Icephobic Coating Improves Solar Panel Efficiency
A team from the University of Michigan recently announced that they have created a coating for solar panels to reduce snow and ice accumulation and improve productivity in cold climates. The clear coating, which can be sprayed or brushed on in cold weather, reportedly enabled panels to generate up to 85% more energy in tests.
“Renewable energy is really taking off right now, but snow is a huge problem in northern climates,” said Anish Tuteja, U-M professor of materials science and engineering, who led the study. “Solar panels might lose 80 or 90% of their generating capacity in the winter. So figuring out a way for them to continue generating energy throughout the year was an exciting challenge.”
According to the release, the coating consists of PVC or PDMS plastic and silicon or vegetable-based oils. The current formulation keeps sheds ice and snow accumulation for up to a year. Using the lab’s previous research, the team recognized that low interfacial toughness and low adhesion strength were key to ice-shedding coatings
“Ice is relatively dense and heavy, and our previous coatings used its own weight against it,” Tuteja said. “But snow can be 10 times less dense than ice, so we weren’t at all certain that the tricks we use on ice would translate to snow.”
Low surface adhesion, or slipperiness, typically works on smaller areas. The larger the surface, the more force is needed to slide snow or ice off, or the precipitation needs to be broken up. The low interfacial toughness reportedly creates cracks between the ice and the solar panel.
Researchers utilized a very rigid PVC plastic for low interfacial toughness and mixed it with a small amount of vegetable oil to create low surface adhesion. According to the release, a second formulation with PDMS plastic and silicon-based oil worked equally well.
The coating was tested at a solar field in Fairbanks, Alaska, in collaboration with the University of Alaska. These panels were monitored by automated cameras for about two weeks, with tests showing that the coated panels had an average snow and ice coverage of approximately 28% over an entire winter season. Uncoated panels had an accumulation of about 59%, in comparison.
U-M reports that the coating was developed as part of a project led by Sandia National Laboratories, a U.S. Department of Energy research and development lab and funded by the DOE’s Solar Energy Technologies Office.
“As the cost of solar energy has dropped and profitability has climbed, much of the growth in solar energy in recent years has been in northern states, where snow is common,” said Laurie Burnham, the project’s principal investigator.
“Snow-phobic coatings, if we can demonstrate their long-term efficacy, will make solar power more reliable and more affordable in snowy regions, helping accelerate our nation’s transition to a more solar-dominated energy economy.”
Tuteja said although the current iteration of the coating could be utilized immediately, there are plans to continue working on the coating with a goal of creating five-year longevity.
The study was recently published in Advanced Materials Technologies.
Previous Ice-Proof Coatings Research
In 2019, Tuteja and his team reported this new class of coatings was moving researchers one step closer to being able to ice-proof airplanes, marine vessels, powerlines and other large structures.
The decades-long goal is finally shining light on the possibility through a “beautiful demonstration of mechanics,” revealing ice shedding effortlessly from large testing surfaces with the help of a light breeze, or in other cases, the weight of the ice itself.
Tuteja and his colleagues decided to test a new method, not common in icing research.
“For decades, coating research has focused on lowering adhesion strength—the force per unit area required to tear a sheet of ice from a surface,” Tuteja said at the time.
“The problem with this strategy is that the larger the sheet of ice, the more force is required. We found that we were bumping up against the limits of low adhesion strength, and our coatings became ineffective once the surface area got large enough.”
By introducing a low interfacial toughness strategy instead, surfaces with LIT encourage cracks to form between the ice and surface it's shaped upon. Once a crack begins to form, it can quickly spread across the entire iced surface and break from it. In previous methods involving breaking an ice sheet’s surface adhesion, cracks would only break the surface free along its leading edge.
Michael Thouless, the Janine Johnson Weins Professor of Engineering in mechanical engineering, compared the LIT strategy like “pulling a rug across a floor.”
(In trying to pull a large rug, one would be more resistant compared to a small rug because of the strength of the interface between the rug and the floor. This friction force should be equivalent to the interfacial strength.)
“But now imagine there’s a wrinkle in that rug,” continued Thouless.
“It’s easy to keep pushing that wrinkle across the rug, regardless of how big the rug is. The resistance to propagating the wrinkle is analogous to the interfacial toughness that resists the propagation of a crack.”
The concept is most popular in the field of fracture mechanics, where it reinforces products such as adhesive-based aircraft joints and laminated surfaces. However, regarding the study, the concept can now begin exploring its use in ice mitigation.
In the mitigation studies, it was important that both the LIT and interfacial strength have an equal focus.
In the testing stage, Tuteja’s team mapped out the properties of a vast library of substances, adding LIT and interfacial strength data into the equation. By doing this, the team was able to mathematically predict the properties of a coating system without having to test all of them.
The mathematical process also enabled them to develop a variety of combinations, each specifically tailored to Thouless’ concept of equal interfacial focuses. In physical testing of the coatings on large surfaces—a rigid aluminum sheet and a flexible aluminum sliver (to mimic a power line)—ice fell off immediately due to its own weight.
Since their discoveries, a paper titled, "Low Interfacial Toughness Materials for Effective Large-Scale De-Icing," has been published in the journal Science.