New research from the University of New South Wales (UNSW) is prompting renewed scrutiny of how solar module durability is assessed, after analysis found a significant minority of systems degrade substantially faster than industry averages.
The study, published in the IEEE Journal of Photovoltaics, analysed performance data from nearly 11,000 photovoltaic (PV) systems worldwide and identified a ‘long tail’ in degradation outcomes. This means that while most systems perform close to expectations, a notable subset experience much higher rates of performance loss.
Across the full dataset, researchers observed a median degradation rate of around 0.9 per cent per year. However, around 20 per cent of systems were found to degrade at least 1.5 times faster than this typical rate, and approximately one in 12 systems degraded at twice the average rate.
According to Yang Tang, Lead Author from UNSW’s School of Photovoltaic and Renewable Energy Engineering, there are material implications for the effective service life of affected systems.
“For the entire dataset, we observed that system performance typically declines by around 0.9 per cent per year,” he said.
“However, our findings show extreme degradation rates in some systems. At least one in five systems degrade at least 1.5 times faster than this typical rate, and roughly one in 12 degrade twice as fast.”
At these higher rates, some systems could see substantially reduced output well before the end of their 25-30 year performance warranty period. In extreme cases, the study suggests output losses could approach 45 per cent by year 25.
Why panels degrade
All solar modules experience gradual performance decline over time due to environmental exposure, including ultraviolet radiation, heat, humidity, salt, temperature cycling, wind loading and long-term chemical changes within materials. These mechanisms are already accounted for in performance warranties, which typically specify a maximum allowable annual degradation rate.
However, the UNSW research focused on systems that fall outside these expected ranges, where degradation is accelerated by defects or interacting failure modes rather than normal ageing alone.
The study identified three dominant contributors to accelerated degradation in the ‘long tail’ group:
- Interconnected failures, where one fault (such as backsheet damage) triggers secondary issues such as moisture ingress and corrosion.
- Early-life failures, caused by manufacturing defects or material issues not detected in quality control, often followed by stabilisation after an initial period.
- Latent minor defects, which may not affect performance initially but can trigger sudden and severe output losses later in life.
Notably, the researchers found no strong correlation between these accelerated degradation patterns and extreme climate exposure. None of the analysed systems were located in harsh desert or similarly extreme environments.
Implications for testing standards
Dr S. Poddar, Co-author of IEEE Journal of Photovoltaics, shared that the findings suggest existing qualification and reliability testing regimes may not fully capture real-world failure pathways.
Current standards typically test module responses to mechanical stress, temperature extremes, ultraviolet exposure, humidity and standardised sunlight conditions. However, the study argues that real-world operating environments involve interacting stresses that can trigger cascading failure modes.
“When modules are operating in the field, many different factors come into play, and these cascading failures can be very significant,” Dr Poddar said.
The researchers are calling for broader use of combined stress testing and for greater use of field performance data from large-scale solar farms across different climate zones to inform future standards development.
Australia’s Clean Energy Council currently lists more than 1,500 approved solar module models meeting IEC 61215:2021 standards. While this ensures baseline compliance, the UNSW study highlights the growing importance of long-term reliability data as solar becomes a core part of national energy infrastructure.