Hollandse Kust Zuid Wind Farm Zone (Sites I-IV)

Hollandse Kust Zuid Wind Farm Zone (Sites I-IV)The Hollandse Kust Zuid Wind Farm Zone project is one of the biggest offshore wind projects in the world and the first in Europe to be totally subsidy free. It will also use the largest offshore wind turbines available to date and feature a new design of monopile foundation.

The project spans four 350 MW sites in the Dutch North Sea, offered to tender in separate lots by the Dutch Government, two in 2017 and two in 2018. In a ground-breaking move, the Government invited companies to submit zero-subsidy bids for these projects, using a full comparative assessment scoring system, rather than price, to award contracts. Vattenfall was confirmed as the winner for Hollandse Kust Zuid Wind Farm Sites I and II (HKZWFS I and II) in March 2018 and HKZWFS III and IV in July 2019.


In total, the four HKZ sites have a combined size of 225 km2 and are being developed by Vattenfall as one project. Construction started in summer 2022. The first operating turbine is already supply electricity to the Dutch grid and by end February 2023, 100 of the 140 Siemens Gamesa 11 MW turbines planned for HKZ had been installed. Full completion of the HKZ project is expected this year (2023).

Siemens Gamesa's 11 MW turbine is an upgraded version of its 10 MW SG DD-193 direct drive offshore wind turbine, originally planned to be used Vattenfall. According to the company, the capacity upgrade, available under certain site conditions, means fewer turbines are needed to generate the same amount of energy. This also reduces installation, operations, and maintenance costs and thereby contributes to further reductions in Levelized Cost of Energy for offshore wind. The environmental impact of installation and operation of the wind farm is also reduced.

Site work close to completion

Scour protection started on site in June 2021, followed swiftly in July 2021 with the first monopile foundations supplied by SIF. Instead of using the traditional transition pieces, SIF's new foundation design sees the work platforms and ladder attached directly to the monopile. Vattenfall believes this will increase installation speeds and reduce costs. Seaway 7 transported (from Maasvlakte in Rotterdam) and installed the foundations using installation vessel Seaway Strashnov. It completed piling work for all 140 foundations in early September 2022.

Cadeler's installation vessel Wind Osprey is being used to transport (again from Maasvlakte) and install the wind turbines, with the final units scheduled for installation in March 2023. By mid-2023, all 140 wind turbines should be fully operational. At that point, HKZ will become the largest operational offshore wind farm in the world.

The 315 km of 66 kW inter-array cables connecting the turbines to TenneT's two offshore substations for the zone are supplied by Prysmian, with Seaway 7 installing them.

The Port of Ijmuiden will serve as the operations and maintenance hub for the project. Windcat Workboats has also been contracted for the supply of hydrogen-powered crew transfer vessels (CTVs) for the maintenance of the wind farm.


HKZ is owned by Vattenfall (50.5%), BASF (24.3%) and Allianz (25.2%). Vattenfall is leading the development of the project.

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At a glance

  • Owner: Vattenfall, BASF, Allianz

  • Total capacity: 1.5 GW (expected to generate enough electricity to power 3 million households)

  • Wind turbines: 140 Siemens Gamesa 11 MW

  • Location: 18 - 36 km off the coast of Zuid-Holland Province

  • Size of the site: 225 km2

  • Water depth: 18.1 -27.8 m

  • Foundation type: Monopiles

  • Construction Start: 2021

  • Fully operational: 2023

  • Operation and maintenance base: Ijmuiden

  • Main suppliers: Siemens Gamesa, SIF, TKF, Prysmian, Windcat Workboats

  • Installation: Seaway 7 (a unit of Subsea 7), Cadeler (previously Swire Blue Ocean)

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