A Cost-Optimization Model for Sizing Grid-Connected PV-Battery Energy Storage Systems with Cyclic Capacity Degradation

Photovoltaic (PV) and battery energy storage system (BESS) capacities are among the fastest-growing renewable energy technologies worldwide. The optimal sizing of these technologies is crucial to achieving a cost-effective integration into existing energy systems and increase competitiveness. However, existing models often neglect cyclic (dynamic) BESS degradation and replacement costs, and assume a calendar aging (static) system lifetime, use low-resolution consumption and solar irradiation data, or determine the optimal size of only one component. This contribution proposes a cost optimization model for the size of a grid-connected PV-BESS system including cyclic battery degradation based on its intensity of use. The model considers the most relevant technical parameters of PV and BESS, including state of charge (SoC), round-trip efficiency, depth of discharge (DoD), and self-discharge rate, and the lifetime based on a maximum number of cycles. The energy flows of the system are based on the principle that PV generation initially covers consumption directly, surplus energy is used to charge the BESS, deficits are covered by discharging the BESS, and any remaining demand is drawn from the grid or surplus electricity is fed into the grid to generate revenue. The model is validated on the basis of a real-world use case, a single-family house in Vienna, Austria, with the hourly load profile and PV generation on site available. The results indicate that assumptions about calendarbased BESS degradation lead to shorter replacement periods and lower available BESS capacity compared to the cyclic degradation model, leading to higher costs for assumptions with calendarbased degradation.