Bats and wind energyCan bat activity patterns make them vulnerable to wind turbine impacts

Tiffany Thwaits NMMU

Prof. G. Kerley Dr. N. Mzilikazi

Energy Postgraduate Conference 2013

WIND ENERGY

RenewableRenewable

CleanClean

Environmentally Environmentally friendlyfriendly

88 applications for SA

40 31

BUT HAS NEGATIVE IMPACTS ON

WILDLIFE

Migratory & tree roosting species at greater risk

Wind farm/facility Total fatalities Reference

Mountaineer Wind Energy Centre (West Virginia, USA)

2092 (over 2 yrs) Kerns & Kerlinger (2004)

Casselman Wind Project (South-central Pennsylvania, USA)

784/yr Arnette et al. (2009)

Coega test turbine (Eastern Cape, SA)

17 (1 yr) Doty & Martin (2012)

Wind turbine associated mortality greater than Natural mortality

Slow to recover from adverse

effects

Long livedSlow reproductive rateSlow population growth

SO WHAT?SO WHAT?

SO WHAT?SO WHAT?

HEIGHTTIME WEATHER

BAT ACTIVITY

MONITORING BATS

BAT PASS

STUDY SITE

MITIGATION & MANAGEMENT

Different bat groups are active at different seasons and occupy

different aerial habitats

BIMODAL PEAK• activity highest 1-2hrs after sunset• 1-2hrs before

sunrise

SINGLE PEAK• activity highest 1-2hrs after sunset

• reduced activity in winter months

WEATHER & BAT ACTIVITY

Variables in global model

▪ Month

▪ Overnight average temperature

▪ Overnight average wind speed

▪ Temperature:Wind speed

▪ Month:Temperature

▪ Month:Wind

▪ Month:Temperature:Wind

Predictor variable χ2 d.f. P

Month* 121.52 4 <0.001Overnight average temperature* 51.55 1 <0.001

Overnight average wind speed 5.96 1 0.016

• Final model = weak High degree of variation in data

• Model may be dependent on other variables not quantified here

Lang et al. 2006Milne et al. 2005

Another factors involved

Temperature

Wind Speed

Barometric Pressure

Humidity

Precipitation

Season

Time of night

Insect abundanc

e

Moon Phase

Cloud cover

MODEL

Mitigation & Management

Bat activity & Monitoring

Mitigation Management

• 2hrs after sunset• High flying bats at great risk (55m)• Autumn = peak season

Increase cut in speed of blades

Curtailment

Blades spin fast so that they are more

“visible” to bats

Switch off turbines during peak seasons

or when wind conditions

unfavourable

• Post construction monitoring (fatalities)• Feasibility of mitigation methods• Evaluations of next turbine locations