Current Methods of Geothermal Power Generation
Geothermal energy takes heat from the earth’s molten core and converts it into electricity or for use in heating. Vast quantities of geothermal heat exist within subsurface rock and underground reservoirs of water. Ninety percent of geothermal energy exists in hot dry rock. Because of the near limitless ability of the earth to produce geothermal heat, and the continuous transfer of heat into subsurface rock and underground water, geothermal energy is considered to be a renewable energy resource. Geothermal resources have been harnessed as an energy source since the dawn of civilization, when natural hot springs were first used for cooking and bathing. Geothermal heat currently used to generate electricity can reside as deep as 10,000 feet below the earth’s surface. Because of the need for extensive drilling, destructive pressures, heat loss and the caustic nature of superheated water, capital costs for the construction of geothermal power plants with current technology have historically been much higher than for large coal-fired plants or new natural gas turbine technologies.
Current geothermal electricity generation technologies consist of Dry, Flash or Binary systems. Dry Geothermal is very rare and requires a source of highly pressurized underground steam, which is used to directly drive a power generation turbine. Limited to natural sources of high temperature water, Flash Geothermal pipes liquid water of 300°F to 700°F from a highly pressurized natural underground reservoir directly into a geothermal power generation facility. When this superheated water is released at surface pressure it flashes into steam driving a turbine generator. With the Binary Geothermal system (depicted below), underground reservoir waters of between 250°F to 300°F are used to heat a second (binary) fluid, which is used to drive electric power generation systems.