An integrated approach to offshore wind energy assessment: Great Lakes 3D Wind Experiment. Part 1. Calibration and testing.
R.J. Barthelmie, S.C. Pryor, C.M. Smith, P. Crippa, H. Wang (Indiana University)
R. Krishnamurthy, R. Calhoun (Arizona State University)
D. Valyou, P. Marzocca (Clarkson University)
D. Matthiesen (Case Western Reserve University); N. Capaldo (SgurrEnergy)
Project Information poster download
An experiment to test wind and turbulence measurement strategies was conducted at a northern Indiana wind farm in May 2012. The experimental design focused on instrument cross-calibration and data integration across a range of temporal and spatial scales to quantify the flow in 3D. Data are also integrated with simulations from the Weather Research and Forecasting model (WRF).
Lidar systems were deployed at 2 meteorological masts on opposite sides of the wind farm, NE (not shown) and SW. A tethersonde and Unmanned Aerial Vehicle (UAV) were operated from a private airstrip 2 km to the SW (Fig. 1).
Focused on independent power supplies (Midwest Portable Power; Fig. 2) and evaluation of IU’s ZephlR lidars vs. the mast measurements. As in the main experiment, correlation coefficients for mast/ZephlR wind speeds were > 0.98 (Fig 3).
Lidar measurement systems
Natural Power’s ZephlR lidar (Fig. 4) uses a continuous wave laser to determine wind characteristics from the backscatter by atmospheric aerosols. The 3 ZephlR’s were operated to measure at 5 fixed heights (40, 80, 120, 160 and 200 m). Wind direction during the experiment was dominated by NE winds (Fig. 5).
Scanning lidar (Galion) (Fig. 6) also uses the Doppler shift of radiation backscatter to determine wind characteristics but with a pulse signal. The range-gate length was 30 m and azimuthal spacing between beam products < 3" with range up to a maximum of 4 km distance/750 m height. Scan types used are given in Fig. 7.
The Tethersonde (Fig. 8) was co-located with the UAV. Approx. 30 hours of measurements were collected in 10-min increments at 40-80-120-160 m heights using 2 sondes separated by ~40 m. Profiling was also undertaken.
Data from the sonic anemometer along with airspeed, components of acceleration and GPS position, heading, and ground speed were collected on the Golden Eagle (Fig. 9) and during 9 flights of ~20-30 minutes duration.
Data integration with WRF
WRF was run for the experiment period with 50 vertical levels, in a nested grid with lateral boundary conditions from the North American Mesoscale Model. The outer grid has 324x274 cells of 9 km, the inner nested grid 310 x 259 grid cells of 3 km. The physics options selected include the Mellor-Yamada-Janjic PBL scheme, and land cover was specified at a resolution of 0.7 km.
Results: May 17, 2012
There is good agreement between the diurnal cycle and vertical profile of wind speed measured by the various instruments and simulated by WRF (Fig. 10).
Results: May 18, 2012
Even in this flat terrain, there are important spatial gradients of wind speed (from WRF, Fig. 11 and the Galion, Fig. 12). Breakdown of the nocturnal boundary layer during 18 May was observed as the wind direction shifted towards southerly. The resulting vertical profiles of wind speed (Fig. 13) indicate good agreement as the atmosphere transitioned from stable to unstable stratification.
Data analysis for the 2012 experiment is ongoing, but initial results are very promising in terms of the cross-calibration. “Lessons learned” are being integrated into the planning for a 2013 Lake Erie experiment.
Many thanks to the two landowners and the owners of the private airstrip. This material is based upon work supported by the Department of Energy under Award Number #DE-EE0005379.
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