Passive management of thermal stratification within long-duration liquid-based thermal energy storage reservoirs

A multi-reservoir thermal energy storage system, comprising:

• a first containment structure configured to hold a thermal energy storage fluid and a dual-media thermal storage medium comprising a packed bed of solid particulate material selected from rock, quartzite, granite, or ceramic particles immersed in the thermal energy storage fluid, wherein the thermal energy storage fluid comprises molten salt;
• a second containment structure fluidly coupled in series to the first containment structure and configured to hold the thermal energy storage fluid, wherein the second containment structure is substantially free of phase change material;
• at least one thermocline management mechanism comprising a layer of phase change material (PCM) encapsulated within a plurality of microcapsules or macro-encapsulated tubes, the PCM being positioned at least proximate to a top region and/or a bottom region of the first containment structure and configured to function as a thermocline damper that flattens the thermocline zone as the thermocline passes through the layer of PCM during charge and discharge cycles;
• a charge/discharge assembly comprising at least one pump and heat exchanger configured to transfer thermal energy into and out of the first and second containment structures;
• and
• wherein thermal energy is stored as sensible heat in the thermal energy storage fluid and the dual-media thermal storage medium;
• wherein the PCM is configured to passively stabilize a thermocline formed in the thermal energy storage fluid held by either the first containment structure or the second containment structure by absorbing and releasing latent heat at a predefined phase transition temperature, wherein the PCM positioned exclusively in the first containment structure provides system-wide thermocline stabilization across both the first and second containment structures;
• by intercepting and damping thermocline broadening as the thermocline zone moves vertically through the first containment structure during charging and discharging operations.