Abstract
Bird collisions with offshore wind turbines can be avoided by curtailment of wind turbines, a so-called curtailment procedure. A curtailment can save the lives of many birds during periods of high bird migration intensity. Rijkswaterstaat is implementing a curtailment procedure for offshore windfarms on the Dutch NCP on behalf of the Ministry of Economic Affairs and Climate Policy. The curtailment procedure is based on a prediction model for mass-bird migration, which is developed by the University of Amsterdam. Part of this implementation is the decision on the height of the threshold for a curtailment.
To get a better insight on an appropriate threshold, Rijkswaterstaat asked Bureau Waardenburg to study the variation in nocturnal migration activity between locations and seasons using radar data collected at two offshore wind farms in the Dutch North Sea: Luchterduinen (LUD) and Borssele (BSA). Migration intensity clearly differed between the locations. Moreover, moments of peak migration did not necessarily coincide.
In addition, we studied the relation between wind speed, bird migration intensity and the power generated by wind turbines, to illustrate how curtailment regimes could be optimized to reduce the number of potential bird collisions and at the same time the power loss due to curtailments. Our exploration of the relation between wind speed category, bird migration intensity and power generation by offshore wind turbines shows how power loss and the percentage of avoided bird collisions are related to threshold combinations at different wind speeds. Generally, curtailments during low wind speeds yield the largest gain in the percentage of avoided bird collisions and the lowest loss in power yield. Hence, thresholds per wind category may be preferred to a single, overall threshold for curtailment, as curtailment during hours with low wind speed will lead to a lower loss of energy yield.