Desert solar farms like the Ivanpah facility (above) need miles of transmission lines. Rooftop solar panels (below) don't.

PHOTO COURTESY OF BRIGHTSOURCE ENERGY, INC. AND LUMINALT

rebeccab@sfbg.com

At a business conference this past May hosted by Wired Magazine, Bill Gates, the billionaire chair of Microsoft and an influential philanthropist, offered his two cents on solar energy. "If you're going for cuteness," he told Wired, "the stuff in the home is the place to go. It's really kind of cool to have solar panels on your roof. But if you're really interested in the energy problem, it's those big things in the desert."

Those big things in the desert are solar farms, designed to concentrate energy from the sun using arrays of mirrors or parabolic troughs spanning vast swaths of land. They're green versions of the types of power plants big energy companies have always relied on — centralized, dependent on transmission lines, and requiring billions of dollars in investment. Some rely on water from desert aquifers for cooling, cleaning, and steam generation. Yet the plants can replace electricity that traditionally has been derived from burning coal, representing a significant advancement away from fossil fuels.

It's too early to say whether California's energy future will follow Gates' maxim that rooftop solar is "cute" while desert solar represents the serious stuff. Others have argued just the opposite, and momentum is building on both fronts. Gov. Jerry Brown has endorsed the idea of installing 12,000 megawatts of rooftop solar, and was expected to bring stakeholders together in late July to discuss how to accomplish that goal.

At the same time, large-scale desert solar is attracting billions in investment, and big-name companies such as Bechtel, Chevron, AECOM, and Pacific Gas & Electric Co. are engaged in its development. The California Energy Commission approved nine desert solar-thermal projects last year, capable of producing 4,100 megawatts.

As California moves toward fulfilling a mandate of generating 33 percent of electricity from renewable power sources by 2020, there's bound to be a political edge to solar development too. Giant utility companies profit by sending power along their transmission lines from desert solar farms to the grid. On the other hand, if energy-conscious customers generate more power than they use with rooftop solar panels, the utility company has to cut them a check. So there's little incentive for utilities to encourage customer-owned, distributed generation of renewable power.

Jeanine Cotter, CEO of San Francisco-based Luminalt, a small solar installer, says it takes her work crew about a day and a half to mount new panels onto a rooftop. "That will produce power for that home for the next several decades," Cotter notes. "It's a rapidly deployable technology that is durable and will last a long time."

Cotter practices what she preaches. "At my house, if you turn on all the appliances, you can look at the meter and see that we're still relying on PG&E to bring us power," she says. Cutting down results in the meter showing that the panels are producing electricity for the grid.

Self-empowerment is a major draw for proponents of rooftop solar. "The choice is pretty clear: pay for the ongoing cost of remote central-station renewable power or pocket the savings of locally-generated renewable power," Al Weinrub of the Sierra Club writes in a pitch for decentralized solar generation in a January 2011 report. "Businesses with large rooftops or parking lots can become small power companies that feed electricity into the grid. Community cooperatives can pool the rooftop area of their neighborhoods to form, for example, an East Oakland Power Company." The revenue could be rolled into job creation and more green-energy development.