The impact of wind farms on winter navigation

Rapport, 2024

In 2022, the Swedish Government adopted the first Swedish marine spatial plans. At the same time, The Swedish Agency for Marine and Water Management (SwAM) was assigned to bring forth proposals for amended marine spatial plans to meet the need for increased electricity production. These plans include and identify several areas in the Gulf of Bothnia that may be suitable for offshore wind power installations in the form of dense wind farms. These farms are planned geographically based on several parameters, including minimizing the impact on commercial shipping in the area, which follows predictable routes during the summer. The Gulf of Bothnia, especially the Bay of Bothnia, is completely or partially covered with ice of varying thickness and concentration during the winter. The ships that operate in these areas during winter therefore require the assistance of icebreakers. Requirements for economic and environmental sustainability are the basis for effective icebreaker planning where, due to the dynamics of the ice, the routes vary greatly from week to week. Offshore wind power hinders and blocks the choice of ship routes and also risks affecting ice formation and the nature of the ice.
 
The project has carried out a literature study to compile current knowledge about ice formation in the vicinity of offshore wind farms. It shows that there is a large knowledge gap in the area. There is therefore a great need for further research to understand if and how the ice formation at wind farms develops to ensure safe installations and how the ice formation may affect, for example, winter navigation. The project has developed a generally applicable methodology for assessing how shipping is directly affected by offshore wind farms both in summer and winter by limiting the range of available shipping routes. The methodology uses historical tracking data (AIS data) of maritime traffic in the years 2018, 2022 and 2023. It has been applied to geographical areas that SwAM specified as areas of special interest in the Gulf of Bothnia. Through a proprietary script in the Python programming language, the data has been filtered, processed and presented ship tracks on maps of desired areas that contain sub-areas where wind farms are planned to be installed. Based on this, the wind farms' impact on shipping was visually analyzed to identify problematic areas and periods. This has been compared with ice data (thickness, concentration and movement) to explain why ship routes follow different patterns at different time periods (eg, months). To systematically track and compare areas, the proportion of ships within an area whose routes cut through the various wind power areas has been calculated. Statistics have been produced for the analyzed years and areas as specified by HaV.
 
All the years that have been analyzed have limited ice extent in the Sea of Bothnia and thus the analysis was limited to summer traffic in this sub-area as the routes do not need to be adapted to the ice and without the need for icebreaker assistance. Potentially problematic areas are identified here: B164 with a crossing frequency of 40% in the third week of November 2023, B149 with 40.4% in the last week of October 2023. In the Bay of Bothnia, large parts are covered by ice in winter and there winter traffic with icebreaker assistance could also be analysed. Here, the results show relatively stable intersection frequencies in summer but highly variable, and generally higher frequencies in winter. This is due to the adaptation of routes due to the dynamics of the ice. Potentially problematic areas are identified here B111 with a cut rate of 60% in the first week of April 2023, B113 with 45.6% in the first week of May.