Lake County geothermal plant Bottle Rock sold to Seattle energy company

A Seattle energy company has purchased a 55-megawatt power facility in The Geysers geothermal field in Lake County.

AltaRock Energy announced last week that its clean energy subsidiary, Baseload Clean Energy Partners, purchased Bottle Rock Power LLC and taken ownership of the geothermal operation from Riverstone Holdings and U.S. Renewables Group for an undisclosed price.

U.S. Renewables had purchased the then-shuttered facility in 2001 from the state for a reported $1.8 million. U.S. Renewables sold 50 percent of its holding in the company to Riverstone in 2006, according to its website.

Bottle Rock is located on 350 acres in The Geysers, which straddles Lake and Sonoma counties and is the world’s largest geothermal field. The largest operator in the area is Houston-based Calpine Corp.

The Cobb-area Bottle Rock facility was constructed by the California Department of Water Resources in 1985. But it failed to live up to the state’s energy production goals and was shut in 1990, according to the California Energy Commission. It was producing only 12 megawatts at the time. Calpine’s Geysers facilities by contrast, have been producing about 540 megawatts and have an operating capacity of 725. Bottle Rock resumed operations in October 2007.

It is being renovated and new wells are being drilled with the intention of operating the facility at its licensed 55 megawatt capacity, the energy commission reported.