State utility regulators late Thursday approved a 20-year geothermal energy contract for Southern California Edison.

The California Public Utilities Commission approved the contract for SCE to purchase geothermal energy from a planned facility in Imperial County jointly operated by Ram Power Inc. and Orita Geothermal LLC.

Southern California Edison and the state’s two other investor-owned utilities – San Diego Gas & Electric and Pacific Gas & Electric – face a state mandate to obtain 20 percent of their power from renewable resources by the end of this year. As of the end of 2009, Edison was closest to that goal with 17.4 percent of its portfolio coming from renewable resources.

The Orita facility is expected to come on line in 2013 with an expected initial capacity of 50 megawatts, which may be expanded to 100 megawatts.

The PUC also authorized Edison to execute two additional contracts with similar terms and conditions for future projects from Ram Power and Orita Geothermal.

Southern California Edison is a subsidiary of Rosemead-based Edison International.