On 22 January 2026, the transmission system operators (TSOs) of the Core capacity calculation region submitted a proposal to their national regulatory authorities to amend the day-ahead capacity calculation methodology. As the national regulators could not reach an agreement, the proposal was referred to ACER on 30 March 2026 under the Capacity Calculation and Congestion Management Regulation.
What is the methodology about?
The Core day-ahead capacity calculation methodology (initially established by ACER in 2019 and first implemented in June 2022) aims to maximise the capacity made available to the market while maintaining operational security.
This methodology is based on a flow-based approach, meaning cross-zonal capacities are calculated by taking into account transmission networks’ physical constraints. This approach significantly improves the efficiency of cross-zonal capacity allocation, as it better reflects real network conditions.
Why change the rules?
Core TSOs propose to amend the methodology to better harmonise it with other electricity market timeframes (i.e. intraday and long-term capacity calculation) operating in the same region.
The main purpose of this amendment is to remove long-term allocations from the day-ahead capacity calculation. Removing long-term allocations from the day-ahead capacity calculation decouples operational safety from long-term capacity volumes, allowing their determination without direct operational security constraints. This will improve the efficiency of the process, as long-term capacities will be calculated independently, reflecting the separation between the day-ahead and long-term frameworks.
What are the next steps?
ACER, in cooperation with relevant energy regulators and TSOs, will reach a decision by 30 September 2026.
