Test-to-Failure of crystalline silicon modules

Abstract

Accelerated lifetime testing of five crystalline silicon module designs was carried out according to the Terrestrial Photovoltaic Module Accelerated Test-to-Failure Protocol. This protocol compares the reliability of various module constructions on a quantitative basis. The modules under test are subdivided into three accelerated lifetime testing paths: 85°C/85% relative humidity with system bias, thermal cycling between -40°C and 85°C, and a path that alternates between damp heat and thermal cycling. The most severe stressor is damp heat with system bias applied to simulate the voltages that modules experience when connected in an array. Positive 600 V applied to the active layer with respect to the grounded module frame accelerates corrosion of the silver grid fingers and degrades the silicon nitride antireflective coating on the cells. Dark I-V curve fitting indicates increased series resistance and saturation current around the maximum power point; however, an improvement in junction recombination characteristics is obtained. Severe shunt paths and cell-metallization interface failures are seen developing in the silicon cells as determined by electroluminescence, thermal imaging, and I-V curves in the case of negative 600 V bias applied to the active layer. Ability to withstand electrolytic corrosion, moisture ingress, and ion drift under system voltage bias are differentiated according to module design. The results are discussed in light of relevance to field failures.

Interlaboratory Study to Determine Repeatability of the Damp-Heat Test Method for Potential-Induced Degradation and Polarization in Crystalline Silicon Photovoltaic Modules

“…A component of the work to arrive at conditions for a standardized test for the effects of system voltage durability comes from field comparisons with accelerated tests [13,14]. Tests show that with system voltage bias applied at 85°C and 85% relative humidity (RH), modules may show seriesresistance degradation outside of the scope of this work.…”

Experimental observations on hot-spots and derived acceptance/rejection criteria

“…1 shows two infrared (IR) images of hot-spots. The anomalies that cause hot-spots can be external to the PV module: shading (Alonso- García et al, 2003;Herrmann et al, 1997;Molenbroek et al, 1991) or dust (Lorenzo et al, 2014); or internal: micro-cracks (Brun and Melkote, 2009;Buerhop et al, 2012;García et al, 2013;Grunow et al, 2005;Paggi and Sapora, 2013;, defective soldering (Buerhop et al, 2012;Chaturvedi et al, 2013;Gabor et al, 2006;García et al, 2013;Muñoz et al, 2008), potential induced degradation (Berghold et al, 2013;Hacke et al, 2010), material imperfections (Vasko et al, 2014). In general, a hot-spot entails a decrease of the operational efficiency of the PV module.…”

Outdoor PV degradation comparison

“…For realistic PV lifespan estimation, the knowledge of power decline over time is essential and important to all stakeholders-utility companies, investors, and researchers alike. Outdoor field testing has played a vital part of determining PV field performance and lifetime for at least two reasons: (1) It is a non-trivial task to correlate indoor testing to outdoor results [2] and (2) it is the typical operating environment of PV modules [3]. A wealth of excellent information has been reported in the literature measuring degradation rates with respect to technologies, age, manufacturers, and geographic locations.…”