Geothermal Dry Steam Power Plants

Many early geothermal projects, such as The Geysers dry steam power plant in Northern California, depend on high temperature steam formations to directly provide the energy to drive power generator turbines. This type of formation is called a "dry steam" power plant because the steam is released from the pressure of a deep reservoir, through a rock catcher, and then past the power generator turbines.

dry steam power plant animation

Dry steam reservoirs use the water in the earth's crust, which is heated by the mantle and released through vents in the form of steam. The dry steam power plant is suitable where the geothermal steam is not mixed with water. Production wells are drilled down to the aquifer and the superheated, pressurised steam (180°-350°C) is brought to the surface at high speeds, and passed through a steam turbine to generate electricity. In simple power plants, the low pressure steam output from the turbine is vented to the atmosphere, but more commonly, the steam is passed through a condenser to convert it to water. This improves the efficiency of the turbine and avoids the environmental problems caused from the direct release of steam into the atmosphere.

The waste water is then reinjected into the ground with reinjection wells.

The underground water reservoirs that feed such a system are refilled when rain falls on the land. The rainwater eventually soaks back into the crust of the earth. Because this occurs on a continuous basis, geothermal energy is considered a renewable resource.

This is the oldest type of geothermal power plant. It was first used at Lardarello in Italy where it has powered electric railroads for since 1904. About 6 percent of the energy used in northern California is produced at 28 dry steam reservoir plants found at The Geysers dry steam fields in northern California. At peak production, these dry steam geothermal power plants are the world's largest single source of geothermal power producing up to 2,000 megawatts of electricity an hour. That is about twice the amount of electricity a large nuclear power plant can produce. These dry steam power plants emit only excess steam and very minor amounts of gases.