ACER publishes today its Opinion on the draft TYNDP 2026 Scenarios Report prepared by the European Network of Transmission System Operators for Electricity and Gas (ENTSO-E and ENTSOG) under the TEN-E Regulation. 

These scenarios, produced every two years, provide the common foundation for EU-wide electricity, gas and hydrogen infrastructure planning, and feed into the Ten-Year Network Development Plans (TYNDPs).

ACER’s Opinion assesses whether the ENTSOs’ scenarios comply with ACER’s Framework Guidelines and provide a transparent and consistent basis for infrastructure planning.

What are the key findings?

ACER welcomes the significant work by ENTSO-E and ENTSOG to improve the scenarios’ accuracy, including:

• the continued delivery of joint scenarios combining electricity, gas and hydrogen; 
• the introduction of economic variants (high- and low-growth cases applied to the central scenario to assess the robustness of the underlying economic assumptions);
• the involvement of the Stakeholder Reference Group, which gives stakeholders structured scrutiny over the scenarios’ assumptions, methods and data; and
• the development of an Innovation Roadmap, which sets out planned improvements to the scenario-modelling tools and methods, and is updated every two years.

ACER also identifies two main areas for improvement:

• Alignment with EU climate and energy targets. The current methodology enables formal compliance with EU targets, but ACER considers that it does not adequately capture the structural changes needed to achieve those targets in practice.
• Stronger economic variants. These should function as meaningful alternative scenarios, with greater transparency and consultation on key scenario assumptions and infrastructure planning inputs, improved consistency with the European Resource Adequacy Assessment (ERAA) and a more timely scenario development process.

What are the next steps?

For the finalisation of the TYNDP 2026 Scenarios Report, ACER calls on ENTSOs to improve transparency on the remaining gap to EU climate and energy targets and the limitations of the current methodology.

For future cycles, ACER expects further improvements in EU targets alignment, economic variants, consistency with ERAA, stakeholder consultation and the overall timeliness of the process.

The European Commission will take ACER’s Opinion into account when assessing the draft TYNDP 2026 Scenarios Report.

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.

On 10 June 2026, transmission system operators (TSOs) submitted a proposal to ACER to revise the harmonised allocation rules (HAR) and the requirements for the single allocation platform (SAP).

To inform its decision-making process, ACER will open a public consultation on 10 July 2026.

What are these rules about?

The harmonised allocation rules apply to all allocations of long-term transmission rights performed in the European Union. They provide specifications for the auctioning of long-term transmission rights (including their use, curtailment and eligibility criteria) and go through a review process every two years. All TSOs issuing long-term transmission rights are required to offer-long term cross-zonal capacity to market participants through the single allocation platform.

Why amend them?

With the implementation of long-term flow-based allocation, long-term transmission rights for all bidding zone borders within a capacity calculation region will be allocated with a single auction. 

Currently, collaterals (i.e. financial security provided by market participants to guarantee their payment obligations) for long-term transmission rights are reserved until the auction is cleared, often leading to an overestimation of collaterals’ needs. As long-term flow-based allocation combines multiple bidding zone borders, this over-reservation further increases collateral requirements for market participants. This, in turn, may result in unnecessary bid rejections by market participants and potential welfare losses.

To address this, TSOs propose to amend the harmonised allocation rules and the single allocation platform's requirements by introducing a new collateral management solution.

What are the next steps?

The public consultation will run from 10 July until 7 August 2026. 

ACER will analyse the feedback received and reach a decision by 10 December 2026.

ACER has launched the first edition of its electricity network tariff repository. 

Why network tariffs matter

Network tariffs are a key part of electricity bills, used to recover the costs of investing in, maintaining and operating electricity networks. As Europe’s power system evolves, the grid needs to support more electrification, more renewable energy and new patterns of grid use. Based on sector estimates, investments in electricity networks could reach up to €2,600 billion by 2050 to integrate the rise of renewable energy (see ACER’s 2024 infrastructure report). With the ramp-up of grid investments, network costs are a big driver of overall electricity costs.

Clear and comparable tariff information is therefore important for understanding how network costs are allocated, how tariff structures differ across countries and how tariff design may support efficient use of the grid. This supports broader EU efforts to improve energy affordability and ensure electricity grids are fit for the future, including the European Commission’s upcoming network charges plan, which is part of its energy package expected on 10 June. 

Network tariff repository 

This new ACER repository brings together tariff information from EU Member States in one centralised platform. It complements national transparency efforts and supports access to electricity network tariff data at European level.

The dashboard aims to improve comparability and understanding of national approaches to network cost recovery and tariff setting.

Who can use ACER’s network tariff repository?

Whether for analysis, benchmarking or strategy the repository offers easy access to electricity network tariff information from across Europe to national regulatory authorities, policymakers, network operators, researchers, analysts, and consumer and industry organisations. 

Use case 1 – Electricity bills: An analyst comparing electricity bills across Europe could use the repository to check whether network charges are mainly fixed, capacity-based or energy consumption-based in different Member States and therefore understand the underlying cost drivers. 

Use case 2 – National tariff methodologies: A regulator reviewing its national tariff methodology could compare how other Member States structure and allocate network charges for households and businesses.

What’s next?

The repository will be progressively updated with data and additional information, including tariff practices and relevant studies underlying key network tariffication choices. 

The dashboard will also provide input for ACER’s future analytical work, including the next edition of ACER’s report on electricity network tariff practices, expected in 2027. 

Disclaimer: This electricity network tariff repository is published as a work-in-progress tool. The repository is intended to improve access to tariff-related information and will support ACER’s future analytical work.

Check ACER's new dashboard.

In summer 2024, Southeast Europe¹ experienced a sustained period of electricity price spikes. In response, the European Commission asked ACER to assess which measures could help prevent or mitigate similar episodes across the region in the future. 

Today, ACER publishes its Monitoring Report to the Energy Union Task Force, setting out recommendations to increase cross-zonal capacity and system flexibility across Southeast Europe.

What did ACER find? 

• The 2024 price spikes were driven mainly by a lack of flexible resources to replace solar generation in the evening, during periods of high demand. 
• Limited cross-border capacity, including due to planned network maintenance, reduced the region’s ability to import lower-priced electricity from the rest of the EU.
• Although prices in 2025 did not reach the same levels as in summer 2024, the price gap between Southeast and Central Europe² persisted into early 2026. This suggests deeper structural challenges in the region. 

ACER found that a better use of the existing network could have helped ease regional system stress in 2024. But increasing interconnection alone is not enough – greater system flexibility is also key. 

What does ACER recommend?

Addressing the challenges observed in Southeast Europe’s electricity markets requires both immediate and long-term action by Member States, national regulatory authorities, transmission system operators and other market actors:

• Faster deployment of grid-enhancing technologies (such as dynamic line rating and advanced line conductors).
• Improved regional coordination, including on outage planning and curative remedial actions in capacity calculation. 
• Continued implementation of EU market integration rules (minimum 70% cross-zonal capacity requirement, flow-based approach across Southeast and Eastern Europe, and market coupling with non-EU neighbours).
• Accelerated network investment projects to strengthen interconnectivity of Southeast Europe.
• Measures to unlock system flexibility by removing market barriers for small market participants and supporting investments in flexibility.
  
  ^{1. For the purpose of this assessment, Southeast Europe refers to the group of Member States affected by the price spikes: Slovenia, Croatia, Hungary, Romania, Bulgaria and Greece. 2. Central Europe refers to Austria and Slovakia.}

Today, ACER publishes a policy paper exploring how Europe could improve the way costs and benefits of cross-border electricity infrastructure projects are shared. The paper aims to support the grid investments needed for a more integrated European electricity market and a more efficient use of Europe’s electricity system. 

Why cost and benefit sharing of energy infrastructure matters

Building an integrated European electricity market requires substantial cross-border grid investments. An effective cost-sharing framework is a key enabler of such investments, especially when infrastructure in one country brings benefits beyond its borders.

However, the current framework does not always ensure that costs are shared fairly when a project benefits several countries (for example, when one country bears most of the investment costs while others receive a significant share of benefits). 

As a result, projects with clear European or regional value might not be realised if costs are largely borne at national level while benefits are distributed more widely across borders.

Several mechanisms currently aim to address this challenge: 

• congestion income distribution, which shares revenues from cross-border congestion; 

• the inter-TSO compensation (ITC) mechanism, which compensates for costs related to hosting cross-border flows; and 

• cross-border cost allocation (CBCA), which allocates costs of new infrastructure based on expected cross-border benefits. 

While each plays an important role, gaps and overlaps remain in how effectively they align costs with benefits. This can make it more difficult to develop infrastructure that is valuable from a European or regional perspective.

What is in ACER’s policy paper?

Already in July 2024, ACER committed to strengthening and improving the existing mechanisms to better reflect the costs and benefits of cross-border network infrastructure. 

As part of this effort, ACER’s 2026 policy paper assesses the current mechanisms, their gaps and overlaps, and explores how they could be improved or redesigned to better align national investments with European and regional needs. 

It sets out several policy options, ranging from targeted improvements to the existing mechanisms to broader changes to the overall cost-sharing framework. These include improving the current mechanisms separately, combining some of them into a single ex-post mechanism, or exploring a new framework with common EU financing for infrastructure used for cross-border trade. 

The policy paper also provides a qualitative evaluation of these options, with the common objective of strengthening investment incentives for cross-border electricity infrastructure.

The policy paper does not provide definitive solutions to the identified challenges. Instead, it aims to inform and stimulate further discussion on how the cost-sharing framework can better support investment in projects of European and regional value. 

Today, ACER releases its Opinion on the All-Island Resource Adequacy Assessments for Ireland, Northern Ireland and the Single Electricity Market (SEM) as a whole. The assessment was jointly prepared by the transmission system operators (TSOs) of both jurisdictions (EirGrid and SONI), complementing the European Resource Adequacy Assessment (ERAA) 2025.

What is a resource adequacy assessment?

The ERAA evaluates electricity resource adequacy across the EU and provides a consistent framework to assess whether additional national measures are needed to ensure security of supply. It is carried out annually by the European Network of Transmission System Operators for Electricity (ENTSO-E) and reviewed by ACER.

Member States can complement the European analysis through national adequacy assessments (NRAAs) to reflect local conditions. When a national assessment identifies differences from the European assessment, ACER issues an opinion.

What did ACER find?

ACER finds that most differences between the All-Island Resource Adequacy Assessment and the ERAA are justified, as they reflect national trends and include additional modelling detail, enhancing accuracy. 

ACER also highlights two factors with a major impact on adequacy:

• The planned second North-South Interconnector is included only in the SEM-wide assessment, meaning its contribution to adequacy is not captured in all three analyses. Once operational (expected by 2031), it would help keep adequacy risks in the SEM within the reliability standard in 2033 and 2035, strengthening security of supply across the island and highlighting the importance of increased cross-zonal capacity for resource adequacy.
• The rapid growth of data centres in Ireland (which accounted for 22% of national electricity demand in 2024 and could reach 31% by 2034) poses a key adequacy risk. New policy updates now require data centres to provide onsite or nearby generation equal to peak demand, helping reduce grid reliance and improve flexibility during stress periods. Future adequacy assessments should better reflect both the demand impact of data centres and the extent to which policy measures can mitigate adequacy risks.

What are ACER’s recommendations?

To further strengthen the assessment, ACER recommends that TSOs:

• Include a viability assessment of adequacy resources in the central scenario to confirm the required resources are realistically available. 
• Ensure revenue consistency between market viability and dispatch models so that both tools reflect aligned market revenues and investment signals. 
• Consider multiple revenue streams in the assessment to provide a more robust evaluation of resource profitability. 
• Include the planned second North-South Interconnector in all the three analyses. 
• Consider greater operational flexibility for gas units during periods of scarcity. 
• Incorporate storage and demand response expansion, including flexibility from data centres, for all target years till 2035. 

What are the next steps?

ACER encourages TSOs to consider these recommendations to ensure a more accurate assessment of adequacy risks.

ACER approves the European Resource Adequacy Assessment proposed by the European Network of Transmission System Operators for Electricity (ENTSO-E) for 2025 (ERAA 2025). This draft ERAA was submitted in December 2025 for ACER’s review.

While this marks an important step towards securing Europe’s electricity supply, the ACER approval decision is accompanied by a letter addressed to ENTSO-E. The letter raises concerns about the assessment, in particular persistent methodological gaps and last-minute changes introduced by ENTSO-E shortly before submission, without proper stakeholder consultation. These include a supplementary approach to modelling investment behaviour, which led to a second, less robust set of results that ACER removed to ensure overall robustness.

As the ERAA is increasingly used to justify national measures (such as capacity mechanisms under the EU State aid framework), ACER emphasises the need to safeguard its technical integrity and ensure early, transparent cooperation. 

What does ACER say about the ERAA 2025? 

While the ERAA 2025 provides an important 10-year outlook on resource adequacy, ACER’s analysis identifies several critical areas where further improvements were needed:

• Address model inconsistencies between the investment and adequacy modules, which may otherwise systematically overstate adequacy concerns, leading to unnecessary or costly market interventions.
• Move towards a revenue-based investment module to better reflect whether market revenues can sustain existing capacity and support new investments, particularly in flexible resources (e.g. batteries).
• Reinforce procedural transparency to ensure significant changes are introduced in a timely manner and subject to proper stakeholder consultation. This includes greater transparency on ENTSO-E’s website on what is still a draft ERAA, hence subject to ACER's approval.

Without these improvements, the ERAA risks losing its usefulness as a reference for policy decisions.

What’s next? 

The ERAA 2025 was the last edition before the entry into force of the amended ERAA methodology (March 2026). From the upcoming 2026 edition, ENTSO-E will progressively integrate the amended methodology into future reports. 

ACER will hold a webinar on the updated ERAA methodology on 26 May 2026.

Full implementation of this methodology is needed to support the fast-track approval of capacity mechanisms under the Clean Industrial State-Aid Framework, such as indicating how much firm capacity is needed and calibrating technology-specific derating factors to determine how much each technology can be relied on to deliver when needed. 

Looking ahead, ACER identifies several priorities for ENTSO-E for the ERAA 2026:

• Adopt a revenue-based investment module to improve model coherence and provide a more realistic view of which capacities remain economically viable.
• Work on the full implementation of the amended methodology, introducing the "Trends and Projections" scenario to reflect the observed pace of the energy transition, and deliver capacity mechanism-related parameters to support the fast-track State aid approval process for capacity mechanisms.
• Ensure a more transparent and cooperative development process, including early alignment on methodological changes to ensure timely and efficient delivery of future ERAA annual assessments.
• Strengthen the hurdle rate method used in the assessment to better reflect investors’ risk aversion.

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.

The Core capacity calculation region comprises of 13 Member States: Austria, Belgium, Czech Republic, Croatia, France, Germany, Hungary, Luxembourg, the Netherlands, Poland, Romania, Slovakia and Slovenia.

Capacity calculation regions define the geographic areas across Europe where TSOs coordinate the capacity calculation and other processes subject to regional methodologies.

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. This change is a prerequisite for the adoption and implementation of the flow-based capacity calculation methodology in the long-term timeframe (Core LT CCM), which is currently under review by ACER following its referral by Core regulatory authorities in February 2026.

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.

Today, ACER publishes its report on distribution system operator (DSO) investments and revenue setting. 

The report: 

• finds a major upscaling in electricity distribution grid investment trends across Europe;
• identifies some factors that may hinder efficient investments; 
• reviews the DSO landscape in Europe; 
• explores ways to address the challenges facing DSOs;
• proposes a set of 10 recommendations to optimise the ramp-up of distribution grid investment and improve services to grid user.

What are the main findings?

To accelerate decarbonisation, significantly more grid capacity is needed for electrification and renewables’ growth. This is driving a visible rise in electricity distribution grid investments across Europe. In 2024, annual distribution grid investments increased by over 50% to €35.3 billion (compared to €23.5 billion in 2021). Distribution grid investment is projected to approach €47 billion in 2027.

Beyond the investment challenge, DSOs face expanded roles under EU legislation. They must be active system operators (e.g. managing the system, utilising flexibility services, optimising electricity flows on the grid), market facilitators, data hubs, and innovation drivers – responsibilities that require new tools, specialised skills, and stronger coordination. 

Europe needs DSOs who provide high quality distribution services. As the system evolves, regulatory frameworks must adapt alongside it. 

This ACER report highlights several elements that might hinder efficient investments:

• Size matters. DSOs must be equipped to deal with evolving responsibilities for grid planning, flexibility solutions, grids’ digitalisation and resilience, to ensure all customers have equal access to high-quality and cost-efficient distribution services. Robust system planning and efficient regulatory scrutiny should not be compromised by fragmented and uncoordinated network development. 
• DSOs should adopt the most efficient solutions for network development – whether grid-based or non-grid (e.g. flexibility). The regulatory focus must expand beyond cost-cutting and maximise the benefits for society. Reducing capital expenditure (CAPEX) bias, still present in several countries, is key for improving regulatory regimes. 
• Rigid expenditure caps should not hinder nor distort key investments needed for the clean energy transition. 
• Distribution grid use and planned development should be more transparent. DSOs should strive to publish their mid-term cost trajectories and monitor grid utilisation to improve planning and operations.

ACER’s report offers 10 recommendations for legislators, regulators and system operators to optimise the ramp-up of distribution grid investment and improve services to grid users. These aim to ensure adequate competences, proper transparency and unlock efficient investments. National regulatory authorities should consider these recommendations when setting or approving their distribution revenue methodologies.

What are the next steps?

ACER will continue to:

• facilitate best-practice sharing among national regulatory authorities; and
• engage with stakeholders to gather insights.

In 2027, ACER will publish the next edition of its report on network tariff practices. ACER’s next report on revenue setting practices will be in 2028.