Researchers in India developed a predictive framework combining degradation experiments, weather data, and environmental stress models to assess how rain affects anti-soiling solar coatings. They found that coating lifetime strongly depends on local climate, installation tilt, and rainwater pH.
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Researchers at the Indian Institute of Technology Bombay have assessed the impact of rain on antisoiling coatings for solar panels and have found that their lifetime can vary significantly depending on local climate and installation scenario.
“The key novelty of this work is the development of a framework to predict the lifetime of anti-soiling coatings under rain exposure by integrating experimentally derived degradation parameters with the Arrhenius-modified Peck model, which separately considers temperature and pH effects on degradation, and Miner’s rule, which predicts the failure of a material under variable cyclic stress,” corresponding author Sonali Bhaduri told pv magazine. “The study investigates how environmental parameters, such as rainwater pH, temperature, and installation conditions, influence coating degradation and lifetime.”
“The results showed that coatings exposed at tilt angles lower than their roll-off angle exhibit substantially lower lifetime due to prolonged water retention on the surface. The work also highlights the greater dependence of some fluoropolymer-based coatings on rainwater pH than that of phenylsilicone-based coatings,” Bhaduri added.
The researchers experimentally determined the activation energy and pH dependence factor for four commercial hydrophobic anti-soiling coatings using accelerated water immersion tests at different temperatures and pH levels. These degradation parameters were then linked with real weather data from different geographical locations to estimate coating lifetime under realistic outdoor conditions.
The research group investigated the durability of four types of hydrophobic coatings on 5 cm × 2.5 cm solar glass samples. Three coatings, labeled A, B, and D, were fluoropolymer-based, while a fourth coating, named C, was phenylsilicone-based. Fifteen samples of each coating were immersed in pH-controlled water solutions at temperatures of 25 C, 45 C, 65 C, and 97 C to evaluate degradation behavior under simulated rainwater conditions.
Contact angle measurements were periodically performed, and coatings were considered failed when the angle dropped below 90°, indicating loss of hydrophobicity and self-cleaning ability. Additional experiments at pH 5, 6, and 7 at 45 C were conducted to determine the pH dependence factor of the coatings.
The testing showed that coating lifetime decreased with increasing temperature for all coating types. Moreover, the scientists found that fluoropolymer-based coatings exhibited significantly greater pH dependence than the phenylsilicone-based counterpart, highlighting differences in degradation behavior under acidic conditions.
The analysis also demonstrated that the coatings exposed to higher rainfall and acidic conditions experienced shorter lifetimes, while Coating C demonstrated the least sensitivity to pH changes and the most stable performance overall. “All coatings showed lower coating life under varying pH when exposed at a tilt angle lower than their respective roll-off angle,” the academics added.
The researchers warned that the lifetime predictions presented in the study should be interpreted as relative indicators of coating performance under specific conditions, rather than precise estimates of actual service life. “In real outdoor environments, coating degradation is governed
by the combined influence of multiple environmental stressors,” they also stated.
“Our approach provides a pathway for climate-specific coating selection and can serve as a foundation for future modeling of combined environmental stressors affecting PV reliability and durability,” Bhaduri concluded.
The research findings were presented in the study “Lifetime Prediction of Antisoiling Coatings Undergoing Degradation due to Rain,” published in Progress in Photovoltaics.
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