‘Opportunity Charging’ for industrial electric vehicles is a term that currently has no strict definition; it is generally accepted as the practice of charging a bus for short periods of time throughout the day. Some perceive it specifically as a quick and intense burst of high power at strategic points along the route. Some see it as the chance for a bus to return to the depot during the day for a quick top up before returning to service. Others explicitly state that it is a method that allows a battery to extend its capacity over working shift but should not be seen as a critical daily requirement.
Opportunity charging can be delivered to vehicles in a variety of ways – from large pantographs that can deliver charges of up to 600kW in quick bursts via the roof of the vehicle, to a standard fast charger that can plug in and deliver up to 150kW for a longer charge from 10 minutes to an hour. TfL even trialled inductive wireless charging through equipment installed under the road surface at the bus stand (https://zeeus.eu/uploads/publications/documents/zeeus-city-sheet-london-en-final.pdf ).
In comparison, depot based charging is the simple method where all vehicles return to the depot daily for a long overnight charge ready for the next day’s service. Depot based charging relies on access to a large amount of power delivered over a relatively short period of time (either via a grid connection or local battery storage), and a fleet of large bus batteries to carry all of that power for the duration of their daily service. Battery technology is improving at a rapid rate – only a few short years ago, the idea of a full electric double decker bus was laughable, and now there are several available in the UK market – so it’s only a matter of years until a single vehicle’s battery capacity can last the majority of daily route schedules.
But just because it will be possible doesn’t mean it is optimal. High depth of daily recharge and discharge (i.e. going from 100% State of Charge all the way down to 5% and back again) can shorten a battery’s operational life, a key asset for operators moving to electric fleets. The ability to secure sufficient grid connection capacity is a postcode lottery and can in cases be prohibitively expensive; on site static storage batteries result in additional costs and management.
Opportunity charging comes with its own challenges, and a longer overnight charge is still recommended food good battery health, so the standard depot-based charging infrastructure is still required. More complex route modelling will need to be undertaken to understand the power requirements and variable factors affecting them. Route schedules will need to be reworked to provide adequate time for vehicles to charge during service; ensuring that they are robust enough to account for late running vehicles that can miss a charge and not run out of power, while also not affecting the passenger’s experience. Maintenance for the new roadside equipment, and training for drivers to use it. All of that, assuming that an ideal roadside location can be identified for this new equipment to be installed in an ideal location to suit as many of the operator’s bus route(s) as possible.
This is where I think the National Bus Strategy for England (https://www.gov.uk/government/publications/bus-back-better ) can truly benefit the future of electric bus services across the country. By working together, local government and bus operators can identify complementary ways of tackling these opportunity charging challenges. Bus stations and transport hubs are the perfect location for pantographs – they are usually central locations that serve multiple routes, and are scheduled to allow more time for passengers to board than a regular stop (meaning that a quick 4 minute charge won’t impact the service). Standard fast chargers near a route end bus stand could also be utilised by other council-owned service vehicles when not in use.
The Bus Back Better is ushering in a new era, driving the industry to reconsider how we can shape our services to not only reflect the need of our passengers and communities, but how we can embrace the transition to net zero to be able to serve the country in a new, sustainable way.
