1. Wind Farm Noise Impact Assessment
WIND SHEAR

2. Wind shear ……. what is wind shear ?
how does wind shear affect wind farm noise ?
how should wind shear be dealt with ?

3. What is wind shear ? VL Vu

4. What causes wind shear ?
ground roughness

5. Modelling wind shear due to ground roughnessVU VL VU VL =
log(HU/z0)
log(HL/z0) x HU
z0 = ground roughness length HL
ground roughness

6. What causes wind shear ?
atmospheric effects

7. What causes wind shear ?
atmospheric effects

8. What causes wind shear ?
atmospheric effects

9. What causes wind shear ?
atmospheric effects

10. Modelling wind shear due to atmospheric effectsVU VL = x HU HL m VU VL HU
m = shear exponent HL
atmospheric effects

11. Diurnal variations in wind speeds
Time of day, hh:mm
Hourly averaged wind speed, m/s 2 4 6 8
00:00
06:00
12:00
24:00
18:00 80 80 40 20 10
Height above ground, m
After G.P van den Berg, WTG Noise 2005, Berlin

12. Diurnal variations in wind shear
Wind shear is generally highest in evening/night which are measured under ETSU-R-97

13. Wind shear as a function of wind speed

14. Diurnal and seasonal variations in wind shear
all wind speeds

15. Diurnal and seasonal variations in wind shear
3 m/s to 5 m/s wind speeds only

16. Diurnal and seasonal variations in wind shear
6 m/s to 8 m/s wind speeds only

17. Why is wind shear important for wind farm noise ?VH
V10

18. Wind shear – effect on turbine sound power

19. ETSU-R-97 sets noise limits as a function of 10m height wind speed
Wind Farm Noise – setting acceptable limits
ETSU-R-97
ETSU-R-97 sets noise limits as a function of 10m height wind speed

20. Calculating wind farm noise at receptors
Source Sound Power Level
Wind turbine noise emissions are also specified as a function of 10m height wind speed
Noise Propagation Calculation Algorithm
Wind Farm Noise Immission Level
ETSU-R-97 Noise Limit
Standardised from hub height

21. Using a hub height mast onlyVH
+ background noise and turbine SWL’s both related to the same ‘real’ wind speed
+ requires no assumptions about site specific shear profile
- typically requires >50m high mast
V10

22. Using measurements at two heightsVH V2
+ Similar to first method
+ Lesser measurement height: use shorter mast and shear measured between two heights to extrapolate up to hub height V1
- typically requires up to 50m high mast
V10

23. Wind speed at 10m height (m/s)
Using a 10m mast only VH
+ cheapest and easiest option
- Need to have data or make assumptions on shear profile on the site
+ IOA GPG provides simplified corrections for use
Wind speed at 10m height (m/s)
V10

24. Wind shear is important for wind farm noise
… and best practice guidance is contained in the IoA GPG