OWEMES 2006, Civitavecchia, Italy

Accuracy of Short-Term Predictions for 25 GW Offshore Wind Power in

Germany

Jens Tambke, L. v. Bremen, N. Saleck, U. Graewe, *J.-O. WolffForWind and *ICBM, Carl von Ossietzky University Oldenburg

John A. T. ByePhysical Oceanography, The University of Melbourne, Australia

Lorenzo ClaveriFMI, Finnish Meteorological Institute, Helsinki, Finland

Carsten Poppinga, Ulrich Focken, Matthias Langeenergy&meteo systems, Oldenburg, Germany

© E

lsam

A/S

Jens Tambke, University of Oldenburg / Slide 2

Overview

Numerical Weather Predictions: ECMWF & DWD

Wind Power Forecasts at FiNO1, North Sea

Combination of Inputs for Power Forecasts

25 GW Forecasts: Spatial Smoothing of Errors

Jens Tambke, University of Oldenburg / Slide 3

Analysed Observationsin North and Baltic Sea

Horns Reef

FINO1

Jens Tambke, University of Oldenburg / Slide 4

Wind Speed Measurements at FiNO1

Location: German Bight / North Sea

45km northerly of Island of Borkum

Investigated Period: Jan-Dec 2004

Heights: 33m to 103m

Jens Tambke, University of Oldenburg / Slide 5

DWD:

Lokal-Modell LM by German

Weather Service (DWD)

Horizontal Resolution:

7 x 7 km2

Vertical Resolution: 35 levels

Temporal Resolution: 1 h

Horizon of Prediction: 48 h

Evaluated Forecast Models at FiNO1

ECMWF:

European Center for Medium

Range Weather Forecasts

Horizontal Resolution:

40 x 40 km2

60 levels

3 h

Jens Tambke, University of Oldenburg / Slide 6

Typical ECMWF Wind Forecast atFiNO1, North Sea

48h

48h

Measured Wind Speed

Pre

dic

ted

Jens Tambke, University of Oldenburg / Slide 7

RMSE of Speed Forecasts at a single offshore site:FiNO1, 100m height, 12 months, 2004

DWD ECMWF

RMSE normalised to the mean wind speed (9.8 m/s):

15% to 30% 15% to 25%

Jens Tambke, University of Oldenburg / Slide 8

Accuracy of Speed Forecasts at FiNO1, 100m height,12 months, 2004

Distribution of Speed Errors : not exactly Gaussian…

Jens Tambke, University of Oldenburg / Slide 9

Calculation of Power Forecasts

Here: typical Multi-Mega-Watt Power Curve „Band Pass Filtering“ of the Time Series

+/- 1m/s +/- 10% Power

Jens Tambke, University of Oldenburg / Slide 10

RMSE of Power Forecasts atFiNO1, 100m Height, 12 months, 2004

RM

SE

% o

f P

(in

st)

DWD: 15% - 26%

ECMWF: 14% - 22%

Combination: 12% - 22%

Jens Tambke, University of Oldenburg / Slide 11

Correlation of Power Forecasts to Obs. atFiNO1, 100m height, 12 months, 2004

DWD: 0.94 - 0.78

ECMWF: 0.94 - 0.84

Combined: 0.95 - 0.84

Jens Tambke, University of Oldenburg / Slide 12

Accuracy of Power Forecasts at FiNO1, 100m height,12 months, 2004

Distribution of Power Errors: Not at all Gaussian!

Jens Tambke, University of Oldenburg / Slide 13

Temporal Speed Gradients at FiNO1, 100m height,12 months, 2004

+/- 1m/s +/- 10% Power

Interpolated ECMWF winds are too persistent

Wind Speed Difference after 1 Hour

Jens Tambke, University of Oldenburg / Slide 14

Temporal Power Gradients at FiNO1, 100m height,12 months, 2004

Interpolated ECMWF power is too persistent

Power Difference after 1 Hour

Jens Tambke, University of Oldenburg / Slide 15

Power Forecasts for 25 GW Offshore Wind Farms,12 months, 2004

Planned Wind Farms in the German Bight Source: www.bsh.de

180km

0

0,2

0,4

0,6

0,8

1

0 500 1000 1500 2000

diameter of region [km]E

rro

r R

edu

ctio

n F

acto

r

0.75

0.45

800km

Offshore Measurements for Forecast-Evaluation?

DWD Wind Speed Analysis proved to be a good substitute!

Spatial smoothing of errors same size as onshore?

Red.-Factor =RMSE(single)RMSE(region)

Jens Tambke, University of Oldenburg / Slide 16

Irish Sea North Sea Baltic Sea

110m Wind Speed Analysis from Weather Service DWDMarch 20th, 2004

Jens Tambke, University of Oldenburg / Slide 17

Correlation of Power Forecasts at 25 single Sites in the German Bight

DWD-Analysis ECMWF-Forecast

agrees well with Obs. Decay too weak

Decay weaker than Onshore!

Jens Tambke, University of Oldenburg / Slide 18

Distance of single sites

Cross correlation of forecast errors at single sites

Decay has same size as onshore

0 km 180 km

ECMWF-Forecasts evaluated against DWD-Analysis, 12 months, 2004

Correlation of Errors of Power Forecasts at 25 single Sites in the German Bight

Jens Tambke, University of Oldenburg / Slide 19

regional 25GW forecast

9%

13%

Single Offshore Sites

12% => 3 GW

RM

SE

%

of

P(i

nst

)

18%

22%

Offshore (180km) Error Reduction Factor

(3h: 0.65) ~ 0.73 (48h: 0.82)

RMSE of Forecasts for 25 GW Offshore Wind Power,12 months, 2004

Jens Tambke, University of Oldenburg / Slide 20

Offshore 25GW

13%

Single Offshore Sites

18%

22%

7% => 3.5 GW

RM

SE

%

of

P(i

nst

)

9%On+Offshore 50GW

5%

10%

Error Reduction Factor:

Offshore (180km) ~ 0.73

On+Offshore (800km) ~ 0.43

RMSE of Forecasts for 25 GW Offshore Wind Power,12 months, 2004

Jens Tambke, University of Oldenburg / Slide 21

Conclusions

Combinations of Forecasts from DWD and ECMWF

increase the Forecast Accuracy

Regional Smoothing of Errors: Same Size as Onshore

Offshore Forecasts (180km area): RMSE of 12%

On&Offshore Forecasts (800km region): RMSE of

7%

Thank you for your Attention!

This work was funded by the EU within the ANEMOS and POW’WOW Projects.

Jens Tambke, University of Oldenburg / Slide 22

Accuracy of Power Forecasts at FiNO1, 100m height,12 months, 2004

Error Frequency

DWDAbs(Error) < 15% at 36hours:230 of 350 forecast runs

ECMWFAbs(Error) < 15% at 36hours:262 of 350 forecast runs

Jens Tambke, University of Oldenburg / Slide 23

Power Forecasts for 25 single Offshore Sites,12 months, 2004

Increase with forecast time due to increasing importance of general upstream errors

Cross correlation of forecast errors at single sites

Look-ahead Time

Jens Tambke, University of Oldenburg / Slide 24

Correlation of Forecasts to Referencefor 25 GW Offshore Wind Power, 12 months, 2004

On+Offshore 50GW: 0.98 – 0.91

Offshore 25 GW: 0.97 – 0.88

Single Offshore: 0.94 – 0.85

Jens Tambke, University of Oldenburg / Slide 25

Temporal Gradients of Power Forecasts in the German Bight

Power Difference after 1 Hour

Jens Tambke, University of Oldenburg / Slide 26

Temporal Gradients of Power Forecasts in the German Bight

Power Difference after 1 Hour