Thursday. 22 April 2010 Wind Lidar measurement optimization in complex terrain Matthieu Boquet, Laurent Sauvage, Rémy Parmentier, Jean-Pierre Cariou - LEOSPHERE/NRG Ferhat Bingöl – Risø DTU Dimitri Foussekis – CRES Armand Albergel – Aria Technologies Guillaume Dupont – Meteodyn Catherine Meissner – WindSim

Lidar measurement in complex terrain 2 Thursday, 22 April 2010 Agenda Introduction: complex terrain requirements Wind Lidar volume measurement vs. cups point measurement: assumptions for direct comparison and validity of these assumptions CFD modeling and WindCube measurement process simulation Geometrical optimization and CFD combination for improving Lidar measurement in complex terrains Conclusions

Lidar measurement in complex terrain 3 Thursday, 22 April 2010 Wind Resource Assessment Program Estimate the wind speed distribution: On-site measurement: masts and remote sensors Meteorological stations and airports records Flow modeling software to extend measurements both in space (hub height and turbines location) and time (long-term scaling) In complex terrain: Requires more on-site measurement locations to gain certainty in the WS estimation A remote sensor is a precious complementary system: But performances need to reach cup standards, i.e. bias<2%

Lidar measurement in complex terrain 4 Thursday, 22 April 2010 Pulsed Wind Lidar principle HOW AND HOW WELL DOES THE WINDCUBE TM RETRIEVE WIND VELOCITY VERTICAL PROFILES?

Lidar measurement in complex terrain 5 Thursday, 22 April m -10m Lidar volume measurement principle 1) Pulse length and beam width 2) Conically scanning Probed volumes are away one from another 3) Sequentially scanning

Lidar measurement in complex terrain 6 Thursday, 22 April 2010 Radial velocities measurement v v rad = v.axis beam Laser shooting direction aerosols v rad Radial velocity is the projection of aerosols velocity on laser beam axis Flow homogeneity assumption: aerosols velocity is the same at every radial velocity measurement location U, V and W can be resolved

Lidar measurement in complex terrain 7 Thursday, 22 April 2010 FlatModerately complexMountainous Terrain complexity influence Lidar + mast Forest Terrain slope 10° Wind direction South- East: Plateau, no trees North- West: 10° slope, trees At 80m Slope = Slope = At Risø test site Høvsøre (onshore 1st phase of Norsewind Project) Observed relative difference:~1% Observed relative difference:~2% Observed relative difference:~6%

Lidar measurement in complex terrain 8 Thursday, 22 April 2010 CFD Modeling analysis USING A CFD MODELING TO BETTER UNDERSTAND THE LIDAR AND ANEMOMETER DIFFERENCES IN COMPLEX TERRAIN

Lidar measurement in complex terrain 9 Thursday, 22 April 2010 Complex Spanish site North-West wind MERCURE/Aria Technologies CFD model adapted to complex topography Stationary CFD: A study of Lidar wind velocity retrieval process under various distorted flow conditions Simulation of Lidar measurement process with MatLab Met mast WindCube North-West wind

Lidar measurement in complex terrain 10 Thursday, 22 April 2010 Lidar vs. cup simulation Lidar overestimation >5% Lidar underestimation <-5% North-West Wind Terrain elevation represented with colors Black stars: locations of Lidar and cup measurement simulation CFD simulation On site measurement -5.8%-6.1%

Lidar measurement in complex terrain 11 Thursday, 22 April 2010 Horizontal gradient of vertical wind speed dependency Lidar-cup relative difference vs. horizontal gradient of the horizontal wind speed No dependency Lidar-cup relative difference vs. horizontal gradient of the vertical wind speed Clearly correlated

Lidar measurement in complex terrain 12 Thursday, 22 April 2010 Geometrical Optimisation HOW CAN WE MODIFY THE LIDAR MEASUREMENT PROCESS TO GET CLOSER TO CUP?

Lidar measurement in complex terrain 13 Thursday, 22 April 2010 Reducing the scanning cone ? Probing a smaller volume then more homogeneous ? No! At a given height, difference depends only on horizontal gradient of vertical wind speed No magical scanning cone angle Dangerous below 15° and above 30° U U U W1W1 W2W2 W3W3 Radial vel. Source of Bias

Lidar measurement in complex terrain 14 Thursday, 22 April ° vs. 15° - CRES data 30° cone angle15° cone angle

Lidar measurement in complex terrain 15 Thursday, 22 April 2010 Adding more lines of sight ? Consider first order variation of wind speed As new unknown variables are introduced, one should add new Lidar equations to retrieve them However, a line of sight LOS i gives the radial velocity S i : No LOS brings info on W i

Lidar measurement in complex terrain 16 Thursday, 22 April 2010 Lidar-CFD combination COULD A CFD MODEL BRING THE MISSING INFO?

Lidar measurement in complex terrain 17 Thursday, 22 April 2010 Using a model to correct Lidar data Model can provide the essential site specific info on the vertical wind speed distribution to correct Lidar data Modeling Relative difference on siteRelative difference with corrected Lidar

Lidar measurement in complex terrain 18 Thursday, 22 April 2010 Methodology validation Meteodyn WT and WindSim correction add-on tested on 2EN and CRES WindCubes on complex Greek site CFD combination gets the bias from 6% down to 1%

Lidar measurement in complex terrain 19 Thursday, 22 April 2010 Conclusion Point and volume measurement leads to wind speed value differences in complex terrain Vertical wind speed loss of homogeneity is the main source of error Scanning cone angles between 15°-30° act similarly for horizontal wind speed More lines of sight are not more useful info Meteodyn WT and WindSim add-on: WINDCUBE ® Lidars data are now quantitatively useable on all types of terrain

Lidar measurement in complex terrain 20 Thursday, 22 April Questions ?