Degradation Studies of PV Technology Modules Operating in Various Applications in Minas Gerais, Brazil
Abstract
The viability of photovoltaic (PV) systems is directly linked to the operating performance and reliability of the PV modules. This study investigates the durability behavior of modules of different technologies under real operating conditions in several climate zones of Minas Gerais, Brazil. These include ground-based fixed and tracking power plants and floating (FPV) systems. Standard evaluations using visual inspections, thermal infrared imaging, I-V and electrical parameter characterization, and electroluminescence (EL) mapping. Trends in degradation patterns are reported for devices studied over the past 3-decades. Pre-2005 crystalline Si experience irreversible light-induced degradation (LID) due to their p-type substrates (and associated B-O complexes). More severe were issues with encapsulant discoloration, contact corrosion, cracked cells, and delamination resulting in annual degradation rates of 4%-9%/year. Early era a-Si:H and CdTe modules exhibited critical problems with TCO decomposition with average average losses in the 3%-5%/year range. Innovation in device architectures and materials post-2015 has resulted in higher efficiency cells and modules with general positive trends in observed reliability. However, the more rapid introduction into commercial product has led to unanticipated degradation mechanisms that have required innovation in mitigation schemes. This study reports reversible LID and possible LeTID in Al-BSF and p-type PERC modules--with elimination of this effect in n-type PERC. More concerning is shunt and polarization potential-induced degradation (PID) observed in PERC modules. Average annual degradation rates of 1.5%-5%/year are reported for ground-based (tracking and fixed) modules. However, systems exposed to higher irradiance, temperature, ultraviolet, and humidity conditions are shown to have higher losses. This is especially determined for the research floating PV (FPV) experiencing significant PID-shunt. In contast, more recent thin-film CdTe and bifacial n-type modules on this same platform exhibit negligible losses over a 2-year period.
Keywords
PV degradation, durability, reliability, PV modules, systems, solar cell technologies