Energy storage plant and process

A process for energy storage, comprising:

• carrying out a closed thermodynamic cyclic transformation through a working fluid different from atmospheric air, wherein
• the closed thermodynamic cyclic transformation is carried out first in one direction in a charge phase and then in an opposite direction in a discharge phase;
• the closed thermodynamic cyclic transformation is carried out between a casing and a tank, the casing being a deformable membrane gasholder;
• in the charge phase, the working fluid, stored in the deformable membrane gasholder in a gaseous phase, is:
• compressed,
• cooled, storing sensible heat,
• condensed by passing it through a saturated vapor zone until it reaches a liquid phase, storing latent heat in a secondary fluid, the condensing taking place at a pressure which depends on a temperature of the secondary fluid to allow heat transfer from the working fluid to the secondary fluid, and
• stored in the liquid phase in the tank with a temperature close to and lower than a critical temperature;
• in the discharge phase, said working fluid, stored in the tank in the liquid phase at a pressure and a temperature which is in equilibrium according to a temperature of the secondary fluid, is:
• vaporized by passing it through the saturated vapor zone until it reaches the gaseous phase, receiving the latent heat by means of cooling the secondary fluid, the vaporizing taking place at a pressure which depends on the temperature of the secondary fluid to allow heat transfer from the secondary fluid to the working fluid,
• heated using the sensible heat stored during the charge phase,
• expanded, and
• stored in the deformable membrane gasholder in the gaseous phase;
• in any operating condition during the closed cyclic thermodynamic transformation, the working fluid in the deformable membrane gasholder is in equilibrium of pressure with the atmosphere with low or no overpressure;
• and
• wherein the temperature of the secondary fluid is close to an ambient temperature.