1. What is Geothermal?
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. These resources can be classified as low temperature (less than 90°C or 194°F), moderate temperature (90°C - 150°C or 194 - 302°F), and high temperature (greater than 150°C or 302°F). The highest temperature resources are generally used for electric power generation. Low and moderate temperature resources can be used for two applications: direct use heat and ground-source heat pumps.
2. What are the Technologies & Applications?
Geothermal Electricity Production - Geothermal power plants use steam produced from reservoirs of hot water found two or more miles below the Earth's surface. There are three types of geothermal power plants: dry steam, flash steam, and binary cycle.
Direct use involves using geothermal resource at temperatures between 38°C (100°F) to 149°C (300°F). A well is drilled and the hot water is brought up through the well, and a mechanical system—piping, a heat exchanger, and controls—to deliver the heat directly for the heating of buildings, industrial processes, greenhouses, aquaculture (growing of fish) and resorts. Geothermal hot water can be used for many applications that require heat. Its current uses include heating buildings (either individually or whole towns), raising plants in greenhouses, drying crops, heating water at fish farms, and several industrial processes, such as pasteurizing milk. With some applications, researchers are exploring ways to effectively use the geothermal fluid for generating electricity as well.
Ground-source heat pumps use the earth or groundwater as a heat source in winter and a heat sink in summer. Using resource temperatures of 4°C (40°F) to 38°C (100°F), the heat pump, a device which moves heat from one place to another, transfers heat from the soil to the house in winter and from the house to the soil in summer. Accurate data is not available on the current number of these systems; however, the rate of installation is thought to be between 10,000 and 40,000.
Find out about more about geothermal technologies from the National Renewable Energy Laboratory Geothermal Technologies Program.
Sources of information: National Renewable Energy Laboratory Geothermal
i Energy Information Association. Geothermal for Electricity Generation. http://www.eia.doe.gov/oiaf/analysispaper/Geothermal/
ii Geothermal Task Force Report – Western Governors’ Association. http://www.westgov.org/wga/initiatives/cdeac/Geothermal-summary.pdf