Avian Collision Risk with Reference Wind Turbines: Effects of Geometry, Operation, and Flight Height Distribution

The expansion of wind energy, while essential for the energy transition, poses serious collision risks to birds, particularly due to the rotating blades of wind turbines. When conducting environmental impact assessments, accurate quantification of these risks is challenging, especially offshore, and it relies heavily on collision risk models. This study investigates the influence of wind turbine geometry and operational parameters on avian collision probability, utilising the Band model in combination with four well-documented reference wind turbines. By systematically varying turbine characteristics and bird flight height distributions, the analysis reveals that both turbine design and the vertical distribution of bird flight critically affect collision risk estimates. Generally, turbines with higher power ratings and larger rotor diameters exhibit lower collision probabilities, which is attributed to their lower rotor speed. The study further introduces an adaptation of the standard Band model, which incorporates a more detailed blade geometry, including local airfoil thickness and twist. With a few exceptions, this updated model increases the predicted collision probabilities. By basing the analysis on open source reference wind turbines, the present study establishes transparent methodologies and improves reproducibility and benchmarking in collision risk assessments. The results highlight the need for species- and site-specific modelling, as well as the value of refined turbine representations, to support effective mitigation strategies and nature-inclusive wind farm planning.