Use of Braking Energy

Use of braking energy in Subway stations by using a Hybrid Storage Systems

The use of surplus energy from various processes is the focus of many efficiency measures. If this energy is to be used at a later date, the use of energy storage is essential. A major challenge is the selection of technologically and economically suitable storage technologies, because each technology has several advantages and disadvantages. Some technologies can store a lot of energy but provide little power. Others can respond very quickly to changing performance requirements or have a very low self-discharge rate. For these reasons, the use of a hybrid storage system is close, ie a storage system consisting of two different storage technologies. The advantages of the respective technologies can be combined and the disadvantages compensated. In the German-Greek cooperation project MetroHESS, a hybrid storage system is to be designed for testing, which absorbs the braking energy of a subway in a short time, in order to deliver it slowly and continuously to the subway station.

Research topic in the project MetroHESS is a hybrid energy storage system (= HESS) for the use of braking energy in urban subways. As a practical example serves the Metro of Athens. The electrical energy generated during the braking of the metro is to be used to supply the 420 V AC network of the individual stations and thus make it available to stationary consumers such as lighting, ventilation, elevators or escalators. The overall objective of this analysis is the reduction of energy consumption and thus the saving of climate-damaging greenhouse gases, as well as the reduction of operating costs. For this purpose, it is expected that such a storage can cover up to three-quarters of the energy consumption of the stations. The memory is periodically charged with high power and discharged over a longer period of low power. This requirement can be ensured by a combination of two memories with different specific powers and capacities, which together form a hybrid memory system.

The research objectives of the MetroHESS project are, on the one hand, the analysis of the technical and economic feasibility of hybrid storage systems using the Athens Metro. Furthermore, the improvement and the application of a method for the design and Dimensioning of hybrid storage systems studied. The development and comparison of various energy management systems for hybrid storage systems are also the subject of research. For this purpose, both measurements of the available braking energy and an energy audit on the energy consumption in the stations should be carried out first. On this basis, the energy storage system is designed taking into account various storage technologies and topologies. In addition, various energy management strategies are tested on the computer. The planned hybrid storage system will then be built and tested as a demonstrator. Finally, on this technical basis, the eco- nomic feasibility and energy saving potentials can be evaluated by using the hybrid storage system.

If the results of the project show that the use of such hybrid storage systems makes sense both energetically and economically, the results could be used in follow-up projects. It is intended on the one hand, the large-scale use in the metro in Athens and the simple transfer to similar applications in other urban rail systems. A research partner and a medium-sized company are involved in the project on the Greek and German sides. Research partners will use the results through transfer to teaching and advice to regional SMEs. The scientific findings on hybrid energy storage design methodology and operations management will be shared with the scientific community in the form of articles and conference papers, and will be used as part of lectures to train future engineers. For medium-sized companies, the research enables the transfer of the developed solutions into new commercial offers. The solutions developed in the project and the insights gained with regard to the demonstrator form the basis for developing commercial products in the market of hybrid storage systems. This makes an important contribution to the more effective shaping of the energy transition in Germany and Greece.

Support Measures:

Greek-German Bilateral Research and
Innovation Cooperation

Project Title:

MetroHESS – Nutzung von Bremsenergie in
U-Bahn-Stationen durch Einsatz eines

(MetroHESS - Use of braking energy in Subway stations by using a Hybrid Storage Systems)

Operational Time:

01.09.2018 – 30.11.2020

Project Number:

Funding volume of the joint project about 380,000 €


Leibniz Universität Hannover
Institut für Elektrische Energiesysteme (IfES)
Prof. Dr.-Ing. Richard Hanke-Rauschenbach
Dr.-Ing. Astrid Bensmann
Appelstr. 9a
30167 Hannover
Phone: +49 511 762-14402
Fax +49 511 762-14403

Project Partner:

Leibniz Universität Hannover
Stercom power solutions GmbH
Centre for Renewable Energy Sources and Savings
Attiko Metro S.A.


Bundesministerium für Bildung und Forschung (BMBF)
Referat Grundlagenforschung Energie, 53170 Bonn

Editorial and Design:

Projektträger Jülich (PtJ),
Forschungszentrum Jülich GmbH

Photo credit:

Attiko metro S.A.
Ishwar Sarpal, Leibniz Universität Hannover
Stand: September 2018