Hollandse Kust (south) Alpha topside installed in the North Sea

The offshore transformer station of the Alpha platform of Hollandse Kust (south) has been successfully installed on the substructure in the North Sea. The station is located some 20 kilometres off the coast of The Hague. The transformer station - also called topside - is one of the two topsides of the Grid at sea Hollandse Kust (south). This grid will connect the offshore wind area of the same name with the Dutch high-voltage grid on the mainland.

The Netherlands is deploying offshore wind farms on a large scale. To generate electricity from these offshore wind farms, a so-called 'grid at sea' is needed. Grid at sea consists of several subgrids:

Grid at sea electricity network transports electricity from the wind farms to the high-voltage grid on land. The 'grid at sea' consists of a platform, sea cables, land cables and a converter station. From Net op zee Hollandse Kust (south), the converter station has now been placed in the North Sea.

Marco Kuijpers, director Large Projects Offshore: "With the installation of the Alpha topside, the Grid at Sea that TenneT is realising in the North Sea is taking more and more shape. Hollandse Kust (south) Alpha is the first connection from an offshore wind farm to the Maasvlakte, with a capacity of 700 MW. Wind energy plays a crucial role in the energy transition, including in industry, and I am proud that TenneT can contribute to a sustainable future in this way."

The Grid at sea will be equipped with two transformer stations: Alpha and Beta. These High Voltage Alternating Current (HVAC) transformer stations were designed by contractor Petrofac last year at the Drydocks World yard in Dubai. The weighing and loading of the 3,830-tonne Alpha topside onto the transport ship Tai An Kou was handled in November by Mammoet, which specialises in heavy transport and lifting. From Dubai, the Tai An Kou sailed to the Alexiahaven on the Maasvlakte in a month. Here, the ship arrived on Tuesday 21 December.

At Alexiahaven, the Alpha topside of the transport vessel was loaded onto the multi-purpose platform installation and removal vessel Pioneering Spirit of offshore company Allseas. This vessel then sailed out to the installation site in the North Sea. After completion of preparatory work, the Alpha topside was placed by Pioneering Spirit on the substructure structure, which is called a jacket.

"It is great to be involved in an energy project with such strategic importance for the Netherlands," says Edward Heerema, President and CEO of Allseas. "Pioneering Spirit has made a name for itself in recent years with pioneering lifts in the oil and gas industry. The successful installation of the Alpha topside demonstrates the vessel's versatility and our added value in the energy transition."

Sami Iskander, Petrofac Group chief executive, adds: "The safe installation of the Alpha topside is a significant milestone in the delivery of this important energy transition project. All those involved should be proud of this achievement. Petrofac has made its mark in offshore wind energy over the past decade. This is reflected in the competence of our engineers and the quality of our products. We are working closely with our partners on the delivery of the Beta topside and a successful grid connection."

Grid at sea will be equipped with two topsides: Alpha and Beta. The Beta topside has a capacity of 700 MW as well. It is expected to be installed in the first quarter of 2022. The Hollandse Kust (south) wind area being realised by Vattenfall should be fully operational by 2023. The energy production of this area should be equivalent to the energy consumption of around two million households.

Beta topside - also with a capacity of 700 MW - is expected to follow in the first quarter of next year. When fully operational in 2023, the Hollandse Kust (south) wind farm to be built by wind farm developer Vattenfall will generate an amount of green electricity equivalent to the annual consumption of more than two million households.

Author: Wouter Hoeffnagel