NIRAS conducts environmental impact assessment for Thor - Denmark’s largest offshore wind farm to date


A multidisciplinary team of NIRAS experts are conducting the environmental impact assessment for the offshore facilities of the 1,080 MW Thor Offshore Wind Farm. Once built, Thor will deliver renewable energy to the equivalent of more than one million households, making it the largest offshore wind farm in Denmark.

January 11, 2024
  • SDG: #7, #13, #14
  • SECTORS: Environment and Ecology, Offshore Wind
  • COUNTRIES: Denmark
  • CLIENT: Thor Wind Farm I/S (RWE)

A team of NIRAS experts are preparing the environmental impact assessment (EIA) on behalf of Thor Wind Farm I/S (RWE) for the offshore facilities of the Thor Offshore Wind Farm, which will be built in the Danish North Sea approximately 22 km off the west coast of Thorsminde in Jutland. The EIA documents the impacts relating to the construction, operation and decommissioning of the wind farm with a planned capacity of more than 1,000 MW. It considers all elements of the offshore installation, including the wind turbines, an offshore substation and the network of submarine cables.

Thor is hitherto Denmark’s largest offshore wind project to date and will be powered by 72 14 MW wind turbines. Thor will be the first offshore wind farm to utilize Siemens Gamesa’s GreenerTowers and will be equipped with the world-wide first recyclable rotor blades in order to make even more sustainable wind power. Once connected to the grid, which is latest in 2027, the wind farm will deliver energy to the equivalent of more than one million households.

NIRAS has produced a range of background reports, including assessments of underwater and airborne noise, a hydrodynamics and sediment analysis as well as visualisations of the wind farm for the EIA reporting. As project manager on the EIA, it has also been NIRAS’ job to coordinate activities between all relevant actors – such as specialists, authorities and the client – while also working closely with specialists from RWE in the preparation of the overall project description.

The location of Thor and the area being investigated
The location of Thor and the area being investigated

Interdisciplinary methods is the backbone of the assessment

Assessing the environmental impacts of the construction of an offshore wind farm includes drawing from a plethora of data across different fields of work, which is why the EIA is drawing from approaches within hydrography and sedimentology, geochemistry, biodiversity, landscape, cultural heritage and archaeology, while also applying methods within fields of risk analysis and noise pollution.

For example, to assess sediment dispersal during the construction phase, a range of input data from the project area must be analysed, consisting of current and wave data, bathymetry, as well as information regarding temperature, salinity, wind and air pressure. This wealth of data is first used to generate two models: a hydrodynamic model simulating water level and currents, and a wave model simulating the wave environment. Next, the dispersal and deposition of suspended sediments across the project area is modelled using the hydrodynamic and wave models in combination with sediment composition data obtained from geophysical and geotechnical surveys.

Aside from being used to assess the potential impacts to marine flora, fauna and coastal morphology, the results from the sedimentation model also underpin the assessments for fish, marine mammals, birds and Natura 2000 areas.

The area is a natural habitat  for guillemots
Lomvien er en av fuglene som lever i området

Examining cumulative impacts

Cumulative impacts describe the combined, incremental effects of human activity and are the result of effects from one project or activity interacting with other effects within a particular place and timeframe.

The environmental impacts arising from the construction and operation of the Thor Offshore Wind Farm are therefore beings assessed in combination with a series of approved projects and adopted plans that, in combination with Thor, have the potential to cause cumulative impacts. Cumulative impacts are especially relevant given the anticipated expansion of offshore wind in the Danish North Sea in the coming years.

Cumulative impacts can stem from individually minor affects from separate projects or activities that, when assessed together, give rise to an incremental or aggregated cumulative impact of increased significance or scope. As part of the EIA for Thor Offshore Wind Farm, NIRAS have assessed the potential for cumulative impacts with respects to the following offshore activities:

  • Offshore wind farms and renewable energy facilities
  • Marine infrastructure (underwater pipes/cables)
  • Offshore raw materials extraction
  • The Danish Coastal Authority’s coastal protection activities along the west coast of Jutland

Bid preparation and consent management

NIRAS is specialist in offshore consultancy and, in addition to the EIA, supported RWE during the bid preparation phase. Here, NIRAS helped review the wealth of data made available by the Danish authorities, including draft permits, baseline studies, various environmental reports as well as the strategic environmental assessment.

NIRAS is also supporting RWE with ongoing permitting and consent management, which focusses on the process of obtaining the necessary permits (and thereby consent) to construct and operate an offshore wind farm. Consent management is a complex task requiring the navigation of different legislative and regulative domains spanning multiple authorities and varying procedures. NIRAS has been supporting RWE by defining requirements, coordinating and preparing applications and supporting documentation, as well as maintaining an active dialogue with the relevant authorities.

The reporting is being completed in collaboration with RWE, with NIRAS assisting ongoing dialogue with the authorities, including with the Danish Energy Agency, the Danish Maritime Authority and The Danish Environmental Protection Agency.

Example of construction work on Horns Rief Windfarm
Eksempel fra oppføringen av havvindmølleparker på Horns Rev

Want to know more?

Rikke Holm

Rikke Holm

Senior Project Manager

Aarhus, Denmark

+45 8732 3262

Lisbeth Errboe Svendsen

Lisbeth Errboe Svendsen

Vice President

Aarhus, Denmark

+45 6039 4483

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