Slow rotation of turbine blades at low wind speeds

Overall effectiveness category Likely to be beneficial
Number of studies: 1
Share Tweet Email

View assessment score

How is the evidence assessed?

Effectiveness

60%
Certainty

40%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

Most wind turbines operate by a ‘cut-in’ wind speed at which the turbine begins to generate electricity and the blades can move at a maximum rotation speed. However, the blades can still rotate below cut-in speeds when electricity is not being generated. Slowing the rotation of turbine blades below the cut-in speed may reduce bat fatalities, which have been found to be higher at low wind speeds (e.g. Horn et al. 2008, Rydell et al. 2010, Wellig et al. 2018).

For studies that prevent turbine blades from turning below the cut-in speed, see ‘Prevent turbine blades from turning at low wind speeds (‘feathering’)’. Cut-in speeds may also be increased in combination with this intervention. See ‘Increase the wind speed at which turbines become operational (‘cut-in speed’)’.

Horn J.W., Arnett E.B. & Kunz T.H. (2008) Behavioral responses of bats to operating wind turbines. The Journal of Wildlife Management, 72, 123–132.

Rydell J., Bach L., Dubourg-Savage M.-J., Green M., Rodrigues L. & Hedenström A. (2010) Bat mortality at wind turbines in northwestern Europe. Acta Chiropterologica, 12, 261–274.

Wellig S.D., Nusslé S., Miltner D., Kohle O., Glaizot O., Braunisch V., Obrist M.K. & Arlettaz R. (2018) Mitigating the negative impacts of tall wind turbines on bats: vertical activity profiles and relationships to wind speed. PLOS ONE, 13, e0192493.

Study locations

Key messages

One study evaluated the effects of slowing the rotation of turbine blades at low wind speeds on bat populations. The study was in Canada.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

Survival (1 study): One replicated, randomized, controlled study in Canada found that bat fatalities were reduced when turbine blades were slowed at low wind speeds.

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, randomized, controlled study in 2006–2007 at a wind farm in an agricultural area of Alberta, Canada (Baerwald et al 2009) found that slowing the rotation of turbine blades at low wind speeds resulted in fewer bat fatalities than at conventional turbines. Average bat fatality estimates were lower at experimental turbines with altered blade angles (8 bats/turbine) than at conventional control turbines (19 bats/turbine). Average bat fatality estimates did not differ significantly between turbines before the experiment (‘experimental’ turbines: 19 bats/turbine; ‘control’ turbines: 24 bats/turbine). Most bats identified during carcass searches were hoary bats Lasiurus cinerus and silver-haired bats Lasionycteris noctivagans (see original paper for data). In 2006, all of 14 turbines were operated using conventional methods (blades rotated freely at low wind speeds). In 2007, six randomly chosen turbines were altered by changing the pitch angle of the rotor blades to slow rotation at low wind speeds (<4 m/s). Eight control turbines were left unaltered. Carcass searches were conducted weekly along spiral transects up to 52 m around each of the 14 turbines in July–September 2006 and 2007. Carcass counts were corrected to account for searcher efficiency and removal by scavengers.
Study and other actions tested
Referenced paper
Baerwald E.F., Edworthy J., Holder M. & Barclay R.M.R. (2009) A large-scale mitigation experiment to reduce bat fatalities at wind energy facilities. Journal of Wildlife Management, 73, 1077-1081.

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

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Bat Conservation

Related Actions

Actions	Effectiveness	Category
Reduce turbine height Action Link	No evidence found (no assessment)	Synopsis Link
Retain a buffer between turbines and habitat features used by bats Action Link	No evidence found (no assessment)	Synopsis Link
Deter bats from turbines using radar Action Link	No evidence found (no assessment)	Synopsis Link