Hornsea Project One, North Sea, United Kingdom

Hornsea Project One is expected to be the world’s biggest offshore wind farm.

Hornsea Project One is an offshore wind farm proposed by DONG Energy that will be located off the Yorkshire coast within the Hornsea Zone in the southern North Sea.

Located in the Humber region, the project is part of a £6bn ($8.7bn) investment to transform the region into a hub for the UK's renewable energy sector.

At 1.2GW, the project will be the world's biggest offshore wind farm and the first offshore wind farm to have more than 1GW of capacity.

In February 2015, DONG Energy acquired 66.66% ownership share of SMart Wind, a consortium of Mainstream Renewable Power and Siemens Financial Services, to become the sole owner of the project. It is also the owner of future offshore developments Hornsea Project Two and Hornsea Project Three, which have a potential capacity of a further 3GW.

The final investment decision on the Hornsea Project One was taken on 3 February 2016 and the project is scheduled to be commissioned in 2020. It will have a life span of approximately 25 years.

The wind farm is expected to power more than one million UK homes and create 2,000 employment opportunities during the construction phase, as well as 300 additional jobs during its operational phase.

Hornsea Project One make-up

Hornsea Project One is being constructed on an area of approximately 407km² and will be equipped with 174 Siemens wind turbines rated at 7MW each.

Turbines will be 190m tall and have a rotor diameter of 178m with a maximum blade tip height of 200m. They will have a clearance level of 22m above mean high water springs (MHWS).

The project will also involve construction of the world's longest ever offshore wind farm, featuring a high-voltage AC electrical system comprising more than 900km of cables that will transfer generated electricity to the shore and national grid.

The selected site for the development has favourable water depths between 20m and 40m and provides good wind and ground conditions.

In addition, the wind farm will include three offshore wind generating stations, two offshore accommodation platforms, up to five HVAC collector substations that will be connected through inter-array cables of 30kV to 70kV, up to two offshore HVDC converter stations, and an offshore HVAC reactive compensation substation.

Onshore infrastructure for the Hornsea Project One

Onshore infrastructure will comprise a substation, underground cable, core buildings and compounds, low-voltage electricity equipment and communication cables, as well as roads, paths, drainage and landscaping.

The onshore substation will be based at North Killingholme in North Lincolnshire and will transfer electricity from the offshore wind farm to the adjacent national grid substation.

It is being constructed on a 32,200m² area, and will include transformers, reactors, high-voltage gas-insulted switchgear systems, static VAR compensator (SVC) or static synchronous compensator (STATCOM) and harmonic filters.

Offshore cables will make a landfall at the Horseshoe Point, south of Grimsby, and will be connected to underground onshore cables via transition joint bays. The cable route will span 40km underground from the landfall site to the onshore substation of the national grid located in North Killingholme.

Hornsea Project One construction

"At 1.2GW, the project will be the world's biggest offshore wind farm and the first offshore wind farm to have more than 1GW of capacity."

Construction of onshore facilities began in early 2016 and will continue until 2019. Offshore construction is scheduled to begin in 2018 and aims to be completed by 2020.

Offshore installation of foundations is planned to be completed within 24 months. Onshore cables will be installed underground using open-cut trenching techniques, while cables at the landfall will be installed using horizontal directional drilling under the saltmarsh and sea defence.

Jointing bays that will be used to connect the cables will have dimensions of 25m x 6m x 2m, and will be constructed at intervals of 750m to 2.5km.

The world's biggest ever seabed investigation campaign was completed in April 2015 in preparation for the project. It involved 2,800m of seabed cone penetration testing and approximately 5,000m of boreholes on all future wind turbine generators and operational support system positions.

Key players involved

Siemens was selected to supply wind turbines for the project. A £25m ($36.2m) contract was awarded to Balfour Beatty for construction of the onshore substation. Atkins was selected to provide engineering design services for three offshore substations.

Fugro Geoconsulting was awarded a £13m ($18.8m) contract for conducting a detailed site investigation using Greatship Manisha and Bucentaur, two of its biggest and best-equipped geotechnical vessels.

A2SEA is responsible for the installation of a part of the 174 Siemens 7MW turbines.

DEME subsidiary Tideway received a design and build cable installation contract from DONG Energy for Hornsea Project One, in June 2016.

Dragados Offshore secured a contract from DONG Energy to provide four substation jackets for the project. The scope of the contract includes procurement and fabrication of the jackets and piles of three offshore substations and a reactive compensation substation.