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S. K. Ghosh Associates Inc.
www.skghoshassociates.com
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Jason Ericksen, S.E.S. K. Ghosh Associates Inc.www.skghoshassociates.com
Solar Photovoltaic Systems Committee
Ronald LaPlante, S.E.Division of the State Architect – State of California
Wind Loads on PV Arrays
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Why are we here?
� Photovoltaic arrays are becoming more popular
� Codes and Standards do not address these directly
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S. K. Ghosh Associates Inc.
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Freestanding
Carports
Arrays
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Residential
Sloped relative to pitched roof
Flush-mounted on sloped roofs
Not covered in this discussion
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Commercial
Flat Roofs – not flush mounted
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ROADMAP
� Building Codes and Standards
� Freestanding Systems
� Flush-Mounted Systems on Sloped Roofs
� Low-Profile Systems on Flat Roofs
SEAOC Solar Photovoltaic Systems Committee report SEAOC PV2-2012
“Wind Design for Low-Profile Solar Photovoltaic Arrays on Flat Roofs”
Ron LaPlante
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S. K. Ghosh Associates Inc.
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ROADMAP
� Building Codes and Standards
• IBC
• ASCE 7
� Freestanding Systems
� Flush-Mounted Systems on Sloped Roofs
� Low-Profile Systems on Flat Roofs
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Building Codes and Standards
� 2009 IBC
• No provisions for ground or roof mounted PV arrays
� 2012 IBC
• No Provisions for ground mounted PV arrays
• New section for roof mounted PV arrays
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S. K. Ghosh Associates Inc.
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2012 IBC Chapter 15 – Roof Assemblies and Rooftop Structures
� 1509.7 Photovoltaic systems. Rooftop mounted photovoltaic systems shall be designed in accordance with this section.
1509.7.1. Wind Resistance. Rooftop mounted photovoltaic systems shall be designed for wind loads for components and cladding in accordance with Chapter 16 using an effective wind area based on the dimensions of a single unit frame.
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Building Codes and Standards
� ASCE 7-05 and ASCE 7-10
• No provisions specifically for ground or roof mounted PV arrays
• Provisions may be adapted to apply
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ASCE 7-05 and ASCE 7-10Freestanding Systems
� Open building? MWFRS
C&C
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ASCE 7-05 and ASCE 7-10Freestanding Systems
� Solid freestanding sign?
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S. K. Ghosh Associates Inc.
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ASCE 7-05 and ASCE 7-10Flush-Mounted Systems
� Standard building roof pressures?MWFRS
C&C
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ASCE 7-05 and ASCE 7-10Flush-Mounted Systems
� Solid attached sign?
This is a SOLID SIGN
Elevation Cross-Section
≤≤≤≤ 3 ft
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S. K. Ghosh Associates Inc.
www.skghoshassociates.com
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ASCE 7-05 and ASCE 7-10Sloped Systems on Flat Roofs
� Rooftop equipment?
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ROADMAP
� Building Codes and Standards
� Freestanding Systems
� Flush-Mounted Systems on Sloped Roofs
� Low-Profile Systems on Flat Roofs
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Freestanding Systems
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Freestanding SystemsICC AC428
� ICC Evaluation Service: Acceptance Criteria for modular framing systems used to support photovoltaic (PV) modules (ICC AC428)
� Just released -November 2012
www.icc-es.org/criteria/pdf_files/AC428.pdf
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S. K. Ghosh Associates Inc.
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Freestanding SystemsICC AC428 – Wind Loads
� 3.1.3.1.2 Freestanding System
• MWFRS elements provide support and stability for the overall structure
� lateral bracing, columns and primary beams
• C&C elements are those that do not qualify as MWFRS elements
� beams supporting PV modules and connections between the PV modules and the beams
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Freestanding SystemsICC AC428 – Wind Loads
� 3.1.3.1.2 Freestanding System
• MWFRS elements: Open buildings with monoslope roofs
� Section 6.5.13 using Figures 6-18A and 6-18D of ASCE 7-05 for 2009 and 2006 IBC
� Section 27.4.3 using Figures 27.4-4 and 27.4-7 of ASCE 7-10 for 2012 IBC
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S. K. Ghosh Associates Inc.
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Freestanding SystemsICC AC428 – Wind Loads
� 3.1.3.1.2 Freestanding System
• C&C elements: Open buildings with monoslope roofs
� Section 6.5.13 using Figure 6-19A of ASCE 7-05 for 2009 and 2006 IBC
� Section 27.4.3 using Figure 30.8-1 of ASCE 7-10 for 2012 IBC
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Freestanding SystemsICC AC428 – Wind Loads
Components and Cladding
Main Wind-Force Resisting System
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Freestanding SystemsICC AC428 – Wind Loads
Main Wind-Force Resisting System
Components and Cladding
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Freestanding SystemsICC AC428 – Considerations
� ASCE 7 provisions for Monoslope Free Roofs
• Figures limited to θ ≤ 45°
� Shielding has not been considered
� Size effects have not been considered
Roof Angle
θθθθLoad Case
Wind Direction, γγγγ = 0° Wind Direction, γγγγ = 180°
Open Wind Flow Obstructed Wind Flow Open Wind Flow Obs tructed Wind Flow
CNW CNL CNW CNL CNW CNL CNW CNL
0°A 1.2 0.3 -0.5 -1.2 1.2 0.3 -0.5 -1.2B -1.1 -0.1 -1.1 -0.6 -1.1 -1.0 -1.1 -0.6
7.5°A -0.6 -1 -1 -1.5 0.9 1.5 -0.2 -1.2B -1.4 0 -1.7 -0.8 1.6 0.3 0.8 -0.3
15°A -0.9 -1.2 -1.1 -1.5 1.3 1.6 0.4 -1.1B -1.9 0 -2.1 -0.6 1.8 0.6 1.2 -0.3
22.5°A -1.5 -1.6 -1.5 -1.7 1.7 1.8 0.5 -1B -2.4 -0.3 -2.3 -0.9 2.2 0.7 1.3 0
30°A -1.8 -1.8 -1.5 -1.8 2.1 2.1 0.6 -1B -2.5 -0.5 -2.3 -1.1 2.6 1 1.6 0.1
37.5°A -1.8 -1.8 -1.5 -1.8 2.1 2.2 0.7 -0.9B -2.4 -0.6 -2.2 -1.1 2.7 1.1 1.9 0.3
45°A -1.6 -1.8 -1.3 -1.8 2.2 2.5 0.8 -0.9B -2.3 -0.7 -1.9 -1.2 2.6 1.4 2.1 0.4
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ROADMAP
� Building Codes and Standards
� Freestanding Systems
� Flush-Mounted Systems on Sloped Roofs
• Modular Framing system
• Roof members
� Low-Profile Systems on Flat Roofs
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Flush-Mounted Systems
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2012 IBC Chapter 15 – Roof Assemblies and Rooftop Structures
� 1509.7.1. Wind Resistance(rooftop mounted photovoltaic systems)
• All elements as components and cladding
• Effective wind area of single unit
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Flush-Mounted SystemsICC AC428
� ICC Evaluation Service: Acceptance Criteria for modular framing systems used to support photovoltaic (PV) modules (ICC AC428)
� Just released -November 2012
www.icc-es.org/criteria/pdf_files/AC428.pdf
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S. K. Ghosh Associates Inc.
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Flush-Mounted SystemsICC AC428 – Wind Loads
� 3.1.3.1.1 Flush-Mounted System
• All elements designed for C&C loads
� Chapter 6 of ASCE 7-05 using Method 2 (Analytical Procedure for Low-Rise Buildings) for the 2006 and 2009 IBC
� Chapter 26 and 30 of ASCE 7-10 using the Envelope Method prescribed in Chapter 30, Part I for the 2012 IBC
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Flush-Mounted SystemsICC AC428 - Wind Loads
� 3.1.3.1.1 Flush-Mounted System
• Internal pressure coefficient = 0
p = qh[(GCp) – (GCpi)]
p = qh(GCp)
• p ≥ 10 psf for the 2006 and 2009 IBC
• p ≥ 16 psf for the 2012 IBC
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S. K. Ghosh Associates Inc.
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Flush-Mounted SystemsICC AC428 - Conditions
� 3.1.3.1.1 Flush-Mounted System
• The distance between the roof or wall surface and the PV module must be between 2 and 10 inches
• PV modules shall not be installed within 10 inches of roof edge or ridge
2 in. ≤ dpv ≤ 10 in.
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Flush-Mounted SystemsICC AC428 - Conditions
� 3.1.3.1.1 Flush-Mounted System
• A minimum gap of 0.75 0.25 inch must exist between PV modules and adjacent rows of modules
• Building height limited to 60 ft
≥ 0.25 in.
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S. K. Ghosh Associates Inc.
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Modular Framing SystemsICC AC428
� Additional load requirements
• Snow
• Seismic
• Dead
• Roof Live
� Serviceability
• loads and limits
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Flush-Mounted SystemsSolar ABCS Report� Solar America Board for Codes and Standards
report: “Wind Load Calculations for PV Arrays”
Stephen Barkaszi, P.E.Florida Solar Energy Center
Colleen O’Brien, P.E.BEW Engineering
June 2010
www.solarabcs.org/about/publications/reports/wind-load/index.html
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S. K. Ghosh Associates Inc.
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Flush-Mounted SystemsSolar ABCS Report
• PV mounting structure and attachment to the roof
• PV modules and attachment to the mounting structure
Main Wind-Force Resisting System
Components and Cladding
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Flush-Mounted SystemsSolar ABCS Report
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S. K. Ghosh Associates Inc.
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Flush-Mounted SystemsSolar ABCS Report
Components and Cladding
Main Wind-Force Resisting System
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Flush-Mounted SystemsResource Comparison
2012 IBC 1509.7 ICC AC428 Solar ABCS
Internal Pressurecoefficient
NA GCpi = 0 ±0.10 ≤ GCpi ≤ ±0.30
Stand off distance
NA 2 in. ≤ dpv ≤ 10 in. dpv ≤ 6 in.
Distance to roof edge or ridge
NA dedge ≥ 10 in. NA
Gap between modules
NA gap ≥ 0.75 in. NA
Building Height NA ≤ 60 ft ≤ 60 ft
C&CAll members and
attachmentsAll members and
attachments
PV modules and attachment to the
mounting structure
MWFRS None NonePV mounting structure and attachment to the
roof
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Flush-Mounted SystemsSupporting Roof Members
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Flush-Mounted SystemsSupporting Roof Members
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Flush-Mounted SystemsSupporting Roof Members
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Flush-Mounted SystemsSupporting Roof Members
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Flush-Mounted SystemsSupporting Roof Members
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Flush-Mounted SystemsSupporting Roof Members
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Flush-Mounted SystemsSupporting Roof Members
With PV Modules
WithoutPV Modules
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Additional Resource
� “Wind Load Analysis for commercial roof-mounted arrays”
Colleen O’Brien, P.E.BEW Engineering
David Banks, Ph.D.CPP Wind Engineering
June/July 2012
http://solarprofessional.com/article/?file=SP5_4_pg6_TOC
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S. K. Ghosh Associates Inc.
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Additional ResourceSolarPro Article
� Low-profile PV arrays on flat roofs
• DNV Wind Load Calculator
� Freestanding systems
• ASCE 7-05: Open buildings with monosloped roofs
• Results will be conservative for interior rows, but conducting wind tunnel tests in compliance with ASCE 7-05 guidelines can reduce this conservatism
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BREAK!
If you are encountering technical difficulties, please call (847) 991-2700
If you have any questions, please type them in
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S. K. Ghosh Associates Inc.
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Question and Answer Session
If you are encountering technical difficulties, please call (847) 991-2700
If you have any questions, please type them in
Solar Photovoltaic Systems Committee
New SEAOC Document for Wind Design of Rooftop Solar Arrays
December 6, 2012Ronald LaPlante, S.E.
Division of State Architect – State of California
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S. K. Ghosh Associates Inc.
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SEAOC Solar Photovoltaic Systems Committee
Outline
� PV Committee and Scope
� Overview of SEAOC Solar PV Wind Design
Report
� Prescriptive Solar PV Wind Design Values
� Effective Wind Area
� Wind Tunnel Procedure
� Example Solar PV Problem
� Solar PV Code Development
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SEAOC Solar Photovoltaic Systems Committee
New SEAOC PV Committee Reports
Available at: http://www.seaoc.org/bookstore
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SEAOC Solar Photovoltaic Systems Committee
PV COMMITTEE AND SCOPE
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SEAOC Solar Photovoltaic Systems Committee
Formation of Committee
� Formed in September 2011 as subcommittee
of SEAOC Wind Committee
� Composed of:
� Structural Engineers
� Code Enforcement Agencies
� Wind Tunnel Experts
� Solar PV Industry Members
� NCSEA & ASCE 7 Wind Committee Members
� SEAOC Seismology Members
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S. K. Ghosh Associates Inc.
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SEAOC Solar Photovoltaic Systems Committee
Solar Photovoltaic Arrays Types
Flat Roofs
Carports Ground Mount
Sloped Roofs
Parking Garages
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SEAOC Solar Photovoltaic Systems Committee
Which Wind Loading Provisions Apply?
What about other installations?
ASCE 7
Open Buildings (ASCE 7-05 Figure 6-18,19) (ASCE 7-10 Figure 27.4-4, 30.8)
Enclosed Buildings – C&C(ASCE 7-05 Figure 6-11)(ASCE 7-10 Figure 30.4-2)
ICC AC 428
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SEAOC Solar Photovoltaic Systems Committee
Which Wind Loading Provisions Apply?
Flat Roofs – not flush mounted
Ground Mount - Sheltering
Parking Garages
Pitched Roofs – not flush mounted
Apply Kzt as if on cliff?
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SEAOC Solar Photovoltaic Systems Committee
Wind Tunnel Procedure
ASCE 7
Wind Tunnel Procedure (WTP)
What’s an appropriate wind tunnel study?
ASCE 7 WTP is written for specific building modeling, not generalized buildings with solar panels.
Should the WTP be peer reviewed?
Is there a minimum wind load?
Does building need to be modeled?
Roof zoning?
Etc…
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Failures do Occur
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SEAOC Solar Photovoltaic Systems Committee
OVERVIEW OF SEAOC SOLAR PVWIND DESIGN REPORT
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SEAOC Solar Photovoltaic Systems Committee
Goals for Solar PV Wind Report
� Develop report to address wind
design provisions for low-profile
solar PV arrays on flat roofs
� Establish wind design
coefficients similar to those in
ASCE 7 figures
� Report provides proposed
changes to ASCE 7-10,
references added for ASCE 7-
05 – equally applicable
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SEAOC Solar Photovoltaic Systems Committee
Goals for Solar PV Wind Report
� Define Effective Wind Area for
unique aspects of solar PV
arrays
� Define minimum Wind Tunnel
Procedure modeling
requirements and minimum
design loads
� Example Problem
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SEAOC Solar Photovoltaic Systems Committee
PRESCRIPTIVE SOLAR PV WIND DESIGN VALUES
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SEAOC Solar Photovoltaic Systems Committee
ASCE 7 Wind Design
ASCE 7
qh=0.00256KzKztKdV2Iand accounts for site parameters:• Kz – building exposure & height• Kzt – site topography• Kd – wind directionality• V – site wind speed
pressure=qhGCn
GCn accounts for aerodynamic effects.Need to create GCnfactors for solar PV so it is generalized for any site and building.
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Wind Tunnel Data
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SEAOC Solar Photovoltaic Systems Committee
� Understanding wind flow environment on roof
Wind Tunnel Data
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� Vortices form at roof corners
� Shear layer forms at roof edge
Wind Tunnel Data
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SEAOC Solar Photovoltaic Systems Committee
Wind Tunnel Data
� Take the guesswork out
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SEAOC Solar Photovoltaic Systems Committee
Wind Tunnel Data
� Following test on 10 degree tilt, lift values (6Hx6H)
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SEAOC Solar Photovoltaic Systems Committee
Lift Coefficients 0°
Wind Tunnel Data
North
70
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SEAOC Solar Photovoltaic Systems Committee
Lift Coefficients 10°
Wind Tunnel Data
North
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SEAOC Solar Photovoltaic Systems Committee
Lift Coefficients 20°
Wind Tunnel Data
North
72
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Lift Coefficients 30°
Wind Tunnel Data
North
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SEAOC Solar Photovoltaic Systems Committee
Lift Coefficients 40°
Wind Tunnel Data
North
74
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SEAOC Solar Photovoltaic Systems Committee
Lift Coefficients 50°
Wind Tunnel Data
North
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SEAOC Solar Photovoltaic Systems Committee
Lift Coefficients 60°
Wind Tunnel Data
North
76
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Lift Coefficients 70°
Wind Tunnel Data
North
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Lift Coefficients 80°
Wind Tunnel Data
North
78
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Lift Coefficients 90°
Wind Tunnel Data
North
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SEAOC Solar Photovoltaic Systems Committee
Lift Coefficients 100°
Wind Tunnel Data
North
80
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Lift Coefficients 110°
Wind Tunnel Data
North
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SEAOC Solar Photovoltaic Systems Committee
Lift Coefficients 120°
Wind Tunnel Data
North
82
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SEAOC Solar Photovoltaic Systems Committee
Lift Coefficients 130°
Wind Tunnel Data
North
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SEAOC Solar Photovoltaic Systems Committee
Lift Coefficients 140°
Wind Tunnel Data
North
84
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S. K. Ghosh Associates Inc.
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SEAOC Solar Photovoltaic Systems Committee
Lift Coefficients 150°
Wind Tunnel Data
North
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SEAOC Solar Photovoltaic Systems Committee
Lift Coefficients 160°
Wind Tunnel Data
North
86
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SEAOC Solar Photovoltaic Systems Committee
Lift Coefficients 170°
Wind Tunnel Data
North
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SEAOC Solar Photovoltaic Systems Committee
Lift Coefficients 180°
Wind Tunnel Data
North
88
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SEAOC Solar Photovoltaic Systems Committee
Wind Tunnel Data
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SEAOC Solar Photovoltaic Systems Committee
Lift Coefficients All directions
Wind Tunnel Data
North
90
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SEAOC Solar Photovoltaic Systems Committee
Prescriptive Solar PV Wind Loads
� Convert data into a
prescriptive procedureBoundary Layer Wind Tunnel Laboratory
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SEAOC Solar Photovoltaic Systems Committee
� Procedure needs to consider:
� Geometric Limitations of PV panels
� Roof Zoning
� Effective Wind Area
� Effect of Building Size (height & width)
� Panel Tilt Angle
� Array edge effects
� Panel Length
� Parapets
Prescriptive Solar PV Wind Loads
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SEAOC Solar Photovoltaic Systems Committee
Geometric Limitations of PV panels
� Based on most common
application and supported by
data
� Steeper, taller, longer
increases loads
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SEAOC Solar Photovoltaic Systems Committee
Roof Zoning
� Roof zoning for open elements on roof
different than enclosed C&C elements
Components & Cladding Solar PV Arrays
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peak pressure on roof
peak pressure on solar panels in NE corner
� Snapshot image of vortex
Roof Zoning
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SEAOC Solar Photovoltaic Systems Committee
� Defined roof zones similar to ASCE 7
� Clarified steps, angled corners, reentrant corners
Roof Zoning
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Effective Wind Area
� GCn values are a function of effective wind area, similar to
ASCE 7 Wind Figures
Wind tunnel test data for solar PV ASCE 7-05 Figure 6-11B C&C
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SEAOC Solar Photovoltaic Systems Committee
Effect of Building Size� Strength of vortex and resulting wind load increases with
size of building
� Kz does not account for this, it addresses gradient velocity
above ground
� SEAOC Method can apply > 60 ft
Height 15 ft 30 ft 60 ft
ASCE 7 C&CPrediction
Conservative Target Unconservative
SEAOC Solar PVGoal
Target entire range
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999 999 999 999 999 999 999 999 999 999 999 999
999 ### ### ### ### ### ### ### ### ### ### 999
999 ### ### ### ### ### ### ### ### ### ### 999
999 ### ### ### ### ### ### ### ### ### ### 999
999 ### ### ### ### ### ### ### ### ### ### 999
999 ### ### ### ### ### ### ### ### ### ### 999
999 ### ### ### ### ### ### ### ### ### ### 999
999 ### ### ### ### ### ### ### ### ### ### 999
999 ### ### ### ### ### ### ### ### ### ### 999
999 ### ### ### ### ### ### ### ### ### ### 999
999 ### ### ### ### ### ### ### ### ### ### 999
999 ### ### ### ### ### ### ### ### ### ### 999
999 999 999 999 999 999 999 999 999 999 999 999
Effect of Building Size
2H x 2H Building 6H x 6H Building
� Wind tunnel data to illustrate
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SEAOC Solar Photovoltaic Systems Committee
Effect of Building Size
An = Normalized Wind Area
� How to address effect of building size?
An=����
��� ���,��
�
Height 15 ft 30 ft 60 ft
A (area to component) 10 sf 10 sf 10 sf
An 44 11 2.8
Result on wind load decrease No change increase
A = Effective Wind Area
100
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SEAOC Solar Photovoltaic Systems Committee
Effect of Building Size
� Illustrate on Solar PV GCrn curve
� No plateau
2.8
441
1
GCrn = 1.4
GCrn = 1.1
GCrn = 0.9
ASCE 7 C&C
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SEAOC Solar Photovoltaic Systems Committee
Panel Tilt Angle
� Similar to open structures, wind pressure
increases as tilt angle increases
Tilt Angle
GCrn
5º 15º 35º0º
Interpolate GCrn 15º-35ºGCrn 0º-5º
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SEAOC Solar Photovoltaic Systems Committee
Panel Tilt Angle
� Tilt angle address through two GCrn Figures
� Uses normalized wind area, no flat plateau
� Values are for sheltered panels
Interpolate
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SEAOC Solar Photovoltaic Systems Committee
Array Edge Effects
104
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SEAOC Solar Photovoltaic Systems Committee
Array Edge Effects
North
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SEAOC Solar Photovoltaic Systems Committee
Array Edge Effects
5 panel x 4 row array
North
North edge factor (En) <=2
South, East, West
edge factor (Es,e,w)
<=1.5
� Apply factor to increase wind load on edges
of arrays and panels exposed from any side
Last 5 ft of row
received East and
West edge factor
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SEAOC Solar Photovoltaic Systems Committee
Array Edge Effects
� Edge Factor:
� If spacing between rows gets large, then
all panels in the array will get an edge factor >1
� Gaps in the middle of an array for mechanical units,
skylights, etc will require all edges around gap to get an
edge factor >1
� Method developed requires each panel to have an edge
factor calculated in 4 principle axis directions (N,S,E,W)
and highest one used to design panel supports
� Edge factor becomes smaller close to building edge
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SEAOC Solar Photovoltaic Systems Committee
Array Edge Effects
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SEAOC Solar Photovoltaic Systems Committee
Array Edge Effects
Evaluate toward adjacent panel
or building edge, whichever is
closer:
Adjacent panel:
dx= distance to adjacent panel
hc= min (h1, 1ft)+lpsin(ω)
(hc≈height of panel above roof)
Building edge:
dx= distance to building edge
hc=0.1*apv
(apv≈height of building roof)
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Array Edge Effects
hc=2 ft
dN= 10 ft
north south
ground
roof
wind
Determine EN
Example:
dN/hc=5,
then EN=1.5
Observations:
-If dN<4 ft, EN=1
-If dN>16 ft, EN=2
-Keep space between
rows less than 2*hc
Shear Layer -
Reattachment
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Array Edge Effects
dN= 10 ft
north south
ground
roof
windDetermine EN
Example:
hc=0.1*apv=3 ft
dN/hc=3.3,
then EN=1.2
Observations:
-If dN<6 ft, EN=1
-If dN>24 ft, EN=2
-Keep space between
edge of building less
than 2*hc≈0.2*h
h= 30 ft(h≈apv)
Shear Layer - Reattachment
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Other Effects
� Panel chord length factor (γc):
� The longer the panel, the higher the
wind pressure
� Panels <= 4’-4”, γc=0.8
� Panels 6’-8”, γc=1.0, interpolate betw.
� Parapet height factor (γp):
� The taller the parapet, the higher the wind
pressure in some areas
� Parapets <= 4’-0”, γp=1.0
� Parapets > 4’-0”, γp=0.25 hpt, need not exceed 1.3
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Final SEAOC Solar PV Figure
Roof Zoning Geometric
Limitations
-Panel Tilt Angle
-Effective Wind
Area & Building
Size Effects
Array Edge
Effects
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Final SEAOC Solar PV Figure
Array Edge
Effects
Building Size
Effects
Panel Length
EffectsParapet
Effects
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BREAK!
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If you have any questions, please type them in
115
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Question and Answer Session
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If you have any questions, please type them in
116
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Strategies to Avoid High Wind Loads
� Place panels > 2 * building height (h) from
building edges
� Avoid isolated panels, need sheltering
� If within 2h of building edge, place close to
building edge below shear layer, best if less
than 0.2*building height from edge
� Keep gap between rows small and aisles
between arrays as small as possible, best if
less 2*height of panel above roof (to highest
point of panel)117
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Strategies to Avoid High Wind Loads
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EFFECTIVE WIND AREA
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Effective Wind Area
� Wind flowing over roof is turbulent and gusty
� Wind pressure is not uniform and varies with
time at any one location
� Members and connections with small tributary
areas are subject to the instantaneous high
peak pressures
� Members and connections with large tributary
areas are subject to lower pressures because
the pressures over the entire area do not peak
at the same time.120
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Effective Wind Area
SEAW/ATC-60 Figure 9-7
Peak pressures to design
roof sheathing attachment
Lower pressures to design
roof purlin (averaging effect)
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Effective Wind Area
� EFFECTIVE WIND AREA, A for solar arrays: The area used to determine GCrnper Figure 29.9-1 is equal to the tributary area for the structural element being considered, except that the width of the effective wind area need not be less than one-third its length. For a fastener attaching solar modules, the effective wind area shall not be greater than the area tributary to the individual fastener.
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Effective Wind Area
� Effective Wind Area
Example
Panel to rack attachment
Roof attachment
Rack beam
Plan View of PV panels
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Effective Wind Area
Plan View of PV panels
Panel to rack attachment:
Effective wind area = ¼ panel area
(i.e. tributary area)
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Effective Wind Area
Plan View of PV panels
Rack beam effective wind area:
Width of effective wind area is larger of:
• Tributary width
• 1/3 span length between supports ( )
Span length
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Effective Wind Area
Plan View of PV panels
Roof attachment effective wind area:
Width of effective wind area is larger of:
• Tributary width
• 1/3 span length tributary to supports ( )
Span length tributary
to support
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Effective Wind Area
� If solar array support system has adequate
strength and interconnectedness to span
across a support or ballast point that is subject
to yielding or uplift, the tributary area (and
effective wind area) can be correspondingly
increased, provided that strengths are not
governed by brittle failure and that the
deformation of the array is evaluated and does
not result in adverse performance.
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Effective Wind Area
Plan View of PV panels
If justified, larger effective area could be
used, see example in Appendix
� For example, say roof attachment spacing reduced, but
rack beam had adequate strength and interconnectedness
to span across multiple supports
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Effective Wind Area
Plan View of PV panels
If rack robust enough, effective area for
sliding could use the entire array area.
� For sliding, if the racking system had adequate strength and
interconnectedness to engage larger areas, then that larger
effective wind area may be used
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WIND TUNNEL PROCEDURE
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Wind Tunnel Procedure
ASCE 7
Wind Tunnel Procedure (WTP)
What’s an appropriate wind tunnel study?
ASCE 7 WTP is written for specific building modeling, not generalized buildings with solar panels.
Should the WTP be peer reviewed?
Is there a minimum wind load?
Does building need to be modeled?
Roof zoning?
Etc…
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Wind Tunnel Procedure
� What are acceptable testing methods?
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Wind Tunnel Procedure
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� Wind tunnel model requirements
� Promote consistency
� Requirements for developing generalized wind loads
� Must comply with ASCE 49-12 “Wind Tunnel Testing
for Buildings and Other Structures”
� Boundary layer wind tunnel
Wind Tunnel Procedure
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� Wind tunnel model requirements
� Model array on generic building
� Roof zones
� Effective wind area
� Panel geometry (size)
� Panel tilt angle
� Row spacing
� Height above roof
� Roof shape (flat, barrel, pitched)
� Some interpolation allowed between multiple tests
Wind Tunnel Procedure
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Boundary Layer Wind Tunnel Laboratory
Wind Tunnel Procedure
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� For solar PV systems that meet the limitations
and geometry requirements of the SEAOC
Solar PV Figure, then:� Minimum is 50% of values in SEAOC Solar PV Figure
� Minimum of 10 psf in ASCE 7-05 not applicable (16 psf in
ASCE 7-10)
� Lower values allowed if qualified peer review
� For other systems:� Minimums in ASCE 7 should apply
� Lower values allowed if qualified peer review
Minimum Design Wind Loads
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� Independent peer review
� Knowledgeable reviewer experienced in
performing wind tunnel studies on buildings in
atmospheric boundary layers.
� Review report, data, modeling, wind loads,
GCrn values, etc
� Prepare a report
� A peer reviewed wind tunnel study can be
used on multiple projects, unless scope of
applicability changes
Peer Review Requirements
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Wind Tunnel Procedure
� Computation Fluid Dynamics is not recognized
by ASCE 7
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EXAMPLE SOLAR PV PROBLEM
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Example Solar PV Problem
� Example Problem in Appendix
� Aid in interpretation and application of method
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� 9 locations selected to provide sample
calculations for (8 attached, 1 ballasted)
Example Solar PV Problem
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� Procedure outlined in Section 3.2.1 of Report
Example Solar PV Problem
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� Step 5 – Determine Roof Zones
Example Solar PV Problem
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� Step 10 – Determine Edge Factors
Example Solar PV Problem
E=2
E=1
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Example Solar PV Problem
� Step 13 – Determine Pressure
p=96 psf (SD)
=56 psf (ASD)
p=30 psf (SD)
=17 psf (ASD)
Pressures
shown for panel
connections,
would be lower
for roof
connections
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� Formulas for GCrn curves provided
Example Solar PV Problem
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Example Solar PV Problem
� Ballasted system example for Location 9
� Illustrates need for wind tunnel tested aerodynamic
systems to make feasible
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SOLAR PV CODE DEVELOPMENT
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SEAOC Solar PV Reports into Code
Current Efforts• SEAOC Solar
PV Systems Committee
• Solar ABC• Technical
Papers• Wind Tunnel
Studies• ASCE 49
ASCE 7(2016)
IBC(2018)
2013 CBC Amendments, 2012 IBC, DSA
IR 16-8
What’s next?
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DSA IR 16-8
� Updated in October 2012 to incorporate SEAOC PV
reports
� Available at: www.dgs.ca.gov/dsa
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DSA IR 16-8
� DSA IR 16-8 addresses:
� Dead load – Check roof, keep mass increase below 10%
� Live load – No need to include where covered by panels < 24” or
signs
� Wind – SEAOC PV paper, Wind tunnel requirements, peer review
� Seismic – ASCE 7 loading, unrestrained systems per SEAOC PV
paper
� Load combinations – Apply load combo’s when checking uplift
� Rack design – ICC AC 428
� PV Installations on Standing Seam Metal Roofs
� BIPV systems – ICC AC 365
� Fire Life Safety requirements
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2013 CBC
� 2013 CBC Amendment to 2012 IBC
Section 1509.7
� Effective wind area should NOT be based
on effective wind area of a single unit frame
� DSA and HCD co-adopt Exception
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SEAOC Solar Photovoltaic Systems Committee
2013 CBC
� 2013 CBC Section 1613.5 – amendment
to modify ASCE 7-10 Section 13.4 to
allow unrestrained solar arrays.
Next Slide
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2013 CBC
� 2013 CBC Section 1613.5 (continued).
SEAOC Seismic PV Paper indicates how to do this
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SEAOC Solar Photovoltaic Systems Committee
� SEAOC Solar PV Reports will be updated
annually +- as we receive feedback
� Spreadsheet developed to automate process
Future Updates to SEAOC PV Reports
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Acknowledgements
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THANK [email protected]
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Question and Answer Session
If you are encountering technical difficulties, please call (847) 991-2700
If you have any questions, please type them in
159
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