EP2427656A2

EP2427656A2 - Method and apparatus for storing mechanical energy by the quasi-isothermal expansion and compression of a gas

Info

Publication number: EP2427656A2
Application number: EP10726147A
Authority: EP
Inventors: Etienne Lebas; Alexandre Rojey
Original assignee: Cogebio
Current assignee: Cogebio
Priority date: 2009-05-07
Filing date: 2010-05-06
Publication date: 2012-03-14
Also published as: WO2010128222A3; FR2945326A1; US20120042643A1; FR2945326B1; WO2010128222A2; US9080574B2

Abstract

The invention relates to a system for storing energy, in particular mechanical energy, comprising a series of containers (14, 15, 16) inside an insulated chamber (11), a medium (10) for storing thermal energy, a tank (13) containing a hydraulic fluid (9) and a system for the pumping-expansion of said fluid (17). According to the invention, energy storage is achieved by compressing the gas (1, 2, 3) contained in the containers (14, 15, 16) by pumping the liquid (9) using the apparatus (17). The heat released by compressing the gas is stored in the medium (10).

Description

Process and equipment for storing mechanical energy by compression and quasi-isothermal expansion of a gas

Technical area

The present invention relates to a system for storing energy, in particular mechanical energy, comprising a system for quasi-isothermal compression of a gas by means of a hydraulic fluid. The stored mechanical energy is then released by quasi-isothermal expansion of said gas.

The present invention also applies to the storage of electrical energy, especially from intermittent sources such as photovoltaic or wind energy. Surplus storage of electricity production can also be considered for use during peak consumption.

State of the art

There are several energy storage systems that can be used for these applications at different power scales. On a small scale, electrochemical systems such as batteries and supercapacitors can be used. These systems nevertheless have a number of disadvantages. Batteries are a danger to the environment and have a limited life. Supercapacitors have insufficient energy density for most applications. On a larger scale, the storage of water in a tank in elevation presents a good option. Water can be released at the chosen time and generate electricity through turbines. The main limitation of this technique is the low number of adaptable sites without heavy and expensive work.

The storage of compressed air in an underground cavity (sometimes known as CAES = Compressed Air Energy Storage), is also an interesting alternative; this has been envisaged in US Patents 4,885,912 (Gibbs & HiII, Inc.), US 3,996,741 (George M. Herberg) and in Patent Applications WO 93/06367 (Arnold Grupping) and EP 106 690 (Shell International Research). On the other hand, the number of sites available is very limited and an economically profitable implementation requires the coupling to a combined cycle. This leads to very large installations, with very heavy investments. Moreover this solution involves the consumption of fossil fuels, and its yield is low. Finally, another alternative is the hydro-pneumatic storage where the compression of a gas is achieved through the pumping of a liquid. But this type of technology needs to be improved in order to increase the yield and reduce the cost.

It is already known, in particular from the document WO 2008/139267 (Ecole Polytechnique Fédérale de Lausanne), such a system which uses, as a device for compressing the gas, a liquid piston system. A sprayer or grid integrated in the upper part of the chamber ensures the gas-liquid contact during the compression and expansion phases of the gas so as to maintain quasi-isothermal conditions. In this system the thermal energy released during the compression phase is discharged to the atmosphere via an exchanger. This same exchanger is used to provide calories during the expansion phase of the gas.

This type of system, although satisfactory, nevertheless has significant disadvantages. Indeed, the effectiveness of this type of storage is limited especially because of the energy loss that is the evacuation of calories during the compression phase of the gas. In addition, the restitution phase of the stored energy is accompanied by a cooling of the liquid associated with the expansion of the gas. It is therefore necessary to spend a significant amount of energy to ensure isothermal expansion of the gas.

The present invention proposes to overcome the drawbacks mentioned above by means of a hydro-pneumatic storage system which makes it possible to obtain a high energy efficiency by using a system for storing the thermal energy produced during the compression phase of the gas. , this energy being restored during the expansion phase of the gas.

Object of the invention

The invention relates to a system for storing energy, especially mechanical energy, comprising (a) at least one container containing a hydraulic fluid and a gas;

(b) at least one storage chamber containing hydraulic fluid;

(c) compression-triggering means capable of "pumping" hydraulic fluid pumping, and "triggering" mode of relieving hydraulic fluid; characterized in that (i) said hydraulic fluid and / or said gas contained in the at least one vessel is in thermal contact with a thermal energy storage medium contained in an enclosure;

(ii) said container is connected to said at least one storage enclosure by lines for conveying said hydraulic fluid from one to the other through said compression-expansion means;

(iii) said compression - expansion means is capable of pumping hydraulic fluid from the storage vessel to the vessel, and capable of expanding the contained hydraulic fluid. in said container to the storage chamber, generating mechanical energy.

Said compression - expansion means may be a reversible compression - expansion device, such as a hydraulic piston pump also functioning as a piston engine. Said compression - expansion means may comprise means for transforming the generated mechanical energy into electrical energy.

In this mechanical energy storage system, the energy storage is obtained by compressing the gas contained in the at least one container by the hydraulic liquid which is pumped with said compression-expansion means.

Said at least one container may be constituted by any volume having a suitable exchange surface with the hydraulic fluid. It may be constituted for example by a tube or plate heat exchanger in which it occupies the compartments in heat exchange with those occupied by the hydraulic fluid. It may also be constituted by a tube or a plurality of tubes arranged in the storage volume of the hydraulic fluid. It may in particular be constituted by a spiral tube.

Said gas is a condensable gas, and preferably a gas selected from the group consisting of hydrocarbons, CO ₂ , fluorinated hydrocarbons, fluorinated alkanes. It can also be a non-condensable gas such as nitrogen or ambient air.

Said thermal storage medium may comprise a phase change material.

Said at least one container may be located inside said enclosure, or it may be located outside said enclosure; in the latter case, it advantageously comprises a fluid loop which ensures a thermal contact between said medium of thermal storage of said enclosure and said hydraulic fluid contained in said container.

In a particular embodiment, the system according to the invention comprises a first group of containers and a second group of containers, said gas is ambient air, and during the mechanical energy storage phase, said first and second Groups of containers operate alternately in air compression or air suction.

In this embodiment, said container may comprise a contactor for improving the gas - liquid contact, and in this system:

- In the mechanical energy storage phase, the hydraulic fluid stored in the storage chamber is conveyed by a line to said compression-expansion means and then by a line to said container to compress the gas; - In the mechanical energy recovery phase, the gas is expanded by releasing the fluid by a line to the compression-expansion means and then by said line to the storage chamber.

During the energy storage phase, said contactor makes it possible to maintain the quasi-isothermal gas and to transfer the calories to the hydraulic fluid, a fluid loop enabling the heat of the fluid to be conveyed to the thermal storage medium; in the energy recovery phase, the fluid loop makes it possible to restore the calories stored in the thermal storage medium to the hydraulic fluid.

In another particular embodiment, the system according to the invention further comprises a device for supplying the thermal storage medium with external thermal energy, such as a solar collector or a heat exchanger operating on combustion gases or other external sources of heat.

figures

Figures 1 to 10 refer to the invention and its various embodiments.

Figure 1 is a diagram illustrating the basic principle of the mechanical energy storage system.

FIG. 2 is a diagram of a first variant of the system of FIG. 1. FIG. 3 is a diagram of a second variant of the system of FIG.

FIG. 4 is a diagram illustrating a variant of the system of FIG. 2. Figure 5 is a diagram illustrating another embodiment of the storage enclosure.

Figure 6 is a diagram illustrating another variant of the system of Figure 1.

FIG. 7 is a detailed view illustrating an implementation possibility of the diagram of FIG. 1.

Figure 8 schematically illustrates a plate heat exchanger, which can be used in the context of the present invention.

Figure 9 is a diagram illustrating another variant of the system of Figure 1, wherein the storage chamber is at a lower level than the containers.

Fig. 10 is a diagram illustrating another embodiment of the invention, wherein the thermal storage medium is heated by a solar collector.

List of landmarks used in the figures

detailed description According to the invention illustrated in Figure 1, the mechanical energy is stored in a gas (1, 2, 3) which is compressed by means of a hydraulic fluid (4, 5, 6). The compressed gas is contained in at least one container (14, 15, 16), and preferably in a plurality of containers (14, 15, 16) interconnected by a line (40). The at least one container (14, 15, 16) is placed in the enclosure (11) which contains a thermal storage medium (10) capable of absorbing and returning the heat generated by the compression of the gas (1, 2, 3) keeping it sufficiently isothermal.

The hydraulic fluid (9) is stored in the storage chamber (13), it is conveyed by the line (8) to a compression - expansion means which is preferably a reversible device P-T (17).

Said compression device - reversible expansion (17) is capable of either pumping the hydraulic fluid (9) receiving a quantity of mechanical energy W, which leads to the compression of the gas (1, 2, 3), or to relax the fluid (4, 5, 6) conveyed by the line (7) producing a quantity of mechanical energy W; advantageously, it has means for converting this mechanical energy into electrical energy. These devices have a very high efficiency, generally greater than 90%. By way of example, it may be a hydraulic piston pump also functioning as a piston engine, or a deformable diamond rotary machine, known for example from US Pat. No. 3,295,50 (Jordan). In a variant illustrated in FIG. 2, said compression-expansion means is constituted by a circuit which comprises, in parallel, a device (P1) capable of pumping the hydraulic fluid (9) while receiving a quantity of mechanical energy W, and a device (T1) for producing a quantity of mechanical energy W by relaxing the fluid (4, 5, 6) conveyed by the line (7); two pairs of valves (V51, V52, V53, V54) make it possible to select either the "compression" mode or the "relaxation" mode. In all the embodiments and variants of the invention described herein, these two compression-expansion means can be used interchangeably; for simplicity, we will describe the invention later referring to us as means of compression - relaxation to the compression device - reversible expansion (17).

Here is described in a simple manner a typical mode of use of the system according to the invention: To store energy, the compression-expansion device (17), or as indicated above, another compression means - relaxation , hydraulic fluid pump (9) through the line (7) in the at least one container (14, 15, 16). The level of hydraulic fluid (4, 5, 6) in said containers (14, 15, 16) rises, the surface of said fluid acting as a piston and compresses the enclosed gas (1, 2, 3) in said containers (14, 15, 16). This compression generates heat, which is transferred to the thermal storage medium (10). This heat can be restored when the gas is released; the temperature rise of the hydraulic fluid (4, 5, 6) in "compression" mode is normally low, of the order of a few degrees at the most, but if it is restored to the "expansion" mode with gas (1 , 2, 3), this makes it possible to increase the pressure of the gas (1, 2, 3) significantly. If the compressed gas (1, 2, 3) is allowed to relax through the line 7 and the compression / expansion device (17) operating in "expansion" mode, the level of hydraulic fluid (9) in the containers (14) , 15, 16), and the hydraulic fluid (9) sets in motion the energy conversion means of said expander (17) to generate mechanical energy; this mechanical energy can be transformed into electrical energy. The hydraulic fluid (9) is transferred through the line (8) into the storage chamber (13) whose liquid level rises.

If the gas (1, 2, 3) is air and if the air pressure (1, 2, 3) in the containers (14, 15, 16) becomes during the expansion of the hydraulic fluid (9) lower than the atmospheric pressure, air can be introduced from the outside into the containers (14, 15, 16) by means of a valve.

The enclosure (11) is preferably surrounded by a thermal insulator (12).

The hydraulic fluid (4, 5, 6, 9) is generally a liquid, and preferably consists of an aqueous phase, water or glycol water to avoid the risk of freezing. It can also be an organic phase, such as glycol, a mineral oil, an ester, a vegetable oil or phosphate esters.

The gas (1, 2, 3) may be a permanent gas such as air or nitrogen. It can also be another gas such as CO ₂ or an organic fluid. The thermal storage medium (10) may consist of a liquid (aqueous or organic) and / or of a solid phase optionally phase-change.

In a variant of the process according to the invention, the fluid (1, 2, 3) is a condensable fluid, and the compression and expansion is performed on a two-phase fluid; this will be explained below. The advantage of this variant is that it makes it possible to maintain a stable pressure in the containers (14, 15, 16).

Figure 3 shows a block diagram of a variant of the invention. The thermal storage medium (10) is constituted at least in part by the hydraulic fluid (9) used for the compression of the gas (1, 2, 3). The hydraulic fluid volume (9) is easily able to maintain the air volume under substantially isothermal conditions. Indeed, if the air is initially at atmospheric pressure (the storage being operated for example between the atmospheric pressure and 200 to 600 bar), the MCp coefficient of air for a given volume is 1, 2/4200 times lower than the coefficient MCp of the same volume of water needed to move it. A heating of 100 ⁰ C of the initial air volume corresponds to a quantity of heat which raises the temperature of the water only by 1, 2/42 = 0.03 ⁰ C

If the containers (14, 15, 16) occupy for example half of the volume of enclosure in which they are placed, the level of liquid in the chamber (11) varies between I ₁ and 1 _h = 1, 5 I ₁ .

It is also possible to have simultaneously a solid storage phase (10) (for example a phase change material), which remains stationary while the hydraulic fluid (9) circulates. The circulation of the hydraulic fluid (9) then ensures the heat exchange in good conditions.

The preceding provision also applies if the gas (1, 2, 3) is condensable. In this case, if the hydraulic fluid (9) is constituted by an aqueous phase, the fluid (1, 2, 3) may consist of a hydrocarbon or a fluid such as ammonia or CO ₂ . This condensable gas must not be miscible with the hydraulic fluid, so that the vapor pressure above the liquid phase resulting from the condensation of said gas (1, 2, 3) is always the saturation pressure. We then have a three-phase system: two liquid phases (hydraulic liquid (9) + liquid phase resulting from the condensation of the gas (1, 2, 3)) and a gaseous phase constituted by the gas (1, 2, 3).

In such an embodiment, during compression and expansion, the pressure in the containers (14, 15, 16) remains constant, which facilitates the operating conditions of the reversible compression-expansion device (17) and prevents a decrease in efficiency of said compression device - trigger (17). In addition, it is possible in this case to operate with moderate pressure, which reduces the investment costs.

Figure 4 shows a variant of the method according to the invention as illustrated in Figure 3, which is distinguished by the use of an open cycle instead of a closed cycle.

The gas used for storing energy is air taken from the environment by the line (18). This gas, once compressed, is stored in the storage chamber (35). This storage enclosure (35) may be constituted by an underground cavity, natural or artificial. The storage system according to the variant illustrated in FIG. 4 operates with at least two containers (B1, B2). During the mechanical energy storage phase, said containers (B1) and (B2) operate alternately in air compression or air suction. In a first step, while the first container (B1) draws air into the environment through the line (18), the second container (B2) compresses the air (20) via the fluid (21). ) pumped by the equipment (KT1). The compressed air (20) is then directed to the storage chamber (35) by the line (19).

In a second step, while the second container (B2) draws air into the environment through the line (26), the first container (B1) compresses the air (30) via the fluid (31). ) pumped by the equipment (KT1). The compressed air (30) is then directed to the storage enclosure (35) via the line (19).

The isolated enclosure (1 1) allows the storage of the thermal energy released during compression of the gas in the thermal storage medium (IO). This energy storage makes it possible to maintain the temperature of the first and second containers (B1, B2) almost constant during the mechanical energy storage phase.

During the restitution phase of the mechanical energy stored via the compressed air in the storage enclosure (35), the first and second containers (B1, B2) also function alternately. At first, the compressed air contained in the storage chamber (35) is directed towards the second container (B2) via the line (19). The second container (B2) expands the air (20) through the fluid (21) expanded by the equipment (KT1). At the same time the first container (B1) discharges air into the environment by the line (18). In a second step, the compressed air contained in the storage chamber (35) is directed towards the first container (B1) by the line (19). The first container (B1) expels the air (30) through the hydraulic fluid (31) expanded by the equipment (KT1). At the same time, the second container (B2) expels air into the environment through the line (18). The thermal energy stored during the compression phase in the thermal storage medium (10) makes it possible to maintain the temperature of said first and second containers (B1, B2) during the expansion phase.

The thermal equilibrium ensuring the isothermal nature of compression and expansion can be achieved by any type of device intended to promote the thermal exchange between the hydraulic fluids (21) and (31) and the thermal storage medium (10) such as a coil, not shown in FIG. 4. The circulation carried out at the time of compression and expansion may contribute to homogenizing the temperatures. Additional means of circulation or mixing can be introduced for this purpose.

It is possible to ensure a constant pressure in the storage chamber (35) by introducing into the chamber containing the compressed gas a variable volume of hydraulic fluid, this volume being regulated so as to maintain the pressure constant. The hydraulic fluid can be introduced from a storage chamber (36) at atmospheric pressure. During the step of generating energy from the storage, a fraction of the restituted energy is used to pump the hydraulic fluid. At the time of the energy storage step, this energy is restored. The system operates because the energy required to compress a liquid from atmospheric pressure to a relatively high pressure P is much lower than the energy required to compress a gas from atmospheric pressure to pressure P.

The variant of FIG. 6 differs from the diagram illustrated in FIG. 1 by the use of an indirect transfer of the thermal energy released during the compression of the gas towards the enclosure (11).

In this variant, it is also presented the possibility of using an internal packing element (44) in the container (43) to improve the gas-liquid contact. For this purpose, a recirculation loop (42) of the hydraulic fluid can also be activated by the use of a recirculation pump (49).

In this configuration, in the mechanical energy storage phase, the hydraulic fluid (9) stored in the storage chamber (13) is conveyed via the line (8) to the pump (17) and then via the line (42). to the container (43) to compress the gas (48). The switch (44) maintains the quasi-isothermal gas and transfers the calories to the hydraulic fluid (47). A fluid loop (45) conveys the calories of the fluid (47) to the thermal storage medium (10).

In the mechanical energy recovery phase, the gas (48) is expanded by releasing the fluid (47) via the line (41) to the compression device - reversible expansion (17) and then by the line (8) to the storage enclosure (13). During this phase, the recirculation of the hydraulic fluid (47) activated by the pump (46) makes it possible to maintain the temperature of the gas (48) almost constant. The fluid loop (45) makes it possible to restore the calories stored in the thermal storage medium (10) to the hydraulic fluid (47).

FIG. 7 shows an exemplary embodiment of the containers (14, 15, 16) of FIGS. 1 or 2 which can each be made in the form of a tube, preferably spirally wound. The use of a tube makes it easier to produce pressure vessels and facilitates heat exchange with the heat exchange medium (10). In another variant, the storage chamber (35) is made in the form of one or more straight tubes, stacked or not, connected to each other (see FIG. 5). In general, the use of tubes is advantageous because a tube is a hollow body capable of withstanding a high internal pressure which has a very simple shape and which can easily be made without welding by spinning processes. A bundle of straight tubes is particularly suitable for large storage systems. For example, a bundle of nine straight steel tubes with a diameter of 122 cm and a length of 10 meters can store about 105 m ³ of air; there are steel grades for making such tubes that withstand an internal pressure of more than 250 bar.

The container (14, 15, 16) may also consist of a plate heat exchanger (60) as shown in FIG. 8. A plate heat exchanger makes it possible to develop a large exchange surface between two thermal media in a small volume . Such an exchanger can typically consist of a stack consisting of a plurality of flat plates (63) and a plurality of corrugated plates (64, 65), which thus form two channel networks (61, 62). In each of said channel networks can flow a fluid. One of the fluids is the hydraulic fluid (4, 5, 6) with the gas (1, 2, 3), and the other fluid is the fluid that constitutes the thermal storage medium (10). Advantageously, a cross-flow or countercurrent configuration is used. Cross flow embodiment is shown in Figure 8, in which the channels formed by two adjoining corrugated sheets are rotated 90 ^e.

The variant of FIG. 9 differs from the diagram illustrated in FIG. 1 by a particular location of the enclosure (11) with respect to the storage enclosure (13). It is indeed possible to combine the principle of a hydro-pneumatic storage with that of a gravity storage: in this variant, the hydraulic fluid (4, 5, 6) contained in the containers (14, 15, 16) drops by gravity through the line (7) and the compression device - reversible expansion (17) in the storage chamber (13) which is at a lower level with respect to the enclosure (11).

In this variant, during the energy storage phases, the pump (17) must supply more mechanical energy (W ") to raise the hydraulic fluid (9) and compress the gas (1, 2, 3). phases of restitution of energy, the relaxation of gas (1, 2, 3) is coupled to the hydraulic fluid level (4, 5, 6) to provide a mechanical energy W ".

FIG. 10 schematically shows another embodiment of the invention in which, before the expansion phase of the gas (1, 2, 3), a thermal energy external to said gas is supplied. This external thermal energy can come from different external sources. Advantageously, such a device comprises a solar collector (52) as external source of thermal energy, which is connected to a heat exchange coil (53) containing a heat transfer fluid and which is immersed in the storage medium (10) contained in a balloon (51). In this figure, the storage of the compressed air is also inside a coil (54), and the storage medium (10) is the hydraulic fluid itself. Of course, other embodiments can be realized, in which the storage medium (10) is heated by a solar collector (52), or by a heat source with a small difference in temperature, knowing that it is one of the special features of the quasi-isothermal system and method according to the invention to be able to value the calories that are brought to it with a very small difference in temperature: if the storage medium (10) is heated by one degree, this already makes it possible to create a significant and usable pressure in the gas (1, 2, 3), which can be converted with high efficiency into mechanical energy via the compression-expansion means.

This embodiment makes it possible, after compression of the gas (1, 2, 3), to heat the thermal storage medium (10) via the solar collector (52). This thermal energy is transferred to the gas (1, 2, 3) by said thermal storage medium (10) and causes an increase in its pressure, which can be converted, with a high efficiency, into additional mechanical energy.

Examples

The present invention will be better understood with the aid of two non-limiting examples of mechanical energy storage described below.

Example 1

Example 1, described with reference to FIG. 1, illustrates a first configuration of implementation of the invention. In this example, the captive gas (1, 2, 3) is nitrogen contained in 3 cylinders of 1 m ³ . The total mass of nitrogen is 344 kg.

It is initially at a pressure of 100 bar and at a temperature of 20 ^° C. At the instant t = 0, water is pumped into the containers (14, 15, 16) with a flow rate of 1.83 m ³ / h. The containers (14, 15, 16) having a limited contact surface with the medium (10), the gas (1, 2, 3) heats up substantially during this compression phase. At time t = 60 min, the gas pressure is 360 bar and its temperature is 75 ^° C. This step stores 9 kWh of mechanical energy. At this time, the system goes into decompression phase by withdrawing an identical flow of 1.83 m ³ / h of water containers (14, 15, 16). At time t = 112 min, the gas found a pressure of 100 bar and a temperature of 1 ⁰ C. This second phase allows to restore 7.5 kWh of mechanical energy. The efficiency of the system is therefore 83%.

Example 2

Example 2 described with reference to FIGS. 1 and 7 illustrates a second embodiment of the invention. In this example, the captive gas (1, 2, 3) is nitrogen contained in 3 coiled tubes as shown in Figure 7. Each tube may contain a gas volume of 1 m ³ . The total mass of nitrogen is 344 kg. It is initially at a pressure of 100 bar and at a temperature of 20 ^° C. At the instant t = 0, water is pumped into the containers (14, 15, 16) with a flow rate of 1, 96 m ³ / h. The containers (14, 15, 16) having a large contact surface with the medium (10), the gas (1, 2, 3) heats very little during this compression phase. At time t = 60 min, the gas pressure is 360 bar and its temperature is 40 ^° C. This step stores 9.4 kWh of mechanical energy. At this time, the system goes into decompression phase by withdrawing an identical flow rate of 2 m ³ / h of water containers (14, 15, 16). At time t = 120 min, the gas found a pressure of 100 bar and a temperature of 17 ° C. This second phase allows to recover 9.0 kWh of mechanical energy. The efficiency of the system is therefore 96%.

The present invention is not limited to the examples described above but encompasses all variants and all equivalents.

Claims

1. A system for storing energy, in particular mechanical energy, comprising

(a) at least one container (14, 15, 16) containing a hydraulic fluid (9) and a gas (1, 2, 3);

(b) at least one storage chamber (13) containing hydraulic fluid

(9);

(c) compression - triggering means capable of "compressing" pump hydraulic fluid (9), and "trigger" mode of expanding hydraulic fluid (9); characterized in that

(i) said hydraulic fluid (9) and / or said gas (1, 2, 3) contained in the at least one vessel (14, 15, 16) is in thermal contact with a thermal energy storage medium (10); ) contained in an enclosure (11); (ii) said container (14, 15, 16) is connected to said at least one storage enclosure (13) by lines (7, 8) for conveying said hydraulic fluid (9) from one to the other through said compression - expansion means;

(iii) said compression-expansion means is capable of pumping hydraulic fluid (9) from the storage chamber (13) to the container (14, 15, 16), and capable of relaxing the hydraulic fluid (9) contained therein in said container (14, 15, 16) to the storage enclosure (13), generating mechanical energy.

2. Energy storage system according to claim 1, characterized in that said compression-expansion means comprises means for converting the generated mechanical energy into electrical energy.

Mechanical energy storage system according to claim 1, characterized in that the energy storage is obtained by compressing the gas (1, 2, 3) contained in the at least one container (14, 15, 16). by the hydraulic fluid (9) which is pumped with said compression - expansion means.

4. System according to any one of claims 1 to 3, characterized in that said container (14, 15, 16) is constituted by a spiral tube or by a plate heat exchanger (60).

5. System according to any one of claims 1 to 4, characterized in that said gas (1, 2, 3) is a condensable gas, and preferably a gas selected from the group consisting of hydrocarbons, CO ₂ , fluorinated hydrocarbons, fluorinated alkanes.

6. System according to any one of claims 1 to 5, characterized in that said thermal storage medium (10) comprises a phase change material.

7. System according to any one of claims 2 to 6, characterized in that it comprises a first group of containers (B1) and a second group of containers (B2), and in that said gas (1, 2, 3) is ambient air, and in that during the mechanical energy storage phase, said first and second groups of containers (B1, B2) operate alternately in air compression or air suction.

8. System according to any one of claims 1 to 7, characterized in that said at least one container (14,15,16) is located inside said enclosure (11).

9. System according to any one of claims 1 to 7, characterized in that said container (43) is located outside said enclosure (1 1), and in that a fluid loop (45) ensures a thermal contact between said thermal storage medium (10) of said enclosure (11) and said hydraulic fluid (47) contained in said container (43).

10. System according to claim 9, characterized in that said container (43) comprises a contactor (44) for improving the gas-liquid contact, and wherein system:

in the mechanical energy storage phase, the hydraulic fluid (9) stored in the storage enclosure (13) is conveyed by a line (8) to said compression-expansion means and then by a line (42) to said container (43) for compressing the gas (48);

- In the mechanical energy recovery phase, the gas (48) is expanded by releasing the fluid (47) by a line (41) to the compression-expansion means and then by said line (8) to the storage enclosure (13).

The system of claim 10, wherein: in the energy storage phase, said contactor (44) makes it possible to maintain the quasi-isothermal gas and to transfer the calories towards the hydraulic fluid (47), a fluid loop (45) making it possible to convey the calories of the fluid ( 47) to the thermal storage medium (10);

in the energy recovery phase, the fluid loop (45) makes it possible to restore the calories stored in the thermal storage medium (10) to the hydraulic fluid (47).