Energy storage system

Abstract

A gravity energy storage device for temporary storage of energy prior to release as electrical energy, comprises a solid load that can be raised up to store energy and subsequently lowered to release the same energy to generate electricity, the raising and lowering being over a vertical travel range which is between one and a half and five times a height of the load, the load radius being at least two orders of magnitude smaller than the height of the load.

Description

[0001] ENERGY STORAGE SYSTEM

[0002] RELATED APPLICATION / S

[0003] This application claims the benefit of priority under 35 USC § 119(e) of U.S. Provisional Patent Application No. 63 / 536,526, filed 5 September 2023, the contents of which are incorporated herein by reference in their entirety.

[0004] FIELD AND BACKGROUND OF THE INVENTION

[0005] The present invention relates to a Gravity Energy Storage System.

[0006] There is an increasing requirement nowadays to use renewable energy sources to produce electricity. The most common renewable sources are Solar panels and wind turbine. However, these sources are intermittent, and the total amount of power that the electric power grid can absorb from renewable sources is limited due to the intermittent availability of these renewable sources power generation.

[0007] In order to increase the total power from renewable sources that can be delivered by the power grid, electricity storage systems must be connected to the grid. These systems should be able to store electric power when there is a surplus of power generated by the renewable sources, and generate electricity when the power grid demand is higher than the available power from renewable sources.

[0008] The electric energy can be stored in many forms, such as chemical (batteries), inertia wheels (kinetic energy), heat and gravity (potential energy).

[0009] Batteries are most commonly used today. Batteries drawbacks include high cost, relatively short life time and massive negative impact on the environment, mainly as they use rare earth materials and produce soil-contaminating waste at end-of-life.

[0010] Inertia wheels have the drawbacks of high cost and short storage time.

[0011] Heat storage is low cost, but low efficiency, i.e., the total power that can be recovered is only a small portion of the power stored in heat.

[0012] Gravity energy storage is well known and has been in use for many years. Most common implementations are pump storage hydroelectric power stations, where water is pumped to an elevated lake when there is a surplus of power, and then is allowed to fall and operate a turbine to generate power during peak demand. A particular advantage of a pump storage scheme is that the additional power can be brought on line very quickly.

[0013] In recent years, gravity energy storage systems using solid material have been proposed. Unfortunately, they are all of low power density per solid material weight, per area of used land and come at a high cost.

[0014] Patents GB 2506133 by Bergland and DE102007057323A1 by Pesch, propose energy storage using a heavy load suspended on a cable, driven up and down by a motor / generator inside a mine well or in holes drilled in ground.

[0015] A drawback of these systems, is that an enormous weight is required and large holes need to be drilled in the ground to store a substantial amount of energy. This implies very high cost.

[0016] Patents and patent applications US 2010 / 0301616 Al by Abdulaziz, US 2009 / 0193808 Al by Fiske, US9,745,963B2 by Boone, WO2018 / 134620A3 by Franklin, US7973420B2 by Scott, US 10683851B2 and US 2021 / 0404445 Al by Pedretti, all describe systems designed a)_to lift heavy loads using electric motors / generators in order to store electric energy as potential energy, and b)_ to generate electricity by lowering the heavy loads to drive electric motors / generator.

[0017] A common feature of these proposed systems, is that the height of the load is short, compared to the height to which it is elevated. This results in a low energy density.

[0018] In an example, using a lift height of 50 meter, and a load height of 5 meter, assuming the load is a concrete block with density 2500Kg per cubic meter, then the stored energy per square meter is less than 1.5kwh. However, a load of 1 square meter section and 5-meter height weighs 12.5 metric tons. The energy density of such a system would be. 0.03 kwh / cubic meter (1.5kwh / (height 50m x 1 square meter)).

[0019] In this example, it is evident that the motor / generator used to move up and down the load is large, and the tower needed to hold the lifting motor / generator needs to be designed for a heavy load, resulting in high cost of construction. However only one and a half kilowatt-hour of energy can be stored by such a system.

[0020] Energy gravity storage with much higher power densities in terms of a)_ stored energy per square meter of used land and b)_ stored energy per installation cost is evidently needed. SUMMARY OF THE INVENTION

[0021] An object of the present embodiments is to provide a Gravity Energy Storage system (GES) having high energy densities in terms of a)_ stored energy per square meter of used land and b)_ stored energy per installation cost.

[0022] According to an aspect of some embodiments of the present invention there is provided a gravity energy storage device, comprising a load raisable to store energy and lowerable to release said energy to generate electricity, said raising and lowering over a vertical travel range, the vertical travel range being between one and a half and five times a height of said load, the load having a radius, the radius being at least two orders of magnitude smaller than the height of said load.

[0023] In embodiments, said vertical travel range is approximately twice the height of said load.

[0024] In embodiments, the radius of the load is approximately three orders of magnitude smaller than the height of said load.

[0025] In embodiments, said load comprises a plurality of cylindrical elements linked together.

[0026] In embodiments, said load is attached to an electrical machine via a winch system, the electrical machine configured to operate as a motor to raise said load and to operate as a generator when said load is being lowered.

[0027] Embodiments may comprise a vertical tube, the load being located within said vertical tube, the vertical tube providing said vertical travel range.

[0028] The vertical tube may provide said vertical travel range, wherein said cylindrical elements are articulated together.

[0029] In embodiments, said load comprises at least a first set of guide wheels for guiding said load within said vertical tube.

[0030] In embodiments, said load comprises at least a second set of guide wheels, the second set of guide wheels being oriented perpendicularly to said first set of guide wheels.

[0031] In embodiments, said vertical tube is an excavation, such as a hole or well, dug into the ground.

[0032] In embodiments, at least one of said cylindrical elements comprises two half cylinders attached together around a central cable. In embodiments, said central cable extends from a lowest cylindrical element of said load up to a pulley, and from said pulley to a spool.

[0033] In embodiments, said pulley comprises a sequence of pulleys connected together by gears.

[0034] According to a second aspect of the present invention, there is provided a gravity energy storage method, comprising: raising a load to store energy and lowering said load to release said energy to generate electricity, said raising and lowering over a vertical travel range, the vertical travel range being between one and a half and five times a height of said load, the load having a radius, the radius being at least two orders of magnitude smaller than the height of said load.

[0035] Unless otherwise defined, all technical and / or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and / or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

[0036] BRIEF DESCRIPTION OF THE SEVERAL VIEW OF THE DRAWINGS:

[0037] Fig 1: is a schematic view of a GES according to the present embodiments;

[0038] Fig 2: shows an implementation of a modular load element for use with the GES of Fig. 1; Fig 3: shows another implementation of a modular load element for use with the GES of Fig. 1;

[0039] Fig 4: illustrates guiding wheels for use with the GES of Fig. 1, the guide wheels being to guide the load in the GES well;

[0040] Fig 5: is a simplified schematic view of an implementation of a winch system to raise and lower the load of Fig. 1 , and Fig. 6 is a simplified schematic flow chart of a process for gravitational energy storage according to the present embodiments.

[0041] DETAILED DESCRIPTION:

[0042] According to the present embodiments there is provided a gravity energy storage (GES) device for temporary storage of energy prior to release as electrical energy. The device comprises a solid load that can be raised up to store energy and subsequently lowered to release the same energy to generate electricity, the raising and lowering being over a vertical travel range which is between one and a half and five times a height of the load, the load radius being at least two orders of magnitude smaller than the height of the load.

[0043] In a GES according to the present embodiments, a load includes a series of modular load elements fixed to each other in a long chain in the vertical direction. Each load element has a vertical dimension substantialy longer than its horizontal dimensions. The load has thus the form of a vertical chain of modular load elements having a total height greater by several order of magnitude than the horizontal dimensions. The load is suspended by means of cable or belt to a winch driven by an electric motor / generator, and can be moved vertically up and down by the winch and motor / generator with minimal friction inside a provided vertical well of height greater than the height of the load. In an embodiment, the horizontal dimensions of the load elements are small, for example under 20cm, and the vertical well is a deep hole drilled in the ground, for example a few hundred meters deep. According to certain embodiments, the height of the vertical well H and the total height of the load h are set according to the relationship H / h ~ 2.

[0044] Energy absorption and storage is obtained by activating the motor / generator in the motor mode and lifting the load toward the top of the vertical well from a lower vertical position. Electric power is obtained by activating the motor / generator in generator mode and driving down the load from a higher vertical position toward the bottom of the vertical well.

[0045] Advantages of a GES of the present embodiments over previous art GES are:

[0046] • High energy storage density: as will be shown further below the maximum energy storage density (D) is obtained when the height h of the load is approximately half the height of the well H. A GES according to the present embodiments is designed to satisfy the H / h ~ 2 condition as close as possible

[0047] • Small weight of the load: due to the small horizontal dimensions of the load, the total weight of the load is relatively small and the winch, motor / generator and constructive elements may be relatively small in size

[0048] • Small footprint, high energy storage density per occupied land area.

[0049] • Modularity due to the small size of one unit of energy storage. • Easy installation: the load is composed of many modular elements and using appropriate tools, the elements may be inserted one by one in the well and attached to the previously inserted element.

[0050] • Low cost of the well: In the case the well is drilled in the ground, the common and relatively economic technique of water well drilling may be used.

[0051] • Large height of the Well: In the preferred embodiment in which the well is drilled in the ground, a depth of several hundred meters may be reached. As will be shown further below, the energy storage density per land area is proportional to the square of depth of the well (H2) and high energy storage density may thus be achieved.

[0052] Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and / or methods set forth in the following description and / or illustrated in the drawings and / or the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

[0053] Referring to Eig 1, there is shown a Gravity Energy Storage (GES) system according to embodiments of the present invention.

[0054] A plurality of modular load elements (MLE), 112a, 112b and 112c are suspended in chained manner, thus being connected to each other in a vertical series. The highest modular load element is suspended on a cable 103. In Fig 1 only 3 such modular load elements are shown for clarity, however a GES of the present embodiments may include a large number of such modular load elements. The entire series of these modular load elements constitute a heavy load the load, 114 suspended on the cable 103, extending over a vertical height h 107. Hooks such as hook 111 between the first and second MLEs, shown in Fig 1 illustrate mechanical link between vertically adjacent modular load elements.

[0055] The load 114 is inserted in a vertical shaft, for example an excavated well 115, of height H 108. According to embodiments of the present invention, the height H 108 of the well 115 may be approximately twice the height h 107 of the load 114. In the scope of this patent application, the term height refers to the vertical dimensions of the well and / or of the load as relevant in the context. In the embodiment shown in Fig 1, the well 115 is a hole drilled in the ground 110, 109. In other embodiments the well may extend upward above the ground. For example, the well may be a vertical tube or shaft as mentioned above. In yet other embodiments, the well may be just a vertical space under a hole, for example a vertical free space of height H under a hole. The hole may be capped with a horizontal plate, and the plate may support various constructions and mechanical components of the GES, so that the mechanical components are above the plate.

[0056] Characteristics of a GES according to the present embodiments may include the load 114 having a height 107 bigger by several orders of magnitude than its horizontal dimension 106. As an example, the height 114 may be 200 meters, and the load horizontal dimension 106 may be 20cm, i.e., a one to a thousand ratio.

[0057] Another characteristic of a GES according to the present embodiments is that the height H 108 of the well 115 or the vertical free space, or travel range, in which the load 114 is inserted, may be approximately twice the height 107 of the load 114. It will be shown further below that this condition may result in a maximum energy storage density.

[0058] A winch assembly includes components schematically shown in Fig 1 inside the dashed line contour 116. It includes a motor / generator 104, a traction pulley 102 and a drum 101 to store the long cable 103. The traction pulley 102 is driven with high torque by the motor / generator 104 to pull the load 114 up or down. When the motor / generator 104 pulls up the load 114, electric energy transmitted to the motor is converted into potential energy of the load 114. When the motor / generator lets the load down, the torque on the motor is reversed vis a vis the rotation direction, and potential energy of the load is converted into electric energy that can be transmitted from the motor / generator to the power grid.

[0059] The winch assembly as shown in Fig 1 is for illustration only. Many types of winch system could be used in a GES according to the present embodiments.

[0060] The energy storage density, in energy per occupied volume and occupied land area, can be calculated using:

[0061] • The material load density: p

[0062] • The well height: H

[0063] • The load height h

[0064] • The gravity coefficient g = 9.81m / S2

[0065] The sectional area of the load S The maximum vertical movement of the load is calculated by:

[0066] L = H - h

[0067] The mass of the load:

[0068] M = p. S. h

[0069] The potential energy of the load when moving from the bottom to the top of the well is thus:

[0070] Etop = M.g. L = p.S. h. g. H — h

[0071] The energy storage density D per occupied volume is thus

[0072] The energy density reaches a maximum when h=H / 2 condition 1

[0073] A GES will then give a maximum of energy storage density when the height of the load is close to half the weight of the well condition 1. However, it must be understood that this maximum is calculated for ideal conditions. An actual maximum may differ from the theoretical maximum due to non-uniformity of the load material or other factors.

[0074] At this maximum, we have the following Energy densities:

[0075] Energy Storage Density per occupied volume: Dmax= p. g.— equation 1

[0076] 4

[0077] _ Hz

[0078] Energy Storage Density per load section area S L)s= p. g. — equation 2

[0079] Installation cost of the system grows with the occupied volume. For example, if the GES is implemented with an underground well, the drilling cost is dependent on the depth and the diameter of the well. If for example, in a first evaluation, we adopt a model in which the installation cost of the system Cuis proportional to the occupied volume V

[0080] Then the cost of system is evaluated by Cu= K. V where K is a constant

[0081] The total stored Energy Capacity of the system is E = Dmax. V = p. g. — . V

[0082] C 4 K

[0083] Then Cost per unit of stored energy Ce= - ■ = ' Equation 3

[0084] Equation 3 indicates that the installation cost of an energy storage system, per unit of energy, decreases rapidly with the height of the well.

[0085] It is thus advantageous to design a GES with the maximum possible height per occupied volume.

[0086] Additionally, occupied land area is also an important cost factor. The occupied land area is directly related to the horizontal section area of the load. The Energy Storage Density per load section area, as shown by equation 2, is proportional to the square of the well height, and thus rapidly increases with the well height.

[0087] It is thus desired to design a GES with a very high or deep well. According to the present embodiments, the height of the load is close to the half the height of the well to optimize the energy density, as per condition 1 above. The weight of the load is proportional to its height and its section area. In order to keep the load weight to practical levels, a thin load profile is chosen, with a small horizontal section area.

[0088] A GES according to the present embodiments may thus have a thin vertical profile, with a height much larger than its horizontal dimensions, preferably by several order of magnitude.

[0089] In the preferred embodiment described in respect of Fig 1 above, a considerable height may be achieved at a relatively low cost for a small sectional area. The GES occupies a small land area, and many GES’s may be installed in a field to implement a large energy storage plant.

[0090] In particular, a GES’ of the present embodiments may be installed in photovoltaic solar fields, for example under the photovoltaic panels, without adding any area to the size of the fields. A single GES may be able to store the energy produced by several solar panel modules. A solar field using a number of underground GES, each GES being covered by a solar panel, may be used to store electrical energy and generate power later on from the stored energy according to the needs of the power grid. Thus the solar energy produced by the solar field may be sold when needed rather than when produced, and thus realize a higher price. Accordingly, the rentability of the solar field may be increased.

[0091] Following are descriptions of two possible designs of the Modular Load Elements MLE. However, many other designs could be conceived for Modular Load Design for GES’s of the present embodiments.

[0092] Referring now to Fig 2, a cylindric Modular Load Element MLE, 200 is shown, The MLE is made of two half cylinders 202 and 203 that can be tightly assembled around the cable 103, also seen in Fig 1. The two half cylinders 202 and 203 are tightly fixed to each other by means of bolts or brackets - not shown, and the cable 103 may be strongly compressed into profiled grooves 204, 205 provided in the two halves. The Modular Load Element 200, formed by the two halves 202, 203 is thus tightly fixed to the cable 103 by friction forces. The desired number of Modular Load Elements is fixed to the cable 103 to form the load of a GES. The cable 103 implements a flexible link between the multiple MLEs of the GES. The MLE may be made of heavy material, such as Iron or Concrete. Scrap Iron may conveniently be used to lower costs. An MLE according to the present design allows for ease of insertion of the load inside the well.

[0093] Referring to Fig 3, a cylindrical MLE 300 is shown. The link between MLEs is implemented by a slot 302 on one extremity, and a connection plate 304 on the other extremity. The connection plate 304 may be designed to fit the slot 302 of the neighbor MLE. Holes 303 and 305 are provided for the introduction of bolts which provide the links between vertically adjacent MLEs. Such a link may have only one degree of freedom. In the case where the well is not perfectly straight, it is required to provide flexibility of the load in two degrees of freedom. For such a purpose, an MLE 300 may be provided with a slot 302 and plate 304 perpendicular to each other, and thus give a flexibility of the load in two horizontal dimensions.

[0094] In a GES according to the present embodiments, the vertical well may have straightness and verticality tolerances. In this event, the load may touch the well walls; the generated friction may reduce the system efficiency and damage the walls. In order to prevent this, guiding wheels may be mounted at some positions between or on a number of MLE’s. Preferably, the number of guiding wheels required will be low for low tolerances of the well straightness and verticality.

[0095] Fig 4 illustrates an assembly 400 of two guide wheels 402a and 402b that can be mounted between two MLE’s. The guide wheels 402a and 402b are shown mounted on a common axis 403 through which a cable 401, the same as cable 103 of Fig 1, is run. The wheel assembly 400 may be fixed to the cable by clamps or brackets - not shown. To prevent the MLE from striking the well wall in both horizontal directions, additional wheel assemblies 400 are mounted in a perpendicular orientation to the first horizontal orientation.

[0096] Guide wheels may minimize eventual friction and avoid wall damage.

[0097] Typically, the straightness and verticality of the well will have some tolerances, and a few guide wheels may be needed.

[0098] Wheel assembly may involve separate components. It must be understood that many designs may be applied to the guide wheels. Optionally, guide wheels may be integrated into the MLE’s.

[0099] The GES of the present embodiments may include a winch system to pull up and lower the load. The winch system may be designed for high efficiency regeneration of electrical power when the load is pulled down. Various designs of a winch system may be applied, according to known techniques and existing products.

[0100] Referring to Fig 5, a design concept for a winch design is shown. The winch system 500 is designed to drive vertically up and lower the load of the GES while that load is suspended on a cable 501, thus applying a vertical tension force 509 on cable 501. A motor / generator 503 is able to apply a high torque to a shaft 505a and to a gear wheel 504a fixed to that shaft. A set of three other gear wheels 504b, 504c and 504d are all engaged with each other with a unity gear ratio. Each gear wheel 504a- 504d is fixed to a corresponding shaft 505a-505d. All shafts 505a-505d have the same diameter and are arranged in a gear box with bearings -not shown to be able to rotate around a fixed position of their rotation axis. The shaft of the motor / generator 503 is coupled to the shaft 505a either by means of a coupling device or directly. The cable 501 is threaded to surround shaft 505a on its upper half circumference, then shaft 504b on its lower circumference, then shaft 505c on its upper circumference, shaft 505d on its lower circumference and then wound on a drum 508. The drum 508 is driven by an auxiliary motor 506 coupled by a shaft 507. The winch system described above may function as follow:

[0101] The load weight applies a high tension 509 on cable 501. The friction on the first shaft 505a opposes this tension so that the tension of the cable 501 between shafts 505a and 505b is reduced. In the same way, tension of cable 501 is further reduced by each shaft and finally the tension on of the cable 501 between shaft 505d and drum becomes minimal but never zero. The auxiliary motor 506 is then driven to maintain the minimal tension. With the arrangement as described, when the shafts 504a- 504-d are blocked, for example by operation of a brake on motor / generator 503, the load may be held with a minimal torque on drum wheel 508.

[0102] Referring now to Fig. 6, using gravitational energy storage device 600, when it is required to convert electric energy into potential energy, the motor / generator 503 is operated in motor mode to pull up the load - 602. All the shafts 505a-505d are driven at the same speed, and the auxiliary motor maintains the minimal tension required, so that there is no slippage of cable on the shafts, and thus no friction power losses.

[0103] When it is required to convert potential energy back into electrical energy, motor / generator 503 is run in generator mode to lower the load - 604.

[0104] The winch system of Fig. 5 permits small shaft 505a-505d diameters to be used. The torque applied by the load on the motor / generator is proportional to the radius at which the high tension - indicated by arrow 509 - is applied. The relatively small diameter of the shafts 505a-505d results in torque in a range that may be generated by motors commercially available. Advantageously, a direct drive motor may be used as a motor / generator, providing a relatively high efficiency.

[0105] The travel range - 606 - is between 1.5 and 5 times the height of the load, and more particularly but not exclusively, approximately twice the height of the load. The load radius is very much smaller than the height of the load, for example two to three orders of magnitude smaller.

[0106] We have described here various implementations of a GES according to the present embodiments. It must be understood that many different specific designs of various components of a GES may be conceived by the person skilled in the art without departing from the invention as claimed.

[0107] According to embodiments of the present invention there may be provided a GES having a load composed of a plurality of modular load elements mechanically linked in a vertical series, which load may be pulled up and lowered using a winch system and one or more cables, chains, or belts. The load may move up and down inside a vertical well. The vertical height of the well may be set to be approximately twice the vertical height of the load. The vertical height of the load may be set to be very significantly larger than the load horizontal dimensions. When the load is moved up by the winch system, electrical energy is stored as potential energy of the load, and when the load is lowered by the winch system, potential energy of the load is converted back into electric power.

[0108] General

[0109] As used herein the terms “about” and “approximately” refer to ± 20 %

[0110] The terms "comprises", "comprising", "includes", "including", “having” and their conjugates mean "including but not limited to".

[0111] The term “consisting of’ means “including and limited to”.

[0112] As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise.

[0113] Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of the range from one and a half to five should be considered to have specifically disclosed subranges such as from 1.5 to 3, from 1.5 to 4, from 1.5 to 5, from 2 to 3, from 2 to 4, etc., as well as individual numbers within that range, for example, 1.5, 2, 3, 4, and 5. Furthermore, the range is meant to include any numeral (fractional or integral) within the indicated range. The phrases “ranging / ranges between” a first indicate number and a second indicate number and “ranging / ranges from” a first indicate number “to” a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

[0114] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment and the present description is to be construed as if such embodiments are explicitly set forth herein. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or may be suitable as a modification for any other described embodiment of the invention and the present description is to be construed as if such separate embodiments, subcombinations and modified embodiments are explicitly set forth herein. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

[0115] Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

[0116] All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting. In addition, any priority document(s) of this application is / are hereby incorporated herein by reference in its / their entirety.

Claims

WHAT IS CLAIMED IS:

1. A gravity energy storage device, comprising a load raisable to store energy and lowerable to release said energy to generate electricity, said raising and lowering over a vertical travel range, the vertical travel range being between one and a half and five times a height of said load, the load having a radius, the radius being at least two orders of magnitude smaller than the height of said load.

2. The gravity energy storage device of claim 1, wherein said vertical travel range is approximately twice the height of said load.

3. The gravity energy storage device of claim 1 or claim 2, wherein the radius of the load is approximately three orders of magnitude smaller than the height of said load.

4. The gravity energy storage device of any one of the preceding claims, wherein said load comprises a plurality of cylindrical elements linked together.

5. The gravity energy storage device of any one of the preceding claims, wherein said load is attached to an electrical machine via a winch system, the electrical machine configured to operate as a motor to raise said load and to operate as a generator when said load is being lowered.

6. The gravity energy storage device of any one of the preceding claims, comprising a vertical tube, the load being located within said vertical tube, the vertical tube providing said vertical travel range.

7. The gravity energy storage device of claim 4, comprising a vertical tube, the load being located within said vertical tube, the vertical tube providing said vertical travel range, wherein said cylindrical elements are articulated together.

8. The gravity energy storage device of claim 7, wherein said load comprises at least a first set of guide wheels for guiding said load within said vertical tube.

9. The gravity energy storage device of claim 8, wherein said load comprises at least a second set of guide wheels, the second set of guide wheels being oriented perpendicularly to said first set of guide wheels.

10. The gravity energy storage device of any one of claims 7 to 9, wherein said vertical tube is an excavation.

11. The gravity energy storage device of claim 4, wherein at least one of said cylindrical elements comprises two half cylinders attached together around a central cable.

12. The gravity energy storage device of claim 11, wherein said central cable extends from a lowest cylindrical element of said load up to a pulley, and from said pulley to a spool.

13. The gravity energy storage device of claim 12, wherein said pulley comprises a sequence of pulleys connected together by gears.

14. A gravity energy storage method, comprising: raising a load to store energy and lowering said load to release said energy to generate electricity, said raising and lowering over a vertical travel range, the vertical travel range being between one and a half and five times a height of said load, the load having a radius, the radius being at least two orders of magnitude smaller than the height of said load.

Images