The numerical modelling of a phase change material (PCM) attached to a hybrid three-dimensional truncated compound parabolic concentrator and thermoelectric module is performed under transient and non-uniform variation in solar radiation. To demonstrate the higher performance of the system, the performance parameters of a stand-alone system (without PCM), SAS, and incorporated system (with PCM), IS, are modelled and studied using the ANSYS 2020 R1 software and MATLAB R2020a Simulink software. The PCM is placed at the hot junction of the solar thermoelectric generator (STEG) in order to act as a re-concentrating lens via the phase-change lensing effect and to decrease the adverse effect of transient and non-uniform solar radiation on the STEG. The results demonstrate an increase in the light transmissivity and refractive index of the PCM after melting and the efficacy of the PCM in shielding the STEG under extremely concentrated solar radiation intensities. The optimum heat input required to maximise the STEG efficiency and power output while minimising the challenge of excess heat dissipation in STEG systems is obtained and discussed. Finally, the results obtained show that the maximum temperature gradient, power output and efficiency from the stand-alone were higher than those from the incorporated system. The results obtained from this study will provide useful information in the design of STEGs under fluctuating meteorological conditions coupled with solar concentrators, which generate varying solar radiation.