Public transport in Solingen: New emission-free trolleybuses

In Solingen, Germany’s largest trolleybus network is being used as a testing ground: in order to implement a public transport system that is sustainable and emission-free, four battery-powered trolleybuses (known locally as BOBs), which will be able to run on electricity even without overhead wires, are initially being deployed. What is more, there are plans to develop the existing trolleybus network into a “Smart Trolleybus System”, an intelligent infrastructure which is integrated into the power distribution network.

Battery-powered trolleybuses in Solingen: the Smart Trolleybus System

Trolleybuses have been operating in Solingen ever since 1952. The vehicles run on electric motors and draw power from an overhead wire. Each bus is also equipped with a diesel unit, which powers a generator to produce electricity for short distances where there are no overhead wires. Due to the rise in particulate matter pollution in cities, electric drive concepts are becoming increasingly important.

Engine for progress:

  • Integrated approach to interlinking public transport and energy
  • Implementing an emission-free public transport system
  • Improved integration of renewable energies
  • Transferability to other trolley wire networks

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Photo: Stadtwerke Solingen

Integrated batteries provide more flexibility

In the first stage, one diesel bus line will be converted; in the medium term, the pilot project will be expanded to include 20 battery-powered trolleybuses operating in Solingen. If this proves a success, the entire bus fleet in the city will gradually be converted. A special feature of the electric vehicles is that they have a battery as well as modern control technology. This means that, on the one hand, they can be charged while running on the wire and, on the other hand, they can also cover sections of the route that have no overhead wires. The buses also offer other benefits: the batteries help to balance fluctuations caused by electricity from renewable energy sources. In the future, there are plans for the entire trolley wire infrastructure to be closely linked to the urban power distribution network.

Moving step by step towards a sustainable integrated urban system

Until now, electricity only flows from the power distribution network into the trolley wire system. In the future, however, it should also be possible for current to flow from the trolley wire system into the power distribution network. This is exciting because, in the course of this project, photovoltaic facilities will be connected directly to the trolley wire system. Since the latter runs on direct current, conversion losses caused by the direct feed-in of solar power are avoided. Prospectively then, only green energy that is produced locally will be used for the public transport system in Solingen. The project also uses the old batteries from the buses to set up stationary storage units in the network and to thus stabilise both the trolley wire system and the upstream power distribution network. By means of an intelligent charging and energy management system, peaks in current load or green energy production in both power systems can be absorbed and the integration of fluctuating renewable energy sources can generally be improved. In addition, those responsible for the project also plan to connect charging stations for private households to the trolley wire system.

The project pursues a holistic approach and views issues of mobility, energy supply and urban development as part of a transdisciplinary integrated urban system. In this way, new business models for transport companies, energy providers and grid operators are to be developed. The project points out possibilities and opportunities and shows how an electrified public transport system can make an important contribution to solving the great challenges of the “transport revolution” and of the successful transformation of the energy system, the “Energiewende”, at a municipal level.


Photo: Stadtwerke Solingen GmbH

“The decision taken in the 1990s to continue using trolleybuses will make it possible for us to carry out further electrification of the public transport network in Solingen in the near future. Our aim is to interweave the diesel bus lines with the trolley wire network and to remove the diesel buses from the transport system in the long term, replacing them with battery-powered trolleybuses or BOBs. It also opens up the opportunity of developing the Solingen public transport company into a virtual power plant and of thus supporting the primary supply network in line with the transformation of the energy system.

Conrad Troullier, Managing Director and Operations Manager of Stadtwerke Solingen GmbH

Partners and sponsors

  • Stadtwerke Solingen GmbH
  • SWS Netze Solingen GmbH
  • Stadt Solingen
  • Bergische Universität Wuppertal
  • Neue Effizienz - Bergische Gesellschaft für Ressourceneffizienz mbH
  • Voltabox AG
  • NetSystem Netzwerk- und Systemtechnik GmbH
  • Bundesministerium für Verkehr und digitale Infrastruktur (BMVI)

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