Wind Loads on PV roof top solar installations.

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This my presentation from the Energytech conference in Israel.
Energytech 2010 27-28/10/2010

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Wind Loads on PV roof top solar installations.

  1. 1. 2010 www.barangroup.com
  2. 2. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Abstract The Israeli Photovoltaic industry must rely on licensed structural engineers, today there are various interpretations of building codes and standards to design PV mounting systems that will withstand wind-induced loads. The new 414 Wind Loads Israeli Standard doesn’t rely to any obstacles like PV array on a roof, but a lot of engineering reports, a large and proved experienced engineers team in Baran Raviv has prepared our interpretation and our detailed engineering process to study and get a good analyze of a roof mounted PV system on an existing structure. Analysis of Structures with roof mounted PV arrays - Presentation Eng David Cohen Eng Claudio Moses Eng Sagiv Azriel
  3. 3. Engineering Process Step 1. Preliminary Survey • General Structure geometry (3D) • Qualitative Characterization of the existing structure; Azimuth, Roof slopes, Obstacles. • Damages in the existing structure, structural imperfections, Advanced rust detection, safety faults . Step 2. Preliminary Report • Total Energy Output Predicted • Maintenance Report of the existing structure Step 3. Advanced Survey • Engineered Mapping of the structure elements. • Structural analysis of the existing structure. • Structural analysis of the existing structure with Roof top PV system. • Reinforcing solutions of the existing structure. Step 4. Quality Assurance • Design and engineering QA checking. • Manufacturing QA checking. • Erection and Installation QA checking. Existing Structures with roof-mounted PV System Baran Raviv Ltd.
  4. 4. Existing Structures with roof-mounted PV System Baran Raviv Ltd. STATIC ANALYSIS OF AN EXISTING STRUCTURE In order to do an accurate analysis of an existing structure we need to know how the structure is composed. Which are the main structural components of the structure and how loads are transmitted to the foundations. All this data is taken during the Advanced Survey. With the completion of all the geometry data, the Analysis with the relevant loads could be done. For the Static Analysis we work accordingly to the relevant Israeli or European Standards: IS:412 – Loads on Structures: Characteristic Loads IS:413 – Design Provisions for Earthquake Resistance of Structures IS:414 – Characteristic Loads on Structures: Wind Loads IS:466 – Concrete Code IS:1225 – Steel Structure Code Eurocode 9: Design of aluminum Structures In most of the cases, the structures that are available for Solar panels are light-weight structures (Steel Structures with thin tin roofs). For this structures we usually need only the Standards that are marked in red.
  5. 5. IS:414 – Characteristic Loads on Structures: Wind Loads This particular Standard is used in order to calculate the most relevant Loadings on light-weight Structures. The Wind Loading is influenced by: - Geographic position of the building - Building Height - Geometry of the building (With or Without walls, two or one sloped roof, slope angle, etc.) The Basic Equation for Wind Load: Where: - qb: Basic wind pressure. - Ce(ze): Exposure parameter (depends on the height and on the terrain roughness). - CsCd: Building parameter (for our kind of structure we will take CsCd=1) - Cp: Aerodynamic force parameter, depends of the geometry of the building. The basic wind pressure Equation: Where: - ρ = 1.25 Kg/m^3 - vb: Basic wind speed, depends on the geographic location of the Structure. Existing Structures with roof-mounted PV System Baran Raviv Ltd. pdseeb ccczcqw ⋅⋅⋅= )( 2 2 b b v q ⋅ = ρ
  6. 6. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Wind Load Map of Israel Vmax= 36 m/sec ( 10min avge) Vmin = 24 m/sec (10 min avge)
  7. 7. Ce(ze) Parameter Existing Structures with roof-mounted PV System Baran Raviv Ltd.
  8. 8. Cp Parameter (Example for a two pitched roof without walls) Existing Structures with roof-mounted PV System Baran Raviv Ltd.
  9. 9. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Modeling of the Structure For the modeling of the structure we need to have a 3D picture of al all the structural components that compose the building. Loads will be applied to this structure using a Finite Elements Static Analysis program.
  10. 10. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Wind Loads on Solar Panels Wind Loads on Solar Panels are required in order to design the aluminum structure that support the panels. This loads are also transferred to the Building, so we need to check the original Building with the relevant panel loads on the relevant zones of the roof. There are different approaches about how to Calculate the Loads on the panels and on the roof as there is no answer for this on the Wind Standard. Our approach is to Calculate the Load on the first row of panels as Wind on a single slope open building. Loading on the next rows is Calculated using the Wind Load on the first row but with the appropriate shielding generated from the first row.
  11. 11. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Example of Loads Calculation on a roof-mounted PV System Parameters for the example: 1- The building is located on an agricultural zone with few bushes or trees. Wind velocity v=24 m/s 2- Three rows of panels are going to be installed on the south pitch of the building (Orientation of the roof slopes is South-North). 3- For the example we are going to take a two-sloped building without walls. The Support Structure of the Building is made of regular steel (St-37), the roof is made of corrugated tin . Geometry of the building is indicated on the next drawing:
  12. 12. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Example of Loads Calculation on a roof-mounted PV System Parameters for the example: 1- For the case study, we will configure the PV array with 3 rows (see picture below) 2- According to the 414 Israeli Standard, the roof is divided into different areas (see picture below).
  13. 13. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Example of Loads Calculation on a roof-mounted PV System DEAD LOADS: - Self Weight of the Support Structure. - Self Weight of the Roof Cover. - Self Weight of panels and panels Support Structure - Extra loading on the roof such as lights pending from the roof, pipes, etc. RANDOM LOADS: - Live Loads: From IS:412 we should take q=20 Kg/m^2 (light weight roof). - Snow Loads: From IS:412. - Wind Loads: Principal Loads, we will Calculate this loads for our example.
  14. 14. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Example of Loads Calculation on a roof-mounted PV System Wind Load Basic Equation: - Geographic Zone II - CsCd = 1 pdseeb ccczcqw ⋅⋅⋅= )( 2 222 360 6.1 24 162 m Nvv q bb b === ⋅ = ρ 86.1)4.4( ≅=⇒ mzce
  15. 15. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Example of Loads Calculation on a roof-mounted PV System - For the example we will assume that the building is empty (φ=0) ZONE A: Cp,net = +0.7/-0.7 ZONE B: Cp,net = +1.8/-1.5 ZONE C: Cp,net = +1.4/-1.4 ZONE D: Cp,net = +0.4/-1.4 From here we have the following Loads: W(A) = +469/-469 N/m^2 W(B) = +1205/-1004 N/m^2 W(C) = +973/-937 N/m^2 W(D) = +268/-937 N/m^2
  16. 16. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Example of Loads Calculation on a roof-mounted PV System - For the example we will assume that the building is empty (φ=0) α = 10º (Roof angle) ZONE A: Cp,net = +0.7/-0.7 ZONE B: Cp,net = +1.8/-1.5 ZONE C: Cp,net = +1.4/-1.4 ZONE D: Cp,net = +0.4/-1.4 From here we have the following Loads: W(A) = +469/-469 N/m^2 W(B) = +1205/-1004 N/m^2 W(C) = +973/-937 N/m^2 W(D) = +268/-937 N/m^2
  17. 17. Existing Structures with roof-mounted PV System Baran Raviv Ltd.
  18. 18. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Example of Loads Calculation on a roof-mounted PV System Wind Load For the first row of panels: Row angle = 27º -> We need to interpolate the parameters of the table: ZONE A: Cp,net = +2.08/-2.76 For the panels we can use only the A zone as the other strips are too small. From here we have the following Load: Wpanels = +1393/-1848 N/m^2 According to the wind obstacle that the first row of panels is causing to the other rows, we could take shelter factors for the rows upwind: x- space between rows = 0.7m h- height of a row = 0.67m x/h= 1 Ys= 0.3 Wpanels = +418/-554 N/m^2
  19. 19. Existing Structures with roof-mounted PV System Baran Raviv Ltd. +1393/-1848 N/m^2 +418/-554N/m^2
  20. 20. Existing Structures with roof-mounted PV System Baran Raviv Ltd.
  21. 21. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Geometry for the Analysis of the Structure
  22. 22. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Geometry for the Analysis of the Structure
  23. 23. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Wind Pressure on the structure without PV Panels
  24. 24. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Loads transfer to the structure by the mounting system points of anchorage: Wind Pressure on the structure with PV Panels
  25. 25. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Wind Uplift on the structure without PV Panels
  26. 26. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Loads transfer to the structure by the mounting system points of anchorage: Wind Uplift on the structure with PV Panels
  27. 27. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Bending Moment Results:
  28. 28. Existing Structures with roof-mounted PV System Baran Raviv Ltd. Final Result: Ultimate Beam Capacity
  29. 29. Baran’s Project VisionBaran’s Project Vision Establish and ProvideEstablish and Provide engineering, technology,engineering, technology, construction solutions andconstruction solutions and Control Capabilities to meet ourControl Capabilities to meet our Client full satisfaction andClient full satisfaction and ExpectationsExpectations 2
  30. 30. THANK YOU! For more information, please contact: Mr. David Cohen Chief Engineering Manager BARAN RAVIV LTD. dcohen@barviv.co.il www.barangroup.com

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