Peng et al., “Microscopy study of snail trail phenomenon on photovoltaic modules,” RSC Adv., vol. Meyer et al., “Silver nanoparticles cause snail trails in photovoltaic modules,” Sol. Lee, “Snail Trail,” Today Energy Solut., vol. Hagendorf, “Understanding the snail trail effect in silicon solar modules on microstructural scale,” 27th Eur. įigure 1: Photograph of a PV module with snail trails. For example, a 50-100 hour damp-heat test at 85 ☌ and 85% relative humidity in combination with a forward bias current of 8 A has been shown to be able to create snail trails in susceptible PV modules. The has been several testing methods developed for susceptibility for snail trails. They have shown some evidence that the glass frits of silver paste and peroxide additives in the EVA (ethylene vinyl acetate) were the cause to form snail trails. Fortunately, Canadian Solar demonstrated that snail trails do not affect actual solar module performance. The silver nanoparticles from the grid fingers may dissolve and migrate into the encapsulant causing a chemical reaction to cause the discolouration. While a solar cell is generally an effective barrier to protect the moisture coming to the front surface, the cell edges or microcracks are sites where moisture can diffuse to the solar cell front surface. Under operating conditions, the moisture in the surrounding enter the PV modules through the back sheet foil.
It was shown that the discolouration can be caused by a high density of silver nanoparticles within the encapsulation foil just above the silver finger, by silver oxide, or silver carbonate nanoparticles. It has been reported to affect the modules from a wide range of PV module manufacturers worldwide. The formation of snail trails has been related to the ingress of moisture and oxygen via microcracks. This phenomenon typically occurs within several months to several years after the initial installation. Snail Trail (also known as snail tracks or worm marks) have been observed in outdoor conditions, which appears as brownish discoloured contact fingers especially around the cell edges and microcrack areas.
Other than light-induced degradation and potential-induced degradation, there has been another failure mechanism, which affects the reliability of the PV modules.
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