TEG powered by hot and cold water project

Projects
#1

Hey guys,

English is not my first language so I’m sorry for the mistakes but I will try to keep it simple.

I’ve been thinking on how to generate power during the winter in Latvia. Here we have almost no sun at all during the winter so solar panels are useless and a wind turbine seems a bit expensive at the moment + the wind is not so consistent here.

So I’ve been thinking about how to utilize what I already have.

My house uses a pellet burner to heat water for consumption and the house heating. The water that exists the burner is around 65-75 Celsius (150-170F) (maybe a bit more) but consistent depending on the settings. I usually have to burn for about 6 months during the year.

After a while looking and studying things about sterling engines I came across some videos on TEGs and seeback effect, I found some people doing experiments with the exhaust of burners and some other small projects but all of them have the same problem: too small, and poor delta of temperatures, often leading to damage to the TEGs.

I thought about something else. Having the TEGs in a sandwich of ‘radiators’ with one side pumping water from my pellet burner and the other radiator pumping cold water from a big tank underground where the temp will be stable all the time at 10C (45F) or lower.

Ideally I would have a constant delta of 65-70C (160F).

The hot water would exit the system and just go to its normal course of heating my house.

As I burn about 6-8hours a day, I would have consistent power generation.

Here is some diagrams and visuals of the idea.

To test the concept, I created a small prototype to charge my phone. I connected 10 TEGs in series, then to a converter and USB exit. It worked but I need to manage the temperature fluctuations and design a better ‘radiator’ as I just used these computer water sinks.

The idea is to have a big panel or a series of panels with these TEGs in series and parallel to generate some 500wh and then charge a battery.

The TEG I’m using is the SP1848 27145 which is good for not so high temps.

With this design I will prevent them of overheating and they will last long.

I know they are not supper efficient and with the desired delta I might get about 1.5.2 watts maximum each, but they cost like a couple of bucks and with this I could actually manage to get some 10kwh a day during winter and without sun doing absolutely nothing different, just using the hot water that I already have to heat anyway.

I’ve calculated the cost of this would be around 1-2k (euros) and I’m ok with this since I’m not looking for a financial investment but only resilience during the winter without having to burn anything else than I already have. My pellet burner accepts also firewood so that’s even better in case I can’t get pellets I have enough wood in my land.

I’m a product designer (software), and I’m not very handy, as you can see by the pictures. However, I’ve used some AI to find problems with the idea, and so far, all my predictions have worked fine. Now, I would like to know if you guys have any suggestions on how to build this for scale, how to design and build these “radiators.”

Any suggestions or ideas are welcome. Thank you!

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#2

Cool project, welcome to the Drive On Wood Forum.
A quick idea, would be to pump antifreeze through the cold side and cool it in the snow.

I am sorry about the rest of my comments, as they would be negative or too logical.

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#3

Yes. Also welcome to the DOW ThiagoC.

You language is fine. Very understandable.
And you been able to lay out most all of the problems and potential benefits to personal home use of solid state Thermal Electric Generators.
A tantalizing possibility that has called to most all of us wood-for-power users.

I myself did dip a toe into this. After a few hundred dollars spent and realizing how just ONE thermal runaway event could kill them then back to IC engine generators for me.
Just a matter of costs of investments effectiveness. At least $1,000 USD to get a few hundred watts for an expected few hundred hours of service life - they don’t just event fail - they degrade in usage.
Or that same $1,000 USD I have now spent out on three 400 to 2000 watt inverter generators with durable service life’s of minimum 1000 to 2000 hours. Generating units that I have now just loaned out to adjacent neighbors in GRID loss failures periods. Recently, Spain and Portugal.
Because my adjacent neighbors will see my lights and me with power running my larger, more expensive woodgas friendly IC generator units with 2,000 to 4000 hour service life’s.

It is really a matter of life experiences and gained perspectives.
Bluntly, your software designer experiences have you with the expectation that whatever developed will be set aside, supplanted every 24-36 months for something better.
Most of us here on the DOW like better working with tools and systems that can stand the test of time in decades, even centuries and still be able to function by a human willing to work it, and learn it characteristics.

Once you are forced to use your own now-harvested wood in the middle of your cold wet no-sun 6 months period because events outside you country mean no more manufactured wood pellets . . . believe me forced speed drying down freshly cut unseasoned wood will show you how to use any “waste” space and water heat made BTU’s/calories.

But go ahead with TEGs, by all means.
You first.
Regards
Steve Unruh

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#4

Hi Steve, thank you for your input.

Yes, the real-life experience is much more valid than just positive thinking + theory :smiley:

As I said before, the TEGs usually die out of too much heat as most examples I found were with them in extreme hot temperatures like woodburner exhaust, etc… The system I’m designing would never exceed those temps, since I would run it in 70-80 Celsius maximum, and they are designed for up to 150 Celsius.

I found information about them saying they are supposed to last 200 thousand hours, and a failure rate of 0.2%

Counting with degradation information, I found that with the Delta and number of cycles, I’m expecting it to work for some 15 years with a 10% loss over time. Hopefully, in that time I can figure out something better to invent :smiley:

but as you said, real life experience is different. I’m still pushing to build at least one big panel with some 300-500 TEGs and see where it leads. I’m doing this for curiosity and also to learn along the way, as I will have to learn hands-on how to do things, tools, thermodynamics, and how different materials behave.

Thank you for your input, I will take the degradation and failure rate more seriously.

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#5

Hi Bruce,

Yes, I thought about that, having glycol in a tank and possibly also a radiator to the outside to cool it down as the temp gets really cold in here during the winter.

Thank you!

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#6

I forgot to ask in my previous comment. If you have any info/data of your previous experiences with TEGs and could share, I will be very grateful, every piece of information can be helpful. Thank you!!

1 Like
#7

Thiago,
Welcome to the forum!
Your English translation is very good! Your documentation is also very good. :grinning:

First thing: Your latitude is South of some of our driveonwood.com members, and a small (for testing) modern solar array might gather more energy than you might believe, even on cloudy, gray days. Maybe much more cost-effective than buying multiples of cheap TEG’s.

I like Bruce’s idea:

Steve U. is right. Many have tried this, and the results are poor, discouraging. Keep your experiments small and practical, and in the intended use (installed in the actual environment the TEG array will be used in) and do a trial use for a month or more. Steve is also right about manufactured hardwood pellets becoming hard-to get in an emergency situation.

I think your 10KWh per day goal is not realistic, and you should start small and scale up. You will invent your own best design for a larger array based on your experiments at your location, and trial and error.
Keep in mind that each TEG is not magic. Each one steals a bit of energy out of your system; plus pumping liquid also requires input to the energy equation.

Please try your ideas and I hope this works well for you! :cowboy_hat_face:

6 Likes
#8

Hi Mike, thank you for your comment.

My coordinates are (57.6018520, 24.5093802)

Unfortunately the winter in Latvia is brutal in the solar sense. My father in law here has a modern (2 years old) solar array setup (12kw) and during November, December, January, February he could only collect about 5-10kwh a month, there are like literally a couple oh hours of sunshine during the months and the rest is just fog, cloudy and darkness, the day light is only a few hours.

But as you see in my diagram, I’m also planing to have a solar array, it’s more a holistic approach, a bit of everything.

About the pellets, it’s true, thank good my burner accepts fire wood too, just exchanging the the door and I always have about 2 winters of dry wood ready to go.

Also, yes I will build a prototype for home scale and test this winter hopefully. I will keep you guys updated on progress. Right now I’m working on the design of the cold and hot plate. Example:

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Once again, thank you for the support!

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#9

Okay you guys have forced me to make my comments.

  1. What do you need the electricity for? You already have grid. If you have a pellet stove you have grid.
  2. What is the thermal efficiency of the pellet stove? How much heat do you reject out the smokestack?
  3. Are you attempting to capture the heat you reject from the smokestack and use it for the peltier junctions? If not this is actually a worse idea than simply burning the pellets.
  4. A much more profitable and obtainable engineering challenge would be to increase the thermal efficiency of the pellet stove. Rejecting no more than 10% of the heat value of the pellets out the stack would be an incredible improvement.
  5. If you are looking for a project because you have too much time on your hands, you would be better off researching exchange traded funds holding European stock. The stock valuations in Europe will be driven up as capital flees the USA. You Europeans are poised to make a big pile of money.
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#10

I’m not planing to use the heat from the stove at all, only the heat from the hot water pipe outside of the stove that is at 65-75 Celsius for the hot side of the TEG and use cold water for the other side having an ideal delta for the specific TEG I mentioned. I’m not burning less or more wood, since 5 degrees difference in my big tank of hot water won’t make a difference. The TEG system I’m designing is to trickle charge a battery when I’m using the pellet burner. I’m currently ongrid and moving offgrid when I’m able to generate enough energy for my house from various sources.

I think the pellet burner youre think is not the same I have at home. Look at this picture, I’ve marked with red the pipe where I will collect the hot water for this design. It has nothing to do with chimney, as I pointed before using the chimney is not a good idea and that’s why 99% of TEG projects are doomed.

I have a big source of heat, I’m not concerned at the moment with that. I want to generate electricity.

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#11

A wood pellet gasifier running a generater with a battery bank and heat exchanger was the first thing I thought of.

There was also a recent discovery that could affect TEG technology that improved efficiency. I can’t find the article right now though.

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#12

Yes if could use it to warm the house water yes. Other than that I would have then 2 stoves burning wood :sweat_smile:

If you find the article let me know, I’m much interested.

#14

Just to clarify — I’m not asking whether TEGs are worth it or not. I’m already committed to building a controlled, low-temp system with long-term degradation planning. I’m only here to discuss efficient thermal block design (like flat plate vs tubing, flow paths, material choices). Any insights from those who’ve designed efficient radiator or cold plate systems — regardless of application — would be appreciated!”

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#15

Still not the article, but interesting for your application since it uses wood and since you want a LOT of TEGs it could be cheaper. But I didn’t look at the efficiency or even read the paper.

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#16

Thank you for the article, this is interesting, but I think the real usage would be more for wearables such as health monitors, watches and etc…

About the TEG I’m using the SP1848-27145 these are the numbers:

  • Size: 40MM * 40MM* 3.4MM
  • 20 degree temperature difference: open-circuit voltage 0.97V, generated current: 225MA
  • 40 degree temperature difference: open circuit voltage 1.8V, generated current: 368MA
  • 60 degree temperature difference: open circuit voltage 2.4V, generated current: 469MA
  • 80 degree temperature difference: the open circuit voltage 3.6V, generated current: 558MA
  • 100 degree temperature difference: open circuit voltage 4.8V, generated current: 669MA

I’m aiming for the 60 degree temperature difference, that’s very achievable if I manage the plumbing well, then having groups in series and parallel, I could actually achieve something around 500wh with the right number of these TEGs.

The biggest difficulty at the moment is the design of it, since I need the metal plate to be entirely at the same temp, without gradients like in regular home radiators. Sizing, internal structures, materials and flow will be key for the success of this.

#17

I live off grid. Everything is based on whether or not it’s worth it. Otherwise, I am wasting money. I do waste a lot of money on engines. I like burning fuel.
Coming here to this forum and trying to limit the topic is fruitless, and a thick skin is required. Still, actual malice here is extremely rare, and never tolerated.
Alright I will behave.
Here is the engineering…
If you have a natural draft boiler, half the fuel goes up the smoke stack to make the draft. The same draft can be achieved more efficiently if you have an electric fan powered draft. It is for this reason I would work at capturing the waste heat. This a problem because of incomplete combustion, and it’s products condensing on the stack. It means more maintenance keeping the flue clean.
I need to discuss the inefficiency of the peltier junctions. 8% or less of the heat is converted to electric power. So you are saying you have a heat sink large enough to handle this steadily? Are you moving the heat to the sink via liquid? You are heating a basement with the heat sink? I was working the conversion, 500wh of electric means 21000 BTUs have to be rejected into the heat sink. I am sure it can be done in the winter in the basement.
A resource I use is to ask ChatGPT if it’s exposed to ASHRAE data. It seems so. Chat can design the cooling plates using ASHRAE heat transfer data. Once you know roughly what you need, I bet the Chinese merchants have something very close.
I found this gas to liquid heat exchanger using that method.

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I guess the difference between the heat you have to make “anyway” and getting useful power is keeping that heat sink from warming up. That is my complaint about the scheme. If the heat sink warms up, then you’re not making any power because you have no temperature Delta. If the heat sink remains cold you’re throwing away the Heat which is not really good idea at 57 North.

One additional comment about the photograph, I saw three circulation pumps on the boiler, I need a 200 amp hour battery to make it through the night operating one of those circulation pumps. It’s just a thought about when you eventually go off grid. I do use LiFePo batteries trickle charged and not heated.

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#18

Thanks a lot for your thoughtful response — this is exactly the kind of grounded feedback I’m looking for.

You’re absolutely right on all main points, especially about:

  • The inefficiency of TEGs (~5–6% in practice, rarely 8%)
  • The importance of maintaining a cold-side temperature to preserve ΔT
  • The risk of over-relying on circulation pumps when off-grid (they are high efficient ones, 3-5 watts each)
  • The critical role of proper thermal rejection

Some clarifications about my system:

  1. My cold-side design is liquid-based , not air or ambient basement air.I’m using external IBC tanks, partially buried and exposed to Latvia’s winter cold — consistently around 0°C or lower at night. That cold water is circulated through manifolded aluminum plates (serpentine-style) mounted behind each TEG array.
  2. The hot side comes from a pellet burner running ~80°C water. The flow hits the TEGs first, then moves into the tank. So the highest ΔT is across the TEGs, and I’m only burning 2–3 × 15 kg bags/day, which I already burn for heating anyway.
  3. I’m accounting for energy loss from the circulation system. The current design uses only two low-power DC pumps (one per loop), and the entire TEG system is designed to run 6–8 hours per night only, when ΔT is highest. Power for the pumps and MPPTs is supplied from a LiFePO₄ battery system with a minimum of 10 kWh capacity.
  4. Yes, I know I’m rejecting ~20x more heat than I’m harvesting electrically. That’s fine — the point of the system is to recover a small but usable amount of electricity while still using the heat for the home. It’s not about 100% energy conversion, but rather making use of the unavoidable ΔT I already create every night in winter.
  5. As for ASHRAE-calibrated design: I’ve been working with ChatGPT to model the cold plate flow, surface area, and rejection rate. So far the numbers look good, and the liquid-cooled plates will keep the ΔT high as long as I stay within my planned runtime and flow rate.

In short:

  • I agree that this wouldn’t work with a natural-draft wood stove or chimney mount — that’s a recipe for poor results and TEG death.
  • But with proper manifold plumbing, liquid-cooling, and a system built for short, cold nighttime runs, I believe this can yield 6–10 kWh/day, using power I’m already burning as heat.

Of course, these estimates are also very optimistic and I might achieve much less, yet the initial goal is actually to provide the minimum to run a couple of freezers, fridges, pumps, and a few lights as the backbone of the needs for my house, which are around 3.5- 4kwh a day.

Appreciate your perspective — and if you have input on optimizing the cold-side loop sizing (e.g., flow rate, surface area per kW rejected), I’d love to hear it.

I can assure you, there is no malice here, and I’m following it purely by curiosity and a deep conviction that I should try to explore all avenues available, and the reasons for going off-grid are mostly personal and individual, which can’t be measured only by cents saved.

Thank you!

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#19

This is my issue. Your heat sink needs to be something that you use the heat for. You can’t be heating Latvia’s winter. I think that will drive you crazy.
Isn’t the whole point of this to do something with the heat you had to make anyway? If you are sending it to totes, you aren’t going to be able to use it.
This why I keep looping back to the wasted exhaust heat from the boiler draft. Run the exhaust through an economizer, send that captured heat to the Peltier junctions and then send it to the totes. This route follows your engineering constraints.
Otherwise, radiators in the basement? Heat the garage? Chicken coop. Something that can use the heat but not get too warm.

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#20

Bruce,

I guess I wasn’t clear, the hot water won’t to go totes outside of the house. There are 2 separate flows. Imagine flow #1: pellet burner > TEG module (hot radiator) > straight back to the original flow my house already has and naturally that water will go back to the boiler.

Flow #2: cold water stored outside with glycol> cold radiator> back to outside

They are separated, imagine a sandwich of radiators and the tegs in the middle.

The hot side will lose almost no heat doing this path, at least none that will cause any issues to the house heating.

The cold side I want to keep as cold as possible, that’s why outside.

This way I create a stable delta during the winter, the colder it gets outside, bigger the delta is and bigger my wattage collection.

The delta of 60-80 celsius is what I want to achieve with the specific teg I have. It is not hot enough to damage them, it’s quite the ideal actually.

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#21

Here is a couple of videos explaining it better.

Thank you!

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