World's largest offshore wind farm opens for business

By James Holloway

Walney wind farm off the coast of Cumbria in the UK yesterday became the world’s largest offshore wind facility. One hundred and two turbines over 73 sq km (28 sq miles) provide a maximum output of 367.2 MW. It’s claimed the facility will provide enough power for about 320,000 homes – half as many again as the total number in Cumbria.

The project’s first phase, Walney 1, has been providing power since January 2011 from 51 137-meter-high (450-ft) turbines, each with a 107-m (350-ft) rotor diameter. The completed second phase, Walney 2, adds another 51 turbines of even greater size to the installation. These 150-m (492-ft) tall turbines have three 18-tonne (19.8-short ton) blades with a total diameter of 120 m (394 ft). Despite the differing dimensions, all turbines are Siemens-made 3.6 MW turbines. All told a single wind turbine weighs a hefty 550 tonnes (606 short tons). The Walney 2 installation was completed in an impressively tight six-month window.

The turbine specs appear well-suited to the UK’s considerable wind assets, functioning at wind speeds between 4 and 25 m/s (9 and 56 mph), operating at a peak in winds of 14 m/s (31 mph), with mean wind speeds for the area thought to be just over 9 m/s (20 mph) at the critical altitude.

The above map shows the Walney wind farm’s position in the Irish Sea. The distance of the turbines to the coast varies between 14.4 and 25.8 km (9 and 16 miles) – a significant distance that helps to reduce the visual impact of the scheme. The blue and red lines indicate the export cables for Walney 1 and 2 respectively.

The facility makes use of offshore substations, stepping up the voltage from 34 kV to 132 kV. This is good news for the environment as transmission at higher voltage minimizes losses, and so reduces the need for inefficient lower-voltage transmission to an onshore substation.

The facility has been built by a company called Walney (UK) Offshore Windfarms Limited, a joint enterprise with DONG Energy and SSE as the major stakeholders. DONG is also the major stakeholder in the even larger London Array wind farm. It is not clear when this 1000 MW wind farm will be complete, though phase 1 should be making a maximum capacity of 630 MW available before the end of the year. Walney, therefore, will not hold the top spot for long. DONG will surely try to improve upon the construction of the Walney facility, phase 2 of which (according to the UK’s Guardian newspaper) DONG claims was the fastest wind farm construction of its type.


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