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Best way to generate energy (electricity) from heat?

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mramos1

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I know this is not really an electronic question, but it will have electrons flowing...

I know heating copper and iron at the junction of them twisted together will generate electric energy at the ends of the wires.

I have never tried this, but is there better material (common material) that will generate a fair ammount of power from the heat?

I bought a fresnel lens for the my kid (and me) to play with. After cooking pennies and aluminum cans we were over the lens. Then I thought let's make a steam engine or something, or use bi-metals for power.
 
It would melt the cell. It melts a penny in 15 seconds. In fact, copper and iron might not be good. The copper would melt.
 
Here in the US, the pennies they make these days are not all copper. They're made of zinc with a thin copper shell. Copper's melting point is ~1083 C (1981 F) while zinc melts at ~420 C (788 F). That's why it's relatively easy to melt those pennies. If they were older pennies (pre-1982), it would be much more difficult.

The problem you have heating a thermocouple junction is that you'll only get millivolts per deg C out of it. Basically of no use, unless you have hundreds (or thousands) of them in series. Even then the current output would probably be miniscule.

Basically, "co-generation" is usually simultaneous production of steam and electricity. The steam is often used for processes that require heat (like oil refining, large-scale distillation, etc.) and the electricity powers control systems, pumps, lights, etc. At least, that's how they do it at a couple of plants I used to work at.

JB
 
Funny project 2 was going to be a water distiller. Last a food dehydrator..

Will scratch that idea then. Thanks for the info.
 
Edmund Scientific used to offer a fresnel lens that was something like 30in X 40in (I don't remember exactly). They said when using the heat of the sun, a solar furnace could be built which would melt a wide variety of metals. It would also ignite the asphalt from their parking lot in seconds (which is no real surprise; asphalt is basically tar, sand & rocks) For instance, **broken link removed** says that the solar energy density is about 1KW per square meter. That's about 0.1 watts per sq cm. Disregarding losses, think of the energy density at the fresnel's focal point!
JB
 
mramos1 said:
It would melt the cell. It melts a penny in 15 seconds. In fact, copper and iron might not be good. The copper would melt.

That would be true - on any day other than April 1st. ;)

Dan East
 
Hi
I think a thermoelectric chip which uses the Peltier effect will work in reverse....
 
Your fresnel lens melted a penny in 15 seconds? How big is your lens?
Copper melts at 1984F and zinc at 787F.

Thats pretty, uh, cool!
 
And copper is good at reflecting light and infrareds in particular.

A thermoelectric "Peltier" cooler can generate small amounts of power via the "Seebeck Effect", which is basically the flipside of the Peltier Effect, another way of looking at it. But be aware that the power it's capable of is quite limited (under a watt), the cold side must be kept quite cool or there's way less power output, and if you exceed the device's max temp then it will permanently degrade in a short period of time.

Seebeck Effect is the same thing that makes the iron-copper junction, and all measurement thermocouples, make current.

It's difficult to make a useful heat engine. As you noted, there's a steam engine. Actually a solar cell with a lot of cooling will probably produce the most electricity. Also, a Stirling Engine will produce much more power than a steam engine. Yeah, look up "Stirling engine" on the web and in particular on eBay, for working small versions. They're expensive though, and again, power output is fairly small.
 
Thanks for the info Oznog. Did not know what was in a Pelitier or that they might handle it. They are a little pricey, but something to try. Or the distiler. I have one that last the heating element a year ago, I can drag out of the closet (yep, pack rat here).

I was gonna list Sterling when I mentioned Steam engine, but figured you guys would think I was an over-unity guy crashing the electronics forum. hahahah.. Most simple one uses a ballon and wood (that might not be good if the wind moves the lens a tad. But that was my actual first plan, they look hard to make if I want a good one.

Hyedenny. $5 for a 12x12 from Anchor Surplus I think they were called, for small some fun, OR $49 for a 31inch by 41inch that melts the penny in 15 secs. It is wicked KEWL! Built a frame and pivot for it. Kids love it, make sure you have welding goggles and never leave it in the sun unattented, trust me on that part.

Dan East, darn, it is 11:30PM on April 1, the only day it will not mely my solar panel, and the sun is gone for April 1.. Will try it next year. hahaha..

Thanks guy.
 
Oh jbeng.. Thanks for your comments too.. Yea, I think sterling will be first, kids will learn from that. And steam, well it can be dangerous and required adding water. I will leave that for second.

Heck, I live in Florida, I can use it for a hot shower next hurricane season.

Oh, I live in West Palm (Boynton Beach), we had the 135MPH+ winds in Wilma at my house and 160 at the airport 10 miles away. So we had no power, water, hot water for a weeks after wilma (no traffic lights, street signs) last year, and Francis and Jean did the same thing, just more like 115MPH the year before.. So I will be able to cook and heat water if nothing else. And so everyone knows the different from 115MPH (scary) and 135MPH+ (thinking about moving elsewhere, moving like the inside drywall flexed inside my house). I could see the drywall bow in the center of the wall about 3/4 of an inch. No joke..
 
The solar power article on Wikipedia is pretty good. https://en.wikipedia.org/wiki/Solar_power
Particularly of interest is the section on Concentrated power solar plants. You can see how they do it to get some good ideas.

I'm sure they spent a lot more man-hours researching the best way to convert that energy than you really have time for. :p No sense in reinventing the wheel.

And yeah, there are real solar power plants that use stirling engines at the focal point. It's a sound technology when used in an approppriate application. Not all that quacky.
 
If you want to research this accurately be sure to use the correct spelling- "Stirling Engine", not 'sterling' which refers to a popular silver alloy.

https://en.wikipedia.org/wiki/Stirling_engine

Don't overlook the solar cells. Solar cells lose efficiency as they heat up, as well as the potential for damage. But the back side on many is a solid metal which is a good heat conductor thus a proper heatsink could keep it at a more acceptable temperature.
 
Yea, I saw them, then I saw the price. I guess I will build a homemade one first, see if it works (does not melt down) and if so, look into a larger scaled unit later.

I am good with wood and have all the tools, but a little lite for metal items.
 
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