A novel real-time fast acting BESS-based control approach is proposed to smooth the solar power by making optimal use of the BESS capacity. The proposed method is implemented on a solar system to compensate for solar power intermittency and improve distribution grid power quality. The novelty of the proposed method is to provide a systematic way to optimize the size of the battery capacity for the desired level of solar power smoothing. The obtained results show a 45 percent reduction in the BESS capacity compared with the common moving average technique.