Energy Storage Units Save 80 Tons of CO2 Per Year

Siemens has launched a new hybrid energy storage system for streetcars. Streetcars equipped with the solution can be driven up to 2,500 meters without an overhead conductor, and the system saves lots of energy. This is possible thanks to a combination of a double-layer capacitor and battery. Running streetcars without an overhead conductor is especially appropriate for historic downtown areas, where the cables spoil the view, or in places where it is simply difficult to install cables — for example in tunnels, under bridges, or at large intersections.

Streetcars with the system consume up to 30 percent less energy and produce up to 80 metric tons less CO2 emissions per year than vehicles without energy storage devices. Another plus is that the systems are mounted on the streetcar roofs and electrically connected to the vehicle’s energy supply point. This new switching concept enables the Siemens technicians to integrate the energy storage system in new rail vehicles and in existing streetcars to realize energy savings.

The Siemens system — called Sitras HES — consists of two energy storage devices: the Sitras MES (double-layer capacitor) mobile energy storage unit and a nickel-metal hydride battery. This concept combines the benefits of the high-performance capacitors with the characteristics of a traction battery. The capacitors recharge faster and deliver the energy faster than traction batteries, which release their stored energy over longer periods. While the streetcar is under way, the energy storage units recharge through the vehicle’s braking. The stored energy makes it possible for a streetcar to be driven for longer distances without drawing power from the overhead conductors. The energy storage systems also can recharge while the streetcars are moving on sections equipped with overhead conductors or by means of stationary charging stations, for example at streetcar stops.

In Portugal the hybrid energy-storage system is being successfully used in everyday passenger-transport operation, linking Almada and Seixal, cities located south of Lisbon. In Germany it also is approved for use in public passenger transportation.