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Onshore/ Offshore Wind: How It Works

Turbines catch the wind’s energy using propeller-like blades (usually three blades), which are mounted on a shaft to form a rotor. The blades use aerodynamic forces (‘lift’ and ‘drag’), in a similar fashion to an aeroplane wing, to produce mechanical power. This power rotates the blades and the shaft. The shaft is connected to a generator, normally via a gearbox, which produces electricity. The rotor blades and shaft are connected to the nacelle, which contains the gearbox and other power/mechanical components and sits at the top of the wind turbine tower. The nacelle can rotate freely, allowing the wind turbine blades to align with the direction of the wind and helping them to extract as much energy as possible.
Wind turbines are mounted on a tower to optimise energy capture. This is because, in general, wind is stronger, more consistent and less turbulent the higher off the ground it is.

Wind generators range in size from kilowatt-sized machines (suitable for domestic buildings) to large multi-megawatt devices (1 megawatt = 1,000 kilowatts) for use onshore and offshore wind farms into the national electricity grid.

Electricity will not be generated when there is no wind. This means that there are some technical challenges with incorporating this form of generation into the electricity network to provide power as needed. However, wind farms are distributed throughout the UK so the changes in power from individual turbines will be evened out; if the wind drops in one area of the UK it is still highly likely to be present in others. The National Grid Company has estimated that the extra amount of conventional back-up power needed to cope with an increasing level of wind generation is likely to be small.

Offshore wind, however, is a larger-scale, more technologically challenging and expensive undertaking than onshore wind. However, it has huge potential due to the UK’s excellent offshore wind resource, which is stronger and more consistent than the wind resource onshore, leading to higher power outputs per turbine and more hours spent generating each year.

Offshore turbines operate in much the same way as onshore turbines, although in general they are larger and more powerful. The construction, delivery and assembly of such large machines require specialist equipment, for example special facilities at ports and installation vessels. Careful scheduling is also needed as offshore turbines can only be installed in calm seas. Changeable weather and sea conditions also mean that offshore turbines need to be extremely robust. Offshore wind turbines also require underwater cabling to transport electricity back onshore and into the grid.

For a useful diagram on how an offshore wind farm works visit the British Wind Energy Association website.