Water is pumped underground where it is heated by the earth's heat, producing steam that spins turbines at the surface to generate electricity. Geothermal power plants have an average cost of $10.5 million to build but produce electricity at a cost of 4.5 to 7.3 cents per kilowatt-hour while releasing less than 1% of the carbon emissions of fossil fuel plants. However, geothermal energy is not widely used and building new plants takes a long time.