How does geothermal energy work?

Earth’s interior is hot, partly from heat left over from its formation and partly from the decay of radioactive elements. In volcanic regions, groundwater is heated by hot rock and can be reached by drilling wells a few kilometres deep. Dry steam plants use steam directly, flash plants let very hot pressurised water turn to steam, and binary plants use hot water to boil a second fluid. The steam drives turbines connected to generators, and the cooled water is often pumped back underground. Iceland generates about a quarter of its electricity from geothermal and heats around 90 percent of its homes with it.