Tuesday, April 25, 2006

Holographic Solar

Continued from page 1

By Prachi Patel-Predd

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But traditional concentrators are complicated. Since the lenses or mirrors that focus light need to face the sun directly, they have to mechanically track the sun. They also heat up the solar cells, and so require a cooling system. As a result, although they redirect light with more intensity than the hologram device, "they're unwieldy...and not as practical for residential uses," says National Renewable Energy Laboratory spokesperson George Douglas.

Holograms have advantages that make up for their relatively weak concentration power. They can select certain frequencies and focus them on solar cells that work best at those frequencies, converting the maximum possible light into electricity. They also can be made to direct heat-generating frequencies away from the cells, so the system does not need to be cooled. "In this way, you are efficiently using only that part of the sunlight that really matters," says Selim Shahriar, director of the atomic and photonic technology laboratory at Northwestern University in Evanston, IL.

Also, different holograms in a concentrator module can be designed to focus light from different angles -- so they don't need moving parts to track the sun.

Prism Solar's system incorporates these advantages. Nevertheless, to be competitive with other solar technologies available today, the company might need to reduce its price below $2.40 a watt, says Christo Stojanoff, professor emeritus of engineering at the Aachen University of Technology in Germany.

CEO Lewandowski says the holographic modules will cost about $1.50 per watt in a few years, using their second-generation technology, which will have solar cells sandwiched between two glass panels containing holograms. At that price, they'll start to compete with fossil fuel-generated electricity, which now costs almost three times less than conventional solar electricity, according to San Francisco, CA-based research and consulting company Solarbuzz.

The modules' intensive use of glass could be adding to their cost, says Douglas. Still, such a novel idea for a concentrator, using holograms, could be a lucrative investment because it needs less silicon than flat-panel modules and therefore saves money. The high demand for solar cells in Germany and other European countries "has now outstripped the supply, which has [led to] a silicon shortage and a shortage of manufacturing in the photovoltaic world," he says.

Although the idea of holographic solar concentrators has been around since the early 1980s, no one has developed them commercially yet, according to Professor Stojanoff, who has investigated the technique extensively. His company, Holotec GmbH in Aachen, Germany, researches and manufactures holographic materials. Also, Northeast Photosciences, a Hollis, NH-based company, came close to manufacture, before it went defunct for reasons unrelated to the technology or to finance, he says.

So, if all goes according to plan, Prism Solar could be the first company to manufacture and sell holographic solar concentrator modules.

Holographic Solar

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