Onshoring renewable energy from the North Sea

The Eastern Green Link 3 and 4 projects are critical to net zero targets

National Grid Electricity Transmission’s planned Eastern Green Link (EGL) 3 and 4 high-voltage direct current (HVDC) schemes will bring 4GW of offshore wind power from Scotland to 4M homes in the Midlands and South of England. The two separate projects form part of National Grid’s Great Grid Upgrade that aims to improve energy security in the UK while also driving up the availability of clean energy. While they are individual projects, they are being delivered in tandem.

Installation of 100km of buried onshore cables for both EGL 3 and 4 make these the largest schemes of their type ever delivered in the UK and they must also be delivered within a tight timescale to support government clean energy targets. Ensuring planning permission and procurement processes run smoothly is critical and Mott MacDonald is supporting National Grid to achieve that in the run up to the anticipated Development Consent Order application in 2026.

The client for the onshore cables is National Grid but the projects involve National Grid in two joint ventures with the transmission companies – one with Scottish Power Energy Networks and one with Scottish and Southern Electricity Networks Transmission.

The onshore cables for EGL 3 and 4 are currently expected to make landfall at either Anderby Creek or Threddlethorpe in Lincolnshire and connect to HVDC converter stations at Walpole in Norfolk and Bilsby in Lincolnshire.

“Our role involves the front-end engineering design (FEED) and technical support for the onshore parts of the project to improve programme certainty and support National Grid through the planning and procurement processes,” explains Mott MacDonald technical director for energy networks John Weeks.

This phase of work is the second undertaken by Mott MacDonald on the projects. The first, which started in 2023 supported the optioneering for the projects that established the preferred corridors for the cable routes. Mott MacDonald was then appointed to undertake the FEED contract and geotechnical services in March 2024. The focus is now on supporting the project through public consultation in summer 2025 to address issues ahead of the DCO application next year.

2023 - Mott MacDonald’s first involvement in EGL 3 and 4

2024 - Mott MacDonald’s appointment to the front-end engineering design contract

Creating planning certainty

The work on the current EGL projects follows on from delivery of similar services to National Grid by teams at Mott MacDonald for EGL 1 and 2, however, those schemes went through the local planning process because they were concentrated in one local authority area.

“The length of cable involved in EGL 1 and 2 was also much shorter,” explains John. “The 100km cables planned for EGL 3 and 4 means that the scheme passes through multiple areas and the DCO process was considered more straightforward for managing the multiple stakeholders.

“Neither project is classified as a Nationally Significant Infrastructure Project, so they don’t automatically have to go through a DCO for planning consent; but the scale of the project makes it possible to apply to use the process. The work is also critical nationally because it is part of National Grid’s Great Grid Upgrade, which will provide the transmission infrastructure to meet the government’s 2050 clean energy target to deploy up to 50GW of offshore wind.

“Using the DCO route means that the project can be driven through the planning process with more certainty, so while it may be slightly slower, it gives National Grid more confidence that consent will be granted within a specific timeframe.”

Detailed design

The scope of Mott MacDonald’s role has evolved since appointment to the FEED contract as it has been recognised that a greater level of design detail is needed in some areas to inform decisions and support the DCO applications. As an example, John points to the area around the planned converter station site in Walpole where more detail was required to take the work through the public consultation stage.

“Originally we were going to define a preferred option and develop that,” adds John. “Instead, we have advanced several options to a greater level of design which will give more clarity on the impact on traffic from the work, especially if the two converter stations are co-located at the site but built by different contractors. The options also consider the constructability of the facilities with a look at how transport of materials to the sites will affect the local area and cause challenges for other planned projects in the region.”

This is key to the success of the overall project as they are on the critical path. According to John, this is one of the reasons that a FEED approach was used for the work as it increases the level of design undertaken in the early stages to provide better programme assurance. “Achieving the 2033 target for the system being operational is critical for National Grid,” he adds.

While the design work is still underway, John has said that the cables will be buried using a mix of trenching and trenchless solutions to minimise the effect of the work during construction, as well as the long-term visual impact.

Construction challenges

Implementing such a project using conventional high-voltage alternating current (HVAC) technology would not be technically feasible. HVDC offers an efficient solution over long distances, requiring converter stations at each end of the link to change from alternating current to direct current and vice versa. This can then be connected to the national electricity transmission system for use in homes and businesses.

It is the long linear nature of the projects, with multiple landowners and stakeholders, that makes this work challenging from a management perspective, while the fast-paced programme adds complexity to the delivery. “Technically the work is more straightforward – the elements of the project are all techniques and solutions that have been used before and we have experience on –  it is the scale here that is different,” explains John. “Drawing together our expertise from past projects, along with learning lessons from other projects delivered in the region is key to supporting National Grid through the DCO process.”

According to National Grid senior project manager for EGL 3 and 4, Roxanne Fisher-Redel, the support provided by Mott MacDonald has been invaluable for progressing the design and assisting with the tender schedules. “The team has shown flexibility and adaptability throughout, responding well to the changing make up of the National Grid team,” she said. “The outputs have been consistently high in quality and the team’s ability to reprogramme sensibly has helped ensure our needs are met without disruption.”

While work to date has progressed well, there are still some more milestones that need to be met before construction can start. Public consultations on the projects are planned for summer 2025 ahead of submitting documents for the DCO in 2026. National Grid hopes the detailed work currently underway will smooth the planning application process to allow construction to start in 2029 to achieve its 2033 operational target for EGL 3 and 4.

“Completion of these projects will enable the UK to make full use of its offshore wind capacity,” says John.