An integrated approach to implementing opportunity charging for electric buses

Abstract

The introduction of electric buses (EBs) is required in order to achieve global greenhouse emission goals. However, operating an electric bus fleet (EBF) requires careful consideration of both the mobility and energy systems in charging strategies. In literature and in real life many cases show careful consideration of only one of the systems and an oversimplification of the other, resulting in failed implementations. This paper focuses on the need for additional charging of EBs during the day using on-route opportunity charging during the on- and offboarding of passengers in residential neighbourhoods. This research aims to provide an integrated approach to bus service design, including both the mobility and energy systems. Additionally, this paper presents insights into the effect of traffic management on the feasibility of on-route opportunity charging. Two simulation tools are used for the integrated decision-making approach: SUMO and Gaia. The Simulation of Urban MObility (SUMO) software provides results regarding the energy consumption behaviour and charging needs of the EBs. Gaia provides results regarding the transformer load rate in the residential distribution grid. This paper proposes five strategies with a varying configuration of charging capacities, charging times and the introduction of traffic management via traffic priority. The five strategies are tested against three requirements: two from the mobility system and one from the energy system. The research presented uses a case study of bus line 36 in Rotterdam, the Netherlands. The results of this research show that residential neighbourhoods are often unable to handle chargers with the maximum capacity of the buses in the case study of 450 kW. A mid-range charger of 200 kW is possible in most cases. With a 200 kW charger, the on- and offboarding time of passengers is insufficient to complete daily operations. Therefore, additional charging time is necessary. Without the introduction of traffic priority, the timetable cannot be completed. With the introduction of traffic priority, travel time and energy consumption are reduced by 9.8% and 4.5%, respectively, and daily operations can be completed while satisfying the requirements of the mobility and energy systems. The results presented in this thesis suggest that an EB route design with opportunity charging is impossible without considering both mobility and energy systems simultaneously. From the mobility perspective, opportunity charging is feasible only if the charging infrastructure can meet the buses' energy needs without disrupting the schedule. From the energy perspective, it is essential that opportunity charging is implemented where and when sufficient charging capacity is available. The introduction of traffic priority allows for the satisfaction of all requirements and displays an example of the connection between mobility and energy systems.