Update on International PV Module Quality Assurance Forum

By Sarah Kurtz, NREL

The 3^rd International PV Module Quality Assurance Forum was held at Iino Hall, in Tokyo, Japan on Tuesday, Nov. 27^th, 2012.  Detailed information can be found at: http://unit.aist.go.jp/rcpvt/ci/update/2012/qafj2/index_e.html.

Here is a brief summary of the meeting:

Task Group 1:

In February, Japan published a national standard (JIS Q 8901) for certification of a PV manufacturing quality system.  So far, about 10 certifications have been issued by JET, TUV-Rheinland Japan or VDE Global Services.  JIS Q 8901 requires that the quality system be aligned with the planned functional lifetime (target service life) of the PV module.  Also, Task Group 1 has been writing a PV-specific version of ISO 9001; international differences are being resolved for paragraphs 7 and 8.  Discussions are underway about how to pay for converting the eventual consensus draft into an international standard.  It is hoped that the consensus draft will be submitted sometime in early 2013.

Task Group 2:

Building on the previously proposed test sequence:

1. Visual Inspection
2. EL image
3. Power Measurements
4. IR image
5. Insulation Resistance Testing
6. Wet Leakage Current Testing
7. Dynamic Mechanical Load (based on NP 62782 Ed 1.0)
8. Temperature Cycling, TC/Humidity Freeze Cycling 
(Details to be determined)
9. Visual Inspection
10. EL image
11. Power Measurements
12. IR image
13. Insulation Resistance Testing
14. Wet Leakage Current Testing

This group is starting an experiment to compare DML+TC with extended TC testing up to 600 cycles. DML testing will apply IEC 62782 Ed. 1.0 (+/- 1,000 Pa, 2-3 cycle/ min, 1,000 cycles) followed by TC200.  The power loss, cell cracks, ribbon fatigue, and solder bond fatigue will be measured.  The EL and LSI (Laser Scanning Image) methods for measuring cell cracks will be standardized by SEMI. The results will be reported with a submission of a NWIP at the WG2 meeting in Jamaica.

Task Group 3:

The discussions of this group have joined those of multiple other groups to consider how to test for Potential-Induced Degradation.  A couple of round robin experiments are in progress.  In parallel, field experience data is being collected to identify failure mechanisms including the role of UV and formation of acetic acid.  Task Group 3 is working closely with Task Group 5 to better understand all of the issues.

Task Group 4:

A study at JET confirmed that thermal runaway of the bypass diodes can be seen during high-temperature reverse bias; the timing of switching from forward to reverse bias affects the results.   The importance of potting (in the junction box) on diode failure is being studied by JET and will be presented in February, 2013.

Task Group 5:

As noted above, this group is collaborating on better understanding of the failure mechanisms; a number of new experiments are being started – results will start becoming available in 2013.

Task Group 6:

A proposal was made for a Rating System to add new tests:

• Added thermal cycling, mechanical stress, and diode testing in response to interconnect failures that are observed in the field.

• Added UV exposure since encapsulant discoloration and/or delamination (sometimes leading to corrosion) are frequently seen and the current qualification tests are inadequate for identifying this.

• Additional high-temperature stress to uncover problems not seen at more common temperatures.

• Additional high-humidity stress to uncover problems not seen in dry climates.

It is proposed that the results of such tests be communicated via:

1. Detailed reports for engineers who want to do thorough analysis
2. A high-level summary on the module nameplate
3. Interpretative maps that would be outside of the standards process, showing the relationship between test results and expected field locations in all locations.

Task Group 7:

Is now more focused on snow loads, but continues to discuss both snow and wind.

Task Group 8:

This new group has a kick-off meeting planned in February, 2013 in Golden, CO.

Task Group 9:

This new group is using a survey to prioritize the work that will be tackled first.

Open Discussion

50min. open discussion was held to collect opinions from the participants.

1. PV module manufacturers would have to make a single top grade product since it is very difficult to know where and how their products are finally used and high volume production is needed for cost reduction.
2. It would be a more realistic approach to create a modified version of 61215 to ensure reliability of PV modules.
3. Incentives like lower insurance rates for higher rated modules would be helpful to support promotion of the rating system.
4. Alignment of test methods with field degradation is critical. More efforts should be made for collection of field data and its scientific analysis to understand degradation mechanisms.
5. It is difficult to evaluate the validity of the ascribed functional lifetime in JISQ8901 audit. Clear criteria are desired.

A vote was taken identifying that 74 individuals supported the rating system proposal, while 44 individuals were against.

SEMI, The Grid, December 2012