Study on optical and thermal performance of a linear Fresnel solar reflector using molten salt as HTF with MCRT and FVM methods

A novel linear Fresnel reflector which employs the evacuated tube, CPC secondary reflector, and uses molten salt as the heat transfer fluid (HTF) was designed and studied in this paper. A 3D optical model was developed to simulate the radiation transmission within the system with Monte Carlo Ray Tracing (MCRT) method. Based on the model, firstly, the optical performance of the systems using cylindrical and parabolic mirrors was compared. Then the local solar flux distribution on the absorber surface and the optical efficiency were computed. Then the effects of the slope error, time and location, etc. were investigated. Finally, the thermal performance was investigated by coupling the MCRT with the Finite Volume Method (FVM). The optical simulation results indicate that the system with optimized cylindrical mirrors can achieve nearly the same performance as the one with parabolic mirrors. The solar flux distribution on the absorber exhibits a non-uniform characteristic which can be improved by using mirrors with proper slope error. The instantaneous optical efficiency of 65.0% at normal incidence and the annual mean optical efficiency which ranges between 55.2% and 34.8% from the equator to N50° can be achieved. The numerical results indicate that the temperature profiles on the absorber follow the non-uniform solar flux. The collector efficiencies are all above 46.0% under the studied conditions. Both the thermal efficiency and the collector efficiency increase with decreasing salt temperature and with increasing radiation. These results suggest that the introduced system is a feasible choice for using molten salt as the HTF in Fresnel system.