Extensive field study in the North Sea shows the way for offshore wind energy with nature in mind

In collaboration with Aarhus University, NIRAS has carried out one of Denmark's most comprehensive environmental monitoring programmes at sea: a two-year field study in the North Sea, which strengthens the knowledge base for future offshore wind farms. The occasion is the current offshore wind tender of at least 2.8 GW capacity with a tender deadline in spring 2026.

The project has provided the scientific basis for environmental impact assessments of birds, bats and marine mammals in the North Sea I area, which covers approximately 1,400 km² 20–80 km off the west coast of Jutland, Denmark. The purpose is to ensure that future offshore wind projects are developed on a solid, documented and environmentally responsible basis.

"Research and consultancy have complemented each other and provided both quality and applicability. The combination of Aarhus University's research experience and NIRAS' environmental sparring as well as project management and data integration has been crucial for the quality and ongoing deliveries throughout the project. We have proven that when consultancy and research work closely together, you can deliver both solid data and a useful basis for decision-making to authorities and project developers," says senior project manager at NIRAS, Søren Granskov.

"Research and consultancy have complemented each other and provided both quality and applicability."

Søren Granskov, senior project manager, NIRAS

Many hours of fieldwork in a risky environment

The environmental monitoring programme has required extensive fieldwork. Over two years, project staff have spent many hours implementing a unique and ambitious field programme that has included aircraft and ship-based observations of birds and marine mammals as well as acoustic recordings of marine mammals and bats from buoys. Data has been collected in a harsh and risky North Sea environment with the aim of collecting consistent data on birds, bats and marine mammals across seasons.

The most important results are:

Birds: Mapping of 27 species and their annual movement patterns. For the first time, there is now a consistent picture of bird life in the North Sea throughout the year - even with solid data over two years. Particularly high occurrences of the species guillemots, kittiwakes and gannets have been recorded.

Bats: Documentation of individual pipistrelle bats (Nathusius’ pipistrelle) over 80 km from land confirms that bats can be found far from land. However, the study documented the vast majority of bats within 25 km of the coast during the autumn migration period and under the right weather conditions.

Marine mammals (especially seals, porpoises and various whale species): Systematic acoustic monitoring and observations show that porpoises occur regularly in the studied area, while seals mainly stay close to the coast. There are clear seasonal patterns, which provide important information for planning construction work during the periods when the animals are least vulnerable.

"The extensive data collected here and in other projects can accelerate the process for the next offshore wind farms in Denmark by giving developers early insight into the area’s natural and environmental conditions during the tender phase."

Louise Rønde Mønster, Expertise Director, NIRAS

Basis for environmental impact assessments in future winning projects

The extensive data collected from the field surveys has now been transferred in separate reports to Energinet and the Danish Energy Agency. The material will be used in future environmental impact assessments of offshore wind farms in the parts of the North Sea I area that are included in the current offshore wind tender. The next step will be for the results to form the basis for environmental impact assessments of specific projects when the winners of the offshore wind tenders are selected in 2026. Here, the collected data will help to ensure that the expansion of offshore wind energy is carried out on a knowledge-based basis.

“The expansion of offshore wind energy remains slow; however, this project provides an important foundation for the current tender in the North Sea I area,” says Louise Rønde Mønster, Expertise Director at NIRAS. She adds: “The extensive data collected here and in other projects can accelerate the process for the next offshore wind farms in Denmark by giving developers early insight into the area’s natural and environmental conditions during the tender phase. Once the tender winners are announced, environmental impact assessments can leverage this data—eliminating the need for several years of additional studies”.

The reports are available at the websites of the Danish Energy Agency and DCE, Aarhus University.