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An enhanced geothermal system (EGS) generates geothermal electricity without the need for natural convective hydrothermal resources. Until recently, geothermal power systems have exploited only resources where naturally occurring heat, water, and rock permeability are sufficient to allow energy extraction. However, by far most of geothermal energy within reach of conventional techniques is in dry and impermeable rock. EGS technologies enhance and/or create geothermal resources in this hot dry rock (HDR) through 'hydraulic stimulation'. When natural cracks and pores do not allow economic flow rates, the permeability can be enhanced by pumping high-pressure cold water down an injection well into the rock. The injection increases the fluid pressure in the naturally fractured rock, triggering shear events that enhance the system's permeability. As long as the injection pressure is maintained, a high matrix permeability is not required, nor are hydraulic fracturing proppants required to maintain the fractures in an open state. This process is termed hydro-shearing, perhaps to differentiate it from hydraulic tensile fracturing, used in the oil and gas industry, which can create new fractures through the rock in addition to expanding the existing fractures. Water travels through fractures in the rock, capturing the rock's heat until forced out of a second borehole as very hot water. The water's heat is converted into electricity using either a steam turbine or a binary power plant system.〔http://www1.eere.energy.gov/geothermal/egs_animation.html〕 All of the water, now cooled, is injected back into the ground to heat up again in a closed loop. EGS technologies, like hydrothermal, geothermal can function as baseload resources that produce power 24 hours a day, like a fossil fuel plant. Unlike hydrothermal, EGS may be feasible anywhere in the world, depending on the economic limits of drill depth. Good locations are over deep granite covered by a layer of insulating sediments that slow heat loss.〔(20 slide presentation inc geothermal maps of Australia )〕 EGS wells are expected to have a useful life of 20 to 30 years before the outflow temperature drops and the well becomes uneconomic. EGS systems are currently being developed and tested in France, Australia, Japan, Germany, the U.S. and Switzerland. The largest EGS project in the world is a 25-megawatt demonstration plant currently being developed in Cooper Basin, Australia. Cooper Basin has the potential to generate 5,000–10,000 MW. ==Research and development== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Enhanced geothermal system」の詳細全文を読む スポンサード リンク
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