This paper presents both the theoretical approach and the HOMER software approach for the planning of optimum long-term microgrid. The proposed microgrid system comprises of solar, wind, energy storage, diesel generator and converter systems. The microgrid objectives of this work are to be at lowest net present costs and emissions. Hence, the theoretical approach will be using modelling equations for the distributed energy resources to generate possible configurations for a preferred configuration of an optimum microgrid. As for the software approach, will be through HOMER, a microgrid simulation software developed by National Renewable Energy Laboratory, which generates optimised low net present costs configurations for the microgrid. In addition, in this paper, the importance of microgrid planning was highlighted alongside with the relevant parameters which affect the overall feasibility of the microgrid. The results obtained presents a comparison between the theoretical and HOMER approach. Followed by case studies of Australia and Ireland simulated by HOMER to determine the cause and effect of the location chosen for the microgrid.