Geothermal energy refers to heat that is found within the Earth. This heat can be used in a number of ways through geothermal energy systems. First, it can be used to directly heat buildings, where hot water near the earth’s surface is piped into buildings. Second, it can be used indirectly using ground source heat pumps, which transfer heat from the ground or hot water reservoirs into buildings in the winter, a process that is reversed in the summer to cool buildings. And finally, steam from hot water reservoirs can be used to generate electricity.