Which renewable technology holds the key for a sunnier (and more democratic) energy future?
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.
Rooftop solar has gained traction in California over the past five years with a $3 billion program to subsidize installations. The California Public Utilities Commission recently touted the California Solar Initiative (CSI) program's success — a 47 percent growth in installations since 2009. All told, the Golden State boasts 924 megawatts of solar generation capability, installed at 94,891 locations. Consultants for the California Public Utilities Commission found that 11,543 megawatts of solar could be generated on large urban rooftops statewide, while another 27,000 megawatts could be generated on empty lots near rural substations.
The potential is huge, but a cost barrier remains. Even with incentives, residential solar remains largely inaccessible to people who aren't rich enough to own property or finance the upfront cost. In San Francisco — recently declared the greenest city in North America by Siemens — roughly 70 percent of residents are renters who almost never have the option of going solar. Proponents of desert solar farms claim that the large-scale, centralized technology offers something that rooftop panels can't — the potential to bring renewable energy to the masses.
The largest desert solar plant under construction worldwide is BrightSource's Ivanpah plant, which Bechtel is building in the Mojave Desert. Spearheaded by an Oakland company, the plant uses sunlight and mirrors to generate steam to power a turbine. The energy will flow onto the grid to serve PG&E and Southern California Edison customers. It's a dramatic improvement compared with burning coal, but there are other issues. On a yearly basis, it will use enough groundwater in the arid desert to cover 100 acres, one-foot deep. And it riled environmentalists who worried that it would affect the habitat of an endangered tortoise.
No one disputes that on a per-watt basis, it's cheaper to install desert solar than rooftop solar. According to estimates from Go Solar California, it costs more than $8 per watt to install small-scale rooftop solar systems, while recent costs for desert solar farms have been calculated at around $4 per watt. "Because they have the economy of scale, they can be built at less cost," notes John White, executive director of the Sacramento-based Center for Energy Efficiency and Renewable Technologies.
Yet a renewable energy expert who formerly worked for the California Energy Commission (CEC) says comparing costs of desert and rooftop solar from the point of view of the customer tells a different story. In April, Sanford Miller delivered a presentation at UC Davis that could have been considered subversive. His analysis essentially found that ratepayers shell out less to subsidize rooftop solar installations than they do to finance the purchase of energy from desert solar farms once the full cost of transmission and environmental mitigation are factored in.
"From a ratepayers' perspective, rooftop solar would be significantly cheaper than the desert solar," Miller says. When he sent his findings around to his colleagues at the CEC, "no one disputed it," he said. "But the view was that desert solar was inevitable."
But that still leaves the question of who can afford solar — and this is where Tom Price, former executive director of Black Rock Solar and now part of a solar investment firm called CleanPath, believes he's found a middle way. As things stand, every utility customer chips in to subsidize the cost of individualized solar panels for the lucky few who are installing them, he points out, and those same customers are footing the bill for energy companies to buy power from giant solar farms. He's pushing the Community Solar Gardens bill as an alternative.
Introduced as Senate Bill 843 by Sen. Lois Wolk (D-Davis), the bill would allow any customer to purchase a subscription to a centralized renewable energy facility, and receive credit on their utility bill in exchange for the monthly fee.
White takes the view that all the different solar technologies are needed — rooftop, desert, and "intermediary" — the kind of small-scale, centralized facility that is located closer to the customers who will use it, like the solar array at the Sunset Reservoir in San Francisco. "After Fukushima [Daiichi Nuclear Power Plant in Japan], we need to begin talking seriously about reducing our dependence on nuclear power," White says. "When you look at what we're trying to replace and what we're trying to avoid, it's like we're trying to assemble a new portfolio."