Monday, May 04, 2009

Cheaper Solar Concentrators

Skyline Solar, a new startup, is combining conventional technologies to lower solar-power costs.

By Kevin Bullis

Skyline Solar, a startup that today announced its existence to the world, has developed a cheaper way to harvest energy from the sun. The company's solar panels concentrate sunlight onto a small area, reducing the amount of expensive semiconductor material needed to generate electricity.

Sun collectors: Skyline Solar combines conventional silicon solar cells with reflective parabolic troughs (shown here).
Credit: Skyline Solar

The technology will bring the cost of solar power in line with the average cost of electricity, at least in sunny areas, says Ben Eiref, Skyline Solar's director of product management. Currently, solar power can be far more expensive than electricity from conventional sources; many governments have resorted to subsidies to increase its use.

Skyline Solar has raised $24.6 million to date and has been awarded $3 million by the Department of Energy to speed up production. It has also installed a pilot power plant that can produce 24 kilowatts of electricity, and has started production of its solar panels with the goal of selling them later this year. They are designed for commercial installations in the 1-to-10-megawatt range, such as on food-processing and water-treatment facilities at the edges of cities or in rural areas.

The startup isn't the first company to attempt to reduce costs by concentrating sunlight onto smaller solar cells. But Skyline Solar says that it can better compete with other energy sources by combining two technologies that can be produced in high volume using existing equipment and that have been demonstrated in the field for decades: conventional silicon solar cells and reflective parabolic troughs, which are used now in solar thermal plants. In these thermal plants, the long, curved troughs concentrate light on tubes, heating up a fluid inside them that, in turn, is used to drive power-generating turbines. Skyline Solar has replaced those tubes with narrow solar panels, adding a heat sink to keep them from getting too hot. The troughs concentrate the light by about a factor of 10, increasing the power output of the panels by about the same amount as conventional solar panels without concentrators. (To compensate for the increased power output, the company has incorporated larger electrical contacts into the panels.)

Other companies are developing systems that concentrate sunlight much more--by hundreds of times--in an effort to further decrease the amount of expensive solar-cell material needed. Indeed, two of Skyline Solar's founders were part of the founding team at another concentrating-solar company, SolFocus, that was also developing a high-concentration system. But they decided that the technology, while promising, faced too many technical hurdles to be brought to market quickly.

While Skyline Solar's technology may be simpler and easier to bring to market, it's not guaranteed success, says Travis Bradford, a professor of management at the University of Chicago and a solar-industry analyst with the Prometheus Institute for Sustainable Development. "Parabolic troughs are known, so they know what the costs are, and they can make them at a predictable rate," he says. But like almost all concentrating-solar systems, they require a tracking system to keep the mirrors pointed at the sun. "Mirrors are probably cheaper to make than solar cells--for now. But when you add in the tracking, whether there's any real advantage is questionable."

What's more, Bradford says that prices for conventional silicon solar panels are falling dramatically, closing the gap between the cost of regular panels and the cost of the mirrors and the tracking system combined. Potentially, this makes it less worthwhile to concentrate sunlight.

Bradford notes, however, that if Skyline Solar does manage to keep its prices lower than those of the competition, it has a large potential market. The application that it's designed for--medium-size solar-power plants at the edges of cities, called distributed utility systems--is the fastest-growing segment of the solar market.