High-Temperature Solar Selective Coatings

Improved Solar collectors (40) comprising glass tubing (42) attached to bellows (44) by airtight seals (56) enclose solar absorber tubes (50) inside an annular evacuated space (54). The exterior surfaces of the solar absorber tubes (50) are coated with improved solar selective coatings (48) which provide higher absorbance, lower emittance and resistance to atmospheric oxidation at elevated temperatures. The coatings are multilayered structures comprising Solar absorbent layers (26) applied to the meta surface of the absorber tubes (50), typically stainless steel, topped with antireflective savers (28) comprising at least two layers (30, 32) of refractory metal or metalloid oxides (such as titania and silica) with substantially differing indices of refraction in adjacent layers. Optionally, at least one layer of a noble metal such as platinum can be included between some of the layers. The absorbent layers cars include cermet materials comprising particles of metal compounds is a matrix, which can contain oxides of refractory metals or metalloids such as silicon. Reflective layers within the coating layers can comprise refractory metal silicides and related compounds characterized by the formulas TiSi. TiSiC, TiAlSi, TiAN and similar compounds for Zr and Hf. The titania can be characterized by the formulas TiO, TiOs. TiOx or TiON with X 0 to 1. The silica can be at least one of SiO, SiO, or SiON with X=0 to 1.