3 d finite element method modeling and simulation of the temperature of crystalline photovoltaic module

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 04 Issue: 09 | September-2015, Available @ http://www.ijret.org 378
3D FINITE ELEMENT METHOD MODELING AND SIMULATION OF
THE TEMPERATURE OF CRYSTALLINE PHOTOVOLTAIC MODULE
Nyanor Peter1
, Oman Emmanuel Kabu2
, Kudadze Stephen3
, Deku Anthony4
1
Lecturer, Mechanical Engineering Department, Accra Polytechnics, Accra, Ghana
2
Senior Lecturer, Mechanical Engineering Department, Accra Polytechnics, Accra, Ghana
3
Senior Lecturer, Mechanical Engineering Department, Accra Polytechnics, Accra, Ghana
4
Lecturer, Mechanical Engineering Department, Accra Polytechnics, Accra, Ghana
Abstract
The temperature reached by solar cells/modules during operation has been simulated to have information about the temperature
distribution in the solar cell/module. A finite element (FE) model of the solar cell/module was created in COMSOL Multiphysics
environment. The simulations enable visualization of the temperature distribution in crystalline silicon solar cell. The effect of
different encapsulating materials, Ethylene-vinyl Acetate (EVA) and silicone on cell temperature are also investigated. An
unwanted side-effect of the encapsulation of solar cells into a PV module is that the encapsulation alters the heat flow into and out
of the PV module, thereby increasing the operating temperature of the PV module. These increases in temperature have a major
impact on the PV module by reducing its voltage, thereby lowering the output power. A finite element (FE) model representing a
real crystalline silicon solar cell/module in terms of size, mechanical and material properties is created. An in-depth study of the
FE software used, COMSOL Multiphysics is done in other to get the best output in terms of solver configuration and memory
considerations. Four different geometries of the solar cell/module are created for these simulations; each representing a stage or
variant in the solar module assembly. At first, the models are validated comparing results from simulations such as the effect of
changes in solar irradiance, wind velocity and incident angle of solar irradiance on temperature with those in literature. The
effect of the type of protective cover used in the encapsulation, either glass-glass or glass-Tedlar on cell temperature is analyzed.
The thickness of the protective cover layers and its optical properties are also investigated based on their effects on cell/module
temperature. All the simulations leading to the conclusions drawn about the cell/module temperature and its distribution were
performed by varying wind velocity, irradiance, material sizes and incident angle among other model modifications. The color
maps and graphs are presented in this study.
Key Words: Modeling, COMSOL Multipysics, Crystalline silicon solar cell/module, FE simulations, Temperature
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1. INTRODUCTION
Solar energy provides a great potential as a renewable
energy source. It is constantly improving and becoming a
competitive energy source for the future. Recently, there has
been an enormous increase in the understanding of the
principle of operation of photovoltaic devices, which led to
a rapid increase in the power conversion efficiencies of such
devices. New methods of harnessing the full spectrum of the
sun’s wavelength and new materials for making solar cells
are paving way for solar power to be the emerging power
resource for the world at large.
A photovoltaic (PV) module exposed to sunlight generates
heat as well as electricity. For a typical commercial PV
module operating at its maximum power point, only 15 to
20% of the incident sunlight is converted into electricity [1],
with much of the remainder being converted into heat. In
dealing with solar module efficiency, one important effect to
consider is the temperature of the module. According to the
theory, the output power of a crystalline solar cell decreases
by 0.4% when the temperature increase is equal to 1°C
above the optimum operating temperature [2]. Thus a
thorough understanding of the sources, distribution and
values of temperature reached in operation by the solar
module is of utmost importance. In addition, increases in
temperature are implicated in several failure or degradation
modes of PV modules, as elevated temperatures increase
stresses associated with thermal expansion and also increase
degradation rates by a factor of about two for each 10°C
increase in temperature [1].
Solar cells are made from semiconductor materials that turn
sunlight into electricity. This effect was first recorded by E.
Becquerel, in 1839 [3]. In 1877 the first solid state device
was recorded to show such an effect. However, it was in
1954 at Bell Labs when the solar electric effect was
demonstrated in silicon (Si) that the idea of producing
useable amounts of electricity from solar cells began.
2. TEMPERATURE MODEL OF SOLAR
CELL/MODULE IMPLEMENTED IN COMSOL
MULTIPHYSICS ENVIRONMENT
To simulate the solar cell/module operating temperature, a
model of the solar cell/module is created in COMSOL
Multiphysics. The geometry needed for each simulation is
created, the material properties are defined based on values

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from the COMSOL materials library and literature.
2.1 Creating the geometry
To simulate the solar cell/module operating temperature, a
model of the solar cell/module is created in COMSOL
Multiphysics. The geometry needed for each simulation is
created, the material properties are defined based on values
from the COMSOL materials library and literature
2.1.1 Model A: Solar Cell Consisting Of Silicon,
Aluminum, Busbars And Fingers
Model A Is A 12.5 Cm X 12.5 cm solar cell consisting of
the following layers from bottom to top: aluminum, silicon,
busbars and fingers. The busbars and fingers are made of
silver. This represents the basic components of the solar cell
without the encapsulation and protective cover. The
components and its arrangement are shown in Fig -1. The
silicon is 300 µm thick, aluminum is 30 µm thick and the
busbars and fingers are 18 µm thick. The bus bars are 1.5
mm wide whiles the fingers are 250 µm wide. There are two
busbars and 30 fingers on the silicon surfaces. The fingers
are the smallest in size and thus determine to a large extent
the mesh size. The percentage coverage of the fingers on
silicon surface of a solar cell is typically estimated to be
between 7 and 9%. The number of fingers was selected to be
as close to reality (percentage coverage range) as possible
and reduce computational cost to a minimum.
Fig -1: Model A - Solar cell consisting of silicon,
aluminum, busbars and fingers
2.1.2 Model B: Solar cell made up of Model A,
Glass, EVA and Tedlar
Model B is made up of Model A described in 2.1.1,
laminated with a 450 µm thick Ethylene-vinyl Acetate
(EVA) on both sides, a protective solar glass 3.2 mm thick
on the upper side and 500 µm thick Tedlar protecting the
back side. The layers are arranged as shown in Fig -2. The
basic cell part (Model A) has the same configuration and is
revealed in a transparent view (a view with glass, EVA and
Tedlar shown as transparent) in Fig -3.
Fig -2: Model B - Solar cell made up of Model A, Glass,
EVA and Tedlar
Fig -3: Transparent view of Model B revealing busbars and
fingers arrangement.
Model B was used in the simulation to analyze the
additional effect of encapsulation materials (Glass, EVA and
Tedlar) on the cell temperature. The laminating material
EVA is replaced by silicone, another laminating material, to
ascertain if the increase in efficiency of the silicone
laminated modules affects the cell operating temperature.
2.1.3 Model C: Solar cell made up of Model A,
glass, EVA
Model C is made up of the same base as Model B but in this
model, the protective back of Tedlar is substituted by glass.
This model has top and bottom glass protective cover. Each
glass layer is 3.2 mm thick.
The model is used to simulate the effect of having glass on
both sides on cell temperature as compared to Tedlar on the
back side. This model is shown both in 3D and as a
transparent structure in Fig -4 and Fig -5, respectively.
Fig -4: Model C: Solar cell made up of Model A, glass,
EVA

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Fig -5: Transparent view of Model C revealing busbars and
fingers
2.1.4 Model D: Solar Module Made Up Of Two of
Model B With Copper Interconnection
Model D is a two cell mini solar module. To conserve
cumputer memory during computation and to take
advantage of the symmetric nature of the geometry, only a
quarter of each cell is used. The cells have the same
structure and composition as the cell in Model B. The two
quarter cells are connected with a copper stripe. The two
cells are placed 7 mm apart and encapsulated with glass,
EVA and Tedlar as in Model B. The entire space around the
interconnecting copper stripe is filled with EVA. The 3D
view as well as the transparent view of the model is shown
in Fig -6 and Fig -7 respectively. The copper stripe is
modeled here as a straight bar due to memory
considerations. A symmetry boundary condition is defined
on three sides of the mini module to form a complete two-
cell module.
Fig -6: Model D: Solar module made up of two of Model B
with copper interconnection
Fig -7: Transparent view of Model D showing the two cells
and copper interconnections.
Model D is used for the simulation of the temperature
distribution in the EVA surrounding the copper
interconnections, the effect of copper on cell/module
temperature as well as the effect of the distance between
adjacent cells on temperature.
2.2 Definition Of Material Properties
The material properties were taken from literature as well as
from the COMSOL material library. The following
materials are used in the modeling: glass, EVA, silicone,
silver, silicon, aluminum, Tedlar and copper.
Table -1: Sample material properties table [5] [6] [7] [8]
Material
Property
[Unit]
Glass
EVA
Silver
Silicon
Aluminum
Density
[kg/m3
]
2200 935 10500 2329.1 2700
Thermal
conductivity
[W/(m.K)]
1.1 0.34 429 163 210
Heat
capacity at
constant
pressure
[J/(kg.K)]
480 480 235 0.703 900
Electrical
conductivity
[S/m]
1e-
14
* 6.16e7 1e-12 3.5e7
Relative
permittivity
4.2 * 11.7 11.7 10
Refractive
index
1.5 1.5 * 3.45 *
Emissivity * * 0.01 0.84 *
*Value not relevant for the simulation
2.3 Physics selection and boundary conditions
The physics selection determines what parameters are
solved for and the physical boundaries of the simulation.
Two physics interfaces, joule heating and heat transfer in
solids with surface-to-surface radiation and radiation in
participating media activated are used in the simulation in
this study. COMSOL allows for the full coupling of the
different physics interfaces. The physical boundaries are
also defined for each simulation according to real values and
conditions.

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2.4 Meshing
The structured mesh type “swept mesh” is used in meshing
all the models. The swept mesher operates on a 3D domain
by meshing a source face. The source face is meshed with
free triangular elements and then the resulting face mesh is
swept along the domain to an opposite destination face. A
swept mesh is structured in the sweep direction and can be
either structured or unstructured orthogonally to the sweep
direction
The mesh size is chosen from one of the predefined mesh
sizes under general physics. The predefined sizes start from
extremely coarse mesh size to extremely fine mesh size. The
model is meshed with coarse size mesh. The mesh is made
finer at the narrow regions like in the finger, busbar areas
and edges and much coarser in the wider regions as shown
in Fig -8.
Fig -8: Fine mesh at narrow regions and edges
2.5 Simulation approach
The models for the simulations were created as explained in
detail in 2.1.1 to 2.1.4. First of all, the models are verified
incorporating standard (common) operating conditions
where the outcome can be speculated based on literature and
experience. Once the initial model was verified to be
working properly, further modifications are made to
investigate material and atmospheric conditions
dependencies.
The simulations are done at the Normal Operating Cell
Temperature (NOCT), which is defined as the temperature
reached by open circuited cells in a module under the
following conditions:
Irradiance on cell surface = 800 W/m2
Ambient air temperature = 20°C
Wind velocity = 1 m/s
Mounting = open back side.
The segregated solver makes it possible to split the solution
process into substeps. Each substep uses a damped version
of Newton’s method. It can be used for both stationary and
time dependent solvers. Each subset can have its own solver
settings. This solver is made use in simulations of Models B
through D in combination with a direct solver PARDISO.
The order in which the segregated steps run can be changed.
3. RESULTS AND DISCUSSION
3.1 Combined effect of Joule heating and solar
irradiance on temperature
COMSOL Multiphysics allows for the metaphysical
analysis of modeled systems. The temperature characteristic
of the solar cell is dominated by both solar irradiance and
Joule heating. These physical effects can be modeled
individually and as a combined effect. Table -2 shows the
temperature difference in the case of applying solar
irradiance only, Joule heating effect only and the
combination of both, at the NOCT conditions. The
simulations demonstrate that the Joule heating effect
produces a small heating of the cell with respect to solar
irradiance, as expected. The values of the third column of
Table -2 affirm that the modeled solar cell shows a quasi-
linear behavior (superposition effect of the two physical
effects). The combined effect leads to a slight lower
temperature increase as the discrete addition of both effects
due to the dependence of heat transfer coefficient on
temperature difference. The simple addition of the
simulation outcome from individual application of the two
physical effects is slightly higher than that from the
combined effect simulation. The simple addition of the two
physical effects is as shown in Chart -1 by a green line and it
is the addition of the blue and magenta lines. The wind
speed is varied over a range for each of the three cases and
the results are shown in Chart -1. This behavior is also
reported in [9].
Table -2: NOCT results of the solar cell under the three
cases (irradiance, Joule heating and a combination of both).
Ta = Ambient Temperature, Tc = Max. Cell Temperature,
ΔT = Temperature difference
Ta (°C) Tc
(°C)
ΔT (°C)
Solar irradiance 20 44.102 24.102
Joule heating effect 20 22.74 2.74
Solar irradiance
and Joule heating
effect
20 46.05 26.05
The confirmation of the existence of the relationship
between the individual physical effects applied alone and as
a combine effect lead to the decision to simulate in most
cases the irradiance physical effect only. This was done
Finer mesh

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because of memory constraints and computational cost. The
Joule heating effect is constant for a given current density
and its effect on overall cell/module temperature is proven
to be minimal.
Due to the accumulation of the generated current in one
direction to be connected to external load or the adjacent
cell, there is more current in the busbar towards one end and
that end turns to heat up more. The surface temperature
color maps belonging to the three cases reported in Table -2
is shown in Fig -10. This also highlights the current
accumulation effect in the Joule heating model.
0 1 2 3
0
2
4
6
16
18
20
22
24
26
28
30
32
34
TemperatureDifference(Tc
-Ta
)[°C]
Wind Velocity [m/s]
Joule Heating & Irradiance (simulated)
Irradiance only
Joule Heating only
Irradiance + Joule heating
Chart -1: Superposition effect of solar irradiance and Joule
heating. The Joule heating effect causes temperature
difference across the cell. The average cell temperature is
plotted and the error bars used to show the deviation from
maximum and minimum temperatures.
Fig -10: Temperature map of combined effect of Joule
heating and solar irradiance
3.2 Effect of Encapsulation Material On Cell
Temperature
Chart -2 shows the temperature of the cell without
encapsulation plotted with the ones encapsulated with EVA
and silicone. The cell was subject to a solar irradiance of
800 W/m2
and the wind velocity on both sides varied from 0
m/s to 3 m/s. There is a clear rise in the temperature due to
encapsulation but not a significant difference when the EVA
or silicone is used.
0 1 2 3
18
20
22
24
26
28
30
32
-Ta
)[°C]
Wind Velocity [m/s]
Cell encapsulated with EVA
Cell encapsulated with silicone
cell without encapsulation
Chart -2: Effect of encapsulating materials EVA and
silicone on cell temperature
The color map for the NOCT condition using EVA as the
encapsulating material is also given in Fig -11. The module
has the highest temperature at the cell and the lowest at the
top of the protective glass cover. The temperature difference
between cell and glass surface is about 1°C in all
simulations.
Fig -11: Surface temperature map of EVA encapsulated
solar cell at NOCT conditions
3.3 Effect of Copper Interconnection On Module
Temperature
In forming a module, two or more solar cells are placed
approximately 7 mm apart in series, electrically connected
with copper ribbons and then encapsulated. The modeling of
a solar module is given in 2.1.4 as Model D. This mini
module was simulated using the same conditions of 800
W/m2
irradiance, 20°C ambient temperature and the wind
velocity varying from 0 m/s to 3 m/s as was used for Model

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B. The result from 3.2 is presented here in Chart -3 to
include the result of simulating the mini module with copper
ribbon interconnection. The resulting plot shows that,
connecting solar cells with copper ribbons and encapsulating
it into a module actually decreases the cell temperature.
Even though the cell temperature is still above that of the
cell without encapsulation the decrease in cell temperature
of the mini module is significant as can be seen in Chart -3.
0 1 2 3
18
20
22
24
26
28
30
32
-Ta
)[°C]
Wind velocity [m/s]
cell encapsulated with EVA
cell encapsulated with silicone
cell without encapsulation
mini module with Cu interconnector
Chart-3: Reduction in cell temperature in the mini module
compared to a single cell
Copper being a good conductor absorbs more heat. The
copper ribbon interconnections are totally surrounded by
EVA which turns to conduct most of the heat away from the
copper interconnections. Therefore, the copper
interconnections do not show any strong contribution in
terms of raising the cell temperature. The region of the mini
module where the gap between the two adjacent cells and
the copper interconnection is located turns out to have the
lowest temperature. The distribution of the temperature in
this area and that in the EVA filling the area around the
copper ribbon interconnections is best seen in a 2D
isosurface temperature map shown in Fig -12.
Fig -12: 2D Isosurface temperature map showing the
temperature distribution in the mini module and around the
copper stripe
3. CONCLUSIONS
In this study, the temperature reached by solar cells/modules
during operation and also information about the temperature
distribution in the solar cell/module is provided by utilizing
a finite element (FE) model of the solar cell/module which
has been created in COMSOL Multiphysics environment.
Four different geometries (models) of the solar cell/module
were created for these simulations; each represented a stage
in the solar module manufacture or a variant.
The models have been verified by checking for the variation
in temperature due to changes in solar irradiance, wind
speed and solar irradiance angle of incident. They showed
good conformance with the values from literature and
experience.
Two major contributors as source of heat for the solar
module have been identified as solar irradiance and Joule’s
heating effect. Joule’s heating effect contributes much less
compared to solar irradiance and the two effects are shown
to have quasi-linear behavior when simulated together. This
allowed for the dropping of the Joule heating effect in the
more complex simulation where memory usage was of
concern. The cell/module temperature maps obtained are
corrected with that from the Joule heating only simulation
which is constant for a given current density.
The subject of encapsulation has been shown to be very
important for the life time of the cell and its electrical parts.
The encapsulants used to protect the solar cell are
responsible for about 11% increase in the cell temperature at
NOCT conditions. EVA and silicone are the most used
encapsulants with silicone giving the highest efficiency due
to its low absorptivity compared to EVA but is more
expensive. There was negligibly small increase in
temperature of silicone encapsulated cells compared with
those with EVA.
Protecting the front of the solar module with glass and the
rear with Tedlar compared to protecting it on both sides with
glass revealed no significant change in temperature. Solar
modules protected by glass on both sides have a slightly
higher temperature due to the thickness of the glass used.
The thickness of glass used in a module is not much of
thermal concern but more of structural.
Two or more cells electrically connected together via copper
ribbons and encapsulated into a module has been simulated
to have a lower temperature than a single cell module due to
the distance between the adjacent cells and the copper
ribbon interconnection not contributing to an increase in cell
temperature. The temperature in the module increases
beginning from the middle of the mini module where the
copper ribbons surrounded by EVA are. The temperature
increases towards the edges of the module in the horizontal
plane but the solar cell itself has a uniform temperature
distribution, though with a lower average temperature.
Position of Copper ribbon interconnection

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REFERENCES
[1]. C. Honsberg and S. Bowden, "Module Materials,"
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-materials
[2]. T. Hausler and H. Rogass, " Latent heat storage on
photovoltaic," in Sixteenth European Photovoltaic
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2267.
[3]. Vignola, "Solar Cells," University of Oregon Solar
Radiation Monitering Lab, 2000.
[4]. National Renewable Energy Lab, "Spectrum Definition
for information, data and resources for solar".
[5]. AZoM.com, "Silicone Rubber material,"
www.grantadesign.com.
[6]. MathWeb, "Material property data,"
http://matweb.com/search/PropertySearch.aspx.
[7]. P. Industries, "Solarphire Glasses by PPG," PPG Glass
Business & Discovery Center:
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r/Pages/default.aspx, Cheswick, PA 15024 .
[8]. COMSOL, "Comsol Material Library," COMSOL.
[9]. S. Vergura, G. Acciani and O. Falcone, "3-D PV-cell
Model by means of FEM," IEEE, Bari, Italy, 2009.

3 d finite element method modeling and simulation of the temperature of crystalline photovoltaic module

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3 d finite element method modeling and simulation of the temperature of crystalline photovoltaic module