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 engineers have exploited this basic phenomenon to develop a technology that improves solar panel performance. 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 discovery 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.
The 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, from infrared rays.
“Solar arrays must face the sun to function, even though that heat is detrimental to efficiency,” says Shanhui Fan, professor of electrical engineering at Stanford University. “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.”
In 2014, the same group 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 the new paper, published in the Proceedings of the National Academy of Sciences, they applied that work to improve solar array performance when the sun is beating down.
The researchers 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 maximize 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 23 degrees Fahrenheit.
Cooler Cars
For a typical crystalline silicon solar cell with an efficiency of 20 percent, 23 F of cooling would improve absolute cell efficiency by over 1 percent, a figure that represents a significant gain in energy production.
