Offshore wind farms have the wind in their sails

wind farms, offshore wind farm, energy efficiency, wind turbine, electricity

©TheWindPower

In July 2011, the French government launched a call for tenders for the construction of wind farms off its coasts as part of an open multi-party initiative on environmental issues referred to as the “Grenelle Environnement”. Contracts were awarded on April 6th: France is indeed going to embark on the construction, installation and exploitation of its first offshore wind farms. These current developments give us the opportunity to review the benefits and constraints of this fledgling renewable electricity source.

France has long relied nearly exclusively on nuclear energy for its electricity production. Today it massively invests in renewable energy, particularly in offshore wind power. By 2016, the four wind farms to be built off the coasts of Normandy and Loire Atlantique (Fécamp, Courseulles-sur-mer, Saint-Nazaire and Saint-Brieuc) will generate an estimated 2 Gigawatts. France is striving to catch up with Germany and the UK and ambitions to triple its expected 2016 output in 2020, i.e. about 6GW, which would represent 1,000 to 1,200 windmills powering 4.5 million households.

Outstanding energy efficiency

Offshore wind farms work the same way as onshore wind farms: the wind’s kinetic energy drives turbines whose movement is turned into electricity, just like a dynamo. Offshore technology greatly benefits from recent advances in onshore technology but has a bigger potential: since offshore winds meet less obstacles, they are steadier, more intense and less stormy. All things being equal, a wind turbine is thought to produce twice more power offshore than onshore. Besides and quite simply, the sea offers almost endless obstacle-free spaces, which makes installing wind farms much easier. Finally, while critics often allege that wind turbines are an eyesore, causing “aesthetic pollution”, 15 km off the coasts they look like tiny needles, hardly more visible than a cargo ship on the horizon.

… entailing new technical and financial constraints

However, one must bear in mind that even offshore wind is intrinsically intermittent: it neither blows constantly nor steadily. For instance, wind blows more at night, whereas energy needs are obviously much bigger during daytime. It is thus extremely important to be able to store off-peak power to make it available during peak periods. Connecting the turbines to the grid is also a challenge of its own, as it requires a network of submarine cables capable of mitigating electricity losses.

Offshore wind farms also entail financial constraints: they are 30 to 50% more expensive than onshore. On the one hand, adequate ships are required to install the turbines and on the other hand, their maintenance is complex: they are subject to moisture and ocean currents and must be equipped with sensors to alert to the risk of corrosion. Finally, fixing a power failure may take several days, which could cause significant losses for the operator.

Producing electricity further off the coasts: the advances of far-shore wind farms

Far-shore wind power is a major improvement from mainstream offshore turbines. Indeed, “conventional” windmills can only be embedded in rather shallow waters, less than 40-metre deep, otherwise they get too expensive. Floating wind turbines, such as the WindFloat concept developed by the US company Principle Power, avoid this stumbling block: they rest on floating foundations attached to the seabed by cables. There are a number of advantages to this system: firstly, it benefits from the strongest winds over 30 km off the coasts; besides, aesthetic pollution from the shore is almost nil. Finally, installation costs are reduced, since turbines can be assembled on the ground and then tugged offshore.

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Picture : © TheWindPower

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