Dirty Silicon + Cali Sun =

Clean energy, ninjas! Cali/Berlin-based start-up company, CaliSolar has developed a way to use lower grade silicon to produce photovoltaic cells, thanks to research done at UC Berkeley by former Professor Eike Weber who is now in Germany at the Frauhofer Institute.

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The difference between the 99.99999% purity of electrical grade silicon that most PV manufacturers use and the 99% purity of ‘dirty’ metallurgical grade silicon is profound. Not only is the lower grade silicon cheaper ($20-$50/kg versus $150-$250/kg for electrical grade), but there is vastly more of it available, with 1.2 million tons/year made, as opposed to only 70,000 tons/year of electrical grade. Both of these qualities – cost and raw material supply, are crucial to the sustainability of the PV solar industry. The reason most PV companies don’t use the cheaper dirty silicon is that impurities in the material get in the way of the capture and conversion of sunlight to energy:

Photovoltaic solar panels generate electricity by separating negative charges from positive charges contained in the sunlight that strikes them. The negative charges (electrons) are then captured, converted to AC power, and then used to power things in your house. Pure silicon is usually needed because impurities prevent electron capture.CaliSolar gets around this by isolating the impurities during manufacturing. The impurities can be channeled into the borders between crystals, Johnson said, which don’t generate electricity anyway. The impurities can also be coaxed, through chemical and physical forces, to “float” to the top of a wafer, where they can be etched off. In other words, it nullifies the effect of the impurities by coming up with ways to ensure that the impurities aren’t uniformly distributed.

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The solar cells coming out of CaliSolar’s labs are already roughly competitive with standard silicon solar cells in terms of efficiency, said Johnson, a former networking executive. If CaliSolar can mass manufacture solar cells with a 14 percent efficiency rating–which means that they will convert 14 percent of the sunlight that strikes them into electricity–these solar cells will cost far less than the 16 percent efficiency cells that are common on the market today.

The key word here is ‘if’. CaliSolar will need to raise $30-50 million in order to get an industrial sized manufacturing plant up and running. They have raised $9 to get a smaller prototype factory going.

[cnet news]

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