Numerical analysis of a modified combined volumetric filtered concentrating PV/T system using MCRT and FVM coupled method

To solve the problem that solar cell temperature limits high-quality thermal output from a traditional concentrating PV/T (CPV/T) system, this paper proposes a linear CPV/T system with a vacuum tube receiver incorporated with a combined volumetric filter. In which a solid absorption glass along with liquid filter is used as the combined volumetric filter for the silicon CPV module. However, the entire photovoltaic/photothermal conversion process in the combined filtered CPV/T system is complicated. To achieve more accurate predicted performance, a three-dimensional numerical model of this system is presented and the combined Monte Carlo Ray-Tracing (MCRT) method with the Finite Volume Method (FVM) is employed. The stated optical models are validated against the experimental results from an indoor test under one sun. And the coupled method of MCRT and FVM is also verified. The optimal filter combination is obtained by optical simulation using LightTools software based on the MCRT method firstly. Then, the solar energy flux distribution on the receiver achieved from LightTools is adopted as a boundary condition for CFD simulation. Based on these models and the MCRT-FVM coupled method, parametric study is conducted to quantify optical efficiency, temperature distribution, energy and exergy efficiency of the system. The results show that the optimal combined filters for silicon PV module are HB700+water and HB700+propylene glycol (PG). Because the optical absorption of water differs from that of PG, the PV maximum temperature is 308.36 K using HB700+water and it is 321.94 K using HB700+PG, whereas the outlet temperature of water and PG exceeds 352 K. The greater thermal and total exergy efficiencies can be achieved at higher inlet temperature and lower mass flow rate, while the electrical exergy efficiency shows slight change. To further reduce heat loss, an indium tin oxide (ITO) coating with low emissivity is applied on the receiver surface. The results reveal the receiver with 240° ITO coating achieves the highest total exergy efficiency of 14.92% and optical efficiency of 88.94%.