A comprehensive model and corresponding code named after SPTOPTIC for analysis of the real-time optical performance of a Solar Power Tower (SPT) with a Multi-Tube Cavity Receiver (MTCR) were developed using Monte Carlo Ray Tracing (MCRT) method. After validation, the model was used to study the optical performance of the DAHAN plant. The model-obtained results show that the solar flux in the MTCR exhibits a significant non-uniformity, showing a maximum flux of 5.141 x 10(5) W m(-2) on the tubes. A comparison of the tracking models indicates that it is a good practice to treat the tracking errors as the random errors of the tracking angles when considering the random effect on the solar flux distribution. Study also indicates that multi-point aiming strategy of tracking helps homogenizing the flux and reducing the energy maldistribution among the tubes. Additionally, time-dependent optical efficiencies were investigated, and the yearly efficiency for the energy absorbed by the tubes was found to be 65.9%. At the end of the study, the cavity effect on the efficiency was revealed quantitatively, which indicates that the optical loss can be reduced significantly by the cavity effect, especially when the coating absorptivity is relatively low. It is concluded that the present model is reliable and suitable for predicting both the detailed real-time solar flux and the real-time efficiency of SPT. (C) 2016 Elsevier Ltd. All rights reserved.