geothermal and fossil energy Geothermal energy uses the Earth’s internal heat and is a renewable energy source; fossil fuels such as coal and petroleum are nonrenewable energy sources.
nuclear energy Large quantity of energy that is released in the form of heat; this occurs during a nuclear reaction (fission of atom nuclei). The heat is used to produce electricity.
solar energy Harnessed solar radiation has many applications, including solar-panel heating and electricity produced with solar cells and solar furnaces.