Recognized as a key for energy-saving, zero energy building (ZEB) is being enforced as a target by Japan’s government for the average of the newly constructed buildings by 2030. In the ZEB environment, local power generation is expected to be enough for supplying all loads. As the solar energy generation that is generated by PV system relies on the availability of solar radiation, an energy storage system is necessary to complement the system. Both PV and battery system need to be optimized in term of size. This paper proposed the sizing method for PV system equipped with battery system by concerning the energy independence condition which includes the zero energy. The optimization method is based on building’s energy independence represented by the self-sufficiency ratio (SSR) and the self-consumption ratio (SCR). By utilizing these two ratios, the hybrid system size is determined efficiently towards zero energy target.