IN Brief:
- ACER will consult on the preliminary EU-Flex electricity market model between 5 November and 17 December 2026.
- The open-source framework will support analysis of electricity flexibility requirements and potential gaps across EU power systems.
- An explanatory paper, methodology and test case will accompany the release, ahead of the first EU-wide assessment in July 2027.
The European Union Agency for the Cooperation of Energy Regulators (ACER) will open a public consultation on 5 November 2026 covering EU-Flex, an open-source electricity market model being developed to assess flexibility requirements across European electricity systems.
The consultation will remain open until 17 December, allowing electricity system operators, regulators, market participants and other stakeholders to examine the proposed methodology before ACER conducts its first EU-wide flexibility needs assessment in July 2027.
EU-Flex is being developed under responsibilities established by the European Union’s 2024 Electricity Market Design reform. The legislation requires ACER to assess electricity flexibility needs, identify potential gaps between those requirements and available resources, and recommend action addressing relevant cross-border issues.
The consultation was announced on 21 October, but the preliminary software and supporting documentation are not due to be released until 5 November. The model should therefore be treated as an upcoming technical release rather than a completed assessment of European electricity infrastructure.
Electricity flexibility describes a power system’s ability to respond when generation and demand change. The resources providing that flexibility can include controllable generation, energy storage, demand response and transfers between interconnected electricity markets.
Their operating characteristics differ considerably. A battery can increase or reduce its power output rapidly, but its discharge duration is constrained by the energy available. Demand response changes electricity consumption, while conventional generating plant can adjust output only within its technical operating limits.
Interconnectors provide another route for balancing electricity supply and demand. Their contribution depends on transfer capacity, network conditions and whether sufficient electricity is available in neighbouring systems when required.
As wind and solar generation expand, electricity system operators must accommodate greater variations in generation patterns. These changes interact with demand fluctuations, plant outages, network constraints and the availability of dispatchable resources.
A flexibility assessment must account for these relationships if it is to distinguish between an apparent shortage of generating capacity and a requirement for resources able to change output or consumption at particular times.
The European approach also presents a geographical challenge. Electricity systems differ in their generation portfolios, interconnection capacity, demand characteristics and available storage. A method developed for one national system may not produce directly comparable results when applied elsewhere without consistent assumptions.
ACER intends EU-Flex to provide a common analytical framework for examining these requirements across member states. The first assessment will identify flexibility needs and potential shortfalls, but the consultation itself will not establish procurement obligations or select particular technologies for deployment.
The preliminary release will include an explanatory paper describing the model and demonstrating its application through a test case. ACER will also provide the preliminary source code, the input data required for that test case and documentation covering the methodology.
Making those materials publicly available should allow stakeholders to examine how the model has been constructed and reproduce the accompanying example. The ability to test a model is particularly relevant where its results may later inform regulatory or investment decisions.
Open-source publication does not automatically establish that a model produces reliable results. Its usefulness depends on whether the mathematical representation, input data and operating assumptions adequately describe the electricity system conditions under examination.
Electricity flexibility requirements also vary with time. Rapid disturbances may require a response measured in seconds or minutes, while changes in renewable generation can create different requirements across hours or consecutive days.
Energy storage technologies cannot be compared solely by their maximum power ratings. A 100MW installation with one hour of usable storage has a different operating capability from a 100MW installation designed to discharge over several hours.
The charging requirements of storage must also be considered. A battery that has already discharged cannot repeat the same response indefinitely without replenishing its stored energy, and opportunities to recharge depend on both electricity availability and network conditions.
Demand response introduces different limitations. Industrial processes, building systems and other electrical loads may be capable of shifting consumption, but the achievable response depends on process requirements, customer participation and how long the reduction or increase can be sustained.
Network conditions can further restrict the use of otherwise available flexibility. A resource may have sufficient power and energy capacity but be unable to deliver the required response at a particular location because of transmission constraints.
ACER has not yet published the preliminary EU-Flex materials, so the extent to which the model represents individual network constraints, temporal operating limits or specific technologies cannot be confirmed from the consultation announcement alone.
These questions will form part of the technical examination once the source code and methodology become available. Stakeholders will be able to identify assumptions that require clarification, test the published example and propose changes before the assessment framework is finalised.
ACER plans to collect feedback on the explanatory paper and methodology through its formal consultation. Comments concerning the model itself will be handled through the agency’s public GitHub repository, allowing technical issues to be examined alongside the software.
An online webinar scheduled for 17 November will introduce EU-Flex and demonstrate how the preliminary version can be configured and run. The session takes place during the consultation period, giving participants an opportunity to examine the model before submissions close.
The consultation audience includes transmission and distribution system operators, national regulatory authorities, public bodies, electricity market participants, academics and other interested organisations.
Their contributions may address different aspects of the framework, from the availability of representative data to the treatment of operational constraints and the interpretation of identified flexibility gaps.
A common methodology could support more consistent comparisons across national markets, although the validity of those comparisons will depend on the quality of the model and its underlying assumptions.
The July 2027 assessment is intended to provide evidence about requirements that may need to be addressed through future market arrangements, network measures or flexibility resources. Decisions about investment and regulatory implementation will remain separate from the modelling exercise.
The first public test begins on 5 November, when ACER is scheduled to release the preliminary software and supporting documents. Feedback collected before 17 December will inform the agency’s preparations for the first EU-wide assessment seven months later.
