Rocket stove electric generator

Has anyone heard of this concept? using a thermoelectric cooler to create electricity with your Rocket stove? My idea is to put about 12 to 14 of these on the outside exhaust stack and allow the 100+ F temps come in contact with one side and the cold winter out side on the other and have it create clean sustainable electricity from my efficient Rocket mag stove and add to the work load my stove already has. Upgrade the stove in to a power machine.

Get you own cheap thermoelectric modules here: http://www.ebay.com/sch/i.html?_odkw=thermal+cooler+modual&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.XPeltier+Thermoelectric+Cooler+Modules.TRS0&_nkw=Peltier+Thermoelectric+Cooler+Modules&_sacat=0

i think every household should generate thier own electricty- and yeah if you can make heat- you can generate power. its more than a great idea , its making the most of your home energy

I think using every bit of everything out of it all. My friends say i can squeeze a penny into a dime. these thermoelectric coolers are super cheap and we all can afford them and a small battery bank.

in the summer you could use solar to maintain the bank and cloudy days you can use my "doomsday exercise bike" for extra charge requirements. that project is on permies under "energy/alternative energy" posted by me in 2015. check it out if you like alternative energy

I would use a bike to generate electricity if a stream didnt run 5 feet behind my house.

thats awesome man. floating water wheel perhaps? i was just plug-advertising my other prior permies energy project lol. most energy stuff is so addictive and captivating- draws my immediate attention. like rocket stove electricity generators for example

It's been discussed many times over here. So far nobody came back to brag, or with amazing results.

Problem with TECs Pelletier thingys, is that they don't produce much. And that they have a temperature limit which is rather low. And to produce electricity with theses, you need the bigger temp differential you can get. Not 80C° hopt face and 20C° cold face.

Satamax Antone wrote:It's been discussed many times over here. So far nobody came back to brag, or with amazing results.

Problem with TECs Pelletier thingys, is that they don't produce much. And that they have a temperature limit which is rather low. And to produce electricity with theses, you need the bigger temp differential you can get. Not 80C° hopt face and 20C° cold face.

In USDA zone 6 virtually every night his nighttime temperatures will be significantly under 0C

So best case scenario? 5 or 10 of the units would power my LED lights and maybe charge the cell phone too?

Yes they are very low output, and if you go to wood stove suppliers chances are you have seen the one place these have become usefull, heat transfer fans, designed to set on your stove and blow the hot air around the room. This is a tiny motor and it takes a 2x2 device to run it......

The best TEG's are only about 8% efficient and 5% is more realistic, and this is at their optimum temperature differential. (that is for the chip alone, not the whole system, which will necessarily be a little less efficient)
The cost per watt (output) is extremely high. It's not just the cost of the peltier chip itself, the heat sinks (you need to keep the cold side, well, cold, or you won't generate any current.) are typical aluminum or copper, intricately machined, and often need additional airflow (fans) to cool the cold side and prevent damage.

There are well-engineered commercially sold, air-cooled units for home use, meant to be directly attached to a wood stove (likely at least 50%-75% higher ΔT than we are discussing here) that produce a claimed 45 watts, at maximum ΔT, for around US $525. (I've seen a liquid-cooled device advertised up to 60w (US $625)) These units are about a foot square and weigh about 20 pounds, to give you some idea of how much it takes to output 45 watts (using 8 pieces of TEG1-12610 peltiers). (typically about US $25 each in small quantities) With a low ΔT (most low temp chips are spec'd at about 270c ΔT, typically 30c and 300c), you would generate far less in the same space.

Extremely high quality TEGs have been used for years in the space industry (called "RTGs") they have attained end-to-end efficiencies of up to 7%, whith these systems, nuclear decay provides the heat source and near-absolute-zero space provides the cold. Even these million dollar units struggle to provide more that a few hundred watts.

Design criteria is rather important, as the power generated is directly related to the ΔT, so you want the maximum hot side temp., and the minimum cold side temp., but the hot side needs to stay below the maximum operating temp. or you will destroy the peltiers.
I've played with this tech for the last 15 years or so, and TBH, have been mostly disappointed. It's such an attractive technology, but it still needs a lot more development to be truly useful to most of us. For now, I consider it a great school science experiment, not a bad rich man's toy, but I've found solar to be a far more user friendly and functional way to generate small amounts of power.

I don't mean to disparage your ideas, I just want to provide a realistic viewpoint, from someone who has played with the technology. Armed with experience of others, hopefully you won't be disappointed with the outcome, if you give it a try.

Thank you all for your input. I seriously have been studying this and in all reality i am aware of the limitations. I only expect to get the results that have been studied for a wood stove and temps i have to provide for it. I plan to use the exhaust stack on the out side which will be well below the high end limit and the cold side will be exposed to outside cold air which can get as low as -19F here. We dont get those extreme cold temps everyday but we do get cold enough not to need electric fans and expensive heat sinks to provide differences in temps for the modules. I will be using enough modules to provide what i need and only expect to trickle charge a 12v battery bank when the stove is in use and on cold dark cloudy days and nights will help when the solar panels are not working as well. I know i can not run an entire house with one of these modules but when you are living off grid every little bit helps.

@Steven Oh: "I've played with this tech for the last 15 years or so, and TBH, have been mostly disappointed. It's such an attractive technology, but it still needs a lot more development to be truly useful to most of us."

Steven, could you perhaps elaborate on a different approach. My thermodynamics and knowledge of thermocoupling is terrible, so please bear with me.

In many climates closer to the poles, one will generally heat the home to about 55 degrees F (~13C) minimum. During the coldest months, the days are short and the sun is weak, thus solar vastly reduced from the summer months. Yet on the northern wall of an average home (obviously not an earth-bermed dwelling), it could be a fairly average 0-10 degrees F (-18 to 12C) on the outside of the wall, given the severity of the season and how close the poles one is. Granted, as you alluded to, there is huge room for improvement and cost of the technology, might it not be useful to (Finally!) have a polar-directed wall that could be "of use".....could in fact be one massive 30 ft X 8 ft thermoelectric generator utilizing the inside-outside of the house as the thermal differential, even if only for trickle charging as a complement to PV for battery maintenance? Even if this temperature gradient is pretty paltry, might it not suffice given efficiency improvements in the technology and a large enough surface area? It would be serving the opposite role as the equatorial facing wall, which is windowed to gain as much passive solar as possible. Again, your average home today is on "the grid"---there is no need to separate power sources with regard to power sinks. But in a more permie home, you might have all of the efficient lighting driven by one pack of batteries....that is maintained by one source of power (PV, wind, thermoelectric, etc.) whereas the other loads are provided by a different source. Maybe?.....thoughts?

Edit: Interesting link in this regard....let me know if the link is blocked: https://pangea.stanford.edu/ERE/pdf/IGAstandard/SGW/2014/Li.pdf

If you watch this video to the end you will see that you can get 200mv from just a few centimeters of graphite and aluminum and some heat. Just think about how easy it would be to create a string of these easy to make thermal electric generators and wrap them around the upper part of the bell on your Rocket stove? Passive cooling only unless you want to get elaborate... but im all about cheap passive energy, especially made from the rocket stove you already have to run to keep your house warm. you could easily trickle charge a 12v battery for small off grid use. why not right, create a bit of electric... while you keep the house warm?

here is the DIY energy idea for your rocket stove:

Nice simple unit... the question is how many of these would you need to make to give a useful amount of power. He doesn't say how many watts (or milliwatts) he gets from this demo setup. Per his first try, 100 cells to get 1 volt, 1200 cells to get 12 volts; how much charge could it put into a battery in one evening?

The second demo with 6 cells and 200 mv suggests 30 cells for one volt, not sure what the actual counts would end up being... and of course the voltage would depend on the barrel temperature. Would a 12 volt battery be helped by a 6 volt feed?

If I'm reading the following spec sheet properly for one such "stove-top" product, your stove surface needs to be at ~500 degrees F in order to produce 1 amp of current (X12V = 12W) and about 550 degrees in order to double that output. This would be easily achieved on the top surface of a RMH; in fact, one would have to be careful regarding the Max. hot surface side temperature on the thermoelectric unit of 840 degrees F. http://www.tegmart.com/datasheets/DW-SM-45W.pdf

just 6 very small pieces of graphite and tabs of aluminum for 200mv times that by what ever your stove can heat up to, to create energy and you have how many you have to make for 12v of power to trickle charge a battery.

with the cost per watt of those things, I really think a Stirling engine driving a small generator would be the better way to go, with the hot side on the stove and the cold side running a passive themal convection water supply to an outside water barrel, or even pipe stream water in and back out if you have a stream but not enough flow or head for hydro power.

John Weiland wrote:@Steven Oh: "I've played with this tech for the last 15 years or so, and TBH, have been mostly disappointed. It's such an attractive technology, but it still needs a lot more development to be truly useful to most of us."

Steven, could you perhaps elaborate on a different approach. My thermodynamics and knowledge of thermocoupling is terrible, so please bear with me.

In many climates closer to the poles, one will generally heat the home to about 55 degrees F (~13C) minimum. During the coldest months, the days are short and the sun is weak, thus solar vastly reduced from the summer months. Yet on the northern wall of an average home (obviously not an earth-bermed dwelling), it could be a fairly average 0-10 degrees F (-18 to 12C) on the outside of the wall, given the severity of the season and how close the poles one is. Granted, as you alluded to, there is huge room for improvement and cost of the technology, might it not be useful to (Finally!) have a polar-directed wall that could be "of use".....could in fact be one massive 30 ft X 8 ft thermoelectric generator utilizing the inside-outside of the house as the thermal differential, even if only for trickle charging as a complement to PV for battery maintenance? Even if this temperature gradient is pretty paltry, might it not suffice given efficiency improvements in the technology and a large enough surface area? It would be serving the opposite role as the equatorial facing wall, which is windowed to gain as much passive solar as possible. Again, your average home today is on "the grid"---there is no need to separate power sources with regard to power sinks. But in a more permie home, you might have all of the efficient lighting driven by one pack of batteries....that is maintained by one source of power (PV, wind, thermoelectric, etc.) whereas the other loads are provided by a different source. Maybe?.....thoughts?

Edit: Interesting link in this regard....let me know if the link is blocked: https://pangea.stanford.edu/ERE/pdf/IGAstandard/SGW/2014/Li.pdf

John,
A lot of fun mental exercises there. There is nothing inherently wrong with your concept, but there is still the limitation of the current technology. TEGs are very inefficient, they require a large temperature differential (on the order of several hundred degrees Celsius) to even get close to their typical (5-8%) rating. They also require a very efficient way of shedding heat from the cold side. My first experience with thermoelectric devices was professional. Back in the 1990's I was designing air and water quality testing equipment for laboratories doing EPA analysis. We used TECs as a VOC trapping technique, with some success. This lead to my curiosity about power generation with these devices, as they obviously were reversible. (power can be used to generate a temperature differential, or a temperature differential can be used to generate power). Unfortunately, the technology has advanced very little, if at all, in the years since I first worked with these devices.

Note that in the Stanford link, they are using liquid cooling (far more efficient that air cooling) to achieve very modest power generation. Also note that they do not consider the power requirements for the electronics, pumps or heat rejection for the coolant side. In the large system they used 600 thermoelectric modules and custom machined heatsinks with the entire unit so cumbersome that it is mounted on wheels (see figure 12). While claims are made that this system is more cost effective than other renewable resources, no cost analysis is made of the expense of the geothermal wells (the stated intent is to use 200c water to generate the amount of power claimed to be cost effective) , or maintenance of those wells, which is significant. Basically, nothing was learned in the Stanford experiment. We already knew you COULD generate electricity with TEGs, and the cost efficiency claims ignore massive investments required for the geothermal heat source and also for a significant cooling system. The lesson learned from this exercise is that; with unlimited funds, you can generate modest power in a laboratory environment.

The concept is, obviously, extremely attractive. But, in practice, there are very few commercial applications where it is utilized. I have never found a practical DIY installation that is producing usable power of any consequence. Most fail because of poor design, for example, F Styles, here, intends to try it without efficient heatsinks/fans and a small temperature differential. No offense intended, it's a common error when people first try TEG, but it's probably going to drain the batteries instead of charging them. TEGs also work in reverse, using large amounts of power (remember they are very inefficient) to transfer heat across their two plates. The difference between a thermoelectric generator and a thermoelectric cooler is the direction of current flow. While I applaud the pioneering spirit, the RMH TEG experiment is almost certainly doomed to failure, due to a lack of understanding of the requirements of the technology.

I have no doubt, that someday in the future, there will be a breakthrough in the technology that will allow for a more mainstream use of this technology. By all means, play with a few TEGs and see what happens. That's what I have done. You'll discover very quickly that, currently, these are niche curiosities, with little application in general use. To net even modest gains requires meticulous engineering. NASA uses them, and as has been noted in this thread, there are a few commercially available units that provide modest power. Even those commercially available systems require constant monitoring to ensure that the energy draw from the load doesn't exceed what is produced by the TEG, otherwise the cold-side fan stops running and the device can be destroyed.

So here's the cliff notes for successfully using current TEG technology:
1.) Keep below device maximum temperature (or it will be destroyed)
2.) Big temperature differential required for modest power gains (low efficiency)
3.) Require very efficient cold side heat removal (see #1)
4.) Prevent the TEG's from becoming TEC's and draining your power source.
5.) Be prepared to spend.

Knowledge is a wonderful thing. I certainly encourage anyone to play with a few TEGs and grow to understand their requirements. Hopefully, in the future, that experience will prove useful, when the tech is improved. Good luck and have fun!

@Steven Oh: " There is nothing inherently wrong with your concept, but there is still the limitation of the current technology.

Thank you for this in-depth response, Steven. Like looking back on the first inventor of the LED, I'm hoping a new wave of minds takes up this challenge and some version of it may become a reality in a PV/battery based dwelling down the road. So many interesting technology tasters and so little time!.....

i dont think i mentioned even imagining i could run a house on this type of modules. i gave a link to a search with a wide range of affordability and quality depending on desire. what i mentioned was trickle charging a 12v bank of some sort and a proof of concept was shown to be built with junk laying around let alone if you put some more thought and time into it and increase performance. creative possibilities are endless especially if there is any opportunity to grab even the smallest amount of energy to reduce your foot print and get close to zero waste. i dont think i have ever seen any one against getting as much out of your wood resource as you can.

I came back to permies to look up thermoelectric due to my interest being piqued with instoves association with firevolt systems to put out a thermoelectric generator. I am looking for a way to balance out the cloudy days to go the rest of the way off grid. We don't have enough wind here for a wind generator, no natural streams, so I am looking for a complement for solar. Have any of you looked at their technology? As I am sure you are more knowledgable than I on thermoelectric power generation, I would be interested in your thoughts. http://www.instove.org/node/130

Using peltiers is very good option as part in off-grid system if designed properly.

Since they last long (life age) and are easy to operate without difficult electric devices between and circuits.

Also they are cheap - 60W peltier is about 2 euros from ebay. Note that it is its maximum power consumption and you will not ever get 60 watts out of one peltier.

As told also here, the main problem isnt to heat them up but to cool down the other side.

Also, you should notice that too much temperature will kill the peltiers or at least, shorten their life age and efficiency greatly.

As they are semiconductors just like LEDs, I would not try to use them at maximum power: just like LEDs, it is best to use them with little power and have more LEDs to produce the same light, or in this case: have more peltiers to produce the same electricity.

There is special peltiers designed for high temperatures up to 200 celsius (392 F).

Normally you shouldnt use them above 80 celsius (176 F) - just like LEDs. That causes them to break down faster and they will produce less and less electricity over time - just as LEDs break down like this, that they dim down.

Also the max temperature difference in the cold side and hot side is about 70 celsius (158 F).

It means basically, that we cannot cool down the other side too much.

So these are the basic limits of the peltiers: we cannot heat them up too much, or even cool them down too much.

So instead we think how to make the hot side very hot and cold side very cold, we should think how we can make them work without that they break down eventually and "dim down" like LEDs - producing less and less electricity.

So like solar panels, we need a big panel of peltiers so it will work properly.

Best way might be, that water would be used to reserve the heat and the container would be coated with peltiers, which produce electricity even after the fire goes out. This will also prevent the peltiers to heat up too much, or that the maximum temperature difference wont be gone over.

So if the water would be 80 degrees celsius, then the cold side can be only 10 celsius, and not anymore below 10 celsius.

I am thinking, that instead of fan (which consumes energy) you would use the energy from the convection from the hot air of burning wood, to move also cold air into other place where it cools down the peltiers.

One option I think, would be install the peltiers inside ground so that the earth would cool down them.

Basic info about peltiers as generators:

https://en.wikipedia.org/wiki/Thermoelectric_generator

The video in the first post does not work anymore, here is another one: