In order to determine the efficiency factors of central receiver systems (CRS) in a reasonable time frame, in particular those relating to shading and blocking, the performance simulation and optimisation codes typically use simplification techniques. One frequent simplification is the assumption that the sunshape model is a point source sun. This paper examines the effect of the sunshape model on the shading efficiency, the findings illustrating a dependent relationship between the two. In particular, if the sunshape model considers the finite size of the solar disk, the performance results depend on the angle that the candidate heliostat forms with the main direction. Additionally, with the objective of reducing both computation times and error levels, a new method for the determination of the shading and blocking efficiency is presented, developed specifically for use in performance simulation and optimisation applications in CRS. The proposed method is compared with other methods, using the results of a conventional Monte-Carlo ray-tracing method as reference, through a study of computation times and error levels. The results demonstrate that the proposed methodology produces a reduction in both computation times and error values. The causes of the main errors associated with each method are also discussed. (C) 2020 Elsevier Ltd. All rights reserved.