Renewable energy sources （RESs）, such as photovoltaic （PV） and wind power generation, have the characteristics of random fluctuation and intermittence. The output of RESs should be smoothed to inhibit the adverse effects of RESs fluctuations on the power grid. The energy storage system （ESS） is playing a more and more important role in the application of RESs due to its discharge/charge characteristic. Therefore, the optimal planning and design of ESS is of vital importance because of the expensive cost of ESS.