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Thermoelectric generator improvements

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fepps:
Hi All! This is my first post here. I might have an unusual background for a site such as this-- I am a bookseller by profession. But in the 90s I got involved in alternative energy research of the more far-out variety, and eventually went on to work for a couple of companies as a database researcher. All this to say that I'm not a builder but a paper pusher :-)
Over the years my focus has narrowed, and gotten much more conventional. I've spent the last few years reading the patent databases in PV and Thermoelectric generators, looking for technologies that might have been lost or forgotten over the years. I found plenty. In particular, it looks to me like Seebeck generators can be made far more efficient than they are now, through use of some pretty simple means, easily developed. None of it is my invention, just what I gleaned from reading a lot of old patents. Frankly, I'm here to promote the possibility of an efficient TEG, and offer some information that might be useful to anyone who is interested in that possibility. I won't waste anyone's time going through it all, unless there is some interest. Thank you for your time!  Fred

Bruce S:
Fred;
WELCOME ABOARD!!
You will find there are plenty of people here you are interested in the TEGs and their counterparts.
Please due post some of your findings and don't be too worried about rambling on, we do that on a regular basis  :o

I have two solid state fridges that I've increased their cooling abilities by merely taking the backs off replaced the single exhaust fan with side mounted squirrel fans to let the hot air out.

Cheers
Bruce

DamonHD:
Hello!

I have some meaty Seebeck generators that I never deployed.  I was considering going big solar thermal and coverting excess heat to electricity, but in the end went PV and I am doing the reverse for a heat battery!

Rgds

Damon

SparWeb:
And we do encourage experimentation.  So put the paper aside and pick up that screwdriver!

Whatever your preference, feel free to share ideas.

Another: Welcome to Fieldlines!

fepps:
Hi Bruce, DamonHD, SparWeb,

Thanks for the warm welcome! I hope you won't regret giving me permission to ramble on about this and that! As to picking up a screwdriver, I've made several starts to it but never get very far. Doing things in the physical world takes a high tolerance for frustration which I never seem to manage.
OK: thermoelectric generators. So much to say. I've surveyed most of the US patent literature on TEGs, and two concepts pop up over and over again in different forms. Neither is in use in current devices, and both show the possibility of great gains in performance.
This is just a broad, general description of the ideas, without references. I can go into the details to whatever degree is wanted.
The first is to create some sort of barrier between the hot and cold side couples that blocks heat flow, but allows electrons to pass freely. This violates the Weidemann-Franz law that says that thermal phonon and electron conduction always go together--one of the main reasons for the low efficiency of TEG. Different patents use capacitive coupling through a dielectric, point contacts, and sparks and arcs, both ionized and vacuum, for this purpose. If the heat flow is blocked then figure of merit Z of the couple increases dramatically. Theoretically, if there were no heat flow at all, you could put a TEG in the wall of a thermos containing hot liquid, and get power until the internal heat dissipated through the walls. This is an exaggeration, but it shows the importance of finding a way to do this. Between the different techniques, capacitive coupling through a dielectric seems the most promising, with the disadvantage that it can't be used with the standard ceramic TEG units because of the way they are put together. One patent simply places a high K dielectric between the ceramic blocks.
The second concept may be more directly usable since it doesn't involve changing the structure of the modules. One of the other major causes of inefficiency in TEG is the high current, low voltage output. This maximizes the I2R losses inside the couple--most of the current produced by heat turns right back into heat. A German inventor solved this issue by using switches to include TEG modules in an AC circuit containing a reactance. The module current doesn't reverse direction of course, but the switches align the module current with the already flowing AC at the zero crossings. Putting a reactance in the circuit and choosing the right operating frequency lowers current and raises voltage through the modules, resulting in increased efficiency. The AC generator is wattless because the voltage rise from the TEG compensates for the voltage drop in the generator.
These two concepts are synergistic in that a capacitive-coupled heat barrier only works if current is changing through the modules, which is the case when the second concept is used. The German inventor does use both concepts with a spark gap for the thermal barrier, and reports very high efficiencies. Interestingly, in his very long patent he also applies the same concept to PV and many other direct energy converters. He states 30% increase in output power for the PV over the MPP. But that's another topic.
I hope you find this of interest!
Fred

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