PV Module Quality Assurance

 

Optimizing Solar Power Plant Investments: 

PV Module Quality Assurance 

  

"Aren't all solar modules basically the same? Is quality control even necessary?"

As the most critical power-generating component of a solar power plant, any module failure can lead to consequences ranging from financial losses to severe safety hazards, such as electrical leakage or fire. It is certainly not something to be taken lightly.

In this article, we will examine what key aspects need to be controlled in PV module manufacturing—and what risks you face if quality control is neglected. 

 

Before Selecting a Supplier: Factory Audit

Prior to selecting a supplier, it is essential to fully understand their production line status, quality control execution, and technical capabilities. Every manufacturer knows how to market themselves, each claiming superior technology and top-tier quality management. However, once professional auditors step onto the production floor, the reality becomes immediately clear. We have encountered many module manufacturers with polished public images, only for their factory management to be deeply disappointing—and even global Tier-1 manufacturers have let us down.

There are many reasons why factory management fails to meet expectations. For instance, acquired facilities or outdated production lines often result in low operational efficiency and unstable product quality. High employee turnover can lead to insufficient staff training, causing low yield rates. Due to these systemic issues, even manufacturers with good intentions often lack the capacity to maintain consistent quality.

A thorough production line audit must identify these underlying issues and oversee necessary improvements. For manufacturers whose capabilities fall significantly short, we advise clients to exclude them from consideration. This prevents high operational risks post-installation or project delays caused by failed pre-shipment inspections.

 

Case Study: While most factory audits conclude with recommendations for localized improvements, this was one of the rare cases where we directly advised halting procurement. This international manufacturer’s overseas facility suffered from poor management due to local cultural factors and language barriers. Worse still, the equipment had severe operational issues: excessive flux residue presented high risks of module delamination. Yet, the technical staff exhibited zero "problem awareness"—since the issues were invisible after module encapsulation, no corrective actions were ever taken. Ultimately, we issued a record-breaking 48 non-conformances, including five major findings. Judging that the factory could not complete the required rectifications in the short term, we recommended that the client switch suppliers.

 

Excessive flux residue can cause severe issues, such as EVA yellowing and delamination.

 

Special Reminder: Do not be misled by glossy marketing brochures or polished websites. Even Tier-1 manufacturers operate both high-performing and sub-par facilities; only an on-site audit can reveal the true quality of the products you are purchasing.

We also strongly advise project owners to conduct factory audits before finalizing supplier selection. If corporate procedures mandate selecting a supplier first, ensure that you reserve sufficient time and flexibility in your schedule. This prevents project disruptions if a supplier change becomes necessary after the audit, or provides the factory with enough time to implement required improvements on the production line.

  

During Module Production: In-line Manufacturing Supervision

The purpose of in-line manufacturing supervision is to ensure that the production of a specific batch strictly complies with required quality control standards. While a factory audit verifies that the facility possesses a viable Quality Management System (QMS), in-line supervision ensures that the factory actually executes its established Quality Control (QC) plan. Today, most PV module manufacturers have comprehensive QMS frameworks with quality documentation as thick as a dictionary; however, much of this is created merely for client audits, and whether these procedures are rigorously enforced in daily operations is another matter entirely.

 In-line supervision verifies QC execution through randomized sampling across incoming quality control (IQC), in-process quality control (IPQC), and final quality control (FQC). Inspectors also conduct routine line walks to ensure proper bill-of-materials (BOM) usage and identify potential risks in manufacturing processes or workmanship. When doubts arise regarding materials or production processes, auditors have the authority to quarantine the affected batch to prevent shipment—or, in severe cases, halt production until corrective actions are fully implemented. As one can imagine, inspectors must possess extensive module manufacturing experience and deep technical knowledge to spot latent risks within routine production activities.

 Case Study: Improper parameter settings during cell tab-soldering (stringing) can lead to poor solder joint quality. The image below shows an example of a cold-solder joint (poor bonding), where the solder ribbon is not securely attached to the cell busbar. This flaw leads to increased internal resistance, power loss, or even complete electrical open-circuiting. When soldering defects stem from incorrect process parameters, they typically affect the vast majority of solar cells, resulting in widespread issues across most modules in the production run. 

Poor soldering quality results in the solder ribbon failing to bond with the solar cell.

 What makes this issue even more problematic is that it becomes invisible once encapsulated. During the lamination process, the solder ribbons and cells are tightly pressed together, allowing electrical conductivity immediately after production and making the defect undetectable during factory Electroluminescence (EL) testing. However, once installed in the field, exposure to thermal expansion and contraction alongside environmental stresses will cause these poorly bonded solder ribbons to detach (as shown in the image below), leading to power degradation loss and hot spots. 

Modules with poor soldering quality deteriorate over time after installation, resulting in dark spots/inactive areas.

 

Special Reminder: Many process-related defects become invisible once the product reaches the finished goods stage. Therefore, in-line manufacturing supervision is essential to uncover these hidden issues—a critical value that pre-shipment inspections alone cannot replace.

  

Before Module Shipment: Pre-Shipment Inspection (PSI)

The purpose of Pre-Shipment Inspection (PSI) is to evaluate the overall quality of a specific batch of products. However, many issues that occur during production become invisible in the finished product—such as the poor soldering quality mentioned earlier. Standard PSI can only inspect physical appearance, Electroluminescence (EL) images, and electrical performance parameters to judge product quality. In addition to these standard checks, our inspection process specifically includes a thorough audit of production logs and records, where experienced auditors can uncover latent product defects.

 Case Study: Some clients believe that power generation capability is the only thing that matters and that cosmetic appearance is secondary; however, this stems from a misunderstanding of the true purpose of inspection. In reality, visual inspections target defects that pose direct risks to module power output, long-term reliability, or even system safety. The image below illustrates a case discovered during our inspection, where solder slag/droplets were present between interconnect ribbons. While a brand-new module may maintain normal electrical insulation due to a thin layer of EVA separation, moisture ingress over time will degrade the insulation properties of the EVA. This eventually leads to short circuits, localized overheating, and burn-through.

 

Inspection revealed solder slag bridging across interconnect ribbons 

A module burned out due to a short circuit between interconnect ribbons 

Special Reminder: Inspections are typically conducted based on the acceptance criteria agreed upon by both the buyer and the seller. Therefore, documents specifying shipment inspection standards, testing methodologies, and non-conformance handling protocols should be explicitly included as contract annexes. Otherwise, if inspection results fall short of expectations, requesting returns or replacements at that stage can lead to major disputes.

Furthermore, the stringency of inspection standards directly impacts module manufacturing costs (and consequently, pricing). Both parties should finalize these standards prior to signing the contract and incorporate them as part of the module specifications to prevent future conflicts.

 

Summary

In practice, return on investment (ROI) and budgetary constraints are always primary considerations. Therefore, we suggest taking a phased approach:

l Tight Budget: Prioritize Pre-Shipment Inspection (PSI) to mitigate baseline risks.

l Moderate Budget: Step up to In-line Manufacturing Supervision for more comprehensive risk reduction.

l New Suppliers: Implement Factory Audit when procuring from unfamiliar suppliers for the first time—especially given the recent trend of project owners sourcing modules overseas, where an audit is essential to avoid costly pitfalls.

 

 

About the Author

Jay Lin, warmly known as Dr. Jay among industry peers:

• 2004: Engaged in solar module R&D at the Industrial Technology Research Institute (ITRI).
• 2005: Partnered with TÜV Rheinland to establish Asia’s first solar testing and certification laboratory in Taiwan.
• 2007: Served as CTO at a2pak Power, a German-backed solar venture.
• 2011: Founded PV Guider, a consulting firm providing professional advisory services and solar power plant quality control solutions. 

Current Roles:

• Chief Consultant, PV Guider
• Task Force Leader / Chairman, SEMI Standard Committee
• Member, Technical Committee of CNS National Standards
• Technical Expert, IEA PVPS Task 13 (Photovoltaic Power Systems Programme - Solar Reliability Workgroup)
• Technical Committee Member, European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC)