Reliability of Silicone Encapsulants in high Pollution Environments.

Photovoltaic cells and their encapsulants are subjected to harsh environments with extremes in solar radiation, thermal/humidity cycling, mechanical stress, electrical bias and increasing levels of pollution. Volcanic action and the escalating use of fossil fuels have increased the threat of atmospheric sulfurous gaseous on silver and other metal contact materials. Twenty years ago Cuddihy et. al., concluded that elastomeric silicone encapsulants were the only technology to meet all the physical, chemical, spectral, and mechanical demands of photovoltaic modules. In the decades since the decision to excluded silicone in this application for cost reasons, the thermal and photo-degradation of Ethylene Vinyl Acetates, EVAs, continues to be well documented. It can be concluded from recent work on water vapor transmission rates that sufficient water can penetrate today´s EVA cells to fuel the corrosion processes mitigating hard fought efficiency gains. Today silicones are in wide-spread use as frame or junction-box sealants in the PV industry to protect against water/moisture ingress into EVA or electrical connections, as well as to protect bypass diodes and soldering points in junction box potting applications. Future forecast are cure speeds will be ramped up, and PV module prices will be progressively driven down, is it time to reconsider this proven silicone technology? Dow Corning Corporation has expanded their studies to include the growing list of sulfur-based industrial pollutants. The results of continuous corrosion rate monitoring of silicone encapsulated silver circuits on glass substrates reconfirms the benefits of silicone encapsulants in this application