Samenvatting

Polymer front-sheets are increasingly considered as lightweight alternatives to glass in photovoltaic (PV) modules, yet their long term soiling behaviour under real outdoor conditions remains poorly understood. This thesis compares five polymer front-sheet candidates against a glass reference over twelve months of outdoor exposure at two climatically distinct sites: Kannur, India (tropical) and Delft, the Netherlands (temperate maritime).Optical transmittance, water contact angle, optical microscopy, Raman spectroscopy, and SEM-EDX were combined to relate surface chemistry changes to the observed soiling trends.

The first finding is that soiling was consistently heavier at Kannur than at Delft, with much larger transmittance losses at the tropical coastal site than at the cleaner maritime one. The second, and more significant, finding is that the soiling-resistance ranking of the materials reverses almost completely between the two sites. At Kannur, glass suffered the heaviest transmittance losses while the pure ETFE front-sheets retained transmission most effectively; at Delft the opposite occurred, with glass remaining essentially unchanged and the most hydrophobic polymer becoming the worst performer. This reversal is driven not by changes in the materials themselves but by the cleaning mechanism each climate activates. Under Kannur's dry, dusty conditions, low surface energy weakens particle adhesion and resists moisture-driven cementation, favouring hydrophobic surfaces. Under Delft's rain-mediated regime, wettable surfaces support continuous water films that lift the deposit, whereas hydrophobic surfaces shed water as droplets that fail to clean.

Contact angle measurements support this interpretation. At Kannur, every polymer shifted markedly towards hydrophilicity, consistent with the original surface being masked by a wetted deposit, while at Delft the surface chemistry was largely preserved.

Front-sheet selection is therefore better understood as a search for the best surface–substrate–climate combination: ETFE is preferable in tropical, high-dust environments, while glass and PET perform best in temperate maritime climates.