WO2018134620A2

WO2018134620A2 - Apparatus and method for electrical energy storage based on the potential energy of a vertically moving massive weight

Info

Publication number: WO2018134620A2
Application number: PCT/GB2018/050170
Authority: WO
Inventors: Miles FRANKLIN; Peter Fraenkel
Original assignee: Gravitricity Limited
Priority date: 2017-01-20
Filing date: 2018-01-19
Publication date: 2018-07-26
Also published as: GB2561529A; GB201701015D0; WO2018134620A3; GB2561529B

Abstract

An energy storage system comprising a plurality of cables, a weight attached to respective end regions of the plurality of cables so that the weight can be raised and lowered through a substantially vertical distance by winch means, wherein the cables extend from the weight, through the winch means and subsequently directed through the substantially vertical distance and attached at opposite end regions to a second weight which is moved in an opposite direction to the first-mentioned weight through the substantially vertical distance, the arrangement being such that the passage of movement of the second weight does not interfere with the passage of movement of the first- mentioned weight.

Description

APPARATUS AND METHOD FOR ELECTRICAL ENERGY STORAGE BASED ON THE POTENTIAL ENERGY OF A VERTICALLY MOVING

MASSIVE WEIGHT This invention relates to an energy storage system, and in particular to a system intended for absorbing electrical energy, storing it with minimal leakage or loss and then exporting it when required.

JP5771792B discloses a device which generates electric power utilizing circulation of water or liquid. In a gravity type power generator, a lifting tank, a balance weight body, and a power generator are connected with a rope in a pair of containers or an integrated container provided on the ground or underground, and the movement of the rope associated with the lifting motion caused by the gravity movement of the lifting tank and the balance weight body rotates the power generator to generate electric power.

CN202338453U discloses an energy storage device which is provided with a driving wheel, wherein the driving wheel is in charge of inputting energy and lifting a weight, is used for lifting a main weight box through a transmission chain and a driving pulley, and drives a driven wheel with a certain load.

JPS5728880 discloses a system to store the energy of wind, by changing it into the potential energy of a body. An input wheel and an output wheel are supported by shafts on the top of a tower, an endless looped transmission means is wound around the wheels and a movable wheel between the wheels. The movable wheel is coupled to a heavy body which can be moved up and down. A windmill is installed at the top of the tower. The input wheel is driven by the motive power of the windmill to move the heavy body up. The energy of wind is thus changed into the potential energy of the body so that the energy of wind is stored.

As described in our earlier International Patent Application Publication WO2013/005056, an energy storage system comprises a weighted object (or weight) suspended from a cable, a lifting device connected to the weighted object by way of the cable and arranged to move the weighted object through a substantially vertical distance, and means for generating electrical energy connected to the lifting device. The system preferably comprises a guidance system for guiding the weighted object. The basic system comprises a weight suspended from a cable. The cable is connected to a winch such that the winches can be simultaneously and harmoniously operated in order to raise or lower the weight in such a manner that the load is shared approximately equally between the winches. The cables may be steel or synthetic. The winches include an electrical drive to interface with the electricity grid, and preferably a gearbox and brake. Alternatively, it is possible to use a hydraulic drive interfacing with a hydraulic motor driven generator to convert hydraulic power into electrical power. The electrical or the hydraulic drive operates as a motor or power source to raise the weight and as a generator or power producer when the weight is permitted to descend. Thereby energy is stored by raising the weight using electrical energy from the grid and energy can be returned to the grid by allowing the weight to descend under the influence of gravity and thereby drive the winches so that electricity is generated and fed into the grid. The physical principle involves conversion of potential energy to electrical energy and vice-versa, the gross stored energy being E = mgh where E is energy, m is the mass, g is the acceleration due to gravity and h is the height the mass has been raised. In general, the weight will be suspended in a vertically aligned hole in the ground, much like the shafts used for mines, such that it has clearance radially around it. Our previous patent application advocated two or more vertical pre- tensioned cables surrounding the weight and extending from the bottom of the shaft to the top. In this earlier embodiment, the weight is fitted with sliders which engage with the pre-tensioned cables such that they can slide up and down them and control the horizontal position of the weight as it ascends and descends and inhibit it from colliding with and damaging the walls of the shaft.

This invention discloses improvements, additions and refinements to the technology described in the aforementioned earlier patent application. According to one aspect of the present invention, there is provided an energy storage system comprising a plurality of cables, a weight attached to respective end regions of the plurality of cables so that the weight can be raised and lowered through a substantially vertical distance by winch means, wherein the cables extend from the weight, through the winch means and subsequently directed through the substantially vertical distance and attached at opposite end regions to a second weight which is moved in an opposite direction to the first- mentioned weight through the substantially vertical distance, the arrangement being such that the passage of movement of the second weight does not interfere with the passage of movement of the first-mentioned weight.

According to a second aspect of the present invention, there is provided a method of energy storage comprising lifting a first weight through a substantially vertical distance by winch means thereby storing potential energy, said winch means connected to means for generating electrical energy, and lowering said first weight, thereby activating the means for generating, for transforming the stored potential energy into electrical energy, wherein a second weight is moveable through said substantially vertical distance in an opposite direction to the first weight and wherein the passage of movement of the second weight does not interfere with the passage of movement of the first weight, the arrangement being such that the first weight is suspended by a plurality of cables, the cables being would around the winch means and then directed to return down the substantially vertical distance, the returning cable ends being attached to the second weight.

Owing to these aspects of the invention, it is possible to provide a system where, instead of having to store large lengths of cable above ground, this can be substantially stored below the ground surface.

Advantageously, the first weight has mounted thereto at least two (but probably more) wheels or skids which extend outwardly of the perimeter of the first weight such that the first weight can travel substantially vertically up and down, for example, in a shaft when the first weight is raised and lowered. The wheels or skids may be sprung radially relative to the centre line of the shaft. The radial spring suspension for the wheels or skids allows for compensation of any unevenness or inconsistency in the surface they contact. In this way, the wheels engaging with the surface prevent the weight from swinging too wildly and even if the first weight does move, the wheels or skids protect the surface from any potential damage caused by contact with the first weight.

This same energy storage principle may also be useful using a weight suspended over the edge of a cliff-like feature or the edge of a trench or canyon rather than in a hole. In this case, the first weight would preferably be long and narrow and hung from a row of winches spaced out along the top edge of the cliff-like feature or the edge of a trench or canyon. Such a first weight may also be fitted with wheels or skids that can prevent it from swinging and impacting the substantially vertical face of the cliff-like feature or the edge of a trench or canyon. Moreover the cliff-like face may be inclined at a small angle from the vertical so that the first weight tends to lie against the face, in which case the wheels become an important feature to allow the heavy first weight to move up and down the face with minimum friction.

In our earlier above-mentioned patent application, it was disclosed that the cables suspending the weight would be either wound directly onto a drum winch or spooled onto a cable storage drum set behind the winch relative to the shaft, such that in both cases the cable is stored at the surface when the weight is raised. With significantly large substantially vertical distances, such as deep shafts, this can involve significant lengths of cable. Therefore, instead of storing the cables at or above the surface, the cables may wind around the winching means in the form of, for example, a traction winch or capstan type winch and then be directed to return down the substantially vertical distance. Each of the returning cable ends will be attached to the second weight or counterweight, or possibly counter-weights, such that the counter-weight(s) will travel in the opposite direction to the main first weight. In this configuration, the counterweight will sit at the lower extreme of the hole when the main first weight is at the upper extreme and vice versa. In order to prevent collisions between the first and second weights, the second counterweight may pass externally of the main first weight, for example, if the substantially vertical distance is formed by a shaft in the ground, the second counterweight may pass in the space between the main weight and walls of the shaft (the counter weight in that case could be a thin walled cylinder of slightly larger internal diameter than the maximum external diameter of the main weight), but the preferred embodiment is to use a long and slim counterweight (or counterweights) which pass through a channel through the central portion of the main first weight. In such a case, the channel may have a tapered entry and exit so that the counterweight can easily centre itself and pass through the main weight when required.

It is anticipated that the main first weight can be constructed as a container that can be filled with dense material. When installed in a circular hole or shaft in the ground, the weight can be similar to a large bucket, probably fabricated from steel, which can be filled with scrap metal such as scrapped railway rails or with some other high density material. Increasing the density of the material will generally result in a smaller, more expensive assembly for a given mass. This trade-off of cost against volume will be optimised in conjunction with other system level considerations, especially the cost of shaft sinking. Various embodiments of the first weight are proposed which could also include a steel tubular core with a circular base with sufficient internal clearance for a counterweight to pass through the tubular core. Scrap metal such as scrapped railway rails can be stacked and clamped or welded to the core.

It is to be expected that means will be required to support the first weight assembly at the upper extreme of its freedom of travel in order to enable installation and maintenance. Various possibilities are envisaged, such as a support beam that can be rolled out of a slot in the side wall of a shaft to span the shaft and thereby support the weight. To release the support beam, the weight can be slightly raised by the lifting cables using the winching means at which point the support beam can be retracted such that the first weight is free to move downwards and so generate power.

In order that the invention can be clearly and completely disclosed, reference will now be made, by way of example only, to the accompanying drawings in which:- Figure 1 is a diagrammatic cross-sectional view of an energy storage system, and

Figure 2 is a diagrammatic perspective view of an alternative embodiment of the energy storage system.

Referring to Figure 1 , an energy storage system comprises a first heavy weighted object or mass 8 (shown in cross-section) hanging from cables 6 in a shaft or hole 10 in the ground providing a substantially vertical distance though which the first weight 8 can be moved up and down. Winch means 3, in the form of, for example, traction winches are arranged for raising and lowering the first weight 8 in the hole 10. It would be possible to use other forms of winch means which are not illustrated here, such as a drum winch or a winch with a separate cable storage drum behind it. Preferably, a plurality of winch means 4 are arranged around the shaft or hole 10.

In the simplest embodiment, each winch 3 will drive a single cable 6. It may also be envisaged that a single winch 3 may drive multiple cables 6. Smaller diameter cables require smaller diameter sheaves to avoid reduced service life due to bending fatigue, and so a larger number of small diameter cables may provide a practical advantage. Additionally, if the requirements of drive units (whether electric or hydraulic) and cables diverge then it is envisaged that a plurality of winches may be driven from a single motor.

In the illustrated embodiment of Figure 1 , the heavy first weight 8 has a channel or through-hole in its central region through which a second weight or counterweight 9 is able pass without interfering with the movement of the first weight 8. The counterweight 9 is attached to the opposite end of each cable 6 suspending the first weight 8. This arrangement of the first weight 8 and the second counterweight 9 therefore avoids the need for a spooled storage or large drum winch and also serves to provide back tension required by the winch means 3 to prevent slippage of the cables 6. The counterweight 9 may also be suspended outwardly the first weight 8 and be in cylindrical form or, for example, as a plurality of counterweights surrounding the main first weight rather than passing through it, so the passage of movement of the counterweight does not interfere with the passage of movement of the first weight 8.

The cables 6 are guided to the counterweight 9 over sheaves 5. In addition, there may also be a tensioned guide wire or cable 2 which is tensioned between a structural support 1 above the shaft or hole 10 and an anchor point 1 1 at the floor of the shaft. The guide wire 2 passes through the channel in the first weight 8 and also a second through-hole in the centre line of the counterweight 9 in order to control its movement. The second through-hole of the counterweight may be lined with a low-friction material that can engage smoothly and with minimum wear of the tensioned guide wire 2. Advantageously, each end of the channel through the first weight may be tapered so that the counterweight 9 can easily centre itself and pass through the first weight when required. In addition, each end of the counterweight itself can be correspondingly tapered to further ease the ability of the counterweight to centre itself in the channel and its pass through the first weight.

Similarly, if the counterweight(s) is/are to be disposed outwardly of the first weight, then respective tensioned guide wires could also be provided for each counterweight.

It may, in some cases, be possible to dispense with the guide wire 2 although to do so risks the possibility that the counterweight 9 might start to swing like a pendulum and thereby cause damage to the first weight 8 and also the internal surface of shaft 10.

The winch means 3 are coupled to means for generating electrical energy such as electrical or hydraulic drives (not shown) which can either power them so as to raise the first weight 8 or which can absorb power which is converted into electricity when the first weight descends.

Advantageously, provision of guide wheels or skids 12 which may contact the sides of the hole or shaft 10 assist in the prevention of the first weight 8 from swinging too wildly and thereby possibly causing impact damage to the sides of the hole or shaft 10 or the first weight 8. The guide wheels or skids 12 are preferably mounted spring-loaded like the wheels of a motor vehicle so that the wheels can follow undulations or unevenness in the sides of the hole or shaft without altering too much the substantially vertical movement of the first weight 8. The wheels or skids 12 would, generally, not be in firm contact with the sides when the first weight is centred, but there would be a minimal radial clearance such that very little lateral movement of the first weight 8 is possible before contact is made between the wheels and the sides of the hole or shaft 10. Only two guide wheels can be conveniently illustrated in Figure 1 , but a larger number are preferably disposed around the periphery of the first weight 8. The guide wheels or skids are preferably located at the top end region of the first weight 8 for optimum effect and also to permit easy access for maintenance when the first weight 8 is fully raised. However, if it proves useful, the guide wheels or skids 12 may be located differently to the arrangement as illustrated. Referring to Figure 2, a different embodiment of the energy storage system is possible whereby the heavy first weight 8' is hung over the side of a cliff-like vertical (or near vertical) face using a plurality of cables 6'. The cables 6' are engaged with winch means 3' connected to electrical or hydraulic drives. One or more second counterweights 9' are hung from sheaves 5 disposed further outwardly than those for the main first weight 8' so as not to interfere with the movement of the first weight 8' (shown without any support structure for clarity).

The first weight 8' in this embodiment can also be fitted with wheels or skids 12' that can roll against the substantially vertical cliff-like face. In some situations, it may be advantageous for the face to be inclined to be almost but not quite vertical so the first weight 8' runs continuously on the wheels or skids 12' and therefore not only prevent any swinging of the first weight 8' but also allow for the minimum of friction with the cliff-like face. Although not shown in Figure 2, the second weight 9' could be shaped so as to avoid colliding on the first weight 8' when the weights pass each other.

This embodiment will normally be used for considerably smaller lift distances than the first weight 8 in the hole or shaft configuration of Figure 1 so to maintain adequate energy storage and where much heavier weights are liable to be used since the energy storage capacity is a function of the total mass and the height raised.

Claims

1 . An energy storage system comprising a plurality of cables (6), a weight (8) attached to respective end regions of the plurality of cables (6) so that the weight (8) can be raised and lowered through a substantially vertical distance (10) by winch means (3), wherein the cables (6) extend from the weight (8), through the winch means (3) and subsequently directed through the substantially vertical distance (10) and attached at opposite end regions to a second weight (9) which is moved in an opposite direction to the first-mentioned weight (8) through the substantially vertical distance (10), the arrangement being such that the passage of movement of the second weight (9) does not interfere with the passage of movement of the first-mentioned weight (8).

2. An energy storage system according to claim 1 , and further comprising a plurality of winch means (3) driven from a single motor.

3. An energy storage system according to claim 1 or 2, wherein the second weight (9) is a long and slim weight which passes through a channel through the central portion of the first weight (8).

4. An energy storage system according to claim 3, wherein the channel has a tapered entry and exit, the arrangement being such that the second weight (9) can easily centre itself and pass through the first weight (8).

5. An energy storage system according to any preceding claim, and further comprising a tensioned guide wire (2) for guiding the second weight (9) and tensioned between a structural support (1 ) above the substantially vertical distance (10) and an anchor point (1 1 ) at the floor of the substantially vertical distance (10).

6. An energy storage system according to claim 5 as appended to claim 3, wherein the tensioned guide wire (2) passes through the channel in the first weight (8) and also a second through-hole in the centre line of the second weight (9).

7. An energy storage system according to claim 6, wherein the second through-hole of the second weight (9) is lined with a low-friction material.

8. An energy storage system according to any one of claims 4 to 7, wherein each end of the second weight (9) itself can be correspondingly tapered to centre itself in the channel and its pass through the first weight (8).

9. An energy storage system according to claim 5 as appended to claims 1 or 2, wherein the second weight (9) is disposed outwardly of the first weight (8) and guided by the tensioned guide wire (2).

10. An energy storage system according to any preceding claim, wherein the first weight (8) is suspended over an edge of a cliff-like feature or the edge of a trench or canyon.

1 1 .An energy storage system according to claim 10, wherein the first weight (8) is relatively long and narrow and hung from a linear row of winch means spaced out along the top edge of the cliff-like feature or the edge of a trench or canyon.

12. An energy storage system according to any preceding claim, and further comprising means to support the first weight (8) at the upper extreme of its freedom of travel.

13. An energy storage system according to claim 12, wherein the means to support is arranged to be rolled out of a slot in the side wall of the shaft to span the shaft and thereby support the weight (8).

14. A method of energy storage comprising lifting a first weight (8) through a substantially vertical distance (10) by winch means (3) thereby storing potential energy, said winch means (3) connected to means for generating electrical energy, and lowering said first weight (8), thereby activating the means for generating, for transforming the stored potential energy into electrical energy, wherein a second weight (9) is moveable through said substantially vertical distance (10) in an opposite direction to the first weight (8) and wherein the passage of movement of the second weight (9) does not interfere with the passage of movement of the first weight (8), the arrangement being such that the first weight (8) is suspended by a plurality of cables (6), the cables being would around the winch means (3) and then directed to return down the substantially vertical distance (10), the returning cable ends being attached to the second weight (9).

15. A method according to claim 14, and further comprising suspending the second weight (9) so as to allow its passage through a channel in the central portion of the first weight (8).

16. A method according to of claims 14 or 15, wherein the second weight (9) is guided by a tensioned guide wire (2).

17. A method according to any one of claims 14 to 16, wherein the first weight (8) is suspended over the edge of a cliff-like feature or the edge of a trench or canyon.