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Cooling transparent coating boosts solar cell efficiency

Posted: 25 Sep 2015     Print Version  Bookmark and Share

Keywords:Stanford University  solar cell  coating  photon 

One of the major problems plaguing the solar industry is when solar cells become hot, they tend to become less efficient at converting sunlight to electricity. Now, Stanford engineers created a transparent overlay that increases efficiency by cooling the cells even in full sunlight.

Every time you stroll outside you emit energy into the universe: Heat from the top of your head radiates into space as infrared light.

Now three Stanford engineers have developed a technology that improves on solar panel performance by exploiting this basic phenomenon. Their invention shunts away the heat generated by a solar cell under sunlight and cools it in a way that allows it to convert more photons into electricity.

The work by Shanhui Fan, a professor of electrical engineering at Stanford, research associate Aaswath P. Raman and doctoral candidate Linxiao Zhu is described in the current issue of Proceedings of the National Academy of Sciences.

The group's discovery, tested on a Stanford rooftop, addresses a problem that has long bedeviled the solar industry: The hotter solar cells get, the less efficient they become at converting the photons in light into useful electricity.

Thin, patterned silica material

When laid over a solar cell, the transparent material shown here can radiate heat away from solar cells, allowing them to produce electricity more efficiently.

The Stanford solution is based on a thin, patterned silica material laid on top of a traditional solar cell. The material is transparent to the visible sunlight that powers solar cells, but captures and emits thermal radiation, or heat, as infrared rays.

"Solar arrays must face the sun to function, even though that heat is detrimental to efficiency," Fan said. "Our thermal overlay allows sunlight to pass through, preserving or even enhancing sunlight absorption, but it also cools the cell by radiating the heat out and improving the cell efficiency."

A cool way to improve solar efficiency

In 2014, the same trio of inventors developed an ultrathin material that radiated infrared heat directly back toward space without warming the atmosphere. They presented that work in Nature, describing it as "radiative cooling" because it shunted thermal energy directly into the deep, cold void of space.

In their paper, the researchers applied that work to improve solar array performance when the sun is beating down.

The Stanford team tested their technology on a custom-made solar absorber, a device that mimics the properties of a solar cell without producing electricity, covered with a micron-scale pattern designed to maximise the capability to dump heat, in the form of infrared light, into space. Their experiments showed that the overlay allowed visible light to pass through to the solar cells, but that it also cooled the underlying absorber by as much as -5°C.

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