ACER has adopted two decisions amending the day-ahead and long-term capacity calculation methodologies for the Core region - the EU’s largest electricity capacity calculation region (CCR), covering 13 Member States.
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 covers electricity capacity available for trading one day before delivery, while the long-term methodology covers yearly and monthly capacity calculations.
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, linking operational security to long-term capacity volumes.
The Core transmission system operators (TSOs) proposed separating these two timeframes to 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 proposed amendments, with some adjustments.
Key changes include:
Long-term methodology:
- introducing transitional benchmark available transfer capacity (ATC) values to better reflect historical cross-border capacities;
- establishing formal amendment procedures for future updates to these values; and
- integrating the Ireland and Northern Ireland–France bidding zone border into the Core region, following the Celtic Interconnector’s commissioning.
Day-ahead methodology:
- removing long-term allocations from the capacity calculation process; and
- reflecting the transmission system’s expansion and new infrastructure (including the Celtic Interconnector).
Next steps
The Core TSOs must implement both amended methodologies for the 2027 capacity calculation processes.
