We conducted a long-term (>6500 h) in-situ PV module humidity monitoring experiment, where digital humidity sensors encapsulated in different encapsulants (EVA, TPO, POE and ionomer) were exposed to different humidity conditions in a climatic chamber. From the acquired data, humidity ingress parameters (moisture diffusion coefficient and solubility) of used materials are extracted. Furthermore, first promising results have been obtained by an ongoing experimental work, where we obtained a correlation between the sensors' RH readings and the water mass concentration in the EVA encapsulant. Such a calibrated monitoring method, capable to measure humidity content in different PV modules using various encapsulants, represents a very cost effective and versatile technique for laboratory and field testing applications.