Uncertainty in a post-construction
energy yield estimate
Sónia Liléo, Johannes Lindvall and Johan Hansson
Contents
Methodologies for post-construction
assessment of the wake reduced gross
production (i.e., gross AEP – wake losses)
Methodologies for the post-construction
assessment of non-full performance losses
Dependence on the operational period length
Uncertainty assessment
ProdOptimize
•
Research project within the Vindforsk IV programme
•
Mainly financed by the Swedish Energy Council and
the branch organization Elforsk.
•
Partly co-financed by:
Assessment and optimization of the energy
production of operational wind farms
Measured short-term wind series
Post-construction assessment methods
4 Modelled long-term wind series A: Nacelle anemometer wsp B: None C: None D: None A: WRF ERA-Interim B: WRF ERA-Interim C: WRF ERA-Interim D: WRF ERA-Interim LTC method to calculate farm’s long-term wind
Used power curve
A: U&N method
C: None
B: None
D: None
A: Sectorwise PC relates nacelle anem wsp and prod power for each wtg
B: Sectorwise PC relates modelled wsp and prod power for each wtg
C: Sectorwise PC relates modelled wsp and modelled power (PPV model)
D: None
Modelled long-term power series
A: 10-min LT power series
C1: Weekly LT power series
D: Monthly wind index
B: 10-min LT power series
C2: Monthly LT power series
Wake Reduced Gross AEP
A: Annual mean value
C1: Linear reg modelled and
actual prod on a weekly basis. Fit applied on remaining series.
AEP = 52.18*Weekly mean value.
C2: Linear reg modelled and
actual prod on a monthly basis; Fit applied on remaining series.
AEP = 12 * Monthly mean value
B: Annual mean value
D: Linear reg wind index and
actual prod on a monthly basis. AEP = 12*Prod normal month
E: None E: WRF ERA-Interim
extrapol. to each wtg position using WAsP
E: None
E: 1-hour LT power series
E: Official PC for density corrected (1h res) wsp
E: Wake model run for each time step and for each wtg. Modelled production adjusted to actual production for full performance periods.
Obtained mean ratio applied on remaining series.
Post-construction assessment methods
5
Used methods
A: Measured wsp ; Measured PC
C1: Modelled wsp; Modelled PC;
Regression weekly basis
C2: Modelled wsp; Modelled PC;
Regression monthly basis
B: Modelled wsp; Measured PC
D: Monthly wind index
Model developed by KVT in partnership with the University of Oslo
(UiO) and Statkraft. The project was financed by the Norwegian
Research Council (50 %), Statkraft (40 %), and KVT (10 %)
Simulates the production of each turbine of a wind farm in the
time domain, including density correction and wake modeling in
the time domain (1 h resolution)
Has been validated against data from the Norwegian wind farms
Smøla and Kjøllefjord owned by Statkraft
Method E: Newly developed model
Comparison of the methods
Wind farm 1
Nr of operational months after the first 6 months of operation
No
rmaliz
ed
W
ak
e
Re
duc
ed
Gro
ss
AE
P
Deviation of up to 8 %
between the methods
based on 2.5 y data
Normalized by the average
Wake Reduced Gross for max nr of months
First 6 months of operation not included in the calculation
Comparison of the methods
Nr of operational months after the first 6 months of operation
No
rmaliz
ed
W
ak
e
Re
duc
ed
Gro
ss
AE
P
Wind farm 2
Deviation of up to 2 %
between the methods
based on 5.5 y operation
Deviation of up
to 8 %
Methodologies for the post-construction
assessment of non-full performance losses
9
Method 1
Historical power curve relating the nacelle anemometer wind
speed and the produced power
Met
hods
presented
in I
EC/TS
61
40
0-26
-2
Method 2
Average production of wind farm
Method 3
Average production of most representative neighbour turbines
chosen subjectively based on proximity/terrain charactieristices
Method 4
Power correlation matrix
Method 5
Production of the most representative neighbour turbine chosen
objectively based on lowest historical sectorwise deviation
Method 6
Nr of operational months after first 6 months of operation
N
or
maliz
ed
non
-full
per
formance
los
se
s
(%)
Comparison of the methods
Wind farm 1
Very large deviation
between the methods
Normalized by the average
non-wake losses for max nr of months
Comparison of the methods
Nr of operational months after first 6 months of operation
Wind farm 2
Deviation of
up to 40 %
Deviation of up
to 25 % of the
estimated loss
Nor
malized
non
-ful
l
performanc
e
loss
es
(%)
In case of a non-full perf loss of 6 % Deviation of 40 % = 2.4 % Deviation of 25 % = 1.5 %Nr of operational months after first 6 months of operation
N
or
maliz
ed
non
-full
per
formance
los
se
s
(%)
Comparison of the methods
Wind farm 1
Very large deviation
between the methods
Normalized by the average
non-wake losses for max nr of months
Nacelle anemometer performance
13Nacelle anemom wsp T1 [m/s]
Na
c
elle
ane
mom
ws
p
T2
[m
/s]
Wind farm 2
Wind farm 1
T1 & T2 full perf
T1 not full perf & T2 full perf
Different accuracy of the
nacelle anemometer wsp when turbine is in full perfrmance compared to when it is not in full performance
Higher uncertainty in
Method 1 for Wind farm 1 than for Wind farm 2
Nr of operational months after first 6 months of operation
Comparison of the methods
Wind farm 1
Deviation of up to
40 % of the
estimated loss
Not reliable
No
rmaliz
ed
non
-full
pe
rfor
man
ce
los
s
es
(
%)
Methodologies for post-construction assessment of the
wake reduced gross production
15
A
MeasWind
MeasPC
B
ModWind
Meas PC
C
ModWind
ModPC
D
Mod
WindIndex
E
WFS
Short operational
period
-
-
+
-
+
Long oper. period but
large amount of
non-full performance
periods
+
+
-
-
+
Non-consistent
nacelle anemometer
wind speed
-
+
+
+
+
Conclusions
+
More recommended
-
Less recommended
Methodologies for post-construction assessment of
non-full performance losses
16
1
Hist
PC
2
Average
WF prod
3
Average
Repres
WTGs
4
PCM
5
Most
Repres
WTG
6
WFS
Large amount of non-full
performance periods
+
-
-
-
-
+
Change in nacelle anemometer
calibration during the oper period
-
+
+
+
+
+
Different accuracy of the nacelle
wind speed for full and non-full
performance periods
-
+
+
+
+
+
Large variation in mean wsp
between wtg positions
+
-
-
+
+
+
Conclusions
Methods presented
in IEC/TS 61400-26-2
Uncertainty
Wind farm 1
Wind farm 2
Based on 2.5 y oper
Based on 2.5 y Based on 5.5 y
Input data 1 – 2 % 1 – 2 % 1 – 2 %
Method for the estimate of Wake Reduced Gross AEP
8 % 8 % 2 %
Estimate of
non-full perf losses 2.4 % 2.4 % 1.5 % Assumption that future turbine performance will be equal to past performance 2 - 3 % 2 - 3 % 2 - 3 % Assumption that future wind climate will be equal to past wind climate
4 % 4 % 4 %
Total 9.0 – 10.0 % 9.0 – 10.0 % 5.0 – 6.0 %
Total uncertainty in the post-construction AEP
Conclusions
First 6 months not included
Uncertainty
Wind farm 1
Wind farm 2
Based on 2.5 y Based on 2.5 y Based on 5.5 y Input data 1 – 2 % 1 – 2 % 1 – 2 %
Method for the estimate of Wake Reduced Gross AEP
8 % 8 % 2 %
Estimate of
non-full perf losses 2.4 % 2.4 % 1.5 % Assumption that future turbine performance will be equal to past performance 2 - 3 % 2 - 3 % 2 - 3 % Assumption that future wind climate will be equal to past wind climate
4 % 4 % 4 %
Total 9.0 – 10.0 % 9.0 – 10.0 % 5.0 – 6.0 %
Total uncertainty in the post-construction AEP
Conclusions
First 6 months not included
For non-full perf loss of 6 %
Uncertainty
Wind farm 1
Wind farm 2
Based on 2.5 y Based on 2.5 y Based on 5.5 y Input data 1 – 2 % 1 – 2 % 1 – 2 %
Method for the estimate of Wake Reduced Gross AEP
8 % 8 % 2 %
Estimate of
non-full perf losses 2.4 % 2.4 % 1.5 % Assumption that future turbine performance will be equal to past performance 2 - 3 % 2 - 3 % 2 - 3 % Assumption that future wind climate will be equal to past wind climate
4 % 4 % 4 %
Total 9.0 – 10.0 % 9.0 – 10.0 % 5.0 – 6.0 %
Total uncertainty in the post-construction AEP
Conclusions
First 6 months not included
For non-full perf loss of 6 %
Uncertainty
Wind farm 1
Wind farm 2
Based on 2.5 y Based on 2.5 y Based on 5.5 y Input data 1 – 2 % 1 – 2 % 1 – 2 %
Method for the estimate of Wake Reduced Gross AEP
8 % 8 % 2 %
Estimate of
non-full perf losses 2.4 % 2.4 % 1.5 % Assumption that future turbine performance will be equal to past performance 2 - 3 % 2 - 3 % 2 - 3 % Assumption that future wind climate will be equal to past wind climate
4 % 4 % 4 %
Total 9.0 – 10.0 % 9.0 – 10.0 % 5.0 – 6.0 %
Total uncertainty in the post-construction AEP
Conclusions
First 6 months not included
For non-full perf loss of 6 %
Uncertainty
Wind farm 1
Wind farm 2
Based on 2.5 y Based on 2.5 y Based on 5.5 y Input data 1 – 2 % 1 – 2 % 1 – 2 %
Method for the estimate of Wake Reduced Gross AEP
8 % 8 % 2 %
Estimate of
non-full perf losses 2.4 % 2.4 % 1.5 % Assumption that future turbine performance will be equal to past performance 2 - 3 % 2 - 3 % 2 - 3 % Assumption that future wind climate will be equal to past wind climate
4 % 4 % 4 %
Total 9.0 – 10.0 % 9.0 – 10.0 % 5.0 – 6.0 %
Total uncertainty in the post-construction AEP
Conclusions
Assuming 2 % unc in wsp First 6 months not includedFor non-full perf loss of 6 %
Uncertainty
Wind farm 1
Wind farm 2
Based on 2.5 y Based on 2.5 y Based on 5.5 y Input data 1 – 2 % 1 – 2 % 1 – 2 %
Method for the estimate of Wake Reduced Gross AEP
8 % 8 % 2 %
Estimate of
non-full perf losses 2.4 % 2.4 % 1.5 % Assumption that future turbine performance will be equal to past performance 2 - 3 % 2 - 3 % 2 - 3 % Assumption that future wind climate will be equal to past wind climate
4 % 4 % 4 %
Total Uncertainty 9.0 – 10.0 % 9.0 – 10.0 % 5.0 – 6.0 %
