Low cost anti-soiling coatings for CSP collector mirrors and heliostats

Most concentrating solar power (CSP) facilities in the USA are located in the desert southwest where open land and sunshine are abundant, but airborne dust is prevalent. The accumulation of dust, sand and other natural pollutants on collector mirrors and heliostats presents a significant operational problem and M&O cost for the CSP facilities in this region. The optical performance of the CSP collectors is key to achieving low electricity costs, where a 1% decrease in reflectance directly leads to a 1% increase in the levelized cost of electricity (LCOE) generated by these facilities. In this paper we describe the development of low cost, easy to apply anti-soiling coatings based on superhydrophobic (SH) functionalized nano silica materials and polymer binders that posses the key requirements necessary to inhibit particulate deposition on, and adhesion to, CSP mirror surfaces, and thereby significantly reducing mirror cleaning costs and facility downtime. The key requirements for these coatings are excellent optical clarity with minimal diffuse reflectance, and coating mechanical and exposure durability in harsh desert environments while maintaining SH and dirt shedding properties. The coatings developed to date have excellent SH properties with water contact angles > 165 degrees and rolling angles < 5 degrees. The solar weighted optical reflectance of the anti-soiling coating over the wavelength range 250 nm to 3 mu m is > 99% that of uncoated mirror surfaces with coating diffuse reflectance being < 1% over this wavelength range. Ongoing mechanical and accelerated solar UVA exposures also indicate these coatings will meet the required durability goals.