Performance and degradation analysis for long term reliability of solar photovoltaic systems: A review

Electricity generated using photovoltaic (PV) technology can only be economical if the PV modules operate reliably for 25-30 years under field conditions. In order to ensure such levels of reliability PV module undergo stringent qualification tests developed as per international standards by International Electro-technical Commission. These tests provide excellent information regarding module design, material and process flaws which can lead to premature failure. Even the well qualified modules are found to fail or degrade more than their expected levels when exposed to the outdoor conditions, indicating that these tests are not adequately addressing the real outdoor conditions and are not sufficient to estimate the module lifetime. Keeping in view this aspect, the performance and degradation analysis studies of solar photovoltaic modules, accelerated aging testing under laboratory and outdoor field testing conditions, are reviewed. The factors affecting the performance of PV module, PV module degradation modes, stress factors responsible for degradation, accelerated aging tests and current PV module qualification standard tests are also discussed along with recently used techniques for the failure mode analysis of PV modules. The main objective of the study is to review the literature on performance and degradation of PV modules under outdoor operation for identifying research gaps for long term reliability of PV modules and improving the PV qualification standards for various geographical and climatic conditions.