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

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 hour

Notice the diurnal wind speed pattern

Daily

average

wind

speeds at

11 met

stations in

India for the

same year

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 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.

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 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

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 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

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%

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

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 onshore (land)

European Wind Atlas

The offshore (sea)

European Wind Atlas

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

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