Developing an Envelope-Based FCA for Battery Storage

Summary

Grid operators across Germany are receiving a growing number of grid connection requests for battery storage systems and are increasingly reaching their capacity limits. This project, carried out in collaboration with a distribution system operator, demonstrates how a structured FCA concept can make this challenge manageable.

Background

The distribution network in question is connected to the upstream high-voltage grid at several transfer points and is already operating close to its load capacity. With additional consumers planned for connection, network utilisation will continue to rise. Under a conventional grid connection agreement, connecting further battery storage systems would hardly be feasible.

Envelope-Based FCA as a Solution

To enable the integration of battery storage into the grid, the project developed power envelopes as the basis for Flexible Connection Agreements (FCAs). These are variable operating limits that allow battery storage systems to feed in and draw power at the highest possible level at any given time, without exceeding the network’s capacity constraints. The analysis draws on a modelling of the future grid situation, taking into account known new consumers and generators. The developed envelopes guarantee storage operators a minimum operating window of their installed capacity, ensuring that economically viable operation remains possible.

As part of the project, the client was provided with an Excel tool to support the further development of the envelopes. It enables the aggregation and visualisation of load profiles with and without installed battery storage for any given envelope (Figure 1). The tool also derives a maximum and a recommended envelope from the modelling, which can then be visualised (Figure 2). This facilitates straightforward communication of storage operating parameters to project developers.

A Toolkit for Structured FCA Concepts

The methodology and Excel tool developed in this project can be applied to other grid areas. For grid operators, this provides a transparent basis for evaluating battery storage connection requests in a structured way and for substantiating FCA contracts. For project developers, a clearly defined operating window creates the planning certainty needed for a sound economic assessment.