Different equivalent circuit models were used to fit the impedance spectra of CdTe solar cells at fixed d.c.-voltages and the resulting C-V (capacitance-voltage)-curves and C-S (capacitance-frequency)-curves were analysed. A simplified equivalent circuit model, which consists of a parallel resistor R-p and capacitor C in series with a resistor R-s, does not give a good fit to the experimental data and is not capable of simulating the: dispersive trend. Also the commonly assumed model for CdTe, which consist of two sub-circuits (R-p and C) does not allow the simulation of the measured impedance spectra. As both models are only consisting of frequency-independent circuit elements they can not be used to describe the frequency dispersion of thin film CdTe solar cells. A phenomenological description of the capacitance behaviour was obtained by replacing the capacitor of the first model by a frequency-dependent non-ideal capacitor, a so-called constant phase element (CPE). This element is described by the two CPE-parameters (T and P). A correlation of these parameters to the capacitance dispersion and to the real cell capacitance are presented and the physical phenomena responsible for the capacitance dispersion are discussed.