Forty Shades of Black: a Benchmark of High Temperature Sprayable Black Coatings Applied on Haynes 230

Abstract

The solar receiver coating opto-thermal efficiency has a significant impact on a central receiver system thermal final system efficiency. The development of durable high solar absorptance coatings with simple application process and minimal thermal treatment can directly improve the receiver efficiency, thus reducing the levelized cost of electricity. During the past years, innovative receiver coatings for solar thermal tower plants have been developed on various substrates and tested under isothermal load at different temperature levels. In this paper, eight commercial black coating formulations are sprayed on Haynes 230 metal coupons. Solar absorptance and thermal emittance are monitored before and after isothermal exposure. Mass deviations are also measured to pinpoint any oxidation or coating outgassing. Isothermal testing is performed in laboratory muffle furnace for 1000 hours, covering the operating temperature range from 700 to 800 °C. After 1000 hours exposure at 800 °C, Pyromark 2500 leads the benchmark, while many black coatings degrade optically. Uncoated samples oxidize significantly and appear darker than some aged black coatings.