Dealing with power distribution system became one of the most important arts in the field of power system, especially in the rapid increase of the distributed generation (DG) penetration to the distribution level which is a vital and important part of the entire power system. In this paper, a very special power distribution system with a unique deployment of distributed generation, such as, photovoltaic and wind generation has been studied. Energy storage system is utilized to play the main role to control the system’s power quality and the system frequency, as load following operation (LFO) and automatic generation control (AGC), respectively. In this paper, a working criterion has been introduced followed by a case study focuses on two important conditions, one of them when the proposed system is connected to the electrical grid (upper system) and the other one when the system is completely islanded. In both cases, the crucial usage of the ECS gives a concrete result which made the system fully recommended to be applied in real life.