ACER updates methodology for a more efficient assessment of regional electricity reserve requirements

In March 2026, ACER received a proposal from the European Network of Transmission System Operators for Electricity (ENTSO-E) to amend the methodology for the regional sizing of reserve capacity. After reviewing the proposal and exchanging with stakeholders, ACER has decided to amend the methodology.

What is the methodology about?

The methodology for the regional sizing of reserve capacity (first approved by ACER in 2023) allows regional coordination centres (RCCs) to assess the reserves needed at regional level, taking into account volumes shared between transmission system operators (TSOs) through bilateral agreements. 

This coordination helps reduce procurement costs and ensure a more efficient distribution of reserves across Europe. Based on their assessment, RCCs provide TSOs with recommendations on how to optimise reserve capacity volumes, leveraging the flexibility of the EU electricity system.

What’s new in the amended methodology?

As previously requested by ACER, the methodology now:

• Establishes that all RCCs must rely on data from the previous 12 months when assessing the minimum volume of reserves needed for the following year. This ensures the data used reflects the most relevant and frequent system conditions.
• Specifies, for each system operation region, how much reserve capacity is needed to cover positive and negative imbalances. 
• Introduces a 24-month rolling implementation deadline for assessing the short-term availability of reserve capacity (for sharing agreements established after 1 July 2026).
• Enhances transparency by strengthening and streamlining RCCs’ reporting obligations.

These changes will help RCCs size reserve capacity more efficiently, address TSOs’ operational risks and enhance the process’ transparency and coordination.

What are the next steps? 

As previously agreed, RCCs must implement the methodology’s main changes by 1 July 2026.