Regarding the continuing increase of renewable energy in smart grid, energy storage system (ESS) has play an important role in deal with the fluctuation of new energy, such as PV and wind. However, the application of ESS in smart grid is limited to its expensive cost, therefore, how to configure a reasonable capacity in a comprehensive scenario of smart grid has become a key concern for researchers. To address this issue, this article first uses a fuzzy clustering algorithm to generate scenarios of wind and PV, and builds an economic operation model for ESS based on profit margin analysis for solving the optimal capacity configuration of ESS. At the same time, an economic criterion for investment of ESS considering the life loss in smart grid is proposed and sensitivity analysis is introduced to study subsidy policies, such as electricity prices and initial investment unit prices.