Geothermal power plants

In geothermal power plants steam or hot water from geothermal reservoirs provides the energy that spins the turbine generators and produces electricity. The used geothermal water is then returned through an injection well into the reservoir to be reheated, to maintain pressure, and to sustain the reservoir.

There exist three basic technologies that are being used to convert thermal fluids to electricity. The type of conversion used depends on the state of the fluid (whether steam or liquid) and its temperature:

Dry Steam Power Plants

Power plants using dry steam systems are the oldest type of geothermal power plants. This system can be used with dry steam reservoirs, which produce steam but no or very little water. It is the most efficient type of plant, but it can only be used with the highest quality steam, as the steam is not separated.

The steam, which flows through the turbine to produce electricity in the generator, is supplied directly from the production well. After passing through the turbine, the steam condenses and is returned to the underground reservoir through the injection well to be reheated, so the process is repeated forming a cycle.

The technology was first used at Larderello in Italy in 1904. Dry steam reservoirs are rare, the largest one in the world, the Geysers, being located in northern California.