Unlike some renewable resources, geothermal power has the ability to be dispatched, meaning that it can be available when needed and can quickly adjust its output to match customer demand.
The power source for geothermal generation is unlimited and comes from the Earth itself. Naturally occurring steam fields below the surface of the earth have been producing power at this location since the early 1960’s. Today, there are currently 18 geothermal plants operating in the area producing 835 megawatts of electricity.
The process of turning steam into electricity begins with molten rock or magma that exists deep within the earth where temperatures are extremely high. At The Geysers location, this molten rock is believed to exist at a relatively shallow depth, approximately four miles below ground. The heat from the magma radiates to the layers of rock above, heating water trapped in the pores and voids of the hot rock. At some locations, a portion of the heated water created by exposure to this extreme heat source may rise to the surface creating hot springs or geysers. At The Geysers, an overlying layer of tight, unfractured rock traps the boiling water below ground.
To harness the power trapped in the boiling water, pressurized steam flows from wells through pipelines to the power plant. The steam is routed to a turbine where it enters at 40-100 pounds per square inch. As the steam expands through the turbine, it causes the turbine to spin which in turn spins a generator and creates electricity.
Once the steam leaves the turbine, it’s cleaned using a gas removal system and hydrogen sulfide abatement before it’s turned back to water or, vented to the atmosphere.
Recharging the Geysers
Today, the Geysers Reservoir continues to be recharged by injecting approximately 20 million gallons a day of treated waste water producing additional electricity. The waste water is pumped up to 50 miles from its source at the Lake County Sanitation Water Treatment Facility and added to the steam field. Injecting treated water into the steam field protects local waterways and produces power without releasing greenhouse gasses into the air.
In addition to the treated waste water, water recaptured by condensing the steam is also reused by injecting it into the reservoir.
The Geysers is one of only two locations in the world where high temperature dry steam exists that can be directly used to move turbines in order to generate electricity.
For more information about The Geysers Steam Field, click here.