What is offshore wind energy

Offshore wind energy is obtained by harnessing the power of the wind at sea, where the wind reaches a higher speed and is more constant because there are no 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.

Because this is a type of renewable energy, there are numerous benefits because it is inexhaustible (wind is an unlimited resource) and does not pollute. (It is a source of energy that produces low greenhouse gas emissions (GHGs), which are the main culprits responsible for global warming).

The wind blows more at sea than it does on dry land and can produce up to twice the power obtained from onshore facilities. What's more, these plants have a lower visual impact and are less noisy which means that their installed power can be far higher than on land, reaching hundreds of megawatts. Likewise, sea transport is easy, allowing unit powers and sizes far higher than those possible on land.

The main difference lies in the technological difficulty of building them because the structures and their maintenance are more complex due to the offshore environment, which is governed by strict safety requirements. The construction and operation of offshore wind farms requires the use of highly specialised logistical resources. On the other hand, the capacity to generate electricity is higher offshore, because the wind resource is superior and more regular than it is on dry land, which means a higher yield of power. It is easier to transport the components required to install a wind farm offshore, which is why wind turbines with unit power of over 10 MW - and even 15 MW - are feasible in an offshore setting. It is more difficult to transport them on land, where unit power of around 5 MW is the norm.

Due to access constraints during operation, wind farm elements require higher reliability and components are designed with higher levels of redundancy than onshore wind farms.

To install an offshore wind farm a positive Environmental Impact Statement (EIS) must be obtained, as well as a favourable study showing the compatibility of the facility with other uses of the maritime space. For this, very rigorous and strict studies must be conducted in the years prior to the start of the project, including an analysis of the compatibility of the wind farm with navigation, marine fauna, avifauna, migration routes, sediment transport dynamics, etc. These studies are complemented by thorough monitoring of these aspects during the construction and operation phases of the farm.

To protect the environment on wind farm sites, the offshore power industry is using cutting edge, extremely innovative solutions. For example, Iberdrola has used advanced noise mitigation systems while building offshore wind farms such as the underwater bubble curtains used for the Wikinger project in the Baltic Sea. This system protects marine mammals from being affected during construction.

There are two types, distinguished by the type of anchorage used to secure the wind turbines:

Marine wind turbines with fixed foundations:

These are installed on a fixed support structure on the seabed. In turn, there are different types of foundations: monopile (the tower is installed on a large steel cylinder embedded in the seabed); gravity-supported (requires a high-mass, large-area concrete or steel platform resting directly on the prepared seabed); or using jackets (reticular steel structures with three or four anchor points on the seabed). Current fixed foundation technology permits structures to be installed up to 60 metres below the surface.

Offshore wind turbines on floating platforms:

This type of technology allows these wind generation farms to be built farther offshore in very deep waters. The floating bases make it possible to harness the enormous potential of the wind in huge offshore areas. With this type of technique, depth restrictions are determined by the laying of underwater electricity evacuation infrastructures, which can be placed hundreds of metres below sea level.

Depending on the system used to fasten the equipment to the sea bed, they are classified as: single floating columns or spars, semi-submersible platforms or tension-leg platforms.