1.1 How to read this document
The TYNDP 2026 Scenarios Methodology Report sets out the key principles and processes underlying scenario development and describes the methodologies applied in scenario development. The document is structured as a step by step description of the scenario building process. It starts by outlining the guiding principles, definitions and governance agreements that frame the methodological choices. It then explains how scenario inputs are collected and processed through an integrated modelling toolchain, before detailing the methodologies applied for demand, supply, grids and weather representation.
Finally, it presents the specific approaches used for gap filling, economic variants and sensitivity analyses.
The purpose of this report is to provide transparency on how those results are derived, and not to interpret scenario findings. It enables the reader to understand the modelling scope and assumptions, assess the internal consistency of the approach, and interpret scenario outputs presented in the TYNDP Scenario Report and associated visualisation tools.
1.2 Key definitions used throughout the report
To support clarity and consistency, the following key terms are used throughout this report:
National Trends (NT)
The term NT reflects the aggregation of national inputs submitted by electricity and gas Transmission System Operators (TSOs), based primarily on National Energy and Climate Plans (NECPs) and other official national strategies available at the time of data collection (cut-off date: December 2024).
National Trends+ (NT+) – Central Scenario
The term NT+ or Central Scenario constitutes the Central TYNDP 2026 Scenario. It is derived from the NT dataset through the application of a dedicated gap filling methodology to ensure consistency with selected EU level targets, while preserving national differentiation . NT+ is the baseline for all target year analyses (i. e. 2030 / 2035 / 2040 / 2050). In the reports the terms NT+ scenario and Central scenario are used as synonyms.
Economic Variants: High and Low Economic Variants (HEV / LEV)
In addition to the Central Scenario, the TYNDP 2026 framework includes two economic variants (High Economic Variant / HEV and Low Economic Variant / LEV) for target years 2035 and 2040. These variants are explicitly anchored to the NT data collection and are designed as stress tests, reflecting alternative macro economic growth assumptions. They do not represent alternative policy pathways.
Scenario Toolchain
The Scenario Toolchain refers to the sequence of modelling tools and data exchanges used to translate annual scenario inputs into hourly demand profiles, market simulation results, and aggregated supply indicators. The toolchain includes, among others, the Energy Transition Model (ETM), hourly demand profiling tools, the market simulation model and the Supply Tool.
Scenario Grid
The Scenario Grid is the network representation used exclusively for scenario modelling in TYNDP 2026. It defines the electricity and hydrogen transmission topology applied consistently across scenario and target years for market simulations (cf. Sec. 7, p. 39).
Weather Year
A Weather Year is a climate year selected to capture the impact of weather variability on demand and renewable generation. For each target year, a limited set of representative Weather Years (cf. Sec. 6, p. 38) is used instead of simulating the full range of possible climate outcomes.
Endogenous / Exogenous
Concepts endogenous and exogenous refer to origin of variables in modelling framework. Exogenous variables are given as inputs to the model and originating from external sources such as national climate and energy plans. Endogenous variables are determined within the model through optimisation or system interactions.
1.3 Core principles and assumptions guiding the methodological development
The methodology for developing the TYNDP 2026 central scenario and variants is grounded in alignment with the latest national and EU energy and climate policies, including the TEN-E Regulation, the ACER Framework Guidelines for the TYNDP scenarios and NECPs. It relies on data collected from electricity and gas TSOs.
The Ten-Year Network Development Plan has hence developed into a future-proofing lookout to a carbon-neutral Europe by 2050. The TYNDP Scenario Report therefore encompasses the short-term (2030) to the very long-term (2050).
Scenario development follows a structured and sequential process. TSOs initially submit data reflecting their national policies as set out in NECPs and mostly validated at national level, forming the National Trends (NT) dataset. These inputs are subsequently assessed against aggregated European objectives. Where gaps are identified, a dedicated gap-filling methodology is applied to derive the National Trends+ (NT+) scenario.
To support transparency and accountability, scenario inputs, methodological choices and key assumptions are subject to stakeholder engagement, including bilateral exchanges, public consultation and the Stakeholder Reference Group (SRG).
In addition to the Central Scenario (NT+), the TYNDP 2026 framework includes two Economic Variants reflecting higher and lower economic growth assumptions (HEV and LEV). These variants are modelled symmetrically, are explicitly anchored to the Central Scenario and therefore act as stress tests of the Central Scenario.
A detailed description of the TYNDP 2026 Scenario Framework and the associated stakeholder engagement process can be found in Chapters four, five and six of the TYNDP 2026 Scenario Report.
1.4 Governance and decision-making process for designing the methodology
This methodology report documents the outcome of a decision-making process within the Working Group Scenario Building (WGSB). This working group is a joint ENTSO-E and ENTSOG platform involving experts from both gas and electricity TSOs, The work carried out within the WGSB is informed by stakeholder input, including feedback obtained through public consultations, the SRG and bilateral exchanges. The work is validated by TSOs and, where possible, stakeholders.
The WGSB is structured into thematic sub-teams responsible for specific topics and modelling aspects. Methodological choices underpinning the TYNDP 2026 Scenarios were assessed and discussed within the relevant sub-teams before consolidation at the WGSB level. These choices were guided by the objective of ensuring model accuracy, while also accounting for practical constraints related to timelines, data availability, and computational requirements. The structure of the joint scenario building team is outlined below (Figure 1).
Figure 1: Decision making groups for the TYNDP 2026 scenario building and methodology definition
