Geothermal Energy
Flash steam plants are the most common type of geothermal power generation plants in operation today. An example of an area using the flash steam operation is the CalEnergy Navy I flash geothermal power plant at the Coso geothermal field.
Binary Cycle
The water used in binary-cycle power plants is cooler than that of flash steam plants, from 107 to 182°C (225-360°F). The hot fluid from geothermal reservoirs is passed through a heat exchanger which transfers heat to a separate pipe containing fluids with a much lower boiling point. These fluids, usually Iso-butane or Iso-pentane, are vaporized to power the turbine. The advantage to binary-cycle power plants is their lower cost and increased efficiency. These plants also do not emit any excess gas and, because they use fluids with a lower boiling point than water, are able to utilize lower temperature reservoirs, which are much more common. Most geothermal power plants planned for construction are binary-cycle.
Enhanced Geothermal Systems
Enhanced Geothermal Systems (EGS), also known as Hot-dry-rock systems, involve pumping water into hot rocks in the earth, rather than harvesting hot water already in the earth. This type of geothermal system has many advantages over the others, as it can be used anywhere, not just in tectonically active regions. However, it requires deeper drilling than the other forms of geothermal energy harvesting.
