Solar Boom

Forward

September/October 2008
By Dean Takahashi

New twists on three leading solar technologies.

As oil prices have climbed, so has venture investment in alternative energy. According to VentureDeal, a venture-tracking service in Menlo Park, CA, solar-power startups in particular have seen a three-year surge, from a low of no venture investment in the third quarter of 2005 to a high of more than half a billion dollars in the second quarter of this year.

The most popular approach to solar power remains photovoltaic panels made from crystalline silicon. But recent years have seen the commercialization of two rival technologies: thin-film solar cells, in which layers of light-absorbing materials are deposited on glass or even flexible plastic, and solar concentrators, which conserve silicon by using mirrors or optics to focus the sun's energy onto a smaller area. With VentureDeal's help, Technology Review has identified solar startups with innovative variations on all three approaches.

CaliSolar
Most solar cells are made from very pure--and thus expensive--silicon. But CaliSolar can make do with silicon that has a thousand times the impurities and can cost a sixth as much. That could mean real savings, since silicon can represent a quarter to a third of the cost of making solar cells. Usually, impurities lower cells' efficiency by reabsorbing freed electrons. But CaliSolar's manufacturing process herds impurities together, so electrons are less likely to hit them. The company's cells convert 15 percent of solar energy into electricity, putting them in the ballpark of conventional cells.

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