Performance of a parabolic trough concentrating photovoltaic/thermal system: Effects of flow regime, design parameters, and using nanofluids

The aim of this study is to simulate a parabolic trough concentrating photovoltaic/thermal (CPV/T) system and to investigate its performance from energy and exergy viewpoints in both laminar and turbulent flow regimes. After validating the proposed model with available experimental data from the literature, the effects of various parameters, including concentration ratio, pipe length, and diameter, on the performance of the system were examined in detail. Further, the effects of glazing the system and using nanofluids as the working fluid on the system efficiency were determined and discussed. The performance of the CPV/T system was also compared to that of a flat-plate photovoltaic/thermal (PV/T) system. The results showed that increasing the pipe length from 0.5 to 5 m decreases the total energy efficiency by about 9.33% in the laminar regime and 1.09% in the turbulent regime, while it increases the total exergy efficiency by about 33.65% and 10.37% in the laminar and turbulent regime, respectively. The increment of the pipe diameter has a negligible impact on the system performance, for a given flow rate. The results also indicated that applying nanofluids in the laminar flow is more effective compared to the case of the turbulent regime. Furthermore, the PV/T system can reach greater energy and exergy efficiency compared to the CPV/T system, whereas employing nanofluid in the CPV/T system is more efficient compared to the case of the PV/T system.