Multiple Nanoparticles Coupling Strategy for Enhancing Optical Filter Performance of Spectral Splitter Used in Photovoltaic/Thermal System

Selective absorptive nanofluid can pre-absorb certain sunlight wavelength that cannot be used by PV and transmits remaining sunlight to the surface of PV, which can decouple PV from the thermal receiver spatially. In order to improve the harvesting of electricity and high-temperature thermal nanofluid, it is important to design an optimal optical filter window (transmit sunlight with wavelengths of 732–1067 nm to the surface of the photovoltaic cell and absorb the remaining sunlight). However, designing optimal optical filter is facing following challenges: (1) inherently narrow selective absorptivity property of single nanoparticle; (2) simplified numerical calculation method calculating transmittance; (3) ignoring the shape of the nanoparticle. In this study, the idea of using multiple nanoparticles coupling effect to design an optical filter is proposed, which can superimpose the narrow absorption bandwidth of different nanoparticles to obtain a wide absorption bandwidth of the whole system. In addition, an improved transmission method considering light-matter interaction at air/vessel and liquid/vessel interfaces is adopted to compute the transmittance. The results calculated by improved transmission method are more accurate than widely used traditional Lambert-Beer law, which is verified by experimental test. Furthermore, the effect of nanoparticle shape on spectral transmittance is also investigated, which shows that spiny Ag can approximately extend absorbance from 400 nm to 600 nm compared to nanosphere silver. Finally, the results show that optical filter efficiency of nanofluids with multiple nanoparticles coupling (Ag, spiny Ag, ZnO, ITO) can reached up to 35%.