Geothermal energy processes utilize the natural heat of the Earth for beneficial purposes when the heat is collected and transported to the surface. Geothermal power plants are compact with a small footprint, using less land per GWh than coal, wind, or solar photovoltaics with a center station. Geothermal energy conversion refers to the power-plant technology that converts the hot geothermal fluids into electric power. Geothermal power plants fall into one of three conversion categories: dry steam, flash steam, or binary cycle. Location-specific, dry-steam geothermal power plants take advantage of subterranean rocks that are so hot that the water vaporizes on its way up through the production well. The great potential for dramatically expanding the use of geothermal energy can be realized by using enhanced geothermal systems, also sometimes called engineered geothermal systems. Geothermal heat pumps, sometimes referred to as geoexchange, earth-coupled, ground-source, or water-source heat pumps, have been in use since the later 1940s.