IEC qualification identifies early design failures but does not establish long-term module durability or production consistency
Extended stress testing revealed significant performance differences among six TOPCon modules, particularly in thermal cycling and damp heat
Factory audits, batch testing, BOM verification, and pre-shipment inspections help identify quality issues before modules reach PV projects
Rapid changes in PV module design and technology are bringing new reliability considerations, making it challenging to assess long-term performance based on standard qualification tests alone. IEC certification helps identify early failures in module designs, but it does not necessarily establish their durability over an expected service life of 25-35 years or ensure consistent quality across production batches.
At the TaiyangNews Reliable PV Module Design Conference 2026, Max Köntopp, Global Business Segment Coordinator for Power Plants at TÜV Rheinland, discussed the gap between standard qualification and long-term reliability assessment. He highlighted the importance of extended stress testing and supply chain quality assurance, particularly as the industry moves from PERC to TOPCon, back-contact (BC), heterojunction (HJT), and eventually perovskite-based technologies.
Every change in module design can introduce new or insufficiently understood failure modes. Project developers and investors need confidence in module performance well before products have accumulated many years of field operation. IEC 61215 and IEC 61730 are the basic qualification standards used to assess PV module design and safety. Köntopp noted that extended stress testing has therefore become increasingly important for assessing potential degradation and failure mechanisms that basic qualification may not adequately cover.
Another limitation of standard qualification is that it is generally a one-time assessment conducted before mass production. Passing the test does not ensure that every module manufactured afterward will maintain the same quality. Differences in manufacturing processes, materials, handling, and transportation can affect the quality of the delivered batch.
The IEC 63209 series provides a basis for extended stress testing, and companies adopt its protocols into their own assessment programs. TÜV Rheinland has also introduced an extended bankability program that combines reliability and performance evaluations to provide a more quantitative comparison of module products.
Köntopp identified three complementary requirements to the standard qualification: extended stress testing to assess product durability, specific test protocols to address newer or emerging failure modes, and batch-level testing and production monitoring to verify that commercial modules maintain the quality demonstrated during qualification.
TÜV Rheinland’s assessment program includes test sequences for ultraviolet-induced degradation (UVID), light and elevated temperature-induced degradation (LeTID), and potential-induced degradation (PID), along with extended UV exposure. The program also evaluates shading response and energy yield under different climatic conditions.
To demonstrate the application of the program, TÜV Rheinland evaluated modules from six TOPCon manufacturers using its extended stress test sequences. All six modules passed the assessment, although the results revealed considerable differences in performance across individual tests.
The assessment results are classified based on reliability and performance. The reliability classification considers results of different stress tests, with greater weight assigned to tests associated with more significant power degradation or product failure. These include temperature cycling, damp heat, PID, and mechanical stress sequences. The performance classification considers energy yield and shading response. Energy yield accounts for 80% of the performance rating and is calculated using module temperature coefficients, low-light performance, and climate profiles representing different regions. Modules assessed in this program get a score based on their performance across the test sequences, allowing products to be compared and ranked. The assessment takes approximately six months.
Köntopp emphasized that even a well-performing module design does not guarantee that the modules delivered to a project will meet the same quality expectations. Manufacturing consistency, material changes, handling, shipping, and installation can all influence the final product. Defects identified only after installation can result in rework, energy yield losses, warranty claims, and additional project costs.
Several measures can reduce these risks, including supplier qualification and factory inspections, continuous production supervision, certificate reviews, sample testing, and bill of materials (BOM) verification during production. Electroluminescence (EL) inspection of modules before shipment can also help identify defects, and for larger-format modules, mechanical configuration testing together with mounting will cover tracker-based installations. Larger modules with thinner glass, particularly thin rear glass in glass-glass configurations, can create mechanical stability challenges when combined with trackers. Increasing hailstorm risks have also led to the availability of extended hail testing.
Köntopp also discussed the importance of verifying the actual power output of delivered modules. According to TÜV Rheinland’s testing experience, most modules tested in its laboratories around 10 years ago delivered power above their nameplate ratings. However, around two years ago, most tested modules were found to be below their stated ratings. The situation has improved somewhat since then, but he advised project buyers to verify that the modules supplied meet the specified power requirements.
Watch the full presentation by Max Köntopp here.