STS is your “eyes and ears” in the manufacturing lines!

Through our on-site inspections at PV module factories worldwide, STS continuously identifies quality risks that could impact the long-term performance and reliability of solar projects. Below, we share examples of non-conformities recently detected by our inspectors, along with root causes and corrective actions taken. These findings reinforce the value of independent quality control to safeguard your investment.

– Insufficient Overlap Area Between Ribbon and Busbar

To ensure stable electrical connections, the ribbon and busbar must overlap by at least 3 mm after soldering.

During a recent inspection, we found modules with an actual overlap of only 2 mm, falling below the required standard.

Such insufficient overlap can lead to weak electrical connections, increasing the risk of contact failure, hotspots, and reduced module performance over time.

The root cause was traced to unstable string length and ribbon reservation after machine maintenance, with string lengths found to be 1.5 mm shorter than required, directly impacting the final overlap area.

In response, the factory has strengthened operator training, introduced mandatory first-piece and periodic overlap checks, enhanced AI detection for this issue, and added post-soldering overlap checks to the lamination process.

– Bubbles on the Rear Side of the Module 

During lamination, proper temperature settings and process control are essential to ensure that the module layers bond uniformly, without trapped air pockets that compromise durability.

In a recent inspection, our team detected bubbles on the rear side of finished modules – an indication of poor lamination quality.

Such bubbles can reduce the module’s mechanical strength and long-term weather resistance, potentially leading to premature field failures.

The root cause was incorrect lamination machine settings, with the temperature in one chamber rising to a high level, beyond the acceptable range, which disrupted the bonding process.

The factory responded by updating lamination requirements, tightening appearance inspection standards, and implementing regular skills assessments for inspection personnel.

– Hidden Cracks at the Module Corner (via EL Imaging) 

During lamination, modules must be properly positioned and supported to avoid excessive stress, especially at the corners where glass warping is common. Without proper support, the risk of microcracks increases significantly.

In a recent inspection, our team detected hidden corner cracks through Electroluminescence (EL) imaging – these cracks are often invisible to the naked eye but can compromise module durability and electrical performance.

Such cracks may lead to cell breakage, electrical leakage, and reduced energy output over time.

The root cause was traced to inadequate corner support during lamination. Glass warping at the corners, combined with positioning misalignment caused by the lamination frame, resulted in uneven pressure and increased cracking risk.

The factory has since standardized the placement of corner padding to ensure full coverage under the cells, optimized the centering of modules in the lamination chamber, reinforced the lamination frame corners, and fine-tuned lamination parameters including inflation rate, temperature, and pressure settings.