ACER’s 2026 Monitoring Report on energy infrastructure development in Europe examines whether electricity, gas and hydrogen networks are adapting to changing energy needs, and what this means for investment costs, delays and consumer costs.  

As renewable generation expands and electricity demand grows (driven by heat pumps, electric vehicles and data centres), electricity grids need to accommodate new connections and shifting generation and consumption patterns. Meanwhile, gas networks must adapt to lower demand, and hydrogen is still at an early stage. Developing the right infrastructure, efficiently and on time, will determine whether Europe can meet its decarbonisation goals and keep energy affordable for households and industry.

What trends did ACER monitoring find?  

• Electricity grid investment is rising fast. Annual investment in electricity transmission nearly tripled, from €10.4 billion in 2019 to €30.5 billion in 2025.
• Cross-border projects are often delayed. On average, 22% of electricity transmission projects of common interest (PCIs) and mutual interest (PMIs) is delayed each year, mainly due to lengthy permitting procedures. A one-year delay can cost around €4 billion in lost economic welfare.  
• Electricity grid congestion is costly. Remedial actions taken by transmission system operators (TSOs) to relieve congestion cost European consumers €5.4 billion in 2025, over 25% more than in 2024.  
• Income collected to manage electricity grid congestion is largely set aside for later use. Annual congestion income from day-ahead markets exceeded €9 billion in 2025, seven times the 2019 level. Yet, 60% (about €12.5 billion) of the total available is set aside rather than reinvested in cross-border grids or used to reduce tariffs.
• Rising electricity network costs weigh on household bills. Electricity network costs for EU households rose by 40% between 2019 and 2025, reaching 84 EUR/MWh. They now account for around 28% of the average electricity bill.
• Gas networks are adapting to lower demand. Gas investments are broadly stable, while demand remains 16% below its 2017-2021 baseline. Average transmission tariffs increased by 40% between gas years 2020/2021 and 2024/2025.
• Hydrogen networks are at an early stage. EU electrolyser capacity (used to produce hydrogen with electricity) reached 0.49 GW, well below the 30-58 GW target envisaged for 2030 in national strategies and EU scenarios.

What are ACER’s recommendations?  

• Make better use of existing networks through demand response, market-based congestion management, full implementation of the 70% cross-border capacity requirement, cost-reflective network tariffs and grid-enhancing technologies.
• Improve infrastructure planning and delivery with transparent, more integrated planning across electricity, gas and hydrogen networks, and simpler, more predictable permitting procedures.
• Address shortcomings in cost-sharing mechanisms by distributing network costs fairly among users over time and reviewing how costs and benefits of cross-border projects are shared. 

ACER published the preliminary version of EU-Flex, an open-source electricity market model developed to assess flexibility needs across the EU.

Electricity flexibility is the power system’s ability to respond to changes in supply and demand. As renewable generation grows and electrification expands across sectors, the EU will need greater flexibility to ensure security of supply, integrate new renewable sources and keep electricity affordable. 

Why estimate flexibility needs?

Under the EU’s (2024) Electricity Market Design reform, ACER is tasked with estimating flexibility needs across the EU, identifying potential gaps between these needs and available flexibility and recommending actions to address cross-border issues. The first assessment is planned for July 2027.

To support this work, ACER developed EU-Flex, an open-source model that simulates the European electricity market. The model provides insights into the flexibility challenges facing the EU power system, and how cross-border cooperation can help address them.

What’s in this preliminary release?

By sharing the model ahead of the 2027 assessment, ACER aims to make its analysis more transparent, allowing stakeholders to explore the proposed approach and contribute to the model’s development.

The release includes:

• a short paper introducing the model and demonstrating its use through a test case;

• a preliminary version of the model, with its source code and test case input data; and

• a document describing the underlying methodology.

Have your say!

Interested stakeholders have until 17 December 2026 to share their views on the:

• paper and methodology, through ACER’s public consultation; and

• preliminary model, via ACER’s GitHub repository.

Want to learn more?

On 17 November 2026, ACER will hold a webinar to present the model, explain its key features and demonstrate how to run it. Register for free.

Integrated electricity markets are central to a secure, affordable and sustainable EU energy system. By enabling cross-border trade, they increase competition, improve affordability for consumers, support more renewables and strengthen security of supply and system resilience.

The ACER 2026 Monitoring Report published today evaluates progress and potential benefits of EU electricity market integration, covering key developments across all market timeframes, as well as cross-zonal capacity and congestion management. 

What trends did ACER’s monitoring find? 

ACER’s monitoring finds progress:

• Cross-border trade generates about €32 billion in economic surplus each year in the day-ahead market alone. Further integration over all markets could deliver at least an additional €4 billion per year. 
• Day-ahead trading has largely moved to 15-minute products. Introduced on 1 October 2025 to better reflect changing system conditions, they now account for almost 90% of all electricity traded in the day-ahead market. 
• Interest is growing in pairing renewables with storage. Power purchase agreements (long-term contracts between sellers and buyers) increasingly combine renewable generation with energy storage, supporting investment in renewable energy and increasing flexibility.

However, significant challenges remain: 

• Forward market liquidity remains concentrated in a few bidding zones and trading activity falls rapidly for electricity contracts traded beyond one year-ahead.
• Price differences between bidding zones are widening, increasing the importance of making sufficient transmission capacity available for cross-zonal trade.
• The availability of cross-zonal capacity is still lagging. The requirement to make at least 70% of capacity available for trading electricity across borders is not yet fully implemented across the EU. Markets that operate closer to real time, such as intraday and balancing markets, are particularly affected by limited access to cross-zonal trade. 
• The cost of managing grid congestion is rising. It reached €5.4 billion in 2025, up from €4.3 billion in 2024, with a growing share linked to voltage control following the Iberian blackout.

Looking ahead

Market integration already brings clear benefits, but its full value has yet to be realised. As renewable generation grows, cross-zonal trading, particularly close to real time, will become increasingly valuable. Further integration and the full application of existing rules, such as the minimum 70% requirement, would deliver significant gains for consumers in the coming years.
 

Today, ACER releases its report on the Slovak gas transmission tariffs directed at Eustream, Slovakia’s transmission system operator (TSO).

The report assesses the compliance of the proposed reference price methodology (RPM) with the requirements of the EU Network Code on Harmonised Transmission Tariff Structures (NC TAR). 

Eustream had previously proposed the application of a new tariff methodology for January 2026 to December 2027, with indicative tariffs calculated for that period (see ACER analysis). In April, the Slovak energy regulator, ÚRSO, approved lower transmission tariffs than Eustream had proposed, to be applied from 1 May 2026. Following this decision, Eustream launched a new consultation on 30 June, proposing the same tariffs as in the previous consultation, with only minor methodological changes. 

On 8 October 2026, ÚRSO discontinued the tariff proposal procedure, which also ended the RPM proceeding. There is a 40-day period to appeal against ÚRSO’s decision. The discontinuation of the Slovak procedure does not affect ACER’s obligation to publish its analysis.

What is the proposed tariff methodology?

The Slovak TSO proposes to:

• Introduce a revised methodology and new tariffs midway through the current tariff period, which would result in a tariff increase of more than 50%. The TSO cites exceptional circumstances (a large drop in cross-system flows) as the reason for this change.
• Apply a uniform postage stamp reference price methodology with an ex-ante entry-exit split.
• Continue recovering transmission revenues through a mix of capacity-based charges (paid for reserving network capacity) and commodity-based charges (linked to the volume of gas transported).
• Adjust capacity tariffs at all entry and exit points (including domestic points) using benchmarking to lower tariffs and make them more competitive. Eustream proposes to use a wide set of European TSO tariffs, including those from Northwestern Europe, as a reference.
• Keep two commodity-based charges in place:
  • a flow-based charge paid in kind (meaning a portion of transported gas is normally used to cover the fee); and
  • a complementary revenue recovery charge, designed to help recover the costs of the Slovakia-Poland gas interconnector.

What are the key findings? 

ACER’s findings remain largely unchanged from its February 2026 report. After analysing the new consultation document, ACER concludes that: 

• The proposed methodology meets the EU requirement on non-discrimination.
• Compliance with the requirements on transparency, cost-reflectivity, avoidance of cross-subsidisation, volume risk and the prevention of cross-border trade distortions cannot be confirmed. This is mainly due to the proposed benchmarking adjustment, which does not meet the tariff network code’s standards.
• The proposed commodity-based charges are non-compliant. Specifically, the flow-based charge is corrected by a discount for domestic flows, which is not allowed under EU rules.

What does ACER recommend? 

Should the procedure be resumed, ACER recommends that ÚRSO:

• Limit benchmarking adjustments to points with clear pipeline competition, ensuring tariffs reflect market conditions and remain predictable for network users.
• Implement measures to improve alignment with the network code’s requirements, despite current challenges to full compliance.
• Phase out the non-compliant discount applied to the flow-based tariff.

See all ACER reports on national tariff consultation documents.