Automatically reduce turbine blade rotation when bat activity is high

Overall effectiveness category Likely to be beneficial
Number of studies: 2
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How is the evidence assessed?

Effectiveness

80%
Certainty

60%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

This intervention involves the use of automatic bat registration systems to monitor bat activity and shut down operation of wind turbines when bat activity reaches a predetermined ‘high’ level.

Study locations

Key messages

Two studies evaluated the effects of automatically reducing turbine blade rotation when bat activity is high on bat populations. One study was in Germany, and one in the USA.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (2 STUDIES)

Survival (2 studies): Two replicated studies (one randomized, controlled and one paired sites study) in Germany and the USAfound that automatically reducing the rotation speed of wind turbine blades when bat activity is predicted to be high resulted in fewer bat fatalities for all bat species combined and for five bat species.

BEHAVIOUR (0 STUDIES)

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A replicated, paired sites study in 2012 at eight pairs of wind turbines in Germany (Behr et al 2016) found that using automated ‘bat-friendly’ operating systems that reduced turbine blade rotation speed resulted in fewer bat fatalities than at conventionally operated wind turbines. Total bat fatalities and average collision rates were lower at automated turbines (total 2 bat fatalities, 0.01 fatalities/turbine/night) than at conventionally operated turbines (total 21 bat fatalities, 0.06 fatalities/turbine/night). At automated turbines, predictive models identified periods of high fatality risk and low energy yield from bat activity and wind speed data. During these periods, rotor blades were moved parallel to the wind to reduce rotation speed according to a target bat fatality rate (0.012 fatalities/turbine/night). Conventionally operated turbines rotated freely. At each of eight sites, automated and conventional operating modes were alternated weekly between two paired turbines over 14 weeks in July–October 2012. Carcass searches were carried out daily. Carcass counts were corrected to account for searcher efficiency and removal by scavengers. If applied to all turbines, it was estimated that automated operation would result in annual energy losses of 2.1%.
Study and other actions tested
Referenced paper
Behr O., Brinkmann R., Korner-Nievergelt F., Nagy M., Niermann I., Reich M. & Simon R. (2016) Reduktion des Kollisionsrisikos von Fledermäusen an Onshore-Windenergieanlagen (RENEBAT II): Ergebnisse eines Forschungsvorhabens. Institut für Umweltplanung, Hannover report, Umwelt und Raum Bd. 7, 369pp.
A replicated, randomized, controlled study in 2015 at a wind energy facility in an agricultural area of Wisconsin, USA (Hayes et al 2019) found that using automated ‘Smart Curtailment’ operating systems that reduced turbine blade rotation speed resulted in 74–91% fewer fatalities of five bat species compared to conventionally operated turbines. Total fatality estimates were lower at automated turbines than conventionally operated turbines for eastern red bats Lasiurus borealis (automated: 34 fatalities; conventional: 220 fatalities); hoary bats Lasiurus cinereus (automated: 11; conventional: 59); silver-haired bats Lasionycteris noctivagans (automated: 5; conventional: 55); big brown bats Eptesicus fuscus (automated: 8; conventional: 31); and little brown bats Myotis lucifugus (automated: 3; conventional: 35). Twenty turbines were randomly selected (10 operated by automated systems, 10 conventionally operated). At automated turbines, fatality risk was calculated by a predictive model using real-time bat activity and wind speed data every 10 minutes. If fatality risk was high (wind speed <8 m/s and >1 bat call detected in the previous 10 minutes), rotor blades were rotated out of the wind and slowed (to ≤1 rpm) for 30 minutes. Conventionally operated turbines were ‘feathered’ to rotate slowly below a cut-in speed of 3.5 m/s. Daily carcass searches were conducted along transects in plots (80 x 80 m) centred on each of the 20 turbines in July–September 2015. Carcass counts were corrected to account for searcher efficiency and removal by scavengers. Electricity generation was reduced by 90 MWh/turbine at automated turbines during the study period.
Study and other actions tested
Referenced paper
Hayes M.A., Hooton L.A., Gilland K.L., Grandgent C., Smith R.L., Lindsay S.R., Collins J.D., Schumacher S.M., Rabie P.A., Gruver J.C. & Goodrich-Mahoney J. (2019) A smart curtailment approach for reducing bat fatalities and curtailment time at wind energy facilities. Ecological Applications, 29, e01881.

Please cite as:

Berthinussen, A., Richardson O.C. and Altringham J.D. (2021) Bat Conservation: Global Evidence for the Effects of Interventions. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

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This Action forms part of the Action Synopsis:

Bat Conservation

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Deter bats from turbines using ultrasound Action Link	Unknown effectiveness (limited evidence)	4	Synopsis Link
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Increase the wind speed at which turbines become operational (‘cut-in speed’) Action Link	Beneficial	12	Synopsis Link