Increasing power demand and encouragement of renewable energy generation appear the importance of Distributed Generation (DG). The Photovoltaic (PV) is considered a resource of distributed generation. The integration of PV-DG unit into the grid has a significant effect on reducing real power losses, operating costs, and enhancing voltage stability. Most of the current researches handle this issue from the point of optimizing the PV-DG unit size and location to enhance the grid performance. In fact and due to optimal design criteria, PV location and size are selected, implemented, and no luxury for a change. In this research, specific selection of sizing and placement of PV-DG unit in radial distribution systems was previously determined and installed. The main goal of this research is to study the grid performance enhancement under these conditions. IEEE 15 bus system has been taken to perform this study based on a MATLAB environment. The idea of this study is to analyze the grid performance when connecting the PV-DG unit to each bus across the transmission line to find the optimally connected bus considering the available transfer capacity of the existing network. For optimal grid performance enhancement, results show that PV-DG unit fragmentation into small units to be connected to all buses was the best solution.