A state-of-the-art review on the multifunctional self-cleaning nanostructured coatings for PV panels, CSP mirrors and related solar devices

Solar energy-based devices are protected using glass surfaces that need to be cleaned periodically to maintain their desired optimum performance. If these devices are large and placed in remote locations or not easily accessible, manual cleaning is not only difficult but prohibitively expensive, which in turn necessitates suitable self-cleaning coatings to be applied on the glass surfaces. Traditionally, sol-gel processes have been used for such coating developments. However, for large volume production, spray based processes have certain advantages, especially their lower cost and ease of manufacturing. The self-cleaning coatings can be either hydrophobic or hydrophilic determined by the contact angle between water and glass surfaces. Further, care must be taken when selecting coating materials and the corresponding coating parameters to maintain the transparency or reflectivity of such glass surfaces used for the particular device applications. The optical transparency of self-cleaning or anti-soiling coating is of paramount importance in the case of solar photovoltaic panels and related solar devices. Therefore, enhancing their performance by additional cost-effective anti-reflecting coatings, is a plausible solution. A state-of-the-art of this effort is being attempted in this review. It includes the necessary basic principles, cost-effective deposition techniques, performance evaluation standards and life expectancy of such coatings. The scope of the present review has been broadened by including specific issues related to concentrated solar power devices and by highlighting recent advances in atmospheric pressure plasma deposition processes. Additionally, use of non-fluorinated polymer materials and related nanostructured materials has been suggested for the fabrication of the self-cleaning coatings.