Wind energy I. Lesson 3. Wind field characterization
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Transcript of Wind energy I. Lesson 3. Wind field characterization

Wind Energy I
Michael Hölling, WS 2010/2011 slide 1
Wind field characterization

Wind Energy I
slideMichael Hölling, WS 2010/2011 2
Class content
4 Wind power
5 Wind turbines in general 6 Wind - blades
interaction
7 Π-theorem
8 Wind turbine characterization
9 Control strategies
10 Generator
11 Electrics / grid
3 Wind field characterization
2 Wind measurements

Wind Energy I
slideMichael Hölling, WS 2010/2011 3
Motivation
Why should we know anything about the wind field ?
Atmospheric boundary layer (ABL)

Wind Energy I
slideMichael Hölling, WS 2010/2011 3
Motivation
Why should we know anything about the wind field ?
Atmospheric boundary layer (ABL)

Wind Energy I
slideMichael Hölling, WS 2010/2011 3
Motivation
Why should we know anything about the wind field ?
Atmospheric boundary layer (ABL)

Wind Energy I
slideMichael Hölling, WS 2010/2011 4
http://www.ecogeneration.com.auhttp://www.wind-energy-the-facts.org
Enercon E-126 BARD 5.0
Motivation

Wind Energy I
slideMichael Hölling, WS 2010/2011 5
Motivation
GROWIAN - Große Windkraftanlage (Big Wind energy converter)

Wind Energy I
slideMichael Hölling, WS 2010/2011 6
Resource wind
Kinetic energy of wind: E =m
2· u2 =
! · V
2· u2 =
! · A · x
2· u2
Wind energy converter can NOT convert 100% of that energy ! Consequently the power of the wind energy converter is also smaller:
PWEC = cp · 12
· ! · A · u3 = cp · Pair
Corresponding power for constant velocity u : Pair =
d
dt
!! · A · x
2· u2
"
=12
· ! · A · u2 · dx
dt
=12
· ! · A · u3

Wind Energy I
slideMichael Hölling, WS 2010/2011 7
Resource wind
Power curve of wind energy converter - theory
0 10 20 300.0
0.4
0.8
1.2
1.6
2.0
u [m/s]
P(u
) [M
W]
P(u)
cut in
cut out
rated

Wind Energy I
slideMichael Hölling, WS 2010/2011 8
Power curve of wind energy converter - reality
Resource wind

Wind Energy I
slideMichael Hölling, WS 2010/2011 9
Resource wind
Annual mean wind speed taken from wind atlas

Wind Energy I
slideMichael Hölling, WS 2010/2011 10
Resource wind
Estimation of Annual Energy Production (AEP) based on annual mean wind speed from wind atlas:
0 10 20 300.0
0.4
0.8
1.2
1.6
2.0
u [m/s]
P(u
) [M
W]
P(u)
500kW!u"annual # 7m/s

Wind Energy I
slideMichael Hölling, WS 2010/2011 11
Resource wind
Is such a calculation realistic ? How does real wind behave ?
Wind velocity time series (20 days)

Wind Energy I
slideMichael Hölling, WS 2010/2011 12
Calculation of 10-minute averaged wind speed
Resource wind

Wind Energy I
slideMichael Hölling, WS 2010/2011 12
Calculation of 10-minute averaged wind speed
Resource wind

Wind Energy I
slideMichael Hölling, WS 2010/2011 13
Resource wind
Distribution of 10-minute averaged wind speeds (u
)

Wind Energy I
slideMichael Hölling, WS 2010/2011 14
Resource wind
Estimation of energy production based on wind distribution
(u)

Wind Energy I
slideMichael Hölling, WS 2010/2011 14
Resource wind
Estimation of energy production based on wind distribution
(u)

Wind Energy I
slideMichael Hölling, WS 2010/2011 14
Resource wind
Estimation of energy production based on wind distribution
E(u)
(u)

Wind Energy I
slideMichael Hölling, WS 2010/2011 14
Resource wind
Estimation of energy production based on wind distribution
E(u)
(u)

Wind Energy I
slideMichael Hölling, WS 2010/2011 14
Resource wind
Estimation of energy production based on wind distribution
E(u)
(u)

Wind Energy I
slideMichael Hölling, WS 2010/2011 14
Resource wind
Estimation of energy production based on wind distribution
E(u)
(u)

Wind Energy I
slideMichael Hölling, WS 2010/2011 14
Resource wind
Estimation of energy production based on wind distribution
E(u)
energy production:
E =N!
i=1
E(ui) =N!
i=1
counts(ui)/6 · P (ui)
(u)

Wind Energy I
slideMichael Hölling, WS 2010/2011 15
Resource wind
Comparison of energy production for mean wind speed and 10-minute averaged wind speed distribution (example based on data of 20 days):
!u" = 6.3m/s 244 kW
E = counts(< u >)[h] · P (< u >)= 24 · 20 · 244 = 117120kWh

Wind Energy I
slideMichael Hölling, WS 2010/2011 16
Resource wind
E(u)
E =N!
i=1
E(ui) =N!
i=1
counts(ui)/6 · P (ui) = 166, 920kWh

Wind Energy I
slideMichael Hölling, WS 2010/2011 17
Resource wind
Description of wind speed distribution (u
)

Wind Energy I
slideMichael Hölling, WS 2010/2011 18
Resource wind
Convert to probability density by normalization

Wind Energy I
slideMichael Hölling, WS 2010/2011 19
Distribution can be fitted by Weibull distribution
Resource wind
A = scaling parameter
k = form parameter
A = 7
k = 2.59

Wind Energy I
slideMichael Hölling, WS 2010/2011 20
Weibull distribution
Resource wind
u [m/s]

Wind Energy I
slideMichael Hölling, WS 2010/2011 21
Resource wind
Atmospheric boundary layer (ABL)
Wind speed variation with height

Wind Energy I
slideMichael Hölling, WS 2010/2011 22
logarithmic profile
roughness length for topographical effects
thermal effects
Wind field characterization
Meteorological approach:
International Electrotechnical Commission (IEC) approach:power law profile
standard for site assessment
Alternative approach: stochastic analysis
high frequency data for better understanding

Wind Energy I
slideMichael Hölling, WS 2010/2011 23
Meteorological approach
Wind speed u (mean values) as a function of height z:
Logarithmic profile:
u* = friction velocity (typically between 0.1m/s and 0.5m/s)
k = von Karman constant, about 0.4
z0 = surface roughness length

Wind Energy I
slideMichael Hölling, WS 2010/2011 24
Meteorological approach
classes 3
2
10

Wind Energy I
slideMichael Hölling, WS 2010/2011 25
Meteorological approach
classes 3
2
10

Wind Energy I
slideMichael Hölling, WS 2010/2011 26
Influence of friction velocity u* on profile
Meteorological approach

Wind Energy I
slideMichael Hölling, WS 2010/2011 27
Influence of friction velocity u* on profile
Meteorological approach

Wind Energy I
slideMichael Hölling, WS 2010/2011 28
Meteorological approach Meteorological approach
Thermal effects make ABL stable, neutral or unstableMonin Obukhov
length

Wind Energy I
slideMichael Hölling, WS 2010/2011 29
IEC approach
Wind speed u (mean values) as a function of height z:
z2
z1
Power law profile:
α needs to be fitted from data !
Commonly used for wind energy applications !
u(z) = u(z1) ·!
z
z1
"!
Velocity at height z can be determined by:

Wind Energy I
slideMichael Hölling, WS 2010/2011 30
What is the difference between the two approaches ?
Wind profile

Wind Energy I
slideMichael Hölling, WS 2010/2011 30
What is the difference between the two approaches ?
Wind profile
u(z1)
u(z2)

Wind Energy I
slideMichael Hölling, WS 2010/2011 31
Wind profile
What is the difference between the two approaches ?
u(z1)
u(z2)

Wind Energy I
slideMichael Hölling, WS 2010/2011 32
Site characterization / assessment
IEC demands information for site characterization:
annual mean wind velocity
parameters for Weibull distribution of 10-min averaged wind speeds
annual mean wind profile
turbulence intensity Ti =!<u>10min
< u >10min

Wind Energy I
slideMichael Hölling, WS 2010/2011 33
Alternative approach
What happens in reality ?

Wind Energy I
slideMichael Hölling, WS 2010/2011 34
What happens in reality ?
Alternative approach