Energy Modeling and Battery Energy Storage System (BESS) Capacity Sizing for Diesel-to-Battery Rail Retrofitting

Decarbonizing the transportation sector requires practical pathways for reducing fossil-fuel consumption and greenhouse gas emissions from existing rail systems. Although railway electrification through catenary systems offers an effective pathway toward low-emission rail transportation, its widespread implementation on existing non-electrified corridors can be constrained by substantial capital costs, infrastructure modifications, and deployment complexity. Battery-electric and battery-supported locomotive technologies provide an alternative pathway for rail decarbonization by enabling progressive fleet electrification while reducing dependence on extensive wayside electrical infrastructure. This study presents a route-level energy assessment to determine the onboard battery energy storage system (BESS) capacity required to retrofit an F59PH diesel passenger locomotive for battery-electric operation on the Piedmont corridor. The journey is simulated using the Single Train Simulator (STS), incorporating route characteristics, speed restrictions, station stops, and vehicle configuration. The resulting traction-energy demand provides the basis for evaluating commercially available battery technologies under battery-only and hybrid battery-supported operating scenarios. The simulation indicates a route-level energy consumption of 25.2 kWh/km. Among the evaluated battery technologies, the configuration requiring the fewest packs for baseline battery-only operation consisted of 142 packs, sufficient to satisfy the total route energy demand. Incorporating the added battery mass into the vehicle-energy model modestly increased this requirement to 146 packs. Under the hybrid battery-supported scenario, approximately 1305 kWh of regenerative braking energy was recoverable, with the lowest-pack-count configuration (Type D) providing sufficient capacity to enable nearly 40 min of battery-only operation. These results demonstrate how onboard energy storage and regenerative braking can support incremental rail decarbonization by reducing diesel operation, recovering otherwise dissipated braking energy, and potentially lowering the infrastructure burden associated with conventional corridor-wide electrification. As a route-level case study, the proposed methodology provides a transferable framework for evaluating onboard battery integration, identifying appropriate battery capacity, and supporting decarbonization strategies across passenger, light-rail, and heavy-rail applications.