Thermoelectric Stoves vs. Solar Panels
lowtechmagazine.com
lowtechmagazine.com
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_37...
So about 0.001-0.002% as efficient as solar, up to 5 orders of magnitude worse. With the advantage of less intermittency, I suppose, but both are solid state energy converters; I wouldn’t claim thermoelectric is “lower tech” except that it’s way less efficient and with more environmental footprint due to that inefficiency. A battery to solve the intermittency would be still a much better trade IMHO.
I’m not saying that biology isn’t great. Self-replicating machinery is pretty awesome. But if you’re using advanced machines anyway, you should skip the biological middleman if you can and go right for the source of energy.
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.
Why not a Stirling engine?
It looks like the Kickstarter turned into https://seftonmotors.com/ , which are about 2000$ for a 1.2kW (full temp, pressurized) engine.
I'm not sure though why you want to burn wood on that scale. It's really expensive to properly filter the exhaust from a wood stove, and economy of scale doesn't hit in the kW range. I mean, yes, if you're in the middle of nowhere, sure, but I'd claim that an install cost of 3~4$/W(electric) for the Melvin Package, including shipping (even to a potentially-remote location, only 100kg for the largest piece allows transport with e.g. a paramotor or two humans, with additional trips for the cooling jacket/firebox/vents/piping) is acceptable for a reliable wood-fueled electricity source.
It's probably not much.. but I imagine you could boost the efficiency by lining the chimney with copper tube and running water through it, using the waste heat there to heat this water. Then use your TEG as a heat-exchanger between that loop and another loop connected to your "domestic water heater" or other cold water supply.
Maybe it's merely teasing the Ig Noble Prize committee though. :-)
We’ve got mains powered one in our current place and it makes a big difference.
> 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/)
[0] https://www.wayfair.com/Ecofan--UltrAir-Wood-Stove-Fan-810CA...
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.
"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.
If energy systems were installed that could heat and power these places without biofuel at all you'd be vastly better off. I did not see that point in there.
What energy system you had in mind?
Solar panels could provide electricity, but they don't produce heat, which is vastly more important in the household. A solar PV installation that powers an electric cookstove and heater is unaffordable, even for many people in rich countries.
Alternatives are different in different places, but are some combo of electrification using wind, hydro, solar, tidal, geothermal, and nuclear.
I get that these things take time. I guess if this article pointed out that wood energy is generally terrible for air pollution and carbon reasons and must be moved away from, I would be less upset by it.
Of course burning wood produces more particulates, though less sulfur or radium. These I imagine would be slightly more upscale ovens though than I think you're talking about, the kind with chimneys so they don't exhaust into the house at least. For those kinds of ovens I feel like demographic wise you're talking semi off-the-grid New Hampshire rather than cooking with coal indoors.
Consider that trees collecting solar energy are maybe 50x worse than solar cells at converting sunlight to biomass energy. But for the kinds of situations I'm imagining they have enough land that the wood is free anyway. And I do believe that in that situation it's carbon neutral, except that the carbon gets released more as soot than it started which does suck.
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.
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.
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.
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.
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.
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.
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!
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.
And the particulate air pollution from wood is a true killer.
This concept is deeply flawed because of carbon emissions and air pollution.
I just don't think the idea of a "life cycle" is meaningful here. It is similar to labelling something as "natural".
The coal in the ground isn't a snapshot of a single point in time in the past. It represents a succession of trees. Some were buried in the ground, and others grew above them. More were buried, and more grew above. Many layers were deposited over millions of years. The totality of coal below ground represents a lot more trees than could ever grow at once on the surface. Burning fossil coal puts CO2 into the atmosphere that cannot be offset in any meaningful way by planting trees. Not on a time horizon shorter than millions or at least thousands of years.
We would have to grow trees, then cut them down, and sequester them below ground again in a way that keeps the carbon from escaping. Almost like, you know... coal.
Sure. In the short term almost nothing humans do can make a difference at Earth scale. It's a very big planet. But we have been burning huge amounts of fossil fuels for centuries now, which has got us into trouble.
> And I don't think wood burning should get a free pass just because somewhere a tree is growing. Ideally a carbon tax would apply.
Agreed.
A book on energy once classified energy as new (biofuel, solar, wind, hydro), old (fossil fuel) and really old (nuclear, geothermal, tidal). I kind of like that. Of course all of the above are derived from nuclear fusion in stars if you track it back far enough.
But it should still be much better than these thermoelectric generators.
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.
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.
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!
[...]
>"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."
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.
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.
Dryer body is already acting as a heat sink for the (air-gapped) hot side and heating interior air at 22 degree c
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/ €0.17 per watt now. 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, 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.
1. "Kris De Decker just really doesn't like plastic!"
Correct. We need to get rid of plastic. Keep reading me if you want to know how.
2. "TEGs tend to get burned up"
Not if you build a well designed stove, which is what all the research in the article is about.
3. "They are not going to run your vacuum cleaner or your e-scooter, contrary to the misleading illustrations in this article."
There are several references in the article to prototypes of thermoelectric heating systems that actually do provide enough power to run a vacuum cleaner or an e-scooter.
4. "The truth is that solar panels are not being recycled because almost all of them still work"
Just read a bit about the recycling of solar panels, OK? You can find the references in the article.
5. "TEGs are not "less costly" than solar panels."
In your calculation, you completely ignore the energy storage and the installation. And that's where the cost advantage of the TEG is. Also, no need to oversize generation capacity. RTFA.
6. "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."
So where are you getting that single kilowatt of electricity from? Also, can your air conditioner also cook your food, heat your water, and maybe even provide you with lighting? No. You need a lot more electric appliances (and infrastructures) for that.
7. "So what could have motivated such a mendacious article?"
You would not have the balls to say these things in my face.