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The idea may not be original, but it has an elegant obviousness: why not use some of the many industrial rooftops in the sprawling southern California megalopolis as sites for megawatt-level, solar-powered electricity-generating plants? The scale of the recently announced Southern California Edison (SCE) project, however, is unprecedented, dwarfing that of any comparable plans, such as Colexon Energy's deployment of First Solar and other PV modules on rooftops of chicken farms and other commercial structures in Germany.

The utility company plans to build 250-MW worth of these stations over the next five years, adding a megawatt of installed power each week (ed.--corrected from "month") on between 100 and 200 leased warehouse roofs, at a total cost of $875 million. Once it's completed, photovoltaic panels will cover nearly 65 million square feet, or two square miles' worth of rooftop real estate, and provide enough juice for about 162,000 homes.

Grid-connected solar utility installations of this magnitude usually use thermal or concentrator technologies to turns the sun's rays and heat into power, are mostly located in the desert or other sparsely inhabited areas, and require substations and miles of power lines to bring the juice back to where it's needed. For example, a day before the SCE announcement, FPL Energy aired its plans to start building a 250-MW solar power plant next year in the Mojave Desert of California, which will use rows of some 500,000 parabolic mirrors to concentrate the sun's energy to produce steam for turbine generators.



SCE's John Bryson on the roof where the first of many
megawatts of panels will be installed. (Photo courtesy SCE)

By contrast, the SCE project will employ hundreds of thousands of PV modules placed on top of commercial buildings that consume little electricity on their own, situated in population and energy-demand growth areas, as company spokesman Gil Alexander explained, where the installations can be connected "to the nearest power pole." One attractive aspect of the project: "the generating characteristics of solar PV coincide with consumption patterns of our customers," in terms of peak generation, especially during the hot California summers when the grid needs all the extra power it can get. Quipped Alexander: "We're designing a very peaky system."

What types of PV panels will be used has not been finalized. "We are looking closely at thin-film products, but not solely," according to Alexander. Since the modules will not include tracking systems and will lie flat on the rooftops, "we're looking for technologies with [conversion] efficiencies on either side of peak...with the capacity to capture less than peak [energy]. He added that "of the multiple types of panel product being analyzed, the characteristic we're looking closest at is weight," although any facility selected will be able to "carry this kind of increased load" on its rooftop.

Starting in August, the first 2.2 MW of modules will be installed on 607,000 square feet of leased rooftop on the Kaiser Distribution Park in Fontana, CA. The owner of the site, ProLogis, happens to be the "world's largest owner, manager, and developer of distribution facilities," and has much smaller rooftop solar installations on a handful of its buildings in France and Spain. Alexander told me that the multinational is one of many businesses seriously negotiating for placement of additional plants on more of the many properties that it owns and manages in Southern California.

How many modules are we talking about? Alexander said that SCE estimates about 10,000 modules per megawatt will be needed, which brings the total required over five years up to a whopping 2.5 million units--a massive, unprecedented product order. ""PV needs a boost, it's still costly," he explained. "We're hopeful that placing orders of this magnitude will reduce costs for everyone. There's lots of negotiations taking place on how to achieve the best price point for a project of this scale." He noted ongoing "intensive discussions with several module suppliers and installers."

SCE posits that it will achieve a cost per installed watt of $3.50, as much as half of the usual expense of installed PV, according to Alexander. The cost metric breaks down to 61 cents for labor, engineering, and installation costs, with the other $2.89 going for hardware, $2.54 of which will be spent on the module and system interconnect expenditures.

Alexander believes the project "could be a breakthrough" in the drive to make utility-scale PV more cost-effective, ubiquitous, and practical. These kind of decentralized, distributed power plants "could end up virtually anywhere it would make sense."

In the vast expanses of sunny southern California, where warehouse-saturated industrial zones sometimes stretch for miles, that's a whole lot of rooftop real estate ready to carry the load of many megawatts of solar-based renewable energy.