Spectrally selective copper oxide films

Temperature- and Angle-Dependent Emissivity and Thermal Shock Resistance of the W/WAlN/WAlON/Al2O3-Based Spectrally Selective Absorber

“…Spectrally selective absorber coatings on the receiver tube of concentrating solar power systems (CSP) should exhibit a high absorptance in the solar spectrum and low infrared emissivity at high temperature, and these properties would enable to realize the capability of spectrally selective absorbers in solar thermal systems. − For an ideal spectrally selective absorber, the absorptance should be ∼0.95 in the solar spectrum with heat loss fraction of 0.05. − The aforementioned criteria indicate that performance of a solar thermal system is limited not only by how efficiently the solar irradiation is captured by the absorber but also by how effectively the absorbed energy can be utilized to heat the fluid flowing through the receiver with minimal heat loss. − This can be determined in terms of the heliothermal efficiency (η), which is calculated by estimating the difference between the absorbed energy by the surface and the radiated energy from the material with respect to total incident concentrated radiation. − The expression of the heliothermal efficiency (η) is the following: where α is solar absorptance, ε­( T ) represents thermal emissivity of the selective coating at a temperature T , σ indicates Stefan–Boltzmann constant, and C and I are concentration factor and solar flux intensity on the earth’s surface (1000 W/m 2 ), respectively.…”