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Post by grahamk on Feb 8, 2012 8:11:23 GMT -8
I'm developing a technique for producing a little electricity from stove waste heat as cheaply as possible.
Is there anyone else working in this field?
GrahamK
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Post by Donkey on Feb 9, 2012 15:28:21 GMT -8
Yep. Look up the T.E.G. Thermo-Electric Generator. Also, there's the Stirling Cycle Engine, which has been around for a LONG time and some folks have used them for converting waste heat to kinetic energy and/or electricity.
Seems to me that if the intent is to make electricity, the TEG or some kind of thermo-couple would be the way to go, fewer conversions.. On the other hand, if the intent is to use the electricity to turn some gizmo or provide some kind of kinetic motion, the Stirling Cycle would be my choice for the same reasons..
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Post by Deleted on Feb 10, 2012 2:30:30 GMT -8
The efficiency of a TEG is typicaly just around 5-10% and very small amounts of watts are produced. TEGs for driving a blower or producing a bit light are relatively cheap. A small Stirling has an efficiency of around 15% to 30% and much larger amounts of watts can be produced. A Beta Stirling would be the cheapest to build stirling. Even a Beta Stirling is expensive to build, at least as high temperature version. en.wikipedia.org/wiki/Thermoelectric_generatoren.wikipedia.org/wiki/Stirling_engineIn Germany the power companies are forced by law to buy electricity from everyone at a good price, thus generating electricity from waste heat is of great financial interest for homeowner. One can buy here stoves with an build in Stirling to raise overall efficiency to near 90%. The other way round is also common, using an Otto engine to produce electricity and heating the house with the waste heat. This third possibility is the most promising for producing a significant mount of electricity with a wood stove. Parts of the gas produced by a gasifying stove could be used to drive an Otto engine. There are Otto engines of any imageable size. An Otto engine is much cheaper to produce as a TEG or Stirling of a comparable power. It would not need any control for varying rotation as it could always run in the most efficient range. One from the Waste could be used to. Even a steam engine could be used, maybe the cheapest way. www.john-tom.com/html/SteamPlans.htmlnpmccabe.tripod.com/steam.htmwww.animatedengines.com/oscillatingsteam.html
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Post by woodburner on Feb 10, 2012 9:54:49 GMT -8
Steam is appealing as the engines are usually quiet and they are interesting to play with. The big problem is that they mostly use pressurised boilers, and these are dangerous and often kill people. One of the reasons for the invention of the Stirling engine.
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Post by Deleted on Feb 10, 2012 11:35:32 GMT -8
Can be build even from a pringles box and a low energy generator can be cheaply build with solenoids. On that can run 7/24 at higher temperatures and do some real work is more challenging. There are reason, why most of them are just models. Some infos, links and plans. www.bekkoame.ne.jp/~khirata/indexe.htmA beta Stirling with a solenoid generator for a little energy would be relatively simple to build.
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Post by carlos on Jul 5, 2013 4:17:29 GMT -8
Not everyone wants noise in his home, so rotating devices are not so welcome.
TEGs make no sound. But the main problem i found using them for some years is overheating. For them to put out more watts, cold side must be as cold as possible and hot side as hot as possible, but not more than 260C. That is very hard to achieve. Yes, you can use pumps, but they make noise and need electricity - usually more than tegs provide.
Relistically one can get night light - enough to see the way to wc at night. And its very nice when some light appears when stove heats up in early morning or dark afternoon. When set up, TEG system does not need any maintenance. Only watch the termometer! Wood heat can make drastic leaps.
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Post by mangyhyena on Jun 19, 2015 10:30:54 GMT -8
Not everyone wants noise in his home, so rotating devices are not so welcome. TEGs make no sound. But the main problem i found using them for some years is overheating. For them to put out more watts, cold side must be as cold as possible and hot side as hot as possible, but not more than 260C. That is very hard to achieve. Yes, you can use pumps, but they make noise and need electricity - usually more than tegs provide. Relistically one can get night light - enough to see the way to wc at night. And its very nice when some light appears when stove heats up in early morning or dark afternoon. When set up, TEG system does not need any maintenance. Only watch the termometer! Wood heat can make drastic leaps. Okay, I joined this forum when I came across this thread during a Google search. I am actively attempting to power TEGs using both a rocket stove and a parabolic reflector, either one, depending of weather conditions. I realize this is an old thread, but I am hoping my idea might assist others here to make this work to produce usable power beyond powering a light or charging a cellphone. Ideally, the goal is to charge deepcycle batteries in a home battery bank. As pointed out in the quote, the idea is to bring an exact amount of heat to the hot side of the TEG, which must not be hotter than the TEG's maximum working temperature, while bringing cold to the cold side of the TEG to create a temperature differential. The bigger the difference between the hot and cold side, the more electricity the TEG can produce. The challenge with a rocket stove or concentrated sunlight is that both generate temperatures well above the maximum working temperature of the TEG, which will destroy the module with that excessive heat. My solution is to sandwich the TEG between 2 square, metal reservoirs, each of which is capable of holding liquid. Put hot mineral oil in the hot side reservoir and cool water in the cold side reservoir. The difference in temperature between the 2 liquids should power the TEG. By using mineral oil as a heat carrier, just the correct portion of the high heat from a rocket stove or concentrated solar can be brought to the TEG. If the TEG's maximum working temperature is 350F, you would put a thermometer in the oil as it heats on the rocket stove, remove the oil once it reaches 350F, then pour the oil into the hot side reservoir of the TEG unit. This will work for lower temperature Peltier modules, as well. Simply use hot water instead of oil, monitor the temperature as it heats, then pour it into the hot side when the desired temperature is reached. This concept is as simple as heating the liquid, monitoring the temperature, then pouring into a reservoir. Larger reservoirs can accommodate more TEG modules for greater electric output, making this a scalable unit to serve specific electric needs. The downside to this setup is the need to add hot liquid to the hot side as the temperature cools and to add cold water as the cold side heats up. This is very hands-on, unlike solar panels. Also, TEG's are not cheap, so this system requires a substantial investment. The upsides are: The TEG can operate from any heat source equal to or higher than the TEG's rated maximum working temperature. There are many fuel sources capable of heating the oil, even cardboard and paper waste in a rocket stove. Anyone with the skills to cook and read a thermometer can operate this generator. It is an on-demand system that is not reliant on weather conditions. TEGs have extremely long working lives if they are not abused and this system, if operated correctly, will not abuse them. I think this system would make an excellent addition to solar panels, allowing both active and passive electric generation from inexpensive energy sources. Thoughts?
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