Hybrid energy storage systems are necessary in the future grids to improve the power quality and maintain the grid stability under high penetration of renewable sources. The use of more than one type of energy storage elements in the grids with different response times will help in improving the efficiency and reliability of the storage systems.
Energy Storage provides Energy when it is needed, just as Transmission provides Energy Where it is needed. Storage could reduce or eliminate use of low efficiency peaking units. Think of storage like memory on a computer. Storage should be treated like a renewable resource.