But the study also found that there are those among the 25 species occurring in Germany that do not look for their prey at heights where wind wind turbine rotors are found: Mouse-eared bats (genus Myotis), for example, do not display any activity at nacelle height. They hunt very largely in the forest and rarely fly higher than the tree tops.
ENERCON was the technical cooperation partner in this study that was conducted in 2008 during an activity period from April to November. Using the SCADA system, the wind speeds at nacelle height were tracked in parallel with the acoustic recordings. As wind speeds increased, smaller species such as the common pipistrelle rarely travelled to the height of the nacelle. Presumably they are too light to stay on course during high winds.
According to the researchers, the data permits some general conclusions. One of them is: The stronger the wind, the lower the risk of collisions. So far, the researchers have not found any conclusive evidence that an increased risk for bats must be assumed for WEC sites in forested areas. This matter is, however, still under investigation; the analyses have not yet been completed.
As far as methodology goes, the acoustic detection systems installed in the nacelles have proven their worth. Their results were matched successfully to high-resolution images from thermographic cameras. The authors also present a possible approach for taking the presence of bat populations into account during the approval process for the construction of wind power converters. It involves determining which species occur in the vicinity of the wind turbines, so that the collision risks can be analysed in relation to time of day and season as well as wind speed. This information can then form the basis for the decision.
Dr. Robert Brinkmann and his colleagues presented their preliminary results during a conference at Leibniz University in Hanover. A first set of data is expected to be published in mid-2010. The short versions of the presentations with the most salient results of the study are available from the Leibniz University website.