Most of the energy used by people today comes from these fossil fuels. But fossil fuels are limited in their supply, can pollute and are sometimes hard to find. The following energy sources not require the sun. They are derived from other aspects of the earth's ecosystem. Water is not an energy source, but water is used to generate energy.
Water falling downhill is used to run turbines, which generate electricity.
This is called hydroelectric power. About 5 percent of the world's power is now produced by hydroelectric dams. A similar type of energy comes from geothermal energy. Pockets of boiling water under the earth's surface send steam to the surface of the earth. This hot water also can be used to generate electricity.