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Welcome to the world of wind energyWind Speed
Wind 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
Typical wind profiles resulting due to different atmospheric stability conditions.
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.
Surface roughness, typical values of z0
Portugal, experimental verification locations
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
Land use
Z0=1 m Z0=0.25m Z0=0.03 m
Land and sea
u*=friction velocity
The power law wind profile
α depends on roughness
wind profile changes from land to sea
Z01
Z02
Wind profiles compared to IEC standard
Wind speed variation with time, δt=1 sec
10 minutes
Wind speed variation with time, δt=1 minute
Wind speed variation with time, δt= 1 hourNotice the diurnal wind speed pattern
Daily average
wind speeds at
11 met stations in
India for the same year
Figure 2. 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
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
Analysis and presentation of wind data.Southeast China - yearly mean wind speeds
How good is a site based upon the average annual
wind speed?
Quality of site
Wind speed at
10 m AGLpoor < 4 m/sPoor-fair 4-5fair 5-6good 6-7Very good 7-8excellent > 8
Make sure you compare speeds measured for the same height above ground or sea when comparing sites. Otherwise vertical extrapolations will be necessary.
Study 11.2014
V(m/s) at 10 m AGL 28 meteorological stations
Meteorological stations
Annual maximum
wind speed from 16-31
m/s
Duration Curve, Frequency Distribution of wind speeds
Monthly Duration Curves
Wind speed, m/s
% time
Time, number of hoursOne year =8760 h
Yearly Duration Curve
The DC coupled with the wt’s PC will give
the AEP
B m/s1 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
Gusts, Ug or Vg
One hour 60 seconds
Wind directions-wind rose
Roman definitions, 30 degrees intervals
Hellenic wind gods
Boreas
16 Wind directions needed for wind energy analysis
symbol nameN 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 nameN 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
Wind rose and power rose or power density
ανεμολόγιο Ξηρολίμνης 1993
05
101520253035
N
NNE
NE
ENE
E
ESE
SE
SSES
SSW
SW
WSW
W
WNW
NW
NNW
ανεμολόγιο "ισχύος", Ξηρολίμνη Κρήτης(% χρόνου*V3)
0
10000
20000
30000
40000N
NNE
NE
ENE
E
ESE
SE
SSES
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 Cretedirection
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 31,12 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%
1-2-3
4-5-6
7-8-9
10-11-12
There are variations
Oman predominate wind directions
WSW
WSW SSW
SSES
S
Oman predominate SUMMER wind directions.Sultan Qaboos University, Renewable & Sustainable Research Group, Research Report, May 2010
ανεμολόγιο 1990
05
1015202530354045
N NE E SE S SW W NW
διεύθυνση
% χ
ρόνο
υ
Ποταμιά Μελανιός
Wind rose
Direction
% time
PotamiaMelanios
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 1983Σκύρος 1984
Wind direction
% time
1983
1984
Question: What does the wind rose look like in a long term analysis?
Μύκονος 1983-1989
05
10152025303540
Διεύθυνση
% χ
ρόνο
υ
Wind direction
% time Mykonos Greece
The onshore (land) European Wind Atlas
The offshore (sea) European Wind Atlas
The Greek land Wind Atlas
www.cres.grwww.rae.gr
Please keep in mind, the atlas is
an indication, measurements are
necessary for bankable projects
www.cres.gr
The Greek offshore Wind Atlas
http://www.irena.org/
3 m/s
6 m/s
9 m/s
The wind atlas and major power lines in Kenya
Power lines
7 m/s
2 m/s
12 m/s
7 m/s