Abstract: In microgrid systems, energy storage devices are employed to mitigate fluctuations in renewable energy sources such as solar and wind power. To address the energy storage capacity optimization problem in these systems, a bi-level, multi-objective optimization model is proposed, based on the NSGA algorithm. The upper-level model aims to minimize investment costs, annual electricity purchases, and annual comprehensive operational costs, while the lower-level model focuses on minimizing daily comprehensive operational costs, reducing maintenance costs, and lowering wind/solar curtailment rates for typical daily scenarios. The bi-level model is solved using a combined NSGA and CPLEX algorithm. This model calculates the optimal energy storage configuration that minimizes the microgrid system′s annual comprehensive operational costs, considering the best single or combined objectives of energy storage investment, wind/solar utilization rates, and annual electricity purchase. The effectiveness of the proposed model and combined algorithm is validated through simulation results across three distinct scenarios.