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LAN_403

Overclocked

Mon Oct 29 2007, 04:15AM

Registered Member #1056 Joined: Thu Oct 11 2007, 11:15PM
Location: CT, USA
Posts: 27

In the recent Months Ive become Intrested in Power Generation (alternative mind you). So Far, there are various ways to generate Power Using Various Sources Around us (excluding Coal, and Oil. Nuclear power FTW IF its used right) such as Wind, Solar, and in some spots, geothermal. Ive heard there are Generators That will use the tides of the ocean in the works, and I myself have been thinking of some idea to use the oceans waves to generate power. However, There is one Form we dont take advantage of.

Thermoelectric Energy, ie, Heat. Sure we can use it to boil water for our hot water heaters, But why not use something to generate power? Im thinking a homemade thermocouple. I have some Forrest M. Mimms Books that show how to make one and which materials one could use. Im thinking if you can get a bunch of these, Put them in the sun OR snow (since they generate power via a difference in temperature) hooked up in series, you could probably get enough voltage to power a battery.

I think they were made of Copper and Steel...err or It was a steel paper clip and 2 copper wires. I Know My idea will work, But will it be Practical? Are the bill of materials just so expensive, that its cheaper to go solar? Still, If there is Heat or cold, there has to be a way to put it to use. Hmm dont diodes or most semiconductors produce a voltage if heated or cooled?

On A side note, I do know there are things such as Peltiers, and I have a couple, But Ive heard pelts arent really a good way to generate electricity from heat.

...

Mon Oct 29 2007, 04:38AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Face it, converting heat back into usable energy just isn't easy.

You will never be able to get any appreciable amount of power using thermcouples, even with pielters you can't recover more than a few precent of the energy.

Really the only way that exists currently to create large amounts of usable energy from heat is to boil something, and then use a turbine and generator to turn a motor.

Coyote Wilde

Mon Oct 29 2007, 05:37AM

Registered Member #175 Joined: Tue Feb 14 2006, 09:32PM
Location: Sudbury, ON
Posts: 111

All of the technologies you 'excluded' are thermoelectric, technically (along with geothermal and some solar) -- they convert heat to electricity.
They don't use peltiers/thermocouples, because thermocouples suck. Peltiers are thermocouples run in reverse, and the ones you have are way more efficient than anything you could make with metals like iron and copper. But compared to a rankine cycle steam system, like the excluded technologies, there's absolutely no contest.
If your Tmax is too low to boil water, you can use another fluid instead of water, or switch to the sterling cycle. A small sterling engine is probably your best bet to work from a small differential, but it still won't work well.
You NEED a heat difference. The bigger, the better.
Also, putting something in the sun to heat up is technically solar power. Use some sun-tracking mirrors and you can get some righchously high temps, plenty to boil water with. An newspaper in Revolutionary France (IIRC) actually powered its printing presses with solar-thermal-steam. It's name? The Sun, of course. (well, translated)

But no, what you want to do is not practical. If you want to leave semiconductors in the sun to get power, get PV.

Since somebody is going to counter my "thermocouples suck" with NASA's use of them in RTGs, it's only because they have no moving parts and won't wear out on a decade-long mission like the Pioneer probes, Voyagers, Galileo, Cassini, or New Horizons. NASA has been looking very hard for alternatives to better use the available power, and have an impressively efficient free-piston sterling generator in testing now.

Bjørn

Mon Oct 29 2007, 07:51AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

First we need to find the teoretical maximum efficiency obtainable. e = 1 - (Tcold / Thot), temperatures in kelvin. Imagine you have smelting snow and an air temperature of 10 deg C. e = 1 -(273/283) = 3.5% efficiency, then you subtract any losses in your system and you are left with hardly a measurable efficiency.

Peltiers are as good as anything for very small generators, I have seen several peltier power generators, I have never seen a small strirling or other mechancal type that is in actual practical every day use. Peltiers can give more than 10% efficiency without moving parts but it is very difficult since you need high temperature differences and you are very close to destroying the peltier. I have reached 10% conversion efficiency using a candle as the power source and used it to power LEDs that made more light than the candle itself. Fun but perfectly useless since other light sources than candles would be a lot more efficient.

Your first step would be to replace all heating of air and water with solar heat and heat pumps. Then reduce your energy use in general as much as possible. Then you have significant savings without spending more than you save. Then look at hydroelectric, solar and wind power. Then look at other forms. The exception would be if you use gas, oil, wood or other sources of high temperature for heating, then you can in theory do very well in combining those with a thermoelectric generator.

Avalanche

Mon Oct 29 2007, 06:27PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

I had a go at making my own thermoelectric generator a while back. I can't remember if I posted it here or on another forum, but here it is, just for interest... It's a 70 watt peltier cooler sandwiched between two heatsinks, on top of a lamp.

I know the open circuit voltage in the photos proves nothing, but the output impedence is quite low. Short circuit current was well over an amp, and by experimenting with different loads I managed a power output of about 3 watts IIRC.

I originally intended to use it for recharging phones and cameras remotely, where the lamp could run for 12 hours overnight on one fill.

I gave up in the end, I never actually used the thing. It sort of worked, you had to run the fan as well to stop the module overheating.

Coyote Wilde

Mon Oct 29 2007, 11:21PM

Registered Member #175 Joined: Tue Feb 14 2006, 09:32PM
Location: Sudbury, ON
Posts: 111

That's actually pretty cool, Avalanche. Too bad it didn't quite work >_>;
I seem to recall the Soviets at one point producing a similar kerosene-lamp/thermal-generator for use in remote Siberia, but they had purpose-made thermocouples to take the heat.

Okay, I'll concede Bjorn's point... but like I said, you use peltiers where the moving parts of a sterling or rankine cycle engine are going to be a problem. I can see that being smallness.
Though small Stirlings are used, just not commonly-- example here, a power-cooler:

A similar size to what they started to fit peltier modules into a few years ago... this is at once way more efficient and more expensive, probably due to those fine machining tolerances. No idea if how well the Stirling unit would work ripped out and run in reverse, however.

Steve Conner

Tue Oct 30 2007, 09:45AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Avalanche, did it take more power to run the fan than what you got out of the Peltier? :(

Avalanche

Tue Oct 30 2007, 07:32PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

The power output from the peltier would have probably been about right to run the fan, taking into account conversion losses from having to step up the output to 12v for the fan. That's why I never bothered taking the project any further. If I really cooked the peltier it would produce a bit more, but not for long!

To make it worthwhile on a small scale a fanless approach is definitely the way forward

Overclocked

Tue Oct 30 2007, 11:40PM

Registered Member #1056 Joined: Thu Oct 11 2007, 11:15PM
Location: CT, USA
Posts: 27

Crap, I kinda figured that it wasnt practical. Oh well, I guess theres always generators.

I did do a little experiment and found that Blue LEDs Do give a lot of voltage when exposed to light, appr 500 mV. Not bad considering Solar Panels give the same. But I wouldnt know how much current it would be able to supply. By the time you a lot of money of LEDs, you can just get surplus solar panels from electronics goldmine.

Conundrum

Fri Nov 02 2007, 09:07PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

or use solar cells directly, they are mostly sensitive to red light which an alcohol burner flame provides in quantity.

-A

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