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back pressure: a devise with controls the pressure of steam commonly found in direct heating units with large volumes of lower pressure steam.
closed system: a type of geothermal generator where the geothermal fluids do not come into contact with the turbines.
condensing exhausts: equipment that condenses turbine exhaust steam into condensate.
continental crust: the relatively thick crust (> 50 km) that underlies the continents composed of less dense silicate minerals.
dry steam: steam in geothermal systems that does not contain water vapor.
fossil fuels: fuel derived from material formed from fossil organic matter and stored in the deep Earth for a long period of geologic time.
geothermal energy: energy derived from hot rocks and/or fluid beneath Earth's surface.
geothermal gradient: the rate of temperature increase in the Earth as a function of depth.
heat exchangers: a devise in a flash steam geothermal plant where geothermal fluids cause a secondary fluid to flash to vapor, which then drives the turbines and subsequently, the generators.
Gigawatt (GW): an electrical unit of power that is equal to 1000 megawatts or one billion watts.
ground source heat pumps: a geothermal system that uses the earth's ability to store heat at a relatively constant temperature as a source for heating and cooling.
hot dry rock: subsurface geologic formations of very high heat content that are found a few kilometers below the ground.
isotopes: variants of an element where the number of neutrons differs in the nuclei of atoms.
Kilowatt (kW): a unit of electrical power that is equal to 1,000 watts.
Kilowatt-Hour (kWh): the amount of energy transferred at a constant rate of 1 kilowatt for 1 hour.
load: the simultaneous demand of all customers required at any specified point in an electric power system.
magmatic intrusions: molten rocks that are injected into the crust from below.
Megawatt (MW): one megawatt is equal to 1000 kilowatts or one million watts.
oceanic crust: the crust that underlies the ocean floor (10-16 km thick) made from dense silicate minerals.
permeable: rocks through which fluids can pass because of interconnected pores and fractures.
petroleum: generic name for hydrocarbons, including crude oil, natural gas and their products, contained in sedimentary rocks.
porous rocks: rocks that contain spaces between their grains or particles, e.g. sandstone.
radioactive decay: the process by which the nucleus of an unstable atom loses particles.
reservoir: a store of hot rocks in geothermal systems and may contain water.
space cooling: the use of geothermal in summer to exhaust heat in buildings into the relatively cooler ground.
superheated steam: steam which has a temperature greater than the boiling point of water.
vapor-dominated: a geothermal reservoir system in which subsurface pressures are controlled by vapor rather than by liquid.
wet steam: steam in geothermal systems that contains water vapor.