• Wind speed • Wind direction • The power law wind profile • Wind profile changes from land to sea

1. 11
Welcome to the world of wind energy
Wind Speed
Wind Direction
Dr. D. V. Kanellopoulos
OPWP Renewable Energy
Training Program
11-14 December 2016
Muscat, Oman

2. 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.

3. Wind speed profiles in the Atmospheric (or planetary) Boundary
Layer, ABL or PBL or BL
Boundary layer thickness varies

4. Typical wind profiles resulting due to different atmospheric stability
conditions.

5. 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.

6. Surface roughness, typical values of z0

7. Portugal,
experimental
verification locations

8. 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

9. Land use
Z0=1 m Z0=0.25m Z0=0.03 m

10. Land and sea
u*=friction velocity

11. The power law wind profile
α depends on roughness

12. wind profile changes from land to sea
Z01 Z02

13. Wind profiles compared to IEC standard

14. Wind speed variation with time, δt=1 sec
10 minutes

15. Wind speed variation with time, δt=1 minute

16. Wind speed variation with time, δt= 1 hour
Notice the diurnal wind speed pattern

17. Daily
average
wind
speeds at
11 met
stations in
India for the
same year

18. 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

19. Analysis and presentation of wind data.
Southeast China - yearly mean wind speeds

20. 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.

21. Study 11.2014
V(m/s) at 10 m AGL
28 meteorological
stations

22. Meteorological stations

23. Annual
maximum
wind speed
from 16-31
m/s

24. Duration Curve, Frequency Distribution of wind speeds

25. Monthly Duration Curves

26. 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

27. 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

28. 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

29. Gusts, Ug or Vg
A discrete gust event: a, amplitude; b, rise time; c,
maximum gust variation; d, lapse time
+ve
-ve

30. Gusts, Ug or Vg
One hour 60 seconds

31. Wind directions-wind rose

32. Roman definitions, 30 degrees
intervals
Hellenic wind gods
Boreas

33. 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

34. 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

35. Wind rose

36. Wind rose and power rose or power density
ανεμολόγιο Ξηρολίμνης 1993
0
5
10
15
20
25
30
35
N
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
40000
N
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

37. 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%

38. 1-2-3
4-5-6
7-8-9
10-11-12
There are
variations

39. Oman predominate wind directions
WSW
WSW SSW
SSES
S

40. Oman predominate SUMMER wind directions.
Sultan Qaboos University, Renewable & Sustainable
Research Group, Research Report, May 2010

41. ανεμολόγιο 1990
0
5
10
15
20
25
30
35
40
45
N NE E SE S SW W NW
διεύθυνση
%χρόνου
Ποταμιά
Μελανιός
Wind rose
Direction
% time
Potamia
Melanios
Question: Is it possible to have differences
even in areas with close proximity?

42. 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 NNW
Διεύθυνση ανέμου
%χρόνου
Σκύρος 1983
Σκύρος 1984
Wind direction
% time
1983
1984

43. 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
N
NNE
NE
ENE E
ESE SE
SSE S
SSW SW
W
SW W
W
NW NW
NNW
Διεύθυνση
%χρόνου
Wind direction
% time Mykonos Greece

44. The onshore (land)
European Wind Atlas

45. The offshore (sea)
European Wind Atlas

47. 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

48. www.cres.gr
The Greek offshore
Wind Atlas

49. http://www.irena.org/

50. 3 m/s
6 m/s
9 m/s
The wind atlas and major power lines in Kenya
Power lines

54. 7 m/s
2 m/s
12 m/s

56. 7 m/s