ACER Opinion 13-2026 on the ENTSO-E and ENTSOG draft Ten Year Network Development Plan 2026 Scenarios Report

No 13/2026

OPINION

on the ENTSO-E and ENTSOG draft Ten Year Network Development Plan 2026 Scenarios Report

8 July 2026

A C E R O P I N I O N N O 1 3 / 2 0 2 6

Executive summary

Purpose and scope of the Opinion

This Opinion concerns the draft TYNDP 2026 Scenarios Report jointly submitted by ENTSO-E and ENTSOG pursuant to Article 12 of Regulation (EU) 2022/869 on guidelines for trans-European energy infrastructure. ACER’s assessment is mainly based on the TYNDP Scenarios Framework Guidelines adopted in January 2023 and focuses on whether the draft scenarios comply with these Guidelines, thereby ensuring that they provide a transparent, non-discriminatory, robust and policy-aligned basis for Union-wide infrastructure planning.

Key observations by ACER

ACER welcomes the substantial work undertaken by ENTSO-E and ENTSOG, with the involvement of hydrogen transmission network operators, in particular the continued development of joint electricity, gas and hydrogen scenarios, the first-time implementation of Economic Variants, the involvement of the Stakeholder Reference Group (‘SRG’), and the development of an Innovation Roadmap. At the same time, ACER identifies several important shortcomings and areas requiring improvement: • The scenarios do not yet provide a sufficiently credible representation of a pathway aligned with the Union’s climate and energy objectives. While the ENTSOs apply a “gap-filling” methodology to formally achieve target compliance, the approach remains overly simplistic and mischaracterises the broader structural transformations required to meet EU targets in practice. • ACER recognises that the ENTSOs are operating within a broader governance gap between EU-level targets and nationally validated implementation pathways. However, the current methodology risks creating the impression of target compatibility without transparently reflecting the remaining gap towards achieving the Union’s climate and energy objectives. At a minimum, ACER considers that future TYNDP cycles should include one scenario that credibly demonstrates compatibility with the Union’s climate and energy targets. • The Economic Variants represent a useful first implementation of ACER’s Framework Guidelines. However, the variants remain relatively limited as alternative scenarios, particularly regarding hydrogen uncertainty and lack of more divergent transition pathways. • ACER also identifies important inconsistencies in the Scenario Grid methodology, particularly regarding the differing maturity criteria applied to electricity and hydrogen infrastructure projects. ACER considers that current and future TYNDP cycles should strengthen transparency, consultation and consistency regarding the assumptions used for the reference infrastructure grid. • ACER positively acknowledges the role of the SRG and the generally constructive stakeholder engagement process. Nevertheless, stronger transparency and public scrutiny remain necessary, particularly regarding deviations between TSO input assumptions and NECP values, as well as the consultation of demand-side input data and Economic Variants results. • The Innovation Roadmap implementation priorities and timelines remain insufficiently clear. • ACER also notes persistent differences between TYNDP and ERAA assumptions; • ACER remains seriously concerned about continued delays in the scenario preparation process, which risk undermining the relevance and credibility of the TYNDP framework and creating significant complexity for scenario-building and network development planning at national level.

Overall conclusion and way forward

ACER considers that the draft TYNDP 2026 Scenarios Report incorporates several improvements, particularly regarding cooperation with the SRG. However, the current scenarios do not yet provide a sufficiently robust and transparent basis for infrastructure planning consistent with the Union’s climate and energy objectives.

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For the finalisation of the TYNDP 2026 Scenarios Report, ACER therefore calls on ENTSO-E and ENTSOG to: • improve transparency regarding the remaining gap to EU climate and energy targets; • strengthen transparency regarding the limitations of the gap-filling methodology; and • ensure transparency about the differences between the TYNDP central scenario (near-term and mid-term) and the corresponding ERAA scenarios. For future scenario cycles, and in particular TYNDP 2028, ACER further expects ENTSO-E and ENTSOG to: • develop a more credible and robust approach to target alignment and gap-filling, including a central scenario that credibly demonstrates compatibility with the Union’s climate and energy targets; • further develop the Economic Variants as meaningful scenarios; • improve transparency, consultation and consistency regarding the Scenario Grid assumptions, particularly concerning the maturity criteria applied to electricity and hydrogen infrastructure; • include scenarios with sensitivities on the main hydrogen demand and supply drivers, to capture uncertainties over the appropriate scale of infrastructure required to meet future needs. • strengthen consistency with ERAA assumptions; • further improve transparency and stakeholder consultation processes; and • ensure a significantly timelier scenario preparation process.

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1. Background

1 This Opinion concerns the draft Joint Scenarios Report prepared for the 2026 Union-wide tenyear network development plan (‘TYNDP 2026’) by the European Network of Transmission System Operators for Electricity (‘ENTSO-E’) and the European Network of Transmission System Operators for Gas (‘ENTSOG’), in cooperation with hydrogen transmission network operators.

2 Under Article 12(1) of Regulation (EU) 2022/869 on guidelines for trans-European energy infrastructure (‘TEN-E Regulation’), ACER must establish framework guidelines for the joint scenarios to be developed by ENTSO-E, ENTSOG and the European Network of Network Operators for Hydrogen (‘ENNOH’) (together, the ‘ENTSOs’). Those guidelines must ensure that the scenarios are developed in a transparent, non-discriminatory and robust manner, in line with best practices in infrastructure assessment and network development planning. They must also ensure consistency with the energy efficiency first principle, the Union’s 2030 climate and energy targets and its 2050 climate-neutrality objective, while taking into account the latest available European Commission scenarios and, where relevant, national energy and climate plans (‘NECPs’).

3 Article 12 of the TEN-E Regulation further requires the ENTSOs to develop the joint scenarios in line with ACER’s Framework Guidelines. The scenarios must include a long-term perspective up to 2050, with appropriate intermediate steps. The ENTSOs must also involve relevant stakeholders, including the EU DSO entity, sectoral associations, consumer representatives and civil society, in particular on key assumptions and on how those assumptions are reflected in the scenario data. The draft Joint Scenarios Report must then be published and submitted to ACER, the Member States and the European Commission for their opinion.

4 Under Article 12(5) of the TEN-E Regulation, ACER must, within three months of receiving the draft Joint Scenarios Report, the consultation input and the explanation of how that input was taken into account, issue an Opinion on the scenarios’ compliance with the Framework Guidelines, including, where appropriate, recommendations for amendments. The Commission must then decide whether to approve the draft report or request amendments.

5 Until 1 January 2027, Article 12 applies subject to the transitional rules in Article 61 of Regulation (EU) 2024/1789 on the internal markets for renewable gas, natural gas and hydrogen. Under those rules, ENTSOG remains responsible for preparing the 2026 Union-wide network development plan for hydrogen, with the full involvement of hydrogen transmission network operators and, once established, ENNOH. During that transitional period, ENTSO-E, ENTSOG and ENNOH must cooperate closely on integrated network planning, including on a single set of joint scenarios under Article 12 of the TEN-E Regulation.

6 On that basis, ACER adopted and published the Framework Guidelines for Joint TYNDP Scenarios on 25 January 2023 (‘Framework Guidelines’). ENTSO-E and ENTSOG, with the involvement of hydrogen transmission network operators pending the formal establishment of ENNOH, then prepared the draft TYNDP 2026 Joint Scenarios Report and submitted it on 11 June 2026 to ACER, the Member States and the European Commission for opinion.

7 This Opinion is based on Article 4(3)(b) and Article 11(c) of Regulation (EU) 2019/942 establishing ACER, and Article 12(5) of the TEN-E Regulation. It mainly sets out ACER’s assessment of whether the scenarios in the draft TYNDP 2026 Joint Scenarios Report comply with the Framework Guidelines. This Opinion is addressed to ENTSO-E, ENTSOG, the European Commission and the Member States A C E R O P I N I O N N O 1 3 / 2 0 2 6

2. Procedure

8 On 11 June 2026, ENTSO-E and ENTSOG jointly submitted for ACER’s opinion the draft TYNDP 2026 Scenarios Report to ACER for its Opinion, together with the consultation input and the explanation of how that input was taken into account.

9 The ACER Electricity Working Group provided its advice on 17 June 2026.

10 The ACER Gas Working Group provided its advice on 17 June 2026.

3. ACER assessment

3.1. Study horizons

12 ACER notes positively that scenarios for 2030, 2035 and 2040 are included in the draft Scenario Report, in line with the Framework Guidelines and improving on past ENTSO practice.

3.2. Increased scenario assumption transparency

13 The Framework Guidelines state that “an open and streamlined process relies on clear communication about the assumptions and proper documentation of the inputs, assumptions, models and scenarios”.

14 ACER welcomes that the TYNDP 2026 Scenarios Visualisation Platform now includes gas demand data for final uses, an improvement over the 2024 visualisation platform, where gasrelated information was absent. Gas demand for other purposes (thermoelectric generation, steam methane reforming) should also be displayed.

15 ACER also welcomes the expanded scenarios results section compared to the 2022 and 2024 editions. However, with few exceptions (e.g. hydrogen imports per corridor), data remains presented only at EU-wide level. The final report should include: • Key figures (electricity demand, total gas demand including biomethane, hydrogen demand, electricity production by type) at country level; • Charts on cross-border flows of electricity, methane and hydrogen across EU Member States.

3.3. The scenarios do not yet provide a sufficiently credible target-aligned pathway

16 ACER recalls that the TEN-E Regulation requires TYNDP scenarios to be “on-target”, consistent with the Union’s climate and energy objectives and the energy-efficiency-first principle. The ACER Framework Guidelines further clarify that scenarios shall comply with the Union’s 2030 climate and energy targets and the 2050 climate-neutrality objective, while taking into account NECPs and the latest European Commission scenarios.

17 ACER acknowledges that ENTSO-E and ENTSOG have developed a methodology intended to ensure compliance with the EU climate and energy framework by amending the final energy consumption in the 2030 National Trends scenario. The methodology distinguishes between A C E R O P I N I O N N O 1 3 / 2 0 2 6 European mandatory target and indicative national efforts and includes a “gap-filling” mechanism to meet the EU climate and energy targets.

18 However, ACER considers that the current approach does not sufficiently demonstrate credible target alignment in practice.

19 The central scenario largely reflects national trends and NECP-based assumptions as of 31 December 2024, while the proposed gap-filling methodology follows the same approach as in the TYNDP 2024 cycle by adjusting final energy consumption for coal and oil downward until the scenario reflects compliance with the EU final energy consumption target. While this approach has the advantage of being relatively simple and straightforward to implement, ACER considers that it is overly simplistic given the scale of the remaining gap toward the EU’s climate and energy targets. Such large cuts in coal and oil demand at this scale require matching deployment of clean alternatives, including renewable electricity, electrification, heat pumps, electric vehicles, hydrogen and energy efficiency measures. The methodology does not reflect these shifts. It does not adjust the corresponding demand and infrastructure assumptions for other energy carriers, including electricity and methane.

20 As a result, while the scenarios may formally satisfy selected indicators after application of the gap-filling methodology, ACER considers that they do not yet provide a sufficiently credible representation of a genuinely target-aligned pathway for the electricity, gas and hydrogen system. ACER also notes that the methodological limitations of the current approach, as well as possible alternative approaches, were highlighted in a recent study carried out for ACER . Stakeholder Reference Group feedback provided to ENTSO-E and ENTSOG in September 2025 reached the same conclusion on the gap-filling methodology . ACER therefore distinguishes between nominal target compliance under the current methodology and a scenario pathway that credibly reflects the structural transformation required to achieve the Union’s climate and energy objectives.

21 ACER further notes that, under Regulation (EU) 2022/869 on the Governance of the Energy Union and Climate Action, the primary mechanism for closing the gap between EU-level climate and energy targets and national implementation should in principle have been the NECPs themselves. The updated final NECPs submitted by Member States were expected to collectively ensure delivery of the Union’s agreed objectives.

22 However, the European Commission’s own assessment of the final NECPs , as well as independent analyses , continue to identify a persistent gap toward achieving the EU’s climate and energy targets, particularly regarding energy efficiency objectives, but as a result also for the EU climate and renewable energy targets. This gap persists even where the European Commission has taken into account indicative national targets that were not underpinned with concrete policy measures within the NECPs.

23 In this context, ACER recognises that ENTSO-E and ENTSOG are operating within a broader governance gap between EU-level targets and nationally validated implementation pathways. The current gap-filling methodology can therefore be understood as a technical workaround intended to reconcile EU-level targets with nationally validated assumptions within the constraints of the current TYNDP framework. ACER also recognises that scenario development necessarily A C E R O P I N I O N N O 1 3 / 2 0 2 6 involves uncertainty and methodological simplifications, particularly where political objectives, and national planning assumptions do not fully align.

24 At the same time, ACER considers that the current methodology risks creating the impression of target compatibility without sufficiently reflecting the scale of transformation still required to achieve the Union’s climate and energy objectives in practice. While no scenario-building methodology can eliminate uncertainty regarding future technology deployment, policy implementation and societal choices, scenarios used for infrastructure planning should transparently present these uncertainties and avoid obscuring the remaining gap between current trajectories and policy objectives.

25 ACER also notes that the current simplified gap-filling methodology risks becoming increasingly distortive in the context of future 2040 climate targets, where the remaining policy and implementation gap relative to the policy ambition is expected to be significantly larger. According the latest EEA Trends and Projections 2025 report, the aggregated net GHG emissions based on existing measures and planned measures are projected to reach 60% and 69% below 1990 levels by 2040, respectively, compared to a target of 90% . Mechanically reducing fossil fuel demand without reflecting the corresponding deployment of clean technologies and efficiency measures risks undermining the realism and policy relevance of the scenarios. As a result, the scenarios may not fully capture the changes in energy demand patterns, technology deployment and associated infrastructure needs that would be expected in a genuinely target-aligned pathway, potentially affecting the assessment and selection of infrastructure projects.

26 Against this background, ACER considers that:

27 For the final TYNDP 2026 Scenario Report: • the limitations of the current gap-filling methodology and the concerns of ACER and the Stakeholder Reference Group should be explicitly acknowledged; and • the remaining gap between the underlying NT scenarios and the EU energy efficiency and renewable energy targets should be transparently quantified, acknowledged and presented. For the future TYNDP 2028 cycle: • further political and governance guidance will likely be required from the European Commission and/or Member States regarding how future TYNDP scenarios should credibly reconcile EU-level targets with nationally validated assumptions. In particular, ACER considers that future TYNDP cycles should ensure that the central scenario credibly demonstrates compatibility with the Union’s climate and energy targets. Such clarification should be developed through an open and transparent process involving relevant stakeholders.

3.4. Greater transparency and consistency are needed for the Scenario Grid assumptions

28 ACER notes that the current Scenario Grid methodology applies significantly different criteria to electricity and hydrogen infrastructure.

29 For electricity infrastructure, ACER considers that the definition of projects categorised as “planned but not yet permitting” remains too expansive. In particular, the methodology allows this category to be supported by elements such as legal requirements, positions regarding a Final A C E R O P I N I O N N O 1 3 / 2 0 2 6 Investment Decision (‘FID’), or references to national frameworks. As already clarified in ACER th Opinion No 07/2023 on the 4 ENTSO-E CBA Guideline, such criteria do not sufficiently satisfy the principle of “reasonable certainty”, as they are either too generic or inappropriate. The “planned but not yet permitting” category represents a significant share of transmission projects submitted for the TYNDP 2026 (26%, 47 of 178) . ACER therefore considers that inclusion in all relevant national network development plans would provide a more prudent and robust basis for categorising projects as “planned but not yet permitting” than the broader criteria currently foreseen.

30 For hydrogen infrastructure, ACER notes that projects may be included in the Scenario Grid based on significantly broader criteria, including Project of Common and Mutual Interest (PCI/PMI) status irrespective of project maturity. For the grid assumed for the short-term (2030 and 2035) ACER reiterates its preference for a more prudent approach based primarily on projects having reached FID and/or included on the latest European Commission PCI/PMI list but with a sufficiently advanced level of maturity. ACER notes that the current approach allows the inclusion of a substantial number of less-advanced hydrogen projects whose timely commissioning remains highly uncertain. According to the data in the ENTSOG Visualisation Tool for projects submitted for the TYNDP 2026, 87% of all projects (212 of 244) were included on the rd 3 PCI/PMI candidate list, of which 67% were categorized as less-advanced (141 of 212) and 54% were categorized as both less-advanced and not part of an NDP (115 of 212) .

31 ACER recognises the nascent nature of the hydrogen market and the challenges associated with modelling a strategically developed hydrogen network at an early stage of market development. But over time, ACER expects the underlying logic and maturity requirements applied across infrastructure categories and time horizons to become more consistent across TYNDPs.

32 A range of scenarios with sensitivities on the main hydrogen demand and supply drivers is necessary to capture uncertainties in hydrogen infrastructure planning. Therefore, ACER recommends that ENTSOG develops scenarios reflecting different assumptions on hydrogen demand and supply, to capture uncertainties over the appropriate scale of infrastructure required to meet future needs.

33 Against this background, ACER considers that future TYNDP cycles, and in particular TYNDP 2028, should focus on improving transparency, consultation and consistency regarding the Scenario Grid methodology. In particular, ACER expects that: • the status and maturity of projects included in the Scenario Grid be transparently documented, particularly for hydrogen PCI/PMI projects with limited maturity and electricity projects categorised as “planned, but not yet permitting”; • electricity projects categorised as “planned but not yet permitting” are limited to projects approved in all relevant national network development plans; • draft project lists and Scenario Grid assumptions be made subject to meaningful public consultation at a sufficiently early stage of the process to allow stakeholder scrutiny before modelling assumptions are finalised; and • the definitions and maturity criteria applied to electricity and hydrogen infrastructure progressively converge over time, including through clearer justification of any deviations from a more conservative starting grid approach. A C E R O P I N I O N N O 1 3 / 2 0 2 6

3.5. The Economic Variants remain too limited as alternative scenarios

34 ACER welcomes the first implementation of the “High Economy” and “Low Economy” variants introduced under the Framework Guidelines .

35 The variants constitute an important step toward more robust planning under differing macroeconomic conditions. ACER positively acknowledges the extensive exchanges between ENTSO-E, ENTSOG, the European Commission, ACER and the SRG during the development of the methodology.

36 The resulting variants provide a broadly coherent and internally consistent adjustment of electricity and hydrogen demand around the central scenario. However, ACER notes that the overall variation between the scenarios remains relatively limited and may not yet provide a sufficiently meaningful spectrum of long-term infrastructure needs, particularly for hydrogen infrastructure planning where uncertainty remains especially high.

37 ACER also notes that the current methodology largely keeps the same supply-side assumptions and generation capacities across the variants. While this simplifies the modelling approach, it also limits the ability of the variants to test more divergent transition pathways and infrastructure needs.

38 In particular, ACER observes that: • the variation in final energy demand remains relatively modest, with the Economic Variants altering EU final energy demand by only around ±1% relative to the central trajectory in both 2035 and 2040. This may not adequately reflect the range of plausible demand outcomes, particularly given continuing uncertainty regarding industrial recovery, electrification rates and energy efficiency developments; • some important assumptions, including on energy efficiency in buildings and supply-side developments, are not significantly differentiated between variants; and • hydrogen demand uncertainty may not be adequately captured through the current symmetric adjustment ranges.

39 ACER therefore recommends that future scenario cycles: • provide greater transparency regarding the justification for the selected adjustment ranges; • strengthen the differentiation between variants to ensure more meaningful validation of infrastructure needs and projects; • allow greater flexibility and asymmetry for hydrogen-related uncertainty; and • make both the Economic Variants methodology and the resulting country-level scenario data subject to meaningful public consultation sufficiently early in the process to allow stakeholder scrutiny and feedback before assumptions are finalised. A C E R O P I N I O N N O 1 3 / 2 0 2 6

40 Overall, ACER considers that the Economic Variants represent a useful and constructive first implementation of the Framework Guidelines, while further methodological refinement will be necessary in future cycles.

3.6. Stakeholder engagement has improved, but transparency remains insufficient

41 From 16 June to 14 July, and from 1 to 29 July 2025, ENTSO-E and ENTSOG carried out a public consultation on the Draft 2026 TYNDP Scenarios input data and methodologies as well as Economic Variants development methodology, respectively .

42 In addition, ENTSO-E and ENTSOG organised several stakeholder workshops in the context of the 2026 TYNDP Scenarios process. In particular, on 4 June 2024, ENTSO-E and ENTSOG held a public workshop marking the closure of the 2024 Scenarios cycle and the launch of the 2026 TYNDP Scenarios cycle. Furthermore, on 4 July 2025, ENTSO-E and ENTSOG held a public stakeholder workshop on the draft input data and methodologies for the 2026 TYNDP Scenarios cycle .

43 ACER notes that ENTSO-E and ENTSOG established a stakeholder engagement process comprising public consultations, stakeholder workshops and the Stakeholder Reference Group (‘SRG’). Based on the information available, ACER considers that the ENTSOs made reasonable efforts to involve a broad range of stakeholders in accordance with Article 12(3) of Regulation (EU) 2022/869, including representatives of transmission and distribution system operators, industry, civil society and demand-side interests. ACER therefore considers that the overall stakeholder engagement process broadly met the requirements of Article 12(3) of Regulation (EU) 2022/869, leaving room for improvements .

44 ACER also considers that ENTSO-E and ENTSOG sufficiently involved hydrogen transmission network operators in the development of the scenarios, notably through the involvement of pre- ENNOH, thereby meeting the requirements of Article 61 of Regulation (EU) 2024/1789 in conjunction with Article 12(8) of Regulation (EU) 2022/869.

45 ACER positively acknowledges the continued efforts of ENTSO-E and ENTSOG to strengthen stakeholder engagement and transparency in the TYNDP scenarios process.

46 In particular, ACER welcomes the involvement of the Stakeholder Reference Group (‘SRG’), which has become an important platform for expert dialogue and methodological scrutiny during the TYNDP 2026 cycle. On 4 May 2026 the SRG adopted an Opinion on the 2026 TYNDP Scenarios, representing the SRG’s advice to the ENTSOs on the 2026 TYNDP Scenarios process. The Opinion summarised the main outcomes of SRG discussions and reflected both majority and minority views expressed by SRG members. The Opinion was shared with ACER and the ENTSOs in accordance with paragraph (67) of the Framework Guidelines. ACER strongly supports the continuation of this process.

47 ACER also welcomes the transparency improvements associated with the Energy Transition Model dashboards and related consultation materials.

48 At the same time, ACER identifies several areas where transparency and public validation should be strengthened.

49 ACER notes that demand-side input assumptions were published together with the consultation materials. However, these assumptions were provided “for information” rather than being the subject of meaningful stakeholder scrutiny. ACER notes that paragraph (52) of the Framework A C E R O P I N I O N N O 1 3 / 2 0 2 6 Guidelines requires data sets to be published in a format agreed with the SRG, and paragraph (48) requires the stakeholder engagement plan to allow stakeholders enough time to evaluate key inputs. Neither condition was met for the demand-side assumptions. Given the central importance of these assumptions for infrastructure planning and target alignment, ACER considers that this approach is insufficient.

50 ACER welcomes the publication of the new TSO survey annex accompanying the draft Scenarios Report, which provides extensive information on national validation processes, alignment with NECPs, consistency between TYNDP and ERAA datasets, and key data uncertainties. ACER considers this a valuable first step towards improving the transparency and traceability of scenario assumptions.

51 However, much of this information became publicly available only at the time of submission of the draft Scenarios Report. As a result, stakeholders were not able to scrutinise these explanations, justifications and validation outcomes during the earlier stages of the scenario development process when they could have most effectively informed the discussion.

52 Paragraphs (31) and (32) of the Framework Guidelines require the ENTSOs to use NECPs as the basis for scenario development and to ensure a process for stakeholder scrutiny of inputs and assumptions. Paragraph (48) further requires the stakeholder engagement plan to allow adequate time for stakeholders to evaluate key inputs. Conducting the NECP consistency check only after consultation had closed is incompatible with these requirements.

53 As a result, stakeholders were not provided with a meaningful opportunity to scrutinise or comment on potentially significant deviations between TSO input assumptions and the corresponding NECP values during the consultation phase itself.

54 This issue is particularly important given the substantial differences observed between certain country-level demand assumptions submitted by TSOs and the European Commission’s assessment of the final NECPs, especially regarding final energy consumption and energy efficiency trajectories.

55 ACER therefore considers that future TYNDP cycles should: • transparently document and justify deviations between TSO assumptions and NECP values already during the public consultation phase; • make these deviations subject to meaningful stakeholder consultation rather than providing them merely “for information”; • provide more systematic country-level comparisons between TYNDP assumptions and NECP values; and • further improve the accessibility of aggregated supply and flexibility assumptions used in the scenarios when providing them for public consultation. More specifically, ACER recommends providing a country-level overview of generation capacity and flexibility data, similar to the ETM demand dashboards, to facilitate stakeholder review.

56 ACER calls ENTSO-E and ENTSOG to develop further an appropriate transparency and validation framework for future scenario cycles.

3.7. The Innovation Roadmap is a positive step, but implementation remains uncertain

57 ACER welcomes the development of an Innovation Roadmap for the TYNDP scenarios process, broadly in line with the expectations set out in the Framework Guidelines. A C E R O P I N I O N N O 1 3 / 2 0 2 6

58 The Innovation Roadmap represents a positive step toward a more structured and transparent approach to methodological improvements across scenario cycles. ACER also positively acknowledges that a number of stakeholder proposals and SRG recommendations have been incorporated into the roadmap.

59 At the same time, ACER notes that many identified improvements remain deferred due to resource constraints and competing priorities. While ACER recognises the practical limitations faced by the ENTSOs, the current roadmap still leaves considerable uncertainty regarding the timing and implementation of several important methodological enhancements.

60 ACER therefore encourages ENTSO-E and ENTSOG in future Innovation Roadmaps to: • provide clearer implementation timelines; and • further consult stakeholders on future methodological priorities.

3.8. Stronger consistency between TYNDP and ERAA assumptions remains necessary

61 ACER recalls that the Framework Guidelines require consistency to be maintained as far as possible between the TYNDP scenarios and the inputs used for the European Resource Adequacy Assessment (‘ERAA’).

62 ACER notes that differences between TYNDP and ERAA assumptions have persisted in recent cycles as highlighted in a recent study carried by the consultancy Artelys for ACER . ACER notes that paragraph (40) of the TYNDP Scenarios Guidelines requires consistency to be maintained 'as much as possible', and that at least the central scenario must be consistent with ERAA inputs. While some divergence may be justified by differences in timing, methodologies or intended use, such differences should remain limited and be clearly explained.

63 ACER welcomes the efforts undertaken by ENTSO-E and ENTSOG in the TYNDP 2026 cycle to document and explain differences between TYNDP and ERAA assumptions, including through the publication of the dedicated TSO survey annex accompanying the Scenarios Report. This represents a useful first step towards greater transparency and traceability of scenario assumptions. ACER nevertheless expects ENTSO-E and ENTSOG to continue strengthening coordination between both processes. For the TYNDP 2026 Scenarios Report and future scenario cycles, any significant deviations between TYNDP and ERAA assumptions should be transparently documented and justified and, where possible, made available at an earlier stage of the process to facilitate stakeholder scrutiny.

64 While the present Opinion concerns the TYNDP Scenarios, ACER further emphasises that discussions on changes to the gap-filling methodology should not be limited to the TYNDP scenarios process alone but should also consider the broader consistency of NECP-based scenario frameworks, including the ERAA. In particular, where modifications to the gap-filling methodology could materially affect electricity or hydrogen system assumptions, including demand projections, ACER considers that consistent treatment across both TYNDP and ERAA processes would be necessary to maintain overall methodological coherence.

3.9. Continued delays risk undermining the relevance and credibility of the TYNDP process

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65 ACER recalls that its Framework Guidelines expected the draft TYNDP Scenarios Report to be published and submitted by 31 December of the odd-numbered year preceding the publication of the TYNDPs.

66 ACER therefore notes with concern that the draft TYNDP 2026 Scenarios Report was submitted only on 11 June 2026, approximately six months later than expected. This is the second consecutive cycle in which the deadline set in paragraph (18) of the TYNDP Scenarios Guidelines was missed. The 2024 report was expected by end-2023, but submitted on 30 May 2024 (Opinion 05/2024, para. 8).

67 ACER further notes that the cut-off date for data collection for the TYNDP 2026 scenarios was 31 December 2024. As a result, continued delays in the scenario development and infrastructure planning process risk leading to the publication of TYNDP deliverables in 2027 that are still based on assumptions and input data originating from 2024.

68 These delays risk undermining the relevance, credibility and timeliness of the TYNDP framework, particularly in a rapidly evolving policy and market environment, while also compressing timelines for subsequent processes such as the PCI and PMI assessment and selection.

69 Repeated delays suggest shortcomings in the current organisation of the scenarios process. ACER therefore strongly encourages ENTSO-E and ENTSOG to improve the planning, governance and sequencing of the process and to present, at the beginning of the TYNDP 2028 Scenarios cycle, a clear action plan setting out how timely delivery will be ensured in future cycles.

4. Conclusions

70 ACER welcomes the significant efforts undertaken by ENTSO-E and ENTSOG in preparing the draft TYNDP 2026 Scenarios Report and acknowledges the progress achieved regarding stakeholder engagement, transparency tools, Economic Variants and methodological governance.

71 At the same time, ACER considers that important shortcomings remain regarding the credibility of target alignment, the robustness of the gap-filling methodology, the transparency and consistency of Scenario Grid and country-level scenario assumptions, the robustness of the Economic Variants, ERAA consistency and the overall timeliness of the process.

72 In particular, ACER considers that the current scenarios do not yet provide a sufficiently credible representation of a pathway aligned with the Union’s climate and energy objectives and risk overstating the degree of target compatibility achieved. ACER also considers that further development of the Economic Variants will be necessary to provide a more meaningful assessment of infrastructure robustness under differing transition pathways.

73 ACER therefore recommends that ENTSO-E and ENTSOG: For the finalisation of the TYNDP 2026 Scenarios Report: • improve transparency regarding the remaining gap between the underlying NT scenario before application of the gap-filling methodology and the EU climate and energy targets; • strengthen transparency regarding the limitations of the gap-filling methodology; and • ensure transparency about the differences between the TYNDP central scenario (nearterm and mid-term) and the corresponding ERAA scenarios . For future scenario cycles, and in particular TYNDP 2028: A C E R O P I N I O N N O 1 3 / 2 0 2 6 • develop a more credible and robust approach to target alignment and gap-filling, including a central scenario that credibly demonstrates compatibility with the Union’s climate and energy targets and appropriately reflects the Union’s evolving climate framework, including the legally binding 2040 climate target; • further develop the Economic Variants as meaningful alternative scenarios; • improve transparency, consultation and consistency regarding the Scenario Grid assumptions, particularly concerning the maturity criteria applied to electricity and hydrogen infrastructure; • include scenarios with sensitivities on the main hydrogen demand and supply drivers, to capture uncertainties over the appropriate scale of infrastructure required to meet future needs. • enhance transparency and public scrutiny of country-level scenario assumptions; • strengthen consistency between TYNDP and ERAA assumptions; and • ensure a significantly timelier preparation process in future TYNDP cycles. This Opinion is addressed to ENTSO-E, ENTSOG, Member States and the European Commission. Done at Ljubljana, on 8 July 2026. — SIGNED — V. ZULEGER, ACER Director ad interim