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May 28, 2012

Under the right circumstances, solar cells from Semprius could produce power more cheaply than fossil fuels

Technology Review - this past winter, a startup called Semprius set an important record for solar energy: it showed that its solar panels can convert nearly 34 percent of the light that hits them into electricity. Semprius says its technology, once scaled up, is so efficient that in some places, it could soon make electricity cheaply enough to compete with power plants fueled by coal and natural gas.

Semprius uses gallium arsenide, which is better than silicon at turning light into electricity (the record efficiency measured in a silicon solar panel is about 23 percent). But gallium arsenide is also far more expensive, so Semprius is trying to make up for the cost in several ways.

By combining the world’s most efficient multi-junction solar cells with superior module design, Semprius holds the world record for module efficiency, reaching 33.9 percent, as confirmed by the Instituto de Energía ­Solar at the Universidad Politécnica de Madrid. Semprius modules are two-to-three times more efficient than traditional silicon and thin-film modules, delivering more than 300 watts per square meter.


Semprius website provides details




They shrink solar cells, the individual light absorbers in a solar panel, to just 600 micrometers wide, 600 micrometers long, and 10 micrometers thick. Its manufacturing process is built on research by cofounder John Rogers, a professor of chemistry and engineering at the University of Illinois, who figured out a way to grow the small cells on a gallium arsenide wafer, lift them off quickly, and then reuse the wafer to make more cells. Once the cells are laid down, Semprius maximizes their power production by putting them under glass lenses that concentrate sunlight about 1,100 times.

Concentrating sunlight on solar panels is not new, but with larger silicon cells, a cooling system typically must be used to conduct away the heat that this generates. Semprius's small cells produce so little heat that they don't require cooling, which further brings down the cost. Scott Burroughs, Semprius's vice president of technology, says utilities that use its system should be able to produce electricity at around eight cents per kilowatt-hour in a few years. That's less than the U.S. average retail price for electricity, which was about 10 cents per kilowatt-hour in 2011, according to the U.S. Energy Information Administration.

The company hopes to expand that to 30 megawatts by the end of 2013, but to do so it must raise an undisclosed amount of money in an atmosphere that is no longer kind to capital-­intensive energy startups.


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