Electricity Generation

There are three different methods to convert geothermal heat into energy: dry steam systems, flash steam, and binary cycle.

Dry steam systems pump steam directly from underground sources to a power generation unit. Because there are only two known major U.S. sources of underground steam (Yellowstone National Park in Wyoming and the Geysers in Northern California) this method of electricity production is fairly uncommon. Currently there is only one dry steam plant, located at the Geysers in Northern California.

Flash steam power plants use reservoirs of hot water (>360°F) located beneath the earth’s surface. Wells are drilled to bring the hot water to the earth’s surface. The water is brought to the surface under pressure to keep it in liquid form. As the superheated water is released into the turbine area, it “flashes” to steam and expands, driving the turbine to generate power. Excess water is pumped back into the reservoir. This is the most popular method of geothermal power generation.

Binary Cycle power plants use two independent cycles or loops. One loop contains thermal water from a geothermal well. The other contains a working fluid with a lower boiling point than water. The thermal water heats the working fluid through a heat exchanger, causing it to convert to a vapor and driving the turbine. These plants can utilize thermal water in the 200-360°F range. Some applications have been successful with temperatures as low as 165°F.

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