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News – What`s happening in energy research

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The lead-acid batteries used are particularly powerful due to the copper grid in the negative electrode. An ecological advantage of the technology is a recycling rate of over 99%.
© Franz Meyer, BINE Informationsdienst
Grid stabilisation
14.09.2016

The project partners jointly press the symbolic start button for the large-scale M5BAT battery storage system. From left to right:Professor Ernst Schmachenberg, Rector of RWTH Aachen, Volker Wachenfeld (SMA), Dr Rainer Busar (Exide), Professor Dirk Uwe Sauer (PGS), Eckhardt Rümmler (Uniper) and Professor Rik W. De Doncker
© Franz Meyer, BINE Informationsdienst

Lithium-ion batteries provide the short-term power storage.
© Franz Meyer, BINE Informationsdienst

Battery types used with M5BAT.
© Franz Meyer, BINE Informationsdienst

Medium-voltage tranformators connect the battery storage with the grid.
© Franz Meyer, BINE Informationsdienst

The transformer station is immediately beside the battery storage.
© Franz Meyer, BINE Informationsdienst

Safety first: For the protection of the lithium-ion batteries the battery rooms are flooded with argon in case of a fire.
© Franz Meyer, BINE Informationsdienst

Research on large-scale battery storage system

The modular, large-scale M5BAT battery storage system recently began operating in Aachen, Germany. With a 5 MW output and a storage capacity of 5 megawatt-hours, it is the largest battery storage system currently being researched. Together with industrial partners, scientists at RWTH Aachen are testing the interaction of five different battery types and are developing business models for decentralised storage systems in actual grid operation.

Since 9 September 2016, a former office building on the campus of the Rheinisch-Westfälische Technische Hochschule in Aachen has acted as a huge battery. Located close to a substation and the research institutes at RWTH Aachen University, it offers an ideal location for the "Modular, multi-megawatt, multi-technology, medium-voltage battery storage system" – or M5BAT for short. The output and capacity of the system are similar to the electricity consumed by 10,000 households in about an hour.

Battery technologies complement one another

The researchers are investigating three different lithium-ion technologies for short-term power storage. These are being supplemented with two lead-acid battery types for short to medium discharge times. They are testing both the OCSM technology, which thanks to a copper grid in the negative electrode has special high-current properties, and the RLA gel technology, which is optimised for high cyclic loads and requires no maintenance. By comparing these battery types, scientists expect to gain important findings about the response time and stability. The thermal behaviour of the batteries is also being analysed to optimise the air-conditioning of the energy storage system and to additionally reduce the energy consumption. The hybrid operation can also utilise synergies. Researchers are investigating which method of operation minimises the overall operating costs and maximises the service life of the system.

At the ceremony to inaugurate the system, Professor Dirk Uwe Sauer from the Institute for Power Generation and Storage Systems (PGS) at RWTH Aachen explained: "More than 25,000 battery cells in six strands with different lithium-ion battery technologies and four different lead battery strings will be closely and individually monitored from day one. This will enable us to gain valuable information about the ageing, reliability and durability. With an intelligent battery management system, we also want to demonstrate how the overall operation can be optimised using a hybrid system with different technologies."

Eckhardt Rümmler, the Uniper executive board member responsible, among other things, for new technologies, highlighted the role of storage systems in the future: "With M5BAT we are testing the usage possibilities provided by combining different battery technologies in the actual grid and in the market. The storage system is already integrated into Uniper's operating trading business and will provide important, short-term insights into the development of business models based on decentralised storage systems. Energy storage systems are a key element for ensuring the success of the energy transition. These help to increase the flexibility of the energy systems and ensure system stability."

Power electronics connects to the electricity grid

The batteries are connected to the medium-voltage grid via inverter systems that either feed grid-compliant alternating current into the substation via medium-voltage transformers or charge the batteries from the power grid. The inverter systems are designed to provide different grid system services and achieve a peak efficiency of 98.6%. These are dimensioned with power reserves. Identical inverters can be used for different battery strings. This reduces the costs and the grid connection is flexible and scalable.

Fully automatic and remote controlled

The large-scale battery storage system runs fully automatically and is remotely monitored and controlled for energy trading by Uniper in Dusseldorf. The modular system is certified for the balancing energy market, i.e. Uniper can sell the stored energy in the electricity market. Various operating strategies are being tested in terms of their economic effectiveness for various application purposes.

Participation in the primary control market currently appears attractive. Here the storage system balances out short-term fluctuations in order to keep the grid frequency stable. However, it is also intended that the battery storage system shall be available for researching other system services in different markets.

"With M5BAT we are testing the usage possibilities provided by combining different battery technologies in the actual grid and in the market. The storage system is already integrated into Uniper's operating trading business and will provide important, short-term insights into the development of business models based on decentralised storage systems," explained Uniper executive board member, Eckhardt Rümmler.

Storage systems for the energy transition

Energy storage systems provide an important component of the energy transition. They help to increase the flexibility of the energy systems and ensure system stability. To date, however, only a few storage technologies have reached the necessary technical maturity at a competitive cost level. With its Energy Storage research initiative, the German government has been supporting innovations for a wide range of storage technologies since 2011.

Battery storage systems can be used at precisely those weak points where grid expansion has not yet managed to solve the problems. They balance out short-term fluctuations in the electricity fed into the energy system by renewable energies. The large-scale M5BAT battery storage system was funded as a flagship project by the German Federal Ministry for Economic Affairs and Energy.

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Addresses

Scientific research, operation and testing
RWTH Aachen, PGS

Scientific research, operation and testing
RWTH Aachen, IAEW

Inverters and power electronics
SMA Solar Technology AG

Provision of technical equipment and development of business models
Uniper SE

Links

M5BAT
Project homepage

Energy storage systems
Recent reports on research, development and demonstration of energy storage systems