Energy Form Possible SourcesThermal energy fireRadiant energy electric light bulbChemical energy living cellMechanical energy moving vehicleOther Forms of EnergySolar, elastic, electrical, wind,...
The sun. Or if you mean more specifically, in some cases the heat radiation from the sun is used to superheat something (water, salt) and that is used to create electricity.
Basically heat comes up from the core of the earth and heats the water in the crust. people drill or tap into these hot water ''pools'' and the pressure naturally pumps the water up. then the steam...