GeoThermal Batteries

Never hear of this specifically, but makes sense.

A Novel Thermal Battery Promises Green Power Around the Clock

Japanese scientists have developed a thermal battery that converts heat into electricity when buried in a geothermal zone   In IEEE Spectrum By John Boyd

You can fry an egg on the ground in Las Vegas in August, but try that in Iceland or Alaska and you'll just end up with the stuff on your face—unless you know how to tap into the Earth's vast reservoirs of geothermal energy. 

Researchers at the Tokyo Institute of Technology have developed a new kind of battery that can reliably generate electric power from heat in environments with temperatures ranging from 60 degrees C to 100 degrees C—which is low enough to mimic geothermal heat.

In an earlier experiment, the researchers developed sensitized thermal cells (STCs) that employed dye-sensitized solar cells to convert light into electric power. In their latest advance, team leader Sachiko Matsushita, an associate professor at Tokyo Tech, explained that they replaced the dye with a semiconductor to enable the cells to operate using heat instead of light.

Several methods for converting heat into electric power already exist, including redox batteries that employ the flow of hot and cold chemical liquids to create electricity, and thermoelectric batteries that use the Seebeck effect to generate electricity when a temperature gradient is applied along a conductor.

But Matsushita points out that whereas the STC battery can literally be buried in the ground and work as is, the other devices would face major physical and operational issues if required to operate in such a way.  .... "