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.
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Solar photovoltaic (PV) electricity is now widely recognised as an affordable, clean and reliable energy source, playing a pivotal role in the energy transition. Its rapid implementation has the potential to help mitigate climate change by phasing out fossil fuel power stations; however, this will require reliable and long-lasting PV modules. While manufacturers typically provide performance warranties of 25 to 30 years, only a few PV modules and systems have demonstrated a proven operational lifetime exceeding 20 years. Current warranties and business plans rely on accelerated ageing tests, which, however, are subject to limitations and provide no insight into the effective lifetime of solar modules. A detailed analysis of six grid-connected PV systems installed in Switzerland during the late 1980s and early 1990s demonstrates that high-quality PV systems (and their components), when built with high-quality materials and components, can achieve lifetimes exceeding 30 years. This highlights their durability and long-term reliability. Through collaborative efforts, we correlated module degradation rates across diverse climates, altitudes, and module bill-of-materials (BOMs); utilised advanced methods to evaluate performance and ageing of modules; and extracted key insights from a 35-year-old solar module technology, highlighting its long-term reliability.