Optimal configuration of energy system in multiple households with power interchange for reduction of CO2 emissions in Japan

As a replacement for conventional sources, which cause CO2 emissions, the installation of photovoltaics (PV) has increased extensively in residential sectors. However, large-scale PV installation causes voltage violations of low-voltage distribution grids, particularly in the residential sector. According to previous studies, energy storage systems and power interchange methods are effective in utilizing PV surplus electricity and saving energy. The objective of this study is to derive the optimal configuration of energy systems in multiple households under power interchange for the minimization of total CO2 emissions. Two methods for solving this complicated and large-scale problem are proposed. First, we considered a calculation of the optimal configuration of energy systems in multiple households as an optimal unit sizing of energy systems in a single household. Second, we examined the operational planning problem as mixed integer linear programming (MILP) with an enumeration method. We found that a heat pump water heater (HP) can be installed as the heat supply equipment regardless of the PV installation ratio by the year 2030 in Japan, when the CO2 conversion factor of the electrical grid will be 0.37 kg/kWh. In addition, the maximum impact of power interchange on CO2 emissions will lead to its reduction by 85 kg, at 75 % of PV installation ratio.