Transcript Document

Wind Farm Noise Impact Assessment
WIND SHEAR
w w w . h o a r e l e a . c o m
Wind shear …….
• what is wind shear ?
• how does wind shear affect wind farm noise ?
• how should wind shear be dealt with ?
What is wind shear ?
Vu
VL
What causes wind shear ?
ground roughness
Modelling wind shear due to ground roughness
VU
VU = VL x
log(HU/z0)
log(HL/z0)
HU
z0 = ground roughness length
VL
HL
ground roughness
What causes wind shear ?
atmospheric effects
What causes wind shear ?
atmospheric effects
What causes wind shear ?
atmospheric effects
What causes wind shear ?
atmospheric effects
Modelling wind shear due to atmospheric effects
m
VU
VU = VL x
HU
HU
HL
m = shear exponent
VL
HL
atmospheric effects
8
Height above ground, m
Hourly averaged wind speed, m/s
Diurnal variations in wind speeds
80
6
40
80
20
4
10
2
00:00
06:00
12:00
18:00
24:00
Time of day, hh:mm
After G.P van den Berg, WTG Noise 2005, Berlin
Diurnal variations in wind shear
Wind shear is generally highest in evening/night which are measured
under ETSU-R-97
Wind shear as a function of wind speed
0.7
0.6
Shear
Shear Exponent
Exponent
0.5
0.4
0.3
0.2
0.1
0
0
0
2
4
6
8
10
12
14
Wind Speed, m/s
16
18
20
22
24
Diurnal and seasonal variations in wind shear
0.7
Jan
Feb
all wind speeds
0.6
Mar
Apr
Shear Exponent
0.5
May
Jun
0.4
Jul
Aug
0.3
Sep
Nov
0.2
Dec
0.1
0
0
2
4
6
8
10
12
14
Hour of Day
16
18
20
22
24
Diurnal and seasonal variations in wind shear
0.7
Jan
Feb
3 m/s to 5 m/s wind speeds only
0.6
Mar
Apr
May
Shear Exponent
0.5
Jun
Jul
0.4
Aug
Sep
0.3
Oct
Nov
0.2
Dec
0.1
0
0
2
4
6
8
10
12
14
Hour of Day
16
18
20
22
24
Diurnal and seasonal variations in wind shear
0.7
Jan
Feb
6 m/s to 8 m/s wind speeds only
0.6
Mar
Apr
Shear Exponent
0.5
May
Jun
0.4
Jul
Sep
0.3
Nov
0.2
Dec
0.1
0
0
2
4
6
8
10
12
14
Hour of Day
16
18
20
22
24
Why is wind shear important for wind farm noise ?
VH
V10
Wind shear – effect on turbine sound power
110
Sound Power output, dB(A)
105
100
95
90
85
80
0
1
2
3
4
5
6
7
8
Wind speed at 10m height, m/s
9
10
11
12
Wind Farm Noise – setting acceptable limits
ETSU-R-97
Calculating wind farm noise at receptors
Wind Turbine Sound Power Output Level
60
Turbine Sound Power Level, dB(A)
55
Source Sound
Power Level
50
45
40
35
30
25
20
15
10
0
1
2
3
4
5
6
7
8
9
10
11
12
13
Wind Speed at 10m (m/s)
Noise Propagation Calculation Algorithm
Assessment Property - Quiet Day-time Periods
60
Standardised
from hub
height
55
ETSU-R-97 Noise Limit
50
L90 dB(A)
45
40
35
30
25
Wind Farm Noise Immission Level
20
15
10
0
1
2
3
4
5
6
7
8
Wind Speed at 10m (m/s)
9
10
11
12
13
Using a hub height mast only
VH
+ 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
Using measurements at two heights
VH
V2
+ Similar to first method
V1
+ Lesser measurement height: use shorter
mast and shear measured between two
heights to extrapolate up to hub height
- typically requires up to 50m high mast
V10
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
Assessment Location 1
70
Assessment Location 1
70 65
65 60
60 55
V10
L90 dB(A)
55 50
L90 dB(A)
50 45
45 40
40 35
35 30
30
25
25
20
15
20
15
10
10
0
0
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
10
10
11
11
Wind Speed at 10m (m/s)
Wind Speed at 10m (m/s)
Wind speed at 10m height (m/s)
12
12
13
13
14
1
14
Wind shear is important for wind farm noise
… and best practice
guidance is contained
in the IoA GPG