Both huge projects will be located in San Luis Obispo County's California Valley, although they are not adjacent to each other. When complete, they are expected to hold the record for the world's largest set of grid-connected solar photovoltaic installations.
Once the solar farms are up and running, they will deliver enough energy to power 239,000 homes a year, nearly 12 times as much electricity as the largest such plant operating today.
Generating 250 megawatts of power, SunPower's California Valley Solar Ranch is the smaller of the two. It is expected to begin power delivery in 2010 and be fully operational in 2012, using high-efficiency crystalline photovoltaic panels that generate up to 50 percent more power than conventional crystalline cells.
The larger of the two projects at 550 megawatts, OptiSolar's Topaz Solar Farm will use its own proprietary thin-film solar cells manufactured in Hayward and Sacramento.
Located on the northwestern corner of the Carrisa Plains in California Valley, this solar farm is expected to begin delivering power in 2011 and be fully operational by 2013. Both projects are contingent upon the extension of the federal investment tax credit for renewable energy.
"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.
Utility-scale PV solar projects convert sunlight directly into electricity and produce the greatest amounts of power during the afternoons, when electricity demand is high, Keenan explained.
The contracts will bring the utility's renewable energy commitment to 24 percent of its portfolio. California requires that by the year 2010 utilities must provide 20 percent of their electricity from renewables - including wind, biomass and geothermal as well as solar power.
OptiSolar's Topaz Solar Farm is expected to deliver approximately 1.1 million megawatt-hours annually of renewable energy.
Randy Goldstein, chief executive officer of OptiSolar said the company is committed to working closely with the local community as the solar project is developed.
"Our solar farms are quiet and emission-free, with solar panels mounted near ground level to minimize visual impact. Implementing cost-competitive solar power on this scale establishes thin-film photovoltaic generation as an important contributor to global sustainability," Goldstein said.
The design of the project requires minimal grading and allows continual growth of vegetation in the rows between panels, preserving some wildlife habitat. OptiSolar is consulting with the California Department of Fish and Game and the U.S. Fish and Wildlife Service to find practical solutions for issues such as kit fox migration and protection.
The other contract is between PG&E and High Plains Ranch II, LLC, a subsidiary of the publicly traded SunPower Corporation.
SunPower's California Valley Solar Ranch is expected to deliver an average of 550,000 megawatt-hours of electricity annually.
The company will install its patented SunPower Tracker solar tracking systems at the site, which tilt toward the sun as it moves across the sky, increasing energy capture by up to 30 percent over fixed systems, while reducing land-use requirements.
"Today, high-efficiency photovoltaic technology is a competitively priced component of utility-scale peak power generation," said Tom Werner, chief executive officer of SunPower. "We design our solar systems to maximize energy harvest while adapting to the natural topography of the site and serving the needs of the community."
SunPower has constructed more than 350 megawatts of solar systems on three continents, including the largest ground-mounted solar power tracking system in the eastern half of the United States now under construction at the world headquarters of the pharmaceutical company Merck in New Jersey.
SunPower also built what is currently the largest solar installation in the United States, a 14 megawatt solar farm at Nellis Air Force Base in Arizona.
PG&E spokesperson Jennifer Zerwer says energy generated by the new solar farms will be connected to the grid via the Midway-Morro Bay transmission line, which still has unused capacity, subject to approval by the California Independent System Operator.
Over the past six years, PG&E has entered into purchase contracts for more than 3,600 megawatts of renewable power, including solar contracts that total more than 2,500 megawatts.