Our network planning process is undergoing major transformation as we transition to the Centralised Strategic Network Plan.

The ESO is working in collaboration with Ofgem on the Electricity Transmission Network Planning Review (ETNPR) to review our network planning processes to ensure that the network design and investment processes in Great Britain are fit for the future. To meet our ambitious decarbonisation targets, the pace and scale of our Electricity Network planning processes must change. We are moving away from an annual network planning assessment cycle to a new Centralised Strategic Network Plan (CSNP).  

The objectives of the CSNP are displayed in the image below. The CSNP will proactively identify, design and progress investments in the network and will ensure that the transmission network is planned holistically, onshore, offshore, and across vectors.  

There will be a shift away from focusing predominately on winter peak thermal flows moving closer to a year-round system needs assessment which includes voltage and stability requirements. 

The below image details the objectives of the current network planning cycle and how they are changing in the new centralised strategic network plan.

The options assessment will be adapted as part of the CSNP to create a level playing field whereby network options are assessed against third party and innovative solutions. In addition to economic assessment, the CSNP will also consider environmental and community factors earlier in the planning cycle.  

As we prepare for these changes, our network planning activities will look very different from previous network planning cycles. 

We are in a state of evolution from the NOA to the CSNP and during this transition there will be some iterations of a transitional CSNP to continue informing network planning and investment decisions whilst we develop the enduring CSNP process. 

The first transitional Centralised Strategic Network Plan (tCSNP1) was published in July 2022. This included the Holistic Network Design (HND) and the NOA 2021/22 Refresh. These publications together provided network designs and onshore network investment recommendations required to deliver the UK Government’s ambition for 50GW of offshore wind by 2030.  

The second transitional Centralised Strategic Network Plan (tCSNP2) will be delivered in 2023 and will include: 

As we prepare the framework and methodology for the enduring CSNP we will continue to adapt our planning processes in order to meet our ambitious objectives. To find out more about the CSNP or the Network Planning Review contact us at: [email protected].

Boundary analysis

Learn more about how we analyse the transmission network: 

As the ESO, we are responsible for the operation of the transmission networks in England, Wales, Scotland and offshore.  

The NETS is mainly made up of 400kV, 275kV and 132kV assets connecting separately owned generators, interconnectors, large demands and distribution systems. 

Here, ‘transmission’ generally means assets at 132kV or above in Scotland or offshore, but in some cases includes other lower voltage assets.  

In England and Wales, it relates mainly to assets at 275kV and above. There are three onshore transmission owners (TOs) in GB: 

The offshore transmission systems are also separately owned. There are 24 licenced offshore transmission owners (OFTOs) appointed through Ofgem’s competitive tendering process. They connect operational offshore wind farms given Crown Estate seabed leases in allocation rounds. 

The TOs and ESO work together to reflect real world changes in network modelling to accurately assess network behaviour under differing conditions. 

Together with the transmission owners, the ESO works to make sure the assumptions made in the analysis are acceptable and any changes in their networks are reflected correctly in the network models. This ensures the ETYS portrays an accurate representation of the current transmission capabilities and identifies future requirements. 

A boundary splits the system into two parts, crossing critical circuit paths that carry power between the areas where power flow limitations may be encountered. 

Defining the boundaries has evolved over many years of planning and operating the transmission system. When significant changes occur, new boundaries may be defined and some boundaries either removed or amended and we communicate any changes with our stakeholders. 

We do not study all boundaries, specifically those where no significant changes are identified in the FES generation and demand data compared to previous years. We assume the same capability as the previous year for these boundaries. 

The boundaries used by ETYS can be split into two different types: 

Local boundaries 

Small areas of the NETS with a high concentration of generation. These small power export areas can give high probability of overloading the local transmission network due to too much generation operating simultaneously.  

Wider boundaries  

Large areas containing significant amounts of both generation and demand. The SQSS boundary scaling methodologies assess the capability of the wider boundaries. 

These consider both the geographical and technological effects of generation, allowing for a consistent capability and requirements assessment. 

Download a larger view of the map

When we assess future requirements, we bear in mind that we have many signed contracts for new generation, demand and interconnectors seeking to connect to the NETS. 

We do not know precisely how much new capacity there will be, when it will connect, or when existing generation will shut down. Our FES provides four credible scenario pathways to 2050 and we use these to identify expected future boundary flows as required by the NETS Security and Quality of Supply Standard (NETS SQSS).  

For each boundary, we work with the transmission owners to undertake power system analysis to determine the boundary capability which is the maximum MW flow that can be transferred across a boundary while maintaining compliance with the NETS SQSS. 

Limiting factors on transmission capacity include:  

  • Thermal circuit rating  
  • Voltage constraints  
  • Dynamic stability  

For the ETYS network assessment, contingencies are applied, and the most severe limitation is used to determine the network boundary capability. 
The base capability of each boundary can be seen in the Electricity Transmission Network section.

The ETYS describes the network capability by looking at the maximum secured power transfer between two regions or the power transfer across a boundary

The numbers above correspond to the points from the map in Key Message 2

To operate the system safely, we must make sure that the power flow across the boundary does not exceed the capability of the system between the two regions. To prevent this, we have to take actions to constrain generation which can incur significant costs.

The heatmap shows that if no reinforcements are made to the system (i.e. the system is the same as it is today, over the next 10 years), the network boundaries defined in the ETYS would lead to incurring significant network constraint costs due to the high flows from the increased generation capacity.