Holistic view of interactions in modules affecting durability - adhesion and snail trails

Abstract

We are introducing our program to study and understand the interactions of photovoltaic module component materials and their impact on module durability from a holistic point of view. While the impact of backsheets and encapsulants on module durability has been studied to a great extent, the role of metallization pastes is significantly less understood. One durability-related aspect of metallization pastes is their adhesion strength to the tabbing ribbons. We have developed methods to control adhesion over a wide range and are among the first to quantify the impact of adhesion on module durability. We present our finding that adhesion does not have a measurable impact on module durability under the conditions tested, even for ultra-low adhesion conditions below 1 N/mm. Another module durability topic that requires a holistic view of interactions between module components is the phenomenon of snail trails on the surface of PV modules, which has become a widespread problem encountered by a large number of module makers and solar farms around the world. Through detailed studies, we have previously been able to link the root cause of snail trails to chemistry in the ethylene-vinyl acetate (EVA), which reacts with silver in the presence of moisture introduced via micro-cracks. We present our continued efforts to develop an in-depth understanding of the mechanisms behind snail trail formation. We investigate the influence of micro-cracks as well as the material properties of encapsulants and backsheets on the rates of water ingression and subsequent snail trail formation. We also discuss the development and effectiveness of accelerated test methodologies replacing the current time-consuming field aging test method to establish snail trail susceptibility and rate of formation and apply them to specific module designs. Data from module field exposure tests is presented to correlate with lab accelerated aging tests.