Story URL: http://news.medill.northwestern.edu/chicago/news.aspx?id=227710
Story Retrieval Date: 8/30/2014 3:23:06 AM CST

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Self-cleaning solar panels reflect a brighter future

by Sarah Kollmorgen
Feb 6, 2014


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Solar panels collect dust, dirt and snow. But solar panels coated with a superhydrophobic coating could shed build-up for a self-cleaning surface.


A slick technology for the solar power industry was announced this week by a group of national laboratory.

The scientists have developed an inexpensive “superhydrophobic” coating that, applied to solar panels, would make them self-cleaning and therefore more efficient.

The superhydrophobic coating has been in the works for a year and a half, said Scott Hunter, the principle scientist on the team from Oak Ridge National Laboratory in Tennessee.

Although superhydrophobic materials have been studied for over a decade, Hunter said he believes his team has developed the best superhydrophobic surface yet for self-cleaning.

“It’s a really useful and important idea,” said Alex Martinson, an assistant chemist in the material science division at Argonne National Laboratory southwest of Chicago. As the price of producing solar technology decreases, the costs of installing and cleaning solar panels becomes more significant, Martinson said. Solar panels that would be self-cleaning “makes the whole system more affordable,” he said.

The coating from Oak Ridge National Laboratory, which could be painted or sprayed onto the surface of solar panels, is superhydrophobic, meaning it is extremely repellant to water molecules.

The hydrophobicity of a surface is measured by its water contact angle, or the angle formed between a liquid droplet and the solid surface it sits on. A surface with a high contact angle will be very difficult to wet, causing more spherical water droplets to form on it. Conversely, a surface that is easy to wet, where a water droplet would flatten out, has a lower contact angle.
 
A material with a water contact angle of 180 degrees, the maximum, would be extremely water repellant. With the coating the scientists have developed, the Oak Ridge team has measured contact angles up to 178 degrees, but routinely has produced surfaces in the 170-175 degree range, Hunter said.

For reference, Teflon has a contact angle of about 115 degrees. “Our contact angles are higher than anybody else’s,” he said.  “We’re close to the maximum possible water repellency that you can achieve.”

The coating from Oak Ridge National Laboratory is different from other superhydrophobic surfaces in that it effectively combines water repellency, optical transparency and durability, which make it ideal for application to the surface of solar panels.  Similar superhydrophobic surfaces struggle to combine these three traits as well as the superhydrophobic coating from Oak Ridge, Hunter said.
   
The super-slick coating would cause dust or dirt particles to simply roll off solar panels with a breeze or rain. Built up dirt particles on solar panels can reduce reflectivity by up to 50 percent in 14 days, according to the Oak Ridge statement. Even in wintery climates, Hunter said snow and ice would more easily slide off solar panels.

“Getting up close and personal with modules usually involves getting people up on a roof,” said Seth Masia, executive director of the American Solar Energy Society and editor of Solar Today magazine. Especially in more wintery environments, scaling buildings to clean off solar panels can cause a safety risk, he said. Self-cleaning solar panels would eliminate risks involved in maintain hard to reach panels.

The Oak Ridge superhydrophobic coating has widespread applicability in other industries as well. Hunter said the next year will be dedicated to finding commercial partners to do further research with. Once they find some interested parties, two to three more years of testing is expected.

“Expect this stuff in two to five years, basically,” Hunter said.