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

1. 2010
www.barangroup.com

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. 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. 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. 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. 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. Ce(ze) Parameter
Existing Structures with roof-mounted PV System
Baran Raviv Ltd.

8. Cp Parameter
(Example for a two pitched roof without walls)
Existing Structures with roof-mounted PV System
Baran Raviv Ltd.

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. 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. 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. 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. 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. 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. 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. 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. Existing Structures with roof-mounted PV System
Baran Raviv Ltd.

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. Existing Structures with roof-mounted PV System
Baran Raviv Ltd.
+1393/-1848
N/m^2
+418/-554N/m^2

20. Existing Structures with roof-mounted PV System
Baran Raviv Ltd.

21. Existing Structures with roof-mounted PV System
Baran Raviv Ltd.
Geometry for the
Analysis of the
Structure

22. Existing Structures with roof-mounted PV System
Baran Raviv Ltd.
Geometry for the
Analysis of the
Structure

23. Existing Structures with roof-mounted PV System
Baran Raviv Ltd.
Wind
Pressure on
the structure
without PV
Panels

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. Existing Structures with roof-mounted PV System
Baran Raviv Ltd.
Wind Uplift
on the
structure
without PV
Panels

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. Existing Structures with roof-mounted PV System
Baran Raviv Ltd.
Bending
Moment
Results:

28. Existing Structures with roof-mounted PV System
Baran Raviv Ltd.
Final Result: Ultimate Beam Capacity

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. THANK YOU!
For more information, please contact:
Mr. David Cohen
Chief Engineering Manager
BARAN RAVIV LTD.
dcohen@barviv.co.il
www.barangroup.com