Optical performance of parabolic trough solar collectors under condition of multiple optical factors

Abstract

Since various optical factors, including sunshape and optical errors, coexist in practice, their coupling effects on the PTC's optical performance deserve in-depth explorations. Previous studies mainly focused on individual effects of several typical optical errors or simple description of optical errors using a unified Gaussian model. Thus, this study is committed to investigating the coupling effects of multiple optical factors on the PTC's optical performance based on the theoretically individual characterization of each optical factor. The Monte Carlo Rays Tracing method was adopted, and the effective sunshape model was established for sampling of incident rays by convolving the incident sunshape model with the specularity error model. It is revealed that larger circumsolar ratio and specularity error produced more uniform heat flux distribution on the absorber. The advantage of high optical quality reflectors in improving optical efficiency was more outstanding in clearer weather. As circumsolar ratio was more than 0.2, improving specular quality to very high degree (<3 mrad) reduced instead the optical efficiency. When tracking error and slope error were maintained respectively less than 4 mrad and 2 mrad, the weakening of optical efficiency was limited. The optical efficiency was more sensitive to slope error than to tracking error. The offset direction along positive Y-axis caused at maximum 2.19 times increase in heat flux density than that without optical errors, which causes threat of overheating to the absorber. When alignment error and tracking error were in the opposite direction, the optical loss could be compensated, whereas that in the same direction enlarged the optical loss. The slope error weakened the compensation effect and aggravated the weakening effect.