Turbulenzdaten für Anwendungen in der Windenergie Evaluation von Lidarmessungen

Transcription

1 Turbulenzdaten für Anwendungen in der Windenergie Evaluation von Lidarmessungen Dr. Carolin Schmitt a David Hilbert b Markus Weimbs a a juwi Energieprojekte GmbH b Senvion SE DMG METTOOLS 2015 Offenbach

2 Wind measurements for Site Assessment Wind speed u Turbulence Turbulence intensity 10 min/1hz data TT = σ u u wind speed [m/s] time [s]?

3 Turbulence Application in Wind Energy Background and Facts Turbulence Estimates: Without Measurements General estimation of TI from surface roughness and theoretical interpolation to hub height Met Tower Measurements Measured TI and theoretical interpolation to hub height Lidar Measurement Measured TI up to hub height, no interpolation necessary, different values compared to cup anemometers due to different measurement systems

4 Turbulenz Definitions (technical) Depending on windpark layout, additional wake effects increase the total turbulence at the turbine Load estimation for single turbines

5 Turbulence Classes Turbines are desígned for different Wind/Turbulence classes according to Reference Turbulence Layout Planning including wake effects, sector management etc.

6 I_ref distribution

7 Measurement devices + previous work Cup anemometer Ground-based Lidar (VAD) Previous work Research (e.g. Sathe et al. 2011) Lidars [...] cannot measure turbulence precisely Industry (e.g. Barker et al. 2011) measure TI values [...] to an accuracy suitable for use in wind energy applications

8 Questions How do practical TI measurements from Lidars compare to those from cup anemometers? How can Lidars improve analytically derived estimates of TI?

9 Measurement basis 12 different sites (A-L) WindCubes only Co-located masts (cup anemometers) 6 flat + simple 2 hilly + partly forested 4 hilly + forested 3 WindCube v1 9 WindCube v2 simple complex 2-9 months of deployment valid data samples after filtering Concurrent time series Wake-free sectors Availability (all heights)

10 Lidar vs. cup anemometers Regression of 10 min data samples different sites y = 1.116x R² = y = 1.001x R² = 0.71 y = 1.131x R² = y = 1.045x R² = 0.76 quality of regression varies significantly Lidar more conservative with high TI

11 Lidar vs. cup anemometers Mean TI over height simple sites Lidar Cup Lidar slightly conservative over all heights (around 0.5-1% pts.)

12 Lidar vs. cup anemometers Mean TI over height complex sites Lidar Cup Lidar strictly conservative over all heights (around +2% pts.)

13 Lidar vs. cup anemometers Standard deviation of TI over height Lidar Cup Lidar in all cases conservative for STD of TI (around 1% pts.)

14 Lidar vs. cup anemometers Distribution over wind speed Lidar Cup Performance quite stable over wind speed

15 Questions How do TI measurements from Lidars compare to those from conventional masts (cup anemometers)? How can Lidars improve analytically derived estimates of TI?

16 Analytical methods Theory for neutrally stratified ABL TT z = 1 IEC distribution over wind speed ln z z 0 Approaches used in expert s reports on estimated TI

17 Real measurements vertical profile Lidar measurements vs. estimated profiles Estimated Measurement Turbulence decay with height: Stronger than suggested by theory

18 Real measurements distribution over wind speed Lidar measurements vs. IEC distributions IEC B Measurement IEC-like distribution may not be representative, even of simple sites

19 Conclusion Lidar vs. cup anemometers for TI Lidars provide a conservative measure of TI Overestimation increases with TI (complex sites!) Standard deviation of TI consistently overestimated Stable performance over all wind speeds Limitation WindCubes only How Lidars can improve analytical estimates Analytical model and IEC profiles not necessarily representative Vertical profile: decay stronger in reality Distribution over wind speed: decay may be weaker / non-existent in reality Outlook / Industry s To Dos Extend study to more sites and other Lidar manufacturers More systematic comparison of different site conditions (simple/complex/forested) Get more experience above 100 m (difficult)

20 Thanks for your Attention