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

• Multilayered nanocrystalline selective solar absorber coatings.
• Chrome-free low-cost sol–gel method including induction heating for thermal annealing.
• Superior thermal stability at 360 °C with respect to black chrome coatings.
• Solar absorptance of 0.95 and thermal emissivity of 0.12 on steel substrates.
• Prototype coatings on 2 m long stainless steel tubes as CSP candidate.

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 2 m 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.