UK researchers have studied the durability and performance of anti-reflective coatings on all solar modules, and said further work is needed to improve industry standards. Their review discusses single and multilayer techniques and provides insight into their costs and profitability.
In the magazine “Performance and durability of solar panel cover glass anti-reflection coatings – a review”, published Solar energy, the research team presented all coating plans, materials and coating methods divided into two categories – single and multi-layer coatings. In addition, it gave an assessment of their durability, paying special attention to their abrasion sensitivity.
Additionally, they discussed incorporating features such as antifouling and bandgap reflection into existing AR coatings.
As for single-layer AC coatings, the researchers said that the sum of their reflectance and transmittance values at each wavelength should be 100%, and this technique is currently the industry standard.
“Because single layers minimize reflection at one wavelength, the reflectance rises on either side of this, making single-layer AR coatings less effective at longer wavelengths,” they said, however, stressing their current limits. “Furthermore, the need for a low refractive index material means that porous materials are usually used, which can lead to durability issues.”
Multi-layer anti-reflection (MAR) coatings, on the other hand, are shown to be able to overcome the typical limitations of single-layer coatings because they have a high and low refractive index, which reduces reflection over a wider wavelength range.
“The most common type of MAR coating is a two-layer coating consisting of one high-index and one low-index material, both of which are quarter-wave thick,” they explained, adding that MAR coatings also offer an advantage in terms of durability, as there is no need for ultra-low index materials. However, they also emphasized that these coatings tend to be more expensive, which limits their adoption at the commercial level.
In terms of durability, the researchers said they found that the coatings have a lifespan of less than 8 years, even though manufacturers usually offer a 25-year warranty on their solar modules.
“Since the AR coating is hydrophilic and the water contact angle is about 20 degrees, increased fouling has been observed in some locations, causing a greater power loss than adding an AR coating,” they pointed out. “This highlights the need to add hydrophobic, anti-fouling functionality to AR coatings on the PV module, especially in locations with high levels of dirt.”
In the future, the team said, research should focus on improving the durability and versatility of AR coatings, paying particular attention to antifouling techniques. “Further work is needed to improve the UV resistance of currently available commercial hydrophobic coatings and this should be an industry focus,” it stated.