The developer, EnergySource, already has a power purchase agreement for a second plant in the southern California area.

"With this team and so much available capacity in this resource, we have a development pipeline of new geothermal projects for the coming decade that will help California and Southwestern utilities meet their state-mandated renewable energy requirements,” says chief executive Dave Watson.

The $400m Hudson Ranch 1, under construction since May 2010, draws on what EnergySource describes as "one of the largest and highest temperature geothermal resources in North America", with an "extremely permeable liquid dominated resource".