When converting the bus fleet to electric operation, the mobility company can benefit from its many years of experience in the field of electric mobility. OVB was one of the first public transport companies to start looking for sustainable solutions for the use of electric buses in local public transport as early as 2011. In Offenbach, the first purely battery-powered bus in Germany was tested in regular service. In 2016, the Supervisory Board of the mobility company gave the go-ahead for a gradual electrification of the bus fleet in the course of vehicle replacement procurement, after a further test run was successfully completed.

The switch from diesel to electric vehicles was also included in the new local transport plan in 2017. The plan defines the scope and quality of public transport in Offenbach for the years 2018 to 2022. The concept adopted by the city council provides for a one-third increase in the range of city bus services with denser cycle times and longer scheduled services, better late service and an expanded network of routes.

A well-functioning public transport system, supplemented by electromobile bike and car sharing, has been an important part of Offenbach’s climate protection concept and air pollution control plan for years. Peter Schneider: “If the city bus fleet is now not only expanded, but also electrified, this is the next logical step towards reducing carbon dioxide and nitrogen oxide emissions and thus improving the quality of life in our city”.

According to Anja Georgi, who heads the mobility division of the Stadtwerke Group, the expansion of public transport and the gradual replacement of the diesel fleet, both are future projects and cannot be seen separately from one another. “Optimising the range of services and switching to eBusse is a major step forward for Offenbach’s transport operators. We now have the opportunity to position ourselves in a modern way and to align ourselves for the future with the latest environmentally friendly technology”.

27 eBusses on 4 lines

The basis for the conversion to emission-free bus operation is a feasibility study commissioned by the Federal Ministry of Transport and Digital Infrastructure (BMVI) in 2017. The eBus concept developed by the Aachen office ebus-plan with an operational, technical and economic evaluation is now available and provides OVB with a guideline for action, also taking environmental impacts into account. The goal is to use a total of 27 electric buses in daily operation by 2023. This corresponds to around 35 percent of the total city bus fleet of currently 72 vehicles (including subcontractors).
In order to implement the new local transport plan in two phases, the number of vehicles is to increase by eleven buses at the timetable change at the end of 2018 and by a further five buses at the end of 2919 to a total of 88 vehicles. The increased demand will initially be met this year by new diesel buses with state-of-the-art exhaust technology. At the same time, however, funding is to be applied for from the federal and state governments as early as 2018 and the procurement of electric buses and the charging infrastructure is to be put out to tender throughout Europe.
The first two e-buses are scheduled to go into service around mid-20199, a further five at the end of 2019 and a total of 20 additional vehicles in the diesel fleet are to be replaced by e-buses in subsequent years as part of the replacement purchase. Although the electric buses will not be used “linearly” but variably, they will nevertheless mainly run on the four so-called priority lines 103, 104, 107 and 108. These lines will gradually be converted almost completely to electric operation.

High environmental effectiveness

Compared to their diesel-powered predecessors with consumption values of 50 litres per hundred kilometres, the 27 eBuses are expected to save 2,300 tonnes of CO2, 1,000 kilograms of nitrogen oxide (NOX) and eight kilograms of fine dust with a total annual output of around 1.9 million kilometres. 21 of the 27 electrically powered vehicles will be solo buses, six will be articulated buses. The vehicles are heated and air-conditioned with the aid of a hybrid heating system. In a certain temperature range this happens electrically, in the frost range a fossil, with bio-diesel or bio-ethanol operated additional heating switches on.

On the recommendation of specialist planner Matthias Rogge, OVB prefers a so-called occasional load to a pure depot load. In most cases, the energy requirements of vehicle use with exclusive depot charging would exceed the battery capacity currently available. With the favoured occasional load, the eBuses are reloaded within a few minutes during the day at fast charging stations with an output of 300 kW at the strategically favourable “Kaiserlei” and “An den Eichen” terminal stops, i.e. at the western and eastern ends of the city. The cargo is loaded overnight in the depot. A current collector (pantograph) is lifted from the bus roof and contacts a charging hood.

The charging points at the end stops and the short recharging times not only allow more flexible operation during occasional charging, but also the use of smaller and thus lighter batteries. Unlike an exclusive depot charge, this system does not require heavy and very expensive batteries to be carried along the entire route.
The battery capacity of the buses will be designed in such a way that at least one complete cycle will be available on each line as a power reserve. The charge level, remaining range and overall condition of the batteries as well as checking the proper functioning of the external charge at the end stops are constantly transmitted electronically to the control station.

The integration of electric mobility into line operation poses a major challenge for the municipal utility subsidiary OVB, also with regard to its technical infrastructure. The workshop and premises on Hebestraße must be comprehensively upgraded, the existing grid connection expanded and the storage halls converted and equipped with chargers and current collection points. Engineering offices provide the technical planning for this. Fire protection experts are also consulted.
The company site of the municipal utility company is to receive its own power supply with transformer systems and 20 kilo volt medium-voltage lines, which will be laid in the yard. The eBuses are parked and loaded overnight in the hall. There are regulated temperatures, so that the vehicles do not need to be preheated in cool weather in the early morning.
In order to make room for the loading technology, a gallery is planned to be installed in each of the depot halls. 28 charging points with an output of 50 kW make it possible to store electricity slowly overnight for a maximum of four hours. A quick charging point is also to be installed in the depot. The workshop will be equipped with special tools and will have a roof workstation with crane system. The employees receive manufacturer-specific training. Drivers are also particularly qualified for handling e-buses and familiarised with topics such as economical driving or energy recovery during braking (recuperation).

Electrical from door to door

With the scheduled use of the first eBus prototype seven years ago and the simultaneous opening of the eMobile rental station with pedelecs and electric cars on the Marktplatz, Offenbach’s central public transport hub, the Stadtwerke Group’s Mobility business unit set the course for an electric-mobile interlinking of means of transport at an early stage.
“According to Managing Director Anja Georgi, “The eBuses now give Offenbach’s passengers the opportunity not only to be demand-oriented, but also climate-friendly mobile. Together with the lending of pedelecs or e-cars to six eMobile stations operated jointly with the RMV, this will result in fully electrified door-to-door mobility”.
The city of Offenbach, praises ebusplan managing director Matthias Rogge, has a “fully electrified multimodal transport concept” with the electrification of city buses and the inter-station rental system for electric vehicles and thus assumes a “pioneering role within Hessen, but also within the Federal Republic”. It will now be even more attractive for Offenbach’s citizens to use public transport and the associated mobility services.