GC: n

CT: Geothermal energy is the heat from the Earth. It’s clean and sustainable. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth’s surface, and down even deeper to the extremely high temperatures of molten rock called magma.
Almost everywhere, the shallow ground or upper 10 feet of the Earth’s surface maintains a nearly constant temperature between 50° and 60°F (10° and 16°C). Geothermal heat pumps can tap into this resource to heat and cool buildings. A geothermal heat pump system consists of a heat pump, an air delivery system (ductwork), and a heat exchanger-a system of pipes buried in the shallow ground near the building. In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger. The heat removed from the indoor air during the summer can also be used to provide a free source of hot water.

S: http://www.renewableenergyworld.com/rea/tech/geothermal-energy (last access: 11 February 2015)

N: 1. geothermal (adj): 1875, from geo– (word-forming element meaning “earth,” ultimately from Greek geo-, comb. form of ge “earth”) + thermal (1756, “having to do with hot springs,” from French thermal (Buffon), from Greek therme “heat, feverish heat,” from PIE gwher- “to heat, warm” -cognates: Latin fornax “an oven, kiln,” formus “warm,” Old English wearm-. Sense of “having to do with heat” is first recorded 1837. The noun meaning “rising current of relatively warm air” is recorded from 1933).
energy (n): 1590s, “force of expression,” from Middle French énergie (16c.), from Late Latin energia, from Greek energeia “activity, action, operation,” from energos “active, working,” from en “at” + ergon “work, that which is wrought; business; action”.
Used by Aristotle with a sense of “actuality, reality, existence” (opposed to “potential”) but this was misunderstood in Late Latin and afterward as “force of expression,” as the power which calls up realistic mental pictures. Broader meaning of “power” in English is first recorded 1660s. Scientific use is from 1807. Energy crisis first attested 1970.
2. Geothermal Energy is heat (thermal) derived from the earth (geo). It is the thermal energy contained in the rock and fluid (that fills the fractures and pores within the rock) in the earth’s crust.
Calculations show that the earth, originating from a completely molten state, would have cooled and become completely solid many thousands of years ago without an energy input in addition to that of the sun. It is believed that the ultimate source of geothermal energy is radioactive decay occurring deep within the earth (Burkland, 1973).
3. Old-fashioned term: red coal (the heat from the Earth).

S: 1. OED – http://www.etymonline.com/index.php?allowed_in_frame=0&search=geothermal+energy&searchmode=none (last access: 12 February 2015). 2. http://www.geothermal.org/what.html (last access: 12 February 2015). 3. OG – https://bit.ly/2LrA1Pb (last access: 19 December 2018).

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CR: cavitation, geothermal deposit, geothermal power station, geothermal gradient, geothermics.