Infrared emissivity of copper-alloyed spinel black coatings for concentrated solar power systems

• Published in: Solar energy materials and solar cells 2019-09, Vol.200, p.109961, Article 109961
• Main Authors: González de Arrieta, I., Echániz, T., Fuente, R., Rubin, E., Chen, R., Igartua, J.M., Tello, M.J., López, G.A.
• Format: Article
• Language: English
• Subjects: Absorptance; Absorptivity; Alloy systems; Alloying; Coatings; Concentrated solar power; Conversion efficiency; Copper; Emissivity; High temperature; Infrared emissivity; Morphology; Nickel base alloys; Porosity; Porous materials; Selectivity; Solar absorbing coating; SOLAR ENERGY; Solar power; Spinel; Superalloys; Temperature; Temperature effects
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2019.109961

The directional spectral emissivities of four new copper-alloyed spinel coatings for concentrated solar power applications were measured up to 800 °C and compared Pyromark 2500®, deposited in the same conditions on Inconel 625. Reproducible results were found for all coatings at all temperatures, with similar spectral features at working temperatures. The temperature and angular dependences are related to the morphology and composition of the samples. The total hemispherical emissivity increases up to 400 °C for all coatings and then stabilizes, with similar values for most materials, except for the porous Cu0.5Cr1.1Mn1.4O4 coating. This coating offers a reduced total hemispherical emissivity due to increased semitransparency at high angles arising from its porosity. This porosity is linked to an increase in both the solar absorptance and the emissivity in the normal direction due to enhanced light trapping, which means that this coating shows signs of directional selectivity. These results, together with the data dispersion reported for Pyromark, suggest that structural properties are key for the high-temperature emissivity of the coatings and highlight the importance of direct emissivity characterization. Combined with absorptance measurements, these emissivity measurements allow for accurate calculations of the high-temperature efficiencies of the coatings, which reach values up to 0.929. •High-temperature directional spectral emissivity study of Cu-containing spinels.•Porosity enhances solar absorptance and lowers the total hemispherical emissivity.•Importance of temperature and directionality for calculating accurate efficiencies.•Conversion efficiency of 0.929 obtained at 1300 suns for porous Cu0.5Cr1.1Mn1.4O4.