Siemens has completed installation of a fourth high-voltage direct current (HVDC) offshore platform in the North Sea, marking a step ahead for grid connections of sea-based wind farms.

Prior to the installation of the 864MW SylWin1 alpha converter platform, Siemens has completed the 690MW HelWin2 converter station near the German island of Heligoland, also in the North Sea.

Siemens is currently under a contract to implement a total of five North Sea grid connection projects for European electricity transmission system operator TenneT.

Located approximately 70km to the west of the island of Sylt, the 864MW SylWin1 platform will convert alternating currents coming from the Dan Tysk, Butendiek and Sandbank offshore wind farms into direct current.

The direct current will be transported to land through a 205km-long subsea cable.

The first four grid connections are due to take up commercial operation successively between the second half of 2014 and the first half of 2015 while the fifth grid connection is expected to go on-line in 2019.

Siemens AG Power Transmission and Smart Grid Divisions CEO Jan Mrosik said: “Once they have been commissioned, these grid connections will supply electricity from offshore wind power for around three million households.”

TenneT Germany offshore director Wilfried Breuer said: “In the past few days, we have erected two platforms in quick succession that will provide approximately 1.5GW of additional capacity for feeding offshore wind energy into the onshore transmission grid.

“The German Government has decided to increase the transmission capacity for offshore wind energy by 6.5GW in the period until 2020. In 2015, two-thirds of that target will already have been achieved.”