Offshore Wind,Power Curves and Wakes
J.Tambke, M.Doerenkaemper, G.Steinfeld, L.v.Bremen
& Prof. J.-O.Wolff
– ForWind & ICBM
University of Oldenburg, Germany
Prof. T. Osahwa
– University of Kobe, Japan
Prof. J.A.T. Bye
– The University of Melbourne, Australia
Slide 2
Overview
1. Offshore Performance of Meso-Scale Models
2. Wind Profiles and Thermal Stratification - FiNO1
3. Influence on Power Curves
4. Influence on Wakes
5. Large Scale Wakes
100m height / mean wind speed / 2km domain100m height / mean wind speed / 2km domain
Capacity Factors
Slide 4
FINO1 - 103m heightFINO1 - 103m height
9.73 m/s
9.62 m/s
-0.11 m/s (-1.2 %)
1.48 m/s (15.2 %)
0.94
8,749Sample Number
Regression Line y = 0.968 x + 0.202
Accuracy
OBS Average
WRF Average
Bias
RMSE
Correlation Coeffi.
y = 0.968 x + 0.202
0
5
10
15
20
25
0 5 10 15 20 25
Sim
ula
ted
win
d s
pee
d (
m/s
)
Observed wind speed (m/s)
WRF y = 1.024 x - 0.000
0
5
10
15
20
25
0 5 10 15 20 25
Sim
ula
ted
win
d s
pee
d (
m/s
)
Observed wind speed (m/s)
COSMO
9.73 m/s
9.96 m/s
0.23 m/s (2.4 %)
1.36 m/s (14.0 %)
0.95
8,312Sample Number
Regression Line y = 1.024 x - 0.000
Accuracy
OBS Average
CSM Average
Bias
RMSE
Correlation Coeffi.
Slide 6
Binned Wind-Speed Ratios
FiNO1: Influence of Thermal Stratification
unstable stable
Slide 7
Binned Wind-Speed Ratios
FiNO1: Influence of Thermal Stratification
unstable stable
Slide 8
Speed Ratio u90./u30 vs. 10m/L
WRF
Obs.
Monin-Obukhov
LES: Large Eddy Simulation of Wakes
@ alphaventus
Temporally
averaged u at hub
height
u
+1,7% -3% -0,2%
+2,6% -1,5% -0,2%
6 month values
Influence of Thermal Stability on Power Curves
Slide 10
Influence of Thermal Stability on Power Curves
Slide 11
Influence of Thermal Stability on Wakes
Slide 12
Influence of Thermal Stability on Wakes
Slide 13
Slide 14
Conclusions
2. Power differs by up to 10%
2. Wake effects differ by up to 20%
1. Thermal Stratification has a crucial Impact
on Offshore Wind Profiles and on Wakes
This work was funded by the German BMU within the Project OWEA (RAVE - Research at alpha ventus)
Slide 15
MO-Profiles and Boundary Layer Height zi
Mixing Length Approach from Peña & Gryning [BLM 2008]:
Unstable:
Neutral:
Stable:
Boundary Layer Height:Rossby, Montgomery [1935]
Slide 16
Speed Ratio (u90./u33) vs. Stability (z/L)
unstable
stable
u(90m)
u(33m)
< 1.05
Stability: 40m./L (Sonic.40m)
Slide 17
Speed Ratio (u90./u33) vs. Stability (z/L)
Stability: 40m./L (Sonic.40m)
Peña/Gryning 2008
Slide 18
Meso-scale Models at FiNO1
Mean Wind Speeds at 100m:~10m/s
Mean Potential Power Production:50% of the installed Capacity
Bias
m/s
RMSE
m/s
ECMWF
Op. Analysis
-0.4 1.6
DWD Op. Analysis
<-0.1 1.4
MM5 with NCEP
<-0.1 2.3
(2004)
MM5
with ECMWF
<-0.1 1.5
WRF
with NCEP
<-0.1 1.8
(2006)
FiNO1, alpha ventus
Slide 19
Mean Wind Profiles at FiNO1: DWD, WRF
WRF(MYJ-Scheme)
Observation
DWD-LME
for wind directions between 190° and 250°
Slide 20
Mean Wind Profiles at FiNO1: 0-200m
WRF
Observation
DWD-LME
for wind directions between 190° and 250°
Slide 21
Mean WRF-Profiles and Stability
-0.6
-0.3
0
+0.3
+0.6
10m/Lunstable stable-0.6 < 10m/L < +0.6
Slide 22
Uncertainty in the Wind Shear due to Temperature Errors
1. Two non calibrated Pt100: (δ(T2-T1) = ± 0.12 – 0.16°C)
2. Two calibrated Pt100: (δ(T2-T1) = ± 0.08 – 0.12°C)
3. Temperature difference sensor: (δ(T2-T1) = ± 0.04 – 0.08°C)
U30m= 10 m/s
Class 1
Class 2
Class 3
Bulk and Gradient Methods to calculate Stability are not accurate enough.
Saint-Drenan et al. EWEC 2009
Slide 23
Comparison of Mean Profiles at FiNO1
MO-ICWP
Observation
WAsP
for wind directions between 190° and 250°
Model Input: time series of wind speed at 33m height
WAsP bias = - 0.4 m/sMO-ICWP bias < +0.1 m/s
RMSE(103m) = 11%RMSE(103m) = 5.5%
Slide 24
FiNO1: Comparison of Mean Profiles
MM5(ETA-Scheme o1.5)
Observation
DWD(prog. TKE o2.5)
wind directions between 190° and 250°
Slide 25
DWD-LME Speed Ratios vs. Stability (z/L)
MM5 (NCEP)
ObservationDWD Analysis
wind directions between 190° and 250°
Slide 26
Inertially Coupled Wind Profiles
σu/u vs. Wind Speed (u) at 103m, Jan-Dec 2004
Motivation for Ekman-Approach:Turbulence Intensities at FiNO1 are very low
Slide 27
FiNO1: u* -Velocity and Wind Speed at 40m
u* (Sonic.40m)
Wind Speed (Cup.40m) [m/s]