OPERATIONAL MITIGATION OF WIND TURBINES TO AVOID BAT FATALITIES: A SYNTHESIS OF EXISTING STUDIES

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1 OPERATIONAL MITIGATION OF WIND TURBINES TO AVOID BAT FATALITIES: A SYNTHESIS OF EXISTING STUDIES Wally Erickson, Greg Johnson, David Young, Ed Arnett, Cris Hein NWCC Webinar January 28, 2013

2 In 2003, between 1,398 and 4,031 bats estimated to have been killed at the Mountaineer Wind Energy Facility in West Virginia

3 Key Patterns and Relationships High estimates of bat mortality have seasonal patterns: bat mortality tends to increase after July 15 and tapers off after October 15. Studies have shown an inverse relationship between mortality and wind speed; more bat fatalities are observed on nights with low wind speeds. Sources: Arnett et al. 2005, 2008 Fatalities/turbine/night MOUNTAINEER Fatalities/turbine/night MEYERSDALE windspeed (m/s) windspeed (m/s)

4 Thermal Imaging Patterns Bat activity positively related to low wind periods and higher ambient temperatures No bats killed at non-moving turbines

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6 Changing turbine cut-in speed Several studies have investigated the effects of raising the turbine cut-in speed on bat mortality. Cut-in speed is the wind speed at which the turbine is able to generate electricity to the grid. This measure effectively reduces turbine operations (and electricity generation) during periods when wind is below the new cut-in speed. Costs Availability of turbines to generate electricity is lowered can have contractual ramifications; Reduced generation while winds are between the normal turbine cut-in speed and the raised cut-in speed economic ramifications.

7 Not all turbines are created equal or operate the same Blade tip speed for different turbines as a function of wind speed.

8 Synthesis of studies a BWEC priority Studies to date 7 completed, several ongoing Germany study (results not publically available) Summerview Wind Power Project, Alberta Casselman Wind Project, Pennsylvania Fowler Ridge Wind Farm, Indiana Mount Storm Wind Energy Facility, West Virginia Two other anonymous facilities Also, others in 2012 (e.g., Sheffield, VT) results pending Studies have typically involved a control-treatment study design with variations in search interval, number of turbines studied, cut-in wind speeds, and feathering of turbine blades.

9 Summerview Wind Power Project, Alberta Study compared normally operating turbines to turbines with (A) an adjusted cut-in speed of 5.5 m/s and (B) turbines that were idled below normal cut-in speed (4.0 m/s) Study Period Aug 1- Sept 7, 2007 Baerwald, E.F., J. Edworthy, M. Holder, and R.M.R. Barclay A Large-Scale Mitigation Experiment to Reduce Bat Fatalities at Wind Energy Facilities. Journal of Wildlife Management 73(7):

10 Summerview Wind Power Project, Alberta Vestas Turbines; Aug 1 Sep ; weekly searches; Control Treatment Treatment Results 15 turbines, 5.5 m/s cut-in speed 8 turbines, normal operation 4.0 m/s cut-in speed 6 turbines, idling blades pitched to reduce rotation in low wind speeds Raised 5.5 m/s cut-in speed = bats/turbine Idling (4.0 m/s cut-in speed) = bats/turbine Control = bats/turbine Experimental treatments showed 57-60% reduction in bat mortality No difference between experimental treatments

11 Casselman Wind Project, Pennsylvania 2008 & 2009 Two year study compared normally operating turbines to two treatment groups (A) an adjusted cut-in speed of 5.0 m/s and (B) an adjusted cut-in speed of 6.5 m/s Study Periods: Jul 27-Oct 9, 2008 & July 26 Oct 8, 2009 Arnett, E.B., M.M.P. Huso, M.R. Schirmacher, and J.P. Hayes Altering turbine speed reduces bat mortality at windenergy facilities. Frontiers in Ecology and the Environment 2010; doi: /

12 Casselman Wind Project, Pennsylvania 2008 & 2009 Casselman, Pennsylvania July 26 October 9, 2008, July 26 October 8, 2009 Control Treatment Treatment Results 12 turbines, 12 turbines, 5.0 m/s cut-in 6.5 m/s cut-in speed speed 12 turbines, normal operation, 3.5 m/s cut-in speed Raised 5.0 m/s cut-in speed = 0.27 (95% CI: ) bats/turbine Raised 6.5 m/s cut-in speed = 0.53 (95% CI: ) bats/turbine Control = 2.04 (95% CI: ) bats/turbine Experimental treatments showed 44-93% reduction in bat mortality. Difference between experimental treatments not statistically significant

13 Fowler Ridge Wind Farm, Indiana 2010 & 2011 Two years of study: Aug 1 Oct 15, 2010 & July 15 Oct 15, study similar to previous study at Casselman with two cut-in speed adjustments (no blade feathering) 5.0 m/s and 6.5 m/s 2011 study investigated feathering turbine blades at 3 different cut-in wind speeds: 3.5 m/s, 4.5 m/s, and 5.5 m/s

14 Fowler Ridge Wind Farm, Indiana 2010 Fowler Ridge, Indiana August 1 October 15, 2010 Control Treatment Treatment Results 9 turbines, 9 turbines, 5.0 m/s cut-in 6.5 m/s cut-in speed speed 18 turbines, normal operation, 3.5 m/s cut in speed Raised 5.0 m/s cut-in speed = 7.0 (95% CI: ) bats/turbine Raised 6.5 m/s cut-in speed = 3.0 (95% CI: ) bats/turbine Control = 14.0 (95% CI: ) bats/turbine Experimental treatments showed approximately 50% and 78% reduction in bat mortality

15 Fowler Ridge Wind Farm, Indiana 2011 Fowler Ridge, Indiana July 15 October 15, 2011 Control Treatment Treatment Treatment Results 9 turbines, 42 turbines, 42 turbines, 42 normal operation, blades feathered blades feathered turbines, blades 3.5 m/s cut below 3.5 below 4.5 feathered in speed m/s cut in speed m/s cut in speed below 5.5 m/s cut in speed 3.5 m/s cut in w/ feathering = 66 bats found 4.5 m/s cut in w/ feathering = 42 bats found 5.5 m/s cut in w/ feathering = 25 bats found Control = 105 bats found Experimental treatments showed 36%, 57%, and 73% reductions in bat fatalities, respectively

16 Mount Storm, West Virginia 2010 & 2011 Intent was to investigate effects of turbines that are not producing electricity on bat mortality. Normally, the Mount Storm turbines freewheel ( hunting the wind, wind-seek mode ) - spin at up to 9 rpm in winds under normal cut-in speed of 4 m/s. Impacts associated with freewheeling turbines (those spinning below the normal cut-in speed when they are not producing electricity) was unknown study used a weather forecast approach to predict when bat mortality might be high; manually feathered 2011 process of feathering blades was automated so turbines self-regulated

17 Mount Storm, West Virginia 2010 July 15 October 13, 2010 Control Treatment Treatment Results 8 turbines, normal operation, turbines, 4.0 m/s cut-in speed blades 8 turbines, 4.0 m/s cut-in speed blades m/s cut in speed feathered for first feathered for half of night second half of night Feathering first half of night = 59 bats found Feathering 2 nd half of night = 86 bats found Control = 111 bats found Experimental treatments showed approximately 47% and 23% reduction in bat mortality when comparing all nights Experimental treatments showed approximately 72% and 50% reduction in bat mortality when comparing only nights feathering was in effect

18 Mount Storm, West Virginia 2011 July 15 October 15, 2011 Control Treatment Results 12 turbines, normal operation, 4.0 m/s cut in speed 12 turbines, blades feathered below 4.0 m/s cut in speed automatically (turbines self monitored and when wind speed dropped below 4.0 m/s for 6 minutes they paused) Automated feathering = 39 bats found Control = 43 bats found Experimental treatment showed 9% reduction in bat fatalities**

19 Other Studies Anonymous site in Midwest region: 47% (4.5), and 72% (5.5) reduction Anonymous site in Southwest region: 20.1% (4.0), 34.5% (5.0 ½ night), 32.6% (5.0 all night), 38.1% (6.0).; No sig differences between 4, 5 and 6 *High % of TABR kills Sheffield, VT 2.7x more fresh carcasses found at control (fully operational) compared to treatment turbines (6.0 m/s)

20 Mean reductions relative to cut-in Results from publicly available operational adjustment studies. Study Name Mean Cut-in Mean Percent Percent Speed Reduction in Mortality Reduction (m/s) Per Cut-in Speed in Mortality Fowler Ridge Mount Storm a 4 64 Summerview Fowler Ridge Casselman Casselman Fowler Ridge 2010 b 5 50 Summerview Fowler Ridge Casselman Casselman Fowler Ridge 2010 b a average reduction from first and second halves of the night b Study did not include feathering below cut-in speed Mean % Reduction in Mortality Cut-in Speed (m/s)

21 Conclusions Studies consistently demonstrate that substantial reductions in bat mortality can be achieved with relatively little loss in operating time but variation can be expected

22 Conclusions May find variable results depending on species composition of fatalities freetail bats can and often do fly at wind speeds > than cut-in speeds tested

23 Conclusions Power loss variable and not all studies currently reporting but <1% total annual production documented

24 Recommendations-Next Steps Look at RMPs/tip speed and operating time relative to kills Tip speed at or below which no bat fatalities occur

25 Recommendations-Next Steps Look at RMPs-operating time relative to kills Add temperature or other variables to decision on when to curtail. Ultimately bat friendly turbine automation that self regulates based on several variables. For example: Date (e.g., August 1 to September 30) Time of day (e.g., between sunset and sunrise) Wind speed (e.g., less than 6.0 m/s) Temperature (e.g., nights when temp is >50 o F) Turbine operational adjustments should include adjusting the turbine blade pitch on lower wind speed nights (< cut-in) to minimize rotation of the rotor

26 Recommendations Implement broadly at sites with moderate to high fatalities

27 Acknowledgements Many folks played a significant role in the studies: Companies operating Mount Storm; Fowler Ridge, Casselman, Summerview, Sheffield provided study sites. Numerous field technicians tirelessly searched plots around turbines daily!

28 THANKS QUESTIONS??