As part of the Pathway to 2030 workstream of the Offshore Transmission Network Review, National Grid ESO has published proposals for holistic network design (HND) of the GB electricity transmission network in which the offshore and onshore elements are integrated, enabling both the connection of offshore generation to shore and transmission of electricity to the points of demand.


The HND is part of a transition towards the Centralised Strategic Network Planning (CSNP) model proposed by Ofgem and expected to be implemented by 2024 – 2025 (see our briefing for background and our latest briefing on the minded-to decision).

Projects in HND

The HND gives a high-level view of the onshore and offshore infrastructure needed to connect 23 GW of offshore wind, which, when combined with existing offshore wind projects and projects at more advanced stages, will deliver up to 50 GW of offshore wind in Great Britain by 2030. It includes the following future projects:

a)    the projects which were successful in The Crown Estate Offshore Wind Leasing Round 4, totalling 8 GW;

b)    the projects which were successful in the ScotWind leasing round, totalling 11 GW;

c)    assumptions on 1 GW of floating wind from the upcoming Celtic Sea leasing round; and

d)    3 GW of other sites located near to Round 4 and ScotWind sites, to test whether there are opportunities for coordination.

Coordinated or radial connections?

Depending on the projects' location, either coordinated or radial connections are recommended. Coordination across wind farms is recommended for:

a)    the East Coast of England and Scotland;

b)    the west coast of Scotland, the north west of England and north Wales (the North West Region);

c)    the South East and South Coast of England; and

d)    the South West Region,

Radial connections are preferable for the North Scotland Region, due to the distance between the projects.

The coordinated design optimises the number of landing points, provides for some projects to connect further south than would have been the case and results in different power flows on the onshore network, by including infrastructure to transfer electricity from north to south, from the point of generation to the point of demand, rather than from generation to the onshore network which would be the case under the usual approach.

For example, for the North West Region an offshore connection is recommended between Scotland and Wales, bypassing onshore grid constraints and enabling transmission of electricity from north to south, towards areas of higher consumption. The design encompasses a connection to a T-point via high voltage direct current (HVDC) cable, with potential for other projects to connect into the T-point in the future.

Benefits of HND

Transporting power from generation to demand will avoid wind energy being constrained off and reduce the need for fossil fuelled generation, lowering cumulative CO2 emissions by 2 million tonnes between 2030 and 2032. Over a ten-year period from 2030, the availability of offshore wind on the system is expected to rise by 32 TWh.

Implementing the recommended design would increase capital costs by £7.6 billion due to additional offshore infrastructure, but would save £13.1 billion in constraint costs thanks to the additional network capacity. These are provisional figures, subject to change in the course of the detailed review, depending on the technology and routes selected.

The total number of offshore cables connecting to shore will be lower by up to a third because of the increased use of HVDC technology, reducing the environmental footprint.

For the existing onshore system, the HND recommends 94 reinforcements costing £21.7 billion by the end of the decade. In addition, delivery of 11 reinforcements already planned must be accelerated in order to meet the 2030 targets. These earlier delivery dates can be achieved with a more efficient consenting process and earlier regulatory approval to key projects.

Delivering the HND

The ESO, UK Government, Ofgem and TOs have committed to work collectively to deliver the HND, including by:

  • expediting the consenting and regulatory approval processes and reducing the time from development to construction of strategic infrastructure projects;
  • creating a regulatory framework to allow for strategic and anticipatory investment within the Pathway to 2030 workstream;
    designating the transmission network infrastructure required for 2030 as strategic;
  • accelerating delivery of reinforcement projects;
  • ensuring supply chain availability for the recommended network; and
  • where needed, considering mitigation and strategic environmental compensation.

Ofgem has recently issued a consultation on accelerating onshore electricity transmission investment which looks at these recommendations in more detail.

Coordinated connections will require changes to industry codes and standards – these will be progressed later this year. The ESO's current view on the changes required is set out in the Industry Code, Standard and Licence Recommendation Report.

Based on known technology, the ESO believes that the design is ambitious but realistic. The technology currently in development will be considered in future network plans to enable an even greater level of integration.

Along with the HND, the ESO has published an updated Network Options Assessment (NOA) for 2021/22. This replaces the NOA 2021/22 published earlier, which was based on radial design, to reflect the HND recommended design.

Next steps

The HND will be followed by a Detailed Network Design (DND) and consenting process, which will be conducted by the party responsible for delivering the relevant asset. The DND will confirm technology choices, transmission routes and locations of substations and converter stations.

Ahead of the DND, Ofgem will determine which of the transmission assets in the HND will be regulated as "onshore transmission" and which will be "offshore transmission". This will be based on each asset's function within the transmission network, rather than its location, so that some "onshore transmission" may be in the sea and some "offshore transmission" may be on land.

In the North West Region example above, the T-point will be treated as part of the onshore transmission system, the developer of the wind farm will be responsible for the link from the project to the T-point, and the other circuits will be described as TO works.

Within "offshore transmission" assets a distinction will be drawn between "radial" and "non-radial" and depending on this classification, different delivery arrangements within the HND will apply.

The party responsible for the DND and consenting process of each asset will be identified following this exercise.


Firstly, it is important to bear in mind that "early opportunities" projects are basically outside of this because they do not fall within the Pathway to 2030 scope.

The decision to continue with radial connection in Scotland is understandable as it is a continuation of approach that has been used in Scotland (particularly in the far north) since before privatisation in 1990.  It is inherently more vulnerable to lost load in adverse weather conditions, but is a reasonable trade off in terms of costs and benefit.  It is perhaps worth noting that as part of the transition to HND, the existing Connection and Infrastructure Options Note (CION) process as described here will come to an end which will entail a licence amendment.

Fundamentally, when taken together with the new Centralised Strategic Network Planning (CSNP) model, it would appear to signal the end to developer led projects.  This raises some significant issues. Just as one example, for generation led projects such as OFTOs where the sizing of the HVDC cables for connection onshore reflects the size of the offshore wind farm being developed, who will underwrite the risks of oversizing the cable so that it more efficiently provides connectivity for more than just that one project where another developer's project fails to achieve final investment decision or financial close?

The HND approach has the potential to deliver significant acceleration towards GB achieving the targets for net zero and decarbonisation but at the project level (which also goes to bankability for financing purposes), a great many issues have yet to have the details worked out and with a generator led approach to offshore grid development, these details are going to be critical to whether or not HND is seen as a successful tool to delivering the UK Government's ambitions for the transition of our energy economy.

Martin Stewart-Smith

Martin Stewart-Smith

Partner, Infrastructure Projects & Energy
London, UK

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Richard Goodfellow

Richard Goodfellow

Head of IPE and Co-head of Energy and Utilities
United Kingdom

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