Lens Arrays Could Enable Rooftop Solar Concentrators

Tiny solar cells sandwiched between lens arrays could bring the promise of concentrator photovoltaics (CPVs) down to a consumer scale.

“Current CPV systems are the size of billboards and have to be pointed very accurately to track the sun throughout the day,” said Penn State professor Dr. Noel C. Giebink. “But, you can’t put a system like this on your roof, which is where the majority of solar panels throughout the world are installed.”

Giebink led an international team that developed a prototype rooftop CPV incorporating high-efficiency GaAs cells less than a millimeter in size that need to move no more than a centimeter to keep up with the sun.

The cells were embedded between a pair of 3-D-printed plastic plastic lens arrays less than a centimeter thick. Each lens in the top array acts like a small magnifying glass, and is matched to a lens in the bottom array that functions like a concave mirror.

With each tiny solar cell located at the focal point of the two optics, sunlight is intensified more than 200 times. An optical oil was used to lubricate the sliding cell array and also to improve light transmission.

“The vision is that such a microtracking CPV panel could be placed on a roof in the same space as a traditional solar panel and generate a lot more power,” said Giebink. “The simplicity of this solution is really what gives it practical value.”

Giebink said improving consumer solar cell efficiency from the current 20 percent for silicon toward 40 percent of better with multijunction CPVs is important because increasing the power generated by a given system reduces the overall cost of the electricity it generates.

He cautioned, however, that CPV systems are not suitable for all locations.

“CPV only makes sense in areas with lots of direct sunlight, like the American Southwest,” he said. “In cloudy regions like the Pacific Northwest, CPV systems can’t concentrate the diffuse light and they lose their efficiency advantage.”

Funding for the project came from the U.S. Department of Energy.

The research was published in Nature Communications (doi: 10.1038/ncomms7223).

For more information, visit www.psu.edu.