Green energy based on a now mature technology – offshore wind power – is at last beginning to really take off all around the world. But how do these offshore wind turbines work? What are their advantages? And what can we expect in the coming years? Decoding keys...
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.
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.
Although Denmark was a pioneer, with its first offshore wind farm commissioned in 1991, this 100% green energy is now being developed all around the globe. In France, for example, seven bottom-fixed offshore wind turbine projects are currently in the pipeline, while three floating offshore wind turbine pilots have been launched. In the UK, an extraordinary wind farm – with 280 turbines almost 30 times more powerful than those installed in Denmark in 1991 – will be completed by 2025/2026, more than 120 kilometres off the coast. It will be capable of producing as much electricity as a nuclear power station with several reactors! Things are also moving fast in the USA and Asia, as well as in Europe, which is still ahead of the game: the region produces more than 80% of the world's wind power, which currently stands at 30 gigawatts. So the future looks bright for the sector: it is estimated that by 2030, the power generated by offshore wind turbines will have increased five to sevenfold.
Power to the wind!