Wind power gains

The HelWin2 converter platform being transported.

More than 3.8GW of offshore wind transmission capacity is being installed by TenneT offshore northern Europe. Meg Chesshyre found out more.

Siemens is making good progress on the five offshore high-voltage direct current (HVDC) grid connections it is installing for the German-Dutch network operator TenneT. The grid connections have a total transmission capacity of more than 3.8 GW. In June, the 10,500-ton HelWin2 converter platform topside was loaded out from Heerema Fabrication Group’s fabrication yard at Zwijndrecht, in the Netherlands.

The topside was installed last month (July), 85km offshore Heligoland, in the German Bight on a 4500-ton jacket, built by Heerema Vlissingen. The installation was be carried out by Heerema Marine Contractors’ derrick barge Thialf. HelWin2 is an unmanned platform with a transmission capacity of 690MW, bridge-linked to HelWin1 (576MW), which was installed in August 2013. HelWin1 should be operational later this year, with HelWin2 following 1H 2015.

The HelWin2 transmission link will connect the offshore wind farm Amrumbank West, located in the HelWin cluster, to the German grid at the Büttel substation. There is capacity on the converter platform for further tie-backs. HelWin1 will convert input from the Meerwind Süd/Ost and Nordsee Ost wind farms, which are currently under construction.

Earlier this year Siemens installed the 12,000-ton BorWin2 (800 MW) offshore converter platform, 130 km off Borkum, built by Nordic Yards at its shipyard in Warnermünde, in Germany. Siemens is in a consortium here with Italian cable specialist Prysmian. This should also be on line in 1H 2015, as will SylWin1 (864MW), also built by Nordic, to be installed 160km off Sylt this summer. The projected windfarms in the BorWin wind farm cluster are: Albatros 1, BARD Offshore 1, Deutsche Bucht, Global Tech 1, and Veja Mate. For Sylwin, the wind farms are Butendiek, Dan Tysk, and Sandbank.

The most recent order has been for BorWin3 (900MW), due to begin commercial operation in 2019, where Siemens is in a consortium with Petrofac. This is still in the engineering phase. Meanwhile, TenneT is mulling bids for BorWin4 (900MW) with a contract award due shortly.

TenneT is also tying in DolWin1, 2, 3 cluster, 165km off Dollard Bay. DolWin1 was also built by HFG, for client ABB, with Heerema Zwijndrecht supplying the topsides, and Heerema Vlissingen the jacket. Commissioning is ongoing. The DolWin2 platform was built in Dubai. The sailaway was June 10. The projected wind farms in the DolWin cluster are: Borkum Riffgrund1, Borkum Riffgrund2, Gode Wind1, Gode Wind2, MEG Offshore1, Nordsee One, and Trianel Windpark Borkum.

Power cables in the HelWin2 platform. Photos from Siemens.

The converter technology used by Siemens is called HVDC Plus. This is a voltage-sourced converter of the modular multi-level converter type. By contract with the conventional HVDC version, which can only be used in networks with sufficient short-circuit capacity, systems using HVDC Plus make it possible to start up island networks from scratch, an important prerequisite for operation offshore.

The converter room on HelWin2.

HVDC technology enables the alternating current generated by the wind farms to be converted to low loss direct current. Siemens says transmission losses per link are less than 3%, not including cable losses. First a number of transformer platforms arranged around the wind farm transform the alternating current before it is converted into direct current on an HVDC platform. It is transported to land via a submarine cable and then converted back into alternating current for onward transmission. HVDC technology is usually used when transmission cable lengths reach 80km or longer.

The HVDC transmission market is expected to double within the next five years from a current €2.5 billion. In the last 40 years, “Orders for HVDC lines with a total capacity of 250 gigawatts (GW) are anticipated for this decade,” commented Tim Dawidowsky, CEO Business Unit Transmission Solutions, Power Transmission Division, Siemens Energy Sector. “This is an enormous boom when you consider that a total of only 100 gigawatts was installed over the last 40 years.” Siemens, as one of the biggest suppliers in the HVDC transmission sector has completed about 50 HVDC transmission projects worldwide, one quarter of which were in China.

Dawidowsky added that offshore wind was still a young industry with potential for standardization and cost reduction through mass production. Siemens itself is eyeing a target of cost reduction of between 30-40% by 2020, which would equate to a reduction to 10 euro cents per kilowatt hour by 2020. It was looking at solutions that could lead to a dramatic 95% reduction of the space requirement for converter platforms from >4000cu m to 200cu m, the first milestone being DC compact switchgear for 320kV.

“We feel confident that with the political frame being set not only in Germany, but also in the UK, the biggest market in Europe moving forward, offshore wind has a future. We would like to be part of that. We have to contribute on cost reduction. We are ready for that,” Dawidowsky concluded.