March 12, 2007 4:00 AM PDT
Full steam ahead for Nevada solar project
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Although solar thermal systems and solar photovoltaic (PV) panels both transform energy from the sun into electricity, they work in vastly different manners. PV panels, which have become very popular in the last five years, split photons from the sun into electrons and positive charges from the sun. The electrons are harvested and funneled into the electrical system of a building or the grid. In general, silicon PV panels convert 15 to 22 percent of the light that strikes them into electricity; mixing other materials into the panels can increase efficiency, but also adds cost.
Solar thermal plants are more efficient, said Cohen, with efficiencies ranging from around 20 percent to 40 percent, according to studies, in part because it's easier to extract heat from sunlight than electrons. Solar thermal water heaters--which heat water for commercial and residential buildings--rely on the same principle.
The molten salt vats also give solar thermal systems insurance against cloudy days, something that PV doesn't have. One hundred thousand square feet of molten salt holds enough heat to provide electricity for four hours.
The big drawback is that solar thermal plants can't be installed everywhere. They work best in warm, dry locations, unlike PV panels which even work well in Germany. Shadows from vapor trails and planes can curb their production. And dust is a major problem. To keep it off, a cart festooned with moist brushes that look like they came from a car wash hoses off the mirrors.
As a result, solar thermal mostly gets deployed for power plants, which cost hundreds of millions of dollars and take up hundreds, if not thousands of acres of land. An individual can put a PV system on a private home, but it will cost about $20,000. Until recently, financing for these projects has been nearly impossible to obtain. Security is a potential issue, too. Venture capitalist Vinod Khosla recently said during a panel discussion that a thermal plant occupying three percent of Morocco's land could provide Western Europe with all of its power. Maybe so, said other panelists, but that would also make it a potential target for terrorists, or even a political tool.
Solar One's location was the result of a host of factors, said Cohen. A lake about 18.5 miles away provides water to the station. Additionally, it's only 3 miles from three electrical substations. It costs about $1.5 million per mile to connect to a substation, so distance counts.
Plus, it's about the sunniest place in America.
"You have a site here that for 360 days is almost like today," Cohen said, nodding toward the bright blue sky. "We had to shut down construction three times because it was snowing. We talked to people who lived here, and they said they had never seen snow in their lives here."
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