If the 2,000 year old windmill is the predecessor of today’s wind turbines, the fireplace and the wood stove are the even older predecessors of today’s solar panels. Like solar panels, trees and other plants convert sunlight into a useful source of energy for humans. Throughout history, the burning of wood and other biomass provided households with thermal energy, which was used for cooking, heating, washing, and lighting.
Photosynthesis also underpinned all historical sources of mechanical power: it provided fuel for both human and animal power, as well as the building materials for water mills and windmills. Neither the old-fashioned windmill nor the old-fashioned wood stove produced electricity, but both can easily be adapted to do so. It suffices to connect an electric generator to a windmill, and to connect a thermoelectric generator to a wood stove.
Thermoelectric Generator
Thermoelectric generators (or “TEGS”) are very similar to “photoelectric” generators – which we now call “photovoltaic” generators or solar PV cells. A photovoltaic generator converts light directly into electricity, and a thermoelectric generator converts heat directly into electricity. 1
A thermoelectric generator consists of a number of ingot-shaped semiconductor elements which are connected in series with metal strips and sandwiched between two electrically insulating but thermally conducting ceramic plates to form a very compact module. 2 They are commercially available from manufacturers such as Hi-Z, Tellurex, Thermalforce and Thermomanic.
Stick a thermoelectric module to the surface of a wood stove, and it will produce electricity whenever the stove is used for cooking, space heating, or water heating. In the experiments and prototypes that are described in more detail below, the power output per module varies between 3 and 19 watts.
As with solar panels, modules can be connected together in parallel and series to obtain any voltage and power output that one needs – at least as long as there is stove surface left. As with solar panels, the electric current that is produced by the thermoelectric module(s) is regulated by a charge controller and stored into a battery, so that power is also available when the stove is not in use. A thermoelectric stove is usually combined with low voltage, direct current appliances, which avoids the conversion losses of using an inverter.
Thermoelectric stoves could be applied in many parts of the world. Most research is aimed at the global South, where close to 3,000 million people (40% of the global population) rely on burning biomass for cooking and domestic water heating. Some of these households also use the stove or fireplace for lighting (1,300 million people have no access to electricity) and for space heating during part of the year. However, there’s also research aimed at households in industrial societies, where biomass stoves and burners have increased in popularity, especially outside of cities.
100% Efficient
Ever since the thermoelectric effect was first described by Thomas Seebeck in 1821, thermoelectric generators have been infamous for their low efficiency in converting heat into electricity. 3456 Today, the electrical efficiency of thermoelectric modules is only around 5-6%, roughly three times lower than that of the most commonly used solar PV panels. 4
However, in combination with a stove, the electrical efficiency of a thermoelectric module doesn’t matter that much. If a module is only 5% efficient in converting heat into electricity, the other 95% comes out as heat again. If the stove is used for space heating, this heat cannot be considered an energy loss, because it still contributes to its original purpose. Total system efficiency (heat + electricity) is close to 100% – no energy is lost. With appropriate stove design, the heat from electricity conversion can also be re-used for cooking or domestic water heating.
More Reliable than Solar Panels
Thermoelectric modules share many of the benefits of solar panels: they are modular, they require little maintenance, they don’t have moving parts, they operate silently, and they have a long life expectancy. 7 However, thermoelectric modules also offer interesting advantages compared to solar PV panels, provided that there’s a regularly used (non-electric) heat source in the household.
Although thermoelectric modules are roughly three times less efficient than solar PV panels, thermoelectric stoves provide a more reliable electricity supply because their power production is less dependent on the weather, the seasons, and the time of the day. In jargon, thermoelectric stoves have a higher “net capacity factor” than solar PV panels.
Even if a stove is only used for cooking and hot water production, these daily household activities still guarantee a reliable power output, no matter the climate. Furthermore, the power production of a thermoelectric stove matches very well with the power demand of householders: the times when the stove is used, are commonly also the times when most electricity is used. Solar panels, on the other hand, produce little or no electricity when household demand peaks.
Note that these advantages disappear when thermoelectric generators are powered by direct solar energy. Solar thermoelectric generators (or “STEGS”), in which thermoelectric modules are heated by concentrated sunlight, don’t compensate for the low efficiency of their modules due to higher reliability because they are just as dependent on the weather as solar PV panels are. 8910
Less Energy Storage
Because of its higher reliability, there’s no need to oversize the power generation and storage capacity of a thermoelectric system to compensate for nights, dark seasons or bad weather days, as is the case with a solar PV installation. Battery capacity only needs to be large enough to store electricity for use in between two firings of the stove, and there’s no need to add extra modules to compensate for periods of low power production.
Solar panels and thermoelectric stoves can also be combined, resulting in a reliable off-grid system with little need for energy storage. Such a hybrid system combines well with a stove that is only used for space heating. The thermoelectric modules produce most of the power in winter, while the solar panels take over in summer.
Cheaper to Install, Easier to Recycle
A second advantage is that thermoelectric modules are easier to install than solar panels. There’s no need to build a structure on the roof and an electric link to the outside world, because the whole power plant is indoors. This also prevents theft of the power source, a significant problem with solar panels in some regions.
All these factors make that power from a thermoelectric stove can be cheaper and more sustainable compared to power from solar PV panels. Less energy, materials and money are needed to manufacture batteries, modules, and support structures.
In terms of sustainability, there’s another advantage: unlike solar PV panels, thermoelectric modules are relatively easy to recycle. Although silicon solar cells themselves are perfectly recyclable, they are encapsulated in a plastic layer (usually “EVA” or ethylene/vinyl acetate polymer), which is critical to the long-term performance of the modules. 11 Removing this layer without destroying the silicon cells is technically possible, but so complex that it makes recycling unattractive from both a financial and energetic viewpoint. 1213 On the other hand, thermoelectric modules do not contain any plastic at all. 141516
Cooling the Modules
The electrical efficiency of a thermoelectric generator doesn’t only depend on the module itself. It’s also, in large part, influenced by the temperature difference between the cold and the hot side of the module. A thermoelectric module operating at half the temperature difference will only generate one quarter of the power. Consequently, improving the thermal management of a thermoelectric generator is a major focus in the design of thermoelectric stoves, as it allows to produce more power with less modules.
On the one hand, this involves locating the hottest spot(s) on a stove and fixing the modules there – provided that they can take the heat. Most stoves have surface temperatures from 100 to 300 degrees Celsius, while the hot side of bismuth telluride modules (the most affordable and efficient ones) withstands continuous temperatures of 150 to 350 degrees, depending on the model.
On the other hand, thermal management comes down to lowering the temperature of the cold side as much as possible, which can be done in four ways: air-cooled and water-cooled forced convection, which involves electric fans and pumps, and air-cooled and water-cooled natural convection, which involves the use of passive heat sinks that do not have a parasitic load on the system.
Active cooling usually has higher efficiency, even when the extra use of a fan or a pump is taken into account. However, passive systems are cheaper, operate silently, and are more reliable than active systems. In particular, the breakdown of a fan can be problematic, as it can lead to module failure due to overheating. 17
Thermoelectric Stoves with Heat Sinks
The first thermoelectric biomass stoves were built in the early 2000s, although the Soviets pioneered a similar concept in the 1950s with mostly electric radios powered by kerosene lamps. 6 In 2004, a team of Lebanese researchers retrofitted a typical cast-iron wood stove from local rural areas with a single 56 x 56 mm thermoelectric module they had made themselves. 18 The stove, which is used for cooking and baking as well as for space and water heating, is rather small (52 x 44 x 29 cm) and weighs 40 kg.
![Image: The cast-iron stove used in the experiments. [^18]](https://solar.lowtechmagazine.com/2020/05/thermoelectric-stoves-ditch-the-solar-panels/images/dithers/lebanese-wood-stove_dithered.png)
The researchers screwed a 1 cm thick smooth aluminium plate to the hottest spot of the stove surface, fixed the module there, and attached a very large (180 x 136 x 125 mm) aluminium finned heat sink to its cold side. At a burning rate of 2.5 kg soft pine wood per hour, their experiments showed an average power output of 4.2 watts. Operating the wood stove for 10 hours per day (excluding the warm-up phase) thus supplies a rural Lebanese household with 42 watt-hours of electricity, enough to cover basic needs.
![Image: TEG installation details and location on stove. [^18]](https://solar.lowtechmagazine.com/2020/05/thermoelectric-stoves-ditch-the-solar-panels/images/dithers/teg-on-wood-stove-lebanon_dithered.png)
More modules and heat sinks can be added to increase power output, but of course the stove surface is limited, and as more modules are added they will be located in areas with a lower surface temperature, decreasing their efficiency. Another way to increase power production is to use an even larger heat sink, and/or a more expensive heat sink made from materials with higher thermal conductivity.
Thermoelectric Stoves with Fans
Most thermoelectric stoves that have been built to date use electric fans to cool the module, in combination with a much smaller heat sink. Although the fan can break and is a parasitic load on the system, it can simultaneously increase the efficiency of the stove by blowing hot air into the combustion chamber – slashing firewood consumption and air pollution roughly by half. Furthermore, fan-powered stoves avoid the building of a chimney and can rely on a horizontal exhaust pipe instead. 19 Consequently, self-powered, fan-cooled stoves make it possible to reduce firewood consumption and indoor air pollution in rural regions of the global South where people neither have access to electricity, nor the means to make a chimney through the roof.
A study of a forced-draft thermoelectric cookstove with one module showed a 4.5 watt power output, of which 1 watt is required to operate the fan. 20 The net power production (3.5 watts) is lower compared to that of the stove with only a heat sink (4.2 watts), but the fan-cooled stove uses only half as much firewood: it generates 3.5 watts net electricity at a burning rate of 1 kg of firewood per hour, while the passively cooled stove requires 2.5 kg of firewood to produce 4.2 watts.
![Image: TEG-powered forced draft cooking stove. [^20]](https://solar.lowtechmagazine.com/2020/05/thermoelectric-stoves-ditch-the-solar-panels/images/dithers/teg-draft-cookstove_dithered.png)
An 80-days field test of a similar portable thermoelectric cookstove design in Malawi showed that the technology was highly valued by the users, with the stoves producing more electricity than was needed. Over the entire period, power production amounted to between 250 and 700 watt-hours of electricity, while electricity use was between 100 and 250 watt-hours. 21
Some fan-cooled thermoelectric cooking stoves are commercially available, often designed with backpackers in mind. Examples are the stoves from BioLite, Termomanic and Termefor, which advertise power outputs between 3 and 10 watts, depending on the design and the number of modules. 17
Thermoelectric Stoves with Water Tanks
The most efficient thermoelectric stoves are those in which the cold side of the module(s) is cooled by direct contact with a water reservoir. Water has lower thermal resistance than air, and thus cools more effectively. Furthermore, its temperature cannot surpass 100 degrees Celsius, which makes module failure due to overheating less likely.
![Image: the principle of thermoelectric stove with passive water cooling. [^17]](https://solar.lowtechmagazine.com/2020/05/thermoelectric-stoves-ditch-the-solar-panels/images/dithers/teg-water_dithered.png)
When thermoelectric modules are water-cooled, the waste heat from their electricity conversion does not contribute to space heating, but to domestic water heating. Water-cooled thermoelectric stoves can be active (using a pump) or passive (no moving parts). 17
Most thermoelectric stoves with passive water cooling are small and only used for heating relatively small amounts of water. In fact, rather than the stove, it is most often a cooking pot that is equipped with thermoelectric modules. For example, the PowerPot is a commercially available backpacking type cooking pot with a thermoelectric module attached to the base, which can be directly placed on the top of a stove and advertises a power generation of 5-10 watts.
![Image: multifunctional wood stove with passive water cooling. [^22]](https://solar.lowtechmagazine.com/2020/05/thermoelectric-stoves-ditch-the-solar-panels/images/dithers/clip-stove_dithered.png)
A much larger and more versatile thermoelectric stove with passive water cooling was designed by French researchers, based on a large, multifunctional mud wood stove design from Morocco. 1922232425 They installed eight thermoelectric modules at the bottom of a built-in 30L water storage tank, which not only serves as the heat sink for the cold side of the generator, but also as the domestic hot water supply for the household. Furthermore, the stove is equipped with a self-powered electric fan and has a double combustion chamber to increase combustion efficiency.
Tests of a prototype generated 28 watts of power using two modules, while burning 1.5 kg of wood for cooking and/or heating. The fan used 15W, meaning that 13W of power remains for other uses. The stove also provided 60 litres of hot water per hour. Depending on the duration of two cooking sessions, between 35 and 55 watt-hour electricity was stored in a battery in a day. Note that here the researchers take into account the losses of the charge controller, the 6V battery, and the fan.
Thermoelectric Stoves with Pumps
Passive water cooling has a downside. As the temperature of the water in the tank increases, the difference between the cold and the hot side of the module will decrease, and so will the electrical efficiency. There either needs to be sufficient time between two firings of a stove to let the water cool down again, or the warm water should regularly be used and replaced by cold water. A pump makes this task more convenient.
![Image: Prototype of a thermoelectric stove with water-cooled modules. [^26]](https://solar.lowtechmagazine.com/2020/05/thermoelectric-stoves-ditch-the-solar-panels/images/dithers/water-cooling-system-goudarzi_dithered.png)
A 2015 prototype, in which a wood stove used for cooking and space and water heating was equipped with 21 thermoelectric modules cooled by a pumped water system, showed a power production from 25W (burning 1 kg of pine wood per hour) over 70W (4 kg wood/hour) to 166W (9 kg wood/hour). 26 The power output per module is as high as 7.9 watts, almost double the power output per module of the stove with natural air cooling. The pump uses 5W and the stove also has a fan to increase combustion efficiency, which consumes 1W. 2728
Thermoelectric Gas Boilers?
Thermoelectric generators with forced water cooling better fit the energy infrastructure in industrial societies, especially in households with central heating systems. More modules could be added, resulting in a power production that matches a relatively high energy lifestyle. However, there’s some caveats. First, central heating systems are only used for space and water heating, not for cooking, which makes their power production less reliable throughout the year. Second, only some central heating systems operate on biomass or wood pellet burners, while many more run on gas, oil or electricity.
![Prototype of a thermoelectric wood-pellet burner. [^30]](https://solar.lowtechmagazine.com/2020/05/thermoelectric-stoves-ditch-the-solar-panels/images/dithers/teg-pellet-moser_dithered.png)
Obviously, when the heat source is electric, it makes no sense to stick a thermoelectric module to it. A thermoelectric system is incompatible with the vision of a high-tech sustainable building where heating is done with an electric heat pump, cooking happens on an electric cooking stove, and hot water is produced by an electric boiler.
However, when the energy source is gas or oil, a thermoelectric boiler is as much of a low carbon solution as a grid-connected solar PV system on the roof. 29 A thermoelectric heating system doesn’t make a household independent of fossil fuels, but neither does a grid-connected solar PV installation. It relies on the (largely fossil fuel powered) power grid to solve energy shortages and excesses, and it usually counts on a fossil fuel powered central heating system for space and water heating.
![Image: A 1 kW thermoelectric generator with forced-water cooling for low temperature geothermal resources. [^31]](https://solar.lowtechmagazine.com/2020/05/thermoelectric-stoves-ditch-the-solar-panels/images/dithers/1-kw-thermo-electric-generator-liu2014_dithered.png)
A thermoelectric heating system that runs on fossil fuels also compares favourably to a large cogeneration power plant, which captures the waste heat of its electricity production and distributes it to individual households for space and water heating. In a thermoelectric heating system, heat and power are produced and consumed on-site. Unlike a central cogeneration power plant, there’s no need for an infrastructure to distribute heat and electricity. This saves resources and avoids energy losses during transportation, which amount to between 10 and 20% for heat distribution and between 3 and 10% (or much more in some regions) for power distribution.
A cogeneration power plant is more energy efficient (25-40%) in turning heat into electricity, meaning that in comparison a thermoelectric heating system supplies a larger share of heat and a smaller share of electricity. This is far from problematic, though, because even in Europe 80% of average household energy use goes to space and water heating.
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Raphaël
Hey!
Great topic! It reminded me of the Peltier effect that was a fad in CPU cooling back in the day.
I’m wondering: could thermoelectric modules be useful if placed between a CPU and its heatsink? Like producing some of the power needed by a Raspberry Pi ? It seems those can be burning hot (but not cooking hot yet!)
M@trixX
I like the idea, but I wouldn’t consider thermoelectric generators as a replacement for photovoltaic but more as a supplement to it. I’m from central Europe and the heating is in use for 6-8 months a year and not entirely regularly in spring and fall, so TEGs could cover maybe half a year. The rest - sunny days and most of summer - could be easily and practically covered by PV.
While cooking on fire makes sense during the cold winter days when one is also heating the space, it has an obvious disadvantage in summer: It heats up the interior people want to keep cool. Also, it takes up a lot of time to heat up and cool down the stove, so the interior is warmed much longer than it would be by stove that can be rapidly turned on and off like gas or electric induction.
This would be obviously different for different locations and the biomass-burning-only solution with TEGs would be perfectly adequate for subarctic climates, but it would supply too much heat and too little electricity in tropical latitudes. There, PVs are clearly better choice - doubly so, when they are used to run air conditioners peaking during the sunniest hours.
TEGs are amazing and maintenance-free, but their low efficiency limits them to rather low-power applications. If a reasonably insulated building is considered, the need for heat is relatively lower than the need for electricity even in colder climates, so scaling the heating up to provide more electricity wouldn’t make sense. There might be a solution: a stirling engine. It has moving parts, so it would require some maintenance, but it could provide more electricity with less heat. Maybe something worth investigating for another article?
Rafael Carrascosa
Thanks Kris, big fan of your articles here.
Afaik TEGs do not use the electromagnetic spectrum to operate, are you sure they do?
Regards,
Rafael
Kris De Decker
@ gareth
I don’t understand what you mean (none of both “things”). Could you be more clear?
Fred Smith
If I were to build a new home, or retrofit my existing one, I would install some version of a rocket mass heater; as it is my understanding based on my extensive research that rocket mass stoves or heaters are the most efficient wood-fired heaters, using the least amount of solid fuel. Plus they are cheap and easy to build. Of course many building codes and/or insurance companies will not approve their installation or insure against them.
Simeon Hope
Once again, this site presents some gadget as a means to avoid the reality of our high energy consumption and the political and economic changes that are required to avoid the worst of the climate disaster. All we have to do is scale this up in our imaginations and consider the consequences.
“Throughout history, the burning of wood and other biomass provided households with thermal energy” while denuding the environment of trees. During the Bronze Age in the UK, vast areas of forest were chopped down for fuel and to clear land for farming. The past is not necessarily where we should be heading.
There are nearly 68 million people in the UK. If everyone switched to wood as a fuel for home energy, where would it come from? As the recent film Planet of the Humans points out, biomass a.k.a. dead trees is not a renewable resource by any means, even though the EU classifies it as such. The USA exports much of that biomass to Europe.
“UK-based researchers found last year that burning wood is a “disaster” for climate change because older trees release large amounts of carbon when they are burned and aren’t always replaced with replanted forests. Even when trees are replaced, it can take up to 100 years to cultivate a wooded area that soaks up as much carbon as was previously released. And the fuel burned in shipping wood pellets to Europe is also a significant source of emissions.”
https://www.theguardian.com/environment/2018/jun/30/wood-pellets-biomass-environmental-impact
“According to the American Lung Association, wood-burning stoves produce harmful toxins that can damage your lungs and increase the risk of cancer, heart disease, and premature death. The fumes from wood-burning stoves are especially dangerous if you have a respiratory condition, such as asthma.”
https://www.verywellhealth.com/the-health-hazards-of-wood-burning-stoves-914956
“The flipside is that wood fires produce vast quantities of particulate matter, tiny fragments of soot like those emitted by diesel cars. These contribute to climate change but can also cause breathing problems or even cancer in humans. In urban areas particularly, wood-burning stoves are therefore not the greenest choice.”
https://www.sciencefocus.com/planet-earth/are-wood-burning-stoves-environmentally-friendly/
David Bourguignon
Thanks a lot Kris for your feedback. I am looking forward to reading your new article!
gareth
Coming back to this, TEG is a mature but very niche technology often used at remote locations where hydrocarbons are available - eg offshore oil/gas platforms, pipeline RTU/SCADA/valve stations, and even nav lights (eg unmanned lighthouse beacons) with refueling required to a tank.
Companies like ecogenthermoelectric in Russia and Global Thermoelectric Generators in US are almost exclusively focused on TEG.
These type of applications typically burn liquid or gas fuel to make hot internals at 350-550 DegC and heatsink to atmosphere for cold, 4-1000W in unit sizes, installations of 5000W are not unheard off.
The main selling point in these applications is they are almost totally maintenance free and therefore lifecycle cost over 25 years beats all other options, plus can be used without batteries due to constant generation, assuming fuel available.
Often TEG is used offshore on unmanned platforms to maintain the 24VDC system for nav lights and other essentials, untended.
Also volkswagon had an experimental car with TEG on the extractors, got rid of the alternator and had some fairly significant economy improvements (can’t remember the number but remembering thinking it was well worth it at the time, better than getting rid of wing mirrors).
There are definitely niches where the TEG technology is viable today and if production is able to be ramped up or simplified by scales of economy, or a few percent extra efficiency comes as a breakthrough, I predict we will only see more of them around in a similar but less spectacular way than solar has grown.
Jay Vaughan
I have a small garden in which I can grow multiple plants that will provide a regular source for my local needs .. from hedge to hazelnut and apple tree and even a bamboo grove. Once you stop living so ‘big’, you can also moderate your needs and manage resources rather than necessitate consumption at scale. Most of the energy produced is used, just to get the energy system working. Local energy means less effort. As a gardener, I applaud this application of an age-old resource, near endless in supply: our Sun. Why not get a little help from healthy plants and things to solve our ills?
kris de decker
@ Martin, and others
Here’s my answer to the sustainability of wood production: https://www.lowtechmagazine.com/2020/09/how-to-make-biomass-energy-sustainable-again.html
Deepack
This is ‘Deepak’ writing to you, i am a German engineer, involved in renewable energy projects in India and Nepal.
ARTI-India, Appropriate Rural Technology Institute (Pune)
www.Samuchit.com
has developed a fabulous pyrolysis/ gasifier high efficient (cooking) stove: ‘Sampada’
https://images.app.goo.gl/aJE5YQhWmciqPmkz9
No fan required and high combustion temperature ==> no smoke; it is sold in India for less than 3000 Indian Rupees, ~ 35€.
A very good device, which can also be used to incinerate trash, for example plastic waste:
https://m.youtube.com/watch?v=KEtqBiUvK1c
The Sampada Gasifier Stove is made by Samuchit Enviro Tech in Pune …
https://images.app.goo.gl/tD7yQMZ9PCzpHEVX7
The thermoelectric effect could also be incorporated and this ‘Sampada’.
Biogas…if biogas is converted into electric power per combusting engine motor, there is always an excess of heat, which cannot be used. Another perfect use for TEG elements.
Great work, you do!
Your truly big fan, during this lockdown, from Nepal, watching the 8000m+ Annapurna range.
Yours, ‘Deepak’
Tony-the-tiger
Excellent article. Obviously, this is a small scale technology. Useful for providing small quantities of high value electricity where wood is used for space heating, water heating, or both. Especially useful where a grid connection is not available and you need 100W of dispatchable power for things like lighting. A lot of the comments about sustainability don’t seem to me to be very valid. This is clearly not intended to be a solution for everyone. More a niche solution, for people that cannot draw kWs of power from the grid but have wood around them and need to keep a few lights going. Those people will be burning wood, or coal or animal faeces anyway and none of that is going to stop anytime soon. A thermo electric device allows them to get more out of the same input.
Sorin Trimbitas
Great article :D Thank you for it.
What, almost all people from hackernews, didn’t understood is that you are not burning wood to get electricity but you get electricity as a by-product of your wood burning :)
Tom Antero
I have thought about harnessing my wood burning, water circulating oven to electric generation. 5 years ago I even ordered bunch of tecs to give them a try. energy generation was just as weak as was conveyed in this article.
From my experience, when it comes to energy-generation from oven, stirling engines are way to go. It can reach efficiency comparable to diesel engine. problem is that there´s no stirling engine designed and sold for that purpose. The economics just don´t make sense. Even on the darkest times in northern Finland, solar panels generate enough energy for my western comfort devices. Panels combined with hot water energy storage from oven, and lion batterypack are working too nicely for me to start developing oventop stirling generator.
toby
Here is an interesting article about themo-voltaics. This uses specially produced pv cells designed to harvest ’low’ temerature infra-red photons.
https://www.pnas.org/content/116/31/15356#sec-4
Abstract
Thermophotovoltaic power conversion utilizes thermal radiation from a local heat source to generate electricity in a photovoltaic cell. It was shown in recent years that the addition of a highly reflective rear mirror to a solar cell maximizes the extraction of luminescence. This, in turn, boosts the voltage, enabling the creation of record-breaking solar efficiency. Now we report that the rear mirror can be used to create thermophotovoltaic systems with unprecedented high thermophotovoltaic efficiency. This mirror reflects low-energy infrared photons back into the heat source, recovering their energy. Therefore, the rear mirror serves a dual function; boosting the voltage and reusing infrared thermal photons. This allows the possibility of a practical >50% efficient thermophotovoltaic system. Based on this reflective rear mirror concept, we report a thermophotovoltaic efficiency of 29.1 ± 0.4% at an emitter temperature of 1,207 °C.
This is like replacing the sun with a gas heater and then totally enclosing the heating-element (substitute sun) with pv cells and then enclosing this whole set up with mirrors to reflect back the lower wavelength photons back onto the heater.
Like a micro dyson-sphere enclosed in a mirror.
I wonder if you could use a system based on this with the cold side of the thermo-voltaic being used to heat water or an oven?
Marcos Buenijo
I wish to point out the rated conversion efficiency of a thermoelectric module does not imply 5% of the heat released by a furnace used to power these modules is converted to electricity. Of course, the figure applies only to the heat that actually moves through the modules.
For a typical installation, the proportion of the heat released by the furnace actually transferred to the hot side of these modules is appallingly low. For this reason, most applications will see extremely low net conversion efficiencies - quite literally on the order of a small fraction of 1%.
Noel Putaansuu
This article is on point for the subject matter. We are researching these TEGs in use with our smoke measurement instrumentation. We find that a wood stove stack and TEG can generate enough to power some sensors. It helps to not run wires along a hot sheet metal pipe. One to 2 net watts is not something most people get interested in, however, modern sensors and micro controllers can work with this power level. For more information our website is www.smokelesschimney.com
Randy Berg
“If a module is only 5% efficient in converting heat into electricity, the other 95% comes out as heat again.” … “With appropriate stove design, the heat from electricity conversion can also be re-used for cooking or domestic water heating.”
While the above statements are true the actual amount of electricity produced is very small. The hot side of the module must be within it’s capabilities and the cold side of the module must be at a hot enough temperature for effective hot water heating. All of this reduces the module’s temperature difference hence it’s efficiency.
hugh sheehy
The emissions from wood stoves are a disaster.
Arturs
It would be more beneficial to run a steam turbine of a stove or use gasification and run an ICE generator instead. It would add complexity to the build. Jet with electricity one can harvest 3x more heat or more depending on the source temperature. At minimum using electricity for computing, it would turn in to heat anyway. So basically using the same energy twice!
Himbeerkuchen
Tile ovens are not as popular as they once were (e.g. in the 1800s), yet many people (in moderate and colder climate zones) in the west still associate them with comfort and coziness. I imagine there might be a case for a TEM ceramic tile module to convert an existing tile oven to an energy-generating one. The outside of the tiles could be finned or otherwise structured to encourage air flow, while they should probably have a surface glaze and glaze color that maximizes infrared emission. Each tile might incorporate a small electronics module so that you can easily interconnect them. Hmm… should I start a small business?
Olivier Hannoun
Any thoughts on using TEG modules not with fire but with hot water generated from solar thermal panels?
Pekka
@Raphaël
This is the Peltier effect. What the author is talking about are what the PC modding scene used to call peltier coolers. However, rather than using electricity to generate a temperature differential they’re using a temperature differential to generate electricity.
Janine Mesu
@34 so, using the Peltier-element backwards.…
Martin
Ah I am not good at making a point. Here condensed:
difference between physical and “non physical” energy source
limited availability of energy source and “resulting energy form” usage devices
widespread (not concentrated like a photovoltaic production plant) environmental damage through millions of inefficient energy production processes
major efficiency increase only by sun/electrically possible as a result of point 1 and 3.
Rob
@kris
Thank you for showcasing this possibility for improvement. I am wondering if anyone has thought of using TEG tech with a rocket mass heater as promoted by Paul Wheaton. The RMH is designed to burn sticks about the diameter of your thumb. Sticks burn at about 800 degrees f., as opposed to firewood that burns at about 600 degrees f.
People in Europe used to manage coppiced woodlands that gave them all of the sticks they needed to make heat and to cook with. Perhaps the old ways are still the best. Using a RMH with coppiced wood will be more efficient than cutting trees and splitting it for heat (at a lower burning temp). I like the fact that TEG is not limited by weather events or sun/no sun limits. Also of note the RMH does not emit smoke like a conventional fireplace or woodstove. Due to superior design this stove actually burns the smoke before it is discharged. This advantage eliminates the previous “emissions disaster” concerns entirely.
Darkest Yorkshire
One of the interesting things about a stove generating electricity is it could charge the battery of an electric fire lighter. That can then light the stove the next time it’s needed, breaking the dependence on matches or other lighters.
Kevin
While glad you mention the backpackers cook stove, there are commercially available modules in the United States that produce up to 100 watts on a wood stove. This can be great in an Alaskan Cabin where there is a wood stove and little sun all winter. It can also lower the need for batteries at night in an off grid electric system. The most popular application to date seems to be the small fans that circulate heat around the cabin, now available for <$40 USD. It should be pointed out that commercially available modules are sold at max power output, but realistically wood stoves are not run at highest heat all the time. For a while the a device called the Devil Watt that produced 100 watts for with an $800USD device. (I am unsure of current availability.) These devices have also been used to pump hot water around a cabin greatly increasing comfort. This small amount of power is easily enough to light several LED lights bulbs around a home and power small electronics.
https://www.tegmart.com/
Matty
It occurs to me that the highest priority usages of electricity in households are lighting and communication electronics. Phones of course already have battery storage, so lighting is the most critical low power electrical usage that can’t be time-shifted to meet supply.
Using a thermoelectric generator to power LED lighting is not a terrible idea, since even at 1% conversion to electricity, the 100 lm/W of LEDs means you could expect 1 lm/W overall, which is about ten times the 0.1 lm/W typical of an orange open flame.
However similar luminous efficacy can be achieved by using a gas mantle (https://en.wikipedia.org/wiki/Gas_mantle) with a flame. What is lost in flexibility is made up in simplicity. Admittedly gas mantles as currently exist are designed very specifically for lamps with small gas flames and not cooking/heating fires, but I see no reason the selective emissivity of the technology couldn’t be adapted.
Rick Otten
Pellet stoves burn pellets made not only from sawdust, but from straw and other lower order or scrap biomass. They are relatively easy to make. The main drawback to pellet stoves is that they require a small amount of electricity to feed the pellets into the burner. If a thermoelectric device could provide enough electricity to keep it going, then all you’d need is the energy required to light it and do the initial warm-up. That would make a pellet stove much more appealing - at least to me!
Andrew M Himmelfarb
Say would it be practical to fabricate motorcar bonnets, cooling fins, and even brake shows out of thermovoltaics? Allied with a force feed pedaling crank too replace the traditional throttle pedal, the scheme could generate enough voltage whilst motoring to bypass the alternator and hence raise fuel economy significantly.
Joel Angiolillo
Error in my previous comment. Burning 1 cord (3624 kg) of wood produces about 6000kg of co2. According to https://paperonweb.com/A1110.htm.
Warren
I don’t know if you’re still watching these comments but I’ll post anyway.
Wouldn’t it be more efficient to output the heat to a Stirling engine?
Sure, there’s moving parts and you need coils and all that produce the electricity but maybe the all-in cost and effort would be worth it.
And why rely on a stove?
Use a Fresnel lens to concentrate the Sun’s rays and point it where it needs to go to provide heat to the engine.
And use that same process to heat a thermal battery of some sort and then, when needed, it’s heat can be output to the Stirling engine.
This isn’t to say that you couldn’t add thermo-electric modules to the system though.
Thermal batteries do lose heat, obviously, as they sit so slapping on some modules to the thing means you could capture that waste heat and turn it directly into energy.