Low Tech Mag
These days, we provide thermal comfort in winter by heating the entire air volume in a room or building, an approach that consumes a lot of fossil fuels. In this book, LOW←TECH MAGAZINE focuses on our forebear’s concept of heating, which was more localized. They used radiant heat sources that warmed only certain parts of a room, creating micro-climates of comfort, and they used personal heating sources that warmed specific body parts. It would make a lot of sense to restore this old way of warming, especially since newer technology has made it much more practical, safe, and efficient. By placing heating technology in a historical context, LOW←TECH MAGAZINE challenges the high-tech approach to sustainability and highlights the possibilities of alternative solutions.
Half of the articles in this book have not appeared in print before.Contents table:
- Restoring the Old Way of Warming: Heating People, not Spaces
- Insulation: First the Body, then the Home
- The Revenge of the Hot Water Bottle
- Energy Labels Oblige Frugal Homeowners to Make Unsustainable Investments
- How to Keep Warm in a Cool House
- Sunbathing in the Living Room: Tile Stoves and Other Radiant Heating Systems
- Heat Storage Hypocausts: Air Heating in the Middle Ages
- The Revenge of the Circulating Fan
Available in our bookshop: Heating people, not spaces, Kris De Decker, 142 pages, Low-tech Magazine, 2023.Other thematic books in the series:
How to build a low-tech internet?, Kris De Decker, Roel Roscam Abbing, Marie Otsuka, 166 pages, Low-tech Magazine, 2023.
How to downsize a transport network?, Kris De Decker, 162 pages, Low-tech Magazine, 2023.
The Low-tech Magazine archives are also available as a chronological series consisting of three volumes.
A year after Low-tech Magazine built and documented a domestic bicycle generator, the Pavillon d’Arsenal in Paris asked if they could borrow it for an exhibition. We agreed to build a new one instead. The result of our work is now part of the exhibition “Énergies légères”, which runs until March 2024. The installation gives visitors an idea of how much energy they can produce as humans.Image: Bike generator in Paris. Photo: Luc Borho, Pavillon d'Arsenal. Bike generator in Rotterdam, Netherlands
In October, we built a third energy bicycle during a workshop at the House of the Future in Rotterdam. This bicycle generator is now used as an energy source in the community center. The House of the Future is open to the public, for details see their website and instagram.
In a future article, we will cover the construction process and technical details of these two new muscular power plants. These machines are based on spinning bikes and are more powerful than the first bike generator we built.Image: Bike generator in Rotterdam. Photo: Marie Verdeil. Bike generator in Barcelona, Spain
Finally, Andy Lagzdins built a pedal-powered air compressor to run the power tools in his motorcycle workshop, a project that he documented on Low-tech Magazine. We have now put a video online showing how the machine works.Image: Bike generator in the US, built by Andy Lagzdins. Photo: Andy Lagzdins.
During the Second World War, many motorized vehicles in continental Europe were converted to drive on firewood. 1 That happened as a consequence of the rationing of fossil fuels. Wood gas vehicles were a not-so-elegant alternative to their petrol cousins, but their range was comparable to today’s electric vehicles. In Germany alone, around 500,000 wood gas cars, buses, and trucks operated by the end of WWII. An even more cumbersome alternative was the gas bag vehicle. 2
Nowadays, there’s much less firewood available than in the 1940s, especially in industrialized regions. So, what would be the solution to the disruption of gasoline or electricity in the Third World War? Dutch artist Gijs Schalkx found another fuel supply, which is abundant: plastic waste. The production of plastics only started in the 1950s, after the Second World War. Since then, plastic has become an increasingly popular material, growing to a global annual production of 460 million metric tons in 2019 – twice as much as in 2000 and eight times as much as in 1976. 34Image: Diesel production on the roof. Image credit: Gijs Schalkx.
Plastics are made from fossil fuels, and the process can be turned around. Gijs Schalkx converted an abandoned Volvo 240 to run on diesel that he makes from the plastic waste he collects. The “de-refinery” converts plastic waste back into fuel and is installed on the luggage carrier of the car, making the vehicle independent of the fossil fuel infrastructure. The plastic waste is heated in a boiler to about 700 degrees Celsius, after which it evaporates. The gas is then cooled down, and turns into a diesel-like liquid one hour later. Gijs collects it in plastic bottles – themselves the raw material for the diesel they contain. The fuel looks like Coca-Cola – one of the largest producers of plastic waste.How far can we drive on plastic waste?
Making fuel can happen while the car drives, but Gijs has kept the two activities separate for safety reasons. At a speed of 80 km/u, his Volvo 240 drives a distance of 7 kilometres per kilogram of plastic (which corresponds to 14 kg of plastic per 100 km driven). That includes the fuel used to heat up the plastic waste on the roof (1 kg of plastic gives 0.5 liter of diesel). Plastic waste is a rather voluminous material, and it takes several garbage bags full of plastic waste to make one liter of fuel. Schalkx plans to use a small shredder to reduce the volume of the plastic waste he collects, but for now he relies on a supply of discarded plastic granulate from a neighbour, consisting of PET and HDPE.Image: Gijs Schalkx adds plastic waste to the de-refinery. Image credit: Gijs Schalkx.
How far could we drive if we would convert all plastic waste into fuel? The Netherlands produced roughly 1,650 kiloton of plastic waste in 2017 (1,650,000,000 kg), enough to drive 11.55 billion km (11,550,000,000 km). 5 That corresponds to about 1/10th of kilometers driven by all passenger cars in the Netherlands in 2021 (114.3 billion km). 6 On a smaller scale, the average passenger vehicle in the Netherlands drives 12,000 km per year, requiring each driver and their passengers to collect 1,714 kg of plastic. On the other hand, even the current amount of plastic waste per capita in the Netherlands (97 kg) would be enough to drive 679 km – perhaps sufficient for those who use their automobile wisely. The amount of plastic waste grows faster than the number of cars so that we could drive increasingly longer distances in the future. 7How sustainable is driving on plastic waste?
Being able to drive a vehicle on plastic waste has benefits in terms of resilience. For example, it could allow medics to operate ambulances without a regular fuel supply in a war zone. However, how does a vehicle driven on plastic waste performs in times of peace? After all, plastic waste is a huge problem, and Gijs Schalkx’s car gets rid of it. With less than 10% of plastic waste recycled worldwide, would it make sense to encourage people to convert their vehicles to run on diesel oil made of plastic waste? Sure, it would be a more affordable alternative to electric cars, but what about the carbon emissions?
On the one hand, the embodied carbon emissions of the Volvo 240 are almost zero: Gijs found most components – including the car itself – in the dump, others on the second-hand market. 8 In contrast, manufacturing new vehicles – especially electric ones – adds a significant carbon footprint before they drive their first kilometer. They also need an extensive infrastructure to produce and distribute fuel and electricity, adding more carbon emissions. In contrast, the Volvo has its fuel infrastructure on the roof, built from scrap.Image: Gijs Schalkx in his car. The design is a nod to wood gas cars built by other Dutchmen, Dutch John and Joost Conijn. Image credit: Frank Hanswijk. Image: The interior of the car. Image credit: Frank Hanswijk.
On the other hand, the CO2-emissions from the fuel production and the fuel combustion are not praiseworthy. First, there is the burning of plastic on the roof of the car. Making 1 liter of diesel requires the burning of 1 kg of plastic, which results in 2-2.7 kg carbon emissions. 9 Second, there is the combustion of the diesel fuel while driving, which emits 2.7 kg of carbon dioxide per liter. 10 Together, that becomes 4.7 to 5.4 kg CO2 per liter. Consequently, with a 14:1 fuel economy, the Volvo emits 65.8 to 75.6 kg of greenhouse gases per 100 km.
In contrast, the emissions of the average fossil fuel powered car in Europe amount to 25.8 kg/100 km, including crude oil production, fuel refining and vehicle manufacturing. 11 The emissions of a small electric car like the Nissan Leaf amount to 10.9 kg/100km in Europe, including the emissions of the fuel that is burned to produce the electricity. 11 The Volvo thus emits 2.5 times more CO2 than the average fossil fuel powered car in Europe, and 7 times more than a small electric car. The difference will be somewhat smaller, because the data for the other cars do not include the emissions for building the oil and power infrastructure. However, this is unlikely to tip the balance.
There are several reasons for the high carbon emissions. First, fuel production by burning plastic on the roof is four times more carbon intensive than producing fuel from crude oil in a refinery. 12 Second, the Volvo dates from 1980, when cars had lower fuel economy. Gijs Schalkx: “Hypothetically, you could convert a newer car to drive on plastic waste and have much lower carbon emissions. Likewise, the de-refinery is one of the first of its kind and could be made more efficient by real engineers. Oil refineries have been developped for more than 100 years. However, newer cars have proprietary electronic motor controls that prevent using alternative fuels.”Externalizing pollution
Carbon emissions are not the only worry. Because of the chemicals added to plastic, burning it to make fuel creates a lot of nasty air pollution. Nobody in their right mind will propose a switch to cars fuelled by plastic waste. However, it is instructive to examine the motives behind this unanimous conclusion. Much of the plastic waste that the Volvo 240 burns burns anyways. Not in cars but incinerators. That is the case for 44% of plastic waste in Europe. 13 That plastic waste burns to produce electricity, which can then charge electric cars. How is that more sustainable than burning plastic on the roof of your car?Image: Burning plastic. Image credit: Gijs Schalkx.
The carbon emissions are the same. So is the air pollution, although it’s easier to put a flue gas scrubber on thousands of incinerators than on millions of cars. The main difference is that burning plastic waste in incinerators to power electric cars allows many of us to externalize the side effects of car driving. An incinerator can be (and always is) located in a poor neighbourhood, where it causes high incidences of cancer and other health problems in spite of air pollution control. Meanwhile, it produces electricity that charges electric cars which drive around low emission zones in well-to-do neighbourhoods.Internalizing pollution
In contrast, Schalkx’s Volvo internalizes all the side effects of driving automobiles. The car is not a pleasure to drive, at least not regularly. It is dirty. Its interior stinks of plastic, which cannot be healthy – Gijs keeps the car windows open no matter the weather. Furthermore, he needs to spend a lot of time collecting plastic and making fuel, and all these disadvantages make him think twice before he gets behind the wheel. It’s unlikely that Schalkx will drive 12,000 km per year, and so, ultimately, he will produce less pollution than the drivers of more sustainable-looking cars that face none of these problems.
Somehow, the Dutch authorities, who are not known for their permissivity, officially approved the car after inspection. Schalkx drives tax-free and – thanks to his car being an oldtimer – can enter low-emission zones, where he parks alongside the latest electric SUV. Justice is not yet out of this world.Image: Plastic fuel bottles. Image credit: Kris De Decker. Image: Part of the de-refinery on the roof, showing the air blower for the oil burner. It was made from an old heater fan from the Volvo. Image credit: Gijs Schalkx. Image: Part of the de-refinery on the roof, showing the Ursutz-style oil burner that stokes the refinery hot. Image credit: Gijs Schalkx. Image: Gijs Schalkx repaired the car with scrap steel. Image credit: Gijs Schalkx. Image: Gijs Schalkx stripped the car down to its essentials. Image credit: Kris De Decker.
Woodgas vehicles: firewood in the fuel tank, Kris De Decker, Low-tech Magazine, 2010. https://solar.lowtechmagazine.com/2010/01/wood-gas-vehicles-firewood-in-the-fuel-tank/ ↩︎
Gas Bag Vehicles, Kris De Decker, Low-tech Magazine, 2011. https://solar.lowtechmagazine.com/2011/11/gas-bag-vehicles/ ↩︎
The plastics industry now consumes 14% of all oil production, compared to only 4% in 2012. By 2050, the share of the plastics industry is forecasted to be 20% of oil production. Sources: https://e360.yale.edu/features/the-plastics-pipeline-a-surge-of-new-production-is-on-the-way & https://www.reuters.com/business/environment/big-oils-plastic-boom-threatens-uns-historic-pollution-pact-2022-03-04/ & https://oilprice.com/Energy/Energy-General/How-Much-Crude-Oil-Does-Plastic-Production-Really-Consume.html See also 3 ↩︎
New parts in the car are fuel hoses, coolant hoses, paint, tyres, brake lines and brake pads. Most of these were required to pass vehicle inspection. ↩︎
Rubio-Domingo, Gabriela, et al. “Making Plastics Emissions Transparent.” COMET. Last modified February 2022. https://ccsi. columbia. edu/sites/default/files/content/COMET-making-plastics-emissions-transparent. Pdf (2022). https://ccsi.columbia.edu/sites/default/files/content/COMET-making-plastics-emissions-transparent.pdf. ↩︎
The workshop takes place on behalf of the “House of the Future”, a spinoff of the Human Power Plant project. The House of the Future will bring the Human Power Plant’s “Human Powered Neighbourhood” scenario to life in Bospolder-Tussendijken, Rotterdam, in the coming years. You can already get a taste of it at the Museum Boijmans van Beuningen’s online exhibition (in Dutch).
Since this community will run largely on human power, we need human power plants. Therefore, Kris De Decker and Marie Verdeil organise an open and collaborative workshop where we will build a fully working bicycle generator based on a second-hand spinning bike. You are welcome to learn, experiment, teach, and help.
During the workshop, we will mount a generator on the bike, build a control panel, and modify devices to run on low voltage. This bicycle generator will be specifically designed to serve as a power source in the communal workshop, so that we can use it to build more stuff we need (including more bike generators).Programme:
- Tuesday 10 October (14h-18h): open day House of the Future
- Wednesday 11 October (15h-17h): introduction workshop
- Thursday 12 October (10h-17h): workshop
- Friday, October 13 (14h-19h): workshop
- Saturday, October 14 (14h-17h): workshop
We speak Dutch, English, French, and Spanish. The introduction (11 oct) will be in Dutch only.
Admission is free. To participate: just walk in (Jan Kobellstraat 56A, Rotterdam) or send an email to contact  huisvandetoekomst  org.
All future events will be published on our events page.Illustration: Future vision of the human powered housing block in Rotterdam. Drawing: Melle Smets.
Fast and cheap transportation props up industrial societies, both for the moving of people and cargo. However, our transport networks are very wasteful of energy and utterly dependent on fossil fuels. In this series of articles, Low-tech Magazine critically examines the call for electrified vehicles, which depend on unsustainable batteries and infrastructures.
Much more important than the chosen power source is vehicle design: size, weight, speed, acceleration, and comfort level. Furthermore, public transport is more resource efficient, and we could electrify it without batteries.
The book’s second part deals with long-distance transportation: planes, trains, sailing ships, and ocean liners. By placing transportation technology in a historical context, Low-tech Magazine challenges our high-tech approach to sustainability and highlights the possibilities of alternative solutions.Contents table:
- How to Downsize a Transport Network: the Chinese Wheelbarrow
- The Citroën 2CV: Cleantech from the 1940s
- The Status Quo of Electric Cars: Better Batteries, Same Range
- Electric Velomobiles: as Fast and Comfortable as Automobiles, but 80 times more Efficient
- Get Wired again: Trolleybuses and Trolleytrucks
- High Speed Trains are Killing the European Railway Network
- Life Without Airplanes: from London to New York in 3 Days and 12 Hours
- How to Design a Sailing Ship for the 21st Century?
How to downsize a transport network?, Kris De Decker, 166 pages, Low-tech Magazine, 2023.Other thematic books in the series:
How to build a low-tech internet?, Kris De Decker, 162 pages, Low-tech Magazine, 2023.
The Low-tech Magazine archives are also available as a chronological series consisting of three volumes.
Conventional solar installations do not question our dependence on fossil fuels and the energy-guzzling lifestyle that results. Both rooftop solar panels and large-scale solar farms provide us with all the power we want, even when the sun is not shining. That is because these systems use the central power grid, which largely runs on fossil fuels, as a kind of battery to cope with power shortages.
Although grid-connected solar panels can reduce the fossil fuel consumption of thermal power plants, these savings are at least partly offset by the additional fossil fuels required to build and maintain what is essentially a dual energy infrastructure. Combining solar and wind power can further increase the share of renewable energy in the power grid, but this requires further infrastructure development. Apart from energy, this also demands a lot of money and time.
Replacing fossil-fuel-fired power plants with energy storage, so that surplus electricity generated on sunny days can be stored for when there is no or insufficient sun, encounters the same problem. Energy storage, whether integrated into a power grid or located at individual households (off-grid systems), is very expensive and carbon-intensive to build and maintain.Autonomous solar installation
The production of solar panels obviously costs money and energy. However, the financial and energy costs of the associated back-up infrastructure are many times higher. For grid-connected solar installations, these costs are very difficult to calculate precisely, but for autonomous solar installations (without grid connection and with their own energy storage) it is a lot easier. As an example, I will therefore take the small autonomous solar installation that powers my living room in Barcelona.
This system consists of two 50W solar panels on the balcony, a 100 Ah lead-acid battery and a 10A charge controller. The energy generated is used for lighting, the music system, and charging laptops and other electronic devices, among other things. The initial financial investment was 340 euros: 120 euros for the solar panels, 170 euros for the battery and 50 euros for the charge controller.
But while the solar panels should last 30 years and the charge controller about 10 years, I have to replace the lead battery on average every three to five years. 1 Over a 30-year lifespan, the costs then amount to €120 for the solar panels, €150 for the charge controllers and – in the best case scenario – €1,020 for the batteries. The batteries (and associated charge controllers) therefore account for about 90% of the total lifetime costs.
Energy storage also dominates the plant’s “embedded” energy (and resulting carbon emissions). Producing my lead-acid battery took 1,200 megajoules (MJ) of energy. 2 Over a 30-year lifetime (six batteries at best), that equates to 7,200 MJ. The three charge controllers add another 360 MJ over a 30-year lifetime, bringing the total energy consumption for the battery system to 7,560 MJ. 3 In contrast, the production of the solar panels costs only 2,275 MJ out of a total of 9,835 MJ. 4 Conclusion: more than 75% of total fossil energy consumption is due to energy storage.Image: To the right on the balcony are the two 50W solar panels that power my flat's living room. Next to it is the 30W solar panel that makes this website work. Photo: Marie Verdeil. Image: The structure for the solar panels, built from waste wood. Photo: Kris De Decker. Image: The 100 Ah lead-acid battery powering the living room after sunset. Photo: Kris De Decker.
Other types of batteries would not significantly change this conclusion. For a comparable off-grid system with lithium-ion batteries, energy storage would account for about 95% of the total lifetime cost (which is almost double that of a system with lead-acid batteries). Assuming an optimistic lifetime (10 years) and including charge controllers, lithium energy storage accounts for some 70% of the energy invested in a solar grid system. 5 6 For nickel-iron batteries, energy storage would account for 85% of the total lifetime cost (there are no energy cost data). 7
The scale and location of the solar installation also make no difference. A larger system needs more solar panels, but also larger batteries and more expensive and powerful charge controllers. The ratios remain the same. 8 The only factor that may give the solar panels a slightly larger share of the total cost is the structures on which they are mounted. I don’t take this into account because I built them myself from waste wood. However, if the solar panels are mounted on a roof, a DIY solution is less obvious. But even in that case, the cost of energy storage remains by far the biggest consideration.Direct solar energy: much cheaper and more sustainable
Unlike fossil fuels, the sun and wind are not available on demand. The problem with our approach to renewable energy is that we insist that power should always be infinitely available, regardless of the weather, seasons or time of day. Matching energy demand to supply – as was done in the past – would lead to dramatic reductions in the cost and use of fossil fuels.
For example, if I omitted the battery storage of my solar installation, my system would become about 10 times cheaper: 120 euros instead of 1,290 euros over a 30-year lifetime. Alternatively, I could spend 1,290 euros on solar panels alone, which would give me a solar system of 1,075 watts. That’s ten times the capacity of the setup with batteries, more than what would fit on the balcony.
Without the battery and charge controller, the energy cost of the installation also drops from 9,835 MJ to 2,275 MJ. In other words, I could generate at least four times as much solar energy with the same investment in fossil fuels.How can direct solar power be practical?
All well and good, but the sun does not shine after sunset and the amount of solar energy varies throughout the day and year. So how then can using solar panels without batteries (or other back-up infrastructure in the case of grid-connected installations) be practical?
To answer that question, we look at a pioneer of “direct solar power”: the Living Energy Farm. This environmental education community in the US state of Virginia is completely “off-the-grid” thanks to solar power, but only 10% of the solar power generated passes through a (nickel-iron) battery. However, the solar panels provide power for several homes, a communal kitchen, a metal workshop, and a farm. 9 10Image: direct solar power at the Living Energy Farm.
The solar installation has been in operation since 2011 and consists of separate systems with a total peak power of 1,400 watts. 11 In comparison, the average peak power of a residential solar installation in the UK and the US – for one household – is 4,000 watts and 6,500 watts, respectively. As in my flat, the Living Energy Farm uses energy sparingly, but the fact that hardly any batteries are used has other reasons.Some appliances are only used during the day
A first reason is obvious: some electrical appliances and machines are only used during the day. This is true, for example, of all machines in the metal workshop, including a band saw, compressor, grinder, circular saw, lathe, milling machine and drilling machine. It also applies to agricultural machinery such as a grain mill and a deep well pump. Linked directly to solar panels, these machines offer all the capabilities of modern grid-powered technology, with the exception that they can only be used during the day. 10
On a much smaller scale, I have used direct solar power for a soldering iron, glue gun and irrigation pump (for the balcony) at home. Other examples of appliances and machines that could be used only during the day include hoovers, sewing machines, washing machines, game consoles, laser cutters and 3D printers. It is not so difficult to imagine a modern society where activities such as vacuuming and DIY chores only take place during the day. It is certainly not a return to the Middle Ages.Image: several workshop tools at the Living Energy Farm, most of them run on direct solar power. Image: Alexis Zeigler. Image: Metal lathe running on direct solar power, Living Energy Farm. Image: Alexis Zeigler. Image: Soldering with direct solar power. Photo: Marie Verdeil. [Watch the video](https://www.youtube.com/watch?v=qozZCJU4IOc).
Moreover, not all electrical appliances require constant attention. Washing machines or dishwashers that trigger automatically when the sun shines are often cited example applications of a “smart” power grid. But that approach relies on an extensive infrastructure of electricity transmission, communication networks, and electronics-packed appliances.
In contrast, in a decentralised direct solar approach, the intelligence is provided by the sun and the rotation of the planet. A direct solar-powered washing machine or dishwasher can be fully charged and switched on in the evening. The machine then starts up “automatically” in the morning. You can even use timers (electronic or mechanical) to run different appliances one after the other.
Whether clouds pose an additional limit to a direct solar installation, and to what extent, depends on the size of the solar panels. Doubling the area of solar panels guarantees sufficient solar power during moderate cloud cover, while the installation remains much cheaper and more sustainable than a system with batteries or other backup infrastructure.
An even larger area of solar panels could provide sufficient energy even during heavy cloud cover, but increasing the size of the system tenfold brings the cost back to the level of an autonomous system with batteries. Quadrupling the area makes the system equally dependent on fossil fuels again.Many appliances already have batteries
Direct solar power does not rule out the use of electrical appliances after sunset either. As mentioned, the Living Energy Farm has a modest battery system, providing power for lights, fans, and electronic devices after sunset, among other things. 10 In addition, many modern appliances already have built-in energy storage. This is the case for all kinds of electric vehicles, for most electronic gadgets, and for older electrical appliances with AA batteries.
Consequently, these types of devices can be charged with direct solar energy during the day and then used for several hours after sunset thanks to the built-in battery. Combined with a lithium-ion power bank, a direct solar panel can also make it possible to charge USB devices after sunset. This strategy can even work for lighting, as there are many battery-powered lamps that you can use as modern torches, hung in different parts of rooms and buildings.Image: A mobile phone on direct solar power. Photo: Marie Verdeil.
Of course, outsourcing chemical energy storage to the device is not the most sustainable option. The production of lithium-ion batteries requires fossil fuels, and (unlike lead-acid batteries) they are not recycled. The best solution, of course, is to reduce the use of electrical devices. But charging them with direct solar energy is a lot more sustainable and efficient than via other batteries or a fossil-fueled electricity grid. If we use high-tech devices, then preferably in the smartest way possible.Non-electric energy storage
A third reason why direct solar power is more practical than it initially seems is that some electrical appliances can be used after sunset thanks to thermal energy storage. This is much cheaper and more sustainable than electrical energy storage. Thermal energy storage is already fairly well established for space and water heating systems, which store solar-heated water in an insulated boiler or (for space heating only) in the building envelope. It is no surprise that the Living Energy Farm has such systems, and solar thermal energy also provides hot water in my flat.
However, the same approach also works for two important household appliances that need to work after sunset and also consume a lot of electricity: the fridge and the cooker. Instead of storing electricity from a solar panel in a battery to then power a fridge or cooker after sunset, these appliances on the Living Energy Farm use thermal insulation. This keeps the heat inside (in the case of the cooker) or outside (in the case of the fridge) when there is no power supply. The thermal insulation also ensures very high energy efficiency, which means that each of these appliances can already operate on a solar panel of just 100-200 watts.A direct solar-powered fridge
It is perfectly possible to connect a conventional fridge or freezer directly to a solar panel, but such an appliance would heat up very quickly at night. Even refrigerators with the most energy-efficient labels have a relatively limited insulation thickness (usually 2.5 cm). However, if that insulation thickness is increased to about 12.5 cm, the energy consumption of a refrigerator drops by a factor of four. 12 13 The passive cooling capacity of a refrigerator can be further increased by adding thermal mass in the form of a water tank inside the appliance. During the day, the solar panel cools the water or converts it to ice. At night, this cold water or ice slows down the heating of the refrigerator. 14
A direct solar-powered fridge also opens at the top, not at the front. Cold air is heavy, and so much less energy is lost that way when someone opens the door. All these design choices add up to spectacular energy efficiency. A study of direct solar refrigerators in very sunny regions (Texas and New Mexico, USA) showed that they maintained their cooling capacity for 6 or 7 days without power supply. The units operated year-round with solar panels of only 80W to 120W. 15 The Living Energy Farm powers its solar refrigerator with a 200W panel. 10Image: The Sundanzer DDR165. A refrigerator designed specifically for direct solar power. Photo: Sundanzer.
Unlike solar heating, solar cooling is optimally tuned to seasonal variations in solar radiation. Cooling requires more energy in summer, when there is more solar energy. The aforementioned refrigerator in New Mexico recorded electricity consumption of 406 watt-hours per day in summer and only 230 watt-hours in winter. 16 Moreover, the technology can be used throughout the cold chain, of which the household refrigerator is only a small (but essential) part. Another application is air cooling, although this is less well researched and more challenging. 17A direct solar electric cooker
In principle, a conventional cooker can also be connected directly to a solar panel, but as with a conventional fridge, it is not very practical. You can only cook during the day, and you have to install a lot of solar panels. A single hot plate needs 1,000 watts of electrical power. A solar electric cooker solves these problems by packing the cooktop with thermal insulation. The technology is basically a combination of an electric cooktop and a haybox.Image: Test of an electric solar cooker. Photo: California Polytechnic State University (Cal Poly).
Thanks to thermal insulation, an electric solar cooker slowly accumulates heat during the day, which can then be used for cooking after sunset. In this way, a much lower power supply can be sufficient to achieve high temperatures. Think of it as “charging” your cooker, not with electricity but with heat.
Researchers at US California Polytechnic State University (Cal Poly) built the first solar electric cooker in 2015. Their 12-volt device, which has since been further developed, needs only a 100W solar panel to work. It boils a litre of water in an hour. With a full day of sunlight, it can cook almost 5 kg of beans, rice, stew or potatoes. 18
Cooking after sunset is possible by using a cooking pot with a much thicker bottom (5-10 kg). Cal Poly’s research team managed to bring the temperature of that solid heat storage to 250°C in five hours with a 100W solar panel. They were then able to boil a litre of water in three seconds after sunset. In another test, they stir-fried 1 kg of vegetables in two minutes. The ideal configuration consists of two cooking pots: one with and one without heat storage. Thus, an electric solar cooker can cook both slowly and quickly, depending on the time of day and the dish. 19Image: The principle of a solar electric cooker with solid heat storage. Drawing: California Polytechnic State University (Cal Poly). Thermal or electric?
Like solar water and space heating systems, cooking and cooling can work both with and without electricity – with PV panels on the one hand and solar thermal collectors on the other. But while solar space and water heating are more cost- and energy-efficient without electricity, for solar cooling and solar cooking it is just the opposite.
Space and water heating require relatively small temperature differences, which can be provided by low-cost solar thermal collectors made of glass plates and water pipes. In contrast, cooling and cooking require larger temperature differences, which require more sophisticated (vacuum tube or parabolic) solar collectors – and these are more expensive than PV panels. 20 21
The only exception is a simple solar cooker – an insulated box with a glass top – but it cannot achieve such high temperatures. Moreover, an electric solar cooker has some additional advantages. With a non-electric appliance, you have to cook outside, which is less practical but also less efficient, especially in winter: a thermal solar cooker will lose more heat to the environment. An electric solar cooker is also more energy-efficient because it is insulated on all sides. It also works better in cloudy weather and can be used after sunset. At the Living Energy Farm, the parabolic solar cooker is only used in optimal conditions – at full sun and high outdoor temperatures.What are the technical challenges?
Although the Living Energy Farm is putting all these applications of direct solar energy into practice, there are some technical challenges for those who want to follow suit. Almost all our modern technology is designed to operate with a stable and uninterrupted power supply. It doesn’t have to be that way, but for now, direct solar power usually requires some tinkering. A direct solar system is much easier to build than an autonomous system with batteries, but it often requires modifications on the appliance side.
Some devices can be connected directly to a solar panel: it is enough to connect the positive and negative contacts of the solar panel and the device. For example, machines with a DC motor tolerate large fluctuations in the power supply. The metal workshop and agricultural machinery at the Living Energy Farm work this way. If clouds block the sun, the combined electrical load can become greater than the power supply from the solar panels, but this does not stop the machines. All the engines will slow down because they share the available energy, but they all continue to do useful work. 10 22
The same applies to all appliances that work on the basis of resistive heating elements, such as kettles, hotplates or electric heating systems. They work regardless of power or voltage, just slower or faster. A direct solar-powered fridge preferably operates on a variable DC compressor, which can adjust its speed according to the varying solar power production. 10 23
Many other devices need a specific and stable voltage input, which usually does not match what the solar panel produces. This can be solved by placing a DC-DC converter (a “buck” or “boost” converter) between the solar panel and the device. This is a small electronic module that converts the fluctuating voltage of a solar panel into a constant output voltage for a low-voltage device (5V, 12V or higher). 24Image: Experiments with direct solar power. Photo: Marie Verdeil.
If you use an inverter in addition to this, even mains appliances can operate directly on a solar panel. 25 DC-DC converters are essential for all appliances that contain electronic components. This is the case for many appliances today, including those, such as washing machines or coffee machines, that until recently operated without electronics. That often gives you two options to run such appliances on direct solar power. You can either fit a DC-DC converter or modify the appliance by bypassing the electronics.DIY manuals & commercial devices
Most direct solar power applications operate at low voltage, so you can safely do it yourself. Low-tech Magazine will soon publish a manual on this. However, the Living Energy Farm uses direct current with higher voltages for a number of applications. Examples are the machine tools in the metal workshop (90V) and a number of powerful electric solar cookers (48V, 180V). It is not a good idea to build these systems yourself unless you have the help of a qualified electrician, as these voltages can lead to fatal accidents.
Those wishing to build their own (low-voltage) electric solar cookers will find comprehensive manuals at both Living Energy Farm and Cal Poly. 26 The devices can be made with simple materials. The insulation material should be fireproof. Example materials are rock wool, fibreglass, natural wool or clay.goed
Different technologies can be used for heating elements, but embedding nichrome wires in cement is the simplest option. These wires can be taken from a variety of appliances such as toasters, ovens and hotplates. In principle, the heating wires can be attached directly to the cooking pot, but it is more practical to make a heated “nest” in which a pot can be placed.Image: Inspired by Cal Poly's work, Living Energy Farm also developed a number of electric solar cookers, one of which they [offer for sale through their website](https://livingenergylights.com/product/roxy-solar-electric-oven/). The Roxy Oven can be used as a hotplate or an oven, for example for baking bread. The door also remains closed when used as a hot plate. This solar cooker has no energy storage. Image: The Roxy Oven without the door and with the glass wool insulation visible. The device - made in the metal workshop with direct solar power - runs on 48V and requires a solar panel of 200 to 500 watts. Living Energy Farm also offers Sunstar's solar refrigerator [for sale online](https://livingenergylights.com/product/sunstar-direct-drive-8-cuft-chest-style-refrigerator-freezer/). Does direct solar power waste energy?
The sustainability of a solar installation depends not only on the energy required to produce and maintain the infrastructure, but also on the energy produced by the solar panels during their lifetime. Some people will argue that direct use of solar power is inferior to conventional grid-connected or battery-powered solar installations in this respect.
After all, the hoover, washing machine and power drill are not used every day, and if no electrical appliance is connected then a solar panel will not produce power either. Consequently, the amount of electricity produced by the panel will decrease over its lifetime, while the energy needed to manufacture the panel remains the same. This makes the power from a direct solar panel more carbon-intensive.
However, because energy storage in batteries (or the grid-connected alternative) accounts for such a large proportion of the total energy invested, a standalone solar panel can waste quite a lot of energy before it becomes less sustainable than its counterpart with battery storage or grid connection.
Moreover, direct use of solar power avoids the charging and discharging losses caused by batteries, or the energy losses in the transmission infrastructure for grid-connected systems. Both have to be offset by additional solar panels. Furthermore, solar panels connected to batteries or the grid also waste power – a consequence of the large difference in energy production between summer and winter.Maximising direct solar power with collective services
Nevertheless, it is important to maximise the energy production of a direct solar panel. In that context, it is useful to return for a moment to the original example system located on my balcony. Direct solar power could be a nice addition to this system, especially for the fridge and cooker. It was because of these appliances that I concluded in 2016 that it was impossible to completely disconnect my flat from the grid.
However, the Living Energy Farm shows that it could be done: there is room for a further 200 watts of solar panels (4 x 50W) on the balcony, enough to power both a thermally insulated fridge and hob. Additional battery capacity would not be needed.
For other appliances, however, direct solar power is of little use in my case. It would not be very efficient to install an extra solar panel for the washing machine or the power drill, as they are only used occasionally. This seems to play into the hands of a “smart” electricity grid, because that way many households can use the same solar power – there is always someone who needs to wash clothes or drill a hole.
However, such a smart grid does require a lot of infrastructure, even if direct solar power were to be used at that scale. It may not require batteries or fossil fuels as backup, but it does require transmission and communication infrastructure.Image: A record player on direct solar power. Photo: Marie Verdeil. [Watch the video](https://www.youtube.com/watch?v=_LjSigJv0-0).
The Living Energy Farm demonstrates an alternative solution: the communal organisation of household tasks and work. Instead of a communal power grid distributing energy to many indidvidual households, we can set up collective services with decentralised energy production.
In the Living Energy Farm communal workshop, direct solar power can be used much more efficiently than in an individual workshop that is only used occasionally. A collective laundry in each street would also use direct solar power much more efficiently. Moreover, we save a lot of energy on building appliances this way, and gain a lot of space.Direct wind power?
This strategy becomes even more important if we choose not direct solar power but direct wind power – or a combination of both. The Living Energy Farm is located in a sunny region, but the same approach could also work in windy places.
However, there is an important difference between solar power and wind power. The efficiency of a solar panel does not depend on its size, which makes solar power ideal for decentralised energy production. In contrast, the efficiency of a wind turbine increases more than proportionally as the rotor diameter increases. Much better than one wind turbine per household, therefore, is a somewhat larger wind turbine for a community of households, e.g. for powering a collective laundry or workshop.
The service life of lead-acid batteries depends on many factors. If they are discharged too deeply or are not fully charged regularly, the service life can be shorter than three years. On the other hand, a lead-acid battery that is hardly used or not discharged at all can last much longer than five years. However, the academic literature states a life expectancy of three to five years and this has also been my experience with the batteries I have used since 2016. See, for example, “Optimal Sizing and Life Cycle Assessment of Residential Photovoltaic Energy Systems With Battery Storage”, A. Celik, in “Progress in Photovoltaics: Research and Applications”, 2008. & “Energy pay-back time of photovoltaic energy systems: present status and prospects”, E.A. Alsema, in “Proceedings of the 2nd World Conference and Exhibition on photovoltaics solar energy conversion”, July 1998. ↩︎
Manufacturing a lead-acid battery (based on largely recycled materials) takes about 1 MJ of energy per watt-hour of storage capacity. My 100 amp-hour battery equates to a storage capacity of 1,200 watt-hours, and so the embedded energy equals 1,200 MJ. Over a 30-year lifespan, I need six of these batteries at best, so 7,200 MJ in total. Source: “Energy Analysis of Batteries in Photovoltaic systems. Part one (Performance and energy requirements)” and “Part two (Energy Return Factors and Overall Battery Efficiencies)” (PDF). Energy Conversion and Management 46, 2005. ↩︎
Not much research has been done on the embedded energy of charge controllers. The most relevant data I found is a value of 1 MJ per watt maximum power: Kim, Bunthern, et al. “Life cycle assessment for a solar energy system based on reuse components for developing countries.” Journal of cleaner production 208 (2019): 1459-1468. For a capacity of 120W (my charge controller has a maximum capacity of 10A x 12V = 120W), this amounts to 120 MJ. For the estimated lifetime, I found values of 7 and 12.5 years: same reference as above, as well as: Kim, Bunthern, et al. “Second life of power supply unit as charge controller in PV system and environmental benefit assessment.” IECON 2016-42nd Annual Conference of the IEEE Industrial Electronics Society. IEEE, 2016. I therefore made the calculation on an estimated lifetime of 10 years. ↩︎
Nawaz, I., and G. N. Tiwari. “Embodied energy analysis of photovoltaic (PV) system based on macro-and micro-level.” Energy Policy 34.17 (2006): 3144-3152. According to this widely quoted source, it takes 3,500 MJ to produce 1 m2 of solar panel. My two solar panels together measure 0.65 m2, representing a total energy cost of 2,275 MJ. A more recent literature review puts the energy cost for producing different types of solar panels at between 1,034 and 5,150 MJ/m2. The most recent studies of silicon solar panels in this review put the energy cost at around 1,000 MJ/m2, much lower than the figure I am using. See: Ludin, Norasikin Ahmad, et al. “Prospects of life cycle assessment of renewable energy from solar photovoltaic technologies: A review.” Renewable and Sustainable Energy Reviews 96 (2018): 11-28. ↩︎
Lithium-ion batteries are a lot more expensive than lead-acid batteries, but unlike lead-acid batteries, they can be discharged deeper (up to 15% of their total capacity) and have a longer lifespan (7 to 10 years). Consequently, fewer and smaller batteries are needed. Taking these factors into account, the lifetime cost of the battery is €750, compared with €1,020 for lead-acid batteries. On the other hand, lithium-ion batteries require a more sophisticated and more expensive charge controller: a 10A charge controller costs between 200 and 600 euros, depending on the quality. Assuming a price of 400 euros for the charge controller and a 10-year lifetime for both the battery and the charge controller, battery storage accounts for 95% of the total lifetime cost (a total of 2,070 euros, much more than the total cost for the system with lead-acid batteries). Sources: https://www.lithiumion-batteries.com/products/product/12v-50ah-lithium-ion-battery & https://www.lithiumion-batteries.com/products/12v-lithium-ion-battery-chargers/ ↩︎
Although the production of a lithium-ion battery costs more energy than the production of a lead-acid battery (1.4-1.9 MJ/Wh versus 1 MJ/Wh), this is offset by a longer lifespan and greater discharge capacity. The energy cost of lithium-ion batteries over a 30-year lifetime is then about 3,000 MJ, significantly less than a comparable lead-acid battery system. In contrast, the charge controller contains more complex electronics. Unfortunately, no data is available for the energy cost of such a charge controller. So there is no alternative but to estimate the energy cost based on the financial cost, which is four to twelve times more expensive than a charge controller for a lead-acid battery. Assuming a four times higher cost, the embedded energy of the charge controller increases to 480 MJ, or 1,440 MJ over a 30-year period. The total energy cost for the system is then 6,685 MJ, less than a comparable system with lead-acid batteries. Of this, almost 70% is attributable to battery storage. ↩︎
Nickel-iron batteries are even bigger and heavier than lead-acid batteries and they need regular maintenance. But they can be fully discharged and have a very long service life (20 years). Moreover, they can be used with the same charge controllers as lead-acid batteries. The lifetime cost over 30 years for the battery is €750, cheaper than the six lead-acid batteries of similar capacity. The total lifetime cost for a nickel-iron battery system with 100W solar panels is €1,020, of which 85% goes to energy storage. Unfortunately, nickel-iron batteries are hard to find, especially the smaller models. Sources: https://beyondoilsolar.com/product/nickel-iron-battery-industrial-series/ & https://beyondoilsolar.com/product-category/batteries/nickel-iron/ ↩︎
Actually, the price of solar panels in a somewhat larger solar installation would be proportionally even smaller. This is because solar panels with small sizes (such as 50W) are proportionally more expensive per watt of peak capacity than solar panels with more conventional sizes (from 250W onwards). More or less the same applies to the energy cost. ↩︎
Alexis Zeigler, founder of the Living Energy Farm, wrote a book about the project, which is available in full online: Empowering Communities. A Practical Guide to Energy Self Sufficiency and Stopping Climate Change. It can also be ordered in hard copy. ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
Since direct solar power does not require a charge controller for each separate system, splitting up a solar system does not involve any additional costs or energy consumption. ↩︎
Research shows that doubling the insulation thickness from 2.5 cm (standard insulation) to 5 cm reduces the annual electricity consumption of a refrigerator (50 litre capacity) from 250 to 125 kilowatt hours. 13 With an insulation thickness of 10 to 12.5 cm, electricity consumption halves again to around 60 kilowatt hours per year. Even thicker insulation brings a smaller reduction in electricity consumption and is no longer attractive because thicker insulation also increases the cost and size of the refrigerator. The study concerns a solar-powered AC fridge that operates thanks to an inverter and a battery, which is less energy-efficient than a direct solar-powered fridge. ↩︎
Gupta, B. L., Mayank Bhatnagar, and Jyotirmay Mathur. “Optimum sizing of PV panel, battery capacity and insulation thickness for a photovoltaic operated domestic refrigerator.” Sustainable Energy Technologies and Assessments 7 (2014): 55-67. ↩︎ ↩︎
This thermal mass can literally be a container of water placed inside the fridge. or some water bottles for drinking. But the water can also be stored in reservoirs along the side of the appliance, behind an inner lining that keeps them in place and hides them from view. Water has a higher heat storage density than air, keeping the temperature stable for longer. ↩︎
Ewert, M., et al. “Photovoltaic direct drive, battery-free solar refrigerator field test results.” Proceedings of the solar conference. American solar energy society; American institute of architects, 2002. ↩︎ ↩︎
This advantage only applies if the fridge is set up in an unheated room. The modern habit of placing a fridge in a heated kitchen when the outside temperature in winter is equal or lower than that in the fridge is obviously absurdly wasteful. But neither is this advantage valid in tropical countries, where temperatures are high all year round. ↩︎
The use of direct solar power for space cooling has not been analysed as thoroughly as for domestic refrigerators. See: Luerssen, Christoph, et al. “Life cycle cost analysis (LCCA) of PV-powered cooling systems with thermal energy and battery storage for off-grid applications.” Applied energy 273 (2020): 115145. Moreover, it is unlikely to achieve equally large energy savings. A refrigerator is always insulated, but in the case of an air-cooled room or building, this is not necessarily the case. Moreover, a refrigerator is set up in a room where there is a stable temperature. A building is subject to greater temperature fluctuations and can also be heated by direct solar radiation. So direct solar air cooling is a lot more complicated. See: Qi, Ronghui, Lin Lu, and Yu Huang. “Parameter analysis and optimisation of the energy and economic performance of solar-assisted liquid desiccant cooling system under different climate conditions.” Energy conversion and management 106 (2015): 1387-1395. ↩︎
Insulated Solar Electric Cooker with Solid Thermal Storage, Andrew McCombs et al., 2022. See also this video. ↩︎
See: Ferreira, Carlos Infante, and Dong-Seon Kim. “Techno-economic review of solar cooling technologies based on location-specific data.” International Journal of Refrigeration 39 (2014): 23-37. ///// Riffat, James, et al. “Development and testing of a PCM enhanced domestic refrigerator with use of miniature DC compressor for weak/off grid locations.” International Journal of Green Energy 19.10 (2022): 1118-1131. ///// Du, Wenping, et al. “Dynamic energy efficiency characteristics analysis of a distributed solar photovoltaic direct-drive solar cold storage.” Building and Environment 206 (2021): 108324. ///// Alsagri, Ali Sulaiman. “Photovoltaic and photovoltaic thermal technologies for refrigeration purposes: an overview.” Arabian journal for science and engineering 47.7 (2022): 7911-7944. ↩︎
For lack of research, whether the same applies to embedded energy consumption is not clear. ↩︎
In both cases, however, it is necessary to bypass the device’s switch, because DC electricity produces more heat than AC electricity. Instead, a suitable external switch can help, but in doing so you bypass the device’s safety mechanism, which is obviously a risk. 10 Again, this does not have to be the case: it is technically possible to make devices suitable for direct solar power. ↩︎
A fixed-speed compressor can only use 50% of the solar power produced in a useful way, while a variable-speed compressor uses about 75% in a useful way. 15 A capacitor is needed to provide the compressor with an energy boost during the start-up phase. ↩︎
Instead of a DC-DC converter, you can also install a small “buffer battery” and a charge controller. Like a DC-DC converter, the charge controller will ensure a stable output voltage. In addition, the small battery can provide limited energy storage that can be useful to handle short spikes in power consumption. For example, some devices have a current spike when charging. The disadvantage of a buffer battery is that the cost and embedded energy increase, and additional components can fail. A capacitor is an alternative technology to absorb power peaks. ↩︎
However, using low-voltage direct current devices is a lot more energy-efficient because solar panels also produce low-voltage direct current: https://solar.lowtechmagazine.com/2016/04/slow-electricity-the-return-of-dc-power/ ↩︎
Insulated Solar Cooker Construction Manual, Living Energy Farm. Insulated solar electric cooker manual, Pete Schwartz, Cal Poly Physics. Roxy Oven Manual, Living Energy Farm. Video presentation manual solar electric cookers, Alexis Zeigler, Living Energy Farm. Video manual for making heating wires. Thermal heat storage: Insulated Solar Electric Cooker with Solid Thermal Storage, Andrew McCombs et al., 2022. Also see this video. ↩︎
We built a pedal-powered generator and controller, which is practical to use as an energy source and exercise machine in a household — and which you can integrate into a solar PV system. We provide detailed plans to build your own, using basic skills and common hand tools.
Image: The bicycle generator in the living room.
- The bike generator
- The art of pedal power: what are the challenges?
- The dashboard: how to address these challenges?
- How to use the bike: experiments
- Alternative configurations
- The bike generator
- The control panel
- Buck and boost converters, dimmer
- Wind charge controller (for charging lead-acid batteries)
- Wires, connectors, diodes, fuses, on-off buttons
- Dashboard instruments
- Dashboard panel and fixation
- Components list
- Max amperage
- First Prototype
Many people have built pedal power generators and published the manuals online and in books. However, when we set out to make a pedal power generator ourselves, we found that these manuals are incomplete when making the bike generator practical to use. The focus is on building the power source itself, with comparatively little attention to what happens with the power that comes out of it.
To try and make human power production more useful, we built not just a pedal power generator but also a control panel in the form of a “dashboard” attached to the handlebars. The dashboard allows powering or charging a wide diversity of devices – no matter what voltage they run on. Furthermore, multiple devices can be powered simultaneously, allowing the cyclist to adjust the resistance on the pedals for an optimal workout.
We also tried to improve the bike generator itself. Although there are good manuals available, we wanted a power source that is easy to build (no welding or complex tools required), comfortable to pedal, as compact as possible, and not an eyesore. The bike generator is set up in a small living room and used regularly. We found the solution in a vintage exercise bike with a flywheel, an approach we have not seen before.
Trial and error
The bike generator and dashboard were designed and made in collaboration with Marie Verdeil as part of her internship at Low-tech Magazine. We could not find the technical information we were looking for, so we followed a trial-and-error approach. That was time-consuming and costly, but we gained insight and learned lessons. We made lots of mistakes that you can avoid.
We are not engineers, and we welcome technical feedback concerning further improvements. Based on that feedback and more experiments with the bike generator – which is now in use for one month – we will update and expand the manual. Our design can be adjusted and adapted to your needs. We appreciate a donation if you find our work interesting. Your support makes it possible to finance further experiments and building projects that we have in mind. Marie Verdeil will continue working with Low-tech Magazine when she finishes her studies at the Design Academy Eindhoven later this year.
Newcomers to this website may want to read some earlier articles that this bike generator project is building further upon: The short history of pedal powered machines (2011), Pedal powered farms and factories: the forgotten future of the stationary bicycle (2011), Bike generators are not sustainable (2011), How to go off-grid in your apartment (2016), Slow electricity: the return of DC Power? (2016), Could we run modern society on human power alone? (2017), and How much energy do we need?(2018).THE BIKE GENERATOR
There are many ways to build a bicycle generator, and each has its advantages and disadvantages. We based our pedal power plant on a vintage exercise bicycle from the 1950s. Our bike was made by Spanish brand BH but similar vintage models can be found anywhere in the industrialised world.
Image: The exercise bike dating from the 1950s. It has a heavy flywheel in front.
Our approach has several advantages. The first and most important is that old exercise bikes have a large flywheel in front. Bike generators without flywheels – which are the majority these days – are likely to end up gathering dust in the garage because they are tiring and uncomfortable to pedal.
A flywheel is essential because pedalling a stationary bicycle is a different experience from riding a bike on the road. The power that our feet put on the pedals peaks every 180 degrees of crank rotation. On the road, this has little effect because of the inertia of the cyclist.
In contrast, on a stationary bike, this uneven power output results in jerky motion and additional stress on parts. The flywheel solves this by its large mass and rotational speed. That evens out the difference between power peaks and makes for comfortable pedalling. The rider tires less quickly and can generate more energy. A flywheel also produces a more steady voltage.
Our approach also makes it possible to build a pedal power generator with simple tools and basic skills. There is no need to cut or weld metal – the bike remains like it is.  Neither is there a need to build a support structure – the bicycle already has one. We only had to add a so-called friction drive – a small roller attached to the generator shaft and pressed against the flywheel.
Image: The friction drive – a small roller attached to the generator shaft and pressed against the flywheel.
Our method also results in a very compact bike generator. It is just over 1m long. Finally, and although this is a matter of personal taste, it results in a bike generator that is beautiful to behold. The bicycle was bought from someone in a neighbouring village who had it standing in the living room as a decoration.
As a disadvantage, one could mention that a friction drive is less energy efficient than a gear or belt drive. However, the higher efficiency of the flywheel compensates for that. Only a combination of flywheel and gear or belt drive would do better – but that would be more difficult to build. Another disadvantage is that our machine has no switchable gears -- more on that later.
The power output (W) of a bike generator corresponds to the voltage (V) multiplied by the current (A). We obtained roughly 100 watts (12V, 8-9A) of power during a short and heavy workout. During a moderate effort – which we can sustain for a longer time – power production is between 45 and 75 watts. The power output not only depends on the bike but also on the person who operates it. Athletes could produce more power, while couch potatoes would (initially!) generate less. 
We measured the power output right after the generator. However, you need to put more power on the pedals to obtain that power output. To start with, no generator is 100% efficient. Our generator achieves its maximum efficiency (75-78%) at a power output of more than 6A (72W). Efficiency decreases when you produce less power: it drops to 60% at 3A and less than 45% at 2A. Second, there are energy losses in the drive train between the pedals and the generator. We cannot measure these, but according to the data we found, a friction drive introduces on average 15% of extra energy losses.
Taking into account efficiency losses in both generator and friction drive, you need to put at least 150 watts on the pedals to obtain a power output of 100 watts. There are additional energy losses in the bicycle drive train. In theory, bicycle gears have low energy losses, at most a few percent. In practice, however, these energy losses can be high. We proved this unintentionally. Power production doubled after we thoroughly cleaned and oiled the bicycle train. We made the mistake of cleaning the bike only at the very end. That forced adjustments to the control panel to manage the higher currents that suddenly came through it.
As a power cyclist, you have to match the voltage (V) and the current (A) of the device you are powering or charging. However, this is easier said than done. Electric devices run on different voltages and they have very different power demands. The voltage refers to how fast you pedal and the current to how hard you pedal.
A bike generator produces low voltage DC power, similar to a solar PV system (12/24V). The voltage output depends on how fast the bike generator spins. The pedalling rate and the gear ratio determine the generator speed. The manual explains in detail how to set up the correct gear ratio. In short, you need to measure the outer diameter of three parts (pedal sprocket, flywheel sprocket, flywheel) and use those data to calculate the correct spindle size for the intended voltage output.
Once you have set the gear ratio, you could produce a lower or a higher voltage by pedalling slower or faster, respectively. That makes it possible to power devices on different voltages. However, assuming your generator provides 12V at average pedalling speed, you would have to pedal in extreme slow motion to produce 5V, and it will be hard to keep your feet at the pedals to provide 24V. Gears would make it easier to vary the voltage output, but our bike has none.
Running an appliance straight from the generator can be a practical solution if it needs roughly 12V. The flywheel helps to maintain a relatively steady voltage output. However, electronic devices and batteries require a precise voltage. Otherwise, they may not work or get damaged. Furthermore, running an appliance straight from the generator prevents you from powering or charging several devices with different voltages simultaneously – which is a solution to the next problem.
Electric and electronic devices can have very different power demands – even if they work on the same voltage. Unfortunately, it’s much harder to adjust the current than the voltage. How hard you have to pedal depends entirely on the device you are powering. In some cases, this results in an optimal resistance. More often, the resistance at the pedals is either too low or too high.
At one extreme, resistance on the pedals is almost zero when charging a smartphone or a relatively small lead-acid battery. At the other extreme, resistance on the pedals is too high when powering a kettle or a refrigerator. Some devices have varying current demands. For example, the printer demands between 25 and 70 watts of power, depending on what it’s doing exactly. There are peaks in power demand following startup and between pages, and printing images requires more effort than printing text.
Off-grid solar PV systems often charge lead-acid batteries. Human power does not depend on the weather and the time of day, but it can be practical to store human energy in a battery for future use.
Based on 100 watts of power production, it’s easy to make overly optimistic calculations about the time you need to charge a battery. For example, if it takes 100 watt-hours to charge a battery, you can do that in one hour. Right? Wrong. Even if you could sustain a power output of 100 watts for an hour, the battery limits how much power you can put into it. It’s not possible to do a short workout to charge the battery faster than it allows you to.
Lead-acid batteries charge between 10 and 25% of their maximum capacity – and we obtained 10% for all batteries tested. Charging one lead-acid car battery (roughly 60-80Ah) requires you to get 85-115 watts out of the generator, which is a heavy workout. A full charge (12V to 13V) will take five hours, not including charge & discharge losses.
However, for smaller lead-acid batteries, the low power demand is problematic. There is little or no resistance on the pedals (so no real workout), it is very inefficient (the generator has high energy losses), and still, it takes as much time as charging a much larger battery. For example, recharging a 12V battery with a storage capacity of 14Ah (similar to the one powering the solar-powered website requires only 1.4A. That is not much of a workout (20W).
The same problem occurs with USB devices. The most cited use of a pedal power generator is charging a smartphone. However, recharging a smartphone requires very little power (5-10W) compared to what the bike can produce. (Some newer models allow faster charging). You may think charging a 10Wh phone battery would take only 6 minutes at a maximum power output of 100W, but it takes just as long as when you plug it into a wall socket. A much smaller hand-powered charger would be sufficient to charge a smartphone, but then you don’t have your hands free.
To overcome all these problems, we built a control panel that distributes the power from the bike generator into switchable circuits with different voltages for the operation of various devices. You can use these circuits separately or in combination, which allows you to adjust the resistance at the pedals precisely for the optimal workout. You can also control some devices directly by lowering their power demand.
There is no need to pedal faster or slower to match the voltage of different devices. Instead, you can use buck converters and boost converters - electronic modules that convert a fluctuating voltage input into a steady voltage output. Buck converters have a higher input voltage than the output voltage (they step down the voltage), while boost converters have a higher output voltage than input voltage (they step up the voltage). There’s more information on buck and boost converters in the manual.
You can build one electric circuit using only one buck or boost converter. You can then adjust the voltage by turning the tiny screw every time you power a device that requires a different voltage. However, building multiple switchable circuits with different voltages brings advantages. Not only can you easily switch between different types of appliances without the need for a screwdriver, but you can also adjust the resistance at the pedals by running several circuits simultaneously. The control panel includes:
- Two circuits for powering or charging USB devices (5V)
- Three circuits for powering 12V appliances
- One circuit for charging lead-acid batteries (14.4V)
- One circuit for powering mains appliances (220V here in the EU)
- One unregulated circuit where the voltage output matches the voltage input
Image: the front of the control panel
Image: the back of the control panel
If there is insufficient power demand, you can increase the resistance on the pedals by switching on more circuits. That will also increase the efficiency of the generator. To address the low power demand of batteries, you can keep the 5V and 14.4V circuits always open. That introduces a basic electric load of roughly 20W (two to five USB devices and a 14Ah lead-acid battery). For a heavier workout, increase the load by opening other circuits and powering more devices. This approach does not shorten the time it takes to charge batteries. However, it makes your effort more worthwhile.
A dashboard with nothing but 5V USB circuits is another option. More so, you use the control panel in that way without small changes. You can hook up a handful of devices to a single USB output, with a maximum power use of 10 watts (5V/2A). Our dashboard has two 5V circuits – one serves primarily for dashboard lighting, but you can add a USB distributor hub to it for another 10W of devices.
You can add six additional USB power outputs by plugging USB connectors into the three 12V outputs, at least when you add three female 12V connectors. That brings total power demand to 80 watts -- enough to recharge 10 to 15 smartphones simultaneously. There’s no shortage of USB devices these days: phones, tablets, ebooks, power banks, bicycle lights, cameras, wireless headphones, AA battery chargers, and so on.
If there is too much power demand, you can switch off one or more circuits. For some more powerful 12V devices, the dashboard also allows you to lower the current and thus the resistance on the pedals directly by using a variable resistor or potentiometer (better known as a dimmer). When you "dim" appliances like the electric kettle or the Peltier refrigerator, they work just as well, only slower. Without a potentiometer, only athletes could power these devices (100-120W). Dimming does not work for all devices. A laptop, for example, will shut down if it does not receive the power it needs.
By switching between and combining different circuits - and by finetuning the current on the 12V circuit - you can adjust the resistance at the pedals as precisely as on an exercise bike. That optimizes endurance but also power production.
A bike generator is best suited for powering electric devices directly – without storing the energy into a battery first. That avoids charge and discharge losses (up to 30% in lead-acid batteries) and reduces the complexity and the costs of setting up a practical human power plant. For this purpose, our control panel has several 12V circuits and a 220V circuit.
Image: Some of the appliances that we tested: air compressor, lights, Peltier refrigerator, dot-matrixprinter, electric kettle, soldering iron.
Among the 12V devices that we powered directly are an experimental Peltier refrigerator, a water kettle, laptops – powered by a 12V adapter, and without battery or with the battery at 100% – lights, a soldering iron, a power drill, and a sander. Many more 12V devices exist, mainly aimed at truck drivers and car drivers, sailors, caravan dwellers (and low-tech tinkerers who wire their apartment as if it was a sailboat).
These are all the devices we have powered or charged so far:
- All types of USB devices (5V)
- Lead-acid batteries of different sizes (14.4V)
- Peltier refrigerator (12V)
- Electric kettle (12V)
- Soldering iron (12V)
- Corded power drill (12V)
- Corded sanding machine (12V)
- Air compressor (12V)
- Model railway (12V)
- Sewing machine (220V)
- Dot-matrix printer (220V)
- Stereo amplifier + cd-player (220V)
- Laptops (12V, 220V)
- Lighting (5V, 12V, 220V)
- Fans (5V, 12V, 220V)
Powering the lights is often more practical with a battery because that allows you to enjoy lighting without having to pedal at the same time. However, it’s perfectly doable to read a book on the bike while providing the lights in real-time, especially in winter – it takes little effort, it’s healthier than sitting still, and it keeps you warm. Other appliances that are well suited for “direct drive” human power production are power tools and heating and cooling devices.
Although 12V power tools are widely used, they are almost always powered by lithium-ion batteries. You could recharge these batteries with human power. However, that will take a long time, is not much of a workout, and introduces significant energy losses. Therefore, it makes sense to convert these devices into corded power tools. In this way, you only need to produce power when you need it, with much higher efficiency. Furthermore, there is no more need to wait for batteries to charge – the tool is always ready to use.
Converting a battery-powered tool to a corded tool can be pretty straightforward. After removing the battery, locate the positive and the negative contacts and solder two wires to them. Note that you only get one chance to decide which one is positive or negative. For the power drill, this was very easy to figure out. For the sander, we asked advice because the wiring is more complicated. 12V power tools with missing or dead batteries sell cheap on the second-hand market.
A corded power drill is perhaps the most versatile tool. You can use it with a whisk (to beat eggs), a stiff brush (to remove paint or clean objects), a grinding wheel (to sharpen knives), or a polishing wheel (to make chrome or other metals and materials shine). Precision tools for jewelry or model making also combine well with direct pedal power. We are still in the early testing phase for converting and using corded 12V power tools.
Hand versus foot-powered tools
Compared to human-powered mechanical hand tools, human-powered electric equipment is less energy efficient. Going electric introduces extra energy losses – in the generator, the buck converter, the wires, and the drive train. However, this is more than compensated for by a more energy-efficient use of the human power source. Our legs are roughly four times stronger than our arms.
Going electric is also more ergonomic because it spares hand joints and muscles. Fixing dozens of screws by hand may be more sustainable than using a power drill, but it can ruin your wrist. A bike generator thus allows you to work faster and more ergonomically without relying on an external energy source. Mechanical hand tools keep some advantages: they are silent, more portable, and less energy-intensive to manufacture. A third option combines these advantages: pedal-powered mechanical equipment. However, it's challenging to build a compact stationary bicycle that can power many different tools. We designed the bike generator to be as compact and multifunctional as possible.
Power tools can have high power demands, but this should not stop you. The sander only needs 30 watts at most, but our power drill can demand up to 20A of current – which is too high for the bicycle generator and control panel (12V*20A=240W). However, the machine will rarely require that power unless you use it to drill through hard materials. The power demand of a power tool will increase whenever the torque increases, so you feel when the drill bit has gone through the material or when the screw has been fixed or loosened. You can handle the tool as precisely with your feet as you can with your hands.
Electric heating and cooling are energy-intensive. Alternatives, such as direct solar heat and fire, are more sustainable. However, heating and cooling can easily be included in your exercise routine and provide results. We apply this principle with an electric kettle and an experimental Peltier refrigerator. Both appliances are very well insulated. Consequently, converting human power into heat or cold becomes another form of energy storage – without all the drawbacks of batteries.
Electric kettles that run on grid power are often very powerful and boil water in a matter of minutes or even seconds. Boiling water using a bicycle generator will take a lot more time, but it’s perfectly possible. We acquired a commercial 12V electric kettle with a vacuum insulated reservoir of one litre. During a test, boiling water for one cup of tea took slightly over one hour at an average power production of 60 watts.
The electric kettle can also prepare hot water bottles for thermal comfort. That requires more water than a cup of tea, but with a lower temperature of around 60 degrees celsius. During a test, heating one litre of water for a (small) hot water bottle took 1 hour and 30 minutes at an average power production of 60 watts. Following this effort, the last thing you need is a hot water bottle. Stronger still, during that effort, you are a space heater with an output of several hundreds of watts, and you may be able to increase the air temperature in a small room. However, the vacuum insulated kettle can be put into a fireless cooker and used up to 24 hours later when you are inactive and need warmth.
Commercial 12V refrigerators are expensive. After researching thermoelectric generators (TEGs), the idea of a Peltier refrigerator was born. A Peltier refrigerator is essentially a well-insulated fireless cooker with a TEG mounted on top. If power is applied, the module will get hot on one side and cold on the other, cooling the box interior. TEG cooling is not particularly efficient. However, it's silent, works without problematic cooling gases, and is the easiest way to make a refrigerator yourself.
The TEG refrigerator is an early prototype, which needs further testing and improvements. Powering one TEG at full power requires roughly 60 watts (12V*5A), measured right after the generator. That is a good workout, and the dimmer allows to lower the resistance at the pedals precisely. However, it quickly became apparent that one TEG is not enough for the size of the cooling space. We will add a second one for a heavier workout (60-100 watts).
Mains Appliances (220V)
Our dashboard also includes a 220V circuit. That makes it compatible with grid-powered devices (110V in the US, 240V in the UK). The 220V circuit requires an inverter. The inverter is too large to include in the dashboard, so we placed it in a box on the luggage rack that we built in front. A 220V socket is not necessary. Many 220V appliances have 12V (or 24V) alternatives which are more energy efficient for decentralised power production. However, we included a 220V circuit for powering devices that have not (yet) been replaced by or converted to low voltage alternatives: the dot-matrix printer, the sewing machine, the stereo system, and the router.
The dot-matrix printer and the sewing machine are challenging to operate because of their rapidly changing power demand. For example, to avoid the voltage dropping below 12V at high power peaks while printing, you need to pedal very fast (around 20V) to provide sufficient inertia to the flywheel. A supercapacitor may be able to solve this — this is something we will try in the coming months. A foot-powered mechanical sewing machine and printer would be much more energy-efficient — but much less space-efficient.
The control panel is designed to power a wide diversity of devices, but you can follow a similar approach with different results. For example, if you only want to charge lead-acid batteries, one 14.4V circuit is enough. You can use a buck and boost converter to create any voltage you need, for example, to build a 3V, 6V, 9V, or 24V circuit.
However, if you mainly want to run 24V appliances, it’s a better idea to adjust the gear ratio. Same if you only want to charge 14.4V lead-acid batteries on a 12V system: adjust the gear ratio to generate 16-17V (to compensate for energy losses in the buck converter). How to do this is explained in the manual.
Images: The luggage rack that holds the inverter, the wind charge controller, the lead-acid battery, and the power outlets.
Our choice to have a large dashboard on the handlebars has advantages and disadvantages. To have the control panel on the bike itself makes it easy to read and manipulate. It also makes the bike generator portable. If the neighbour needs emergency power, you pick up the bike, and you are there in a minute. On the downside, having the dashboard on the bike adds vibrations, which increase noise and energy losses. It also makes it necessary to adjust the voltage output from the buck and boost converters from time to time.
Most importantly, having such a large control panel on the bike prevents you from placing a large desk on top of the handlebars instead. That could be useful to operate power tools or a laptop while simultaneously providing power. Our present set-up is not ideal for using power tools. It requires two people - one to cycle and one to operate the power tool. Likewise, you can power another person’s laptop, but you can’t power yours while using it.
We plan to build a bike generator with a smaller dashboard -- one 12V circuit and two USB ports -- and a large workspace on the handlebars. Such a bike generator harks back to similar (mechanical) bicycle machines from the early twentieth century. Another option is to screw the control panel to the wall or put it on a shelf -- and place the bike generator next to it. The inverter, lead-acid battery, and wind charge controller – now on the “luggage rack” – can also move away from the bike.
Some of you may think that our bike generator is more of a gimmick than a practical power source for the household. In part, this is true. Our human power plant is the perfect exercise machine – power production is motivating. It is also practical in emergencies, especially if enough people power is available – it can produce up to 2.4 kWh per day. However, it won’t provide enough energy daily – not even for a low-tech household. In practice, there are not enough people willing to cycle.
On the other hand, a bike generator is an excellent addition to an off-the-grid solar PV system, at least in a low-energy household. The power output of the bicycle generator does not depend on the weather, the seasons, or the time of day. Human power can provide extra energy during bad weather, which reduces the need for expensive and unsustainable batteries. That is especially useful in winter, when the solar PV system produces much less power, and when the effort required to operate the bike also keeps you warm. There is enough solar power in summer -- when it’s often too hot to use a stationary bicycle.
Image: The bike generator stands right next to the solar PV systems. The ultimate plan is to integrate both power systems.
With a power production of 50-100 watts, the bike generator is more powerful than the two solar panels that are standing on the balcony next to it: the 50 watts solar panel that is powering the lights in the living room and the 30W solar panel that runs the solar-powered website. The solar panels rarely – if ever – reach their maximum power production, and during bad weather, they produce much less power than the bike generator. With dark clouds overhead, energy production almost drops to zero, and if this lasts for two days, the lights and the website go down. One or two hours per day on the bike generator could fix this. Alternatively, pedal power could operate power tools or other devices without draining the energy storage from the solar PV system.
It's also possible to use the dashboard with a solar panel instead of a bike generator. It suffices to replace the wind charge controller with a solar charge controller. You can then use solar energy to power devices directly -- without necessarily using a solar charge controller and battery. Replace the wind charge controller with a hybrid solar/wind charge controller, and you can use both energy sources to charge batteries and power devices directly. Solar and human power can also be combined, increasing the power output.
Combining solar and human power should make it possible to take further steps towards an off-grid urban household. The plan is to add another 50W solar panel, take more devices off the grid (most notably the refrigerator) and keep the battery storage as it is.
Image: the friction drive.
To convert the mechanical energy of the flywheel into electricity, you need a 12V/24V permanent magnet DC generator with a maximum power output of about 150-250 watts. Not any generator will do. You need one that runs at a relatively low speed (<5000 no-load rpm) to obtain 12 or 24V with a practical gear ratio (see further). Many generators need to run at higher speeds to generate 12V or 24V, and you won’t be able to produce more than a few volts at an average pedalling rate.
Be sure to get a brushed DC motor. Brushless DC motors won’t work because they need a very high rotation speed. Note that a generator is a motor working in reverse. When searching online, “DC motor” will give you more results than “DC generator”. Car alternators also work, and many pedal power plants use them because they are cheap and easy to obtain. However, they are very inefficient and require a 9V battery to start.
You can scavenge DC generators from discarded electric scooters or bicycles, but we bought a brand new one: the Ampflow Pancake Motor P40-250. It has a no-load RPM of 1700 at 12V and a maximum power output of 250 watts. You can tighten it securely to a metal or wooden surface, which saves a lot of trouble.
The voltage created by the generator is directly proportional to the rotating speed of the generator (the RPM or “rounds per minute”). However, the rotating speed of the generator is not a given. It depends on how fast you pedal (the RPM of the pedals). It also depends on the gear ratio between the pedals and the generator. The average RPM of the pedals on a stationary bike – a comfortable pedalling rate that you can sustain for a long time – is roughly 60 RPM. It can be calculated precisely by a tachometer or using low-tech tricks. 
Our bike generator uses a friction drive. It consists of a small wheel (the spindle) attached to the generator shaft that will spin in contact with the flywheel. Calculating the gear ratio involves measuring the outer diameter of four parts: the pedal sprocket, the flywheel sprocket, the flywheel, and the spindle. The first three are known, while the latter was for us to figure out. The spindle size you need depends on the specifications of your generator and on the exact voltage that you would like to produce. Figuring this out can be mind-boggling unless someone provides you with the right formula (thank you, Gabriel Verdeil!).
First, you need to find the “no-load RPM” of your generator. This information should be provided by the manufacturer. Our generator has a no-load RPM of 3400 at 24V. This ratio is proportional -- you can calculate the required no-load RPM for any voltage you want. For example, at 12V it’s 1700 RPM (3400/24*12), and at 16V it’s 2267 RPM (3400/24*16). Next, measure the outer diameter of the pedal sprocket, the flywheel sprocket, and the flywheel. Whether you use mm, cm, or any other unit doesn’t matter but be consistent. Now you have all the data you need to calculate the spindle size. Below is the formula, followed by the calculation for our specific case (assuming 60 RPM at the pedals):
Spindle diameter = (PS*W*RPM pedals)/(WS*RPM generator)
- PS = pedal sprocket diameter
- W = flywheel diameter
- RPM pedals = how fast you pedal
- WS = flywheel sprocket diameter
- RPM generator = the no-load RPM of the generator
Spindle diameter for our configuration (in mm) to produce different voltages:
- 12V = (190*525*60)/(60*1700) = 58.68mm spindle diameter.
- 13V = (190*525*60)/(60*1842) = 54.15 mm spindle diameter.
- 14V = (190*525*60)/(60*1983) = 50.30 mm spindle diameter.
- 15V = (190*525*60)/(60*2125) = 46.94 mm spindle diameter.
- 16V = (190*525*60)/(60*2267) = 44.00 mm spindle diameter.
- 17V = (190*525*60)/(60*2408) = 41.42 mm spindle diameter.
- 24V = (190*525*60)/(60*3400) = 29.34 mm spindle diameter.
The exact voltage you need – and thus the exact spindle size – depends on what exactly you want to do with the bike. We address this in detail in the manual for the control panel. Imagine you want to charge lead-acid batteries (which require 14.4V). You use a buck converter (which steps down the input voltage), so you will need to produce close to 17V to make up for the losses in the voltage conversion. That results in a spindle diameter of 41.42mm. This configuration shows in the illustration below.
You can use the formula in different ways. You can use it to calculate the minimum RPM at the pedals for a given spindle; to calculate the generator RPM based on a given RPM at the pedals and spindle size; and to calculate the voltage that will be produced by a given configuration. Find the formulas below, followed by an example based on the configuration illustrated above:
Calculate the minimum RPM at the pedals for a given spindle size (S):
- RPM generator/[(PS*W)/(FS*S]
- 2260/[(190*525)/(60*41)] = 55.81 RPM at the pedals.
Calculate the generator RPM for a given spindle size and RPM at the pedals:
- (PS/FS)*(W/S)*RPM at the pedals
- (190/60)*(525/41)*55 = 40.61 (gear ratio)*56 = 2274 RPM
Calculate the voltage for a given RPM at the generator:
- Generator RPM*No load RPM ratio
- 2274*(3400/24) = 16.1V
Figuring out the spindle size is only half of the work. It can be challenging to find a spindle with the correct diameter, made from the required materials, and compatible with the generator shaft. We tried a dozen spindles until we got the right one. A flywheel has a hard surface and requires a soft spindle made of rubber or polyurethane. We found that a solid metal and rubber buffer allowed optimal friction with our flywheel. We took it to a metal workshop where they drilled a 10 mm hole into the piece.
Image: A sample of our test spindles.
Other options are small solid polyurethane wheels and rubber suspensions. Skate wheels have a larger inside diameter which is not ideal for an 8-10mm shaft. Be careful to choose a material that can handle friction: some plastic tends to heat up and melt. Keep in mind: this is a trial and error process. You won’t get this right from the first time. Another route you could take is to design a custom lathed piece, as is described in magnificientrevolution.org’s tutorial. A universal mounting hub can help attach wheels featuring bolt holes, such as robot wheels.
Buying a DC generator with a pre-installed spindle seems the easiest solution. For example, Pedal Power Generator offers a 360W generator with a spindle size of 37.5 mm. However, you can’t choose a spindle with a different diameter. That means you cannot control the output voltage unless you replace the sprockets in the bicycle drive train. In our case, a 37.5mm spindle would produce 18V, which is too much.
The generator comes with an integrated sprocket or pulley drive. You need to remove it to attach the spindle. A nylon lock nut with a reverse tread holds the sprocket or pulley drive. You need to unscrew it to the right. You probably need a clamp to manage this. Our generator features an 8 mm shaft, while our spindle fits on a 10 mm shaft. Therefore, we use a two-part spindle featuring a “shaft arbor” and a wheel. To properly attach the spindle, you can take advantage of the D-cut on the shaft (a “round shaft with drive flat”). Our first try was a threaded fixation, but that did not work. Because of the reversed thread, it will come loose when the generator starts spinning.
Image: the generator with a threaded shaft arbor.
Image: The generator with the 41mm spindle.
We found that a threaded shaft arbor with set screws was the most versatile solution to test different wheels. We fixed the shaft arbor with grub screws placed on the flat section of the shaft. It’s an M10 threaded rod. You can secure a wheel on it with a couple of washers and a nut. A Bore Rigid Coupling could also serve as a small spindle. You can also use it to attach the generator’s shaft to another axle with a wheel. However, we found this was not ideal for our setup because the set screws stick out of the coupling, damaging the flywheel.
We screwed the generator to a wooden board and then pressed it against the flywheel using a wood support structure. The board is attached to the bike with a strong door hinge. That allows adapting the angle at which the spindle is in contact with the flywheel. The stand is resting on a cork wedge that buffers the vibrations. See our first prototype for another method.
Image: the friction drive.
Buck converters and boost converters are electronic modules that convert a fluctuating voltage input into a steady voltage output. Buck converters have a higher input voltage than the output voltage (they step down the voltage), while boost converters have a higher output voltage than input voltage (they step up the voltage).
You can adjust the output voltage by turning a tiny screw on the module. Some buck and boost converters come with a small digital screen that shows the output voltage. If this is not the case, you can use a multimeter to adjust the voltage output.
Note that you need either a buck or a boost converter. Do NOT use a buck/boost converter. This is a sort of micro bench supply that requires the output voltage to be adjusted every time the system is powered up. This is unpractical and risks damage to your appliances. In contrast, a buck or boost converter remembers the output voltage whenever you start it up.
Also, do NOT buy a voltage regulator. This device allows you to regulate the output voltage but only in relation to the input voltage. If the voltage input changes, so will the voltage output. You want a buck or boost converter, in which the voltage input can fluctuate but the voltage output is stable.
Finally, you should check the maximum current rating before buying a buck or boost converter. Some only take 2A, which is not powerful enough for a bike generator. You need at least one that can take 5A and preferably one that can take 10A or 15A, depending on your power output.
Buck or boost converter?
Whether you opt for a buck or a boost converter depends on the voltage produced by the generator -- and by the voltage of the device(s) you want to power or charge. If the bike generator puts out 12V and you want to charge 5V USB devices, you need to step down the volume and thus use a buck converter. These small modules with a USB connector convert a fluctuating voltage input into a steady 5V voltage output. 
If you want to power 12V devices or recharge lead-acid batteries (14.4V), both a buck and a boost converter could work. If you opt for a buck converter, the bike generator needs to have a voltage output that is slightly above 12V or 14.4V (13-14V and 16-17V, respectively). This higher input voltage is necessary to compensate for energy losses in the power conversion. If you use a boost converter, the voltage output of the generator needs to stay below 12V or 14.4V.
A buck converter will never exceed the chosen voltage output, no matter how many volts the generator produces. In contrast, a boost converter guarantees you a minimum voltage output, but it does not set a maximum output voltage. If you pedal too fast, the voltage output may exceed the set voltage output and damage the appliance or battery you are powering or recharging.
For our first dashboard prototype, we used only buck converters. We used a boost converter to charge lead-acid batteries for the next version. The generator needs to produce 16-17V to obtain a voltage output of 14.4V with a buck converter. That is fine if you only want to charge lead-acid batteries because you can then adjust the gear ratio to produce 16-17V at a comfortable pedalling speed. However, if you optimize the gear ratio for lower voltages, you have to pedal very fast whenever you include the charging of batteries in your workout.
The bike generator needs to supply 14.4V to charge lead-acid batteries -- the maximum voltage that a lead-acid battery needs. In principle, all you need is a buck or boost converter, but there’s one caveat: you may overcharge the battery, which can lead to an explosion. You can avoid this risk in a low-tech way – by keeping an eye on the amperemeter. Once the current drops to 3% of the rated storage capacity of the battery (in Ah), the battery is fully recharged -- and you should stop pedalling. Because you are the power source and thus certainly present and awake, this approach is less risky than charging a lead-acid battery from a DC power supply or a solar panel without a charge controller.
However, it’s a good idea to add more security. A solar charge controller provides this security in a solar PV system. It cuts the power input whenever the voltage rises above 14.4V. However, a solar charge controller does not work when coupled to a bike generator. Instead, you need a wind charge controller, which operates the other way around. Instead of cutting the load to zero, a wind charge controller suddenly increases it and “brakes”. If you use a buck converter, the wind charge controller will rarely activate the break because the buck converter will limit the voltage output to 14.4V. It will only brake when you threaten to overcharge the battery. If you use a boost converter, the wind charge controller will brake whenever you accidentally exceed a voltage output of 14.4V.
Wind charge controllers have three green wires to connect to the power source. You can take any two of these three wires and connect them to the plus and the minus of the power input – it doesn’t matter which goes where. Most wind charge controllers commercially available are way too powerful for a pedal power generator, so get the smallest one you can find. We sent two charge controllers back to the manufacturer. One wind charge controller with a screen came without a manual, and nobody could figure out how it works. The only hybrid wind/solar controller that we tried, for now, was dangerous. The solar panel overcharged the battery. It also maintained the electric brake for half an hour whenever we crossed the threshold, thus blocking human power production.
You need wires, connectors, diodes, fuses, and on-off buttons to connect everything. All these parts can confuse you, so here’s what you need to know.
Wires. The control panel includes roughly ten meters of electric cable. However, the main thing to worry about is not the length but the thickness of the cable. Opt for too thin wires, and your dashboard may catch fire during a heavy workout. Making the right choice can be confusing because there are several standards. We wired the dashboard with a 20AWG 0.52mm2 cable, which takes 11A. A better option would have been an 18AWG 0.82mm2 cable, which takes 16A. Take care when stripping the wires: if you cut too deep the cable can take less current.
Connectors.Wires can be connected using very different methods. We choose lever connectors — bulky and expensive but handy. They help to connect wires securely without soldering or screws. These connectors come with two to ten pins. Wiring the dashboard can become disorderly. Make sure you don’t cut the cables too short.
Fuses.You can build a bike generator and controller without fuses, but it’s not a good idea. A fuse will break the electric circuit when you exceed a current threshold, preventing fire and damage to components. We placed a 12A fuse at the entrance of the dashboard (our max power production is 8-9A). We also added fuses to most of the devices we power.
On-off switches. Switchable circuits require on-off buttons. Our dashboard has nine of them. We wanted switches that light up when active because that quickly shows which electric circuits are in operation when starting the pedal power generator. However, lights make wiring the on-off switches more complex.
We bought switches with the wires already attached because we preferred not to solder the connections. However, we had to solder them anyways because the thick wires took too much space. On-off buttons without lights and with prefixed thinner wires simplify this part.
Schottky Diode. A Schottky diode ensures that the current can only flow in one direction through a cable. This tiny part is essential when there are batteries attached to your system. Without a diode, the battery could power the generator (and turn the pedals) instead of the other way around. We put a Schottky diode right after the generator to prevent this. It needs to be rated for the correct amperage: above your expected power production. Our maximum power production is 8-9A, the Schottky diode takes 10A.
The control panel includes several displays that show the voltage and current in different electric circuits. The analog volt- and amp meter on top is the most important one. It shows how much power the generator is producing (V*A=W). The voltmeter tells you how fast you are pedaling, the amp meter how hard you are pedaling.
Analog V&A meters are most precise in the middle of their range, so we choose a voltmeter that goes up to 30V and an amp meter that goes to 15A. A digital V&A meter is more compact, but analog meters display variations better. Above the meter, there is a USB circuit to plug in a small LED light. That allows you to keep an eye on the V&A meter when dark. It’s also handy to quickly check if the system is working.
Image: how to wire the analog voltmeter and ammeter.
Below the V&A meter are three voltage meters for every buck and boost converter. These show the voltage output for each of the circuits. The voltage output should be 12.0V for the 12V and 220V electric circuits and 14.4V for the 14.4V circuit. The first two may fall below that value if you don’t pedal fast enough, while the last one may go above that value if you pedal too quickly -- the wind charge controller will also make this clear to you). There is also a voltage and current meter on the 5V circuit. That helps to maximize power production by adding as many USB devices as possible (up to 2A).
Two more instruments are not on the dashboard itself: the voltage meter of the lead-acid battery and the temperature meters of the electric kettle and the Peltier refrigerator. None of these are essential. However, they can motivate the power cyclist. On the road, your efforts result in distance covered. Stationary cycling can be boring -- you are not going anywhere. The instruments help you to set goals. For example: let’s get the refrigerator temperature down by 2 degrees C before you take a shower.
We attached the control panel to the handlebars and added a luggage rack in front that holds extra parts such as an inverter, a wind charge controller, and a lead-acid battery. On top of the box are the power outputs for each circuit and a USB distribution hub. The box has an open lid and holes for the dashboard’s cables to pass through (they first go inside the handlebar).
We used a laser cutter at a maker space (MADE Barcelona) to produce the panel. All components are fitted in or sandwiched between two layers of 4mm MDF. You can easily remove the front panel if something needs to be changed or repaired. A transparent acrylic plate protects the buck and boost converters. You can take it off to adjust the output voltage. We attached the dashboard to the bike handle with rubber pipe clamps, M8 cap nuts, and bolts.
1: Schottky diode. 2: Fuse. 3: Cables. 4: Analog ammeter and voltmeter. 5: On/Off switches. 6: Wire connectors. 7: USB Led Light.
8: USB Buck converter. 9: USB Voltmeter & Ammeter. 10: USB Multi-plug and cable.
13: Boost converter. 14: Wind turbine charge controller. 15: Lead-acid battery. 16: Battery electronic voltmeter.
17: Buck Converter. 18: Inverter.
- Motor (x1). Ampflow P40 - 250W Pancake DC. Brushed Motor 24-12V https://www.ampflow.com/motors/pancake/
- Shaft arbor (x1). Threaded Shaft Arbor conversion from 8mm to M10.
- Wheel (x1).
- Schottky diode (x1). BOJACK Diode Schottky 10SQ045 (10A 45V)
- Fuse (x1).
- Analog ammeter (x1). Analog Ammeter DH-670 0-5A Class 2.0 & Analog voltmeter (x1) — Analog Voltmeter DH-670 DC 0-30V Class 2.0
- On/Off LED Switch (x8) — KR1-5 Series Rocker ON/OFF Switch 12V 20A 3 pins with LED
- Wire Connector (≈16 of different formats)
- 5V USB Led Light. Any USB flexible arm LED light will do.
- 5V Buck converter (x2). Buck Converter MH KC24 DC-DC 24-12V Charging Step Down to 5V USB with Fast Charging Protocol.
- 5V USB Voltmeter & Ammeter.
- 5V USB Multi-plug.
- 12 V 5A Buck Converter (x1). Buck Converter DC-DC Adjustable 12-24-36V 5A
- 12V DC Socket (x1). RUIZHI DC 12V waterproof Female Car Cigarette Lighter Socket
- Boost Converter (x1).
- Wind turbin charge controller (x1) — Asixx Waterproof Wind Charge Controller 24-12V 300/600W
- Battery Electronic Voltmeter.
- 12V 15A Buck Converter (x2, one is for our test circuit) — Buck Converter 200W 15A DC 3-60V to 1-36V step-down adjustable voltage regulator synchronous rectifier module.
- Inverter (x1) — 300W or less Inverter DC 12V to AC 220-240V (Any with these specifications will do)
- M3 Bolts. They fit with the electronic components to secure them to the dashboard.
- M6 Bolts. To attach the motor to the wooden board.
- M8 Bolts. To attach the two parts of the dashboard.
- Big door hinge. To attach the motor at an angle.
- Metal mounting brackets (all sizes and shapes). To strengthen the structure.
- Rubber metal clamps. To attach the dashboard to the bike handle.
- Wood glue, screws (all sizes), bolts, washers and nuts (normal, lock, rounded, wing-shaped),
- wooden cleats and boards, black acrylic paint, etc.
We only include the components we effectively used:Generator
- Vintage exercise bike (second hand): 60 euro
- Generator: 60 euro
- Arbor shaft: 10 euro
- Spindle: 3 euro
- Total: 133 euro
- Wires: 17 euro
- Connectors: 25 euro
- Analog volt meter: 9 euro
- Analog ampmeter: 9 euro
- On-off buttons: 20 euro
- Diode: 1 euro
- Fuse: 1 euro
- Total: 82 euro
- 5V USB buck converter (2x): 8 euro
- 5V USB V&A meter: 8.50 euro
- USB distribution hub: 30 euro
- Total: 46.5 euro
- 12V 5A buck converter (2x): 24 euro
- 12V 5A boost converter: 8 euro
- 12V 15A buck converter: 25 euro (extra circuit we added later)
- Dimmer: 7.50 euro
- Total: 64.5 euro
- Inverter: 50 euro
- Battery (14Ah): 31 euro
- Wind charge controller: 34 euro
- Total: 115 euro
- To fix the dashboard and the generator: +/-30 euro
- Grand total: 471 euro
All components used must sustain the power that goes through it. The voltage is usually not a problem, but you have to watch the amperage. Power production was limited to 60 watts (12V, 5A) — but that was before we thoroughly cleaned and oiled the bike drive train. After cleaning, we discovered the bike could produce almost double that power (12V, 8-9A). That required us to make some updates.
Components get more expensive as their maximum rated amperage increases. For the 12V, 220V, and 14.4V, we stuck to a limit of 5A. Although the bike generator can produce more power, we usually combine several circuits — each limited to 5A. We added an extra 12V circuit with a 15A buck converter and thicker wires to run a more powerful appliance. This circuit bypasses the dashboard entirely. We plan to move this to the unregulated electric circuit on the dashboard (and upgrade the wiring).
- Cables: 11A, 18A for the extra circuit
- USB buck converters: 2A
- 2x Buck converters: 5A
- 1x Buck converter: 15A
- Boost converter: 5A
- On-off switches: 20A
- Diode: 10A
- Fuse: 12A
- Connectors: 20A
- Wire cutter
- Tiny screwdriver (to adjust voltage output on buck and boost converters)
- Calculator, multimeter, tachometer
- Soldering iron. We soldered the on/off switches and the two USB buck converters. However, this can be avoided. Switches can be bought prewired and there are alternative options for the USB converters.
- Wood saw: to make the luggage rack
- Metal saw: to cut custom threaded rods
- Drill: to mount the luggage rack and the dashboard
- Wrench socket set: very handy when working on a bike.
The control panel can take different forms and use other tools and materials. We first built a proof of concept with scrap wood and Meccano then strapped it to the handlebars with iron wire and some wooden blocks.
Initially, we screwed the generator on a large wooden board and put the bike on top. We made holes in the board for the four legs so that the bike was always right where it had to be. This set-up worked and was handy to try out different spindle sizes, but it takes much more floor space than our final configuration.
We welcome technical feedback concerning further improvements.
Kris De Decker, Marie Verdeil.
Special thanks to Adriana Parra, Eris Belil, Gabriel Verdeil, and Manvel Arzumanyan.
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One exception, though. We had to remove the friction roller and screw that adjusts the resistance on the pedals of the exercise bicycle. We cut this part with a small metal saw.
It’s important that your saddle is at the correct height to maximize power production. The saddle on our bike is too low. We need to find a longer seat post.
The resistance on the pedals depends on the device that you are powering. If you are charging a smartphone, then you will only be able to produce a few watts – as much as the smartphone needs. Therefore, to find out the maximum power output of a bike generator you need an appliance or multimeter that is more powerful than yourself. We did the test with an electric air compressor.
To calculate the RPM at the pedals cycle for 15 seconds and count the number of complete pedal turns (the left or right pedal takes a complete turn). Multiply this number by four.
There are many other types of USB connectors but those require a steady 12V input.
Imagine a personal heating system that works indoors as well as outdoors, can be taken anywhere, requires little energy, and is independent of any infrastructure. It exists – and is hundreds of years old. The hot water bottle could save a great deal of energy and money without sacrificing thermal comfort.
Hot water bottles work both indoors and outdoors. Illustration: Marie Verdeil.
A hot water bottle is a sealable container filled with hot water, often enclosed in a textile cover, which is directly placed against a part of the body for thermal comfort. The hot water bottle is still a common household item in some places – such as the UK and Japan – but it is largely forgotten or disregarded in most of the industrialised world. If people know of it, they usually associate it with pain relief rather than thermal comfort, or they consider its use an outdated practice for the poor and the elderly.
Nevertheless, when I sent two dozen hot water bottles to friends and family as a Christmas present, the reactions were almost unanimously enthusiastic. People show themselves very much surprised that such a humble object can provide so much comfort. Because I don’t have the time nor the budget to send hot water bottles to everyone, I have written this article. It’s largely based on my personal experience – I have been using hot water bottles for many years and they are the only heat source in my apartment.The history of the hot water bottle
Croation inventor Eduard Penkala patented the rubber hot water bottle – which he dubbed the “Termofor” – in 1903. However, it did not come out of nowhere. In fact, the history of the hot water bottle goes back thousands of years, albeit in different guises.
Rubber hot water bottle, made in Germany (1925-35). Source: Museum Rotterdam.
The first “hot water bottles” – quite literally – were other people and animals. Since time immemorial, people have warmed themselves by huddling together. For example, it was common for the whole family to sleep together in the same bed – and this included potential visitors.  People also took advantage of the heat from animals – “hot water bottles” with a standard fur cover.
They snuggled up against cows and pigs, which were either sharing the living space or lived in the stables below it. In the eighteenth century, wealthy women kept specially bred “hand dogs” – toy poodles – around to keep their lap and hands warm.  Personal heating devices also took the form of objects – stones, bricks, potatoes – that were heated in or near the fire, wrapped in cloth or paper, and kept in people’s laps, in pockets, or in the bed.
As early as the 1500s, people started to use all kinds of portable containers filled with hot coals from the fire. These were used as foot warmers, hand warmers, and bed warmers.  Most were made of metal, either brass or copper, and placed inside wooden or ceramic enclosures to prevent skin burns. Over time, hot coals were replaced by hot water, which is a cleaner and safer heat storage medium.
Initially, these first “real” hot water bottles were made from hard materials such as glass, metal, or stoneware. It was only with the invention of vulcanised rubber in the nineteenth century that more comfortable lightweight and flexible hot water bottles became an option. Spanish friends told me that hot water bottles used to be made from animal skins, but I could not verify this. It may well be true, because all over the world there’s a long tradition of using “water skins” for storing liquids.
An example of a hot water bottle in common use in households in the mid 20th century before the use of rubber ones (1940s, Melbourne, Australia). Source: Victorian Collections. https://victoriancollections.net.au/items/5a2622e921ea6a17dcba0799
A foment can is filled with hot water and used very much like a hot-water bottle to apply warmth to the body. Fomentation actually means “to apply warm liquids to treat the skin.” This oval-shaped can is curved to fit the body. Maker: Kenworthy Son and Company. Place made: Southport, Sefton, Merseyside, England, United Kingdom. Source: Science Museum, London. (CC BY 4.0). https://wellcomecollection.org/works/gf42542b
Hexagonal hot-water bottle, Austria, 1791-1798. This hexagonal hot-water bottle is made of pewter and is engraved with a forest scene. Source: Science Museum, London. (CC BY 4.0). https://wellcomecollection.org/works/b452vwjm
This foot warmer was used to give warmth and comfort to patients who were resting in the hospital wards. Made from tinned iron, the warmer would have been filled with hot water and secured with a cork. This copy was made in 1927 to commemorate one hundred years since Joseph Lister’s birth. Place made: Glasgow, Glasgow, Scotland, United Kingdom. Source: Science Museum, London. (CC BY 4.0). https://wellcomecollection.org/works/mfjujndv
French foot warmer, date unknown. Source: Musée Départemental Albert DemardHot water bottles today
The classical hot water bottle for sale today is either made from rubber or PVC plastic. The latter material has few advantages. It’s often a bit cheaper and can be made transparant, but unlike rubber it contains toxic chemicals (which make the plastic flexible). A third option – a bit harder to find – are plastic hot water bottles without chemical softeners, which are rigid instead of flexible.
The distinctly shaped Japanese hot water bottle – the “yutampo” – is usually of that type. Its use dates back to the fifteenth century when it was made from metal or stoneware. Of course any sealable container can function as a hot water bottle. I have successfully used metal drinking bottles and even plastic PET-bottles – more about those later.
In spite of its dull image, the hot water bottle has seen some interesting innovations lately.
The typical hot water bottle has a rectangular shape and holds up to two litres of water. However, in spite of its dull image, the hot water bottle has seen some interesting innovations lately. A first novelty are much smaller rectangular bottles, which hold between 0.2 and 0.8 litres of water. Judging by their covers, these are mostly aimed at children, but they can be just as useful for adults who can carry them in pockets or put them inside clothing.
There are now also larger hot water bottles available, which hold up to three litres of water or more. Finally, the most successful novelty has the form of a hot dog: it’s a hot water bottle 80 centimetres long. It can be tied around the waist but is just as practical as a companion on the couch or in the bed. It can easily be shared by two people and its shape makes it luxuriously comfortable. It holds up to two litres of water.
Rubber and PVC hot water bottles. Image by Marie Verdeil.
Rubber hot water bottles. Image by Marie Verdeil.
A Japanese hot water bottle, or yutampo, made of hard plastic. Source: All About Japan. https://allabout-japan.com/en/article/6244/
The Japanese yutampo is still available in metal. Source: Maruka.How to use hot water bottles?
People who know hot water bottles usually think of them as bed companions. However, they can keep you warm wherever you are, throughout the day. This includes the sofa, of course, but you can also surround yourself with one or more hot water bottles when seated at a desk or a table. I use one, two, or exceptionally three hot water bottles simultaneously, depending on the indoor temperature. They usually end up in my lap, behind my lower back, and/or under my feet. Although only some body parts are directly heated, the warmth from the bottle(s) is distributed throughout the body by skin blood flow.
Hot water bottles can be combined with a blanket, which further increases thermal comfort. If I put a blanket over the lower part of my body when seated at my desk, it traps the heat from the bottles and keeps them warm for longer. Even better is a blanket with a hole in the middle to stick your head through – a basic poncho – or a blanket with sleeves. If it’s large enough, it creates a tent-like structure that puts your whole body in the warm microclimate created by the water bottles. Draping long clothes over a personal heat source was a common comfort strategy in earlier times.
A blanket traps the heat of hot water bottles. Illustration by Marie Verdeil.
You can go one more step further and put a large blanket over the desk or table and then put your legs underneath it. Such heating arrangements have been used in different parts of the world, usually with hot coals as the heat storage medium. Examples are the Japanese “kotatsu”, the Middle-Eastern “korsi”, and the Spanish “brasero de picon”. The first two are rather low to the ground – people sit on the floor – while the latter fits the common seat height in the Western world. It’s easy to build such a heating arrangement – and a few hot water bottles are the ultimate heat source for it.Hot water bottles outdoors & on the move
The arrangements described above only work for people who stay in one place. The need for an external heat source decreases when we move around and are physically active, because our body produces more heat. Nevertheless, hot water bottles can also keep you warm when you are standing up doing things or when you are moving through a space or a building. They can be worn underneath clothing or even put in specially designed pockets or backpacks. A small backpack holding a hot water bottle – positioned between the shoulder blades – also works great while sitting on a chair.
Hot water bottles provide thermal comfort with all the windows open. Illustration by Marie Verdeil.
Hot water bottles work both indoors and outdoors – provided that the body is protected from wind and rain – or indoors with the all the windows open. Modern central heating systems provide thermal comfort mainly by heating the air in a space, an approach that obviously won’t work well outdoors or in a well-ventilated indoor space. In contrast, hot water bottles transfer heat directly to people through physical contact (a heat transfer method called “conduction”). They heat people, not spaces. This makes hot water bottles a safe and sustainable alternative for terrace heaters in bars and restaurants. The investment is minimal: a collection of hot water bottles and a kettle – the water can be re-used over and over again. Alternatively, everyone could bring their own hot water bottle and fill it up on the terrace.
Hot water bottles are a safe and sustainable alternative for terrace heaters in bars and restaurants.
One could take this idea even further and envision a public infrastructure for refilling hot water bottles, not just on bar terraces but in multiple locations such as schools, offices, and public buildings.  People could gather around the hot water dispenser just like they gather around the water cooler. Historically, hot water bottles – and their predecessors using hot coals – were also taken out of the house. Their use was common in coaches and trains, as well as in churches, which were unheated. Smaller hot water containers with carrying strings and fabric covers were put into fur muffs or pockets. Nowadays, you could also store hot water in a vacuum flask and then pour it into a hot water bottle hours later.
Stoneware Queens Muff Warmer. Source: Antiques Atlas. https://www.antiques-atlas.com
Curved rectangular hot-water bottle, France, 1751-1810. Made of pewter, an alloy of tin and lead, this hot-water bottle is engraved with birds and plants and has a curved shape to fit close against the body. Source: Science Museum, London. (CC BY 4.0). https://wellcomecollection.org/works/g5ufhayn
Foot warmers on the floor of a railway carriage (1929). Source: The History Trust of South Australia.900 hot water bottles per day: energy savings
Unsurprisingly, there’s little – or actually no – academic research into the energy savings potential of hot water bottles. Instead, in recent years scientists have investigated more sophisticated personal heating devices such as electrically heated desks and seats, radiant heat bulbs, or battery-powered heat pillows. [5-7] These alternatives look needlessly complex in comparison to the hot water bottle. Water can be heated in many ways both high-tech and low-tech, and containers can be made from locally available materials.
Nevertheless, these studies show that personal heating sources with similar effects as hot water bottles could save a great deal of energy while maintaining and often even improving thermal comfort. For example, one study revealed that lowering the air temperature in an office from 20.5 to 18.8 C and giving employees a heated chair to compensate for the discomfort leads to 35% less energy use and consistently higher scores for thermal comfort. There are few interventions in the building envelope that can achieve such large energy savings for such a small investment, and yet the decrease in air temperature was far from radical in this experiment. If personal heating devices would be combined with a change in clothing insulation and/or blankets the energy savings could become much larger still.
Another way to investigate the energy savings potential of the hot water bottle is to calculate how much energy it takes to prepare one and compare that to the energy use of a central heating system. Because rubber or PVC bottles can only be filled up to two-thirds for safe and comfortable use, I assume a somewhat larger model – 3 L – which can hold two litres of water in practice. This makes the calculation also valid for containers that can be filled completely, such as the Japanese yutampo. It takes 4,200 joule to raise the temperature of 1 litre of water by 1°C, meaning that heating two litres of water from 10°C to 60°C requires 420 kilojoule or 116.7 watt-hours.
Advertisement for Westbrook & Thompson Ltd's 'Cosimax' hot water bottles, made with Dunlop rubber. 1938. Science Museum / Science & Society Picture Library. Source: https://www.ssplprints.com/image/95677/sleep-well-hot-water-bottle-august-1938
In comparison, the average household energy use for gas heating in Belgium – which has a moderate climate – is 20,000 kWh per year. Assuming that the average Belgian heating system is used for six months per year, daily energy use corresponds to 109.6 kWh per day. This energy could heat roughly 900 water bottles per day – enough to keep the whole neighbourhood comfortable. Imagine that four household members each use two hot water bottles simultaneously and reheat them every two hours throughout their waking hours (16 hours). Total energy use is then below 4 kilowatt-hours, almost 30 times less than the heating energy consumed by the average Belgian household.
This is not to suggest that hot water bottles need to replace a central heating system. The rather short and mild winters here in Barcelona allow me to use hot water bottles as the only heating system because it rarely gets colder than 12°C in my unheated apartment. In less hospitable climates, hot water bottles can be combined with a central heating system. The hot water bottles create islands of thermal comfort for low metabolism activities while the rest of the indoor space is comfortable to move through or be physically active in.Safety
Hot water is a safer heat storage medium than hot coals, but it is not without its risks and hot water bottles need to be used carefully. They carry the instruction not to use boiling water, which is very sound advice, but hot water doesn’t need to boil to be dangerous. Water above a temperature of 60°C can scald you and lead to very serious injuries. Therefore, it’s recommended to use only hot tap water, or any other hot water source below 60°C. This temperature is sufficiently high to make you comfortable and the only advantage of using hotter water is that you need to reheat it less often.
Too hot water can hurt you in several ways. First, there’s always a chance you spill water on your hands while filling the bottle. Second, a rubber or plastic hot water bottle can start leaking, either through the cap or through the seams. Third, and this is the worst-case scenario, a hot water bottle can burst and release two liters of hot water on your body. Such accidents are rare, because nowadays hot water bottles are made according to quality standards. However, they do occur, usually because the bottle has worn out.
Created by Don Poynter for his Poynter Products company, the Jayne Mansfield Hot Water Bottle hit the market in 1957. The Mansfield figure—in a pin-up pose with hands behind her neck and wearing a painted-on black bikini—is made of “blushing” pink–colored plastic with a screw-on “hat” cap and measures close to two feet head-to-foot. Source: https://vintagenewsdaily.com/at-the-height-of-her-career-in-the-1950s-jayne-mansfield-even-modeled-for-this-awesome-hot-water-bottle/
To safely use rubber or PVC hot water bottles at higher water temperatures, it’s important to replace them after a few years of use, and to store them properly. If you really want to use higher water temperatures, metal hot water bottles – inside a cover to prevent skin burns – are the safest option. However, if you keep the temperature below 60°C, the worst-case scenario is just getting wet. If you use PET-bottles, you should surely stick to this maximum temperature, because at higher temperatures they could melt. Furthermore, a PET-bottle should not be used for drinking after it has been used for heating, because the higher temperatures may release chemicals in the water.Water use & infrastructure
Hot water bottles also require a source of water. It’s possible to reheat the same water over and over again, thus limiting the water use to a few litres during the lifetime of the bottle. However, that’s not always the most practical solution. In modern households, hot water can be sourced from an electric kettle, a pot on the cooking stove, or the hot water tap. Although hot tap water is the safest source of water for a hot water bottle, once the water has cooled down there’s no way to get it back into the pipes for reheating. Furthermore, it takes time before the water comes up to temperature, meaning that more than two litres of water will be consumed.
Even a slightly lower shower frequency easily provides you with the water and energy for continuous hot water bottle use.
Using an electric kettle – or a pot on the cookstove – makes it easy to reuse the same water over and over again, but it faces some problems too. First, if your electric kettle does not come with a programmable water temperature, you need to make sure the water does not get too hot. I solve this by dipping the probe of a digital thermometer in the kettle while warming the water. Second, if you reheat the water from rubber bottles, the kettle (or pot) can no longer be used to heat water for human consumption because it will taste bad. So, either you use a separate kettle for use with hot water bottles, or you warm the water in the only household kettle and discard it after use.
Even if the water is not reused for other purposes (such as watering the plants) the waste is quite limited. The average shower consumes enough water to fill 37 hot water bottles. Likewise, the energy use of the average shower corresponds to the energy use for heating 17 hot water bottles (which use water with a higher temperature than a shower). Consequently, even a slightly lower shower frequency easily provides you with the water and energy for continuous hot water bottle use.
Stoneware hot water bottle (1901-1910). Source: Auckland War Memorial Museum
The use of metal and ceramic hand warmers has a long tradition in China and Japan. The Japanese offered guests a small roundish ceramic pot with fuel inside, called a “te-aburi”. Copper or bronze box-shaped hand warmers a few inches across, often with perforations and carrying handles, were called “shou lu” in China. Image in the public domain. Read more: https://homethingspast.com/2011/11/26/hand-warmers-muff-warmer/Cold water bottles
Hot water bottles can be used for cooling as well. In this case, they are filled with cold water or put in the freezer. Cooling people is much more energy efficient than cooling spaces. I don’t have air conditioning and rely entirely on fans and cold water bottles in summer, when temperatures are usually above 30°C. I use “cold water bottles” in a similar fashion to hot water bottles – they go into the bed, under my feet, or behind my back. For cooling I use plastic PET-bottles and metal drinking containers, not rubber water bottles as they get hard and brittle. Keep in mind not to fill the bottle completely – water expands when it’s frozen – and to put the bottle inside a protective cover to prevent iceburn. Also keep in mind that they will get a bit wet on the outside as the ice melts – although this effect only enhances the cooling. Like hot water bottles, cold water bottles work outdoors as well as indoors.
Kris De Decker
Proofread by Alice Essam
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 This custom was accompanied by strict rules. For example, male visitors ended up sleeping on one side of the bed, while the family’s daughters were on the other side. Source: Ekirch, A. Roger. At day's close: night in times past. WW Norton & Company, 2006.
 The “warming pan” or “bed warmer” was a metal container filled with hot coals and fitted with a long handle. It was slid between the bedsheets and then moved across the bed to warm all corners before someone got into it. Yet another solution to warm the bed was the so-called “bed wagon”: a wooden frame or sledge designed to hold a pot of hot coals, which was slid below the bed and covered with a metal sheet. Unlike a warming pan, the bed wagon provided warmth throughout the night. See: http://www.oldandinteresting.com/warming-the-bed.aspx
 Some cities had public hot water supply systems. For example, in the first half of the twentieth century, the Dutch city of Rotterdam counted hundreds of "water distilleries" where people came to fill buckets with hot water for domestic use. China has a long and continuing tradition of providing its citizens with hot water everywhere they go – mainly for drinking. By the 1830s, hot water stores – known as “laohuzao” or “tiger stoves” – popped up in major cities all over the Yangtze river delta. Today, almost every government body, business and school administrative office in China has hot water dispensers – even high speed trains have them. Read more: https://www.sixthtone.com/news/1000919/the-history-behind-chinas-obsession-with-hot-water
 Verhaart, Jacob, Michal Veselý, and Wim Zeiler. "Personal heating: effectiveness and energy use." Building Research & Information 43.3 (2015): 346-354. https://www.tandfonline.com/doi/abs/10.1080/09613218.2015.1001606
 Deng, Qihong, et al. "Human thermal sensation and comfort in a non-uniform environment with personalized heating." Science of the total environment 578 (2017): 242-248.
 Mishra, A. K., M. G. L. C. Loomans, and Jan LM Hensen. "Thermal comfort of heterogeneous and dynamic indoor conditions—An overview." Building and Environment 109 (2016): 82-100. https://www.sciencedirect.com/science/article/pii/S0360132316303560
The printed archives of Low-tech Magazine now amount to four volumes with a total of 2,398 pages and 709 images. All books are printed on demand.
The newest Low-tech Magazine book collects 18 articles published between 2018 and 2021. At 368 pages it’s a thin book compared to earlier volumes. When we started the book series, the challenge was to unlock an archive of almost 12 years. It made sense to pack this content into as few volumes as possible.
However, looking ahead, we will publish more often, once every one to three years, depending on the number of articles written. From now on, the articles will be arranged chronologically, from oldest to newest, and no longer the other way around. This volume contains 184 images in black and white.Low-tech Magazine: The Comments
We also launched a book which collects almost 3,000 comments on the roughly 100 articles which are published in the three other books. This volume has 688 pages and no images. We included all feedback up to November 7, 2021. Read more about the comments book here.
Over the years, readers have often stated that the comments on the website are (at least) as interesting as the articles themselves. We agree. Low-tech Magazine would not have been even half what it is now without the comments. You can even take this literally, because this is one of the thickest books we have published so far, despite the extra small font we use.New Edition
Finally, we have published a second edition of the first book we published in 2019. This new edition has almost twice as many images and follows the same design as the other volumes. In contrast to the first edition, the images are not "dithered" and of higher quality. We use a smaller font to pack more content on fewer pages. This second edition also fixes some errors in the articles and the references.
The printed archives of Low-tech Magazine now amount to four volumes with a total of 2,398 pages and 709 images.
- Low-tech Magazine Volume I (2007-2012).
- Low-tech Magazine Volume II (2012-2018).
- Low-tech Magazine Volume III (2018-2021).
- Low-tech Magazine: The Comments (2008-2021).
Around the 17th century, the Dutch started reinforcing their dykes and harbours with sturdy mats the size of football pitches – hand-woven from thousands of twigs grown on nearby coppice plantations. These “fascine mattresses” were weighted with rocks and sunk into canals, estuaries, and rivers.
This article contains many images and would be a 12.1 MB download from this website. Therefore, I kindly invite you to read the article on our solar powered website, where it has been compressed to 1.90 MB.
George Cove, a forgotten solar power pioneer, may have built a highly efficient photovoltaic panel 40 years before Bell Labs engineers invented silicon cells. If proven to work, his design could lead to less complex and more sustainable solar panels.
Above: George Cove stands next to his third solar array. Source: "Generating electricity by the sun's rays", Popular Electricity, Volume 2, nr. 12, April 1910, pp.793.More efficient, less sustainable
Ever since Bell Labs presented the first practical solar PV panel in the 1950s, technological development has focused on reducing costs and increasing the efficiency of solar cells. According to these standards, researchers have made a lot of progress. The efficiency of solar panels increased from less than 5% in the 1950s to over 20% today, while the costs decreased from 30 dollars per watt-peak in 1980 to less than 0.2 dollars per watt-peak in 2020. Lower costs – to which higher efficiencies contribute – are considered of paramount importance because they allow solar PV panels to compete in the market with electricity generated by fossil fuels.
However, in terms of sustainability, very little progress has been made. To start with, ever since the 1950s, solar panels have been unfit for recycling, resulting in a waste stream that ends up in landfills. This waste stream will grow significantly during the coming years. Solar panels are discarded only after at least 25 to 30 years, and most have been installed only in recent years. By 2050, researchers expect that almost 80 million tonnes of solar panels will reach the end of their lives. [1-3] That is a significant waste of resources and a danger to the environment – discarded solar PV panels contain toxic elements and present a fire hazard.
The manufacturing of solar PV panels is just as problematic. It produces toxic waste and requires a global supply chain, including capital-intensive factories, complex machinery, mined materials, and a steady input of fossil fuels. In life cycle analyses of solar panels, scientists calculate how much energy and materials are required to build a solar panel. However, they ignore the massive amount of energy and materials needed to set up and maintain the solar PV supply chain itself. [4-11] Consequently, these studies do not reveal the actual cost of solar panels in terms of fossil fuel dependence, emissions, and other environmental pollution. Furthermore, the need for capital-intensive technology and long supply lines prevents the local production of solar panels by less affluent societies or DIY communities.Finding inspiration in the past
Are solar PV panels inherently unsustainable, unrecyclable, and dependent on high-tech and capital-intensive manufacturing processes? Or, is it possible to build them with local, recyclable and less energy-intensive materials and production methods? In other words, can we build low-tech solar panels? And, if so, what would that mean for costs and efficiency?
Before we try to answer this question, it’s important to note that the best low-tech alternative for a high-tech solar panel is often not a low-tech solar panel but direct use of solar energy. That is, putting solar energy to use without converting it to electricity first. For example, a clothesline and a solar thermal water boiler are much more efficient, sustainable, and economical than an electric tumble dryer and a water boiler powered by solar PV panels. Direct use of solar energy can happen with local materials, relatively simple manufacturing technologies, and short supply lines.
Nevertheless, in this article, I take the question literally: can we build low-tech photovoltaic devices, which convert sunlight into electricity? In a previous article, we have seen that history offers inspiration for building more sustainable wind turbines. Can history also inspire us to make more sustainable solar cells?The prehistory of solar cells
Bell Labs’ solar PV panel, presented in 1954, came not out of nowhere. The silicon solar cell had its roots in less complex devices that could produce electricity from either light or heat.
In 1821, Thomas Seebeck found that an electrical current will flow in a circuit made from two dissimilar metals, with the junctions at different temperatures. This “thermoelectric effect” formed the basis for the “thermoelectric generator” -- which converts heat (for example, from a wood stove) directly into electricity. In 1839, Antoine Becquerel discovered that light could also convert into electricity, and during the 1870s, several scientists proved this effect in solids, most notably in selenium. This “photoelectric effect” formed the basis for the “photoelectric generator” -- which we now call a “photovoltaic” generator or solar PV cell. In 1883, Charles Fritts constructed the first photovoltaic module ever made, using selenium on a thin layer of gold. [12-14]
Throughout this period – and until the 1950s – the practical uses of thermoelectric and photoelectric devices were limited. Inventors built many experimental thermoelectric generators, usually powered by a gas flame, but their efficiency did not exceed 1%. Likewise, Charles Fritts’ solar panel, and the selenium solar cells made afterward, obtained just 1-2% efficiency in converting sunlight into electricity.  In short, the period before the 1950s doesn’t seem to offer much inspiration for building more sustainable solar PV panels.A forgotten pioneer of solar power
However, the prehistory of the solar panel may be incomplete. In 2019, I received a mail from a reader of Low-tech Magazine, Philip Pesavento:
“I have been studying an early pioneer in solar cell technology from the pre-WWI era since the early 1990s. I am getting too old to continue doing anything with this, and even though there have been one or two scholarly articles about Mr. Cove, they have completely missed what he accomplished. I am enclosing a PDF of a PowerPoint that I put together back in 2015 and never presented to anyone. If you are interested in pursuing writing a paper yourself, I could mail you a thumb drive with all the background material that I have collected.”
If Philip Pesavento’s historical account and hypotheses are correct, George Cove set out to build a thermoelectric generator but accidentally made a photovoltaic generator – a PV solar cell. Although this happened in the early 1900s, Cove obtained a comparable power output and efficiency to the Bell Labs scientists in 1954. His design also showed much higher performance than the selenium solar cells built between the 1880s and the 1940s.  Philip Pesavento:
“It would be quite exciting to prove that relatively high-efficiency solar cells were invented 40 years before the development of silicon cells. More importantly, if it turns out there was a solar photovoltaic cell and panel system before World War I, it might also have some advantages concerning the cheapness of raw materials, low embodied energy to convert the ores into metallic materials, the efficiency of the final PV cells, and ease of fabrication.”
In other words, if Philip Pesavento’s historical account and hypotheses are correct, it may be possible to build low-tech solar panels.George Cove’s solar electric generator
George Cove presented his first “solar electric generator” in 1905 in the Metropole Building in Halifax, Nova Scotia, Canada. Apart from an image, there are no data about this panel.  However, its power output and efficiency were remarkable enough for US investors to send an expert to Halifax. Based on this expert’s examination of the machine, they then brought Cove to the US (Sommerville, Mass.) to continue the development of his device.
Cove presented his second solar electric generator there in 1909. This 1.5m2 panel could produce 45 watts of power and was 2.75% efficient in converting solar energy into electricity. By mid-1909, Cove had moved to New York City, where he presented his third prototype, a solar array consisting of four solar panels of 60 watt-peak each, which charged a total of five lead-acid batteries. The total surface area was 4.5 m2, the maximum power output was 240 watts, and efficiency rose to 5% – similar to the first solar panel presented by Bell Labs. 
Above: George Cove's first solar panel, demonstrated in 1905. Source: Technical World Magazine 11, nr.4, June 1909.
Above: Cove's second solar panel, with one section missing. Source: Technical World Magazine 11, nr.4, June 1909.
Above: George Cove's third solar panel. Source: "Harnessing sunlight", René Homer, Modern Electrics, Vol. II, No.6, September 1909.
Above: George Cove's third solar panel. The panels are now tilted at an angle as opposed to lying flat. Source: Literary Digest 1909.
Above: One of the solar panels of Cove's third solar array, with the glass cover removed. Source: "Harnessing sunlight", René Homer, Modern Electrics, Vol. II, No.6, September 1909.
Although George Cove is absent from most historical accounts of solar power, his solar electric generator impressed some popular tech media of the day. For example, in 1909, Technical World Magazine wrote that “such a machine is cheap and indestructible as a kitchen range. Even in its present and somewhat crude and experimental state, given two days of sun, it will store sufficient electrical energy to light an ordinary house for a week. The inventor has proved this now for months in his establishment”. Plugs set in asphalt
How did George Cove manage to build a solar panel that was 40 years ahead of its time? According to Philip Pesavento, who has a background in semiconductor engineering, Cove intended to build a better thermoelectric generator (TEG). He exposed his generator to the heat from a wood stove and direct solar energy -- Edward Weston had made the first experimental solar thermoelectric generator (or STEG) in 1888. Cove’s intentions are also clear from how he described his device:
“The frame contains a number of panes of violet glass, behind which are set, through an asphalt compound backing, many little metal plugs. One end of the plugs is always exposed by sunlight, while the other end is cool and sheltered.”
Creating the largest possible temperature difference is key to thermoelectric power production, so Cove’s design makes sense. The problem is that when he measured the power output of his generator, it did not respond to heat like a thermo-electric generator was supposed to do. Initially, Cove observes that his invention uses both heat and light to produce electricity when exposed to solar energy:
“The principal part of my invention is the peculiar composition of the metallic plugs which are acted upon by the sun in such a way that the current is generated not only by heat rays but the violet rays as well”.
However, after further experiments with both the wood stove and solar energy, Cove states:
“When the machine is exposed to various sources of artificial heat it gives no electricity whatsoever. Other than the heat rays of the sun (short-wave infrared), perhaps the violet or ultraviolet rays are active in setting up the electrical current”.
The primary cell of Cove’s solar PV panel was a three-inch-long plug or rod of metallic composition, an alloy of several common metals. The 1.5 m2 panel had 976 rods, while the 4.5 m2 array had 4 x 1804 plugs. However, keeping the rods cool on one side and hot on another – separated by an asphalt layer – did not matter. What mattered is that Cove had unknowingly built a metal-semiconductor contact.The semiconductor bandgap
George Cove did not understand how his solar generator worked, and neither did anyone else at the time. It was only with Einstein’s work on the photoelectric effect (in 1905) and later work in quantum mechanics (1930s and beyond) that the concept of a *semiconductor bandgap* was realized. Electrons orbit the nucleus of an atom in different “states”, which form regions that are called “bands”. These bands keep their electrons firmly in place. In between these bands are “bandgaps” – states in which no electron can be.
Conductors have no bandgaps, and so electrons flow through them. That is why a copper wire conducts electricity, for example. In insulators (like wood, glass, plastics, or ceramics), there is a very wide bandgap, which blocks the flow of electricity. Finally, in semiconductors, there’s a relatively narrow bandgap. That allows them to either act as an insulator or a conductor. Semiconductors can become conductors when they absorb a “photon” (an elementary particle of light) with an energy potential equal to or greater than the bandgap of the semiconductor material. 
The understanding of semiconductors led to the birth of the modern solar PV cell in the 1950s. It also improved the performance of thermoelectric generators – be it for different reasons. Thermoelectric generators do not take advantage of the semiconductor bandgap. However, semiconductors have higher thermo-voltages and lower thermal conductivities than metal and metal alloys with no bandgap, making thermoelectric generators more efficient.The Schottky Junction
For a photovoltaic effect to exist, there must be some inhomogeneity in the system. In the 1950s, Bell Labs scientists managed to do this with the so-called p-n junction, which forms a boundary between a positively charged and a negatively charged semiconductor. P-type semiconductors have electron vacancies called “holes” (which attract electrons), while N-type semiconductors have extra electrons. At the junction between both is an electric potential.
However, it's also possible to create a PV cell from a so-called Schottky junction, which connects a semiconductor with a metal. In this case, the metal functions as the n-type semiconductor. Philip Pesavento:
“My hypothesis is that George Cove stumbled upon a Schottky contact photovoltaic cell, decades before it was described by Walter Schottky.  There is the possibility of both photovoltaic (predominantly) and thermoelectric responses from these devices. The plug was an alloy of zinc and antimony – which we now know is a semiconductor. It was alternately capped by German silver (a nickel, copper, and zinc alloy) and copper on opposite ends. This formed an ohmic contact and Schottky contact, respectively. This is a photovoltaic device.”Accidental discovery
According to Philip Pesavento, George Cove probably started with “German silver” as the negative material on both ends of the plugs, and an antimony-zinc alloy (ZnSb) as the positive material. These were the best available thermoelectric materials at the time:
“He probably ran out of German silver and substituted copper to finish making up a bunch of plugs since the difference in thermoelectric voltage between using copper and German silver was small. Then, during testing, Cove noted that these plugs (with a German silver cap at one end and a copper cap at the other end) gave a much greater voltage: 100s of mV’s versus the usual 10s of mV for a thermoelectric generator.”
What happened? By using copper, Cove had unknowingly built a Schottky junction. That converted his thermoelectric generator into a “thermophotovoltaic generator.” Such a device works the same as a photovoltaic solar cell but on a different wavelength. The solar spectrum covers a range of approximately 0.5 to 2.9 electron-Volts (eV), from infrared to ultraviolet. A semiconductor with a bandgap between 1 and 1.7 eV efficiently converts visible light into electricity (a photovoltaic generator) -- while a semiconductor with a bandgap between 0.4 and 0.7 eV efficiently converts short-wave infrared solar energy into electricity (a thermophotovoltaic generator).
Above: This drawing from Cove's 1906 patent shows the zinc-antimony alloy “b”; the german silver (ohmic) end cap “c”; and the copper or tin (Schottky) end cap “f”. All these are press-fit because soldering the connections lowered the efficiency.
We now know that ZnSb – the negative material in Cove’s plugs – is a semiconductor with a bandgap of 0.5 eV. That largely explains why the inventor initially observed that his solar generator converted both heat and light into electricity. A thermophotovoltaic generator matches not only the infrared tail of the solar spectrum -- it also matches the direct spectrum of a burning flame or a red hot emitting surface which is heated by burning wood or natural gas. It also converts the lower portion of the visible spectrum into electricity, be it very inefficiently.
According to Philip Pesavento, Cove then managed to refine the composition of the alloy close to Zn4Sb3 – a zinc-antimony alloy with proportions of 4 parts zinc to 6 parts antimony. That, we now know, is also a semiconductor. However, it has a bandgap of 1.2 eV – very close to the bandgap of silicon (1.1 eV). Consequently, it turned his thermophotovoltaic generator into a photovoltaic generator:
“In his enthusiasm, Cove probably made up a larger number of plugs and somehow got the proportions “wrong” on one batch. He then measured an even larger voltage. Finally, he made a careful study of zinc-antimony alloys and found that the 40-42% range zinc alloy gave the highest voltage (compared to 35% zinc in ZnSb). Having – accidentally – discovered Zn4Sb3, the higher bandgap of this semiconductor meant that it no longer worked when it was exposed to the heat from a wood stove. However, it worked even better when it was exposed to solar energy – because it was now converting far more of the visible spectrum of sunlight efficiently into electricity.”
Using colored glass filters, George Cove determined that most of the response was from the violet end of the spectrum and only a little from the so-called heat rays. His earlier PV plugs had responded equally well to heat rays and violet rays, while the older thermoelectric generators (German silver at both sides) did not respond to the violet rays at all.Bring back the Schottky solar cell?
Schottky junction solar cells have commanded only a small amount of attention from researchers and corporations – few solar cell designs use metals in the active region, other than for contacts.  Nevertheless, Philip Pesavento believes that it would be worthwhile to attempt to fabricate some Schottky solar cells according to Cove’s design:
“If it could be demonstrated that Zn4Sb3 (bandgap 1.2 eV) can be used in a photovoltaic cell, there is a good chance that such a solar cell design will be sustainable. It would be a good candidate for a quick EROI and have an acceptably long operational life with a surplus energy output over several decades. It’s astounding that everyone seems to have missed this material and its application to photovoltaic cells and that no development has been done – even after researchers briefly recognized it as being a possible option in the early to mid-1980s. It fits in the category of a premature discovery which should mean it could be developed very quickly in this day and age.”
Apart from solar PV, Philip Pesavento sees potential in thermophotovoltaics for a wood stove, solar thermal, or dual junction tandem applications, using ZnSb instead of Zn4Sb3. Furthermore, if the plug-type solar cells prove to be effective, he believes that they would allow line concentrator solar collectors – such as parabolic troughs or non-imagining CPC concentrators – to be built at greatly reduced costs.Low-tech manufacturing
The primary advantage of Cove’s design would be its low-tech fabrication method. In the 1970s and 1980s, scientists investigated Zn4Sb3 for use in photovoltaics and concluded that the material’s “obvious advantages are apparent simplicity and relatively low temperature of the preparation procedure.”  The melting point for Zn4Sb3 is 570 degrees Celsius, while it’s 1,400 degrees for silicon.
Researchers studied metal-semiconductor junction solar cells based on other types of semiconductors than Zn4Sb3 in the 1970s. Again, their motivation was the simple and cost-effective fabrication procedure compared to silicon p-n junction solar cells at the time. [24, 25] Schottky cells do not require a high-temperature phosphorus-diffusion step, which ordinarily creates the n-layer of the p-n junction in silicon today. This alone reduces the energy input into the solar cell production process by 35%. 
During the 1980s, researchers made important advances in silicon p-n junctions, and interest in alternative configurations waned. However, there has been renewed interest in recent years. For example, research into graphene/silicon Schottky solar cells concludes that “simple and cost-effective device fabrication that does not require high temperatures is one of the advantages.”  In other recent studies, scientists conclude that Schottky-type “selenium devices are… extremely simple and cheap to fabricate”. [27-30]Easier recycling
Another advantage of Schottky solar cells may be easier recycling. Silicon modules are sandwiched between two laminate encapsulant layers (usually EVA, an ethylene/vinyl acetate copolymer). These layers are essential to ensure module service lifetime. [1-3] To recycle the silicon – the most valuable component of a solar panel – these layers need to be separated, but burning them also destroys the modules. Silicon cells can only be recycled by a combination of thermal, chemical, and metallurgical steps. That is an expensive process with an impact on the environment. Although you can find statements claiming that around 10% of solar panels are “recycled", they are more likely to be “downcycled”. The modules are shredded, and the resulting material is used as a filler material in asphalt and cement industries.
In contrast, the solar cells built by George Cove were entirely recyclable. They required no protective layer and did not even contain solder. Philip Pesavento:
“If you were to build the cells exactly the way Cove did by press-fitting the caps and then overwrapping them with wire to try to keep them tight, they would also be easier to recycle, being strictly a mechanical operation, no chemicals need to be involved. It would be labor-intensive to put them together and take them apart again, but it could be automated, too.”
Pesavento believes that it’s also possible to build flat solar cells from Cove’s material. However, whether or not those would need a protective layer that interferes with recycling remains to be seen. In the 1970s, Schottky solar cells based on other materials did not always need protective layers to reach more than 20 years of life expectancy. Efficiency
If we could build more low-tech solar panels, how efficient could we make them? According to Philip Pesavento, Schottky cells are slightly less efficient for the same materials than p-n junctions because p-n junctions generate a higher voltage – they get more of the energy in the photons they absorb.
“When every bit of efficiency counts, you do that. If making solar cells easier to manufacture using manual or artisan methods is your goal, the Schottky diode would be a more logical choice.”
On the other hand, it may be possible to build Schottky cells thinner than silicon solar cells – and that would increase their efficiency. Philip Pesavento:
“I have not found the specific numbers for the parameters – carrier velocity, recombination lifetime, absorption coefficient – to say this unequivocally. But the fact that Cove made such long skinny cells and got as high efficiencies as he did bodes well for making them thinner.”
Again, recent research into Schottky cells based on other materials seems to confirm this. For example, recent experiments with Schottky selenium cells brought layer thickness back to only 100 µm, compared to between 200 and 500 µm for silicon cells.   Scientists also reached 17% experimental efficiency for a graphene/silicon Schottky cell, up from 1.5% ten years earlier. 
We can also question the current obsession with higher efficiencies. Many people will argue that if low-tech solar panels are less efficient, we would need more solar panels to produce the same power output. Consequently, the resources saved by low-tech production methods would be compensated by the extra resources to build more solar panels. However, efficiency is only crucial when we take energy demand for granted. A decrease in efficiency may just as well be compensated by lowering energy demand, especially when it leads to more sustainability and lower resource use throughout the supply chain. As with wind turbines, sacrificing some efficiency may gain us a lot in sustainability.What happened to George Cove?
If Cove’s solar panel was so revolutionary, why is it forgotten? On this question, Philip Pesavento’s research material reads like a crime novel. Cove’s attempt to produce and market his solar energy device failed in mysterious ways.
The inventor became involved with a stock manipulator – Elmer Burlingame – who in 1909 and 1910 issued stock from businesses that were not his, including Cove’s start-up the Sun Electric Generator Company. In October 1909, Cove was allegedly kidnapped, and his life was threatened if he did not cease the development of his solar invention. However, the police dismissed Cove’s kidnapping as a hoax. In 1911, both Cove and Burlingame were arrested for stock fraud and spent a year in jail. Although Cove worked on other inventions after that, none of those were related to solar energy. 
Was George Cove a charlatan? Was he the victim of one? Or was his reputation destroyed because the solar electric generator threatened other companies’ interests? There are many historical examples of suppression of technological innovations by large US corporations. George Cove was active in the same period as the Edison Electric Illuminating Company of New York, whose unscrupulous practices against competitors are well-documented. If Cove’s solar electric generator worked, it could have reduced the growing demand for Edison’s coal and oil-fired power stations.  Earlier, in the 1880s, Edison had bought the company that produced the best thermoelectric generator at the time – Clamonds’s Improved Thermopile – and subsequently stopped the development of the machines. More Mysteries
However, while it’s tempting to see George Cove as a victim, we can only speculate. Philip Pesavento’s archive material contains more mysteries, such as Cove’s patent – applied for in 1905, granted in 1906. In his patent, the inventor describes the making of his Zn4Sb3 plugs in detail, which helped Pesavento to calculate the power output and efficiency of the solar arrays. However, Cove describes these plugs for converting heat from a wood stove into electricity, which is not compatible with his choice of material. To make the stove generator work, it required ZnSb plugs with a bandgap of 0.5 eV. Philip Pesavento:
“Was this misdirection on the part of Cove to prevent folks from copying his stove patent and getting it to work? I don’t know.”
Even more surprisingly, an image that shows Cove standing beside one of his solar panels also appears in John Perlin’s 2013 historical overview of solar power *Let It Shine: The 6,000-Year Story of Solar Energy*. However, the solar panel in the image is attributed to Charles Fritts, the inventor of the selenium solar cell. Furthermore, George Cove himself has disappeared from the image. Excerpts from the book, as well as the photo, have appeared on several websites. Philip Pesavento was not surprised when I got back in touch:
“I made this discovery several years ago. I guess that somebody badly needed an image of Fritts’ solar panels, found this image, and then photoshopped George Cove out of it. After all, Cove is totally unknown and when known is thought to have invented a solar thermoelectric generator, not a solar PV panel. If you look closely at the two photos, you can see that the top of the right column portico behind him was cut and pasted to where Cove had been standing, it’s not quite right in its perspective.”
Kris De Decker
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: Weckend, Stephanie, Andreas Wade, and Garvin A. Heath. End of life management: solar photovoltaic panels. No. NREL/TP-6A20-73852. National Renewable Energy Lab.(NREL), Golden, CO (United States), 2016.
: Xu, Yan, et al. "Global status of recycling waste solar panels: A review." Waste Management 75 (2018): 450-458.
: Sica, Daniela, et al. "Management of end-of-life photovoltaic panels as a step towards a circular economy." Renewable and Sustainable Energy Reviews 82 (2018): 2934-2945.
: Hornborg, Alf, Gustav Cederlöf, and Andreas Roos. "Has Cuba exposed the myth of “free” solar power? Energy, space, and justice." Environment and planning E: Nature and space 2.4 (2019): 989-1008.
: Cederlof, Gustav, and Alf Hornborg. "System boundaries as epistemological and ethnographic problems: Assessing energy technology and socio-environmental impact." Journal of Political Ecology 28.1 (2021): 111-123.
: Bartie, N. J., et al. "The resources, exergetic and environmental footprint of the silicon photovoltaic circular economy: Assessment and opportunities." Resources, Conservation and Recycling 169 (2021): 105516.
: Powell, Douglas M., et al. "The capital intensity of photovoltaics manufacturing: barrier to scale and opportunity for innovation." Energy & Environmental Science 8.12 (2015): 3395-3408.
: Dehghani, Ehsan, et al. "An environmentally conscious photovoltaic supply chain network design under correlated uncertainty: A case study in Iran." Journal of Cleaner Production 262 (2020): 121434.
: Carvalho, Maria, Antoine Dechezleprêtre, and Matthieu Glachant. Understanding the dynamics of global value chains for solar photovoltaic technologies. Vol. 40. WIPO, 2017.
: Dehghani, Ehsan, et al. "Resilient solar photovoltaic supply chain network design under business-as-usual and hazard uncertainties." Computers & Chemical Engineering 111 (2018): 288-310.
: Kumar, Abhishek, et al. "Economic viability analysis of silicon solar cell manufacturing: Al-BSF versus PERC." Energy Procedia 130 (2017): 43-49.
: Fritts, Charles E. "On a new form of selenium cell, and some electrical discoveries made by its use." American Journal of Science 3.156 (1883): 465-472.
: Effect of Light on Selenium During the Passage of An Electric Current*. Nature 7, 303 (1873).
: Green, Martin A. "Silicon photovoltaic modules: a brief history of the first 50 years." Progress in Photovoltaics: Research and applications 13.5 (2005): 447-455.
: Perlin, John. Let it shine: the 6,000-year story of solar energy. New World Library, 2013.
: Selenium Cells, Thomas William Benson, 1919.
: Extrapolating from the performance of the next panel, we can guess that this one had a power output of about 25W and just under 3% efficiency.
: Cove claimed to have built an even larger panel of 9 m2, but no image has survived. It was said to have had a power output of 768 watt at 8% efficiency assuming 100 W/ft2 solar insolation. This array consisted of 8 panels with a total of 14,432 plugs.
: Winthrop Packard, Technical World Magazine 11, nr.4, June 1909.
: Why don’t we use conductors for solar panels? When light hits a conductor surface it mostly reflects, and little or no energy is absorbed. Furthermore, in conductors, the free electrons move randomly, there is no flow of current, no directional capacity.
: Cove was not the first, though. Charles Fritts’ solar cell was also based on a Schottky junction.
: Byrnes, Steve. "Schottky junction solar cells." (2008).
: Tapiero, M., et al. "Preparation and characterization of Zn4Sb4." Solar Energy Materials 12.4 (1985): 257-274. See also: Mozharivskyj, Yurij, et al. "A promising thermoelectric material: Zn4Sb3 or Zn6-δSb5. Its composition, structure, stability, and polymorphs. Structure and stability of Zn1-δSb." Chemistry of Materials 16.8 (2004): 1580-1589.
: Rothwarf, A., and K. W. Böer. "Direct conversion of solar energy through photovoltaic cells." Progress in Solid State Chemistry 10 (1975): 71-102..
: Anderson, W. A., A. E. Delahoy, and R. A. Milano. "An 8% efficient layered Schottky‐barrier solar cell." Journal of Applied Physics 45.9 (1974): 3913-3915.
: Yavuz, Serdar. Graphene/Silicon Schottky Junction Based Solar Cells. University of California, San Diego, 2018.
: Todorov, Teodor K., et al. "Ultrathin high band gap solar cells with improved efficiencies from the world’s oldest photovoltaic material." Nature communications 8.1 (2017): 1-8.
: Selenium can be deposited by thermal evaporation at only 200°C. This temperature is within easy reach of solar thermal technologies, which means that in principle these processes could be run by direct use of solar energy.
: Hadar, Ido, et al. "Modern processing and insights on selenium solar cells: the world's first photovoltaic device." Advanced Energy Materials 9.16 (2019): 1802766.
: Ferhati, H., F. Djeffal, and D. Arar. "Above 14% efficiency earth-abundant selenium solar cells by introducing gold nanoparticles and Titanium sub-layer." Optical Materials 86 (2018): 24-31.
: Zhu, Menghua, Guangda Niu, and Jiang Tang. "Elemental Se: fundamentals and its optoelectronic applications." Journal of Materials Chemistry C 7.8 (2019): 299-2206.
: More details in “George Cove’s solar energy device”, Dennis Bartels, 1997.
: Polozine, Alexandre, Susanna Sirotinskaya, and Lírio Schaeffer. "History of development of thermoelectric materials for electric power generation and criteria of their quality." Materials Research 17 (2014): 1260-1267.
It is surprisingly difficult to build a carbon neutral sailing ship. This is even more the case today, because our standards for safety, health, hygiene, comfort, and convenience have changed profoundly since the Age of Sail.
On board the ship `Garthsnaid' at sea. A view from high up in the rigging. Image by Allan C. Green, circa 1920.
The sailing ship is a textbook example of sustainability. For at least 4,000 years, sailing ships have transported passengers and cargo across the world’s seas and oceans without using a single drop of fossil fuels. If we want to keep travelling and trading globally in a low carbon society, sailing ships are the obvious alternative to container ships, bulk carriers, and airplanes.
However, by definition, the sailing ship is not a carbon neutral technology. For most of history, sailing ships were built from wood, but back then whole forests were felled for ships, and those trees often did not grow back. In the late nineteenth and early twentieth century, sailing ships were increasingly made from steel, which also has a significant carbon footprint.
The carbon neutrality of sailing in the 21st century is even more elusive. That’s because we have changed profoundly since the Age of Sail. Compared to our forebears, we have higher demands in terms of safety, comfort, convenience, and cleanliness. These higher standards are difficult to achieve unless the ship also has a diesel engine and generator on-board.The revival of the sailing ship
The sailing ship has seen a modest revival in the last decade, especially for the transportation of cargo. In 2009, Dutch company Fairtransport started shipping freight between Europe and the Americas with the Tres Hombres, a sailing ship built in 1943. The company remains active today and has a second ship in service since 2015, the Nordlys (built in 1873).
Since then, others have joined the sail cargo business. In 2016, the German company Timbercoast started shipping cargo with the Avontuur, a ship built in 1920.  In 2017, the French Blue Schooner Company started transporting cargo between Europe and the Americas with the Gallant, a sailing ship that was built in 1916.  All these sailing ships were constructed in the twentieth or nineteenth century, and were restored at a later date. However, a revival of sail cannot rely on historical ships alone, because there’s not enough of them. 
The Noach, built in 1857.
At the moment, there are at least two sailing ships in development that are being built from scratch: the Ceiba and the EcoClipper500. The first ship is being constructed in Costa Rica by a company named Sailcargo. She is built from wood and inspired by a Finnish ship from the twentieth century. The second ship is designed by a company called EcoClipper, which is led by one of the founders of the Dutch FairTransport, Jorne Langelaan. Their EcoClipper500 is a steel replica of a Dutch clipper ship from 1857: the Noach.
“Old designs are not necessarily the best", says Jorne Langelaan, "but whenever proven design is used, one can be sure of its performance. A new design is more of a gamble. Furthermore, in the 20th and 21st century, sailing technology developed for fast sailing yachts, which is an entirely different story compared to ships which need to be able to carry cargo.”More economical sailing ships
These two ships – one under construction and one in the design phase – have the potential to make sail cargo a lot more economical than it is today. That’s because they have a much larger cargo capacity than the sailing ships currently in operation. As a ship becomes longer, her cargo capacity increases more than proportionally.
The EcoClipper500 is a full-scale replica of the Noach.
The 46 metre long Ceiba is powered by 580 m2 of sails and carries 250 tonnes of cargo. The 60 metre long EcoClipper500 is powered by almost 1,000 m2 of sails and takes 500 tonnes of cargo. For comparison, the Tres Hombres is not that much shorter at 32 metres, but she takes only 40 tonnes of cargo – twelve times less than the EcoClipper500. A larger ship is also faster and saves labour. The Tres Hombres requires a crew of seven, while the EcoClipper500 only has a slightly larger crew of twelve.Life cycle analysis of a sailing ship
Although the EcoClipper500 is still in the design phase, she will be the focus of this article. This is because the company conducted a life cycle analysis of the ship prior to building it.  As far as I know, this is the first life cycle analysis of a sailing ship ever made. The study reveals that it takes around 1,200 tonnes of carbon to build the ship.
Half of those emissions are generated during steel production, and roughly one third is generated by steel working processes and other shipyard activities. Solvent-based paints as well as electric and electronic systems each account for roughly 5% of emissions. The emissions produced during the manufacturing of the sails are not included because there are no scientific data available, but a quick back-of-the-envelope calculation (for sails based on aramid fibres) signals that their contribution to the total carbon footprint is very small. 
The EcoClipper500 has a carbon footprint of 2 grammes of CO2 per tonne-kilometre, which is five times less than the carbon footprint of a container ship.
If these 1,200 tonnes of emissions are spread out over an estimated lifetime of 50 years, then the EcoClipper500 would have a carbon footprint of about 2 grammes of CO2 per tonne-kilometre of cargo, concludes researcher Andrew Simons, who made the life cycle analysis for the ship. This is roughly five times less than the carbon footprint of a container ship (10 grammes CO2/tonne-km) and three times less than the carbon footprint of a bulk-carrier (6 grammes CO2/tonne-km). 
Looking aft from aloft on the 'Parma' while at anchor. Alan Villiers, 1932-33. Villiers's work vividly records the period of early 20th century maritime history when merchant sailing vessels or ‘tall ships’ were in rapid decline.
Transporting one ton of cargo over a distance of 8,000 km (roughly the distance between the Caribbean and the Netherlands) would thus produce 16 kg of carbon with the EcoClipper500, compared to 80 kg on a container ship and 48 kg on a bulk carrier. The proportions are similar for other environmental factors, such as ozone depletion, ecotoxicity, air pollution, and so on.
Although the sailing ship boasts a convincing advantage, it may not be as big as you might have expected. First, as Simons explains, there’s scale. A container ship or bulk carrier enjoys the same benefits over the EcoClipper500 as the EcoClipper500 enjoys over the Tres Hombres. It can take a lot more cargo – on average 50,000 tonnes instead of 500 tonnes – and it needs only a slightly larger crew of 20-25 people. 
Second, fossil fuel powered ships are faster than sailing ships, meaning that fewer ships are needed to transport a given amount of cargo over a given period of time. The original ship on which the EcoClipper500 is based, sailed between the Netherlands and Indonesia in 65 to 78 days, while a container ship does it in about half the time (taking the short cut through the Suez canal).Building a fleet of sailing ships
There’s two ways to further lower the carbon emissions of sailing ships in comparison to container ships and bulk carriers. One is to build ships from wood instead of steel, such as the Ceiba. If the harvested trees are allowed to grow back (which the makers of the Ceiba have promised), such a ship may even be considered a carbon sink.
However, there’s a good reason why the EcoClipper500 will be made from steel: the company’s aim is to build not just one ship, but a fleet of them. Jorne Langelaan: “There are few shipyards who can deliver wooden ships nowadays. Steel makes it easier to build a fleet in a shorter period.”
A possible compromise would be a composite construction, in which a steel skeleton is clad with timber keel, planks, and deck. Andrew Simons: “This would reduce the carbon footprint of construction by half. It could also be feasible to make superstructures and some of the mast sections and spars from timber instead of steel.”
Driving sprays over the main deck of the 'Parma'. Alan Villiers, 1932-33.
Towards the future, another possibility to further decrease a sailings ship’s emissions per tonne-km is to build it even larger. While the EcoClipper500 has much more cargo capacity than the cargo sailing ships now in operation, she is far from the largest sailing ship ever built.
Historical ships such as the Great Republic (5,000 tonnes), the Parma (5,300 tonnes), the France II (7,300 tonnes), and the Preussen (7,800 tonnes), were more than 100 metres long and could take more than ten times the freight capacity of the EcoClipper500. Langelaan already dreams of a EcoClipper3000.Passengers
Most cargo sailing ships travelling across the oceans today can also take some passengers. Fully loaded with cargo, the EcoClipper500 takes 12 crew members, 12 passengers, and 8 trainees (passengers who learn how to sail). If the upper hold deck is not used for cargo, another 28 trainees can join, so that the ship can take up to 60 people on board (with a smaller cargo volume: 480 m3 instead of 880 m3).
The carbon footprint for passengers amounts to 10 g per passenger-km, compared to roughly 100 g per passenger-km on an airplane.
Consequently, and since ocean liners have disappeared, the EcoClipper500 also becomes an alternative to the airplane. According to the results of the life cycle analysis, the carbon footprint for passengers on the EcoClipper500 amounts to 10 grammes per passenger-kilometre, compared to roughly 100 grammes per passenger-kilometre on an airplane. Transporting one passenger thus produces as much carbon emissions as transporting 1 tonne of freight.Engine or not?
Importantly, the life cycle analysis of the EcoClipper500 assumes that there is no diesel engine on-board. On a sailing ship, a diesel engine can serve two purposes, which can be combined. First, it allows to propel the ship when there is no wind or when sails cannot be used, for example when leaving or entering a harbour. Second, combined with a generator, a diesel engine can produce electricity for daily life on board of the ship.
For most of history, energy use on-board of a sailing ship was not too problematic. There was firewood for cooking and heating, and there were candles and oil lamps for lighting. There were no refrigerators for food storage, no showers or laundry machines for washing and cleaning, no electronic instruments for navigation and communication, no electric pumps in case of leaks or fire.
However, we now have higher standards in terms of safety, health, hygiene, thermal comfort, and convenience. The problem is that these higher standards are difficult to achieve when the ship does not have an engine that runs on fossil fuels. Modern heating systems, cooking devices, hot water boilers, refrigerators, freezers, lighting, safety equipment, and electronic instruments all need energy to work.
Crewman of the 'Parma' with a model of his ship. Alan Villiers, 1932-33.
Modern sailing ships often use a diesel engine to provide that energy (and to propel the ship if necessary). An example is the Avontuur from Timbercoast, who has an engine of 300 HP, a 20 kW generator, and a fuel tank of 2,330 litres. Large sail training vessels and cruising ships have several engines and generators on-board. For example, the 48m long Brig Morningster has a 450 HP engine and three generators with a total capacity of 100 kW, while the 56m long Bark Europa has two 365 HP engines with three generators – and burns hundreds of litres of oil per day.
Depending on the lifestyle of the people on board, the emissions per passenger-km may rise to, or surpass, the levels of those of an airplane.
Obviously, the emissions and other pollutants of these engines need to be taken into account when the environmental footprint of a sail trip is calculated. Depending on the lifestyle of the people on board, the emissions per passenger-km may rise to, or surpass, the levels of those of an airplane. To a lesser extent, electricity use on-board also increases the emissions of cargo transportation.Energy use on board a sailing ship
The EcoClipper500 has no diesel engine on board, which is a second reason to focus on this ship. Obviously, a sailing ship without an engine cannot proceed her voyage when there’s no wind. This is easily solved in the old-fashioned way: the EcoClipper500 stays where she is until the wind returns. A ship without an engine also needs tug boats – which usually burn fossil fuels – to get in and out of ports. For the EcoClipper500, these tug services account for 0.3 g/tkm of the total carbon footprint of 2 g/tkm.
Without a diesel engine, the ship also needs to generate all energy for use on board from local energy sources, and this is the hard part. Renewable energy is intermittent and has low power density compared to fossil fuels, meaning that more space is needed to generate a given amount of power – which is more problematic at sea than it is on land.
Renewing caulking on the poop of the 'Parma'. Alan Villiers, 1932-33.
To make the EcoClipper500 self-sufficient in terms of energy use, a first design decision was to shift energy use away from electricity whenever possible. This is especially important for high temperature heat, which cannot be supplied by electric heat pumps. The ship will have a pellet-stove on board to provide space heating, as well as a biodigester – never before used on a ship – to convert human and kitchen waste into gas for cooking. Thermal insulation of the ship is another priority.
Nevertheless, even with pellet-stove and biodigester (which themselves require electricity to operate), and with thermal insulation, energy demand on the ship can be as high as 50 kilowatt-hours of electricity per day (2 kW average power use). This concerns a “worst-case normal operation” scenario, when the ship is sailing in cold weather with 60 people on board. Power use will be lower in warmer weather and/or when less people are taken. During an emergency, the power requirements can amount to 8 kW, while more than 24 kWh of energy can be needed in just three hours.Hydrogenerators
How to produce this power? Solar panels and wind turbines are only a small part of the solution. Producing 50 kWh of energy per day would require at least 100 square metres of solar panels, for which there is little space on a 60 m long sailing ship. Vulnerability and shading by the sails make for further problems. Wind turbines can be attached in the rigging, but their power output is also limited. The low potential of solar and wind power are demonstrated by the earlier mentioned sailing ship Avontuur. She has a 20 kW generator, powered by the diesel engine, but only 2.1 kW of solar panels and 0.8 kW of wind turbines.
The hydrogenerator is the only renewable power source that can provide a large sailing ship with enough energy for the use of modern technology on board.
The hydrogenerator is the only renewable power source that can provide a large sailing ship with enough energy for the use of modern technology on board. Hydrogenerators are attached underneath the hull and work in the opposite way as a ship’s propeller. Instead of the propeller powering the ship, the ship powers the propeller, which turns a generator that produces electricity. In spite of its name and appearance, the hydrogenerator is actually a form of wind energy: the sails power the propellers. Obviously, this only works when the ship is sailing fast enough.
Furling sail on the main yard of the Parma. Alan Villiers, 1932-33.
The EcoClipper500 will be equipped with two large hydrogenerators, for which Simons calculated the power output at different speeds, taking into account the fact that the extra drag they produce slows down the ship somewhat. He concludes that the EcoClipper500 needs to sail at a speed of at least 7.5 knots to generate enough electricity. At that speed, the hydrogenerators produce an estimated 2,000 watts of power, which converts to roughly 50 kWh of electricity per day (24 hours of sailing).
At a lower speed of 4.75 knots, the generators produce 350 watts, which comes down to 8.4 kWh of energy over a period of 24 hours – only 1/6th of the maximum required energy. On the other hand, at higher speeds, the hydrogenerators produce more energy than necessary. At a speed of almost 10 knots they provide 120 kWh/day, at a speed of 12 knots this becomes 182 kWh/day – 3.5 times more than needed.Saltwater batteries
According to her hull speed, the EcoClipper500 will be able to sail a little over 16 knots at absolute top speed – this is double the minimum speed required to generate enough power. Achieving this speed will be rare, because it needs calm seas and strong winds from the right direction. Nevertheless, in good wind conditions, the ship easily sails fast enough to produce all electricity for use on board.
Good wind conditions can last for days, especially on the oceans, where winds are more powerful and predictable than on land. However, they are not guaranteed, and the ship will also sail at lower speeds, or find herself in becalmed conditions – when hydrogenerators are as useless as solar panels in the middle of the night.
Because she has no engine, the EcoClipper500 faces a double problem when there’s no wind: she cannot continue her voyage, and she has no energy to maintain life on board.
Because she has no engine, the EcoClipper500 faces a double problem when there’s no wind: she cannot continue her voyage, and she has no energy to maintain life on board. The first problem is easily solved but the second is not. Life on board goes on, and so there is a continued need for power. To provide this, the ship needs energy storage.
To cover the needs for three days drifting in cold weather, an energy storage of 150 kWh would be required, not taking into account charge and discharge losses. Five or seven days of energy use on-board would require 250 to 350 kWh of storage. For emergency use, another 25 kWh of energy storage is needed.
Scraping the deck onboard the 'Parma'. Alan Villiers, 1932-33.
Not having an engine, generator and fuel tank saves space on board, but this advantage can be quickly lost again when one starts to add batteries for the hydrogenerators. Lithium-ion batteries are very compact, but they cannot be considered sustainable and bring safety risks. That’s why Jorne Langelaan and Andrew Simons see more potential in – very aptly – saltwater batteries, which are non-flammable, non-toxic, easy to recycle, have wide temperature-tolerance, and can last for more than 15 years. Like the biodigester, they have never been used on a sailing ship before.
Unlike lithium-ion batteries, saltwater batteries are large and heavy. At 60 kg per kWh of storage capacity, a 150 kWh battery storage would add a weight of 9 tonnes, while a 350 kWh storage capacity would add 21 tonnes. Still, this compares favourably to the total cargo capacity (500 tonnes), and the batteries can serve as ballast if they are placed in the lower part of the ship’s hull. The space requirements are not too problematic, either. Even a 350 kWh energy storage only requires 14 to 29m3 of space, which is small compared to the 880m3 of cargo volume.
The emissions that are produced by the manufacturing of the hydrogenerators, biodigester, and batteries are not included in the life cycle analysis of the ship, because there are no data available. However, these emissions must be relatively small. Hydrogenerators have much higher power density than wind turbines, and thus a relatively low embodied energy. A quick back-of-the-envelope calculation learns that the carbon footprint of 350 kWh saltwater batteries is around 70 tonnes of CO2. Human Power
There’s another renewable power source and energy storage on board of the EcoClipper, and that’s the humans themselves. Like the pellet stove and the biodigester, the use of human power could reduce the need for electricity. Nowadays, cargo ships and most large sailing ships have electric or hydraulic winches, pumps, and steering gear, saving manual labour at the expense of higher energy use. In contrast, EcoClipper sticks to manual handling of the ship as much as possible.
Crew at the capstan of the Parma, weighing anchor. Alan Villiers, 1932-33.
Simons and Langelaan are also considering the addition of a few rowing machines, coupled to generators, to produce emergency power. Two rowing machines could provide roughly 400 watts of power. If they are operated around the clock in shifts, they could supply the ship with an extra 9.6 kWh of energy per day (ignoring energy losses) – one fifth of the total maximum electricity use.
In fact, as I tell Simons and Langelaan ten rowing machines operated continually in shifts would provide as much power as the hydrogenerators at a speed of 7.5 knots. If there are 60 people on board, and everybody would generate power for less than one hour per day, no hydrogenerators and batteries would be needed at all. “A very interesting thought”, answers Simons, “but what impression would we be painted with?”Hot Showers?
Even with a biodigester, hydrogenerators, batteries, and rowing machines, the passengers and crew on board the EcoClipper500 would be far short of luxurious, and perhaps too short of comfortable for some. For example, if 60 people on board the ship would take a daily hot shower – which requires on average 2.1 kilowatt-hours of energy and 76.5 litres of water on land – total electricity use per day would be 126 kWh, more than double the energy the ship produces at a speed of 7.5 knots.
The ship could supply this energy at a higher sailing speed, but there would also be a need for 4,590 liters of water per day, a quantity that could only be produced from seawater – a process that requires a lot of energy. Even a crew of 12 taking a daily hot shower would require 25.2 kWh of energy per day, half of what the hydrogenerators produce at a sailing speed of 7.5 knots. The Bark Europa is the only sailing ship mentioned in this article that has hot showers in every (shared) cabin, but it is also the ship with the biggest generators and the highest fuel use.
On the forecastle head of the Parma in fine weather. Image by Alan Villiers, 1932.
Andrew Simons: “On the EcoClipper500 there needs to be a manageable compromise between energy use and comfort. Energy use on board will have to be actively managed. Resources are finite, just like for the planet. In many ways the ship is a microcosm of challenges that the wider world has to face and find solutions to.”
Jorne Langelaan: “At sea you are in a different world. It doesn’t matter anymore if you can take a daily shower or not. What matters are the people, the movements of the ship, and the vast wilderness of ocean around you”.Measuring the right things
This article has compared the EcoClipper500 sailing ship with the average container ship, bulk carrier, and airplane in terms of emissions per tonne- or passenger-kilometer. However, these values are abstractions that obscure much more important information: the total emissions that are produced by all passengers and all cargo, over all kilometres.
The international ocean freight trade increased from 4 billion tonnes of cargo in 1990 to 11.2 billion tonnes in 2019, resulting in more than 1 billion tonnes of emissions. International air passenger numbers grew from 1 billion in 1990 to 4.5 billion in 2019, resulting in 915 million tonnes of emissions. Consequently, lowering the emissions per tonne- and passenger-kilometre is neither a necessity nor a guarantee for a reduction in emissions.
If we cut international cargo traffic more than fivefold, and passenger traffic more than tenfold, then the emissions of all container ships and airplanes would be lower than the emissions of all sailing ships carrying 11.2 billion tonnes of cargo and 4.5 billion of passengers. Vice versa, if we switch to sailing ships, but keep on transporting more and more cargo and passengers across the planet, we will eventually produce just as much in emissions as we do today with fossil fuel powered transportation.
The mizzen of the 'Grace Harwar'; view aft from the main crosstrees. Alan Villiers, 1932-33.
Of course, none of this would ever happen. The amount of cargo that was traded across the oceans in 2019 equals the freight capacity of 22.4 million EcoClippers. Assuming the EcoClipper500 can make 2-3 trips per year, we would need to build and operate at least 7.5 million ships, with a total crew of at least 90 million people. Those ships could only take 0.5 billion passengers (12 passengers and 8 trainees per ship), so we would need millions of ships and crew members more to replace international air traffic.
We should not be fooled by abstract relative measurements, which only serve to keep the focus on growth and efficiency.
All of this is technically possible, and as we have seen, it would produce less in emissions than the present alternatives. However, it’s more likely that a switch to sailing ships is accompanied by a decrease in cargo and passenger traffic, and this has everything to do with scale and speed. A lot of freight and passengers would not be travelling if it were not for the high speeds and low costs of today’s airplanes and container ships.
It would make little sense to transport iPhones parts, Amazon wares, sweatshop clothes, or citytrippers with sailing ships. A sailing ship is more than a technical means of transportation: it implies another view on consumption, production, time, space, leisure, and travel. For example, a lot of freight now travels in different directions for each next processing stage before it is delivered as a final product. In contrast, all sail cargo companies mentioned in this article only take cargo that cannot be produced locally, and which is one trip from producer to consumer. 
This also means that even if sailing ships have diesel engines on board, they would still bring a significant decrease in the total emissions for freight and passenger traffic, simply because they would reduce the absolute number of passengers, cargo, and kilometers. We should not be fooled by abstract relative measurements, which only serve to keep the focus on growth and efficiency.
Kris De Decker
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 Between 1978 and 2004, the Avontuur was operated as sail cargo vessel under Captain Paul Wahlen. The Apollonia, originally built in 1946, is another cargo sailing ship in operation since 2014. It is 19.5 metres long and carries 10 tonnes of cargo.
 Very recently, Grain de Sail was buillt and launched for Trans-Atlantic shipping of wine and cocoa. She is a modern sailing ship without an engine, built from aluminium, and can take 35 tonnes of cargo.
 Andrew Simons: “There are plenty historical sailing ships, but either very costly to get into service as a regulatory compliant cargo vessel, because they are still used for other purposes, or not suitable.”
 Unfortunately the envelope got lost.
 In the case of the EcoClipper, most of the emissions are produced during the construction of the ship, while in the case of bulk carriers and container ships, they are mainly produced during operation and fuel production.
 The largest container ships now take 190,000 tonnes of cargo.
 There is not much data available on saltwater batteries, but they are less energy-intensive to build than many other types of batteries. The calculation is based on an estimate of 66 kg CO2/kWh of storage capacity and three generations of batteries over a period of 50 years.
 Almost one third of all cargo transported are fossil fuels themselves.
 The study can be downloaded when you subscribe to EcoClipper’s newsletter. The research is based on a typical life cycle analysis, but note that this is not a peer reviewed study.
In the mid 20th century, whole cities' sewage systems safely and successfully used fish to treat and purify their water. Waste-fed fish ponds are a low-tech, cheap, and sustainable alternative to deal with our own shit -- and to obtain high protein food in the process.
After we eat and drink, we excrete into toilets, which use water to flush our effluent into municipal sewage systems. By and large, the resulting sewage is either untreated, or treated in different kinds of wastewater treatment plants, the most advanced of which are expensive to run and have high energy demands. 
But even if sewage is treated, effluent is still high in levels of nitrogen, phosphorous, dissolved oxygen, and biological matter—essential nutrients for life on Earth. This causes eutrophication. The high levels of these nutrients lead to algal blooms, which in turn may produce toxins leading to mass fish deaths and biodiversity loss in rivers, lakes, and oceans. 
Essentially, the core of the issue is that rather than nutrients being recycled, as occurs in most ecosystems, it’s a one-way flow. Fixing these problems by, for example, making water use more efficient, or using more energy-intensive sewage treatment plans, doesn’t solve the root of the problem: the nutrient cycle is leaky. And you can’t fix a leaking sink by changing the amount or kind of water you use.Too much of a good thing
If we want to fix the leaking sink, we need to move away from the idea that human waste is inherently toxic, or that human activity is always bad for the environment. This way of thinking is grounded in the assumption that humans are somehow separated from nature. The logical conclusion of this assumption, then, is to separate us from natural cycles even more: building more refined, chemically and energy-intensive sewage treatment, building hard boundaries between food production and watersheds, and, failing that, using large-scale geoengineering experiments to clean our rivers.
But the main issue here is not that we are somehow toxic and so a burden to our environment. It’s that the nutrients we are releasing into the environment are too highly concentrated. This is especially the case when it comes to the “problem” of eutrophication. Caused by high-nutrient wastewater and agricultural run-off, it is generally thought as a bad thing. But consider the Greek root of the word: “becoming well fed.”The main issue is not that we are somehow toxic and so a burden to our environment. It’s that the nutrients we are releasing into the environment are too highly concentrated.
Eutrophication is only bad because good nutrients like nitrogen, carbon, and phosphorous, necessary for the majority of biotic life, are too concentrated—causing rapid algal growth, leading to too little oxygen in the water, as well as too many toxins produced by algae, both of which are deadly to fish. However, fish eat algae, so if algae growth were to be slowed down a bit, fish populations would multiply instead. The problem is not that wastewater is polluted, but that there is too much of a good thing, too highly concentrated for the ecosystem to absorb.How to fix a leaking sink
I first learned about the system of treating sewage through aquaculture when I lived in Hanoi. There, I found out that it’s actually very common, especially in poor agricultural communities, to reuse human waste for production.
This basic idea can also be brought to scale. During the communist period in China, many fish farmers had limited access to fish feed and local state cooperatives started organizing human waste collection systems. Eventually, in many Chinese cities, up to the 1990s, trucks and boats collected human manure in cities—some run by the state and some clandestine, illegal operations—and transported them to aquaculture operations in peri-urban land. From 1952 to 1966, about a third of fertilizers (which includes fish feed) used in China came from nightsoils, and by 1966, 90% of excreta were recycled.  Incidentally, today, massive seaweed production off the coast of China has likely greatly reduced the likelihood of eutrophication—an accidental form of bio-remediation and nutrient recycling. 
Image: Sewage water being pumped into a fish pond in the outskirts of Hanoi, Vietnam. Source: Edwards, 2005. 
Image: Wastewater after treatment in fishponds, Hanoi. Source: Edwards, 1996. 
One interesting large-scale example is the system that emerged in the outskirts of Hanoi in the 1960s. Hanoi, the capital of the newly independent communist nation, fighting a drawn-out war against Western occupying forces, had no municipal wastewater treatment. Sewage led out into two rivers, which flowed south and eventually merged with the Red River. During the communist period of collectivization of farmland, Vietnamese farmer cooperatives were excluded from the international market and so often used whatever resources available to them to feed fish, such as slaughterhouse wastes or spoiled grains. Seeing the untreated wastewater in the canals—a resource out of place—farmers started pumping it into large ponds.Seeing the untreated wastewater in the canals—a resource out of place—farmers started pumping it into large ponds. After trial and error, and investing the little they had in infrastructural improvements, they determined the right sewage-and-freshwater ratio needed that would dilute the wastewater enough so the fish wouldn’t die. They also let the untreated sewage water sit in primary and secondary ponds before mixing it into fish ponds, effectively killing harmful pathogens and allowing large solids to sediment, further promoting algal growth. Image: A local retail fish market in Yen So commune. Anders Dalsgaard. Source: Thi Phong Lan, Nguyen, et al. "Microbiological quality of fish grown in wastewater-fed and non-wastewater-fed fishponds in Hanoi, Vietnam: influence of hygiene practices in local retail markets." Journal of Water and Health 5.2 (2007): 209-218.
Farmers also grew plants such as duckweed and water hyacinth on the water and on its banks, which could then be fed to livestock—and had the dual benefit of drawing out heavy metals from the water. They also practiced fish polyculture, where species like catfish, carps, and tilapia were farmed together, and thus were more effective in cleaning the water and protecting small fry from predators. Every year, the ponds were drained, and the sludge at the bottom was then applied to nearby fields, further reusing available nutrients.
Eventually, these farmers developed a system that, by 1995, provided 40-50% of Hanoi’s total fish supply every year. Scientific measurements showed that the water from the fish ponds, when pumped back into the river, was well below the World Health Organisation’s recommended level for biological oxygen demand—an indicator to determine the efficiency of water treatment systems.  Essentially, they had created a water treatment plant for a city of 1.5 million people, at almost no cost to the state.A “low-cost folk technology” serving an entire city
You might be thinking: sure, this is one example of an interesting, but ultimately doomed, alternative to wastewater treatment. It is an aberration, and couldn't possibly be maintained for long. Unfortunately for your internal cynic, it actually can be. The city of Kolkata (formerly Calcutta), India—population 14.8 million—has the largest sewage-fed aquaculture system in the world. Though farmers had been using sewage to feed fish in different ways since the 19th century, the system became more developed starting in the 1940s.
Image: Fish ponds in the East Kolkata Wetlands, the largest sewage-fed aquaculture system in the world today. Source: iStock.
During the British colonial period, administrators built a series of canals through the city that functioned as its sewers. These let out into the Bidyadhari River. However, this river quickly silted up and became unusable. As a result, an adjacent wetland area transformed from tidal salt marshes to primarily freshwater marshes. Two sewage canals were then built in 1940 to further extend the city’s effluent to the ocean. It was at this point that local farmers started rerouting the sewage water into fish ponds in the former salt marshes, growing vegetables on the banks of the sewage canals, and forming cooperatives to manage the wastewater.
Though the Kolkata system was developed over time, it is quite systematic. Every year, ponds are first drained and sludge is applied to fields. Sewage water is fed into the pond slowly at low depth and allowed to sit for two weeks. This basically mimics conventional sewage treatment systems, where sewage is first treated through stimulating algal and bacterial growth, harmful sediments are left to settle, and most parasites are killed because their eggs and worms die if they don’t find a host within two weeks. Then, fish are stocked in another pond, and slowly sewage water is introduced into the pond at a sewage-to-water ratio of 1:4. All of this requires skill and knowledge developed over generations, allowing farmers to know when oxygen levels are too low, which could kill the fish.   The resulting effluent can reach the water quality of conventional treatment. 
Image: A sluice gate made of bamboo at the Eastern Kolkata Wetlands. Water hyacinth is grown to help purify the water and to feed livestock. Source: Mukherjee, 2020. 
Image: Every year, the ponds are drained, and the sludge at the bottom is applied to nearby fields, further reusing available nutrients. Source: Take pride in the East Kolkata Wetlands (Facebook-page).
Through trial and error and good judgement, local farmers have developed a wastewater treatment system that is extremely efficient and adaptive to local conditions. They can distinguish the kind of effluent—industrial or domestic—through the hues it gives off, and will control or dilute it when necessary. For example, sewage from tanneries can be toxic to fish, so they will not use it. They vary water levels according to season, weather, and available quantities of effluent. They know the hue of greenish-black the water needs to be to have an optimal oxygen and ammonia level for fish. They can tell whether there is too little oxygen by paying attention to the degree by which fish come up to the surface to gulp air. Farmers harvest snails in the water to protect fish growth, which are then crushed and fed to ducks, whose droppings in turn fertilize fish ponds and nearby soils. They plant water hyacinths and duckweed to absorb heavy metals from the sewage water.  The Kolkata fish farms provide 40% of the region's fish production and process 80% of the city’s sewage. The Kolkata fish farms provide 8000 tons of fish per year to the city, or 40% of the region’s fish production. It processes 80% of the city’s sewage, and reduces the nutrient and organic loads of the city’s sewage water by 50-90%, while keeping bacterial loads to an acceptable level under WHO guidelines. It is calculated to save the city an equivalent of $64,400,000 per year in sewage treatment costs—making Kolkata an “ecologically subsidized city”.  The system provides farmers a return over investment of 28% and provides 200,000 people with a livelihood.  While profit shouldn’t itself be the goal of this system—it’s a public service, after all—it certainly helps to defray costs of wastewater treatment. In a small municipality in Karnal, northern India, one study showed that municipal sewage-fed fish ponds, installed in the 2010s, provided over $25,000 of net profit per year to the municipality, as well as indirect benefits such as improving nearby soils through the sale of treated wastewater to farmers.  Image: Waste-fed fish ponds provide steady sources of protein for small-holder farmers. Source: Fish Farming in the East Kolkata Wetlands, Ramble On, Priya Mallic. Image: Fish harvested from the East Kolkata Wetlands. Source: Fish Farming in the East Kolkata Wetlands, Ramble On, Priya Mallic. Still, when introduced into small rural communities, the benefits extend far beyond monetary profit, to the social, cultural, and ecological services provided by the fish ponds. This includes improving soil quality, adaptability of local communities to climate change, leisure (e.g. fishing with friends), and steady sources of protein for small-holder farmers. For example, even if they don’t sell the fish, a small sewage-fed fish pond can provide a family of six with 8kg of fish, per person, per year—a significant raise in protein intake for many rural communities.  In the case of the Eastern Kolkata Wetlands, the fish ponds also help to recharge the ground water—a serious issue in India where many aquifers are nearing depletion.  Kolkata’s wetlands are a “low-cost folk technology”  treating the majority of the sewage of a city with a population the size of New York. This is made possible through the development of a vast human-fish-plant ecosystem, a city-scale wastewater treatment plant that emerged through the creativity, ecological knowledge, and direction of local farming communities. Over 90 systems in Germany in the early 20th century By this point, your internal cynic might have come up with another counter-argument: sure, so it works at scale. But you would have to be pretty desperate, and poor, to stoop down to farming fish in sewage water. While it might work in India, and worked for a while in Vietnam and China, it would never work in developed countries, where there are higher sanitation standards, and where no one would want to eat the fish farmed in sewage anyway. Image: A view of the former sewage-fed aquaculture system in Munich, Germany, today a bird sanctuary. Photo: Peter Schleypen, 2012. Source: Historisches Lexikon Bayerns. You may be surprised to learn that, in fact, over 90 such systems existed in Germany in the early 20th century.  Up until the 1990s, the city of Munich still processed most of its wastewater through fish farming. Indeed, Germany has pioneered some of the more detailed and rigorous scientific investigation into the large-scale viability of sewage-fed fish ponds, as early as the 1890s. Up until the 1990s, the city of Munich in Germany still processed most of its wastewater through fish farming. Like in China, wastewater-fed fish ponds have a long but unappreciated history in Europe. Castle moats, monasteries, and villages often had wastewater-fed fish ponds. As cities grew rapidly in the 19th century, untreated wastewater was simply flushed into rivers, leading to the collapse of fisheries across Europe as well as generally unsanitary conditions and the spread of disease. There was a growing recognition that sewage should be treated; one common indicator of adequate treatment methods was that trout are able to live in the treated water. As a result, civil engineers and scientists constructed small fish ponds to test the quality of municipal sewage treatment plants. Gustav Oesten, a civil engineer charged with wastewater treatment in Berlin, began to experiment in the late 1880s with using fish to treat wastewater, and to harvest fish as a secondary product of sewage treatment. He was able to spend the good part of a decade conducting experiments with different fish species, designs for ponds, and various local and weather conditions.  Image: Feed channel for the fish ponds of the Munich sewage-fed aquaculture system. Image by Bjs (CC BY-SA 3.0), Wikimedia Commons. Through these experiments, he showed conclusively that fish growth accelerates in sewage water, and that fish in turn help purify sewage water. Trout were not very good fish for this purpose, because they cannot tolerate water with high oxygen levels—common in wastewater systems, a byproduct of rapid algae growth. Carp, who can come up for air when oxygen levels are intolerable, grew very well—those fed with sewage far exceeding production of those in normal fish ponds. But, using trout, he proved that the water was of high enough quality to enter back into the water shed. His experiments suggested that fish ponds could be designed to help address Europe's water crisis and, at the same time, provide an economic return through the sale of fish. By the beginning of the 20th century scientists throughout Germany started conducting more small-scale experiments. Bruno Hofer, a fish scientist better known for pioneering the study of fish pathologies, started scaling up these experiments, showing in the early 1900s that wastewater of larger institutions like hospitals, breweries, and factories, as well as smaller municipalities could theoretically be treated with fish ponds. He even went further, and “dared” to propose such a system for a city as large as Munich—a notion that was perhaps considered outlandish at the time. Image: A sprinkler introducing secondary treated wastewater diluted with river water into a wastewater-fed fishpond in Munich, Germany. Source: Edwards, 2005.  By 1929, however, after several successful implementations of Hofer’s design around Germany, the city of Munich built its own fish pond wastewater treatment system, which served the whole city until the 1990s. This was the largest such system implemented at the time in the world, initially designed to process the wastewater of 500,000 people. The system was so efficient that the water leaving the ponds, fully treated, was comparable to natural water in quality and nutrient level.  Many applications As these examples illustrate, sewage-fed aquaculture is a solution to many interlinked problems. It processes waste—from agriculture, livestock, and cities—and cycles those nutrients back into the system through food and agricultural production. It reduces nitrogen and phosphorous levels in the water, preventing eutrophication further downstream. It reuses available water, slowing down the water cycle and replenishing groundwater. It further reduces unnecessary inputs like chemical fertilizers, phosphates, and energy-intensive fish feed. Finally, it creates jobs and a source of income, especially necessary in poor countries. If we were to calculate the fertilizer potential of sewage water alone, this would be reason enough to develop systems to reuse it. For example, one study estimated that, in the year 2000, all of India’s sewage was worth an equivalent of $2,000,000 per day in fertilizer costs.  In other words, on any given day, all of India is flushing several million dollars down the toilet. Waste-fed fish ponds would be of great help in capturing this wealth. Perhaps counter-intuitively, scientists have found that waste-fed fish ponds may actually be especially useful for arid countries, where water is scarce, by re-using wastewater for protein production.  Fish ponds don’t have to be for productive use alone. They can be integrated into wetlands and conservation areas, leisure fishing, tourism areas, or educational sites. They provide opportunities for improving biodiversity and making urban life more permeable for nature. Fish ponds don’t have to be for productive use alone. They can be integrated into wetlands and conservation areas, leisure fishing, tourism areas, or educational sites. Another reason waste-fed fish ponds continue to be relevant is that it is low-cost and low-tech, and therefore has little barriers for implementation. While high-tech, high-input systems like hydroponics, vertical gardening, and automated agriculture are getting a lot of press these days, the fact is that the majority of the world’s farmers have little to no access to capital and relies on small, but mostly sustainable, interventions to feed a stunning 70% of the global population.  Waste-fed fish ponds offer a source of subsistence at little financial risk to these small farmers.  Equally, when developed at the municipal level, they offer small towns, villages, and resource-poor communities opportunities to defray the costs of wastewater treatment, as well as generating local employment and improving sanitation.   Why don't we do this more often? Despite many advantages, most sewage-fed aquaculture systems have either been totally stopped or are in decline. So what happened? The first possible reason, and the one that most people might raise, is the “yuck factor”. Perhaps it's just too gross for most people to eat fish grown from poop. By and large, this wasn't the problem: consumers' surprising acceptance of waste-fed fish is a constant in the research on urban fish ponds.  Furthermore, about 10% of the world’s population probably already consumes food irrigated with wastewater , and, even in the European Union, where agricultural regulations are famously strict, many farmers already apply sewage sludge to their fields—but European consumers don’t seem to care too much. Image: Tilapia. The second possible reason for their decline is that it's not safe. And, it’s true, here is where the most care needs to be taken in designing effective wastewater treatment. There is good evidence showing that sewage treatment in fish ponds can be as safe as conventional methods. Some of the strongest evidence to support this comes from a city-sized experiment conducted in the 1980s in Lima, Peru, sponsored by the World Bank and the United Nations Development Project. Aid agencies worked closely together with the city government to design a large-scale aquaponic sewage treatment site.  The site was basically a city-sized proof-of-concept. Endless measurements were taken over its two decades of operation, adjusting different variables throughout the project’s lifespan, and controlling for changes in volume of sewage and weather. It was found quite conclusively that fish-based sewage treatment was not only a viable and economical alternative for low-income countries, it also met stringent World Health Organization guidelines for water sanitation. The fish were also tested for human consumption. In all three trials, 100% of fish tested were rated at “very good” in safety levels.  This study wasn't alone: numerous studies have investigated the safety of fish grown in sewage ponds.  More than just a leaking sink If it's not the “yuck factor” or safety, then what was it? In Hanoi, the waste-fed fishponds were not fully recognized for their potential, and peri-urban development in the 1990s began to encroach on the fish ponds. As the communist era came to an end, land near the city became increasingly valuable, and ponds were filled up for housing construction. Sewage became mixed with untreated industrial effluent, leading to large amounts of sewage being poisonous to fish, in turn leading farmers to switch to pelleted feed, by then increasingly available as Vietnam’s domestic market was opened to foreign trade.   Today, Hanoi only treats 22% of its sewage, the rest flows directly into its river systems, and 180,000 cubic meters of waste water are discharged every day into the To Lich river, the same river that serviced the fish ponds.   The disappearance of fish ponds in Germany can also be largely attributed to urban growth. As cities grew, peri-urban areas—where fish ponds necessarily needed to be placed due to them having to be close to sewage lines and sources of fresh water—became more valuable. Pressured by booming real estate prices, less availability of land, high costs of labour, as well as diminishing returns on investment as domestic fish breeding had to compete with international markets, governments inevitably chose to close the fish ponds, or convert them into more conventional sewage treatment plants. Even in Munich, the largest system built in Germany, management was costly and became less and less appealing to the municipality. Munich’s fish ponds were eventually converted into an estuary, where migrating birds come to rest. Fish production is no longer its primary goal, and the estuary only absorbs a small percentage of Munich’s wastewater.  Image: The East Kolkata Wetlands in 2005. Source: Google Earth. Image: The East Kolkata Wetlands in 2019. Source: Google Earth. The system at Kolkata is still operational, but suffering from similar symptoms. At their peak, fish ponds in the East Kolkata Wetlands were as large as 12,000 hectares. This has shrunk to 4,000 hectares due to encroaching urban development. In Kolkata, too, workers struggle to deal with industrial effluent such as that from the sizeable leather tanning industry, which is poisonous to the fish and indiscriminately dumped into the municipal wastewater system.     Thankfully, unlike Hanoi’s government, the city of Kolkata and the Indian government recognized the importance of this system, and put in a series of regulations to protect it from further development. Still, informal and illegal development—where developers fill up ponds with debris overnight and then build on it as farmers are forced to abandon it—is slowly chipping away at the wetlands. So the main driver of their disappearance is urban expansion into the peripheries. This is largely due to the global speculation on real estate—which constitutes 60% of all capital investments today.  When given a choice between selling peri-urban land to the highest bidder, and pairing sewage treatment with some fish production, most officials won’t think twice—the fish ponds have got to go! A second reason is the high prevalence of toxic chemicals in our water systems—which are too concentrated for ecosystems, and aquaculture systems, to absorb. We should ask ourselves if it’s really worth it to permit these products if they make it harder for us to mend the ecological rift between our settlements and their surroundings. More messy, organic systems are often derided as backwards and primitive, when in fact they may be far more appropriate and sustainable than the energy-intensive, easily replicable “solutions” valued by planners and engineers. A third reason is the relatively cheap cost of fossil fuels. In most industrialized countries, it is much more rational to choose for sewage treatment plans with a small land footprint but a large carbon footprint. In a world where energy is cheap, environmental costs can be pushed further and further downstream. But they will eventually circle back to us, and already are. Finally, a significant factor, and one which we shouldn’t ignore, is the bias of our leaders and of professional engineers against more messy, organic systems like that of wastewater-fed aquaculture. Such low-tech solutions are often derided in popular culture as backwards and primitive, when in fact they may be far more appropriate and sustainable than the energy-intensive, easily replicable “solutions” valued by planners and engineers.  Each reason points to a deeper problem: our economy's inability to value the right things. Like so many sustainable solutions today, and many of those discussed on this website, sewage-fed fish ponds suffer from the “you can’t change this one thing without changing the whole system” problem. These systems are beset by global real estate speculation, toxic chemicals in our food and household products, contamination by industry, the cheap price of fuel, and the deep-seated idea that humans are separate from the ecosystems they are embedded in. At the root of it all is a system of value that is not in line with our ecological needs as a species, and as a member of Earth’s living community. Fish ponds are a low-tech, low-cost, safe, and sustainable way to fix our society's leaking sink. But when we get down there on our hands and knees, we might find a lot of other things that need fixing. Aaron Vansintjan Thank you to Henning Fehr for doing research on the fish pond system in Germany, Michael DiGregorio for telling me about the Vietnamese system, Phuong Anh Nguyen for the extra research into it, and Geert Vansintjan for always keeping me inspired. * Support Low-tech Magazine via Paypal or Patreon. * Subscribe to our newsletter. * Buy the printed website. References  For example, in many developed countries, sewage treatment often involves constant automated stirring of large ponds of water—a system which is hard to maintain and takes a lot of energy. While sewage treatment only accounts for 4% of national energy use in the US, they account for up to 50% of municipal energy use—a significant portion of the domestic energy footprint. That means that towns and cities could actually decrease their energy impacts significantly if they switched to different treatment plants. See https://betterbuildingssolutioncenter.energy.gov/sites/default/files/Primer%20on%20energy%20efficiency%20in%20water%20and%20wastewater%20plants_0.pdf  It also contributes to a little-understood phenomenon called coastal darkening, where our ocean floors become muddier and darker, leading to a lower albedo, or reflectivity, of the Earth’s surface, in turn triggering global heating as well as reduced ability for marine life to receive daylight. https://www.hakaimagazine.com/news/the-environmental-threat-youve-never-heard-of/  Edwards, P. (2003) Philosophy, principles and concepts of integrated agri-aquaculture systems. In: Gooley, G. J., & Gavine, F. M. (Eds.), Integrated agri-aquaculture systems: a resource handbook for Australian industry development. Rural Industries Research and Development Corporation.  Edwards, P. (2015). Aquaculture environment interactions: past, present and likely future trends. Aquaculture, 447, 2-14.  Edwards, P. (1996). Wastewater reuse in aquaculture: Socially and environmentally appropriate wastewater treatment for Vietnam. The ICLARM Quarterly, January.  Mukherjee, J. (2020). Blue Infrastructures. Springer Singapore.  Ho, L., & Goethals, P. L. (2020). Municipal wastewater treatment with pond technology: Historical review and future outlook. Ecological Engineering, 148, 105791.  Edwards, P. (2009). Traditional asian aquaculture. In New Technologies in Aquaculture (pp. 1029-1063). Woodhead Publishing.  A term attributed to Dhrubajyoti Ghosh, a high-profile activist for the Eastern Kolkata Wetlands.  Banerjee, S., & Dey, D. (2017). Eco-system complementarities and urban encroachment: A SWOT analysis of the East Kolkata Wetlands, India. Cities and the Environment (CATE), 10(1), 2.  Kumar, D., Chaturvedi, M.K., Sharma, S.K. and Asolekar, S.R., 2015. Sewage-fed aquaculture: a sustainable approach for wastewater treatment and reuse. Environmental monitoring and assessment, 187(10), pp.1-10.  Lightfoot, C., Bimbao, M.A.P., Dalsgaard, J.P.T. and Pullin, R.S., 1993. Aquaculture and sustainability through integrated resources management. Outlook on Agriculture, 22(3), pp.143-150.  Datta, S. (2006). Waste Water Management Through Aquaculture. Journal of Environmental Management. 1. 339-350.  Mukherjee, J. (2020) citing Dhrubajyoti Ghosh.  Edwards, P. (2005). Development status of, and prospects for, wastewater-fed aquaculture in urban environments. Urban Aquaculture. Costa-Pierce B, Desbonnet A, Edwards P, Baker D, editors. Wallingford Oxfordshire: CABI Publishing, 45-59.\  Prein, M. (1988, December). Wastewater-fed fish culture in Germany. In Edwards, P. and Pullin, RSV Wastewater-Fed Aquaculture. Proceedings of the Internation al Seminar on Wastewater reclamation and Reuse for Aquaculture, Calcut ta, India (pp. 6-9).  One issue with the fish ponds in the German case was the high variability of the weather. Less sun in the Fall and Spring meant that algal production was much lower, in turn impacting fish growth and the ability of the system to treat wastewater at constant rates. In the winter months, ponds will often freeze, leading to oxygen deficiencies and fish deaths. As solar radiation can fluctuate throughout the day, the fish ponds require daily management to balance fish growth, algal growth, nutrient removal, and too much sewage that would lead to fish deaths.  Calculated using the Indian Rupee to US Dollar exchange rate in 2000, adjusted by the author for inflation of USD in 2021 from data provided by Jana, B. B., Heeb, J., & Das, S. (2018). Ecosystem Resilient Driven Remediation for Safe and Sustainable Reuse of Municipal Wastewater. In Wastewater management through aquaculture (pp. 163-183). Springer, Singapore.  In Israel, for example, mid-century kibbutzim colonies, which were often limited in the groundwater available to them, experimented in the 1960s with reusing sewage for fish production.In Egypt, the government has put its hope in wastewater-fed aquaculture, in an attempt to increase domestic protein production and maximize use of water.   See also Kolkovsky, S., Hulata, G., Simon, Y., Segev, R., & Koren, A. (2003). Integration of agri-aquaculture systems the Israeli experience. In: Gooley, G. J., & Gavine, F. M. (Eds.), Integrated agri-aquaculture systems: a resource handbook for Australian industry development. Rural Industries Research and Development Corporation.  El-Zohri, M., Hifney, A. F., Ramadan, T., & Abdel-Basset, R. (2014). Use of Sewage in Agriculture and Related Activities. In: Pessarakli, M. (Ed.), Handbook of plant and crop physiology. CRC Press.  In Germany in the 20th century, consumers at first rejected these fish, but municipalities engaged in public communication campaigns to convince people otherwise.  In Lima, Peru, researchers conducted a study of whether the fish were accepted by consumers at the market, and were surprised to find out that people weren’t so bothered when they found out where the fish came from.  In Kolkata, too, sewage-fed fish still constitute 40% of the local fish market, even when consumers have alternatives available.  WHO (2015) Sanitation. Fact sheet no. 392. World Health Organization, Geneva  Cointreau, S. J. (1990). Aquaculture with treated wastewater: A status Report on studies conducted in Lima, Peru. Applied Research and Technology (WUDAT), Technical Note No. 3. The World Bank Water Supply and Urban Development Department: p. 1-56.  In a fourth trial, only 6% were rated as “unacceptable”, but this was because they deliberately increased the ratio of sewage-to-water above the acceptable level, to mimic an “accident”. Still, these same fish were then rated as “very good” when the sewage level was decreased for a subsequent 30 days. This shows that even in the case of an accident, fish can easily recover to being safe for consumption. See UNEP International Environmental Technology Centre. (2002). Environmentally Sound Technologies for Wastewater and Stormwater Management: an International Source Book (Vol. 15). International Water Assn. : Where there are insufficient resources to build sanitary requirements into the system, researchers recommend that cleaning, butchering, and packaging be done in sanitary conditions, so that fish muscle does not risk being contaminated with pathogens on the skin or in intestines. Cooking fish thoroughly is also recommended—and in Kolkata, local cuisine fortunately does not include raw fish. Another proposal is to transfer fish to clean water ponds two weeks before harvest; this both reduces the risk of pathogens being present in fish muscle and intestines, and helps to eliminate possible unpleasant odours. Edwards P. (1990) Reuse of human excreta in aquaculture: A state-of-the-art review. Draft Report. World Bank, Washington DC. And when it comes to the presence of toxic chemicals, there is also good evidence to show that this is not a significant problem. However, this does depend on local conditions. For example, people in industrialized countries use many more detergents and pharmaceuticals that may impact the fish. This includes a broad category of toxins called “emerging contaminants” which are found in new products like beauty products and certain pharmaceuticals. There have been little recent studies in industrialized countries on the effects of these products on sewage-fed fish—in large part because these systems had largely been phased out by the time these household commodities became more prevalent in the last fifty years.         Edwards, P. (2004). Decline of wastewater-fed aquaculture in Hanoi. Aquaculture Asia, Volume IX (4, October-December): 13-14.  Hoan, V. Q., & Edwards, P. (2005). Wastewater reuse through urban aquaculture in Hanoi, Vietnam: status and prospects. Urban aquaculture. CABI International, Wallingford, 103-117.  Saigoneer (2019). Only 13% of Vietnam's Urban Sewage Is Treated Before Discharge. The Saigoneer. https://www.saigoneer.com/saigon-environment/17571-only-13-of-vietnam-s-urban-sewage-is-treated-before-discharge  Kiet, Anh. (2019). No technology can radically clean Hanoi's polluted river if sewage not treated: Mayor. Hanoi News. http://hanoitimes.vn/no-technology-can-clean-hanois-heavily-polluted-river-if-people-keep-pouring-sewage-into-it-mayor-300420.html  Bunting, S. W. (2007). Confronting the realities of wastewater aquaculture in peri-urban Kolkata with bioeconomic modelling. Water Research, 41(2), 499-505.  Jana, B. B. (1998). Sewage-fed aquaculture: the Calcutta model. Ecological Engineering, 11(1-4), 73-85.  Stein, S. (2019). Capital city: Gentrification and the real estate state. Verso Books.  Mara, D. (2013). Domestic wastewater treatment in developing countries. Routledge.
If the electricity for a vertical farm is supplied by solar panels, the energy production takes up at least as much space as the vertical farm saves.
Urban agriculture in vertical, indoor “farms” is on the rise. Electric lights allow the crops to be grown in layers above each other year-round. Proponents argue that growers can save a lot of agricultural land in this way. Additional advantages are that less energy is needed to transport food (most people live in a city) and that less water and pesticides are required.Which crops?
The vertical farms that have been commercially active for several years all focus on the same crops. These are agricultural products with a high water content, such as lettuce, tomatoes, cucumbers, peppers, and herbs. However, these are not crops that can feed a city. They contain hardly any carbohydrates, proteins, or fats. To feed a city, it takes grains, legumes, root crops, and oil crops. These are now grown globally on 16 million square kilometers of farmland - almost the size of South America. 1Growing wheat vertically
An art installation currently presented in Brussels - The Farm - explores what it would take to grow wheat in a vertical farm. For the experiment, 1 square meter of wheat was sown in a completely artificial environment. By measuring the input of raw materials such as energy and water, the project shows the extent to which natural ecosystems support our food production. When wheat is planted in the ground next to each other, instead of above, the sun provides free energy and the clouds free water.A loaf of bread for 345 euros
The experiment shows that growing 1m2 of wheat in an artificial environment costs 2,577 kilowatt-hours of electricity and 394 liters of water per year. The energy required for the hardware production (such as lighting) is not included in these results, so this is an underestimate. The building’s energy cost is also not taken into account, and that concerns both the construction and its use, for example, for heating, cooling and pumping water.
The cost calculation does include the price of the equipment (1,227 euros). The lifespan of the infrastructure is estimated at 8 years. Converted, the production of 1 m2 of wheat in an artificial environment costs 610 euros per square meter per year (including infrastructure, electricity, and water). Of this, 412 euros goes to electricity consumption and only 1 euro to water consumption. This calculation may be an overestimate because the installation is set up in an exhibition space.
The “farm” produces four harvests per year. With every harvest, enough wheat is grown to make one loaf of bread (580 grams), which has a cost of at least 345 euros. Each loaf contains 2,000 kilocalories, the amount that an average person needs per day. As a result, 91 m2 of artificially produced wheat is necessary for each person, with a total cost of 125,680 euros per year.The paradox of vertical farming
Artificial lighting saves land because plants can be grown above each other, but if the electricity for the lighting comes from solar panels, then the savings are canceled out by the land required to install the solar panels. The vertical farm is a paradox unless fossil fuels provide the energy. In that case, there’s not much sustainable about it.
Calculated at a yield of 175 kilowatt-hours per square meter of solar panel per year, the indoor cultivation of 1 m2 of wheat requires 20 m2 of solar panels. This is a underestimate because the calculations are based on the average yield of a solar panel. There is much less sunlight in winter than in summer. In reality, the vertical farm requires many more solar panels to keep operating all year round. There is also a need for an energy storage infrastructure, which costs money and energy too. Finally, solar panels’ production also requires energy, which would demand even more space if the production process itself were to run on solar panels.Innovation?
All this criticism also applies to vertical farms where lettuce and tomatoes are grown. In this case, there is a significant reduction in water use. These companies are profitable, but only because the process relies on a supply of cheap fossil fuels. If solar panels supplied the energy, the extra costs and space for the energy supply would again cancel out the savings in terms of space and costs. The only advantage of a vertical farm would then be the shorter transport distances. Still, we could just as well make transport between town and countryside more sustainable.
The problem with agriculture is not that it happens in the countryside. The problem is that it relies heavily on fossil fuels. The vertical farm is not the solution since it replaces, once again, the free and renewable energy from the sun with expensive technology that is dependent on fossil fuels (LED lamps + computers + concrete buildings + solar panels). Our lifestyle is becoming less and less sustainable, increasingly dependent on raw materials, infrastructure, machines, and fossil energy. Unfortunately, this also applies to almost all technology that we nowadays label sustainable.
Kris De Decker
Proofreading: Eric Wagner
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Can we make modern health care carbon-neutral and maintain the levels of care, pain relief, and longevity that we have come to take for granted?
Illustration: The human powered hospital. By Golnar Abbasi & Arvand Pourabbasi. Taken from Human Power Plant: Human Powered Neighbourhood, Melle Smets & Kris De Decker.The environmental footprint of the health care sector
Health care is one of the most important economic sectors in high income countries, but its environmental footprint is underreported and not often considered. Most research into sustainable health care is less than five years old. A 2019 research paper calculated that the sector accounts for 2-10% of national carbon footprints across all OECD countries, China, and India, with an average share of 5.5% overall. [1-2]
The data refer to the year 2014, when the health care sectors of all these 36 countries combined were responsible for 1.6 Gt of greenhouse gas emissions. This corresponds to 4.4% of the global total emissions that year (35.7 Gt) – almost double the share of aviation. The US has the most carbon-intensive health care system, accounting for up to 10% of national carbon emissions.  It also produces 9% of national air pollution, 12% of acid rain, and 10% of smog formation nationally.
The environmental footprint of health care keeps increasing. For example, in the US, the health care sector’s greenhouse gas emissions grew by 30% between 2003 and 2013.  The rise in emissions couples an increase in spending – in fact, the emissions are often calculated based on spending. US national health expenditures as a percentage of Gross Domestic Product (GDP) increased from 3% in 1930, to 5% in 1960, to 10% in 1983, to 15% in 2002, and to 17.7% in 2019. [4-5] In the EU, health care spending per capita more than doubled between 2000 and 2018, and total spending is now at 9.9% of GDP. 
If the whole world would copy today’s US health care system, the global carbon footprint of the health care sector would amount to almost half of total emissions worldwide in 2014.
The 36 countries whose health care systems together cause 4.4% of global emissions only have 54% of the worldwide population. The remaining 46% of the population produces little or no health care related emissions because they don’t have access to health care. If we were to extend the OECD-China-India health care system globally, emissions would double to about 8% of the worldwide total. Furthermore, there are very large differences between these 36 countries. If the whole world were to copy the US health care system, the global carbon footprint of the health care sector would amount to around 16 Gt – almost half of total emissions worldwide in 2014.Intense spotlights, high power medical equipment
What makes modern health care so resource-intensive?  To start with, modern hospitals are high energy users, primarily because of large plug loads from medical devices, lighting, ventilation and air-conditioning. [3, 8-12] In operating rooms, the high power use is mainly due to the use of intense spotlights and ultra clean ventilation canopies. In intensive care units and diagnostic imaging departments, medical equipment dominates the power load. 
Technologically Advanced Operating Room. iStock.
An MRI-scanner in Taipei, Taiwan (2006). Image: Kasuga Huang (CC BY-SA 3.0).
Like so many other sectors in modern society, health care has come to rely on all types of machines and devices.  Some of this medical equipment has very high power use. For example, an MRI-scanner, one of the most powerful diagnostic imaging technologies, can use as much electricity as more than 70 average European households. A 2020 study calculated that high-tech medical diagnostic technology (both MRI- and CT-scanners) was responsible for a whopping 0.77% of global carbon emissions in 2016. 
The power use of smaller medical equipment is poorly researched, but an inventory of two US hospitals showed that they had 14,648 and 7,372 energy using devices, of which the infusion pumps alone consumed more electricity on aggregate than an MRI-scanner.  The high density of medical equipment also increases the electricity use of air-conditioning in hospitals. Resource use along the supply chain
Even more energy – around 60% of the total – is used indirectly along the supply chain. [1,3,10,15]. This concerns the procurement of medical equipment, pharmaceuticals, and other medical products.
To start with, the growing number of medical devices used in hospitals also needs to be manufactured and brought to market. This requires activities such as the mining of resources and the construction and operation of research laboratories, factories and transport vehicles. This "embodied energy" of the medical equipment supply chain is very poorly researched. A study calculated that the production of an MRI-scanner requires more than half the fossil fuels used in the production of a passenger jet, and that the embodied energy is one third of the total energy use of the machine. 
Modern health care is also highly dependent on pharmaceuticals, which account for between 10 and 25% of total health care emissions, depending on the country. [15,17] A 2019 study revealed that the global pharmaceutical industry produces more greenhouse gases than the global automotive industry: 52 MtCO2 versus 46 MtCO2.  However, there is almost no data about the environmental footprint of specific pharmaceuticals, because corporate secrecy prevents scientists from making life cycle analyses.
Pharmaceutical Manufacturing Laboratory. Source: iStock.
Rubber gloves production line. Source: iStock.
Face mask production line. Source: iStock.
Single-use disposable products are another source of health care energy use and pollution. [19-24] These products are worn by medical personnel and patients (face masks, gloves, overshoes, hats, drapes, gowns). Towels, basins, sterile plastic packaging, and utensils such as syringes, laryngoscopic handles and blades, anaesthetic breathing circuits, and even surgical instruments are also provided for single use. These disposable products are supplied to hospitals in so-called custom packs, which are sets of prepackaged sterile products for any specific medical procedure you can imagine. In principle, once a pack is opened, all items are discarded, even if they were not used.
When these practices are questioned, it is often for the hospital waste they create -- the average patient in a hospital produces at least 10 kg of waste per day.  However, the environmental footprint increases significantly if the embodied energy and waste in the supply chain for making these disposable products is considered too. A study of cataract surgery in the UK – cataracts are the main cause of blindness worldwide – shows that the manufacturing of disposable materials accounts for more than half of the total carbon footprint of the procedure. Anesthetics & Vaccines
Finally, some specialist medical drugs produce emissions too. Inhalation anesthetics, which suppress the central nervous system and are a cornerstone of surgery, are potent greenhouse gases, which evaporate into the atmosphere after they have been inhaled by the patient (vented to the outside through the high energy ventilation systems of modern operating rooms).  Maintaining a 70 kg adult anesthetized for an hour produces from 25 kg (using isoflurane) to 60 kg (desflurane) CO2-equivalents, which corresponds to the emissions of driving an average European car (121gCO2/km) for 200-500 km (or driving it for around 4 hours). 
Pressurized dose inhalers, which are used to treat asthma and chronic obstructive pulmonary disease, also release potent greenhouse gases. Globally, around 800 million pressurized dose inhalers are manufactured annually, with a total carbon footprint that corresponds to the yearly emissions of more than 12 million passenger cars. [17,27] Vaccines are another key element of modern health care. They release carbon emissions not only through their development and production, but also by their resource-intensive distribution, which involves a dedicated cold chain. I could not find any reference to its environmental footprint.Carbon footprint of medical procedures
Health care services often involve all of the above mentioned sources of emissions: medical devices, pharmaceuticals, and disposable materials. When the emissions in hospitals and along the supply chain are combined, it becomes possible to calculate the environmental footprint of medical procedures.
Operating room in cardiac surgery, 2020. Source: iStock.
For example, studies of cataract surgery and reflux control surgery in the UK estimated the carbon footprint to be 182 kg and 1 ton of emissions, respectively, which corresponds to between 1,517 km and 8,333 km of driving. [28,29] Renal dialysis, a treatment to replace kidney function, produces 1.8 to 7.2 tonnes of emissions per patient per year, equal to the emissions of 15,000 to 60,000 km of driving. [28,30]The limitations of carbon and energy efficiency
Although data on its environmental footprint is still incomplete, it seems quite clear that modern health care is not compatible with a transition to a low carbon society. The big question is whether or not this can be fixed without lowering the levels of care, pain relief, and longevity that people in high income societies have grown accustomed to.
Many efforts and studies into health care sustainability aim to reduce energy use and emissions without affecting the quality of medical treatments, often explicitly so. For example, the authors of a 2020 study into the Austrian health care system write that it’s “crucial to understand how the health care sector can reduce its emissions without undermining its service quality”.  Elsewhere, researchers write that “any solution that would reduce environmental impacts while reducing performance at the same time cannot be deployed”. 
As a consequence, many researchers tend to focus on improving carbon and energy efficiency. These strategies aim to deliver the same "performance" or "service quality" but with less energy (thanks to more energy efficient equipment), or with less emissions (owing to more renewable energy sources). 
The quality of medical treatments continues to improve, resulting in extra energy use that erases the carbon or energy savings that result from efficiency.
The problem is that the quality of medical treatments continues to improve, resulting in extra energy use that erases the savings that result from carbon and energy efficiency. For example, in 2012 researchers calculated that MRI-scanners could be made 10-20% more energy efficient with relatively simple changes in design and operation.  Some of their proposed changes are now in use, but the energy use of MRI-scanners has not decreased, on the contrary.
Medical Scientist working on brain tumor cure in a Research Center. Source: iStock.
A first reason is that MRI-scanners now come with higher field strengths (which offer diagnostic images of higher accuracy) and with larger boreholes (which improve patient comfort and allow obese or very muscular patients to be scanned). These innovations have improved the quality of care, but they have done so at the expense of extra energy use. In the 2012 study, the average power consumption per scan before the energy efficiency improvements was 15 kWh. A 2020 study measured an energy use of 17 kWh and 23.6 kWh per scan for an MRI-scanner with a field strength of 1.5 and 3 Tesla, respectively. 
Second, MRI-scanners with better diagnostic capabilities also increase energy use in unexpected ways, because medical equipment, pharmaceuticals, and treatments shape and change each other.  For example, doctors used to diagnose a patient through physical examination and communication, and only used diagnostic services to confirm the diagnosis, if necessary. Now, diagnostic tests happen upfront and drive the decision process, resulting in more tests and higher energy use. The introduction of new pharmaceuticals can foster increasingly energy-intensive diagnostic practices, too. For example, certain cancer treatment drugs are now being designed to treat a very specific tumor subtype, which requires more and more accurate medical imaging to identify the tumor subtype. 
Adding more renewable energy sources could potentially lower the emissions of health care both on-site and throughout the supply chain, but as the energy use of medical treatments continues to increase, this outcome is unlikely. Besides, a quick calculation shows that, even without further growth in energy use, a carbon neutral US health care system would gobble up the entire US renewable energy production – sun, wind, hydroelectric, wood, geothermal, biofuels, and waste.  The challenge is only slightly smaller in other high-income countries. Finally, renewable energy would not solve all of the health care sector’s environmental damage, and would not even eliminate all of its carbon emissions.Sufficient health care?
To reduce the environmental footprint of modern health care, we need to question the trend towards ever greater reliance on energy-intensive technologies and services. The same holds true in other domains of life. 
However, while some people see the charm and real advantages of frugal and past ways of living when it comes to comfort or convenience, few would be tempted to apply the same principles to health and longevity. After all, the health care equivalent of travelling more slowly or wearing an extra sweater at home may be living a shorter life, suffering more pain, or being less mobile in old age. For example, if we would stop using MRI-scanners, or only use those with a field strength up to 1.5 Tesla, the lower diagnostic accuracy will lead to some cancers not being detected, resulting in lower cancer survival rates, and a lower average life expectancy. Or at least, so it seems.
The surgeon, a painting by David Teniers, 1670s.
Barber-surgeon extracting a tooth, a painting by Adriaen van Ostade, 1630.
If health care is viewed in a historical context, it seems clear that there is a powerful connection between the use of energy-intensive medical technologies on the one hand, and the health and longevity of a population on the other hand. Even looking back less than a century shows much lower health outcomes and survival rates for all kinds of diseases, and today’s global average life expectancy (72.6 years) is higher than in any high-income country back in 1950.
Hospitals date back to antiquity, but they merely welcomed those gone mad or awaiting death. In the middle ages, surgery happened at the barbershop, where “barber-surgeons” offered blood-letting, tooth extractions, and amputations alongside the more usual haircuts and shaves. They brew their own anesthetics based on herbs and alcohol, which could be just as deadly as the treatment itself.  A look at the “developing” world today also seems to suggest a clear connection between health care emissions, which are very modest, and life expectancy, which can be 20 to 30 years below that in high income countries. [37-41]
However, if one digs deeper, the connection between energy use and longevity is not as strong as it seems. This is proven by the USA, which has the most expensive and unsustainable health care system in the world, but ranks behind most European countries on the Health Care Access and Quality Index (which measures death rates from 32 causes of death that could be avoided by effective medical care). US citizens also have a lower life expectancy than European citizens. Clearly, there are other factors at play, too.Resistance to disease
To start with, the quality of a health care system is not the only determinant of health and longevity. Here’s where history does have an important lesson to teach us. Medical knowledge dating back to antiquity viewed health in a more holistic way and placed great emphasis on building up the body’s inherent resistance to disease. For example, Hippocrates, often referred to as the father of Western medicine, prescribed diet, gymnastics, exercise, massage, hydrotherapy, and swimming in the sea. 
One could argue that our forebears had no other choice than to focus on preventing disease, because they had few treatments available. However, the wisdom of their approach is more obvious than ever. Nowadays in high income societies, many patients need medical treatment because of so-called lifestyle diseases – those caused by poor or excessive nutrition, lack of physical activity, stress, or substance abuse. Typical health risks are cardiovascular disease, diabetes type 2, depression, obesity, some types of cancers, and higher susceptibility to infectious diseases. Industrial society has given us effective medical treatments, but it's also making us sick.
This means that health and longevity can be promoted in other ways than through an increasingly resource-intensive health care system. By addressing the broader determinants of health and longevity, we could make a switch from curative to preventive medicine. [15,43] Preventive medicine is not about the government telling us not to smoke (and then cashing in tax money on the sales of cigarettes). Rather, it concerns systemic changes that go beyond behavioural change.
Rush hour in São Paulo, Brazil, 2005. Public domain.
For example, significantly reducing the use of cars in our societies would bring a surprisingly large number of health benefits that would lower the need for energy-intensive medical treatments. It would decrease the health damage done through traffic accidents and through air and noise pollution. It would make people more physically active (preventing many lifestyle diseases), and it would free a lot of public space for people to come together, for kids to play, and for trees to grow (all important factors for the mental health of a population). Finally, reducing the use of cars may easily save more greenhouse gas emissions than the health care system produces.
Switching to a healthier food production system, addressing the environmental damage done by the plastic industry, reducing poverty and social inequality, introducing shorter work hours, and more meaningful jobs are other examples of preventive medicine. We have not achieved the higher life expectancy of today only because of better health care systems. We also got it because of better education, sanitation, safety and traffic regulations, welfare systems, crime control, and a more reliable food supply. The low average life expectancy in poor countries is also partly due to these factors.
Preventive medicine would also reduce the health damage done by the medical treatments themselves. This concerns health damage resulting from medical errors or side effects of pharmaceuticals and more indirectly from the pollution that the health care sector generates. For example, air pollution from health care services contributes to the prevalence of asthma, which in turn increases the demand for health care. Climate change and other environmental damage threaten younger and future generations with even larger health impacts, for example through crop failures, spread of diseases, extreme weather events, and natural disasters. The law of diminishing returns
Second, within a health care system, medical practices with higher energy use do not necessarily lead to increased health outcomes in a proportional way. Like so many other sectors in industrial society, curative health care is vulnerable to the law of diminishing returns: it takes ever more energy to gain ever smaller increases in health outcomes.  Conversely, this means that a relatively small decline in the quality or specifications of medical treatments could yield comparably large reductions in resource use and emissions.
Infection control is a good example. The development of general anesthesia in the 1840s made surgery possible, but at the time over 90% of surgical wounds became infected, often leading to death.  The first major decrease in infection rates followed antiseptic practices (1880-1900), and the second followed the introduction of antibiotics (1945-1970). By 1985, the overall infection rate had decreased to about 5%. Since then, a lot of resources have been invested to achieve incremental gains towards 100% sterility, mainly by replacing reusable supplies by single-use, disposable products. 
Operating room nurse preparing instruments for surgery at the 3rd Station Hospital, Korea. 1951. Source: US National Library of Medicine.
If properly decontaminated, reusable supplies carry no increased infection risks, but cross-contamination between patients sometimes happens by mistake. Nevertheless, some scientists have advocated for a return to reusable products, which have a much lower environmental footprint in most cases. For example, the use of reusable laryngoscope handles produces 16-25 times less greenhouse gases than single-use, disposable ones. . The researchers admit that their approach may increase deaths from surgical infections. Still, they argue that the health damage caused by the production of single-use disposable supplies is even more considerable.
When it comes to maximizing returns, less affluent societies can teach us some lessons. Comparisons of cataract surgery in the UK and in India have shown that the same treatment (phacoemulsification) in India's Aravind Eye Clinics is much cheaper and produces only 5% of the emissions and 6% of the solid waste in the UK. This is mainly because the Indian surgeons reuse as many supplies, devices, and drugs on as many patients as possible. [26,46-49] In addition, they use locally manufactured supplies, implants, and drugs, and they apply a dual-bed system in which one patient is operated while another one is being positioned and prepared in the bed next to it.
Although these practices flout regulations for infection control in high income countries, cataract surgery in India achieves similar or better outcomes and does not cause any more infections than it does in the UK or the US. [26,46-49] Consequently, it may well be that the law of diminishing returns has reached its ultimate limit, in the sense that an expensive and unsustainable medical practice does not seem to bring any health benefits at all. The Indian eye clinics demonstrate that an effective model of care is possible without expensive and unsustainable supplies and resources. Medical innovation can happen without new technology.Driven by profit
The law of diminishing returns and the focus on curative medicine are both rooted in the fact that medical innovation is primarily driven by profit. [50,51] Private companies who develop and sell medical equipment, pharmaceuticals, and other health care products have nothing to win or earn if the demand for new curative health care technologies and products declines, or if medical technologies were to be judged in relation to their resource use. The medical industry -- logically -- wants to increase the sales of its products, and has enormous marketing budgets and lobbying power at its disposal to achieve that goal. 
King George Military Hospital, electrical treatment and x-ray room. 1915. Source: US National Library of Medicine.
The WHO estimates that 20-40% of health care spending is wasted, and argues that “the cost-effectiveness, real need, and likely usefulness of many innovative technologies are questionable”. [44, 37] An increasing body of academic literature shows the extent to which patients in high income countries are “overdosed, overtreated, and overdiagnosed”. [44, 14]
None of this is inevitable. A modern health care system could also work in another economic context. For example, some have suggested the open source development of medical equipment and pharmaceuticals, in which health care technology would become a commons. Shifting the tax burden from labour to resources could be another part of the solution. In high income countries, medical equipment, pharmaceuticals, and disposable products partly serve to reduce the expensive human labour force in health care.Age and Sustainability
Based on the fragmented data available, it seems likely that the resource use of modern health care systems could be reduced significantly, without bringing us back to the barber-surgeons of the middle ages. A health care system that is more focused on preventive medicine, and which operates outside the logic of the market, could reduce emissions without negatively impacting health, maybe even improving it.
The law of diminishing returns highlights additional opportunities to lower the environmental footprint of health care services. For example, if the environmental footprint of health care was halved, it’s very unlikely that life expectancy would decrease proportionally. Nearly half of lifetime health care expenditures – and thus energy use and emissions – is incurred during the senior years (+65 years old). For those up to age 85, more than one-third of their lifetime expenditures will accrue in the remaining years. 
Advocating for a shorter average life expectancy, even if it may concern a very modest decrease, sounds problematic. However, avoiding the topic is just as problematic. Because of modern health care’s enormous (and still growing) environmental footprint, today’s health and longevity comes at least partly at the expense of the health and longevity of younger and future generations, who have no voice in this debate.  If we cure one person today, at the expense of making other people sick tomorrow, health care becomes counter-productive. Health is not only a private good but also a public one, and as medical treatments become increasingly resource-intensive, the chances increase that the public health damage of a treatment outweighs the individual gain of a patient, especially at old age.
Kris De Decker
Thanks to Elizabeth Shove
Proofread by Alice Essam & Eric Wagner
 Pichler, Peter-Paul, et al. "International comparison of health care carbon footprints." Environmental Research Letters 14.6 (2019): 064004. https://iopscience.iop.org/article/10.1088/1748-9326/ab19e1/pdf
 National estimates of health care sector greenhouse gas emissions have been performed for the UK (2009), the USA (2009 & 2016), Sweden (2017), Australia (2018), Canada (2018), China (2019), Japan (2020) and Austria (2020). For an overview, see . However, because each study has its own methodology, the results are not perfectly comparable. That’s why I quote this source, as it gives comparable estimates.
 Eckelman, Matthew J., and Jodi Sherman. "Environmental impacts of the US health care system and effects on public health." PloS one 11.6 (2016): e0157014. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0157014
 US National Health Expenditure Data. Centers for Medicare & Medicaid Services. https://www.cms.gov/Research-Statistics-Data-and-Systems/Statistics-Trends-and-Reports/NationalHealthExpendData/NationalHealthAccountsHistorical
 Tainter, Joseph. The collapse of complex societies. Cambridge university press, 1988. Page 102 & 103.
 Current healthcare expenditure, 2012-2017, Eurostat. Current health expenditure per capita (current US$) - European Union, World Bank. Current health expenditure per capita, PPP (current international $) - European Union, World Bank. Health spending, OECD.
 In what follows, I ignore the resource use and emissions caused by transportation to and from health care facilities, as well as the resource use and emissions caused by the building of the health care facilities themselves.
 Research in different countries has shown an electricity use of 130 to 280 kilowatt-hour per square metre per year, representing around 50% of total on-site building energy consumption. [11-12] For comparison, residential electricity use in European households is on average 70 kWh/m2/year, and total energy demand is dominated by heating, not electricity. According to a 2016 study, for which scientists collected power data over a period of 18 months in a German hospital, operating rooms have the highest electricity use (438 kWh/m2/year), followed by intensive care units (135 kWh/m2/yr). 
 Christiansen, Nils, Martin Kaltschmitt, and Frank Dzukowski. "Electrical energy consumption and utilization time analysis of hospital departments and large scale medical equipment." Energy and Buildings 131 (2016): 172-183.
 Wu, Rui. "The carbon footprint of the Chinese health-care system: an environmentally extended input–output and structural path analysis study." The Lancet Planetary Health 3.10 (2019): e413-e419. https://www.sciencedirect.com/science/article/pii/S2542519619301925
 Bawaneh, Khaled, et al. "Energy consumption analysis and characterization of healthcare facilities in the United States." Energies 12.19 (2019): 3775. https://www.mdpi.com/1996-1073/12/19/3775/pdf
 Rohde, Tarald, and Robert Martinez. "Equipment and energy usage in a large teaching hospital in Norway." Journal of healthcare engineering 6 (2015). http://downloads.hindawi.com/journals/jhe/2015/231507.pdf
 Black, Douglas R., et al. "Evaluation of miscellaneous and electronic device energy use in hospitals." World Review of Science, Technology and Sustainable Development 10.1-2-3 (2013): 113-128. https://www.osti.gov/servlets/purl/1172701
 Picano, Eugenio. "Environmental sustainability of medical imaging." Acta Cardiologica (2020): 1-5. https://www.tandfonline.com/doi/abs/10.1080/00015385.2020.1815985
 Sherman, Jodi D., et al. "The Green Print: Advancement of Environmental Sustainability in Healthcare." Resources, Conservation and Recycling 161 (2020): 104882. https://www.researchgate.net/profile/Brett_Duane/publication/343137350_The_Green_Print_Advancement_of_Environmental_Sustainability_in_Healthcare/links/5f216962299bf134048f8960/The-Green-Print-Advancement-of-Environmental-Sustainability-in-Healthcare.pdf
 Martin, Marisa, et al. "Environmental impacts of abdominal imaging: a pilot investigation." Journal of the American College of Radiology 15.10 (2018): 1385-1393. https://www.sciencedirect.com/science/article/abs/pii/S1546144018308639. The researchers write that “when production and use phases are combined, the total energy consumption of MRI (>309 MJ/examination, abdominal scan, 1.5 Tesla) is comparable with cooling a three-bedroom house with central air-conditioning for a day”.
 Weisz, Ulli, et al. "Carbon emission trends and sustainability options in Austrian health care." Resources, Conservation and Recycling 160 (2020): 104862.
 Belkhir, Lotfi, and Ahmed Elmeligi. "Carbon footprint of the global pharmaceutical industry and relative impact of its major players." Journal of Cleaner Production 214 (2019): 185-194. https://www.sciencedirect.com/science/article/abs/pii/S0959652618336084
 Laufman, Harold, Luther Riley, and Barry Badner. "Use of disposable products in surgical practice." Archives of Surgery 111.1 (1976): 20-26. https://jamanetwork.com/journals/jamasurgery/article-abstract/581229
 Gilden, Daniel J., K. N. Scissors, and J. B. Reuler. "Disposable products in the hospital waste stream." Western journal of medicine 156.3 (1992): 269. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1003232/pdf/westjmed00091-0045.pdf
 Sherman, Jodi D., and Harriet W. Hopf. "Balancing infection control and environmental protection as a matter of patient safety: the case of laryngoscope handles." Anesthesia & Analgesia 127.2 (2018): 576-579. https://www.researchgate.net/profile/Jodi_Sherman/publication/322407715_Balancing_Infection_Control_and_Environmental_Protection_as_a_Matter_of_Patient_Safety_The_Case_of_Laryngoscope_Handles/links/5a82ba12a6fdcc6f3eadcfab/Balancing-Infection-Control-and-Environmental-Protection-as-a-Matter-of-Patient-Safety-The-Case-of-Laryngoscope-Handles.pdf
 Thiel, Cassandra Lee, et al. "Life cycle assessment of medical procedures: Vaginal and cesarean section births." 2012 IEEE International Symposium on Sustainable Systems and Technology (ISSST). IEEE, 2012.
 Campion, Nicole, et al. "Sustainable healthcare and environmental life-cycle impacts of disposable supplies: a focus on disposable custom packs." Journal of Cleaner Production 94 (2015): 46-55.
 “Reusables, Disposables each play a role in preventing cross-contamination”, Elizabeth Srejic, Infection Control Today, April 2016
 Sustainability roadmap for hospitals, American Association of Hospitals. http://www.sustainabilityroadmap.org/topics/waste.shtml#.YCsEOXyYXWc.
 Thiel, Cassandra L., et al. "Cataract surgery and environmental sustainability: waste and lifecycle assessment of phacoemulsification at a private healthcare facility." Journal of Cataract & Refractive Surgery 43.11 (2017): 1391-1398. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5728421/
 Vollmer, Martin K., et al. "Modern inhalation anesthetics: potent greenhouse gases in the global atmosphere." Geophysical Research Letters 42.5 (2015): 1606-1611. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014GL062785
 Salas, Renee N., et al. "A pathway to net zero emissions for healthcare." bmj 371 (2020).
 Brown, Lawrence H., et al. "Estimating the life cycle greenhouse gas emissions of Australian ambulance services." Journal of Cleaner Production 37 (2012): 135-141.
 Connor, A., R. Lillywhite, and M. W. Cooke. "The carbon footprint of a renal service in the United Kingdom." QJM: An International Journal of Medicine 103.12 (2010): 965-975. https://academic.oup.com/qjmed/article/103/12/965/1584174
 Herrmann, C., and A. Rock. "Magnetic resonance equipment (MRI)–Study on the potential for environmental improvement by the aspect of energy efficiency." PE INTERNATIONAL AG, Report (2012).
 Shove, Elizabeth. "What is wrong with energy efficiency?." Building Research & Information 46.7 (2018): 779-789. https://www.tandfonline.com/doi/pdf/10.1080/09613218.2017.1361746
 Heye, Tobias, et al. "The energy consumption of radiology: energy-and cost-saving opportunities for CT and MRI operation." Radiology 295.3 (2020): 593-605. https://pubmed.ncbi.nlm.nih.gov/32208096/
 Blue, Stanley. "Reducing demand for energy in hospitals: opportunities for and limits to temporal coordination." Demanding Energy. Palgrave Macmillan, Cham, 2018. 313-337.
 Duffin, Jacalyn. History of medicine: a scandalously short introduction. University of Toronto Press, 2010.
 WHO compendium of innovative health technologies for low-resource settings, WHO; 2016-17. WHO, 2018. https://www.who.int/medical_devices/publications/compendium_2016_2017/en/
 Medical devices: managing the mismatch: an outcome of the priority medical devices project: methodology briefing paper, WHO, 2010. https://apps.who.int/iris/handle/10665/70491
 Global Atlas of Medical Devices, WHO, 2017. https://www.who.int/medical_devices/publications/global_atlas_meddev2017/en/
 Page, Brandi R., et al. "Cobalt, linac, or other: what is the best solution for radiation therapy in developing countries?." International Journal of Radiation Oncology* Biology* Physics89.3 (2014): 476-480.
 In a survey of surgeons across 30 African nations, 48% reported at least weekly power failures, 29% had operated using only mobile phone lights, and 19% had experienced poor surgical outcomes as a result of it. 
 Parker, Steve. Medicine: The Definitive Illustrated History. DK Publishing, 2016.
 Hall, Peter A., and Michèle Lamont, eds. Successful societies: How institutions and culture affect health. Cambridge University Press, 2009.
 Borowy, Iris, and Jean-Louis Aillon. "Sustainable health and degrowth: Health, health care and society beyond the growth paradigm." Social Theory & Health 15.3 (2017): 346-368.
 Sherman, Jodi D., and Harriet W. Hopf. "Balancing infection control and environmental protection as a matter of patient safety: the case of laryngoscope handles." Anesthesia & Analgesia 127.2 (2018): 576-579.
 Steyn, A., et al. "Frugal innovation for global surgery: leveraging lessons from low-and middle-income countries to optimise resource use and promote value-based care." The Bulletin of the Royal College of Surgeons of England 102.5 (2020): 198-200. https://publishing.rcseng.ac.uk/doi/pdf/10.1308/rcsbull.2020.150
 Haripriya, Aravind, David F. Chang, and Ravilla D. Ravindran. "Endophthalmitis reduction with intracameral moxifloxacin in eyes with and without surgical complications: Results from 2 million consecutive cataract surgeries." Journal of Cataract & Refractive Surgery 45.9 (2019): 1226-1233. https://www.aurolab.com/images/JCRS%202%20million.pdf
 Venkatesh, Rengaraj, et al. "Carbon footprint and cost–effectiveness of cataract surgery." Current opinion in ophthalmology 27.1 (2016): 82-88.
 Thiel, Cassandra L., et al. "Utilizing off-the-shelf LCA methods to develop a ‘triple bottom line’auditing tool for global cataract surgical services." Resources, Conservation and Recycling 158 (2020): 104805.
 Relman, Arnold S. "The new medical-industrial complex." New England Journal of Medicine 303.17 (1980): 963-970. https://www.nejm.org/doi/full/10.1056/NEJM198010233031703
 Smith, Richard. "Limits to medicine. Medical nemesis: the expropriation of health." Journal of Epidemiology & Community Health 57.12 (2003): 928-928. https://jech.bmj.com/content/57/12/928
 In health care, there is a thin line between marketing and corruption, especially when the target audience is medical personnel that may gain benefits from using or prescribing a medical device or drug, or when regulators are influenced to facilitate practices that increase profits. Transparancy International ranks the procurement of drugs and medical equipment fourth on a list of seven processes that carry high risk of corruption, and calls the problem "widespread in all countries". 
 Alemayehu, Berhanu, and Kenneth E. Warner. "The lifetime distribution of health care costs." Health services research 39.3 (2004): 627-642. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1361028/