Impact of Incident Angle Dependent Optical Properties and Dirtiness on the Optical Performance of Parabolic Trough Collectors

A novel methodology for analysing the optical performance of a parabolic trough collector is presented. It intends to address the realistic behavior of the receiver tube when absorbing the incident radiation; it means that the reflectivity, absorptivity and transmittance depend on the incident angle of the sun rays. The optical properties of the glass envelope and the selective of the absorber tube are provided by real data from previous studies. The analysis is performed using a ray tracing tool and by comparison of the optical performance using the incident angle modified curves and the efficiency for a reference case as the merit indicators. The results demonstrate the significant loss of efficiency, in general terms, when this realistic effect is considered. In addition, the relevance of the dust accumulation on the receiver tubes is demonstrated by means of a sensitivity analysis as function of the dirtiness factor, which was previously calculated based on experimental data and theoretical assumptions.