Jacket for Hollandse Kust (zuid) Alpha platform installed

08.09.2020

The offshore wind area Hollandse Kust (zuid) is located 22 kilometres off the coast of the Dutch province of Zuid-Holland. The Dutch-German transmission system operator (TSO) TenneT will connect the wind farms in this area to the onshore substation in the industrial and port area of Maasvlakte via two offshore platforms – Alpha and Beta – and submarine cables. The jacket for the Hollandse Kust (zuid) Alpha platform was transported to the operation site by a heavy-duty vessel on 5 September and successfully installed on the seabed. The Alpha jacket is 29 meters long, 20 meters wide, 46 meters high and weighs 3200 tonnes. It will be further installed in the coming days.

The two 220kv submarine cables will be connected to the jacket over the next few months. In 2021, the platform top side will be placed on the jacket. The Hollandse Kust (zuid) Alpha platform is expected to be operational by the end of 2021. The projects in this new wind area are part of the large-scale offshore expansion programme of TenneT. By the end of 2023, the TSCNET shareholder will have installed 3.5GW of offshore grid connections in the Netherlands, of which the first 1.4GW have already been achieved with Borssele Alpha and Beta. The connection to follow Hollandse Kust (south) will be Hollandse Kust (nord). For all the wind farms in these two areas, TenneT will deploy five identical 700MW transformer platforms and identical 220kV cable connections. “Such standardisation enables TenneT to complete these projects more efficiently, more quickly, and more economically,” explains TenneT COO Tim Meyerjürgens.

The Dutch national roadmap for offshore development provides for an additional 6.1GW of offshore wind farms in the wind energy areas Hollandse Kust (West), Ten Noorden van de Waddeneilanden, and IJmuiden Ver from 2024 to the end of 2030. For the first two areas, TenneT will again use standardised 700MW offshore platforms. The efficient connection of IJmuiden Ver, which is located further out in the North Sea, partly requires other technologies based on DC instead of AC. IJmuiden Ver will have two offshore transformer platforms with a capacity of 2GW each, which is unique in the offshore wind industry.

TenneT has installed the jacket for the Hollandse Kust (zuid) Alpha platform (picture: TenneT)

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Deep Dig-It trencher at work for TenneT

09.03.2020

The Hollandse Kust (South) offshore wind area in the Dutch North Sea is located 22 kilometres off the coast of the Dutch province of Zuid-Holland. TSCNET shareholder TenneT is responsible for connecting the wind farms under construction there via two corresponding offshore platforms to the onshore high-voltage substation in the industry and port area of Maasvlakte, from where the green electricity is transmitted further to the Randstad 380kV South Ring power line in the Dutch Randstad region, the most densely populated area in Europe, and further.

But there is a major challenge to be met by the Dutch-German transmission system operator (TSO): On the first ten kilometres of the offshore route, the four submarine cables to be laid are crossing the entrance to Europe’s busiest cargo port, the port of Rotterdam. To pass through the busy Rotterdam-Maasmond shipping lane, the cables here must be buried more than 5 metres deep into the seabed. For this specific job, the Dutch maritime contracting company Van Oord designed and built the Deep Dig-It trencher, a gigantic remote-controlled trencher.

Last Friday, final tests were carried out in the Aleksiahaven of Maasvlakte in preparation for the actual laying of the submarine cables in July. The innovative device is a so-called Tracked Remotely Operated Vehicle, which drives unmanned over the seabed, creates a deep trench for the cables, inserts the cables and closes the trench again. The Deep Dig-It is the largest and most powerful machine in its class. The trencher weighs 125 tonnes, is more than 17 metres long, well over 8 metres high and 11 metres wide. This makes it possible to bury cables in very hard ground, while the burial depth that can be achieved with the Deep Dig-It is well over 5 metres.

TenneT employs the powerful Deep Dig-It trencher to connect the Hollandse Kust (South) wind farms to the onshore grid (picture: Van Oord nv)

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