Blackbody-cavity ideal absorbers for solar energy harvesting

Abstract

Spectrally selective solar absorbers (SSAs), which harvest heat from sunlight, are the key to concentrated solar thermal systems. An ideal SSA must have an absorptivity of unity in the solar irradiance wavelength region (0.3–2.5 upmu m), and its infrared thermal emissivity must be zero to depress spontaneous blackbody irradiation (2.5–25 upmu m). Current SSA designs which utilize photonic crystals, metamaterials, or cermets are either cost-inefficient due to the complexity of the required nanofabrication methods, or have limited applicability due to poor thermal stability at high temperatures. We conceptually present blackbody-cavity solar absorber designs with nearly ideal spectrally selective properties, capable of being manufactured at scale. The theoretical analyses show that the unity solar absorptivity of the blackbody cavity and nearly zero infrared emissivity of the SSA’s outer surface allow for a stagnation temperature of 880 ^circ C under 10 suns. The performance surpasses state-of-the-art SSAs manufactured using nanofabrication methods. This design relies only on traditional fabrication methods, such as machining, casting, and polishing. This makes it suitable for large-scale industrial applications, and the “blackbody cavity” feature enables easy integration with existing concentrated solar thermal systems using the parabolic reflector and Fresnel lens as optical concentrators.