Current testing standards have been called into question after new research found that 20% of solar panels tested in one study had a degradation rate 1.5 times worse than average.
Why do solar panels deteriorate?
All solar panels deteriorate over time. This is largely due to natural wear and tear caused by environmental factors such as ultraviolet rays, heat, humidity, salt, temperature changes (causing expansion/contraction, microcracks), wind, and inherent chemical changes.
This results in gradual (and should be small) annual losses in efficiency over the life of a panel. A permissible maximum annual loss is specified in the panel’s performance warranty (more on warranties below), which is typically 25 – 30 years.
Then there are the modules that degrade more and faster than they should due to manufacturing defects and poor quality control. Or fail completely prematurely.
What has research found about solar panel performance?
Researchers from UNSW’s School of Photovoltaic and Renewable Energy Engineering analyzed previously collected information; obtained from almost 11,000 different photovoltaic samples worldwide. They observed a so-called “long tail” in the probability distribution of performance data; This means that up to 20% of all samples perform 1.5 times worse than average.
“For the entire data set, we observed that system performance typically degrades by approximately 0.9%1 per year.” said Yang Tang, one of the authors of the article on the subject. “However, our results show that some systems experience extreme rates of degradation. At least one in five systems is degrading at least 1.5 times faster than this typical rate, and about one in 12 systems is degrading twice as fast.”
This has a major impact on the service life of such panels; This could be closer to 11 years – long before the 25 to 30 years of a warranty ends.
“Or in other words, they could lose about 45% of their production by the 25-year mark,” Tang said.
3 main reasons for panel failures
There were three main reasons for failure in the long tail group:
- Interrelated failures, where different types of problems can interact with each other; e.g. B. damage to the back film, which leads to corrosion damage.
- “Infant mortality” when relatively new panels have critical manufacturing defects or material defects that are not detected during quality control. They tend to show slight recovery and a slower degradation rate after the initial installation phase.
- Minor errors that may not be a problem at first, but then cause a sudden, severe loss of performance at a random time.
The researchers emphasize that the accelerated degradation is not related to the climatic conditions to which the solar modules were exposed. No samples were installed in locations with extreme environmental conditions such as very hot deserts.
What does the study aim to achieve?
Dr. S. Poddar, co-author of the paper, says it is time to think about new testing standards as current standards only report on several parameters. This is the response of a module to mechanical stress, extreme temperatures and exposure to ultraviolet radiation – also often to moisture tests and the response to a standardized amount of sunlight (AM1.5 spectrum).
“But when they’re actually operating in real-world conditions, there are so many different factors at play, and these cascading failures can be very significant,” Poddar said.
The team wants to get even more data from large solar farms and understand different factors that contribute to module failures in different types of climates.
“Third, testing authorities should be aware of real-world degradation patterns in different climates and consider combining stress tests to better replicate outdoor operating conditions.”
The UNSW study was published in the IEEE Journal of Photovoltaics.
Product vs. Performance Guarantees
There are two different warranties for solar panels. There is a product guarantee on materials and workmanship (often 25 years). Then there is the performance guarantee, which guarantees that the performance of the system will not decline beyond a certain point each year, regardless of the number of years; usually 25 – 30 years as mentioned.
For example, the 440-watt JA Solar Deep Blue 4.0 Pro solar module has a 25-year product warranty and a 25-year performance warranty. The guaranteed annual performance degradation is 1% per year in the first year and 0.4% per year in years two through twenty-five. This results in a guaranteed output of 87.4% in year 25.
You can view the product and performance warranties of a range of models in the SolarQuotes solar panel comparison table.
On a related note, last week we published an article about solar panels installed in the 1990s that were subjected to performance testing, which suggested that the maximum degradation levels specified in their long performance warranties were realistic. However, these researchers (a different team) mentioned that the degradation pathways seen in advanced solar cell technology today were not present in the old solar panels tested.
Selection of solar modules
Australians are spoiled for choice when it comes to solar panels; and spoiled with affordable prices. The Clean Energy Council approved module list includes over 1,500 solar module models that comply with international standards IEC 61215:2021.
And given today’s prices for high-quality devices, there is no reason to save – there are many solar panels in the affordable price range.
But how do you find them?
You can use the SolarQuotes comparison table as mentioned earlier. However, an easier way to look in the right direction is to use SolarQuotes’ recommended solar panel brand chart. Since any of these manufacturers should be a safe bet. On this page you will also find recommended brand tables for inverters, home batteries, electric vehicle chargers and heat pumps.
Footnotes
- This 0.9% is still much higher than the annual allowable rate of deterioration stated in major solar panel manufacturers’ warranties, which is typically in the range of 0.25% to 0.55% per year in years 2 to 25. ↩
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