The battery electric buses (BEB) are set as key tools to enable cities to meet their challenging transport environmental targets, i.e. the reduction of Greenhouse gas (GHG) emissions, improvement of local air quality, as well as to provide a quieter system for both passengers and the urban community. The recent evolutions of the traction battery technology, with increasing battery energy and power densities, battery durability and dynamic performance, driven by both the light and heavy duty vehicles segment, has opened the way for a series of transit bus electrification initiatives, focused on the evaluation of the feasibility of the BEB technology for the zero local emission bus fleet targets, already set by transit authorities in some important cities worldwide.
In this context, as important as the onboard electric traction technology itself, currently already mature for BEB test trials, is the required electric charging infrastructure and its inherent operational effects, which ultimately might affect the service levels and costs of transit bus service.
The roll out of BEB fleets is challenging for i) the utilities companies, given the required (high) electric power capacities; ii) the city planning authorities, due to the required land for charging stations in large and densely populated cities and iii) the transit operators, that might redesign their operational strategy, to cope with battery charging and range limits. To deal with these stringent boundary limits, it is required from the stakeholders a coordinated effort, focused on the development of a transition plan, that necessarily might take into account strategic topics, such as: i) the BEB minimal operational requirements; ii) the design of the required charging facilities, such as the charging strategies (overnight, on-route, as well as conductive or inductive charging) and the required power levels; iii) the charging management tools, such as smart charging management, to minimize the BEB impact on the electric grid and electricity rates; iv) utility grid reliablity/resilience approaches, to circumvent the effects of grid outages; v) the operational and infrastructure costs; vi) the charging hardware interoperability requirements; and vii) the required operational staffing for the innovative technology.
This work provides a review of the BEB charging infrastructure technology and the associated effects on the bus transit system operability, such as the operational BEB range, that ultimately is not just only a matter of battery size or capacity, but rather a combination of charging strategies (i.e. low powered depot and high powered opportunity/top-up charging) and operational conditions, such as passenger loads, route topography, speed and acceleration regimes. The adopted charging strategy, that might range from a single to a mix of slow and fast charging approaches, might affect the BEB fleet availability and required size, as well as the total costs (both capital and operational) of the BEB systems.