Multi-year operational minimization study in West Virginia: Potential novel strategy to reducing bat fatalities at wind turbines

Limiting blade rotation at relatively low wind speeds (e.g. [ view full abstract ]

Limiting blade rotation at relatively low wind speeds (e.g. <5.0 m/s or <6.5 m/s) has proven to be successful in reducing bat fatalities at wind turbines. Yet, this operational minimization strategy appears to be cost prohibitive and is rarely implemented. Thus, strategies to reduce the economic impact to the industry, while maintaining the conservation value, are needed to maximize adoption. In 2012, we initiated a 3-year study at a wind energy facility in West Virginia to test the effectiveness of different operational minimization strategies to reduce bat fatalities. In 2012, we tested normal turbine operation (3.0 m/s cut-in; control) versus turbines that were feathered below 5.0 m/s for the first four hours of the night (5m/s-half-3min) and the entire night (5m/s-all-3min), with all operational changes based on 3-minute wind speed averages measured at the meteorological (met) tower. In 2013, we tested normal turbine operation versus increased cut-in speeds of 5.0 m/s all night (5m/s-all-10min) and 6.5 m/s all night (6.5m/s-all-10min), with operational changes based on 10-minute wind speed averages measured at the met tower. In 2015, we used 5.0 m/s all night based on 10-minute wind speed averages at the met tower (5m/s-all-10min-met) as the control group since turbines were operating under that regime as a minimization strategy at the site during the autumn migration period. We compared this control group to two treatments using 20-minute wind speed average measured either at the met tower (5m/s-all-20min-met) or at each individual turbine (5m/s-all-20min-turbine). In 2012, we found a significant difference between 5m/s-all-3min and the control group, but no difference between the control and the 5m/s-half-3min treatment. In 2013, we found a significant difference for both the 5m/s-all-10min and 6.5m/s-all-10min treatments versus the control, but no significant difference between the two treatment groups. In 2012, the 5m/s-all-3min treatment showed an average reduction of47%. In 2013, the 5m/s-all-10min treatment showed an average reduction of 58% and the 6.5 m/s-all-10min treatment showed an average reduction of 75%. In 2015, our results indicated significantly fewer bat fatalities occurred when turbine operations were based on the met tower rather than individual turbines. Furthermore, extending the decision time, from 10 to 20 minutes, to initiate start-up, may have contributed to lower fatalities by reducing the number of transitions (i.e., turbine start-ups and shut-downs). Minimizing the number of start-ups/shut-downs also may assist in reducing wear-and-tear on turbines and, at least in this study, may reduce the power loss related to this minimization strategy. Thus, 5m/s-all-20min-met represented a decision framework with fewer fatalities, significantly fewer than 5m/s-all-20min-turbine, and compared to 5m/s-all-10min-met had less transitions (i.e., potential turbine wear-and-tear) with slightly more power production. Therefore, the 5m/s-all-20min-met may be the most cost effective option of the 3 treatments studied in 2015. To better determine the cost-effectiveness of this novel strategy, future research should investigate the potential of modifying traditional operational minimization strategies by increasing the decision time to initiate turbine operation in other regions and as an alternative to raising the cut-in speed greater than 5.0 m/s.