selective surface coating
Copper Sun integrated collector and storage solar collector utilizing SOLKOTE selective coating technology on tubular copper solar absorbers. Credit: Sun Systems Solar, Inc.
A selective surface coating is a material with high absorbence and low emittance properties applied to or on the surface of solar absorbers. The usual coatings provide a degree of absorption of over 90%.
Solar paints, which can be mechanically applied to the absorbers (with either brushes or sprays), are less or not at all selective, as they have a high level of emission. Galvanically applied selective coatings include black chrome, black nickel, and aluminum oxide with nickel. Relatively new is a titanium-nitride-oxide layer, which is applied via steam in a vacuum process. This type of coating stands out not only because of its quite low emission rates, but also because its production is emission-free and energy-efficient.