TEG Power Anyone?

Longknife Posted By Longknife, Jul 16, 2018 at 10:13 PM

  1. Longknife

    Longknife
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    I did a search and didn't see much on here.

    Just curious if anyone has tried out a thermoelectric generator with their woodstove? I came across the website tonight and thought some of the stuff looked interesting. I don't have solar, so not much need for anything but one of the lower cost systems might be neat for an ice shack or cabin.

    I've had an Ecofan for a few years, but other than that, no experience.

    https://www.tegmart.com/wood-stove-thermoelectric-generators/
     
  2. peakbagger

    peakbagger
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    Its pretty expensive for what you get in output. More of a geewhiz factor than practical to do much work. The higher the temperature difference on the two sides of the TEG, the more power. The actual TEG is as close to reliable as possible as there are no moving parts.
     
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  3. CaptSpiff

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    I'll start by saying I have no knowledge on this subject technically, but the above website sends up red flags for me:

    1. Their "About Us" section does not disclose any physical location, or which State they are incorporated in.

    2. The first line of their "Terms & Conditions" is: "RETURNS-All sales are final. We regrettably cannot accept returns on any electrical items. It is impossible to accurately determine their condition. Defective merchandise may be returned for store credit or exchange." But they list no stores.

    3. Their "Privacy Policy" disclosure section has the boilerplate language from the website developer: "Add your privacy policy here. This is required by most credit card processors."

    In their Shipping section they state that their information is current as of JAN 28, 2014. That's a long time to be in business and not update their Privacy Policy, especially since this website has multiple pages where they seek you to provide them personal details. One section even asks you to create a log-in and password, and that is the golden egg for hackers because people commonly reuse their PWs multiple times.

    Just saying.
     
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  4. Longknife

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    Good catches. I hadn't looked that close. Thanks.

    I will definitely be avoiding this particular retailer.
     
  5. begreen

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  6. peakbagger

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  7. olddawgsrule

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    Nice link! You find a link to a possible webcast of the event? I'm looking, but not seeing one..
     
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  8. olddawgsrule

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    This is a good example of a working TEG.

    https://www.bioliteenergy.com/products/campstove-2?variant=180482965518&utm_medium=cpc&utm_source=google&utm_campaign=Google%20Shopping&gclid=Cj0KCQiA2o_fBRC8ARIsAIOyQ-k9zuRih9_PvSzOwWEqnKKan_0jZIF6ggF_9w90ExjqKVIUE23gs48aAgRIEALw_wcB

    These folks I would buy from. Shame they did not incorporate the technology into their Fire Pit (I own the fire pit).
    This is not something you can use on your wood stove, but does show the tech is good.

    The issue at hand (to me) is like the BioLite CampStove, the heat transfer must come from 'inside' the firebox to create the large temperature difference required. Meaning, the 'stove' needs to be built to do this. I don't see a great running TEG that can be mounted, placed or hung on a wood stove and work efficiently. Takes far to much cooling (coolant) on the other side.

    I love this Technology! I hope to see someone design a small wood stove (or pellet) that works. I've always thought that would be a fun retirement project!
     
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  9. spirilis

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    Might work as a flue pipe inline section though (with TEG hot side exposed directly to flue gases)? Close enough to the stove, it may be hot enough... but doubtful as hot as the BioLite gets inside.

    edit: Likely not, in fact, this is an interesting approach - put a catalytic combustor in the fluepipe to boost the temp first - https://www.adn.com/energy/article/presto-alaska-inventor-turns-wood-stove-heat-electricity/2013/02/19/

    I am trying to find a day to visit that Wood Stove Design Challenge down in DC this weekend (or a day next week), I will report back some info if I'm there.
     
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  10. olddawgsrule

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    Please do! Interested minds here!
     
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  11. Corey

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    I've done a bit of research, but it keeps coming back to the same issues:

    1) For the power generated vs cost, you'd be MUCH better off with just about any other source for power... gas generator, solar, steam engine, stirling, etc. At best, these are sort of a laboratory curiosity and even in virtually perfect application they typically cost way more per watt.

    2) If you are willing to accept #1, or have a very niche use, the next big thing is not getting the TEG hot, it's keeping it cool. If you get a true, graphite 'TEG', it might reach a red line temp at ~300C / 570F, but the cheaper / generally available ones (ebay) have a limit around 150C / 300F. Sure there are places on a stove that hit 300F, but you have to be careful - and consider what the temp is under 'full fire'. Putting them in a spot that is 300F 'most of the time' won't do. Then one day you decide to light a roaring fire due to bitter cold and melt your TEGs.

    You could put them in some sort of movable box...ideally with a hot side temp read out... but now you're tending the fire and tending the TEGs. Not a huge deal, but something to consider.

    3) Next up is consistency. From above, max power likely comes with the hot side close to 300F, and you might run the cold side close to room temp ~70F, but the stove typically won't run a perfect set temp all the time. You reload, the stove warms up, cruises for a while, then cools back down and reload again. Assuming the cold side (room) is relatively constant at ~70F, that only gives you about 230 degrees of 'delta T' to play with and likely the stove will be transitioning through that range almost constantly.

    4) Power. Given the narrow operating temp range above, you also have to consider that your TEG cycles from zero to full power in that same range. Any individual TEG will swing from about 0-5V. Very few things will accept such a wide swing in voltage, so then you need a buck/boost power converter. If you need to run something 12V, now you need 3 TEGs in series and they are swinging from 0-15V so that only magnifies the problem.

    Even considering these issues...and more I haven't even listed, I've still considered setting something up 'just for the heck of it'!
     
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  12. begreen

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    Yep. I am not impressed with TEG output in this application. To get some reasonably useful power of 1-200 watts the cost is high and cooling is complicated.
     
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  13. olddawgsrule

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    This is my little 'proof of concept' TEG.

    Configured as shown, it would be placed over an open flame. Example, a candle.
    For the wood stove configuration the bottom exchanger would be removed to the module would be in direct contact with the stove.

    This concept follows this design http://www.thermonamic.com/BfGenerator-English.pdf and adapted slightly.

    Can I produce 5v's from this... No.. Not as shown. I did, but I removed the top fan and used ice to cool.

    I love playing with Technology. Mainly I love proving I can build/make something new!

    I mentioned the Bio-Light CampStove in the previous comment. I really like what they did with this technology. Small amounts of fuel, generating enough power to run their battery, charge their battery and charge another device (or run lighting). Oh ya... cook your meal on it.

    ToyEv74.jpg
     
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  14. Corey

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    A good start to be sure. You say "removed the top fan and cooled with ice", so I take it the cold side is on the top as shown.

    I would consider reversing that configuration - at least heat sink wise. Reason being - hot is generally no trouble. If you figure a max redline at 300F - a wood stove can do that, large candle could likely do it, kerosene lamp, gas camp stove, etc. You could get the hot side up to full operating temp with a very small heat sink, or likely no heat sink at all... just touch the hot side of the appliance.

    You want the cold side to be as cold as possible but you only have ambient air and a fan. So you want all the heat sink area you can get, all the fan power you can spare, etc. That is one slight benefit to these on a wood stove- you want the heat in the house anyway, so if it travels through the TEG and makes a few measly watts of power, all the better.

    I've wanted to take a shot at a ~100 watt system to run some 12V fans on my insert and a bluetooth temperature sensor/transmitter. But the latest hurdle is that I thought a buck/boost converter might help smooth the wide power swings coming out of the TEGs as they warm/cool. But it turns out if the converter input power goes slightly over/under the output demand, it goes into shutdown and needs a 'hard reset'. So while it can take a 6-30V input and make a 1-35V output, it needs to be a 'constant' input/output. Otherwise, you have to unplug it, bring the loads back in range and restart.

    I had also toyed with the idea of making a 'smoke bell' for my Aladdin lamps with a TEG. These fit on top of the glass chimney and are exposed to the heat of the kerosene mantle. With 4-5W of output power, it would likely drive LEDs to put out more light than the actual lamp does. An interesting demonstration of how far technology has come!
     
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  15. olddawgsrule

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    Will love to hear your progress Corey!

    As mentioned earlier, the main issue is not heat, but cooling. The units I read about that work very well (the Bio-Light being the exception) use liquid cooling. One gent used a ice bath, but you now how that went.. worked great till the bath warmed up.
    The others are so large (some larger than the wood stove) that I find it impractical.

    Now, I would love to hear the Delta T Wood Stove Generator made it to the competition this weekend! That's a interesting direction of working a TEG.
     
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  16. begreen

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    There is also the “Condens-E” by Maine Energy Systems pellet boiler there that is charging a Tesla. It generates up to 5KW! With a PowerWall battery this could be an interesting option or alternative to grid life. It uses a stirling powered generator.
    http://www.maineenergysystems.com/chp/
     
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  17. spirilis

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    Got pics & some literature! Went there with my 6 y/o son this afternoon. That 5kW condensing boiler was a beast. It's 60kW thermal output btw (200K BTU; not at all for a home, more like small commercial applications).

    Helium-filled stirling engine. I wasn't quite sure what the guy was saying about the water routing but all I remember is the stirling engine cold side receives the coldest of the intake water from the storage tank, and obviously hot water storage is necessary here. They had a bank of 4 heat exchanger+blower assemblies outside the tent venting the heat to keep the system running.

    Teaser from the hot-side of the stirling:
    20181111_150744.jpg
     
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  18. begreen

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    It's great that you made it there. Did you take more pics? Can you post a summary in the main hearth forum?

    200K btus is about what some McMansions require. I'm wondering what the boiler costs and the rate of fuel consumption. It sounds like if has a lot of moving parts. Was it noisy?
     
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  19. spirilis

    spirilis
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    Yeah I'm going to do a big write-up once I collect the images & thoughts... hopefully before bed tonight while it's fresh in my mind :)

    It did have a hum to it, though there was a bit of noise in the tent so hard to say but it definitely had some noise.

    Maine Energy Systems also had their homeowner-grade boiler and forced-air furnaces on display, just not running. Attractive appliances - and I asked the guy about using one of their boilers as primary heat & DHW, he said it's approved with insurance co's as primary heat for your house (alluding to some political help getting that in place from Sen. Susan Collins). I tried to ask about price but he didn't go there... as for the Pellematic e-max, there are 2 units running out in the field right now and those are in laboratories, so it's mostly a prototype and/or curiosity of theirs for now.

    Another person asked about the claim of them being "condensing" pellet boilers; the short answer is, if your demand can get the water intake temp on the boilers down to ~110F, it's condensing, otherwise it's not.
     
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  20. spirilis

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    Here's my boy posing in front of the MESys lineup-
    20181111_153725.jpg
     
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  21. peakbagger

    peakbagger
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    MES is a about a 20 minute drive from my place. The owners are very good at promotion, one of them Les Otten ran for the governor of Maine several years ago and they have been very successful in the past leveraging state and federal dollars to get their product installed.

    Les Otten the lead owner is a fairly controversial person in the area. He is a "developer" that is very good at leveraging other peoples money. He was a minority player in the Red Sox's sale several years ago yet his involvement seems to increase every time he talks about it. He is also a ski resort developer and a lot of folks lost a lot of money when the company he founded went belly up https://www.newenglandskihistory.com/skiareamanagement/americanskiingcompany.php. He has been developing a defunct ski resort in Northern NH for several years with promises that ground would be broken "very soon" and has done so for four years. It turns out that a major source of the early stage funding was a utility that paid him under the table for him to support a nearby power project. I would not bet on his firm coming out with a successful commercial product anytime soon. For a couple of years the city next to me had a combination of incentives which cut the out of pocket cost of a pellet boiler installation down to less than 5K including bulk storage. In addition to the homeowner incentives on the boilers, they also got a 50% match up to $4000 in subsidies for energy improvements. Along with the incentives there was money to hire people to beat the bushes to get folks sign up. MES ended up supplying the majority of the equipment and also happens to be the only bulk delivery supplier of pellets in the area. They dont talk a lot about their early product they imported that turned out to be rather maintenance intensive to the point where many were pulled out by early adopters.

    They have been occasionally talking on about the potential for co-generation off their boilers. If you search for the supplier of the Sterling engines its pretty obvious that its an early stage company. It has a lot of similarities of the Sunpower design from 20 years ago. https://sunpowerinc.com/1kw-stirling-engine/ Sunpower even sold a few research prototypes at one point but their focus has been to sell the IP to some other firm and then get paid to do the research to make it commercial. Dean Kamen of Segway fame also has been claiming to have a Sterling Cycle design ready for production for years and claims that his home is supplied power from one of his units. He also wants to license his IP to some other firm to produce the actual engines. He even toured the media circuit and I think he plugged it on 60 Minutes as the next best thing. It occasionally still pops up but to date I havent seen any firm plans for production. There was also a firm based in New Zealand that had a similar free piston design that got a trial in England for home heating. which I believe ended up with the units withdrawn from the market I think Honda even dabbled in them. STM back in 2001 had a so called commercial design that they were selling https://www.power-eng.com/articles/print/volume-105/issue-10/features/stirling-engine-stirling-technology-engines-shooting-for-dg-market-penetration.html. The company I worked for installed several STMs in a biodiesel facility, and our techs spent a lot of time replacing the piston seals which usually is the downfall for Sterlings. The company was always promising they had the seal issue licked (as have many others) and did so until the day they went bankrupt. There was lot of hype on PBS several years ago on tracking solar dish generators that had been developed by Sandia National labs, they licensed the technology to a company called Razor who got a lot of federal and state money to build large solar fields. The problem they had is the Sterling cycle generators that was the heart of the equipment never proved to be reliable. Back in college I remember Chicago Bridge and Iron touring with their free piston Sterling cryocooler The point of this is Sterling cycle units have been too good to be true for many years and always just down the road waiting for funding and subsidies.

    Maybe MES will crack the code of a viable unit but the history seems to bet against them.
     
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  22. spirilis

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    Ah ok, so MESys is just reselling an imported product... thanks for this insight.

    http://www.okofen-e.com/en/pellematic_e_max/

    That explains the "Okofen" reference I kept seeing on their units.
     
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