[1] Sited in the North Sea 120 km (75 miles) off the east coast of England, the eventual wind farm group is planned to have a total capacity of up to 6 gigawatt (GW).

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.

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.

In July 2023, British government officials gave the final approval for Hornsea Four, the fourth phase of the wind project.

[9] The Hornsea development zone was awarded to a joint venture (SMart Wind) of Siemens and a consortium Mainstream Renewable Power including Hochtief.

[31][32] A £25 million contract to construct the onshore substation at North Killingholme had been awarded to Balfour Beatty in late 2015.

[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] Construction of the onshore cable route was begun in late 2016 under J. Murphy & Sons.

[2] The export cables were installed by Tideway Offshore Solutions, a subsidiary company of the Belgian DEME Group.

[41] Hornsea 1 began supplying power to the UK national electricity grid in February 2019,[42][3] with full completion expected in the first quarter of 2020.

[46][47][4] In 2019 the failure of the plant was partially responsible for a large scale nationwide power cut on the evening of 9 August.

[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] By the time construction commenced in 2020, the selected area was to the east and north of Hornsea One and the specification had been set as 165 8 MW turbines giving a rated capacity of 1.4 GW.

During 2018 and 2019, consultation with the local communities which will be affected by the project took place, with a Development Consent Order application originally intended in the first quarter of 2020.

[77] 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.

[78] 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.