Multiple 3-d Scanning Doppler Lidar and Wind Energy Resource Assessment Raghu Krishna Environmental Remote Sensing Group, Arizona State University Co-Authors: Ronald Calhoun & Aditya Choukulkar, ASU Gregory S. Poulos, V-Bar, LLC Keith Barr, David Mcreavy LMCT, Inc.
AWEA Wind Resource Assessment Seminar September 13th, 2012
Multiple 3-d Scanning Doppler Lidar and Wind Energy Resource Assessment
• • • •
Scanning Doppler Lidar Overview Scanning Lidar for WERA Dual-Doppler Lidar for WERA Value proposition of 1 year lidar deployment integrated into WERA and P-Values
Scanning Lidar: Principles of Operation Doppler Lidar Characteristics
Beam is Scanned to Provide 2-3D Spatial Coverage
Return Light is Doppler Shifted Moving Aerosols
Nd-Yag laser
Operating Wavelength
1.6/2µm
Energy per pulse
2mJ
Pulse repetition Pulse Envelope (50 – 80 m) frequency
50 – 80 m Pulse transmitted 500 times a second
‘Pencil’ Beam Width 10 – 30 cm
Doppler Doppler LIDAR Lidar
Transmitter
Portion of Scattered Light Collected By Transmit/Receive Telescope
Relative wind induces a Doppler frequency shift in the backscatter light; This frequency shift is detected by the sensor
Data Rate
5 Hz
Range resolution
~ 50 - 100 m
Min range
436 m
Max range
10/15 km
vr ( R, , ) U sin cos V cos cos W sin Vr =Radial Velocity, ϕ = Azimuth Angle , θ = Elevation angle U, V, W = Components of wind speed
500 Hz
“LASER”
Scanning Lidar for WERA Terrain-following Surface 1hour RMS Difference
Mean (ms-1) 9.67 9.61
Instrument Tower @ 50 m Lidar @ 50 m
(ms-1) 0.72
1 hour RMS Difference
Mean Instrument Tower @ 50 m Lidar @ 50 m Wind speed RMS difference @ 50 m
(deg) 168.24 170.34
10 minute RMS (ms-1) 1.18
1 Hour RMS (ms-1) 0.72
(deg) 9.20
24 hour RMS (ms-1)
0.46
94% Correlation of wind speed Distance between tower and lidar – 3.2 km Krishnamurthy et al. 2012
Single Doppler Lidar Challenges vr ( R, , ) U sin cos V cos cos W sin 1. Why does lidar retrieval accuracy reduce in the off-mean wind direction? Radial velocity ~ 0 – No new information is provided! 2. What is the retrieval accuracy in the off-mean wind direction?
Conditional analysis with tower measurements shows correlation of 90% in wind speed. Krishnamurthy et al. 2012
Vr =Radial Velocity, θ = Elevation angle, ϕ = Azimuth Angle U, V, W = Components of wind speed
Dual-Doppler for Wind Energy Resource Assessment v
vr_L1
u u
Y • Intersecting lidar beams for 3-d wind vector •Sample – 250 MW Wind Farm • No. of Turbines – 125 • Rotor Diameter (RD) – 80m
vr_L2
X
• Spacing – Prevailing mean wind direction – 13 RD Off - mean wind direction – 3.5 RD Wind Farm Coverage – 14 km x 3 km
• Hub-height winds for 90% of the wind farm – ~42 sq km • Winds speed spatial accuracy – ~100 m
L2 15 km
L1
Dual-Doppler Lidar • Why? – – – – – –
Higher confidence in velocity retrievals Reduces directional dependence Measured hub-height winds at nearly all turbine locations Turbulence parameters (u* , σu ,σv ,σw , u' w',v' w' etc.) Input to mesoscale models – data assimilation Can track atmospheric events – harmful to turbines
• Challenges – Synchronizing lidar beams from two instruments – Pointing accuracy and complex terrain blockage/placement Newsom et al. 2005, Calhoun et al. 2006, Krishnamurthy et al. 2010
Value Proposition of Dual-Doppler Lidar in Wind Energy Resource Assessment 90% wind farm area dual-Doppler coverage at hub height • Cost of dual 3-d Doppler lidar deployment for 1 year: ~$1.5 M • ROI for a 250MW Wind Farm with 60-m towers? Uncertainty
60-m Towers a
dual 3-d Doppler
Shear
2%
0.25%
Micro-siting
6%
2%
a
Lower range of uncertainty estimates Other uncertainties in P-value calculation remain the same
95% Confidence limits
P95/P50 ratio
P95 Production (D )
20 Year NPV (@$60/ MWh)
ROI
1 Year
Drops ~250 basis points
D 0.781 to 0.801
17,500 MWh
~ 9.4 M
~650%
20 Year
Drops ~400 basis points
D 0.852 to 0.883
27,500 MWh
~ 14.8 M
~1000%
Depends on your wind farm’s financing terms
Dual-Doppler to Track & Quantify Harmful Atmospheric Events
L1
15 km
L2
2.9 km
• Coplanar scans along 80 degree azimuth • Height difference between Lidars • Validation - Pointing accuracy Hill et al. 2009
15 km
Dual-Doppler to Track & Quantify Harmful Atmospheric Events Colors – Vorticity (s-1); Contour – Swirl Strength; Arrows – Wind Direction
Lidar can quantify: a. Vorticity b. Sub-rotors c. Dissipation rate Turbine not to scale
Hill et al. 2009
Scanning Lidar’s Tool or Toy? • Scientific advantage over towers for WERA? – Large spatial extent coverage – reduces micro-siting uncertainty – Dual-Doppler – Higher retrieval accuracy – Dual-Doppler – reduces directional challenges
• Financially viable or good ROI? – Uncertainty reduction by ~ 4% in WERA – 5x or 10x ROI for a 250MW wind farm
• Year long dual-Doppler lidar deployment is promising both financially and scientifically amidst PTC uncertainty!
Questions?
References Choukulkar, A., 2012: A Modified Optimal Interpolation Technique for Vector Retrieval for Coherent Doppler Lidar. IEEE GeoScience and remote sensing letters. Krishnamurthy, R et al., 2012: Coherent Doppler lidar for wind farm characterization. Wind Energy, doi: 10.1002/we.539 Krishnamurthy, R. 2011: Wind Turbulence Estimates in a Valley by Coherent Doppler Lidar, Meteo. App, doi: 10.1002/met.263. Hill, M et al., 2010: Coplanar Doppler Lidar Retrieval of Rotors from T-REX. J. Atmos. Sci., 67, 713–729.
Calhoun, R 2006: Virtual towers using coherent Doppler lidar during the Joint Urban 2003 Experiment, J. App. Meteo. Newsom et al. 2005: Linearly Organized Turbulence Structures Observed over a suburban area by dual-Doppler lidar, Bound. Layer. Meteo. Boccippio, D 1995: A diagnostic analysis of the VVP single-Doppler retrieval technique, J. Atmos. Ocean Tech Browning and Wexler, 1968: The determination of kinematic properties of a wind field using Doppler radar. J. Appl. Meteor.
Email: Raghu.Krishna@ asu.edu Contact: 480-234-4807
http://more.engineering.asu.edu/windlab/
Additional Slides
Dual-Doppler Lidar “Virtual Towers”
Cautions: Height difference between Lidar’s should be taken into account Pointing accuracy Calhoun et al. 2006,
