IEC 61215-2 provides a set of qualification tests that indicate that a PV module design is likely to be free of flaws that will result in early failure. However, IEC 61215-2 does not address the long term wear-out of PV modules. This part of IEC 62788-1 is designed as a more rigorous qualification test, using accelerated UV exposure at elevated temperature to determine whether polymeric encapsulants can suffer loss of optical transmittance. IEC 61215-2 already includes a UV preconditioning test (MQT 10), however, the parameters for that test only represent a limited level of exposure (~weeks of UV dose). This test procedure is intended for representative coupon specimens, applying stress at a greater intensity (designed relative to Phoenix, AZ), using a radiation spectrum that is more similar to the terrestrial solar spectrum, and using a duration of exposure that is more relevant to the PV application (i.e., equivalent to several years of outdoor exposure). This test quantifies the degradation rate of encapsulants so that the risk of the materials losing optical transmittance during operation in the terrestrial environments can be managed. The quantitative correlation between climate (or location of use), a specific application (utility-installation, residential-installation, roof-mount, rack-mount, use of a tracker, the system electrical configuration and its operation), and the test can be established for each specific encapsulant material, but is beyond the scope of this document.
The method herein is intended to qualify encapsulants for use in a PV module. This document is intended to apply to encapsulants used in PV modules deployed under temperature conditions of normal use, as defined in IEC TS 63126. The use of this method for encapsulants in modules deployed under conditions of higher temperature is specified elsewhere, for example IEC TS 63126. The method here is intended to be used to examine a particular encapsulant and does not cover incompatibilities between the encapsulant and other packaging materials. This document covers PV technology constructed using a transparent incident surface/encapsulant/photovoltaic device construction, the relevance to other geometries where the encapsulant layer is located behind the photovoltaic device layer, is outside the scope of this document. In the case of bifacial cell technology, the module can accept light from its front and back surfaces – the transmittance of a frontsheet (if used), encapsulant, and transparent backsheet (if used) is relevant for both active surfaces. The optical durability of frontsheets and backsheets, however, is addressed separately in the IEC TS 62788-2. Thin coatings that might be added for antireflection or anti-soiling purposes are outside the scope of this document. The method in this document can be used for other purposes (e.g., research and development); many details of alternate uses of the method (e.g., alternate test durations or measurement increments) are not described here.
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