March 9th, 2022
Researchers from Chiang Mai University in Thailand reported that they have developed a new antireflective, hydrophilic and photocatalytic coating for solar panels. Using this coating, scientists were able to increase the panels’ power yield by over 6 percent.
The study, “Antireflective, photocatalytic, and superhydrophilic coating prepared by facile sparking process for photovoltaic panels,” was recently published in the journal Scientific Reports.
About the Coating
According to the research, photovoltaic panel cover glass is highly transparent but has a natural reflectance. One way to increase the panel’s effectiveness would be to reduce the optical loss and natural reflectance with an antireflective coating.
To achieve this, researchers used a “simple and inexpensive” sparking process to produce an AR film. The developed method uses basic equipment that can be operated in ambient environments without a high-vacuum system. Additionally, no toxic waste is produced from any chemical precursors or agents.
The synthesis method reportedly creates porous nanostructured films with well-controlled thickness and uniform composition, allowing for large-scale, one-step coating and making it ideal for commercial use.
For the sparking process, researchers used 0.25-millimeter titanium wire with a 99.5 percent purity, supplied by United Kingdom-based Advent Research Materials Ltd. The wires were cut, aligned with a gap of one millimeter between the anode and cathode and then “sparked off” with a high DC voltage of around 3 kilovolts discharged from a 24-nF capacitor.
“The high applied voltage induced arcing in the tip gap via a field ionization process. During sparking, electrons and ions produced from the neutral air molecules migrate toward the anode and cathode, respectively,” wrote researchers. “The bombardment of high-energy electrons and ions melt the metal tips. Hence, the nanodroplets are nucleated, which move toward the substrate and oxidized in atmospheric air.”
Then, the surface morphology and film thickness were characterized using scanning electron microscopy, water contact angles were measured using a custom-made tensiometer and optical transmittance reportedly measured via spectrophotometer reached a range of 350-800 nm.
Researchers used eight monocrystalline solar panels for the field experiment, manufactured by Sun Solar Ecotech and installed at the Faculty of Science at the university. Four coated and four uncoated solar panels were exposed to the sun at an inclination of 19 degrees, facing south with a power output of 5 watts.
The uncoated panels were placed in the middle, while the uncoated panels were placed on the edges. All the panels were also connected to two identical resistors and a microcontroller unit, which calculates the electrical power generated by each panel and sent to the scientists for analysis.
During testing, researchers looked at reflectiveness, surface topography, hydrophilicity, photocatalytic properties and the coating’s anti-soiling properties.
According to the study, the average power difference per day was 5-9% between the coated and uncoated panels. Overall, an average power gain of 6.62 percent due to the coating was reported over the entire study period.
The highest value difference showed coated panels operated with a power yield of 14.22 percent more than the uncoated panels. This result was reportedly due to rainy weather, allowing the coating to produce more power by light entrapment, and the super-hydrophilic property of the coating allowed less dust due to rain to cover the panels.
Other Solar Panel Coating Research
In 2020, the United States Department of Energy Solar Energy Technologies Office awarded Arizona State University spin-out company, Swift Coat, $1 million to commercialize a dirt-eating solar glass coating that also aims to increase energy generation.
Using two coatings—a preexisting antireflection coating and a photocatalytic titania (titanium dioxide)—Swift Coat is aiming to create a material that both repels dirt and breaks down organic compounds.
Over the 18-month program, Swift Coat will be using titanium dioxide to develop the photocatalytic titania coating. When absorbing UV light, the material creates a chemical reaction that breaks down organic soilants.
Once developed, the coating will be applied using a technique that sprays dry nanoparticles through a gas deposition process called “aerosol impact-driven assembly.” In choosing this type of application, the coating avoids possessing a high refractive index and thus matches the industry standard for anti-reflection coating performance.
Additionally, the coatings applied make the module surface hydrophilic, making it easier for rain or dew to wash away the already loosened inorganics.
While the coatings could potentially increase energy generation by 3% percent over standard panels, it would also reduce operation and maintenance costs due to its self-cleaning properties. When completed, Swift Coat’s hardware aims to coat single-module-wide coating line at 10 meters-per-minute, producing roughly 300 60-cell solar modules per hour.
Last year, a team from the University of Michigan 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 percent more energy in tests.
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.
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% percent over an entire winter season. In comparison, uncoated panels had an accumulation of about 59 percent.
