step by step procedure for accurate soldering of solar pv cells. The soldering is done carefully to reduce the thermal mechanical stresses on the cells which prevent cell cracking.

1. Soldering of
Polycrystalline Silicon
Solar Cells
For making DIY customised solar modules
depending on power requirements
by
manav shah (mechanical engineering student)

2. Solar cell basics
The figure shows the description of different parts of the solar cell to
get a understanding of its workings

3. Working station
Availability of right equipment is necessary to achieve optimum results.
The figure shows the workstation where the soldering process was
conducted

4. Electrical layout
Tabbing wire at negative conducting strip
Tabbing wire at negative conducting strip
Efficiency – 18% minimum
Power (1 cell) –1.148W
By connecting all the cells in series configuration
Voltage –8.4V Current –0.5A
Power –4.2W
Busbar for series connection

5. Materials required
Wooden board
Soldering iron (operating at maximum temperature of 340oc)
Solder wire (40% tin and 60% lead)
Paper tape (3M)
Scissors
Flux pen
Polycrystalline solar cells (MarsRock 18% having dimensions of 52mm*156mm)
Tabbing wire (1cm wide)
Ruler
Copper gauge
Voltmeter (measuring DC voltage and current with constant frequency)
Insulating wire

6. Methodology
Soldering of PV cells is to be performed for university project involving
the integration of PV cells on flat surfaces. The procedure is devised
after many trials to minimise the thermo-mechanical stresses on the
cell during soldering

7. Step 1
The cell is taken carefully from the stack. Avoid
lifting the cells with fingers. Instead, rest the cell
on the palm of the hand to distribute the weight
evenly and prevent stresses to concentrate on a
small surface area.

8. Step 2
The cell is then placed on the board.
A wooden board is used while
soldering as wood has better heat
dissipation property. The use of
plastic board will result in uneven
heat dissipation which will result in
melting of the plastic while applying
solder.

9. Step 3
The cell is then taped on both ends to prevent
the movement of the cell while soldering. Paper
tape was used in this case due to its
characteristics of easy removal and leaving
minimum gum residue on the surface of the cell.

10. Step 4
On the positive side of the cell, flux is applied on
all the three conducting strips with the help of
flux pen. Afterwards, small dots of solder wire
(40% tin and 60% lead) are applied evenly on the
entire surface of the three metallic conducting
strips with the help of soldering iron.
Flux application is the most important part of the
process as it allows the tabbing wire to stick to
the surface of the conducting strip. Not applying
solder dots within few minutes after flux
application will result in drying of flux on the
surface which may result in metal not sticking to
the surface.

11. Step 5
A set of cells in this process refers to the two
52mm * 156mm cells connected in series. For
each set, 3 pieces of 114mm tabbing wire and 6
pieces of 72mm tabbing wires are cut into
pieces. The width of the tabbing wire was
limited to 0.5cm which is the half of supplied
width of 1cm in order to align the width of the
conducting strip and the width of the tabbing
wire. This promotes accurate soldering.

12. Step 6
The temperature of the soldering iron is kept at 340c and must be
placed gently on one end of the cell for few seconds for the heat
to start flowing and melt the solder dots. As, the tabbing wire is
coated with solder metal, heat from the soldering iron will melt
the lead on the tabbing wire as well as the solder dots which
results in the attachment of the tabbing wire to the surface of the
conducting strip. After the surface of the wire is heated up, the
soldering iron is moved evenly on the entire strip length by
applying even pressure. Try to move the soldering iron over the
strip in one stroke to prevent cooling of the metal before the
entire strip is being soldered

13. Step 7
The angle of the soldering iron is the vital part
of the entire soldering process. The angle
determines the amount of heat flow to the
surface. As maximum heat flow is required,
angle of 15 degrees is required for maximum
heat transferred to the surface of tabbing wire
which results in instant melting of the metal.
Avoid touching the tabbing wire from the tip
of the soldering iron as this will lead to less
heat flow and uneven soldering.
15o

14. Step 8
After the wire is soldered, do not remove the tape immediately
as the wire and the cell are not completely cooled off and can
lead to removal of the tabbing wire from its position. If the
tabbing wire is removed slightly at a certain area, avoid repairing
it immediately. After heat to the surface as part of the repairing
process can heat the entire wire surface which can result in
dislocation of the wire from the other areas of the strip.
The application of soldering iron results in the transferring of
heat from the iron to the cell which can increase the
temperature of the cell to about 80C. The most efficient option is
to allow the cell to cool down completely before reapplying the
iron. As the cooling of the cell is very important part of the
soldering process, temperature can be determined with the help
of infrared thermal camera. The figure shows the temperature
after soldering the tabbing wire which is around 65C.
Cell should be allowed to cool down until temperature reaches
25C-35C. The figure below shows the cell temperature has
dropped from 65C to 34C
Hot cell
Cold cell after
cooling

15. In case of the entire removal of the wire, the
surface of the conducting strip is deposited
with bunt residue from the soldering wire
and flux which is hard to remove. As the
reapplication of the flux and solder dots is
not possible on the burnt surface, the cell is
removed from its position and the same
process is being implemented on a new cell
(recommended)
Success rate of making the perfect set for
the electrical circuit is 20%. Due to the low
thickness and brittle nature of the cell, the
cell is prone to cracking. Occurrence of
minor crack can significantly impact the
electrical performance of the cell which can
provide less output.

16. Step 9
• Success rate of making the perfect
set for the electrical circuit is 20%.
Due to the low thickness and brittle
nature of the cell, the cell is prone
to cracking. Occurrence of minor
crack can significantly impact the
electrical performance of the cell
which can provide less output.
• If a formation of minor crack is
noticed, it is not recommended to
proceed forward. Do not try to
repair or strengthen the cracks as
the power output is being reduced
after cracking

17. Step 10
Exposure to high temperature can
result in expansion of the cell. This
expansion can permanently
deform the cell which increases
the probability of the cell while
soldering. It becomes very difficult
to handle and solder the cell in its
deformed position due to its brittle
nature.

18. To reduce the effect of expansion and contraction, a procedure should be set in order to
improve the accuracy of soldering and minimise cell cracking

19. a) Positive strip ‘B1’ is soldered first with 114 mm wire and wait for the cell to cool down.
The wire is placed on the solder dots and is taped on the either sides to prevent
movement. The cell will expand and deform from the heat of the soldering iron.
b) The cell is now flipped to its negative side and the procedure of the application of flux
and solder dots is iterated to make the cell ready to solder. Then, strip ‘A3’ and ‘A2’ is
soldered to balance out the expansion of the cell. During the application of the soldering
iron, the cell will deform back to its previous position (flat). Allow the cell to cool before
starting the next step.
c) Strips ‘B3’ and ‘A1’ are then soldered respectively. The cell will expand again. At the
end, solder ‘B2’ is soldered to balance the possible deformation. By following this process,
the deformation will be kept to its minimum.
d) Meanwhile, prepare the second cell by applying flux and solder dots and attaching the
tabbing wire on conducting strips ‘D1’, ‘D2’ and ‘D3’ in a continuous process by allowing
adequate cooling time in between. The cell will expand and deform significantly.
e) Then, both the cells are brought side by side and the desired position is set and each
corner of both the cells are taped. Gap of 10mm is kept between the two cells to allow the
tabbing wire to expand and contract during heating an cooling

20. f) After that, both the cells are brought side
by side and the desired position is set and
each corner of both the cells are taped. Gap
of 10mm is kept between the two cells to
allow the buffer when they are placed on
two sides of the absorber tube with an angle
of 60o.
g) Strip ‘C1’, ‘C2’, ‘C3’ are soldered without
applying pressure. To prevent excess
pressure from being applied, the hand is
restricted from touching the ground.
The sensitivity of the cell should be kept in
mind as in the case of cracking of the cell
during the ‘C2’ or ‘C3’ process, it is very hard
to recover both the cells in the set as both
the cells were connected through ‘C1’ and it
cannot be reversed.

21. Step 11
After completion of the soldering process,
tapes are removed after 5 minutes in order to
cool both the cells. The tapes are then
discarded and are not reused in the second
set as the gum on it is heated and burnt which
makes the tape less sticky and its purpose is
reduced to its minimum. The cell is then
transported to the container by lifting the
wooden board and sliding the set in the
desired location.

22. Prototype
• Working of the cells is required to be tested
under the heat of the sun to check the
efficiency of the cells. A prototype of three
sets was made and all the sets were
connected in series. They were connected
with electrical wires as they can be
removed after testing with the help of
copper gauge. The use of copper gauge is to
extract the solder metal from the desired
area by applying heat on it.
• They were connected with electrical wires
as they can be removed after testing with
the help of copper gauge. The use of copper
gauge is to extract the solder metal from
the desired area by applying heat on it.

23. Thank you for your time