In this research, an optimisation for building integrated hybrid PV/diesel generator system for zero load rejection for Malaysia is performed. The optimisation is performed considering a loss-of-load probability (LLP) less than 0.01. However, the daily averages of solar energy for Malaysia and a mathematical model of a hybrid PV/diesel generator system are used in this optimisation. The optimisation presented in this paper aims to calculate the optimum capacities of a PV array and diesel generator, which investigate the minimum system cost. An optimisation problem in terms of system units' cost is solved graphically in this study. Moreover, the optimised system is compared to other energy source choices to highlight its feasibility. The recommended configuration of a PV/diesel system located in Malaysia is C-A = 1.2, C-DG = 0.3, while the optimum C-B is 0.1. The results of the optimisation show that a PV/diesel generator choice is more feasible compared to a standalone PV system or diesel generator system because it reduces the system cost by 35%. (C) 2011 Elsevier B.V. All rights reserved.