What is geothermal energy, and what methods, application distributions, and performance potentials characterize its utilization in global energy systems?

Q: What is geothermal energy, and what methods, application distributions, and performance potentials characterize its utilization in global energy systems?   A: Geothermal energy refers to the thermal energy stored within the Earth's crust, harnessed through extraction of subsurface hot water or steam for both heating and electricity generation. Three primary conversion technologies drive its practical use: dry steam systems directly employ underground steam to rotate turbines; flash steam processes utilize high-pressure hot water that vaporizes upon pressure reduction to drive mechanical generators; and binary cycle systems transfer heat from geothermal fluids to a low-boiling-point working fluid (like isobutane), whose vapor expansion powers turbine systems.   Geographically, deployment spans approximately 25 nations, with leading producers including the United States, Indonesia, the Philippines, Turkey, and New Zealand. Iceland exemplifies intensive utilization, where 87% of buildings rely on geothermal sources for space heating and domestic hot water. Global installed capacity reached 15.6 gigawatts (GW) by 2020, with theoretical potential exceeding 2 terawatts (TW) based on accessible subsurface resources. Despite this promise, adoption faces geographical constraints—high-enthalpy resources concentrate in tectonically active regions—though low-temperature ground-source heat pumps enable decentralized applications in most climates, expanding its practical reach beyond traditional volcanic zones.