In this paper, an optical-irradiance model is developed for analyzing the performance of a fa ade integrated solar collector. The collector is constructed in a reflector-on-top configuration with a finite, flat booster reflector and a receiver. The model can subsequently be used for optimizing the collector geometry, also demonstrated in this work. The optical model uses the three-dimensional ray-tracing technique, in conjunction with Latin hypercube sampling (LHS) for statistically generating the sampled incoming rays. This makes it suitable for urban applications. For validation, the optical model was solved with a single ray in four different geometrical scenarios and the results were compared with the 3D modeling program. The sampled rays were then simulated using the optical model to obtain the complete booster reflection in these scenarios. The total solar irradiance incident on the receiver's surface, which is the sum of direct and booster reflected irradiance, is obtained by using the results of the optical model in the irradiance model. The two applications: (i) finding the optimum installation angles; and (ii) evaluating the day -round performance, are also explained via a case study conducted in Auckland (New Zealand).