Yesterday, Southern California Edison (SCE) said it reached an agreement to purchase 250 megawatts (MW) of First Solar’s (Nasdaq: FSLR) Silver State South solar farm in Primm, Nev. With this buy, SCE now has 771 MW of First Solar’s projects under contract.

This 2,500-acre, ground-mounted project will interconnect with SCE’s proposed Eldorado-Ivanpah 220-kilovolt transmission line. The project should start producing electricity as early as 2014 and be fully operational by May 2017.

The announcement is the latest in a series of large-scale solar contracts that the Edison International (NYSE: EIX) subsidiary has made as it adds in more renewable generation to meet California’s renewable energy portfolio. Recently, it also announced plans to buy a combined 831 MWs of solar electric generation from SunPower, Corp. (Nasdaq:SPWRB) and Fotowatio Renewable Ventures, Inc.

California’s standard requires utilities to purchase 33 percent of their power from renewable sources by 2020.

“Right now we’re at 19 percent or higher in 2010, with about 14 billion kilowatt hours [of renewable energy produced],” said Mike Marelli SCE’s director of contracts for the renewable and alternative power. “We have a lot of projects coming online here in a couple of years.”

Among those, he said, are two large-scale solar farms being built by First Solar, comprising 550 MW of generation. The company will buy 250 MW of First Solar’s 550-MW Desert Sunlight project and 300 MW of First Solar’s Stateline project.

SCE is procuring new renewable-energy projects on a “high-needs scenario,” Marelli said. He explained that SCE is prepared for some projects to fail before completion for a variety of reasons.

According to Marelli, the development side of such projects can be more difficult than the utility side of the contract.

“It’s kind of a benefit of contracted project,” he said. “We have an easier job of just doing the contract and buying the power out of it.”

But First Solar, Marelli said, “Has proven they have the ability to [develop projects] at least in the 20-megawatt range.”

SCE previously bought the 21-MW Blythe photovoltaic farm, developed by First Solar. Marelli said he thought the project went online within the promised timeline.

“Actually,” he said, “I think they were a little ahead of schedule.”

Building enormous-scale solar farms shouldn’t be too difficult for First Solar.

“It’s not like redesigning a whole new process. It’s more like refining and optimizing an existing process,” he said.

And First Solar’s been building ever larger plants as it refines that process.

The company recently completed one of the largest solar farms in the world, the 80-megawatt Sarnia, Ontario, solar farm in Canada, which it delivered ahead of schedule.

Image courtesy of First Solar.