Giant Wind Power Sockets Installed in the North Sea

A tremendous amount of offshore wind capacity—from 100 MW to 13,000 MW—is expected to play a major role in Germany’s transition to sourcing 80% of its power from renewables by 2050. However, Energiewende —the country’s energy transformation—has often been hampered by disruptions to the connection of offshore wind parks in the North Sea, stemming from delays in planning and building. This August, to the relief of grid operator TenneT, which bought the 11,000-kilometer-long grid network from E.ON in 2011 and has been tasked with connecting all wind parks in the North Sea, the infrastructure for connecting offshore wind farms has finally begun to take shape.

On Aug. 26, ABB installed the DolWind1 offshore wind connector platform—what it says is the “world’s highest-voltage offshore converter station” in the North Sea. The 320 kV station has an 800-MW power transmission capacity and will convert alternating current from three wind farms off the coast of Germany into high-voltage direct current (HVDC) for transmission to the mainland. And on the same day, Siemens Energy finished installing the 576-MW HVDC HelWin1 offshore platform, also in the North Sea, to link two offshore wind farms—Nordsee Ost and Meerwind—to the mainland (Figure 2).

The projects stem from separate contracts awarded in 2011 to the companies by TenneT: ABB received a $1 billion order, and Siemens a $710 million order. Siemens and Prysmian are also implementing a number of other connection projects: HelWin2 off of Helgoland, BorWin2 off of Borkum, and SylWin1 off of Sylt. For ABB, delays to DolWin1 led to charges of $50 million last year. The company is meanwhile readying the DolWin2, a 900-MW offshore connection, for commissioning in 2015.

The installation of both platforms was challenging. ABB says the 9,300 metric ton DolWin 1 platform, including the converter station, was transported offshore by barge 75 km around the German coast. Then it was lifted by the world’s largest crane vessel, Thialf, and positioned on top of the already installed jacket. “Putting such a huge platform in place is one of the most delicate operations in the delivery of an offshore transmission link, requiring strong cooperation between the many stakeholders involved” said Brice Koch, head of ABB’s Power Systems division.

For Siemens, transport of the HelWin1 platform took seven days, plus four additional days to install it 22 meters above sea level to protect it against giant waves. The 75-m by 50-m surface of the platform features a helipad, and it has seven decks to accommodate 16 cabins for crew members. Both projects are now expected to be fully commissioned in 2014.

2. A marine socket. When HelWin1, the first offshore converter platform in the North Sea goes online in 2014, it will link the offshore Nordsee Ost and Meerwind wind farms and convert power from up to 576 MW of capacity at offshore wind farms to direct current (DC) and transmit it via submarine cable to the German mainland about 85 kilometers (km) away. The DC power will then be converted back into alternating current at a converter station on land. The floating jack-up platform weighs about 11,000 tons and was towed around the northern tip of Denmark in a seven-day journey that covered 990 km. Courtesy: Siemens