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Penn State develops CPV system for rooftops


Researchers at Penn State have developed a concentrating photovoltaic system that is small enough and light enough to be mounted on a building’s roof.

“Concentrating photovoltaic (CPV) systems leverage the cost of high efficiency multi-junction solar cells by using inexpensive optics to concentrate sunlight onto them,” explained Noel C. Giebink, assistant professor of electrical engineering, Penn State.

“Current CPV systems are the size of billboards and have to be pointed very accurately to track the sun throughout the day. 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,” he added.

Using multi-junction solar cells can improve a system’s efficiency at converting sunlight to electricity by 40 percent. By increasing the power generated by a system, CPV reduces the overall cost of the power it generates.

To enable CPV on rooftops, the researchers combined miniaturized, gallium arsenide photovoltaic cells, 3D-printed plastic lens arrays and a moveable focusing mechanism to reduce the size, weight and cost of the CPV system and create something similar to a traditional solar panel that can be placed on the south-facing side of a building’s roof.

The Penn State researchers collaborated with colleagues from the University of Illinois to make very small, very efficient multi-junction solar cells. The cells are less than 1 square millimeter.

To focus sunlight on the cells, the cells were embedded between a pair of 3D-printed plastic lenslet arrays. The lenslet on the top array act like a small magnifying glass and are matched to a lenslet in the bottom array that works like a concave mirror.

With each tiny solar cell located in the focus of this duo, sunlight is intensified more than 200 times. Because the focal point moves with the sun over the course of a day, the middle solar cell sheet tracks by sliding laterally in between the lenslet array.

Because the total panel thickness is only about a centimeter and 99 percent of it — everything except the solar cells and their wiring — consists of acrylic plastic or Plexiglas, this system has the potential to be inexpensive to produce.

According to Mr. Giebink, CPV arrays make sense in areas with a lot of direct sunlight. In cloudy regions, these systems will not be able to concentrate the diffuse light and will lose their efficiency.

Others working on this project include Jared Price, graduate student, Penn State; Xing Sheng, postdoctoral fellow; John A Rogers, professor of materials science and engineering, University of Illinois, Urbana Champaign; and Bram M. Meulblok, technical representative, LUXeXcel Group B.V., The Netherlands.

The U.S. Department of Energy funded this research.



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