In this paper, a simplified model for optimal sizing of the off-grid PV system regarding value of loss of load probability is described. The model gives optimal size of system in terms of required number of PV modules, peak power, number of batteries and cost of system regarding the defined value of loss of load probability, load curve and period for which optimal size will be determined. The model is applied for determination of optimal size of the off-grid PV system for the city of Osijek. Based on measured load curve, optimal size of the system is determined for values of loss of load probability from 0.00 to 0.10 in steps of 0.01, and additionally for 0.15.