Optimal integration location and sizing of renewable energy systems in AC railways for cost optimisation

This study presents a bi-level optimisation framework for the optimal integration of photovoltaic (PV) systems and energy storage systems (ESS) in AC railway traction power supply networks. The framework addresses two key objectives: determining the optimal capacities and selecting effective integration locations for PV and ESS to enhance energy efficiency and reduce operational costs. At the master level, a grid search explores combinations of PV and ESS sizes and locations, while the slave level employs a mixed-integer linear programming (MILP) model solved with CPLEX to optimise ESS charge/discharge operations under variable energy conditions. Case studies demonstrate that integrating a 10 MW PV system with a 1 MWh, 2 MW ESS can reduce daily operational costs by 30% (from £20k to £14k per day). The system shows resilience to short-term fluctuations in solar irradiance but exhibits higher sensitivity during extended low-irradiance periods. These findings highlight the importance of carefully balancing system configuration, operational strategies, and renewable energy variability. Overall, the proposed approach provides a structured methodology for achieving cost-effective and sustainable PV-ESS integration in railway electrification systems, supporting both economic and operational performance objectives.