The efficient and reliable production of solar energy is essential for a sustainable future. However, the deposition of particulate matter (PM) on photovoltaic (PV) modules, commonly referred to as soiling, remains a significant economic concern for the solar industry. Soiling can reduce solar energy production by as much as 70%, depending on the location. Consequently, frequent cleaning of PV modules is required to maintain optimal performance, leading to increased operating and maintenance costs for solar power plants. Researchers have previously explored various methods to mitigate soiling on PV surfaces, with a particular focus on the application of hydrophobic and super-hydrophobic coatings. These coatings have shown promise in reducing PM deposition by increasing the particle rebounding rate, resulting in lower mass loading on the coated surfaces Additionally, dew formation on PV surfaces exacerbates soiling issues, leading to cementation, particle caking, and capillary aging. Dew events can occur frequently in certain regions, further complicating the challenge of maintaining clean PV surfaces. In a new field study led by Professor Michael Valerino from the Civil and Environmental Engineering Department at Duke University, published in the peer-reviewed Journal Solar Energy addresses the combined effect of hydrophobic coating and dew suppression on soiling in PV systems. Conducted in the western part of India, the research provides valuable insights into the potential of these techniques to improve the efficiency of solar panels and reduce maintenance costs.
Hydrophobic coatings have demonstrated their ability to repel water and, consequently, reduce the adhesion of dust and PM on PV surfaces. The coating process involves the conversion of hydrophilic silanol groups on silica particles into hydrophobic groups (≡Si-O-Si-(CH3)3), resulting in an amorphous hydrophobic layer on the glass surface. Scanning electron microscopy images confirm the presence of these particles on coated surfaces, while atomic force microscopy reveals increased surface roughness due to the coating. This enhanced roughness and altered surface chemistry contribute to a significantly higher water contact angle (WCA), making the surface highly hydrophobic. Additionally, the coating reduces reflection, leading to increased hemispherical glass transmittance compared to uncoated surfaces.
One of the challenges associated with maintaining clean PV surfaces is dew formation. Dew events can lead to the repositioning of particles on PV panels, resulting in localized regions of high mass loading, commonly referred to as Milli-Scale Non-Uniformity (MSNU) The study shows that multiple dew events can significantly increase MSNU, causing concentrated mass loading regions on both hydrophilic and highly hydrophobic surfaces. In contrast, surfaces subjected to dew suppression exhibit lower MSNU values, indicating effective prevention of dew formation.
The authors also investigated the impact of hydrophobic coating on the particle size distribution of deposited PM. Notably, particles in the 10–30 μm size range dominate the mass loading on both uncoated and coated surfaces, consistent with previous findings in various regions. Hydrophobic coatings reduce the adhesion forces between dust particles, leading to increased particle rebounding and lower mass deposition on coated surfaces. This effect is most pronounced for particles in the 10–20 μm and 20–30 μm size bins, demonstrating the effectiveness of hydrophobic coatings in mitigating soiling.
The research team quantified mass loading and soiling loss for coated and uncoated samples with and without dew suppression over the entire sampling period. Unsurprisingly, uncoated samples exposed to dew exhibit the highest mass loading and soiling loss. Hydrophobic coating and dew suppression individually reduce mass loading and soiling loss compared to the UCWODS samples. However, the combination of hydrophobic coating and dew suppression demonstrates the most significant reduction in mass loading and soiling loss. These findings emphasize the importance of considering both hydrophobic coating and dew suppression strategies to maximize soiling mitigation. Dust Potency (DP) represents the soiling potential of dust deposited per unit mass on PV surfaces. The study also evaluated DP values for different samples, including uncoated and coated surfaces with and without dew suppression. Surprisingly, no statistically significant differences in DP are observed between these samples throughout the sampling period. This result contrasts with some previous studies, highlighting the need for further research to understand the impact of anti-soiling coatings on DP.
In conclusion, the research conducted by Professor Michael Valerino and his team at Duke University offers valuable insights into soiling mitigation strategies for solar PV panels. The combination of hydrophobic coating and dew suppression has shown remarkable promise in reducing mass loading and soiling loss, ultimately improving the efficiency and maintenance of PV systems. However, the complex interplay between coating, dew formation, and dust characteristics requires further investigation. This study serves as a crucial step toward enhancing the reliability and sustainability of solar energy production and paves the way for future advancements in the field of PV surface protection. As the demand for clean and renewable energy sources continues to grow, innovative research in the realm of solar panel maintenance and performance optimization remains essential. The findings presented hold the potential to significantly impact the solar industry by reducing operational costs, increasing energy yields, and contributing to a more sustainable energy future.
Aniket Ratnaparkhi, Drashti Dave, Michael Valerino, Mike Bergin, Chinmay Ghoroi, Reduction in solar PV soiling loss using hydrophobic coating with and without dew suppression, Solar Energy, Volume 253, 2023, Pages 332-342,