Abstract: A refrigeration, or thermal, energy storage system for storing refrigeration, or thermal, energy, comprising a body, closed and insulated, the body being configured to contain two fluids, respectively a Phase Change Material (PCM) type fluid and a secondary fluid, the two fluids being immiscible with each other and having different densities, so as to be stratified within the volume of the body; withdrawal means configured to draw the secondary fluid from the body, and to convey the same inside a heat exchanger configured to exchange frigories, or calories, with the secondary fluid; and distribution means configured to draw the secondary fluid from the heat exchanger, and distribute the secondary fluid into the PCM type fluid, so that the secondary fluid exchanges with the PCM type fluid frigories, or calories, absorbed in the heat exchanger, the secondary fluid having a solidification temperature substantially lower than that of the PCM type fluid.