Determination of optimal size and depth of discharge for battery energy storage in standalone microgrids

Battery energy storage (BES) has a critical role in standalone microgrids to improve reliability and reduce operation costs. Two major factors affecting the economic viability of integrating a BES to a microgrid are its investment cost and lifetime. The BES investment cost greatly depends on its size, while the BES lifetime, which can be defined as the total number of charge/discharge cycles that it can perform, depends on how deep the battery is discharged each time. Therefore, it is imperative to determine both the BES optimal size and depth of discharge when integrating BES to a microgrid. This paper presents a standalone microgrid expansion model with the ability of determining the optimal BES that minimize the microgrid expansion cost. The BES long-term investment and short-term operation models, as well as complicated constraints relating the charge/discharge schedules to the BES lifetime, are further developed and formulated. A mixed integer programming approach is used to formulate the microgrid expansion problem. Numerical simulations on a test standalone microgrid are performed to validate the proposed models.