Seite - 136 - in Water, Energy, and Environment - A Primer

for spaceheating sinceRoman times.Theseuses are still present and growing, and the first district heating system in the US, in Boise, Idaho in 1892, was powered by geothermal energy. In Iceland 90% of households are heated by geothermal energy. Other applications include desalination, agricultural drying and industrialheating, fora totalof about30 thermalgigawatts. 8.6.3.1 Geothermalpowergeneration In modern times geothermal energy is best known for its application to power generation, where its potential is huge. Today’s hydrogeothermal power plants tap geothermal heat in the formof dry steam issuing from the ground, or hotwater that can be flashed into steam, to drive a turbine generator. Geothermal heat can also be tapped to vaporize volatile liquids suchas isobutane,whichcan thenalsodrivea turbinegenerator. The U.S. currently leads the world in geothermal power generation (3567MW), followed by the Philippines (1868 MW), Indonesia (1450MW), andNewZealand (980MW) (see Figure 8.15). Figure8.15 Installedgeothermal capacity (GW)2017 (50). Water,Energy, andEnvironment–APrimer136