Investigation on the correlation between solar absorption and the size of non-metallic nanoparticles

Solar heating with nanoparticles (NPs) exhibits great potential for photo thermal applications, such as direct absorption solar collector and photovoltaic photothermal system. The performance of NPs suspended in base fluid plays a major role in improving solar harvesting efficiency. Most researchers are focused on the optical properties of mental NPs due to their strong localized surface plasmon resonance (LSPR), resulting in a great solar absorption. To our best knowledge, theoretically and systematically studying on optical properties of non-metal NPs is still open. Therefore, we present a thorough investigation on the correlation between solar absorption and the size of CuO, carbon and graphite with the diameter range of 20-200 nm though using the finite-difference time-domain (FDTD) method. Results show that absorption and scattering cross sections of NPs have great sensitivity to particle size. The absorbed power increases with particle size growing. And solar absorption power for per unit volume of the three NPs has optimal diameter about 60 nm, 100 nm, 160 nm for carbon, graphite, and CuO, respectively. Graphite exhibits best average solar absorption efficiency, following by carbon and CuO except for particles smaller than about 30 nm. For particle diameter of 30 nm, carbon has better sunlight absorption property than that of graphite. This work aimed to provide guidelines for choosing non-metal particles and their optimal size for solar thermal utilization.