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Solar energy is important for all countries due to increasing energy needs. Rapid depletion of fossil fuels provide us this greater energy source. Also, air and water pollution and global warming happens due to use of fossil fuels which known as major energy sources. For this reason, countries began to give importance to renewable energy sources like solar energy. In this study, the production of solar cells and solar panels was demonstrated.
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Solar Cell and Solar Panel Production
BERK BOZKURT *
1Department of Electrical – Electronics Engineering, Antalya Bilim University, Antalya/Turkey
*Corresponding author: berk.bozkurt@std.antalya.edu.tr
Received 31 May 2019
1. ABSTRACT
Solar energy is important for all countries due to
increasing energy needs. Rapid depletion of fossil
fuels provide us this greater energy source. Also,
air and water pollution and global warming
happens due to use of fossil fuels which known as
major energy sources. For this reason, countries
began to give importance to renewable energy
sources like solar energy. In this study, the
production of different types of solar panels and
their working principles was demonstrated.
Key Words: Solar Panel, Renewable Energy.
2. INTRODUCTION
Why do we waste time for non-renewable energy
sources when there is legendary energy sources in
the sky with ceaselessly and free? The Sun has
energy more than we need for billion years and
with the help of solar panels we can convert that
energy to electricity. As global warming caused by
non-renewable energy sources continues to
increasing day by day, there is no doubt that solar
energy become more important energy source in
future. To save our world, we have to use solar
energy as a electricity.
With the help of solar cells, we can convert solar
energy to electricity. Solar panels occur by
combining solar cells. Photovoltaic (PV) is
another name of solar energy and it is consist from
“photo” (Greek word for light) and “voltaic”
( reference to Alessandro Volta who invented
battery) [1]. We can think a sunlight as a heap of
photons, and solar cells catches these bunch of
photons, and convert them to electrons. Every
cells at solar panels create a volts, so solar panel’s
mission is combining these volts and make them
bigger electric current and voltage.
3. PRODUCING SOLAR CELLS
Solar cells are very thin silicon disk that convert
sunlight to electricity and silicon is called as a
semiconductor. Then, what is semiconductor? In
nature, some substances do not conduct electricity
but some of them can conduct electricity. For
example, metals allow electricity to flow and they
called conductors. Otherwise, plactics and wood
don’t allow electricity to flow and they called
insulators. Semiconductors like Silicon (Si),
Germanium(Ge) and Gallium Arsenide(GaAs)
neither conductors nor insulators. For making
solar cells we generally use silicon. We can change
the behavior of silicon and make it conductor by
doping it. If we add small amount of impurity into
silicon crystal, it will conductive. There are 2
types of impurities; N-type and P-type. In N-type
doping, Phosphoros(P) or Arsenic(As) added to
silicon. Phosphoros and Arsenic have five outer
electrons so, when they making bond, one outer
atom will be free to move. These free electrons
allow electric current flow to the silicon. In P-type
doping, Boron(B) or Gallium(Ga) added to silicon.
Boron and Gallium have three outer atom so,
when they have bond with silicon atoms, one
silicon atom can not have bond. Because of this
event, holes can be generated and these holes takes
electrons from other atoms. Both types of
semiconductors are good conductors and solar
cells made by these two types silicons. So far, this
paper mentioned about how solar cells produced in
a simple way, now let’s explain in more detail.
There are four types of solar panels;
1- Monocrystal
2- Polycrystal
3- Thin Film (have low efficiency)
4- Transparent Solar Panel (not common yet.)
3.1 MONOCRYSTAL AND
POLYCRYSTAL SOLAR CELL
For the production of solar cells, we must follow
the 9 stepes.
Fig.1 Schema of the solar panel production from
beginning to end.[4]
3.2 RAW MATERIALS
Firstly, for producing solar cells we need to have
sand, because naturel sands are main components
of silicon [2]. In this step as shown in Fig. 1, sand
and coal placed in an arc furnace and we heat
them until 1,800 C. Then, the products are carbon
dioxide and metallurgical grade silicon. [3]. It has
%98 purity, but it is not enough. So that, with the
help of next step we can achieve more purity.
Fig.2 Sand to Mg-silicon process. [4]
3.3 POLYSILICON
In this process, our input materials are MG-silicon
and HCI (Hydrochloric acid). We mixed them at
the Silane (SiH4) tank, then we can distillate the
silicon for making pure. At the last step silicon
moves to heated zone many times and after that
we will have 99.99% pure polysilicon ingots.
Fig.3 MG-silicon to Polysilicon process.[4]
3.4 CZOCHRALSKI PROCESS
In this step, we increase the temperature until the
silicon melts.After that we dip monocrystalline
silicon into melted polycrystalline silicon. When
we take out slowly, we create monocrystalline
ingot [5]. This process known as Czochralski
Process(Cz) invented by Jan Czochralski. By
rotating melted tank, controlling temperature and
take out speed, we can made specific
monocrrystalline silicon. [6] This process works
for monocrystalline silicon for the polycristal we
have to use step 3.2.
Fig.4 Czochralski Process [4]
3.5 CRYSTAL FORMATION
In this step, we increase the temperature for
melting the silicon like step 3.1. After that, when
we cool the tank, at the bottom crystals form. By
controling the temperature we can make a silicon
with the size of a tank. In this way, we will have a
big block of multicrystalline silicon at the end [3].
Fig.5 Crystal Formation [4]
3.6 SILICON WAFER
In this step, we cut into slices the ingots. Because
of the sturdiness of silicon ingots, with the help of
diamond edge multiwire saw use for make it
slice[7].
3.7 TEXTURING
The reason why we need the texturing is that it
ensures better light traveling inside the solar cell.
Before texturing the wafers, they have a flat
surface so that incoming lights can easily
reflected back. For decreasing the reflection
losses, we have to do texturing process. With the
texturing wafer’s surfaces have pyramid structure.
In this way, when the incoming lights hit the one
pyramid also it must hit the next pyramid. So that
we minimize the reflection losses in this
process[8].
Fig.6 Scanning electron microscope photograph of
a textured silicon surface[9].
3.8 DOPING
The most common way to doping is adding
impurities to silicon wafers. If we want to do this
process we have to add
impurities(phosphorous).In order to do this, we
have to put wafers and phosphorus gas in a
furnace. Then, when we heat the furnace(900 C),
phosphorus atoms diffuse into silicon wafer’s top
side. In this way, our silicon wafers become a p-n
junction[10].
3.9 ANTI-REFLECTIVE COATING
This step is very significant. If we do not have
anti-reflective coating, lights will stay under
mirror effect because pure silicon is shiny. For
anti-reflection coating we can use titanium dioxide
and silicon oxide. Generally 75 nanometers thick
and combined the front surface of the solar cells
[11-13].
4. PRODUCING SOLAR PANELS
Before starting production of solar panels, what is
the differences between monocrystillane (mono-c)
and polycrystalline (p-ci)? The easiest way to
distinguish these cells from each other is to look at
the corners of the cells. As shown in Fig.6 , Poly
cells are 4 corners, but there are 8 corners in mono
cells. Also, monocrystalline cells do not have color
difference over the surface, but polycrystalline
cells have some crystal areas. Monocrystalline
cells can provide less sunlight, more production
than the other. They have better performance than
poly cell panels in low light conditions. The
disadvantage of monocrystalline panels is that
they are expensive. In addition, when the panel is
shadowed, or the panel is covered with snow, its
performance is very badly affected. While the
productivity of monocrystalline cell panels was
between 16% and 20%, polyacrylic cell the
efficiency of the panels is between 13% and 16%
[14-15].
Fig.7 Poly-Crystalline and Mono-Crystalline
Solar Cells [16].
4.1 STRINGER MACHINE
After having a solar cells now our aim is making
them a solar panel. Stringer machine is the first
machine of this process. Stringer machine’s
mission is combining the cells which is called
string. The strings vary generally 10 or 12 pieces
of solar cells. It can be changed from the stringer
machine’s screen. The settings are entered
manually on the screen of the stringer machine;
cell size, cell space, string cells, such as soldering
power and soldering time. These settings have
significant role because if settings are more or less
than it should be, solar cells will broke. Than,
solar cells placed in cell slot carefully. Since the
cells are so sensitive in the stringer machine, it is
necessary to use gloves to prevent them from
breaking. After settings and place the cells,
vacuum arms align the cells to band. While
combining the cells, the fluid called flux is being
used to bond the ribbons and the ribbons to the
cells. With the high heat given to flux, the flux
sticks to the cell. In this step, some problems can
occur which are broken of cell, cracked cell or
ribbon shift[17]. Before passing the next machine,
stringers check carefully and if there is no issue,
they can pass the other machine. Whether stringers
have problem, they collect and dispatched the
small solar panel production line.
4.2 LAY-UP AND GLASS LOADING
MACHINE
After having a stringsi the next step it is align the
strings according to the desired panel’s voltage. At
this process, Glass loading machine sends the
glass with the eva sheet to lay-up machine.
Eva(ethylene vinyl acetate) is protect solar cells
from the weather conditions[18]. The lay-up
machine is responsible for placing strings to eva
sheet. Each Lay-up machine has two vacuum arms
so that strings from two stringer machines are
arranged in one Lay-up machine. We can adjust all
the settings as if they were the same string on the
monitor of the layout machine. Also, if the wrong
string is sent from the stringer by mistake, the
string can be restored with the lay-up machine.
4.3 EL-TESTER MACHINE
El tester(electroluminescence test) is the next step.
In this section, the general panel is controlled
again. The anode and cathode ends of the
incoming panel are connected to the current
terminals of the el tester. DC current is given to
the panel and by the glow in the panel mistakes
are clearly shown in el tester machine’s screen as
shown in Fig.7. These mistakes are;
Broken Cell
Cracked cell
Solder failure
Short circuit
Ribbon shift
Foreign matter detection
If one of these faults comes to the cell, the error
determination form is put on the panel, taking note
that the panel is in trouble and the problem is in
the string. Subsequently, the products are barcoded
and the ones that are faulty are sent to the other
station, not the next one.
Fig. 7. Screen of el tester machine and it shows
three cracked solar cells[19].
4.4 LAMINATOR
Products that are error-free and barcoded at EL
Tester, are placing in the elevator, respectively.
Since the process in the laminator takes a long
time, it is necessary to wait until end of process.
The purpose in this section is to completely empty
the air in the panel and to melt the eva, which is
laid under and over the cell, to fill the spaces
between the cells. The small cracks are covered by
eva. Panels are entering each laminator as four.
The process in the laminator consists of four steps.
Vacuum
Lamination
Press
Cool down
Vacuuming takes about three minutes and the air
in the panel is emptied and then laminated at about
160 degrees for about six minutes. Then, with a
press operation for about three minutes, the melted
eva completely surrounds the panel. In the next
period, with the help of the propellers, the panel
leaves the laminator and starts to cool down.
4.5 FRAMING AND SANDING
The backsheet and glass surface are cleaned
properly by pouring alcohol onto the panes that
come into the glass. After the panels are cleaned,
aluminum frames are placed on all four sides of
the panel and the pane is fixed with the aid of a
sledgehammer. Frames need to be fixed exactly
because they can be cut when not fully seated,
which can cause problems for the company in any
accident after the panel is sold. After the frame
operation is finished, the four corners of the panel
are sanded. The purpose of sanding is to reduce
the sharpness of the corners of the panel.
4.6 FLASHER
It is the last step of production of solar panels.
After this part, panels are ready for the utilization.
In this process flasher check the data of the panel.
The positive and negative poles of the solar panel
is connected to the flasher and the barcode of the
product is entered on the computer. Then the
current given to the panel and these results shown
in the flasher’s monitor;
Max Power
Efficiency
Fill Factor
Light intensity
Power Load
Voltage Load
Current Load
If the values come less than they should be, the
products are written "heavy solar" on the
backsheet. Heavily solar panels produce much less
energy than normal panels, so they are sold in very
cheap quantities.
Than the junction box is fitted to cover the
positive and negative poles of the panes and the
anode and cathode ends of the panel are soldered.
The Junction box has an important role: housing
all the electric bits on a solar panel and protecting
them from the environment. Wires are connected
to diodes inside, providing an easy way to link
panels together. Also, junction box are prevent
current flowing. The Junction Box generally
consists of five parts:
Bypass Diode
Conducting Strip
Bypass Diode Terminals
Connection for PV-Cable
Suitable Suitable Connectors.
5. CONCLUSION
In this study, I have shown that, producing solar
cell from sand to a wafer. These process are little
bit complicated but all of them are important.
Than, I mentioned about the differences between
monocrystalline and polycrystalline solar cells.
Finally, I mentioned about producing solar panel
starting from basic solar cells.
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