Brussels Use Case leader, STIB, has completed a feasibility study to optimise the braking energy recovery in their tram network. The feasibility study was completed thanks to a thorough measurement campaign and the development of models and simulations of tram lines 7, 19 and 94.
One of the possible ways to reduce energy consumption in a tram network is to capture the braking energy that is generated by tramways during braking. In regular operation, a small share of this energy is reused by the vehicle auxiliaries, another part is sent back to the overhead line to power other vehicles. This latter share depends on the traffic conditions and characteristics of the network. The remaining energy, i.e., the part that could not be re-used, is dissipated in the tramway braking resistor.
This braking resistors energy can however be recovered and reused with different technologies such as energy storage or reversible substations and the aim of this study was to estimate the amount of energy that is dissipated and to propose means to capture and reuse it.
The measurement campaign was carried out in order to study and analyse the energy flows in the tram network and to validate the models. The results of the measurement campaign show that most of the braking energy generated by the tramway is already reused and there is a very small share that is dissipated by the braking resistors. In line 94 and line 7 around 97% of the braking energy generated by the vehicles is reused and only around 3% is wasted in the braking resistors. Thus, even if STIB could reuse all the wasted energy, the potential to reduce the energy consumption is very low.
The feasibility study shows in which part of the line there is a higher receptivity and where the energy is wasted in the resistors. Where there is a strong traffic density and line interconnections, the line receptivity is high, and almost no energy is wasted. On parts that are more isolated, a higher share of energy is wasted in the resistors.
Another reason that explains the receptivity of the lines is the high consumption of the auxiliaries during the periods of measurement. The average auxiliaries’ consumption during the measurements represented around 40 to 49% of the tram net consumption during the summer months and up to 60% when the heating is on. This energy share depends on the weather conditions, but even during a day with no HVAC, this value represents around 30% of the total consumption of the tramways.
Finally, several measurements to reduce the energy consumption have been proposed, but it seems clear, given the already high receptivity of the lines, that the focus should be given to the reduction of the auxiliaries’ consumption if a significant reduction wants to be achieved.
More information: Roelands Benjamin, Benjamin.Roelands@stib.brussels