Master Thesis Defense by Bianca Eline Sandvik

Title: Impact of Wind Turbines on Local and Regional Winds Across Denmark

To satisfy an increasing demand for green energy, wind turbines and other renewables are being deployed at increasingly larger scales. Wind turbines extract kinetic energy from winds and thereby create wake effects – areas of lower wind speeds and more turbulence – downstream. Previous research show that wake effects can be traced several tens of kilometres downwind resulting in decreased wind energy production and local changes in climate. This thesis analyses changes in wind speed and wind direction across Denmark for the period 1990-2022 due to historical wind turbine expansion. Trends in mean monthly wind speed and angular wind directional change (a) between an observational dataset (DMI) and a simulation-based dataset (ERA5) was compared for 25 locations to identify whether a gradual increase in friction at the surface was detectable. The impact of potential wakes generated by wind turbines in the vicinity of each station is discussed.

While this study finds a general trend of decreasing wind speeds across the country, the results for changes in wind direction are inconclusive. Most locations showing significant trends were located close to the coast or airports potentially due to them being relatively open landscapes where new obstructions are easier to detect. These findings indicate that mean wind speeds are declining across Denmark due to increased surface friction. As many of the meteorological stations providing surface observations have changed locations within the study period; these discontinuities prevent several locations from achieving trend significance for either parameter for a period of at least 20 years. Results for both parameters (wind speed and wind direction) are also not always in agreement, potentially due to differences in calculation method. Direct attribution of the changes observed to wind turbine expansion was not possible.

Supervisors: Eigil Kaas and Harald Rieder (BOKU, Wienna)
Censor: Peter Aakjær