11

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