Offshore wind installations show distinct, profitable features as opposed to installations hinterland, namely:
The wind resource existing in the sea is higher than on the nearby coasts.
Given their position offshore, the visual and acoustic impact is lower than the ones on wind farms on land; this enables a greater exploitation of the existing wind resource, with larger machines and the use of more efficient blade geometries. In like manner, the fact that the sea surface is less rough accounts for the use of lower tower heights.
The above involves a greater job creation activity at the building, assembly and maintenance stages, given a greater complexity during the installation and exploitation phases.
Possibility of getting integrated in mixed sea complexes.
Nevertheless, these sea installations also have remarkable disadvantages as compared to the land ones, which are limiting their development due to: lack of electric infrastructures; more severe environmental conditions; more complex and expensive assessment of the wind resource; and above all, a larger investment and exploitation expense ratios, as they need specific technologies for the building and the foundations works, the transport and assembly offshore, the laying of underwater electric lines and the operation and maintenance tasks.
The unit capacity of the sea wind turbines is higher than the ones by turbines on land. Even though there is not any wind installation currently on the Spanish shoreline, the first wind generators on our coastline in this decade are likely to go over 4 MW, enabling a better exploitation of the sites.
The average depth of the existing wind farms in the world at the end of 2010 (almost virtually the whole of the Northern Europe) is lower to 20 m. Exceptionally, the odd business farm slightly exceeds a 50-m depth, which can be considered as the bathymetric limit for current technology, and for the entire totality of the commercial wind farms to be set up in Spain up to year 2020.
Possibly, the greatest challenge in offshore installations remains the reduction of the foundation costs, for which different variants are found: monopile, tripod, gravity and floating. The monopile ones are the most widely used in medium-depth waters (up to 25 metres); the gravity ones for small depths (less than 5 metres), and the tripod ones for larger depths (up to 50 metres). On the other hand, the commercial feasibility of floating platforms for the installation of wind turbines in deep waters remains unknown, even if there is the odd experimental installation that has accounted for its technical feasibility.