Analysis of Shading Impact Factor for Photovoltaic Modules

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Analysis of Shading Impact Factor for Photovoltaic Modules
Salih Mohammed Salih, Mohammed Qasim Taha
Renewable Energy Research Center, University of Anbar, Iraq
dr_salih_moh@yahoo.com, eng_mk_elc@yahoo.com
Abstract:
PV modules are very sensitive to shading. Unlike a solar thermal panel which can tolerate
some shading, many brands of PV modules cannot even be shaded by the branch of a leafless
tree due to high reduction of its output power. The effect of shading on solar Photovoltaic (PV)
models will be evaluated by using a simulation model for simulating both the I-V and P-V
characteristics curves for PV panels. Different percentages of shading are taken into
consideration of this paper which is: 25%, 50%, 75%, 100%, and without shading. The
irradiation and temperature are constant during test. The results are simulated by using the
Matlab software. A typical Kyocera-54W and Solara-130W solar modules are used in the
simulation part. The output power of models is widely decreased as the shading percentage
increased. The Shade Impact Factor (SIF) is proportional to area of panels, so the systems build
with big panels was higher affected by shading effect
Keywords: Shading, Photovoltaic, PV, MPP, Solara, Kyocera, I-V, P-V, Shading Impact Factor
1. Introduction
When a small section of a photovoltaic panel is shaded by the branch of a tree or other
sources of shading, then a significant drop in power output from the panel will result. This is
because a PV solar panel is made up of a string of individual solar cells connected in series with
one another. The current output from the whole panel is limited to that passing through the
weakest link cell. If one cell (out of for example 36 in a panel) is completely shaded, the power
output from the panel will fall to zero. If one cell is 50% shaded, then the power output from the
whole panel will fall by about 50%, so a very significant drop for such a small area of shading
can happen. This paper reviews and analyzes the behavior of a photovoltaic device (cell or
module) under partial shading conditions [1]. To do this, the implementing a simulation model
in an open tool (MATLAB) that takes into account the electrical and thermal equations of the
photovoltaic device was did. The knowledge of the behavior of PV device under partial shading
conditions is a main topic to optimize its operation. Simulations carried out taking into account
the weather conditions (irradiance, ambient temperature and wind speed) as well as suitable
time to analyze both transient and steady state. Partial shading of photovoltaic modules is a
widespread phenomenon in all kinds of Photovoltaic (PV) systems. In many cases the PV arrays
get shadowed, completely or partially, by the passing clouds, neighboring buildings and towers,
trees or the shadow of one solar array on the other, etc. This further leads to nonlinearities in
characteristics [2]. In this study, the simulation and experimental results of uniform and partial
shading of PV modules are presented. Different shading pattern have been investigated on series
and parallel connected photovoltaic module to find a configuration that is comparatively less
susceptible to electrical mismatches due shadow problems. Partial shading in photovoltaic
arrays renders conventional maximum power point tracking (MPPT) techniques ineffective [3].
The reduced efficiency of shaded PV arrays is a significant obstacle in the rapid growth of the
solar power systems. Thus, addressing the output power mismatch and partial shading effects is
of paramount value. Extracting the maximum power of partially shaded PV arrays has been
widely investigated in the literature. The proposed solutions can be categorized into four main

groups. The first group includes modified MPPT techniques that properly detect the global
MPP. They include power curve slope, load-line MPPT, dividing rectangles techniques, the
power increment technique, instantaneous operating power optimization, Fibonacci search,
neural networks, and particle swarm optimization. The second category includes different array
configurations for interconnecting PV modules, namely series-parallel, total-cross-tie, and
bridge-link configurations. The third category includes different PV system architectures,
namely centralized architecture, series-connected micro converters, parallel-connected micro
converters, and micro inverters. The fourth category includes different converter topologies,
namely multilevel converters, voltage injection circuits, generation control circuits, module-
integrated converters, and multiple-input converters. In centralized or string photovoltaic (PV)
systems, PV modules must be connected in series in order to generate a sufficiently high voltage
to avoid further amplification and to efficiently drive further converters. This always requires
dozens of PV modules; however some of them maybe suffer from partial shadow caused by
trees, clouds or other things. In this case, power generated from each PV module becomes
unbalanced so that total output powers greatly decrease. Furthermore, hot-spot effect caused by
partial shadow is likely to damage the PV cells and affect the security of PV system. In order to
solve these problems, the topology of PV system composed of many series-connected PV
modules with corresponding energy feedback circuits is proposed in this paper, a feedback
circuit is independently utilized to feed the output energy of PV system to the corresponding
circuit including shadowed PV module. The simulation and experimental results verify that the
proposed topology can make each PV module operate on the maximum power point
individually regardless of partial shadow [4]. The energy feedback circuits do not operate
without partial shadow, they have no power loss under this condition, and therefore the circuit
efficiency is improved.
2. The Modeling of Photovoltaic Panels
To prevent the entire string of cells failing when one cell under shading; the installation can be
fitted with ‘by-pass diodes’. The current around the underperforming cells can be rerouted. The
disadvantage is that rerouting the current loses not only potential energy from these cells, but
also lowers the voltage of the entire string. Finding a clear solution to the shading problem will
help guarantee a reliable power supply for the owners of Solar PV system. By reducing shading
induced power losses, installers can potentially increase the available roof area for Solar PV
arrays. The existing Photovoltaic modules in renewable energy research centre (University of
Anbar-Iraq) consist of 36 cells. These modules (Kyocera and Solara) are often used for
experimental researches. In this experiment PV modules were placed in a dark in order to study
their behavior without illumination. Our results contain both experimental with some
mathematical calculation used to determine the effect of some the junction parameters through
an equivalent circuit model of PV.
A single solar cell consists of a photo current source is the simplest equivalent circuit in
addition to a diode, and a series resistor describing an internal resistance of cell to the current
flow. More precise mathematical description of a solar cell, which is called the double
exponential model that derived from the physical behavior of solar cells constructed from
polycrystalline silicon. The details algorithm for fig. 1. is given in ref [5].

Fig. 1. Equivalent circuit of a solar cell.
Equation (1) is commonly referred to as the diode model, where all parameters except V and I
are constants and could be used as a good model for a solar cell, as well as a module
IPV=Iph - Isat*( exp (Vcell +IPV*Rs)/Vt*N) -1) (1)
Vt = A*k*T/q (2)
Where:
G - solar irradiance
Iph- photo-generated current,
Isat- dark saturation current,
Rs- panel series resistance,
IPV - cell out put current,
Vcell - cell out put voltage,
A - diode quality (or ideality) factor,
K- Boltzmann’s constant = 1.38×10-23,
q - electron charge 1.6×10-19,
N- number of cells connected in series = 36
T - cell temperature.
The calculation is considered of both series along with the junction ideality factor (A). The
components of the diode diffusion experimentally collected I-V and P-V curves were introduced
into specially designed software that performs numerical calculations [6].
The effect of shade on power output of typical PV installations is nonlinear in that a small
amount of shade on a portion of the array can cause a large reduction in output power. For
instance, completely shading one cell of an array will cause the bypass diode protecting that cell
to begin conducting, reducing the power of the module by as much as 1/3–1/2 (depending on
the number of groups of cells in the module). Equation (3) is used to compute Shade Impact
Factor (SIF) of PV systems [7].
SIF = [1- Pshade / Psys)] × Asys / Ashade (3)
Where:
Psys and Asys are the nominal system power and area,
Ashade is the shaded area, and Pshade is the power produced under shaded conditions

3. Simulation Results
The electrical performance of a solar module is represented by I-V and P-V characteristic
curves of concentrator arrays due to mismatch between series-connected high concentration PV
modules and between single junction cells within a module. The mismatch between cells was
caused by a number of factors including: misalignment of optical elements and cells, uneven
shading due to dust or delaminating of the cell-secondary lens interface, degradation of the main
Fresnel lens and non-uniform cell material parameters. Small amounts of mismatch that would
go unnoticed at one-Sun insulation levels are vastly amplified at high concentration ratios. This
paper reports on, and interprets the regular I-V measurements that were recorded over a period
of two years under various conditions. The effect of bypass diodes on the module I-V curves is
also investigated. The general characteristics of the measured resultant I-V curves are explained.
The degradation of the PV concentrator modules over a period of two years is also confirmed
from the I-V measurements. Electrical Output power of PV panels is badly affected by shading
that caused by clouds and trees and other blocks that prevent sun's radiation with constant
irradiation and temperature. In this research it can be shown the effect of panels’ efficiency of
Kyocera and Solara PV modules by using Matlab program calculation and lab equipments to
compute o/p characteristics. The technical specifications for the simulated PV models are
summarized in table (1).
Table. 1. Specification of Kyocera and Solara PV models with 1000 (W/m²) irradiation.
Parameter
Kyocera
Solara
Isc (Ampere)
Current at Peak Power (Ampere)
Voc (Volt)
Voltage at Peak Power (Volt)
Peak Power (Watt)
Effective Panel Area (cm)
3.31
3.11
21.7
17.4
54
64 x 65.3
8.18
7.30
21.7
17.8
130
64 x 65.3
The current that is provided and depending on the voltage generated for a certain solar radiation
the generated current is directly proportional to (G), while the voltage reduces slightly with an
increasing of shading. P-V characteristic curve represents the amount of power that a panel
provides and it depends on the voltage generated for a certain solar radiation). The impact of
shading on the I-V and P-V curves of a solar panel clarified the basic mechanism that estimates
the reduction in output power. Such degradation in maximum power production clearly depends
on the shaded area as well as the layout of the modules and the bypass diodes. The analysis was
illustrated by experimental data. Many states of shadings is used (No shading, 25%, 50%, 75%
and 100%) and many connection ways are used to compute the shading effect on the o/p power.
The data are collected in same time and location (In 20th of November 2012, 12:30 AM, at
the University of University of Anbar campus. The I-V characteristic curve for Kyocera model
is shown in fig. 2

0 5 10 15 20
0
0.5
1
1.5
2
2.5
3
3.5
4
V (volt)
I (amp)
no shading
25% Shade
50% Shade
75% Shade
100% Shade
Fig. 2. I-V characteristic with shade effect of one Kyocera PV panels (54 W)
From fig. 2. it can be seen that the current of PV model deceases as the shading percentage
increase from zero to 100%. Note that when the shading percentage is near equal to or more
than 75%, the o/p of current is so effected and less than amount of current that required to use
such model for direct connection to load. Note that if the shading is 75% or 100% the charging
current is not enough for charging batteries of 12 V even the shading used is soft shading
instead of hard shading. Fig. 3. Shows the PV characteristics curves for Kyocera PV module.
The SIF of 50% cell shading state = 0.72 and power of this module is reduced by about 36% (1-
37W / 53 W) as the shading is 50% of the module size with respect to non-shading case. Also;
the maximum o/p power at non-shading is about 53 W instead of 54 W given in the data sheet
of such module and this is due to a difference between the simulation modules (which gives an
approximate result) and the real generated power in the factories, when they used a solar
module tester with constant irradiance and temperature. Ref [8] gives more details of the
extracted results for models by using the existing solar module tester in renewable energy
research center – university of Anbar – Iraq.

0 5 10 15 20
0
10
20
30
40
50
60
V (volt)
P (watt)
no shading
25% Shade
50% Shade
75% Shade
100% Shade
Fig. 3. P-V characteristic with shade effect of one Kyocera PV (54W)
Single Solara PV panel testing under shading effect was investigated by I-V and P-V
characteristics curve that shown in fig. 4. and fig. 5. respectively. Fig. 4. shows that the voltage
generated at shade up to 50% is gradually decreased. As the shading increased to 75% or 100%
the o/p voltage will be less than 12V, which means the charging of batteries will stop, if the
module is used with battery back up.
0 5 10 15 20
0
2
4
6
8
10
V (volt)
I (amp)
no shading
25% Shade
50% Shade
75% Shade
100% Shade
Fig. 4. I-V characteristic with shade effect of one Solara PV module (130W)
In fig. 5. the practical maximum o/p power at non-shading is about 118W which is less than the
maximum rating power of this module ( i.e. 130W) which taken in ideal environment with no
efficiency limitations such as dust, humidity and temperature. The maximum power at 50% of

shading is 60W. This is less than the maximum power by about 49% (1- 60W/118W) and SIF =
0.96
0 5 10 15 20
0
20
40
60
80
100
120
V (volt)
P (watt)
no shading
25% Shade
50% Shade
75% Shade
100% Shade
Fig. 5. P-V characteristic with shade effect of one Solara PV module (130W)
The previous results show that the Kyocera PV panel is less affected by shading than Solara PV
panel when the same percentage of shading was applied. Next, the PV modules are connected in
parallel or in serial in order to increase the generated to be close to or greater than the level of
voltage of the required batteries to be charged.
The series connection of two modules is shown in fig. 6. The output voltage in this connection
type will be increased with a constant current. This type of connection is suitable for
overcoming the problem of hard drop voltage due to shading effect.
Fig. 6. Solar PV panels in series connection
The parallel connection of modules is shown in fig. 7. At this type of connection, the output
voltage is constant while the current increases. This type of connection is suitable for fast

charging of batteries due to high current can be obtained from the panels, and also it is suitable
for direct connection to the driven current load.
Fig. 7. Solar PV panels in parallel connection
Table (2) shows more explanation of shading impact factor and maximum power point
(MPP). SIF of Kyocera modules and series connection is less than SIF of solara modules and
parallel connection respectively. That prove shading has less effect on models with smaller size
and it has higher effect of parallel than series connected PV panels. So series effect connection
has more immunity to shade effect than parallel connection.
Table. 2. Shading impact factor and maximum power
Model \ Connection
Shading
Asys / Ashade
MPP (watt)
SIF
One panel
Kyocera
No shading
∞
54
-
25%
4
45
0.668
50%
2
37
0.63
75%
1.333
7
1.161
100%
1
4
0.925
Two parallel panels
Kyocera
No shading
∞
107.2
-
25%
4
90
0.666
50%
2
74
0.626
75%
1.333
15
1.145
100%
1
8.2
0.921
Two series panels
Kyocera
No shading
∞
107.4
-
25%
4
92
0.593
50%
2
75.35
0.604
75%
1.333
18
1.11
100%
1
11
0.898
One panel
Solara
No shading
∞
116.3
-
25%
4
79
1.282
50%
2
60
0.968
75%
1.333
7
1.25
100%
1
3
0.974

Two parallel panels
Solara
No shading
∞
234.5
-
25%
4
160.9
1.255
50%
2
124
0.942
75%
1.333
14
1.253
100%
1
7
0.97
Two series panels
Solara
No shading
∞
236
-
25%
4
167.87
1.154
50%
2
125
0.940
75%
1.333
17
1.23
100%
1
9
0.916
Despite panels is identical and radiation and temperature is constant but there are deference of
characteristics between series and parallel ones. The details results of experimental tests given
in table (2) are summarized in fig. 8. and fig. 9.
0
20
40
60
80
100
120
025 50 75 100
Shading %
Power (W)
seri es
parall el
Fig. 8. Comparison of power generation between two connected Kyocera
PV panels
0
50
100
150
200
250
025 50 75 100
Shading %
Power (W)
seri es
para ll el
Fig. 9. Comparison of power generation between two connected Solara
PV panels

Table (3) gives some of practical types of shading extracted from ref [9]. This table shows
that there are different resources of shading, the shading in the next figures (figures 10, 11, and
12) is considered as a soft shading and for this reason the o/p of PV will not drop to a high
values as in the hard shading case. Also our extracted results are in the case of soft shading.
Figures 10 and 11 show the shading type which comes from tree effect. While figure 12 shows
the shading comes from railing source.
Table. 3. Types of shading effect.
place
Test description
Out of doors
-Area has no shade
-panels stationary
-panels positioned horizontal
Out of doors shown in fig. 10.
-Area shaded by tree
-panels constant movement
-panels positioned horizontal
Out of doors shown in fig. 11.
-Area shaded by tree
-panels constant movement
-panels positioned at 70 degree to the horizon
Out of doors shown in fig. 12.
-Area shaded railing
panels stationary
panels positioned horizontal
Fig. 10. Shaded panel, stationary panel, panels tilted positioned

Fig. 11. Area shaded by tree, panels constant movement
Fig. 12. Area shaded by railing, panels is stationary
Even panels that have identical performance ratings will usually display some variance in their
characteristics due to manufacturing processes, but the actual operating characteristics of two
panels from the same manufacturer can vary by as much as ±10%. Whenever possible, it is a
good idea to test the real-world performance of individual panels to verify their operating
characteristics before assembling them into an array.
4. Shading Effect of Batteries Charging in PV Systems
Stand-alone photovoltaic systems (The electrical energy produced by the PV array) can not
always be used when it is produced due to shading effect or dusty weather. As the demand for
energy does not always coincide with its production, electrical storage batteries are commonly
used in PV systems [10]. The primary functions of a storage battery in a PV system are to store
electrical energy when it is produced by the PV array and to supply energy to electrical loads as
needed or on demand, to supply power to electrical loads at stable voltages and currents, and
supply surge or high peak operating currents to electrical loads or appliances. Table (4) gives
the concluded results of shading effect on charging performance of batteries from above I-V and
P-V characteristics curves to all states related to the shading effect of batteries charging.

Table. 4. Shading effect on battery’s charging in single PV module [at 12 volt].
Type of PV
Shading state
Ia
Power
Kyocera
No shading
3.31
39.72
25%
3.05
37.8
50%
2.85
33
75%
0.48
5.7
100%
0.31
4.2
Solara
No shading
8.75
104.64
25%
7
68
50%
5.1
58
75%
0.3
4.5
100%
No charging
No charging
Fig. 13. shows the performance Comparison between the percentage charging powers under
shading effect with charging power. From table (4), it can conclude that the model with a small
size (Kyocera–54W) is less affected by shading than the module with a big size (solara–130W).
for example, at 25% shading the percentage of charging power is 37.8/39.72= 95.1 % for
Kyocera, while it is about 68/104.64= 64.9 % for Solara–130 module. As the shading increases
the module with a small size still has better performance than the bigger one at same percentage
of shading.
0
20
40
60
80
100
120
025 50 75 100
Shading ( % )
Percantage charging power ( % )
kyocera
sol ara
Fig. 13. Percentage of charging power
5. PV evaluation based on Solar Module Tester
The solar module tester can be used for evaluation of PV modules. The I-V and P-V
characteristic curves can be obtained directly from the tester module under STCs (T = 25 °C, G
= 1000 W/m2, and Air Mass (AM) = 1.5). the values of solar irradiance can also be changed at
different specified values. Fig. 14 shows the I–V and P–V characteristic curves and the other
key specifications (i.e. Isc, Voc, Pm, Ipm, Vpm, and FF) for the Solara PV module. Note that the

output of this module is the same as the output value in the nameplate of the module from the
supplied company which is 130W. So, the solar module tester can confirm the output values
from the manufacturing companies at standard solar irradiance [8].
Fig. 14. I–V and P–V characteristics of Solara PV model at 1000 W/m2
6. Conclusion
The analysis of shading impact factor on the performance of two PV models (Kyocera–54W
and Solara–130W) is tested under different percentage of shading effect. The results showed
that the shading can has more effect on current of PV than generated voltage, which causes a
reduction of the generated power. Because the generated voltage is less than (12 volt), the
charging of batteries will stop if the shading near 75% or more. The photovoltaic systems with
small modules sizes (dimensions) are less affected by shading than the systems with larger
modules sizes. The solar module tester can be used for extracting the power values of the new
fabricated PV modules.
Acknowledgments
This work is supported by the University of Anbar-Iraq /Renewable Energy Research Center
with Grant No. RERC-TP15.
6. References
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[3] Bidram, Ali, Davoudi, Ali, Balog, Robert S., "Control and Circuit Techniques to Mitigate
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[4] Zhang, Qi, Sun, Xiang-Dong, Zhong, Yan-Ru, Matsui, Mikihiko,“A novel topology for
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Salih Mohammed Salih (Member, IEEE) received his B.Sc. degree in
Electrical Engineering from the University of Baghdad-Iraq in 1999, and his
M.Sc. and Ph.D. degrees in Communication Engineering from the University
of Technology-Iraq in 2003 and 2008, respectively. Since 2005, he has
worked with the University of Anbar-Iraq as a lecturer in the Electrical
Engineering Department. He is currently the director of the Renewable
Energy Research Centre (RERC). His research interests include OFDM,
space time coding, modulation techniques, security, wireless communication,
radar, computer networks, and renewable energy resources. He has published
more than 35 papers in local and international journals and conferences.
Mohammed Qasim Taha received the B.S. degree in Electrical Engineering
from University of Anbar-Iraq in 2010. Since 2010 he works in Renewable
Energy Research Centre (RERC) at the University of Anbar. He is interested
in renewable energy resources, Solar tracker systems, Wind turbines,
Electrical power, Communication, Digital Signal Processing (DSP), Control
applications, and Microcontrollers. He has published many papers in local
and international journals and conferences. Currently he is working toward
the M.Sc. degree in Electrical Engineering Science of University of New
Haven, USA.
.