There are many different and efficient ways of charging electric buses. In this article, the experts from Daimler Buses Solutions explain which strategies are the most simple and cost‑effective.
Omnibus Magazine
The four principal charging strategies for electric buses.
An overview of the best solutions for charging electric buses.
The four principal charging strategies for electric buses.
Simply purchasing an all‑electric vehicle is not the end of it – the many possible methods of charging high‑voltage batteries safely and efficiently are very diverse and complex. A range of options is available for electrifying depots, from simple, mobile chargers as an entry-level solution to complex pantograph systems for fully automated, future‑proof depots.
An overview of the best solutions for charging electric buses.
Charging concept 1: Chargers with CCS plug.
Variant A of the CCS plug: the mobile charger.
The easiest and most flexible option for charging the all‑electric eCitaro is a mobile charger, which is primarily used for initial vehicle tests or for workshop use, particularly in places where no suitable charging infrastructure is yet available. The charger with CCS plug has an output of up to 80 kilowatts, can be carried in the vehicle and can be used on the move.
Variant B of the CCS plug: the built-in charger.
The next evolutionary stage is a permanent charger with one or two CCS plugs, which can be connected directly to the charging sockets on the buses. This cost‑effective, fixed system can be installed both in enclosed depots and outdoor areas.
The charging stations, which usually offer up to two times 150 kilowatts of charging capacity, can also be designed in compliance with calibration laws and AFIR and monitored and controlled via a charging management system. This system also controls the preconditioning function, so that the bus can be thermally preconditioned before use. Charging anomalies can also be displayed directly in the backend. The variable installation options for the charging sockets on the eCitaro with Performance Package (from model year 2023) help customers to install their charging stations precisely to fit.
“A split system allows the space in the electric bus depot to be utilised flexibly and efficiently.”
Expert opinion:
A split system is a useful way to optimise the distances between vehicles and charging stations. This involves installing a distribution station to which several charging points can be directly connected. The electrical wiring of the satellite charging stations is usually routed underground, which keeps the operating routes between the buses clear and makes optimal use of the depot’s capacity. The power unit can be installed up to 100 metres away, so the layout options are very flexible. Although this increases costs slightly, it is still the cheapest way to design a professional depot.
Charging concept 2: Plug charging from above with cable reels.
The next expansion level for a fully electrified depot involves installing charging reels (suspended cable reels) in the hall ceiling. In this relatively elaborate and cost‑intensive construction with a solid steel cross‑member, the CCS plugs are lowered or pulled manually or electrically from the reel to connect the bus in the conventional way. Additional installations for fire protection (e.g. thermal imaging cameras) or monitoring can be attached to stable crossbeams as required. Charging stations of this kind can also be installed outdoors.
Expert opinion:
As the charging infrastructure is largely housed in the hall ceiling, parking areas can be set up in the same way as for diesel buses. This means that very little additional space is required, apart from the space needed for the power units, which can be flexibly installed. In this concept, the power units may be larger and can be designed as compact, central container solutions that are used as charging arrays for multiple vehicles.
Charging concept 3: Roof-mounted pantographs.
The most complex and advanced charging option in series production is the pantograph. These are charging arms that are permanently installed on buses or in charging stations and connect to the power supply automatically. Perhaps their greatest benefit is that they can also be used in everyday operations without the need for qualified specialist personnel – essential for the fully automated depot of the future.
In the panto-up version, the pantograph is usually installed on the front section of the bus. To charge the vehicle, the pantograph lifts and connects to a charging hood installed in a depot or bus stop.
“We installed an innovative solution for our customer HTM in The Hague. It provides 109 charging points for 109 buses using a similar amount of area as was previously used.”
Expert opinion:
These systems can achieve up to 300 kilowatts of charging capacity – twice as much as plug charging. This partially compensates for the loss of a battery module. They are primarily used for what is known as opportunity charging, where vehicles are charged with less power overall in more frequent and faster sessions. Vehicle communication and thermal preconditioning can be carried out in the same way as when charging from a plug. This means that, in a best-case scenario, buses can be operated around the clock without being stuck at the depot for hours on end.
Charging concept 4: Pantographs and charging rails.
“Advanced charging” is how we could describe this combination of pantographs and charging rails. In this configuration, inverted pantographs are fixed to the infrastructure and are usually not fully exposed to the weather. The charging capacity and automation are the same as those of conventional, vehicle-mounted pantographs. Advantage: The only elements installed on the vehicles are very compact, heatable charging rails (the pantograph is lowered onto the rails). This means that no battery modules have to be sacrificed as the charging rails can easily be installed on top of them.
Expert opinion:
This system has obvious benefits in terms of space requirements, charging capacity and automation and is thus becoming increasingly popular. It also allows vehicles to be thermally preconditioned before setting off, as with other solutions. A further safety benefit: In emergencies, all pantographs can be lifted at the same time across the depot to disconnect the power – a great advantage in the event of a fire.
