NOVELTY - The method involves providing heat-transfer fluid (328) e.g. water, that comprises an additive e.g. surfactant, for reducing surface tension of the heat-transfer fluid and enhancing lubricity of the heat-transfer fluid. Gas (326) e.g. air, is compressed to store energy originating from an intermittent renewable energy source of wind or solar energy. The gas is expanded to recover energy when the renewable energy source is nonfunctional. Heat is exchanged between the gas and the additive-containing heat-transfer fluid to increase efficiency of energy storage and energy recovery.    USE - Method for improving efficiency of liquid-based heat exchange in a compressed-gas energy storage and recovery system (claimed) connected to a solar panel and a wind turbine to harness and recover sources of renewable energy e.g. wind energy and solar energy.    ADVANTAGE - The method enables the additive to retard or prevent corrosion and to prevent formation of microorganisms or to kill microorganisms. The method enables reducing energetic losses caused by dissolution of air in heat-exchange liquids under high pressure, thus enabling more-efficient isothermal gas compression and expansion. The method enables reducing time available for air to dissolve in the water, thus reducing amount of air ultimately dissolved in the water. The method enables recovering the energy from dissolved gas using a regenerative piston stroke. The method enables increasing heat-transfer potential of liquid sprays provided to enable isothermal expansion and compression inside cylinders or other mechanical devices for expanding or compressing the gas with resulting gain in efficiency of an overall energy-storage and energy-recovery process. The method enables altering properties of heat-exchange liquid by using the additive, so that efficiency of a liquid-based heat-transfer system can be increased by reducing power needed to produce a suitably atomized spray of liquid, thus increasing overall efficiency of the energy storage and recovery system.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a compressed-gas energy storage and recovery system comprising a cylinder assembly.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic cross-sectional view of a cylinder with a closed-loop liquid-injection system within a compressed-air energy storage and recovery system.    Heat-transfer subsystem (304)    Control system (305)    Vessel (306)    Vent (308)    Gas (326)    Heat-transfer fluid (328)