Thermal energy storage system including a vessel having hot and cold liquid portions separated by floating piston

A thermal energy storage system for storing thermal energy produced by a heat source and for supplying the thermal energy to a thermal load, the thermal energy storage system comprising:

• a working fluid configured to store the thermal energy and transfer the thermal energy between the heat source and the thermal load;
• a vessel configured to store the working fluid;
• the vessel having a first end, a second end, an interior region, and a floating piston located in the interior region to separate a hot portion of the working fluid towards the first end from a cold portion of the working fluid towards the second end;
• wherein the floating piston comprises a piston body having a first end, a second end, and a central region, and a compressible member which is disposed in the central region of the floating piston and which is configured to engage with an inner surface of the vessel;
• and
• wherein the compressible member has a porosity level that results in a thermal loss due to leakage of the working fluid from the first end of the piston to the second end of the piston of no more than 5% of an overall thermal loss in the thermal energy storage system;
• a first manifold configured to be thermally coupled to an output of the heat source and to an input of the thermal load and fluidly coupled to the interior region proximate the first end of the vessel;
• a second manifold configured to be thermally coupled to an input of the heat source and an output of the thermal load and fluidly coupled to the interior region proximate the second end of the vessel;
• and
• a controller configured to maintain the working fluid in a liquid state.