A Hybrid Energy System (HES) consisting wind/solar/Battery has been analyzed for a particular load profile. This analysis is done with the aim of obtaining optimal sizing of HES. Optimal sizing results are obtained with considering important factors such as reliability, cost and other unexpected uncertainties. Dependency of Sources on atmospheric factors introduces nonlinearity in the system and on the demand side also load is fluctuating. For highly non-linear problem it is not preferable to do analysis with conventional optimization technique. Further this paper proposed an Ant Colony Optimization (ACO) based approach to get optimal sizing of HES. The outcome is compared with the previously applied technique to confirm the efficacy and compatibility of proposed technique for considered HES.