The United Kingdom (UK) has set ambitious plans of achieving a zero-carbon electricity system by 2035 and net zero by 2050. Offshore wind (OSW) capacity is a key component in achieving these goals, with the government aiming to achieve a target of 50 GW of OSW capacity with up to 5 GW from floating OSW by 2030. The UK pioneered the world’s first commercial floating offshore wind farm (OWF), the 30 MW Hywind Scotland, in 2017. Thereafter, in 2022, the ScotWind leasing round resulted in the award of 14 floating OSW projects (aggregating 19.2 GW) of the 20 projects (30 GW) awarded in the Scottish North Sea waters. There are further plans to expand floating OSW capacity in the Scottish North Sea as well as Celtic Sea through innovation and targeted oil and gas leasing and Celtic Sea leasing rounds.
Parallelly, efforts to develop the necessary supply chain have been initiated through the UK’s OSW Industrial Growth Plan (IGP), published in April 2024. IGP offers an opportunity to grow the OSW supply chain and contribute GBP 25 billion in gross value added to the economy by 2035, with shared efforts from the industry, the government and key stakeholders such as The Crown Estate (TCE). A major IGP initiative is the supply chain accelerator programme, which focuses on enhancing capabilities for floating OSW in the Celtic Sea, starting with a pilot stage of GBP 10 million and expanding to GBP 50 million over five years.
To accelerate innovation and investment in OSW, in July 2024, the UK government set up a new publicly-owned energy company, Great British Energy, with a capitalisation of GBP 8.3 billion of new money. This company has formed a partnership with TCE to work together to bring forward new OSW developments, with the potential to deliver up to 20-30 GW of extra OSW seabed leases to the market by 2030.
TCE has been advancing the award of floating OSW leases in the Celtic Sea. In December 2023, it released an Information Memorandum, outlining details of the Celtic Sea Floating OSW Leasing Round 5 (LR5) opportunity to establish a new generation of floating wind farms (up to 4.5 GW) in the Celtic Sea off the coasts of South Wales and South West England by 2035. This will be enough to power over four million homes, making it one of the world’s largest floating OSW initiatives. The concession notice confirming the launch of the LR5 tender process for three project development areas (PDAs) was published in February 2024. The invitation to tender Stage 1–ITT1 is currently underway. The final stage of the tender process (ITT2), which involves the eligible bidders participating in the auction for the three PDAs, is expected in spring 2025. The process will conclude with the awarding of lease agreements in the summer of 2025.
TCE’s LR5 has become the first leasing round to be brought to market with an agreed plan for connecting new windfarms to the UK’s electricity grid, with the National Grid Energy System Operator (NGESO) (soon-to-be National Energy System Operator [NESO]) publishing the Beyond 2030: Celtic Sea Report containing the network design recommendation for floating OSW. The report, released in August 2024, is an enabler of LR5. For the first time, developers will be able to move through the OSW leasing round with an understanding of how OWFs will be connected to the grid, allowing them to make a more informed bid, thus reducing risk.
NGESO has undertaken this assessment as a continuation of its Holistic Network Design (HND) publications Pathway to 2030 (July 2022) and Beyond 2030 (March 2024), which charted a course to facilitate up to 86 GW of OSW up to and throughout the 2030s at an investment of GBP112 billion. The Beyond 2030 report incorporated the ScotWind elements of the HND follow-up exercise (HNDFUE), which will facilitate the connection of 21 GW of OSW from the ScotWind leasing round.
The latest Celtic Sea report is the second element of HNDFUE, which creates opportunities for the South Wales and South West regions to continue to play an important part in Great Britain’s green industrial revolution, with connections into the region providing a catalyst for future coordination with green energy developments in these areas. NGESO worked with the transmission owner (TO), National Grid Energy Transmission (NGET) and a group of representatives from local councils across South Wales and the South West to discuss optioneering exercises and invited feedback, which was considered as part of the design development.
HNDFUE process
HND takes a more integrated approach than the existing network planning process in assessing future network needs. NGESO considered both the offshore and onshore network needs of the National Electricity Transmission System to ensure a comprehensive and coordinated planning strategy. As the TO, NGET examined the onshore works required to facilitate the connection of LR5 OWFs, ensuring an understanding of the infrastructure required, based on their assessment against the construction planning assumption provided by NGESO.
NGESO considered 21 unique design options, as well as several variations and sensitivities, for connecting the Celtic OWFs to the transmission network. These included a wide variety of designs, exploring ways of coordinating connections between leasing areas, and different configurations of connection from the wind farms to shore. It also explored connections to 23 interface points, some of which already exist on the onshore electricity network, and some of which would be new substation sites.
A high-level appraisal of identified environmental and community constraints as well as substation capacity constraints led to the selection of five interface points for the offshore network design. This included two 400 kV substations – Pembroke and Carmarthenshire – and the 275 kV Baglan Bay substation in South Wales as well as two 400 kV substations in the South West – North Devon and Cornwall. Following the completion of TO’s onshore studies for the shortlisted designs, NGET advised that connecting to the interface point at the 275 kV Baglan Bay substation would require reinforcement of the whole 275 kV network in South Wales. This extensive upgrade would involve significant onshore works and pose a risk to the delivery date. To avoid this, NGET proposed the establishment of a new 400 kV substation near Baglan Bay. This new substation has been designated as the South Wales Connection Node (SWCN).
The finalisation of the HND marks the strategic optioneering phase of the detailed network design (DND) process, to coordinate the connection of several areas earmarked for OSW generation at given capacities. The DND will include planning and consenting phases and will follow this exercise. These are conducted by the party responsible for developing and maintaining the offshore assets and onshore networks (OWF developer and TO respectively).
Recommended design
Design C_011z has been identified as the best-performing design. It connects 3 GW to South Wales (Carmarthenshire and SWCN) and 1.5 GW to the South West (North Devon). The connection to SWCN is via high-voltage direct current (HVDC) technology, while the connection to the remaining interface points is via high-voltage alternating current (HVAC) technology. Although it is more expensive than C_011a (the second-best performing design), C_011z offers a better balance across the environmental, community, deliverability and operability objectives and has the lowest level of known risk to its timely development and delivery among all designs considered. With a design configuration of 3 GW to South Wales, it avoids the immediate requirement for a new onshore 400 kV overhead double-circuit line and the associated delivery risk, significantly reducing its environmental and community impact and potential delays to connection dates.
Design C_011z performed favourably compared to the other shortlisted designs when balanced across all four design objectives and showed the lowest level of known risk to timely development and delivery of the shortlisted designs. While the recommended design is less economic than some other designs, it does offer advantages in terms of environmental impact and community impact. NGESO considered that the HVDC connection to a new SWCN does add some cost and complexity in terms of the deliverability and operability; however, the route to the landing point does avoid several designated environmental areas. The reduction of onshore works is also an advantage for the recommended design C_011z. Some of the other designs did indicate onshore reinforcement in the South West in the form of a new overhead line to meet the specific need of the HNDFUE Celtic Sea, while the C_011z design did not.
In developing the design, the location of interface points has been considered to reduce the impact on the environment and local communities. The HVDC connection of PDA 2 to South Wales reduces the overall number of cables in the marine environment, and NGESO has assumed buried cables will be used for all routes from offshore platforms to the onshore transmission interface point.
The connection of HNDFUE Celtic Sea to substation sites that are located strategically to address multiple needs is an advantage. NGESO’s recommended design makes use of two such sites in Carmarthenshire and North Devon, while a new connection hub in South Wales will allow more major projects to connect in these regions, further boosting local economic growth and aligning with Welsh policy on green jobs and net zero. It could also pave the way for the connection of future OSW developments. This would be subject to further assessments of the onshore network.
The way forward
Once the successful developers are identified under LR5, NGESO will work with each developer to produce connection contract offers, allowing the projects to connect to the electricity network. Its unique approach with the Celtic Sea will allow it to efficiently manage and remove more than 20 GW of registered connection capacity with little anticipated disruption to other customers and connections.
NGESO will also work with NGET to continue development on relevant works for this recommendation as it progresses into the DND stage. Onshore reinforcement needs outlined in this report focus on those essential for connecting the Celtic Sea OWFs. NGET has conducted an initial assessment of wider system works; however, further detailed analysis will be required in subsequent phases to develop a comprehensive recommendation of broader system needs to ensure compliance with the Security and Quality of Supply Standard. NGESO will also continue to work closely with TCE for consideration of seabed leasing opportunities and the associated network designs to meet future OSW generation ambitions.
The UK is making pioneering efforts to develop floating OSW at scale, along with a more coordinated approach to electricity transmission network planning for OSW. The industry is keenly watching the developments as the country prepares to implement the blueprints on the ground.