Abstract: With an increased penetration of distributed generation (DG) in the distribution network, the impact of DG's intermittency and volatility becomes more significant. Energy storage system (ESS) is a key solution for the problem associated with intermittent DG. However, research to date has not been able to establish the capacity relationship between energy storage and DG. This paper examines the ratio between ESS and DG based on the spectral analysis method, and proposes a practical estimating method. First, the principles and algorithm for optimizing ESS capacity are introduced. In addition, the spectral analysis method is used to optimize EES capacity based on actual operation data of intermittent DG. The relationships are analyzed between the maximum fluctuation and the ESS rated capacity, as well as the rated capacity and the rated energy of EES. As rated capacity is often available for DG projects, additional analysis is undertaken to assess the relationship between rated capacity and the maximum fluctuation, which can then be used to determine the relationship between ESS capacity and DG rated capacity. Based on this approach, the optimal size for capacity and energy can be approximated for EES with a simple manual calculation instead of complex energy storage optimization. Finally, we compare the algorithm of ESS capacity optimization with the practical method using a case study. The results indicate the practical method is simple and effective.

Key words: distributed generation, energy storage, plan, capacity ratio