Wiktionary
n. heat under the ground used to heat water and make steam to turn generator turbines and make electricity.
WordNet
n. energy derived from the heat in the interior of the earth
Wikipedia
Geothermal energy is thermal energy generated and stored in the Earth. Thermal energy is the energy that determines the temperature of matter. The geothermal energy of the Earth's crust originates from the original formation of the planet and from radioactive decay of materials (in currently uncertain but possibly roughly equal proportions). The geothermal gradient, which is the difference in temperature between the core of the planet and its surface, drives a continuous conduction of thermal energy in the form of heat from the core to the surface. The adjective geothermal originates from the Greek roots γη (ge), meaning earth, and θερμος (thermos), meaning hot.
Earth's internal heat is thermal energy generated from radioactive decay and continual heat loss from Earth's formation. Temperatures at the core–mantle boundary may reach over 4000 °C (7,200 °F). The high temperature and pressure in Earth's interior cause some rock to melt and solid mantle to behave plastically, resulting in portions of mantle convecting upward since it is lighter than the surrounding rock. Rock and water is heated in the crust, sometimes up to 370 °C (700 °F).
From hot springs, geothermal energy has been used for bathing since Paleolithic times and for space heating since ancient Roman times, but it is now better known for electricity generation. Worldwide, 11,700 megawatts (MW) of geothermal power is online in 2013. An additional 28 gigawatts of direct geothermal heating capacity is installed for district heating, space heating, spas, industrial processes, desalination and agricultural applications in 2010.
Geothermal power is cost-effective, reliable, sustainable, and environmentally friendly, but has historically been limited to areas near tectonic plate boundaries. Recent technological advances have dramatically expanded the range and size of viable resources, especially for applications such as home heating, opening a potential for widespread exploitation. Geothermal wells release greenhouse gases trapped deep within the earth, but these emissions are much lower per energy unit than those of fossil fuels. As a result, geothermal power has the potential to help mitigate global warming if widely deployed in place of fossil fuels.
The Earth's geothermal resources are theoretically more than adequate to supply humanity's energy needs, but only a very small fraction may be profitably exploited. Drilling and exploration for deep resources is very expensive. Forecasts for the future of geothermal power depend on assumptions about technology, energy prices, subsidies, and interest rates. Pilot programs like EWEB's customer opt in Green Power Program show that customers would be willing to pay a little more for a renewable energy source like geothermal. But as a result of government assisted research and industry experience, the cost of generating geothermal power has decreased by 25% over the past two decades. In 2001, geothermal energy costs between two and ten US cents per kWh.
Usage examples of "geothermal energy".
Moon Mary was packed with geothermal energy, easily extracted through steam wells.
Phil only came to suspect his device might be developed for weaponry instead of geothermal energy.
Maybe you can send out some of your kitchen staff, after you build them stoves, geothermal energy is available under every one of those home caverns.
The mines and the major industrial centers appeared to be deep underground, where the planets geothermal energy was easily tapped.
Pho Ph'eah orbits far from its star and receives little sunlight, but is warmed by active geothermal energy.
And the vast drowned ranges of volcanic rifts, oozing geothermal energy.
Atmosphere's so occluded radio reception's marginal at best, but I hear reports of concentrations of population in places like Iceland and Japan, where geothermal energy's been used longest.
There was too much talk about volcanic effects and not enough about geothermal energy.
Who could stand against the organization that had reduced government research spending on solar, wind, tidal, and geothermal energy to a placating trickle, so as to avoid competition with their own atomic and fossil-fuel consorda?