Thanet Offshore Windfarm Case Study

First pioneered on this project was Subocean’s cable plough-equipped DP2 vessel, the Polar Prince, to install cables under the seabed. The innovative modification of the main deep water array cable installation vessel has reduced cable installation time by 50% and significantly reduced operational activity.

The Thanet project, which comprises 100 Vestas V90 wind turbines, is located in a challenging environment spanning an area of 35km² with water depths of 20-25 metres.

Conditions were particularly difficult because there are large areas of chalk seabed and one of the biggest challenges was to achieve the required depth of burial in what is essentially a hard chalk rock formation. The only way this can be reliably achieved is with the use of the subsea cable plough.

Subocean successfully installed 15 power cables one metre under the seabed in 30 metres of water using the Polar Prince. The cables were each installed within 30 hours which, compared with conventional methods, represents a substantial timescale reduction for both operational activity and exposure to adverse weather conditions.

The Polar Prince’s capabilities are significantly more advanced than conventional barges because it does not require anchors to be run while manoeuvring the vessel is significantly quicker. Traditional barge methods take up to two days to lay and bury one cable. Subocean has saved a day’s operational activity for one cable which is exceptional particularly when put into full project perspective - the Thanet project alone involves installing 100 array cables in total.

The Polar Prince also withstands hostile weather conditions. During the cable installation on Thanet, the Polar Prince remained on site during winds of up to 60 knots when all other vessels retreated to the port for shelter.

Subocean chartered the Polar Prince, a DP2 subsea support vessel, in what represented a £35 million investment for the company. The vessel was installed with Subocean cable laying and burial equipment including tensioners, haulers, cable tank and cable plough spreads.

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Vattenfall acquired the Thanet Offshore Wind Farm project in November 2008. On completion the wind farm will comprise 100 Vestas V90 wind turbines and have a total capacity of 300 MW. This is sufficient to supply approximately 240,000 homes per year with clean energy.

It will be the largest operational offshore wind farm anywhere in the world and will make a significant contribution to the Government’s national and regional renewable energy targets.

The Thanet project is located approximately 12 km off Foreness Point, the most eastern part of Kent. The development work is due for completion during 2010. Some elements of the onshore construction work commenced at the former Richborough power station in January 2008 where the onshore substation is being built.

Vattenfall is one of the biggest wind power operators in Britain and is the fifth largest energy producer in Europe. The Kentish Flats wind farm off Herne Bay/Whitstable, Kent is also owned by Vattenfall.