A liquid energy storage system where the mixed refrigerant may include the following components with concentrations in mole volume percentages as follows: about 12.0% Nitrogen, about 15.0% Ethylene, about 39.0% Methane, about 20.0% Ethane, about 10.0% Propane, and about 4.0% Iso-Butane. A liquid energy storage system where the thermodynamic relationship for lost work is characterized by: Wlost=TOIntegral(T1−T2)/(T1×T2)dH, where To is the ambient temperature and T1, and T2 are the temperatures of the hot and cold streams, respectively, all temperatures are absolute temperatures, and H represents the enthalpy or heat content of the fluids in the heat exchange process.