Testing Lab Perspective: Evolving Trends In PV Module Degradation
Source：taiyangnews
Kiwa PVEL shares insights on module degradation trends using in-house test data at the TaiyangNews Virtual Conference
Evolving nature of degradation: Kiwa PVEL provided an insightful presentation of the latest trend in module degradation modes, inferred from the last 3 years' PQP test results. (Photo Credit: TaiyangNews)
Key Takeaways
- Kiwa PVEL delivered an insightful presentation of recent trends in PV module degradation, inferred from the last 3 years' PQP test data
- Recent TC600 test cycle results show there is a slightly higher risk with TOPCon modules compared to PERC and HJT
- The DH2000 test cycle results show multiple manufacturers are compromising on encapsulant quality
- The mechanical stress test (MSS) shows a trend of compromise in modules' frame quality
The growing trend of submitting sample modules with various cell technologies and bills of materials (BOMs) to third-party testing agencies is driven by several key objectives. These include validating new designs and BOMs through extended environmental stress tests, providing value to module manufacturers, and aiding decision-making for buyers, developers, bankers, and insurers.
Kiwa PVEL, a leading independent PV module testing agency based in California, USA, offers a Product Qualification Program (PQP), which forms the basis of its annual PV Module Reliability Scorecard report. At the TaiyangNews Reliable PV Module Design Conference, Tristan Erion-Lorico, VP of Sales & Marketing at Kiwa PVEL, delivered an insightful presentation on PV module degradation trends derived from 3 years of PQP data.
The PQP, which involves extended reliability and performance testing, goes beyond the requirements of IEC 61215 to ensure its relevance to emerging module technologies and potential failure modes. The 10th Edition of the PV Module Reliability Scorecard 2024 includes data from 53 manufacturers recognized as Top Performers and introduces new categories, such as hail performance and stricter criteria for LID+LeTID Top Performers.
Soldering-related degradation: Multiple TOPCon modules are showing soldering degradation issues, caused by cell metallization, as observed in the thermal cycling stress test of the PQP program. (Photo Credit: TaiyangNews)
Thermal Cycling (TC600) test results
The extended thermal cycling (TC600) test, in which a module undergoes up to 600 thermal cycles from - 40°C to + 85°C, helps in identifying cell soldering, metallization, and junction box reliability issues. The degradation rates of PERC and TOPCon cell technology for the last 3 years are aligned, noted the company. However, the 2024 scorecard shows 5 TOPCon BOMs recorded power degradation failure before reaching TC600 compared to just 1 PERC BOM, indicating a slightly higher risk for TOPCon. These TOPCon degradation failure modes have been observed due to the cell metallization issues at the edge of the cell, observed in the EL images as a dark horizontal line. For HJT modules, the TC600 degradation rate is wider compared to peers, while the sample size is much smaller for the last 3 years between Q3 2021 and Q3 2024. However, the testing agency observed an improvement in HJT modules’ BOM in 2023 compared to 2022. The scope of improvement for HJT manufacturers lies in the low-temperature soldering process which is much different for PERC and TOPCon, shared Kiwa PVEL.
Damp Heat (DH2000) test results
Next stress test, the extended damp heat (DH2000), in which a module undergoes + 85°C and 85% relative humidity for 2,000 hours, reveals degradations such as corrosion and delamination. Kiwa PVEL’s last 3 years’ result shows an alignment in PERC and TOPCon degradation results, while the HJT has a wider degradation range of up to 6%. The company has experienced one or more damp heat-related failures, including delamination of the junction box, electrical insulation failure, and power losses of up to 11% BOM. The re-emergence of small bubble formation around the transversal ribbon of the module, which even extends to the cell, is the result of poor lamination quality and the use of thinner encapsulants, suspected the testing agency. The company further warned about the potential risk of this degradation, where the reduction in electrical insulation between the ribbon, cell circuit, and frame can lead to electrical arcing and subsequent fire risk.
Mechanical endurance: Multiple modules showed breakage issues in the mechanical stress test (MSS), caused by the compromise on frame quality, in the PQP test results. (Photo Credit: TaiyangNews)
Mechanical stress sequence (MSS) test results
To validate the module’s mechanical durability and susceptibility to cell cracking-related power loss, the company adopted a mechanical stress sequence (MSS) test, where the module undergoes 3 rounds of 1,800 Pa mechanical loading using either tracker mount or corner mounting. This is followed by 1,000 cycles of dynamic mechanical loading and TC50 + HF10 stress tests. Irrespective of cell technologies, the degradation rates were fairly stable, while module breakage rates during SML and DML have been on the rise, shared Kiwa PVEL. The company shared an instance of a 30 mm frame module breakage issue during the DML stage, placed on top of a 400 mm Nextracker rail system. Additionally, the testing agency has started the mechanical load test for large-size modules including 2,382 mm and 2,384 mm. It shows frequent instances of breakage issues due to the use of thinner frame walls, added the company.
Potential-induced degradation (PID) test results
The PID stress test, featuring a damp heat test and application of 1,500 V maximum system voltage across the module frame and cell circuit for up to 192 hours, doesn’t show any major statistical difference in degradation rate irrespective of cell technology and configuration (glass-glass or glass-backsheet configuration). However, the company has observed major variations in degradation with different encapsulant materials. Further, the company shed some light on the rise of a polarized type of PID degradation, reversible in nature.
Hail stress test results
In the hail stress test sequence, the company impacted 2 glass-glass modules, equipped with 2 mm thick glass each, with a 40 mm hail and conducted subsequent tests with a 45 mm hail impact if there was no glass breakage in the initial test. For the glass-backsheet configuration, the company started with 50 mm dia hail which goes up to 55 mm. The test results show up to 89% of glass-glass modules with 2 mm thick glass experience glass breakage issues, while the rate drops by up to 40% for glass-backsheet with 3.2 mm thick glass.
Additional insights
Kiwa PVEL also discussed other degradation trends, including LID+LeTID, UVID, PAN, and IAM results, providing a comprehensive overview of the evolving challenges in PV module reliability.