Battery systems are one of key factors in the effective use of renewable energy systems because self-production of electricity by renewables for self-consumption has become profitable for building applications. This study investigates the appropriate capacity of the Battery Energy Storage System (BESS) installed in all electric zero energy power houses (AEZEPHs). The AEZEPH used for this study is a high energy-efficient house, and its criteria indicates that all the electricity energy within the house is covered based on the generated electricity from on-site renewable energy systems, including that the annual net site energy use is almost equal than zero. The AEZEPHs used for this study is located in Daejeon, South Korea, and the experiment for measured data of electricity consumed and generated in the buildings is carried out for a year (i.e., Jan. through Dec. 2014). Based on the measured data, patterns of the electricity consumed by the AEZEPH and generated by an on-site renewable energy system (i.e., photovoltaic (PV) system), and the appropriate capacity of BESS is then analyzed and evaluated using the EES analysis tool, named Poly-sun. Results from this study indicate that the self-consumption can be increased up to 66% when the ESS system is installed and used during operated hours of the PV system, and the amount of received electricity during the week tends to be reduced by about two times.