Swift Coat Spray Paints Nanomolecules on Solar Panels

Swift Coat, an Arizona State University startup has developed a new vacuum deposition method of spray painting TiO2-based nanomolecules on different types of surfaces, including solar panels. This application will help control soiling that can lead to double-digit losses in electricity generation.

The process is being tested with an unnamed glass manufacturer, and will be field proven at the National Renewable Energy Laboratory, in Golden, Colorado, then scaled up for commercial production said Zachary Holman, the CTO of Swift Coat, and professor at ASU.

“The buildup of dirt can reduce the power output of panels by up to 30 percent, and, if you aren’t the type to climb up on your roof and clean them, this loss of efficiency can persist for months,” noted Peter Firth, Swift Coat’s CEO.

The key to the soiling application is the use of TiO2 to catalyze UV light to decompose airborne dirt particles. “The special nanoparticles in our coating perform a chemical reaction powered by ultraviolet sunlight that actively breaks down dirt, keeping the panel clean and operating at optimal efficiency,” explained Shannon Poges, Swift Coat’s senior engineer. The economic impact of the new coating is that it may increase the electrical production of a solar panel by three percent per year with no increase in manufacturing expense, suggests Holman.

With the help of venture capital and the U.S. Department of Energy, Swift Coat developed its Aerosol Impact-Driven Assembly, or AIDA nanomaterial deposition method in which aerosolized nanoparticles are accelerated at sonic speed through a slit-shaped nozzle by a gas flow and attached to a substrate, according to a synopsis by the National Science Foundation (NSF).

The thickness of these nanocoatings can vary from a few nanometers (a billionth of a meter) to a few millimeters with less than 10 percent non-uniformity across a 5-inch diameter substrate, NSF says. This is roughly the size of modern silicon solar cells used in solar panels.

The nanocoating application that will help control soiling on solar panels is being supported by a DOE project grant of $1 million.

The 18 month project, Reducing Module Soiling with Scalable and Robust Photocatalytic Coatings, is being developed at Arizona State University, and will begin in March. The project will make and scale multilayer, anti-reflective and anti-soiling coatings for solar glass, DOE summarizes. DOE’s Energy Solar Energy Technologies Office supports early-stage research and development to improve the affordability, reliability, and performance of solar technologies on the grid.

These anti-soiling coatings will be deposited by a technique that sprays dry nanoparticles that are about five nanometers in diameter. The coatings have the potential to increase annual energy yield by reducing the loss of energy output that results when light gets reflected or when dirt lands on the modules, DOE explains. They will also reduce operation and maintenance costs because the modules won’t require as much cleaning, the agency adds.

Unlike other vacuum deposition processes in the solar industry today, based on massive vacuum pumps, the AIDA works much closer to normal atmospheric pressure, notes Holman. This reduces the cost of solar coatings and can help a company avoid adding a new pumped-vacuum production line, which can cost millions of dollars, he suggests.

The porosity of the nano coating is also highly controlled under the Swift Coat process, providing porosity between five percent and 95 percent, Holman noted. This porosity control enables the company to also control the reflective index of the material, which the solar industry seeks to minimize so that a maximum of convertible light hits the solar cell within the glass-encased panel.

Another feature of the AIDA process is that it can control surface roughness for a given thickness and density. It is important to have smooth glass coatings for scratch resistance, or rough coatings for enhanced adhesion.

Part of the design of the DOE project still underway is determining what sorts of materials may be added to the multi-layer coating that Swift Coat will deposit on the panel glass. Apart from helping to keep solar panel glass clean, nanoparticles deposited by the AIDA process can help boost reflected light in mono-facial and bi-facial solar panels, or those which absorb light on both sides.

When incorporated into the rear reflector of silicon solar cells, properly designed nanoparticle coatings result in an internal rear reflectance greater than 99 percent – the best measured, notes the NSF.

One type of material that may be incorporated into the multi-layer Swift Coat coating is organic dye nanoparticles, which help capture non-visible light in solar cells. “The dyes act as molecular-scale solar concentrators, funneling energy from near-infrared photons into the nanoparticles,” a researcher at Lawrence Berkeley National Laboratory said in a statement. Since the particles themselves are largely transparent to visible light, they would allow other usable light to pass through the glass. LBNL has a separate DOE grant to study and develop organic dye materials and manufacturing processes for solar energy application.

Once the Swift Coat process is perfected for this soiling application in cooperation with the glass manufacturer, the mechanical process will be scaled up to the point that an entire solar panel can be sprayed at once, Holman noted.

Swift Coat, formed to commercialize its vacuum deposition process, can coat hundreds of square feet per minute while maintaining thickness tolerances better than 10 percent, enabling consumers, industries, and the military to coat any surface irrespective of hardness, smoothness and shape, the company said.