Reimagining the subway: making public transport more energy-efficient
Buses and trains are climate-friendly means of transportation. But they also consume electricity. For example, the Berlin transport authority (BVG) alone consumes around 450 gigawatt hours per year, which is as much as 180,000 Berliners in the same period. Current projects in Vienna, Munich, & Cologne demonstrate how we can also save electrical energy when it comes to public transport. One possible solution involves recycling electricity several times, which is made possible by new technologies.17 May 2022
“Electricity recycling” is one possible solution for keeping energy hunger at bay in the transport sector. The keyword here is “regenerative braking.” This involves converting the energy that is released during braking back into electrical energy. Transport operators in the City of Vienna have launched the “Brake Energy” project so that they can make the most of this phenomenon: subway stations functioning like little power stations. Braking energy is fed from these “Brake Energy” stations into Wiener Linien's AC grid, where it converts the subway's direct current into an alternating current. This alternating current is needed in turn to power escalators and elevators or to power lamps. Braking generates around three gigawatt hours of electricity per year according to Vienna’s transport authority. This consumes the same amount of energy as an average of 720 households and saves around 400 metric tons of CO2.
New technologies that save energy and reduce maintenance costs in public transport are also in demand elsewhere. For example, Münchner Verkehrsgesellschaft (MVG), a subsidiary of Stadtwerke München (SWM), has taken a close look at approx. 770 escalators at its subway and overground stations.
It is the largest network of escalators in Germany. MVG transports over half a billion passengers around the Bavarian capital every year, and this whole operation would fall to pieces without escalators. The transport authority relies on using frequency converters as actuators for this purpose. The escalators move when you need them to and, in the direction you need them to go in. Devices known as matrix converters, which combine the converter and regenerative unit in one device, are installed into the escalators so that the energy they generate when they brake can be harnessed. This feeds the energy back into the grid, where it can be used to light subway stations, for example. Another advantage of using the Yaskawa model: Braking resistors are rendered superfluous, which in turn saves on the energy needed for cooling and ventilating the escalators. An ever-increasing number of escalators are being fitted with matrix converters following a successful pilot scheme at Fraunhoferstrasse subway station a few years ago.
Cologne's public transport authority also uses the energy generated when their overground trains brake to charge electric buses and cars. “Multimodal charging module integration,” or “MuLi” for short, is the name of the project on which the energy provider Rheinenergie and the car manufacturer Ford have collaborated.
The special thing about this is that hundreds of discarded battery cells store electricity. The modules are connected together in a gray terminal located at Cologne's Bocklemünd station. Here, the electricity generated by braking is stored inside six battery stacks within a charging station which is then used to power e-buses and electric vehicles. The batteries also temporarily store electricity inside a repository to prevent voltage fluctuations. The voltage would fluctuate if a light rail train were to be driving past as a road vehicle were being fast charged, for example.
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