One size does not fit all for solar PV module reliability

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The results of the PVEL Module Reliability Scorecard 2014, released today by GTM Research and PV Evolution Labs, are likely to disappoint those looking to draw easy conclusions about comparative solar PV module reliability.

The scorecard looks at the performance of modules under six different reliability tests, including damp heat, thermal cycling and vulnerability to potentially induced degradation (PID). In reviewing the findings, GTM Research reports that companies whose modules scored well on one test did not necessarily score well on another.

The tests are based on PVEL’s highly accelerated lifetime testing (HALT) programs, which are designed to imitate real-world conditions and identify potential long-term quality issues and failure modes. As such, the test goes beyond the IEC 61215 and UL 1703 standards, which can identify early failures but do not look at lifetime degradation.

GTM Research notes that not only did the performance of individual manufacturers’ modules vary from test to test, but that results also did not suggest larger conclusions based on geographic origin of modules, or the size of manufacturers. “There weren’t any discernible trends,” notes GTM Research Director of Solar Research MJ Shaio. “Every test was different.”

The company notes that one module maker did perform relatively well across all test categories; however it is not revealing which one. Each test included randomly selected modules from at least 10 manufacturers, and GTM Research has named Yingli, Trina and Kyocera among the participating companies.

The company has noted that the tests revealed potential concerns about certain failure modes. One of the widest ranges of performance was recorded in the PID test on negatively biased modules, where a number of modules performed very poorly.

“Though manufacturers are claiming to be PID-free, we don’t see those results very clearly in our analysis,” notes MJ Shaio. “We saw manufacturers who did not degrade, we also saw manufactures to degraded completely after the test.”

However, negatively biased/positive ground modules make up only a small portion of overall installations, and on the PID test for positively biases modules performance was much better.

Another area of concern identified was thermal cycling. “No module manufacturer was immune to thermal cycling,” notes GTM Research Solar Analyst Jade Jones. She also notes that in coming years many PV modules will be installed in regions where this is an important factor.

Overall, GTM found that the modules performed relatively well, and Shiao says that the report can help installers and buyers make more careful purchases based on specific properties. “Module quality isn’t a single characteristic,” notes Shiao. “You have to look at where the system is being installed and what is the system topology that we are looking at.”