Solar Cell Coating to Increase Efficiency from 20 to 21 Percent
Kagan Pittman posted on September 28, 2015 |

Stanford engineers have invented a solution to the drop in energy efficiency solar panels experience due to heat from the sun. And no, it’s not an advanced form of sunscreen lotion.

Their thin, transparent patterned silica material is laid over top of a conventional solar cell, which allows sunlight to pass through, but captures heat and thermal radiation and then expels it as infrared rays.

The team behind the invention developed a material that radiated infrared heat back in 2014, which they described as “radiative cooling.” 

A thin, patterned silica material allows sunlight to pass through, while trapping and releasing heat to increase solar cell efficiency. (Image courtesy Aaswath Raman.)
A thin, patterned silica material allows sunlight to pass through, while trapping and releasing heat to increase solar cell efficiency. (Image courtesy Aaswath Raman.)

Using these findings, the team developed their latest technology on a custom-made solar absorber, essentially a solar cell that can’t produce electricity. In experiments, the material cooled the absorber by up to 23 degrees Fahrenheit.

“The patterned design used enables a gradual interface between air and the silica, which allows thermal radiation to escape optimally,” Aaswath Raman, research associate and co-first-author of the paper told ENGINEERING.com

The reduction in heat by 23 degrees Fahrenheit leads Raman and his team to believe that the one percent increase in efficiency is possible.

“It's one absolute percent improvement in efficiency. So, in principle, that could mean going from 20 percent efficiency in the field to 21 percent,” Raman explained. “In practice it might be lower or even higher depending on the location.”

A one percent increase in efficiency doesn’t sound like much at first, but let’s take a step back and consider the significance.

One percentage point is equal to a five percent of improvement in overall panel efficiency.

A five percent increase in current efficiency sounds a bit more significant, but it’s still quite small. Added together with future technological advancements, however, and that overall one percent increase may change to three and then five, and maybe even 10 down the line.

Various Applications

The material works best in dry and clear environments, optimal for solar arrays. Raman’s team believe they can scale the material up for commercial and industrial applications using nanoprint lithography to produce nano-meter-scale patterns.

However, “That’s not necessarily the only way,” Raman added. “New techniques and machines for manufacturing these kinds of patterns will continue to advance. I’m optimistic.”

That optimism is going to be important as experiments continue and once marketability becomes a priority.

How will the solar panel coating be introduced? Will it be manufactured with the solar panels, or will it be sold separately? How much will consumers and/or manufacturers have to pay?

For areas with poor weather conditions, the effectiveness of the coating may be seasonal, forcing a “sold separately” situation. The coating will be redundant for areas that experience harsh winters unless it can protect the solar cells from possible corrosion from water damage.

Linxiao Zhu, doctoral candidate and co-author, believes the technology has potential for any outdoor device that could benefit from external cooling.

“Say you have a car that is bright red,” he said. “You really like that color, but you’d also like to take advantage of anything that could aid in cooling your vehicle during hot days. Thermal overlays can help with passive cooling, but it’s a problem if they’re not fully transparent.”

This is because to perceive color, the objects must reflect visible light.

“Our photonic crystal thermal overlay optimizes use of the thermal portions of the electromagnetic spectrum without affecting visible light,” Zhu added. “So you can radiate heat efficiently without affecting color.”

To learn more, read the Stanford team’s paper, published in the current issue of Proceedings of the National Academy of Sciences.

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