The Geothermal Power Plants of Lake County

One of the Geothermal Power Plants operated by Calpines. Photo from Calpines

Comprising of 45 square miles along the Lake and Sonoma County border is the world’s largest complex of geothermal power plants in the world. The Geysers is geothermal power energy derived from the heat of the earth’s core. So what is Geothermal: “Geo” means “from the earth” and “thermal” means “heat.” This type of energy is clean and predictable, offering a reliable and renewable energy source.

The Geysers is the World’s largest geothermal field, containing a complex of 22 geothermal power plants drawing steam from more than 350 wells, located in the Mayacamas Mountains which is a mountain range and is part of the Northern Inner Coast Ranges. The Mayacamas Mountains are located south of the Mendocino range, west of Clear Lake and the ranges’s highest point is Cobb Mountain at 4,724 feet in elevation.

Calpine, the largest geothermal power producer in the U.S., owns and operates 13 power plants at The Geysers.

HISTORY: Native American tribes built steam baths at the fumarole’s which is an opening in the planet’s crust which emits steam and gases such as carbon dioxide, sulfer dioxide, hydrogen chloride and hydrogen sulfide. The steam forms when superheated water condenses as its pressure drops when it emerges from the ground. When European Americans first entered the area in 1847, it was inhabited by 6 Indian tribes. 3 bands of Pomo people, 2 bands of Wappo people, and the Lake Miwok people.

The Geyser Resort Hotel
photograph taken by Andrew Price

It was later on when Archibald C. Godwin developed The Geysers into a spa named The Geyser Resort Hotel, which attracted tourists including Ulysses S. Grant, Theodore Roosevelt and Mark Twain. In the mid 1880’s the resort declined in popularity and the resort was rebranded to appeal to lower income people. The main building was destroyed in 1938 in a landslide although the bar and restaurant with small cabins and the swimming pool stayed open, despite another fire which happened in around March 1957.

The first power plant at the Geysers was privately developed by the owner of the Geysers Resort and opened in 1921, producing 250 kilowatts of energy to light the resort. Pacific Gas and Electric in 1960 began operation of their 11 megawatt geothermal electric plant at the Geysers. The original turbine lasted for more than 30 years. It was finally in 1980 when the Unocal Corporation dismantled the remains of the resort.

RECHARGING THE GEYSERS: By the latter part of the 1990’s the steam power extraction started depleting the Geysers steam field and production began to drop. 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.

The Geysers Reservoir is recharged by injecting 20 million gallons a day. This waste water is treated and pumped 50 miles from its source at the Lake County Sanitation water treatment facility and added to the steam field. This method of injection treated water into the steam field helps protect local waterways and produces power without releasing greenhouse gasses into the air. Plus the treated waste water is recaptured by condensing the steam and then reused by injecting it into the reservoir.

GEOCHEMISTRY: In 2005, abatement equipment was installed at two of the Geysers plants to reduce the amount of mercury released by the waste vapor even though the amount released was below the legal limit for such releases. The Geysers Air Monitoring Programs (GAMP) has shown limited releases of arsenic, but again below a significant level.

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