The Sandbank offshore windfarm features 72 Siemens SWT-4.0-130 turbines. Image: courtesy of
ABB installed the subsea link connecting the Sandbank offshore windfarm to the SylWin alpha platform.
The SylWin1 converter platform was built by Siemens and is 83m-long. Image: courtesy of

The Sandbank offshore windfarm is located 90km west of the island of Sylt in an exclusive economic zone off the German North Sea coast. Developed by a joint venture of Vattenfall and Stadtwerke München (SWM, Munich city utility), the windfarm is built in 25m to 37m-deep waters located north-west of the existing DanTysk windfarm, which was also developed by the same joint venture.

The new windfarm has a gross installed capacity of 288MW and produces up to 1.4TWh per year, enough to power approximately 400,000 households and cut down carbon emissions by 1.5 million tonnes a year.

Vattenfall owns 51% and has invested SWK5.6bn ($818m) in the €1.2bn (approximately $1.4bn) project. Construction began on the windfarm in June 2015 and the first wind turbine was installed in July 2016. The windfarm was commissioned in January 2017, while operations started in July 2017.

Sandbank offshore windfarm equipment

The 400MW Borkum West II wind farm is being built 45km offshore the Borkum island in the North Sea, Germany.

The offshore windfarm features 72 Siemens SWT-4.0-130 turbines rated 4MW each, with a blade length of 63m. The turbines are based on monopile foundations.

The SWT-4.0-130 turbines have a rotor diameter of 130m and height of 158m to the blade tip from the sea level. The large rotor diameter enables efficient operation of the turbine even at low to moderate wind speeds. The blades are made of aeroelastic material, which helps to reduce their mass by up to 20%.

A specially designed service operation vessel (SOV), featuring accommodation facilities and a workshop with spare parts is placed between the DanTysk and Sandbank windfarms. Service crew will be able to ferry between land, the service vessel and turbines on-board a helicopter. The project’s maintenance costs are expected to be minimal due to a common joint operations base for the two windfarms.

Power transmission from Sandbank windfarm

The power generated by the windfarm is transmitted to the high-voltage direct current (HVDC) converter station SylWin alpha by an alternating current (AC) power transmission link.

The 864MW SylWin1 platform built by Siemens transmits the windpower generated by three offshore windfarms DanTysk, Butendiek, and Sandbank. The 56m-wide and 26m-high platform started commercial operations in April 2015.

Contractors involved with the German North Sea wind project

“Two 36km-long, three-core AC submarine cables of 155kV are used for the connecting the windfarm to the project.”

Siemens was awarded the contract to supply 72 turbines for the windfarm in August 2014. The contractual scope also includes maintenance services for the first five years of operation.

ABB was awarded a turnkey contract by TenneT in October 2013 for the design, engineering, supply and installation of the transmission link, which includes a subsea alternate current (AC) cable system and two shunt reactors to absorb reactive power and increase energy efficiency. Two 36km-long and three-core AC submarine cables of 155kV are used for the connection.

In August 2014, Visser & Smit Marine Contracting (VSMC) was awarded a contract worth €90m ($120m), which includes the supply of cables, CPS, installation, post-lay burial, and termination and testing of 76 infield cables. The work began in 2015 and was completed in 2016.

Rambøll was contracted for designing the monopiles, whereas EEW Special Pipe Constructions was contracted for the production of the monopiles and the transition pieces. The transition pieces were, however, produced by Bladt under a subcontract. Bladt Industries was also responsible for the construction of the offshore substation.

Bilfinger Construction was responsible for the installation of the turbine towers. Work began in mid-2015 and was completed in February 2016. The turbine installation vessel was provided by MPI Contractors.

Bladt Industries subcontracted Seaway Heavy Lifting in December 2014 to provide transportation and installation services for the Sandbank substation.

NRI Energy Technology