In Solingen, the debate about the long-term future of battery trolleybus operations has once again resurfaced. A study focusing solely on operating costs proposes replacing the proven battery trolleybuses (BOB) with fully battery-electric buses by 2044. Implementing such a proposal would mean abandoning the strategy adopted only a few years ago to achieve the medium-term full electrification of urban bus services largely through the deployment of BOB vehicles.
Starting point
With its battery trolleybus system (BOB), Solingen possesses an established electrical infrastructure of considerable strategic value. This system did not emerge by chance. It is the result of decades of investment, technological development and operational experience. Generations of engineers, planners and transport operators have built, stabilised and continuously improved it.
This infrastructure represents more than just emission-free transport. It stands for reliability in everyday mobility, for technological expertise at the Solingen location, and for an energy system that is visibly embedded in the urban landscape and moves thousands of people every day.
The currently discussed prospect of a complete dismantling by 2045 is therefore not merely a question of vehicles. It raises the fundamental issue of whether Solingen will continue to develop a functioning electric backbone – or abandon a proven infrastructure. It is a system decision with implications for the next 30 to 40 years: technically, economically, in terms of energy policy and for society as a whole.
IMC vision – Strategic potential for Solingen
The existing overhead line infrastructure in Solingen can be understood as the foundation of a modern In-Motion Charging (IMC) system. IMC is neither a transitional technology nor a hybrid compromise, but an integrated electric solution for bus networks consisting of vehicles, route structure, charging infrastructure and operational strategy.
The Solingen BOB system already reflects this logic today, with its systemic strengths:
- Continuous charging during operation rather than exclusive depot charging
- High energy efficiency through temporally distributed energy intake
- Long-lasting infrastructure components with lifespans of up to 70 years
- Technical robustness without complex digital interfaces between vehicles and infrastructure
- High system availability due to reduced complexity
Experience from numerous cities shows that electrifying around 20–40% of the network is sufficient to operate an entire bus system electrically. Modern batteries allow ranges of up to 100 kilometres between electrified sections. This means that a strategically developed core network is enough to organise urban, suburban and regional services entirely electrically.
Energy management as a strategic advantage
An IMC system distributes energy consumption over 18–24 hours, thereby reducing peak loads.
- Even load distribution lowers installed peak capacity
- Local renewable energy can be fed directly into the system
- Stationary intermediate storage is not necessarily required
- The system supports the grid rather than burdening it
In the future, vehicles can function as controllable energy consumers – potentially even enabling vehicle-to-grid applications and the use of the bus fleet as a flexible urban energy buffer.
IMC therefore represents not an isolated transport system, but a strategic infrastructure platform linking mobility, energy and urban development.
The depot decision – the financial heavyweight of system choice
The question of the depot is not a technical detail but the financial and structural heavyweight of any system decision.
With full depot charging, the entire energy demand is concentrated at a single location during a few night-time hours. This requires grid connection capacities in the double-digit megawatt range, new medium-voltage connections, additional transformers, switching installations, fire protection infrastructure and extensive structural adaptations to the depot. These investments are structural: they arise regardless of the individual vehicle type and have effects lasting for decades.
Whereas the existing system spreads energy intake across the entire operating day, pure depot charging shifts the load to a single central point. This increases technical dependencies, raises complexity and ties up substantial financial resources in the depot over the long term.
Anyone discussing system costs, however, must therefore begin with the depot.
What Solingen would lose through dismantling the network
Dismantling the overhead line infrastructure would not merely represent a technical change but a strategic turning point with long-term consequences. It would terminate a functioning infrastructure before its full development potential had been realised – an infrastructure that already operates reliably today and whose strategic possibilities are far from exhausted.
Solingen would lose structurally:
- the possibility of further developing the existing network as an urban energy backbone
- the option of expanding it into an integrated microgrid with renewable generators and intelligent load management
- the systemic integration of transport and the energy transition
- scalability towards high-capacity eBRT corridors
- a technological platform for digitalisation, energy optimisation and grid integration
From a sustainability perspective, dismantling would also have significant consequences:
- larger batteries imply greater resource binding over the lifecycle and increasing dependence on lithium, nickel and cobalt
- shorter lifespans for key components compared with overhead line systems
- concentration of energy supply at high-power depot charging points
- reduced structural resilience of the overall system
An IMC system enables smaller batteries, lower vehicle weights, higher passenger capacities and reduced strain on road infrastructure. At the same time, the material use per vehicle decreases significantly. This is not a transitional solution but an infrastructure platform designed for decades. Dismantling it would therefore not merely replace technology – it would abandon strategic development potential.
Methodological separation – requirements for a sound system decision
A system change of this magnitude must not be based on a one-sided focus on short-term operating costs. Concentrating solely on supposedly lower vehicle or energy costs falls short of the scale of this decision. Anyone considering only short-term operating costs ignores structural, infrastructural and long-term effects.
The issue concerns around 100 kilometres of existing electrical infrastructure with substantial asset value. This infrastructure forms part of municipal public services and cannot be treated like a variable calculation parameter.
A well-founded system decision must therefore be interdisciplinary. In addition to business-economic aspects, energy-economic, infrastructural, macroeconomic and long-term resilience considerations must also be included.
In particular, depot and grid connection costs, system availability, resource dependency, battery replacement cycles and long-term lifecycle costs must be evaluated transparently and comprehensively. A simple comparison of energy or maintenance costs for individual vehicles is not sufficient for a system decision.
Service development is ultimately a political choice. It does not automatically result from a change in technology, but from the strategic objectives of the city.
International experience – why other cities rely on route-based electrification
The discussion in Solingen does not take place in isolation. Numerous international cities face or have faced similar decisions – and have consciously chosen to develop their trolleybus and IMC systems further.
- Lucerne (Switzerland) is systematically expanding its trolleybus network. New IMC vehicles are gradually replacing diesel buses, the network is being selectively extended and understood as a long-term infrastructure platform. The combination of overhead lines and batteries enables flexible routes without full electrification of every section.
- Prague (Czech Republic) has newly electrified key corridors and is introducing modern trolleybus routes, including on high-demand connections such as the airport axis. The aim is a robust, energy-efficient system with strategically placed overhead line sections instead of full depot dependence.
- Verona (Italy) is implementing several new lines using IMC technology. Overhead lines serve as the energy backbone, while battery operation provides flexibility outside the core corridors.
- Linz (Austria) uses high-capacity trolleybus corridors as an alternative to expensive rail projects. Electric trunk corridors are regarded as the structural backbone of the network.
These cities view their systems as strategic infrastructure elements for energy efficiency, capacity and supply security. Their decisions are not driven by nostalgia but by a pragmatic assessment of energy efficiency, reliability and long-term economic viability. They are modernising, expanding and integrating trolleybus and IMC systems into broader energy and mobility strategies.
Within the EU project eBRT2030, standards for electric high-performance bus rapid transit systems are currently being defined. In this context, IMC systems are regarded as particularly robust and scalable platforms for high-capacity corridors.
International developments therefore show not a retreat from route-based electrification, but its targeted modernisation and strategic expansion. Other cities are safeguarding and strengthening their electric infrastructure because they recognise its long-term stability, energy security and development potential.
Long-term responsibility
This decision must not become a political turning point but should be understood as a long-term strategic choice for the future of the city of Solingen. Electrification strategies extend over decades and affect future generations. Accordingly, the evaluation should be fact-based, technology-neutral and mindful of intergenerational responsibility.
Conclusion
The electrification of public transport is both correct and necessary. However, before irreversible infrastructure decisions are taken, a comprehensive analysis should be carried out that considers not only operating costs but also depot and grid connection costs, resilience, lifecycle costs, circular economy aspects and the development of high-capacity eBRT corridors.
Peter Brandl (trolley:motion) summarises:
“Anyone who focuses only on short-term operating costs today overlooks the real system decision. Full depot charging fundamentally changes the energy architecture of public transport – technically, economically and strategically. Depot and grid connection costs in particular are often underestimated. Solingen should not take an irreversible infrastructure decision without making these factors fully transparent.”
