The purpose of this study was to conduct optimal renewable energy analysis of the freezer and boiler application of a typical office building using a Homer (Hybrid Optimization Model for Electric Renewables) program developed by the NREL (National Renewable Energy Laboratory) program. The Stand Alone Model and Grid-Connected MODEL were use to derive the optimum combination of NPC (Total Net Present Cost). The results indicated that the optimum value for the Stand Alone Model is 30 kW PV, 50 KW FC, 30 KW Battery, and the GRID-Connected Model was derived to be optimal to use only GRID. Since there is no renewable energy that has not yet reached Grid Parity, this was considered a predictable result, which further analyzed the optimal combination according to the change in electricity prices and gas prices. The result was optimal (GRID + PV combination) when the current electric dermal is about 2.5 times (gasprices). In conclusion, when the new renewable energy is applied, the PV was more economical than other renewable energy sources, and even if the gas struggle (if the electricity price of$1.2/kWh) is constantly rising, gas prices were not a major factor in the selection of energy combinations.