German Federal Agency for Nature Conservation (BfN)

Mainmenu



Construction and operation


Construction of alpha ventus. Photo: Thomas Merck (BfN)
Construction of alpha ventus. Photo: Thomas Merck (BfN)

Implementation of the many and increasingly widely spread plans for offshore wind farms in the German EEZ inevitably means major changes in marine habitats and species. As they involve an entirely novel use of the seas, these large-scale plans bring with them not just technical challenges, but as-yet poorly understood impacts on the natural environment. Examples include habitat loss for disturbance-sensitive seabirds, disturbance of marine mammals and other marine organisms by pile driving noise during wind turbine construction, and the risk of migrating sea and land birds colliding with wind turbines upwards of 150 m tall.

Preliminary findings from German studies conducted during wind farm construction and operation are now available, mostly in connection with the alpha ventus test site. The cumulative impacts of numerous wind farms, such as the cumulative barrier effects on migrating birds, are especially hard to estimate and so far have only been assessed on the basis of forecasts.

Construction-related impacts

Impacts from wind turbine construction include:

Pile-driving noise

Noise from shipping

Sediment shifting/overbuilding


Pile driving, Photo: Klaus Betke
Pile driving, Photo: Klaus Betke

Construction of the foundation for an offshore wind farm conventionally starts with pile driving, which generates a huge amount of noise. A hydraulic ram is used to drive a single pile (for a monopile foundation) or up to four piles (for a jacket foundation) as much as 50 metres into the sea floor. Pile driving noise can harm marine mammals such as the harbour porpoise. More information on this topic is provided under Offshore Wind Power:
Impacts on Marine Species and
Underwater Noise.

Installing the foundations, which can weigh over 1,000 tonnes, has direct effects on the sea floor round about. These include the destruction and permanent overbuilding of benthic communities and possibly of protected habitats. Work on the sea floor and the relocation of sediment create turbidity plumes that can block out the light needed by phytoplankton and harm filtering organisms.

The nature and scale of the impacts mostly depend on the type of foundation and site ecology.

Transporting components and laying cables also increase shipping traffic between the construction site and the mainland. Further information on the impacts of shipping on the marine natural environment is provided under Shipping.


Crane vessel with tripod foundation Photo: Trianel
Crane vessel with tripod foundation Photo: Trianel

Installation and operation-related impacts

Impacts from completed installations and their operation include:

Overbuilding/introduced hard substrates

Collision risk and barrier effect

Shipping and aviation

Collision risk for shipping


The foundations for wind turbines and the in some cases very extensive measures used to secure them result in permanent overbuilding and the destruction of benthic communities. Geotextile scour prevention mats can release pollutants or disintegrate into microparticles. Large areas of stone fill make for an artificial, introduced hard substrate with uncharacteristic vegetation growth.

Alongside the impacts on marine species (see:
Impacts on Marine Species) operating wind farms can come into major conflict with an often overlooked natural phenomenon that is not restricted to the seas: twice-yearly bird migration. Both the North Sea and the Baltic Sea are traversed by global bird migration routes. Each year, between 10 and 100 million land birds cross the sea to reach their breeding areas and winter quarters. Most are songbirds, but there are also birds of prey and large birds such as storks and cranes. Many more are coastal waders and waterfowl. Numerous seabird species also migrate across the oceans.

The main problem involved is the danger of birds flying into wind turbine blades as they rotate. The risk of this is biggest at night and in conditions of poor visibility. Some species are also attracted or confused by the lights on wind turbines. Collision risk is lower in good weather, when many birds fly at greater altitudes and the turbines are more easily seen.

It has also been shown that wind farms act as barriers for some migratory bird species. Many migrating birds such as ducks, geese, swans and waders give them a wide berth. As more and more wind farms are built particularly in the path of bird migration routes, there is an increasing danger of birds either having to risk flying through a wind farm or being forced to fly greater distances – thus expending more energy, which can likewise affect the survival and breeding chances of a species.

As well as migrating birds, migrating bats can also be affected by offshore wind farms in similar ways. Systematic scientific studies in Scandinavia, for example, have shown that some bat species migrate south across the Baltic Sea from the southern Swedish coast in autumn and return when they migrate back north in spring. No such systematic research has yet been conducted for the North Sea, although on Heligoland during the migration period there are regular sightings of bats that are not normally found there and are known to be long-distance migrants.

Maintenance work makes for an increase in helicopter and shipping movements both to and within wind farms throughout their operation. This can cause noise and disturbance to fauna.

Risk of collision with shipping

Given the large extent of wind farms and the large numbers of wind turbines often in close proximity to very busy shipping lanes, there is a constant risk of passing ships colliding with the structures as a result of technical problems or human error. Such accidents can pose a threat to large areas of our seas and coasts far outside the wind farms themselves, for example due to oil or chemical spills.

 

Map North Sea

Offshore Wind Farms, Grid Connections and Natura 2000 Sites in the German Exclusiv Economic Zone (EEZ) of the North Sea.

Offshore Wind Farms, Grid Connections and Natura 2000 Sites in the German Exclusiv Economic Zone (EEZ) of the North Sea. (As of 03.2015)

Map Baltic Sea

Offshore Wind Farms, Grid Connections and Natura 2000 Sites in the German Exclusiv Economic Zone (EEZ) of the Baltic Sea.

Offshore Wind Farms, Grid Connections and Natura 2000 Sites in the German Exclusiv Economic Zone (EEZ) of the Baltic Sea. (As of 03.2015)

 Print