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Solar Expansion

Technologies are scaling up quickly to meet industry needs.

Fortnightly Magazine - December 2009

in the American Southwest, mainly California. All of them are being financed and built by the technology suppliers themselves.

Which design will prove the most cost-effective remains to be seen. Parabolic trough technology, with its curved mirrors that direct heat to absorber tube receivers filled with heat transfer fluid, has been employed in California and other parts of the world for decades. As such, the technology generally is viewed as proven, and massive utility-scale projects are now in development. For example, Israel’s Solel Solar Systems Ltd., acquired by Siemens in October, is building what will be one of the largest parabolic trough plants ever. The 533-MW Mojave Solar Park will cover up to 6,000 acres, or nine miles, of California’s Mojave Desert. The plant, which will include 1.2 million mirrors and 317 miles of vacuum tubing, is scheduled to begin operation in 2011. PG&E has contracted to buy its output.

Similarly, Spain’s Abengoa Solar is building a smaller 280-MW parabolic trough plant 70 miles southwest of Phoenix, near Gila Bend. The Solana Generating Station is unique because it will employ a thermal storage system consisting of large insulated tanks filled with molten salt that will store heat generated during the daytime. The heat will then be used to produce energy during periods of low or no sun, including the evening hours. The plant is scheduled to go into operation in 2011, with Arizona Public Service buying the output.

But as impressive as such projects are, some analysts believe trough technology ultimately will give way to the more advanced CLFR and power tower technologies, both of which are under development.

A 2008 report by San Francisco-based Cleantech Group, which monitors the solar power industry for the investment community, predicts trough-based systems will be most prevalent until 2012 or 2013, but could then be displaced by power towers, CLFR and dish-engine developers.

“Troughs will dominate the first generation of CST,” states Brian Fan, Cleantech’s senior director of research. “It’s project financeable today because we know the costs, we know the technologies, and there are no technology risks. Developers have a roadmap to bring down the cost. But if the power-tower concept is proven in the field in test operations, because of higher thermodynamic efficiency and higher scalability, it will be the next generation of CST plants past 2012.”

Like a trough design, the CLFR technology uses the reflectors to concentrate sunlight on transfer fluid-filled pipes. However, the pipes run directly above the mirrors, which, developers say, increases the amount of heat generated. Power tower designs do away with the transfer fluid and piping altogether. Instead, they use mirrors to direct sunlight directly to a boiler system located within a tower.

Developers of both technologies have 5-MW pilot plants operating commercially. In October 2008, Australian-based developer Ausra started up its Kimberlina CLFR plant in Bakersfield, Calif. And in August, Pasadena-based eSolar brought on-line the 5-MW Sierra SunTower plant in Lancaster, Calif. Like Ausra, eSolar intends to scale-up the technology with a 245-MW solar thermal power plant in the Antelope Valley region of southern California. SCE