Bat fatalities at wind turbines have been reported at many sites and sometimes in alarming numbers. Reducing bat fatalities is important both for species protection and for positive public perception of wind turbines. Currently the only way to substantially and reliably reduce fatality numbers is to run turbines with curtailment algorithms that stop the rotor during times of high collision risk (operational mitigation).
Curtailment algorithms that reduce the number of bat fatalities are usually denied based on the wind speed measured at the nacelle of the turbine. Sometimes the time of year, time of night, temperature, and precipitation are also considered. These variables have a great influence on bat activity, and can therefore be used to predict collision risk. In an earlier study, RENEBAT I, we developed a method to quantify and reduce the collision risk for bats at wind turbines using curtailment algorithms tailored to the specific turbine or wind facility. The algorithms are based on the acoustic recording of bat activity in the rotor-swept area, as well as the wind-speed data recorded at the wind turbines in question. A “bat-friendly” curtailment algorithm then determines the times of low energy-yield and high predicted number of bat fatalities. During these periods the blades of the wind turbine rotor are feathered (adjusted parallel to the wind) with the rotor moving at a low speed (free-wheeling). This kind of turbine operation can reduce the risk of bat collisions to an annual average set by the relevant public authorities, while at the same time keeping the resulting loss in energy-yield at a minimum. Careful site-selection is however important, because at sites with low bat activity the idling times will be correspondingly short.
The English summary is available on page 17.