Unitized regenerative proton exchange membrane fuel cell (URPEMFC) performs the functions of an electrolyser and a fuel cell. Currently, power hysteresis effect (PHE) is a key technological challenge for the URPEMFC because it reduces the efficiency of the system as it switches from electrolyser mode to fuel cell mode and vice versa. Here, a modelling and simulation approach is used to investigate the PHE based on its thermodynamic and electrochemical attributes. URPEMFC model was validated against an experimental study and then used for parametric studies. The results indicate that the PHE occurs when the number of cells is 1, 5 and 10. Moreover, an increase in the lost internal current density and total resistance resulted in an increase in overpotentials of the system. Although the theoretical thermodynamic efficiency of a URPEMFC is about 68.86%, the current study predicted an efficiency of 44% for a stack of 10 cells at current density of 0.5 A cm-2. A case study of an integrated photovoltaic-URPEMFC system for power generation using actual meteorological data is also presented. If optimised, URPEMFC can be applied with renewable energy sources for power-to-gas technologies, power-to-power technologies, hydrogen filling stations or distributed hybrid energy systems.