Quantifying the influence of encapsulant and backsheet composition on PV-power and electrical degradation

Although the technical and economic properties of the standard polymer photovoltaic
(PV) materials (ethylene-vinyl acetate (EVA) encapsulant and fluorine-containing
polyethylene terephthalate (PET) backsheet) meet the basic technical requirements,
more sustainable polyolefin-based encapsulants and backsheets have been developed.
These new polyolefin materials have to prove their performance compared to
the established standard materials in terms of the electrical performance of the modules
and in terms of reliability. The long-term stability of the new materials is tested
and evaluated using accelerated aging tests and degradation modelling. Based on
experimental results, the influence of the type of encapsulant and backsheet (i) on
the electrical output power of PV test modules and (ii) on the aging-related electrical
and material degradation under accelerated stress tests was estimated using statistical
modelling approaches. First results showing significant effects for encapsulant,
backsheet and the combination of both on the initial power output are presented. In
general, modules with polypropylene-based backsheets have a higher initial power
(PMPP) than those with PET-based backsheets, with the combination of thermoplastic
polyolefin (TPO) encapsulation material and polyolefin backsheet being superior to
the other material combinations. A comparison of the material-dependent degradation
rates obtained from the mixed-effects models clearly shows that the degradation
rate upon damp heat exposure for modules with EVA is significantly larger than that
using polyolefin encapsulants. The derived relations aim to provide valuable input for
innovative material developments as well as predictive maintenance specifications.