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

Abstract

The presence of soiling on photovoltaic modules reduces light transmission through the front cover glass to the active absorber, thereby reducing efficiency and performance. Current soiling mitigation techniques are expensive and/or ineffective. However, anti-soiling coatings applied to the solar cover glass have the potential to reduce soiling for long periods of time without continuous maintenance. This paper reports the performance of two transparent hydrophobic coatings (A and B) exposed to the outdoor environment of coastal Denmark for 24 weeks. A comparison was made between the performance of coated and uncoated glass coupons, periodically cleaned coupons, and accelerated laboratory tests. Although initial results were promising, water contact angle and transmittance values were found to decline continuously for all coated and uncoated coupons. Surface blisters, film thickness reduction, changes in surface chemistry (fluorine loss), and abrasion damage following cleaning were observed. Coupons cleaned every 4 weeks showed a restoration in transmittance. Cycles of light rainfall and evaporation combined with a humid and salty environment led to cementation occurring on all coupons. The development of an abrasion-resistant, super-hydrophobic coating with a low roll-off angle and high water contact angle is more likely to provide an anti-soiling solution by reducing the build-up of cementation.

Degradation of Hydrophobic, Anti-Soiling Coatings for Solar Module Cover Glass

“…We also observed a loss of fluorine functionalization. These effects were previously observed in outdoor tests [18,26].…”

“…We also observed heavy blistering on the surface of the thicker hydrophobic coatings during damp heat and UV exposure. This was also observed in outdoor testing [26]. There was evidence that the blistering was caused by retention of solvents within the bulk of the coating and inefficient curing after deposition.…”

“…Coatings on module cover glass are exposed to the outdoor environment 24/7. This is very challenging and we have already reported on the effects of exposing hydrophobic coatings in an inland location the UK [18] and in a coastal location in Denmark [26]. In both cases, the hydrophobicity of the coatings degraded more quickly than anticipated.…”

Study of Cellulose Nanocrystals (CNC) & Polyvinyl Alcohol (PVA) Composite Film Modified Using Silica and Polybutylene Terephthalate(PBT) As a Transparent, Hydrophobic, Self-Cleaning Cover

“…CNC at this time was highly acidic. To make CNC acid free, the CNC suspension was centrifuged using a Virtuose PCF01 Lab Grade Centrifuge at 4000 rpm at room temperature (25°C) for 20 minutes, while replacing de-ionized distill water each at replacement batch until the pH was approximately 6.53 (~7) measured using a Measuretech PHS-3C digital pH meter [16,19]. To separate unreacted MCC in the suspension, a 0.22µm Whatman membrane filter was used in a vacuum filtration process using a Joan VT335, vacuum filtration apparatus [22].…”

“…This leads to decrease in primary traits where the hydrophobic coating are used which makes the coating usable i.e. hydrophobic [6,7]. Economically, this becomes expensive as it needs to apply the coating periodically.…”