With higher depletion rates of fossil fuels and the ever growing environmental concerns on Green House Gas (GHG) emissions it has become important to investigate the impact of Internal Combustion Generator (ICG) capacity in Hybrid Energy System (HES)s for standalone applications. In order to accomplish this objective HES modeling, simulation, and optimization was done for three different system configurations based on the renewable energy source. Both mono and multi objective optimization was carried out using Evolutionary Algorithm considering Levelized Energy Cost (LEC) and unmet load fraction as objective functions. Results clearly depicts that seasonable variation of renewable energy sources having a strong impact on system component selection under higher power supply reliability which gradually reduce with the increase of ICG capacity. Published by Elsevier Ltd.