From NPR:
A Lot Of Heat Is Wasted, So Why Not Convert It Into Power?
"One factor working in Scullin's favor: There's plenty of waste heat out there to be harvested. "We waste heat because of the laws of thermodynamics," he says.
Those laws state that it's impossible to use the energy in fuel to power a car or generate electricity without some of that energy going to waste.
"Thermoelectrics haven't attracted much attention in the alternative-energy world, but Scullin seems to be drawn to areas others have overlooked."