In the power systems community, there is active research on different aspects of integration of renewable energy sources. One such aspect is the effect of renewable sources on voltage profiles and power flow. A different aspect is the dynamics of the system, where the effects on power quality and system stability are studied. In this project we focused on the subject of system stability and the role of energy storage in this context. In conventional power systems, the large synchronous generators, which have significant rotational inertia, benefit greatly to the stability of the system. There is a trend in the world of replacing these generators with small distributed renewable source which little, if any, rotational inertia. It is possible to replace the rotational inertia with energy storage systems, as both are forms of storage elements. An important research topic in this context is the relation between the size of energy storage systems and the system stability. In this work we tried to prove that any power system can be stabilized by using large enough energy storage, thus showing explicitly this relation. A different direction we took was to research the benefits of energy storage sharing for system stability, and how this property can be used to determine a lower bound for minimal energy storage required for stability.