Environmental aspects of offshore wind power

Environmental aspects of offshore wind power

As with all forms of energy production, offshore wind power also has negative environmental impacts. The environmental impacts of an offshore wind farm planned for the Finnish territorial waters are assessed in the environmental impact assessment procedure (EIA) and/or in the plan drawn up for the wind farm. Offshore wind farms planned for the territorial waters also require building permits granted by the municipality in order to verify that the application meets the technical requirements of the plan. The environmental impacts of an offshore wind farm planned for the exclusive economic zone are assessed in the EIA procedure. In an exclusive economic zone, the building permit is granted by the Government. Projects located both in territorial waters and in the exclusive economic zone need a permit under the Water Act.

An offshore wind power project may also require an assessment of environmental impacts across state borders according to the Convention on Environmental Impact Assessment in a Transboundary Context, depending on the location and conditions.

Environmental impacts

The environmental impacts of offshore wind power are highly dependent on the location, which means that the choice of location plays a key role in terms of the significance of environmental impacts. Generally, it can be said that biodiversity in the underwater marine environment is at its highest in shallow areas where more light is filtered into the water. Normally, the most modern of offshore wind turbines require a slightly higher depth of water where also the biodiversity of species in the Baltic Sea conditions is smaller.

The environmental impacts of an offshore wind farm can be divided into those above surface, below surface (water column and seabed) and impacts on land areas due to electricity transmission. However, here we shall focus on the environmental aspects of the sea area. On the other hand, the impacts can also be divided into those during construction and during operation, and these differ greatly from one another. All of these are taken into account in the assessment of environmental impacts.

Marine conditions in Finland

The Baltic Sea is a special sea area not only due to its conditions having an impact on construction and planning, as discussed above, but also due to its natural conditions. Especially the fluctuation of salinity within the sea area has a strong impact on the species: In the vicinity of the Danish straits, water salinity is close to the levels in the Atlantic Ocean, but the levels are gradually reduced when travelling towards the northernmost part of the sea area in the Bay of Bothnia. In the Bay of Bothnia, salinity is very low and not many marine species survive there. In addition, salinity in the Baltic Sea varies strongly even locally according to the occurrence of so-called saltwater inflows.

In the sea and shore areas, there are protected areas in the same way as in land areas, and they restrict construction activities. In terms of protected areas, more far-reaching impacts on them and impacts on the protection principles, such as clouding, must also be taken into account. In terms of Natura areas, a separate Natura assessment is carried out, if necessary.

Observation of bird life

In terms of bird life, especially the main migratory routes, birds resting and feeding in the area, and the actual nesting areas are important when building offshore wind power. On the other hand, impacts on the bird population can be divided into collision impacts, disturbance and barrier effects, and impacts caused by habitat changes. The impacts on the bird population are also highly specific to the locations and species. In addition to birds, bats flying in the air within the area of impact of the rotors are also a potential group of animals to be taken into account. The Tahkoluoto offshore wind farm uses a bird radar for monitoring the impacts of the wind farm on the bird populations and, when necessary, the turbines are stopped when a bird representing a certain species approaches the turbine.

The bird radar material from Tahkoluoto indicates that the birds usually go round the turbines and the wind turbines have not had a negative impact on the bird population in the area. The impacts on the bird population by the Tahkoluoto offshore wind farm are smaller than estimated in the environmental impact assessment procedure.

Read more in the Tuulivoima magazine

Photo: Markku Saiha

Marine mammals and the seabed

The marine mammal species in the Baltic Sea, especially along the coast of Finland, are fairly few in numbers in the same way as other species. In practice, there are only three marine mammal species resident in the Finnish marine area: the grey seal, the Baltic ringed seal, and the porpoise. However, the population of the porpoise is very low. The impacts on these species include habitat changes or disturbance impacts during construction and operation.

The species on the seabed consist of seabed vegetation and benthic animals and can be classified roughly into species of hard and soft substrata habitats. With respect to these, especially areas most valuable in terms of their species and habitat types, as well as species requiring special protection, are to be taken into account. The saline levels of seawater have a great impact on the consistency and number of the species: on the southern coast there are considerably more marine species, whereas in the Bay of Bothnia there are mainly freshwater species. The underwater nature values in the Baltic Sea have for long been so-called unknown territory because there has been no basic data available. The VELMU surveys have provided valuable basic knowledge about the underwater marine environment. However, current data concerning many areas is still limited or based only on modelling.

VELMU Map Service

Fish stocks

Offshore wind power can have an impact on fish stocks, for example, due to temporary clouding of water or to power plant structures. Noise, changes in the currents or water quality may cause displacement or behavioural changes. There may also be impacts on spawning. These depend highly on the area and its fish stocks and require individual assessment. The impacts are generally higher during construction and level off after the turbines have been completed. The turbine foundations may also act as artificial reefs, creating new habitats.

Impact assessment

Environmental impacts are always assessed in each case separately in connection with every wind power project. In the same way as in onshore wind power, an impact assessment is also carried out in offshore wind power projects in relation to anthropogenic activities, for example, in terms of the landscape, trade, cultural heritage, population, territorial surveillance, and seafaring.

According to a study published by SYKE in 2022, there are areas suitable for offshore wind turbines in all sea areas of Finland. The study sought sea areas where wind power can be built cost-effectively and without major disadvantages to other lines of business, people, or marine biodiversity. (Virtanen et al 2022). However, it is necessary to carry out diligent surveys and planning in order to find suitable areas.

Further information about offshore wind power:

Tuulivoima magazine, Construction of offshore wind turbines: a successful project is based on sufficient research data