The Hydrostor system efficiently converts electrical energy to compressed air via an advanced adiabatic compression system. This air is then sent to a series of flexible accumulators located 50-500 meters below the surface of a water. Once in the accumulators, the energy can be stored until required by the grid. When the energy is required, the weight of the water pushes the air back to the surface where our system directs it through an expander driving a generator thus supplying energy to the grid and completing the storage cycle. This rapidly deployed, low cost system uses non toxic substances with minimal environmental disturbances while offering high round trip efficiencies without the need for additional fossil fuel heat.