Energy, Mechanics, Power systems, Renewable energy, Sea and ocean, Sustainability

Offshore wind turbines

How are offshore wind turbines kept at sea, and how is the generated energy transmitted to the shore? This is the subject of this post.

Click on the link below to know the operation of a wind turbine.

Wind turbines: how do they work?Click here

Transmitting energy from offshore wind turbines to the consumers

Why build offshore wind turbines? Sea winds are stronger and more constant than the ones inland, therefore, have more energetic potential. In addition, inland wind turbines cause noise pollution and occupy areas that could be used for agriculture or urban development. Offshore wind turbines can be much bigger than inland, to make better use of energy potential.

offshore wind turbines transmitting energy
Array cables transmit generated energy, an offshore substation increases the voltage, to repass electricity to an onshore substation, whose function is to reduce transmission voltage, to arrive at consumer units. Source: Orsted.

Platforms for offshore wind turbines

At depths of up to 50 meters, it is viable to install foundations on the seabed to sustain wind turbines. However, at greater depths, where winds are even stronger and more constant, floating platforms are necessary for support.

offshore wind turbines
Fixed structures and floating platforms for the turbines. Source: (Konstantinidis e Botsaris, 2016).

Platforms are attached to the seabed using metal chains, steel cables, or synthetic fiber ropes.

Barge

This platform floats due to area in contact with water, the empty space serves to absorb waves. It is the cheapest and easiest to install, but it’s more subject to buoyancy forces, therefore, the construction is only viable on spots where tides are weaker.

Tension leg platform (TLP)

Source: paperblog.

With the goal to reduce costs, dimension and weight are reduced, consists of a central axis with three, four or five “arms”. The stabilization comes from interaction between the buoyancy and the high tension on cables. Therefore, it depends much on soil conditions on seabed. The installation of this type of platform is only viable at depths between 50 and 60 meters (164 to 196 ft).

Semisubmersible

Source: WindTAIWAN.

Created to minimize area exposed to water and maximize volume. It has vertical floats united by pontoons with cross braces and filled with ballast water, to improve stability. In addition, most part of floats are underwater. A controller can change the floats’ mass and buoyancy to adjust turbine’s position, which increases complexity.

Spar

A large column below the turbine and most of the mass is on the turbine’s opposite side, as a result, gravity center is much lower than buoyancy center, making the platform stable. However, this type is only viable where depth is higher than 100 meters.

Currently, new platform designs are being developed and proposed, with the finality to obtain the advantages of current models and a better cost-benefit.

Limitations and challenges of offshore wind turbines

  • Installation, maintenance, and operation costs are still too high.
  • Environmental impacts by offshore wind turbines on marine life and birds are still not yet fully understood.
  • Violent weather may force a temporary shut down. However, turbines that resist typhoons have been built in China
  • Depending on the spot, visibility of offshore wind turbines from shore may be unpleasant for local residents. 

About Pedro Ney Stroski

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