The performance and durability of single-layer sol-gel anti-reflection coatings applied to solar module cover glass

Abstract

A significant source of energy loss in photovoltaic (PV) modules is caused by reflection from the front cover glass surface. Reflection from the cover glass causes a loss of~4% at the air-glass interface. Only a single air-glass interface can be coated on crystalline silicon solar modules as an ethylene-vinyl acetate (EVA) layer is inserted between the cover glass and the silicon absorber. A single-layer anti-reflection coating (ARC) on the outer surface of the cover glass is effective at reducing reflection losses over the wavelength range of most PV devices. The coating investigated in this work reduces the reflectance loss at the glass surface by 74%. However, the longterm durability of sol-gel coatings has not been established particularly for use in hot and humid climates. In this work, we investigate the damage resistance of a single-layer closed-surface hard coat ARC, deposited using solgel methods by applying a variety of accelerated weathering, scratch and abrasion test methods. The reflectance of the sol-gel ARC was measured and then the coating was put through a series of durability and environmental tests. The coating is resistant to damage from heating and can withstand temperatures higher than the phase change temperature of soda-lime glass. Scratch testing demonstrated that the sol-gel AR is relatively hard and difficult to remove from the substrate surface. Pull tests and cross-hatch testing also confirmed the strong adhesion of the coating. Weathering experiments show some degradation in weighted average reflectance, particularly an increase in reflectance of 0.6-0.9% after 1000 h of exposure to damp heat. Testing also showed a vulnerability to exposure to acid. These results indicate that the performance of this type of ARC could deteriorate and possibly delaminate in humid climate conditions The ARC had a low water contact angle, which means the coatings are hydrophilic and, therefore, hygroscopic increasing the risk of water damage over extended periods of time. This work shows that sol-gel anti-reflection coatings are currently unsuitable for use on PV and are unlikely to remain durable across the 25 year industry standard.

Testing the Durability of Anti-Soiling Coatings for Solar Cover Glass by Outdoor Exposure in Denmark

“…These tests use controlled conditions to determine the vulnerability of a coating to a particular environmental stress. We have previously reported on the development of the tests for hydrophobic coatings [9] and the use of these tests on different types of anti-reflection coatings [28][29][30]. These tests are now being used on candidate hydrophobic coatings to discover the degradation mechanisms that must be addressed before the coatings can be used in the field.…”

Cam Güneş Panelleri: Bir Derleme

“…demonstrated how the optical model of the oxide-metal-oxide (OMO) stack being necessary for accurate tuning of the color was developed for OMO/glass samples [116]. The damage resistance of a singlelayer closed-surface hard coat ARC deposited by sol-gel methods and applying various accelerated weathering, scratch, and abrasion test methods was investigated by Womack et al, reporting the lowered reflectance loss at the glass surface by 74 % [117]. PV panels of different technologies (polycrystalline Si, a-Si, and CdTe) mechanically treated in pilot-scale by single shaft shredder were examined [118].…”

Abrasion resistance of hydrophobic, anti-soiling coatings for solar cover glass

“…Abrasion is simulated in the laboratory using linear abrasion testing equipment with a range of abrasive pads with increasing hardness [3]. Washability testing can also be carried out to include the effects of water or solvents.…”