Dong Energy is to construct the 660MW Walney 3 offshore wind farm after making a final investment decision in the Round 2.5 wind farm off northwest England.

The wind farm is an extension of the existing 367MW Walney 1 and Walney 2 wind farms, which Dong Energy owns a 50.1% stake.

The Danish company said it has secured all necessary consents from authorities and has signed the majority of contracts to supply and build the project, which will be the world’s biggest offshore wind farm once complete.

The project will boast two different turbines in two phases: 40 8MW turbines from MHI Vestas Offshore Wind and 47 Siemens 7MW offshore turbines.

Siemens has confirmed the order is the first for its new 7MW machine, each which will have a rotor diameter of 154 meters.

Walney 3 is expected to be fully commissioned in 2018 and will be constructed and operated under the UK’s FID-enabling regime with a fixed price for the first 15 years of production.

Dong executive vice president Samuel Leupold said:

“Walney Extension will deliver clean electricity to more than 460,000 UK homes and I’m very pleased that we can now start construction of what will be the world’s biggest offshore wind farm when completed. Building this offshore wind farm will bring us significantly closer to realising our strategy of having 6.5GW of installed capacity online by 2020.”

Then Siemens offshore chief executive Michael Hannibal added:

“This marks the first order for the innovative Siemens 7MW wind turbine. We introduced this upgraded version of our proven 6MW model into the market only last March, and today we are proud to announce that Dong has chosen our new flagship offshore turbine. Our 7MW turbine will leverage the energy output of the Walney 3 East offshore wind farm and contribute significantly to lowering the cost of offshore wind power.”