Siemens received another order from the German-Dutch grid operator, TenneT TSO, for a grid connection for offshore wind power plants in the German waters of the North Sea.
The company will supply the entire technology for efficient direct-current transmission for the DolWin6 grid connection. Spanish partner, Dragados Offshore SA, is responsible for construction and offshore installation of the associated platform. French supplier Nexans will supply the direct-current cables. TenneT tendered the supply and laying of the cables separately, and these services are therefore not part of Siemens’ scope of supply.
The order placed with Siemens is valued in high three-digit millions euros range. After it is completed, DolWin6 will be able to transmit enough electricity to supply just under one million German homes. Commercial commissioning is scheduled for 2023.
Siemens will supply the entire technology for efficient high-voltage direct-current transmission (HVDC) and will use DC CS direct-current compact switchgear for the first time. The new gas-insulated switchgear for 320 kilovolts (kV) requires as much as 95% less space compared to the current air-insulated solutions. If they are used on an offshore platform, the size of the platform can thus be reduced by approximately 10%. As a result, Siemens is significantly helping to lower the cost of grid connections for offshore wind farms and thus to the cost parity of offshore wind energy in general. The switchgear is manufactured in Siemens’ switchgear factory in Berlin. Other components, such as HVDC transformers and converters for converting current, are produced in Siemens’ factories in Nuremberg. The offshore platform is being built by partner Dragados in Cadiz, Spain, and will then be transported to its installation site.
The DolWin6 grid connection, which is around 90km in length, can connect multiple offshore wind turbines to the mainland. A number of offshore wind farms are competing for a connection to DolWin6 in an auction held by the German Gederay Network Agency. The Gode Wind 3 project has already been awarded a contract, and additional offshore wind warms will bid on the coveted grid connection in the next round of the auction. The 155 kV alternating current supplied by the wind turbines will be converted into 320 kV direct current on the DolWin6 offshore platform and transported to Hilgenriedersiel on the mainland via a 45km subsea cable. On the ocean, the cable will pass underneath the island of Norderney by means of horizontal bore holes. Once on land, the electricity will be transported by another 45km underground cable to Emden, East Frisia, where Siemens is building another converter station for converting the direct current back into three-phase current and feeding it into the high voltage grid.
“This makes Siemens the technology partner in six out of 10 DC projects. After BorWin3 and DolWin6 are commissioned, approximately 4.7GW of electrical power will be converted and transmitted to shore using Siemens technology alone. This is enough to supply just under five million homes,” says Ralf Christian, CEO of Siemens’ Energy Management Division.
Siemens is now implementing a total of six out of 10 DC North Sea grid connections for TenneT. The earlier projects were HelWin1 (576MW) and HelWin2 (690MW) off the coast of Helgoland, BorWin2 (800MW) off the coast of Borkum and SylWin1 (864MW) off the coast of Sylt. These grid connections have been placed into service successively since 2015; the BorWin3 (900MW) and DolWin6 (900MW) are currently being executed. The grid connections equipped with Siemens technology now have a total transmission power of 4.7 GW.
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