1. Introduction
The use of wind and solar energy systems have become widespread because they are clean, renewable and accessible. Energy storage systems (ESS) are used for a wide range of purposes in grids that are equipped with renewable energy sources (RES) with intermittent and variable production profiles. With the inclusion of renewable energy sources in distribution grid, the structure of conventional radial or ring networks have turned to distributed networks. Contrary to the conventional ones, distributed networks include generation and consumption together, which makes difficult keeping load consumption and power generation balance equal. Since the generated power from wind generators and solar PV systems depend on wheather conditions, unexpected occur in generated power yielding difficulties in power management in such systems. Therefore, accurate estimation of the power generation from wind turbines and PV systems, at least one day ahead, gain a great importance in terms of system management in order to keep consumption and generation balance tight. The power systems with distributed generation are used to improve voltage fluctuations, reduce power losses, store energy when renewable generation is high, and support high demand when it is low [1]-[4]. These systems can also balance electricity supply and demand once the unexpected changes are predicted and precautions are taken earlier on time. With one day ahed estimation of wind and solar PV power generation, the distributed generation (DG) also improve the reliability and efficiency of the power system, besides enabling a more flexible management of electrical energy [5]-[6].