7 ms·

Thermoelectric Stoves: Ditch the Solar Panels? (2020)

58 points by mastazi 5y ago

ctdonath 5y ago
Interesting related product: BioLite camp stove https://www.bioliteenergy.com/products/campstove-2-plus https://www.bioliteenergy.com/products/campstove-2-plus
- aspenmayer 5y ago
  That would be great for camping or other off-grid use. I had no idea this was a product that existed.
nemo1618 5y ago
> 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. Doesn't this imply that you can just keep recirculating the heat back into the module until it's converted 100% of the energy? I suppose you would need to power the recirculator somehow, but you can do that using the output of the module, so you're back to 100% efficiency again. What's the catch?
- ummonk 5y ago
  You can’t just recirculate heat like that. The TEG requires a temperature difference to generate voltage and power. Any recirculated hot air is not going to be any hotter than the air on the other side of the TEG.
- intrepidhero 5y ago
  Efficiency drops as the temperature delta goes down. The trick is maintaining that difference. That section of the article is a bit misleading. Even really expensive stoves are only about 95% efficient. You need some heat loss out the chimney for the thing to work. I'd guess that stoves typically in use in the rural global south are much less
- invalidator 5y ago
  The waste heat flows out the cold side of the junction, through the heat sink, and is lost into the ambient air. You can't feed that heat back into the hot side because it's been diluted into the air, and thus it's a lower temperature. You can't concentrate the waste heat by enclosing the heat sink in a small volume because that would eliminate the temperature differential across the junction. You won't gain much by making a stack of junctions with each one passing its waste heat to the next one. They effectively insulate each other, reducing the temperature differential across each one. There's an optimization opportunity here, but commercial junctions are usually already sold as a stack. Adding more layers gives rapidly diminishing returns at best. Thermodynamics is cruel.
  - jiggawatts 5y ago
    "No such thing as a free lunch." should be tattooed onto to foreheads of every charlatan claiming to be able to use water as fuel.
intrepidhero 5y ago
I think Seebeck junctions are neat. A friend has one sitting on his wood stove powering a little fan. But you're not going replace a solar system. Example systems in the article produce 10s of watts. If you're running your stove all day (ie winter) that's replacing the output of maybe one 100W solar panel. In the summer when you want to use your stove as little as possible solar will be a much better proposition. Now if you convert your wood stove into a gasifier and drive a converted diesel generator... That be would something viable, a ton more complexity and maintenance but at least you'd have abundant power.
k__ 5y ago
This reminds me that I heat my office in the winter only with my PC. Don't know if this is good or bad, though.
- adrianN 5y ago
  Well, it would be better if you used a heat pump and a more efficient PC, it would probably be worse if you used oil.
ummonk 5y ago
I’ve played a lot with thermoelectric generators and experimented with lots of proposed devices such as this. The simple reality is that thermoelectric generators are just not well suited for drawing significant amounts of power.
Animats 5y ago
3.5 watts net electricity at a burning rate of 1 kg of firewood per hour This is a phone charger at best. That could be useful as an emergency stove accessory.
- ummonk 5y ago
  Right that’s like an order of magnitude less than you’d get off an exercise bike.
- TheSpiceIsLife 5y ago
  Try plugging a modern smartphone in to an old 5 watt USB socket, the charge indicator will probably indicate charging, but it probably won’t do much unless the phone is completely off.
  - NullPrefix 5y ago
    Regular USB is 5V * 0.5Amps = 2.5Watts It's called slow charge and it's healthy for your battery
- mprovost 5y ago
  I remember seeing photos of people in Brooklyn charging phones with Biolite camping stoves after hurricane Sandy: https://gothamist.com/news/oh-just-brooklyn-survivalists-charging-cell-phones-with-camp-stoves-as-the-national-guard-rolls-by https://gothamist.com/news/oh-just-brooklyn-survivalists-cha...
mrtweetyhack 5y ago
100% Efficient. 100% False
ashika 5y ago
youtube channel schematix did a two-part series of iteratively improving a TEG rocket stove. very entertaining but i dont think i'll be building one. https://www.youtube.com/watch?v=_dvbN2vKrc4 https://www.youtube.com/watch?v=_dvbN2vKrc4 https://www.youtube.com/watch?v=B8b1OYy-b5I https://www.youtube.com/watch?v=B8b1OYy-b5I
- KennyBlanken 5y ago
  Entertaining but also a lot of nonsense. I stopped watching after he made a show of wandering around aiming a pair of cheap folding solar panels at the sky. "These tiny solar panels won't charge my phone on a cloudy day!" 1)He compares $30 worth of solar panel to a device that probably cost several hundred dollars to build (each of those heatsinks he used cost as much as the solar panel he was waving about.) A $100 (~100W) solar panel would, even on an overcast day, produce 5-10W pretty easily. 2)You don't just use solar for power. You use solar with batteries. The panels are sized based on solar equivalent hours. There are charts that tell you what areas get in terms of "full hours of sun" each day, in summer and winter. You then figure out your typical load, how much battery capacity you want (ie how many days of zero solar output can you tolerate), and how long you want your system to recover from being completely drained while powering your typical load.
  - Gibbon1 5y ago
    I feel there is a certain irony in Deckers hate of solar cells. Because they're pretty low tech functionally. And it's not like every other material you can acquire isn't tied to some complex industrial infrastructure.
dsizzle 5y ago
OP doesn't comment on the air pollution from wood stoves, except to say it can be "cut in half". Half the pollution from wood stoves is still a lot of pollution. I'm reminded of this essay by Sam Harris https://www.samharris.org/blog/the-fireplace-delusion https://www.samharris.org/blog/the-fireplace-delusion
- aaron695 5y ago
  100% this. It's only for pre existing fireplaces. Like pre-existing cigarette smokers. Even as a prepper you need to be dogfooding so you should limit stuff like this. But if you are going to do it... heres a little fan that uses the principal. I'm unsure if the wind chill is worse that mixing the heat..but it's a cute use of a Peltier https://www.amazon.com/WAPEMORK-Fireplace-non-Electric-Circulating-Accessorie/dp/B09BTVGHM8/ https://www.amazon.com/WAPEMORK-Fireplace-non-Electric-Circu...
- kseistrup 5y ago
  This! As somebody who lives in an area where people mainly uses wood stoves to heat their houses during the winter, I think it's a terrible idea.
- phonypc 5y ago
  I like Sam. I've noticed several instances of him speaking/writing as if rural areas don't exist though. The sentence "If you are burning wood in the United States, Europe, Australia, or any other developed nation, you are most likely doing so recreationally" is just monumentally silly. It's also odd to reference the WHO on the harms of burning solid fuel (not just wood) for heat in an essay condemning recreational fire-burning. Anyway, it's all just an analogy for religion here. Not a serious treatment of the problem of air pollution.
  - dsizzle 5y ago
    He says “most likely” and only 20% live in rural areas. Also there are other sources of heat in rural areas.
karaterobot 5y ago
>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. So if you need a ton of heat and a tiny bit of electricity, this is perfect for you. Otherwise, it doesn't sound like a replacement for solar panels as much as a complementary technology for certain situations.
- neocodesoftware 5y ago
  article says in europe 80% of household energy use in for space and water heating so europe needs a ton of heat and tiny electricity
14 5y ago
The energy from this type of system is far to low for what the author describes. Instead I have a coil on my stove and it is connected to a thermostat to know when the stove is hot and a hot water pump and 2 hot water tanks. Cold city water enters the first tank and circulated through the coil on top my stove. This does a great job of heating a lot of water during a day. Then the second tank pulls from the first one and it is already heated saving lots of money. The first tank is not plugged in just runs off the stove. If you could take a lot of energy from the stove (my hot water set up can do that) you also have to worry about creosote build up. It is important to have a high air hot fire occasionally to get rid of it and to also clean your chimney yearly.
hannob 5y ago
If you don't have extremely sophisticated filter equipment, every form of burning wood is a terrible source of air pollution. Calling that "sustainable" is... maybe a sign how meaningless the word sustainable is. Though it's definitely not something to be recommended.
- fivea 5y ago
  > Calling that "sustainable" is... maybe a sign how meaningless the word sustainable is. There's a huge difference between burning fossil fuels, with all the logistics that involves, and burning whatever trimmings you're getting from your surroundings.
  - simondotau 5y ago
    Yes, a huge difference. The latter is orders of magnitude worse.
    - fivea 5y ago
      > Yes, a huge difference. The latter is orders of magnitude worse. Do you base your personal assertion on any evidence? I'd love to see the basis for this line of reasoning. I mean, carbon emissions-wise the difference between biomass and burning oil/coal is already undisputed.
      - simondotau 5y ago
        When you're talking about people living in an area of medium or high population density, burning tree trimmings for energy is an impractical solution which is grossly inefficient and has multiple disastrous externalities for the environment, even if it's technically carbon neutral. It's better for the environment to sequester biomass inputs (e.g. tree trimmings) back into the soil and burn more efficient fossil fuels instead. Far from being merely carbon neutral, use of fossil fuels combined with sequestration of biomass could easily be carbon positive.
      - Retric 5y ago
35mm 5y ago
PV solar panels might not be the most efficient system overall, but they’re modular, easy to maintain, safe to DIY (for low voltage off grid systems), keep getting cheaper per watt due to economies of scale, and have lots of easily available information on how to make the best use of them.
2Gkashmiri 5y ago
what is the "big" version of those peltier 12v modules called? if i had to find a say 50Watt model, am i stuck with chaiming those tiny toy hobby grade stuff? lets say i live in a place where people have lots of wood burning going during winters and this can be a nice experiment if it gives something substantial
deleted 5y ago
[deleted]

58 points by mastazi 5y ago

Interesting related product: BioLite camp stove https://www.bioliteenergy.com/products/campstove-2-plus https://www.bioliteenergy.com/products/campstove-2-plus

aspenmayer 5y ago
That would be great for camping or other off-grid use. I had no idea this was a product that existed.

nemo1618 5y ago

> 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. Doesn't this imply that you can just keep recirculating the heat back into the module until it's converted 100% of the energy? I suppose you would need to power the recirculator somehow, but you can do that using the output of the module, so you're back to 100% efficiency again. What's the catch?

ummonk 5y ago
You can’t just recirculate heat like that. The TEG requires a temperature difference to generate voltage and power. Any recirculated hot air is not going to be any hotter than the air on the other side of the TEG.
intrepidhero 5y ago
Efficiency drops as the temperature delta goes down. The trick is maintaining that difference. That section of the article is a bit misleading. Even really expensive stoves are only about 95% efficient. You need some heat loss out the chimney for the thing to work. I'd guess that stoves typically in use in the rural global south are much less
invalidator 5y ago
The waste heat flows out the cold side of the junction, through the heat sink, and is lost into the ambient air. You can't feed that heat back into the hot side because it's been diluted into the air, and thus it's a lower temperature. You can't concentrate the waste heat by enclosing the heat sink in a small volume because that would eliminate the temperature differential across the junction. You won't gain much by making a stack of junctions with each one passing its waste heat to the next one. They effectively insulate each other, reducing the temperature differential across each one. There's an optimization opportunity here, but commercial junctions are usually already sold as a stack. Adding more layers gives rapidly diminishing returns at best. Thermodynamics is cruel.
- jiggawatts 5y ago
  "No such thing as a free lunch." should be tattooed onto to foreheads of every charlatan claiming to be able to use water as fuel.

intrepidhero 5y ago

I think Seebeck junctions are neat. A friend has one sitting on his wood stove powering a little fan. But you're not going replace a solar system. Example systems in the article produce 10s of watts. If you're running your stove all day (ie winter) that's replacing the output of maybe one 100W solar panel. In the summer when you want to use your stove as little as possible solar will be a much better proposition. Now if you convert your wood stove into a gasifier and drive a converted diesel generator... That be would something viable, a ton more complexity and maintenance but at least you'd have abundant power.

k__ 5y ago

This reminds me that I heat my office in the winter only with my PC. Don't know if this is good or bad, though.

adrianN 5y ago
Well, it would be better if you used a heat pump and a more efficient PC, it would probably be worse if you used oil.

ummonk 5y ago

I’ve played a lot with thermoelectric generators and experimented with lots of proposed devices such as this. The simple reality is that thermoelectric generators are just not well suited for drawing significant amounts of power.

Animats 5y ago

3.5 watts net electricity at a burning rate of 1 kg of firewood per hour This is a phone charger at best. That could be useful as an emergency stove accessory.

ummonk 5y ago
Right that’s like an order of magnitude less than you’d get off an exercise bike.
TheSpiceIsLife 5y ago
Try plugging a modern smartphone in to an old 5 watt USB socket, the charge indicator will probably indicate charging, but it probably won’t do much unless the phone is completely off.
- NullPrefix 5y ago
  Regular USB is 5V * 0.5Amps = 2.5Watts It's called slow charge and it's healthy for your battery
mprovost 5y ago
I remember seeing photos of people in Brooklyn charging phones with Biolite camping stoves after hurricane Sandy: https://gothamist.com/news/oh-just-brooklyn-survivalists-charging-cell-phones-with-camp-stoves-as-the-national-guard-rolls-by https://gothamist.com/news/oh-just-brooklyn-survivalists-cha...

mrtweetyhack 5y ago

100% Efficient. 100% False

ashika 5y ago

youtube channel schematix did a two-part series of iteratively improving a TEG rocket stove. very entertaining but i dont think i'll be building one. https://www.youtube.com/watch?v=_dvbN2vKrc4 https://www.youtube.com/watch?v=_dvbN2vKrc4 https://www.youtube.com/watch?v=B8b1OYy-b5I https://www.youtube.com/watch?v=B8b1OYy-b5I

KennyBlanken 5y ago
Entertaining but also a lot of nonsense. I stopped watching after he made a show of wandering around aiming a pair of cheap folding solar panels at the sky. "These tiny solar panels won't charge my phone on a cloudy day!" 1)He compares $30 worth of solar panel to a device that probably cost several hundred dollars to build (each of those heatsinks he used cost as much as the solar panel he was waving about.) A $100 (~100W) solar panel would, even on an overcast day, produce 5-10W pretty easily. 2)You don't just use solar for power. You use solar with batteries. The panels are sized based on solar equivalent hours. There are charts that tell you what areas get in terms of "full hours of sun" each day, in summer and winter. You then figure out your typical load, how much battery capacity you want (ie how many days of zero solar output can you tolerate), and how long you want your system to recover from being completely drained while powering your typical load.
- Gibbon1 5y ago
  I feel there is a certain irony in Deckers hate of solar cells. Because they're pretty low tech functionally. And it's not like every other material you can acquire isn't tied to some complex industrial infrastructure.

dsizzle 5y ago

OP doesn't comment on the air pollution from wood stoves, except to say it can be "cut in half". Half the pollution from wood stoves is still a lot of pollution. I'm reminded of this essay by Sam Harris https://www.samharris.org/blog/the-fireplace-delusion https://www.samharris.org/blog/the-fireplace-delusion

aaron695 5y ago
100% this. It's only for pre existing fireplaces. Like pre-existing cigarette smokers. Even as a prepper you need to be dogfooding so you should limit stuff like this. But if you are going to do it... heres a little fan that uses the principal. I'm unsure if the wind chill is worse that mixing the heat..but it's a cute use of a Peltier https://www.amazon.com/WAPEMORK-Fireplace-non-Electric-Circulating-Accessorie/dp/B09BTVGHM8/ https://www.amazon.com/WAPEMORK-Fireplace-non-Electric-Circu...
kseistrup 5y ago
This! As somebody who lives in an area where people mainly uses wood stoves to heat their houses during the winter, I think it's a terrible idea.
phonypc 5y ago
I like Sam. I've noticed several instances of him speaking/writing as if rural areas don't exist though. The sentence "If you are burning wood in the United States, Europe, Australia, or any other developed nation, you are most likely doing so recreationally" is just monumentally silly. It's also odd to reference the WHO on the harms of burning solid fuel (not just wood) for heat in an essay condemning recreational fire-burning. Anyway, it's all just an analogy for religion here. Not a serious treatment of the problem of air pollution.
- dsizzle 5y ago
  He says “most likely” and only 20% live in rural areas. Also there are other sources of heat in rural areas.

karaterobot 5y ago

>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. So if you need a ton of heat and a tiny bit of electricity, this is perfect for you. Otherwise, it doesn't sound like a replacement for solar panels as much as a complementary technology for certain situations.

neocodesoftware 5y ago
article says in europe 80% of household energy use in for space and water heating so europe needs a ton of heat and tiny electricity

14 5y ago

The energy from this type of system is far to low for what the author describes. Instead I have a coil on my stove and it is connected to a thermostat to know when the stove is hot and a hot water pump and 2 hot water tanks. Cold city water enters the first tank and circulated through the coil on top my stove. This does a great job of heating a lot of water during a day. Then the second tank pulls from the first one and it is already heated saving lots of money. The first tank is not plugged in just runs off the stove. If you could take a lot of energy from the stove (my hot water set up can do that) you also have to worry about creosote build up. It is important to have a high air hot fire occasionally to get rid of it and to also clean your chimney yearly.

hannob 5y ago

If you don't have extremely sophisticated filter equipment, every form of burning wood is a terrible source of air pollution. Calling that "sustainable" is... maybe a sign how meaningless the word sustainable is. Though it's definitely not something to be recommended.

fivea 5y ago
> Calling that "sustainable" is... maybe a sign how meaningless the word sustainable is. There's a huge difference between burning fossil fuels, with all the logistics that involves, and burning whatever trimmings you're getting from your surroundings.
- simondotau 5y ago
  Yes, a huge difference. The latter is orders of magnitude worse.
  - fivea 5y ago
    > Yes, a huge difference. The latter is orders of magnitude worse. Do you base your personal assertion on any evidence? I'd love to see the basis for this line of reasoning. I mean, carbon emissions-wise the difference between biomass and burning oil/coal is already undisputed.
    - simondotau 5y ago
      When you're talking about people living in an area of medium or high population density, burning tree trimmings for energy is an impractical solution which is grossly inefficient and has multiple disastrous externalities for the environment, even if it's technically carbon neutral. It's better for the environment to sequester biomass inputs (e.g. tree trimmings) back into the soil and burn more efficient fossil fuels instead. Far from being merely carbon neutral, use of fossil fuels combined with sequestration of biomass could easily be carbon positive.
    - Retric 5y ago

35mm 5y ago

PV solar panels might not be the most efficient system overall, but they’re modular, easy to maintain, safe to DIY (for low voltage off grid systems), keep getting cheaper per watt due to economies of scale, and have lots of easily available information on how to make the best use of them.

2Gkashmiri 5y ago

what is the "big" version of those peltier 12v modules called? if i had to find a say 50Watt model, am i stuck with chaiming those tiny toy hobby grade stuff? lets say i live in a place where people have lots of wood burning going during winters and this can be a nice experiment if it gives something substantial

deleted 5y ago

[deleted]