# Turning heat into electricity to recharge batteries



## Sunking (Aug 10, 2009)

Phil I know a little bit about it, but it is like solar PV systems just too expensive to justify or ever pay for itself.


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## jackbauer (Jan 12, 2008)

Considering how much waste heat a combustion engine produces an automotive thermoelectric generator would surely be a good idea?


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## PhantomPholly (Aug 20, 2008)

It's coming.



Passive, energy-neutral cooling by converting infrared radiation into radiation that we don't feel as heat (like radio waves)
Passive heating by turning radiation we don't feel as heat into infrared radiation
Extremely efficient lighting by basically broadcasting photons from the nantennas. As it's basically the solar process in reverse (photons from electrons, instead of electrons from photons), this is just as feasible as the solar applications
Passive heating or cooling within clothing
Electricitiy production in clothing by harnessing our bodies' radiation.


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## SimonRafferty (Apr 13, 2009)

TAPEC's are a bit too new so it's unlikely anyone will have that much experience outside R&D.

The big advantage over Peltier effect devices seems to be that they do not rely on a temperature difference between two junctions.

In the mean time, so long as you can arrange a cold junction, Peltier effect devices might be a reasonable alternative. Quite good value too.

Si


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## weber (Apr 22, 2009)

I've never heard of Thermal Acoustic Piezo Energy and have no idea what it is but I can tell you that any process or device that converts heat into electricity must work between two different temperatures and an upper limit on the efficiency of that conversion is given by the temperature difference between hot source and cold sink divided by the absolute temperature of the hot source. 
eff < (Th - Tc)/Th

This is Carnot's law (pronounced "car knows law"), one of several equivalent statements of the second law of thermodynamics. Known since at least 1824.

There is no way around it. It is a logical consequence of the fact that heat is the random motion of very large numbers of particles.

-- Dave Keenan


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## Big-Foot (Jun 8, 2008)

In my 8th grade science class (oh about a hundred years ago) - we studied the generation of electricity. I'll not forget the small coil of electric wire that we had hooked up to a galvanometer and passed a lit candle under the coil.. Current flow... Not a lot - but it was there...

And it's my curiosity of such things that has me intrigued and the very basis of why I'm here...


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## SimonRafferty (Apr 13, 2009)

weber said:


> I've never heard of Thermal Acoustic Piezo Energy and have no idea what it is but I can tell you that any process or device that converts heat into electricity must work between two different temperatures and an upper limit on the efficiency of that conversion is given by the temperature difference between hot source and cold sink divided by the absolute temperature of the hot source.
> eff < (Th - Tc)/Th


You are right - and I was wrong to say they do not rely on a temperature difference - of course they do. The difference between these and other previous devices appears to be the size of the difference required to get the thing to work at all. 

Agreed, you may not get as high a conversion efficiency as if the difference were greater - but if a given difference is all you've got, this at least gives you something!

I know there are things like Stirling engines that will work over small energy gradients - but these are potentially much easier to manufacture and have almost no moving parts (in the traditional sense).

There is a better explanation of them here: http://unews.utah.edu/p/?r=053007-1

Si


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## philrp (Mar 13, 2009)

SimonRafferty;
There is a better explanation of them here: [URL said:


> http://unews.utah.edu/p/?r=053007-1[/URL]
> 
> Si


Yes Si this is the item I was talking about, this report is about 2 years old and there was talk of a smaller device.

Unlike other technology it all about heat and appears not to need a cool side.

My though was that you could build some form of water chamber/rad with these device either attached to the case or better still installed inside the chamber extracting the heat thereby cooling the water and producing power at the same time. 

Assuming that you had a water cooled motor and controll you may find yourself producing a number of KW's of power.

The problem as always is finding the compontents and the cost of them.

any thoughts

Phil


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## weber (Apr 22, 2009)

philrp said:


> Unlike other technology it all about heat and appears not to need a cool side.
> 
> ... extracting the heat thereby cooling the water and producing power at the same time.


Phil, if you believe that, there's some prime swampland I'd like to sell you. 

The great and eloquent physicist Sir Arthur Eddington once wrote:

"If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations—then so much the worse for Maxwell's equations. If it is found to be contradicted by observation—well these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation."

But I expect I just wasted several minutes of my life trying to convince others not to waste theirs. 

-- Dave Keenan


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