National Renewable Energy Laboratory 

Innovation for Our Energy Future 

A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 

Development of Automated 

Production Line Processes for 

Solar Brightfield Modules 

Final Annual Technical Progress Report 

1 July 2004 — 15 October 2005

M.J. Nowlan, J.M. Murach, S.F. Sutherland, 

D.C. Miller, S.B. Moore, and S.J. Hogan 

Spire Corporation 

Bedford, Massachusetts 

Subcontract Report 

NREL/SR-520-40406 

August 2006 
Development of Automated 

Production Line Processes for 

Solar Brightfield Modules 

Final Annual Technical Progress Report 

1 July 2004 — 15 October 2005

M.J. Nowlan, J.M. Murach, S.F. Sutherland, 

D.C. Miller, S.B. Moore, and S.J. Hogan 

Spire Corporation 

Bedford, Massachusetts 

NREL Technical Monitor: B. Keyes 

Prepared under Subcontract No. ZDO-3-30628-12 

Subcontract Report 

NREL/SR-520-40406 

August 2006 

National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401-3393 

303-275-3000 • www.nrel.gov 

Operated for the U.S. Department of Energy 

Office of Energy Efficiency and Renewable Energy 

by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337
This publication was reproduced from the best available copy 

Submitted by the subcontractor and received no editorial review at NREL

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TABLE OF CONTENTS 

Page

1 INTRODUCTION ................................................................................................................................ 1

1.1 Objective....................................................................................................................................... 1

1.2 Approach....................................................................................................................................... 1

2 TECHNICAL DISCUSSION................................................................................................................ 2

2.1 Task 6 – Fabricate and Test Module Lay-up System ................................................................... 2

2.2 Task 7 – Fabricate & Test String Busing System......................................................................... 4

2.2.1 Bus Ribbon Fabrication ........................................................................................................ 4

2.2.2 Bus Ribbon and Diode Installation....................................................................................... 7

2.2.3 Development Work at ARRI............................................................................................... 10

2.3 Task 8 – Design Advanced Lamination Process Tool................................................................ 15

2.4 Task 9 – Design Lamination Automation................................................................................... 20

2.5 Task 10 – Design Large Area Solar Simulator ........................................................................... 21

2.5.1 Single-Flash Long Pulse Xenon Light Source.................................................................... 22

2.5.2 Large Area Optical Test Bed .............................................................................................. 24

2.5.3 High Power Electronic Load............................................................................................... 26

2.6 Task 11 – Develop Soldering Process for Thin Cells................................................................. 26

3 CONCLUSIONS................................................................................................................................. 29

4 REFERENCES ................................................................................................................................... 31

 iii
LIST OF ILLUSTRATIONS 

Page

1 Automated module lay-up system. ......................................................................................................... 2

2 Punched slots in EVA-on-fiberglass sheet............................................................................................. 4

3 Ribbon fabrication machine design........................................................................................................ 5

4 Main operating window for the ribbon fabrication machine. ................................................................ 6

5 Bus ribbon fabrication machine. ............................................................................................................ 6

6 Close-up view of bus ribbon fabrication machine components. ............................................................ 7

7 CAD model of four-axis Cartesian robot for busing assembly.............................................................. 7

8 Robot end effector with soldering heads and vacuum pick-up arm....................................................... 8

9 Module-size aluminum sheet on the automated busing system. ............................................................ 9

10 Bus ribbon tray, flux applicator, and diode pack retainer on front tooling plate................................... 9

11 Main operating screen for the automated busing system. .................................................................... 10

12 Slide-mounted solder head suspended from robot arm........................................................................ 11

13 90° pull strengths of bus-diode-bus solder joints................................................................................. 12

14 Experimental molybdenum solder head............................................................................................... 12

15 Temperature control of revised soldering tip with PID controller....................................................... 13

16 90° pull strength data for solder joints formed at 260°C. .................................................................... 13

17 90° pull strength data for solder joints formed at 270°C. .................................................................... 14

18 90° pull strength data for solder joints formed at 280°C. .................................................................... 14

19 Shear strength for bus-diode-bus solder joints..................................................................................... 14

20 Vacuum chamber base design, 2 m x 4 m laminator............................................................................ 16

21 Chamber cover deflection under vacuum............................................................................................. 16

22 Chamber cover stress under vacuum.................................................................................................... 17

23 Large area laminator vacuum chamber design..................................................................................... 17

24 Laminator vacuum chamber design, cross-section view...................................................................... 18

25 Large area laminator design model. ..................................................................................................... 18

26 Blanket heater vacuum test setup......................................................................................................... 19

27 Laminator automation design............................................................................................................... 21

28 Module conveyor drive design for laminator automation.................................................................... 21

29 Large area solar simulator design with 2 m x 4 m test plane............................................................... 22

30 Spire lamp regulator circuit board for a single-flash long-pulse solar simulator................................. 23

31 Scope trace of light intensity during a xenon lamp flash using an active lamp control circuit ........... 24

32 Solar simulator optical test bed with 2 m x 2 m test area. ................................................................... 25

33 Monitor cell gantry for measuring light uniformity over a 2 m x 2 m test area................................... 25

34 String of 220 μm cells soldered with 178 μm thick flat copper ribbon. .............................................. 27

35 Cell strings made with 220 μm thin cells and 178 μm thick corrugated interconnect ribbons............ 27

36 Ribbon spool drive assembly with corrugators and close-up of the ribbon corrugator assemblies..... 28

 iv
LIST OF TABLES 

Page

1 Program tasks. ........................................................................................................................................ 1

2 Dimensional variations in sheet placement, cut length, and punch locations for nominal 

2540 mm long TPE sheets...................................................................................................................... 3

3 Dimensional variations in sheet placement, cut length, and punch locations for nominal 

2540 mm long EVA sheets..................................................................................................................... 3

4 Process parameters for soldering bus-diode-bus joints........................................................................ 13

5 Simulation results for large area laminator chamber deflection and stress under vacuum 

for three chamber designs. ................................................................................................................... 15

 v
1 INTRODUCTION 

This is Spire Corporation’s Annual Technical Progress Report for Phase 2 of a program entitled 

“Development of Automated Production Line Processes for Solar Brightfield Modules.” This program is 

supported by the U. S. Department of Energy under the National Renewable Energy Laboratory’s 

Photovoltaic Manufacturing R&D (PVMRD) project. Phase 2 efforts extended from July 1, 2004 to 

October 15, 2005. 

1.1 Objective 

Spire is addressing the PVMRD project goals of improving PV manufacturing processes and products 

while reducing costs and providing a technology foundation that supports significant manufacturing 

scale-up. To accomplish this, we are focusing our efforts on the design of a large area utility-scale 

module and the development of the necessary manufacturing techniques and equipment to manufacture 

such a module in a high-volume production environment. 

1.2 Approach 

A three-phase program is underway for developing and demonstrating new automated systems for 

fabricating very large photovoltaic (PV) modules ideal for use in multi-megawatt grid-connected 

applications. We designed a large area (1.57 m x 3.68 m) 800 W module and we are developing 

associated module production equipment that will minimize the total installed system cost for utilityscale PV arrays. Activities in Phase 2 focused on the development of automation for module materials 

lay-up, cell string busing, and module lamination; enhancements to the cell stringing and lamination 

processes; and performance testing of large area modules. Program tasks are listed in Table 1. 

Table 1 Program tasks. 

Phase Term Task 

1 June 2003 through 

June 2004 

1 Design Brightfield Module and Production Line 

2 Develop Cell String Inspection Process 

3 Develop Advanced Lamination Process 

4 Design Module Lay-up System 

5 Design String Busing System 

2 July 2004 through 

October 2005 

6 Fabricate & Test Module Lay-up System 

7 Fabricate & Test String Busing System 

8 Design Advanced Lamination Process Tool 

9 Design Lamination Automation 

10 Design Large Area Solar Simulator 

11 Develop Soldering Process for Thin Solar Cells

3 October 2005 through 

December 2006 

12 Fabricate & Test Advanced Laminator 

13 Fabricate & Test Laminator Automation 

14 Fabricate & Test Large Area Solar Simulator 

15 Develop Computer Integrated Manufacturing System 

Spire partnered with the Automation & Robotics Research Institute (ARRI) at the University of Texas at 

Arlington (UTA), a lower-tier subcontractor, in Phases 1 and 2. In Phase 2, ARRI provided process 

support for automated bus and diode soldering under Task 7. 

1 
2 TECHNICAL DISCUSSION 

2.1 Task 6 – Fabricate and Test Module Lay-up System 

In Task 6 we demonstrated a new automated system for assembling module materials for lamination. 

Spire and the Automation & Robotics Research Institute (ARRI) worked with Rosenthal Manufacturing 

to define a system that is customized to handle the lay-up process requirements for Spire’s Brightfield 

module. We specified a system with the capacity for handling material up to 72 inches wide, large 

enough to handle our 62 inch wide module glass. 

The custom lay-up system, shown in Figure 1, is capable of feeding, cutting to length, and placing two 

different sheet materials (encapsulant and back sheet) simultaneously. The material feed system is 

synchronized with a servomotor-driven module conveyor to place the sheet materials directly on the 

module. An in-line punch feature was designed and installed to punch a rectangular cutout along one 

edge of the sheet for feeding bus leads through to the module output boxes. The system can also 

dispense a single layer of material, with the punch feature disabled, to place the first layer of encapsulant 

on the glass sheet, prior to placing the solar cell strings. 

05-091WA 

Figure 1 Automated module lay-up system. 

The system was tested with ethylene vinyl acetate (EVA) encapsulant sheet and Tedlar1

-polyester-EVA 

(TPE) back sheet. Both the EVA and the TPE ran successfully through the system, including feeding, 

punching, cutting, and placing. Repeatability data was measured for material length, punched hole 

location, and placement on a moving substrate, such as a glass sheet that forms a module front surface. 

Since the back sheet has low elongation, it did not stretch during unwinding and feeding, and the 

dimensional variation was within ±0.75 mm (see Table 2). Similar data measured for EVA shows higher 

variation, up to ±3 mm, due to the elastic nature of the material (Table 3). 

2 
Table 2 Dimensional variations in sheet placement, cut length, and punch locations for 

nominal 2540 mm long TPE sheets. 

 Placement (mm) Length (mm) Location (mm) 

Run # Left Right Left Right Punch #1 Punch #2 

1 461.0 462.0 2542.0 2542.0 9.0 2448.0 

2 462.5 461.0 2541.5 2542.0 8.0 2447.5 

3 462.5 462.0 2542.0 2541.5 8.0 2447.5 

4 462.5 462.0 2541.0 2541.5 8.0 2447.5 

5 462.0 462.0 2541.5 2541.0 8.5 2447.0 

6 462.0 462.0 2542.0 2542.0 8.0 2447.5 

Average 462.1 461.8 2541.7 2541.7 8.3 2447.5 

Max - min 1.5 1.0 1.0 1.0 1.0 1.0 

Table 3 Dimensional variations in sheet placement, cut length, and punch locations for 

nominal 2540 mm long EVA sheets. 

 Placement (mm) Length (mm) Location (mm) 

Run # Left Right Left Right Punch #1 Punch #2 

1 467.0 467.0 2495.0 2496.0 12.0 2408.0 

2 468.0 470.0 2494.0 2495.0 12.0 2406.0 

3 466.0 467.0 2495.0 2495.0 12.0 2407.0 

4 468.0 470.0 2493.0 2494.0 12.0 2406.0 

5 465.0 468.0 2494.0 2495.0 13.0 2408.0 

6 469.0 472.0 2494.0 2494.0 12.0 2406.0 

7 469.0 470.0 2495.0 2495.0 13.0 2408.0 

8 471.0 473.0 2493.0 2491.0 13.0 2405.0 

9 469.0 470.0 2492.0 2493.0 13.0 2404.0 

10 470.0 471.0 2493.0 2493.0 13.0 2405.0 

Average 468.2 469.8 2493.8 2494.1 12.5 2406.3 

Max - min 6.0 6.0 3.0 5.0 1.0 4.0 

We found that EVA stretches in the machine length direction during feeding and shrinks after cutting, 

resulting in a length that is shorter than expected. The observed shrinkage was 1.8% of the sheet length. 

For the module’s front EVA layer, where only one layer is being dispensed, we can compensate for the 

amount of shrinkage by adding this percentage to the desired length as an offset. For the back layer, the 

shrinkage causes misalignment in the punched holes and the cut sheet lengths between the EVA and the 

TPE. This problem can be solved by using an EVA-on-fiberglass material, which has much lower 

elongation than EVA alone. This material is a standard component used behind the cells in Spire’s 

modules. 

The lay-up machine was tested with a roll of EVA-on-fiberglass material to compare with the EVA 

material. The EVA-on-fiberglass ran successfully through the system, including feeding, punching, 

cutting, and placing. The EVA-on-fiberglass showed much less stretch during feeding than EVA without 

fiberglass. 

Our original punch design called for a 25 mm square hole, large enough so that cut sheets could be fed 

from the top down over an output bus ribbon that is bent up from the surface of the module at a 90°

3 
angle. Upon review, we realized that this results in an area with no encapsulant or back sheet behind a 

section of the bus ribbon and an edge of a solar cell. While a terminal box will cover the hole, the design 

provides inferior environmental protection for the cell and the bus ribbon. 

The punch design was changed to create a slot, 3 mm wide by 16 mm long. A photo of the punched slots 

in EVA-on-fiberglass sheets is shown in Figure 2. With this design, the hole is narrow enough for the 

EVA to flow and fill in during lamination, fully encapsulating the cell and bus ribbon. To make the sheet 

lay-up process work with such a narrow slot, the output bus ribbon is not bent up, but lies flat on the 

module when the back EVA and Tedlar sheets are dispensed. The slot lines up with the flat output 

ribbon at the location where the ribbon feeds through. In the original design with the bent ribbon, an 

operator is required to press the ribbon flat after the back sheets are dispensed, prior to lamination. In the 

new design, an operator is required to feed the bus ribbon through the slot prior to lamination. 

05-056WA 

Figure 2 Punched slots in EVA-on-fiberglass sheet. 

2.2 Task 7 – Fabricate & Test String Busing System 

Engineering design work for a production prototype string busing system was completed, and the system 

was built and tested. The system consists of automation for transporting and aligning 5 ft x 12 ft 

modules, cutting and placing bus ribbon, applying flux, placing diodes, and soldering bus ribbons. Two 

separate systems were built, one for fabricating bus ribbons off-line, and one for installing bus ribbons 

and diodes in a module, on an assembly line. 

2.2.1 Bus Ribbon Fabrication 

Mechanical and electrical designs were completed for the bus ribbon fabrication machine, which 

automatically feeds ribbon from reels, straightens it to remove coil set, cuts or punches it to length, and 

fills a tray with a stack of ribbon. Assembly and detail drawings were completed for all system 

subassemblies. A view from the SolidWorks CAD model of the machine is shown in Figure 3. Electrical 

and pneumatics schematics were created. 

4 
RIBBON STAND 

ASSEMBLY 

PUNCH 

SHEAR CUTTER 

RIBBON PICK & 

PLACE 

RIBBON TRAY 

STRAIGHTENER 

RIBBON DRIVE 

ENCODER 

04-113WA 

Figure 3 Ribbon fabrication machine design. Main support frame and controls cabinet not 

shown. 

Software was written for controlling the bus ribbon fabrication machine. A Visual Basic graphical user 

interface (GUI) was coded and debugged. The main window is shown in Figure 4. Controls are provided 

for cutting ribbons continuously or in batches, selecting the number of ribbons per batch, and setting the 

ribbon length, feed velocity, and feed acceleration. A counter displays how many ribbons have been cut. 

The System section of the window displays the status of the machine sensor inputs, including end of 

ribbon reel, cutter and punch positions, ribbon pick-and-place positions, vacuum, and ribbon presence in 

the tray. Buttons are provided for manually actuating outputs for jogging (advancing) ribbon; punching, 

cutting, and ejecting ribbon; moving the pick-and-place actuators; and turning the pick-and-place vacuum 

on and off. Motor controller programs were written for automatic operation, to allow the controller to 

run the machine without connection to a PC if desired. 

Mechanical, pneumatic, and electrical assembly work was completed, software was installed, and the 

machine was tested. The completed system is shown in Figure 5. Figure 6 shows a close-up view of the 

main components, including (left to right) the ribbon straightener (removes coil set), ribbon feed encoder 

(measures ribbon length), ribbon drive wheels, punch (punches a tab for the diode), knife set, pick-andplace hand, and ribbon tray. 

5 
04-102WA

Figure 4 Main operating window for the ribbon fabrication machine. 

05-092WA 

Figure 5 Bus ribbon fabrication machine. 

6 
05-093WA 

Figure 6 Close-up view of bus ribbon fabrication machine components. 

2.2.2 Bus Ribbon and Diode Installation 

Mechanical and electrical designs were completed for the bus ribbon and diode installation system, 

which automatically picks, aligns, and places bus ribbons and diodes, applies no-clean flux for diode 

soldering, and solders bus ribbons to diodes and string ribbons. Mechanical assembly and detail 

drawings were completed for all system subassemblies, and electrical and pneumatics schematics were 

created. 

A large four-axis (x, y, z, and θ) Cartesian robot was specified. A CAD model of the robot is shown in 

Figure 7. The robot can travel 3935 mm in the x axis, 2250 mm in the y axis, and 150 mm in the z axis. 

Servomotors drive all four axes. The x and y axes have belt driven slides, the z axis has a lead screw, 

guide rods, and a brake, and the θ axis has a 127 mm diameter rotary table. 

Z-AXIS 

Y-AXIS 

X-AXIS 

θ-AXIS

04-103WA

Figure 7 CAD model of four-axis Cartesian robot for busing assembly. 

7 
An end-effector was designed for the robot, including a safety clutch, a vacuum pick-and-place arm, and 

two soldering tips. The robot end-effector is shown in Figure 8. The clutch stops all robot motion in the 

event of a collision that applies torque on the end-effector. Each solder tip assembly includes a vertical 

air cylinder to move the solder tip below the vacuum cups during soldering, an air jet for rapid solder 

joint cooling, a heated spring-loaded solder tip, and a spring-loaded pin for holding the solder joint in 

contact while the solder freezes. 

05-070WA 

Figure 8 Robot end effector with soldering heads and vacuum pick-up arm. 

Mechanical and electrical assembly of the bus and diode installation system was completed. The system 

is shown in Figure 9. A large 1.68 m x 6.10 m (66 inch x 240 inch) roller conveyor and a 4-axis 

Cartesian robot were installed on the main steel frame. A module stop assembly, two pneumatic module 

aligner assemblies, and three roller lift assemblies were built and installed on the conveyor for module 

alignment. 

Tooling plates were installed on the frame on both sides of the conveyor. The two rear tooling plates 

hold the solder tip cleaner and three bus insulators for rear bus soldering. The robot places these 

reusable insulators under the bus ribbons to keep the EVA encapsulant from melting during soldering. 

The two front tooling plates hold three bus insulators for the front buses, seven bus ribbon trays (two 

short and two long trays for the front buses, and three trays for the rear buses), two diode pack retainers, 

and two flux applicator assemblies. A diode pack retainer, ribbon tray assembly, and flux applicator are 

shown in Figure 10. Each ribbon tray assembly has an optical sensor to signal when the tray is empty. 

The flux applicator has a float switch connected to a flux supply pump to maintain the proper flux level. 

8 
05-068WA 

Figure 9 Module-size aluminum sheet on the automated busing system. 

05-030WA 

Figure 10 Bus ribbon tray (top), flux applicator (left), and diode pack retainer (center) on front 

tooling plate. 

Electrical and pneumatics components were debugged. The digital and analog I/Os were verified, the 

robot actuators were configured, and the servomotors were tuned for the four robot axes (x, y, z, and θ). 

Software was written, installed, and debugged for the main operating screen (Figure 11), the I/O and 

motion diagnostics screens, the system parameters screen, and the process parameters screen. 

9 
05-094WA 

Figure 11 Main operating screen for the automated busing system. 

Robot speed and position parameters were fine tuned for the bus ribbon and diode pick and place 

processes. Solder head motions were adjusted to eliminate ribbon bending when the soldering tips move 

down and contact the ribbon. Vertical (z axis) motions were minimized during the soldering moves to 

reduce process cycle time. A video of the busing system in operation was recorded and delivered to 

NREL. 

2.2.3 Development Work at ARRI 

ARRI designed and fabricated a prototype clamping mechanism to secure the bus bars in position during 

the soldering operation. The robot end effector acquires bus bars from a supply stack with vacuum cups, 

places them on the module, releases them, and retracts to allow placement of the soldering tips. A 

clamping mechanism was demonstrated that clamps the buses before the end effector releases the 

vacuum. The clamping devices are small and placed such that no interference occurs between the clamps 

and the soldering head. Once the joints are formed and solidified, the clamps are removed from the bus 

without disturbing the bus position on the module. 

ARRI worked on developing and testing the bus-diode-bus soldering process with the Spire-designed 

solder head to establish ranges for soldering parameters, including reflow temperature, dwell time, tip 

pressure, and cool down period. The soldering parameters were initially refined using a manual process. 

Subsequent soldering tests were performed using an Adept 1 SCARA robot for automated processing. 

10 
In preparation for the solder tests, 610 mm lengths of 13 mm wide bus bars were cut, and one end of each 

strip was notched to match the diode area. Flux was applied in the robot-controlled process to the bottom 

surface of the diode and to the underside of the notched tab. The solder head temperature was 

maintained in the range from 264 °C to 278 °C. A reflow time of 8 s was used, followed by a cool down 

period of 2 s. The solder head assembly (shown in Figure 12) was mounted on a weighted slide that 

applied 2.4 kg of force to the joint during soldering. 

05-004WA

Figure 12 Slide-mounted solder head suspended from robot arm. 

Forty bus/diode/bus solder joints were formed and the joint strengths were measured using 90° pull tests 

(force applied perpendicular to the diode solder joints). All diodes were checked following soldering and 

prior to pull testing, and all tested good. Results from the 90° pull tests are plotted in Figure 13. The 

values are much more consistent than those observed with the manual soldering tests, implying that the 

previous variation was due to uneven contact or pressure between the solder tip and the materials to be 

joined. The majority of the strength values fall in the range of four to six pounds, and all are well above 

the target value of one pound. All joints are tested to complete failure. Once failure of the joint is 

initiated, complete failure occurs very quickly. It should be noted that, for all 40 joints, not one failed at 

the solder bonds between the diode and the buses. The consistent failure mode is through the center 

layer of the silicon diode. 

ARRI designed and fabricated an experimental molybdenum solder head. The primary reason for 

modifying Spire’s solder head design was to achieve better temperature control of the soldering tip, to 

determine whether the variations in solder joint strength observed in earlier tests were due to fluctuations 

in the tip temperature. Dimensions of the revised solder head are 0.75 inch by 0.75 inch by 1.94 inches. 

Two internal cylindrical cavities are machined to house a cartridge heater and a spring-loaded plunger 

pin assembly that holds the solder joint securely during the cool-down period. The solder head is shown 

in Figure 14. 

11 
0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

0 10 20 30 40

Sample No.

Pull Strength (lbs)

50

05-005WA

Figure 13 90° pull strengths of bus-diode-bus solder joints. 

05-045WA 

Figure 14 Experimental molybdenum solder head. 

The solder head was connected to a PID temperature controller. During earlier soldering tests with the 

original solder head, the temperature of the soldering tip varied over a range of 14 °C, with the controller 

set at 270 °C. The temperature of the revised solder head was allowed to reach steady state, and then 

temperature measurements were taken just to the side of the soldering surface and recorded over a three 

minute time span. This was done for three temperature set points: 260 °C, 270 °C, and 280 °C. The 

temperature was very stable for all three settings. The greatest variation in temperature was 4 °C, 

observed at the 270 °C setting. Figure 15 plots the temperatures for the three settings over three-minute 

periods. Soldering experiments for the bus-diode-bus joint were performed using these three temperature 

settings. The process parameters are shown in Table 4. 

12 
05-046WA 

Figure 15 Temperature control of revised soldering tip with PID controller. 

Table 4 Process parameters for soldering bus-diode-bus joints. 

Reflow 

Temperature (°C) 

Reflow 

Force (kg) 

Reflow 

Period (s) 

Cool-down 

Period (s) 

Cool-down 

Force (kg) 

260 2.4 8 5 0.23 

270 2.4 5 5 0.23 

280 2.4 5 5 0.23 

Twenty solder joints were formed for each temperature setting, and then subjected to 90° pull tests to 

determine the joint strength and the failure mode. In 90% of the joints, failure occurred through the 

center of the diode, fracturing the bulk silicon. In the remaining 10% of the cases, the soldered interface 

between the diode and the bus bar failed. This type of failure had high strength, typically over 8 pounds. 

Pull strength data for joints made at 260 °C, 270 °C, and 280 °C are plotted in Figures 16 to 18. This 

data shows that, despite a more constant soldering tip temperature, the failure strength still varies. Based 

on this information, it was concluded that the moderate temperature fluctuations (±7 °C) of the original 

soldering head were not responsible for the variations in joint pull strengths. Since the lowest pull 

strengths occur when the silicon fractures, the variations may be due to stress in the diode caused by the 

difference in thermal expansion between the silicon diode and the copper bus bar. 

05-047WA 

Figure 16 90° pull strength data for solder joints formed at 260°C. 

13 
 

05-048WA 

Figure 17 90° pull strength data for solder joints formed at 270°C. 

05-049WA 

Figure 18 90° pull strength data for solder joints formed at 280°C. 

Additional joints were soldered for the purpose of determining the shear strength of the bus-diode-bus 

joints. All joints were soldered at 270 °C using the parameters in Table 4. Pull tests were done with the 

force applied parallel to the diode solder joints. Joints that failed at the soldered interface had shear 

strengths ranging from 25 to 44 pounds. In other tests, the copper bus bar failed before the solder joint 

sheared, with shear strengths in the range of 42-54 pounds. A plot of the shear strength values is shown 

in Figure 19. This data shows that the shear strength of the bus-diode-bus joints far exceeds the level 

required for the module. 

05-050WA 

Figure 19 Shear strength for bus-diode-bus solder joints. 

14 
2.3 Task 8 – Design Advanced Lamination Process Tool 

We designed an advanced laminator for large area PV modules in this task. Given the size of our module 

(1.57 m x 3.68 m), we decided to specify the lamination area at 2.00 m x 4.00 m. Initial design work 

focused on vacuum chamber structural design and heated platen design. 

Solid models were created in CAD (SolidWorks) and a series of structural FEA simulations was done 

(with ANSYS) for various chamber plate thicknesses and reinforcing rib designs. Chamber deflection, 

stress, and factor of safety were calculated for each design. The load on the vacuum chamber is 

atmospheric pressure, set to 15 psi for these analyses. The resulting force on the chamber plates, which 

are 424 cm x 235 cm (167 inch x 92.5 inch), is 1,031 kN (231,700 lbf). Our design goals are to limit the 

total chamber deflection to 10 mm (0.39 inch) or less and to limit the stress on the chamber to obtain a 

factor of safety of 3 or more. 

An early design iteration used 23 aluminum I-beams for reinforcing each of the two aluminum chamber 

plates. The chamber base has side walls around the perimeter to form the chamber cavity. The chamber 

cover design is similar to the base, except it has no side walls, which add stiffness to the base. The 

engineering simulation results are summarized as Case 1 in Table 5. The total maximum chamber 

deflection was 0.48 inch (base plus cover) under vacuum. The maximum stress was 18,000 psi, resulting 

in a safety factor of only 2.26. Thus both the deflection and the safety factor failed to meet our design 

goals in Case 1. 

Table 5 Simulation results for large area laminator chamber deflection and stress under 

vacuum for three chamber designs. 

Case 

 

Chamber 

Component

I-beam 

Type 

I-beam 

Quantity 

Chamber 

Weight 

(lbs) 

Maximum 

Deflection 

(inch) 

Maximum 

Stress 

(psi) 

 

Factor of 

Safety 

1 Cover 

Base

Total 

4 x 4 

4 x 4 

23 

23

46 

2377 

2633

5010 

0.330 

0.150

0.480 

14,072 

17,998 

2.89 

2.26 

2 Cover 

Base

Total 

8 x 5 

8 x 5 

19 

19

38 

2486 

2742

5227 

0.096 

0.057

0.153 

8,512 

5,377 

4.77 

7.55 

3 Cover 

Base

Total 

8 x 5 

8 x 5 

13 

13

26 

2189 

2445

4635 

0.133 

0.080

0.213 

10,768 

7,702 

3.77 

5.27 

We then switched to a taller, wider I-beam, and attached 19 of them, the most that would practically fit, 

to each plate. The total deflection decreased to 0.153 inch and the maximum stress decreased to 8,512 

psi, for a safety factor of 4.77 (Case 2 in Table 5). Given that these results exceeded our structural 

design criteria by a wide margin, we reduced the number of I-beams to save cost and weight. 

The final vacuum chamber design has 25 mm (1 inch) thick plates, each reinforced with 13 I-beams. The 

base chamber is shown in Figure 20, with a heating platen in place. The chamber deflects a total of 

0.213 inch under vacuum (Case 3 in Table 5). The maximum stress is 10,768 psi, resulting in a 3.77 

factor of safety. Results of the FEA simulations for cover deflection and stress for this design are shown 

in Figures 21 and 22. 

15 
05-013WA

Figure 20 Vacuum chamber base design, 2 m x 4 m laminator (perspective view). 

05-014WA

Figure 21 Chamber cover deflection under vacuum (inch). 

16 
05-015WA

Figure 22 Chamber cover stress under vacuum (104 psi). 

Once the chamber structural design was complete, design work focused on the remaining features of the 

vacuum chamber, the heated platen, and a module pin lift system. A perspective view of the complete 

vacuum chamber assembly design is shown in Figure 23. The chamber consists of top and bottom plates, 

side rails attached to the bottom plate to create the chamber cavity, and I-beams attached to both plates to 

limit the chamber deflection and stress under vacuum. 

05-023WA 

Figure 23 Large area laminator vacuum chamber design. 

17 
A quick-release diaphragm clamping system was designed that will significantly reduce the time required 

to change the flexible diaphragm that applies pressure to the module during lamination. The diaphragm 

clamp has an open rectangular shape, similar to a picture frame, which is attached to the bottom surface 

of the top chamber plate to hold the diaphragm in place. The new design uses a set of locking toggle 

clamps to hold the diaphragm clamp in place, instead of the large number of screws used in our previous 

designs. Figure 24 shows a cross-section view of the chamber assembly, while Figure 25 shows the 

overall laminator design. 

05-024WA 

Figure 24 Laminator vacuum chamber design, cross-section view. 

05-095WA 

Figure 25 Large area laminator design model. 

18 
A module pin lift design was also completed for the large laminator. The pin lift is important to prevent 

large modules from curling when placed on a heated platen. Curling occurs because the surface of the 

glass in contact with the platen is hotter than the opposite surface of the glass, and therefore longer due to 

thermal expansion. The pins hold the glass slightly above the surface of the platen during the initial 

evacuation step in the lamination process. The pin lift system uses sliding cam bars under the heated 

platen to push pins, located in holes in the platen, from a position slightly below the surface of the platen 

up to a maximum height of 5 mm above the platen. The pin up height is adjustable, with a nominal 3 mm 

recommended for production. 

We investigated the use of a novel blanket heater for the laminator’s heated platen. Our current 

laminators use electric rod heaters attached to the platen with long machined clamps and thermal grease. 

Platen temperature uniformity is typically ±4 °C to ±5 °C. Improved uniformity can be obtained with rod 

heaters, either by making the platen thicker or by spacing the heaters closer together, which requires 

more heaters and clamps. Both options increase the cost of the laminator. 

We identified a source of thin heaters that can be made in large areas, potentially at low cost. The flat 

geometry of these heaters may allow us to significantly improve the platen temperature uniformity. We 

obtained two 28 cm x 38 cm (11 inch x 15 inch) 230 V blanket heaters from the manufacturer for 

evaluations. 

Our experience powering heaters in vacuum has shown that insulated power leads can produce 

conductive plasmas that arc to ground when operated at pressures in the 300 to 1000 mTorr range, which 

is the normal operating pressure in the laminator. These arcs can damage the insulation and the electrical 

controls while creating a potential safety hazard. Thus we designed and fabricated a simple vacuum 

chamber from two aluminum plates to test the blanket heater for potential arcing in vacuum. The 

chamber and heater controls were assembled and tested. A current sensor was installed on the heater 

power line and connected to an oscilloscope that would trigger if an arc occurs. The test setup is shown 

in Figure 26. 

05-034WA 

Figure 26 Blanket heater vacuum test setup. 

19 
Several scope triggers were detected, indicating possible arcing. We ran more tests to increase the 

chance that we would see the effects of arcing, then opened the chamber and examined the inside of the 

chamber and the heater. We found no direct evidence of arcing, such as carbon tracks or burned 

insulation. However, the heater insulation was delaminated internally from the heater element in some 

areas, probably due to overheating. We obtained information from the manufacturer on the temperature 

rating of the insulation used on the heater. We repeated this test with an identical heater, this time 

controlling the temperature below the rating for the insulation material. This time no arcs were detected. 

Thermal cycling tests were completed for evaluating a graphite composite heat transfer material that may 

replace thermal grease in the laminator platen assembly. If the graphite material is suitable, it would 

eliminate the laminator maintenance and downtime that is sometimes required to replace grease that 

migrates away from the heater-platen interface due to thermal cycling. 

The graphite material was installed around rod heaters and cooling lines in a test platen assembly and 

subjected to 2478 thermal cycles, typically between 100 °C and 160 °C. We then disassembled the 

platen and found that the graphite material was worn in some areas due to mechanical stress from thermal 

cycling. The graphite was removed and the test platen was reassembled with our standard thermal 

grease. Thermal cycles were then run while monitoring the platen temperature for comparison with the 

graphite data. 

These tests showed that the temperature uniformity of our test platen is substantially better with thermal 

grease (±3.5 °C average) than with the graphite material (±6.7 °C average). This was a surprising result, 

given that the graphite material has a higher thermal conductivity (5 W/mK) than the thermal grease 

(0.95 W/mK). We suspect that the ability of the grease to flow and fill in gaps caused by irregularities in 

the mating surfaces is more important for uniform heat transfer than the difference in conductivity of the 

materials. 

2.4 Task 9 – Design Lamination Automation 

Mechanical design work was completed for an automated conveyor system for transporting modules 

through the large area laminator (2 m x 4 m module size capacity). The design is shown in Figure 27. 

The drive components for the conveyor were sized and selected. Mechanical design models for the drive 

conveyor and a conveyor cleaning brush were created. Detail design drawings and assembly drawings 

were generated from the models. 

The conveyor belt will be fabricated from a Teflon®-coated fiberglass material, similar to the release 

sheets we use to keep EVA encapsulant from sticking to the interior surfaces of the laminator. A motordriven cylindrical brush will be included to remove any EVA or other material that may accumulate on 

the belt. 

A view from the CAD model of the conveyor drive design is shown in Figure 28. The laminator vacuum 

chamber will sit inside the drive system, with the heated platen and chamber side walls coplanar with the 

conveyor belt. Belt travel is left to right in Figure 28. 

20 
05-096WA 

Figure 27 Laminator automation design. 

05-026WA 

Figure 28 Module conveyor drive design for laminator automation (conveyor belt not shown for 

clarity). 

2.5 Task 10 – Design Large Area Solar Simulator 

Spire currently produces upward flashing solar simulators that can test modules up to 1.37 m x 2.00 m. 

In Task 10 we designed a simulator with a significantly larger 2.0 m x 4.0 m test area for the Brightfield 

module. We maintained the flash up geometry for the larger simulator, since it simplifies product 

handling by allowing modules to be transported over the simulator on a conveyor. 

A view of the solid CAD model of the simulator is shown in Figure 29. The simulator has four 2.0 m 

long xenon lamps positioned side-by-side under the test plane. Adjustable reflecting surfaces direct light 

to the test plane, while optical filters correct the spectrum to Air Mass 1.5 Global, per ASTM E 927-042

. 

A pair of motor-driven belt conveyors supports the module at its edges and transports it through the 

simulator. The conveyor positions are adjustable to suit the module width. 

21 
05-097WA 

Figure 29 Large area solar simulator design with 2 m x 4 m test plane. Side panels removed for 

clarity. 

2.5.1 Single-Flash Long Pulse Xenon Light Source 

We developed a single-flash, long pulse xenon light source for our solar simulator. Our standard 

simulator uses multiple (50 to 200) short pulses (1 ms per pulse at 7 to 10 Hz) for each module I-V curve. 

A single flash approach, in which an I-V curve is measured in a single lamp flash, shortens the test time 

from ~20 s to less than 1 s per module. A longer pulse, on the order of 100 ms, allows the simulator to be 

used for solar cells with slow response times, such as SunPower Corporation’s high efficiency (20%) 

back contact cells and Sanyo’s Heterojunction with Intrinsic Thin Layer (HIT) cells. 

We successfully developed a unique active feedback lamp control system that uses power 

semiconductors (MOSFETs) to control the flash profile of a xenon lamp. This lamp control method 

allows us to build a long pulse, single flash simulator without a large number of big, heavy, and 

expensive inductors. 

We designed, assembled, and tested a prototype lamp regulator printed circuit board (Spire no. 909-

0401), shown in Figure 30. The board controls the gate drive of a bank of high voltage power MOSFETs 

in response to an applied reference signal. Initial checkout involved applying signals to the board from a 

function generator and observing the behavior of the board. Changes were made to some board 

components as a result of these tests. 

Work then began on discharging a large (2400 μF, 3600 VDC) capacitor with a regulated current, in 

preparation for a controlled flash of a xenon arc lamp. An electrical panel was assembled, including the 

Spire lamp regulator board, four power MOSFETs, and several high voltage relays and power resistors, 

which provide backup discharge capability. 

22 
05-058WA 

Figure 30 Spire lamp regulator circuit board for a single-flash long-pulse solar simulator. 

The capacitor was first discharged through a 180 Ω power resistor network. This was successful up to 

the point where MOSFET failures occurred, due to transient over-voltage during turn-on. We then 

substituted a 1955 mm long xenon arc lamp in place of the resistor network, since its terminal voltage is 

effectively independent of current. The lamp flashed successfully at a constant current set point of 6.3 A. 

Two additional MOSFETs were installed on the panel, and lamp current was increased in steps up to 

16 A, at an operating voltage of 2350 V. The pulse width under these conditions was about 65 

milliseconds at constant current. 

A reference cell was then installed and used as the feedback source for the light pulse, which is our 

ultimate lamp control scheme. This circuit produced flashes with very uniform light intensity for 66 ms. 

The light pulse has an initial spike followed by a long flat region, which ends when the capacitor is 

discharged to the point where it can no longer provide sufficient current to the lamp. The pulse length 

was then increased by adding more capacitance to the circuit. Figure 31 shows a 78 ms flat light pulse 

generated by a 1.955 m long xenon lamp with 3600 μF capacitance. The lamp current was 24 A during 

the flash, sufficient to produce 1 sun (100 mW/cm2

) of light intensity in a solar simulator. 

The controlled flash has much better intensity stability than obtained with a traditional passive pulseforming network composed of capacitors and inductors. Initial tests show the temporal instability of 

irradiance is less than 0.1%, which is an order of magnitude better than that obtained with a passive 

network, and well below the 2% Class A specification in ASTM E 927-042

. Additionally, active control 

provides excellent flash-to-flash repeatability. As a consequence, more accurate I-V data can be 

obtained. 

23 
0

1

2

3

4

5

-0.02 0.00 0.02 0.04 0.06 0.08 0.10

Time(s)

05-098WA 

Figure 31 Scope trace of light intensity during a xenon lamp flash using an active lamp control 

circuit. The flat portion of the pulse is 78 ms long. 

2.5.2 Large Area Optical Test Bed 

We investigated methods for improving the light spatial uniformity of the large area solar simulator. Our 

current simulators are able to achieve ±3% uniformity over the test plane, which is remarkable given the 

short lamp to test plane distance (less than one meter). A considerable amount of effort goes into the 

uniformity tuning process for each simulator, to meet the ±3% specification. An alternative optics design 

is being evaluated that may allow us to improve our uniformity with less tuning. Another benefit of this 

design is that it reduces the area of spectral filters, which will save considerable cost. 

A two-lamp optical test bed assembly was designed and built (Figure 32) to test the feasibility of the new 

optics over a 2 m x 2 m test plane. An electrical control box was completed and installed near the test 

bed. Two lamp trigger boards were assembled and installed on the test bed. 

Reflector assemblies were fabricated by attaching 76 μm (0.003 inch) thick reflector film onto flat 

substrates. The substrates were spray coated with a contact adhesive and the reflector film was rolled 

onto the substrate with a roller laminator, which has motor driven pinch rollers with pneumatic pressure 

control. Unfortunately, the resulting reflector surface had an orange peel texture, due to the thinness of 

the reflector film and the unevenness of the spray coated adhesive. Since this texture might reduce the 

spatial uniformity of the light at the test plane, we replaced the thin reflector film with 760 μm 

(0.030 inch) thick reflector sheets. The sheets were cut to size and attached to the substrates with contact 

adhesive. The resulting reflector surfaces are smooth. The reflector assemblies were installed on the test 

bed. 

24 
05-051WA 

Figure 32 Solar simulator optical test bed with 2 m x 2 m test area. 

The two lamp assemblies will illuminate a 2 m x 2 m test plane. Normally, a reference cell is placed on 

the test plane and moved in a grid pattern to measure the spatial uniformity of the light intensity. 

However, our 2 m x 2 m test bed has no physical test plane on which to rest a reference cell. (The 2 m x 

4 m sun simulator will also have no physical test plane, as we plan to transport modules across the 

simulator supported by a pair of narrow belt conveyors at the module edges.) Thus we designed and built 

a gantry, shown in Figure 33, that suspends a monitor cell at a fixed height over the test bed. The 

monitor cell is mounted on a small carriage that is moved incrementally in x and y directions as the lamps 

are flashed to map the simulator spatial uniformity. 

05-071WA 

Figure 33 Monitor cell gantry for measuring light uniformity over a 2 m x 2 m test area. 

25 
2.5.3 High Power Electronic Load 

We are increasing the power capacity of our electronic load and measurement circuitry, which measures 

module I-V curves. Our Brightfield module will produce 811 W at Standard Test Conditions (100 

mW/cm2

, 25 °C) when fabricated with 15% efficient solar cells. Since this is well beyond the 500 W 

rating of our current electronic load circuit board, we are redesigning it to handle module power levels up 

to 1000 W when illuminated by a long pulse single flash solar simulator. 

Commercial bipolar power supplies were rejected due to cost ($6500 unit price), size (19-inch rack 

mount) and weight (24 kg). A passive capacitor type system was considered but rejected, due to the 

potential difficulty of matching appropriate module characteristics with varying pulse lengths. An active 

current control system composed of parallel power MOSFETs was ultimately selected, as the I-V sweep 

can be controlled precisely. 

The circuit will operate by sweeping device current from Isc to Voc. A power MOSFET was selected for 

this purpose due to its optimization for linear use and its voltage and current ratings. Depending on the 

selected range, current is diverted through one or two shunt resistors and the resultant signal is fed to a 

programmable gain amplifier. This arrangement allows four current ranges to be selected by two control 

signals. The device voltage, after passing through an attenuator (approximately 25:1), is amplified by 

two successive stages. The first features selectable gains of 1, 2.5, and 10; the second features gains of 1 

and 10. In this way, five voltage ranges (gains of 1, 2.5, 10, 25, and 100) can be obtained using three 

control signals. An on-board capacitor bank will compensate for voltage drops in the semiconductors 

and shunt resistors. The capacitors will be pre-charged through a relay and then isolated prior to 

measurement. 

2.6 Task 11 – Develop Soldering Process for Thin Cells 

Our objective in this task is to develop a high-yield soldering process for joining thick copper 

interconnect ribbon to thin silicon solar cells. As cells become larger and more efficient, the amount of 

current they produce increases. If the interconnect ribbon cross-section remains constant, power loss in 

the ribbon increases as I2

R. Therefore, it would be beneficial to increase the ribbon thickness to reduce 

its series resistance without increasing its width, since the width shadows the cell. However, the stress 

on a cell’s solder joints increases with the thickness of the copper, so there is a limit where the copper 

thickness begins to cause fracturing of the silicon. This limit is typically 125 μm (0.005”) for soft 

annealed copper. The problem is worse for thin cells, less than 250 μm thick, which fracture more easily 

than thicker cells. In this task we developed a method of forming shallow fine-pitch corrugations in 

copper ribbon that act as stress-relief features to enable the use of thicker ribbon. 

We ran a test with thin cells to evaluate cell stress cracking with thick flat ribbon. Cell strings were 

fabricated from thin 220 μm cells and thick 178 μm (0.007 inch) ribbon on our automated solar cell 

stringing equipment, the Spi-AssemblerTM 5000. When flexed after soldering, the thin cells consistently 

break at the same spot, where the maximum stress occurs, as shown in Figure 34. The location is the end 

of the solder joint on the back of the cell. 

26 
05-099WA 

Figure 34 String of 220 μm cells soldered with 178 μm thick flat copper ribbon and flexed to show 

crack locations. 

A ribbon spool drive assembly with corrugators was designed to integrate the ribbon corrugation function 

into our Spi-Assembler 5000. The assembly includes support rollers for two ribbon spools and two 

motor-driven corrugator assemblies. Components were fabricated, assembled, and tested with thick 

copper ribbon at Spire in Bedford, MA. The assembly was then shipped to our Chicago module 

fabrication facility, where it was installed on an Assembler. Solar cell strings made with thin cells and 

thick corrugated interconnect ribbons were produced with this equipment. The type of consistent 

cracking seen previously with flat ribbon was not evident in these strings. Two of these strings are 

shown in Figure 35. 

05-072WA 

Figure 35 Cell strings made with 220 μm thin cells and 178 μm thick corrugated interconnect 

ribbons. 

Each string consists of four cells soldered in series. We used 220 μm thick x 125 mm square Cz-Si cells 

from Shell Solar and 178 μm (0.007 inch) thick x 2.0 mm (0.080 inch) wide copper ribbon with 13 to 

18 μm (500 to 700 micro-inch) thick Sn62/Pb36/Ag2 solder coating. 

While we were able to produce good strings, these tests showed the need for some improvements to the 

corrugator assembly. The drive motors had trouble pulling the ribbon from the heavy (5 kg) spools, a 

problem that will be solved by using higher torque motors. The corrugated ribbon had variable camber 

(bow in the plane of the ribbon) because the spools are wide (101 mm between flanges), resulting in a 

27 
large variable angle as the ribbon feeds into the corrugator. This will be corrected by increasing the 

ribbon path length between the spools and the corrugators. Design work for the larger motor and the 

longer ribbon path was completed and is shown in Figure 36. 

05-100WA 

Figure 36 Ribbon spool drive assembly with corrugators (left) and close-up of the ribbon 

corrugator assemblies (right). 

28 
3 CONCLUSIONS 

Spire has completed the second phase of a three-phase program for developing automated production line 

processes for solar Brightfield modules. In the first phase, a large area (1.57 m x 3.68 m) 800 W module 

for utility-scale PV arrays was designed, with emphasis on minimizing Balance of System (BOS) costs. 

Unique module features include internally laminated by-pass diodes, which greatly simplifies the 

module’s internal busing and output terminals, and a cantilevered superstrate that allows for a reduced 

glass thickness and a simpler frame design. Another key Phase 1 accomplishment was the development 

of a cell string inspection system with machine vision and microcrack detection capabilities. Spire 

applied for a U.S. patent on the infrared crack detection technique.3

In Phase 2 we worked on the design and development of automated tools for producing such modules in 

multi-megawatt per year quantities. Major achievements include: 

• An automated system for dispensing and laying up module materials (encapsulant and back 

sheet) was fabricated and tested. The system feeds material, cuts it to length, and places it in 

position directly on the module. An in-line punch cuts a narrow rectangular hole along one edge 

of the sheet for feeding bus leads through to the module output boxes. Testing was done to 

measure the accuracy of cut lengths, hole locations, and sheet placement on the module for stable 

and elastomeric sheets. 

• We fabricated and tested an automated system for installing and soldering bus ribbons and diodes 

in modules prior to lamination. The system comprises two machines, a bus ribbon fabrication 

machine and a bus and diode installation machine. 

o The bus ribbon fabrication machine automatically feeds ribbon from reels, straightens it 

to remove coil set, cuts or punches it to length, and fills a tray with a stack of ribbon. 

The punch trims one end of the bus to match the diode width, to prevent the positive and 

negative buses from shorting out the diode. 

o The bus and diode installation system consists of a conveyor and aligner for 1.6 m x 

3.7 m modules and a 4-axis robot with a custom end-effector for placing bus ribbon, 

applying flux, placing diodes, and soldering bus ribbons. The robot also places reusable 

insulator strips on the module to prevent the encapsulant from melting during the 

soldering process. Spire’s constant temperature hot-bar solder tip was used for soldering 

the cell string ribbons and the diodes to the bus ribbons. Solder joint pull strengths far 

exceeded the 450 g target value when pulled at a 90° angle and in shear. 

• We designed an advanced vacuum laminator for large PV modules. The lamination area (2.0 m x 

4.0 m) is more than twice the size of our current largest model. Vacuum chamber structural 

design work was done using finite element analysis to optimize the chamber structure while 

maintaining deflection and stress within acceptable limits. A new heated platen design was 

conceived in which a blanket heater is used in place of rod heaters for improved temperature 

uniformity. A module pin lift design was incorporated to prevent glass bowing during the initial 

pump-out phase of the lamination cycle. A quick-release diaphragm clamp system was designed 

to reduce equipment downtime during diaphragm replacement. A vertical cover lift was 

designed to reduce the time needed for loading and unloading modules. 

• Mechanical design work was completed for an automated conveyor system for transporting 

modules through the large area laminator (2 m x 4 m module size capacity). The drive 

components for the conveyor were sized and selected. Mechanical design models, assembly 

drawings, and detail drawings were created for the drive conveyor and a motor-driven conveyor 

cleaning brush assembly. 

29 
• We designed a solar simulator with a 2.0 m x 4.0 m large test area for measuring the electrical 

performance of the Brightfield module under simulated sunlight. This test area is nearly three 

times the size of our current largest simulator. We used a flash-up geometry to simplify product 

handling by allowing modules to be transported over the simulator on a conveyor. The simulator 

has four 2 m long xenon lamps positioned side-by-side under the test plane. Adjustable 

reflecting surfaces direct light to the test plane, while optical filters correct the spectrum to Air 

Mass 1.5 Global, per ASTM E 927-042

. 

o We developed a single-flash, long pulse xenon light source for the solar simulator, in 

place of our standard multiple-flash short-pulse xenon lamp. The single flash shortens 

the measurement time from ~20 s to less than 1 s per module. The long pulse increases 

the illumination time up to 100 ms, compared to our standard 1 ms pulse, to allow the 

simulator to measure the performance of high efficiency and thin film modules with slow 

response. 

o A unique active lamp control scheme was devised for the long pulse lamp. Lamp 

intensity is controlled by active feedback from a reference cell. Extremely flat, wellcontrolled pulses up to 78 ms were demonstrated. Tests showed the temporal instability 

of irradiance is less than 0.1%, which is an order of magnitude better than that obtained 

with a passive network. The pulse length can be increased to 100 ms or beyond simply 

by increasing the capacitance of the lamp circuit. 

• We demonstrated a method for forming shallow, fine-pitch features in thick copper ribbon to 

reduce stress and maintain high yield in the cell string soldering process. We designed an 

automated ribbon forming assembly that was incorporated into our automated cell string 

assembly equipment. This equipment successfully assembled cell strings made with 220 μm 

thick Cz-Si cells and 178 μm thick copper ribbon. This technology can be applied to reduce the 

breakage rate of thin cells in the string soldering process, and to allow the use of thicker copper 

ribbon to reduce module power loss due to ribbon series resistance. Spire has filed a provisional 

application for a US patent for this technique.4

In the remaining third phase of our program, we plan to fabricate and test the improved large area 

laminator, the module transport automation for the laminator, and the large area sun simulator. We will 

also develop a computer integrated manufacturing system for module line supervisory control and data 

acquisition. 

30 
4 REFERENCES 

1 Tedlar® is a registered trademark of DuPont for its polyvinyl fluoride (PVF) film. 

2 ASTM E 927-04, “Standard Specification for Solar Simulation for Photovoltaic Testing,” ASTM 

International, West Conshohocken, PA, 2004. 

3 U.S. Patent Application No. 10/709,529, “Infrared Detection of Solar Cell Defects Under 

Forward Bias,” filed May 12, 2004. 

4 Provisional US Patent Application, “Corrugated Ribbon and Process for Low-stress Soldering of 

Leads to Solar Cells,” submitted November 2005. 

31 
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1. REPORT DATE (DD-MM-YYYY)

August 2006 

2. REPORT TYPE

Subcontract Report 

3. DATES COVERED (From - To)

1 July 2004–15 October 2005 

5a. CONTRACT NUMBER

DE-AC36-99-GO10337 

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

Development of Automated Production Line Processes for Solar 

Brightfield Modules: Final Annual Technical Progress Report, 1 July 

2004 – 15 October 2005 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/SR-520-40406 

5e. TASK NUMBER

PVB66101 

6. AUTHOR(S)

M.J. Nowlan, J.M. Murach, S.F. Sutherland, D.C. Miller, S.B. Moore, 

and S.J. Hogan 

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Spire Corporation 

One Patriots Park 

Bedford, Massachusetts 01730-2396 

8. PERFORMING ORGANIZATION 

REPORT NUMBER

ZDO-3-30628-12 

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NREL 

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National Renewable Energy Laboratory 

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14. ABSTRACT (Maximum 200 Words)

Spire Corporation is addressing the Photovoltaic Manufacturing R&D project goals of improving photovoltaic (PV) 

manufacturing processes and products while reducing costs and providing a technology foundation that supports 

significant manufacturing scale-up. To accomplish this, we are focusing our efforts on the design of a large-area utilityscale module and the development of the necessary manufacturing techniques and equipment to manufacture such a 

module in a high-volume production environment. A three-phase program is under way for developing and 

demonstrating new automated systems for fabricating very large PV modules ideal for use in multi-megawatt gridconnected applications. We designed a large-area (1.57 m x 3.68 m) 800-W module, and we are developing associated 

module production equipment that will minimize the total installed system cost for utility-scale PV arrays. Activities in 

Phase 2 focused on the development of automation for module materials lay-up, cell string busing, and module 

lamination; enhancements to the cell stringing and lamination processes; and performance testing of large-area 

modules. 

15. SUBJECT TERMS

PV; automated production line processes; modules; manufacturing; large area; utility-scale; high-volume; cell string 

busing; lamination; scale-up 

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