Solar Array Lamination Guide

Overview

To us, lamination is simply the process of coating the solar modules in a layer of protective polymer. The degree of care and precision we take in laminating each module can have a significant effect on the effectiveness of the entire solar array. We want to avoid bottlenecking the professionally laminated array by being careless with our own.

Step 1: Binning

The process of binning means performing measurements on each unit of a product to determine its relative performance. In our case, we will measure the IV curve of each cell under identical irradiance and temperature. Follow the following procedure to bin the cells:

Wash your hands and put on latex gloves. Avoid touching the top blue part of the cells; hold them by the edges as much as possible.
Hold the cell to your ear and gently bend it in each direction. If you hear any “tick” sounds that indicates microfractures in the crystal that will impact performance. Place this cell aside; it should not be used.
Place the cell face up on the UV test bench, optimally in a room with no windows and low light conditions. Connect the cell to the curve tracer** and record the Voltage at max power(Vmp), Current at max power(Imp), Voc, and Isc.
The most important characteristic we test for is Imp since a poor performance in that parameter would limit the rest of the module, and possibly the array. Separate into bins by Imp performance, or by max power. Make modules using the highest bin first, then move on to lower bins.

**If you don’t have access to a curve tracer, cells can be primitively binned by Isc and Voc alone

Step 2: Soldering

Soldering is the step where you are most likely to crack a cell. If possible, use a heat gun and solder paste. It is possible to do it with a soldering iron, but avoid putting pressure on the cells or applying too much heat.

Wash your hands and put on latex gloves.
Place each cell in the module in the spacing grid face down, ensuring that you face the positive ends of each cell to the negative end of the next cell. It should have a +/- symbol on the back of the cell, but you can also check with a voltmeter.
Connect each cell to the adjacent ones with Kapton tape between the solder pads. Peel each side of the tape so that the dog bone connectors stick to it. This is easiest to do with a razor blade. Be very careful not to press your hands on the cells when you do this.
Put solder paste on each solder pad, use less than you think you need, and solder only one cell at a time. Lay the dog bone connector on the joint, sticking to the Kapton tape, and melt the solder paste with the heat gun. You can use tweezers to hold the dog bone connector down if it resists.
Repeat step four for all cells. There will be one pair of cells that must be connected that can’t be done with dogbone connectors because the cells aren’t facing each other. Solder a strip of aluminum across these pads to make the connection.
Solder a bypass diode from the negative terminal of the entire module to the positive terminal of the module. Run the aluminum strip along the side of the module to complete this connection. Ensure that the diode points from the negative to the positive terminal. Check this with the multimeter.

Step 3: Assembling the stack

Wash your hands and put on latex gloves.
Preheat the oven to x temperature.
Cut a piece of vaccum bag about an inch larger than the module in each dimension.
Cut two pieces of release fabric about a half inch larger than the module in each dimension.
Cut single and double-sided teflon to about a half inch larger than the module in each dimension. If you need to determine which is single-sided and double-sided, you can draw a small line on each side with a Sharpie. The Sharpie ink will stick to the textured side of the single-sided teflon, but not to the untextured sides.
Cut EVA about a quarter inch larger than the module in each dimension. It is important that it extends outside of the module, but is not larger than the teflon. This ensures that it seals the sides of the teflon to each other, but does not get glue stuck on the vacuum bag.
Use Isopropyl alcohol or Isopropyl alcohol wipes to thoroughly clean both sides of both teflon pieces and the vacuum bag.
Put 4 squares of double-sided Kapton tape on each cell, peeling the film from the back using a razor blade. Be careful not to press down on the cells when doing this step. This is one of the easiest steps to damage cells.
Assemble the stack as follows: On the bottom is the first release fabric piece, then double-sided teflon, then you place the module face up on top of the teflon, sticking the kapton tape to the teflon. Do not press down on the cells to secure them to the tape. It only needs to be secure enough to prevent the teflon from shifting around. Then, put the EVA on top of the module, then the single-sided teflon with the textured side facing down towards the EVA, finally, place the second piece of release fabric on top of the teflon.
Once the stack is assembled on the tray, stick the thick double-sided sealing tape in a tight rectangle around the edge of the module. Avoid getting this tape dirty; it is your seal and will be a significant factor in ensuring the quality of the module.
Pull the vacuum bag taught and lay it over the stack, pressing down on the parts over the tape to ensure a good seal.

Step 4: Pulling Vacuum and Baking

Wash your hands and put on latex gloves.
Make a small slit in the vacuum bag, use this to insert the vacuum nipple, tightening it down to ensure a tight seal.
Connect the nipple to the hose on the vacuum pump and place the tray in the preheated oven. Close the oven door with the tube closed in the door and turn on the vacuum. Optimally, you want the vacuum to have a pressure of around -13 to -14 psi. If our pump can’t get there, just set it to the lowest pressure it can go.
Allow the stack to cook for 30 minutes.
Remove the tray from the oven carefully and set it on a heat-resistant surface. Allow the stack to fully cool to room temperature before turning off the vacuum and removing the bag.