September 19, 2007
Solar Nation: Can the Sun Power the U.S.?
Big Solar - those massive megawatt power plants to be built in California's Mojave Desert - has been seen at best as an add-on to the power grid. Solar, the conventional wisdom goes, might provide "peaking power" when demand spikes during the day but can never replace the so-called baseload power supplied round-the-clock by coal or natural-gas fired power plants. But in a paper to be presented today at the International Solar Energy Society conference in Beijing, scientist David Mills argues that huge solar farms can replace carbon-spewing power plants and produce electricity at competitive prices for the entire nation.
How? By combining solar thermal power plants with energy storage systems to keep the lights on long after the sun has set, according to Mills, chairman and chief scientific officer of Silicon Valley solar company Ausra. Solar thermal plants like the ones being developed by Ausra use rows of mirrors to focus the sun's rays on tubes of liquid - water in Ausra's case - to create steam that drives an electricity-generating turbine. The solar farms would store energy in tanks of liquid that would release the heat for nighttime operation or when clouds pass over. Mills and co-author Robert Morgan calculated that a 92-mile by 92-mile solar farm in the desert southwest could power the entire country. Analyzing electricity demand data from California and Texas, they figured that solar power plants with 16 hours of energy storage capacity could supply 92 percent of those states' power at about 8 cents a kilowatt hour - roughly the current cost of fossil fuel-generated electricity. Mills and Morgan believe the same would hold true on a national scale. "Zero emissions technology is required to replace most of current generation by mid-century to meet stringent climate goals," they wrote. "What is now required as a climate safety, economic, and security imperative is a rethink of the function and form of electricity grid networks, and the inclusion of high capacity factor solar electricity technology in the design of continental electricity systems."
That would mean replacing the current AC grid with a DC grid to get solar electricity from sunny states to the rest of the country with minimal transmission losses - an undertaking on the scale and cost of the construction of the interstate highway system in the 1950s. And of course the fossil fuel industry isn't about to march quietly off to the coal-bin of history. But Mills's "thought experiment" is less a blueprint for a solar nation than an opening shot in a campaign to shift the power paradigm away from the constraints imposed by coal and nuclear technologies. "Baseload is what those older technologies provided, not what we need," Mills told Green Wombat recently. "We need something that follows the natural load."
In other words, the grid is currently constructed to accommodate capital-intensive fossil fuel plants that need to run 24/7 to be most efficient and economical. The natural load, on the other hand, is the demand for electricity created by people's and the economy's daily rhythm. That demand naturally peaks when people are up and about and falls at night when they're asleep. Renewable energy sources, Mills argues, more closely mirror human behavior. Solar electricity production soars when demand does during the day. At night, stored solar energy and other renewable sources like wind, which tends to blow strongest in the evening, can more closely match lower demand as people and machines wind down.
For its part, Ausra is developing solar storage technology that will be commercially available in about 18 months, according to Mills. The company is expected to file a development application for a 175-megawatt solar power plant next week, a spokesperson for the California Energy Commission told Green Wombat. Ausra has been negotiating with PG&E (PCG) and other utilities. (Along with PG&E, California's two other big utilities, Southern California Edison (EIX) and San Diego Gas & Electric (SRE) so far have signed deals to buy nearly 3 gigawatts of solar power.)
"We're hoping to make announcements at the end of the month for multiple projects," Mills says.
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