Comparison of Operational Curtailment Strategies for Reducing Bat Mortality at Wind Facilities

Wind power offers an alternative source of energy with a smaller carbon footprint compared to traditional fossil fuels; however, more operating wind turbines could increase bat mortality due to collisions with turbine blades.... [ view full abstract ]

Wind power offers an alternative source of energy with a smaller carbon footprint compared to traditional fossil fuels; however, more operating wind turbines could increase bat mortality due to collisions with turbine blades. One approach to reduce bat mortality at operating wind facilities is to raise the cut-in speed (the wind speed which the turbine begins to generate electricity) from the standard 3.5 m/s to a higher level. We conducted a 2-year research study at the Raleigh Wind Energy Center in southwestern Ontario to compare bat mortality at wind turbines curtailed at 3.5 m/s vs 4.5 m/s (2014) and 4.0 m/s vs 4.5 m/s (2015). Estimated bat mortality rates were calculated using the Ontario Ministry of Natural Resources and Forestry (OMNRF) estimator using raw carcass counts, searcher efficiency trials, and scavenger rate trials collected using standardized searches. Within each year, comparisons between control and treatment turbines were performed by using a non-parametric permutation test and by examining 90% confidence intervals for overlap. In 2014, bat mortality at turbines with a 3.5 m/s cut-in speed were significantly higher than turbines curtailed at 4.5 m/s across all species (P = 0.001). During 2015, bat mortality at turbines curtailed at 4.0 m/s was similar to mortality at turbines curtailed at 4.5 m/s (P > 0.10). While the results of the 2014 study mirror those of other mitigation studies in North America, the 2015 study did not show significant differences in estimated bat mortality between 4.5 m/s and 4.0 m/s cut-in speeds. This suggests that implementing the 4.0 m/s cut-in speed compared to a 4.5 m/s cut-in speed would not increase estimated bat mortality, would increase the electricity generated at the project through increased operational time, and keep the mortality below the 10 bats/turbine/year threshold prescribed by the OMNRF.