INDUSTRY FOCUS: Alternative Propulsion Systems
1. Introduction
In the last few years, transport planners have increasingly been concerned about the need to move towards a low carbon/zero carbon future. Even for cities with extensive electric metro and light rail services, the aim is to replace fossil fuels in their bus systems. The most popular answer has been to look at the battery-electric bus (“BEB”). On the face of it, this seems such a simple and attractive solution. Just buy the bus and, as the Americans would say, “it’s good to go”. If anybody in a city with trolleybuses suggests that the trolleybus system could play a significant role, battery-bus advocates will point to the BEB and say, “Look! No wires!”.
But in life there are few magic solutions. The proposition that BEBs are much simpler and cheaper to install than trolleybuses may well be illusory. After all, there is so much in common between BEBs and battery-trolleybuses: traction motor; power electronics for control of speed and braking, batteries and chargers are shared in common. And weight for weight, power consumption will be very similar. The main difference is how power is transferred and stored, but this does not seem so fundamental a difference that it should lead to a significant difference in the capital investment required.
The aim of this document is to raise a question in the reader’s mind about the alleged simplicity and relative cost-efficiency of battery bus deployment compared with electrification using battery-trolleybuses with In Motion Charging (“IMC”). It attempts to examine the real-life capital costs of various bus electrification strategies and compare the estimated capital investments needed for:
- a BEB system based on slow overnight charging;
- a BEB system based on fast on route charging, often called opportunity charging;
- a battery-trolleybus system using partial wiring and In Motion Charging
If this causes transit planners and politicians to avoid automatic assumptions on the question of bus electrification, it will have achieved its purpose.
It is not possible to produce conclusive proof that one solution or the other is “better”, whatever that would mean to an individual planner. First, obtaining precise costs for individual components is very difficult because of issues such as commercial confidentiality. Moreover, much will depend on the individual local circumstances of a particular city and specific routes.
