US Patent 9394807 Apparatus, system, and methods for mechanical energy regeneration

Systems and methods for storing and retrieving thermo-mechanical energy are disclosed. The systems and methods generally include a thermodynamic loop or cycle (e.g., a reversible transcritical, trilateral, or Rankine/vapor compression cycle) that works as a heat pump in a charging mode and as a heat engine in a discharging mode. The thermodynamic loop or cycle includes a gas pressure changing device, a liquid pressure changing device, and a working fluid. The system further includes one or more heat storage devices with solid heat storage material(s). Heat is transferred between the working fluid and the solid heat storage material(s) in the high and low pressure sides of the thermodynamic cycle, respectively.