Navigating Transmission Curtailment can be a critical challenge. Here we explore the concepts of curtailment and constraints, shedding light on the reasons behind their emergence. We also delve into our innovative approach to modeling transmission constraints and highlight how we can support your projects in overcoming these challenges.
Supporting Curtailment Analysis for Energy Projects
Blake Clough Consulting’s GB Transmission Grid Model provides a structured approach to addressing curtailment and system constraints. The model is designed to help developers manage challenges and achieve project objectives effectively. Whether working on Tranche 2 or other transmission initiatives, we can assist with reducing timelines for transmission connections by offering alternative connection arrangements, reliable system analysis and in-depth transmission system expertise.
Curtailment. Constraints. Bottlenecks. What are they Exactly?
The transmission system, also referred to as the National Electricity Transmission System (NETS) consists of high voltage network infrastructure within Great Britain and is normally operated at the 275kV and 400kV levels, except for Scotland where the 132kV network is also treated as the transmission system.
As the nation progresses towards Net Zero, system operation costs have increased significantly over the last decade, as shown in the figure below, with a large percentage of these costs constituting curtailment or constraint costs. Curtailment on the transmission system is defined as power output instructed to decrease or switch off completely due to either thermal, voltage or stability driven constraints.
This article will mainly focus on thermal constraints, although voltage and stability constraints are increasingly presenting themselves on today’s network.
Image Courtesy National Energy System Operator (NESO): System Operation Cost Growth
What is Driving Curtailment?
Over the last decade, the transmission system has seen a huge increase in renewable assets deployed on the system, with a majority of this coming from Offshore Wind based in Scotland. In 2010, there was approximately 1.3GW of offshore wind, and this rose to 14GW in 2023.
Image Courtesy of Statista: Offshore Wind Growth in GB
All this power needs to be transmitted to where it is needed, and in the case of GB, wind power will transmit from the North to the South resulting in bottlenecks on the transmission system. This bottleneck or thermal boundary is what will set the limit for cumulative generation, as NESO must ensure the circuits are not overloaded.
These boundaries are visible in publications such as the Electricity Ten Year Statement (ETYS) and in the case of Scottish Wind, these would be the B6 and B4 boundaries illustrated in the image below. The ratings of the overhead lines and other transmission infrastructure will determine the thermal limit set at these boundaries; in summer lower ratings are used on overhead lines due to the lack of ambient cooling, and higher ratings are used in winter. This results in the boundary limits changing at different times of the year and the limit is also influenced by outages on the network, followed by the impact assessment of faults.
Image Courtesy of NESO: ETYS Appendix A Figure 3
The above is an example of the most prevalent curtailment boundary, but curtailment can also become an issue even at the substation level especially with the huge rise in projects queuing to connect at transmission level. It is for this reason that transmission curtailment is often very difficult to model outside of NESO, and reduced model networks are created to simplify networks, but understanding the impact of a project on the wider network is vital.
Navigating Transmission Curtailment – What Can Impact Curtailment?
There are several key factors that can impact curtailment, and these must be considered when assessing the network. These include, but are not limited to:
- The ratings of assets, including seasonal ratings
- Location of the asset and its size
- Generation patterns on individual days
- Years of study and what the network may look like at the time of connection
- Impact of High Voltage Direct Current (HVDC)
- Demand Growth Forecasts
- Distribution Connected Assets
- Outage and Fault Patterns
These are just some of the factors that need to be taken into account when building Power System Models and conducting curtailment analysis. Taking the above into account, analysis can then be carried out to determine if curtailment may be present. To calculate the amount of curtailment exposure, the above datasets need to be implemented across multiple years and at 30 minute – 1 hour intervals. This analysis will produce a load flow profile and can be studied for various outage plus fault combinations.
If a project is due to connect in 2030, then the virtual environment in the Power Systems model should reflect this. For example, the figure below illustrates the impact that building transmission system infrastructure could have on curtailment costs, according to NESO. The Accelerated Strategic Transmission Infrastructure (ASTI) projects are a list of Network Options Assessments brought forward by OFGEM, so that they may be built well ahead of schedule.
Image Courtesy of NESO: Envisaged Reduction in Curtailment on the NETS Due to Reinforcement Works
Navigating Transmission Curtailment – Uncertainties
How Are Uncertainties Like CP2030 and Demand Growth Factored into Curtailment Studies?
When studying curtailment, there are several uncertainties around components such as the demand growth projections, new asset ratings and what the actual transmission queue may look like and who is competing for the same capacity. These can all be factored into a power system study via sensitivity studies, where demands can be tuned as can the rate of attrition to competing projects.
Blake Clough Consulting are actively involved in CP2030 consultations and have developed automated scripts that can screen the transmission generation queue, and this in turn allows the formation of an approximate queue to gauge the possibility on projects that may be pushed back into the late 2030s. This is important when carrying out curtailment analysis as the results will depend on the amount of competing projects.
Blake Clough Consulting and Our National GB Model
We have conducted hundreds of curtailment studies for clients on the distribution network and have a deep understanding of curtailment. This knowledge and expertise has been combined with our extensive scripting, power systems and transmission network know-how which has resulted in the creation of a National Transmission Model.
Blake Clough Consulting has developed a comprehensive Great Britain (GB) Transmission System Model to support Transmission Curtailment Analysis. Built in-house, this model reflects the current GB transmission network and future scenarios. Following our work on Tranche 1, we are now deploying the model for Tranche 2 projects to provide detailed analysis and insights.
Geographical Map of the GB Transmission Network:
The map below provides a geographical representation of the transmission system across England, Scotland, and Wales. This view is instrumental in understanding regional infrastructure and designing location-specific renewable energy profiles.
PowerFactory Model Representation:
The figure below showcases the GB transmission system modelled within DIgSILENT PowerFactory, including critical transmission lines, nodes, and boundaries. This model also incorporates High Voltage Direct Current (HVDC) interconnectors, reflecting the increasing importance of cross-border electricity flows and the integration of renewable energy sources.
Locational Generation Profiles
A key feature of our model is its ability to generate and compare location-specific renewable energy profiles. The plot below compares solar generation profiles for two substations: Indian Queens in Cornwall and Dunbeath in Scotland. The data illustrates how geographical location significantly influences solar output, with differences in irradiance levels and seasonal variability.
- Indian Queens (Cornwall): Located in the south, Cornwall benefits from higher solar irradiance, reflected in greater generation levels throughout the year.
- Dunbeath (Scotland): In contrast, the northern location of Dunbeath results in lower solar generation due to reduced sunlight availability.
This analysis highlights the importance of location-specific modelling to optimise renewable generation forecasts and inform project planning. The model also takes into account wind coefficient factors for both onshore and offshore installations, depending on where in the country they are located. Historical data and forecast data generated through the use of Artificial Intelligence is also used in the model when conducting curtailment analysis for future years.
Developing the GB Transmission System Model
Our model was created using DIgSILENT PowerFactory, a widely used platform in power systems analysis. It includes geographically accurate representations of the GB transmission network. One key feature is the ability to generate custom wind and solar generation profiles for renewable generators. This is made possible by geographical precision enabled through Python scripting and peer-reviewed energy data sources, ensuring detailed and relevant analysis.
The model also incorporates:
- HVDC interconnectors: Enabling the simulation of cross-border energy flows and the integration of large-scale renewables.
- Operational dispatching simulations: Reflecting real-world scenarios.
- Dynamic load and generation profiles: Adjusting for evolving energy demands and infrastructure changes.
- Geographical accuracy: Supporting site-specific renewable energy analysis.
Curtailment and Constraint Analysis
The model provides load flow analysis to study system behaviour under various operational conditions. Key capabilities include:
- Thermal boundary analysis: Identifying transmission system limits.
- Contingency analysis: Evaluating system resilience under different constraints.
These tools allow for a detailed evaluation of curtailment risks and system constraints, helping developers optimise project planning and operations. We can help clients understand the local network and present scenarios that we would deem prudent for further analysis.
Supporting Future Energy Scenarios and Transmission Connections
The model incorporates data from National Grid ESO’s Future Energy Scenarios (FES) to forecast half-hourly demand for every Grid Supply Point (GSP) through to 2050. This provides a foundation for integrating renewable energy, battery storage, and future infrastructure developments.
Navigating Transmission Curtailment – Key Insights for Developers
Blake Clough Consulting provided significant support to Battery Energy Storage System (BESS) developers for the accelerated storage scheme Tranche 1 offers. We have further enhanced our capabilities, combining our National Transmission model, with CP2030 learnings and Transmission network knowledge. We are ready to assist developers who have been issued transmission connection offers, and who wish to carry out curtailment assessments to gauge loss of output risk. We have previously carried out the following:
- Tranche 1 Contributions: Supported the acceleration of standalone Battery Energy Storage Systems (BESS) under operational constraints.
- Scalable demand forecasting: Simulating merit order dispatch using DIgSILENT PowerFactory’s unit commitment module.
- Custom renewable profiles: Enabling site-specific generation forecasting for wind and solar assets across GB.
- Client-specific regional modelling: Allowing for analysis tailored to individual project needs and local conditions.
For more information or to discuss your project, please contact us at [email protected].