Storage, offshore structure, and method of adding storage capacity

Abstract

A storage (200) for a fluid is disclosed. The storage comprises a storage tank (500) for storing the fluid; piping (510) for conducting fluid to and from the storage tank (500); a valve (520) for sealing off any fluid in the storage tank (500); and at least one holder (300) for rigid attachment of the storage (200) to a partly submerged floating offshore structure (100). The storage (200) is configured to float entirely below a sea surface (20) and above the seabed (10), such that the storage (200) can be attached to the offshore structure (100) without adding weight to the offshore structure (100). An offshore structure comprising one or more storages (200) for a fluid is also disclosed, as well as a method of adding fluid storage capacity to a partly submerged floating offshore structure (100).

Description

[0001] STORAGE, OFFSHORE STRUCTURE, AND METHOD OF ADDING STORAGE CAPACITY

[0002] Technical Field

[0003] The present disclosure relates to a storage for a fluid, an offshore structure comprising one or more storages for a fluid, and to a method of adding fluid storage capacity to of a floating offshore structure. More particularly, the present disclosure relates to subsea storage of hydrogen and how to realise such storage safely and efficiently in the field of renewable energies.

[0004] Background

[0005] Storing hydrogen is a problem because hydrogen is highly combustible. There are regulations that must be followed when storing hydrogen. A hydrogen storage tank is usually placed on top of an offshore structure or inside the offshore structure. Both these possibilities have disadvantages. For example, a hydrogen storage tank that is placed on top of an offshore structure can get damaged, for example by a rotating blade of a wind turbine, weather or other objects. A leaking hydrogen storage tank inside an offshore structure may result in loosing the whole offshore structure. A hydrogen storage tank place on the sea bed requires a riser and facilities to keep it in place.

[0006] It is a problem to store safely hydrogen that can be accessed by an offshore structure. It is a problem to comply with the relevant regulation technically and in a cost effective manner. It is further a problem to avoid damage to any storage tanks and keeping in mind that a storage tank may leak. It is also desirable to reduce wear on the tanks and increase their life span. Preferably storing hydrogen should allow for the storage to be movable.

[0007] A further technical problem is that any part of storing hydrogen must function without a possibility to fail, fulfil technical and legal requirements, and be easy to use. It is desirable that any solution is simple, not expensive to produce, and is reliable. It is further a technical problem to avoid cumbersome arrangements that are expensive to manufacture or assemble or use in connection with an offshore structure.

[0008] Summary of the Invention

[0009] It is an object of the present invention to provide a storage for a fluid, an offshore structure comprising one or more storages for a fluid, and a method of adding fluid storage capacity to a partly submerged floating offshore structure. This object can be achieved by the features as defined by the independent claims. Further enhancements are characterized by the dependent claims. The invention is defined by the claims.

[0010] According to one embodiment, a storage 200 for a fluid is disclosed. The storage comprises a storage tank 500 for storing the fluid; piping 510 for conducting fluid to and from the storage tank 500; a valve 520 for sealing off any fluid in the storage tank 500; at least one holder 300 for rigid attachment of the storage 200 to a partly submerged floating offshore structure 100. The storage 200 is configured to float entirely below a sea surface 20 and above the seabed, such that the storage 200 can be attached to the offshore structure 100 without adding weight to the offshore structure 100. Preferably the storage 200 can be attached to and detached from the offshore structure 100. Adjust buoyancy means 430 may be used for floating the storage 200 above and below the sea surface, such that the storage 200 may be entirely below the sea surface, or partly above the sea surface. When attached to the offshore structure, the one or more storages 200 are subsea, above the seabed 10, below the sea surface 20, submerged. Preferably, the storage 200 is attached to a part of the offshore structure 100 that is subsea. The storage 200 may comprises multiple storage tanks 500 arranged in a rigid support.

[0011] The at least one holder 300 for attaching the storage 200 to an offshore structure 100 may comprise at least two holders 300, 310; one holder 300 being configured for attaching the storage 200 to an offshore structure 100 and the other holder 310 being configured for attaching the storage 200 to another storage 210.

[0012] The piping 510 may be configured for conducting fluid between the storage tank 500 and one of the offshore structure 100 and a second storage 210. The buoyancy means may be further configured for floating the storage 200 at least partly above the sea surface.

[0013] According to one embodiment, an offshore structure comprising one or more storages 200 for a fluid is disclosed. The offshore structure 100 is a floating offshore structure 100, preferably a partly submerged floating offshore structure 100. The one or more storages 200 are subsea, above the sea bed 10, below the sea surface 20, and in the proximity of the offshore structure 100; and each storage 200 is rigidly attached to a subsea part 110, 120 of the offshore structure 100. The one or more storages may not be supported by, or standing on, the sea bed 10. Preferably, the storage 200 is attached to a part of the offshore structure 100 that is subsea. Each storage 200 may be a storage according to any one of the storages disclosed herein. The offshore structure may have a first storage 200 attached to a first part 110, of the offshore structure 100, which is subsea; and a second storage 210 attached to the first storage 200. The second storage 210 may further attached to a second part 120, of the offshore structure 100, which is subsea. The weight of the offshore structure 100 is configured to remain substantially unchanged by adjustable buoyancy means 530 for floating the one or more storages 200. The adjustable buoyancy means 530 allows for the weight of the offshore structure 100 to remain substantially unchanged. The offshore structure may further comprise a support 350 arranged between a first part 110 and a second part 120 of the offshore structure 100 that are subsea, wherein the support 350 holds a plurality of the storages 200. The offshore structure 100 may be a floating offshore structure. The offshore structure may comprise a wind turbine generator and the fluid may be hydrogen. The one or more storages 200 may be releasably fixed to the offshore structure 100. In some embodiments, the storage 200 may be welded to the offshore structure 100.

[0014] According to one embodiment, a method of adding fluid storage capacity to a partly submerged floating offshore structure 100 is disclosed. The offshore structure may be an already installed for production offshore structure. That is, the offshore structure may be floating and installed for producing energy, in other words the offshore structure may have been installed and now produces energy. The offshore structure 100 may be an embodiment of the offshore structure as described herein. The method comprises placing 410 the one or more storages 200, preferably positively buoyant storages, in the proximity of the offshore structure 100; and rigidly attaching 420 the one or more storages 200, entirely submerged above the seabed 10 and below the sea surface20, to one or more parts 110 of the offshore structure 100 that is subsea without adding weight to the offshore structure. The method may further comprise adjusting buoyancy to float the one or more storages 200 entirely below the sea surface, such that the storage 200 can be rigidly attached to the floating offshore structure 100 fully submerged. This may allow rigidly attaching storages 200 without adding weight to the floating offshore structure 100. The method may comprise placing 410 the one or more storages 200 subsea in the proximity of the offshore structure 100; adjusting buoyancy means 430 for floating the storage 200 entirely below the sea surface 20 and above the sea bed 10, such that the storage 200 can be attached to the offshore structure 100 without adding weight to the offshore structure 100; and rigidly attaching 420 the one or more storages 200 to one or more parts 110 of the offshore structure 100 that is subsea. For example, the rigid attachment may be a subsea attachment that is between the sea surface 20 and above the seabed 10, and may be a subsea attachment between the one or more storages 200 and an offshore part that is between the sea surface 20 and above the sea bed 10.

[0015] Attaching 420 the one or more storages 200 to one or more parts 110 of the offshore structure 100 that is subsea may comprise attaching 422 a first storage 200 to a part 110 of the offshore structure 100 that is subsea; and attaching 424 a second storage 210 to the first storage 200 and to a second part 120, of the offshore structure 100, that is subsea. The method may further comprise sailing away with the offshore structure 100 and the one or more storages 200. The method may further comprise arranging the one or more storages 200 subsea such that the offshore structure 100 and that the one or more storages 200 can move relative to each other without contacting each other.

[0016] According to one embodiment, in combination or independently, a method is disclosed where the offshore structure 100 can be moved on the sea together with the one or more storages 200 arranged as described herein.

[0017] The storage as described herein, or the offshore structure as described herein, or the method as described herein, may further comprise that the floating offshore structure 100 comprises a wind turbine generator and / or that the fluid is hydrogen.

[0018] At least one of the above embodiments provides one or more solutions to the problems and disadvantages with the background art. Other technical advantages of the present disclosure will be readily apparent to one skilled in the art from the following description and claims. Various embodiments of the present application obtain only a subset of the advantages set forth. No one advantage is critical to the embodiments. Any disclosed embodiment may be technically combined with any other disclosed embodiment or embodiments.

[0019] Brief Description of the Drawings

[0020] The accompanying drawings illustrate presently exemplary embodiments of the disclosure and serve to explain, by way of example, the principles of the disclosure. Fig 1 is a diagrammatic and schematic illustration of an offshore structure comprising one or more storages for a fluid according to an exemplary embodiment of the disclosure;

[0021] Fig 2 is a diagrammatic and schematic illustration of an offshore structure comprising one or more storages for a fluid according to an exemplary embodiment of the disclosure;

[0022] Fig 3 is a diagrammatic illustration of a method of storing a fluid in the proximity of an offshore structure according to an exemplary embodiment of the disclosure; and

[0023] Fig 4 is a diagrammatic and schematic illustration of a storage for a fluid according to an exemplary embodiment of the disclosure.

[0024] Detailed Description

[0025] Figures 1 to 4 illustrate exemplary embodiments of the storage, the offshore structure, and the method for adding fluid storage capacity to a partly submerged floating offshore structure. The fluid may by hydrogen. Figures 1 and 2 a diagrammatic and schematic illustration of a floating, partly submerged, offshore structure 100 comprising one or more storages for a fluid according to an exemplary embodiment of the disclosure. In figure 1 the seabed 10 and the sea surface 20 have been illustrated, but in figure 2 only the sea surface 20 has been illustrated. The offshore structure may be any floating offshore structure, for example a semisubmersible platform with a plurality of columns, such as a partly submerged floating offshore structure. Figure 3 illustrated a flow chart of a method of storing a fluid in the proximity of an offshore structure according to an exemplary embodiment of the disclosure. Figure 4 illustrates a storage 200 for a fluid with a storage tank according to an exemplary embodiment of the disclosure. The storage 200 illustrated in figure 4 may be the storages 200, 210, 220 illustrated in figures 1 and 2.

[0026] Turning first to figure 4, a storage 200 for a fluid is illustrated. The storage comprises a storage tank 500 for storing the fluid; piping 510 for conducting fluid to and from the storage tank 500; a valve 520 for sealing off any fluid in the storage tank 500; at least one holder 300 for rigidly attachment of the storage 200 to a partly submerged floating offshore structure 100; and the storage 200 is configured to float entirely below a sea surface 20 and above the sea bed 10, such that the storage 200 can be attached to the offshore structure 100 without adding weight to the offshore structure 100. The storage 200 may be rigidly attached to, and detached from, a part of the floating offshore structure that is subsea. The rigid attachment may be a stiff or unyielding attachment, not pliant or flexible attachment, resulting in that the storage 200 moves in unison with the floating offshores structure 100. The rigid attachment may be an inflexible attachment, such as for example bolting the storage 200 to the offshore structure 100. The rigid attachment is not a flexible attachment, such as for example chains or wires. The storage tank 500 may be completely inside the storage 200. The storage tank 500 may be suitable for storing hydrogen, preferably pressurised hydrogen. The piping 510 may be conduits that are configured for transporting the fluid stored in the storage tank 500. The piping 510 may lead between the storage tank 500 and an outside of the storage 200, to allow stored fluid to enter and leave the storage tank 500. The piping 510 may have a connector on the conduit reaching out of the storage 200, to allow the piping 510 to connect to, for example, another storage 200 or to a separate receiving unit of the stored fluid on an offshore structure 100 or elsewhere. The valve 520 may be positioned on the piping 510 to seal off any fluid in the storage tank 500. The at least one holder 300 may be a plurality of holders 300 on each side of the storage 200, making it possible to rigidly attach the storage 200 to an offshore structure or to another storage 200. The storage 200 is self-contained, for example the storage 200 may be configured to be used and moved independently and may have necessary safety features, such as for example pressure gauges and safety valves. The storage 200 may be shaped in the form of a cuboid, a tetrahedron, a polyhedron, or a ball. The adjustable buoyancy means 530 may be evenly distributed within the storage 200 to give the storage 200 stability. The at least one holder 300 may be at least on releasable holder 300. The adjustable buoyancy means 530 may change the weight of the storage 200 such that the storage floats in the sea, for example entirely below the sea surface 20, or for example at least one part of the storage 200 above the sea surface 20. For example, the adjustable buoyancy means 530 may add sea water into the storage 200 to make it heavier, or remove sea water from the storage 200 and replace it with air to make the storage 200 lighter. The storage 200 may comprise a pump configured for this purpose. The adjustable buoyancy means 530 may be ballast, for example by adding additional, permanent or temporary, ballast one may sink the storage below sea surface for installation purposes. The ballast may be dead weight, such as for example water or metal or sand or stone. By adjusting the adjustable buoyancy means 530 the storage 200 can be attached to an offshore structure 100, or another storage 200, without adding weight to whatever it is attached to. The storage 200 may thus be buoyed up by a force equal to the weight of the storage 200. It is advantageous that the overall weight, for example that of an offshore structure and one or more storages 200, does not change when a storage 200 is attached with the holder 300. Storages can therefore be added to already installed floating offshores structures that produce energy since the attachment of the storage 200 to the offshore structure 100 is rigid and does not alter the integrity or weight that the floating offshore structure must support. It is advantageous to be able to submerge, and adjustably submerge, the storage 200 because of the possible hazard the stored fluid may pose. Buoyancy, or up-thrust, may be the upward force exerted by the sea water that opposes the weight of the partially or fully immersed storage 200. The buoyancy means 530 can adjust this buoyance. Embodiments of the storage 200 described herein may be adjusted to be at a certain predefined depth in the sea, and releasably attachable to an offshore structure 100, to allow safe storage of fluids, such as for example hydrogen.

[0027] As best illustrated in figures 1 and 4, the at least one holder 300 for rigidly attaching the storage 200 to an offshore structure 100 may comprise at least two holders 300, 310. One holder 300 may be configured for rigidly attaching the storage 200 to an offshore structure 100 and the other holder 310 may being configured for rigidly attaching the storage 200 to another storage 210. The rigid attachment may be configured to be inflexible, such that the storage 200 moves in unison with the floating offshores structure 100. For example, two holders 300 on the left side of the storage 200 in figure 4 may be configured to releasably, or permanently, rigidly attach the storage 200 to an offshore structure 100. For example, the two holders 310 on the left side of the storage 200 in figure 4 may be configured to releasably, or permanently, attach the storage 200 to another storage 200, or to another part of the offshore structure. In this way a plurality of storages may be attached like and form a chain, with the ends of the chain attachable to an offshore structure 100, preferable attachable in a subsea position in the proximity of the offshore structure 100. The at least two holders 300, 310 may be arranged on opposite sides of the storage 200. The storage 200 may comprise one or more holders 300 on each side of the storage 200. Each holder may be configured to rigidly attach, subsea, each storage 200 to a subsea part 110, 120 of the offshore structure 100.

[0028] The piping 510 may be configured for conducting fluid between the storage tank 500 and one of the offshore structure 100 and a second storage 210. In this way fluid can be transported between the storage tank 500 and the offshore structure 100, and fluid can be transported between the storage tank 500 and another storage tank 500. The piping 510 may include a coupling for coupling the piping 510 to conduit fluid. The piping may comprise quick connect couplings. The piping 510 may be flexible and / or extendable conduits or pipes.

[0029] The adjustable buoyancy means 530 may be further configured for floating the storage 200 at least partly above the sea surface 20. This would allow the storage 200 to come up above the sea surface 20 so that it can be accessed for use and / or service. For example, when connecting the piping 510 it may be convenient to float the storage 200 above the sea level 20 to make a connection above water, not subsea. The adjustable buoyancy means 530 may be configured to adjust the buoyance of the storage 200 proportional to the amount of fluid in the storage tank 500, the amount of fluid being for example the amount of hydrogen in gaseous form, pressurised or not.

[0030] The offshore structure described herein may be an offshore structure that comprises a wind turbine generator. The offshore structure may be a floating offshore structure. The offshore structure may be a semi-submersible platform with at least three columns 110, 120, 130, each storage 200 may be releasably fixed to at least two of the columns 110, 120 subsea. The offshore structure 100 may be a partly submerged floating offshores structure 100. The offshores structure may be an already installed for production offshore structure. That is, the offshore structure may be floating and installed for producing energy, in other words the offshore structure may have been installed and now produces energy. The offshores structure may be in the process of being installed. For example, the offshores structure may be ready for being transported from the quay-side to its production location for its final installation. One or more storages 200 may be rigidly attached to such an offshores structure 100 at the quay-side, and, for example, sail away with the offshores structure to its production location. The fluid described herein may be hydrogen. The fluid may be a mixture of liquid and gaseous substance. The tank 500 may be configured for storing a fluid at pressure, for example a high pressure, for example several time the atmospheric pressure. The one or more storages 200 are subsea, above the sea bed 10, below the sea surface 20, and may be below the footprint, and in the proximity, of the offshore structure 100.

[0031] Turning to figures 1 and 2, an offshore structure comprising one or more storages 200 for a fluid is illustrated. The one or more storages 200 are subsea, above the sea bed 10, below the sea surface 20, and in the proximity of the offshore structure 100; and each storage 200 is rigidly attached to a subsea part 110, 120 of the offshore structure 100. The one or more storages 200 may not be supported by, or standing on, the sea bed 10. Each storage 200 may not add weight to the offshore structure. The attachment may be releasable or more permanent, such as welding. The rigid attachment may be configured to attach and detach a storage 200. Each storage 200, 210, 220 may be a storage 200 as described herein. A first storage 200 may be rigidly attached to a first part 110, of the offshore structure 100, which is subsea; and a second storage 210 may be rigidly attached to the first storage 200. The second storage 210 may be subsea. The second storage 210 may be further rigidly attached to a second part 120, of the offshore structure 100, which is subsea. The second storage 210 may be further rigidly attached to a third storage 220, and the third storage 220 may be rigidly attached to the second part 120, of the offshore structure 100, which is subsea. Each storage 200 may be releasably fixed to two different parts 110, 120, of the offshore structure 100, that are subsea.

[0032] The weight of the offshore structure 100 is configured to remain substantially unchanged by the adjustable buoyancy means 530 for floating the one or more storages 200, for example by adding ballast. In this way fluid may be stored in the proximity of the offshore structure 100 without adding additional weight to the offshore structure 100.

[0033] As illustrated in figure 2, the offshore structure 100 may further comprise a support 350 arranged between a first part 110 and a second part 120 of the offshore structure 100 that are subsea. The support 350 may hold a plurality of the storages 200. The support 350 may rigidly attach a plurality of the storages 200 to the floating offshore structure 100. The support may extend between two parts 110, 120 subsea and hold one or more storages 200, 210, 220. The buoyance of the storages 200, 210, 220 may be adjusted, for example by adding ballast, so that the storages 200, 210, 220 are buoyant at the same level, depth, as the support 350 is positioned. This allows the support 350 to carry no weight from the storages 200, 210 220 and therefore support the storages 200, 210, 220 better.

[0034] According to one embodiment, a method adding capacity to a partly floating offshore structure 100 is disclosed. The offshore structure 100 may already comprising one or more storages 200 for the fluid. The storages 200 may be any embodiment of the storages 200 described herein. The method comprises placing 410 one or more storages 200 in the proximity of the offshore structure 100; and rigidly attaching 420 the one or more storages 200, entirely submerged above the seabed 10 and below the sea surface 20, to one or more parts 110 of the offshore structure 100 that is subsea without adding weight to the offshore structure 100. This may be done using any of the features described herein. These steps may be taken in any order. The one or more storages may not be supported by, or standing on, the seabed 10. Preferably the buoyancy is adjusted, for example by adding ballast, before attaching the storage 200 to the offshore structure. This method allows a safe place for the storages 200 of a fluid like, for example, hydrogen without storing the hydrogen inside or on the offshore structure 100, and without the storages 200 being an integral part of the offshore structure 100. This stores hydrogen safely in the proximity of an offshore structure 100 and at the same time avoiding damage to any storage tanks 200. In case of a leakage in a storage 200, the leakage is away, and separate, from the offshore structure. This also reduces wear on the storages 200 and increases their life span. The storages 200 may in this way be storages separate from the offshore structure 100 and when the storages are entirely below the sea surface 20 then other safety aspects apply to the storages 200 compared with when the storages are floating or above the sea surface 20. As described herein, a partly floating offshore structure that does not have the capacity to store a fluid, such a hydrogen, or cannot store more fluid, can be given fluid storage capacity or additional fluid storage capacity.

[0035] The method may comprise adjusting buoyancy to float the one or more storages 200 entirely below the sea surface, such that the storage 200 can be rigidly attached to the floating offshore structure 100 fully submerged. The adjustable buoyancy means, as also described elsewhere herein, may comprise adding ballast, or adding additional ballast, for the purpose of sinking the storage 200 below surface to a predetermined subsea level for installation purposes. The ballast may be dead weight, such as water, sand, stone, or metal. The ballast may be permanently attached to the storage 200, or may be temporarily attached to the storage 200. The storages 200 may assist with the buoyancy of the floating offshore structure 100.

[0036] The part of the method of rigidly attaching 420 the one or more storages 200 to one or more parts 110 of the offshore structure 100 where the one or more parts 110 are subsea may further comprise rigidly attaching 422 a first storage 200 to a part 110 of the offshore structure 100 that is subsea; and rigidly attaching 424 a second storage 210 to the first storage 200 and to a second part 120, of the offshore structure 100, that is subsea. This may be done like a sequence as described herein, and as illustrated in figures 1 and 2. The method may comprise arranging the one or more storages 200 subsea such that the offshore structure 100 and the one or more storages 200 can move in unison with each other and without contacting each other.

[0037] A support 350 may be used to arrange the storages 200 in relation to the offshore structure 100. The support 350 may be arranged between a first part 110 and a second part 120 of the offshore structure 100 that is subsea. The support 350 may hold a plurality of the storages 200 in a spaced way away from, and in the proximity of, the offshore structure 100, as elsewhere described herein. The storages 200 may be separately removable from the offshore structure 100 and / or the support 350. The support 350 together with the storages 200 may be rigidly attached to the offshore structure 100.

[0038] The method may further comprising sailing away with the offshore structure 100 and the one or more storages 200. Embodiments disclosed herein allow that when the offshore structure 100 is moved, sailed away, then any storages 200 attached to the offshore structure 100 can move, sail away, with the offshore structure 100 without any further arrangement. The storages 200 are rigidly attached to the floating offshore structure 100 such that they move in unison with the floating offshore structure 100. A vessel may arrive at the offshore structure and one may detach a storage 200 from the offshore structure 100 and attach that storage 200 to the vessel. In this way a storage may be transported to and from the offshore structure, with the benefit that the storage 200 is configured to be self-contained.

[0039] Turning to the figures, an offshore structure comprising one or more storages 200 for a fluid is illustrated. The offshore structure 100 may be for a wind turbine, or any other energy producer. The offshore structure 100 may be a semi-submersible platform 100 with a plurality of parts 110, 120, 130, for example columns. The parts may be structures that are perpendicular to the main top deck or body of the offshore structure 10. The plurality of parts may be two, three, four, or more of parts. The entire part, or at least a section of the part, may subsea, i.e. under water. In the figures 1 and 2 the parts 110, 120, and 130 of the offshore structure 100 are at least partially subsea. In figure 1 the offshore structure 100 has three parts 110, 120, 130, while the offshore structure 100 in figure 2 has two parts 110, 120. Alternatively, the offshore structure 100 in figure 2 has four parts, two of the parts not being visible behind the two front columns, parts 110, 120. The parts in figures 1 and 2 are for example columns, hollow structures, part of the offshore structure 100. The parts may be in corners or junctions of the offshore structure 100. The offshore structure 100 may have a deck that is substantially parallel to the sea surface 20. For example, as in figure 1, if the offshore structure 100 comprises a substantially triangular top surface, then the parts 110, 120, 130 may be one in each corner. For example, as in figure 2, if the offshore structure 100 comprises a substantially square top surface, then the parts may be one in each corner. A hydrogen generation package 150 may be located on the offshore structure 100. Hydrogen may be lead between the hydrogen generation package 150 and the one or more storages 200 using the piping 510 of the one or more storages 200.

[0040] As illustrated in figures 1 and 2, the one or more storages 200 are subsea, above the seabed 10, below the sea surface 20, and in the proximity of the offshore structure 100. Each storage may be completely, entirely, in the water, below the sea surface. Each storage 200 may be rigidly fixed to a subsea part 110, 120, 130 of the offshore structure 100. Each storage 200 may comprise one or more storage tanks for hydrogen. Each storage 200 may be positioned below the footprint of the offshore structure 100, but completely inside the water, and not on the seabed. Each storage may be fixed indirect or direct to a part 110, 120, 130 of the offshore structure 100 that is subsea. In this way the one or more storages 200 are connected, anchored, to the offshore structure 100. This location protects the storages from damages, for example from a wind turbine blade. This location is advantageous since it is below the sea surface, i.e. in the water. There is no need for a riser since the storages 200 are not on the seabed 10. The storages 200 may assist with the buoyancy of the offshore structure 100.

[0041] As illustrated in figures 1 and 2, each of the one or more storages 200 may be rigidly fixed to a part 110, 120, 130 that is subsea. Each storage may be rigidly fixed, and may also be releasably fixed, to a subsea part 110, 120 of the offshore structure 100 in such a way that there is a distance, space, between each storage and the structures, the parts 110, 120, 130, of the offshore structure 100. The rigid fixation and attachment may be only subsea, in the water. The storages are rigidly attached and are therefore not an integral part of the hull of the offshore structure 100. Each storage 200 may be rigidly fixed to two or three or all four of the parts 110, 120, 130 subsea. In one embodiment, a storage 200 may be welded to the offshore structure for a permanent position.

[0042] As best illustrated in figure 1, a first storage 200 may be rigidly attached to a first part 110, of the offshore structure 100, which is subsea. A second storage 210 may be rigidly attached to the first storage 200. The second storage 210 may be further rigidly attached to a second part 120, of the offshore structure 100, which is subsea. Alternatively, the second storage 210 may be further rigidly attached to a third storage 220. The third storage 220 may be further rigidly attached to the second part 120, of the offshore structure 100, which is subsea. A fourth, fifth, and / or sixth storage may be correspondingly rigidly attached between the first part 110 and the second part 120.

[0043] As illustrated in figure 2, the offshore structure may further comprise a support 350 arranged between a first part 110 and a second part 120 of the offshore structure 100 that is subsea. The support 350 may hold a plurality of the storages 200. The support 350 may bridge subsea two parts 110, 120 of the offshore structure 100. The support 350 may comprise a compartment, an opening, where each storage 200 may be releasably and rigidly attached via the at least one holder 300. By the adjustable buoyancy means 530 the storages may not change the overall weight of the offshore structure 100. Since the storages 200 in figures 1 and 2 are not an integral part of the hull of the offshore structure 100, a fluid like hydrogen can be stored safely away from the offshore structure 100, but still in the proximity of the offshore structure 100. The support 350 may bridge subsea three parts 110, 120, 130 of the offshore structure 100.

[0044] According to one embodiment that may be combined with any embodiment disclosed herein, the offshore structure may further comprise a flexible pipe for transporting the fluid to and from the one or more storages 200. The flexible pipe may be part of the flexible holder 300. The flexible pipe may also be between two storages 200. The storages 200 may be connected in parallel or in series, but preferably in parallel. The piping 510 may comprise the flexible pipe.

[0045] According to one embodiment that may be combined with any embodiment disclosed herein, the offshore structure may comprise a wind turbine generator, or a wave generator, or solar energy generator. The fluid mentioned herein may be hydrogen. The energy electric power may be used to split water into hydrogen and oxygen by electrolysis. A hydrogen generation package may be located on the offshore structure 100. The hydrogen can then be stored for future use in the one or more storages 200, the hydrogen may be converted back into electricity when needed.

[0046] At least one embodiment described herein provides that the one or more storages 200 avoids being in the hull of the offshore structure 100 or part of the hull or a permanent attachment to the hull. This avoids large and costly safety measures against possible leakage at the hull and all decks above of the offshore structure 100. To store hydrogen inside the hull needs a specific hull that is expensive and would otherwise compromise the purity of the hydrogen stored. Connecting the storages in the described way above reduces the weight of the offshore structure because the storages provide buoyancy.

[0047] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using the storage, the offshore structure, and performing the methods of adding fluid storage capacity. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

[0048] List of elements:

[0049] 10 sea bed

[0050] 20 sea surface

[0051] 100 offshore structure

[0052] 110 first part

[0053] 120 second part

[0054] 130 third part

[0055] 150 hydrogen generation package

[0056] 200 storage

[0057] 210 storage 2nd

[0058] 230 storage 3rd

[0059] 300 holder

[0060] 310 holder 2nd

[0061] 320 holder 3rd

[0062] 350 support

[0063] 410 placing the one or more storages 200 subsea, above the sea bed 10, below the sea surface 20, and in the proximity of the offshore structure 100

[0064] 420 attaching the one or more storages 200 to one or more parts 110 of the offshore structure 100 that is subsea 422 attaching a first storage 200 to a part 110 of the offshore structure 100 that is subsea

[0065] 424 attaching a second storage 210 to the first storage 200 and to a second part 120, of the offshore structure 100, that is subsea 430 adjust buoyancy means for floating the one or more storages 200 entirely below the sea surface, such that the storage 200 can be rigidly attached to the floating offshore structure 100 without adding weight to the offshore structure 100 500 storage tank 510 piping 520 valve

[0066] 530 adjustable buoyancy means

Claims

Claims1 A storage (200) for a fluid, the storage comprising a storage tank (500) for storing the fluid; piping (510) for conducting fluid to and from the storage tank (500); a valve (520) for sealing off any fluid in the storage tank (500); and at least one holder (300) for rigid attachment of the storage (200) to a partly submerged floating offshore structure (100); wherein the storage (200) is configured to float entirely below a sea surface (20) and above the seabed (10), such that the storage (200) can be attached to the offshore structure (100) without adding weight to the offshore structure (100).2 The storage according to claim 1 , wherein the at least one holder (300) for attaching the storage (200) to an offshore structure (100) comprises at least two holders (300, 310); one holder (300) being configured for attaching the storage (200) to an offshore structure (100) and the other holder (310) being configured for attaching the storage (200) to another storage (210).3 The storage according to claim 1 or 2, wherein the piping (510) is configured for conducting fluid between the storage tank (500) and one of the offshore structure (100) and a second storage (210).4 The storage according to any one of the preceding claims, further comprising adjustable buoyancy means (530) for floating the storage (200) at different levels between the sea surface (20) and the seabed (10).5 The storage according to any one of the preceding claims, wherein the storage (200) comprises multiple storage tanks (500) arranged in a rigid support.6 An offshore structure comprising one or more storages (200) for a fluid, the offshore structure is a floating offshore structure, characterised in that the one or more storages (200) are subsea, above the seabed (10), below the sea surface (20), and in the proximity of the offshore structure (100); andeach storage (200) is rigidly attached to a subsea part (110, 120) of the offshore structure (100).7 The offshore structure according to claim 6, wherein each storage (200) is a storage according to any one of claims 1 to 5.8 The offshore structure according to claim 6 or 7, wherein a first storage (200) is attached to a first part (110), of the offshore structure (100), which is subsea; and a second storage (210) is attached to the first storage (200).9 The offshore structure according to claim 8, wherein the second storage (210) is further attached to a second part (120), of the offshore structure (100), which is subsea.10 The offshore structure according to any one of the preceding claims 7 to 9, wherein the weight of the offshore structure (100) is configured to remain substantially unchanged by adjustable buoyancy means (530) for floating the one or more storages (200).11 The offshore structure according to any one of the preceding claims 6 to 10, further comprising a rigid support (350) arranged between a first part (110) and a second part (120) of the offshore structure (100) that are subsea, wherein the support (350) holds a plurality of the storages (200).12 The offshore structure according to claim 11 , wherein the support (350) is configured to receive a plurality of storages (200, 210, 220) in the proximity of the offshore structure (100) in a horizontal plane.13 A method of adding fluid storage capacity to a partly submerged floating offshore structure (100), characterised in placing (410) one or more storages (200) in the proximity of the offshore structure (100); and rigidly attaching (420) the one or more storages (200), entirely submerged above the seabed (10) and below the sea surface (20), to one or more parts (110) ofthe offshore structure (100) that is subsea without adding weight to the offshore structure (100).14 The method of claim 13, further comprising adjusting buoyancy (430) to float the one or more storages (200) entirely below the sea surface, such that the storage (200) can be rigidly attached to the floating offshore structure (100) fully submerged.15 The method of claim 13 or 14, wherein attaching (420) the one or more storages (200) to one or more parts (110) of the offshore structure (100) that is subsea, comprises attaching (422) a first storage (200) to a part (110) of the offshore structure (100) that is subsea; and attaching (424) a second storage (210) to the first storage (200) and to a second part (120), of the offshore structure (100), that is subsea.16 The method of any one of the preceding claims 13 to 15, further comprising sailing away with the offshore structure (100) and the one or more storages(200).17 The storage according to any one of the preceding claims 1 to 5, or the offshore structure according to any one of the preceding claims 6 to 12, or the method according to any one of the preceding claims 13 to 16, wherein the floating offshore structure (100) comprises a wind turbine generator and / or the fluid is hydrogen.

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