Evaluation of Battery Requirements for Hybrid and Electric City Buses

This paper presents an evaluation of battery requirements for hybrid and electric city buses. Technical specifications of recently developed lithium based batteries and vehicle simulation results are used as basis for the evaluation. The battery requirements are evaluated in terms of power and energy capacity, calendar and cycle life as well as costs. Conventional diesel, parallel and series hybrid, plug-in hybrid, and electric city bus were chosen as different bus applications. The simulation results of the diesel powered city bus were used as reference for performance requirement and a point of comparison in operation cost analysis. Simulations were carried out in four different types of driving cycles. The evaluation shows that lithium based batteries offer sufficient specific power and energy capacity meanwhile requirements for costs and cycle life durability are dependent on the bus application, the driving cycle, and the operation schedule. Especially a power intensive driving cycle can be challenging for the high energy batteries in terms of cycle life. There are also noticeable differences in performance between different battery chemistries. For plug-in hybrid and electric city buses, fast recharge capability can increase significantly the costeffectiveness in bus fleet operation. The operation cost analysis also indicates that the battery cost is more important for the plug-in hybrid and electric buses whereas the initial cost of the bus is a major factor for the charge sustaining parallel and series hybrid buses.