Heerema’s heavy lift vessel Sleipnir has installed the jacket foundation for TenneT’s Hollandse Kust Zuid (HKZ) Beta offshore transformer platform some 22 kilometres off the coast of The Hague. The topside is expected to follow early next year. HKZ Beta is one of two platforms that will collect and transform the electricity produced by Vattenfall and BASF’s 1.5 GW Hollandse Kust Zuid offshore wind farm which is expected to be fully operational in 2023..
The jacket left the fabrication yard end of May in the United Arab Emirates, where it was built. The 2,852-tonne structure was placed on the bottom of the North Sea by special lifting vessel Sleipnir of Heerema, on behalf of main contractor Petrofac. The jacket is 50 metres long, 34 metres wide and 44 metres high and is anchored to the seabed by six piles, each weighing 162.5 tonnes. The 57.7 metre long piles were drilled 46.5 metres into the seabed. The jacket was then attached to the piles.
The installation of the second jacket is an important milestone for TenneT. “The past year has been characterised by uncertainty and challenges due to the COVID pandemic. Not only for TenneT, but also for our contractors and suppliers. Nevertheless, together we succeeded in achieving this performance. We can be proud of that,” said Marco Kuijpers, TenneT’s Director Offshore Projects.
Hollandse Kust Zuid connection
The transformer platforms have a capacity of 700MW each. The first jacket for the Hollande Kust (zuid) wind farm was installed in the North Sea in September last year, also by Heerema’s Sleipnir. The topside for the Alpha station will be installed at the end of this year. The topside of the second jacket is expected to follow early next year. Once the topsides have been lifted onto the jacket, the last systems will be connected, tested and put into operation. The cables of the wind turbines will then be connected and the wind farm. The connection will be ready for use in 2022.
The platforms will be connected to shore with two 220kV alternating current export cables each. TenneT has built a new onshore transformer station onshore and is expanding the high-voltage ‘Maasvlakte 380kV’ substation. From this high-voltage substation, offshore wind energy will be fed into TenneT’s Randstad 380kV South ring. The wind energy goes to the electricity consumers in the country via the national high-voltage grid.
Connecting offshore wind energy up to 2023
The HKZ grid connection is part of TenneT’s 3.5 GW of offshore grid connections until 2023. With the completion of Borssele Alpha and Beta, the first 1.4 GW has been realised in 2020. This will be followed by HKZ Alpha and Beta and Hollandse Kust (Noord). TenneT uses the same type of 700 MW transformer platform here, located close to a wind farm, and the same type of 220kV cable connection to the coast.
Programme Net at Sea 2024-2030
According to the follow-up “Wind at Sea Roadmap”, a further 6.1 GW of offshore wind farms will be developed between 2024 and 2030. This concerns the wind farms in the wind energy areas Hollandse Kust (west) and Ten Noorden van de Waddeneilanden, TenneT is again using three standardised 700 MW platforms (2.1GW) for the first two areas. For the efficient connection of the wind energy areas further out in the North Sea, such as IJmuiden Ver (4GW), other techniques are needed based on direct current instead of alternating current. At least two offshore connections of 2 GW each will be developed for IJmuiden Ver. In addition, a third 2 GW connection is being studied for IJmuiden Ver, in parallel with the other IJmuiden Ver projects.