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Question on thermocouples?

I understand that thermocouples are extremely inefficient. I was wanting to build a solar trough, but instead of running a pipe containing a fluid for a heat exchanger, I wanted to directly have the ‘hot’ wire in the concentrated solar line, and have the ‘cold’ wire just outside with heat sinks on it. Would it be able to produce enough electricity to do anything, or should I stick with a stirling engine to power a generator?

Thermocouples can have very low resistance, so even though they generate only millivolts per thermocouple pair, they can produce reasonable currents. But it takes a lot of couples in series to generate more than a few volts. Remember that you can make electrical contact at the couples any way you like, but low resistance junctions waste less of your voltage as current passes through them. Silver soldering the junctions works well for iron and copper. Keep the wire lengths as short as you can manage between hot and cold areas, to minimize resistance that wastes voltage. Remember to use a heaver gauge for the iron because of its higher resistivity (both thermal and electrical). You might want to build a small pilot generator to get some idea whether or not it is practical to scale up with the materials you can get.

http://en.wikipedia.org/wiki/Thermocouple

The thermoelectric coolers made of semiconductor junctions can also act as a thermopile generator if you heat one side and cool the other.

http://en.wikipedia.org/wiki/Thermoelectric_cooling

Edit: Remember that it is not the joint between the two dissimilar metals that generated the voltage. The temperature change along each piece of metal generates voltage across the length of the metal, and this voltage is different (and possibly even different polarity) for different metals. It is the difference between the voltages generated in each of the metals, as they pass from one temperature to another, that is the thermocouple output. That is why it doesn’t matter if other metals (like silver solder) are involved in the electrical joint between them.

A piece of heavy gauge “J” thermocouple lead wire (lower, cheaper grade than measurement wire) is made up of iron and constantan, which produce a pretty good output per thermocouple compared to other commonly available wire materials.

http://www.electronics-cooling.com/2006/11/the-seebeck-coefficient/

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Regards,

John Popelish

Tub of Water Solar Heat Exchanger Experiment: Mar. 22, 2010

solar heat exchanger

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