Partnering with WREN, questionnaires are sent to offshore wind energy developers around the world who are involved in environmental monitoring. This page provides contextual project information and highlights environmental monitoring, providing links to available data and reports. Content is updated annually.

Kriegers Flak

Description

The Kriegers Flak offshore wind farm has a capacity of 604 MW which makes it Denmark's and Scandinavia's largest offshore wind farm. Since it began operation in 2021, it has increased Danish production of wind power by 16% and its 72 offshore wind turbines are able to cover the annual energy consumption of approximately 600,000 Danish households. The wind farm covers an area of 132 km2 and about 170 kilometres of underwater cables have been laid. 

As part of the Combined Grid Solution project, Kriegers Flak is interconnected with the German wind farm Baltic II, which is located less than 30 km southeast of Kriegers Flak. This was the first time ever an offshore power grid connected wind farms located in two different countries, Germany and Denmark. 

A research collaboration with Danish universities has successfully cultivated seaweed on lines inside the borders of the wind farm. This project aims to explore synergies between wind energy and sustainable food production at the same time and place, with cultivation starting for sugar kelp, sea lettuce, dulse, and blue mussels. Research efforts will also focus on monitoring the effects of turbine foundations and their potential for creating artificial reefs.  

Location

Kriegers Flak is located in the Baltic Sea, 15-40 kilometers off the Danish coast and is installed at the intersection of the Danish, German, and Swedish exclusive economic zones (EEZ). During the installation phase the turbines were preassembled and shipped out of the Port of Rønne on the island of Bornholm. The wind farm is serviced out of Vattenfall’s service facility at the Port of Klintholm on Møn, approximately 100 kilometers south of Copenhagen.

Project Timeline

  • 2021: Turbines operational 
  • 2021: All 72 turbines were installed 
  • 2021: First turbine was installed 
  • 2020: First foundation was installed 
  • 2019: Construction started   
  • 2018: Power purchase agreement signed 
  • 2016: Cable works started 
  • 2012-2016: EIA investigations 
  • 2012: Construction is decided by Danish Parliament 

Licensing Information

On December 22nd, 2016, the Kriegers Flak Concessions Agreement was signed and the licences for pre-investigations and establishment were awarded.

Key Environmental Issues

The fauna in the seabed in the area is very sparse, and there are no endangered species present. Grey seals, harbor seals, arctic ringed seals, and harbor porpoise are known to inhabit the waters surround Kriegers Flak. Several species of birds fly through the area, including cranes, and geese, however bats are not present. Twenty-six species of fish are present, the most common being herring and cod. The impact of noise on marine mammals from construction was the largest concern, but with mitigation measures such as a bubble curtain, soft start procedures, and deterrent devices, the noise impact of construction and pile driving was determined to be negligible. In 2023 Vattenfall conducted a study monitoring bat presence and behavior near the Kriegers Flak wind turbines using ultrasound detectors. Results from this study will be compared with a similar study using thermal cameras to monitor bat presence. This research was conducted as part of the Kattegat West Baltic Bats Project, initiated in 2022, to investigate bat presence and behavior in offshore wind farm areas. The project is a coordinated effort between several countries including Denmark, Sweden, Germany, and Norway, and over 140 bat detectors have been deployed over the study areas. 

Metadata Documents

Environmental Papers and Reports

Environmental Monitoring: Kriegers Flak

Phase Stressor & Receptor Design and Methods Results Publications Data
Baseline Displacement

Marine Mammals 		Pile driving disturbance index
A pile driving disturbance index was calculated to determine the percentage of total habitat unavailable to animals due to deterrence by pile driving noise. The index was calculated with disturbance distance, area occupied by local population, duration of pile driving event, average turnaround from the start of pile driving one foundation to the start of another foundation, and the fraction of the impact zone that falls into the total area. 		Complete
Disturbance without a bubble curtain was calculated to be the largest for harbor seals, with a disturbance index of 9%, followed by the Baltic Proper porpoises (winter) at 7%, and the Belt Sea porpoises and grey seals, both at 4%. With the use of a bubble curtain, all disturbance indices were below 1%. 		Tougaard and Mikaelsen 2018 No data publicly available.
Baseline Noise

Marine Mammals 		Sound pressure level model for operational wind turbines
The sound pressure levels from two turbines that are 1000 meter apart are modelled to determine cumulative noise level in relationship to ambient noise and distance from turbine. 		Complete
Harbor porpoises have poor hearing at the low frequencies of turbine noise; therefore, the turbine noise is expected to be inaudible to the porpoises unless they are close to the turbine, within 100 meters. Harbor seals have good low frequency hearing, well below ambient noise. Their ability to hear the turbine will be determined by the ambient noise level rather than their hearing threshold. The model suggests that the noise is audible to seals within the wind farm area and extending at least 1 km outside of the wind farm. 		Tougaard and Mikaelsen 2018 No data publicly available.
Baseline Avoidance

Marine Mammals 		Individual based simulation model
A simulation model was built to reproduce the natural movement patterns of porpoises using data from a previous satellite tracking study. The model also incorporated food resource patches to predict porpoise densities. Other parameters that we built into the model included porpoise energy requirements, dispersal behavior, disturbance simulations, and porpoise reproduction and mortality. 		Complete
The model showed that the post-construction effects of the wind turbines resulted in substantially reduced porpoise densities up to 200 m from the turbines. However, the turbines are not expected to have an impact on long-term dynamics of the population. 		Nabe-Nielsen et al. 2011 No data publicly available.
Baseline Bats Passive acoustic monitoring (PAM)
In 2013, passive acoustic monitoring was used to record bat presence from two PAM stations over a 250 km2 pre wind farm investigation area. These surveys were completed from August to November. The surveys took place at the southeastern edge of the investigation area. 		Complete
Bats were recorded on 17 of the nights between the months of August and November. Overall, 287 bats were recorded. Bats were identified as Nathusius’ pipistrelle, noctule bat, parti-colored bat, and serotine bat. 		Brinkløv et al. 2025 No data publicly available.
Baseline Birds Radar
This study used radar to determine how many birds flew below 200 meters at the site, which puts them at higher risk of collision. 		Complete
Between 60 and 64% of birds flew below 200m during the day and between 30 to 39% flew below 200m during the night. Birds flying at night will be more at higher risk for collision. 		Sweden Offshore Wind AB 2007 No data publicly available.
Baseline Invertebrates Benthic surveys, sonar, and echosounder
The conditions of the seabed were studied in five transects using an underwater video camera. The area was then re-searched using side viewing sonar and multidirectional echosounder. 		Complete
The richest diversity of macrozoobenthic species found were polychaetes, mollusks, and crustaceans. The epifauna was sparse in species and completely dominated by blue mussels. 		Sweden Offshore Wind AB 2007 No data publicly available.
Baseline Fish Fishing and trawling surveys
Three rounds of fishing and trawling were completed per year from 2002 to 2004. A special trawl was used to catch small fish. Where conditions made it impossible to fish, divers were used. 		Complete
27 species of fish were identified in 2002, and average occurrence was measured at 172 individuals per hectare, none of which were listed as endangered. In 2004, 13 species of fish were found, and average occurrence was measured at 122 individuals per hectare. 		Sweden Offshore Wind AB 2007 No data publicly available.
Baseline Birds Visual transect and aerial surveys
Surveys were carried out between April 2002 and March 2004. An area of 508 km2 was searched from ships over 35 different sampling events. Observations were also made from planes over 16 different sampling events in an 840 km2 area. 		Complete
24 different bird species were observed in the area. Sea gulls dominated the population, occupying 60% of the observations. Loons and razor bills can be found during the winter months. 		Sweden Offshore Wind AB 2007 No data publicly available.
Baseline Birds Visual observation and radar
Visual observations were made from 2002 to 2004 during the day and at night to observe migrating birds. Radar observations were carried out above 10m height interval in which visual observation was no longer viable. 		Complete
139 species of birds were observed migrating through the area. The eider was the species that occurred most frequently. Of the 139 species, 21 are listed in the EU bird protection directive, 26 are also registered on the Swedish red-list of endangered species. 		Sweden Offshore Wind AB 2007 No data publicly available.
Baseline Marine Mammals Visual transect and aerial surveys, T-POD acoustic detection
Visual transect and aerial surveys were conducted from 2002 to 2004. An area of 505 km2 was surveyed from ships over 35 survey events and an area of 560 km2 was surveyed by plane over 21 survey events. T-PODS were used to detect porpoises and were positioned on an anchored ship, sampling 15 occasions over 36 days. 		Complete
During the two years of sampling, three porpoises and three grey seals were observed at Kriegers Flak. No harbor seals were observed. 		Sweden Offshore Wind AB 2007 No data publicly available.
Baseline Noise

Marine Mammals 		Pile Driving Noise Modeling
A noise exposure model using a pile driving scenario was run for 4.5 hours for seals and porpoises, with and without a bubble curtain, and included a soft start phase, a ramp-up phase, and a full hammer energy phase. 		Complete
The sound exposure model resulted in higher received sound levels for seals than for porpoises. The bubble curtain appeared to be an effective mitigation measure for sound exposure levels to pile driving, leading to a 20 dB reduction in received levels for porpoises and 10 dB reduction for seals. Without a bubble curtain, the cumulated noise from pile driving was above the exposure thresholds for PTS for seals and porpoises. 		Tougaard and Mikaelsen 2018 No data publicly available.
Operations Collision

Birds 		Ultrasound sensors
Ultrasound detectors were deployed on buoys, masts, lighthouses, wind turbines, and other installations to study bats as they are at or pass through the wind farm. 		In process
The results from this study will be compared with results from a study using a thermal camera to observe how bats fly around wind turbines and their ability to detect collision events. 		No data publicly available.
Operations Bats Passive acoustic monitoring (PAM)
In 2022 and 2023, after the wind farm became operational, a survey was conducted to take passive acoustic recordings from 10 wind turbines. From August to November 2022, all 10 PAM stations were running, but due to technical difficulties, only five of the PAM stations were active from April to August 2023. 		Complete
The five active PAM stations recorded 2,058 bats from the offshore wind turbines. The bats consisted of noctule bats, parti-colored bats, Nathusius’ pipistrelle, soprano pipistrelle and common pipistrelle. The noctule bat was one of the most frequently recorded at the turbines, and likely there during migration. The parti-colored bat was recorded at the stations closest to land, indicating that these are likely foraging individuals. Besides the noctule bat, the other species generally did not venture out to the turbine over 20 km from land. Continued bat detection studies are planned to occur in 2024-2025 to be used for direct comparison with these results to determine the effect of the turbines. 		Christensen 2024 No data publicly available.
Operations Habitat Change

Invertebrates 		Epibenthic surveys and eDNA sampling
Epibenthic surveys completed utilizing scraping samples from wind turbine towers. Species coverage was also recorded using an ROV down the length of the tower, across the scour protection, and out 100 meters beyond the tower over the original seabed. Environmental DNA samples were collected downstream of the turbines. 		Complete
The upper section of the towers and the lower section of the towers (about 0.5 m above the seabed) had less epibenthic cover. Mytilus mussels were dominant on the towers and observed on the seabed in a long linear line, likely on the power cable. Species compositions were highly similar when comparing eDNA from water samples taken within the wind farm to those taken outside the wind farm, however 9 species were unique to the wind farm, indicating that the additional substrate could support growth of new species in the area. 		Dahl et al. 2025 No data publicly available.
Operations Displacement, Habitat Change

Birds 		Vessel based surveys
Vessel based transect surveys were completed from December 2022 to February 2023 throughout the Kriegers Flak wind farm to assess the influence of operational wind turbines of long-tailed duck distribution. Observers recorded long-tailed duck sightings along the transect lines. From the observed data, abundance and density estimates were extrapolated and maps were created of duck distribution within the wind farm. 		Complete
154 flocks of long-tailed ducks were observed over the sample period. 63 flocks were observed west of the wind farm, 37 flocks were observed east of the wind farm, and 54 flocks were observed in the wind farm, between the operational wind turbines. Duck density gradually increased from December to February. The ducks appeared to prefer the area west of the wind farm, as evidenced by the higher density. There was no clear sign of habitat displacement caused by the wind farm. 		Nielsen et al. 2023 No data publicly available.