STS is your “eyes and ears” in the manufacturing lines!
As we do every month, we’re reporting here on our findings from the latest PV module manufacturing inspections, where we’ve identified a few non-conformities worth sharing:
– Lack of “Positioning Tape” on the Pre-lamination Layup
The cells are held in place during lamination by applying, before lamination, what is known as “positioning tape”.
The module shown on the picture did not have any positioning tape applied, running a risk of the cells being displaced during lamination. This can potentially cause many issues, such as shorts, hotspots, misfunctions, etc.
The root cause analysis performed by STS staff identified several issues occurring in parallel: first, it appeared that factory personnel did not follow the schedule of maintenance of the tape-applying tool. One of the suction cups from the taping machine got clogged and therefore did not work properly. Additionally, the alarm systems in place were not setup properly and failed to inform the staff of the malfunction. Maybe even more importantly, there was no proper inspection performed by the factory staff; the issue was not identified before STS intervened.
Following STS’ inspection, the factory implemented corrective actions, which include regular maintenance intervals, switching cleaning agents, verifying tape thickness, and implementing automatic shutdowns for timely maintenance reminders.
– Insufficient Soldering Area for Cell and String Connectors
The cell strings are connected to the junction box via tin-plated cupper ribbons called “string connectors”. The area of soldering between the last cell of the string and the string connector should be sufficiently large to avoid any parasitic series resistance.
In this case, only the tip of the wires are connected to the string connector. This may create hotspots, or even complete disconnection from the wires to the connector, potentially reducing the conversion efficiency of the module.
Root cause analysis revealed that the equipment positioning the string connector was not maintained properly, and the parameters were not adjusted properly. This caused the string connector to be positioned too far from the cell.
After the issue was pointed out by STS, the factory implemented some additional training for process control and introduced a belt replacement plan with the responsible personnel assigned to monitor performance.
– Edge Bubbles on the Laminated PV Module
Modules should not display any air bubble trapped into the encapsulant material. Air bubble may expand during the lifetime of the module, may merge into larger bubbles, with the potential to delaminate the materials, and create path for leakage current, or insulation faults.
This module shows numerous bubbles on the edge of the laminate.
The root cause was traced to dust accumulating inside the laminator and blocking air flow. The laminator was therefore not evenly applying pressure, leading to bubble formation.
In response of this non-conformity identified by STS, the factory implemented corrective actions: modifying the maintenance schedule to include cleaning of the inflation valve; confirming machine condition post-maintenance with quality inspection personnel; and adopting double valve inflation channels to minimize the risk of future blockages.
– Bubbles Trapped in Frame Adhesive
Similarly, we expect no air bubbles in the adhesive used to attach the frame to the laminate. These bubbles may reduce the mechanical stability of the assembly, and create a conductive path which may lead to a ground fault.
The root cause analysis identified two main root causes. First, an adhesive gun head was found to be damaged, and not replaced on time. Secondly, the line was not purged well when the adhesive barrel was replaced. Air was trapped in the line and dispensed on the module together with the adhesive.
Following STS inspection, the factory implemented regular glue gun head replacements, increased purging times, increased spot check frequency, and provided staff training on identifying and reporting glue line bubbles to prevent further occurrences.
– Bubbles in Junction Box Glue Potting
Similarly, the material which is used to pot the junction box needs to be free of any air bubble. Bubbles trapped in this material can trigger short-circuit between the different live elements of the junction box, damaging the junction box as well as the module.
The root cause identified that the operating instructions for cleaning the dispensing system were not adequate. The maintenance was therefore not performed correctly, and some crystals formed inside the lines. These crystals were hindering the flow of potting material, creating bubbles during dispensing.
In response of this non-conformity identified by STS, the factory introduced cleaning protocols for the adhesive pump, re-trained staff on cleaning steps and frequency, ensured stable flow rates, revised the adhesive sample inspection method, and increased personnel for inspections during curing to verify proper potting and cleanliness.
– POE Residue on Rear Glass
The glass surfaces (front or rear) are expected to be free of any stain or contaminating materials.
On this module, we see visible stains of what was identified as encapsulating material (“POE” or “polyolefin encapsulant”). This material may collect dirt and other contaminant, increasing parasitic absorption and therefore reducing the module efficiency.
The root cause identified a chain reaction starting with a production issue at the downstream frame assembly step. During the time the frame assembly was being fixed, the line was stopped and modules upstream from this step stayed in place, instead of moving forward. Some modules were stopped at the exit of the laminator, on a hot zone. Because of this extra heat, the POE overflew onto the laminator’s belt. When the line started again, this overflow contaminated the rear side of subsequent modules.
Following STS inspection, the factory implemented new measures to avoid that modules are stopped at the lamination step when a manufacturing problem occurs downstream. They also cleaned the affected modules and the laminator itself and implemented enhanced cleanliness checks at the following inspection and cleaning stations.
Having a third-party inspection body conduct quality checks before shipment is crucial for PV module buyers to protect their investment and ensure long-term performance of their solar systems. These inspections identify manufacturing defects, such as those detailed above, that can affect the modules’ efficiency, durability, and safety.