Storage arrangement

Abstract

A flow battery electrolyte storage arrangement 1 comprises a first pile 2 at least partly, but preferably completely, provided within a first bore 11, the first pile defining a first pile volume 3 that is at least partly filled with the electrolyte 4. Preferably, two electrolytes comprising an anolyte and catholyte are provided in first and second piles. The piles may comprise an internal lining and may include a cured material between the pile and its respective bore. Multiple piles for each electrolyte may be provided to increase capacity (figure 5). A flow battery (100, figure 2) comprising such a flow battery electrolyte storage arrangement is also described.

Description

Field of Invention The present invention relates to the storage of flowable compositions. In particular, the present invention relates to a flow battery composition storage arrangement. The present invention further relates to a use of a pile, a flow battery, a flow battery electrode arrangement and a method of providing flow battery composition within a flow battery. Background Flow batteries, or redox flow batteries, are a type of electrochemical cell, and have been known for many years (for example, see US224404, US3713888, US4068043 and US4469760). Two electrolytes, often known as the anolyte and the catholyte, are pumped across opposite sides of a membrane in order to produce a potential difference. The energy capacity of the flow battery is determined by the volume of electrolyte that can be stored. It is therefore desirable to be able to store a large volume of electrolyte. The electrolytes are typically stored in tanks above ground. Such tanks occupy a large amount of space, and the widescale deployment of flow batteries may be hindered by the economic and / or practical issues related to electrolyte storage. The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved way of storing electrolyte for flow batteries. Summary of Invention In accordance with a first aspect of the present invention, there is provided a flow battery composition storage arrangement comprising a first pile at least partly within a first bore, the first pile defining a first pile volume that is at least partly filled with a first composition comprising an electrolyte for a flow battery. The storage of a flow battery electrolyte in a pile may be advantageous since such piles can provide a large storage volume. Furthermore, such piles are typically located in the ground, and therefore provide a storage solution that typically does not occupy a significant amount of space above ground. It is further anticipated that storage in a pile may provide a more stable thermal environment that may be less vulnerable to changes in atmospheric temperature. The first composition is flowable, in so far as it may be caused to flow from the first pile. The first composition optionally comprises a fluid, such as a gas or liquid. The first composition may comprise a solution and / or a suspension. For example, the first composition may comprise a solution in which particles are suspended. For the avoidance of doubt, the term “bore” includes, but is not limited to, a cavity that may be formed by a drill or other rotary tool. The bore is optionally substantially cylindrical. Optionally, a majority of the length of the first pile is within the first bore. Optionally, the first pile is substantially within the first bore. The first composition may comprise any electrolyte suitable for use in a flow battery. For example, the first composition may comprise an anolyte. Anolytes typically come into contact with the anode during use. The first composition may have a pH of from about 2 to about 9. The first composition may comprise a catholyte. Catholytes typically come into contact with the cathode during use. The first composition may have a pH of from about 9 to about 13, optionally from about 10 to about 13, optionally from about 11 to about 13 and optionally from about 12 to about 13. The first composition may comprise one or more of sodium, potassium, hydrogen, lithium, iron, chromium, tin, titanium, zinc, manganese, lead, cerium and bromine. These species may be in any suitable oxidation state. Those skilled in the art will realise that the oxidation state of such species may depend, amongst other things, on the operational status of a flow battery (for example, depending on whether the battery is in a charged or discharged state), and therefore the oxidation state of such species may change. The first pile volume may optionally be defined by one or more walls of the first pile. The first pile volume is therefore optionally a volume inside the pile. In this connection, the first pile may optionally be a hollow pile. The first pile is optionally configured to store the first composition. For example, the first pile may be provided with a first composition-contacting surface (provided, for example, by a lining) to facilitate the storage of first composition. The first composition-contacting surface may optionally be inert to the first composition. The first composition-contacting surface may be chemically resistant to the first composition. For example, if the first composition is acidic, then the first composition-contacting surface may be resistant to acids. Alternatively, if the first composition is alkaline, then the first composition-contacting surface may be resistant to alkalis. Optionally, the first pile comprises an outlet for delivering the first composition to a flow battery electrode arrangement. Those skilled in the art will realise that the flow battery electrode arrangement is not part of the flow battery composition storage arrangement. Optionally, the first pile comprises an inlet for receiving the first composition from a flow battery electrode arrangement. The flow battery composition storage arrangement may optionally comprise a second pile volume that is at least partly filled with a second composition comprising an electrolyte for a flow battery. The second pile volume may be provided by the first pile. However, it may be preferred that the second pile volume is provided by a second pile. The second pile volume may be located within a second pile. The second pile may comprise one or more walls. The second pile volume may be defined by one or more walls of the second pile. The second pile may optionally be at least partly within a second bore. Optionally, a majority of the length of the second pile is within the second bore. Optionally, the second pile is substantially within the second bore. Optionally, the second pile comprises an outlet for delivering the second composition to a flow battery electrode arrangement. Those skilled in the art will realise that the flow battery electrode arrangement is not part of the flow battery composition storage arrangement. Optionally, the second pile comprises an inlet for receiving the second composition from a flow battery electrode arrangement. The second composition is flowable, in so far as it may be caused to flow from the second pile volume. The second composition optionally comprises a fluid, such as a gas or liquid. The second composition may comprise a solution and / or a suspension. For example, the second composition may comprise a solution in which particles are suspended. The second composition may comprise any electrolyte suitable for use in a flow battery. For example, the second composition may comprise an anolyte.. The first, composition may have a pH of from about 2 to about 9. The second composition may comprise a catholyte. The second composition may have a pH of from about 9 to about 13, optionally from about 10 to about 13, optionally from about 11 to about 13 and optionally from about 12 to about 13. If the first composition comprises an anolyte, then the second composition optionally comprises a catholyte. Conversely, if the first composition comprises a catholyte, then the second composition optionally comprises an anolyte. The second composition may comprise one or more of sodium, potassium, hydrogen, lithium, iron, chromium, tin, titanium, zinc, manganese, lead, cerium and bromine. These species may be in any suitable oxidation state. Those skilled in the art will realise that the oxidation state of such species may depend, amongst other things, on the operational status of a flow battery (for example, depending on whether the battery is in a charged or discharged state). More than one pile may be used to store each of the first and second compositions. In this connection, the flow battery composition storage arrangement may comprise a first set of two or more piles and a second set of two or more piles, the first set of piles being provided with the first composition and the second set of piles being provided with the second composition. Optionally, the first composition is located within each of the first set of two or more piles. Optionally, the second composition is located within each of the second set of two or more piles. One or more conduits may be provided between two or more of the first set of piles to facilitate movement of the first composition between two of more of the first set of piles. One or more conduits may be provided between two or more of the second set of piles to facilitate movement of the second composition between two of more of the second set of piles. The first, second and other piles may have certain features, some of which are listed below. The statements below in relation to “a pile” or “the pile” refer to the first pile, the second pile and other piles mentioned above. Optionally, the pile is configured to facilitate the transfer of a load from a structure, such as a building or bridge, for example, to a solid underlying substrate. Optionally, the pile has a length of at least 5m, optionally at least 10m, optionally at least 15m, optionally at least 20m, optionally at least 25m, optionally at least 30m, optionally at least 35m, optionally at least 40m, optionally at least 45m, optionally at least 50m, optionally at least 55m and optionally at least 60m. Optionally, the pile has a length of no more than 100m, optionally no more than 90m, optionally no more than 80m and optionally no more than 70m. Optionally, the pile has a length of from 10m to 100m, optionally of from 20m to 100m, optionally of from 10m to 80m, optionally of from 10m to 70m and optionally of from 10m to 60m. Optionally, the pile has an internal dimension (for example, an internal diameter) of at least 0.2m, optionally at least 0.3m, optionally at least 0.4m, optionally at least 0.5m, optionally at least 0.6m, optionally at least 0.8m, optionally at least 1.0m, optionally at least 1.2m, optionally at least 1.4m and optionally at least 1.6m.Optionally, the pile has an internal dimension (for example, an internal diameter) of no more than 3.0m , optionally no more than 2.8m, optionally no more than 2.6m, optionally no more than 2.4m, optionally no more than 2.2m, optionally no more than 2.0m, optionally no more than 2.2m, optionally no more than 2.0m, optionally no more than 1.8m, optionally no more thanl.6m, optionally no more than 1.4m, optionally no more than 1.2m and optionally no more than 1.0m. Optionally, the pile has an internal dimension (for example, an internal diameter) of from 0.4m to 3.0m, optionally of from 0.5m to 2.6m and optionally of from 0.6m to 2.0m. Optionally, the pile has a length of from 10m to 100m and an internal dimension (for example, an internal diameter) of from 0.4m to 3.0m; optionally, a length of from 10m to 80m and an internal dimension (for example, an internal diameter) of from 0.5m to 2.6m; and optionally a length of from 10m to 70m and an internal dimension (for example, an internal diameter) of from 0.6m to 2.0m. Optionally, the pile is in the form of a column. The column may comprise one or more walls, the one or more walls defining an internal void. The internal void may provide a space for the storage of the first or second composition. Optionally, the column comprises a plurality of stacked pile sections. Optionally, one or more pile section is annular or cylindrical. Optionally, one or more of the pile sections may be formed form a plurality of pile section segments that are assembled to form a pile section. Optionally, the pile may comprise a base. If the pile comprises a column, then the base may be located at the bottom of the column. Optionally, the pile may comprise a cap. If the pile comprises a column, then the cap may be located at the top of the column. Optionally, the pile may be at least partly within a bore. Optionally, a cured material (such as grout) may be provided between the pile and the bore. Optionally, the pile is made from any suitable material, such as concrete. Optionally, the pile comprises one or more reinforcement members, such as rods, cables or lattices, which may be formed from any suitable material, such as steel. In accordance with a second aspect of the present invention, there is provided use of a pile to store a flow battery composition comprising an electrolyte for a flow battery. The applicant has discovered that it may be beneficial to store a flow battery composition comprising an electrolyte in a pile. The storage of an electrolyte in a pile may be advantageous since such piles can provide a large underground storage volume that does not occupy a significant amount of space above ground. It is further anticipated that storage in a pile may provide a more stable thermal environment that may be less vulnerable to changes in atmospheric temperature. The flow battery composition may comprise any of the features of the first or second composition described above in relation to the storage arrangement of the first aspect of the present invention. For example, the flow battery composition may comprise an anolyte or a catholyte. The pile may comprise any of the features of the piles described above in relation to the storage arrangement of the first aspect of the present invention. The pile may optionally define a pile volume that is at least partly filled with a flow battery composition comprising an electrolyte for a flow battery. The pile may optionally be at least partly within a bore. Optionally, a majority of the length of the pile is within the bore. Optionally, the pile is substantially within the bore. The pile may be substantially located below the surface of the surrounding ground. A structure may be located above the pile. The pile may be configured to transmit the load from the structure to the ground surrounding the pile. The pile may be coupled to the structure to facilitate transfer of load from the structure to the pile. The use of the second aspect of the present invention may comprise any of the features of the flow battery composition storage arrangement of the first aspect of the present invention. In accordance with a third aspect of the present invention, there is provided use of a first pile to store a first composition comprising an electrolyte for a flow battery and a second pile to store a second composition comprising an electrolyte for as flow battery, one of the first and second compositions being an anolyte for a flow battery and the other of the first and second compositions being a corresponding catholyte for a flow battery. The use of the third aspect of the present invention may comprise any of the features of the flow battery composition storage arrangement of the first aspect of the present invention. The first and / or second pile may comprise any of the features of piles described above in relation to the flow battery composition storage arrangement of the first aspect of the present invention. The first composition may comprise any of the features of the first composition described above in relation to the flow battery composition storage arrangement of the first aspect of the present invention. The second composition may comprise any of the features of the second composition described above in relation to the flow battery composition storage arrangement of the first aspect of the present invention. In accordance with a fourth aspect of the present invention, there is provided a flow battery comprising a flow battery electrode arrangement, and a flow battery composition storage arrangement in accordance with the first aspect of the present invention, wherein the flow battery electrode arrangement is arranged to receive the first composition from the flow battery composition storage arrangement of the first aspect of the present invention. As mentioned above, the storage of flow battery electrolyte in a pile may be advantageous since such piles can provide a large storage volume. Furthermore, such piles are typically located in the ground, and therefore provide a storage solution that typically does not occupy space above ground. It is further anticipated that storage in a pile may provide a more stable thermal environment that may be less vulnerable to changes in atmospheric temperature. Optionally, the battery comprises a means for transferring the first composition to the flow battery electrode arrangement, such as a pump. Optionally, the flow battery composition storage arrangement comprises a second pile volume that is at least partly filled with a second composition comprising an electrolyte for a flow battery. Optionally, the second pile volume is located within a second pile. Optionally, the flow battery electrode arrangement is arranged to receive the second composition from the flow battery composition storage arrangement. Optionally, the battery comprises a means for transferring the second composition to the flow battery electrode arrangement, such as a pump. The flow battery electrode arrangement may optionally comprise an anode and a cathode, one of the first composition and the second composition contacting the anode, and the other of the first composition and the second composition contacting the cathode. One or both of the anode and the cathode may optionally be porous. Optionally, the flow battery electrode arrangement may comprise one or more current collectors. A current collector may optionally be in electrical contact with an anode. A current collector may optionally be in electrical contact with a cathode. The flow battery electrode arrangement may comprise a membrane (optionally an ion-selective membrane) separating the first composition and the second composition. The membrane is typically located in an ion flow path between the anode and the cathode. The membrane is typically physically located between the anode and the cathode. The flow battery electrode arrangement may comprise a first inlet arranged to receive the first composition from the first pile volume. The flow battery electrode arrangement may comprise a second inlet arranged to receive a second composition from the second pile volume, for example, from a second pile. The flow battery electrode arrangement may be arranged to deliver the first composition to the first pile. For example, the flow battery electrode arrangement may comprise a first outlet in fluid communication with the first pile. For example, the first outlet of the flow battery electrode arrangement may be in fluid communication with an inlet of the first pile. A means for transferring the first composition to the flow battery electrode arrangement, if present, may facilitate transfer of the first composition from the flow battery electrode arrangement to the first pile. Similarly, the flow battery electrode arrangement may be arranged to deliver the second composition to a second pile. For example, the flow battery electrode arrangement may comprise a second outlet in fluid communication with the second pile. For example, the second outlet of the flow battery electrode arrangement may be in fluid communication with an inlet of the second pile. A means for transferring the second composition to the flow battery electrode arrangement, if present, may facilitate transfer of the second composition from the flow battery electrode arrangement to the first pile. In accordance with a fifth aspect of the present invention, there is provided a flow battery electrode arrangement for use in the flow battery of the fourth aspect of the present invention. The flow battery electrode arrangement of the fifth aspect of the present invention may comprise one or more features of the flow battery electrode arrangement as described above in relation to the flow battery of the fourth aspect of the present invention. In accordance with a sixth aspect of the preset invention, there is provided a method of operating a flow battery comprising moving a first flow battery composition from a first pile to a flow battery electrode arrangement. Optionally, movement of the first flow battery composition from the first pile to a flow battery electrode arrangement is associated with the generation of electrical power. Typically, in order to facilitate this the method may optionally comprise moving a second flow battery composition from a pile (and optionally a second pile) to a flow battery electrode arrangement. The method may comprise using a pump to move the first flow battery composition from a first pile to a flow battery electrode arrangement. The method may comprise moving the first flow battery composition from the flow battery electrode arrangement to the first pile. This may be effected using the pump that moves the first flow battery composition from the first pile to the flow battery electrode arrangement. If the method comprises moving a second flow battery composition from a pile (and optionally a second pile) to a flow battery electrode arrangement, then a pump may be used to move the second flow battery composition from a pile to a flow battery electrode arrangement. The method may comprise moving the second flow battery composition from the flow battery electrode arrangement to a second pile. This may be effected using the pump that moves the second flow battery composition from a second pile to the flow battery electrode arrangement. Those skilled in the art will realise that actuation of a pump will cause movement of the first flow battery composition from the first pile to the flow battery electrode arrangement, through the flow battery electrode arrangement and from the flow battery electrode arrangement back to the first pile. Similarly, actuation of a pump will cause movement of the second flow battery composition from the second pile to the flow battery electrode arrangement, through the flow battery electrode arrangement and from the flow battery electrode arrangement back to the second pile. The flow battery electrode arrangement may comprise one or more features of the flow battery electrode arrangement described above in relation to the flow battery of the fifth aspect of the present invention. The flow battery may comprise one or more features of the flow battery described above in relation to the flow battery of the fifth aspect of the present invention. The first flow battery composition may comprise one or more features of the first composition described above in relation to the storage arrangement of the first aspect of the present invention. The pile may comprise one or more features of the piles described above in relation to the storage arrangement of the first aspect of the present invention. In accordance with a seventh aspect of the present invention, there is provided a first pile suitable for use in the storage arrangement of the first aspect of the present invention. The first pile may comprise one or more features of the piles described above in relation to the storage arrangement of the first aspect of the present invention. It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa. DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: Figure 1 shows a schematic cross-sectional view through part of a flow battery composition storage arrangement according to a first embodiment of the invention; Figure 2 shows a schematic cross-sectional view through a flow battery according to another embodiment of the invention; Figure 3 shows a schematic representation of the flow battery of Fig. 2 and its relationship to an applied load and a potential source of electricity for charging the flow battery; Figure 4 shows a schematic representation of a method of operating a flow battery according to another embodiment of the invention; and Figure 5 shows a schematic representation of a flow battery according to yet another embodiment of the invention. DETAILED DESCRIPTION An example of a flow battery composition storage arrangement will now be described by way of example only with reference to Figs. 1 and 2. The flow battery composition storage arrangement is denoted generally by reference numeral 1, and comprises a first pile 2 at least partly within a bore 11, the first pile 2 defining a first pile volume 3 that is at least partly filled with a first composition 4 comprising an electrolyte for a flow battery. Flow battery composition storage arrangement 1 comprises a second pile 22 at least partly within a bore (not shown), the second pile 22 defining a second pile volume 23 that is at least partly filled with a second composition 24 comprising an electrolyte for a flow battery. Each of the first 2 and second 22 piles is cylindrical in shape, has a length of 50m, an internal diameter of 2.0m, and is entirely located in the ground G. Each of the first 2 and second 22 piles provides a large volume of about 160m3 for the storage of the respective first 4 and second 24 flow battery compositions. Furthermore, the entire storage volume is located underground and therefore takes-up substantially no space above ground, leaving space above ground for overlying structures. The storage of the first 4 and second 24 compositions underground also isolates those compositions from changes in ambient climate conditions (such as high or low temperatures) that could potentially have a deleterious effect on one or both of the first 4 and second 24 flow battery compositions. First 2 and second 22 piles are essentially identical, and first pile 2 will now be described in detail with reference to Fig. 1. First pile 2 comprises a plurality of tubular pile sections 5, 6, 7, 8 that are stacked one upon another to form a hollow column located in bore 11. The hollow column is located on a pile base 9. The pile base 9 may either be formed in situ in the bore 11 or may be a pre-fabricated piece that is placed in the bottom of bore 11. A pile cap 10 is located on top of pile section 5. A cured grout 13 fills the space 12 between the outside of first pile 2 and the inner surface of bore 11. The grout 13 helps couple first pile 2 to ground G. The manufacture of first pile 2 will now be briefly described. A drill (not shown) is used to form bore 11 in ground G. Pre-formed pile base 9 is placed at the bottom of bore 11. Pile section 8 is then placed on top of pile base 9. Pile section 7 is then placed on top of pile section 8, pile section 6 placed on top of pile section 7, and pile section 5 placed on top of pile section 6. A pile cap 10 is placed on top of pile section 5. A non-cured, liquid grouting is then provided in the space 12 between the external surface of first pile 2 and the internal surface of bore 11. The grouting then cures over time to produce a solid that fills the space 12 between the first pile 2 and bore 11, and also couples the first pile 2 to bore 11. As mentioned above, the structure of second pile 22 is essentially the same as first pile 2. The method of pile assembly is described in more detail in GB2580041, the teaching of which is fully incorporated herein by reference. A raft 14 of concrete is provided above both first 2 and second 22 piles. This raft 14 couples first 2 and second 22 piles to an overlying structure (not shown) so that load transmitted from the structure is transmitted through raft 14 to the first 2 and second 22 piles and into the ground G. First flow battery composition 4 comprises an anolyte comprising a solution of sodium disulfide (Na2S2). Second flow battery composition 24 comprises a catholyte comprising a solution of sodium tribromide (NaBrfi. Each of first pile 2 and second piles 22 comprises an inlet (not shown) for the initial introduction of the respective anolyte or catholyte. Referring to Fig. 2, each of the first pile 2 and second piles 22 comprises a respective outlet 31, 41 for delivering the respective first 4 and second 24 flow battery composition to a flow battery electrode arrangement (shown as 50 in Fig. 2 and described in more detail below). Those skilled in the art will realise that flow battery electrode arrangement 50 is not part of the flow battery composition storage arrangement 1. Each of the first pile 2 and second piles 22 comprises a lining (not shown) that facilitates the storage of liquids within the first 2 and second 22 piles. An example of an embodiment of a flow battery according to the present invention will now be described by way of example only with reference to Fig. 2. The flow battery is denoted generally by reference numeral 100 and comprises flow battery composition storage arrangement 1 and a flow battery electrode arrangement shown generally by reference numeral 50. First flow battery composition 4 is pumped by pump 32 from first pile 2 through first pile outlet 31 and conduit 33 to the flow battery electrode arrangement 50 via inlet 51 into anolyte volume 55. Similarly, second flow battery composition 24 is pumped by pump 42 from second pile 22 through second pile outlet 41 and conduit 43 to the flow battery electrode arrangement 50 via inlet 52 into catholyte volume 56. Anolyte volume 55 is defined by anode 57 and ion-permeable membrane 59. Catholyte volume 56 is defined by cathode 58 and ion-permeable membrane 59. Those skilled in the art will realise that a flow battery may operate in a discharge mode, in which electrical power is provided to an electrical load, and in a charging mode, in which electrical power is provided to the battery from an external source of electricity. In the discharge mode, the following reactions occur at the anode and the cathode: Anode: 2Na2S2 Na2S4 + 2Na+ + 2e Cathode: NaBrs + 2Na+ + 2e’ —> 3NaBr In the charging mode, the reactions are reversed, with sodium polysulfide forming sodium disulfide and sodium bromide forming sodium tribromide. Flow battery electrode arrangement 50 is provided with a first outlet 53 that permits egress of first flow battery composition 4, which is transferred via conduit 34 into inlet 35 provided in the first pile 2. Flow battery electrode arrangement 50 is further provided with a second outlet 54, which permits egress of second flow battery composition 24, which is transferred via conduit 44 into inlet 45 provided in the second pile 22. For the avoidance of doubt, pump 32 provides the necessary force to urge the first flow battery composition 4 out of the flow battery electrode arrangement 50 into first pile 2. Likewise, pump 42 provides the necessary force to urge the second flow battery composition 24 out of the flow battery electrode arrangement 50 into second pile 22. The operation of the flow battery 100 will now be described by way of example only with reference to Fig. 3. Flow battery 100 is typically connectable to an electrical load 110 and a source of electrical power 120. In a first mode of operation, a charged flow battery 100 is connected to the electrical load 110, and electrical power is supplied to the electrical load 110. Once the battery has been discharged, it is connected to a source of electrical power 120 to recharge the flow battery 100. The source of electrical power 120 in this particular case comprises a bank 130 of photovoltaic cells. Photovoltaic cells are of particular benefit because they provide a low-carbon way of recharging the flow battery. Alternative low-carbon sources of electrical energy may be used, such as wind turbines. An example of an embodiment of a method of operating a flow battery in accordance with the present invention will now be described with reference to Figs. 2 and 4. A method of operating a flow battery is denoted generally by reference numeral 200, the method 200 comprising moving 201 a first flow battery composition 4 from a first pile 2 to a flow battery electrode arrangement 50. The method 200 also comprises moving 202 a second flow battery composition 24 from a second pile 22 to a flow battery electrode arrangement 50. The method 200 also comprises moving 203 first flow battery composition 4 from the flow battery electrode arrangement 50 to the first pile 2, and moving 204 second flow battery composition 24 from the flow battery electrode arrangement 50 to the second pile 22. A further embodiment of flow battery in accordance with the present invention will now be described with reference to Figure 5. The flow battery is denoted generally by reference numeral 300, and comprises flow battery composition storage arrangement denoted generally by reference numeral 301 and a flow battery electrode arrangement shown generally by reference numeral 350. Flow battery electrode arrangement 350 is essentially the same as flow battery electrode arrangement 50 as described above. Flow battery storage arrangement 301 comprises a first set 301’ of piles 302, 303, 304 that are at least partly filled with first composition 4, and a second set 301” of piles 305, 306, 307 that are at least partly filled with second composition 24. First composition 4 comprising anolyte is supplied from piles 302, 303, 304 to the flow battery electrode arrangement 350 via conduit 333. Second composition 24 comprising catholyte is supplied from piles 305, 306, 307 to the flow battery electrode arrangement 350 via conduit 343. First composition 4 is returned to the piles 302, 303, 304 from flow battery electrode arrangement 350 via conduit 334. Second composition 24 is returned to the piles 305, 306, 307 from flow battery electrode arrangement 350 via conduit 344. Conduits may be provided between each pair of piles 302, 303, 304 in the first set 301’ of piles to facilitate movement of the first composition 4 between piles. Similarly, conduits may be provided between each pair of piles 305, 306, 307 in the second set 301” of piles to facilitate movement of the second composition 24 between piles. Piles 302, 303, 304, 305, 306, 307 are essentially the same as first pile 2 and second pile 22 described above, and are all located substantially below ground. Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described. The examples above describe the use of piles that are formed by stacking sections of a pile in a bore to form a column located in the bore. An alternative method of making piles by stacking is disclosed in GB2606724. Those skilled in the art will realise that other piles may be used. For example, a 1-piece pile may be lowered into the bore. Alternatively, a hollow pile may be formed in situ in the bore, as described in WO2008 / 047151. The examples above describe the use of a concrete raft above the piles. Those skilled in the art will realise that such a raft need not be used in all cases. The examples above described the use of pile linings. Such linings are merely optional and need not be used in all cases. The examples above describe the use of a flow battery with an ion-selective membrane. Those skilled in the art will realise that a membrane need not be used. For example, a laminar flow arrangement may be used, in which laminar flows of the first and second compositions contact one another. The examples above describe the first and second compositions being in the form of solutions. One or both of the first and second compositions need not be solutions. For example, one or both of the first and second compositions may be suspensions. The examples above describe the use of sodium disulfide and sodium tribromide electrolytes. These are non-organic or inorganic electrolytes. Those skilled in the art will realise that organic electrolytes may be used, such as methyl viologen and TEMPOL. The liquid used to dissolve the electrolytes in the Examples above is water. Those skilled in the art will realise that the liquid in which the electrolyte is dispersed or dissolved may be aqueous or non-aqueous, and will depend to some extent on the nature of the electrolyte. For example, if the electrolytes are non-organic, then typically the liquid in which the electrolyte is dispersed or dissolved would be aqueous. If the electrolytes are organic, then the liquid in which the electrolyte is dispersed or dissolved may optionally be aqueous or non-aqueous. The examples above describe the use of a sodium disulfide-sodium tribromide electrolyte system. Those skilled in the art will realise that other combinations of electrolytes are possible, such as vanadium-vanadium, zinc-bromine, zinc-cerium, lead-acid, zincmanganese, iron-iron, iron-tin, iron-titanium, iron-chromium, bromine-hydrogen, hydrogenlithium bromide and hydrogen-lithium chlorate. Some examples of flow batteries comprising different electrolyte systems are described in US224404, US3713888, US4968043 and 5 US4469760. Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. 10 It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments. 15

Claims

1. A flow battery composition storage arrangement comprising a first pile at least partly within a first bore, the first pile defining a first pile volume that is at least partly filled with a first composition comprising an electrolyte for a flow battery.

2. The flow battery composition storage arrangement according to claim 1, in which the first pile is substantially within the first bore.

3. The flow battery composition storage arrangement according to claim 1 or claim 2, in which the first composition comprises an anolyte or a catholyte.

4. The flow battery composition storage arrangement according to any preceding claim, in which the first pile volume is defined by one or more walls of the first pile.

5. The flow battery composition storage arrangement according to any preceding claim, in which the first pile comprises a lining that provides a first composition-contacting surface to facilitate the storage of first composition.

6. The flow battery composition storage arrangement according to any preceding claim, in which the first pile comprises an outlet for delivering the first composition to a flow battery electrode arrangement.

7. The flow battery composition storage arrangement according to any preceding claim, in which the first pile comprises an inlet for receiving the first composition from a flow battery electrode arrangement.

8. The flow battery composition storage arrangement according to any preceding claim, in which the first pile is configured to facilitate the transfer of a load from a structure to a solid underlying substrate.

9. The flow battery composition storage arrangement according to any preceding claim, in which the first pile has a length of from 5m to 70m.

10. The flow battery composition storage arrangement according to any preceding claim, in which the pile comprises one or both of a base and a cap.

11. The flow battery composition storage arrangement according to any preceding claim, in which a cured material is provided between the pile and the bore.

12. The flow battery composition storage arrangement according to any preceding claim, comprising a second pile volume that is at least partly filled with a second composition comprising an electrolyte for a flow battery.

13. The flow battery composition storage arrangement according to claim 12, in which the second pile volume is provided by a second pile.

14. The flow battery composition storage arrangement according to claim 12 or claim 13 when dependent on claim 3, in which, if the first composition comprises one of an anolyte and a catholyte, and the second composition comprises the other of the anolyte and a catholyte.

15. The flow battery composition storage arrangement according to any of claims 12 to 14, comprising comprise a first set of two or more piles and a second set of two or more piles, the first set of piles being provided with the first composition and the second set of piles being provided with the second composition.

16. A flow battery comprising a flow battery electrode arrangement, and a flow battery composition storage arrangement in accordance with any preceding claim, wherein the flow battery electrode arrangement is arranged to receive the first composition from the flow battery composition storage arrangement of the first aspect of the present invention.

17. The flow battery according to claim 16, in which the flow battery composition storage arrangement comprises a second pile provided with a second pile volume that is at least partly filled with a second composition comprising an electrolyte for a flow battery, the flow battery electrode arrangement comprising an anode and a cathode, one of the first composition and the second composition contacting the anode, and the other of the first composition and the second composition contacting the cathode.

18. The flow battery according to claim 17, in which the flow battery electrode arrangement comprises one or more of:a current collector in electrical contact with the anode;a current collector in electrical contact with the cathode;a membrane separating the first composition and the second composition;a first inlet arranged to receive the first composition from the first pile volume; and a second inlet arranged to receive a second composition from the second pile.

19. Use of a pile to store a flow battery composition comprising an electrolyte for a flow battery.

20. Use of a first pile to store a first composition comprising an electrolyte for a flow battery and a second pile to store a second composition comprising an electrolyte for as flow battery, one of the first and second compositions being an anolyte for a flowbattery and the other of the first and second compositions being a corresponding catholyte for a flow battery.

21. A flow battery electrode arrangement for use in the flow battery of claims 16 to 18.

22. A first pile for use in the flow battery composition storage arrangement according to5 any of claims 1 to 15.

23. A method of operating a flow battery comprising moving a first flow battery composition from a first pile to a flow battery electrode arrangement.

24. The method of claim 23, comprising moving a second flow battery composition from a second pile to the flow battery electrode arrangement.

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