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International Journal of Power Electronics and Drive System (IJPEDS)
Vol. 11, No. 3, September 2020, pp. 1508~1518
ISSN: 2088-8694, DOI: 10.11591/ijpeds.v11.i3.pp1508-1518 1508
Journal homepage: http://ijpeds.iaescore.com
Theoretical and experimental analysis of photovoltaic module
characteristics under different partial shading conditions
Ali Hussein Numan, Zahraa Salman Dawood, Hashim A. Hussein
Department of Electromechanical Engineering, University of Technology, Baghdad, Iraq
Article Info
ABSTRACT
Article history:
Received Jul 6, 2019
Revised Dec 2, 2019
Accepted Feb 16, 2020
Recently, the renewable energy resources have gained more attention in the
electricity sector as promising technology to tackle the depletion in the
traditional energy resources. Solar energy grows rapidly due to its vast
applications. The performance of Photovoltaic (PV) system is affected by
partial shading that results from building, clouds, and fallen leaves. This
paper investigates theoretically and experimentally the impacts of various
cases of partial shading; such as vertical string, horizontal string, and single
cell at environmental conditions on the current-voltage and power-voltage
characteristics of 88 W PV panel. In addition, diagonal shading with multi
steps is considered in the analysis. The experiments are conducted with
considering various parameters; such as shading position and ratio to validate
the simulated results. The results show that at 100% shading condition, the
maximum power drops by 99.36 %, 43.7%, and 41.15% for horizontal,
cellular and vertical shading at the same solar radiation level comparing with
their initial state value. Horizontal string shaded has the highest negative
impact on the power and efficiency among other types of shadings. The
comparison between the theoretical and experimental results reveals
considerable agreement between the theoretical and experimental results.
Keywords:
PV module
Solar radiation
Partial shading,
Power losses
This is an open access article under the CC BY-SA license.
Corresponding Author:
Ali Hussein Numan
Electromechanical Engineering Department
University of Technology
Al-Sana'a Street ,Tel Mohammed,Baghdad,Iraq
Email: 50059@uotechnology.edu.iq
NOMENCLATURE
PV Photovoltaic
I current (A)
Iph photon current (A)
Irs reverse saturation current of diode (A)
V voltage (V)
Rs series resistance of PV cell (Ω)
A ideality factor
VT junction thermal voltage
Ns number of cell in series
K Boltzmann constant (1.3806503 × 10^-23 J/K)
Tc cell temperature (°C)
Q electron charge (1.6021765× 10^-19 C)
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Fs shading factor
Gt,s shaded surface irradiances (W/m2)
Gt unshaded surface irradiances (W/m2)
SA shading area
Imax current at the maximum power point (A)
Vmax voltage at the maximum power point (V)
Pmax power at the maximum power point (W)
ΔP power loss of PV panel (W)
F.F fill factor
1. INTRODUCTION
The emission of carbon from the traditional electrical power generation technology is one of the
most important reasons that lead to employ the renewable energy as alternative sources of electrical power
generation. Solar energy is the best choice for electricity generation [1] because it is clean [2], cheap [3],
silent [4], abundant and environmentally friendly energy resources [5].
Among different forms of renewable energy, PV represents one of the most promising renewable
energy in the world [6, 7] due to its great advantages; such as zero emission of greenhouse gases, low
maintenance cost, not rotating or moving parts [8, 9]. A PV cell is basically a semiconductor diode with a
large barrier layer exposed to light allowing portion of the energy in the light photons arriving at the cell
convert directly to DC electrical power [10]. The most notable factors that have a clear impact on the
performance of PV system are: Partial shading, dust [5], sand [11], temperature [12], and solar radiation [13].
Partial shading is the most common encountered problem in a PV system. In this phenomenon, the received
sunlight is reduced significantly and results in lower system efficiency [14]. In the design stage, the shadow
of nearby objects avoided as possible. However, parts of PV module face unexpected shadows; such a sun
melted snow, bird dung, fallen leaves, the neighboring buildings, towers, and passing clouds [15, 16].When
the PV module partially shaded, the shaded cell operates at current levels lower than unshaded cell. As
consequence, the shaded cells are forced into reverse bias and begin consuming power instead of generation
power. This lead to undesired increase in cell temperature this is lead to localized overheating (hot spot).
When this temperature reaches the critical limit, the effected cell (shaded cell) can be damaged [17].Passive
and active methods are used for decreasing the power losses which are caused by partial shading. In the first
method, the bypass diode is connected in antiparallel with the photovoltaic cells in order to pass the current
and avoid the destructive impact of shading. Current flow in the diode causes losses in power, therefore, it is
not possible to avoid losses completely. On the other hand, the dynamic reconfigurations between the panels
of photovoltaic represent second method (active method) [18, 19]. H. H. Khaing et al [20]: Studied the effect
of different partial shading on four various types of PV modules that involve amorphous thin-film, CIGS
thin-film, CdTe thin-film and multi-crystalline PV modules. The module tested along the length side and
along the breadth side with different shading rate varied from 10% to 60% from the PV area with increase of
10%. The result showed that shading along the breadth side more effected than shading along it’s length side.
G. S. Reddy et al. [21] Presented PV module model by MATLAB/ Simulink to analyze their performance
under nonuniform irradiance condition. Moreover, Various PV array simulation schematic could be created
by the proposed model, and parameters of irradiance of each PV module can be set independently. Different
simulation process is conducted and compared for different array configurations (2 series, 3 series, 2series ×
2parallel and 3 series × 2 parallel) under nonuniform irradiance conditions of I-V and P-V characteristics
curves. M. Abdullah et al [22], investigated the impact of shading on the effectiveness of PV panel. The
experiments have been accomplished with a 90-W solar panel under constant and changeable irradiations.
Horizontally shaded area which changed from 0 to 80% has been applied to detect the impact of varying
irradiation at appointed shading points. The results showed that for each 100W/m2 increase in radiation level
leads to enhance the output power by 3.89 W, 3.37 W, 2.27 W, and 2.02W at 0 %, 25%, 50%, and 75%
shaded area respectively. In addition, the efficiency has been raised by 0.29 %, 0.27%, 0.25%, and 0.22% at
0 %, 25%, 50%, and 75% shaded area respectively. The drop in output power and efficiency were 12.41W
and 2.3% respectively when the shading area increased by 10%. However, this study considers the horizontal
shading and ignored the other types of shading. F. Bayrak et al (2017) [23], analyzed thermodynamic and
electrical performance under the shading shape and shading ratios on 75 W polycrystalline PV. Horizontal,
vertical and single cell shading at different percentage were applied. The results showed that at 100% shading
rate, the power losses were 99.98 %, 66.93% and 69.92% for horizontal, vertical and cellular shading
respectively. The gap of this research is that the results are obtained from a practical study only without
simulating study. Gutierrezet al [24] presented the effortless approach to model and analyze the performance
of PV module under partial shading using shading ratio. The shadow opacity and characteristics of shaded
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area integrated in this approach. J. C. Teo et al (2018) [25], investigated the partial shading effect and the
critical point that reduced the sensitivity of shading heaviness. Under various numbers of shaded modules
and shading heaviness, The P-V characteristics showed that the PV string became impervious to gravity shad
when the irradiance of shaded panels arrived a critical point. The results showed that when irradiation on the
shaded modules on the PV system was between 1000 and 700 W/m2, the power dropped by about 6.2% for
each 100W/m2 drops in the irradiation. However, when irradiation was between 700 and 0 W/m2, each 100
W/m2 drops in the irradiation, leads to drop the power by 0.24%. In [21] and this research, the results
obtained from MATLAB/SIMULINK did not validated experimentally. In the present paper, different cases
of partial shading with different percentages are analyzed experimentally and theoretically to determine its
impact on power and efficiency of mono crystalline PV panel with 36 series connected cells and three bypass
diode. Insulated material is employed as shading element in different cases with different percentage of
shaded area. The I-V recorded and P-V calculated before and after applying shadow is utilized to find the
power loss corresponding to this shadow.
2. MODELING OF PHOTOVOLTAIC MODULE
PV module is the basic unit of power PV generation system. PV module has non-linear
characteristics which depend on solar radiation and cell temperature. In this paper, PV module with 36 series
connected solar cell is chosen. Figure 1. Shows the PV module model that is employed in this study. Besides,
the irradiance (G) and temperature (T) with the electrical characteristics parameter of PV module such as,
open circuit voltage (Voc), short circuit current (Isc) are shown in the figure. It is having 23.42V, 5.192A and
1.5 as open circuit voltage (Voc), short circuit current and ideality factor respectively, while series resistance
value (Rs) is 0 ohm. Different cases are carried out using Matlab/Simulink to determine I-V and P-V
characteristics (Table 1). To develop the model of PV, the solar cell block is taken from Sim Electronics
block set-Matlab. The parameters of solar cell are defined in equations (1) and (2) [25].
I = [exp
] (1)
:
(2)
The output powr is [26]
(3)
Fill factor (FF) represents the ratio of maximum power divided by the open circuit voltage and short
circuit current [26]
(4)
I ,IPh and Irs are the output, photo-generated and the diode saturation currents respectively, V is the
output voltage, RS is the series resistance, NS is the number of cells, VT is the junction thermal voltage, A is
the ideality factor, k is the Boltzman constant (1.3806503 ×10-23 J/K), T is the cell temperature and q is the
electron charge (1.6021765 ×10-19 C).
Different cases were conducted as illustrated in Table 2. The adopted PV module includes 36 solar
cell which are divided into two group, each group consist of 18 cells. Different solar irradiations and constant
temperature (25°C) were applied to find their effect on the I-V and P-V curve of the PV model. Shading
factor (FS) represents the ratio of irradiance on the shaded Surface (GT,S) to the irradiance on the unshaded
surface (GT) [27].
FS=
(5)
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Table 1. Cases studies carried out
Case study
Solar Cell Irradiance (W/m2)
Shading Factor
(FS)
Unshaded group (18 cells)
Shaded group (18 cells)
Case 1
1000
1000
1
Case 2
1000
800
0.8
Case 3
1000
600
0.6
Case 4
1000
400
0.4
Case 5
1000
200
0.2
Case 6
1000
0
0
Figure 1. Photovoltaic module model with three bypass diodes
In addition, other cases were considered by applying different irradiation level on three groups of
solar cells (each group 12 cells) as shown in Table 2 the model in Figure 1 used in these cases with
simple changes.
Table 2. Illustration of random radiation levels for PV module.
Case study
Solar Cell Irradiance (W/m2)
Unshaded group A (12 cells)
Shaded group B (12 cells)
Shaded group C (12 cells)
Case1
1000
1000
1000
Case 2
1000
900
800
Case 3
1000
800
600
Case 4
700
600
200
Case 5
800
950
300
Case 6
300
500
700
Case 7
300
200
400
Case 8
200
200
200
Figure 2. Photovoltaic module model (three group with different irradiation levels)
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Figure 3 shows the PV module, the vertical string shading with 100% shading area are applied to the
model and the results are compared with the experiment results.
Figure 3. PV module and the experiment results
3. EXPERIMENTAL SETUP
In order to obtain the I-V and P-V characteristics of the PV panel under partial shading, the current
and voltage were measured. Solar radiation and ambient temperature affect these characteristics therefore; it
is necessary to measure these parameters. At environmental conditions, the change in atmospheric condition
may lead to rapid change in the solar radiation therefore; the data must be recorded quickly in short time
as possible.
Figure 4 shows the experimental setup, where the experiment was set up in Baghdad (33.33° N
latitude and 44.39° E longitude) for collecting the required data. The utilized PV pane is Monocrystalline PV
panel with 36 cells connected in series, where each 12-cell connected to one bypass diode. The panel is
placed on a mobile metallic holder and it is installed to face the south with an inclination of 31.2. Table 3
explains the electrical characteristics of the PV panel under standard test condition. The required data are
radiation intensity, ambient and module temperatures, wind speed and relative humidity therefore; two digital
multi- meters used to measure the current and voltage. Thermocouple type k was used for obtaining the
panels temperature by using a digital data recorder. Relative humidity and ambient temperatures were
measured by using UNI-T UT332 digital Thermo-hygrometer devise. The measurement of wind speed was
obtained using wind gage type Kaindl Wind master 2.
Solar radiation was measured by solar meter pyrometer type TES 1333R and rheostat (100W, 10)
were used as load to measure the maximum current and maximum voltage. Many experiments were carried
out in clear sky condition during September, 2018 to investigate partial shading on the panel. Different cases
with different percentage of shading were applied on the panel by using non-transparent material as shading
element to closing as 0, 25, 50, 75, 100% shaded area of horizontal string, vertical String and single cell as
illustrated in Figure 5 and 6. Moreover, diagonal shading also investigated as shown in Figure 7.
Table3. Electrical characteristic of monocrystalline solar panel
Designation
Abbreviation
Values
Maximum power
P
88
Open circuit voltage
23.42 V
Short circuit current
5.192 A
Voltage at maximum power
18. 33 V
Current at maximum power
4.801 A
Voltage temperature coefficient
Kv
-2.10 mV/cell/℃
Current temperature coefficient
Ki
15 micro A/cm2/℃
No. of cells connected in series
36
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Figure 4. The schematic view of the experimental setup
Figure 5. Different percentage of shading for horizontal string, vertical string and single cell by employed
insulated materials; (X1) SA=25%, (X2) SA=50%, (X3) SA=75% and (X4) SA=100%, (Y) SA=25%, (Z1)
SA=25%.
Figure 6. Diagonal shading profile of the photovoltaic panel with different steps
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Figure 7. PV panel with different cases of shading (A) horizontal, (B) vertical, (C) single cell and (D)
diagonal.
4. RESULTS AND DISCUSSION
4.1. Simulation results
Figure 8 Shows the I-V and P-V characteristics of the photovoltaic module. This module consists of
two groups, each group with 16 solar cells. The irradiance level on the first group (unshaded) is constant
(1000W/m2), while the irradiance level on the second group (shaded) between 1000 and 0W/m2. Figure 8 (a)
represents the I-V characteristics under the cases study in Table1. Figure 8 (b) illustrates the P-V
characteristics of the same cases. From these results, it can be notice that the short circuit current decreases
when the irradiance decreases, while the open circuit voltage is less affect by shading. The maximum power
output decreases with decreasing in the shading factor. However, the output power is 88W at Fs=1 and then
dropped to 72.52, 53.5, 36.7, 15.5 and 11.86 W for 0.8, 0.6, 0.4, 0,2 and 0 of Fs respectively.
(a)
(b)
Figure 8. Photovoltaic module characteristics (a)I-V, (b)P-V.
When the irradiance on the module is non-uniform as illustrated in Table 2, multi steps in the I-V
characteristics and multiple peaks in the P-V characteristics curves are observed. This is because the bypass
diodes are activated, where this bypasses the shaded group cells and allow the unshaded group cells to have
different P-V characteristics from the shaded group cells. Figure 9 (a) shows the simulation results of the
cases study in Table 2. The same figure shows that the short circuit current is negatively affected by
decreasing the irradiance levels. This leads to decrease the maximum current and consequently, the
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maximum power as well, whereas the open circuit voltage is less affected by partial shading in comparing
with short circuit current under these conditions. The maximum power values for these cases are 88, 76, 56.9,
33, 44.3, 29, 16.1 and 15W for first, second, third, fourth, fifth, sixth, seventh, eighth case respectively.
(a) (b)
Figure 9. Photovoltaic module characteristics under nonuniform irradiation levels (a)I-V, (b)P-V.
4.2. Experimental results
An experiment was conducted to analyze the performance of PV panels under shading conditions.
Figures 5, 6 and photo of Figure 7. Show the cases of shading with different shading area.
I. Horizontal string with 0, 25, 50, 75, and 100% shaded area.
II. Vertical String with 0, 25, 50, 75, and 100% shaded area.
III. Single cell with 0, 25, 50, 75, and 100% shaded area.
IV. Diagonal shading with multi step (one, two, three, and four steps).
Each case were applied on monocrystalline panel which shaded by 25, 50, 75, 100% respectively
under radiation changes between (985±7 W/m2). In addition to that, the recorded environmental temperatures
were close during measurement days. The outside temperature is 42±2°C while, the module temperature is
approximately 66.2±2 °C. In general Isc, Im decreasing with increasing shaded area, consequently Pm
decreasing with increasing shading area as showed in Figure 10, Figure 11 and Figure 12. Figure (5.10) a and
b show I-V and P-V for different shading ratio of horizontal shading. Table 4 presents the Imax, Vmax,
Pmax, ΔP, Plosses (ΔP/P (%)) and FF values which are calculated from Figure 10. Fill factor (FF) is
decreased from 70.61% to 0.42%. It can. In comparison with current at no shading, the current is decreased
by 98%. The maximum power at no shading 63.45W while, at 100% shading conditions, the power was
drops to 0.504 W. In the other words, the power decreased by 99.36 % for 100% shading condition. In this
case of shading, each string in the photovoltaic module affected by shading, therefore, the bypass diodes
which connected between them completely disabled.
Case II: Vertical string shaded as previous case applied and the results explained in Figure 11. It can
be noticed that the power output at 0% shading was 63.62W. While, at 100% shading condition, the power
was decreased to 29.1W. In comparison with power at no shading, it mean that the power output dropped by
54.26% at 100% shading condition. At these condition, the F.F decreasing from 69.84% to 48.92%.
Case III: In this case single cell shaded by 25%, 50%, 75% and100%, the result clarified in
Figure12. It can be noticed that at no shading (0% shading) the current is 4.7A, however, at 100% shading
conditions, the current was 2.81A. The same figure showed that the power at no shading is 63.87W, and then
dropped to 26.33 W. This means that power decreased by 68.71 % as the shading increased to100%, as
compared With power at no shading condition.
Table 4. The shading results of three cases
Shading
Area
(SA)
Horizontal string Shading
Case I
Vertical string Shading Case II
Single cell Shading
Case III
ΔP
(W)
Plosses(%)
F.F
(%)
ΔP
(W)
Plosses(%)
F.F
(%)
ΔP
(W)
Plosses(%)
F.F
(%)
0%
0
0
70.61
0
0
69.17
0
0
70.5
25%
21.11
33.27
67.62
17.09
26.86
50.24
16.9
26.46
57.04
50%
36.78
57.96
63.43
20.15
31.67
50.07
21.69
33.96
50.04
75%
51.44
81.07
54.31
23.37
36.73
47.78
26.43
41.38
45.47
100%
62.95
99.21
0.4
34.52
54.26
48.92
37.5
58.71
49.3
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(a)
(b)
Figure 10. Recorded characteristics of PV panel under horizontal string shading (a) I –V; (b) P-V.
(a)
(b)
Figure 11. Recorded characteristics of PV panel under vertical string shading (a) I –V; (b) P-V.
(a)
(b)
Figure 12. Recorded characteristics of PV panel under single cell shading(a) I –V; (b) P-V.
By comparing the results of the three cases, it can be concluded that the decreasing in maximum
power output in the third case is less than the decreasing in the first cases (horizontal and vertical shading).
Diagonally shading with multi step (one, two, three, and four steps) investigating at 860 W/m2 radiation
level, as illustrated in Figure (5.19a & b). The results of this type of shading appeared that in the first step
where no shading applied the Im was 4.38, then it decreased to1.9, 4.11, and 2.11A for second, third and
fourth steps. On the other hand he power dropped from 61.32W at no shading to 2.43W for the fourth steps.
The comparison is done for two cases random reading for no shading condition and 100% of vertical
string shading when solar radiation is 743 Wlm2 and module temperature is 57℃. The I-V and P-V curves of
the collected data that were achieved experimentally and theoretically are explained in the Figures 14 a and b.
The error between the experimental and theoretical results is about 3.3 and 6.28% for first and second cases
respectively.
A comparison between present experimental results of power losses of PV module as a function of
shading area with the experimental results of previous studies explained in Figure 15. This figure presented a
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comparison of the present work with F. Bayrak et al [23]. It can be observed that the present experimental
results have obvious agreement in the behavior as compared with the existing literature.
(a) (b)
Figure 13. Recorded characteristics of PV panel under diagonally shading (a) I-V; (b) P-V.
(a)
(b)
Figure 14. Recorded characteristics of theoretical and experimental results for no shading and 100% vertical
string shading. (a) I-V; (b) P-V.
5. CONCLUSION
In this paper, non- transparent material with different shading position and different percentage of
area are applied on monocrystalline solar panel. The importance of the presence of diodes in the PV panels is
their ability to divide each panel into several sections. The results showed that the Photon current under
partial shading decreases. This reduces Isc and Im, which leads to decrease the output power. Besides, the
results reveals that when the radiation changes between 965 to 975 W/m2 and 100% shading condition is
considered the power decreases by 99.36 %, 43.7 % and 41.15% for horizontal, single cell, and vertical
respectively comparing with their initial value at no shading condition. Further, when considering the
diagonal shading with no shading at first step the power is 62.06W. However, the power decreases by 48.56
%, 63.3% and 96.22% for second, third and fourth steps respectively. The parameters of PV panel are
simulated by using MATLAB to investigate the partial shading effect at different irradiation levels. The
results show noticeable agreement between the experimental and the theoretical results.
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