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Kentish Flats Offshore Wind Farm
8-10km offshore from Whitstable, Kent, UK
associated engineer
Not known
date  August 2004 - September 2005
era  Modern  |  category  Power Generation  |  reference  TR145780
The array of 30 wind turbines located off the north Kentish coast on a sandbank plateau is know as Kentish Flats Offshore Wind Farm. At completion, it was the largest wind farm in the UK, and was the joint-largest offshore facility in the country until the completion of the London Array, also in the Thames Estuary, in 2013.
The £105m scheme was built by Vestas and is now owned and operated by Vattenfall, and is managed from Esbjerg, Denmark. It has a design life of 20 years, over which time it is estimated to save some 4.4 million tonnes of carbon dioxide emissions compared with burning fossil fuels.
The site covers an area of 1,000 hectares on a plateau of sandbanks. The seabed is generally 0.5m of silt and sand overlaying 10-12m of London clay. The wind turbines are arranged east-west in five rows of six turbines, at 700m spacing. Each of the Vestas V90 turbines has an output of 3MW, giving a total 90MW capacity.
The turbines were positioned using GPS. They are founded on monopiles 4.5m in diameter and 38-44m long, driven 28-34m into the seabed from a purpose-built jack-up barge working in 5-8m depth of water. The piles are formed from steel plate 45mm thick.
A transition piece caps the top of each monopile with a landing and maintenance platform. This enables the mast to be mounted vertically, even if the monopile is not vertical. The mast is pre-fitted with ladders, lifts, power cables and lighting. The turbine hubs stand 70m above mean sea level. The nacelle, hub and two rotor blades are assembled onshore and brought to site to be lifted to the top of the mast. The last operation is to fit the third rotor blade on to the hub.
Mean wind speed at the turbine hub is 8.7m per second. The blades begin to turn at 4m per second, have full power output from 14m per second and stop operating at wind speeds over 25m per second.
The rotor diameter is 90m and each of the three rotor blades attached to the hub is 22.5m long and weighs 6.6 tonnes. Each wind turbine weighs between 487 and 532 tonnes, of which the mast weighs 108 tonnes, the nacelle 68 tonnes and the rotor 39.8 tonnes.
The transmission line from offshore to onshore has three buried cables, comprising copper conductors and fibre optics, which were installed before the turbines. The wind turbines generate power at 33kV, which is transformed up to 132kV at a sub-station at Herne Bay and then fed into the UK's National Grid.
Piling began in August 2004 and turbine erection in June 2005. Commissioning was completed in September 2005.
Monopile installation: MT Højgaard
Turbine supply: Vestas
Research: ECPK
bibliography
www.4coffshore.com
www.kentishflats.co.uk
www.nce.co.uk
www.northsealogistics.co.uk
www.vattenfall.com
Location

Kentish Flats Offshore Wind Farm