Is it possible to make a thermoelectric generator using solar hot water?

[Massacure]

Let's say 100 watts during a hot summer day. What about a cold winter day? How big would the collecters be and how expensive would the parts be? Could a high school senior do it.

[don954]

1. yes, but it is way more efficent to use photocell solar panel

you only want 100 watt hours per day? Get a 20-25 watt solar panel, that will more than do it.

http://store.solar-electric.com/solarpanels.html

[Massacure]

3. I meant an hour. Are PV panels cheap though?

[don954]

6. a thermo-electric generator at this amperage isn’t going to be

cheep either. The Kyocera 120 Watt solar panel is $538 + 30-50$ shipping right now, I have used it and it works well.

BTW, I used to build solar power systems to power remote radio relay sites so I have a bit of professional experience with this..

If you NEED 100 watts an hour, you may want to oversize your system in order to insure proper generation. Also be sure to pick up a battery for night time, and a charge controller.

[skids]

10. Oh, they aren't too horribly more expensive.

You can get an 8W panel for $54.71 in singles, and the price goes down for quantities.

The advantage to using thermoelectric over PV is that you can store heat in a hot water tank, instead of having to use a large battery array.

[queeg]

2. try this

http://www.wind-power.com/

not just wind but several "off the grid" type energy ideas, including both solar-electric and solar-hot water

[EVDebs]

4. Someone mentioned a 'mexican hat' style system

with a base of glass enclosure and a hot-air stack where the rising hot air would turn fans and spin a generator. I think this was in a Peter Hoffmann book Hydrogen The Forever Fuel if I'm not mistaken. Anyway, I don't know if anyone has tried it. A desert area (Mexico's Sonoran for example) would be the place to try this I guess.

[skids]

12. Yeah that's called a "thermal chimney"

They are making a huge one in Australia. But it's really a design that only puts out decent power at a very large scale (the chimney has to reach way up to get a nice cool, low-pressure outlet.)

[EVDebs]

20. Yo skids, as a total 'aside' from this topic, have you seen ZAFCs

Zinc Air Fuel Cells ? This fuel cell, not based on the hydrogen/PEM based system that is getting all the funding but is based upon platinum and is rare/expensive, is way cheaper and more 'doable'.

Zinc Air Fuel Cells are based upon potassium hydroxide and zinc oxide pellets. The system mimics cellular energy and not photosynthesis as hydrogen fuel cells do.

Anyway Metallic Air just went belly up but eVionyx and Arotech are still going on with ZAFCs.

[skids]

29. Yeah, there's a lot of neat stuff going on in metal oxides.

One company even has a UPS system that regenerates the zinc pellets. Aluminum-air batteries are also neat, and a possible route to fuel storage if you just use and discard the aluminum feed.

When they get to the point where I can power my house off of coke cans, let me know :-) In the meantime, I think I'll keep looking into thermal systems and, for the electricity portion (which is not the major portion of our energy use) thermoelectrics.

[htuttle]

5. You could use a Stirling engine heated by a parabolic mirror

In the winter, the engine might actually become more efficient than on a very hot day, since the cold cylinder could be far colder. Stirling engines' efficiency is related to the temperature differential between the two cylinders.

I've seen experimental designs where this was done on a large scale, with a mirror field heating a rather tall 'hot' cylinder. The same basic design should be shrinkable to a 'personal' size.

http://en.wikipedia.org/wiki/Stirling_engine
http://www.stirlingengine.com/

The only drawback is that the engine might have to be awkwardly large to run a decent sized generator -- unless you can come up with a very efficient mirror to generate quite a bit of heat, or can keep the cold cylinder quite cold (such as in a running river or in the winter, for example).

[Viking12]

14. Or the "solar death ray"

http://www.solardeathray.com/index.html

[phantom power]

15. I almost built one of those in college.

I had the giant fresnel lense, but my wife refused to swipe the columnating optics from her physics lab. Curse her. I could have ruled the campus with an iron fist.

[Viking12]

17. The solar death ray doesn't use a lense

in the FAQ the designer says;

What about mounting a magnifying glass in the focus?
I don't think this would do anything. When using a magnifying glass (or similar lens, like a Fresnel lens), every point on the lens is
associated with a specific direction of incoming light (upper image). However this is not the situation in the focus of the Solar Death Ray, because all of the light from the focus is reflected off of mirrors at different angles (lower image). Because of this, a conventional lens would not help concentrate the light, and would most likely dilute ("de-concentrate") the sunlight. There are
ways to minimize the effect, but the Solar Death Ray would have to be explicitly designed to use a magnifying glass or other
secondary concentrator.



He also addresses the possibilities of a Sterling generator:



What about hooking it up to a Sterling engine?

Yeah, that would be cool. The thermodynamic efficiency should be decent (maybe over 60%) assuming I can reject heat near room temperature (about 300 K). I haven't seen a kilowatt-class Sterling engine for sale, but that might be because the guy who makes them hasn't seen a kilowatt-class solar concentrator for sale.

[phantom power]

18. That makes sense. My design was a bit different.

I started out with a (very large) lense, where all rays were traveling toward a focal point. My idea was to use a concave lense to bend these rays back into parallel, near the focal point. My big lense didn't really have the kind of quality it would have taken to seriously work, but I wanted to try. If it had worked, I could have directed this beam more or less anywhere, with a mirror. Assuming the beam didn't melt the mirror. Which might have happened. I've melted glass with my lense.

[phantom power]

19. This design is interesting.

Using mirrors to focus light onto a relatively small area of PV cells. One little-used property of PV cells is that they can operate at higher efficiencies in more intense light.
http://www.energyinnovations.com/sunflower250.html

[Dogmudgeon]

24. There is one small catch

If you heat a PV cell too much, it will "crash"; even modest levels of heat destroys them.

IIRC, Pelletier devices have the same problem, although they can tolerate more heat than most semiconductors.

Yes? No?

--p!

[phantom power]

26. I did notice they had a fan to keep the PV cells cool.

[Coastie for Truth]

27. With Peltier/Sabbatier devices

The ones I worked with were semiconductors of (Pb,SN) with all sorts of cats and dogs (Ga, In, Tl//As,Sb, Bi//Se, Te) and the "dopants" were thermally mobile - migrated like bats out of the bat cave on heating. We are talking dopant level concentrations - so it doesn't take much to convert an expensive electrode into a paper weight.

As to PV cells - I have worked with amorphous Si -- and you really have to get to temperatures where the metal in the Cu leads and bus bars begins to migrate. (Part of the fabrication process is plasma CVD -- and some manufacturers use a thermal anneal for Staebler-Wronski control.) But my trickle charger has survived hot summer afternoons in my windshield - no problems. Instead of a "reflector" - I put an amorphous Si PV cell on a flexibe substrate in my windshield when parked.

[Dogmudgeon]

28. My EE experience is limited to hobby electronics

So naturally, I ask around, but one thing that I learned from the first time I plugged in a soldering iron was "don't overheat the semiconductors". This was around 1968 (I was 10) and simple general-purpose transistors were still a buck a pop. (ICs were still exotic, horrendously expensive, and the stuff of sci-fi.)

It's good to hear that PV cells are more thermally "robust" than I feared. I assume that someone had studied this in detail -- just how much heat can the easily-available PV cells withstand, day after day?

--p!

[Coastie for Truth]

7. Solar collector +Peltier/Sabbatier effect Generator

I saw a prototype of one of these -- Peltier/Sabbatier is a thermocouple type device. Japanese sell a Peltier/Sabbatier desk top refrigerator. Cute little "Sharper Image" type thing.

The "Solar collector +Peltier/Sabbatier effect Generator" integrated unit was constructed to meet a development contract for the DOE and have an "actual reduction to practice" for a patent filing. Nothing commercial ever came of it -- and the investigator went on to other Federal grants and contracts.

;)

[skids]

9. Stirling if size matters, peltier if it doesn't

Stirlings will get more power out of the heat generated by a reflective dish, but peltiers are easier to maintain, so if you have the real-estate, just make a larger collector.

You can get seebeck-optimized peltiers at the below two URLs. Per watt, they are running a little bit more than PV panels right now.

http://tellurex.com/
http://www.hi-z.com/

The peltier cooling modules are not meant to generate power. They can, but the ones made specifically for that purpose are probably better, and the wattage ratings charts given on websites are for driving it, not using it as a generator.

As a demonstration of totally screwed up the world is, there are lots and lots of companies that sell the peltier effect cooling modules, and they are cheaper than the seebeck effect generator optimized modules. Go figure, it's the same basic thing. Anyway, to add insult to injury, a lot of the companies that resell Chinese modules do not offer the generator modules, even though the same company produces them, and of those who do offer the generator modules, they rarely list the prices on the website -- a clear indication that they don't keep them in inventory. There just isn't demand, because we dumbass Americans only seem to want to buy products that use electricity, not generate it.

[kestrel91316]

21. I am so proud of myself ..............

all on my own, about 5 years ago I thought up a cool way to generate solar power using a Fresnel lens and Seebeck/Peltier thermocouple thingie. Too much time on my hands and too much browsing in the library I suppose............not bad for veterinarian who took one physics class way back in 1978.

But then I found out somebody had already thought it up and dreams of patents and billionaire status went down the drain.

I guess I will stick to fixing kitty booboos.

[Porcupine]

8. Thermoacoustic resonance generators

Try this link here: http://www.io.com/~frg/ or this http://www.freeenergynews.com/Directory/ThermalAcousticResonator/

Research rigs only but interesting nonetheless.

[skids]

11. Yeah, I'm eagerly awaiting those.

But right now they are still vaporware.

Someone really needs to pull together a price-tracking website for
mini-cogen products. I mean something like streetprices.com, not the "popular science" type sites that do new product announcements and reviews.

[phantom power]

16. Something about this nags me.

Thermodynamics would seem to imply that it requires some kind of heat gradient to operate. An example of what bugs me would be their suggested application of operating medical implants. If a TAR chip is sitting inside a human body, then the entire device would be at body-temp. The system would be iso-thermic, and there would be no useable heat gradient.

I'm not quite as sure about something like a rooftop application, but I wonder if it would suffer the same problem. The entire chip would be more or less the same temperature, and I don't see how useable energy could be extracted from that.

[RONSTOO]

13. wtf?

:o

[Coastie for Truth]

22. Sabbatier/Peltier on cars

One thing that gets periodically looked at is a Peltier/Sabbatier/Seebeck thermoelectric generator for cars.

The "hot side" is bonded to the catalytic converter - or better yet the exhaust manifold (years ago when I played with these things there was an "issue" the solder thermally diffusing into the Sabbatier/Peltier/Seebeck electrode - contaminated the semiconductor and killed performance -- this diffusion was highly temperature dependent).

The cold side is bonded to the radiator.

You can get a fair amount of watts out of this.

With a hybrid - this could be very interesting.

ARPA and the USMC have put out a "Request for Proposals" on this (sorry - no link).

[Massacure]

23. How can I build a thermoelectric generator though?

I don't have a car to toy with it on but I do want to try it with a loop of hot water heated by the sun and a loop of cold water cooled by the Earth.

[Coastie for Truth]

25. At various times

Radio Shack and Edmund Scientific had Sabbatier/Peltier Effect generator demo kits and hobbyist kits.

Tellurex (http://www.tellurex.com/) has ones a bit bigger then hobbyist/demo size.

In my travels - I have seen thermeoelctric modules (toys, hobbyist, co-gen sizes) in Tokyo's Akihabara (http://www.akiba.or.jp/english/) -- if you are into electronics hobbies - Akihabara will make you think that you have died and gone to heaven!

[Massacure]

30. Those are expensive. Perhaps I would be better of with a sterling engine?

Maybe it would be cheaper to build either of the options from scratch or near scratch? Is it even possible?