27 Mar 2017


The project «SwissTrolley plus» aims to replace the diesel-powered auxiliary power unit of standard trolley buses with a high-performance traction battery. This replacement offers ta number of advantages like the possibility to extend existing trolley bus lines without having to extend expensive infrastructure. .

Further advantages are a reduced noise and pollutant emissions during off-grid operation, around 15% reduced energy demand due to regenerative braking, and active peak load balancing in the electricity grid.

This project is a cooperation of Carrosserie HESS AG (Bellach, Solothurn), Verkehrsbetriebe Zürich (VBZ), Berner Fachhochschule (BFH), and ETH Zürich. It is sponsored by the Bundesamt für Energie (BFE) and the Swiss Competence Center for Energy Research (SCCER).

State-of-the-art trolley buses need a diesel-powered auxiliary power unit (APU) to ensure maneuverability during a shortage of electricity. The engine, despite being rarely used, leads to increased vehicle weight and thus increases the energy consumption. When eventually in use, the undersized APU runs mainly in cold-start mode, leading to extreme noise and pollutant emissions.

The goal of «SwissTrolley plus» is to avoid those drawbacks by replacing the APU with a high-performance traction battery. The traction battery enables regenerative braking, which allows to reduce the energy demand of the vehicle by about 15% compared to a state-of-the-art trolley bus. Furthermore, the battery allows purely battery-electric driving outside the overhead wire network for several kilometers. This feature is used to extend existing bus lines and remove parts of the overhead wire network, thus in both situations saving infrastructure building maintenance costs. Finally, the battery capacity can be used to stabilize the electricity grid by balancing the unsteady power demand, which is a major factor for energy pricing in trolley networks.

This project is a follow-up project of the very successful and trusting cooperation between ETH and Carrosserie HESS AG during the project. As a new partner, Verkehrsbetriebe Zürich (VBZ) provides the needed know-how and experience from the view of a public transportation operator in order to achieve the ambituous goals. The Berner Fachhochschule (BFH) investigates the differences of currently available battery types and tests their operating characteristics in various load scenarios. One aspect of this research is the process of battery aging. Accurate aging models are especially of interest for financial aspects and the electrochemical degradation due to fast load transients.


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