BorWin3 grid connection is a 900MW high-voltage direct current (HVDC) offshore interconnection project located in the North Sea, approximately 130km off the coast of Borkum, Germany.

It is the third HVDC grid connection project by the German-Dutch transmission network operator TenneT to bring onshore the clean electricity from wind farms offshore Borkum, after BorWin1 and BorWin2.

The BorWin3 grid connection project involves 160km of transmission lines and two converter stations.

The engineering, procurement, construction, and installation (EPCI) contract for the project was awarded in 2014, while construction was started in 2015 with the laying of onshore cables.

Construction on the onshore converter station of the project was started in May 2016 and completed in the beginning of 2018. The laying of offshore cables and the installation of the offshore converter station were completed by October 2018.

The DC transmission between the offshore and onshore converter stations was successfully tested in February 2019.

Scheduled to commence commercial operations by the end of 2019, the BorWin3 grid connection is expected to supply clean offshore wind power to approximately one million German households.

Power supply for BorWin3 grid connection

The BorWin3 grid connection project will evacuate power from the under-construction 497MW EnBW Hohe See offshore wind farm and the 400MW Global Tech I offshore wind farm, which has been operational since 2015.

Equipped with 71 Siemens SWT-7.0-154 turbines, the Hohe See wind farm being developed by the German utility Energie Baden-Württemberg (EnBW) is scheduled for commissioning in 2019.

The Global Tech I offshore wind farm uses 80 AREVA M5000 wind turbines and is currently connected with the BorWin2 grid connection system, which will be reconnected with the BorWin3 grid connection system.

BorWin3 project details

The BorWin3 project comprises an offshore convertor platform named BorWin gamma, which is installed in 40m-deep waters to convert the alternating current (AC) produced by the wind turbines into direct current (DC).

The DC electricity from the BorWin gamma platform will be sent onshore through a 130km-long 320kV submarine cable connecting Hamswehrum, which is located to the west of Borkum.

The electricity from Hamswehrum will be further transmitted through a 30km-long underground cable to the converter station at Emden, for DC to AC conversion and connection to the German national grid.

Details of the BorWin gamma offshore platform

Installed on jacket foundation, the topside of the BorWin gamma offshore platform weighs approximately 18,500 tonnes (t) and houses a 900MW HVDC converter supplied by Siemens.

The topside of the platform was constructed and fabricated by Drydocks World in Dubai and was transported to the installation site in the North Sea by the heavy lift vessel Xiang He Kou in September 2018.

Contractors involved

Petrofac  in a consortium with Siemens was awarded the EPCI contract for the BorWin3 offshore platform in April 2014.

Petrofac was responsible for the construction and installation of the BorWin gamma offshore platform, while Siemens supplied the HVDC converter station on the platform.

Siemens also provided the project’s onshore converter station located at Emden.

Drydocks World was engaged for the construction and fabrication of the BorWin gamma platform topside, while Heerema Fabrication Group was contracted to construct the 6,000t jacket and 5,000t piles for the BorWin3 offshore platform in December 2015.

The Prysmian Group won a contract worth €250m ($345m) to supply and lay transmission cables the BorWin3 grid connection project in April 2014.

COSCO SHIPPING, in partnership with DNV GL's Noble Denton marine services, performed the transportation and installation of the BorWin gamma offshore platform.