Building an offshore wind farm

Building and operating an offshore wind farm in a harsh sea environment is no easy task presenting many challenges related to scale, water depth and distance from shore.

The pace of technological advancement and innovation in the wind industry has been rapid over the past decade. The scale and power of machines is increasing helping to bring new efficiencies and reduced costs. Already 5-10MW machines with rotor diameters over 150 metres are coming onto the market.

From top to bottom, the main parts of an offshore wind turbine are the nacelle (housing the rotor, drivetrain and generator); the blades; the tower; the transition piece; the support structure/foundation.

Installing an offshore wind turbine to date has typically involved driving a foundation monopile into the seabed. Erosion protection similar to sea defences is then placed around the base to prevent damage. A transition piece is fitted at the top of the foundation painted a bright colour to make it visible to ships and with an access platform to allow maintenance vessels to dock and transfer personnel. The tower, nacelle and blades are built up from the foundation using a jack up vessel with a large crane facility.

As larger turbines are brought forward and projects move into deeper waters different types of foundation and support structures will be needed. This could include gravity base, tripod, tripile and floating designs.

Once turbine assembly is complete, sensors on the turbine detect the wind direction and turn the nacelle and blades to face into the wind so that they collect the maximum amount of energy. The movement of the wind over the aerodynamically shaped blades makes them rotate around a horizontal hub, which is connected to a shaft inside the nacelle. This shaft, via a gearbox, powers a generator to convert the energy into electricity. Some manufacturers have moved away from gearboxes to direct drive systems reducing the number of parts and weight of components within the nacelle.

Subsea cables are laid to take the electricity generated by the turbines to an offshore substation where it is boosted to a higher voltage to reduce transmission losses. An export cable runs from the offshore substation to an onshore substation where the power is fed into the National Grid. The electricity is then carried through the grid and local networks into homes, businesses and industry.

Operation and maintenance is carried out from bases located at ports near to projects. Turbine performance and diagnostic checks can be remotely managed from these bases. Regular maintenance and servicing is carried out by crews who travel out to the wind farms via fast catamaran vessels. In the future projects further from shore and in deeper waters are likely to be serviced by larger vessels anchored close to the wind farm for several weeks at a time.

For more information about developing an offshore wind farm and to understand more about the requirements of the industry, a helpful guide has been published by the Crown Estate – please click here to access the guide.

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