Novel black selective coating for tubular solar absorbers based on a sol–gel method

Abstract

Multilayered chrome-free black selective surfaces for solar thermal energy conversion were produced by a low-cost sol–gel dip-coating method. The optical properties of the Cu–Co–Mn–Si–O based nanocrystalline thin films have been characterized by spectrophotometry and spectroscopic ellipsometry. After optimization of the multilayer design, a solar absorptance of 0.95 and a thermal emissivity of 0.12 at 100°C have been achieved.The stability of the coatings at 360°C in air surpasses the one of the conventional robust black chrome coatings existing on the market. Additionally, the corrosion resistance has been tested in acidic environment. The novel black selective coatings were deposited with satisfactory homogeneity on 2m long stainless steel tubes. Fast and energy-efficient induction heating was used for thermal annealing.Receiver tubes coated in this manner are especially interesting candidate for applications working with concentrated solar power (CSP) such as power plants for solar thermal electricity generation, co- and tri-generation.