The Pacific Gas and Electric Co. announced new contracts Thursday to buy 800 megawatts of power from two solar-power plants to be built by OptiSolar and SunPower.

OptiSolar plans to build a 550-megawatt plant using thin-film solar panels while SunPower plans to construct a 250-megawatt plant using more common and efficient crystalline panels.

PG&E said the deals demonstrate the possibility of building large-scale power plants using solar panels. If they were built today, the plants would be the largest solar-panel projects in the world. 

The companies have declined to say how much the projects will cost, however.

Previous photovoltaic power-purchasing contracts signed by PG&E involved much smaller projects.

To buy power from large-scale power plants, PG&E has generally turned to companies that develop solar-thermal technology. Unlike solar panels, solar-thermal technology uses the sun's heat instead of its light to generate electricity.

Solar-thermal proponents say the technology allows power plant developers to build large-scale, or utility-scale, projects that cost less per kilowatt-hour than those built with solar panels

In April, BrightSource said it would build a 900-megawatt solar-thermal plant and sell the electricity to PG&E. The utility also inked a 177-megawatt power-purchase agreement with Ausra last November (see Ausra to Build 177-Megawatt Solar-Thermal Plant and California to Get More Solar-Thermal).

"These landmark agreements signal the arrival of utility-scale PV solar power that may be cost-competitive with solar thermal and wind energy," said Jack Keenan, chief operating officer and senior vice president for PG&E, in a statement.

The 250-megawatt project marks the first-ever deal between PG&E and San Jose, Calif.-based SunPower, which only last month called a 25-megawatt power plant it is developing for Florida Power & Light as the largest photovoltaic power plant in the country (see SunPower to Build 35MW Plants in Florida).

SunPower refers to its new project with PG&E as a utility-scale development, which the company defines as a plant capable of producing 50 megawatts of electricity or more. Other companies have set the floor lower.

SunPower, through its subsidiary High Plains Ranch II, plans to build the project on 2,200 acres of land in California's San Luis Obispo County. The construction date hasn't been set yet, said Julie Blunden, vice president for public policy and corporate communications at the company.

The company is scheduled to begin delivering electricity in 2010, although the plant is expected to come online fully in 2012. Blunden said SunPower can install 1 megawatt worth of panels a day, so meeting the delivery schedule won't be difficult.

OptiSolar also plans to build its 550-megawatt project in San Luis Obispo County through its subsidiary, Topaz Solar Farms. OptiSolar, based in Hayward, Calif., first announced the project in April but didn't name the power purchaser (see Can OptiSolar Make Thin-Film Dreams Real?).

According to a Greentech Media Venture Power Report released Thursday, OptiSolar raised an unconfirmed $132 million in the second quarter. MoneyTree also reported the round last month (see Earth2Tech posts here and here).

The company plans to begin construction in 2010. The power plant is scheduled to begin producing electricity in 2011 and coming online fully by 2013.

The two projects are tied to the fate of a set of expiring federal investment tax credits. Congress has repeatedly failed to extend the tax credits, which can offset 30 percent of a project's cost. The solar industry has lobbied for a one-year extension if Congress isn't able to extend the existing, multi-year tax credit (see Senate Rejects Renewable Tax Credits Bill and No Tax Credit, No Solar Power).

"We sure would like to see the [tax credits] delivered as soon as possible. The uncertainty is having an impact across the solar spectrum, especially in the commercial sector," said Blunden. She declined to say whether there is a deadline for when the tax credits must be in place in order for the project to move forward.

"Depending on the timing – there are a bunch of dynamics that I can divulge because those are details in the contract," she said.