Improvement of optical properties of AISI 304 as a solar absorber using a pulsed fiber laser.

Solar energy is an environmentally friendly and inexhaustible natural resource. It can be converted into thermal energy by using concentrated solar power (CSP) methods. One of the key components of CSP is a solar absorber, which absorbs concentrated solar radiation and converts it into heat. Recently, there have been many studies on enhancing the solar-to-thermal conversion efficiency of solar absorbers. In this work, a pulsed fiber laser was used to modify the surface of AISI 304 stainless steel as a solar absorbing material. By varying the energy density, surface roughness and oxide films can be formed, which affect the solar absorptance and thermal emittance of the substrate. The surface characteristics and corresponding optical properties were investigated. The surface roughness was measured to be in the range of 9-158 nm. Due to heat generated during engraving, metal surface oxidation occurs on the AISI 304 substrate, resulting in different values of solar absorptance and thermal emittance. Compared with the unmodified surface, the modified AISI 304 surfaces resulted in solar absorptance ranging from 58.57% to 91.78%, and the thermal emittance ranged from 10.56% to 32.90%. Consequently, the solar-to-thermal conversion efficiency was improved from 50.09% to 81.69%, and the technique can be used for solar absorbing applications.