Lamination of solar cells

Lamination of solar cells

1. Purpose

Arrange the battery strings according to the process design to prepare for the next step of lamination. The main purpose of lamination is to precisely control the position of the cells in the battery pack (assuming that the cells do not move in position during the lamination process).

2. Bill of Materials

1) 1 piece of tempered glass.

2) Connect 6 battery strings in series.

3) Flux.

4) Bus bars.

5) EVA 2 sheets.

6) 1 backplane.

7) Absolute ethanol.

8) EVA and backboard gaskets.

3. Equipment and tools

1) Stacking table.

2) Constant temperature welding station.

3) Scissors.

4) Sharp mouth deterrent.

5) Templates.

6) Teflon pads.

7) Ruler.

4. Process requirements

1) According to the production arrangement, the team leader is responsible for receiving the battery strings and distributing them to the hands of the stacking operators in each group.

2) The battery strings used are transported by carrying carts, and it is strictly forbidden for personnel to take them directly.

3) The stacking team members go to the designated carrying cart to receive the battery string, and at the same time obtain the process sheet together, and place it in the designated position of the stacking table.

4) Pre-stacking work needs to be prepared before stacking. Take a piece of standard glass from the tempered glass storage place and move it to the stacking table. The stacking staff is responsible for re-confirming whether the tempered glass has obvious defects. If necessary, contact the online IPQC and the team leader of this process in time.

5) Clean the glass surface with a dust cloth and return essence, and ensure that the alcohol is thoroughly swept away, and pay attention to the rough surface of the glass.

6) Take a piece of cut EVA and lay it on the glass surface, the EVA should cover the glass all around.

7) Place the laminated template on the EVA and position it according to the edge of the glass.

8) Clean and check the battery string again. The treatment method is the same as the string welding process. If the solder joints are not flat or the battery pieces cannot be pressed naturally, rework should be performed.

9) Operate with two people, hold the interconnecting bars at both ends of the battery string, and place the battery string on the EVA.

10) Based on the arrangement template, arrange the batteries in series and fix them with 3M tape.

11) When the operator adjusts the spacing of the battery strings, the battery sheets should be in a natural straight state. Due to the tolerance of the module template on the glass surface of the stacking table, when aligning the battery strings, the side should be used as the criterion for adjustment. If the battery string is lifted due to the string tab, it should be reworked.

12) When soldering the head and tail, the actual temperature of the soldering iron is 290~300 ℃.

13) The welding sequence is to weld the tail first, then the head.

14) Under the tail interconnection bar, place a tetrafluorocloth gasket against the battery sheet, and take 3 195mm long busbars to connect the interconnection bars of the 6 groups of battery strings. The bus bar is located under the interconnection bar 3~5mm away from the edge of the cell.

15) Clamp the edge of the solder joint with the left hand and lift it gently, use the electric soldering iron to solder the solder joint with the right hand, remove the soldering iron after the tin is melted, and remove the deterrent after the tin is cooled.

16) Do the rest of the welding on the tail in the same way.

17) Uniformly cut off redundant interconnection bars and busbars, and clean up the waste.

18) Take out the PTFE pad and the lamination template.

19) Under the head interconnection bar, place a tetrafluoro cloth gasket against the battery sheet, take two 220mm busbars and place them under the middle 4 groups of interconnection bars, one on each side of the center line. The bus bar is required to be 3 to 5 mm away from the edge of the cell, and the welding requirements are the same as Article 15.

20) Weld the two bus bars with a length of 75mm on both ends of the 220mm bus bar, pay attention to the alignment when welding, and do not expose the ends.

21) Take two bus bars with a length of 330mm, and lead out the interconnecting bars of the battery string at both ends in parallel, to ensure that the distance between the battery and the battery is 35mm, and the welding requirements are the same as Article 15.

22) Take out the PTFE cloth gasket for welding and the alignment template, and place it in the designated position.

23) Insert the first EVA gasket, the process requirements are shown in Figure 1, pay attention to insert it between the 75mm long bus bar and the battery, and the edge is flush with the edge of the battery.

Lamination of solar cells
Figure 1 – The placement process of the EVA gasket on the head of the module

24) Insert the backplane spacer, the process requirements are shown in Figure 2, pay attention to insert the barcode facing down between the 75mm long busbar and the EVA spacer, and the long side should be aligned with the two 220mm long busbars.

Lamination of solar cells
Figure 2 – The placement process of the backplane gasket on the head of the module

25) The barcode on the backing strip should be the same as the barcode on the flow sheet.

26) Fold the interconnecting strips of the two battery strings on the head in half along the edge of the backboard gasket, and use a deterrent to clamp the folds flat.

27) After folding in half, fix all the bus bars as necessary.

Note that in the overall stack, all the bus bars at the head and tail must be flat, without bending and skewing, the bus bars are folded in place, and there is no short circuit phenomenon.

28) Solder the last two 75mm long busbars to the 330mm busbars, paying attention to the spacing between the busbars.

29) Cover the top layer of EVA, pay attention to cover the glass.

30) Use scissors to cut along the direction of the arrow according to the requirements of Figure 3, here only need to cut regularly.

Lamination of solar cells
Figure 3 – EVA shearing method for the outer layer of the modul

31) Take a backboard and check whether there are quality problems such as scratches, wrinkled skirts, stains, etc. If there is any, contact IPQC and the process leader to replace it. Cover the backplane to the module, and pull out the bus bar from the slit, pay attention to the front and back of the backplane.

32) Lay the 4 bus bar lead wires flat, adjust the position of the backplane, and require that the entire glass must be covered around.

33) Use burlap tape to fix the 4 bus bar lead wires.

34) After the above operations are completed, the components are transferred to the inspection area through the slideway of the stacking table for basic electrical performance inspection.

35) Connect the two outermost lead wires to the black and red alligator clips on the test bench. Note that the left “+” is connected to red, and the right “-” is connected to black. If the connection is reversed, there will be no voltage display on the digital measuring meter.

36) Switch the test meter to the voltage test, turn on all halogen lamps, and record the measured value; then switch the test meter to the current test, and record the measured value. If the voltage is less than 30V or the current is less than 1A, it means that there is a quality problem in the semi-finished product of the module, and inspection and necessary repairs are required.

(Note: Usually, you should do a good job of recording the electrical performance data of the components, and set a lower limit current value. If the data measured by the stacking table is less than this value, you should check the serial connection of the components and the welding of the bus bars.)

37) Turn off all halogen lamps, transfer the qualified semi-finished components to the transfer car, and pay attention to the method of lifting the components.

38) Carefully record all recorded data, operators, brands and models of raw materials in the “Process Flow Sheet” and transfer them to the next process together with the semi-finished components.

5. Quality requirements

1) The spliced components are positioned accurately, the gap between the strings is consistent, the requirement is 2mm, and the error is ± 0.5mm.

2) The positive and negative poles of the series connection bar are placed correctly, and the distance between the battery string and the glass edge is uniform.

3) The selection of bus bars meets the requirements of the pattern, and the bus bars are straight and without creases.

4) The distance between the rear bus bar and the edge of the cell is 35 mm.

5) EVA and backplane should be covered with glass, and be at least 1 mm beyond the boundary.

6) During the splicing process, ensure that there are no impurities, dirt, fingerprints and welding strip residues in the components.

7) The “rough side” of glass, backplane, and EVA faces the battery.

8) The welding quality of the bus bars directly affects the maximum power of the components after the components are laminated, especially if there is virtual welding, the bus bars will fall off and shift during the lamination process, which directly affects the performance and life of the components. The flatness and appearance of the bus bar are also very important, so we must pay attention to the welding method.

6. Notes

1) Note that during the stacking process, the back of the battery is placed upward, and the polarity must not be wrong.

2) Do not use EVA that has been exposed to the air for more than 24 hours.

3) There must be no battery fragments or broken corners entering the module.

4) Do not touch EVA directly with bare hands.

5) The lamination operator is the inspector of the previous process and also the reviewer of the raw materials.

6) The process of cleaning the battery is also a process of inspection. We must pay attention to find out the virtual welding and cracks of the battery in time.

7) It is not allowed to weld the bus bar on the spacer.

8) For some EVA defects that cannot be determined whether they will affect the appearance of the components, the corresponding records should be made after the lamination of the components is completed, and documents should be made for similar situations in the future.

9) The battery string should be kept in a natural straight state.

10) The bus bars should be aligned and pressed firmly before welding, so as to avoid welding crooked for rework. Use deterrents to lift the welding as much as possible. The general principle is to ensure the appearance on the basis of solid welding.