Photos: Six unusual power sources

German scientists have produced thermo-generators (pictured) that use human body heat to generate power and could be used to run mobile devices in future.

The thermo-generators use the difference between the body's surface temperature and the surrounding temperature to produce electrical energy using semiconductor elements.

Currently it is "not realistic" to try to power a mobile phone using the thermo-generators, said Peter Spies, group manager at the Fraunhofer Institute for Integrated Circuits, because the energy from the human body is too low compared with ambient temperatures - so not enough power is produced.

However, Spies is hopeful the technology's efficiency will improve, making thermo-generators for mobile devices a future possibility.

Photo credit: Fraunhofer Institute