Gravitational potential energy storage

Abstract

An energy storage system comprises a cable (13) and a mass 20 suspended from the cable (13) in a shaft (12). The cable (13) is attached to a winch 11 by which the mass may be raised in the shaft (12) to store potential energy, and the mass is lowerable in the shaft (12) to release the potential energy. The mass comprises at least two sections clamped together around the cable (13). More particularly, the system comprising a plurality of cables (13) and a plurality of multi-section masses each suspended in the shaft (12) by a respective cable (13), the masses being raised and lowered in synchronism in the shaft (12). The multi-section masses fit together side-by-side in the shaft (12) to form an overall cylindrical mass body, the multi-section masses each forming a quadrant of the cylindrical mass body.

Claims

1. An energy storage system comprising at least four cables (13) and at least four multi-section masses (21) each suspended by a respective cable (13) in a shaft (12), the cables (13) being attached to a winch means (11) by which the multi-section masses (21) may be raised in synchronism in the shaft (12) to store potential energy, and the multi-section masses (21) being lowerable in synchronism in the shaft (12) to release the potential energy, wherein each multi-section mass (21) comprises at least two sections (22, 23) clamped together around the cable (13), wherein the multi-section masses (21) nest together side-by-side in the shaft (12) to form an overall composite mass body (20), and wherein the multi-section masses (21) comprise circumferentially adjacent multi-section masses (21), wherein the circumferentially adjacent multi-section masses (21) are fixed to only oppositely wound cables (13).

2. An energy storage system as claimed in claim 1, wherein each cable (13) is attached to a respective winch means (11).

3. An energy storage system as claimed in claim 1, wherein the composite mass body (20) is cylindrical and there are four multi-section masses (21) each forming a quadrant of the cylindrical mass body.

4. An energy storage system as claimed in claim 3, wherein each quadrant (21) comprises an inner section (22) and an outer section (23) together defining a conduit (27) through which the cable (13) passes and in which the cable (13) is gripped.

5. An energy storage system as claimed in claim 1, wherein there are a plurality of composite mass bodies (20) suspended by the cables (13) one above the other in the shaft (12), each mass body being spaced from the adjacent mass body(s).

6. An energy storage system as claimed in claim 1, wherein the outer surface of each multi-section mass (21) of the composite mass body (20) has at least one hardened steel strip (24).

7. An energy storage system as claimed in claim 1, wherein to store potential energy each multi-section mass (21) is raised by power derived from a source of renewable energy.

8. An energy storage system as claimed in claim 7, wherein the source of renewable energy comprises wind, wave or solar energy.

9. An energy storage system as claimed in claim 1, wherein to store potential energy each multi-section mass (21) is raised by electrical or hydraulic energy.

10. An energy storage system as claimed in claim 1, wherein the released potential energy is converted to electrical or hydraulic energy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which;

(2) FIG. 1 is a schematic view of an embodiment of an energy storage system according to the invention;

(3) FIG. 2 is a schematic view of a winch unit and shaft of the system of FIG. 1;

(4) FIG. 3 is another schematic view of the winch unit and shaft of FIG. 2;

(5) FIG. 4 is a schematic cross section view of the apparatus of FIG. 1 and a shaft;

(6) FIG. 5 is a perspective view of a mass body according to the invention;

(7) FIG. 6 is a perspective view of a mass quadrant unit of the mass quadrant unit of the body of FIG. 5;

(8) FIG. 7 is a perspective view of one mass quadrant unit of FIG. 6;

(9) FIG. 8 is an exploded perspective view of the mass quadrant unit of FIG. 7; and

(10) FIG. 9 is a perspective view of a number of the mass bodies and quadrant units fixed on respective cables.

DETAILED DESCRIPTION

(11) Referring now to the drawings wherein similar numerals have been used to indicate like parts, there is shown therein an energy storage system generally indicated at 10 according to the invention.

(12) The energy storage system 10 comprises a plurality of traction winch units 11a, 11b, 11c and 11d disposed around a purpose-build or suitable pre-existing substantially vertical subterranean shaft 12. Each winch unit 11a-11d comprises a steel cable 13a-13d engaged on a fraction type winch system 14 and has a storage reel 15. Spooling guides 16 lead each cable 13a-13d from a respective winch system 14 to an associated storage reel 15. Respective leading sheaves 17 guide the cables 13 into the shaft 12 to support a series of composite mass bodies 20 spaced vertically one above the other in the shaft. A series of motor-generators 18 (FIG. 3) are provided to either drive the traction winches 14 in a forward direction to raise the mass bodies (20) in the shaft (12) to store potential energy, or to generate power as the winches 14 are driven in reverse by the mass bodies 20 falling in the shaft 12, as will be described below.

(13) Referring now to FIGS. 5-9, there is shown a composite mass body 20 which is attached to the four cables 13 and suspended in the shaft 12. Each mass body 20 comprises four quadrant units 21 which co-operate or nest together side by side in the shaft to form the overall composite mass body 20. Each quadrant unit 21 comprises an inner section 22 and an outer section 23. The outer surface of the outer section 23 has a plurality of hardened steel strips 24 fixed thereon. The inner and outer sections are clamped together by a means of bolts 25 engaging in corresponding holes 26 to define a vertical cylindrical recess or conduit 27 to accommodate a respective steel cable 13. The cable 13 passes through and is gripped by the conduit 27 so that the quadrant unit 21 is clamped to the cable.

(14) The quadrant units 21a, 21b, 21c and 21d (FIG. 6) are mounted on respective cables 13a, 13b, 13c and 13d in the manner aforesaid so that the circumferentially adjacent cables are of the opposite right and left hand “lay”. The overall arrangement (FIG. 9) is such that a plurality of quadrant units 21a-21d are mounted on and spaced one above the other on a respective cable 13a-13d, each set of quadrant units 21a-21d being horizontally aligned to form the composte mass bodies 20. The cables 13a-13d are attached to the respective traction winches 11a-11d.

(15) A particular example of a gravitational potential energy storage system that can be numerically demonstrated to have a gross capacity of just over 5 MWh is disclosed as follows.

(16) A vertical shaft 12 may be constructed having a depth of 1,700 meters. This shaft 12 may be lined with suitable material to provide structural stability to the shaft wall throughout its projected lifespan, the finished internal diameter of the shaft may be 850 mm.

(17) The total required mass being used to store a 5 MWh capacity in this shaft may be in the order 1,600.00 tonnes.

(18) The mass units 21a-21d may be suspended in the shaft in 4 separate “lengths” each of 400 tonnes.

(19) Each “length” is suspended on a separate steel cable, i.e. in this example there are four separate cables 13 required to suspend the total mass of 1,600 tonnes in the shaft.

(20) Each steel cable 13a-13d may have a diameter of 92 mm each with a minimum breaking force of 670 tonnes.

(21) For ease of construction installation and operation each “length” is assembled in modular units to make up the total of 400 tonnes in each case.

(22) These modular units may be cast using Lead and may be designed to be individually held in position on their respective steel cables by means of each module having been fabricated in two parts 22, 23 through a vertical cross section, the resultant two parts may bolt together around the cable in a manner that can exert perpendicular pressure upon the cable to which it is attached.

(23) Each modular unit 21a-21d may be manufactured so as to form, when fixed in position on the cable, a quarter segment of a vertical cylindrical section 21 that may have a total diameter of 740 mm.

(24) Each modular unit 21 may be 2.9 meters long and fitted along its length with vertically aligned hardened steel “protective strips” 24. The “protective strips” may serve to isolate the Lead material of each “modular unit” from contacting with the shaft lining and also may reduce friction.

(25) The radius of each modular unit 21 may be 370 mm in total, including tolerances which may provide an element of dynamic flexibility when moving in the vertical shaft.

(26) Each individual length of “modular units” which may form 400 tonnes of mass, together with its respective steel cable will be independently attached to “Traction Winch” type hoisting and lowering equipment, i.e. a total of four “Traction Winches 14a-14d may be employed in this example.

(27) Each “Traction Winch” may have its own cable storage reel 15 with sufficient capacity for the required function of the system.

(28) The four “Traction Winches” may have control systems facilitating them to operate in a synchronous manner with respect to each other, throughout the cycle of storage and regeneration of energy.

(29) The “modular units” 21 that comprise the “lengths” of the 400 tonne masses may accordingly be aligned horizontally in the shaft, and may be raised and lowered as one unit by the four synchronised “Traction Winches”.

(30) In this manner they form cylindrical sections vertically “stacked” along the lengths of the four steel cables. There may be a gap of 150 mm allowed between each aligned cylindrical section to facilitate flexibility during operation.

(31) A total of thirty five cylindrical sections 21 may be mounted in this manner, resulting in the total mass required of 1,600 tonnes being achieved, and culminating in the total installed length of the mass to be 427 meters overall, not accounting for any torsional elasticity that may occur in the cables.

(32) The total combined mass in the shaft may increase with depth due to the additional mass of the lengthening cable, load cells may detect this and the control system may react to impede the rate of descent in order to stabilise the rate at which power is being discharged.

(33) If the modular weight system is configured in the manner described there may be a total of 413 tons of suspended mass on each length of cable at its maximum depth in the shaft, this would include the weight of the 92 mm steel cable 13 at 36 kg's per meter.

(34) Mounted at surface ground level and positioned over the shaft so as to facilitate their attachment to their respective steel cables may be four “Traction” type winches 14a-14d.

(35) The four “Traction Winches may be installed to have equal spacing relative to each other of 90 degrees around the shaft opening. A “leading roller” may be aligned at the shaft opening to guide the transfer of the cable to and from the “Traction Winch” during energy storage and dispatch. Load cells may be positioned in the shafts of the rollers for the acquisition of data by the control system.

(36) Although each “traction winch” may be attached to its own cable length and mass, the collective installation of “traction winches” may control the vertical movement of the total mass jointly in a synchronised mode of operation.

(37) Rotational steel cable 13 is composed of many cores of smaller diameter steel wire which is wound together in a manufacturing process producing either a left or right handed pitch, called a “lay”. To offset any rotational forces that may be present in the cable as a result of this, the four cables may be installed with an alternating sequence of right and left handed “lays” to induce a contra torsional component during their collective operation.

(38) The sequence of energy storage may be initiated by raising the mass vertically in the shaft, the greater the distance that the mass is raised during this sequence can result in the greater the amount of energy stored. This sequence may be either partly or wholly carried out, depending on the quantity of energy being made available for storage, the maximum capacity of the system being the maximum available height/depth of the shaft.

(39) The physical process of raising the mass may be accomplished when each of the “Traction Winch” driving systems 14 are provided with power from a source of energy that is required to be stored. The type of power that may be fed to the “Traction Winch” driving systems may be any combination of electric, hydraulic etc. consequently the driving motors may be matched to be either electric or hydraulic accordingly depending on the designated medium.

(40) In order to provide each “Traction Winch” 14 with the means by which they maybe enabled to raise their respective masses, each individual “Traction Winch” may be driven with at least one electrically or hydraulically powered motor 18 coupled to appropriate gearing which may facilitate the cable being drawn around a system of sheaving rollers, this being configured specifically to exclude loss of traction of the cable during the energy storage sequence.

(41) The driving motors 18 may be directly coupled to the running gear of the “Traction Winches” or coupled via rotational shafting.

(42) All “Traction Winch” driving motors may be configured to facilitate a synchronised process of lifting the combined attached masses vertically in the shaft when they might be powered with energy from various sources for the purpose of conversion to stored potential energy.

(43) Each individual “Traction Winch” may be fitted with at least one electrical generator 18 or hydraulic pump.

(44) Each individual “Traction Winch” electrical generator or hydraulic pump component may be directly or indirectly coupled to the “Traction Winch” running gear so as to form a power take off drive for these components.

(45) Accordingly in order to permit the stored energy to be reactivated a controlled sequence may be initiated whereby these components may be driven to produce either electrical power or pressurised fluid during the rotation of the winch.

(46) The production of kinetic energy during the controlled lowering of the mass 21 may be transmitted via the cables drawn around the “Traction Winch” sheave rollers thereby causing rotation and useful torque which may in turn be converted into electrical energy or hydraulic pressure.

(47) It may suit that the driving and generating components of the “Traction Winches”, whether they may be electric or hydraulic motors, would be configured to act as dual purpose components. In this way the electric motors would also act as electrical generators and accordingly the hydraulic motors would act as hydraulic pumps.

(48) It may also be convenient for specific purposes that any electric or hydraulic combination of these components may be installed to each “Traction Winch” unit. This scenario would for example enable a “Traction Winch” during a storage time sequence to be driven hydraulically whilst, in a following time sequence, being able to reactivate stored energy electrically or vice versa.

(49) The storage and reactivation of energy may be processed using any form of suitable energy from any appropriate source. This may typically be alternating current, direct current, hydraulic pressure circuits and pneumatic systems. The system may successfully convert any type of energy which might be configured to raise the mass partly or wholly in the shaft to potential energy thereby resulting in what may effectively be an indefinite storage period without losses.

(50) A mechanical friction type master brake may fitted to the winch system which when applied will have sufficient capacity to indefinitely halt any downward movement of the suspended mass.

(51) The master brake will be subject to a “normally on” configuration to immobilise the suspended mass in the event that the control system is subjected to total power loss.

(52) A series of sensors may be installed to facilitate a multi-function control system which, inter alia, may be configured to detect the capacity level of the stored energy within the system at any given moment. The controller can then support the diversion of available energy to any vacant storage capacity by further raising the mass using this energy.

(53) Each “Traction Winch” may be driven by motors which are capable of functioning at various levels of power supply inputs and additionally or alternatively be provided with suitable variable gearing at their output shafts. This would facilitate the energy storage process when sources are producing minimum rates of power, while accepting a variance of the velocity at which the mass is being raised. In this way energy that has been stored with relatively low rates of power during a certain time sequence may be regenerated at a much greater rate of dispatch during a shorter time sequence.

(54) Each “Traction Winch” may be coupled to drive generators, pumps, or mechanical systems capable of producing regenerated power at various output levels and additionally or alternatively be provided with variable gearing to their input shafts during a sequence of energy regeneration. Power output levels may consequently be regulated in order to dispatch the stored energy capacity during a selection of time periods. To enable this function a system to control electronic or mechanical components may be provided as a means of varying the allowable time periods for capacity discharge by varying the average descent velocity of the mass.

(55) The control system may regulate the average descent velocity of the mass in a selection of pre-programmed stages, or steps, or by means of a system of infinite variance between a set of maximum and minimum values. It may be commercially expedient at times, to rapidly dispatch stored energy to an electrical grid, especially during circumstances where energy may be continuously available for storage on a routine basis.

(56) The control system function of regulating the mass descent velocity may be accomplished by means of generator load sensing, whereby the electrical load on the generator may be increased or decreased electronically, momentarily causing additional consequent loading on the “Traction Winch” to reduce the pay-out velocity of the cable.

(57) Additionally or alternatively the regulation of the mass descent velocity may be achieved by means of a second stage generator or pump being coupled to a power take off point on the low torque end of the “Traction Winch” output gearing. This second stage generator or pump may be less powerful than the primary generator or pump installations. This second stage component may also be regulated to provide a regenerative braking system during the stored energy retrieval sequence.

(58) Regenerative attenuation of the mass descent velocity may be of significant importance in terms of the overall efficiency of the system.

(59) The control system may be software based using analogue and digital methods to acquire data from a number of various types of sensors, encoders, transducers, load cells etc.

(60) The invention is not limited to the embodiments described herein which may be modified or varied without departing from the scope of the invention.