On the surface of a new photovoltaic prototype, microscopic nanotube towers perform best when they catch light on their sides.
By David Talbot, April 17, 2007
source: MIT Technology Review
http://www.technologyreview.com/Energy/18539/
Solar cells generally crank out the most power at noon, when the sun is at its highest point and can strike the cell at a 90-degree angle. Before and after noon, efficiencies drop off. But researchers Georgia Tech Research Institute have come up with a prototype that does the opposite. Their solar cell, whose surface consists of hundreds of thousands of 100-micrometer-high towers, catches light at many angles and actually works best in the morning and afternoon.
“It may be intuitive: when the light goes straight down, the only interaction is with the tops of towers and the ‘streets’ below,” says Jud Ready, senior research engineer at the institute’s Electro-Optical Systems Laboratory. “But at an angle, the light has an opportunity to reflect off the sides of the towers.” When the sun is at a 90-degree angle, the prototype delivers only 3.5 percent efficiency. But it delivers better efficiencies at many other angles and is actually at its peak efficiency–7 percent–when light comes in at a 45-degree angle. That means the device operates at relatively high efficiencies during much of the day and has two efficiency peaks: one before noon, and one after noon.
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