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nickjayr
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Join Date: Jan 2011
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Efficient Way to Harvest Electrical Energy From Heat?

03/09/2011 12:21 PM

I'm very interested on, how to convert heat energy(eg. in fire place) to electrical energy so that it can be used to charge a small battery like a cell phone battery. Is it possible? Because as i have learned heat transducers(eg. thermocouple) cannot produce enough power or current output. If there are other efficient methods be kind to inform me.Thanking in advance for sharing your knowledge :)
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lyn
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#1

Re: Efficient way to harvest electrical energy from heat?

03/09/2011 12:25 PM

Not my field. Check out the Seebeck effect, the Peltier effect, and the Thomson effect.
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nickjayr
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#4
In reply to #1

Re: Efficient way to harvest electrical energy from heat?

03/09/2011 1:04 PM

Thank you :)
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chrisg288
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#7
In reply to #1

Re: Efficient way to harvest electrical energy from heat?

03/09/2011 10:53 PM

and the steam effect.

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PWSlack
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#13
In reply to #7

Re: Efficient way to harvest electrical energy from heat?

03/11/2011 8:40 AM

...and the Stirling Engine effect too?

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tcmtech
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#2

Re: Efficient way to harvest electrical energy from heat?

03/09/2011 12:30 PM

Peltier cooling devices make fair small scale power sources when ran in reverse. Heat one side and keep the other side cool and you get solid state DC power generation.

Plus you can buy them fairly cheap and in countless sizes. The down side is that they have a roughly 350 degree F upper working temp limit and when producing power they put out about 10 -15% of their rated cooling power which means that a 100 watt peltier cooler will only produce around 10 - 15 watts of usable electrical power at best if the temperature difference is high enough.
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nickjayr
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#3
In reply to #2

Re: Efficient way to harvest electrical energy from heat?

03/09/2011 1:02 PM

Thank you very much for the quick response. Are there any other practical limitations when implementing a battery charging system with the above technology? I'm thinking of using few different kinds of sources(solar, heat, wind) to optimize the performance of the charger, which will be useful in a rural area. Any advice on this project is highly appreciated. Thank you :)
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tcmtech
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#5
In reply to #3

Re: Efficient way to harvest electrical energy from heat?

03/09/2011 1:47 PM

Just don't over heat them and try to keep the greatest possible temperature differential across them as you can for maximum output. After that its just a mater of regulating the output to work with what every battery you are trying to charge.

As I tell everyone else you can ask questions all day or you can go spend some money and buy a few them and learn things yourself.

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alba16384
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#8
In reply to #3

Re: Efficient way to harvest electrical energy from heat?

03/10/2011 4:26 AM

Put a diode in series with the Peltier device to make sure the battery does not discharge through the device if there is insufficient heat to provide a high enough voltage for charging!

Regards,

Tony Lee.

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nickjayr
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#9
In reply to #8

Re: Efficient way to harvest electrical energy from heat?

03/10/2011 5:29 AM

Thanks for sharing the Knowledge
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Winfield Hill
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#6

Re: Efficient Way to Harvest Electrical Energy From Heat?

03/09/2011 6:03 PM

Yes indeed. The Peltier effect tells us that a junction of dissimilar metals will have a voltage difference proportional to the temperature difference of the two sides. And, if a voltage difference is asserted, the two sides will attempt to create the temperature difference associated with that voltage.

A thermopile is a stack of Peltier, or thermoelectric, or thermocouple, junctions, where the series stack is intended to insure that larger voltages correspond to smaller temperature differences.

The picture shows five thermopile elements with their attached plus and minus leads.

Often used for small-scale refrigeration, etc., e.g., in a Colman camping cooler, these can be surprisingly effective. In this YouTube video (link) someone is using one to create instant ice.

They have also become popular for use in a recent technique, called energy harvesting. Here small temperature differences create small voltages across thermopile leads, and special electronics is used to step up the low voltages for use in charging batteries, etc.

Linear Technology is a leader in this field. The drawing shows a thermopile with a small transformer and an LTC3108 chip (link), creating energy stored in a supercapacitor at 5 volts, to power a microprocessor and a small RF datalink.

The trick inside the IC is for depletion-mode FETs to start operating with the small voltage and run as an oscillator with the transformer's primary. Then on the secondary a large enough voltage is created to run the rest of the ship. Once it gets going it can be very efficient.

Explore the LTC page for application notes and articles. They also have an LTC3109 chip, which has autopolarity sensing. In this case either side can be hotter than the other. An entire cottage industry has sprung up around these energy harvesting concepts and clever chips like these.

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nickjayr
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#10
In reply to #6

Re: Efficient Way to Harvest Electrical Energy From Heat?

03/10/2011 6:22 AM

Thank you very much for the detailed explanation. As i have learned Peltier elements have a temperature limitation where maximum is about 150'C. With this limitations do i have to consider when connecting where temperature difference of the two sides will be like, temperature from a gas cooker(250'C not sure exactly) & the other @ room temperature? Ratings such as voltage, current for specific temperature difference of a specific device will be very useful in this project if you can help me with. Any advice on this is highly appreciated. Thank you

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rhkramer
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#12
In reply to #6

Re: Efficient Way to Harvest Electrical Energy From Heat?

03/10/2011 2:39 PM

I'm going to give you a GA (I started this reply before I thought to do that).

I should warn you that I'm a certified, card-carrying smartass, so gauge my reply accordingly. ;-)

Re: And, if a voltage difference is asserted, the two sides will attempt to create the temperature difference associated with that voltage.

So, I thought, this is a true over-unity energy resource--I can just assert a voltage difference and get an actual temperature difference, which means real work was (or could) be done. So I asserted, and I berated, and I cajoled, but all to no avail. ;-)
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nickjayr
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#11

Re: Efficient Way to Harvest Electrical Energy From Heat?

03/10/2011 6:25 AM

Thank you for the support
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Users who posted comments:

alba16384 (1); chrisg288 (1); lyn (1); nickjayr (5); PWSlack (1); rhkramer (1); tcmtech (2); Winfield Hill (1)

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