REFLECTIVE COATINGS FOR LARGE-AREA SOLAR CONCENTRATORS

Reflective/protective coatings were applied to pre-formed 2.5-m-long s olar concentrator panels by the magnetron sputtering process. Low-cost manufacturing processes such as hydrostatic forming of aluminum solar concentrator panels are needed to keep the costs of domestic power ge neration low. Without treatment, the specular reflectance of the alumi num panels was less than 20%. As expected, silver (Ag) and aluminum (A l) coatings applied directly over the untreated panels did not signifi cantly increase specular reflectance. To provide a specular base surfa ce, approximately 100-mu m-thick urethane layers were applied to the p anels before deposition of the reflective coating. This smoothing laye r filled in scratches and defects. Reflective Ag and Al layers, with p rotective overcoats of Al2O3 and Si3N4, were deposited onto the uretha ne-coated panels by reactive magnetron sputtering with ion assist in P acific Northwest National Laboratory's 3 m coating chamber. The specul ar reflectance of the panels increased to an average of 92% at visible wavelengths, very near the reflectance of Al coatings on highly polis hed glass. Panels with Ag metal layers displayed similar increases. Th e optical performance uniformity of the coating was better than +/-5%. The measured primary concentration ratio of the panels was 800:1, whi ch far exceeded the design ratio of 500:1. The total concentration rat io was 2400:1. The coatings passed MIL-spec environmental and durabili ty tests. Field testing of the concentrator dishes and coatings is con tinuing, and test results will be reported. (C) 1996 American Vacuum S ociety.