GB2475295A

GB2475295A - Energy storage apparatus with two linked chambers

Info

Publication number: GB2475295A
Application number: GB0919869A
Authority: GB
Inventors: Derek Hunter
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-11-13
Filing date: 2009-11-13
Publication date: 2011-05-18
Anticipated expiration: 2029-11-13
Also published as: GB0919869D0; GB2475295B

Abstract

Apparatus 10 for storing energy, the apparatus comprising a first chamber 64 and a second chamber 60, the chambers 60,64 each having a variable volume and being operably linked, such that expansion of the first chamber 64 causes expansion of the second chamber 60, and contraction of the second chamber 60 causes contraction of the first chamber 64; the second chamber 60 being adapted to contain a volume of reduced pressure relative to ambient pressure in its expanded configuration. The apparatus 10 has a charging configuration wherein the first chamber 64 is charged with fluid for increasing the volume of the first chamber 64, thereby causing expansion of the second chamber 60. The apparatus 10 may also have a discharging configuration wherein the second chamber 60 is contracted, causing contraction of the first chamber 60 which causes fluid to be discharged. A second apparatus comprising a single variable volume chamber, an enclosing wall, a moveable closure and a deformable seal is also disclosed.

Description

I

Title: Improvements relating to apparatus for storing energy This invention relates to apparatus for storing energy.

A wide variety of apparatus exists for storing energy, with many being electrical or mechanical in nature. Examples include electrochemical cells, capacitors, thermal storage apparatus, and mechanical apparatus utilising compressed gas, spring-loading and/or raised weights.

Apparatus for storing energy has many applications. In particular, such apparatus may be used to store energy supplied by a power source over a relatively long period of time, and then discharge that energy in a much shorter period of time.

Alternatively, such apparatus may be used to store energy from a power source during periods of low demand, and then discharge that energy in periods of high demand. Furthermore, such apparatus may be utilised to provide a transportable source of energy.

Mechanical energy storage apparatus is often referred to as an "accumulator", an example of which is a weight-loaded accumulator. This is typically a very large device, with concrete disks loaded onto an oversized piston. Often found in older, high-demand applications, such as steel mills, weight-loaded accumulators have a large capacity and uniform output pressure, but present problems with installation and servicing. Another example of mechanical energy storage apparatus is a spring-loaded accumulator, which is generally small and lightweight; they are useful in mobile applications and have the added benefit that a spring gives a repeatable output force. However, spring-loaded accumulators are limited to small volumes and pressure.

The most common accumulator is a gas-loaded accumulator, which uses the compressibility of a gas (usually nitrogen) for storing energy. In most cases, they have hydro-pneumatic components including a fluid compartment, a gas compartment and a gas-tight element separating the two (except for air receivers which have no separating element). The fluid section connects to the hydraulic circuit so that as pressure rises in the hydraulic circuit, fluid enters the accumulator and the gas compresses. Then, as pressure in the hydraulic circuit falls, the compressed gas expands and forces the stored fluid back into the hydraulic circuit.

Hydro-pneumatic accumulators that use compressed gas have inherent disadvantages when required for storing and distributing energy over long periods.

Storing large amounts of energy in the form of compressed gas generates excessive heat, and the pressures reached mean that substantially engineered vessels are required for manufacture. Furthermore, the construction of suitable seals for use in such accumulators is often problematic. These problems often limit the usability of such apparatus.

There has now been devised improved apparatus for storing energy which overcomes or substantially mitigates the above-mentioned and/or other

disadvantages associated with the prior art.

According to a first aspect of the invention, there is provided apparatus for storing energy, the apparatus comprising a first chamber and a second chamber, the chambers each having a variable volume and being operably linked, such that expansion of the first chamber causes expansion of the second chamber, and contraction of the second chamber causes contraction of the first chamber, the apparatus having a charging configuration in which the first chamber is adapted to be charged with fluid for increasing the volume of the first chamber, thereby causing expansion of the second chamber, the second chamber being adapted to contain a volume of reduced pressure relative to ambient pressure in its expanded configuration.

The apparatus preferably also has a discharging configuration in which the second chamber is adapted to contract, thereby causing contraction of the first chamber, and the first chamber is adapted to discharge fluid from the first chamber.

According to a further aspect of the invention, there is provided a method of storing energy, which method comprises the steps of: (a) providing apparatus as described above; (b) increasing the volume of the first chamber by charging the first chamber with fluid, thereby causing expansion of the second chamber; and (c) containing a volume of reduced pressure relative to ambient pressure in the second chamber in its expanded configuration.

The method according to the invention preferably also includes a step of releasing energy by enabling the second chamber to contract, thereby causing contraction of the first chamber and discharge of fluid from the first chamber.

The apparatus and method according to the invention are advantageous principally because the creation of a volume of reduced pressure within the second chamber stores energy provided by the fluid within the first chamber. Furthermore, contraction of the second chamber preferably causes that energy to be discharged to the fluid within the first chamber. The apparatus according to the invention therefore provides a means for storing energy that may have a simple construction, and which may be efficient and readily controllable. In particular, the apparatus according to the invention may provide a constant output force, but without the inherent problems encountered by those of the prior art. The invention also allows for more efficient design than for conventional accumulators as the pressures reached during operation are readily calculable and therefore allows accurate manufacture of the apparatus.

The volume of reduced pressure relative to ambient pressure is preferably an approximate vacuum.

The first chamber preferably comprises an inlet and an outlet for the fluid. The inlet and outlet may be defined by the same fluid passageway, or may be defined by separate fluid passageways. The inlet and the outlet preferably each include a valve, such that in the charging configuration the inlet valve is open and the outlet valve is closed, and in the discharging configuration the outlet valve is open and the inlet valve is closed. The apparatus may also have a storage configuration in which both the inlet and outlet valves are closed, which is preferably sufficient to maintain the apparatus at equilibrium.

A controller is preferably provided that enables the configuration of the apparatus to be controlled. This controller may be programmable and/or manually controllable, depending upon the application.

The inlet is preferably adapted to be connected to a source of fluid having a pressure sufficient to cause expansion of the first chamber. This source of fluid may therefore be a hydraulic system, and the fluid may be a hydraulic fluid. In particular, charging of the first chamber with fluid is preferably achieved by opening the inlet valve. The outlet is preferably adapted to be connected to means for extracting energy or providing useful work from a fluid flow, eg a turbine. Similarly, discharge of energy from the first chamber, and hence extraction of energy from the fluid flow, is preferably achieved by opening of the outlet valve.

The first and/or second chamber is preferably adapted to have a variable volume by the provision of a wall element that is movable relative to another wall element of the chamber.

The first and/or second chamber preferably comprises an enclosing wall and a closure, which together define the chamber, wherein the closure is movable relative to the enclosing wall, such that the volume of the chamber is variable. In one embodiment, the first and/or second chamber comprises an enclosing wall having a closed end, a length of wall having a constant internal cross-sectional area and a closure slidably mounted therein. For instance, the closure may be a conventional piston or ram slidably mounted within the walls of a cylindrical enclosing wall.

Where the first and/or second chamber is adapted to have a variable volume by the provision of a wall element that is movable relative to another wall element of the chamber, the first and/or second chamber may comprise an enclosing wall including one or more portions of variable dimensions. In particular, the enclosing wall may include a portion of variable length, ie along a linear axis, such that a variation in the length of this portion varies the volume of the chamber. For example, the enclosing wall may include a deformable portion, such as a bellows-type structure or an inflatable structure, or alternatively two or more elements that are movable relative to one another, such as a telescopic arrangement of elements.

The first chamber is preferably configured to receive fluid at a pressure sufficient to cause expansion of the first chamber. In particular, the first chamber is preferably adapted such that introduction of a fluid at a pressure at or above a threshold pressure causes the volume of the first chamber to increase. In the embodiments discussed above, the fluid preferably causes two wall elements to move relative to each other, typically apart from each other, for example by movement of a closure relative to an enclosing wall, or by variation of the length of a portion of the enclosing wall. The first chamber is preferably sealed, save for the inlet and outlet discussed above, to prevent leakage of the fluid from the chamber. This sealing may be provided by conventional sealing arrangements suitable for the particular chamber construction. The seals preferably also allow concurrent sliding and sealing engagement of the moveable elements of the chamber, in the various chamber constructions discussed above.

In a particularly advantageous arrangement, the first and/or second chamber comprises an enclosing wall, a closure movably mounted within the enclosing wall, and a deformable sealing member that is fixed at one end to the enclosing wall, and fixed at the other end to the movable closure. This arrangement is particularly advantageous because a chamber may have a variable volume, without the need for a seal that engages a movable element. The deformable sealing member therefore wears less quickly than other sealing arrangements. This arrangement may therefore be advantageous in any energy storage apparatus that includes a chamber having a variable volume, and being adapted to contain a volume of reduced pressure relative to ambient pressure in its expanded configuration.

Hence, according to a further aspect of the invention, there is provided apparatus for storing energy, the apparatus comprising a chamber having a variable volume and means for expanding the chamber, the apparatus having a charging configuration in which the chamber is adapted to be expanded, the chamber being adapted to contain a volume of reduced pressure relative to ambient pressure in its expanded configuration, and a discharging configuration in which the chamber is adapted to contract, wherein the chamber comprises an enclosing wall, a closure movably mounted within the enclosing wall, and a deformable sealing member that is fixed at one end to the enclosing wall, and fixed at the other end to the movable closure.

The deform able sealing member is preferably adapted to extend between the enclosing wall and the closure, such that the chamber is defined by a combination of the enclosing wall, the deformable sealing member and the closure. The deformable sealing member will typically be generally tubular in form, and is preferably adapted to deform during movement of the closure relative to the enclosing wall, without significant extension of the deformable sealing member.

If the deformable sealing member has sufficient strength, the enclosing wall and the closure may have a wide variety of forms, provided that the deformable sealing member is able to maintain an effective seal between those components during use. However, in presently preferred embodiments, the deformable sealing member is preferably accommodated, at least partially, within a space between adjacent walls of the enclosing wall and the closure.

The closure may therefore be slidably mounted within the enclosing wall, with the deformable sealing member at least partially disposed between those components.

Hence, in presently preferred embodiments, the enclosing wall has a closed end and a length of wall having a constant internal cross-sectional area, the closure has a closed end and a length of wall having a constant external cross-sectional area, and these walls of the enclosing wall and the closure are separated sufficiently to accommodate, at least partially, the deformable sealing member.

The deformable sealing member is preferably fixed to parts of the enclosing wall and the closure that are substantially adjacent in a contracted configuration of the chamber. In addition, the deformable sealing member preferably has a length that is substantially equal to, or greater than, the distance moved by the closure to its expanded configuration, during use.

The deformable sealing member may be inextensible in form. Alternatively, however, the deformable sealing member may be resiliently extendible, which would allow some extension of the deformable sealing member during use. In this embodiment, the deformable sealing member is preferably formed of an elastomeric or rubber-like material.

The apparatus is preferably adapted to connect to a suitable source of fluid at a pressure sufficient to cause expansion of the first chamber, and indeed such fluid source may form part of the apparatus according to the invention. The fluid source is preferably connectable to an energy source, such that the energy source causes pressure to be applied to the fluid, which pressure causes expansion of the first chamber. The fluid source is preferably therefore a hydraulic system, and the fluid is preferably a hydraulic fluid.

The second chamber is adapted to contain a volume of reduced pressure relative to ambient pressure in its expanded configuration, and is most preferably hermetically sealed. In particular, the first chamber is preferably sealed to substantially prevent the ingress of ambient gas into the second chamber. This sealing may be provided by conventional sealing arrangements suitable for the particular chamber construction. The seals preferably also allow concurrent sliding and sealing engagement of the moveable elements of the chamber, in the various chamber constructions discussed above.

The second chamber may be adapted to generate a volume of reduced pressure relative to ambient pressure as its volume increases, during use. Alternatively, or in addition, the second chamber may be connectable to a pump for extracting gas from the second chamber. In particular, the second chamber may include an outlet with a one-way valve. The extraction pump may be operated before, during or after actuation of the chamber, in order to reduce the pressure within the second chamber relative to the ambient pressure. In presently preferred embodiments, the apparatus includes an extraction pump adapted to substantially evacuate the second chamber of gas, before expansion of the second chamber, in order to create an approximate vacuum within the second chamber. This arrangement maximizes the energy that is able to be stored by a particular configuration of second chamber.

The operable linkage between the first and second chambers may be provided by a coupling between a movable element of the first chamber and a movable element of the second chamber. This coupling may be provided by a connecting member that extends between the movable elements. For example, the movable elements may be piston heads, separated by a connecting shaft. Alternatively, the movable elements may be formed integrally as a single component of the apparatus, for example by an upper member of the apparatus that defines the upper ends of the first and second chambers.

Where the first and/or second chamber is adapted to have a variable volume by the provision of a wall element that is movable relative to another wall element of the chamber, the apparatus may be adapted to raise one of those movable elements in order to store gravitational potential energy. In this arrangement, weights may be coupled to that movable element, which are also raised, in order to increase the amount of gravitational potential energy that may be stored by the apparatus.

The sealing arrangements described above and according to the invention are preferably of the type commonly used for hydro-pneumatic systems. However, the sealing arrangements will be configured to withstand the pressures that the apparatus is adapted to generate during use.

The fluid may be a gas or a liquid. Nevertheless, in presently preferred embodiments, the fluid is a liquid.

Where the fluid is a liquid, the fluid source is preferably a hydraulic system, and the fluid is preferably a conventional hydraulic fluid. Examples of conventional hydraulic fluids include synthetic compounds, mineral oil, water, or a water-based mixture. The fluid may also be biodegradable such as rapeseed (Canola) oil, or vegetable oil (eg oils available as ISO 32, Iso 46, and ISO 68 specification oils).

The hydraulic fluid may also include one or more additives, including oils, butanol, esters, phthalates, adipates (eg bis (2-ethylhexyl) adipate), polyalkylene glycols, phosphate esters (eg tributylphosphate), silicones, alkylated aromatic hydrocarbons, polyalphaolefins (eg polyisobutenes), corrosion inhibitors and preservatives. Where the fluid is a gas, the fluid source is preferably a pneumatic system, and the fluid is preferably a conventional pneumatic gas. Examples of pneumatic gases include, air, carbon dioxide, nitrogen, and other inert gases.

There may be provided a plurality of first chambers and/or a plurality of second chambers. In particular, the number and size of the first and second chambers is preferably chosen to be appropriate for the particular application of the apparatus, and preferably also the particular construction of each chamber. Where a plurality of first chambers and/or a plurality of second chambers are provided, the first chamber(s) and the second chamber(s) are preferably operably linked, such that an increase in the total volume of the first chamber(s) causes an increase in the total volume of the second chamber(s), and a decrease in the total volume of the second chamber(s) causes a decrease in the total volume of the first chamber(s).

In another embodiment, one of the chambers is surrounded by the other chamber, for example in a concentric arrangement, and those chambers are each fixed to a common base and a common upper member. For instance, the inner chamber may be defined by a telescopic housing, and the outer chamber may be defined by a housing having a generally bellows-type structure. The bellows housing preferably includes a plurality of horizontal platforms with deformable side walls extending therebetween to improve stability. The bellows housing may also include alignment members for maintaining the horizontal relationship between the plafforms. In addition, a plurality of inner chambers may be provided, which are preferably regularly spaced within the outer chamber.

The apparatus according to the invention has many applications. In particular, such apparatus may be used to store energy supplied by a power source over a relatively long period of time, and then discharge that energy in a much shorter period of time. Alternatively, such apparatus may be used to store energy from a power source during periods of low demand, and then discharge that energy in periods of high demand. Furthermore, such apparatus may be utilised to provide a transportable source of energy, and hence in this embodiment the apparatus according to the invention is preferably portable. The particular size and configuration of the apparatus will be adapted for the particular application, and in particular the amount of energy that the apparatus will be required to store.

The device according to the invention may be used to store the energy produced by power stations (including geothermal power stations, nuclear power stations, hydroelectric power stations, wave power stations and wind farms), when it is in excess of requirement. In so doing this makes the usage of energy more efficient and ultimately more environmentally friendly.

Preferred embodiments of the invention will now be described in greater detail, by way of illustration only, with reference to the accompanying drawings, in which Figure 1 is a schematic, cross sectional view of a first and preferred embodiment of apparatus according to the invention in a rest configuration; Figure 2 is a schematic, cross sectional view of the first embodiment in a storage configuration; Figure 3 is a schematic, cross sectional view of a second embodiment of apparatus according to the invention in a rest configuration; Figure 4 is a schematic, cross sectional view of the second embodiment in a storage configuration; and Figure 5 is a schematic, cross sectional view of a third embodiment of apparatus according to the invention in a storage configuration.

Figure 1 shows a first and preferred embodiment of apparatus according to the invention, which is in its rest configuration and is generally designated 10. The apparatus 10 comprises an end plate 20, and two generally cylindrical housings 30,40 adapted to accommodate a piston 50. The first cylindrical housing 30 has a greater diameter than the second cylindrical housing 40.

The first cylindrical housing 30 is closed at one end by the end plate 20, which has a diameter greater than that of the first cylindrical housing 30. A plurality of support bars 34 are connected at one end to the periphery of the end plate 20 and extend the length of the exterior of the first cylindrical housing 30. At the other end, the support bars 34 are connected to an annular support 36. The annular support 36 extends about the circumference of the first cylindrical housing 30, at its rim, in a plane x which is perpendicular to the longitudinal axis of the apparatus. A further series of separate support bars 34 are connected at one end to the annular support 36, at positions between the connections of the support bars 36 that extend around the exterior of the first cylindrical housing 30. These separate support bars 36 also extend parallel to the longitudinal axis, but at the other end are connected to a top support plate 46. The connections of the support bars 34 at the end plate 20, at the annular support 36 and the top support plate 46 are by a threaded connection, so that a rigid structure is constructed.

The second cylindrical housing 40 is fixed at one end to the centre of the top support plate 46. The piston 50 comprises a shaft 52, and heads 54 and 56 at each end of the shaft 52. The first piston head 54 has cylindrical walls 58 which extend along the length of the first cylindrical housing 30 in the rest configuration.

The first piston head 54 is slidably mounted within the first cylindrical housing 30.

The second piston head 56 is slidably mounted within the second cylindrical housing 40. The shaft 52 of the piston 50 is slidably mounted within an opening in the base of the second cylindrical housing 48.

The apparatus 10 defines three distinct chambers 60,62,64, which are hermetically sealed from each other. An ambient air chamber 62 is defined within the piston head cylinder 58, between the walls of the first piston head 54 and a bracing ring 90. A hydraulic chamber 64 is defined within the second cylindrical housing 40, between the second piston head 56 and the base of the second cylindrical housing 48.

A vacuum chamber 60 is defined within the first cylindrical housing 30, between the end plate 20 and the first piston head 54, and between the first cylindrical housing and the piston head cylinder 58. The vacuum chamber 60 is entirely sealed, and preferably has a negligible volume in the rest configuration. The sealing of the vacuum chamber 60 is achieved by an elastomeric tubular sheath 94, which is approximately the diameter of the piston head cylinder 58. At one end, the sheath 94 is clamped around its entire circumference between the annular support 36 and the rim of the first cylindrical housing 30. The sheath 94 extends into and out of the space 66 between the first cylindrical housing 30 and the piston head cylinder 58, along approximately half the length of the piston head cylinder 58. At the point where the sheath 94 extends out of this space 66, it extends around and over the rim of the piston head cylinder 58 and is clamped in place against the interior of the piston head cylinder 58 by means of the bracing ring 90.

The bracing ring 90 is arranged co-axially with the first and second cylindrical housings 30,40, and has an internal diameter that is greater than the external diameter of the second cylindrical housing 40. In particular, the bracing ring 90 travels over the exterior of the second cylindrical housing 40, during use, whilst at all times defining an opening between the interior surface of the bracing ring 90 and the exterior surface of the second cylindrical housing 40 that enables the ambient chamber 62 to be in fluid communication with the ambient atmosphere.

0-ring seals 55,57 are provided about the second piston head 56, and within an opening in the base of the second cylindrical housing 48, in order to hermetically seal the hydraulic chamber 64 within the second cylindrical housing 40. The hydraulic chamber 64 is sealed save for a hydraulic fluid conduit 70, which extends through the wall of the second cylindrical housing 40 and opens into the hydraulic chamber 64 at the opposite end to the second piston head 56. The hydraulic fluid conduit 70 is connected via a control valve 72 to an energy source 74 and an electrical generator 76. The energy source 74 is adapted to supply a hydraulic fluid at pressure to the hydraulic fluid conduit 70, and the generator 76 is adapted to generate electricity from a flow of hydraulic fluid. The pressure at which the hydraulic fluid is supplied is sufficient to cause movement of the piston 50, such that the vacuum and hydraulic chambers 60,64 increase in volume.

The control valve 72 is adapted to enable flow of fluid from the energy source 74 to the hydraulic chamber 64 in a charging configuration, prevent flow of fluid into, or out of, the hydraulic chamber 74 in a storage configuration, and enable flow of fluid from the hydraulic chamber 64 to the generator 76 in a discharging configuration.

In use, the apparatus 10 is initially in a rest configuration, and an extraction pump (not shown) is used to evacuate the vacuum chamber 60 of air. The evacuation of air causes the sheath 94 to be brought into contact with a substantial portion of both the interior surface of the first cylindrical housing 30 and the external surface of the piston head cylinder 58. This creates a seal between the piston head cylinder 58 and the entrance of the first cylindrical housing 30.

When the vacuum chamber 60 is evacuated of air, an approximate vacuum is formed in the vacuum chamber 60. The control valve 72 is switched to enable flow of hydraulic fluid, at pressure, from the energy source 74 to the hydraulic chamber 64, such that the apparatus 10 is in a charging configuration. In this configuration, the hydraulic chamber 64 charges with hydraulic fluid. Once the hydraulic chamber 64 is fully charged with fluid, the pressure at which the hydraulic fluid is supplied causes the second piston head 56 to move away from the base of the second cylindrical housing 40, and towards an open end of the second cylindrical housing 40. The first piston head 54 therefore slides within the first cylindrical housing 30 away from the end plate 20, thereby causing the vacuum chamber 60 to increase in volume, and further hydraulic fluid to flow into the hydraulic chamber 64.

As the first piston head 54 slides within the first cylindrical housing 30 away from the end plate 20, the sheath 94 remains fixed to the piston head cylinder 58 and the first cylindrical housing 30, and therefore maintains a seal between those components 30,58. In particular, as the piston 50 is withdrawn from the first cylindrical housing 30, the sheath 94 will unfurl against the exterior surface of the piston head cylinder 58.

As the first piston head 54 slides within the first cylindrical housing 30, ambient air contained within the ambient air chamber 62 escapes through the opening defined by the interior of the bracing ring 90. The bracing ring 90 maintains the sheath 94 fixed to the interior of the rim of the piston head cylinder 58. In doing so, the bracing ring 90 moves with the piston head 54, as it slides within the first cylindrical housing 30, and travels over the second cylindrical housing 40.

Since the vacuum chamber 60 has a negligible volume in its rest configuration and is hermetically sealed from the surroundings, a volume of reduced pressure relative to ambient pressure will be created within the vacuum chamber 60 as the volume of that chamber 60 increases. Indeed, an approximate vacuum may be created within the vacuum chamber 60.

Hydraulic fluid is supplied to the hydraulic chamber 64 until the desired amount of energy has been stored. The apparatus stores a maximum amount of energy when the first piston head 54 is adjacent to the base of the second cylindrical housing 48. Once the desired amount of energy has been stored, the control valve 72 is closed, such that the apparatus is in its storage configuration. An example of this storage configuration is shown in Figure 2.

In order to discharge energy from the apparatus 10, and in particular generate electricity from the stored energy, the control valve 72 is switched to enable flow of hydraulic fluid from the hydraulic chamber 64 to the generator 76. In this discharging configuration, the pressure of the air within the ambient air chamber 62 will cause the first piston head 54 to move towards the end plate 20, thereby causing the vacuum chamber 60 to reduce in volume. The second piston head 56 will therefore move towards the base 48 of the second cylindrical housing 40, such that the hydraulic chamber 64 also reduces in volume. This reduction in volume of the hydraulic chamber 64 causes hydraulic fluid to be discharged from that chamber 64, via the hydraulic fluid conduit 70 and the control valve 72, to the generator 76. The hydraulic fluid is discharged from the hydraulic chamber 64 at a pressure sufficient to enable the generator 76 to generate a supply of electricity.

This embodiment of the invention may be used for small or relatively large-scale applications. Large-scale applications include storing excess energy generated by power stations, wind turbines, etc. Indeed, this embodiment may be constructed to be of the order of I 0-50m in height or 20 metres in diameter, and hence of similar dimensions to present day gas holders.

Figure 3 shows a second embodiment of apparatus according to the invention, which is in its rest configuration and is generally designated 100. The apparatus 100 comprises an end plate 120, and two generally cylindrical housings 130,140 adapted to accommodate a piston 150. The first cylindrical housing 130 is closed at one end by the end plate 120, and at the other end by a flange 142 at one end of the second cylindrical housing 140. In particular, the end plate 120 and the flange 142 are both fixed to the first cylindrical housing 130 by a threaded connection.

The first cylindrical housing 130 has a greater diameter than the second cylindrical housing 140. In addition, the flange 142 includes a central opening within which the piston 150 is mounted, and the other end of the second cylindrical housing 140 is open.

The piston 150 comprises a shaft 152 and a head 154,156 at each end of the shaft 152. A first piston head 154 is slidably mounted within the first cylindrical housing 130, and the second piston head 156 is slidably mounted within the second cylindrical housing 140. The shaft 152 of the piston 150 extends through the central opening in the flange 142. This central opening includes an 0-ring seal 144 that hermetically seals the interior of the first cylindrical housing 130 from the interior of the second cylindrical housing 140. In addition, 0-ring seals 155,157 are provided about the first and second piston heads 154,156, in order to form a hermetic seal with the interior surface of the associated housing 130,140.

The apparatus defines three distinct chambers 160,162,164, which are hermetically sealed from each other. In particular, a vacuum chamber 160 is defined within the first cylindrical housing 130, between the end plate 120 and the first piston head 154, an ambient air chamber 162 is defined within the first cylindrical housing 130, between the first piston head 154 and the flange 142, and a hydraulic chamber 164 is defined within the second cylindrical housing 140, between the flange 142 and the second piston head 156.

The vacuum chamber 160 is entirely sealed, and preferably has a negligible volume in the rest configuration. The ambient air chamber 162 is open to the surrounding atmosphere by means of a plurality of openings 132 in the wall of the first cylindrical housing 130, adjacent to the flange 142.

The hydraulic chamber 164 is sealed, save for a hydraulic fluid conduit 170, which extends through the flange 142 and opens into the hydraulic chamber 164 at the opposite end to the second piston head 156. The hydraulic fluid conduit 170 is connected via a control valve 172 to an energy source 174 and an electrical generator 174. The energy source 174 is adapted to supply a hydraulic fluid at pressure to the hydraulic fluid conduit 170, and the generator 176 is adapted to generate electricity from a flow of hydraulic fluid. The pressure at which the hydraulic fluid is supplied is sufficient to cause movement of the piston 150, such that the vacuum and hydraulic chambers 160,164 increase in volume.

The control valve 172 is adapted to enable flow of fluid from the energy source 174 to the hydraulic chamber 164 in a charging configuration, prevent flow of fluid into, or out of, the hydraulic chamber 174 in a storage configuration, and enable flow of fluid from the hydraulic chamber 164 to the generator 176 in a discharging configuration.

In use, the control valve 172 is switched to enable flow of hydraulic fluid, at pressure, from the energy source 174 to the hydraulic chamber 164, such that the apparatus 101 is in a charging configuration. In this configuration, the hydraulic chamber 164 charges with hydraulic fluid. Once the hydraulic chamber 164 is fully charged with fluid, the pressure at which the hydraulic fluid is supplied causes the second piston head 156 to move away from the flange 142, and towards the open end of the second cylindrical housing 140. The first piston head 154 therefore moves away from the end plate 120, thereby causing the vacuum chamber 160 to increase in volume, and further hydraulic fluid to flow into the hydraulic chamber 164. Since the vacuum chamber 160 has a negligible volume in its rest configuration and is hermetically sealed from ambient air, a volume of reduced pressure relative to ambient pressure will be created within the vacuum chamber as the volume of that chamber 160 increases. Indeed, an approximate vacuum may be created within the vacuum chamber 160.

Hydraulic fluid is supplied to the hydraulic chamber 164 until the desired amount of energy has been stored. The apparatus stores a maximum amount of energy when the first piston head 154 is adjacent to the flange 142, but without covering the openings 132. Once the desired amount of energy has been stored, the control valve 172 is closed, such that the apparatus is in its storage configuration.

An example of this storage configuration is shown in Figure 4.

In order to discharge energy from the apparatus 100, and in particular generate electricity from the stored energy, the control valve 172 is switched to enable flow of hydraulic fluid from the hydraulic chamber 164 to the generator 176. In this discharging configuration, the pressure of the air within the ambient air chamber 162 will cause the first piston head 154 to move towards the end plate 120, thereby causing the vacuum chamber 160 to reduce in volume. The second piston head 156 will therefore move towards the flange 142, such that the hydraulic chamber 164 also reduces in volume. This reduction in volume of the hydraulic chamber 164 causes hydraulic fluid to be discharged from that chamber 164, via the hydraulicfluid conduit 170 and the control valve 172, to the generator 176. The hydraulic fluid is discharged from the hydraulic chamber 164 at a pressure sufficient to enable the generator 176 to generate a supply of electricity.

The second embodiment of the invention is particularly suitable for relatively small-scale applications, such as transportable energy storage apparatus.

Figure 5 shows a second embodiment of apparatus according to the invention, which is in its charged configuration and is generally designated 200. This embodiment of the invention is more suitable for relatively large-scale applications, such as apparatus for storing excess energy generated by power stations, wind turbines, etc. Indeed, the second embodiment may be of the order of 10-50m in height, and hence of similar dimensions to present day gas holders.

The apparatus 200 comprises a base 220, an inner telescopic housing 230, an outer bellows housing 240, and an upper plate 250. The telescopic housing 230 and the bellows housing 240 are both generally cylindrical and mounted on an upper surface of the base 220, with the bellows housing 240 arranged concentrically about the telescopic housing 230.

The telescopic housing 230 has four cylindrical sections, with the lowermost section mounted to the base 220, the uppermost section having a closed upper end that is fixed to the upper plate 250, and the sections reducing in diameter with increasing height.

The bellows housing 240 comprises a cylindrical support member 242, upon which is mounted four annular plafforms 246, each connected at their periphery by deformable walls 244. The deformable walls 244 bow inwards, such that the platforms 246 may be located substantially adjacent to one another, with the deformable walls 244 located therebetween, or separated from one another, with the deformable walls 244 becoming generally cylindrical walls of the bellows housing 240. The uppermost platform 246 is fixed to the upper plate 250.

The annular platforms 246 are separated from the outer surface of the telescopic housing 230 by a short distance, such that the entire interior of the bellows housing 240 is in fluid communication. In addition, alignment rods 248 extend downwardly from each platform, and pass through a corresponding opening in the platform 248 immediately beneath, with a close fit. These alignment rods 246 maintain the platforms with a constant horizontal position, relative to the other platforms 248 and the base 220. The alignment rods 248 also include stops at their lower ends, which determine the maximum separation between the platforms 248, and prevent damage to the deformable walls 244 by overextension. In order to enable the bellows housing 240 to fully collapse, the platforms include openings that enable the alignment rods to extend into the interior of the cylindrical support member 242 in the collapsed configuration.

The apparatus 200 defines two distinct chambers 260,264, which are hermetically sealed from each other. In particular, a vacuum chamber 260 is defined within the bellows housing 240, between the outer surface of the telescopic housing 230, the base 220 and the uppermost platform 246, and a hydraulic chamber 264 is defined within the telescopic housing 230, between the base 220 and the close upper end of the housing 230.

The vacuum chamber 260 is entirely sealed, and has a volume defined by the cylindrical support member 242 in the collapsed configuration. An extraction pump 280 is provided that is adapted to evacuate the vacuum chamber 260 of air, such that an approximate vacuum is formed within the vacuum chamber 260 before use.

The hydraulic chamber 264 is sealed, save for a hydraulic fluid inlet 270 and a hydraulic fluid outlet 271, which extend through the upper plate 250 and the closed end of the telescopic housing 230, and open into the hydraulic chamber 264 at its upper end. The hydraulic fluid inlet 270 is connected via a control valve 272 to an energy source 274. The hydraulic fluid outlet 271 is connected via a separate control valve 273 to an electrical generator 276. The energy source 274 is adapted to supply a hydraulic fluid at pressure to the hydraulic fluid inlet 270, and the generator 276 is adapted to generate electricity from a flow of hydraulic fluid from the hydraulic fluid outlet 271. The pressure at which the hydraulic fluid is supplied to the hydraulic chamber 264 is sufficient to cause the telescopic housing 230 to extend, such that the vacuum and hydraulic chambers 260,264 increase in volume.

The inlet control valve 272 is adapted to enable flow of fluid from the energy source 274 to the hydraulic chamber 264 in a charging configuration, but prevent flow of fluid into the hydraulic chamber 274 in storage and discharging configurations.

The outlet control valve 273 is adapted to prevent flow of fluid out of the hydraulic chamber 264 in the charging and storage configurations, but enable flow of fluid from the hydraulic chamber 264 to the generator 276 in the discharging configuration.

In use, the apparatus 200 is initially in a collapsed configuration, and the extraction pump 280 is used to evacuate the vacuum chamber 260 of air, such that an approximate vacuum is formed in the vacuum chamber. The inlet control valve 272 is then switched to enable flow of hydraulic fluid, at pressure, from the energy source 274 to the hydraulic chamber 264, such that the apparatus 200 is in a charging configuration. In this configuration, the hydraulic chamber 264 charges with hydraulic fluid. Once the hydraulic chamber 264 is fully charged with fluid, the pressure at which the hydraulic fluid is supplied causes the telescopic housing 230 to extend, such that the upper plate 250 moves upwardly and further hydraulic fluid flows into the hydraulic chamber 264. This causes the bellows housing 240 to extend, thereby increasing the volume of the vacuum chamber 260. Since the vacuum chamber 260 is hermetically sealed from ambient air, the approximate vacuum will be maintained within the vacuum chamber 260.

Hydraulic fluid is supplied to the hydraulic chamber 264 until the desired amount of energy has been stored. The apparatus stores a maximum amount of energy when the bellows housing 240 is fully extended, as allowed by the alignment rods 248 and associated stops. Once the desired amount of energy has been stored, the inlet control valve 272 is closed, such that the apparatus is in its storage configuration. An example of this storage configuration is shown in Figure 3.

In order to discharge energy from the apparatus 200, and in particular generate electricity from the stored energy, the outlet control valve 273 is switched to enable flow of hydraulic fluid from the hydraulic chamber 264 to the generator 276. In this discharging configuration, the pressure of the air above the upper plate 250 will cause the telescopic housing 230 and the bellows housing 240 to contract towards the collapsed configuration. This will cause both the vacuum chamber 260 and the hydraulic chamber 264 to reduce in volume. The reduction in volume of the hydraulic chamber 264 causes hydraulic fluid to be discharged from that chamber 264, via the hydraulic fluid outlet 271 and the outlet control valve 273, to the generator 276. The hydraulic fluid is discharged from the hydraulic chamber 264 at a pressure sufficient to enable the generator 276 to generate a supply of electricity.

Claims

Claims 1. Apparatus for storing energy, the apparatus comprising a first chamber and a second chamber, the chambers each having a variable volume and being operably linked, such that expansion of the first chamber causes expansion of the second chamber, and contraction of the second chamber causes contraction of the first chamber, the apparatus having a charging configuration in which the first chamber is adapted to be charged with fluid for increasing the volume of the first chamber, thereby causing expansion of the second chamber, the second chamber being adapted to contain a volume of reduced pressure relative to ambient pressure in its expanded configuration.
2. Apparatus as claimed in Claim 1, wherein the apparatus has a discharging configuration in which the second chamber is adapted to contract, thereby causing contraction of the first chamber, and the first chamber is adapted to discharge fluid from the first chamber.
3. Apparatus as claimed in Claim I or Claim 2, wherein the first chamber comprises an inlet and an outlet for the fluid.
4. Apparatus as claimed in Claim 3, wherein the inlet and the outlet each include a valve, such that in the charging configuration the inlet valve is open and the outlet valve is closed, and in the discharging configuration the outlet valve is open and the inlet valve is closed.
5. Apparatus as claimed in Claim 4, wherein the apparatus has a storage configuration in which both the inlet and outlet valves are closed, which is sufficient to maintain the apparatus at equilibrium.
6. Apparatus as claimed in any one of Claims 3 to 5, wherein the inlet is adapted to be connected to a source of fluid having a pressure sufficient to cause expansion of the first chamber.
7. Apparatus as claimed in any one of Claims 3 to 6, wherein the outlet is adapted to be connected to means for extracting energy or providing useful work from a fluid flow.
8. Apparatus as claimed in any preceding claim, wherein the first and/or second chamber is adapted to have a variable volume by the provision of a wall element that is movable relative to another wall element of the chamber.
9. Apparatus as claimed in Claim 8, wherein the first and/or second chamber comprises an enclosing wall and a closure, which together define the chamber, wherein the closure is movable relative to the enclosing wall, such that the volume of the chamber is variable.
10. Apparatus as claimed in Claim 9, wherein the first and/or second chamber comprises an enclosing wall having a closed end, a length of wall having a constant internal cross-sectional area and a closure slidably mounted therein.
11. Apparatus as claimed in Claim 10, wherein the closure is a conventional piston or ram slidably mounted within the walls of a cylindrical enclosing wall.
12. Apparatus as claimed in any one of Claims 8 to 11, wherein the first and/or second chamber comprises an enclosing wall including one or more portions of variable dimensions.
13. Apparatus as claimed in Claim 12, wherein the enclosing wall includes a portion of variable length, such that a variation in the length of this portion varies the volume of the chamber.
14. Apparatus as claimed in Claim 13, wherein the enclosing wall includes a deformable portion, or alternatively two or more elements that are movable relative to one another.
15. Apparatus as claimed in any preceding claim, wherein the first chamber is configured to receive fluid at a pressure sufficient to cause expansion of the first chamber, such that introduction of a fluid at a pressure at or above a threshold pressure causes the volume of the first chamber to increase.
16. Apparatus as claimed in any preceding claim, wherein the second chamber is hermetically sealed to substantially prevent the ingress of ambient gas into the second chamber.
17. Apparatus as claimed in any preceding claim, wherein the second chamber is adapted to generate a volume of reduced pressure relative to ambient pressure as its volume increases, during use.
18. Apparatus as claimed in any preceding claim, wherein the second chamber is connectable to a pump for extracting gas from the second chamber.
19. Apparatus as claimed in any preceding claim, wherein the fluid is a liquid.
20. Apparatus as claimed in Claim 19, wherein the fluid source is a hydraulic system, and the fluid is a conventional hydraulic fluid.
21. Apparatus as claimed in any preceding claim, wherein the fluid is a gas.
22. Apparatus as claimed in Claim 21, wherein the fluid source is a pneumatic system, and the fluid is a conventional pneumatic gas.
23. Apparatus as claimed in any preceding claim, wherein the apparatus comprises a plurality of first chambers and/or a plurality of second chambers.
24. Apparatus as claimed in Claim 23, wherein the first chamber(s) and the second chamber(s) are operably linked, such that an increase in the total volume of the first chamber(s) causes an increase in the total volume of the second chamber(s), and a decrease in the total volume of the second chamber(s) causes a decrease in the total volume of the first chamber(s).
25. Apparatus as claimed in any preceding claim, wherein one of the first and second chambers is surrounded by the other chamber, and those chambers are each fixed to a common base and a common upper member.
26. Apparatus as claimed in Claim 25, wherein the inner chamber is defined by a telescopic housing, and the outer chamber is defined by a housing having a generally bellows-type structure.
27. Apparatus as claimed in Claim 26, wherein the bellows housing includes a plurality of horizontal platforms with deformable side walls extending therebetween.
28. Apparatus as claimed in any one of Claims 25 to 27, wherein the apparatus comprises a plurality of inner chambers.
29. Apparatus as claimed in any preceding claim, wherein the first and/or second chamber comprises an enclosing wall, a closure movably mounted within the enclosing wall, and a deformable sealing member that is fixed at one end to the enclosing wall, and fixed at the other end to the movable closure.
30. A method of storing energy, which method comprises the steps of: (a) providing apparatus as claimed in any preceding claim; (b) increasing the volume of the first chamber by charging the first chamber with fluid, thereby causing expansion of the second chamber; and (c) containing a volume of reduced pressure relative to ambient pressure in the second chamber in its expanded configuration.
31. A method as claimed in Claim 29, wherein the method includes a step of releasing energy by enabling the second chamber to contract, thereby causing contraction of the first chamber and discharge of fluid from the first chamber.
32. Apparatus for storing energy, the apparatus comprising a chamber having a variable volume and means for expanding the chamber, the apparatus having a charging configuration in which the chamber is adapted to be expanded, the chamber being adapted to contain a volume of reduced pressure relative to ambient pressure in its expanded configuration, and a discharging configuration in which the chamber is adapted to contract, wherein the chamber comprises an enclosing wall, a closure movably mounted within the enclosing wall, and a deformable sealing member that is fixed at one end to the enclosing wall, and fixed at the other end to the movable closure.
33. Apparatus as claimed in Claim 32, wherein the deformable sealing member is adapted to extend between the enclosing wall and the closure, such that the chamber is defined by a combination of the enclosing wall, the deformable sealing member and the closure.
34. Apparatus as claimed in Claim 32 or Claim 33, wherein the deformable sealing member is generally tubular in form.
35. Apparatus as claimed in any one of Claims 32 to 34, wherein the deformable sealing member is adapted to deform during movement of the closure relative to the enclosing wall, without significant extension of the deformable sealing member.
36. Apparatus as claimed in any one of Claims 32 to 35, wherein the deformable sealing member is accommodated, at least partially, within a space between adjacent walls of the enclosing wall and the closure.
37. Apparatus as claimed in any one of Claims 32 to 36, wherein the closure is slidably mounted within the enclosing wall, with the deformable sealing member at least partially disposed between those components.
38. Apparatus as claimed in any one of Claims 32 to 37, wherein the enclosing wall has a closed end and a length of wall having a constant internal cross-sectional area, the closure has a closed end and a length of wall having a constant external cross-sectional area, and these walls of the enclosing wall and the closure are separated sufficiently to accommodate, at least partially, the deformable sealing member.
39. Apparatus as claimed in any one of Claims 32 to 38, wherein the deformable sealing member is fixed to parts of the enclosing wall and the closure that are substantially adjacent in a contracted configuration of the chamber.
40. Apparatus as claimed in Claim 39, wherein the deformable sealing member has a length that is substantially equal to, or greater than, the distance moved by the closure to its expanded configuration, during use.
41. Apparatus substantially as hereinbefore described, and as illustrated in Figures 1 and 2.
42. Apparatus substantially as hereinbefore described, and as illustrated in Figures 3 and 4.
43. Apparatus substantially as hereinbefore described, and as illustrated in Figure 5.