Inherent uncertainty and variability in energy production from variable renewable energy (VRE) sources such as wind and solar, require Energy Storage Systems (ESS) to enable continuous availability of supply. The 100% renewable electricity grid with a mix of generators, therefore, needs to be integrated with optimum sized ESS to ensure power demand is fully met while avoiding underutilized assets. In this paper, we analyze, at the macro level, the ESS requirements for the Australian national grid in terms of energy and power capacities as a function of renewable penetration. It is found that the ESS energy capacities tend to decrease almost linearly with increased VRE penetration. However, the maximum power capacities are practically unaffected by high VRE penetration, and it is found that higher power capacity dispatchable generators are required to support high levels of VRE sources.