Power plants make electricity out of other forms of energy. Most electricity in the U.S. today comes from converting the heat energy released from burning fossil fuels--coal, natural gas and oil. The rest is generated from nuclear reactors and from renewable sources, such as sunlight, wind, falling water and geothermal heat (see Renewables, Unit 5).
In a typical power plant, a primary energy source like coal is burned to create heat, which is converted in a boiler to mechanical energy in the form of superheated, high-pressure steam. The steam is directed into a turbine, where it pushes on blades attached to a central shaft or rotor. The rapidly spinning rotor powers a generator.