Three decades, three climates: environmental and material impacts on the long-term reliability of photovoltaic modules

Abstract

As the world has entered the terawatt age of photovoltaic (PV) deployment, ensuring long-term reliability is more critical than ever for the global energy transition. This study analyses the long-term performance of six PV systems in Switzerland over three decades, with more than 20 years of high-quality monitoring data. The plants feature modules from the same family (AM55 and SM55) installed across varying altitudes and climates, providing a unique dataset to compare performance trends under different operating conditions. Using the multi-annual year-on-year (multi-YoY) approach, system-level performance loss rates (PLR) were assessed, averaging just −0.24 ± 0.16% per year, well below the commonly reported range of −0.75% to −1% per year in the literature. Laboratory analyses further revealed that higher thermal stress in low-altitude systems (up to 20 °C warmer) accelerated encapsulant degradation and acetic acid formation, contributing to localised corrosion and higher performance losses. Importantly, the bill of materials (BOM) is identified as the most critical factor in ensuring PV module longevity – with modules manufactured with lower-quality materials showing markedly higher degradation rates – followed by climatic influences. Indoor laboratory measurements confirmed that most modules retained over 80% of their initial nominal power after 30–35 years in the field. These findings highlight the durability of early 1990s module designs featuring EVA encapsulants, Tedlar backsheets, and robust framed glass/foil structures, supporting lower levelised cost of energy (LCOE), reduced carbon footprints, and extended performance warranties.