DANSK DSF/FPREN IEC 62788-6-2 PDF

This part of IEC 62788 describes methods to measure the permeation properties of polymeric materials. The degradation of PV modules is known to proceed by many different corrosion processes. These degradation processes may depend upon moisture ingress into the encapsulant, edge seal, frontsheet, or backsheet materials. Typical polymeric materials used include (amongst other polymers) ethylene-vinyl acetate (EVA) and polyolefins for encapsulants, polyisobutylene (PIB) for edge seals, and polyethylene terephthalate (PET), polyvinyl fluoride (PVF), or polyvinylidine fluoride (PVDF) for backsheets. Therefore, knowing the moisture permeation characteristics of polymeric materials is relevant to module design. These properties can be determined as a function of temperature and relative humidity. With these parameters, simple scaling rules for time and distance can be used to extrapolate to the use environments. This standard provides methods for measuring the steady state water vapor transmission rate (WVTR), water vapour permeability (P), diffusivity (D), solubility (S), and moisture breakthrough time (Ƭ10%) (defined as the time to reach 10 % of the steady state WVTR) for polymeric materials such as encapsulants, edge seals, frontsheets and backsheets. These measurements can be made at selected temperatures and humidity levels as deemed appropriate for evaluation of their performance in PV modules. Measurement is accomplished by inspection of the transient WVTR curve and by fitting it to a theoretical fickian model. This standard is best applied to monolithic films. If multilayer films are used, the D and S values are only apparent values, but the steady state values can still be measured. This standard was written for the measurement of water permeation, but it may equally be used for other permeants such as O2. In this case the same diffusion equations, fitting procedures, and scaling arguments may be used