Danish energy company Dong Energy has signed a contract with Siemens Power Generation to extend the Horns Rev offshore windfarm by more than 200 MW. The contract is the largest order the company has ever received for offshore wind turbines.

Siemens will deliver and install its SWT-2.3-93 type units for the project, which will extend Horns Rev capacity to around 360 MW. The array, when it was built the largest in the world, has since been overtaken but will still rank among the largest in Europe. The contract marks a new phase for the Horns Rev development, the first stage of which hit technical difficulties in 2004.

“This order is … an important signal to the international market with regard to the expansion of Danish wind power capacity – both when it comes to positioning Denmark in the rapidly growing offshore wind power market and particularly for the global efforts to reduce CO2 emissions,” said Andreas Nauen, head of Siemens Wind Power Division.

The selection of Siemens for this project will disappoint Vestas, which supplied the offshore machines for the first phase of Horns Rev. In 2004 all these units were extensively overhauled owing to generator failures but are now fully operational.

The Danish government is planning to install 4000 MW of offshore wind turbines in its waters by 2030.

Installation of the 91 new turbines is expected to begin in early 2009, with startup slated for the end of 2009. The 2.3 MW units will be installed at water depths of 9-17 m.

Siemens’ contract also includes a service and maintenance agreement.

This is the sixth offshore wind farm Siemens will provide to Dong Energy. Siemens recently signed a contract with Dong for thirty 3.6 MW turbines for the Gunfleet Sands project off the British coast. This year, Siemens also completed the Burbo Bank offshore wind project with 25 turbines off the coast of Liverpool in the UK.

“With the signing of this contract, all major agreements concerning the Horns Rev II project are in place,” said Per Holmgaard, CEO of Dong Energy. “This means that we can now look forward to installation of Denmark’s largest offshore wind farm.”

The original Horns Rev wind farm was constructed in 2002 and was then the largest offshore wind farm in the world. It consisted of 80 Vestas V80-2.0 MW machines and was the first step in the Danish government’s plans to expand renewable energy generation.

The project at the time was pioneering but the equipment at the site suffered from the harsh North Sea conditions, which affected the units’ transformers and generators. In 2004 Vestas announced that it would dismantle all 80 of the V80 nacelles at Horns Rev for testing and upgrading.

Horns Rev I was installed by Elsam at a cost of DKK 2 billion and is now owned by Vattenfall (60 per cent) and Dong Energy (40 per cent).