The Ardour Solar Energy Index, covering all forms of solar power, climbed 55 percent in the 12 months through yesterday, outperforming an 8.5 percent decline in the Standard & Poor's 500 Index.
Unlike photovoltaic solar panels that convert sunlight to electricity, solar thermal focuses sunrays with mirrors to heat oil in glass pipes to about 700 degrees Fahrenheit (370 degrees Celsius). The oil turns water to steam, which spins an electric turbine.
Nine solar thermal plants built in the California desert from 1985 to 1991 still operate, with Juno Beach, Florida-based FPL Group Inc. running seven. They have combined capacity of 354 megawatts, enough to power 230,000 Southern California homes.
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