Optimal Charging Scheduling of Electric Bus Fleets with Photovoltaic-Storage-Charging Stations

Research conducted at Tongji University has led to the development of an innovative charging scenario for electric buses (EBs) using photovoltaic-storage-charging (PSC) stations and the existing electricity grid. The study found that relying solely on the grid's energy supply may not fully overcome economic and environmental problems due to its overdependence on non-renewable energy sources. A new modeling and optimization approach was introduced to determine the optimal internal allocation scheme of electricity within each PSC station, minimizing the total charging cost of the EB fleet.

Key Takeaways:

• The study models and optimizes an emerging bus charging scenario where PSC stations and the electricity grid jointly supply electricity to an EB fleet, taking into account photovoltaic (PV) generation, battery storage, and time-of-use (TOU) electricity tariffs.
• The optimal charging cost of the fleet is calculated in terms of the sum of PV generation cost and TOU electricity tariff minus the revenue of supplying electricity to the grid.
• A Lagrangian relaxation procedure is designed, implementing a dynamic programming algorithm as a bi-criterion labeling procedure for the decomposed single-bus charging scheduling subproblem.
• The research selected an electric bus fleet operating in Jiading, Shanghai, to validate the model and algorithm, using weather and operational data to gain managerial insights.
• A sensitivity analysis was conducted to examine how key model parameters such as charging demand and supply, PSC battery capacity, and electricity discharging price influence the charging schedule of the EB fleet.
• The algorithm demonstrates comparable solution optimality while significantly saving computing time compared to a state-of-the-practice commercial solver.

Statistics:

• The study uses a time-expanded network with time discretization to model the EB fleet's charging and discharging behavior.
• The research finds that the optimal internal allocation scheme of electricity within the PSC station minimizes the total charging cost of the EB fleet, achieving a cost reduction of 15.6% compared to the baseline scenario.
• The PSC station's PV generation capacity is 400 kW, with a battery storage capacity of 1,200 kWh.
• The TOU electricity tariff is obtained from the Shanghai Municipal Grid Company, with a peak-hour price of 1.20 yuan/kWh and an off-peak-hour price of 0.60 yuan/kWh.

Sources:

• Xie, C., Hu, X., Li, H., et al. (2025). Optimal Charging Scheduling of an Electric Bus Fleet With Photovoltaic-storage-charging Stations. Applied Energy, 2025;390.
• Elsevier Sci Ltd (www.elsevier.com)
• Tongji University (www.tongji.edu.cn)
• Shanghai Municipal Grid Company (www.shanghai.gov.cn)