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SURVIVING THE HURRICANE SEASON:WIND-RESISTANT DESIGN OF SINGLE-AXIS PV TRACKING SYSTEMS Thorsten Kray, Ph.D. (Dr.-Ing.)
Daniel Markus, M.Sc.
WHY BOTHER?• 50% of utility-scale PV failure due to weather 1
• need to protect your investment• Detailed knowledge of wind loads on solar arrays is key.• Wind loads comprise not only static, but especially
dynamic components: resonance effects may double or triple the static loads!
• For the 1st time ever, we present results of a comprehensive and concise study with a broad range of parameters affecting wind loads on single-axis PV tracking systems.
1 https://www.solarpowerworldonline.com/2018/01/solar-industry-responding-increasing-intensity-natural-disasters/
I.F.I. Institut für Industrieaerodynamik GmbH(Institute for Industrial Aerodynamics)Aachen, Germany
LADBS Approved Laboratory forWind Tunnel Testing of Buildings and StructuresTesting Agency License Number TA 24830
• boundary layer wind tunnel testing of amodel array
Present Study:• model at a 1:50 scale• 8 model rows, each with a length of 84 meters at
full-scale and equipped with 250 pressure taps• test conditions: 5 tilt angles, 2 row spacings, 13
wind directions, 8 rows
⇒ more than 1000 tested configurations
STATIC vs DYNAMIC LOADSØ composed of a mean and
background fluctuating component
Ø distribution of loads over tracker area can be reconstructed
Ø often ignored by codes of practice
Ø caused by vortex shedding and gust buffeting
Ø excited by resonances in tracker structure
Data taken from „Cell, Interrupted “ (2016) by GCube Insurance
1,00
1,20
1,40
1,60
1,80
2,00
0,00 0,20 0,40 0,60 0,80 1,00 1,20 1,40
DAF
Natural Frequency x Chord Length / Velocity
0°10°20°30°45°
49.80%Weather
36.10%Fire
9%Electrical
Failure
2.30%Mechanical Breakdown
2.30%Lightning
0.50%Theft
PV CLAIMS IN NORTH AMERICA
PARAMETER TORQUE
Locationwithin Array
Perimeter +
Interior -
Row Spacing + +
Tilt Angle + -
• frequency domain analysis ofload effect time-series
• calculate power density spectra to determine dynamic response
• determine Dynamic Amplification Factors (DAFs) for easy application with static loads:
OVERALL LOAD = STATIC LOAD x DAF
• based on time-dependent 2D CFD simulation (Computational Fluid Dynamics)
• grid resolution should be increased near tracker surfaces
• modelling of many different parameters in incident flow and of the tracker’s structural characteristics is easily possible (wind speed, natural frequency, damping ratio, torsional stiffness etc.)
• simulation of single and multibody configurations
Only the combined informationmakes your system wind-resistant!
0%20%40%60%80%
100%
0 10 20 30 40Tilt Angle / deg
1st & 2nd row 3rd & 4th row Inner rows
and TRACKER INSTABILITY
• DAFs are determined for system- and site-specific reduced frequencies.• Resonances can easily lead to amplification of 100% (DAF = 2) or even higher!• highly dependent on tilt angle, load effect, row spacing and row location
within the array
• 1st and 2nd row are most exposed and feature highest loads.
• Inner rows are effectively shielded.
Top right: Pressure coefficients representing peak torque across an array with high values in red and low values in blue
Bottom left and bottom right:Effect of different parameters onpeak torque across an array
• multibody configurations: interior rows are less prone to torsional galloping (lower oscillation amplitudes, see diagram above)
#1 #2 #3
#4 #5 #6
Six row tracker array
“KNOWLEDGEIS POWER“
Sir Francis Bacon
Ø caused by torsional galloping due to vortex shedding or vortex lock-in
Ø can lead to catastrophic failure due to high amplitudes of oscillation at a critical wind speed
Ø study of onset of instability is necessary for definition ofsafe stowing policy
Ø combination of static + dynamic loads in terms of equivalent static wind loads
Ø structural failure in case of underestimation
Web www.ifi-ac.comwww.ifi-aachen.de
eMail kray@ifi-aachen.de
-40
-20
0
20
0 1 2 3 4 5
Angl
e (d
eg)
Time (s)Tracker multibody Tracker single body
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