SiliconBeat

eSolar, the Pasadena startup funded by Google.org, Idealab and Oak Investment Partners, signed an agreenment with NRG Energy today to build a series of solar-thermal power plants in California and the Southwest U.S. When finished, the companies said, the plants will produce 500 MW of power, or enough for 400,000 homes.

NRG said it had invested $10 million to “develop, build, own and operate” 11 eSolar power plants on three different sites. The company will turn and sell the power to local utilities it said, without naming them.

NRG, based in New Jersey, operates 40 power plants that generate 24,000 MW of electricity, but this is its first solar venture.

eSolar uses concentrating solar power (CSP), where mirrors track the sun and reflect its light to a tower where water is boiled to make steam. That steam power a turbine and generates electricity.

Google.org invested $10 million in eSolar and BrightSource Energy of Oakland, another solar-thermal company using a similar technology.

You can read more at eSolar’s Web site.

NRG was the company that made an unsolicited offer to buy Calpine, the San Jose and Houston based energy company in May 2008. The deal was rejected by Calpine’s board.