Patent ID: 12218499

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure relates to the field of sustainable energy systems, and more specifically, but not exclusively, to a hydraulic compressed air energy storage system capable of storing compressed air at extremely high pressure while controlling the charging and discharging of the system so as to minimize inefficiencies. The system is capable of consuming electrical power, for example, during low-demand periods, to compress air and thereby charge the system. The system is further configured to release the compressed air, for example, during periods of peak energy demand, to thereby pump liquid through a liquid turbine to thereby generate electrical power.

Energy Storage Systems

Referring now toFIG.1, system10includes two or more air and liquid tanks12. Air and liquid tanks serve a dual function: housing a liquid piston for compressing air, and receiving compressed air for pumping liquid through a liquid turbine.

Each air and liquid tank may be generally shaped as a cylinder. A central tube may extend from the top of the cylinder to nearly the bottom of the cylinder, thus defining an annulus section between the central tube and the external walls of the cylinder. In exemplary embodiments, the central tube is connected to piping for the inflow and outflow of liquid. The annulus section is connected to piping for the inflow and outflow of air.

Each of the air and liquid tanks12is interconnected with the other air and liquid tanks, for example with piping. As a result, liquid and air that are pumped out of one air and liquid tank12may enter another air and liquid tank12.

Air and liquid tanks12may be of any suitable materials and dimensions for carrying out the functions described herein. In exemplary embodiments, air and liquid tanks12have a volume of approximately 1,000 L. Likewise, the liquid may be any liquid suitable for carrying out the functions describe herein. The air may be atmospheric air, and may alternatively be any suitable gas. For example, the air may be carbon dioxide or nitrogen. In exemplary embodiments, the liquid is water, and the air is conventional atmospheric air.

Each air and liquid tank12is connected to an air inlet11. Air inlet11may be a valve that is open to the atmosphere. When the system10uses air other than air, or when the system10is located in a location without access to atmospheric air (for example, underwater or underground), the air inlet11is connected to a suitable source of uncompressed air, for example a large air tank.

At least one pump18is included along a fluid path of the air and liquid tanks12. The pump18is used to pump liquid between air and liquid tanks12during charging of the system10. Operation of the pump is controlled by controller20, and power for the operation of the pump is supplied by power source21. Power source21may be any suitable power source, such as electrical power from a power grid. In exemplary embodiments, power source21is an array of solar panels.

Each air and liquid tank12may have one or more nozzles23associated therewith. The nozzles23are used to pump a volume of cooling fluid onto the exterior of air and liquid tanks12, during compression of the air. In exemplary embodiments, the nozzles are directed at the upper portions of the air and liquid tanks12, which is the location at which the air is compressed within the air and liquid tanks. This cooling fluid counteracts the natural thermodynamic heating of air during compression thereof. An advantage of cooling the air is that performing the compression and expansion of the air as isothermal processes is more energy-efficient than the equivalent adiabatic processes. Calculations supporting this contention will be provided at the end of the present disclosure. Although operation of the nozzles does require some infusion of energy, the mass flow of water used for cooling is very small compared to the mass of water used for compression. Typically, pump18may, in addition to pumping the liquid during compression of the air, also supply the small mass flow needed for cooling the air.

Nozzles23, or a different set of nozzles, may also be used to pump a volume of warm fluid at the air and liquid tanks12, during decompression or discharge of the air, so that discharge of the system also proceeds isothermally.

System10further includes a plurality of compressed air tanks14. Compressed air tanks14receive compressed air from the air and liquid tanks12. The pressure in each compressed air tank14may be monitored by a pressure sensor24, which may communicate its pressure readings to a central controller20. On the basis of these pressure readings, the controller20determines which compressed air tank14to open to receive therein compressed air or to release therefrom compressed air.

Compressed air tanks are made of any suitable material, such stainless steel. In exemplary embodiments, the compressed air tanks are made of carbon fiber.

In exemplary embodiments, the compressed air tanks14are configured to maintain the compressed air at a pressure of at least 40 bar. The pressure may be maintained significantly higher than 40 bar, such as 80 bar, and even as high as up to 400 bar, to thereby increase the energy storage density. In theory, the only upper limit for the pressure of the air is the pressure at which the air liquefies, for a given temperature of the air. One advantage of maintaining this higher pressure is that more energy is stored for the same volume of apparatus. However, storage of the air at higher pressures also poses physical challenges. For example, the container bodies must be sufficiently strong to maintain the compressed air at such pressures. Furthermore, a single container at high pressures may be prone to leaking, which results in inefficiency. In preferred embodiments, to address this concern, rather than using a single compressed air tank with extremely thick walls, system10uses multiple compressed air tanks14. These multiple compressed air tanks14each have a comparatively, often significantly, smaller volume than the air and liquid tanks12. The smaller volume tanks may maintain the same pressures with thinner walls. Moreover, when a smaller volume tank leaks, the resulting loss of compressed air is less than that when a larger volume tank leaks.

In exemplary embodiments, air tanks may be repurposed from other uses for compressed air, for example for medical oxygenation, underwater diving, or workshop burners.

Another challenge raised by maintaining the compressed air at extremely high pressure is that the air heats significantly when compressed and correspondingly cools when expanded. According to Gay-Lusssac's law, when volume is maintained constant, temperature of a gas is directly proportional to pressure of the gas. Thus, increasing a pressure of a gas within a container from 40 bar to 80 bar, for example, has an effect of doubling its temperature. Uncontrolled cooling of air from 80 bar down to atmospheric pressure causes diversion of the stored energy from the turbine, and thus reduced efficiency. Use of multiple small tanks also helps address this challenge. It is easier to control the volume and rate of release of air from many small tanks as compared to from a single large tank.

Yet another advantage of the use of multiple small compressed air tanks14is the flow rate of compressed air from the different compressed air tanks14may be more easily regulated. This may be desirable in situations in which it is desired to generate a consistent stream of power over a period of time, as opposed to a cumulative amount of power.

An additional advantage of storing the air at as high a pressure as possible is cost savings. Maintaining the compressed air at a higher pressure helps maximize the energy that is capable of being generated, for every unit of area on which the system is implemented. This, in turn, helps manage the cost of the system, and in particular renders the cost of implementation of such a system to be comparable to, or even more favorable than, the cost of alternatives such as batteries.

In exemplary embodiments, there may be as many as hundreds of compressed air tanks14. These compressed air tanks14may be contained in a container, built as a wall, may be connected in one group or several remote groups, and may be installed below or above ground. Compressed air tanks14may also be thermally insulated, for example within a water bath. Compressed air tanks14may particularly be located at the bottom of a body of water, such as an ocean. Advantageously, the pressure of the water on the outside of the tanks14helps equalize the pressure of the compressed air within the tanks14, thus enabling thinner construction of the tanks14. Examples of suitable arrangements of compressed air tanks14are described below in connection withFIGS.5A-7.

System10further includes at least one turbine16. Turbine16is, in preferred embodiments, a liquid turbine. This is in contrast to conventional compressed air energy systems which use air turbines. During discharging of system10, compressed air is released from the compressed air tanks14through the air and liquid tanks12. This, in turn, causes flow of liquid from the air and liquid tanks and through the turbine16. Turbine16is operatively connected to generator22, so that rotational energy of turbine16may be converted into electrical energy.

The use of a liquid turbine is particularly advantageous when working with pressures as high as 80 bar, or even higher. When air at pressures of up to 80 bar or higher is depressurized at an air turbine, there is a high likelihood of formation of ice. Formation of ice would stop the operation of the air turbine. One solution for avoiding such ice formation is to warm the air when the air passes through the turbine. However, such warming would be energy-inefficient. Using a liquid turbine instead of an air turbine minimizes this concern. Since the water is incompressible, and has a much higher heat capacity than air and other gases, the water temperature does not decrease below the freezing point. Optionally, the liquid that is delivered through the liquid turbine is heated, which further prevents the formation of ice. The liquid may receive heat from the compressed air or other air during the compression of the air or other air, when it is injected into the compression tanks to ensure isothermal compression. The liquid may alternatively be heated by a liquid nozzle, similar to nozzle23. The same liquid that is used for cooling during compression of the air may subsequently be heated and used to provide heat during decompression of the air. This nozzle may be operated by a feed line from the high pressure air storage tanks14, and the energy required to operate the nozzle expends a small amount of energy relative to the energy used to compress the air.

FIG.2is a schematic diagram illustrating the use of the air and liquid tanks as a liquid piston, according to embodiments of the present disclosure. A liquid piston concept is advantageous for improving the efficiency of air compression. Because a liquid can conform to an irregular chamber volume, the liquid may substantially fill an entire air and liquid tank during compression of air, thereby maximizing the surface-area-to-volume ratio. A liquid piston also eliminates air leakage and replaces sliding seal friction (which is present with solid pistons) with viscous friction. The liquid may also be used as a medium to carry heat into and out of the air and liquid tanks12. When the air is compressed, it generates heat, which is transferred to the liquid. When the air is decompressed, it cools, and this cooling is transferred to the liquid. The use of a liquid piston thus assists in the maintaining of near-isothermal operation.

As illustrated inFIG.2, motor26drives pump18. Pump18drives fluid to and from the liquid pistons according to the configuration of switching valve28. A conventional liquid piston arrangement includes two air and liquid tanks12, in which one air and liquid tank12is always filling with liquid while another air and liquid tank12is always emptying of liquid. In the embodiment illustrated inFIG.2, there are three air and liquid tanks12a,12b,12c. Tank12ais filling with liquid to thereby compress air, while one of the tanks12bor12cis emptying of liquid and filling with air. In general, when three or more air and liquid tanks12are used, the switching valve28may be configured such that, at any given time, one air and liquid tank12is filling with liquid and at least one of the other tanks12is filling with air. This three tanks arrangement enables different compression stages schemes to be implemented easily and with maximal control and efficiency of the compression process.

The air and liquid volumes of tanks12a,12b, and12care interconnected. This interconnection enables configurable work cycles of system10, in a similar manner to a multiple piston liquid fuel engine, in which the air and liquid tanks12circulate air and liquid between each other.

As any given air and liquid tank12is emptied of liquid, the volume of air and liquid tank12is filled with air, via an air inlet32and non-return valve30. Following the filling of an air and liquid tank12with air, the switching valve28, is switched to cause liquid to enter the air and liquid tank12. The incoming liquid compresses the air within the tank12up to a predetermined volume. The compressed air is then transferred through non-return valve31into compressed air tank14.

FIGS.3A and3Bfurther illustrate different components of system10, and in particular the flow of fluid and air during charging and discharging of system10. System10includes three air and liquid tanks12a,12b,12c, each of which stores controllable interdependent volumes of liquid and air. Dedicated air and water passages42,44,46connect between the air and liquid tanks12a,12b,12c.

During charging of system10, incoming liquid is fed into air and liquid tanks12through passages44or46to force compression and outflow of air, via passage42, toward compressed air tank14. During discharging of system10, compressed air is fed in the reverse direction, namely from compressed air tank14, through passage42to tanks12. The compressed air forces outflow of liquid through passage44to turbine16. One or more integrated pumps are connected inline to the passages44,46, for pumping liquid into the air and liquid tanks during charging of the proposed system. A generator is connected to the turbine for generating electric power when liquid is forced from the air and liquid tanks12towards the turbine during discharging of the system.

In the embodiment ofFIGS.3A and3B, the same air and liquid tanks are used during both the charging and discharging of the system10. One advantage of this configuration is that it requires less space for the entire system10. Another advantage of this configuration is that the liquid may act as a medium for equalizing heat transfer. During the compression of the air, heat is transferred from the air to the liquid. During the decompression of the air, cold is transferred from the air to the liquid. As a result, little heat or cold is lost to the outside environment.

As shown inFIG.3A, there are three air and liquid tanks12a,12b, and12c. Each air and liquid tank12a,12b,12cincludes a central tube13a,13b,13c. Annulus regions11a,11b,11care defined between the tube and the outer walls of the tank12a,12b,12c. Each annulus region11a,11b,11cis operatively connected to piping42, which may be galvanized piping. Galvanized piping42extends between each air and liquid tank12a,12b,12cand the compressed air tank14, via a flow control valve31a,31b,31cand pressure regulating valve38. The compressed air tank14also includes pressure safety valve40. In typical embodiments, there are multiple compressed air tanks14, each with its own pressure safety valve40, as discussed above in connection withFIG.1. Each annulus region11a,11b,11calso includes an air intake pressure safety valve36a,36b,36c, and an additional air outlet safety valve34a,34b,34c. The central tubes13a,13b,13care operatively connected to turbine16, via piping44, which may be, for example, carbone steel piping. The flow path between the central tubes13and turbine16includes check valves and flow control valves38a,38b,38c. An additional piping network46connects fluid from an outlet of the turbine16back to the air and liquid tanks12.

The arrows inFIG.3Adepicts the flow of air and liquid through system10when the system10is being charged. Charging of the system10is also referred to herein as the compression stage. In each air and liquid tank12, liquid enters the tank12via pipe13, while air enters the annulus portion11of the tank12from outside the tank12. The liquid rises within the annulus portion11to thereby compress the air that is therein. This compressed air is output through piping42to the compressed air tank. The liquid is then recirculated through piping44,46back to the pipe13, while the annulus portion11refills with air. The liquid during the compression stage is pressurized in a pump41connected to pipe44, and a valve45to the turbine16is closed. Only in the discharge stage is the valve to the turbine opened and water flow through the turbine16produces electricity.

Optionally, system10further includes one or more liquid tanks (not shown). The liquid tanks are used to store liquid exiting the air and liquid tanks12through piping44. In exemplary embodiments, during the charging stage, the liquid is routed through piping44,46and optionally the storage tank without entering turbine16, so that it is not necessary to exert energy to rotate the turbine during the charging stage.

The arrows inFIG.3Bdepict the flow of air and liquid through system10when system10is being discharged. Compressed air exits compressed air tank14and enters each air and liquid tank12through the annulus section11. The compressed air forces liquid from the tank through tube11and up through piping44, through the liquid tank if present, and through turbine16. The compressed air remains in the air and liquid tank12and expands to fill the entire volume of the air and liquid tank12. The liquid then recirculates through piping46, refilling air and liquid tank12, expelling the expanded air from the annulus11. An additional round of compressed air is then pumped into the annulus11, and the cycle is repeated anew, until all the air is restored to atmospheric pressure.

Notably, unlike standard discharge systems, which discharge a store of compressed air in a single burst, often thereby displacing a single, large volume of liquid, the discharge of the compressed air according to the embodiment ofFIG.3Bis a cyclical discharge system. This cyclical discharge system uses a small volume of fluid during the entire process. The fluid is circulated between two or more air and liquid tanks12, using the air expanded from the compressed air tanks14, or a part of this compressed air.

Optionally, turbine16is equipped with a flywheel. The flywheel smooths delivery of power through the turbine, during a change-over between air-and-liquid tanks12.

The discharge system, according to embodiments of the present disclosure, may be operated in various modes, ranging from full storage discharge (e.g., the entire volume of compressed air, from the maximum pressure to atmospheric pressure) to partial discharge discharged in series. The discharge system may also run in a predetermined cycle optimize to achieve best efficiency and moderate variations in the total integrated power output.

FIG.4depicts a second embodiment of a compressed air energy storage system200. System200is similar in most respects to system10, and accordingly similar reference numerals are used to refer to similar elements, except that the reference numerals begin with “2.” System200differs from the previous embodiment in that, during charging of the system200, air is compressed in multiple stages. Similarly, during discharge of system200, the air is decompressed in multiple stages. By way of example, suppose that the maximum pressure achieved in the compressed air tanks is approximately 80 bar. Reference to 80 bar is merely an example, and, in exemplary embodiments, even higher pressures may be reached. However, increasing air pressure directly from 1 bar to 80 bar, in a single stage, may cause an uncontrollable increase in temperature of the air, thus causing loss of energy to thermal processes. To enable more precise control over the compression and resulting temperature effects, the compression may proceed in stages. For example, tanks212aand212bare used as liquid pistons, in the manner set forth above, to compress air from atmospheric pressure to a first pressure level (for example 20 bar). Tanks212aand212bshare a single volume of liquid which is passed between tanks212a,212bvia piping241. This compressed air is introduced into tank252. While the illustrated embodiment depicts only two tanks212a,212b, there may also be a third air and liquid tank at this stage, as disclosed in the previous embodiments. In tank252, the air is compressed to a second pressure level, (for example 40 bar). This compressed air and liquid is then introduced into tank254, where the air is compressed again until it reaches a third pressure level (for example 80 bar). The liquid in tanks252and254is interconnected via piping243and tank260. The volume of tank254may be less than the volume of tanks212a,212b, and252, owing to the high pressure at which air is maintained therein. In the illustrated embodiment, tank254is approximately a quarter the volume of tank252and tanks212a,212b. From tank252, the compressed air is transferred and stored into the compressed air tanks214.

Similarly, during the discharge of the system200, the depressurizing of air proceeds in stages. Depressurizing the air from 80 bar to atmospheric pressure in a single stage may result in an undesired loss of energy due to uncontrolled cooling of the air. In order to control the expansion process, during a first stage of discharge, the compressed air drives liquid between air and liquid tanks262a,262band liquid turbine270. As discussed above, it is also possible for there to be a third air and liquid tank at this stage. Liquid turbine270is designed to receive liquid between the pressures of 40 and 80 bar. When the air has expanded sufficiently that its pressure is below, for example, 40 bar, the air continues to be circulated through air and liquid tanks262a,262b, but is routed through turbine272. Turbine272is configured to receive liquid at a lower pressure than turbine270, for example, at 10 to 40 bar. When the air pressure has reached the lower range of turbine272, the air and liquid are routed from turbine272to air and liquid tanks264and266. The air and liquid are exchanged between air and liquid tanks264,266and through a third turbine274. Turbine274is designed to receive liquid at a lower pressure than turbine272, for example, at pressures of between 3 and 10 bar. Following expansion of the compressed air to the equilibrium pressure through turbine274, the system is completely discharged.

An advantage of using multiple turbines270,272,274is that turbines used during discharge of the disclosed hydraulic compressed air energy storage systems are subjected to a very wide head range. For example, the head range may extend from 800 meters at highest pressure to 20 meters at lowest pressure. Since 1 meter of head is equivalent to 0.098 bars, this translates to approximately 80 bar to 2 bar. Rather than attempting to incorporate a turbine that operates efficiently at this vast pressure range, system200uses a number of turbines, each operating at only a part of the range.

In an alternative use for the system200, instead of carrying out all of the compression stages to raise the pressure of the compressed air to 80 bar, a user may stop compressing the air after the first or second stages. As a result, the user may raise the pressure to a pressure that is lower than the maximum that may be achieved with system200. For example, the pressure may be raised to 40 bar. Such implementations may be desired when there is less time available to charge the system, or when the power needs from the system are sufficiently low that a lower pressure is sufficient to meet them.

In addition or in the alternative to the use of multiple turbines, other mechanisms are possible for controlling the discharging of the compressed air. For example, any of the turbines used in connection with any of the above-described embodiments may employ a counter-pressure mechanism. The counter-pressure mechanism may be a computer controlled variable valve. This counter-pressure mechanism may prevent the turbine from spinning unless the pressure against the turbine exceeds a predefined minimum. The force of the counter-pressure may be controlled as desired, for example gradually decreased, in order to regulate the pace of the decompression of the air. In addition or in the alternative, a blade angle or guide vane angle of the turbine may be adjusted to meet different flow conditions and to keep the efficiency stable, despite any variations in flow rate of liquid through the turbine.

As discussed above in connection withFIG.1, isothermal compression of the air provides greater energy efficiency than adiabatic compression, with all other factors being the same. The below calculations demonstrate this principle. In the given example, the compressed air is first compressed from standard temperature and pressure conditions into a volume of 50 cubic meters and a pressure of 10 bar. The calculations demonstrate that, although more work is initially required to compress the air under isothermal conditions, the overall efficiency of the system under isothermal conditions, as defined by the percentage of work released during discharge as a percentage of the work introduced during charge, is higher.

Adiabatic Compression

Suppose that air is compressed from atmospheric pressure and temperature into a vessel having a volume of 50 cubic meters, and to a pressure of 10 bar. At the start of the compression, P1=1 bar, and T1=300 K. The mass of the air may be derived according to the following equation:

M1=P1⁢VR⁢T1=1⁢05[Pa]*50[m3]831429[Jk⁢g*K]*300⁢K=58.13kg
At the end of the compression, P2=10 bar. In an adiabatic chamber, and assuming the compression is isentropic, the final temperature and mass of the gas are derived according to the following equation:

P11-k*T1k=P21-k*T2k-→T2=T1(p1p2)1-kkT2=3⁢0⁢0⁢(1⁢01)k-1k=3⁢0⁢0*1⁢0⁢1.4-11.4=578⁢KM2=P2⁢VR⁢T2=1⁢0*1⁢05[Pa]*50[m3]8⁢3⁢1⁢42⁢9[Jk⁢g*K]*578⁢K=301.7kg
The change in energy during this compression is governed by the following equations. As can be seen, the final value for the work is negative, meaning that work is invested.

d⁢E=d⁢Q-d⁢W+∑ihi⁢d⁢mi-→d⁢U=-d⁢W+h0⁢d⁢m0⁢h0=cp⁢T0U2-U1=-W+h0(m2-m1)⁢m2⁢Cv⁢T2-m1⁢Cν⁢T1=-W+Cp⁢T0(m2-m1)W=Cp⁢T0(m2-m1)+Cv(T1⁢m1-T2⁢m2)=-36,494⁢kj=-10.1kwh
Given enough time between charge and discharge of the pressure tank, and depending on the features of the heat transfer of its surroundings, the compressed air in the container cools back to the environmental temperature, and the pressure drops accordingly from 10 bar to 5.17 bar.

P3=M2⁢R⁢T3V=301[kg]*0.2⁢867[Jkg*K]*300[K]/50[m3]=517.7[K⁢pa]=5.1⁢7[Bar]
In summary, there is now 301 kg of compressed air at a pressure of 5.17 bar at 300 K.
Isothermal Compression
Once again, the initial pressure P1=1 bar and initial temperature T1=300 K. Accordingly, at the start of compression, the mass of the air is 58.13 kg, as before.

M1=P1⁢VR⁢T1=58.13kg
At the end of the compression, P2=10 bar, and T2=300 K. As a result, the final mass is calculated as:

M2=P2⁢VR⁢T1⁢2=1⁢0*1⁢05[Pa]*50[m3]8⁢3⁢1⁢42⁢9[Jk⁢g*K]*300⁢K=581⁢kg
Notably, this total mass is almost two times the 301 kg mass achieved with adiabatic compression. Furthermore, because the gas is at environmental temperature, there is no need for the gas to cool, and no resulting loss of pressure.

Applying the first law of thermodynamics under a controlled volume:

d⁢E=d⁢Q-d⁢W+∑ihi⁢d⁢midU=-dW+h0⁢d⁢m0>-U2-U1=Q-W+h0(m2-m1)W-Q=m1⁢Cv⁢T1-m2⁢Cν⁢T2+Cp⁢T0(m2-m1)T2=T1=T0>-W-Q=Cv⁢T0(m1-m2)+Cp⁢T0(m2-m1)=R⁢T0(m2-m1)

In addition, assuming that the process is reversible and isothermal:

d⁢S≥d⁢QT+∑iSi⁢d⁢midS=d⁢QT0+S0⁢d⁢miS2-S1=QT0+S1(m2-m1)⁢S0=S1=Constm2⁢S2-m1⁢S1=QT0+S1(m2-m1)>-Q=T0⁢m2(S2-S1)Q=T0⁢m2(Cp⁢ln⁢T2T1-R⁢ln⁢P2P1)>-Q=-R⁢T0⁢m2⁢ln⁢P2P1=-1⁢15,064⁢kj=31.96kwhW=Q+R⁢T0(m2-m1)=-70,080⁢kj=-19.46kwh

Thus, the work invested into the system is 19.46 kWh for obtaining 581 kg compressed air at 10 bar. By contrast, in the adiabatic case, an investment of 10 kWh is applied to get 301 kg compressed air at 10 bar. When considering a difference in the resulting masses from the initial mass of 58 kg, it is evident that, for isothermal compression, less than twice the work is needed to achieve more than twice the increase in mass. This increase in mass of the compressed air is directly proportional to the amount of energy that can be obtained from decompression of the compressed air.

Accordingly, these calculations exemplify the established principle that the minimum work required to compress air is with an isothermal process.

Combined High Pressure Storage Receptacles

Referring now toFIGS.5A-7, as discussed above in connection withFIG.1, it is more efficient and cost-effective to store large volumes of high pressure air, or other gases, in multiple small containers as compared to a single large container. Embodiments of arrays of high pressure receptacles are accordingly described below.

High pressure receptacles that may accommodate pressures higher than 40 bar, such as 150 bar or even higher, are hard and costly to produce. The cost of production stems from mechanical and safety constraints that require a material strong enough for the production of the receptacle, as well as high-quality production processes for ensuring a hermetic volume. The cost of the receptacle exponentially grows with the volume of the receptacle. For example, a 50 m3receptacle adapted for 40 bar pressure may cost $100,000, but a receptacle adapted for 150 bar may cost four times as much as the 40-bar vessel. Generally, the cost of production and deployment of a high-pressure vessel increases linearly according to the nominal pressure, but exponentially based on the volume.

Referring now toFIG.5A, a combined receptacle300includes an array of low volume and high pressure cylinders312. Cylinders312may be of a type that are used for storing compressed gases in other industrial contexts, such as assisted breathing, underwater diving, or workshop burners. These conventional cylinders are generally inexpensive; for example, the cost of an industrial high-pressure cylinder, having a gas volume of 40 liter and nominal pressure of 150 bar, is $30-50. A plurality of high pressure cylinders312may be stacked together. Each cylinder312is connected to a piping system314for transferring the compressed air in and out of the combined receptacle300, and including pressure sensors and valves for regulating the volume of air in each individual cylinder312. The piping system314includes a central port315for transferring pressurized air in and out of the combined receptacle300. For example, the piping system may be connected to a liquid piston arrangement for compressing the air, as described above. Alternatively, the cylinders312may be implemented in any system that requires storage of a large quantity of compressed air.

In the illustrated embodiment, the cylinders312are arranged in a 6×6 array. The 6×6 array thus forms a combined receptacle with36different cylinders312. In a case in which each receptacle312contains 40 liters and holds air at a pressure of 150 bar, the combined receptacle300provides, in total, storage of 1440 liters at 150 bar. The expected cost of this combined receptacle300is approximately half of that of a single receptacle with the same characteristics. This ratio is expected to grow as the total volume of the combined receptacle300increases. In alternative embodiments, the arrays may include, for example twelve or twenty four cylinders312.

Combined receptacle300may be adapted for use deployed on the ground, underground, or underwater. Typically, high-volume, high-pressure containers require only minimal maintenance. Therefore, it is typically cost-effective to store such containers underground or underwater, where the storage space may be less expensive, so long as an adequate approach is left for maintenance. Deployment on ground or underground may require insertion of the combined receptacle in a protective casing, such as a shipping container. Deployment underwater requires insertion of the combined receptacle300in a water-tight casing, in order to protect the combined receptacle from undesired exposure to moisture and salinity.

FIG.5Billustrates an exemplary above-ground combined receptacle300a. The cylinders312are stored in a storage receptacle316a. Receptacle316amay be made of any material suitable for protecting the cylinders312from their environment. For example, receptacle316may be a commercial shipping container. Receptacle316ahas a service hatch318through which maintenance staff may access the cylinders312and piping314.

FIGS.5C and5Ddepict an under-sea deployment system for a combined receptacle300b. Combined receptacle300bis stored in a storage receptacle316b, which may be of plastic material formed as a watertight structure, adapted to protect the combined receptacle300from under-sea ambient and weather-related hazards. Receptacle316bmay have a maintenance entry318on a top portion thereof. The entry318may be positioned in an optimal location for an underground storage tank.

In preferred embodiments, the cylinders312are arranged with their longitudinal axes parallel to each other, and parallel to the horizontal axis of the storage container316aor316b. In addition, the cylinders may be stacked in a configuration that matches the geometry of the storage receptacle, such as in a rectangular configuration (as inFIG.5B) or in a substantially cylindrical configuration (as shown in FIG. Advantageously, orienting the cylinders in this way allows for easier filling of the compressed air from the piping system314into each cylinder312, as well as easy access to all of the pipes of the piping system314for an individual standing within the storage receptacle316aor316b.

Referring now toFIGS.6A and6B, in certain advantageous embodiments, it is desirable to anchor a receptacle underwater so that the receptacle will remain stationary despite ocean storms and currents. InFIG.6A, system350includes receptacle356installed on a surface364of a body of water366. The receptacle356includes an entry hatch355and arrays of high pressure storage containers352. The system further includes anchoring pillars comprised of piers360and foundations358embedded in the surface364. An anchoring arm362extends between the piers360and runs along the entire length of receptacle356. The anchoring arm362, in conjunction with piers360and foundations358, anchors the array to the surface364.

FIG.6Billustrates another embodiment of a receptacle array370with an anchoring system. The main difference between the embodiment ofFIG.6Band that ofFIG.6Ais that, in the embodiment of array370, entry hatch375is at the side of receptacle376, rather than in the center of receptacle376. A staircase379and ladder381optionally provide access from the hatch375to the bottom of receptacle376. As illustrated inFIG.6B, an array of cylinders372is supported internally by vertical beams371and373, and by horizontal beams377. In addition, the entire array370is anchored to surface384of body of water386by foundations378, piers380, and anchoring arm382.

Referring now toFIG.7, systems for storage of energy using compressed air are characterized by two different requirements for the storage tanks. On one hand, it is necessary to have an array of high pressure tanks for storing air at pressures of 150 bar and up. This requirement is addressed by the embodiments addressed above. The other requirement relates to the very large storage volumes required for the uncompressed air. In certain embodiments, the uncompressed air may be drawn from ambient atmosphere. However, when the compressed air storage tanks are stored underwater, it may be advantageous to likewise retain a store of uncompressed air underwater, so that the entire system may be run entirely underwater.

FIG.7depicts an exemplary low-pressure underwater large volume storage system400. According to embodiments of the present disclosure, system400may contain one or more large tanks410. The tanks400may be made of plastic, rubber, or a similar lightweight material. The tanks410may be deployed under sea-level not far away from the shore, at depths of 20-40 meters, thereby taking advantage of the sea water pressure at the installation level, which may be as high as a few bars. Tank410may be tied or anchored to by bottom of the sea by heavy objects404, which may be, for example, concrete blocks or sand bags. One or more pipes402may connect tank410to an on-shore installation. In alternative embodiments, pipes402connect tank410to an underwater installation.

Although embodiments of the present disclosure have been described by way of illustration, it will be understood that disclosed embodiments may be carried out with many variations, modifications, and adaptations, without exceeding the scope of the claims.