European researchers have compiled a comprehensive guide to the degradation of PV modules, studying the literature and case studies on the subject as far back as the 1990s. Their paper details the primary stressors encountered by modules in the field, the most common degradation and failure modes, and clear definitions for reliability, quality, and testing standards. Their main findings include that methods for assessing and improving system reliability still lack a complete understanding of how combinations of different stresses over different periods of time.
There is a wealth of research into the many different mechanisms that can begin to affect the individual components of a solar module when it is installed outside for long periods of time, and the industry has proven to be able to adapt quickly when unexpected problems arise.
A team of researchers led by Eindhoven University of Technology in the Netherlands has conducted a comprehensive review of the literature on the degradation of PV cells and modules published over the past 30 years. Their work aims to provide a detailed guide to the main stressors encountered by PV modules in the field, and a component-specific guide to the common degradation and failure modes encountered by each.
Their guide, Review of degradation and failure Phenomenon in photovoltaics, has been published in its entirety Estimates of renewable and sustainable energy. The key findings they make from examining existing research in this way is that the next step to improve module reliability is to understand the interaction of multiple stresses over different time periods and develop tests that can take this into account.
“Quality and reliability testing has progressed to a stage where the durability of each component under individual stress can be well predicted, but accurate reliability estimates for a combination of materials under a combination of time-varying stresses are still challenging,” the group explains. “On the basis of this information, strategies can be designed to improve the lifetime of solar power systems and thus reduce electricity costs and improve sustainability, as well as extend the life of solar power modules.”
They note DuPont’s efforts with modular accelerated sequential testing, the US National Renewable Energy Laboratory’s combined accelerated modular testing, and Europe’s Solliance in situ degradation method as leading to progress in this area.
“All three combine multiple stressors, such as light, moisture, temperature, rain, mechanical load, and voltage stress,” the team states. “It is worth reminding that stressors and stress levels outside are uncontrollable and time-varying, while traditional accelerated life testing methods are more monotonous in nature.”
The paper also commends the quick reactions of the PV industry and research communities in developing tests that provide advance warning of weaknesses in degradation mechanisms when they are detected – for example, in the event of a potential breakdown. And scientists warn that the whole combination of factors must be considered in any new materials that solar power producers plan to adopt.
“The new materials must work within the whole package of modules and together with other existing materials,” the researchers add. “Agnostic combined stress tests must be used so that unknown, new special models related to failure modes or BOMS can also be triggered during the development phase. Standardization of such agnostic stress tests is key to the further development of long-life modules and the necessary market acceptance and appreciation of long-life claims.