Energy - Rocket Stove Mass Heater

Hello,

has anyone used peltier-elements together with a mass heater to produce electric energy while heating?

I want to build a mass heater that produces electric energy during the heat period to support my (comming) offgrid electric energy system during the month with the least solar returns.

And I think during winter the temperature difference between the smoke extrakt near the heater and the uninsulated wall should be great to have peltier elements produce electric energy at a good rate.

I have found a source for buying peltiers elements at reasonable prices, but those have a maximum temprature of 125 Celsus or 257 Fahrenheit.

So I wonder where to place them and what construction, to allow heat to the one side and cold (from outside) to the other side of the element.

If you have any ideas for construction this as cheap as possible, please let me know.

And the peltier elements can even be used to use the thermal mass of the heater as a cooler using surplus solar energy in hot summer days.

Greetings from Germany and happy thanksgiving!

Martin

Martin Doering : Recently I saw an RMH build that had the system you describe - Probably on You tube or reposted here from U-Tube, and his trickle charger could keep a
battery charged continuously to allow him to run low watt lights until the battery was drained, but as a back up it was kinda interesting !

More interesting was the Rain Wall he ran his used cooling water to with just a fish tank pump, as the water trickled down the rain wall it gave up its heat so that It could be
run back thru the system again and again continuously.

On further reflection I Think the gentleman said the trickle charger could keep the pump running AND the battery charged !

Does this strike a cord with anyone else ? Big AL !

Hello Allen, thanks for your reply. I hope, I can find the vid on youtube.

I am not a native speaker so I don't really get, what you mean by Rain Wall. And how this could be implemented.

What I want to use are peltier-elements, that are used to in 12V cool backs as source for cooling. But they also can produce energy, if they get a temperature difference.

Those peltiers used in cool backs are made to produce some cooling but don't use up too much energy. But there are peltiers elements that have like 60 or 80 watts if you manage to get the enough temprature difference between both sides.

As rocket stove mass heaters are quite large and those are very small, this could be a decent energy source. As I haven't yet build a mass heater, I lack the knowledge neccessary to find a good implementation.

My idea would be to mount them on a metal plate with good heat transportation on the hot side and link this also in metal to the smoke extract. And have some construction to get as much of the outside cold to the cold side of the peltiers. Maybe also a metal plate, that is linked to outside wall.

But I guess, I first have to build the mass heater then work out the temperatures and figure out how much energy a single hightecn peltier-element can produce, before buying a bunch of them.

Martin Doering : While English is my First language sometimes I do not do well in it ether! For rain wall substitute a portable Water Fall, as your used cooling water gets pumped back
to the waterfall it is directed to run down the wall surface in a continuous sheet, with as large a surface area as possible, there is an immediate cooling effect that occurs to that
portion of the water that is not evaporated, as the Rocket stove is Designed to add in providing the multiple air exchanges needed in a healthy home much of that water vapor gets
exhausted with the rest of the Rockets Exhaust.

Properly Constructed Cob benches absorb lots of water vapor in high humidity, and release water vapor into the air as the rooms relative humidity falls !

If any of this is unclear come back here and tells and someone will help you get a good mental picture ! Just a thought but you might want to post this in Alternate Energy Forum
as that way many more additional people will look at it ! For the Craft Big AL !

Martin Doering : Found IT ! As usually happens, I was looking for something else, it actually took longer to find you again ! It is with some trepidation and Guilt that I am sending
you to U-tube Land, please be aware that you are traveling in an area filled with mines and booby traps, people have posted videos of things that can not be operated safely and
can kill you ! Or in your absence members of your family ! This set of 2 videos appears benign, I have NOT looked at all the ones posted here.

At permies.com everthing is peer reviewed, if someone thinks a proposed practice or use of a project is unsafe it will be closely examined ! On U-tube there is no way anyone
can get a bad movie deleted and six months later, there will be 100 copies of Franken-clone Units of Flaming Death !

The Romans had a saying "Caveat Emptor''- let the buyer beware! - O.K. time to get off of my soap box ! Goto >youtube.com/watch?v=eQ6S5WH2n9w
as far as I personally know, this is close to the state of the Art ! For the Good of the craft ! Big AL

P.S. Thanks Alan M. for finding this in the first place !

Allen: Thanks a lot for seeking out the vid.

Now I understand, what you mean by the water fall. It is exactly what I was seeking for. He is using peltiers for the power and water cooling system integrating a waterfall.

I probably will not build it that way on the top of the barrel, but see if I can use the higher temperatures at the exhaust. But I probably could use a watercooling as well using the cold at the outside maybe together with a car part engine cooler.

30 Watt for such a small installation is not bad, especially in winter. And even at the top of this barrel is a lot of unused space.

And I am aware of safety precausions. It might be quite unsafe, if you use your peltier-elements at temperatures outside their specifications. And using electric energy includes the risk of fire, if done wrong.

Anyway you gave me some ideas how to work it out. I guess, I will build the bone of the mass heater and then take the actual heat at certain areas of the construction while burning and think of the best area to place the peltiers. And then build a watercooling connected to the outside.

I will report back, if I get it going.

Cheers Martin

Martin Doering : mostly for your fellow members who will be following in the future I want to point out that I Think this Peltier's power comes from stacking a series of plates
on top of the drum, that there needs to be ~100 * F ~ between the hot side and the cold side, these devices are very inefficient, and in a self limiting way can decrease the Barrels
ability to radiate off the necessary heat to create the 'heat pump' that makes the Rocket Mass Heater RMH work ! Of course, this can happen due to applying a thick coat of cob to the
sides of the barrel by people who 'want a better look' !

You might also want to keep an eye on the area of aerogels. The science now has evolved to the point you can use pour into place aerogel granules as as stable form of high
temperature insulation, 1,000s of times more rugged than the original product ( from the '30s ) Hope this helps, and is timely ! For the Good of the Craft Good luck !!

Think like Fire, Flow like a Gas! Don't be the Marshmallow! As always, your Comments, and/orQuestions are solicited and Welcome ! PYRO - Logically - Big AL !

Hi Martin,

Could you please tell us that source “for buying peltiers elements at reasonably prices” ?

Some thoughts:
the speaker in that video mentioned in this thread says at a point “it's for free”. He means the electrical energy produced by the thermo-electric-generator (TEG). I guess he did not mean this too literal because it's wrong. True is, a part of the thermal energy is transformed into electric energy, i.e. this part of the heat is not longer available for heating your home – so electricity it's not for free.

Looking closer: A certain amount of the heat produced by burning wood is traveling through the TEG from the hot side to the cold side. A very small part of this energy (something like 1%) is transformed into electricity and 99% is released on the cold side to the cooling agent. You want to use the outside air for cooling. In this case 99% are lost.
This is still ok if you use a small TEG, i.e. the amount of heat “used” by the TEG is very small compared with the amount produced by the RMH. For instance the ventilator placed on top of the barrel in that video will not cool remarkable the barrel. But if you really wand to produce electricity for your whole house you should at least use the heat released by the cold side of the TEG e.g. for preheating the fresh air before let it enter the combustion chamber.

The converted ratio of energy depends on the temperature difference between the hot and cold side of the TEG. The 99/1 mentioned before is just a guess. But the real value will not be to far away from that.
I am (and I'm sure I'm not the only one) curious about your progress. Keep us informed!

regards
Peter

Hello Peter,

the cheapest source I have found, is direct import from China. If you choose the standard ones TEC 1-12706 you get them at a resonable pricing.

I currently found the Seebeck effect values for the TEC 1-12708. It is about 49mV and 15.7mA per Kelvin. At max of 68Kelvin (68 degree Celsius tempreture difference) you get about 3.3 Watt from these.

The more common TEC 1-12706 is working at 6A while the other is 8A. My guessing is, that you can generate at max 2.47 Watt from those.

It is no cheap system considering that you need the heat exchange system as well. But it definitly can generate all the energy you need in winter. And it is a good source of energy for off grid use, because if you keep your thermal mass warm all day it does produce all day.

I definitly will try this.

I will post this, when I am finished. But I can not guarantee, that I build my rocket mass heater this winter. But I hope so.

Martin Doering : I for one will be following up on this, or at least watching this space waiting for your further posts/threads ! I have two quick Suggestions one you post something
in the Alternative Energy Forum/ Threads, that way you will reach more like minded fellow members! Two, for your fellow members who would like to follow your progress can
you post a listing of Peltier/T.E.G. 101 resources so we can 'catch-up ! Thank you, Please come back and Post often ! For the Good of The craft !

It appears that I was misinformed/wrong about the necessary temperature difference between hot and cold side the deference will be much closer to 160*F, but if we were running
a simple gasifying, charcoal producing, system we could have two heat streams (that with gas storage do not have to be simultaneous) Cooking ,gas incandescent light And the
potential for two low watt electrical heat streams.

With the need to provide the necessary Temperature spread a Rocket 'tuned' to produce barrel top temps close to 660*F could in theory produce several collection areas, and any
use of water for cooling could be run through a 'Distillation tube' under safe conditions i.e. vented to the open air, and produce potable, hot water as a by product, this operation
being done at a separate location.

Peter Peterson has suggested recycling much of the 'Wasted Heat Energy' by using it to preheat the incoming 'make-up' air for our Rocket Mass Heater RMH and the beauty of that is
almost of that heat will ether be re-used in our Peltier low watt electrical generation, or passing Horizontally through our Cob be stored as heat to warm our backsides !

The potential benefits then include, prompt and stored heat, low watt electrical D.C. Generated Electricity which can be stored in batteries, the possibility of a secondary heat stream
from wood gas generation for cooking and additional incandescent lighting, and the safe production of hot or at the least Tempered water, and a proven method of recycling most of
our largest by product heat energy !

Give me a cave and I can survive ! Give me a cave and heat and I will be happy!! Give me a cave (or a Yurt) and heat and hot water and my wife will be happy ! -and I can get
electricity as a byproduct?! Yikes, to many Win,Win,Wins to count ! For the Craft ! BigAL !

Late Note, we are all part of the 'pClould' , one long chain, but I wanted to point out how Alan Mikoleit found the video of a Peltier being used on an RMH in You-Tube land and Posted
it hereat Permies and we are all growing there by THanks ! Big AL !

I have researched the TEG technology and came up with this info. There are many sellers of TEG modules and completed units that can be air or water cooled. They operate at different temperatures and temperature differentials. The hotter they get in their working range the more power they put out. Its much cheaper to buy the modules and wire them together on your own heat sinks than to buy completed units if you have the skills for it. The modules are not very efficient but once installed it's a source of free electric. I really like the water fall set up and will go well with my vertical heater. I am about to buy fire clay so I can make the pizza oven style arch top for my horizontal burn box.