DolWin4 (NOR-3-2) and BorWin4 (NOR-6-3) are High Voltage Direct Current (HVDC) offshore grid connection systems being developed in Germany.
Both projects are being owned and developed by Amprion Offshore, a subsidiary of German transmission system operator Amprion.
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Construction works commenced in July 2022. DolWin4 is scheduled to start operations in 2028, while BorWin4 will become onstream in 2029.
DolWin4 and BorWin4 will be used to transport offshore wind energy from the North Sea to Lingen in southern Emsland, Germany.
The combined transmitted capacity of both grid integration systems is 1.8GW. This is equivalent to the energy demand of Hamburg with a population of 1.8 million.
Background
In March 2021, Amprion submitted the public planning procedure documents to the Federal Maritime and Hydrographic Agency (BSH) for the Exclusive Economic Zone (EEZ) section of both the offshore grid connection systems.
Amprion started the bidding process for the converter platforms and cables for DolWin4 and BorWin4 in the same year.
In April 2022, Amprion commenced the planning approval procedure for DolWin4 in the EEZ of the North Sea.
The company used Hanekenfähr substation to connect the Emsland nuclear power plant to the transmission network. The power plant was shut down in 2023, freeing 1.4GW of service capacities at this grid node.
Once complete, DolWin4 and BorWin4 are expected to replace the generation capacity.
The first components for the DolWin delta converter platform were completed in October 2024.
DolWin4 and BorWin4 Route
The offshore HVDC converter platforms will be located in the German sector of the North Sea to connect wind farms in Area 3 (DolWin4) and Area 6 (BorWin4).
BorWin4 will have a total route length of around 280km, of which around 125km will be at sea. On the other hand, 215km long DolWin4 will have a 60km offshore section.
The two connection systems will run parallelly on land and for the majority of their route at sea. They will pass under the island of Norderney through to the coastal area of Hilgenriedersiel towards Hanekenfähr substation.
DolWin4 and BorWin4 Development
The DolWin4 and BorWin4 offshore grid connection systems will comprise two standalone offshore converter platforms.
The structures will feature topsides weighing approximately 11,930 tonnes each. They are supported by 7,000-tonne (DW4) and 8,000-tonne (BW4) jackets at water depth of 30.8m and 38.8m, respectively.
The offshore converter platforms will receive alternating current (AC) power from several wind farms in the German North Sea.
The wind farms will be connected to the offshore platforms by 66kV direct connection systems.
The AC power will be converted into 320kV direct current (DC) by the converter platforms and then transmitted onshore via 320kV HVDC submarine cables.
The submarine cables will reach Hilgenriedersiel coast after crossing the island of Norderney from below.
From the coast, the cables will run further to two HVDC onshore substations, which will convert DC electricity back to AC for transmission to the German transmission network.
The onshore substations will be connected to the Hilgenberg switchgear and the 380kV link which will be developed to the grid access point at Hanekenfähr for transmission to the grid.
Both HVDC substations will convert DC back into AC and transmit it to the German transmission network via Hanekenfähr substation.
Contractors Involved
In July 2022, Dragados Offshore, in consortium with Siemens Energy, received a contract to develop the HVDC grid connection platforms of DolWin4 and BorWin4.
Dragados will deliver the two offshore platforms including the jackets and topsides. The scope of works includes design, engineering, procurement, construction, transportation, installation, and commissioning of the platform systems.
Construction will be carried out at the company’s yard in Cádiz, Spain.
Siemens Energy will be responsible for the HVDC system and the onshore HVDC substations. It will also be in charge of the complete maintenance of the converter solutions for an initial period of ten years.
With an order value in the high three-digit million-euro range, the contract represents the largest offshore grid connection order for Siemens Energy.
Dragados and Siemens consortium awarded Meyer Werft, a German shipbuilding company, a contract to produce parts of the converter platforms.
On behalf of Siemens, Convex ZT will construct, execute, and design the onshore converter stations including receiving construction permit.
TÜV SÜD Industrie Service, a German subsidiary of UK-based sustainable solutions provider TÜV SÜD, has been selected as the owner’s engineer for DolWin4 and BorWin4. The scope of the contract includes supervision of the fabrication and assembly of the components at various sites as well as monitoring the assembly and commissioning of the platforms.
German civil engineering firm SETREO serves as the logistics partner for the systems.
SETREO will survey heavy transport routes for 155km of underground cables, prepare concepts and feasibility studies for logistics, and provide consulting with VEMAGS test applications.
Dutch offshore pipelay and subsea construction company Allseas will transport and install topsides and jackets.
Allseas will also perform jacket cut-off and Remotely Operated Vehicle (ROV) debris survey for the projects.
In September 2022, Amprion awarded a more than €800m contract to energy and telecom cable systems industry solutions provider Prysmian. Under the contract, Prysmian will supply approximately 1,000km of HVDC ±320 kV single core XLPE copper cables.
The offshore cables will be produced in Pikkala, Finland and Arco Felice, Italy. The onshore cables will be developed in Gron, France and Abbeville, the US.
SD Engineering, part of Socotec group, is providing advisory and Building Information Modelling (BIM) project management services for the projects since 2021.
VBW Weigt, a subsidiary of GEOS, provided geophysical and geotechnical exploration for approximately 180km corridor, as part of the exploration of the cable routes of the offshore grid connection systems.
