To support regional decarbonization, this study focuses on designing an optimal green energy management system in which renewable energy (onshore, offshore wind power, solar power, and biomass power) are made as prioritized sources to meet the temporal energy demand. The optimization algorithm is applied in the Kitakyushu City of Japan. At first, the annual renewable energy supply and energy demand were estimated and disaggregated to an hourly level, considering the temporal patterns. The storage battery is introduced to rebalance the supply and demand sides. Through its control, the surplus of balance between renewable energy and demand is stored by the battery without supplying from grid power. Meanwhile, the grid power is only supplied when the total green energy supply is less than the demand. The minimum carbon dioxide (CO₂) emission is defined as the objective function. The constraints are considered as including the battery capacity, charging and discharging balance, hourly and annual supply potential for each type of energy, and hourly supply should meet the demand. As our solution, 99.9% of onshore wind power, 56.8% of offshore wind power, 69.8% of solar power, and 45.4% of biomass power were essential in a year to meet each hourly demand and achieve the minimum CO₂ emissions.