STANFORD University researchers have found a way to keep solar cells cool, extending their efficiency and lifespan.
By adding a specially patterned layer of silica glass to the surface of ordinary solar cells, the researchers say, the solar cells can cool themselves by shepherding away unwanted thermal radiation.
According to the researchers, under normal operating systems, solar cells can easily reach temperatures of 55 degrees Celsius or more, which quickly reduce the conversion efficiency, and can markedly shorten the lifespan of a solar cell. For every one-degree Celsius increase in temperature, the efficiency of a solar cell declines by about half a percent.
While it's possible to actively cool solar cells, the use of ventilation or coolants would be very expensive and can reduce exposure to the sun's rays.
The use of the special layer of silica glass is a passive approach to cooling. By embedding tiny pyramid- and cone-shaped structures on an incredibly thin layer of silica glass, the researchers found a way of redirecting unwanted heat—in the form of infrared radiation—from the surface of solar cells back out.
To passively cool the solar cells, the researchers exploited the basic properties of light. Different wavelengths of light interact with solar cells differently. Visible light is used to generate electricity. Infrared carries heat.
The researchers engineered the silica layer to allow visible light to pass through unimpeded while reflecting away the wavelengths of the electromagnetic spectrum that carry heat. This meant the added layer did not degrade the performance of the solar cell, while still protecting it from heat.
The researchers precisely controlled the geometry on the surface of the silica glass, tuning them to refract and redirect only the unwanted infrared wavelengths away from the solar cell and back out into space.