Increasing the operating lifetime of photovoltaic (PV) modules is a key factor in further reducing their levelized cost of electricity. Analytical degradation models typically use the external relative humidity (RH) as a stress factor, rather than the moisture concentration inside the module. This study presents a Finite Element Method (FEM) model, built in COMSOL Multiphysics, to simulate the moisture ingress inside a PV module. We explore the effects of different encapsulant and backsheet materials, as well as various climatic conditions, on moisture penetration. Overall, the impact of the climate has a larger impact on the moisture ingress than the choice of material, implying that the PV module design should be adjusted for different climates. As FEM simulations are computationally intensive, we also present an analytical model, based on empirically determined characteristics, to simulate the moisture ingress. This reconstruction can be done with a deviation lower than 0.05 for all conditions. Finally, our findings indicate that the relative moisture content (RMC) within the module serves as a more accurate stress factor than outdoor RH. Degradation rates over time found in literature are captured more accurately when deploying RMC.