Thermoelectric Generator

 Thermoelectric Generator or a Seebeck generator works via a heat transfer though a material to convert 'heat' into electricity.

A thermoelectric generator also known as a TEG, is a solid state device that converts heat flux (temperature differences) directly into electrical energy through a phenomenon called the Seebeck or Peltier effect which is a form of thermoelectric effect. this type of generator is being used by NASA and the Martian Rovers to power without the uses of solar panels, because of how inefficient they are!