Germany automakers Volkswagen and BMW have developed thermoelectric generators (TEG) that recover waste heat from a combustion engine.
According to a report by Prof. Rowe of the University of Wales in the International Thermoelectric Society, Volkswagen claims 600W output from the TEG under highway driving condition. The TEG-produced electricity meets around 30% of the car's electrical requirements, resulting in a reduced mechanical load (alternator) and a reduction in fuel consumption of more than 5%.
BMW and DLR (German Aerospace) have also developed an exhaust powered thermoelectric generator that achieves 200 W maximum and has been used successfully for more than 12,000-km road use.
I copied the above off the web. I wonder how much research on this subject has been done for cooling and heating houses. I have heard a company here builds TEG's as air conditioners. They can cool or heat 1500 BTU/hr which is about 1/20th of that needed for the average house using conventional cooling/heating systems.