NRG Solar and Sunpower are to begin constructing a 250MW solar power plant in San Luis Obispo County, California.
The California Valley Solar Ranch solar power plant will be one of the largest photovoltaic solar power plants in the world when completed.
NRG Solar plans to invest up to $450m (£290m) in the project over the next four years, subject to final total project cost and negotiation of the financing terms and conditions.
Under an agreement between the two companies, NRG will assume all ownership and financing responsibilities, while Sunpower will design, build, operate and maintain the solar power plant.
Construction is expected to start in the second half of 2011; the plant will begin producing some power by the end of 2011, with the balance coming on line in 2012 and 2013.