Photovoltaic (PV) systems, grid-connected or stand-alone, use the power conditioning unit (PCU) to optimize the energy transfer from the PV generator to the user load by using the maximum. power point tracker, and also to invert, regulate, and wave shape the power between the components of the system. To study and optimize this system, different PCU models are applied. In this work different empirical models of the PCU have been set up. The purpose of this investigation is to verify the possibility of the PCU application to this system and study the different mathematical energy efficiency models. All these models have been simulated and compared with a typical real system to show which one is better. The second part of the paper includes the optimal size of the PCU with the PV system and also an application comparison between two possible locations for varied geographical latitudes, in Kassel/Germany, (middle Europe) and Cairo/Egypt (North Africa).