Dutch transmission system operator TenneT has awarded contracts for the 900MW BorWin5 offshore grid connection system to the consortium of Siemens and Dragados Offshore, as well as Danish industrial group NKT.

The consortium of Siemens and Dragados Offshore has won a contract to build onshore and offshore converter stations. Meanwhile, NKT HV Cables has been awarded a contract for the direct current underground and submarine cables for the offshore grid connection system.

TenneT COO Tim Meyerjürgens said: “With regard to our latest offshore project, we are delighted to not only award the contract to Siemens and Dragados, two companies that are both proven and innovative in the construction of converters, but also to NKT, another powerful supplier in the market for plastic-insulated direct current cables.”

BorWin5 is the 12th direct current connection and the 15th offshore grid connection system implemented by TenneT in the German North Sea.

Meyerjürgens added: “With the award of BorWin5, we are proceeding with the continuous cost reduction in the construction of offshore grid connection systems. Compared to the predecessor project DolWin5, we were again able to achieve a significant cost reduction for the converter stations.

“One reason is that for BorWin5 the smart platform concept is being used for the first time. This not only keeps the costs for the platform construction manageable but also allows us to extend the intervals for maintenance and servicing to once a year.”

BorWin5 is the second project following DolWin5 that has wind turbines directly linked to the BorWin Epsilon offshore platform through 66kV three-phase power cables. This subsequently removes the need for transformer stations usually required in wind farms.

Moreover, three-phase 155kV current cables are not required to link the TenneT offshore platform with the wind farm.

Following conversion, TenneT will use a 230km-long high-voltage direct current cable to transmit power to the Garrel/East converter station on land, through low-loss direct current technology. In this case, the direct current is transformed back into three-phase alternating current and then fed into the extra-high voltage grid.

The company says BorWin5 is a new generation, cost-efficient offshore grid connection.

After the first three BorWin projects, BorWin5 is the fourth offshore grid connection that TenneT has installed off the coast of Borkum using high-voltage direct current transmission technology.

With a 900MW transmission capacity, BorWin5 will connect the wind farm EnBW He Dreiht with the German transmission grid.

TenneT expects to commission BorWin5 in 2025. Once online, this offshore grid connection system will allow the He Dreiht wind farm to power more than 1.1 million households.