Charging for electric buses

Getting sufficient power from the grid to charge a fleet of electric buses requires connected thinking. By Richard Simpson

The case for electrifying bus fleets is a strong one: not only are electric buses around 80% more energy-efficient than diesels, they can also make a substantial improvement to local air quality. There are, however, barriers to their introduction: a major one being provision of adequate capacity to charge the fleet in terms of both electrical input and output. The UK actually led Europe when it came to introducing electric buses: back in 2017 the ‘national’ fleet boasted 191 battery-electric (BE) buses and 153 plug-in hybrids. This meant the UK faced all the typical ‘early adopter’ problems, the most prominent of which was charging.

Municipal Nottingham City Council was a pioneer of electric buses in the UK – and encountered conflicts between the companies supplying chargers, the bus manufacturers and local government when the chargers initially proved incompatible with the vehicles. One of the vehicle types chosen for Nottingham required top-up charging for two hours during the day and this had to be scheduled to coincide with drivers’ breaks. Ultimately, the lesson learned was that vehicle manufacturers had to supply a turnkey solution, including chargers, that was tailored to the operator’s needs. Driver education also emerged as vital if electric buses were to perform to their potential. Once trained, Nottingham’s drivers said they preferred the electric buses.

In York, council-supported park-and-ride services were converted to electric buses from 2017 and similar conflicts emerged between the charger supplier and the bus manufacturer. It emerged that the operator was treating the buses as though they were diesels, with little or no training or monitoring. Again, education and training were vital to the success of electric buses, together with the gathering of accurate data and free and honest exchanges of information between the various parties.


The conversion programme ultimately saw a £1 million investment in charging provision, including the installation of a new sub-station. Now, many of these problems can be effectively outsourced. Zenobē is an international company that designs, builds and operates battery solutions and is playing a leading role in the electrification of Britain’s buses. Steve Meersman, director and co-founder of Zenobē, says that the key to successful depot electrification is to “get all the stakeholders around the table from the start”.

“We’ve electrified 78 bus depots in the UK, and each one is unique,” he reveals. “Every part of the operation needs to be discussed, including how the buses come in and park at the end of the day – and how they leave the depot in the morning. That has a huge influence on charger provision: for instance, you don’t need a high-capacity fast-charger at the back of the depot for the bus that is first home at night and last out in the morning. Every decision made on any aspect of the design and operation of the depot will have an impact elsewhere.”

Meersman says his experience is that more than 40 different layouts have had to be proposed and discussed before a satisfactory solution is found. The key, he says, is that the sooner the correct solution is found and agreed, the lower the costs involved.

“You need to ensure that the decision is based on reality: for instance, the way buses actually enter and leave the depot, not the way that people think that they should in theory,” says Meersman. “Ask if power requirements can be reduced by change: for instance, if the last bus in isn’t the first bus out, then you have longer to recharge it.

“Our experience with National Express in Coventry indicates it is vital to get drivers on board from the start,” he says. “With diesel buses, the difference in energy consumed between a good driver on a good day and a bad driver on a bad day may be in the order of 20%. That can easily go to 50% with electric buses, and then heating and cooling requirements depending on the weather can add another 30% variation on top of that!”

One of the most important aspects of the process, says the Zenobē man, is to get all the depot teams together and look at real data generated by trial vehicles. At that point, work out how to tighten the margins between the best and worst.

A bonus is that the simplicity and proven reliability of today’s electric buses means that fleet sizes can often be reduced. “You don’t need as many spare ‘engineering’ vehicles, as workshop times are reduced,” reasons Meersman. “Typically, a diesel bus fleet will have between 15 and 30% spare buses to cover those that are in the workshop: with battery-electric you can halve that. That, in turn, reduces the need for parking capacity at the depot, but in many cases we find parking capacity can be retained even with chargers in the depot.”


Bus operators have an understandable desire to ensure there is adequate charging capacity at a depot. “People want to introduce risk adjustments at each stage and, if they do, it’s quite easy to end up with a 300% over-capacity,” reports Meersman.

“Where an operator has 100 buses, they might want 100kW of charging for each one, plus 2kW for power lost to the cables: you end up with a 12MW requirement. You can’t have that amount of power in the heart of a city.

“The power requirement can be much reduced by smart charging: there’s no need to charge all the buses at once,” he states. “Six megawatts is, in reality, sufficient for 100 buses and in Coventry, where we have good drivers and a back-up battery, we support 180 buses on that amount. We actually started with 15MW and have been able to downgrade the supply as the drivers got better at handling the electric buses. As service partners, we shoulder the financial risk if buses can’t be charged, which enables operators to be braver in their decision-making.”

One of Zenobē’s key offers is to provide battery back-up for mains power. For this solution, it uses repurposed batteries that have ‘done their time’ on buses and have depleted capacity, but can still hold enough power to meet peak demands when the mains supply may not be adequate. They also have the advantage of being able to hold surplus power from the grid, which can be produced when output from renewables is high but demand low, and either used to charge buses, or sold back into the grid when output is low and demand high.

Zenobē will also assist bus operators with harvesting their own energy, by installing solar panels on suitable buildings, and storing this energy in batteries until it is required.


Existing grid connections at Stagecoach’s Guildford depot had capacity issues that threatened a fleet electrification project. A traditional grid upgrade required to charge a nine-bus fleet would take over 12 months and cost an estimated £2-3 million. Stagecoach indicated it was likely to move its operating centre in the future, further reducing the case for a grid upgrade.

Zenobē supplied a stationary battery on site which incorporated charging infrastructure, and installed a custom management software system. Charging infrastructure and software was installed in six weeks with minimal disruption to operations, and is highly mobile should Stagecoach relocate its operation.

The total cost was substantially less than a grid upgrade, saving Stagecoach around 80% of the predicted costs. Furthermore, payment is spead over the seven-year contract, eliminating high upfront costs.

Stagecoach gains a share of the additional income generated by Zenobē from the battery feeding the National Grid when not charging the buses.

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