California's big plans for solar power keep getting bigger.

Pacific Gas and Electric Co. and a young Oakland company on Wednesday signed what may be the world's largest solar deal, one that will create a string of seven solar power plants generating enough electricity for 530,000 homes.

BrightSource Energy of Oakland will build the plants in the Southern California desert and sell the power to PG&E for an undisclosed amount of money. Fields of mirrors at each plant will focus sunlight on centralized towers, boiling water within the towers, creating steam and turning turbines. The first plant could open in 2012 at the Ivanpah dry lake bed in San Bernardino County.

San Francisco's PG&E needs the juice.

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California law requires the state's electrical utilities to get 20 percent of their power from renewable sources by the end of 2010, although they have three more years to comply if necessary. PG&E has been frantically signing contracts with solar and wind companies, even agreeing to buy power from a startup that wants to build large solar arrays in space. But the credit crisis may kill or delay some of those projects.

Expanding the agreement

PG&E and BrightSource already have a history. Last year, PG&E agreed to buy as much as 900 megawatts from three solar power plants BrightSource planned to build. The deal announced Wednesday greatly expands that agreement, with PG&E potentially buying 1,310 megawatts.

"We are continuing to contract with a variety of renewable developers - that hasn't changed at all," said PG&E spokeswoman Jennifer Zerwer. "But we did decide to renegotiate with BrightSource because they have made strides with demonstrating their technology, moving forward with their (government) permits and getting financing."

Although one megawatt can power about 750 homes, the output from solar plants varies with the seasons and the time of day. So PG&E estimates that BrightSource's seven plants will be able to supply 530,000 homes.

For BrightSource, Wednesday's deal represents another coup.

Earlier this year, the 5-year-old company signed an agreement to supply 1,300 megawatts of electricity to Southern California Edison in what was then considered the world's largest solar deal. The new PG&E agreement just barely tops it.

Technology studied

At a time when some solar companies are collapsing - victims of the credit crisis - BrightSource has been able to demonstrate to the utilities that its technology works. The company built a demonstration facility in Israel that the utilities have extensively studied.

"PG&E looked hard at what we'd done," said John Woolard, BrightSource's chief executive officer. "They looked at the results from our plant in Israel, and that built a lot of confidence that we were meeting milestones and delivering. That's what we're proudest of."

Governor's blessing

Wednesday's deal was big enough to draw praise from Gov. Arnold Schwarzenegger, who has made renewable power a cornerstone of California's policies to fight global warming.

"By committing to increase the amount of solar power, this announcement serves as more evidence that reliable, renewable and pollution-free technology is here to stay, and sunshine will eventually power hundreds of thousands of homes and businesses across our Golden State," he said in a statement.