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11
Welcome to the world of wind energy
Wind SpeedWind Direction
Dr. D. V. KanellopoulosOPWP Renewable Energy
Training Program11-14 December 2016
Muscat, Oman
In the earth’s atmosphere, the ABL is the air layer near the ground affected by diurnal
heat, moisture or momentum transfer to or from the surface.
Wind speed profiles in the Atmospheric (or planetary) Boundary
Layer, ABL or PBL or BL
Boundary layer thickness varies
Surface roughness, or roughness length, Z0 or z0
Is a parameter of some vertical wind profile equations that model the horizontal mean
wind speed near the ground. In the log profile, it is equivalent to the height at which the
wind speed theoretically becomes zero.
In reality the wind at this height no longer follows a mathematical logarithm. It is so named
because it is typically related to the height of terrain roughness elements.
Whilst it is not a physical length, it can be considered as a length-scale a representation
of the roughness of the surface.
As an approximation, the roughness length is approximately one-tenth of the height of the
surface roughness elements.
For example, short grass of height 0.01m has a roughness length of approximately
0.001m.
Surfaces are rougher if they have more protrusions.
Forests have much larger roughness lengths than tundra, for example.
Roughness length is an important concept in urban meteorology as the building of tall
structures, such as skyscrapers, has an effect on roughness length and wind patterns.
When estimating the AEP of a wind farm, it has to be taken as accurate as possible.
Digitally available for use for
modeling wind energy resource
http://www.eea.europa.eu/data-and-
maps/data/corine-land-cover-2000-clc2000-
seamless-vector-database
Annual average wind speed in km/h at Canberra
Airport from 1943 to 2002. Note: the long-term (1961-
90) average is indicated by the horizontal line through
the centre of the graph
How good is a site based upon
the average annual
wind speed?
Quality of
site
Wind
speed at
10 m AGL
poor < 4 m/s
Poor-fair 4-5
fair 5-6
good 6-7
Very good 7-8
excellent > 8
Make sure you compare speeds measured for the same height above ground or sea when
comparing sites. Otherwise vertical extrapolations will be necessary.
Wind speed, m/s
% time
Time, number of hours
One year =8760 h
Yearly Duration Curve
The DC coupled with
the wt’s PC will give
the AEP
B m/s
1 0.8 - 1.7
2 1.9 - 3
3 3.3 - 5.3
4 5.5 - 7.8
5 8 - 10.5
6 10.8 - 13.6
7 13.9 - 16.9
8 17.2 - 20.5
9 20.8 - 24.4
10 24.7 - 28.3
Wind Turbulence
Fast time-scale fluctuations of less than 10 minutes in the wind
speed are associated with turbulence.
The Reynolds number of the atmospheric wind speed is
around 10^8 , which corresponds to a turbulent wind field.
The wind speed can then be decomposed in a 10 minute averaged
velocity and a turbulent fluctuation , such that during a 10
minutes sample:
The main causes of turbulence is the friction of
the wind with the earth surface, and local
fluctuations of temperature in the atmosphere.
Thus, the turbulence will depend on the
surface roughness Z0
To measure the level of turbulence,
the Turbulence intensity (TI or I) factor is used.
It is generally defined for a time scale of 10
minutes
Vw=U10
σ=wind speed standard deviation
Gusts, Ug or Vg
A discrete gust event: a, amplitude; b, rise time; c,
maximum gust variation; d, lapse time
+ve
-ve
16 Wind directions needed for wind energy analysis
symbol name
N North
NE Northeast
E East
SE South east
S South
SW Southwest
W West
NW Northwest
12 Wind directions for wind data, Oman met stations,
sectors every 30 degrees.
symbol name
N North
NNE North-North East
ENE East-North East
E East
ESE East-South East
SSE South- South East
S South
SSW South-South West
WSW West- South West
W West
WNW West- North West
NNW North-North West
Wind rose and power rose or power density
ανεμολόγιο Ξηρολίμνης 1993
0
5
10
15
20
25
30
35N
NNE
NE
ENE
E
ESE
SE
SSE
S
SSW
SW
WSW
W
WNW
NW
NNW
ανεμολόγιο "ισχύος", Ξηρολίμνη Κρήτης(% χρόνου*V3)
0
10000
20000
30000
40000N
NNE
NE
ENE
E
ESE
SE
SSE
S
SSW
SW
WSW
W
WNW
NW
NNW
1993 wind rose, Eastern Crete 1993 power rose EC, % time* Vdir^3
Predominant wind directions: NW , WNW Predominant power direction: NW
YEAR 1993 Station: Eastern Crete
direction
Speed m/s N NNE NE ENE E ESE SE SSE S SSW SW WSW W WNW NW NNW
0,5 έως 1 0,09 0,01 0,02 0,02 0,04 0,01 0,04 0,16 0,01 0,04 0,12
1 έως 2 0,02 0,19 0,14 0,11 0,11 0,1 0,11 0,12 0,27 0,35 0,17 0,27 0,57 0,19 0,31 0,36
2 έως 3 0,07 0,4 0,22 0,21 0,24 0,2 0,3 0,26 0,37 0,31 0,32 0,42 0,91 0,77 0,62 0,76
3 έως 4 0,02 0,12 0,09 0,05 0,16 0,35 0,3 0,19 0,37 0,55 0,51 0,76 1,76 1,31 1,33 0,7
4 έως 5 0,01 0,02 0,06 0,15 0,2 0,36 0,24 0,51 0,72 0,6 2,1 2,33 2,07 0,21
5 έως 6 0,02 0,05 0,05 0,05 0,09 0,21 0,26 0,4 0,75 0,86 0,27 1,9 3,54 2,18 0,29
6 έως 7 0,05 0,02 0,01 0,02 0,01 0,09 0,15 0,36 0,25 0,45 0,71 0,16 1,11 3,26 2,56 0,35
7 έως 8 0,04 0,01 0,06 0,27 0,34 0,2 0,59 0,65 0,14 0,56 3,05 2,59 0,56
8 έως 9 0,02 0,06 0,19 0,22 0,27 0,75 0,78 0,04 0,25 2,9 2,93 0,4
9 έως 10 0,02 0,01 0,01 0,07 0,21 0,16 0,12 0,39 0,75 0,06 0,11 1,73 2,94 0,5
10 έως 11 0,01 0,04 0,2 0,14 0,09 0,26 0,56 0,04 0,01 1,84 2,38 0,5
11 έως 12 0,04 0,1 0,09 0,07 0,21 0,36 0,06 1,01 2,54 0,51
12 έως 13 0,01 0,04 0,04 0,04 0,22 0,19 0,01 0,75 2,58 0,5
13 έως 14 0,06 0,09 0,05 0,19 0,12 0,01 0,36 2,29 0,98
14 έως 15 0,04 0,09 0,1 0,04 0,14 1,77 0,88
15 έως 16 0,04 0,01 0,05 0,01 0,01 1,05 0,46
16 έως 17 0,01 0,01 0,01 0,61 0,29
17 έως 18 0,11 0,11
18 έως 19 0,01 0,01 0,12 0,12
19 έως 20 0,01 0,01 0,09 0,02
>20 0,01 0,01 0,01
total 0,26 0,88 0,46 0,48 0,66 1,26 2,44 2,77 2,82 5,71 6,76 2,88 9,44 23,19 31,1
2
8,63
Combining a
duration curve
and wind rose
in one single
table, % time
for each wind
bin and each
direction. The
bin here is 1
m/s
Total =99,76%,
calm=0,24
Predominant wind
directions:
• WNW = 23.19%,
• NW = 31.12%
Oman predominate SUMMER wind directions.
Sultan Qaboos University, Renewable & Sustainable
Research Group, Research Report, May 2010
ανεμολόγιο 1990
0
5
10
15
20
25
30
35
40
45
N NE E SE S SW W NW
διεύθυνση
% χ
ρόνο
υ
Ποταμιά
Μελανιός
Wind rose
Direction
% time
Potamia
Melanios
Question: Is it possible to have differences
even in areas with close proximity?
Question: Is it possible to have differences
even in successive years in one location?
0
2
4
6
8
10
12
14
16
18
20
N ENE SE SSW W NNWΔιεύθυνση ανέμου
% χ
ρόνο
υ
Σκύρος 1983
Σκύρος 1984
Wind direction
% time
1983
1984
Question: What does the wind rose look like in
a long term analysis?
Μύκονος 1983-1989
0
5
10
15
20
25
30
35
40
NNNE
NEENE E
ESESE
SSE SSSW
SWW
SW WW
NW NWNNW
Διεύθυνση
% χ
ρόνο
υ
Wind direction
% time Mykonos Greece
The Greek land Wind
Atlas
www.cres.gr
www.rae.gr
Please keep in
mind, the atlas is
an indication,
measurements
are necessary for
bankable projects