It is possible to use the heat of under the earth in volcanic regions. Cold water is pumped into earth and comes out as steam. Steam can be used for heating or to power turbines creating electricity. Potentially infinite energy supply. Is used successfully in some countries, such as New Zealand. Can be expensive to set up. Only works in areas of volcanic activity. Geothermal activity might calm down, leaving power station redundant. Dangerous underground gasses have to be disposed of carefully.