Flexibility is rapidly becoming one of the most powerful tools available to system operators to manage congestion, optimise grid capacity and support the large-scale integration of renewable energy. However, as flexibility markets grow and mature across Europe, one critical challenge has become increasingly evident: flexibility activation without proper coordination between Transmission System Operators (TSOs) and Distribution System Operators (DSOs) can compromise grid security instead of improving it.

Within the EU-funded OPENTUNITY project, partners are addressing this challenge head-on by developing and validating practical solutions that enable coordinated, market-based flexibility procurement across grid levels.

The Coordination Challenge Behind Flexibility Markets

Historically, TSOs and DSOs have operated within clearly separated technical and organisational boundaries. Today, with a rising number of flexible assets connected at distribution level, these boundaries are becoming blurred.

Uncoordinated flexibility procurement may lead to:

• Conflicting activations across transmission and distribution networks.
• Local congestion being shifted rather than resolved.
• Increased operational uncertainty for system operators.

To fully unlock the potential of flexibility, coordination must be embedded directly into market processes, supported by shared data, aligned operational rules and real-time communication.

OPENTUNITY’s Approach: Coordination by Design

A core ambition of OPENTUNITY is to demonstrate how secure, interoperable and coordinated flexibility markets can be implemented in real-world conditions. One concrete outcome of this work is the Market Coordination Module, developed by NODES in close collaboration with the Greek DSO HEDNO and the Greek TSO IPTO, developing the OPENTUNITY Greek pilot site.

Rather than treating coordination as an external or manual process, the module integrates it directly into the flexibility trading environment, ensuring that system-level constraints are considered throughout the entire procurement cycle.

Key Features Supporting Secure Operations

The Market Coordination Module introduces several capabilities that are essential for coordinated grid operation:

• A central coordination role, enabling oversight of market activities and supporting system-level decision-making.
• Dynamic grid node thresholds, allowing capacity limits to reflect real-time grid conditions.
• A traffic-light signalling mechanism, providing immediate visibility of potential or actual constraint violations.
• Real-time operator-to-operator communication, facilitating fast, transparent collaboration between TSOs and DSOs.

Together, these functionalities create a shared operational framework where flexibility can be activated safely and efficiently.

Real-World Validation Through OPENTUNITY Pilots

In OPENTUNITY, these coordination mechanisms are being tested in practice. In Greece, HEDNO and IPTO are jointly using the Market Coordination Module to procure flexibility for congestion management and balancing services within a common market environment.

This pilot allows the consortium to assess how coordinated market-based solutions can:

• Improve system security.
• Enhance transparency between system operators.
• Enable more efficient use of distributed flexibility.

The same coordination concept has also proven transferable beyond OPENTUNITY, with applications in Finland, reinforcing the scalability and robustness of the approach.

Building the Foundations for Europe’s Future Flexibility Markets

By embedding coordination into flexibility markets, OPENTUNITY contributes to a future where:

• Market-based solutions and grid security go hand in hand.
• TSOs and DSOs collaborate through shared digital tools.
• Flexibility can scale without increasing operational risk.

These developments are a key step toward a more resilient, efficient and integrated European energy system, one where flexibility supports both system needs and market innovation.