Key Terms

Geothermal Energy– Steam and hot water that is extracted from geothermal reservoirs. This can be used for geothermal heat pumps, water heating, and electricity generation.

Geothermal Plant- A plant with the main driver being a steam turbine. The turbine can be driven either by steam from hot water, or by steam from natural sources such as geysers.

Geothermal Heat Pump– A heat pump that uses the constant temperature of the earth as the heat source in the winter, and a heat sink in the summer instead of the outside air temperature.

Conventional Hydrothermal – the development of a geothermal resource where levels of geothermal reservoir temperature and reservoir flow capacity are naturally sufficient to produce electricity.

Binary – geothermal power conversion technology that operates in a closed-loop system and therefore maintains zero emissions. Highly efficient nationwide potential.

Flash – geothermal power conversion technology in which high-pressure and temperature geothermal fluids are segregated into steam and water in a separator. As a result, pressure decreases.

Dry Steam – geothermal power conversion technology in which steam is taken directly from a geothermal reservoir  and used to run turbines and a generator.

Enhanced Geothermal Systems (EGS) – the development of a geothermal system where hydraulic fracturing of the system can allow the production at a commercial level. EGS’s are engineered reservoirs created where there is geothermal energy but a lack of permeability. Fluid is injected into the earth‘s surface which causes pre-existing fractures to open again, creating permeability. Nationwide potential with engineered reservoirs 6-km to 8-km deep

Potential Capacity Additions (PCA) – the expected power plant’s estimated installed capacity.

Resource Capacity – the megawatt (MW) value of the total recoverable energy of a the subsurface geothermal resource.

Direct Use – use of geothermal heat with first converting it to electricity. Highest potential located in western United States, Alaska and Hawaii.

Closed-Loop System-A geothermal system where gases that rise from the well are injected back into the earth and are not exposed to the atmosphere.

Capacity Factor-The ratio of a power plant’s actual electrical output to the theoretical, maximum output of the plant for a given period of time.


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Matek, Benjamin, and Brian Schmidt. The Values of Geothermal Energy. Rep. Geothermal Energy Association and Geothermal Resources Council, Oct. 2013. Web. 14 Apr. 2014.

“Geothermal Glossary.” Geothermal Technologies Office. United States Department of Energy, 7 Oct. 2008. Web. 14 Apr. 2014.

“State Geological Surveys: Tapping Geothermal Energy in the 21st Century.” The Arizona Geological Survey. The Department of Energy Geothermal Technologies Program, n.d. Web. 14 Apr. 2014.

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Co-Authors: Kyle Brennan, Jessica Ross, Allison Scoular