Parasitic impedances of PV panels play an important role in the common mode circuit. This work has investigated parasitic impedance model including capacitances and inductances, against the one with only capacitances considered in the literature. Further, the effects of geometrical and environmental factors on the parasitic capacitances are analysed using Finite Element Method (FEM) and Design of Experiments (DoE). The analysis has revealed that the water layer above panels is significant for cell-to-frame capacitance and not for cell-to-ground capacitance. Frequency domain analysis of total parasitic impedances is presented which shows that the total impedance exhibits resonances and inductive behaviour in the MHz range. These features are not captured if only capacitive model is considered.