ACER updates Core region’s electricity rules to support long-term flow-based capacity calculation

ACER has adopted two decisions amending the day-ahead and long-term capacity calculation methodologies for the Core capacity calculation region (CCR).

The Core CCR is the EU’s largest electricity capacity calculation region, covering 13 Member States: Austria, Belgium, Croatia, Czech Republic, France, Germany, Hungary, Luxembourg, the Netherlands, Poland, Romania, Slovakia and Slovenia.

ACER Decisions follow referrals by the regional national regulatory authorities under the Capacity Calculation and Congestion Management and the Forward Capacity Allocation Regulations.

What are the methodologies about?

Capacity calculation methodologies determine how much cross-border transmission capacity can be made available to electricity markets.

The day-ahead methodology determines how much electricity capacity is available for cross-border trading one day before delivery. The long-term methodology covers yearly and monthly capacity calculations, enabling long-term planning and hedging opportunities.

In the Core region, both methodologies apply a flow-based approach, meaning capacities are calculated by accounting for actual transmission network constraints. This improves efficiency compared to simpler methods.

Why amend them?

Currently, long-term capacity allocations are included in the day-ahead capacity calculation process. The Core transmission system operators (TSOs) proposed separating these two timeframes so that operational security, which is central to day-ahead capacity calculation, is no longer linked to the volume of capacity allocated in the long-term timeframe. 

This separation aims to better harmonise the region’s market timeframes and facilitate the transition towards long-term flow-based capacity calculation, planned for 2027.

What did ACER decide?

After reviewing the TSOs’ proposals and consulting with stakeholders, ACER approved the amendments, introducing changes to strengthen legal clarity and ensure compliance with EU electricity market rules.

Key amendments include:

Long-term methodology:

• introducing benchmark available transfer capacity (ATC) values as a transitional measure to support flow-based capacity calculation, better reflecting historical cross-border transmission capacities;
• establishing formal amendment procedures for any future changes to these values; and
• integrating the Ireland and Northern Ireland single electricity market–France bidding zone border into the Core region, following the commissioning of the Celtic Interconnector.

Day-ahead methodology:

• removing long-term allocations from the capacity calculation process; and
• updating the methodology to reflect the transmission system’s expansion and new infrastructure (including the Celtic Interconnector).

ACER’s Decisions support consistent capacity calculation in the Core region and facilitate the implementation of long-term flow-based capacity calculation.

Next steps

The Core TSOs must implement both amended methodologies for the 2027 capacity calculation processes.