Effects of Cerium Removal from Glass on Photovoltaic Module Performance and Stability

Photovoltaic modules are exposed to extremely harsh conditions of heat, humidity, high voltage, mechanical stress, thermal cycling and ultraviolet (UV) radiation. The current qualification tests (e.g. IEC 61215) do not require sufficient UV exposure to evaluate lifespans of 30 years. Recently, photovoltaic panel manufacturers have been using glass that does not contain Cerium. This has the advantage of providing about 1.3% to 1.8% more photon transmission but potentially at the expense of long term stability. The additional transmission of light in the 300 nm to 340 nm range can cause delamination to occur about 3.8 times faster. Similarly, UV radiation will cause polymeric encapsulants, such as ethylene vinyl-acetate (EVA), to turn yellow faster losing photon transmission. Silicones do not suffer from light induced degradation as hydrocarbon based polymers do, therefore if silicone encapsulants are used, a 1.6% to 1.9% increase in photon transmission can be obtained from removal of Ce from glass, with no tradeoff in long term stability. Additionally antimony can be added to non-Ce containing glass to further improve photon transmission (principally in the IR range) by an additional 0.4% to 0.7%; however, this does not significantly affect UV transmission so the same UV induced reliability concerns will still exist with common hydrocarbon-based encapsulants.