For many cities around the world, bus electrification is a key priority in order to tackle air pollution. And Europe is no different. Just recently, Transport for London announced that three of the city’s bus routes are now running fully electric. In 2019, the EU’s “Clean Vehicles Directive” set binding procurement targets for zero or low emission vehicles by authorities and public transport operators.
In Germany, public transport operators use 22,000 diesel-powered buses. They account for up to 20% of vehicle emissions in cities The aim is to gradually replace them with environmental-friendly vehicles. By 2025 almost a quarter of newly procured public transport buses will have to be zero or low emission vehicles. By 2026, the quota will even be 65 percent.
Electric Bus ≠ Bus
Electric buses play an important role in implementing the Clean Vehicles Directive. Since operation of electric vehicles (EVs) differs greatly from traditional public transport, operators are now facing numerous questions: Which system should be used – battery, hybrid or trolley? Which vehicles fit best in terms of range, capacity and charging time? How many buses are needed to provide a constant service? How does an efficient charging infrastructure look like? And what impact do charging stations have on the route network?
“The shorter range of batteries compared to diesel engines is certainly one of the biggest challenges. The capacity of electric batteries is often not sufficient for a complete day of duty”, says Sebastian Sielemann, a PTV expert in this field. “An intelligent, well-planned charging strategy is essential.”
In order to enable operation according to the timetable, public transport operators combine single journeys to circulation chains. In this way, all trips of each chain, can be done by one vehicle. Numerous factors must be considered, to ensure that the range of the e-bus covers the entire route. EVs not only use energy when driving, but also when heating or using the windscreen wipers. In addition, breaks within the circuit (for example planned pauses in the timetable) are usually not enough for recharging. And the charging infrastructure is not always available where the bus pauses.
Smart charging strategies
There are different approaches to setting up the appropriate charging strategy. In Paris, for example, officials opted for “overnight charging”. In order to preserve the historic cityscape, they did not want to switch to overhead lines. Electric buses are only charged during nighttime at the depot. Vehicles are therefore equipped with high-capacity batteries that have a large range.
The Zurich public transport authority on the other hand decided on “in motion charging”. E-buses are not only charged at the depot, but also while riding via overhead lines. Thus, a smaller battery size is enough.
Amsterdam’s Schiphol Airport chose the “opportunity charging” strategy. Its 100 electric buses are “refueled” at terminal stops during operation at rapid charging stations with 450 kW in 12 minutes. They cover 500 kilometers a day, seven days a week.
“There is no generally valid solution. The charging strategy for electric buses depends on respective local conditions and must be considered individually,” states Sebastian Sielemann. “For public transport operators, the shift towards electric vehicles is a major investment for the future. This must be well planned. Using what-if scenarios in simulations with PTV software, the various issues can be precisely analyzed, modeled and tested as early as the planning phase”.