Thermoelectric generators

I noticed a topic recently talking about off grid power ideas and I was thinking of one myself recently and would like some feedback.

Disclaimer: I am not trying for over-unity or any "magical" type idea here, just efficient use of resources (I think!)

I was recently looking at the idea of thermo-electric power generation and more specifically from the website:

http://www.tegpower.com/

The home power station model put forward the idea of a small building that houses a burner which can then convert the heat to electricity through the teg product as well as provide heating and hot water.

I considered the power and heating as obvious methods, but the water heating I thought may be improved. If it is using something like a standard wetback, it would seem that I could harness even further power. So here is the idea:

I would use water heating through a standard wetback or similar method. The difference I was considering was hooking up a steam turbine on top of the furnace. The condensation from the steam may be used in the water heating system, but that is not essential.

So, putting aside all the dangers of steam turbines and needing valves etc., what are the disadvantages here and would it provide any benefit in extra usable power?

Thermoelectric generators are extremely low-maintenance, but nor particularly efficient.

When the exhaust of a heat engine (steam turbine, diesel, etc.) is much warmer than the desired water temperature, a thermoelectric system can harvest some of the (otherwise wasted) heat as usable electricity.

In my humble opinion, a thermoelectric generator only makes sense as the main source of electricity in circumstances where maintenance would be particularly difficult, such as on space probes.

Thanks for you feedback, but can I ask what levels of efficiency you would be expecting from such a system? The reason I ask is that even PV panels are not classed as efficient in that they are lucky to get 25% conversion rate. So I would be interested in some idea of how you class efficiency here?

Not that I disagree, just that I want to understand your logic better. I am going off sales info at the moment, so am not 100% trusting in what they say, but this is the comparison they use:

"NOTE: One 165 watt Sharp PV panel produces 0.6 kWh of electricity per day in sunny Southern California. One 25 watt TEG also produces 0.6 kWh of electricity per day (with a continuous heat source) day or night."

My conclusions from this is that the electricity output will be the same, but you are not dependent on the sun (although you do need a good source of wood), and that the TEG panel is a fraction of the size of solar panels.

Just to clarify the reason for my thoughts overall - I am looking at complementing my solar system to keep power up all the time (living off grid). Most of the obvious choices like wind power are still dependent on weather, so I am looking at options for energy sources independent of weather conditions

That quoted power output assumes a continual heat source of 450 F and a cool water source od 68 F. I don't get high a temp as a constant (we would over cook ourselves greatly). 68 degree water would also be a problem much of the year. Color me skeptical.

What do you figure your heat source would be? Water?

The heat source is the wood burner and this is all set up in a small outside shed/building of some sort so will not necessary cook anyone to death (although could supply warmth in Winter time). I live next to a permanent river that is quite cool all year and also have high rainfall, so sourcing water is not really an issue.

When I was looking at the web site late last night, I had an odd thought.  The last device they were showing as a product was the long strip version, where they had the water hooked to a radiator and a small pump to circulate the water.  I wonder how difficult it would be to cobble together a stirling engine to do the actual water circulation?

There are videos on Youtube from these guys as well as a plethora of videos from others, all trying to show how great their stuff works. Some have meters hooked up to show power generated.

The one thing that is missing from the handful I viewed is what I would consider genuine proof. I'd like to see one of these self-promoters shoe me their house or workshop, anything, that is actually being reliably powered in day to day operation. The first person that does that in a credible presentation might actually convince a few of the skeptics, like myself.

Photovoltaics were much a tinkerers delight some years ago. I powered a small home built radio with a small PV cell decades ago. It took a while for PV to get where it is today, but I can now find many working systems (some better than others) within a 5 mile radius of where I live. So perhaps this technology may develop too. However, it should be noted that this is not new tech, it's only newly hyped tech. I had a Peltier effect cooler back in the mid 70's. My brother in law has one he purchased last year. After seeing it in operation for a week it seems to work as well as the one I had back then; a power hog. I guess I don't hold out much hope for improvements, but if it can be made to work, as mentioned above, show me a real life working prototype model, not a lab setup.

Hi Mountain Don, thanks for your input into the discussion and I totally agree with you! This is not something I am going to rush out and by in place of solar (already being upgraded to bigger system). Proof is something that will have quite an impact for me as well, or I would volunteer to be a test case if they want to give it to me

As I said, my main line of thought is looking at alternative energy technologies that are not weather dependent in any way.

I am still looking at picohydro at the moment since my property along the river is actually quite flat, so there is limited head available, but it is still an option I would like to investigate further.

MountainAussie wrote:
Hi Mountain Don, thanks for your input into the discussion and I totally agree with you! This is not something I am going to rush out and by in place of solar (already being upgraded to bigger system). Proof is something that will have quite an impact for me as well, or I would volunteer to be a test case if they want to give it to me

As I said, my main line of thought is looking at alternative energy technologies that are not weather dependent in any way.

I am still looking at picohydro at the moment since my property along the river is actually quite flat, so there is limited head available, but it is still an option I would like to investigate further.

My thought is that rather than rely on any one power generation type, a variety might make more sense. The primary purpose of a stove is to generate heat though... if you start trying to make power from it there will be less heat left to heat the home. Burning wood at a fast enough rate to make power in the summer means less fuel left for the winter. It may in the long run mean no forest land left close to you. If you have a river you are to be envied, most of us would love to have that. There are some pretty high power hydro projects that use not much head but more volume.... Even one or two meters is enough to get as much as 40K, more than enough for a home.

Hi Len, I certainly am not limiting to one energy source as I already have solar and am in the process of putting up a wind turbine to complement that as well. The thing I want to avoid is the dependency on the weather conditions and so I have been looking at alternatives.

I would be curious to see what hydro systems you would recommend as 40K seems to require a lot of head from what I have seen?! I might be able to get 1-2m worked out, but I doubt I would get much more, if that.

Some locations have more different viable options than others.

Here at home in the SW desert and mountains PV solar it "IT". 310 sunny days a year and the cloudy days are spread around nicely so we never have more than a day or two in a row with lousy PV production.

We have no running water we can use for hydro.

After computer logging the winds for slightly over a year I proved to myself that wind generation does not make sense. For a short time in the spring the winds do come, but most of the year the winds are far below speeds needed.

There is no need to make heat, other than to cook, in the summer, a little need in the spring and fall. Heat is needed in the winter, but last winter only used

Heating is required in winter so there could be excess used for TEG use. But even on the coldest days we do not need much heat; built the house with 'too much' insulation'  and it now has a 92% efficient furnace so there is little waste there. Not to mention we have no wood to burn on the desert mesa. I could haul wood from the mountains but it doesn't seem worth the bother when last winter we only paid the gas company an average of $12 a month for gas (plus $10 for the privilege of being connected).

MountainAussie wrote:
Hi Len, I certainly am not limiting to one energy source as I already have solar and am in the process of putting up a wind turbine to complement that as well. The thing I want to avoid is the dependency on the weather conditions and so I have been looking at alternatives.

That is where batteries come from

I would be curious to see what hydro systems you would recommend as 40K seems to require a lot of head from what I have seen?! I might be able to get 1-2m worked out, but I doubt I would get much more, if that.

I don't know if this is the one I saw before...
http://www.treehugger.com/files/2007/06/gravitational_vortex_power.php
Google "hydro vortex generator" for more.  This one is 50000kwh per year or about 7.5kw. I thought I had seen one that was 40k output, but it may have been the per year thing. Still,it is quite a lot of power. This says he has a patent on part of it... I am not sure what part and there are others out there that are similar too.

I don't think the intent of these things is to provide enough power to run a house, but they would still be handy in off grid applications, or as a supplement to on grid homes.  I'm thinking that they could be wired to a fan in ducting run through rocket mass to circulate air.  I also wonder if the pump is strong enough to locate the radiator in another room?  If so one could mount the radiator in a small room (maybe a bathroom?) to add some heat.

I don't know about generating any substantial amount of electricity, but here's one application of the thermoelectric effect that I'm fond of.  a bit delicate, though, so maybe not recommended for those clumsy among us.

Something occurs to me. Their website talks about 50watts of TEG being worth much more solar power because solar PVs are limited only a few hours per day. However, with a rocket mass heater you have the same problem.... maybe worse. A mass heater runs fast and hot for only a few hours then it radiates at a low temp for many hours... all the sudden PVs sound cheaper for the same power over time. The web site shows a wood heater but it is an iron slow burning stink box.. They do show a rocket stove (cooking kind) but they show it as a temporary set up for charging small electronics.

Hi Len, thanks for the reference to the hydro, I am not sure I will have enough flow for this type, but will certainly look into it further.

Also, your last message is the type I was interested in for my idea and how teg would work. I think it will all come down to "show me how it works" before I put any money on the table.

For the money, I think you could get much more electricity from a methane digester, gas scrubber, and internal-combustion generator.

I haven't worked with methane digesters, but I think it might be easier to schedule feeding of the digester (or a couple of them, running as a relay) and maintenance of the engine, than feeding of the wood-fired furnace and cleaning of the heat-exchangers on a thermoelectric generator. I'd have to do the math, but my intuition is that it would consume less biomass, both in terms of calories and in terms of market value.

MountainAussie wrote:
Also, your last message is the type I was interested in for my idea and how teg would work. I think it will all come down to "show me how it works" before I put any money on the table.

I am pretty sure it works as advertised... my question is more is that good enough, does it fill in a part of my power acquisition picture? It does rain a lot here... However, I think the amount of power they feel the two 165w panels would get per day(3.6 hours worth) is under estimated too. I think rather than looking at their comparisons, it is best to look at straight specs and how those relate to what resources are available in any one situation.

If I was going to burn wood 24/7 cleanly and efficiently, I would probably need a lot of those modules to use all the heat, I would have to have a use for the waste heat too. I can only use so much hot water in the summer.... though perhaps in the summer i could use solar heat to run it... making a solar cell part time... If I had the right insulation around the foundation of my house, I could pump the heat down about 9 feet from that... maybe the heat would show up in time for winter heating. The install does start to get pretty expensive though.... at what point does a sterling gen-set become cheaper to install/maintain? Or how can I make a tiny stove that self feeds? (can we make a 2inch rocket stove? <not mass heater>)

It easy to get excited or pass off as useless these things. The good thing with this one is that you don't have to have one in hand to experiment.... I can play with finding a suitable heat source first ... I wonder where they get the cells from, I don't think they are manufacturing them, there may be a cheaper source.

Len wrote:Or how can I make a tiny stove that self feeds? (can we make a 2inch rocket stove? <not mass heater>)

I would worry about solid fuel self-feeding. It's possible to predict the way uniform particles behave, up to a point, but it might be risky to change to another sort of solid fuel.

On another thread, Ernie mentioned that 6" is about as narrow as you can make the ducting on a practical rocket system. I think he said something like this: the boundary layer around the outside ends up dragging too heavily on the updraft, as you go narrower than that, and the whole effect you are going for with "rocket" ceases to work properly.

Joel Hollingsworth wrote:
I would worry about solid fuel self-feeding. It's possible to predict the way uniform particles behave, up to a point, but it might be risky to change to another sort of solid fuel.

I wasn't thinking of something I could leave for 24 hours or a week, but with a small system like that, something that would self feed for 4 to 8 hours would be nice. I was thinking of something like a 1inch willow stick 6 to 8 feet long (depending on top clearance) with a tube around it and an air inlet at the right height.

On another thread, Ernie mentioned that 6" is about as narrow as you can make the ducting on a practical rocket system. I think he said something like this: the boundary layer around the outside ends up dragging too heavily on the updraft, as you go narrower than that, and the whole effect you are going for with "rocket" ceases to work properly.

Yes, I read that.... in fact it may have been in answer to one of my replies. However, The problem seems to be rocket mass heaters where you are expecting the rocket to push the exhaust through a long tube through the mass and then out the flue. A rocket cook stove can be smaller and in fact you can buy smaller ones. The reason then for a rocket stove is not to store heat in mass, but rather clean burning and heat concentration. Normally they do not have a barrel and the exhaust is straight up like the pocket rocket for example.

Oh, I get it now.

I still think you'd want a relatively strong updraft to drive the flames into a heat exchanger, for the hot side of the Seebeck device. That might be accomplished with a tube that's narrow, but tall, and with a heat exchanger that allows flames to continue upward un-impeded.

Joel Hollingsworth wrote:
Oh, I get it now.

I still think you'd want a relatively strong updraft to drive the flames into a heat exchanger, for the hot side of the Seebeck device. That might be accomplished with a tube that's narrow, but tall, and with a heat exchanger that allows flames to continue upward un-impeded.

Ya, you would feed, go through the short tunnel, go up a long enough insulated riser to burn completely and then through an uninsulated riser with the generators on it (if we are going to hake heat, we want to use it all).  I am thinking 4 generators on square sided tube... maybe 8 depending on the heat left after the first 4 or if I have to have a wide enough square tube that two would fit to a side (or I could obtain individual modules and arrange them as needed instead of all in a row). I would want to have something more fool proof than just a water/coolant tube on each side... if the water stops flowing your modules die. From what I can tell, the 450F is pretty close to the devices max temp. So either make sure the riser is always less by that point or put a water reservoir around the whole mess and cool that, so that if the coolant stops flowing, it can be sensed soon enough to kill the input air and shut it down.

Hmmm, it gets less trivial the more you look at it... Still, it may be worth while developing a small heat generator for any use first.

yea thats only a "simple" thermocouple (aka peltier) can be had cheap on ebay i have several around to cool a computer .. i never finished
they work both ways lots of power in it gets cold one side hot the other.. used on those 12 volt mini fridges and the sharper image neck coolers as i recall
and as they are being sold here if you make one side hot and one cold it will put out SOME power

they need to be sealed well best to bond them to what ever your doing or bond copper(or better 999 silver) to each face

i thought the best use for this or a sterling motor(negative not usually self starting) is a solar heat pump. where as one side is the large panel input and out put or one side in the top/hottest part of the solar panel.

If you want cheap solar energy, go coppice >> wood gas >> cheap genset.  If you want durable and hands off, go solar PV. If you want expensive and experimental, go TEG.

They are charging a lot for those units.  PV can be had for under $2 a watt these days.

I have 200 rated watts of PV at my place.  I get in excess of 1,200 Watt hours (1.2kWh) per day (more in the summer).  I spent around $500 for these panels a few years ago.

TEG sounds great, but I don't use a fire very often (maybe once a week during the winter, and only for a couple of hours), so it wouldn't work that well.  I have considered a solar concentrator, it can hit 450 degrees no problem.  But with tracking, cooling water, concentrator, etc, you are looking at at least 2-3 times the cost of simple solar PV.

Another idea would be to make a compost pile, let it heat up, and somehow use a TEG with that heat.  The only problem is the heat is low (150 degrees or less), so you'd need a lot of TEGs.  Again, very expensive for the output.

A decent wind generator and some solar PV, and you are set.  My PV has a 25 year warranty.  What does the TEG come with?

One area for experimenting: get an old satellite dish -- not a big one -- cover it with this stick-on mirror material, determine the focal point, and use that to heat the TEG.  Granted, it's not "on-demand" like running the TEG off a stove would be, but it strikes me as MUCH safer than trying to use the dish as a parabolic mirror to generate steam.

http://www.greenpowerscience.com/ for examples.

yeah, that is a decent idea, Muzhik.

The problem is tracking the satellite to follow the sun.  And then also cooling the cold side of the TEG.  Before you know it, you have a fairly complex (and expensive) system.

velacreations wrote:
yeah, that is a decent idea, Muzhik.

The problem is tracking the satellite to follow the sun.  And then also cooling the cold side of the TEG.  Before you know it, you have a fairly complex (and expensive) system.

FWIW, I did a quick Google search and found a number of systems available that will control the motors to automatically track the sun, including one that looks like it works like an old clock, with weights and springs to control the movement (no electricity required).

As for cooling the cool side of the TEG, I don't see why the cooling system for use with a stove and the cooling system for a solar array have to be different.

No, they don't have to be different, but you have to get rid of a lot of heat, so you need a pump, a radiator, and transfer tube/hose for the cooling system.

For the tracker, you need something firm and steady, it has to stand up to winds.  Even trackers for solar PV are not simple and/or that cheap.

To make it worth while, you would need a system of a decent size (not like 10 watts or something).

I can't see how it would be any more efficient or easier to manage than a PV array.  It would definitely be more expensive.

The better solution would be to set up a tracker system, and use that to track your solar array, increasing its power.

The way PV module prices have dropped some PV installers who used to recommend building PV systems with trackers have changed their tune. In many cases it is less expensive to buy some extra panels than a tracker. Just thought I'd throw that tidbit into the pot about getting best bang for the buck.

I did a case study for development of a low temperature hydrothermal resource. What really gets you with heat engines and thermoelectric devices is that the efficiency depends on the difference between source and cooling temperature (delta T) (see Carnot cycle). Even with "free" hot water, if delta T is less than about 80F, the economics don't justify a mechanical heat engine, and AFAIK those are still more efficient than TE devices. Just a random data point to consider.

Google Chena, Alaska for a really cool case where technology triumphed at capturing energy that was previously considered "out of reach".

This makes me wonder if anyone here has access to a hydrothermal resource, and what they are doing with it. Maybe i should start a new thread?

well tracking with a old 7-12 foot c band dish that people re purpose to solar trackers anyway can be done 'easy' and cheap. there are cheap sensors that come on if they are shaded. so you put a small divider inline with the axis  with one ssensor oon either side connected once the shade hits the sensor the jack will move the dish. i would power this with a small solar panel so no light no move as for resetting the dish pointing east at the end of every day  havent thought of that you can adjust the height of the arc with the bolt on the old mount

I'd like to hear some thoughts on tying in a steam engine into your rocket stove. There is a guy last name Brown out of Ozark, MO I believe. He has written some books and has a very efficient steam engine designed to be hooked up to a generator or alternator. I am thinking that the rocket stove would be a great dual source if not just a primary source to power such a thing. I believe it is a closed loop steam engine. I am sorry, I don't have his contact info handy.

well tracking with a old 7-12 foot c band dish that people re purpose to solar trackers anyway can be done 'easy' and cheap. there are cheap sensors that come on if they are shaded. so you put a small divider inline with the axis  with one ssensor oon either side connected once the shade hits the sensor the jack will move the dish. i would power this with a small solar panel so no light no move as for resetting the dish pointing east at the end of every day  havent thought of that Smiley you can adjust the height of the arc with the bolt on the old mount

That won't work if you have a dish concentrator, you need 2 axis tracking.

And although it can be done for a trough setup, the sensor costs around $40, plus the motor, your small solar panel, a small battery, etc, you are looking at least $200 for the tracking mechanism.  You can get 100 watts of solar PV or more fr that money.

So, for tracking you have $200 invested, then you need the dish (free), the TEG ($5/watt), the cooling system ($100), the mirrored surface ($$$).  For a 100 watt system, you are looking at almost $1,000.  That's not cheap, that's $10/watt, whereas PV is under $2/watt.

I'm interested in TEC Peltier and alternate energy conversions too. I bought a 100 watt one on eBay today for .77 cents plus $5.99 shipping to experiment with. I have a small but crystal clear Fresnel lens too that I picked up at a garage sale for a dollar, also for experimenting. We heat our home with wood, it's a constant heat source more or less and we have extreme cold out of doors where I live in the Atlantic Province of New Brunswick. The only thing I'm missing in this mix is a heliostat to mount the Fresnel lens and track the sun. My principal concern about the TEC is the melting point of the solder, at 250F degrees. I believe the Fresnel can focal a spot point of almost 3000 degrees so my concern with it is how dang dangerous it is, in fact I showed my wife the focal point at an inside window by the stairs and set the banister on fire instantly! That's something that has to be contained or I'd never be able to walk away from it. Anyway it all seems do-able, just got to iron out the bugs before it's a stand alone system.