In this paper the water uptake by PV-modules during weathering tests of the type approval standard IEC 61215 was simulated and compared with the water ingress under ambient outdoor conditions. For this purpose, the base materials, one encapsulant (EVA) and one back sheet (TPT), were analyzed regarding their water vapor permeability. The micro climate a PV-module sees at its surface was monitored during accelerated IEC tests and at outdoor test sites located in four different climatic regions. These measured values were used for FEM based simulations of the water ingress into PV-modules. The results show the speed and the amount of water uptake under IEC-test conditions as damp heat, humidity freeze and thermal cycling tests compared with the water ingress under the different climates. It can be stated that the IEC-damp-heat test provokes almost two times higher water concentrations in the encapsulant between cell and glass than outdoor weathering can adjust over 20 years. The humidity freeze test shows a similar behavior and even the thermal cycling test results in a slightly water uptake in the back sheet. (C) 2015 Elsevier Ltd. All rights reserved.