Considerable optimisation expected on the basis of present materials and construction principles and improvement by < factor 2 in all fields

The development of more powerful and more efficient storage systems will improve stationary storage solutions.

• Energy savings
• Stabilise catenary voltage
• Smoothen power demand

Smoothened power demand

The demand peaks are cut down by the use of a storage system. This saves energy costs, not only due to a reduced energy demand but due to a price effect as well. The energy price is determined by electricity suppliers in a way that basic demand is much cheaper than peak demands. Therefore, a smoothened power demand substantially reduces the price per kWh.

Stabilisation of catenary voltage

The use of a storage system has a stabilising effect on catenary voltage. Tests in Cologne indicate that an energy storage system may even replace a rectifier of a substation, under specific conditions.

Increased peak performance of DC system

With storage systems acting as boosters for accelerating trains, the system gains a peak performance not achievable by the DC system alone.

Stationary energy storage in Cologne light rail network

Since 2000 an energy storage system is tested in service in the Cologne local transportation network. The flywheel with an maximum energy content of 6,6 kWh and a maximum power of 600 kW was installed in a substation of the DC supply grid. Braking energy which would otherwise be lost in brake resistors is stored and can be used later for an accelerating train. Comprehensive tests demonstrate that energy storage saves about 24 % of the total energy consumption. Additional cost effects can be realised due to the fact that energy storage reduces power peaks and thus the energy price. Encouraged by positive experience with the first energy storage, it was decided to equip a second substation with an energy storage system, this time realised with a double-layer capacitor developed by Siemens. Experiences are as positive as in the case of the flywheel.