Analysis of the impact of high-flux irradiation in accelerated aging testing of solar absorber coatings

• Solar absorber coatings are compared under different thermal cycling aging tests. • A furnace-based method is compared to on-sun and simulated high-flux methods. • Solar absorptance differed by less than 0.3 % between the three testing methods. • Morphological changes and phase formation of coatings were similar across methods. • The simpler furnace test method may be sufficient for many applications. Solar absorber coatings play a critical role in concentrating solar thermal (CST) plants by impacting receiver efficiency. To study the lifetime of coatings, they are typically subjected to accelerated aging tests using various methods. In this study, thermal cycling tests designed to simulate the effects of cloud passage were conducted using three methods: (1) a furnace method using a vertical split tube furnace; (2) an on-sun flux method using a solar furnace; (3) and a simulated flux method using a high-flux solar simulator. The simplest of these three methods, cycling heating in a programmable furnace, avoids the requirement for a concentrated radiation source. The main aim of the testing was to compare these methods and understand if high-flux irradiation impacts the optical degradation rate. After 500 cycles (around 62 h of total testing time) using the simulated flux method and 300 cycles (around 40 h of total testing time) using the on-sun flux method, the maximum difference in solar absorptance between these two high-flux methods and the furnace test method was less than 0.3 %, a result consistent for both coating types tested in this study, Pyromark and a coral-structured coating. We suggest the effects of UV radiation or operating with higher flux gradients across samples may not be important to aging characteristics of coatings, and that the simpler furnace test method may be sufficient for many applications.