An analysis comparing different unlimited simulations is included in the final IGI for 2030 and 2040:

• unlimited internal pipeline capacity (no bottlenecks due to unlimited connections between nodes)
• unlimited storage (unlimited storage withdrawal, injection and working gas volume in existing storage countries)
• unlimited imports (unlimited import capacities for external EU supply defined in infrastructure level and years).

Streamline IGI report development process

(Opinion – point 2, assessment – point 22)

TYNDP process / TYNDP Infrastructure Gaps Identification Report

Recent TEN-E revisions added formal opinion and approval periods of up to 20 months to a cycle that should between three and four years.

The TYNDP 2024 Hydrogen IGI report was submitted to ACER on 10 March 2025. Key factors affecting its timeline included the joint Scenarios development, which received EC approval in January 2025, and the approval of the Hydrogen CBA methodology in February 2025. These approvals are essential as they provide core assumptions used in simulations and project assessments.

To address process delays, ENTSOG began work on the Hydrogen IGI report in autumn 2024, using preliminary assumptions and simulation results. Until the relevant methodology and the 2024 Scenarios were formally approved, ENTSOG took into account feedback received during periodic exchanges with the EC and ACER in order to progress with the IGI simulations and report. While this allowed submission in March 2025, it caused duplicated work and a series of unnecessary simulation efforts. The guidance documents, produced before final CBA approval, were more extensive than needed, further prolonging the drafting and stakeholder validation processes.

It must also be acknowledged that TYNDP 2024 in particular had an experimental nature, with a consolidated hydrogen project base, a new model, interlinking the hydrogen and electricity sectors, a new CBA methodology and an updated TEN-E process, all in the same cycle. In future, ENTSOG will consolidate on the experience from TYNDP 2024, as well as on the learnings from its exchanges with ACER and the EC.

It must nevertheless be acknowledged that the increasing complexity of sector integration and the involvement of a growing number of stakeholders are making the TYNDP process lengthier.

Perform the IGI assessment under several scenario variants and sensitivity analyses

(Opinion – point 3, key findings and recommendations – point 7)

TYNDP Infrastructure Gaps Identification Report – Choice of reference scenarios

In TYNDP 2024, ENTSOG followed the European Commission’s guidance to solely focus on the National Trends+ scenario for IGI simulations, adding 3 simulation cases in the final TYNDP 2024 Hydrogen IGI report, for 2 hypothetical infrastructure levels, called “PCI/PMI” and “Advanced”.

ENTSOG acknowledges that incorporating additional scenario variants and sensitivity analyses would provide a broader perspective, thereby potentially improving infrastructure planning. ENTSOG will continue exchanging with stakeholders, including the EC, ACER and ENNOH for the choice of scenarios and sensitivities for the TYNDP 2026 hydrogen IGI.

Reconsider measurement of security of the supply risk for hydrogen projects until the market matures

(assessment – point 37)

TYNDP Infrastructure Gaps Identification Report – Stress-case assessment for hydrogen

While IGI indicator 2.1 was designed to assess the curtailed hydrogen demand in DHEM and DGM for the reference weather year, indicator 2.2 provides a complementing assessment, of hydrogen demand curtailment in climatic stress cases.

Even though the hydrogen market and infrastructure are in their early stages, the lessons learned from the gas and electricity sectors demonstrate how important stress testing is in order to ensure credibility and to help identify bottlenecks before they turn into systemic risks.

Additionally, hydrogen production will depend heavily on variable renewable generation, making it more exposed to extreme weather variability compared to today’s gas system.

Disregarding such weather-related stress-case scenarios – especially in the early stages of planning – risks underestimating flexibility and storage needs from the onset. It could lead to costly retrofits in the long run, damaging trust in a secure energy carrier – hydrogen.

Pass from interlinked energy sector models to a unified model, improve the chosen starting grid for the IGI assessment and generally improve the alignment of assumptions with ENTSO-E

(Opinion – point 3., assessment – sub-section 2.4.)

TYNDP Process / TYNDP Infrastructure Gaps Identification Report / PS-CBA

In its previous opinion, on TYNDP 2022, ACER requested that ENTSOG implement the interlinked model jointly with ENTSO-E – with specific focus on electrolyser projects, to support individual project assessments, as well as their impact at grid-level for the purpose of the first PCI/PMI process under the revised TEN-E.

In ENTSOG’s TYNDP 2024, electrolyser projects are fully considered in the hydrogen infrastructure needs assessment. ENTSOG has performed, for the second consecutive time, electrolyser project assessment, to support the EC’s second PCI/PMI selection under the revised TEN-E.

While the interlinked model is under development between ENTSOG and ENTSO-E, the best approach continues to be use of interconnected individual sector modelling, with successive data validation improvements over cycles. The Dual Hydrogen-Electricity Model (DHEM) was used for this purpose in TYNDP 2024.

With regards to the cross-sectoral coverage of TYNDP assessments, the TYNDP 2024 PS-CBA included a dedicated indicator (B4) that measures benefits and costs across energy carriers for individual projects, including an electricity-hydrogen synergy measurement.

ENTSOG is continually collaborating with ENTSO-E to ensure the same assumptions are used from the basis of TYNDP process, which are the Scenarios. Under the new Scenario Framework for TYNDP 2026, ENTSOG and ENTSO-E have been jointly working closing will both Gas and Electricity TSO’s with regard to all input data from gas and electricity TSO. This has been reviewed and a dedicated Taskforce set up for Quality Control. Alongside this, the ENTSO-s have completed an alignment survey in order to validate the input data in line with the new framework guidelines and ensuring consistency and alignment to the NECP’s and if deviated justification has been provided. This shows new improvements in the process to ensure sector alignment.

Use only one infrastructure level used for the IGI assessment and several for PS-CBA

(assessment – point 33).

TYNDP Infrastructure Gaps Identification Report

Only three hydrogen projects, namely two storage and one transmission project were declared in TYNDP 2024 as having the start of the construction phase ahead of the project collection. Moreover, environmental impact assessment was not required as part of the project timeline. Therefore, this proposed IGI starting grid would have not been possible to implement in the TYNDP 2024 assessment.

Following the ACER recommendation, ENTSOG will request the specified information to project promoters in the upcoming, TYNDP 2026, cycle.

Depending on the number of projects in the two levels of maturity and in case there exist sufficient interconnected countries, ENTSOG will reassess the choice of the starting grid and may consider to change it, taking into account ACER’s indication.

Increase stakeholder engagement, including consider extending of scope of the Stakeholder Reference Group (SRG) to the IGI assessment

(ACER opinion – point 4, key findings and recommendations – point 7, assessment – point 26)

TYNDP process – stakeholder engagement

Inclusive and extensive stakeholder engagement constitute an essential pillar in the development of ENTSOG’s work, including the TYNDP. In the 2024 cycle, a series of improvements have been done to extend stakeholder engagement and deepen cross-sector modelling:

• The provisions of the revised TEN-E Regulation were fully applied, amplifying stakeholder engagement and adding extensive consultation requirements to key-phases of the TYNDP process. Five stakeholder consultations have been organised for assumptions, guidance documents, as well as final deliverables, including presentation and discussion events.
• In particular for the TYNDP 2024 Scenarios process, the SRG was established in November 2023. The complementing expertise from this balanced group brought improvements to engagement efficiency and effectiveness of Scenarios.
• The revised TEN-E added new processes for provision of formal opinions by the EC and ACER, in particular to scenario development, infrastructure gaps identification and the cost-benefit analysis methodology for project assessment. It must be noted that while reinforcing alignment between organisations, these changes also extended the TYNDP process duration.

The priority for TYNDP 2026 is to consolidate current collaboration with the SRG and stakeholder engagement in line with the updated TEN-E. In addition, the TYNDP 2026 will involve a new stakeholder: ENNOH.

As a final comment, echoing ENTSOG’s 2022 answer to a related request, it is important to underline that in the implementation in each new TYNDP, new updates due to feedback from stakeholders create inevitable impact on the timeline, adding a dose of uncertainty for final publication. Several interactions with stakeholders and potential delays in responses have an impact on the timeline.

In general, the priority for ENTSOG is to ensure, besides through validation of results, that all stakeholders have an opportunity to provide their feedback, while aligning as well as possible with the European Commission’s PCI/PMI process timeline.

Streamline and anticipate the development of the IGI methodology, though early testing

(Key findings and recommendations – point 6, Opinion – point 5)

TYNDP process

As a general practice, TYNDP simulations are usually run with the most recent available data during a preparation phase. ENTSOG is committed to ensure model readiness as early as possible. Modelling innovations however, might require extensive testing, to confirm results are accurate and trust-worthy.

In the TYNDP 2024, the model used for IGI simulations (the DHEM) had been newly developed and therefore required extensive testing. When a new model is introduced, testing results can either be related to its configurations or to the data inputs. Repeated iterations are usually required to reach an accurate model set-up, cross-check and validate results.

In TYNDP 2026, the approach will be maintained. While model improvements will still require testing, with the most recent available data, the robust base from TYNDP 2024 is likely to ensure tenting is faster and earlier than in the previous cycle. ENTSOG shall continue informal exchanges with the EC and ACER, where preliminary results are discussed as soon as available and verified.

Implement ACER’s recommendations regarding last-minute data updates to scenarios, as provided in its framework guidelines for the joint TYNDP

(assessment – point 28).

TYNDP Scenarios – Data collection and processing

As the ACER-commissioned study on the development of scenarios for EU-wide infrastructure planning also finds, there indeed exists a misalignment between the availability of NECP data and the development of the joint TYNDP Scenarios, as well as in the time horizons covered. In addition, the hydrogen market in particular is at an early stage, during which projections are more likely to change, as well as supporting policies.

The TYNDP 2024 Scenarios data collection was completed ahead of draft NECP publication, for which the European Commission requested updated hydrogen supply and demand data for the PCI/PMI selection process. While ENTSOG agrees data updates can be necessary in specific cases, we support a standardised, transparent approach, where data is scrutinised by relevant stakeholders.

In addition, ENTSOG and ENTSOE adjusted specific country data of the National Trends scenario, so as to respect the energy and climate target compliance. This was done in line with a publicly consulted ‘Gap Closing Methodology’.