  The viscoelastic response of backsheet materials significantly affects the
durability of the photovoltaic (PV) module. In this study, the viscoelastic
response of commercially available backsheet materials is experimentally
characterized and computationally modeled. An extensive viscoelastic
experimental study on backsheet materials is carried out, considering the
temperature-dependent properties for characterizing the mechanical properties.
Based on an experimental campaign, small-strain viscoelastic models based on
the Prony-series (PS) and Fractional Calculus (FC) Models are proposed here.
The form of the constitutive equations for both models is summarized, and the
finite element implementation is described in detail. Following identifications
of relevant material parameters, we validate the model with the experimental
data that shows good predictability. A comparative study of model responses
under different loading conditions is also reported to assess the advantages
and disadvantages of both models. Such an extensive experimental study and
constitutive modeling will help design and simulate a more comprehensive
modeling of PV modules, as illustrated by the benchmark problems.
