ABSTRACT
Approximately 4000 miles below the Earth’s surface is the core, where temperatures can reach 9000°F. This heat-geothermal energy (geo meaning “earth” and thermos meaning “heat”)—flows outward from the core, heating the surrounding area, which can form underground reservoirs of hot water and steam. These reservoirs can be tapped for a variety of uses, such as to generate electricity or heat buildings. The geothermal energy potential in the uppermost 6 miles of the Earth’s crust amounts to 50,000 times the energy of all oil and gas resources in the world. In the United States, most geothermal reservoirs are located in the western states, Alaska, and Hawaii; however, geothermal heat pumps (GHPs), which take advantage of the shallow ground’s stable temperature for heating and cooling buildings, can be used almost anywhere. Again, it is important to point out that there is nothing new about renewable energy. From solar power to burning biomass (wood) in caves and elsewhere, humans have taken advantage of renewable resources from time immemorial. Hot springs have been used for bathing since Paleolithic times or earlier (USDOE, 2010), and the early Romans used hot springs to supply public baths and for underfloor heating systems. The world’s oldest geothermal district heating system has been operating in France since the 14th century (Lund, 2007). The history of geothermal energy use in the United States is interesting and lengthy; following is a brief chronology of major geothermal events in this country (EERE, 2006).
