Offshore Wind Energy - Basic techniques

The desire to develop wind power in certain countries has led to the need to install offshore wind turbines to take advantage of large areas where wind is abundant.

The installation and operation of wind turbines at sea is fundamentally different from that on land. Wind turbines are firmly anchored to the seabed, requiring the design and construction of subsea support structures capable of transferring the forces of the wind to the ground and withstanding the onslaught of waves. Special submarine cables are used for cabling.

On the other hand, large-scale equipment can be transported by sea without being hampered by road transport limitations. The installation of wind turbines and cables requires the use of appropriate naval resources. Workboats are designed to lift masses of several hundred tonnes to the required height, often over a hundred meters. They are built specifically for offshore wind energy, and each represents an investment of several hundred million euros.

All these features make offshore wind turbines more expensive than onshore wind turbines. In order to reduce costs, developers are looking for the best possible return on investment, based on the following principles:

• the power of the wind farm must be as large as possible, limited only physically by the capacity of the power grid to evacuate the energy or the space available. We're aiming for power ratings of several hundred megawatts;

• by using larger machines, the cost of support structures becomes relatively lower (for a given water depth);

• for a given power farm, the more powerful the wind turbines, the smaller the number of machines to be installed and maintained;

• the larger the project, the greater the justification for specific investments, such as installation vessels.

Offshore wind farm projects are major industrial projects, each involving investments and financial risks of several hundred million euros.

It should be added that the maintenance of wind turbines at sea is much more difficult than on land, if only because of the difficulties of accessing the machines and handling spare equipment.

Finally, it should be stressed that safety issues are particularly acute, since we combine the problems of working at heights and handling heavy loads with those of working at sea, which must take into account the limitations imposed by the weather and sea conditions.

This article does not claim to cover the whole subject exhaustively. The state of the art is evolving very rapidly in this field, and any description of...