Public transit electrification planning with energy storage via second-life batteries – a stochastic programming approach

As part of decarbonization strategies, public transit systems are aiming to electrify their fleets in response to climate targets and net-zero goals. However, the resulting increase in electricity demand may lead to energy stress on the electrical grid. Second-life batteries (SLBs) offer a potential solution, yet their financial, energy, and environmental impacts remain underexplored, as does the long-term planning for their integration. This study proposes a strategic planning model for transitioning a public transit fleet to battery electric buses (BEBs), incorporating the deployment of SLBs as a battery energy storage system (BESS). The model jointly optimizes decisions on asset procurement, replacement, route-level fleet assignments, the integration of SLBs as BESS, and the installation of a supporting renewable energy system (RES). A multi-period stochastic programming framework is employed to optimize planning under uncertainties, such as vehicle and battery costs, and the model is formulated as a mixed-integer linear program. A case study of Metro Vancouver's transit system is conducted to evaluate three electrification pathways. Results show that SLBs can meet up to 84 % of the fleet's recharging energy demand, reduce annual operating costs by up to $107 million, and lower total system costs by $78 million. A sensitivity analysis of battery and electricity prices provides insights into the integration of SLBs under different market and policy conditions.