Regional Electricity Reserve Sizing Methodology Amendment

1.4.2026

ACER to amend the methodology for assessing regional electricity reserve needs

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ACER to amend the methodology for assessing regional electricity reserve needs

What is it about?

On 25 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.

What is the methodology about?

Balancing resources are necessary to manage differences between electricity supply and demand, keeping the grid stable in real time. To maintain this balance, transmission system operators (TSOs) determine the volume of reserve capacity needed at national level.

At regional level, the methodology for the regional sizing of reserve capacity allows regional coordination centres (RCCs) to assess reserve needs across countries, taking into account volumes shared between 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, thereby leveraging the flexibility of the EU electricity system.

Why amend the methodology?

As requested by ACER in 2023, ENTSO-E proposes to:

• determine the appropriate time span of historical data that RCCs should use to assess the minimum volume of reserves needed for the following year, ensuring the data used reflects relevant system conditions;
• specify how much reserve capacity is needed to cover positive and negative imbalances for a defined percentage of time. These changes will help RCCs size reserve capacity more efficiently, address TSOs’ operational risks and enhance the process’ transparency and coordination.

ENTSO-E also proposes a new 24-month implementation deadline for assessing the short-term availability of reserve capacity that TSOs have agreed to share, starting from the date each agreement is signed. This deadline concerns only newly established agreements and reflects the voluntary nature of the task (i.e. it applies only where sharing agreements between TSOs are in place).

What are the next steps?

ACER will decide whether to amend the methodology by 25 June 2026.

Interested parties are encouraged to submit comments or questions to ACER-ELE-2026-002@acer.europa.eu by 30 April 2026.

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