NEW YORK (Reuters) - Utility Southern California Edison said on Thursday it would spend $875 million to build a network of 250 megawatts of photovoltaic solar power generation, making it the biggest solar cell project in the nation.

SCE, a subsidiary of Edison International, said the photovoltaic cells on 65 million square feet of rooftops in southern California would generate enough power to serve 162,000 homes.

The project, which was submitted to state regulators for approval, is an effort to meet the state’s mandate that 20 percent of California’s electricity be generated from renewable sources by 2010.

Utilities and power companies are increasing their portfolios of renewable energy to meet ever-increasing state demands to help reduce their output of carbon, the greenhouse gas blamed for contributing to rising global temperatures.

At 250 megawatts, the installation would be about half the size of the newest coal or natural gas-fired power generation units.

So far, companies behind the largest solar projects have favored solar thermal technology, in which parabolic mirrors are used to concentrate sunlight to heat a liquid that drives a power-generating turbine.

Photovoltaic technology converts sunlight directly into electricity inside the solar cells.

On Wednesday, FPL Group Inc, the nation’s largest generator of wind and solar power, announced it planned to build a 250-megawatt thermal solar plant in California’s Mojave Desert.

SCE said its new photovoltaic project was possible because recent advances had cut in half the traditional cost of installed solar generation in California.

The utility plans to begin installing the solar arrays immediately on to the rooftops of commercial buildings in southern California’s Inland Empire, San Bernardino and Riverside counties.

“These new solar stations, which we will be installing at a rate of one megawatt a week, will provide a new source of clean energy directly in the fast-growing regions where we need it most,” Edison International Chairman and Chief Executive John Bryson said in a statement.