Do you know how offshore wind farms work?

#wind power #renewable energy #Iberdrola projects

Offshore wind energy is the clean and renewable energy obtained by taking advantage of the force of the wind that is produced on the high seas, where it reaches a higher and more constant speed than on land due to the absence of barriers. In order to make the most of this resource, mega-structures are installed that are seated on the seabed and equipped with the latest technical innovations. Discover what these real sea giants are like and how they work.


  • Offshore wind energy is renewable, unlimited and non-polluting.
  • There are more wind resources offshore than onshore (up to twice as much as in a medium onshore wind farm).
  • When located offshore, the visual and acoustic impact is very small, so much larger areas can be used. Thanks to this, offshore wind farms typically have several hundred megawatts of installed capacity.
  • The ease of maritime transport, which has few limitations with regard to cargo and dimensions in comparison with land transportation, has made it possible for offshore wind turbines to reach much larger unit capacities and sizes than onshore wind turbines.


Currently, offshore wind farms are located in shallow waters (up to 60 metres deep) and away from the coast, marine traffic routes, strategic naval installations and spaces of ecological interest.

According to the latest report from WindEurope, the European wind energy Association, Offshore wind in Europe: trends and key statistics 2018, published in February 2019, European farms have an average depth of 27.1 metres (only slightly less than the year before) and are at an average distance of 33 km from the coast, as opposed to the 41 km average recorded in the 2017 report. The United Kingdom is the country with the highest installed capacity in Europe, with a total of 44% of all offshore wind energy installations (in MW). It is followed by Germany (34%), Denmark (7%), Belgium (6.4%) and Holland (6%).


How does an offshore wind farm work?
How does
an offshore wind farm work?
The force of the wind turns the blades.
The blades are attached to the nacelle through the hub.
The low-speed shaft spins at the same speed as the blades (7 - 12 turns per minute).
The gearbox increases this speed more than 100 times and transfers it to the high-speed shaft.
The high-speed shaft (+1,500 revolutions per minute) transmits this speed to the generator.*
The generator transforms the kinetic energy it receives into electricity.
The electricity produced by the generator is fed down through the inside of the tower.
The converter converts the direct current into alternating current.
The transformer raises the voltage (33 kV - 66 kV) in order to transport it across the wind farm.
The electricity is transmitted via underwater cables to the substation.
At the substation, the electricity is converted to high voltage current (+150 kV).
Electricity is transported through the distribution network until homes.
(*) Some technologies use low-speed generators coupled directly to the low-speed shaft.


 SEE INFOGRAPHIC: How does an offshore wind farm work? [PDF]

Know the process in detail

Electrical energy is produced in the wind turbine, a mammoth structure that is fixed to the seabed using different types of supports. It has a controller that starts and stops the turbine depending on the weather conditions, as well as a mechanism that determines the wind direction which allows it to be orientated correctly. The structure, whose height depends on the sea surface topography, is equipped with a beaconing system with specific lights and colours that make it very visible to maritime and air traffic to ensure maximum safety.

The force of the wind turns the blades, which are designed to capture the maximum kinetic energy: they can move even in very light winds, down to 11 kilometres per hour. The blades are connected to the turbine through the hub, which in turn is connected to the low-speed shaft, which rotates at the same speed as the blades (between 7 and 12 revolutions per minute). A gearbox increases this speed more than 100 times and transfers it to the high-speed shaft, which moves at more than 1,500 revolutions per minute and transmits this force to the generator (some technologies use low-speed generators coupled directly to the low-speed shaft). This is where the kinetic energy is transformed into electricity.

The electricity is fed down the inside of the tower to the base, where a converter transforms it into alternating current. It is then transported via underwater cables to a transformer where the voltage is raised (to between 33 and 66 kV) so that it can be transported across the wind farm. From there, it goes to the substation, where the electricity is converted to high voltage current (more than 150 kV) and transported through the distribution network.

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The capacity of offshore turbines has increased by 102% over the last decade, according to WindEurope's report Offshore Wind in Europe: key trends and statistics 2017. This meant that in 2017 the average installed capacity of the new wind turbines was 5.9 MW, 23% more than in 2016. The largest turbines have been erected in the United Kingdom and Germany, with an average of 6 and 5.6 MW, respectively. Followed by Denmark and Finland, with an average of 3.4 MW.

This evolution can be clearly seen in the offshore wind projects developed by the Iberdrola group: West of Duddon Sands, Wikinger, East Anglia ONE, Saint-Brieuc, Vineyard Wind and Baltic Eagle.

Evolution of unitary capacity

and rotor of our offshore wind turbines

120 m 3.6 MW

West of Duddon sands

Irish Sea
(United Kingdom)
In operation since 2014
135 m 5 MW


Baltic Sea
In operation since 2017
154 m 7 MW

East Anglia One

North Sea
(United Kingdom)
Under construction
8 MW 167 m


Saint-Brieuc Bay
Under construction
164 m 9.5 MW

Vineyard Wind 1

Under construction
174 m 9.5 MW

Baltic Eagle

Baltic Sea
Under construction


 SEE INFOGRAPHIC: Evolution of unitary capacity and rotor of our offshore wind turbines [PDF]

Find out how the power of the turbines has increased

West of Duddon Sands was the first wind farm of its kind launched by the company in 2014. Located in the Irish Sea, off the British coast, it has 108 wind turbines which provide a total of 388.8 MW of power, 3.6 MW each. The circumference traced by the blades of each turbine (also called the rotor) reaches 120 metres.

Since then, the power of wind turbines has undergone a breakthrough. In the Wikinger offshore wind farm, located in the Baltic Sea off the coast of Germany and operational since late 2017, each of the 70 turbines provides 5 MW and has a diameter of 135 metres. This results in a total installed capacity of 350 MW, just 30 less than West of Duddon Sands but with 38 fewer wind turbines.

Even more significant are the improvements introduced in the East Anglia ONE, a large-scale offshore wind energy project that is expected to come into operation in 2020. With 102 turbines, each with a unit capacity of 7MW and a rotor diameter of 154 metres, East Anglia ONE will become the largest offshore wind farm in the world, supplying 714 MW. This means that with six fewer turbines than West of Duddon Sands, East Anglia ONE will be able to provide almost twice the power.

At the Saint-Brieuc wind farm, the group's first major offshore wind project in Brittany, 8 MW turbines will be installed, each with a rotor diameter of 167 metres. This will result in a total installed capacity of 496 MW with only 62 turbines.

However, the highest unitary capacity will be found in Vineyard Wind and Baltic Eagle, the two new wind farms that Iberdrola has in the pipeline. Vineyard Wind, the first offshore wind farm developed by the company in the US, will have an installed capacity of 800 MW supplied by wind turbines of over 8 MW and with rotors exceeding 167 metres in diameter. Baltic Eagle, meanwhile, will be built next to Wikinger and will have 476 MW of capacity generated by turbines that are expected to have the same characteristics as those of Vineyard Wind.

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The development of new types of foundations that allow these installations to be located further away from the coast and the continuous evolution in the power and design of wind turbines are just some of the progress we will see in the coming years. These advances undoubtedly augur a long and prosperous future for offshore wind farms.

 Evolution of wind energy in Europe

 Utility of the future