Located between ten and several dozen kilometres off the coast, offshore wind turbines can be either bottom-fixed – meaning they have foundations on the seabed, at maximum depths of 50 to 60 metres – or floating. Floating turbines are installed on a platform that floats on the surface of the water and is attached to the seabed by mooring lines, allowing them to be installed in very deep water. At present, bottom-fixed turbines are much more common, but floating wind turbines are expected to really take off over the next decade. Like their onshore “cousins”, offshore wind turbines consist of a mast equipped with a rotor, usually with three blades. They convert the kinetic energy of the wind into electrical energy, which is sent to a substation at sea and then, via underwater cables, to an electrical substation on land, in turn connected to the electricity grid.
Offshore wind turbines: power and stability
Specially designed to withstand corrosion and currents, offshore wind turbines are generally larger than their onshore counterparts. Projects are currently being studied to build offshore wind turbines over 200 metres high with blades around a hundred metres long! The added bonus is that these giants benefit from winds that are more constant and more powerful, since they are not slowed down by obstacles. They start rotating as soon as wind speeds of 10 km/h are reached and stop automatically for safety reasons whenever they exceed 108 km/h (30 m/s). Offshore wind turbines are therefore two to four times more powerful than onshore turbines and also have a significantly higher load factor, or use rate.