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 at 700, 750 and 800 °C in a muffle furnace for 1000 hours. After 1000 hours isothermal exposure, Coterill 750 leads the benchmark in front of Pyromark 2500, while other black coatings degrade optically. Uncoated samples oxidize significantly and appear darker than some aged black coatings.