Hornsea Wind Farm is a Round 3 wind farm which began construction in 2018.^[1] Sited in the North Sea 120 km (75 mi) off the east coast of England, the eventual wind farm group is planned to have a total capacity of up to 6 gigawatt (GW).

The development has been split into a number of subzones. The 1.2 GW Project 1 gained planning consent in 2014. Construction of Hornsea One started in January 2018,^[2] and the first turbines began supplying power to the UK national electricity grid in February 2019.^[3] The turbines were all installed by October 2019 and the equipment fully commissioned in December 2019. ^[4] With a capacity of 1,218 MW, it was the largest in the world on its completion.

A second 1.4 GW Project 2 was given planning consent in 2016. First power was achieved in December 2021, and it became fully operational in August 2022 overtaking Hornsea One as the largest offshore wind farm in the world.^[5]

In 2016 a third subzone was split into two projects Hornsea 3 and 4, with approximate capacities of 1–2 GW and 1 GW, increasing the capacity of the developed project to a maximum of 6 GW.

In July 2023, British government officials gave the final approval for Hornsea Four, the fourth phase of the wind project.^[6] Hornsea Four is expected to generate 2.6GW, have 180 giant wind turbines, and has the capability to generate enough renewable energy to power 1 million homes in Britain.^[7][8]

The tendering process for Round 3 offshore wind farm opportunities was begun by the Crown Estate in 2008. Bids were received in March 2009, and Zone Development Agreements signed in December 2009.^[9] The Hornsea development zone was awarded to a joint venture (SMart Wind) of Siemens and a consortium Mainstream Renewable Power including Hochtief. The development had an estimated potential generating capacity of 4 GW.^[10]

The Hornsea site is one of three off the British coast in the North Sea, roughly halfway between the other two: Dogger Bank Wind Farm and East Anglia Wind Farm.^[11] The Hornsea site ('Zone 4', also known as 'Holderness' zone) has a total area of 4,730 square kilometres (1,830 sq mi), and is 38 kilometres (24 mi) from land at the closest point; water depth in the zone is from 22 to 73 metres (72 to 240 ft), with a tidal range of 2 to 5 metres (6 ft 7 in to 16 ft 5 in), and typical annual wave height of 1.35 to 1.78 metres (4 ft 5 in to 5 ft 10 in). The surface of the seabed consists primarily of sands and gravel.^[12]

In 2011 the Danish firm Ørsted A/S (then named DONG Energy) became a partner in SMart Wind.^[13] In early 2015 Ørsted A/S became the 100% owner of the first phase, Project 1, of the scheme.^[13] Ørsted acquired rights to the remaining subzones of the Hornsea development (2 & 3) by August 2015.^[14]

In 2016 Ørsted reached an agreement with the Crown Estate for amended plans for the Hornsea Two and Hornsea Three phases. Hornsea Three was split into two new projects, Hornsea Three and Hornsea Four; the new phases were expected to be developed in the 2020s.^[15] The changes increased the potential generating capacity of the wind farm to 6 GW, with Hornsea Three estimated at 1–2 GW and Hornsea Four at about 1 GW.^[16][17]

The initial scoping report for "Project One" within the Hornsea zone identified it as a subzone of 629.6 square kilometres (243.1 sq mi) in the centre of the Hornsea zone, with an estimated potential wind farm of 1.2 GW, divided into two further subzones of 600 MW capacity each. The zone was to connect to an existing 400 kV National Grid substation at Killingholme.^[18] A variety of configurations were considered – foundations of pile jacket, monopile or gravity base; turbines from 3.6 to 8 MW rated power; with electrical power export by HVDC.^[19] Later DONG Energy added the consideration to use HVAC export cables.^[20] The chosen cable export was planned to make landfall at Horseshoe Point (northeast of Marshchapel, East Lindsey), then passing 40 kilometres (25 mi) west and northwest to a substation near Killingholme Power Station, North Killingholme in North Lincolnshire.^[21]

Within the zone of Project 1 the primary underlying geology consisted of deposits from the Quaternary Period consisting of Bolders bank, Botney Cut and Eem formations – primarily sediments or tills – gravelley/sandy clays, overlying sediments were sands or gravels up to 2 to 3 metres (6 ft 7 in to 9 ft 10 in) thick, with waves within the area varying in height by 1 to 3 metres (3 ft 3 in to 9 ft 10 in). Project 1 water depths were generally 25 to 30 metres (82 to 98 ft).^[22]

In 2011 Smart Wind signed lease agreements with the Crown Estate for "Heron Wind" and "Njord" areas making up the zone.^[23] The zone was given provisional contract for difference renewable subsidies by the UK government in April 2014.^[24] Hornsea Project 1 was given planning consent in December 2014.^[25] The 'contract for difference' strike price was £140 per MWh.^[26] In early 2015 DONG acquired all of the project, becoming 100% owner.^[13]

Seabed investigation including boreholes at turbine foundation positions was completed by Fugro by April 2015.^[27] In mid 2015 DONG selected Siemens Wind Power 7 MW turbines with 154 metres (505 ft) rotor turbines for the project – around 171 turbines would be used for the wind farm.^[28] In its 2015 financial report DONG stated it had chosen to use suction bucket foundations on a third of the turbines at Hornsea.^[29] The rationale for use of the new foundation type is thought to be a simplified foundation installation, requiring only a heavy-lift crane to lower the foundation to the sea bed, reducing costs.^{[30][note 1]}

DONG Energy formally committed to building the wind farm in early 2016. The expected completion date for the project was 2020.^[31][32] A £25 million contract to construct the onshore substation at North Killingholme had been awarded to Balfour Beatty in late 2015.^[33]

NKT Cables and ABB were awarded €139 (c. $158) million and $250 million contracts to supply 220 kV AC export cables in March/April 2016.^[34][35] In late 2016 JDR Cables was contracted to supply 242 kilometres (150 mi) of inter-array subsea power cables for the wind farm;^[36] Nexans was awarded a contract for 139 kilometres (86 mi) of inter-array cables;^[37] and EEW was awarded a contract to supply 116 monopiles.^[38] Bladt Industries/Offshore Structures (Britain) Ltd. was awarded a contract for 96 tower transition pieces in early 2017, to be constructed at Aalborg, Denmark and Billingham, UK.^[39] Dragados Offshore was awarded in early 2016, a contract for construction of four jacket type foundations for the AC platforms at its yard in Cádiz, Spain.^{[citation needed]}

A scoping report for "Project Two" was published in October 2012.^[51] The subzone was expected to be developed in a number of phases, with a potential wind turbine capacity of 1.8 GW, in an area of around 400 square kilometres (150 sq mi) located in the centre of the Hornsea wind farm zone. Project 2 was use the same route for its electrical export cable as Project One, and to use either HVAC or HVDC with a separate onshore substation.^[52] Suitable areas for the Project 2 development were identified as being adjacent to the north, east or west of the Zone 1, which was located in the shallowest area of the whole Hornsea zone.^[53] The design considered piled, suction pile, monopile or gravity base foundations for wind turbines of 5 to 15 MW rated power.^[54]

As with Project 1 sea bed conditions and geology consisted of Quaternary period deposits, primarily sediments of sand, till and clays, with the overlying gravel or sand seabed including sandwaves, with the average water depth of 25 to 30 metres (82 to 98 ft).^[55]

In 2013 SMart wind signed lease agreements with the Crown Estate for the "Optimus Wind" and "Breesea" areas making up Project 2 of Hornsea wind farm.^[23] A planning application for Project 2 was submitted and accepted for examination in early 2015;^[56] its wind turbine area was located adjacent northwest of the Project 1 area, with the cable export route following that of Project 1 adjacent on the northward side.^[57] Planning permission for the development was awarded in August 2016,^[58] for 300 turbines covering 300 square miles (780 km²) at a height of 620 feet (190 m) each. At the time of the award, Dong had committed to building 174 turbines, but the whole project is the biggest marine wind farm in the world.^[59]

Project 3 will be to the east of Projects 1 and 2, with a capacity of 2.9 GW over 696 square kilometres (269 sq mi). DONG Energy (which in November 2017 changed its name to Ørsted^[68]) began consultation on the project's development in May 2016.^[69] Ørsted submitted a Development consent application in 2018 and consent was granted on 31 December 2020.^[70] In early 2023, consent was also given to a battery storage power station at Swardeston.^[71] The project began construction in 2023, and is expected to complete at the end of 2027.^[72][73]

Ørsted put forward a plan to add a fourth area to the Hornsea wind farm in 2018, with the area covering 600 square kilometres (230 sq mi), and being located adjacent, north-west of Hornsea Project 1. During 2018 and 2019, consultation with the local communities which will be affected by the project occurred, with a Development Consent Order application originally intended in the first quarter of 2020.^[76] However additional consultations and revisions delayed the submission until September 2021, with further analysis needed on the impacts to kittiwake, razorbill and guillemot populations in the Flamborough and Filey Coast Special Protection Area.^[77] Part of the site is also scheduled for an underground carbon dioxide storage, leading to conflict over the use of the seabed and the ocean surface.^[78]

The project's capacity is unknown by Ørsted due to the ever increasing size of available wind turbines for the project. Government approval for phase four was given by Grant Shapps in July 2023.^[79] Pre-construction site enabling works are expected to commence in the first half of 2025 and completion is expected by 2030.^[80]

• List of offshore wind farms