  It is of significance to incorporate spectral selectivity technology into
solar thermal engineering, especially at high operational temperatures. This
work demonstrates spectrally selective solar absorbers made of multilayer
tungsten, silica, and alumina thin films that are angular insensitive and
polarization-independent. An overall absorptance of 88.1% at solar irradiance
wavelength, a low emittance of 7.0% at infrared thermal wavelength, and a high
solar to heat efficiency of 79.9% are identified. Additionally, it shows the
annealed samples maintain an extremely high absorption in solar radiation
regime over at least 600 C and the solar absorbers after thermal annealing at
800 C still work well in a CSP system with an even high concentration factor of
over 100.
