The next time you fly into Los Angeles International Airport, get a window seat, look down at the vast ocean of warehouses. There’s a black and grey sea of rooftops, just sitting there, burning in the sun. These warehouses are now beginning to provide more than just storage space in southern California. In a few months, islands of shiny black photovoltaic panels will be added to those bare rooftops. It’s part of Southern California Edison’s (SCE’s) warehouse rooftop project, which will install 250 megawatts (MWs) of photovoltaics on warehouses by 2015 (enough to power about 162,000 homes).

The project, when completed, will likely be the largest photovoltaic installation in the U.S. and maybe even the world. As of June 2010, the largest installed photovoltaic plant is Parque Fotovoltaico Olmedilla de Alarcón, a 60 MW installation in Olmedilla, Spain. The park produces enough to power 40,000 homes or about 87.5 gigawatt hours a year. Utilities in other states, like Arizona, New Jersey and New Mexico and other countries are also now planning or developing huge installations like this warehouse project in California.

One of the great things about the warehouse installations is the speed at which they are brought online. The first SCE installation was completed in a total of 4 months to complete, according to SCE spokesperson Gil Alexander. It took 2 months to get all the permitting together and 2 more months to complete the project and get it tied into the grid, allowing the power to be used locally, where it’s needed. The company plans to install 50 MW of solar this year and each following year, Alexander said. It already has completed two warehouse rooftop installations in Fontana and Chino, CA, providing a combined 3 MW of power with First Solar thin-film photovoltaic panels.

SCE also is offering long-term contracts to independent solar power providers for another 250 MW of photovoltaic installations. Altogether, the two initiatives will allow the company to generate 500 MW of electricity from photovoltaics. SCE is undertaking these efforts to meet California’s renewable energy standard mandate, under which utilities must generate 33% of their power from renewable resources by 2020.

The company says it will install large-scale photovoltaics at more than 100 sites over the next five years, spanning between 1.5 and 2 square miles of warehouse rooftops. SCE approaches building owners who would not be thinking about installing solar themselves and offers them the additional revenue option, Alexander explained. He said the company is leasing rooftops for about $20,000 a year per installed megawatt, and adds that the agreements are designed much like those for leasing space for a traditional power plant.

SCE announced on Mar. 10 that it chose SunPower to provide 200 MW of its T5 Solar Roof Tiles for its project. The tiles have monocrystalline silicon photovoltaic panels that are 18.4% efficient (the average solar panel is about 14% efficient as of 2010). The units are interlocking and combine the panel, its frame, and the mounting system into a single unit. This allows for quick installation with minimal additional weight on a rooftop. The large SunPower order, the lightweight panels and frames, will reduce the cost of the photovoltaic panels to roughly $3.5 per installed watt (prices  can be as high $7 per installed watt otherwise).

Eight days after announcing its contract with SunPower, SCE announced its third warehouse rooftop installation, a 1 MW installation in Rialto, CA, on the roof of a 436,000-square-foot warehouse. Alexander said that construction on this project is ongoing as of June 2010, but it is expected to come online this summer between July and September to help meet peak demand needs of customers in the region. .