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Het Flux-Collision Model voor de berekening van aantallen vogelslachtoffers bij windturbines
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The Flux-Collision Model for calculating potential bird collisions with wind turbines

In order to meet conditions of climate agreements, many countries are expanding in the area of renewable energy. Wind energy is an important part of this. Bird mortality resulting from collisions with wind turbines can be an issue in certain areas. Therefore, it is important to be able to predict the number of victims per type (group) as accurately as possible for planned new wind farms.

In a publication in Ecological Modeling we have compared two different models for calculating the numbers of bird collisions with wind turbines. The first model is introduced in the article and concerns the Flux-Collision Model developed by Bureau Waardenburg. This model has recently been adopted by the Dutch commission for EIAs and the Dutch advisory council for administrative jurisdiction (STAB) as the best available method for the quantification of bird mortality at wind turbines. The Flux-Collision Model uses a species (group) -specific collision probability as determined in existing wind farms (the reference wind farm). The model includes various correction factors that correct for differences between the reference wind farm and the planned wind farm. Based of the number of flight movements through the planned wind farm, in combination with the aforementioned collision probability, the number of collision victims can be calculated per species.

In the article, the Flux-Collision Model is compared with the (SOSS) Band model. This is a theoretical model in which the collision probability is calculated on the basis of species- and turbine-specific properties. In such a theoretical model, no use is made of knowledge about collision rates from existing wind farms. The (SOSS) Band model is often used in assessments of offshore wind farms.

In the research presented in the publication, the Flux-Collision Model and the SOSS Band model are compared on the basis of two case studies, one on land and one at sea. In addition, the model results for the case study on land are also compared with the results of victim surveys in the relevant wind farm. In this way it has been investigated to what extent the model results reflect the actual mortality of birds in the wind farm.

The research shows that the results of the Flux-Collision Model and the SOSS Band model are comparable. Both models are sensitive to (changes in) avoidance behaviour. However, the effect of this in the Flux-Collision Model is smaller, because in this model only a deviation for the entire wind farm (macro deviation) has to be entered, while for the SOSS Band model the total avoidance must be estimated (including avoidance of individual rotors, so-called micro-avoidance). The latter is much more difficult to measure in the field as is often much higher than the macro-avoidance. Consequently, the sensitivity of the SOSS Band model for realistic variation in avoidance is many times higher than that of the Flux-Collision Model.

When (good-quality) collision probabilities are available from an existing wind farm, we recommend applying the Flux-Collision Model. If this is not the case, but good data of avoidance behaviour (total avoidance) are available for the relevant species (group), the use of the Band model may be preferable. The location of the planned wind farm (at sea or on land) is of less importance than the availability of suitable data.

One of the important conclusions in the article is that future research should focus on measuring collision probabilities and avoidance in existing wind farms at sea, but also on land, so that this can serve as input for model calculations for future wind farms.

For questions, please contact Jonne Kleyheeg-Hartman via the contact details below.