Four energy companies have emerged from a group of 11 competing to become the main electricity supplier to Sonoma County’s planned public power agency.

Sonoma County supervisors Tuesday approved Calpine’s $700 million plan to build two new power plants at The Geysers geothermal field. It is the most expensive construction project since Lake Sonoma was built 30 years ago. “This will be a long-term benefit for Sonoma County,” Supervisor Mike McGuire said.

Sonoma County’s open space district and associated owners will get $7.9 million as part of a settlement of a lawsuit against Calpine Corp. over damage to lands in the 2004 Geysers Fire.