The first supercap tram from Stadler Rail has been successfully in service for the Geneva transport company TPG since early July. The supercap energy-saving system allows braking energy to be stored during normal operation and reused when the vehicle starts to move in order to conserve energy. The energy stored in the supercaps allows the vehicle to travel at least 400 metres without mains power in an emergency situation. If driven economically, the distance can even be increased to over a kilometre.

The first few of a total of 32 Tango trams have been in regular service for Geneva-based TPG since December 2011. Of the 32 vehicles ordered, one was equipped as a prototype with the supercap energy-saving system. This system stores braking energy in condensers fitted to the roof of the vehicle. During regular service, this is fed back into the system when the vehicles start to move, i.e. when most energy is needed.

1,500 metres without power
In an emergency, the vehicle can even travel without mains power, for example, if there is a power failure or a fault with the contact wire or pantograph. During the first tests on 6 July, a vehicle covered a distance of 1,500 metres on a TPG depot circuit without mains power. This required economical driving, i.e. slow acceleration and low speed. Since then, the vehicle has been in service on the Geneva tram network and has performed excellently.

The supercap units on the TPG vehicle weigh about a tonne and can store energy equivalent to the entire kinetic energy of the empty vehicle at 55 km/h. The benefit of the supercaps over batteries is that they can absorb and release the temporarily very high levels of current produced during braking.

Retrofit option across whole series
The supercap prototype is being extensively tested by TPG and Stadler in conjunction with ABB, the manufacturer of the traction converters, on the TPG network, and its energy consumption is compared to that of the other Tangos, which also absorb braking energy and feed it back into the contact wires. If the tests prove positive, the remaining 31 series vehicles could be fitted with supercap modules relatively easily.