Design of near-ideal and omnidirectional selective solar absorber for high-temperature applications

Efficient absorption of solar radiation with minimal thermal losses is required for efficient solar-to-thermal energy conversion. For this purpose, spectrally selective and omnidirectional surfaces are required that have strong, ideally unity, absorption in the solar spectral window for all incident angles and low, ideally zero, emissivity in the spectral range of blackbody radiation at operating temperature. In this article, we propose theoretically and experimentally lithographic free broadband and omnidirectional solar absorber for high-temperature applications made in a dielectric-metal-dielectric-metal fashion. We have used chromium (Cr), titanium (Ti), and tungsten (W) as a metal layer in the designed absorber due to their high thermal stability at high temperatures and compared their performance. The power balance equation is used to calculate the steady-state temperature considering free and forced convection conditions. W-based absorber shows >90% absorption in the solar window below cutoff wavelength for blackbody working at 600 K with <10% emissivity in the thermal window. Finally, we fabricate the W- based sample and experimentally measure the temperature rise of 100 K under one sun condition. The designed absorber can be used for several solar-thermal applications including solar-steam to electricity generation, water purification, space heating, and solar-thermal energy storage.