Coastal effects on offshore wind farms
Study coordinated by Hereon provides an overview of coastal effects on offshore wind farms.
Although they are 100 kilometres away, offshore wind farms can still be strongly influenced by the land – they are located in the atmospheric transition area from land to sea: the coast. The wind from the land towards the sea plays a particularly important role here: it accelerates over water. Furthermore, the temperature difference between land and water as well as the current sea state have an additional influence. These and other factors together are called coastal effects.
The project partners analysed simulation and observation data and used it to prove that the wind speeds in individual offshore wind farms depend strongly on the wind direction. This is mainly due to the special shape of the coastline in the German Bight. In addition, the researchers found that the interactions between ocean and atmosphere – such as the exchange of heat – should be taken more into account. Another result: the mechanical and thermal properties of the tidal flats, such as the roughness of the surface and their impact on coastal effects, are not yet sufficiently understood.
“The interactions of wind shadowing behind offshore wind farms with coastal effects have also been insufficiently investigated,” says first author Dr. Johannes Schulz-Stellenfleth of the Hereon Institute of Coastal Systems – Analysis and Modeling. (Source: Hereon News)
Read the complete Hereon News:
==> Offshore wind farms: In the transition zone between land and sea
Schulz-Stellenfleth, J., Emeis, S., Dörenkämper, M., Bange, J., Canadillas, B., Neumann, T., Schneemann, J., Weber, I., zum Berge, K., Platis, A., Djath, B., Gottschall, J., Vollmer, L., Rausch, T., Barekzai, M., Hammel, J., Steinfeld, G., & Lampert, A. (2022): Coastal impacts on offshore wind farms – a review focussing on the German Bight area. Meteorologische Zeitschrift (2022), doi:10.1127/metz/2022/1109
Abstract:
The atmospheric boundary layer experiences multiple changes in coastal regions, especially with wind directions from land towards the sea, where the wind speed usually increases due to the smaller roughness of the ocean surface. These effects are of particular relevance for offshore wind energy utilization; they are summarized under the term coastal effects. This paper provides an overview of coastal effects and their potential impact on the operating conditions of offshore wind farms with a focus on the German Bight. Common numerical and experimental tools to study coastal effects and developing internal boundary layers (IBL) are introduced, and a review on the current state of research is given. The German Bight is an interesting example to illustrate impacts of coastal effects on offshore wind energy, because of the large number of wind turbines with a coastal distance of 100 km or less. Phenomena related to the stability of the boundary layer, like low level jets, are discussed. Spatial variations of vertical heat fluxes in the coastal zone related to variable water depths or Wadden Sea areas are analysed. The study illustrates that due to the increasing size of offshore wind farms, horizontal wind speed gradients caused by coastal effects can lead to significant wind variations within a single farm. Research topics which still need further attention are discussed in the framework of the rapidly developing wind energy sector with increasing wind turbine hub heights and rotor diameters as well as growing wind farm sizes. One example is the interaction of coastal effects with offshore wind farm wakes. The necessity to consider a large spectrum of spatial and temporal scales to understand and describe coastal effects is highlighted. We summarize modelling and observation tools, which are suitable for the investigation and prediction of the boundary layer dynamics in coastal areas. Existing applications and results are described based on several examples with collocated observation and model results obtained in the X‑Wakes project. The study puts particular focus on the large potential provided by the combination of different measurements and modelling techniques and gives recommendations for future developments of integrated approaches including the formulation of priorities.
