FIELD OF INVENTION
This invention relates to a Solar Cell String Transfer Device adaptable in the
manufacturing systems of large wattage Photovoltaic (PV) modules, typically PV
modules having at least 72-nos. of solar cells with power output in a range
between 150 to 170 watts. The invention further relates to a method for

automatic transfer and reversal of the PRBCF (Phenolic Resin Bonded Cotton
Fabric) cell jig and the glass superstrate during manufacture of PV modules with
power output of 150 to 170 watts and comprising at least 72 nos. of 125-mm
crystalline silicon solar cells connected in series configuration.
BACKGROUND OF THE INVENTION:
Solar cells are manufactured using 125-mm or 156-mm size mono / multi
crystalline silicon wafers. Typically, each 125-mm solar cell generates a power
output of 2.2 to 2.3 watts. 36 os. of these cells are interconnected in series to
get PV Modules of 75 to 85-watts power output (12-V application) and 72-nos. of
cells are interconnected in series to get PV Modules of 150 to 170-watts power
output (24-V. app ication). The demand for larger wattage (150 to 170-watts)
modules is increasing due to its reliability, cost-benefits, reduced
interconnections a id other hardware requirements in PV Power Plants.
PV Module assembly process basically comprises the steps of Tabbing, Stringing,
String Transfer, Lay-up, Lamination, Framing and Module Testing. The step of
Stringing (interconnection) of the cells is carried out on a PRBCF Stringing Jig
after which the Stringed Cells are transferred onto a glass superstrate with a

EVA (Ethylene Vinyl Acetate) sheet as an intermediate layer. In a semi-automated assembly
lines, this String Transfer operation is carried out manually in a two-step process involving a
first step of physical transfer of the strung cells and followed by a step of reversing the string
so that the front of the Stringed Cell faces the glass superstrate. This string transfer operation
using manual method is well adapted for the 75-Wp PV Modules (size : 1200-mm*525-mm,
weight : 7.5 Kg). However, due to large size and weight of the 150-Wp Modules (size: 15,90-
mm x 785-mm, weight: 15-Kg), manual handling becomes very tedious for the operators and
further increases the possibilities of module breakage. One of the solutions to ease this string
transfer operation and to minimize the risk of module damages, could be the development of
an automated solar string transfer equipment.
Further, the commercially available equipment handles only a part of the string with 12-cells
resulting in 6 operations for achieving the complete transfer. Besides, the interconnection is to
be carried out after each of the transfer operation over the glass superstrate, which is
cumbersome.
The US patent US 20130122639 A1 is for interconnection of Thin Film solar cells whereas the
present invention is for crystalline silicon solar cells. The US patent is for series connection of
individual thin film solar cells whereas the present invention is for transfer of entire solar cell

string on to the glass superstrate with encapsulant (EVA).
The patent WO 2003059570 A1 is for assembly of individual solar cell into string by
interconnecting the solar cells whereas the present invention is for transfer of entire solar cell
string on to the glass superstrate with encapsulant (EVA).
OBJECTS OF THE INVENTION
It is therefore an object of this invention to propose an automated Solar Cell String Transrer
device adaptable in the manufacturing systems of Photovoltaic modules with power output
rating of 150 to 170 watts and comprising at least 72 nos. of 125-mm crystalline silicon so ar
cells connected in ser es configuration.

Another object of this invention is to propose a method for automatic transfer
and reversal of the PRBCF - cell jig and the glass superstate during manufacture
of photovoltaic modules with power output of 150 to 170 watts and comprising
at least 72 nos. of 125-mm crystalline silicon solar cells connected in series
configuration.
Still another object of this invention is to propose a method for automatic
transfer and reversal of the PRBCF - cell jig and the glass superstrate during
manufacture of photovoltaic modules with power output of 150 to 170 watts and
comprising at least 72 nos. of 125-mm crystalline silicon solar cells connected in
series configuration which simplifies the process steps and reduce the process
time.
Yet another object of this invention is to propose a method for automatic
transfer and reversal of the PRBCF - cell jig and the glass superstrate during
manufacture of photovoltaic modules with power output of 150 to 170 watts and
comprising at least 72 nos. of 125-mm crystalline silicon solar cells connected in
series configuration, which is capable of simultaneous pickup of all the 72
soldered solar cells and transfer to the lay-up station.
A further object of the invention is to propose a method for automatic transfer
and reversal of the PRBCF - cell jig and the glass superstrate during manufacture
of photovoltaic modules with power output of 150 to 170 watts and comprising
at least 72 nos. of 125-mm crystalline silicon solar cells connected in series
configuration, in which the complete interconnection of the strings is carried out
in the jig itself and after transfer it will be in a ready state for lamination.

A still further object of the invention is to propose a method for automatic
transfer and reversal of the PRBCF - cell jig and the glass superstrate during
manufacture of photovoltaic modules with power output of 150 to 170 watts and
comprising at least 72 nos. of 125-mm crystalline silicon solar cells connected in
series configuration, which utilizes PLC based electronic controls for conveyorised
movement of PRBCF cell jig under the vacuum cups such that the transfer of all
72-solar cells on to the glass superstrate achieves an appropriate string
alignment.
Another object of this invention is to propose an automated string transfer
device adaptable in a manufacturing process of PV modules which incorporates a
dual redundant operator control enabling the operator to operate the device
either in automatic mode or in manual mode from either end of the device
installation.
SUMMARY OF THE INVENTION
Accordingly, there is provided a solar cell string transfer device adaptable in the
manufacturing systems large wattage Photovoltaic modules. The device
incorporates a PLC based electronic control for conveyorised movement of the
PRBCF cell jig to ensure its precise positioning under the vacuum cups including
simultaneous transfer of all 72-solar cells on to the glass superstrate in an
accurate string alignment which leads to reduction of operator fatigue and
improved cycle time. Necessary interlocks are provided to ensure safe operation
of the equipment. The invention further proposes a method for automatic
transfer and reversal of the PRBCF-cell jig and the glass superstrate during

manufacture of Photovoltaic modules with power output of 150 to 170 watts and
comprising at least 72 nos. of 125 m crystalline silicon solar cells connected in
series configuration.
DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig 1: Shows a pictorial view of PV Module manufacturing process in a
manufacturing system according to the prior art.
Fig 2: Shows a line diagram of a String Transfer device according to the
invention.
Fig 3: Shows an automated String Transfer device according to the invention.
Fig 4: Shows a loading station (moving platform) of the automated string
transfer
device of Fig. 2.
Fig 5: Shows a line 2 diagram of vacuum station of the automated string transfer
device of Fig. 2
Fig 6: Shows a vacuum station of the automated string transfer device of Fig. 2.
Fig 7: Shows a Conveyor mechanism with Servo Motor assembly incorporated in
the automated string transfer of the invention.
Fig 8: Shows a line: diagram of Conveyor mechanism with Servo Motor
assembly incorporated in the automated string transfer of the invention.
Fig 9: Shows a line diagram of jig loading platform of the automated string
transfer device of Fig. 2
Fig 10: Shows a line diagram of stringing jig of the automated string transfer
device of Fig. 2

Fig 11: Shows a Programmable Logic Controller incorporated in the device of
Fig. 2.
Fig 12: Shows an operational sequence of String Transfer operation with manuah
process according to prior art.
Fig 13: Shows an operational sequence of String Transfer operation with
automated process according to the present invention.
Fig. 14:Shows a flow chart of the String Transfer operation with
automat 3d process according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
According to this nvention there is provided a method and a device for solar cell string transfer suitable for the manufacturing process of Photovoltaic Modules of
power output in the range of 150 to 170-watts consisting of 72-nos. of 125-mm
crystalline silicon solar cells connected in series (12*6) configuration ;
The device incorporates a PLC-based electronic controls for conveyorised
movement and positioning of PRBCF jig under the vacuum cups transfer all 72
nos. of soldered and interconnected solar cells on to a glass superstrate resulting
in better string alignment;
Redundant operator controls for either operating the equipment in an automatic
mode or manual mode is possible;

PLC controller provides the necessary interlocks during the steps of transporting
the cells, picking-up the cells and placing the cells on the Glass superstrate. The
PLC controller is interfaced to two sets of Operator push-button controls,
mounted on either side of the equipment for easy operator access from either
side.
As shown in figure 1, the sequential steps of a typical PV module assembly
process comprises the steps of Tabbing, Stringing, String Transfer, Lay-up,
Lamination, Framing and Module Testing. Stringing (interconnection) of the Solar
Cells is carried out on a Stringing Jig after which it is transferred onto a glass
superstrate with a EVA sheet as an intermediate layer. The String Transfer
operation is carried out manually in a two-step process involving physical
transfer of the strung cells and reversing the string so that the front of the Solar
Cell faces the Glass superstrate.
As shown in figures 2 to 11 the automated String Transfer device of the
invention is characterized by comprising a Loading Station (1) for loading and
unloading a stringing jig / glass (9) with EVA has been incorporated in the
existing device; a removable means (4b) for the existing string pick-up fixture
(4b) with 72-vacuum suction cups (4a) suitable for a 150-Wp PV Modules; a
conveyorised mechanism (3,2,7) for moving and positioning the loading station
(1) under the vacuum pick-up station; a Vacuum generator and 72-cup vacuum
cup assembly (4a, 4b); and a dual operator controls (5) with PLC (6). The line
diagram and a picture of the automated string transfer device are shown in
figure 2 and 3 respectively.

Details of these features are described below.
LOADING STATION (MOVING PLATFORMS
As shown in figure 4, the strings of cells along with the stringing jig (9) (on
which the cell strings are formed) are placed in the loading station (1). The
loading station (1) is supported on a moving platform (2), which is moved both
in forward and reverse direction by means of a conveyor-motor assembly (3,7),
as shown in figure 7. The loading station (1) is designed for supporting either the
stringing jig (9) or glass superstate or both and is provided with edge guides (8)
to hold them firm y in place during the movement (Fig. 9).
VACUUM STATION
As shown in figure 6, the vacuum station (4) comprises a removable fixture (4b)
with 72 vacuum suction cups (4a) positioned exactly to align with the 72 cells of
a 150-Wp Module The fixture (4b) is detachable by means of two sets of screws
(not shown). Similar fixtures are designed for use in 100-Wp & 120-Wp modules
and attached in place of the existing one. This allows for flexibility and future up-
gradation of the device of the invention. A line diagram of the vacuum station
(4) is shown in figure 5.
Compressed air is used in the vacuum generators (not shown) to generate
vacuum and at least two such generators are used for achieving higher level of
vacuum suction (4). The vacuum cups (4a) are further strengthened using 'O'
rings (not shown) for effective sealing of air at these points. In addition, non-

return valves (not shown) are provided at these suction cups to provide further
protection against leakage of one of the vacuum cups (4a) and thereby affecting
the other vacuum cups as well. The vacuum station (4) is provided with at least
one preumatic cy inder (10), and a slider (11).
CONVEYOR SYSTEM
As shown in figure 7, the conveyor mechanism (3,2,7) transports the Stringing
Jig (9) and the glass superstate alternately between the loading station (1) and
the vacuum station (4). This transportation is programmed to take place either
automatically or under manual control. A line diagram of the conveyor system (3)
is shown in figure 8, which further indicates the moving platform (2) fixed on the
conveyor (3) at 'IN' and 'OUT' positions.
The conveyor mechanism (3) is driven by servomotors (7) and is capable of
handling the weight of the fixture (4b) or glass superstate (9) or both together.
Limit switches arcs provided at the ends of the loading and vacuum station ends
to sense the extreme points and if necessary, stop the motor (7) which drives
the conveyor (3,2). As shown in fig - 9, the conveyor (3,2) carries the loading
platform (12) on which the stringing jig (9) is loaded. The stringing jig is having
a plurality of cavit es (9a) to accommodate the vacuum suction cups (4a).
ELECTRONIC CONTROLS
The automated string transfer device of the invention is controlled by a
Programmable Logic Controller (PLC) (6) housed in an enclosure at the bottom of

the device as shown in figure 11. The PLC-controller (6) provides all necessary
interlocks during transportation, pick-up of the cells as well as during placement
on the glass superstrate. It is interfaced to two sets of operator push-button
controls (5), mounted on either side of the device for easy operator access from
either side.
The manual string transfer operation and automated string transfer operation
(with the aid of the present invention) are illustrated in figure 12 and figure 13
respectively. A flow chart showing the steps followed in the string transfer device
with the PLC (6) is shown in figure 14.

ADVANTAGES
Major advantages of this equipment over the conventional equipment are as
follows.
The device of the present invention can handle a complete cell string consisting
of 72-Cells in one operation whereas the conventional device can handle only
part string with 12-Cells resulting in 6 operations for achieving the complete
transfer
In the inventive device, the entire string remains stationary and the glass
superstate is moved under it for positioning. In case of conventional devices,
the glass superstate is kept stationary whereas the string is physically moved.
This poses a potential threat to cause string damage in case of vacuum failure
when the string or individual cell is likely to be released from suction.
According to the method of present invention, the complete interconnection of
the string is carried out on the jig itself and after transfer, it is ready for
lamination; whereaS, in case of conventional devices, the interconnection is to be
carried out after the step of transfer operation over the glass superstate is
completed, which is very cumbersome and may also introduce impurities in the
lamination.

BENEFITS ACHIEVED
Installation of the device and implementing the method of the invention in the
150-Wp PV Module assembly system gives the following benefits.
Minimisation of damage to string / glass during string transfer operation
Better string alignment
Improved handling of modules during String Transfer operation & reduction of
operator fatigue
The total cost of development of the Automated String Transfer Device is
comparatively lower than the available devices.

WE CLAIM

1. An automated solar cell string transfer device adaptable in the manufacturing

systems of large-wattage photovoltaic modules with power output of 150 to 170
watt, and constituting of at least seventytwo numbers of 125-mm crystalline
silicon solar cells connectable in series configuration, the device comprising and is
Characterized by;
- a loading station (1) for loading and unloading a stringing jig glass (9)
with an intermediate layer of ethylene vinyl acelate, the stringing jig (9)
accommodating a plurality of stringed cells;

- a conveyor system (3) having a moving platform (2) which supports the
loading station (1), the conveyor system (3) comprising at least one servo
motor (7) for moving and positioning the loading station (1) alternately at
predetermined locations;

- a vacuum station (4) having a removable fixture (4b) with at least
severitytwo vacuum suction cups (4a), the removable fixture (4b)

accommodating the stringing jig (9) with the plurality of stringed cells, the

conveyor system (93, 2, 7) alternately transporting the stringing jig (9)
between the loading station (1) and the vacuum station (4); and

- a programmable logic controller (PLC) (6) disposed at a bottom of the
device for a programmed transportation of the stringing jig (9) including
its accurate positioning at predetermined locations.
2. The device: as claimed in claim 1, wherein the loading station (1) is provided with
at least one edge guide (8) to firmly hold the stringing jig (9) during the latter's
movement,
3. The device; as claimed in claim 1, wherein the removable fixture (4b) is
detachable from the vacuum station (4) and configured to enable
accommodation of a 72-cell, 150-Wp module.
4. The device as claimed in claim 1, wherein at least one vacuum generator is
provided for the vacuum station (4) and wherein at least one pneumatic cylinder
(10), and a slider (11) is provided.
5. The device as claimed in any of the preceding claims wherein the conveyor
system (2,3)) is driven by at least one servomotor (7).
6. The device as claimed in claim 1, wherein the stringing jig (9) is provided with
plurality of cavities (9a) to accommodate therein the vacuum suction cups (4a).

ABSTRACT

AN AUTOMATED SOLAR CELL STRING TRANSFER DEVICE ADAPTABLE
IN THE MANUFACTURING SYSTEMS OF LARGE-WATTAGE
PHOTOVOLTAIC MODULES
The invention discloses an automated solar cell string transfer system for the
manufacture of large wattage Photovoltaic modules. The system incorporates a
Programmable Logic Control (PLC) based electronic control for conveyorised
movement of the PRBCF cell jig to ensure its precise positioning under the
vacuum cups including simultaneous transfer of all 72-solar cells on to the glass
superstrate in an accurate string alignment which leads to reduction of operator
fatigue and improved cycle time. Necessary interlocks are provided to ensure
safe operation of the equipment.