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While buying solar panels, often we ask:

• Will solar panels perform as expected?
• Are they durable?
• Can I trust warranties?

With rapid decline in prices, solar panels are being deployed to save electricity bills or to get electricity. As initial cost of investment on solar panels is high, customers have more concerns on reliability.

This article examines how solar panels (especially crystalline technology – Poly and Mono) fared on performance and durability over years. Crystalline technologies are chosen as they are the most common panels used for commercial applications.

What Field Studies from Reputed Institutes Reveal?

NCPRE, IIT Bombay Field Surveys

National Centre for Photovoltaic Research and Education (NCPRE), IIT Bombay and National Institute of Solar Energy (NISE), Gurugram have been testing solar panels from various installations across India. The results of the testing are reported in All-India Survey of Photovoltaic Module Reliability – 2016 & 2014.

In 2016, NCPRE tested 1,000 modules of different technology from 37 sites spread across India. It reported results of 397 crystalline technology panels as Group X. The results threw interesting results on performance and durability of solar panels.

• Panels from large plants (>100kWp) performed as expected.
• Panels from Small plants (<100 kWp) performed poorly.
• On durability, plants that are older are performing well compared to recent plants.

Performance is measured as decrease in power output from first year. The average decrease of power was about 0.71% per year in large plant and 0.98% per year in smaller plants. Also, the spread of degradation is very narrow among panels of larger plants and wide among small plants. The degradation reported in large plants is in-line with expectations.

Reasons for more degradation in smaller plants were explained by results from Electroluminescence tests (EL Tests). The tests showed more cracks in panels from small plants compared to panels form large plants. These cracks are often related to poor quality and practices of installation.

Durability is delivering performance over life time. From the study, Modules used in older plants performed better compared to younger modules irrespective of size of plant. The degradation in younger modules is higher.

The study explains “lower performance of younger modules indicate that the quality of the modules themselves or the installation practices being adopted in recent years are inadequate. Also, the possibility that some of the young modules are over-rated cannot be ruled out.” 

It also observes price pressures on suppliers could have led to lower quality in recent times.

The National Renewable Energy Laboratory (NREL)’s Field Study

The National Renewable Energy Laboratory (NREL) has been studying degradation and failure rates of solar panels deployed in the field. According to NREL study on 54,500 solar panels of various ages, the failure rate of the solar panels is on the decrease. From a median failure rate of 10 panels per 10,000 panels installed in between the year 1980 to 2000, the failure rate has decreased to 5 panels per 10,000 annually for the panels installed between 2000 to 2015 i.e. a median failure rate of 0.05 percent.

NREL defined failures as number of panels returned for replacement. Though this definition is conservative, the decrease in failure rates indicates improvement in solar panel’s reliability.

NREL’s Dirk Jordan, a Senior Reliability Engineer and Data Analyst since 2009 at NREL, contributed for the study and reporting of solar panels reliability. “Compendium of Photovoltaic Degradation Rates, NREL 2015” authored by him published degradation data of about 1,500 crystalline silicon panels deployed across world.

About 80% of the modules’ degradation rate is in-line or better than warranties promised by panel manufacturers.

NREL claims well-built solar modules last for an average of 30 years while having a manufacturer’s warranty of 25 years which is way more than the average payback period of the solar panel.

What Reputed Lab Tests Reveal?

PVEL and DNV GL conduct independent lab tests every year to understand reliability of solar panels. In six years, the test covered 50 manufactures and 300 BoMs. The sample represents over 70% of 2018’s Bloomberg New Energy Finance “Tier 1” manufacturers list. The tests are more rigorus compared to tests done by module certification bodies and reflect field performance better. Every year, they publish PV Module Reliability Scorecards.

In 2018 report, DNV GL observes overall improvement in reliability compared to previous years.

• 9% of BOMs submitted failed one or more of the test criteria
• 12% of model types failed one or more of the test criteria
• 22% of manufacturers had at least one failure according to the test criteria

It also concludes that with 22% of manufacturers experiencing at least one failure in overall testing, buyers being conscious of the specific Bill of Materials (BOM) that identifies specific models as Top Performers is crucial.

Conclusion

When quality standards and good practices in installation were followed, solar panels delivered results. This is validated by results from rigorous lab tests as well as field studies. Therefore, as a Technology, solar panels are reliable.