Thermo-electric generators?

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bkt

bkt

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Does anyone have any experience with these? Where I am in the winter, skies are usually gray and we get a lot of snow making solar a non-starter. But we burn firewood routinely in either a stove or fireplace insert. Hence the interest in these.

Here's one place selling them: Home-Thermoelectric-generator TEG modules 100W wood stove generator

I have no idea about quality or actual results...just curious what you think.
 
apparently it all comes down to the peltia unit, the little hat powered stove top fans seem to last for ever. the function is based on temperature differential so somehow providing cool air to the fins would help
 
Thermoelectric Generators (TEGs) have a have a long history in space applications and the Russians have used them for some applications in the field. The US has explored using them on vehicles but the need for a large heat sink and a good source of high quality (300C+) heat has always been an issue. I remember when the term "waste heat recovery" was first used and it is correct. Only a part of the heat from your exhaust stack will be used ~25% but it is going up the chimney anyway. Most fireplaces operate most efficiently between 350F and 600F, (175-315C) so they will provide a medium quality heat to the TEG. Having cold water going into the TEG will enhance the output of the TEG and the water/coolant output would most likely be someplace between 120F and 190F depending on the flow rate and the temperature of the flue gas.

When I was heating with my wood fireplace it usually hovered around 425F +/- 175F a TEG would work well in this range.

I have been using solar this year and considering you only get about 6 hours of high quality time (yearly average) per day, I could see where a 100 watt TEG operated 24 hours a day could give you an output similar to a 300 or 400 watt solar arrangement. If you have a battery storage system you could use it to great effect, plus you would be extracting more heat out of your fireplace giving you warm/hot water. I have seen Soviet systems that used an external (out of the cabin) heat exchanger to improve the efficiency, so if you had cold feed water you could get a similar result.

I did notice that they suggested using a 100 gallon water supply and had a discussion of using it to supply base board heating, all very interesting. I would be concerned about having the water in the cooling system freeze if the stove was not in use or the cabin was left vacant for a while, designing you water system to allow for your cooling water to drain when not in use would be a good idea if you were in a harsh environment, otherwise I could envision broken pipes and fittings.

I also noticed that it needs 24" of straight run flu pipe, some places may not have space for this part of the installation. I always wanted to install something like this but I would need a flat plate heat exchanger and I have not seen one other than something that was home made.... And unfortunately the cost has always been a big sticking point here.

I could see where this would be a nice addition to a place that already had some solar and used wood stove heat.

All this assumes that you have the funds available to make the investment without any major hardship.
 
It appears to be a pelter junction. Put cold on one side and heat on the other and get power out of it. Run electricity into it and get heat on one side and cold on the other. Cruising sailboats like to use them for refrigeration. They are also used, as previously mentioned, for wood stove fans.

It is an expensive technology so it is underused.
 
The technology is inefficient. A steam engine would be more efficient and close to the same cost to run.
 
Caribou said:
It appears to be a pelter junction. Put cold on one side and heat on the other and get power out of it. Run electricity into it and get heat on one side and cold on the other. Cruising sailboats like to use them for refrigeration. They are also used, as previously mentioned, for wood stove fans.

It is an expensive technology so it is underused.
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I wrote an application for the a secure national lab to characterize TPV (Thermo Photo Voltaic) diodes. They are diodes that produce a voltage potential when exposed to light or heat while also acting as a diode. They what results if a solar panel had sex with Peltier junction....

We used a pelier junction to keep the device at a constant temp while varying the light intensity. The characteristic curves were mind blowing. Current would dlow backwards when forward biased... :confused2:


https://aip.scitation.org/doi/abs/10.1063/1.1867275
(Ben Wernsman was a good guy but has since passed).

Back on topic!

The peltier junctions required a lot of power but they work. I have seen beer coolers for a car that run of the cigarette lighter.

But they also run backwards if you a heat source and a cold sink.

Ben
 
SheepDog said:
The technology is inefficient. A steam engine would be more efficient and close to the same cost to run.
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Well, there's my face-palm moment for the week. A steam engine generator might be the answer I'm looking for. There seems to be a good amount of information out there about making them.
 
bkt said:
Well, there's my face-palm moment for the week. A steam engine generator might be the answer I'm looking for. There seems to be a good amount of information out there about making them.
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Please share what yo find.


Ben
 
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perhaps we need to rethink the boiler a bit, perhaps a better way to join the tubes to the end plates or figure out how to run lower head pressures and just use automotive propane tanks and some kind of a blast shield
 
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The one thing about Thermoelectric Generators is that they are solid-state, you only have to clean off the heat exchanger fins from time to time. Maintenance on steam has always been an issue, you have to deal with the soot in your flu pipes, you have to deal with scale on the inside of your boiler, and you need to keep the steam engine cleaned, oiled, and lubed.

Many of the TEGs that NASA uses have continued in service for decades without maintenance using a degrading nuclear power source. Voyager probes were still putting out 84% of their original power after 23 years and that was due to degradation of the heating source.

The fireplace TEG would need maintenance at the flu gas interchange and at the cooling loop, but it would be a fairly simple system with no high pressure issues.
 
GaryLa said:
The engine is easy to build. The boiler is the real issue.
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Absolutely on the mark, the boiler is a huge factor, safety being at the top of the list and then there's, how are you going to fuel it? This question sort of pushes the answer back to using the most efficient fuel to run a generator and to me that would likely be diesel or, if you are so blessed, water power which would mean having a year around stable continuous water supply that provides enough flow pressure and volume.
 
GaryLa said:
The engine is easy to build. The boiler is the real issue.
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Yes because I dont have one or the ability to make one from bear skins and stone knives. ;)

Take look at this video that came up on my radar (who says you can't exploit the Youtube algorithm?).




I have four of those motors. Two on the shelf and 2 in a 9-track tape drive (I have yet to dismantle).

What say ye?

Ben
 
Tirediron said:
perhaps we need to rethink the boiler a bit, perhaps a better way to join the tubes to the end plates or figure out how to run lower head pressures and just use automotive propane tanks and some kind of a blast shield
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How much pressure is a water heater rated at?

Ben
 
UrbanHunter said:
The one thing about Thermoelectric Generators is that they are solid-state, you only have to clean off the heat exchanger fins from time to time. Maintenance on steam has always been an issue, you have to deal with the soot in your flu pipes, you have to deal with scale on the inside of your boiler, and you need to keep the steam engine cleaned, oiled, and lubed.

Many of the TEGs that NASA uses have continued in service for decades without maintenance using a degrading nuclear power source. Voyager probes were still putting out 84% of their original power after 23 years and that was due to degradation of the heating source.

The fireplace TEG would need maintenance at the flu gas interchange and at the cooling loop, but it would be a fairly simple system with no high pressure issues.
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True but...

Can we create TEGs in our shop?

Can we create a boiler?

Ben
 
viking said:
Absolutely on the mark, the boiler is a huge factor, safety being at the top of the list and then there's, how are you going to fuel it? This question sort of pushes the answer back to using the most efficient fuel to run a generator and to me that would likely be diesel or, if you are so blessed, water power which would mean having a year around stable continuous water supply that provides enough flow pressure and volume.
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Seven years ago I found this...

DSCN1318.jpg


A coal seam that should get me pretty far..

Ben
 
Tirediron said:
perhaps we need to rethink the boiler a bit, perhaps a better way to join the tubes to the end plates or figure out how to run lower head pressures and just use automotive propane tanks and some kind of a blast shield
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At about 7 minutes.




Ben
 
viking said:
Absolutely on the mark, the boiler is a huge factor, safety being at the top of the list and then there's, how are you going to fuel it? This question sort of pushes the answer back to using the most efficient fuel to run a generator and to me that would likely be diesel or, if you are so blessed, water power which would mean having a year around stable continuous water supply that provides enough flow pressure and volume.
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IMO, diesel/gas/propane generators make entirely too much noise. They also require availability of the fuels.

My interest is with having power generation under the worst of conditions.

I have been drawing up a stacked-plate boiler borrowing concepts from Stanley Steamers and Bryan Boilers. They both use the "just-in-time" steam method which means there is no large boiler with steam "storage". This requires a better management of the firebox, but should eliminate a devastating explosion.
 
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I spent better than a year playing with making steam electric power. Repurposed a bunch of stuff and made a working system. I learned enough to build a working system and that I don't have time to babysit a steam engine while it runs. YMMV

An up side is the fact if we have to fall back to that we can................
 
I agree that a steam system needs to be actively monitored, but I don't think it needs to run 24 hours a day.
 
GaryLa said:
I agree that a steam system needs to be actively monitored, but I don't think it needs to run 24 hours a day.
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No it wouldn't have to if you have a power storage of some sort. IE: batteries. But it does have to be closely monitored constantly while it's running. You can most likely figure on 4 to 8 hours a day devoted to power production with a small system.

I've been toying with the idea of a hybrid solar and hydro with pumped water storage. Currently we use solar and a honda generator
 
I think that if we are trying to build an independent power source, perhaps we need to rethink the whole concept a bit, pahase changes are a huge energy drain, if one were to build small unit specific engines to replace the motors in refrigeration and freezers , and go with a direct drive well pumping system instead of trying to store electricity in batteries for extended periods. and does your freezer need to be in your house?? The way things are shaping up it would probably be prudent to figure some of this stuff out while we still have access to the internet and the brain trust that this forum provides,
 
Tirediron said:
I think that if we are trying to build an independent power source, perhaps we need to rethink the whole concept a bit, pahase changes are a huge energy drain, if one were to build small unit specific engines to replace the motors in refrigeration and freezers , and go with a direct drive well pumping system instead of trying to store electricity in batteries for extended periods. and does your freezer need to be in your house?? The way things are shaping up it would probably be prudent to figure some of this stuff out while we still have access to the internet and the brain trust that this forum provides,
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What would be wrong with a big Sterling engine instead of steam?
No boiler to worry about exploding.:)
Apply heat to the cylinder, and rotational power comes out. :thumbs:


It could fill in for solar panels at night.
 
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Stirling is probably one of the better ways to convert heat into power, and the no explosion thing is rather handy to, and could be almost silent in operation,
 
SLADE said:
A little over 1100 watts.
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Correct.

Sterling engine run off the temp gradient across them and the challenge is often keeping the cold sink cold. So to run at 1100 watts the sink would have to radiates 1100 watt and stay cool doing so.

A large copper bar embed in a running stream may work but keep mind it would it has to stay cool at the engine end.

Mechanical engineers (not me!) spend a lot of time studying what is called "heat on a bar" see this video.



But without diving into boring math anyone 5hat has soldered or welded knows the closed you are to the end where he heat is applied the hotter the metal is. If one has ever tried to solder a big chunk of copper with a small soldering iron the metal never gets hot enough because the heat dissipates and gets radiated away.

That is what we are after for a 1.5 hp sterling engine. A bar big enough to conduct 1100 watts away from the engine and still stay cool.

Since this is a mech-E question and I once swore an oath to never practice outside my area of expertise, I will leave it to others to figure how big a cross section of what type of material with one end at what temp to keep the engine.

Ben
 
Neb said:
Correct.

Sterling engine run off the temp gradient across them and the challenge is often keeping the cold sink cold. So to run at 1100 watts the sink would have to radiates 1100 watt and stay cool doing so.
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Likely far more than that.
Remember, the 1100 watts is the net output power of a wildly inefficient engine.
There is likely ten times that amount moving thru it as thermal energy, which explains why they are not everywhere.
They would probably be fine if you had an unlimited power source like a geothermal steam vent, or an active volcano. :rolleyes:
 
Supervisor42 said:
Likely far more than that.
Remember, the 1100 watts is the net output power of a wildly inefficient engine.
There is likely ten times that amount moving thru it as thermal energy, which explains why they are not everywhere.
They would probably be fine if you had an unlimited power source like a geothermal steam vent, or an active volcano. :rolleyes:
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I had a buddy with a big transformer in his lab that was always radiating heat. He had a sterling engine sitting on it taking advantage of the controlled environment.

Ben
 
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