Energy-recovery system for trams

Summary

Zagreb aimed to use energy efficient trams in the public transport fleet to make it more attractive to citizens. This was done by gradually substituting the existing fleet with state of the art air-conditioned low-floor trams.

Implementing sustainable mobility

Tramways are the backbone of public transport in Zagreb. They operate at short intervals and often beyond capacity. Before CIVITAS ELAN implementation, Zagreb Holding Co - Department ZET operated 17 tram lines with 267 cars and 129 trailers over 117 km tracks with 1,000 mm gauge. Due to the prevalence of energy consumption, inaccessible, uncomfortable, overcrowded and noisy vehicles, transport by tram was not attractive enough for the public. Therefore, a shift towards individual motorised transport was obvious. To counteract this, ZET started a large scale fleet renewal in 2005, introducing 100 new trams by 2009. Aside from being more accessible and attractive, these vehicles produce less noise than the old ones. A particularly interesting feature is the energy recovery system that allows the team to generate electrical power when braking and feeds it back to the electrical network. Through this feature and lighter construction materials, energy efficiency can be increased substantially. ZET plan was to introduce another 70 energy efficient tramways in the coming years.

Progress

  More than 700 tram drivers have been trained on how to return braking power into electrical supply network, as well as on how to operate new trams. ZFOT conducted a quality of service in public transport survey in February/March 2010 and February/March 2012. Trained students carried out the survey by posing questions to citizens at the main railway station and the tram station terminal. The measure leader regularly participated in all relevant events such as workshops in elderly homes, mobility workshops, Wednesdays in tram, other towns and similar activities.
ZET has concluded the public tender for introducing 70 innovative tram vehicles and they have been integrated into the tram fleet. Furthermore, each instalment of a new tram was followed by a press conference attended by the Mayor of Zagreb, Mr. Milan Bandic and representatives of ZET in order to promote these activities. ZET also ran an interesting promotion campaign, by creating a “caterpillar” of new trams, driving through Zagreb.

As mentioned above, new trams have the ability to generate energy while braking which can then be re-used in the same tram or it can be accumulated in the power network. However, this requires additional investments into power network and power accumulators. In order to reach full potential of this new technology, investments in rolling stock must be followed by the investments into infrastructure. However, for now this remains financially too demanding task because it considers reengineering of the whole tram power network.

Outcomes

• 70 new energy efficient trams were introduced as a part of CIVITAS ELAN as well as 70 additional trams (not a part of the project).
• Tramway noise level in curves decreased from 85 dB to 76.7 dB; tramway noise level on the straight line decreased from 83.09 dB in to 83 dB.
• Increase in the energy consumption is recorded. The MJ consumption per vehicle km increased by 10.6%. Two key factors influenced these results:
o New trams are more powerful – new trams have 6 engines and the continuous power output of 390 kW, while the old trams had one engine and power output of 240 kW, i.e. power output is increased by 62.5%.
o New equipment – new trams are equipped with new systems and therefore they consume more energy (e.g. air-conditioning and heating system, information system etc.).
• The level of public satisfaction is considerably increased by all subjective evaluation criterions: vehicle comfort, vehicle quality, interior design, noise level inside vehicle, build quality, vehicle performance and others.