Design of manual solar tracking system wps

1
Design of solar module mounting structure for
manual seasonal single axis tracking capable of
surviving high wind loads on rooftops
Introduction
As global temperature increases and the increasing levels of fossil fuel emissions in the environment, the
energy sector is taking drastic steps to make a transition from the fossil fuels era to the sustainable energy
era.Many developing nations have taken a drastic steps to increase their electric energy generation from
renewable sources,like solar ,wind ,hydro , wave and tidal power. In many developing countries like
India and China, solar energy accounts for a large chunk of electricity generated from renewable sources.
Seasonal trackers help to increase output from solar energy farms because the array tilt is adjusted
throughout the year,most commonly on a monthly basis so that the solar panel arrays remain at an
optimum angle of tilt for each month. For this purpose the adjustable tilt solar mounting structure must
have a rotary joint that allows single degree of freedom movement.
Objective
Our objective here is to ensure the use of lightest square hollow sections and rectangular hollow sections
and design a solar panel structure with tilting capability that can withstand winds up to 160~180kmph.
Analysis and assumptions
Load on a solar dual axis tracker can be divided into two types: Dead load and Wind load.
Dead load is that load which acts on the structure when there is no wind. Hence,it consists of weight of
solar panels and structural members.
In our analysis we have:
1. Assumed dimensions of solar panel to be 2m*1m i.e. each solar panel has a flat surface area of 2m2
.
2. Weight of solar panel = 26kg.
3. Estimated life of structure = 25 years.
4. Estimated height of building on which PV module will be installed = 20m (Class A).
5. Average height of surrounding objects is not greater than 1.5m.
6. Assumed factor of safety for is 1.5 i.e. permissible longitudinal stress is 165N/mm2
.
7. Dimensions given in drawing are in meters.
8. Bending moment diagrams for heaviest members selected have been given only.

2
9. The binding strength of steelwith concrete (σb)= 0.6N/mm2
.
10. Cube strength or compressive strength of concrete (σcu) = 2.1N/mm2
.
Methodology:
1. Calculate dead load acting on particular member and corresponding bending moment.
2. Calculate load due to the wind and corresponding bending moment.
3. Add bending moment due to components of dead load and wind load along major and minor axis,
check if stress developed in member due to a total moment around major axis exceeds
permissible limit.
4. If stress is not within permissible limit, check for higher dimensions.
5. The maximum stress in members (1-5) occurs when the wind acts on the array from the front,
however, maximum stress in structural member 6 (anchor bolts) occurs when wind blows from
the back of the PV array causing uplift forces.
Diagrams of Photo Voltaic array with structure
Figure 1
Number and type of solar tracking structure components:
Serial number Structure Element
No
Section Description Number
1 1 Square Hollow
Section
Panelfixing
member
8
2 2 Rectangular Supporting 4

3
Hollow Section member
3 3 Rectangular
Hollow Section
Base member 1
4 4 Circular Hollow
Section
Steel post 1
5 5 Base plate 1
6 6 Anchor bolt 4
Table 1
Figure 2

4
Figure 3
Conditions under wind load
Figure 4

5
Figure 4 shows the condition under which the forces and moments on structure elements 1-5 is maximum.
Figure 5
Figure 5 shows the condition under which forces on structure element 6 is maximum. Hence,calculation
of stresses on anchor bolts have been made to check for failure under this condition.
Figure 6

6
Example showing direction of force components
Figure 7
Figure 7 shows how forces and moments on structure elements 1-3 have been calculated. Moments about
X’-X’ is maximum hence elements have to be placed such that those moments are balanced on its major
axis.
Only structure element 1 has been shown in the diagram. However,the same analogy can be applied to
structure elements 2 and 3.
Calculations
Calculation of design wind speed:
Design wind speed Vd = k1.k2.k3.Vb,where k1 = risk coefficient for different classes of structure, k2=
terrain factor for difference in design height and terrain type and k3=topography factor.
Vb = basic wind speed which for eastern coastalregions of India = 50m/s.
K1 = 0.9 for estimated life of structure = 25 years.
K2 = 1.12 for terrain category 1 and building class A.
K3 = 1 considering upwind slope at site lesser than 3˚.
Vd = 50.4 m/s.
Calculation of design wind pressure:

7
Design wind pressure (pd) = 0.6Vz
2
= 0.6*(50.4)2
= 0.6*2540.16 = 1524.096n/m2
= 155.36 kg/m2
~150kg/m2.
Selection of suitable section for structural member type 1
Figure 6 shows the portion of load supported by structural member 1. The shaded region represents just
that and it shows that load acting on each ½ solar panel in a single row is supported by it. Hence for 32
solar panels we need 8 nos. of structural member 1.
Figure 8
Figure 9
Dead load moment on square hollow section
Weight of each solar panel = 26 kg
Area of each solar panel = 1 * 2 m2
= 2m2
Weight of solar panel per unit area = 13kg/m2
Considering one square hollow section to support 4 half solar panels,
We calculate the U.D.L. of the solar panels = 13 kg/m2
* 0.5 m = 6.5 kg/m
As shown in the figure the square hollow section is subjected to dead weight consisting of panel load and
its own self-weight.

8
Self weight of square hollow section will be varying with the dimensions of square hollow section we
choose.
1. For SHS 30.0*30.0*2.6, s.w. = 2.1 kg/m and Zx = Zy = 2.15 cm3
.
Design against dead load:
Total value of U.D.L acting on SHS, = (6.5+2.1)kg/m = 8.6kg/m
Maximum value of moment acting on the SHS, = 8.6 * 1 *0.5 kg-m = 4.3 kg-m = 4.3 * 9.81 N-m =
42.183 N-m.
Maximum value of stress induced in the SHS due to dead load = 42.183/2.15 N/mm2
= 19.62 N/mm2
.
Maximum value of stress induced when PV array tilted at 45˚ to vertical = 42.183*0.707/2.15 = 13.87
N/mm2
.
Design against wind load(PV array tilted at 45˚ to vertical):
U.D.L due to wind load acting on SHS = 150 * 0.5 *0.707kg/m = 53.025 kg/m.
Maximum moment due to wind load acting on SHS = 53.025 * 1 * 0.5 kg-m 26.5125 kg-m = 26.5125*
9.81 N-m = 260.087 N-m.
Adding component of dead load total bending moment acting on structural member 1 =
260.087+(42.183*0.707) = 289.91 N-m.
Maximum stress induced in the SHS due to wind load = 289.91/2.15 N/mm2
= 134.84 N/mm2
.
f(x)=(-((2.1+6.5+75)*0.707*x^2)/2)*9.81
f(x)=[(-((2.1+6.5+75)*0.707*x^2)/2)+(132.9867*(x-1))]*9.81
f(x)=[(-((2.1+6.5+75)*0.707*x^2)/2)+(132.9867*(x-1))+(103.4341*(x-3))]*9.81
f(x)=[(-((2.1+6.5+75)*0.707*x^2)/2)+(132.9867*(x-1))+(103.4341*(x-3))+(103.4341*(x-5))]*9.81
f(x)=[(-((2.1+6.5+75)*0.707*x^2)/2)+(132.9867*(x-1))+(103.4341*(x-3))+(103.4341*(x-5))+(132.9867*(x-7))]*...
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5
-300
-200
-100
100
200
300
x
y
BMD for structure element 1 about major axis under influence of wind pressure acting from front of array
when tilted at 45 degrees w.r.t. vertical.

9
Maximum deflection at free end during maximum wind pressure= {Ml2
/(2EI)} = ((28991) * 1002
)/(2 *
20000000 *5.43) = 1.33 cm
Angular deflection of structural member at free end = (1.33/100)*(180/3.14) = 0.76˚.
As both stresses,that due to dead weight and one due to wind load are within the limit of 165N/mm2
, we
can safely use SHS 30.0*30.0*2.6 as a structural member for fixing of PV panels at the assigned location,
as shown in the diagram.
Selection of suitable hollow tube section for structural member type 2
Figure 10

10
Figure 11
1. For RHS 127.0*50.0*3.6 self weight = 9.34kg/m, Zx = 35.76cm3
and Zy = 20.82 cm3
.
Maximum moment due to reactions from structural members = {(19.35 * 2) + (38.70 * 1)} kg-m = 77.4
kg-m = 759.294 N-m.
Maximum moment due to self weight of RHS = 9.34 * 2 * 1 kg-m = 18.68 kg-m = 183.25 N-m.
Total dead load moment at the center of the RHS = (759.294+183.25) N-m = 942.54 N-m.
Maximum stress induced due to dead load moment = 942.54/35.76 N/mm2
= 26.36 N/mm2
.
Maximum stress induced due to dead load when array tilted at 45˚ to vertical = (666.375/20.82) N/mm2
=
32 N/mm2
.
Design against wind load:
Wind pressure = 150 kg/m2
.
U.D.L due to wind load = 150 kg/m2
*2m*0.707` = 212.1 kg/m.
Maximum moment due to wind load = 212.1 *2 *1 kg-m = 424.2 kg-m = 4161.402 N-m.
Total moment after adding component of dead load causing moment about major axis =
(4161.402+(666.375) )N-m = 4827.78 N-m.

11
Maximum stress induced in RHS due to wind load =4827.78/35.76 N/mm2
= 135N/mm2
N/mm2
.
Maximum deflection considering (dead load + wind load) = ((482777) * 2002
)/(2 * 20000000 * 276.33) =
2.12cm
Angular deflection of structural member = (2.12/200)/(180/3.14) = 0.61˚.
As both the stresses are with the limit of 165N/mm2
, RHS 127.0*50.0*3.6 may be safely used as
structural member type 2, as indicated in the drawing.
Selection of suitable hollow tube section for structural member type 3
-0.2 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8
-5000
-4500
-4000
-3500
-3000
-2500
-2000
-1500
-1000
-500
500
x
y
BMD of structure element 2 under influence of wind pressure acting from front of array
when tilted at 45 degrees w.r.t. vertical

12
Figure 12
Figure 13
1. For RHS 240.0*120.0*6.0, self weight = 32.05 kg/m, Zx = 252.16cm3
and Zy = 171.74cm3
.
Maximum moment about major axis due to reactions from supported members = [(192.16*3) +
(157.76*1)]= 644.24 kg-m = 6320 N-m.
Moment due to self weight of member = 32.05*4*2 kg-m = 256.4 kg-m = 2515.284 N-m.

13
Total moment due to dead load about major axis = (6320+2515.284) N-m = 8835.284 N-m.
Maximum stress induced due to dead load = ((8835.284)/252.16) N/mm2
= 35.038 N/mm2
.
Maximum stress induced when PV array is tilted at 45˚ to vertical = (8835.284*0.707)/171.74 =
(6246.55/171.74) = 36.37N/mm2
.
Design against wind load:
Wind pressure = 150 kg/m2
.
Wind pressure acting normal to PV array = U.D.L due to wind load = 150 * 4 * 0.707 kg/m = 424.2 kg/m.
Maximum moment due to wind load induced at the point of support = 424.2 * 4 * 2* kg-m = 3393.6 kg-m
= 33291.216 N-m.
Adding component of dead weight causing moment about major axis = (33291.216+6246.55) N-m =
39537.766 N-m.
Figure 14
Maximum stress induced due to wind load = (39537.766/252.16) N/mm2
= 156.79 N-m.
Maximum deflection considering (dead load + wind load) = ((3953776.6) * 4002
)/(2 * 20000000 *
3025.91) = 5.22 cm
Maximum angular deflection = (5.22/400)*(180/3.14) = 0.74˚.
As the above induced stress values are within the limit of 165N/mm2
, RHS 240.0*120.0*6.0 can be safely
used as structural member in places indicated in the diagram.
f(x)=[-(((600+32.05)*0.707*x^2)/2)]*9.81
f(x)=[-(((600+32.05)*0.707*x^2)/2)-(192.16*0.707*(x-1))]*9.81
f(x)=[-(((600+32.05)*0.707*x^2)/2)-(192.16*0.707*(x-1))-(157.76*0.707*(x-3))]*9.81
f(x)=[-(((600+32.05)*0.707*x^2)/2)-(192.16*0.707*(x-1))-(157.76*0.707*(x-3))+(4069.43544*(x-4))]*9.81
f(x)=[-(((600+32.05)*0.707*x^2)/2)-(192.16*0.707*(x-1))-(157.76*0.707*(x-3))+(4069.43544*(x-4))-(157.76*0...
f(x)=[-(((600+32.05)*0.707*x^2)/2)-(192.16*0.707*(x-1))-(157.76*0.707*(x-3))+(4069.43544*(x-4))-(157.76*0...
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5
-40000
-35000
-30000
-25000
-20000
-15000
-10000
-5000
x
y
BMD of structure member 3 under the influence of wind pressure from front of array
whentilted at 45 degrees w.r.t. vertical.

14
Design of structural member type 4(Base column)
Figure 15

15
Figure 16
1. For CHS, 200.0 * 219.1 * 6.0, self weight = 31.51 kg/m, cross sectional area = 40.17 cm2,
, I =
2281.95 cm4
and Z=208.30 cm3
.
Design against axial forces:
Maximum vertical load acting on structural member 4 = (Weight of supported members + Vertical
component of force acting on PV array+self weight) = (956.24+(424.2*8*0.707)+(31.51*1.2)) = (956.24
+ 2399.2752) kg = 3393.33 kg = 33288.54 N.
Therefore,compression stress induced = (33288.54/4017) = 8.29 N/mm2
.
Slenderness ratio = 1200/110 = 10.9.
The permissible compression stress for structural member with slenderness ratio of 10.90 will be around
150N/mm2
.
Design against moments:
Moment due to wind acting from the front of the PV array when it is tilted at 45˚ with respect to the
vertical = 23536.89*1.2 N-m = 28244.268 N-m
Principal stress induced due to bending = (28244.268/208.30) = 135.59 N/mm2
.

16
Deflection of circular hollow section = (Ml2
/2EI) = (28244.268 * 1202
)/(2 * 20000000 * 2281.95) mm =
0.0045 cm.
CHS 200.0 * 219.1 * 6.0 can be safely used as structural member type 4 as indicated in diagram.
Design of base plate (structural member 5)
Figure 17
Maximum axial load = 32.92kN (compressive)
For annular columns the load from the base plate to the concrete can be assumed to be transferred through
an annular area with equal distances c on both sides of the walls of the column. Figure 12 shows the
annular area that is being discussed.
Area required to carry load = (32.92*103
)/(0.6*σcu) = 26127mm2
Area of annular resistive area = (2c+t)(D-t)π = 26127 or, c= 16.51mm.
Thickness of plate (tp) = c*((3*w)/(σyt))0.5
= 16.51*((3*(0.6*2.1))/(165))0.5
~ 2.5 mm.
Therefore we can say 300mm*300mm*5mm base plate would have been sufficient for this application.
However due to large moment acting on the structure we choose plate having dimension
750mm*750mm*10mm to reduce stress on anchor bolts.
Selection of suitable bolt for structural member type 6
The number of bolts used in this application is 4.

17
Figure 18
For M24 bolts, rb = 12mm and distance of hole from edge of plate should be minimum 44mm.
Figure 19

18
As shown in figure, M = 28.24 kN-m and N = 32.28 kN. Also a = 0.331m and b = 0.215m.
𝑁 = 𝐶 − 𝑇
𝑀 = ( 𝑇 ∗ 𝑎) + ( 𝐶 ∗ 𝑏) = 𝑇 ∗ ( 𝑎 + 𝑏) + 𝑁 ∗ 𝑏 𝑜𝑟, 𝑇 =
{ 𝑀− ( 𝑁 ∗ 𝑏)}
( 𝑎 + 𝑏)
𝑜𝑟, 𝑇 = 38.62 𝑘𝑁.
𝐶 = 𝑇 + 𝑁 = 38.612 + 33.28 = 71.90 𝑘𝑁.
Compressive stress on concrete = {71.90*1000/(320*750)} N/mm2
= 0.413 N/mm2
<cube strength of
concrete(2.1N/mm2
).
Pull out force experienced by each bolt (Fpullout) = 19.31 kN.
Cross sectional area = (π/4)db
2
= 452.4 mm2
.
Stress developed in bolt = (19.31*1000/452.4) = 42.68 N/mm2
.
As of now, there are no problems with using M24 bolts for anchoring purpose. However the greatest
tensile stress induced will occur when wind acts from the back of the PV array. Hence we need to check
for possibilities of failure under those circumstances also.
Figure 20

19
Figure 21
Values of normal force on the array have been obtained simply by multiplying wind pressure by the
projected frontal area of the PV array after adjusting it for specific component and adding to weight.

20
Figure 22
The maximum tension in bolts will occur in case of wind blowing from the back of the array.
−𝑁 = 𝐶 − 𝑇 𝑜𝑟, 𝐶 = 𝑇 − 𝑁
𝑀 = ( 𝑇 ∗ 𝑎) + ( 𝐶 ∗ 𝑏) 𝑜𝑟, 𝑇 =
{ 𝑀 + ( 𝑁 ∗ 𝑏)}
𝑎 + 𝑏
=
28.24 + (13.79 ∗ 0.215)
0.331 + 0.215
= 57.15 𝑘𝑁.
Therefore,load carried by each bolt = 28.58kN.
The tensile stress generated in the bolt = (28575/452.4) = 63.16 N/mm2
.
Area of contact between bolt and concrete = 28575/(0.6) = 47625 mm2
= 476.25cm2
.
Contact area of 140 mm * 140 mm plate =2*{ (15*15)-π.rb
2
} = 440.96 cm2
~ 441 cm3
.
Length of bolt required = (476.25-441)/(π.rb) = [35.25/( π.rb)] ~ 10cm.
Results
The following are the results of the analysis:
1. For structural member type 1, SHS 30.0 * 30.0 * 2.6 and 32.0 * 32.0 * 2.0(TATA STRUCTURA) have
found to be suitable for use.
2. For structural member type 2, RHS 122.0 * 61.0 * 3.6 for use.

21
3. For structural member type 3, RHS 240.0 * 120.0 * 6.0 has been found suitable for use.
4. For structural member type 4, CHS 200.0 *219.1 * 8.0 has been found to be suitable for use.
5. Suitable dimension of structural member type 5 i.e. base plate have been found to be 750mm * 750 mm
* 10mm.
6. For structural member type 6, M24 bolts having 15cm depth and 150mm*150mm*6mm plate at mid
length in cement have been found to be suitable for anchoring the structure to foundation.
Suggestions
1. Stiffeners are suggested to be used made of 6mm thick sheet, 4 numbers in total at the base of the
annular column, in between the anchor bolts. The height and width of the stiffeners may be
assumed to be equal to the diameter of the annulus = 219.1mm.
2. Same can be done to fix base member on to plate of rotational member.
Terminology
UDL = Uniformly Distributed Load.
Zx = Elastic section modulus about major axis.
Zy = Elastic section modulus about minor axis.
Vb = Basic wind speed in m/s.
Vd = Design wind speed in m/s.
Pd = Design wind pressure N/m2
.
SHS = Square Hollow Section
RHS = Rectangular Hollow Section
CHS = Circular Hollow Section
Acknowledgment
I would like to thank Mr. Durjati Prosad Chattopadhayay for giving me an oppotunity to work on this
project. Also, I would like to thank Mr. Krishnendu Roy Choudhury for guiding me through the project
and providing me with reference material. Without these two persons this project would not have been
possible.
References
1. Steel Designer Manual - Buick Davison and Graham W. Owens.

22
2. IS-875, IS-4923, IS-808.

Design of manual solar tracking system wps

More Related Content

What's hot (20)

Similar to Design of manual solar tracking system wps (18)

Recently uploaded (20)

Design of manual solar tracking system wps