Originally conceived as a support tool for renewable energy sources, storage systems have evolved into a versatile and valuable technology with applications across a wide range of energy environments. This work begins by introducing the concept of energy storage systems, outlining their various functions and roles within modern energy infrastructures. The main focus will be on Battery Energy Storage Systems(BESS) and the manifold applications developing in recent years. After discussing the future role of BESSs in frequency regulation and what that regulation actually comprehends, the focus will move on exploring real-word implementations carried out by the energy company Iren in the piedmont and lombardy region.