Work is set to begin in the new year on the 48-megawatt expansion of Sempra Generation’s 10-megawatt El Dorado site in Nevada with the approval last week of the Pacific Gas and Electric’s plan to purchase power the new facility.

The California Public Utilities Commission OK’d the PG&E contract to buy power from the Copper Mountain solar plant on Thursday.

PG&E already is purchasing power from El Dorado facility. California utilities are required to get 20 percent of their power from renewable energy resources in 2010 and that requirement increases to 33 percent in 2020.

The two solar power sites are located near Boulder City, Nevada, which is 40 miles southeast of Las Vegas.

Together, the combined installations will be largest operational photovoltaic solar-power facility in North America when the Copper Mountain expansion project is complete in late 2010, Sempra Generation says.

Almost 1 million photovoltaic panels will used at the combined sites.

Image of the El Dorado solar plant courtesy of Sempra Generation.