- Docket Number
- 41 MW
- Sonoma County
- Steam Turbine
- Project Status
- Operational (Geothermal)
- Project Type
- Application for Certification
The Grant Geothermal Project (Unit 20) is in an unincorporated area of Sonoma County in the Geysers Known Geothermal Resource Area along the ridgeline of the Mayacamas Mountains with moderately steep terrain near the Lake County line, approximately 15 miles west of the town of Cobb. Unit 20, originally known as Pacific Gas & Electric Company’s (PG&E) Geysers Unit 20 Geothermal Project was certified by the California Energy Commission (CEC) in February 1983. Commercial operation began in October 1985.
Unit 20 was designed to provide 110-megawatts; however, due to reduced steam pressures, the plant currently (as of January 2021) supplies approximately 41-megawatts of baseload electricity to northern California's power grid. Unit 20’s major structures on the plant site are enclosed with a seven-foot security fence. These structures include a power cycle consisting of a turbine-generator and condensate and circulating water systems; a multiple cell mechanically induced crossflow cooling tower; a transmission switchyard, adjacent to the turbine generator building; and, a hydrogen sulfide (H2S) abatement system. Primary treatment will be through a Stretford system, in which H2S is scrubbed from the vent gas stream and catalytically oxidized to elemental sulfur.
In April 1999, the CEC granted a transfer of ownership of Grant Geothermal (Unit 20), the former PG&E Geysers Unit 20 Geothermal Project to Geysers Power Company, LLC, a wholly owned subsidiary of the Calpine Corporation.
Power Plant Certification and Exemption Processes
As required by the Warren-Alquist Act, the Energy Commission monitors Commission-certified energy projects throughout construction, operation, and closure to ensure compliance with the conditions of certification imposed by the Commission’s Final Decision for approving the projects.