Cooling Solar Cells, Even at High Noon

There's been a lot of research in the past few years into how to improve the efficiency and lower the cost of solar energy technology. But only now has one rather obvious problem been addressed, and apparently solved: How to keep solar panels cool on a hot, sunny day.

At the same time, the technology makes solar panels more efficient and therefore capable of generating more electricity.

Researchers at Stanford University report in Optica, the journal of The Optical Society, that they simply added a layer of textured silica glass to the surface of traditional solar panels to divert unwanted solar heat, which can hamper the cells' efficiency and longevity.

Solar cells are fairly easy to manufacture and therefore accessible to virtually every budget. But they're not particularly efficient at converting solar energy into usable electricity. Some of this wasted solar energy may be unavoidable, but much of it is due simply to overheating.

Solar cells often heat up to 130 degrees Fahrenheit (55 degrees Celsius), and sometimes even more. Reducing the heat with liquid coolants or even ventilation isn't an option because either method would reduce the panels' exposure to sunlight and make them costlier to manufacture.

The solution, developed by the Stanford team led by electrical engineer Shanhui Fan, doesn't block sunlight, nor does it add unwanted expense to the panels. It simply involves embedding small cone- and pyramid-like structures onto a very thin layer of silica glass to reflect hot infrared radiation away from the panel while maintaining the panel's access to usable solar energy.

"A carefully designed layer of silica would not degrade the performance of the solar cell," Fan explains, "but it would enhance radiation at the predetermined thermal wavelengths to send the solar cell's heat away more effectively."

At best, current solar panels can convert less than 30 percent of the solar energy they collect into electricity. The wasted energy saps the panel's strength even further. In fact, the efficiency of a solar cell declines by about a half of a percentage point for every increase in temperature by 1.8 degrees F, or 1 degree C.

"That decline is very significant," said Stanford postdoctoral scholar Aaswath Raman, a co-author of the Optica paper. "Our method of carefully altering the layers that cover and enclose the solar cell can improve the efficiency of any underlying solar cell. This makes the design particularly relevant and important."

Plus, the waste head shortens the effective life of a solar panel. It's rate of aging doubles for every temperature increase of 18 degrees F (about 8 degrees Celsius).

Zhu's team is now continuing tests of their design in a laboratory, but eventually plan to demonstrate it