How Human-scale Thermoelectric Power Generation Works
If you're puzzled as to how your sweaty body could power an iPad on a warm summer day, think of it this way: Almost all the electricity that humans use -- about 10 trillion watts -- is generated by releasing heat energy (usually by burning fossil fuels to heat water) and then converting that heat into mechanical energy. Mechanical energy is then used to crank generators and produce electrical current. This tried-and-true method, called thermoelectric power generation, produces a lot of energy, to be sure. But it also wastes a lot of energy, because the mechanical process isn't that efficient at using heat. In fact, more than half of that heat simply escapes into the atmosphere [source: Jacques].
It would be a lot better, at least in theory, if we could find a practical way to generate electricity directly from heat itself. Scientists have long known that it's possible to do that, because when there's a difference in the temperature of the surroundings and that of an object, a conductive material between the two can use that contrast to generate electrical current, without any turbine or mechanical generator. This is known as the Seebeck effect [source: Timmer, Ozcanli].
The trick to generating and harvesting that non-mechanical electricity is to find the right conducting material. For a while, researchers have been building direct thermoelectric generators that use a metal alloy, bismuth antimony telluride, which has the ability to generate electricity from heat. But that material is expensive and it's not all that efficient [source: DOE].
That's why everyone is so excited about power felt, which -- despite its name -- isn't actually a cloth woven from wool, like the stuff they use on pool tables. Instead, power felt is made up of plastic fibers wrapped around tiny -- and by tiny we mean one atom in thickness -- structures called carbon nanotubes, which are really, really good at conducting electricity. It's also potentially cheap to manufacture, which means we could use it all over the place [source: Neal, Zhang].