External pressure fluid reservoir for storing energy

Abstract

The invention relates to an external pressure fluid reservoir which has: an interior for receiving a fluid; an external wall to which, during operation, pressure is applied by an external pressure from the external environment and which separates the interior from the external environment in a fluid-tight manner; and a connection, which is provided between the interior and the external environment, for selectively exchanging fluid between the interior and the external environment; wherein the interior is formed by a bulk material filling and the wall is designed such that, during operation, said wall absorbs an external pressure exceeding the pressure in the interior and introduces it into the bulk material filling which in turn supports said wall, in its operating position, against the excess external pressure.

Description

[0001] External pressure fluid storage for energy storage

[0002] The present invention relates to an external pressure fluid reservoir according to the preamble of claim 1 and a method for producing such an external pressure fluid reservoir according to claim 21.

[0003] Energy storage has become increasingly important since renewable energy production as such is expected to increase. Many renewable energy sources are weather-dependent (sun, wind), resulting in a temporal gap between production and consumption. Accordingly, the provision of energy generated by solar or wind, for example, in the form of heat or electricity only makes sense if intermediate storage is possible, either until the energy consumer needs it, or while weather-related insufficient energy production persists.

[0004] Thermal storage systems have become well-known for heat storage, while pumped-storage power plants or pressure storage systems are used for electricity storage. In pumped-storage power plants, the electricity is used to pump water to a higher level, which can then drive generators to generate electricity during periods of power shortages. In pressure storage systems, a compressible fluid, such as air, is compressed by electrically driven compressors and stored in a pressure vessel until, when electricity is needed, the compressed fluid can drive turbines coupled to generators, thus allowing electricity to be produced on demand, thus storing energy for a period of time.

[0005] Energy storage on an industrial scale is technically demanding and expensive, and with the exception of pumped storage power plants, it is largely uncharted territory.

[0006] The storage of energy using compressed gas has become known as CAES (Compressed Air Energy Storage). However, the compression of the gas to be stored generates a significant amount of heat, which must be stored separately to prevent it from being gradually lost through the walls of the high-pressure storage device during the storage period. Importantly, the necessary storage pressure for efficient pressure energy storage should exceed 50 bar, up to 100 bar, so that the fluid can heat up to 500°C or more above the ambient temperature. In addition, it is technically extremely challenging to construct suitable pressure storage devices to absorb the necessary internal pressure, even if the heat is stored separately.

[0007] To avoid such significant disadvantages of the otherwise desirable pressure storage, considerations have emerged to locate the pressure accumulators underwater in order to utilize the pressure of the water column acting on the accumulator to absorb the necessary internal pressure. Thus, if a compressible fluid is compressed on land or at the water surface and pumped into a high-pressure energy storage device located underwater at a depth of several hundred meters, the pressure difference between the internal and external pressure is largely eliminated, thus eliminating one of the main problems of CAES (the pressure storage device design). However, separate heat storage at the water surface is still necessary, and the high-pressure lines to the pressure accumulators in the water also remain problematic in terms of design and the loss-making flow resistance.

[0008] In this regard, the StEnSEA (Stored Energy in the SEA) project for deep-sea storage has become well-known. It proposes the installation of underwater pressure vessels containing an electrically driven pump turbine. When discharged, the pressure vessel is flooded except for a residual air pocket; the water contained within it and the residual air pocket have the external pressure of the surrounding water. To charge the pressure reservoir, the pump turbine is driven by electricity generated at the water surface, acting as a pump that pumps the water contained in the pressure vessel out against the external pressure. Initially, the internal pressure is equal to the external pressure; as the loading progresses, the gas bubble in the pressure vessel expands in proportion to the volume of water pumped out. As the internal pressure drops, the pressure drops in proportion to the volume of water pumped out. This increases the pressure difference to the external pressure and, in turn, the required pumping work.The pump absorbs energy until the required amount of water has been pumped out of the pressure vessel and the vessel is emptied. This charges the StEnSEA pressure accumulator.

[0009] When the StEnSEA pressure reservoir is to be discharged, ambient water under external pressure is admitted via the pump turbine, which now operates as a turbine, into the emptied pressure vessel, which has a low internal pressure. The turbine then generates electricity, which is delivered to the water surface. The StEnSEA pressure reservoir discharges in the process and is discharged as soon as it is flooded with ambient water again.

[0010] Accordingly, the internal pressure in the charged StEnSEA pressure reservoir is significantly lower than the external pressure, with the pressure difference increasing with the amount of stored energy. At the proposed water depth of 500 m to 700 m and a diameter of the spherical pressure reservoir of, for example, 30 m, the concrete pressure hull is expensive; for example, the planned pressure difference of 50 to 70 bar requires pressure reservoir walls of 2.5 m or more. For a planned 20 MWh of StEnSEA pressure reservoir, more than $3,000,000 per MWh of storage capacity would be required, which is not financially viable. The project was not pursued beyond the concept phase.

[0011] In other words, the electric underwater pump turbine now advantageously eliminates the need for CAES heat storage at the water surface and pressure lines in the depths, but instead of a CAES internal pressure storage, an external pressure fluid storage for energy storage must be provided in accordance with STEnSEA, the costs of which are prohibitive for economic use.

[0012] Accordingly, it is the object of the present invention to provide an economically usable external pressure fluid storage device of simplified construction which is suitable for underwater energy storage with low internal pressure.

[0013] This object is achieved by the characterizing features of claims 1 and 22.

[0014] Because the external pressure fluid reservoir has a bulk material filling in addition to the fluid-tight wall that forms its interior, it is easily sufficiently pressure-resistant even at great depths. Since the wall rests on the bulk material filling when the internal pressure is lower than the external pressure (charged state), it does not have to be pressure-resistant and, although fluid-tight, can be designed in a simplified and cost-effective manner. The pressure-resistant bulk material filling itself is cost-effective and offers sufficient storage space for a fluid such as air and water in the interstices within it. Because a skeleton arrangement is provided for the external shape of the bulk material filling in one embodiment, this allows not only smaller external pressure fluid reservoirs or those reduced to a few shapes, where the wall itself is sufficient to hold the bulk material together.A skeleton arrangement can also be used to provide fluid storage of any size or shape, since the skeleton arrangement holds the mass of the bulk material in the intended operational shape or form against the effect of gravity (which is independent of the depth) and prevents the bulk material from flowing due to gravity.

[0015] By constructing the wall and a skeleton assembly over a pneumatic body, the wall and skeleton assembly can be easily manufactured. This construction method allows the finished wall / skeleton assembly to be placed in the water first and then filled with bulk material. The compressive strength of the wall is subject to only minimal, gravity-related requirements, which do not increase with depth. On land, the wall and skeleton assembly essentially only need to be inherently stable, as they do not yet support the heavy bulk material there. In the water, the wall and skeleton assembly only need to maintain the external, operational shape of the now-filled bulk material, counteracting the effect of gravity, which is reduced by buoyancy, and not with regard to the large compressive forces at depth.

[0016] According to the invention, the bulk material filling absorbs the pressure acting on the external pressure fluid reservoir, while its wall is fluid-tight to enable the storage of fluid (e.g., air as well as water) and also to maintain the bulk material filling in its operational shape against the force of gravity acting on it. This eliminates the need for a pressure-resistant wall, making it simple and cost-effective to manufacture. If a skeleton arrangement is also provided, which at least supports the operational shape of the bulk material filling, the wall can be designed even more simply.

[0017] Further preferred embodiments have the features of the dependent claims.

[0018] The invention is described in more detail below with reference to the figures.

[0019] It shows: Figure 1 schematically an embodiment of an external pressure fluid reservoir according to the invention in a cross-section sphere

[0020] Figure 2 schematically shows another embodiment of an external pressure fluid reservoir according to the invention in a cross-section cylinder

[0021] Figures 3 a to 3e schematically show a comparative view of the operating states of an external pressure fluid reservoir according to the invention,

[0022] Figures 4a to 4e schematically show a comparative view of the operating states of an external pressure fluid reservoir with snorkel according to the invention,

[0023] Figures 5a to 5d schematically show the manufacturing process for an external pressure fluid reservoir according to the invention, and

[0024] Figure 6 is a diagram showing a cost estimate.

[0025] Figure 1 shows a cross-section through one embodiment of a spherical external pressure fluid reservoir 1 positioned on the seabed 2 at, for example, a depth of 800 m (a foundation has been omitted to reduce the load on the figure and can be easily implemented by a person skilled in the art). A fluid-tight wall 3 surrounds the body of the external pressure fluid reservoir 1 and encloses a bulk material filling 4, which, due to its spherical volume, forms a spherical interior 5 of the external pressure fluid reservoir 1. A device chamber 6 with a pump turbine 7 is arranged at the bottom of the external pressure fluid reservoir 1. The device chamber 6 is connected to the outside world—here, the surrounding sea 9—via a central fluid channel 8 through the wall 3.

[0026] The pump turbine 7, for its part, is operationally connected, for example, via lines 10 to the interior 5 and thus to the bulk material filling 4, and via the fluid channel 8 to the outside world 9. Thus, the external pressure fluid reservoir 1 has a connection between the interior 5 and the outside world, here the sea 9, via lines 10, the device chamber 6, and the channel 8. It goes without saying that the connection can be interrupted by the pump turbine 7 or by a valve provided in the connection between the interior 5 and the sea 9 (which is not shown to reduce the pressure in the figure), so that the interior 5 is separated from the sea 9.

[0027] Finally, the pump turbine 7 is provided with a power line 11 leading to the water surface and capable of supplying power to the pump turbine 7 in pumping mode from an installation located there, and of discharging power to the installation in turbine mode. As mentioned above, for example, solar or wind-generated power can be used to drive the pump turbine 7 in pumping mode, while the pump turbine 7 in turbine mode can supply power to the water surface or onshore to a suitable installation for power utilization. It should be noted that the pump turbine 7 (including the equipment chamber 6 and the installations provided therein) can, in principle, be arranged not necessarily in, but also next to the external pressure fluid storage 1 (and thus in the outside world).

[0028] The bulk material 4 comprises, for example, coarse sand, gravel, crushed stone, and / or broken stones, etc. In principle, all pourable materials are suitable whose particles are sufficiently pressure-resistant for the intended depth of the external pressure fluid reservoir 1 (see below). By their very nature, there are gaps between the bulk material particles that may be only loosely connected in a two-dimensional section, but are connected in all three dimensions in such a way that the bulk material 4 can easily be completely permeated by a fluid, be it air or seawater, i.e., across all areas of the bulk material. For example, in the case of gravel, the volume of the gaps between the bulk material particles is approximately 30% of the volume occupied by the bulk material, so that the fluid storage volume of the external pressure fluid reservoir 1, in the case of a bulk material filling 4 consisting of gravel and a radius of 10 m, is approximately 1250 m. 3The flow resistance is basically acceptably small for the present purpose, but increases the finer the bulk material is, or the smaller the individual particles are. The expert will therefore prefer to use at least coarse sand, i.e. a sand filling with comparatively large sand grains, i.e. acceptable flow resistance in the specific case, or a bulk material with even larger particles. In the present case, sand is regarded as coarse sand if its average grain size is in the range of 6 mm or more. In the case of the above-mentioned radius of 10 m, a bulk material filling of gravel has a mass of approx. 6,800 t, whereby the buoyancy is approx. 2,800 t. Even under water, the bulk material therefore still has a considerable weight of approx.4,000 t, but must be mechanically maintained in its intended, operational external shape (here a sphere), since bulk material, as a heap of interlocked but loose particles, by its very nature tends to flow out of a given volume or from an external form or shape into a bulk material cone due to gravity.

[0029] Depending on the size or external shape of the external pressure fluid reservoir and the design of the wall, the external shape of the bulk material filling can be defined and maintained by the wall itself. This is the case, for example, with small external pressure fluid reservoirs where the wall's load-bearing capacity is not exceeded by the flow pressure of the bulk material, or when the external shape is already constructed in the manner of a bulk material cone, i.e., with no overhangs, but rather with side walls that widen towards the bottom.

[0030] However, in addition to the wall 3, a skeleton arrangement can also be used, which in the embodiment shown in Figure 1 is designed as an intermediate layer 12 and encloses the bulk material filling 4 or the interior space 5. The skeleton arrangement thus counteracts gravity and prevents (depending on the design of the wall 3 together with the latter) the bulk material 4 from sliding sideways or downwards, thus preventing the bulk material 4 from undesirably spreading on the seabed 2. It follows that the external pressure fluid reservoir 1 preferably (but not necessarily) has a skeleton arrangement for shaping the operational, external shape of the bulk material filling 4.

[0031] In the embodiment shown, the skeleton arrangement is designed as a rigid intermediate layer 12 in the manner of a spherical shell. In a specific case, however, the person skilled in the art can also limit it to, for example, a lower shell, which supports the bulk material filling 4 and encompasses it across its height to such an extent that it does not change its intended external shape (optionally in conjunction with the wall). It follows that the external pressure fluid reservoir 1 preferably has a rigid intermediate layer provided between the wall 3 and the bulk material filling 4, which encloses the bulk material filling 4 at least to the extent that it retains its operational external shape under the influence of gravity. The skeleton arrangement designed as an intermediate layer 12 is preferably made of shotcrete, which is well suited for producing a three-dimensionally curved, flat intermediate layer.It should be noted here that in an embodiment not shown in the figure, the skeleton arrangement can also be designed as a steel mesh spanning the bulk material filling, for example, or as a composite of a thin intermediate layer with a steel mesh, etc.

[0032] Figure 1 shows in particular that the interior space 5 of the external pressure fluid reservoir 5 is formed by the bulk material filling 4.

[0033] During operation, as mentioned above for the STEnSEA project and shown in detail, for example, in Figures 3a to e, the external pressure fluid reservoir 1 is flooded with seawater in one embodiment, except for a residual air bubble 15, to an upper fill level 16 of the interior space 5 or the bulk material filling 4, so that the spaces between them or the interior space 5 are filled with water up to the volume of the residual air bubble 15 (the bulk material filling 4 naturally also extends through the volume of the residual air bubble 15). If, during operation of the external pressure fluid reservoir 1, water is pumped out of the interior space 5 by the pump turbine 7, e.g., down to a lower fill level 17, the air volume increases accordingly, with its pressure, and thus the pressure in the interior space 5 or the bulk material filling 4, falling with the increase in volume.

[0034] If, thanks to flooding, the residual air bubble 15 has the pressure of the surrounding seawater 9, which is 80 bar at the aforementioned 800 m depth, the internal pressure in the interior 5 or the bulk material filling 4 is also 80 bar. If water is pumped out of the interior 5 or the bulk material filling 4 to a lower fill level 17 by the pump turbine 7, supplied with power via the power line 11, the internal pressure continuously drops and is, for example, 1 bar as soon as the lower fill level 17 is reached. The pressure difference between the constant external pressure of 80 bar and the internal pressure then rises to a maximum of 79 bar.

[0035] Depending on the specific design of the external pressure fluid reservoir 1 (operational depth, i.e. water depth at the location of the fluid reservoir 1, upper 16 and lower fill level 17, etc.), this maximum pressure difference reaches a specific value and is referred to here as the predetermined maximum operating differential pressure, in contrast to a current operating differential pressure, as occurs when the current fill level of the interior 5 in a general operating phase lies between the minimum 17 and maximum fill level 16. In general, the predetermined maximum operating differential pressure refers to the maximum prevailing differential pressure as it prevails in the charged state of an external pressure fluid reservoir according to the invention.

[0036] The wall 3 separates the interior space 5 or the bulk material filling 4 from the outside world (here, the sea 9) in a fluid-tight manner, so that the residual air bubble or generally a gas volume present in the external pressure fluid reservoir remains trapped in the interior space 5, and the water contained therein can be pumped out via the fluid channel 8 and forced back in by the operating pressure differential. As a result, the wall 3 is pressurized by the external pressure, here by the pressure of the sea 9, with a magnitude corresponding to the current operating pressure differential, which extends up to the maximum predetermined operating pressure differential. The wall 3 is not designed to withstand the predetermined maximum operating pressure differential, and is therefore not pressure-resistant, but is pressed by the external pressure against the skeleton arrangement, which in the illustrated embodiment is designed as an intermediate layer 12.

[0037] Likewise, the intermediate layer 12 is not designed to withstand the predetermined maximum operating differential pressure, and is therefore not pressure-resistant, but is in turn pressed against the bulk material filling 4 by the wall 3 (the purpose of the intermediate layer 12 is to shape the bulk material filling 4 and thus the interior space 5).

[0038] The bulk material filling 4, in turn, is pressure-resistant and thus pressure-resistant by nature, does not collapse under the predetermined maximum operating pressure difference, and thus supports the wall 3 via the intermediate layer 12 (both of which would otherwise give way to the pressure and collapse).

[0039] As a whole, the wall is designed in such a way that during operation it absorbs a predetermined maximum operating differential pressure given by the difference between an external pressure and an internal pressure and introduces it (here via the skeleton arrangement) into the bulk material filling, by which it is in turn supported in its operating position against the exceeding external pressure.

[0040] This allows the expert to limit the design of wall 3 and intermediate layer 12 to fluid tightness and shaping for the bulk material filling 4, while eliminating the compressive strength required in the prior art for the predetermined maximum operating pressure differential. Given the large operating depth desirable for a large energy storage capacity, this is crucial for a simple and cost-effective construction of both wall 3 and a skeleton arrangement, designed here as intermediate layer 12.

[0041] Depending on the bulk material 4 used and the operating depth at which the external pressure fluid reservoir 1 is located, the bulk material filling 4 may deform slightly when the predetermined maximum operating differential pressure is built up. The bulk material particles, especially on the surface of the bulk material filling 4, may shift slightly, but only slightly, until the mutual wedging of the bulk material particles is sufficiently high everywhere to prevent further displacement of the bulk material particles. This may also locally change the support surface for the wall 3 or the intermediate layer 12, and therefore also the supporting effect of the bulk material filling 4 for the intermediate layer 12 and, through it, for the wall 3.

[0042] Since the intermediate layer 12, consisting of shotcrete, for example, is rigid and (intentionally) not pressure-resistant under the predetermined maximum operating pressure differential, it develops cracks and breaks during the initial build-up of the maximum predetermined operating pressure differential. The fragments can then follow a displacement of the surface of the bulk material filling 4 or the interior space 5 by slightly changing their position and are stable in a new position. This stability in the new position can be supported, for example, by lightweight steel reinforcement of the intermediate layer 12 designed for deformation, and also by the wall 3, which holds the fragments in a position clamped between it and the bulk material filling in such a way that the fragments are mutually fixed. Thus, the intermediate layer 12, if necessary in conjunction with the wall 3, can still maintain the external shape of the bulk material filling 4.The depth of operation and thus the maximum operating differential pressure, even if it leads to the rupture of the intermediate layer 12, is still not relevant, with the exception that the wall 3 must then also be designed for a ruptured intermediate layer 12, which is, however, irrelevant compared to the effort required for compressive strength under the predetermined maximum operating differential pressure.

[0043] The fluid-tight wall 3 is now, for example, elastically or plastically deformable or formed with joints such that it continues to bear against the intermediate layer 12, or now against its slightly changed position fragments, and thus continues to introduce the predetermined maximum operating differential pressure via the fragments into the bulk material filling 4. The wall 3 can, for example, preferably be formed as a flexible skin enclosing the interior space 5 or the bulk material filling 4. Particularly preferably, at least one region of the wall comprises a plastic film, a plastic fabric and / or a flat sheet section. Most preferably, the wall 3 is formed entirely from a deformable plastic film or a plastic fabric.Since the fracture boundaries of shotcrete are not very sharp-edged, but rather follow the curve of the aggregate used, such as sand, commercially available plastic films can be used in conjunction with an appropriately selected shotcrete. A person skilled in the art can easily determine a suitable shotcrete in conjunction with a suitable film in a specific case. It is therefore preferable for the wall 3 to be deformable, such that it can follow a pressure-induced displacement of the supporting bulk material 4 in a fluid-tight manner under the predetermined operating pressure differential.

[0044] It should be noted at this point that the preferred features described above in connection with the intermediate layer 12 are not tied to the presence of an intermediate layer 12 or a skeleton arrangement at all, but also have an advantageous effect when the wall rests directly on the bulk material.

[0045] Since concrete is generally highly compressive, the intermediate layer 12, preferably made of shotcrete, is inherently pressure-resistant under the external operating pressure, i.e., the prevailing water pressure at the location of the external pressure fluid reservoir 1. This is advantageous because the necessary displacement of the deformable wall 3 is then limited to the displacement of the fragments of the intermediate layer 12 and is not further increased by a volume change of the broken material of the intermediate layer.

[0046] In general, this results in an external pressure fluid reservoir according to the invention that preferably the wall 3 itself is not pressure-resistant with respect to a predetermined maximum operating pressure difference between the external pressure and the pressure in the interior 5, but is pressure-resistant due to the support on the bulk material filling 4. As mentioned above, not pressure-resistant means that the wall 3 cannot withstand the operating pressure difference, but would collapse on its own. Pressure-resistant due to support on the bulk material filling 4 means that the wall 3, adjacent to the pressure-resistant bulk material filling 4, does not collapse under the predetermined maximum operating pressure difference, i.e. it retains its operational shape and also remains fluid-tight. Whether this support takes place via an intact or broken intermediate layer 12 or directly, without an intermediate layer 12 or without a skeleton arrangement, is irrelevant.

[0047] This allows the design of the external pressure fluid reservoir to be fundamentally independent of the intended operating depth and, as mentioned above, allows for a simple and cost-effective construction even if the bulk material filling deforms slightly depending on the bulk material and operating depth. The wall and, if provided, the skeleton arrangement are dimensioned with regard to the shape of the bulk material and any possible depth deformation of the bulk material, but not with regard to the operating depth itself.

[0048] In other words, according to the invention, the wall is designed in such a way that, during operation, it absorbs an external pressure that exceeds the pressure in the interior and introduces it into the bulk material filling, by which it is in turn supported in its operating position against the exceeding external pressure.

[0049] Figure 2 shows a further embodiment of an external pressure fluid reservoir 20 which, in contrast to the embodiment according to Figure 1, has a cylindrical bulk material filling 21 and a skeleton arrangement with shaped elements, which are preferably designed as rings 22 made of steel. The bulk material filling 21 is enclosed in a flexible wall 23, on which the rings 22, arranged vertically and spaced one above the other, rest, in such a way that the cylindrical shape of the bulk material filling 21 is maintained. As in the embodiment according to Figure 1, the bulk material filling 21 forms the interior space 24 of the external pressure fluid reservoir 20.

[0050] The wall 23 is preferably formed from a polyester / PVC fabric. A central fluid channel 8 has a device chamber 6, in which, as in the embodiment according to Figure 1, a pump turbine 7 is arranged, which is in operative connection with the bulk material filling 21. It follows that the skeleton arrangement preferably has shaped elements, which are more preferably arranged on the outside of the wall. The shaped elements are very preferably designed as rings 22. In the embodiment shown in Figure 2, the wall 23 rests directly on the bulk material, so that the current and the predetermined maximum operating differential pressure is introduced directly, without an intermediate layer 12 (Figure 1), into the bulk material filling, which in turn supports the wall 23 in its operating position against the current up to the predetermined maximum operating differential pressure.The rings 22 are located above the wall 23 and thus prevent the cylindrical shape of the bulk material filling 21 from bulging beyond its height.

[0051] On the other hand, the wall 23 bulges between each two superimposed rings 22, which is entirely intentional: the tensile stress in the wall 23 is thus comparatively small, as it depends on the radius of the bulge, particularly when the cutting pattern of the wall 23 is dimensioned such that the bulge forms a circular arc or even a semicircle in cross-section. The skilled person can therefore keep the tensile stress in the cylindrical side wall small by the spacing between the adjacent rings 22 and the cutting pattern of the wall 23, which correspondingly reduces the material requirements of the wall 23 and is reflected in low costs for the wall 23. It should be noted here that the bottom surface 25 and the top surface 26 of the wall 23, clamped in the lowest and top ring 22, are subjected to virtually no or only local tensile stress thanks to their position.

[0052] From Figure 2 it can be seen that in the cylindrical shape of the bulk material filling 21 or the interior 24, apart from the bulges, the entire bulk material is located above its ground plan area, so that the lateral forces to be absorbed by the wall 23 for maintaining the cylindrical shape are minimal, which in turn simplifies the formation of the wall 23 and the mold rings 22.

[0053] The functional principle of the external pressure fluid reservoir 20 is the same as that of the fluid reservoir according to Figure 1. Likewise, all embodiments of an external pressure fluid reservoir according to the invention can have a dimension that is greater than 5 m, preferably greater than 10 m, very preferably 15 m and particularly preferably greater than 20 m. The dimension can also be a radius and / or a height, for example the spherical radius of the embodiment according to Figure 1 is 10 m or more, the radius and the height of the embodiment according to Figure 2 are each 15 m. More preferably, the radius of the bulge between two rings 22 is then in the region of 1 m. The interior spaces 5 (Figure 1) or 24 (Figure 2) can be spherical or cylindrical as shown, but also cubic or have a different geometry.

[0054] As in the embodiment shown in Figure 1, the external pressure fluid reservoir 20 has a pump turbine 7, which is operatively connected to the connection for the optional exchange of fluid (lines 10, device chamber 6, channel 8). However, the pump turbine 7 can also be arranged outside the reservoir 20.

[0055] This results in an external pressure fluid reservoir 20 whose interior 24 has a cylindrical structure and which preferably has a number of shaped rings 22 over its height, with a common radius, which lie above a flexible wall 23, and wherein in the interior 24 a vertical channel 8 is provided which is designed as a connection for the selective exchange of fluid and in which a pump turbine 7 is arranged.

[0056] Figures 3a to 3e schematically show the different operating states of an external pressure fluid reservoir 1 positioned operatively on the seabed 2, which is realized in an embodiment according to Figure 1, but in the specific case can generally also be realized with a different shape or with other preferred features.

[0057] Figure 3a shows the external pressure fluid reservoir 1 in the "discharge" operating state: the interior space 5 or the bulk material filling 4 is flooded except for a residual air bubble 15, and the internal pressure corresponds to the external pressure of 80 bar (at the operating depth of 800 m assumed in the description of Figure 1). The current operating differential pressure is zero. The fluid-tight wall 3 prevents air from escaping from the residual air bubble 15 to the outside. The intermediate layer 12, together with the wall 3, ensures that the bulk material filling 4 retains its spherical shape. The connection between the interior space 5 and the sea 9 is preferably closed, but can also be open.

[0058] Figure 3b shows the external pressure fluid reservoir 1 in the "energy storage" operating mode: the connection between the interior 5 and the sea 9 is open, the pump turbine 7 pumps water out of the interior 5 through the line 11, absorbing current, and the water flows through the channel 8 into the outside world according to the arrow 30. Depending on the volume of the drained water, this results in a falling current fill level 31 of the water present in the bulk material filling 4. The residual air bubble 15 (Figure 3a) expands in the spaces between the bulk material filling 4 above the falling current fill level 31 (see the expansion arrows shown) 32 as the current falling fill level 30 decreases towards the lower fill level 17. As a result, the pressure in the bulk material filling 4 continuously decreases, i.e.The current operating differential pressure continuously increases, acting as external pressure on wall 3 and being transmitted through the intermediate layer to the bulk material filling 4, so that the latter absorbs the operating differential pressure. As the operating differential pressure increases, the power required by the pump continuously increases, and thus the energy supplied and consumed (but recoverable) through the power line 11.

[0059] Depending on the design of the external pressure fluid reservoir 1, in particular depending on the bulk material used, the design of the intermediate layer 12, and the intended operating depth, as the current operating pressure differential increases, a moment is reached at which the intermediate layer 12 ruptures, as peripheral bulk material particles shift slightly, but somewhat, due to the increased pressure load; see the description above. This moment can lie anywhere between zero operating pressure differential and the predetermined maximum operating pressure differential and is determined by a specialist such that the effort for the wall and the intermediate layer (possibly also regarding the bulk material) is at an optimal value desired in the specific case.

[0060] Figure 3c shows the external pressure fluid reservoir 1 in the "charged" operating state: the pump turbine 7 has pumped the water out of the interior space 5 down to the lower fill level 17, the air in the residual air bubble 15 (Figure 3a) has expanded into the entire volume of the interstices in the bulk material 4 down to the lower fill level 17 and still maintains a pressure of, for example, 1 bar or, depending on the design, 0.05 bar. The power consumption via line 11 has reached approximately 20 MWh (radius of the interior space 5: 10 m, operating depth: 800 m, see the description for Figure 1). The bulk material filling 4 continues to support the now predetermined maximum operating differential pressure and, via the possibly fractured intermediate layer 12, supports the wall 3 against the external pressure. The connection between the interior space 5 and the sea 9 is closed.

[0061] The external pressure fluid reservoir 1 can remain in the "charged" state until the stored energy is to be withdrawn. Of course, a partially charged fluid reservoir 1 can also remain in the partially charged state as needed. Figure 3d shows the external pressure fluid reservoir 1 in the "discharging stored energy" operating state: The connection between the interior space 5 and the sea 9 is open. Water from the sea 9, driven by the operating differential pressure, penetrates the fluid channel 8 according to arrow 33 and thus reaches the pump turbine 7, which runs in turbine mode, driving a generator that generates electricity and delivers it via line 11. The water filling the interior space 5 or the bulk material filling 4 has a rising current fill level 34, which compresses the air volume located above it in the spaces between the bulk material 4 according to the compression arrows 35. The current operating differential pressure continuously decreases.The bulk material filling 4 still carries the current operating differential pressure and supports the wall 3 against the external pressure via the possibly broken intermediate layer 12.

[0062] Figure 3d shows the external pressure fluid reservoir 1 in the discharged operating state, as achieved after the rising current fill level 34 (Figure 3d) has reached the upper fill level 16. The configuration corresponds to that of Figure 3a.

[0063] Figures 4a to 4e schematically show the different operating states of an external pressure fluid reservoir 40 operatively positioned on the seabed 2 in a further embodiment, in which the embodiment according to Figure 1 is supplemented by a snorkel 41 which connects the interior space 5 or the bulk material filling 4 with the atmosphere above the water surface 42 of the sea 9.

[0064] Thanks to the snorkel 41, atmospheric pressure always prevails inside the external pressure fluid reservoir 40. The upper fill level 43 is no longer designed for the volume required for a residual air bubble 15 (Figure 1), but can, in principle, reach the highest point of the interior space 5.

[0065] Figure 4a shows the external pressure fluid reservoir 40 in the "discharge" operating state: the interior 5 or bulk material filling 4 is flooded, and the internal pressure is 1 bar thanks to the connection to the atmosphere. The current operating differential pressure is equal to the predetermined maximum operating differential pressure of 80 bar. The connection between the interior 5 and the sea 9 is closed; otherwise, water would rise in the snorkel, which is undesirable. The fluid-tight wall 3 prevents water from passing through it into the interior. The intermediate layer 12 is already fractured, depending on the bulk material used (see the description for Figure 3b), ensuring that the bulk material filling 4 retains its spherical shape.

[0066] Figure 4b shows the external pressure fluid reservoir 1 in the "energy storage" operating mode: the connection between the interior 5 and the water 9 is open, the pump turbine 7 pumps water out of the interior 5 by absorbing current through the line 11, and the water flows through the channel 8 into the outside world according to the arrow 30. Depending on the volume of the drained water, this results in a falling current fill level 31 of the water present in the bulk material filling 4. Air originating from the snorkel 41 fills the spaces in the bulk material filling 4 above the falling current fill level 31 (see the arrow 44) as the current falling fill level 31 decreases towards the lower fill level 17.The pump of the pump turbine 7 always operates against the full intended maximum operating differential pressure and therefore consumes more energy supplied by the power line 11 than is the case in the case of the external pressure fluid storage 1 (Figure 3b).

[0067] Figure 4c shows the external pressure fluid reservoir 1 in the "charged" operating state: the connection between the interior space 5 and the sea 9 is closed, the pump turbine 7 has pumped the water out of the interior space 5 down to the lower fill level 17, and the air supplied from the atmosphere via the snorkel 41 has filled the entire volume of the interstices in the bulk material 4 down to the lower fill level 17. The pressure remains at 1 bar. The power consumption via line 11 has reached approximately 21 mWh (radius of the interior space 5: 10 m, operating depth: 800 m). The bulk material filling 4 still supports the predetermined maximum operating differential pressure and supports the wall 3 against the external pressure via the possibly fractured intermediate layer 12.

[0068] The external pressure fluid reservoir 41 can remain in the "charged" state until stored energy is to be withdrawn. Of course, a partially charged fluid reservoir 41 can also remain in the partially charged state as needed.

[0069] Figure 4d shows the external pressure fluid reservoir 1 in the "stored energy discharge" operating state: the connection between the interior 5 and the sea 9 is open. Water from the sea 9, driven by the predetermined maximum operating differential pressure, penetrates the fluid channel 8 according to arrow 33 and thus reaches the pump turbine 7, which operates in turbine mode, driving a generator that generates electricity and delivers it via line 11. The water filling the interior 5 or the bulk material filling 4 has a rising current fill level 34, which discharges the air volume located above in the interstices of the bulk material 4 through the snorkel 41 from the interior 5 to the atmosphere, as shown by arrow 45. The predetermined maximum operating differential pressure is maintained. The bulk material filling 4 continues to absorb this pressure and supports the wall 3 against the external pressure via the possibly broken intermediate layer 12.

[0070] Figure 4d shows the external pressure fluid reservoir 1 in the discharged operating state, as achieved after the rising current fill level 34 (Figure 3d) has reached the upper fill level 43. The configuration corresponds to that of Figure 4a.

[0071] According to the invention, an external pressure fluid reservoir is provided with an interior space for receiving a fluid, an outer wall which is pressurised during operation by an external pressure from the outside world and which separates the interior space from the outside world in a fluid-tight manner, and with a connection provided between the interior space and the outside world for the selective exchange of fluid between the interior space and the outside world, wherein the interior space is formed by a bulk material filling and the wall is designed such that it absorbs an external pressure which exceeds the pressure in the interior space during operation and introduces it into the bulk material filling, by which it is in turn supported in its operating position against the exceeding external pressure.

[0072] Figure 5a schematically shows the production of an external pressure fluid reservoir 50 in an embodiment according to Figure 1. Production takes place in a mold 51 for the lower half of the fluid reservoir 50, into which a plastic film 52 is inserted, forming the wall of the finished fluid reservoir. The plastic film 52 receives a first shotcrete layer 53 from the inside, which forms an intermediate layer 12 (Figure 1) for the lower half of the fluid reservoir 50.

[0073] Figure 5b shows a pneumatic body 54 inserted into the first shotcrete layer 53 after it has hardened. When inflated, this body forms the interior 5 (Figure 1) of the finished fluid reservoir. A second shotcrete layer 55 is applied to the pneumatic body 54, which is operatively connected to the first shotcrete layer 53 and thus forms the complete intermediate layer 12 (Figure 1). Subsequently, a further plastic film, not shown in the figure, is applied to the second shotcrete layer 55 and operatively connected to the plastic film 52 to form wall 3 (Figure 1). The intermediate layer 12 and wall 3 are then completed, so that the pump turbine 7 and the power line 11 (Figure 1) can finally be inserted into the body 56 formed by the intermediate layer 12 and wall 3 (Figure 5c). All that is missing is the filling with bulk material 4 (Figure 1).

[0074] Figure 5c shows the body 56 formed from the wall 3 and the shotcrete layer 53, 55, which has been placed in the water. Floats 57 are attached to the body 56 so that it floats and can be loaded with bulk material 4, thus completing the external pressure fluid reservoir 50. Figure 5d shows how, by reducing the buoyancy of the floats 57 at the future operating location, the external pressure fluid reservoir 50 can be lowered to the operating depth according to arrow 58.

[0075] The invention relates to a method for producing an external pressure fluid reservoir with an interior space for accommodating a fluid, and with an outer wall which is pressurised by external pressure during operation and which separates the interior space from the outside in a fluid-tight manner. The interior space is formed by a bulk material filling which supports the wall against an operating differential pressure. First, a lower part of the external pressure fluid reservoir is produced, then a pneumatic body is inserted into the lower part and inflated until, in the inflated state, it follows the intended contour of the interior space, and then a skeleton arrangement and the wall are arranged on the pneumatic body. An opening is provided at an upper end of the wall such that, in a later step, the bulk material filling can be operatively filled into the interior space formed by the wall.Preferably, the bulk material is poured in after the prepared wall, held in shape by the mold skeleton, has been immersed in water, and can be lowered into this water at a designated location. Further preferably, the pneumatic body is spherical in the inflated state, and particularly preferably, the mold skeleton is formed as a layer of shotcrete sprayed onto the pneumatic body.

[0076] It should be noted that an external pressure fluid reservoir according to the invention can in principle be provided in any body of water, ie in salt or fresh water, also for example in a water-filled borehole inserted into the subsurface, which has a

[0077] Cavern in which the external pressure fluid storage is then arranged.

[0078] Figure 6 shows diagram 60, on whose vertical axis the costs of an external pressure fluid storage device according to the invention are plotted in $ / kWh, and on whose horizontal axis the operating depth is plotted. Assuming a spherical fluid storage device, the solid curve 61 shows the costs for a radius of 5 m, the dash-dotted line 62 shows the costs for a radius of 10 m, and the dotted line 63 shows the costs for a radius of 15 m. These costs are significantly lower than those of an external pressure fluid storage device according to the prior art.

Claims

Patent claims 1. External pressure fluid accumulator (1, 20, 50), comprising an interior space (5, 24) for receiving a fluid, an outer wall (3) which is pressurized by an external pressure during operation and which separates the interior space (5, 24) from the external world in a fluid-tight manner, and a connection provided between the interior space (5, 24) and the external world for the selective exchange of fluid between the interior space (5, 24) and the external world, characterized in that the interior space (5, 24) is formed by a bulk material filling (4) and the wall (3) is designed such that during operation it absorbs an external pressure exceeding the pressure in the interior space (5, 24) and introduces it into the bulk material filling (4), by which it is in turn supported in its operating position against the exceeding external pressure.

2. External pressure fluid storage tank (1, 20, 50) according to claim 1, wherein the wall (3) itself is not pressure-resistant against a predetermined operating differential pressure between the external pressure and the pressure in the interior (5, 24), but is pressure-resistant due to the support on the bulk material filling (4).

3. External pressure fluid storage tank (1, 20, 50) according to claim 1, wherein the wall (3) is designed to be deformable in such a way that it can follow a pressure-induced displacement of the supporting bulk material (4) in a fluid-tight manner under the predetermined operating differential pressure.

4. External pressure fluid storage tank (1,20,50) according to claim 1, wherein the wall (3) is designed as a flexible skin enclosing the interior (5,24).

5. External pressure fluid storage tank (1, 20, 50) according to claim 1 or 4, wherein at least one area of ​​the wall (3) comprises a plastic film, a plastic fabric and / or a flat sheet metal.

6. External pressure fluid storage tank (1, 20, 50) according to claim 1, with a skeleton arrangement for shaping the operational, outer shape of the bulk material filling (4).

7. External pressure fluid storage tank according to claim 6, wherein the skeleton arrangement has a rigid intermediate layer (12) provided between the wall (3) and the bulk material filling (4), which encloses the bulk material filling (4) at least to the extent that it retains its operational external shape under the influence of gravity.

8. External pressure fluid reservoir according to claim 7, wherein the intermediate layer (12) comprises a material which as such is substantially pressure-resistant under the operating external pressure.

9. External pressure fluid storage tank according to claim 7, wherein the intermediate layer (12) consists of shotcrete.

10. External pressure fluid storage tank according to claim 6, wherein the skeleton arrangement has shaped elements which are preferably arranged on the outside of the wall (3).

11. External pressure fluid reservoir according to claim 10, wherein the form elements are designed as rings (22).

12. External pressure fluid storage tank according to claim 1, wherein the bulk material (4) comprises coarse sand, gravel, crushed stone and / or broken stones.

13. External pressure fluid storage device according to claim 1, wherein the interior (5,24) is spherical, cylindrical or cubic.

14. External pressure fluid storage tank according to claim 1, wherein the interior (5, 24) has a dimension greater than 5 m, preferably greater than 10 m, most preferably 15 m and particularly preferably greater than 20 m.

15. External pressure fluid reservoir according to claim 13, wherein the dimension is a radius or a Height is.

16. External pressure fluid storage unit (1, 20, 50) according to claim 1, wherein it further comprises a pump turbine (7) which is operationally connected to the connection for the selective exchange of fluid. An external pressure fluid storage tank according to claims 1, 4, and 11, wherein the interior (5, 24) has a cylindrical structure, and a number of shaped rings (22) with a common radius are arranged along its height, lying above a flexible wall (3), and wherein a vertical channel is provided in the interior (5, 24) as a connection for the selective exchange of fluid, in which a pump turbine (7) is arranged. An external pressure fluid storage tank according to claim 16, wherein the pump turbine (7) is configured for pumping water. An external pressure fluid storage tank according to claim 1, wherein it is arranged underwater. An external pressure fluid storage tank according to claim 1, wherein it further comprises a snorkel (41) connecting the interior (5, 24) to the atmosphere. Method for manufacturing an external pressure fluid storage device (1,20,50) with an interior space (5,24) for receiving a fluid, and with an outer wall (3) pressurized by an external pressure during operation,which fluid-tightly separates the interior (5, 24) from the outside world, wherein the interior (5, 24) is formed by a bulk material filling (4) which supports the wall (3) against an operating differential pressure, characterized in that first a lower part of the external pressure fluid reservoir is produced, then a pneumatic body (54) is inserted into the lower part and inflated until, in the inflated state, it follows the intended contour of the interior, and then a skeleton arrangement and the wall (3) are arranged on the pneumatic body (54), wherein an opening is provided at an upper end of the wall (3) such that, in a subsequent step, the bulk material filling (4) can be filled into the interior (5, 24) formed by the wall (3) in an operational manner. Method for producing an external pressure fluid reservoir (1, 20, 50) according to claim 21, wherein the bulk material filling (4) is filled after the prepared,The wall (3), which is held in shape by the form skeleton, has been immersed in water and can be submerged in this water at a designated location. A method for manufacturing an external pressure fluid reservoir (1, 20, 50) according to claim 21, wherein the pneumatic body (54) is spherical in the inflated state. A method for manufacturing an external pressure fluid reservoir (1, 20, 50) according to claim 21, wherein the mold skeleton is formed as a layer of shotcrete (55) sprayed onto the pneumatic body (54).

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