Altdorfer Flexmarkt and comax: Interaction of Distribution & Transmission Grid for Efficient Grid Congestion Management

As part of the field test of our Altdorf Flex Market (ALF) in the C/sells project, the ALF and comax flexibility platforms were coupled. ALF was developed by the Forschungsstelle für Energiewirtschaft e. V. (FfE) in cooperation with Bayernwerk as part of the project and tested with test persons in the Altdorf region. Via ALF, existing flexibility in the distribution grid can be tapped and used to eliminate grid bottlenecks. The flexibility platform comax was also developed by TenneT within the framework of C/sells and offers the possibility of bringing together the supply and demand of flexibility. This expands the flexibility supply that the respective grid operators can draw on for congestion management by linking the platforms. In this context, the targeted charging of redox flow batteries, which were brought into the field test by the Zentrum für Angewandte Energieforschung e.V., as well as the control of PV systems in the distribution grid could help to prevent overloads.

In the project region, which is located in Bayernwerk’s grid area, there were no bottlenecks on the day of the call, so there was no need to use flexibility. The unused flexibility offers of ALF were therefore transmitted to comax. For this purpose, on the one hand, the offers of all PV plants in the field test area were aggregated, and, on the other hand, the flexibility offer of three battery storage units was submitted in aggregated form. Thus, two additional flexibility offers were available on the comax platform at one grid node. In the TenneT grid area, an overload was forecast on a test basis so that there was a need for the deployment of flexibility. The flexibility offered by ALF as the deployment manager for the plants on the distribution grid level was finally contracted by comax.

The figure shows the flexibility demanded as well as the flexibility offered and provided by the storage and PV systems. The majority of the required flexibility is provided by battery storage, which is charged. In order to provide the remaining demand for flexibility, the feed-in of the PV plants is reduced somewhat. Thus, further curtailment of the PV plants could be avoided by selective control of the plants. The call-off was performed in a limited test environment, which is why low outputs could be called off (in the figure, the relative power value of 1 corresponds to an output of 25 kW). However, this call-up can be scaled as desired.

The two schedule offers aggregated from the ALF offers were transmitted to comax by e-mail. The call-off was also sent by e-mail from the comax platform to ALF. ALF implements the switching actions for the call-off as the deployment manager via the infrastructure of intelligent metering systems (iMSys). The measured values for proving the switching operations are also recorded via the iMSys and collected in ALF’s performance register. Thus, ALF provides the metering values necessary for billing. The discrepancies between flexibility demand and provision result from the following circumstances: PV systems are controlled with a small delay, small deviations may occur in the control of scheduling systems, and in addition, the control levels of PV systems are currently limited to certain values (0 %, 30 %, 60 %, 100 %).


For Prof. Dr.-Ing. Wolfgang Mauch, Scientific Advisor of FfE, the coupling was an important milestone:

  • „Die Koordination und das Matching von Flexibilitätsangebot und -nachfrage im Netzgebiet des Altdorfer Flexmarkts hatten wir bereits erfolgreich demonstriert. In Zukunft wird das aber nicht ausreichen, denn die Netzebenen werden zusammenarbeiten und sich koordinieren müssen. Der Abruf der Anlagen in Altdorf und Arzberg für die Unterstützung der Stabilität im Netz hat erfolgreich gezeigt, wie das künftig funktionieren kann. Dies ist ein ganz wichtiger Schritt, um unser Stromnetz fitter für den weiteren Lauf der Energiewende zu machen, wo die vielen dezentralen Anlagen die Aufgaben der Kraftwerke ergänzen werden."