18 ms·

Thermoelectric Stoves vs. Solar Panels

98 points by MaurizioPz 6y ago

makomk 6y ago
The trouble with this approach is that the thermoelectric modules are expensive and don't generate much power compared to solar. Also, whilst the fact that they can theoretically generate power regardless of the time of day or the weather is nice, you're probably not going to want to run your stove all day and produce twenty times as much heat as electricity in the middle of a baking hot summer.
- Gibbon1 6y ago
  Bought a van that has a secondary battery and a 2kw inverter. It'll run a toaster, electric kettle, or a microwave no problem. Also runs a Engel Fridge for 4 days. Over the years I've read lots of stuff about supposed better mouse trap low tech stoves for people the third world. I suspect what they'd rather is a cheaply financed high tech solar powered mini-kitchen.
chewbacha 6y ago
I think the flaw here is that historically, we have quickly stripped the land for firewood: https://www.history.com/news/the-firewood-shortage-that-helped-give-birth-to-america https://www.history.com/news/the-firewood-shortage-that-help... While it might be more efficient now, it's still a slightly more locally finite than the sun is. In addition, operating a wood stove is still a manual process that needs to be tended to constantly, making the solar panel much easier to operate, and likely much safer as there is no deliberate heat source in a solar array.
- joshdance 6y ago
  Pellet stoves are almost 100% automatic. Pellets can be produced from junk wood, and if we really wanted more wood, we could plant and harvest the forests.
  - close04 6y ago
    Wood has the slight disadvantage that it grows slower than it burns. Wood stoves still need active input for the "supply chain", you have to deal with some additional complexity, maintenance, and extra safety concerns. The forced draft stove in the article needs an electric fan to work. A solar panel on the other hand is passive, with no maintenance, or safety concerns. The setup in the article is OK if you already had the stove for heating and a lot of additional parts lying around to build the thermoelectric generator. In theory any electricity it generates is "free electricity" but the complexity is high, efficiency is low, and a bit of the little electricity it produces may be needed to just keep the whole thing going.
  - biomcgary 6y ago
    Unfortunately, most pellet stoves depend on electricity for the fan and controller and stop if the power goes out. Gravity fed pellet stoves exist but have problems with consistency (and avoiding backdraft fires). I've thought about building a pellet stove with an integrated Stirling engine generator, but it's a bigger project than I have time for. It should be more efficient than thermoelectric.
- deleted 6y ago
  [deleted]
Animats 6y ago
2.5 kg soft pine wood per hour ... average power output of 4.2 watts That's 1.68wh/kg of wood. Pine has a stored energy of about 15 million BTU/Cord (2380 lb)[1], or 4,396Kwh / 1080 kg, or 4000 wh/kg of wood. 0.04% efficiency. That's terrible by the standards of 19th century steam engines, let alone anything newer. It might be a way to get enough power to charge a cell phone from a stove used for other purposes. But burning wood just to make electric power this way is going to need a lot of forest for very little energy. Note that the article has drawings, but not pictures, of a vacuum and scooter being powered with a thermoelectric unit. They probably can't do that. Thermoelectric systems are often used to power heating controls, where little power is required. Some bigger ones can power heating fans as a backup. The U.S. Army has a portable heater with a fan powered this way. [1] https://www.engineeringtoolbox.com/wood-combustion-heat-d_372.html https://www.engineeringtoolbox.com/wood-combustion-heat-d_37...
- makomk 6y ago
  Huge losses at every stage, I guess. A good chunk of the heat is going to go right up the chimney, then most of the heat that doesn't escape is going to directly heat the room the stove is in without going through the thermoelectric elements, and then only a tiny fraction of the tiny fraction that passes through them is going to get converted to electricity. What might be better is something more like a steam engine, except without the complicated maintenance and operation requirements and the annoying tendency to explode if not carefully maintained. Sadly no-one seems to have been able to design such a device.
  - vkou 6y ago
    > Sadly no-one seems to have been able to design such a device. Why not a Stirling engine?
    - namibj 6y ago
      https://www.microgen-engine.com/ https://www.microgen-engine.com/ seems to be a commercial source, and https://www.kickstarter.com/projects/672465444/low-cost-sterling-engine/ https://www.kickstarter.com/projects/672465444/low-cost-ster... was a (failed?) attempt at developing a cheap 1kW generator. The more recent remains are in this blog: http://volodesigns-sterlingproject.blogspot.com/ http://volodesigns-sterlingproject.blogspot.com/ It looks like the Kickstarter turned into https://seftonmotors.com/ https://seftonmotors.com/ , which are about 2000$ for a 1.2kW (full temp, pressurized) engine.
neltnerb 6y ago
I just want to comment that the author for this one is a fantastic writer. At each section I was wondering, "wait, why wouldn't you..." and it was consistently literally the next section. Very impressive ability to predict a reader's interpretation of what they're saying. But back to the article -- totally makes sense to me, as a materials scientist with a smidge of chemical engineering, for places that already use a wood stove for heating. I can't really imagine people redesigning gas stoves and obviously electric stoves are a non-starter. Though a gas boiler for central HVAC could probably generate a little bit. Getting say 100W out of a boiler in your basement seems like a pretty minor increase, but I suppose it does add up over time since themoelectric modules are practically indestructible as long as you don't exceed the temperature limits. I liked the idea of retrofitting places that already use wood stoves to also heat water a lot though. A replacement for an existing wood heating system makes a lot more sense if you're off the grid already (which in my observation is often true even for US homes with wood heating). But I love the idea of a subsidized (or unsubsidized if it's that easy) retrofit if it brings people enough power to charge their phone and some lights and such to get access to communication services.
- acidburnNSA 6y ago
  The author absolutely didn't come through for me. "Wait, isn't air pollution from wood burning as bad or worse than coal?" "Wait, don't the carbon emissions from biofuels like wood concentrate in the atmosphere and cause global warming even though it's technically renewable but system dynamics matter and the fact that you can burn a log that took 20 years to grow in an hour is a fundamental problem?" Yeah this is a terrible idea.
  - Taniwha 6y ago
    Depends on the coal and the wood, if you have high sulfur coal wood can certainly be cleaner
  - elric 6y ago
    Large parts of the world heat their homes by burning wood (or peat etc). I think the point they were trying to make is that if you're already burning wood, and you need electricity, you can convert some of the heat to electricity. I don't think they were advocating for the replacement of conventional power plants with wood burning thermoelectric stoves.
deleted 6y ago
[deleted]
ekr 6y ago
Funnily enough, just the other day I was thinking of a wood gas generator. It would be interesting to see an efficiency comparison, as the wood gas generator also gives out a lot of waste heat. The internal combustion engine is itself not more than 25% efficient so you won't get great efficiency there either, if you add up the losses from generating the wood gas. But it should still be much better than these thermoelectric generators.
slavik81 6y ago
Traditional small wood stoves are absolutely atrocious for the environment. Compared to an industrial-scale power plant, small wood fires don't burn as cleanly, have fewer scrubbers on their exhaust, and are much less efficient. Their only saving grace is that they're small, and thus the scale of the problem is also small, but that only holds as long as they're also rare. Even with the relatively few wood fires we have today, the effects on air quality are noticeable: > Toronto Public Health (2002) estimated that residential wood burning accounts for 11 percent of the PM2.5 found in Ontario’s air, 0.8 percent of the total particulate matter (TPM) and 15 percent of the VOCs. (http://cleanairhamilton.ca/wood-burning/ http://cleanairhamilton.ca/wood-burning/)
- klodolph 6y ago
  Came here to say this. Wood is an incredibly dirty fuel. It makes coal look as clean as driven snow, by comparison.
  - abstractbarista 6y ago
    Looks are not everything. Wood ash isn't (nearly as?) carcinogenic.
    - klodolph 6y ago
      Wood smoke is carcinogenic. Compared to cigarette smoke, wood smoke is 12x as carcinogenic. Of course, it depends on the wood.
- patall 6y ago
  I have wondered about this before: are there standard available solutions to clean your wood stove exhaust air in an economically sensefull way. I mean, my garden produces that much wood each year, I better use that somehow. And I cannot use all of it for growing mushroom.
  - chipsa 6y ago
    To clean the exhaust of an existing stove, not really. But if you replace your stove with a more efficient one, possibly. The problem with most wood stoves is incomplete combustion, which results in smoky, sooty exhaust. Rocket stoves are a solution. Also, electric blowers are a solution.
ggm 6y ago
As long as you want heat energy otherwise, why not? But if you want electricity, and not heat, but have sunlight, I wouldn't run here. It has a niche, as long as YOU WANT HEAT
xt00 6y ago
One major annoyance of using TEG's (from my own experience) is that they need heat to flow through the TEG rather than "heat it up".. so if you don't have a way for the heat to flow through the TEG (such as a fan or heatsink on the opposite side of the TEG -- the "cold side"), you rapidly end up with a situation where both sides of the TEG are roughly the same temperature and as a result you end up generating very little power. So if the wood stove heats up the ambient air around you, then the result is the efficiency goes down tremendously. These things are more suited for places where you have a very high temperature and a cold sink -- like the outside surface of a metal chimney in your cabin in the woods type thing -- such as outside, where you have the greatest sustainable delta T.
- gkop 6y ago
  Silly question, but could you use one of those nifty wood stove fans [0] to move the heat? [0] https://www.wayfair.com/Ecofan--UltrAir-Wood-Stove-Fan-810CABX-L181-K~ECFN1004.html https://www.wayfair.com/Ecofan--UltrAir-Wood-Stove-Fan-810CA...
  - energ8 6y ago
    The fans like this I've seen are powered by TEGs, just like the article is talking about. So, yes, but there is a trade-off. For those familiar with ICE engines, I'd compare it to the trade-off of a turbo/super charger.
    - rcxdude 6y ago
      They are a quite neat niche for TEGs: you have a ready supply of heat, lower power demands, and the fact that you need to get rid of the heat on the cold side is also what you're trying to achieve with the fan in the first place. I don't think they will generate too much excess power though.
jccalhoun 6y ago
I remember seeing reviews of camp cooking stoves that had USB chargers. https://www.bioliteenergy.com/ https://www.bioliteenergy.com/ They didn't seem to be too good at charging but, as the article says, if you are already using a fire why not make a little electricity as well? I grew up in a house partially heated by a wood fireplace. After hauling wood my childhood I'm never using a wood fireplace again!
smileysteve 6y ago
I was thinking about peltier heated clothes dryer the other day. Traditional electric dryers heat to approximately 210 degrees using 240v and about 2500 watts. Recently, (compressor) heat pump dryers have come to the US for ventless options. So to produce 210 degree, 2000 watt of heat where peltiers are at least more efficient as generating heat than resistors, seems possible with a 750 computer power supply.
- londons_explore 6y ago
  Check your math. Peltiers get much less effective as the difference in temperature of the hot and cold sides increases. I imagine a drier would need a hot side ~100C (the equivalent electric elements get red hot after all!). Peltier units with 80C of temperature difference between the sides have very very low efficiency.
  - smileysteve 6y ago
    I always thought the low efficiency was in cooling, not in heating. Dryer body is already acting as a heat sink for the (air-gapped) hot side and heating interior air at 22 degree c
ip26 6y ago
Total system efficiency (heat + electricity) is close to 100% – no energy is lost. I saw this the other day. I stopped reading here. A wood stove may be nearly 100% efficient at converting wood to heat, but half the heat goes right up the chimney. I was surprised to see lowtechmagazine skip over that.
- acidburnNSA 6y ago
  Wait till they hear about district heating from large central power plants.
  - lowtechmagazine 6y ago
    Maybe read the article before you comment? Here's the last two paragraphs: 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.
    - acidburnNSA 6y ago
      I read it! I meant a large central non combustion power plant with district heating that doesn't emit air pollution or carbon. Not a biofuel cogen plant! Yes you have to transfer the power and yes infrastructure is needed. These are important activities in the quest for not killing people via air pollution and stopping climate change.
avsteele 6y ago
If you do any camping or backpacking there is a great little application of this: https://www.bioliteenergy.com/collections#cooking https://www.bioliteenergy.com/collections#cooking This little stick burner can get a super hot fire going and boil water easily, or grill a burger. With the electricity generated in excess of that needed for the fan you can charge your phone/devices or use its port for an LED lamp . That it runs on little sticks is super convenient.
fencepost 6y ago
I suspect many of the folks who'd be interested in this kind of thing (lowtechmagazine) are the same ones very concerned about climate change and pollution. Maybe I missed it by just skimming, but is there any discussion in there of the particulates and CO2 output of burning wood? In a very real sense burning wood is the same thing as burning coal, minus millions of years of pressure. Perhaps for their next article on low-tech stoves they can investigate the higher energy density and improved generation capabilities of coal. Why, in some places you can even find convenient coal chutes!
- tom_mellior 6y ago
  > In a very real sense burning wood is the same thing as burning coal, minus millions of years of pressure. Burning wood only emits CO2 that was in the atmosphere recently. Regrowing an equal size tree in the same place captures that CO2 again. This means net zero CO2 emissions (in theory). In comparison, you would need to plant new trees in new places (and not cut them down) to offset the CO2 from fossil coal.
  - acidburnNSA 6y ago
    Biofuel is almost as bad as coal from a carbon emission point of view. Lifecycle emissions are about 740 gCO₂-eq/kWh, c.f. 840 for coal (Source: Schlomer 2014 IPCC meta-analysis). The problem is that you can burn a log that took 20 years to accumulate carbon in 1 hour. Sure it renews, eventually. But if lots of people do this the concentration of carbon in the atmosphere would equilibriate at a level inconsistent with solving climate change. And the particulate air pollution from wood is a true killer. This concept is deeply flawed because of carbon emissions and air pollution.
    - tom_mellior 6y ago
      Agreed with all your points, I wouldn't want us to return to more burning of wood. I was just pointing out the categorical difference to burning fossil fuels, which even theoretically aren't part of the same life cycle and cannot be offset in the same way -- we can't grow back forests from millions of years ago.
marsdepinski 6y ago
Much better turning excess heat into steam to drive a turbine or flywheel than this. If you have a large water tank you can store heat for days to keep a house warm. I have 27kw cast iron wood burning fireplace and a wood/coal brick / ceramic kitchen and oven on the other side of the chimney. If I run both in -10c the house gets too hot. Once heated the house needs about 4 18inch logs a day. This is the only heating system. Burn oak, beech and birch. Burning pine or any conifer is a disaster for your chimney. Burns like gasoline and you have to keep feeding it.
thescriptkiddie 6y ago
Randall Munroe (xkcd) did a video [0] a while back to promote his book "How To" where he addressed several (mostly silly) ways of powering a hypothetical home using only energy gathered on-site. In it, he calculated that 0.2 acres of trees only produces about 38 watts of usable power, if you burn them to generate electricity at the same rate they grow. [0] https://www.youtube.com/watch?v=j1tcyEo2tQk https://www.youtube.com/watch?v=j1tcyEo2tQk
- slavik81 6y ago
  I look forward to reading about Christopher Robin's adventures in the 19 Kilowatt Wood.
peter_d_sherman 6y ago
>"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." [...] >"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." [...] >"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. [19][22-25] 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."
kragen 6y ago
This article is full of errors, from the details up to the overall idea. TEGs are not "more sustainable" than PV panels. As the article points out, they're made from similar materials, using the same fabrication technologies, except that PV panels include some plastic; and TEGs typically use exotic, scarce semiconductors based on heavy metals, like bismuth telluride or lead telluride, rather than abundant, cheap semiconductors like silicon. (Silicon is too good at conducting heat to make a good TEG.) I guess Kris De Decker just really doesn't like plastic! But a much bigger issue is that PV panels usually last decades, except for the small minority that get smashed, while TEGs tend to get burned up because you have to put them in a fire to make them work, and even aside from the danger of accidental overheating (because your water tank emptied out, say, or the air currents in your wood stove were different from usual) the Arrhenius equation governs a wide variety of TEG and PV failure mechanisms. So TEGs are not "more reliable". The article argues that solar panels are not being recycled because they have plastic in them. This is false. The truth is that solar panels are not being recycled because almost all of them still work, even those manufactured decades ago, and manufacturing is growing rapidly, so there is not a sufficiently large pool of broken solar panels to supply any significant fraction of the demand for silicon. TEGs are not "less costly" than solar panels. Solar panels are https://www.solarserver.de/pv-modulpreise/ https://www.solarserver.de/pv-modulpreise/ €0.17 per watt now. https://www.dx.com/p/yb3981-diy-150-c-thermoelectric-power-generator-peltier-module-white-silver-2050639.html https://www.dx.com/p/yb3981-diy-150-c-thermoelectric-power-g... is a TEG rated for 150° which can theoretically produce about 3 watts for US$9: 15 times as expensive. Typical PV capacity factors are around 20%†, so even if the TEG got a 100% capacity factor — which it won't, since you don't have a constant 3-watt load to hang off it — it would be three times more costly. (Is there a cheaper source for TEGs somewhere?) This also tends to show that more energy and materials are needed to manufacture TEGs than equivalent solar panels, since that's what most of your money goes to buy. (150° is about the limit for bismuth-telluride TEGs — bismuth alloys and intermetallics tend to melt at low temperatures. It is not true that, as the article says, that "the hot side of bismuth telluride modules withstands continuous temperatures of 150 to 350 degrees", nor are Bi₂Te₃ modules "the most efficient ones".) The article argues that TEGs are "100% efficient" because any energy not harvested by the TEG is used to heat your house. Aside from this being undesirable in the summer — a significant concern for many of us here in the "global south" that Kris De Decker pretends to care about, from his apartment in Spain — it's also the case that burning up kilowatts of precious energy directly into low-grade heat is an extremely inefficient way to heat your house. The apartment I'm in here is primarily heated by an air conditioner with the capability of functioning backwards, in which mode it produces about 3 kilowatts of heating in exchange for a single kilowatt of electricity, for 300% "efficiency". (This is not a violation of thermodynamics; the Carnot cycle is reversible, and the indoor and outdoor temperatures just aren't that far apart.) Producing the same amount of heating with the oven or a wood stove would waste two kilowatts of gas or wood. Additionally, wood stoves are seriously fucking bad for your health. They produce massive amounts of carcinogenic smoke. TEGs do have real merits — I've loved them since I was a kid. They can provide small amounts of power, at very low efficiency, in a totally autonomous, independent, and portable way. You might be able to charge your phone, run a reading light, or trickle-charge a battery. But they are not an alternative power source for your house. They are not going to run your vacuum cleaner or your e-scooter, contrary to the misleading illustrations in this article. A normal household vacuum cleaner needs 500–2000 watts, and at 5% efficiency that would mean running 10 to 40 kilowatts of heat through your TEG, a power level at which you will quickly cease to appreciate the space heating effect. However, as John Nagle pointed out in https://news.ycombinator.com/item?id=23356206 https://news.ycombinator.com/item?id=23356206, the end-to-end efficiency in the Lebanese study cited was not 5% but 0.04%, because most of the energy in the fuel goes right out the chimney, and most of the rest goes directly into the house, not through the TEG. So what could have motivated such a mendacious article? Did Low Tech Magazine get an advertorial contract, similar to The Atlantic's famous David Miscavige Leads Scientology to Another Banner Year deal? Does Kris De Decker simply have no interest in whether what he's writing is true or false, scraping together whatever argument he thinks he can trick people into believing in order to support his preconceived conclusion? Either way, this article destroys the credibility of Low Tech Magazine. (Unless it's a false-flag operation? Maybe someone is impersonating Kris De Decker to discredit him?) † In polar countries like Germany, the Netherlands, or England, PV capacity factors may worsen to 10%. Near the Arctic or Antarctic Circle things are even worse, and within them of course you can't use solar power without a seasonal energy store, which is totally impractical for most uses.

98 points by MaurizioPz 6y ago

The trouble with this approach is that the thermoelectric modules are expensive and don't generate much power compared to solar. Also, whilst the fact that they can theoretically generate power regardless of the time of day or the weather is nice, you're probably not going to want to run your stove all day and produce twenty times as much heat as electricity in the middle of a baking hot summer.

Gibbon1 6y ago
Bought a van that has a secondary battery and a 2kw inverter. It'll run a toaster, electric kettle, or a microwave no problem. Also runs a Engel Fridge for 4 days. Over the years I've read lots of stuff about supposed better mouse trap low tech stoves for people the third world. I suspect what they'd rather is a cheaply financed high tech solar powered mini-kitchen.

chewbacha 6y ago

I think the flaw here is that historically, we have quickly stripped the land for firewood: https://www.history.com/news/the-firewood-shortage-that-helped-give-birth-to-america https://www.history.com/news/the-firewood-shortage-that-help... While it might be more efficient now, it's still a slightly more locally finite than the sun is. In addition, operating a wood stove is still a manual process that needs to be tended to constantly, making the solar panel much easier to operate, and likely much safer as there is no deliberate heat source in a solar array.

joshdance 6y ago
Pellet stoves are almost 100% automatic. Pellets can be produced from junk wood, and if we really wanted more wood, we could plant and harvest the forests.
- close04 6y ago
  Wood has the slight disadvantage that it grows slower than it burns. Wood stoves still need active input for the "supply chain", you have to deal with some additional complexity, maintenance, and extra safety concerns. The forced draft stove in the article needs an electric fan to work. A solar panel on the other hand is passive, with no maintenance, or safety concerns. The setup in the article is OK if you already had the stove for heating and a lot of additional parts lying around to build the thermoelectric generator. In theory any electricity it generates is "free electricity" but the complexity is high, efficiency is low, and a bit of the little electricity it produces may be needed to just keep the whole thing going.
- biomcgary 6y ago
  Unfortunately, most pellet stoves depend on electricity for the fan and controller and stop if the power goes out. Gravity fed pellet stoves exist but have problems with consistency (and avoiding backdraft fires). I've thought about building a pellet stove with an integrated Stirling engine generator, but it's a bigger project than I have time for. It should be more efficient than thermoelectric.
deleted 6y ago
[deleted]

Animats 6y ago

2.5 kg soft pine wood per hour ... average power output of 4.2 watts That's 1.68wh/kg of wood. Pine has a stored energy of about 15 million BTU/Cord (2380 lb)[1], or 4,396Kwh / 1080 kg, or 4000 wh/kg of wood. 0.04% efficiency. That's terrible by the standards of 19th century steam engines, let alone anything newer. It might be a way to get enough power to charge a cell phone from a stove used for other purposes. But burning wood just to make electric power this way is going to need a lot of forest for very little energy. Note that the article has drawings, but not pictures, of a vacuum and scooter being powered with a thermoelectric unit. They probably can't do that. Thermoelectric systems are often used to power heating controls, where little power is required. Some bigger ones can power heating fans as a backup. The U.S. Army has a portable heater with a fan powered this way. [1] https://www.engineeringtoolbox.com/wood-combustion-heat-d_372.html https://www.engineeringtoolbox.com/wood-combustion-heat-d_37...

makomk 6y ago
Huge losses at every stage, I guess. A good chunk of the heat is going to go right up the chimney, then most of the heat that doesn't escape is going to directly heat the room the stove is in without going through the thermoelectric elements, and then only a tiny fraction of the tiny fraction that passes through them is going to get converted to electricity. What might be better is something more like a steam engine, except without the complicated maintenance and operation requirements and the annoying tendency to explode if not carefully maintained. Sadly no-one seems to have been able to design such a device.
- vkou 6y ago
  > Sadly no-one seems to have been able to design such a device. Why not a Stirling engine?
  - namibj 6y ago
    https://www.microgen-engine.com/ https://www.microgen-engine.com/ seems to be a commercial source, and https://www.kickstarter.com/projects/672465444/low-cost-sterling-engine/ https://www.kickstarter.com/projects/672465444/low-cost-ster... was a (failed?) attempt at developing a cheap 1kW generator. The more recent remains are in this blog: http://volodesigns-sterlingproject.blogspot.com/ http://volodesigns-sterlingproject.blogspot.com/ It looks like the Kickstarter turned into https://seftonmotors.com/ https://seftonmotors.com/ , which are about 2000$ for a 1.2kW (full temp, pressurized) engine.

neltnerb 6y ago

I just want to comment that the author for this one is a fantastic writer. At each section I was wondering, "wait, why wouldn't you..." and it was consistently literally the next section. Very impressive ability to predict a reader's interpretation of what they're saying. But back to the article -- totally makes sense to me, as a materials scientist with a smidge of chemical engineering, for places that already use a wood stove for heating. I can't really imagine people redesigning gas stoves and obviously electric stoves are a non-starter. Though a gas boiler for central HVAC could probably generate a little bit. Getting say 100W out of a boiler in your basement seems like a pretty minor increase, but I suppose it does add up over time since themoelectric modules are practically indestructible as long as you don't exceed the temperature limits. I liked the idea of retrofitting places that already use wood stoves to also heat water a lot though. A replacement for an existing wood heating system makes a lot more sense if you're off the grid already (which in my observation is often true even for US homes with wood heating). But I love the idea of a subsidized (or unsubsidized if it's that easy) retrofit if it brings people enough power to charge their phone and some lights and such to get access to communication services.

acidburnNSA 6y ago
The author absolutely didn't come through for me. "Wait, isn't air pollution from wood burning as bad or worse than coal?" "Wait, don't the carbon emissions from biofuels like wood concentrate in the atmosphere and cause global warming even though it's technically renewable but system dynamics matter and the fact that you can burn a log that took 20 years to grow in an hour is a fundamental problem?" Yeah this is a terrible idea.
- Taniwha 6y ago
  Depends on the coal and the wood, if you have high sulfur coal wood can certainly be cleaner
- elric 6y ago
  Large parts of the world heat their homes by burning wood (or peat etc). I think the point they were trying to make is that if you're already burning wood, and you need electricity, you can convert some of the heat to electricity. I don't think they were advocating for the replacement of conventional power plants with wood burning thermoelectric stoves.

deleted 6y ago

[deleted]

ekr 6y ago

Funnily enough, just the other day I was thinking of a wood gas generator. It would be interesting to see an efficiency comparison, as the wood gas generator also gives out a lot of waste heat. The internal combustion engine is itself not more than 25% efficient so you won't get great efficiency there either, if you add up the losses from generating the wood gas. But it should still be much better than these thermoelectric generators.

slavik81 6y ago

Traditional small wood stoves are absolutely atrocious for the environment. Compared to an industrial-scale power plant, small wood fires don't burn as cleanly, have fewer scrubbers on their exhaust, and are much less efficient. Their only saving grace is that they're small, and thus the scale of the problem is also small, but that only holds as long as they're also rare. Even with the relatively few wood fires we have today, the effects on air quality are noticeable: > Toronto Public Health (2002) estimated that residential wood burning accounts for 11 percent of the PM2.5 found in Ontario’s air, 0.8 percent of the total particulate matter (TPM) and 15 percent of the VOCs. (http://cleanairhamilton.ca/wood-burning/ http://cleanairhamilton.ca/wood-burning/)

klodolph 6y ago
Came here to say this. Wood is an incredibly dirty fuel. It makes coal look as clean as driven snow, by comparison.
- abstractbarista 6y ago
  Looks are not everything. Wood ash isn't (nearly as?) carcinogenic.
  - klodolph 6y ago
    Wood smoke is carcinogenic. Compared to cigarette smoke, wood smoke is 12x as carcinogenic. Of course, it depends on the wood.
patall 6y ago
I have wondered about this before: are there standard available solutions to clean your wood stove exhaust air in an economically sensefull way. I mean, my garden produces that much wood each year, I better use that somehow. And I cannot use all of it for growing mushroom.
- chipsa 6y ago
  To clean the exhaust of an existing stove, not really. But if you replace your stove with a more efficient one, possibly. The problem with most wood stoves is incomplete combustion, which results in smoky, sooty exhaust. Rocket stoves are a solution. Also, electric blowers are a solution.

ggm 6y ago

As long as you want heat energy otherwise, why not? But if you want electricity, and not heat, but have sunlight, I wouldn't run here. It has a niche, as long as YOU WANT HEAT

xt00 6y ago

One major annoyance of using TEG's (from my own experience) is that they need heat to flow through the TEG rather than "heat it up".. so if you don't have a way for the heat to flow through the TEG (such as a fan or heatsink on the opposite side of the TEG -- the "cold side"), you rapidly end up with a situation where both sides of the TEG are roughly the same temperature and as a result you end up generating very little power. So if the wood stove heats up the ambient air around you, then the result is the efficiency goes down tremendously. These things are more suited for places where you have a very high temperature and a cold sink -- like the outside surface of a metal chimney in your cabin in the woods type thing -- such as outside, where you have the greatest sustainable delta T.

gkop 6y ago
Silly question, but could you use one of those nifty wood stove fans [0] to move the heat? [0] https://www.wayfair.com/Ecofan--UltrAir-Wood-Stove-Fan-810CABX-L181-K~ECFN1004.html https://www.wayfair.com/Ecofan--UltrAir-Wood-Stove-Fan-810CA...
- energ8 6y ago
  The fans like this I've seen are powered by TEGs, just like the article is talking about. So, yes, but there is a trade-off. For those familiar with ICE engines, I'd compare it to the trade-off of a turbo/super charger.
  - rcxdude 6y ago
    They are a quite neat niche for TEGs: you have a ready supply of heat, lower power demands, and the fact that you need to get rid of the heat on the cold side is also what you're trying to achieve with the fan in the first place. I don't think they will generate too much excess power though.

jccalhoun 6y ago

I remember seeing reviews of camp cooking stoves that had USB chargers. https://www.bioliteenergy.com/ https://www.bioliteenergy.com/ They didn't seem to be too good at charging but, as the article says, if you are already using a fire why not make a little electricity as well? I grew up in a house partially heated by a wood fireplace. After hauling wood my childhood I'm never using a wood fireplace again!

smileysteve 6y ago

I was thinking about peltier heated clothes dryer the other day. Traditional electric dryers heat to approximately 210 degrees using 240v and about 2500 watts. Recently, (compressor) heat pump dryers have come to the US for ventless options. So to produce 210 degree, 2000 watt of heat where peltiers are at least more efficient as generating heat than resistors, seems possible with a 750 computer power supply.

londons_explore 6y ago
Check your math. Peltiers get much less effective as the difference in temperature of the hot and cold sides increases. I imagine a drier would need a hot side ~100C (the equivalent electric elements get red hot after all!). Peltier units with 80C of temperature difference between the sides have very very low efficiency.
- smileysteve 6y ago
  I always thought the low efficiency was in cooling, not in heating. Dryer body is already acting as a heat sink for the (air-gapped) hot side and heating interior air at 22 degree c

ip26 6y ago

Total system efficiency (heat + electricity) is close to 100% – no energy is lost. I saw this the other day. I stopped reading here. A wood stove may be nearly 100% efficient at converting wood to heat, but half the heat goes right up the chimney. I was surprised to see lowtechmagazine skip over that.

acidburnNSA 6y ago
Wait till they hear about district heating from large central power plants.
- lowtechmagazine 6y ago
  Maybe read the article before you comment? Here's the last two paragraphs: 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.
  - acidburnNSA 6y ago
    I read it! I meant a large central non combustion power plant with district heating that doesn't emit air pollution or carbon. Not a biofuel cogen plant! Yes you have to transfer the power and yes infrastructure is needed. These are important activities in the quest for not killing people via air pollution and stopping climate change.

avsteele 6y ago

If you do any camping or backpacking there is a great little application of this: https://www.bioliteenergy.com/collections#cooking https://www.bioliteenergy.com/collections#cooking This little stick burner can get a super hot fire going and boil water easily, or grill a burger. With the electricity generated in excess of that needed for the fan you can charge your phone/devices or use its port for an LED lamp . That it runs on little sticks is super convenient.

fencepost 6y ago

I suspect many of the folks who'd be interested in this kind of thing (lowtechmagazine) are the same ones very concerned about climate change and pollution. Maybe I missed it by just skimming, but is there any discussion in there of the particulates and CO2 output of burning wood? In a very real sense burning wood is the same thing as burning coal, minus millions of years of pressure. Perhaps for their next article on low-tech stoves they can investigate the higher energy density and improved generation capabilities of coal. Why, in some places you can even find convenient coal chutes!

tom_mellior 6y ago
> In a very real sense burning wood is the same thing as burning coal, minus millions of years of pressure. Burning wood only emits CO2 that was in the atmosphere recently. Regrowing an equal size tree in the same place captures that CO2 again. This means net zero CO2 emissions (in theory). In comparison, you would need to plant new trees in new places (and not cut them down) to offset the CO2 from fossil coal.
- acidburnNSA 6y ago
  Biofuel is almost as bad as coal from a carbon emission point of view. Lifecycle emissions are about 740 gCO₂-eq/kWh, c.f. 840 for coal (Source: Schlomer 2014 IPCC meta-analysis). The problem is that you can burn a log that took 20 years to accumulate carbon in 1 hour. Sure it renews, eventually. But if lots of people do this the concentration of carbon in the atmosphere would equilibriate at a level inconsistent with solving climate change. And the particulate air pollution from wood is a true killer. This concept is deeply flawed because of carbon emissions and air pollution.
  - tom_mellior 6y ago
    Agreed with all your points, I wouldn't want us to return to more burning of wood. I was just pointing out the categorical difference to burning fossil fuels, which even theoretically aren't part of the same life cycle and cannot be offset in the same way -- we can't grow back forests from millions of years ago.

marsdepinski 6y ago

Much better turning excess heat into steam to drive a turbine or flywheel than this. If you have a large water tank you can store heat for days to keep a house warm. I have 27kw cast iron wood burning fireplace and a wood/coal brick / ceramic kitchen and oven on the other side of the chimney. If I run both in -10c the house gets too hot. Once heated the house needs about 4 18inch logs a day. This is the only heating system. Burn oak, beech and birch. Burning pine or any conifer is a disaster for your chimney. Burns like gasoline and you have to keep feeding it.

thescriptkiddie 6y ago

Randall Munroe (xkcd) did a video [0] a while back to promote his book "How To" where he addressed several (mostly silly) ways of powering a hypothetical home using only energy gathered on-site. In it, he calculated that 0.2 acres of trees only produces about 38 watts of usable power, if you burn them to generate electricity at the same rate they grow. [0] https://www.youtube.com/watch?v=j1tcyEo2tQk https://www.youtube.com/watch?v=j1tcyEo2tQk

slavik81 6y ago
I look forward to reading about Christopher Robin's adventures in the 19 Kilowatt Wood.

peter_d_sherman 6y ago

>"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." [...] >"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." [...] >"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. [19][22-25] 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."

kragen 6y ago

This article is full of errors, from the details up to the overall idea. TEGs are not "more sustainable" than PV panels. As the article points out, they're made from similar materials, using the same fabrication technologies, except that PV panels include some plastic; and TEGs typically use exotic, scarce semiconductors based on heavy metals, like bismuth telluride or lead telluride, rather than abundant, cheap semiconductors like silicon. (Silicon is too good at conducting heat to make a good TEG.) I guess Kris De Decker just really doesn't like plastic! But a much bigger issue is that PV panels usually last decades, except for the small minority that get smashed, while TEGs tend to get burned up because you have to put them in a fire to make them work, and even aside from the danger of accidental overheating (because your water tank emptied out, say, or the air currents in your wood stove were different from usual) the Arrhenius equation governs a wide variety of TEG and PV failure mechanisms. So TEGs are not "more reliable". The article argues that solar panels are not being recycled because they have plastic in them. This is false. The truth is that solar panels are not being recycled because almost all of them still work, even those manufactured decades ago, and manufacturing is growing rapidly, so there is not a sufficiently large pool of broken solar panels to supply any significant fraction of the demand for silicon. TEGs are not "less costly" than solar panels. Solar panels are https://www.solarserver.de/pv-modulpreise/ https://www.solarserver.de/pv-modulpreise/ €0.17 per watt now. https://www.dx.com/p/yb3981-diy-150-c-thermoelectric-power-generator-peltier-module-white-silver-2050639.html https://www.dx.com/p/yb3981-diy-150-c-thermoelectric-power-g... is a TEG rated for 150° which can theoretically produce about 3 watts for US$9: 15 times as expensive. Typical PV capacity factors are around 20%†, so even if the TEG got a 100% capacity factor — which it won't, since you don't have a constant 3-watt load to hang off it — it would be three times more costly. (Is there a cheaper source for TEGs somewhere?) This also tends to show that more energy and materials are needed to manufacture TEGs than equivalent solar panels, since that's what most of your money goes to buy. (150° is about the limit for bismuth-telluride TEGs — bismuth alloys and intermetallics tend to melt at low temperatures. It is not true that, as the article says, that "the hot side of bismuth telluride modules withstands continuous temperatures of 150 to 350 degrees", nor are Bi₂Te₃ modules "the most efficient ones".) The article argues that TEGs are "100% efficient" because any energy not harvested by the TEG is used to heat your house. Aside from this being undesirable in the summer — a significant concern for many of us here in the "global south" that Kris De Decker pretends to care about, from his apartment in Spain — it's also the case that burning up kilowatts of precious energy directly into low-grade heat is an extremely inefficient way to heat your house. The apartment I'm in here is primarily heated by an air conditioner with the capability of functioning backwards, in which mode it produces about 3 kilowatts of heating in exchange for a single kilowatt of electricity, for 300% "efficiency". (This is not a violation of thermodynamics; the Carnot cycle is reversible, and the indoor and outdoor temperatures just aren't that far apart.) Producing the same amount of heating with the oven or a wood stove would waste two kilowatts of gas or wood. Additionally, wood stoves are seriously fucking bad for your health. They produce massive amounts of carcinogenic smoke. TEGs do have real merits — I've loved them since I was a kid. They can provide small amounts of power, at very low efficiency, in a totally autonomous, independent, and portable way. You might be able to charge your phone, run a reading light, or trickle-charge a battery. But they are not an alternative power source for your house. They are not going to run your vacuum cleaner or your e-scooter, contrary to the misleading illustrations in this article. A normal household vacuum cleaner needs 500–2000 watts, and at 5% efficiency that would mean running 10 to 40 kilowatts of heat through your TEG, a power level at which you will quickly cease to appreciate the space heating effect. However, as John Nagle pointed out in https://news.ycombinator.com/item?id=23356206 https://news.ycombinator.com/item?id=23356206, the end-to-end efficiency in the Lebanese study cited was not 5% but 0.04%, because most of the energy in the fuel goes right out the chimney, and most of the rest goes directly into the house, not through the TEG. So what could have motivated such a mendacious article? Did Low Tech Magazine get an advertorial contract, similar to The Atlantic's famous David Miscavige Leads Scientology to Another Banner Year deal? Does Kris De Decker simply have no interest in whether what he's writing is true or false, scraping together whatever argument he thinks he can trick people into believing in order to support his preconceived conclusion? Either way, this article destroys the credibility of Low Tech Magazine. (Unless it's a false-flag operation? Maybe someone is impersonating Kris De Decker to discredit him?) † In polar countries like Germany, the Netherlands, or England, PV capacity factors may worsen to 10%. Near the Arctic or Antarctic Circle things are even worse, and within them of course you can't use solar power without a seasonal energy store, which is totally impractical for most uses.