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Solar thermal tech soars as alternative energy

Posted: 18 Jul 2008 ?? ?Print Version ?Bookmark and Share

Keywords:solar? thermal? energy? fossil fuel?

Solar thermal technology that attempts to harness the efficient phase change from water to steam is emerging as the preferred alternative energy technology in the race to replace fossil fuels with sustainable energy sources.

Along with cost per watt, solar thermal's biggest selling point is its ability to store energy and deliver electricity to consumers during peak power demand periods. Experts at a solar conference this week said "concentrating" solar thermal power could allow utilities and other emerging operators to store steam energy us to 6hr. Super-heated steam is used to drive turbines that generate electricity.

Concentrating, or suntracking, photovoltaics and solar thermal power collectors like parabolic troughs follow the sun across the sky at one of more axis points, focusing sunlight to improve the efficiency of solar panels.

Source of electricity
Experts noted that solar thermal's so-called "dispatchability" means stored power could be used to generate electricity that could then be sold to utilities during load peaks on electric grids, usually after 5 p.m. The approach would make solar thermal power far more valuable for plant operators than photovoltaic energy that must be used immediately.

"Thermal energy storage is the killer application of concentrating solar power technology," said Andrew McMahan, Skyfuel VP for technology and projects, during the recent solar technology conference in conjunction with Semicon West. "Solar thermal collector technologies like parabolic troughs have a good track record after more than 20 years for use," he added. "The technology has steadily improved and is being demanded by utilities when negotiating power supply agreements with solar operators," he noted.

Fit for large projects
Industry analysts like Jim Hines, research director for semiconductors and solar, Gartner Inc., agreed that solar thermal appears best suited to large power projects aimed at supplying electricity to utilities. Other technologies like traditional photovoltaics and concentrating photovoltaic systems work best in residential and commercial applications, Hines said.

Among the solar thermal projects discussed were several "power tower" projects that use concentrating solar collectors to refocus sunlight on "solar boilers." For example, solar developer Brightsource Energy is building a 400mW solar thermal complex in California's Mojave Desert, a prime location for a number of planned solar thermal projects. Along with other industry executives, John Woolard, CEO, Brightsource, noted that the primary challenge for solar thermal is efficiency transmitting power from remote desert locations to population centers.

Energy savings
Still experts agreed that for large alternative energy projects, solar thermal for now appears to be the best approach. According to estimates compiled by the Prometheus Institute fro Sustainable Development, solar thermal power-generating costs could drop from about $4.25/W in 2008 to $2.5/W by 2020.

"Solar thermal is an extremely cost-effective technology compared to other solar technologies," said Travis Bradford, founder, Prometheus Institute, adding that, "however, costs may not drop as fast as competing technologies like traditional and concentrating photovoltaics."

- George Leopold
EE Times

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