Learnings
Outcomes
Programme Outcomes – THERMAL
The THERMAL programme has delivered a coherent set of analytical methods, modelling frameworks, and evidence to support National Grid Electricity Transmission (NGET) in understanding and managing thermal risk under future climate change. Collectively, the projects have progressed the state of knowledge from exploratory research towards decision‑relevant, probabilistic assessment of thermal impacts on network assets.
Project 1 – Climate Data and Probabilistic Temperature Modelling
Key Outcomes
Project 1 delivered a robust, shared climate data foundation for the THERMAL programme. The project developed and demonstrated a generalised methodology for downscaling and bias‑correcting climate model outputs, enabling the derivation of probabilistic metrics relevant to network planning and resilience assessment.
Key outcomes include:
- A consolidated view of future climate conditions relevant to GB energy systems, including temperature extremes.
- Probabilistic characterisation of climate variables (e.g. 1‑in‑n‑year events), supporting scenario‑based and stress‑test‑style analysis.
- Clear guidance on the definition of “extreme” events, highlighting that extremes must be tailored to the specific asset or decision context.
- Provision of a common climate dataset that was subsequently used by Projects 3, 4 and 5.
These outcomes directly support the programme aims of enabling probabilistic future temperature modelling and providing a common weather dataset.
Interim Conclusions
- Climate risk assessments for high-voltage (HV) assets are most effectively stress-tested using 1-in-10 year climate event probabilities, providing a more realistic basis for evaluating asset resilience than reliance on average climate conditions alone.
- Probabilistic representation of climate uncertainty provides materially more value than deterministic scenarios alone.
- Localised, asset-by-asset climate analysis risks missing spatially coherent extreme events that affect the system as a whole.
Impact on subsequent work
These conclusions informed downstream modelling approaches and the refocusing of visualisation activities in Project 5. In particular, they supported the adoption of probabilistic methods for climate risk assessment and reinforced the need to consider both asset-level vulnerabilities and system-wide impacts arising from widespread extreme weather events.
Final TRL (Technology Readiness Level)
TRL 5 – Technology validated in a relevant environment.
The methodologies were demonstrated using real climate datasets and applied to representative network use cases, but are not yet embedded into operational planning systems.
Future phase potential (low‑mid TRL):
Integrate the climate data and probabilistic metrics directly into NGET planning tools, digital twins, and stress‑testing processes.
Project 2 – Asset Taxonomy and Cable Thermal Risk
Key Outcomes
Project 2 delivered an asset taxonomy framework to support structured asset down‑selection and prioritisation for thermal risk assessment, alongside a focused probabilistic assessment of underground cable thermal risk.
Key outcomes include:
- Development of a taxonomy of HV assets, demonstrating how asset attributes can be combined to support risk‑based prioritisation.
- Delivery of a literature review, identifying that: Evidence that many cable rating assumptions remain consistent with those adopted in the 1960s, raising concerns about suitability under future climate conditions.
- Delivery of a probabilistic analysis of soil thermal properties, highlighting that:
1.Soil dry‑out risk is highly localised;
2.Some cable assets are therefore exposed to significantly elevated thermal risk.
3. Delivery of modelling pathways undertake the next stages of probabilistic assessment including generating a thermal resistivity map and reanalysis of cable thermal ratings.
These outcomes support programme success criteria around identifying assets most at risk and informing probabilistic assessment.
Interim Conclusions
- Asset taxonomy is an effective tool for prioritising analytical effort where data availability is uneven.
- Underground cables represent a priority asset class for future thermal risk mitigation.
- Assessment criteria cannot be meaningfully applied without better soil thermal property data.
These conclusions informed the cancellation of a planned assessment‑criteria deliverable and shaped recommendations for future thermal resistivity mapping.
Final TRL
TRL 3 – Analytical and experimental critical function or characteristic proof-of-concept.
The taxonomy and probabilistic methods were demonstrated using representative data but have not yet been applied systematically across the full asset base.
Future phase potential (low‑mid TRL):
Extend the taxonomy and probabilistic cable models using curated datasets and thermal resistivity maps to support operational re‑rating and investment decisions.
Project 3 – Component, Circuit, and System‑Level Thermal Modelling
Key Outcomes
Project 3 delivered a scalable thermal modelling framework linking component‑level behaviour to circuit, substation, network, and system‑level capacity assessment.
Key outcomes include:
- Improved and refined component thermal models, accounting for climate change and heatwave effects.
- Demonstration of progressive integration from:
components → circuits → substations → network → system level.
- Analysis showing the importance of solar irradiance when assessing heatwave impacts.
- Quantification of heatwave impacts on fault rates and accelerated ageing.
These outcomes directly address success criteria relating to generic modelling frameworks, extraction of quantities of interest, and system‑level assessment.
Interim Conclusions
- System‑level thermal constraints can emerge even when individual assets appear compliant.
- Meaningful insight can be delivered without new field measurements, provided modelling limitations are clearly understood.
- Targeted, well‑designed measurement campaigns are preferable to broad, exploratory testing.
These findings influenced the decision to defer field measurement campaigns and focus Phase 1 on model development.
Final TRL
TRL 3 – Analytical and experimental critical function or characteristic proof-of-concept.
The framework was demonstrated across multiple scales but not yet embedded in live operational or planning workflows.
Future phase potential (mid TRL):
Apply the modelling framework to a wider set of real network scenarios and integrate with planning and security‑of‑supply assessments.
Project 4a – Multi‑Hazard Resilience Framework (OHL Exemplar)
Key Outcomes
Project 4a delivered a generic, fragility‑based probabilistic resilience framework designed to represent the interaction between environmental hazards and asset degradation mechanisms. The framework integrates climate data with thermal and degradation modelling to assess how combined stresses influence asset condition, failure probability, and expected life.
The framework was demonstrated using overhead lines as an exemplar asset, focusing on the interaction between extreme heat and windstorms. Key outcomes include:
- Development of models linking environmental conditions to asset degradation and risk progression over time.
- Demonstration of multi‑hazard modelling, showing that extreme heat and windstorms interact materially in determining failure probability and resilience outcomes.
- Application of probabilistic simulation techniques to support risk‑based resilience assessment under future climate scenarios.
These outcomes address success criteria relating to probabilistic assessment, extraction of risk‑relevant quantities of interest, and identification of assets most at risk under extreme conditions.
Interim Conclusions
- Extreme heat should be assessed alongside other hazards, not in isolation.
- Multi‑hazard interactions can materially change risk profiles compared to single‑hazard assessment.
- Generic, extensible frameworks provide greater long‑term value than asset‑specific tools alone.
These conclusions informed programme‑level recommendations on holistic resilience planning and future modelling priorities.
Final TRL
TRL 4 – Technology validated in a laboratory / demonstrator environment.
The framework was applied to realistic scenarios using validated models, although it is not yet operationalised at full network scale.
Future Phase Potential (mid TRL)
Scale the generic resilience framework to multiple asset types and integrate it into asset investment planning and risk‑based operational strategies.
Project 4b – Experimental Studies of OHL Ageing and Clearance Risk
Key Outcomes
Project 4b delivered laboratory‑based experimental evidence to support understanding of overhead line conductor behaviour under thermal and environmental stress. This work focused on conductor ageing, mechanical performance, and clearance risk, providing essential evidence to inform and interpret modelling outputs developed in Project 4a.
Key outcomes include:
- Experimental evidence on Zebra conductor ageing and life expectancy under elevated thermal conditions.
- Improved understanding of the relationship between thermal exposure, mechanical degradation, and clearance risk.
- Identification of ground clearance as a critical constraint influencing safe operation and resilience.
These outcomes strengthened the evidence base for thermal ageing assessment and provided experimental grounding for probabilistic resilience modelling.
Interim Conclusions
- Ground clearance, rather than temperature alone, is a dominant constraint in managing OHL thermal risk.
- Risk‑based approaches informed by experimental evidence can avoid overly conservative derating while maintaining safety.
- Further testing is warranted for assets exposed to combined stresses (e.g. thermal and coastal corrosion).
Final TRL
TRL 5: Technology basic validation in a relevant environment
Experimental findings are directly applicable to modelling and scenario analysis but require further integration for operational deployment.
Future Phase Potential (mid TRL)
Extend laboratory and field‑based testing to a wider range of conductor types and environments to support calibration and validation of resilience models at network scale.
Project 5 – Visualisation and Exploitation
Key Outcomes
Project 5 demonstrated how visualisation tools can make complex climate and risk datasets more accessible and decision‑relevant.
- Delivery of a visualisation demonstrator focused on Project 1 climate data.
Evidence that visualisation significantly improves stakeholder understanding of probabilistic climate risk.
- Identification of straightforward pathways to integrate additional datasets as they mature.
- This supports the programme aim of presenting findings in accessible, web‑based formats.
Interim Conclusions
- Value is maximised by visualising high‑quality, mature datasets rather than attempting premature full integration.
- Visual tools are an important enabler for translating research outputs into strategic discussions.
These conclusions influenced the refocusing of Project 5 scope during delivery.
Final TRL
TRL 3 – Analytical and experimental critical function or characteristic proof-of-concept.
The tool demonstrated concept value but is not production‑ready.
Overall Programme Outcome
Across Projects 1–5, THERMAL has collectively progressed:
- probabilistic climate‑informed risk assessment,
- generic, extensible modelling frameworks,
- and evidence‑based understanding of asset thermal vulnerability.
While several components remain at mid or low TRL, the programme has established a coherent technical foundation and clear roadmap for future phases focused on operational integration, asset investment, and system resilience.
Develop a production‑grade visualisation platform integrated with operational and planning datasets.
Collectively, the 2025/2026 activities delivered integrated modelling capability, clearer evidence of thermal risks to key asset classes, and a consolidated set of lessons learned and recommendations to inform future innovation, operational planning, and long‑term climate adaptation strategy for NGET.
Recommendations for Further Work
The THERMAL programme has successfully demonstrated methodologies for assessing climate-related thermal risks across transmission assets. Future work should focus on transitioning these outputs from analytical studies towards operational application by addressing key data gaps, scaling proven models, and embedding risk-based approaches into planning and asset management processes. Particular emphasis should be placed on validating models with real-world data, extending assessments across a broader range of assets and network scenarios, and ensuring that climate resilience insights directly inform investment and operational decisions. Strengthened programme governance, improved data management, and earlier stakeholder engagement will also be important to maximise the value and impact of future phases.
Key priorities for future work include:
- Address critical data gaps through targeted monitoring and measurement campaigns, including soil conditions, weather data, asset loading, and asset condition information.
- Embed probabilistic climate datasets within network planning, resilience assessments, and stress-testing activities to support evidence-based decision making.
- Scale asset-level models to network level, applying methodologies across additional asset classes and incorporating multi-hazard assessments.
- Adopt risk-based asset management approaches, using probabilistic outputs and fragility curves to support maintenance, mitigation, and investment decisions.
- Expand visualisation and exploitation tools to improve accessibility of results and support stakeholder engagement, training, and operational use.
- Strengthen programme governance through improved data management, clearer success criteria, aligned project timelines, and early SME involvement.
Overall, future phases should concentrate on targeted trialling, validation, and operational integration to increase technology maturity, enhance network resilience, and maximise the benefits of the learning generated during Phase 1.
Lessons Learnt
The section summarises the key lessons learned from deliverables completed during the 2025/2026 reporting year, their relevance to the original project objectives, and interim conclusions that influenced programme direction and next‑stage decisions.
Project 1 – Climate Data and Probabilistic Characterisation
Key Deliverables (2025/26):
- Deliverable 2: State of Climate 2050 Report
- Final downscaling and bias‑correction methodology documentation
Key Learning
- The work demonstrated that definitions of “extreme” temperature must be use‑case specific (e.g. operational ratings vs asset ageing), rather than relying on a single threshold.
- Probabilistic climate metrics (e.g. 1‑in‑10‑year events) proved more decision‑relevant than single deterministic scenarios, particularly when used as inputs to asset and resilience models.
- Analysis showed that location‑by‑location assessment risks missing spatially coherent extreme heat events, reinforcing the need for system‑level perspectives.
Relevance to Project Objectives
- Directly supports the objective to develop a probabilistic modelling approach to predict future temperature and to provide a common weather dataset for downstream projects.
- Enabled integration with Projects 3, 4, and 5, validating the role of Project 1 as an enabling foundation.
Interim Conclusions and Influence on Programme
- These findings influenced later modelling choices, notably:
the move towards Monte Carlo and scenario‑based analysis in Project 4; and
the decision in Project 5 to prioritise climate data visualisation as a cross‑cutting enabler.
- Climate datasets and methods were judged sufficiently mature to support progression into asset‑level resilience analysis.
Project 2 – Asset Taxonomy and Cable Thermal Risk
Key Deliverables (2025/26):
- Asset taxonomy tool and supporting documentation
- Cable soil dry‑out literature review
- Probabilistic soil dry-out assessment
Key Learning
- The taxonomy approach proved effective for asset down‑selection and prioritisation, even where data completeness was limited.
- Analysis demonstrated that soil dry‑out risk is highly localised, meaning network‑wide assumptions can mask high‑risk individual assets.
- Legacy assumptions underpinning cable thermal ratings were found to be broadly unchanged since the 1960s, indicating a structural risk under future climate conditions.
Relevance to Project Objectives
- Directly addressed objectives around asset cataloguing and evaluation of existing rating methodologies, particularly for underground cables.
- Supported the programme’s success criteria around probabilistic risk identification and prioritisation.
Inteim Conclusions and Influence on Programme
- Early findings led to:
1.cancellation of a planned assessment‑criteria deliverable, which would have been insufficiently evidence‑based;
2.prioritisation of underground cables as a key risk class for future phases.
- These outcomes triggered recommendations for future work on thermal resistivity mapping and more targeted data acquisition.
Project 3 – Component, Circuit, and System‑Level Thermal Modelling
Key Deliverables (2025/26):
- Deliverables D2.1–D2.4 (model refinement and measurement datasets)
- Deliverables D3.1–D3.3 (substation, network, and system‑level modelling)
- Deliverables D4.1 and D4.2 (heatwave impacts on ageing and fault rates)
Key Learning
- The modelling framework demonstrated the feasibility of extending thermal analysis from components through to system level, using representative use cases.
- Results highlighted the importance of solar irradiance in heatwave impact assessment, which is not always treated explicitly in traditional studies.
- The absence of new field measurements confirmed that model development and scaling can proceed using existing datasets, provided limitations are properly characterised.
Relevance to Project Objectives
- Strongly supported objectives relating to:
1.evaluation of component rating methodologies;
2.integration of thermal limits into substation, network, and system‑level analysis.
- Demonstrated the programme’s generic modelling framework success criterion.
Interim Conclusions and Influence on Programme
- The decision to defer physical measurement campaigns was influenced by early results showing modelling value could still be delivered.
- Findings triggered clear recommendations for future targeted measurement campaigns to address specific data gaps rather than broad, exploratory testing.
Project 4 – Overhead Line Resilience and Ageing
Key Deliverables (2025/26):
- Fragility‑based resilience framework documentation
- Thermal ageing and multi‑hazard modelling outputs
- Supporting experimental report (Project 4b)
Key Learning
- The work demonstrated that extreme heat risk cannot be assessed in isolation; windstorms and other hazards materially influence failure probability.
- Modelling showed that Zebra conductors can tolerate limited extreme loading without immediate life reduction, supporting risk‑based operation rather than conservative derating.
- Ground clearance, rather than conductor temperature alone, emerged as a dominant constraint.
Relevance to Project Objectives
- Met objectives related to:
1.experimental and modelling approaches to OHL thermal stress;
2.provision of a resilience framework for extreme heat impacts.
- Delivered strongly against success criteria on ageing models, failure probability, and probabilistic assessment.
Interim Conclusions and Influence on Programme
- Multi‑hazard insights influenced the programme‑level conclusion that holistic, system‑level modelling is essential.
- Results supported progression toward future investment planning and operational strategy reviews.
Project 5 – Visualisation and Exploitation
Key Deliverables (2025/26):
Climate data visualisation demonstrator
Key Learning
- Visualisation significantly improves accessibility and comprehension of complex probabilistic climate data for non‑specialist stakeholders.
- Attempting full integration of immature datasets adds limited value; focused demonstration of high‑quality data is more effective.
Relevance to Project Objectives
Supported the objective of presenting findings in a web‑based or visual tool, aligned with exploitation and future operationalisation.
Interim Conclusions and Influence on Programme
- The outcomes influenced the recommendation to expand visualisation only once datasets are operationally robust.
- Triggered proposals for future workshops and exploitation planning.
Overall Programme‑Level Lessons
Across all deliverables, the key lessons for future projects are:
- Early clarity on data availability and success criteria is critical to avoid rework.
Probabilistic, scenario‑based approaches provide greater decision value than deterministic analysis alone.
- Integration across projects requires planned interaction points, not just shared reporting milestones.
- Modelling frameworks should prioritise extensibility and reuse, even where immediate end‑to‑end deployment is not feasible.
These lessons directly informed the programme recommendations and support clear progression pathways for future innovation phases.
Dissemination Arrangements – THERMAL Programme
The THERMAL programme has coordinated, and will continue to coordinate, the dissemination of project outputs to ensure that learning is appropriately shared across internal stakeholders, GB electricity networks, and relevant external forums. Dissemination activities have been structured to reflect the maturity of the outputs, their intended application, and any commercial or confidentiality considerations.
In line with Learning from Experience (LfE) commitments, the programme will:
- Coordinate the dissemination of project outputs to relevant stakeholders.
- Clearly define the intended use and application of the outputs; and
- Identify and develop use cases to support potential follow-on activities where appropriate.
Events, Workshops, and Forums
2.1 Presented/ discussed historically)
THERMAL Programme Workshops and Reviews
- Quarterly THERMAL Programme Review Meetings
Dates: 2024–2026 (quarterly)
Audience: NGET, project partners, asset and policy stakeholders
Content: Quarterly Progress meetings to share project updates, interim findings, integration discussion, risk and dependency management.
- THERMAL Close‑Out Workshop
Date: 30th March 2026
Audience: NGET, all project partners
Content:
1.Final project summaries (P1–P5)
2.Mapping of outcomes to ENA objectives and success criteria
3.Lessons learned (LfE)
4.Recommendations and prioritised next steps
Outcome: Agreed actions and formal programme recommendations.
Project‑Specific Technical Engagement
- Inter‑project technical workshops and bilateral meetings
Dates: 2024–2026 (ad‑hoc)
Audience: Relevant project pairs (e.g. climate, modelling, resilience)
Content: Alignment of methodologies, requirements definition, and integration of climate and asset models
2.2 Planned / Forthcoming Dissemination
NGET Dissemination Webinar
- THERMAL Programme Dissemination Event
Planned: July 2026
Audience: GB licensed electricity networks, ENA representatives, selected external stakeholders
Content:
Summary of key findings and lessons learned
NGET formal response to programme recommendations
Discussion of potential follow‑on activities and use cases
Clarification of how outputs can be accessed and applied
3 Published and Planned Technical Publications
CIGRE and Industry Publications
- Gruffudd Edwards, Oscar Hlustik, Mohamed Galeela, Gordon McFadzean, Gordon Wilson and Aisha Ali. Failure Modelling of Overhead Lines Exposed to Worsening Gradual and Instantaneous Weather Hazards Due to Climate Change. Accepted for presentation at the CIGRE Paris Session 2026, to be held in Paris, France, from 23–28 August 2026.
- Chris J. Dent, James Mollard, Gabi Hegerl, Gruffudd Edwards, Claire Turle, Aninda Bhattacharya and Gordon Wilson. Climate Data for Overhead Line Resilience to Extreme Events. Accepted for presentation at the CIGRE Paris Session 2026, to be held in Paris, France, from 23–28 August 2026.
- Supergen Risk and Resilience Day (19 March 2026): The project was presented at the poster session, contributing to the programme’s aim of improving energy system resilience through enhanced understanding of emerging grid challenges and mitigation strategies.
Dissemination activities are explicitly linked to:
- informing strategic and asset‑group planning for long‑term climate adaptation;
- supporting the development of risk‑based, probabilistic asset management approaches;
- identifying where further innovation phases (e.g. targeted measurement campaigns, expanded modelling, digital twin integration) would provide greatest value.
NGET will use dissemination events and publications not only to share findings, but also to identify practical use cases and partners for follow‑on activities, ensuring that THERMAL outputs progress beyond research into operational and strategic application.
