Twofold spectrum split enabling spectral selectivity tailoring and deep temperature decoupling for high exergy efficiency in a concentrating photovoltaic/thermal (PV/T) system

Photovoltaic/thermal (PV/T) systems are improved from PV systems to harvest both electrical and thermal energy from the solar radiation, as well as cooling the PV cells. While the previous configurations with liquidabsorptive filters have partly solved the temperature coupling of PV cells and heat collector, the unsatisfactory spectral selectivity and inevitably interlayer heat transfer remain restrict the improvement of total exergy efficiency in PV/T systems. In this study, a twofold spectrum split configuration with both Therminol VP-1/Ag nanofluid and pure water is proposed. The complementary optical properties and free flow rate controls open a window to tailoring the spectral selectivity and deep temperature decoupling. A coupling model is constructed to describe the system, which is well validated by our simplified PV/T experiment and literature. Results show that the nanofluid absorbs the shorter unsuited radiation, and water captures the longer, leading to a high spectral match parameter (0.71) and low heat generation parameter (0.26) when for nanofluid thickness of 1 mm, water thickness of 10 mm and Ag nanoparticle volume fraction of 0.01 %. Total exergy efficiency increases with solar concentration, and the highest value of 0.276 is reached for solar concentration of 30 when flow rates of nanofluid and water are 0.032 and 0.029, with an accompanying total energy efficiency of 0.829. As a comparison, two previous PV/T systems have highest total exergy efficiencies even lower than 0.25. Temperature distributions revealed that the deep temperature decoupling in the proposed PV/T system enables a hightemperature heat collection during the low-temperature work of PV cells, which is responsible for the improvement. Our study points out an approach to combine the advantages of two liquid filters, to achieve both good spectral selectivity and deep temperature decoupling.