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TransnetBW operates the transmission grid in Baden-Württemberg (Independent Transmission Operator). With more than 3,200 kilometers of high-voltage lines, the EnBW subsidiary ensures that electricity is available everywhere in the southwest whenever it is needed. Operating the transmission grid used to be a relatively straightforward process. The electricity was distributed across the area from a few large power plants. However, due to the increasing amount of electricity being generated by the sun and wind, the entire energy system has become more complex. This presents the grid operators with considerable challenges.

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Even today, bottlenecks occur time and again in the transmission grids.

A prime example: When it is windy, the wind farms in northern Germany produce a lot of electricity. The industries in the south of the country could really do with this. However, the line capacity is insufficient – leading to transmission congestion. Accordingly, less wind power is fed into the grid. In order to meet the demand in the south, conventional power plants generate the required electricity here instead. This measure – which experts refer to as “redispatching” – is expensive and often not particularly climate-friendly. In order to transport the required electricity from the north to the centers of consumption in southern Germany, TransnetBW is working with the three other transmission grid operators to build additional north–south high-voltage lines. At the same time, however, they are also working on measures to make better use of the existing grid.

The existing high-voltage grid capacity is by no means fully utilized at present. The reason for this is the number-one rule of grid operation, known as the (n-1) principle. This ensures that the power grid remains stable even if one transmission line fails, because the other lines can compensate for the outage and absorb the load. Since transmission line failures occur rather rarely, the “safety buffer” generally remains unused, which means that the individual lines transport significantly less electricity than would be possible.

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How does a grid booster work?

Dies ist eine vorläufige Visualisierung der Anlage. Um den sicheren Betrieb gewährleisten zu können, werden die zu Modulen zusammengefassten Batteriezellen in räumlich und technisch getrennten Containern auf dem Gelände angeordnet. In einem zentralen Betriebsgebäude befindet sich die Mess- und Steuerungstechnik. (Quelle: TransnetBW)

One way of making better use of the lines without compromising grid security is the grid booster. TransnetBW project manager Severin Mosek explains the planned facility: “Normally, the battery system is charged with energy so that the transmission grid can be operated at a higher capacity than is currently the case.

If a circuit in the grid fails, the remaining circuits are temporarily overloaded. In such cases, the grid booster serves as a kind of airbag. Within seconds, we can supply energy at a strategically important point in our grid – 250 megawatts of power for an hour – and simultaneously reduce generation in the north accordingly. In the meantime, we have time to manage the bottleneck, either by means of switching measures or by starting up power plants.”

TransnetBW has brought on board Fluence Energy GmbH as the general contractor for the construction project. The company is the world’s leading supplier of energy storage products and services as well as cloud-based software for renewable energies and storage. TransnetBW CEO Dr. Werner Götz commented confidently on the partnership: “To have secured the industry leader for our grid booster is very pleasing, but it is also a testament to our high standards.” The lithium-ion battery technology that will be used in the grid booster is well-established and proven. One major innovation, on the other hand, will be the integration into transmission grid operations for the first time. The result will be the increased transmission capacity of existing lines while ensuring full security in terms of the grid and the supply. Herein lies the innovative character of the project.

The approval documents for the Kupferzell grid booster were recently submitted to Stuttgart Regional Council for a completeness check. The public will be involved in the further course of the approval procedure. Construction work is scheduled to begin in 2024 and the plant is set to enter operation in 2025.

More Information

  • Find out more about the “Netzbooster” project on the website of TransnetBW:
  • Detailed information on how the grid booster technology works and the role it will play in the grid management of the future is available in English on the website of Fluence Energy: