As the offshore wind energy technology is rapidly progressing and because wind turbines at sea have a relatively short life span, repowering scenarios are already being discussed for the oldest wind farms. Ongoing developments result in larger wind turbines and an increased open airspace between turbines. Despite taller towers having larger rotor swept zones and therefore a higher collision risk area compared to smaller-sized turbines, there is increasing evidence that fewer but larger, more power-efficient turbines may have a lower collision rate per installed megawatt. As such, turbine size can offer an opportunity to mitigate seabird fatalities by increasing the clearance below the lower rotor tip. We assessed the seabird collision risk for a hypothetical repowering scenario of the first offshore wind farm zone in Belgian waters with larger turbines and the effect of an additional increase in hub height on that theoretical collision risk. For all species included in this exercise, the estimated collision risk decreased in a repowering scenario with 15 MW turbines (40.4% reduction on average) because of higher clearance between the lower tip of the turbine rotor and the sea level, and the need for a lower number of turbines per km². Increasing the hub height of those 15 MW turbines with 10 m, further decreases the expected number of seabird collisions with another 37% on average. However, terrestrial birds and bats also migrate at sea and the effect of larger turbines on these taxa is less clear. Possibly even more terrestrial birds and bats are at risk of collision compared to the current turbines. So, while larger turbines and increasing the hub height can be beneficial for seabirds, this likely needs to be applied in combination with curtailment strategies, which stop the turbines during heavy migration events, to reduce the impact on other species groups.
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RBINS Staff Publications 2022
