GB2527195A

GB2527195A - Method and apparatus for generating clean renewable energy through the application of hydrostatic pressure gradients associated with liquid reservoirs

Info

Publication number: GB2527195A
Application number: GB1507475.0A
Authority: GB
Inventors: Ian Robert Fothergill
Original assignee: Julia Ann Fothergill
Current assignee: Julia Ann Fothergill
Priority date: 2014-05-07
Filing date: 2015-04-30
Publication date: 2015-12-16
Also published as: GB201507475D0; GB201408059D0

Abstract

An apparatus is claimed to generate or store energy using a submersible vessel 1 which includes a compressible medium. The vessel 1 is lowered within a liquid reservoir, and then liquid is admitted through a turbine 16, to generate energy as the compressible medium is compressed. The vessel is them moved to a higher level, and liquid is then expelled through a turbine 16 as the compressible medium expands. The invention claims to minimise the energy required to move the vessel by using a counterbalance mechanism which may include a beam 62 with movable weights 71, 73, and a counterweight 68 which is submerged for part of each cycle, connected to the vessel via a pulley mechanism 65, 66, 67 on the beam 62. The compressible medium may comprise a gas, a vapour or a spring biased piston 6 or bellows. As an alternative to using a turbine for energy generation, the compressed gas may be stored in a compressed gas or vapour storage container external to said vessel for later use, see figures 13-15.

Description

Method and Apparatus for Generating Clean Renewable Energy through the Application of Hydrostatic Pressure Gradients associated with Liquid Reservoirs This invention relates to a method and apparatus for generating and or storing clean renewable energy by the utilisation of hydrostatic pressure gradients existing in natural or artificial liquid reservoirs.

The generation of clean energy from thermal gradients within tropical oceanic reservoirs has been successfully exploited using prototype OTEC (Ocean Thermal Energy Conversion) systems together with numerous design proposals see Pearson R.O. US Patent Application No. 681.003, Flynn et.al US Patent Application No. 298664 Ridgeway. S.L. Patent Application No. 680.352 and more generally WEC Survey of Energy Resources 2001 -Ocean Thermal Energy Conversion.

Such methods typically involve evaporating a low boiling point liquid such as ammonia by heat transfer from relatively warm tropical ocean surface waters with useful power being generated by large vapour driven turbines, typically employing a Rankin cycle with exhaust vapour from the turbine being condensed by heat transfer from cold water drawn through long cold water delivery pipes from cool ocean depths. Such closed cycle methods potentially produce clean energy from vapour turbine driven generators. Alternatively open cycle system designs have been proposed whereby warm water from tropical ocean surface layers is used to boil this water when under a low pressure with the potential for energy generation and advantageously production of clean salt free potable water.

The efficiency with which thermal energy associated with relatively warm tropical ocean surface water can be converted into useful power is very small -typically less than 4% -due to the small temperature difference existing between tropical ocean surface regions (typically 25C) and cool ocean depths typically 1,000 metres deep with temperatures approximately 4CC.

Thus to generate reasonably high power output levels operating OTEC facilities would demand enormous cold water delivery pipes, heat exchangers and vapour turbines with resultant very high capital costs and structural integrity implications. Further, OTEC systems can only operate where adequate thermal gradients exist thereby confining them to tropical ocean regions.

It is the objective of this invention to obviate or mitigate the aforementioned disadvantages.

According to a first aspect of this invention there is provided a method for utilising gravitational potential energy associated with hydrostatic pressure gradients within a liquid reservoir and atmospheric pressure acting on said reservoir for the generation of useful power through the steps of alternately transferring a submersible vessel containing a compressible medium between a first and second level within said reservoir said first level being deeper than said second level whereby said compressible medium is compressed at said first reservoir level through the inflow of hydrostatically pressurised liquid into said submersible vessel at this level with said compressible medium expanding at said second reservoir level from reduced environmental hydrostatic pressure at this level thereby driving residual liquid from said submersible vessel with useful power being generated from inflow or outflow of said liquid from said submersible vessel at said first or said second reservoir levels respectively through one or more hydraulic turbines associated with said submersible vessel and with energy to transfer said submersible vessel between said first and said second reservoir levels for direct power generation using said one or more hydraulic turbines minimised through the implementation of a counterbalancing mechanism associated with a support facility for said submersible vessel or as an alternative to said direct power generation using said associated hydraulic turbines and where said compressible medium is a gas or vapour this may be introduced into said submersible vessel at said second reservoir level prior to compression at said first reservoir level followed by transference to a compressed gas or vapour storage container external to said submersible vessel for subsequent utilisation.

According to a second aspect of this invention there is provided apparatus for utilising gravitational potential energy associated with hydrostatic pressure gradients within a liquid reservoir and atmospheric pressure acting on said liquid reservoir for the generation of useful power said apparatus comprising a submersible vessel containing a compressible medium and alternately transferable between a first and second level within said reservoir said first level being deeper than said second level whereby said compressible medium is compressed at said first reservoir level from flow into said submersible vessel of hydrostatically pressurised liquid with said compressible medium expanding at said second reservoir level from reduced environmental hydrostatic pressure at this level thereby driving residual liquid from said submersible vessel with one or more hydraulic turbine means associated with said submersible vessel energised from flow of said liquid into or out of said submersible vessel at said first or second reservoir levels respectively or as an alternative to direct power generation using said associated one or more hydraulic turbines means and where said compressible medium is a gas or vapour this may be introduced into said submersible vessel at said second reservoir level prior to compression at said first reservoir level followed by transference to a compressed gas or vapour storage containment means external to said submersible vessel for subsequent utilisation and with means to support said submersible vessel and alternately transfer it between said first and second reservoir levels together with a counterbalancing means associated with said submersible vessel supporting means to minimise energy requirements for submersible vessel transfer operations between said first and second reservoir levels.

The liquid reservoir may be an ocean or lake or a man-made water containment facility but in all such cases the reservoir depth should be sufficient to provide as large a depth hence hydrostatic pressure difference between said first and second reservoir levels as is technically and economically practical. Further the second relatively low hydrostatic reservoir level should be advantageously located close to the reservoir surface but in the case of oceanic reservoirs the depth of the second reservoir level should be sufficient to prevent potential damage to the submersible vessel from wave action. The inflow of reservoir water into the submersible vessel at the first relatively deep reservoir level will compress the compressible medium contained within the submersible vessel together with increasing its weight by the weight of the volume of water forced into the submersible vessel. On transference of the submersible vessel to the second reservoir level with reduced hydrostatic pressure the water payload will be forced out of the submersible vessel from expansion of the residual compressible medium with a resultant reduction in the weight of the submersible vessel. The option exists to generate clean energy from the inflow and outflow of water into or from the submersible vessel using one or more associated hydraulic turbines. Where a compressible medium is a gas or vapour then as an alternative to direct power generation through energisation of one or more hydraulic turbines from water flow, compressed gas or vapour at the first reservoir level may be fed to a submerged gas or vapour containment facility preferably at or close to the first reservoir level depth with hydrostatic pressures comparable to the gas or vapour pressure within the submersible vessel thereby minimising any stresses within the submerged gas or vapour containment due to minimal pressure gradients across its walls. Alternatively transfer of compressed gas or vapour to a surface or near surface containment in the form of a pressure vessel may be facilitated through pipe work extending from the submersible vessel to the pressure vessel. In such cases the structural integrity of the pressure vessel would need to be significantly greater than that for a submerged gas or vapour containment facility including the requirement for relatively thick pressure vessel walls due to the large pressure differential across them generated by the relatively high compressed gas or vapour internal pressure but low atmospheric external pressure.

Where a gas or vapour is potentially interactive with reservoir water it can be isolated from this water by means of a piston within a preferably cylindrical submersible vessel thereby isolating the compressible contents from the water payload.

In order to minimise energy requirements for submersible vessel transfer operations between first and second reservoir levels a counter balancing facility may be deployed but to accommodate variations in the submerged weights of the submersible vessel corresponding to its flooded and voided conditions at the first and second reservoir levels respectively a counter balance must be responsive to such weight changes thereby confining submersible vessel transfer energy requirements to overcoming viscous drag forces from movement through the reservoir. These can be minimised through submersible vessel streamlining. Also energy demands from inertial forces during acceleration periods are potentially recoverable.

It has been explained herewith how a compressible medium in the form of a gas or vapour may be deployed for direct energisation of one or more hydraulic turbines associated with the submersible vessel or in its compressed condition transferred to a locally submerged or relatively remote near surface submerged pressurised gas or vapour containment facility in the form of a pressure vessel thereby providing a long term energy storage facility for subsequent local or remote utilisation. However for energisation of one or more hydraulic turbines alternative compressible media may be deployed including mechanical springs, cellular rubber or thermo plastic substances, sponge of natural or synthetic rubber or one or more impermeable pressurisible gas or vapour containment bags. In all such cases and others a compressible medium must preferably behave elastically with no permanent creep or deformation from successive compression and expansion cycling. Further reference has been made herewith to a cylindrical geometry submersible vessel with a piston to isolate an internal compressible medium from environmental water. However alternative configurations of a submersible vessel may be deployed including a bellows secured within a cylindrical chamber or an impermeable bag contained within a rigid chamber and formed from flexible plastics for example with both options providing the means for gas or vapour containment and direct energisation of one or more hydraulic turbines or storage through transfer in compressed form to a local submerged or relatively remote near surface compressed gas or vapour storage facility. For direct power generation using one or more hydraulic turbines on board the submersible vessel gas or vapour compressed at the first reservoir level may be valved into an additional pressure chamber within the submersible vessel's main chamber for release and discharge of residual water in the main chamber of the second reservoir level to drive hydraulic turbines.

In circumstances where only energy storage is required rather than on board direct power generation a bellows or impermeable bag in the absence of a rigid container may be deployed. If a gas or vapour from an external source to be compressed prior to transfer to an external container has a pressure greater than that at the second reservoir level then the bellows or impermeable bag can be inflated at this level through appropriate valving and on lowering of the bellows or impermeable bag-possibly with the aid of ballast to create neutral or negative buoyancy for compression at the first reservoir level. The resultant compressed gas or vapour can then be transferred to an external storage container. Alternatively for a gas or vapour source less than the hydrostatic pressure at the second reservoir level a compressible medium such as an open cell sponge or foam substance or spring -with properties to expand at the second reservoir level but compress at the first reservoir level -can be deployed by locating and securing the compressible medium within the bellows or impermeable bag as appropriate. With the bellows or impermeable bag expanded at the second reservoir level from expansion of the contained compressible medium and with appropriate ballasting lowering to the first reservoir level will compress the compressible medium and hence gas or vapour contained within the bellows or impermeable bag thereby facilitating transfer of the resultant compressed gas or vapour to an external containment facility. With the bellows or impermeable bag depleted of their gas or vapour contents but remaining in their compressed condition by an appropriate securing mechanism applied to the compressible medium contained within the compressed bellows or impermeable bag these can be transferred back to the second reservoir level where the securing mechanism can be released allowing expansion of the compressible medium hence bellows or impermeable bag-void of gas or vapour-and thereby depressurisation and drawing in of gas or vapour from a relatively low pressure source which may be atmospheric air or gas or vapour from an external submerged or floating low pressure containment facility.

It will be understood that the means for depressurising the aforesaid bellows or a bag for gas or vapour introduction using a resilient internal member and vent valving can equally be deployed for piston and cylinder configurations or a bellows or bag in a rigid containment thereby facilitating accumulation of successive compressed gas or vapour charges within an external submerged or surface containment facility as an alternative to direct power generation using associated hydraulic turbines.

In the case of a gas such as air, nitrogen or any other gas or vapour non-reactive with reservoir water isolation from the water using a piston, bellows or bag may prove unnecessary where the submersible vessel's gas containment volume is essentially vertically orientated with its closed end uppermost and outlet or opening lower most. This will provide a liquid piston formed from the reservoir water free surface within the submersible vessel which will be forced into the gas containment volume through a valved inlet port at the first reservoir level from relatively high hydrostatic pressure forces. These will compress residual gas or vapour within this volume with this gas or vapour expanding at the second reservoir level from reduced environmental reservoir hydrostatic pressure thereby driving residual water out of the submersible vessel through a power generating hydraulic turbine. For such direct power generation one or more hydraulic turbines would be located at the base of the submersible vessel with associated residual water outlet ports having geometrical configurations such as contouring designed to minimise flow impedance and any bypass flow for optimisation of hydraulic turbine or turbines power generation levels. Note the inlet port would be closed during this power generation period at the second reservoir level.

Instead of compressing residual gas or vapour at the first reservoir level for power generation at the second reservoir level as described herewith direct power can be generated at the first reservoir level by closing the inlet port and driving a bi-directional hydraulic turbine from flow of relatively high pressure water into the submersible vessel or by using two hydraulic turbines one energisable from water flow into the submersible vessel at the first reservoir level as for the bi-directional turbine deployment and the other energisable from water flow from gas or vapour expansion at the second reservoir level. However by driving a hydraulic turbine at the first reservoir level the resultant water pressure at the turbine outlet would be reduced from that from direct inflow via the inlet port or ports thus reducing the level of compression of residual gas or vapour hence power generation output at the second reservoir level. However for power generation at the first reservoir level power output levels may be increased by venting the gas or vapour containment in the submersible vessel to either atmosphere for air or to a relatively low pressure external gas or vapour container for air or other gases or vapours. Such a gas or vapour container may comprise of an inverted chamber supported by a floating vessel or pontoon or by anchor lines secured to the reservoir bed or for relatively shallow reservoirs supported by a platform or rig secured to the reservoir bed. In all such cases the inverted chamber would be located close to the reservoir surface to provide a volume above the water free surface under the chamber with a pressure equal to the surrounding reservoir relatively low hydrostatic pressure. For gases or vapours interactive with water the chamber volume may be isolated from the reservoir by means of a piston or flexible impermeable membrane or by deploying a chamber with a bellows configuration.

S

In circumstances where a gas or vapour is compressed at the first reservoir level it may be stored if required in an external submerged or surface storage container. Hydraulic turbines deployed for direct power generation on the submersible vessel would in this case be closed with pressurised water flowing through one or more flow inlet ports to facilitate compression of residual gas or vapour these ports being closed during direct power generation. For direct power generation only at the second reservoir level the ports would be open at the first reservoir level but closed at the second with the hydraulic turbine or turbines closed at the first reservoir level and open at the second reservoir level.

For compressed gas or vapour storage the flow inlet ports would be opened during the gas compression period at the first reservoir level as herewith described with resulting compressed gas being forced through an outlet pipe or conduit located at or towards the closed end, when uppermost, of the gas or vapour containment volume within the submersible vessel and into a remote gas storage container. To facilitate multiple charging for accumulation of compressed gas or vapour in a remote storage container when deploying a liquid piston all turbine closures and inlet ports would be closed with gas being drawn from an external source into the submersible vessel containment volume at the second reservoir level from expansion of a compressible medium within this volume as here before described and with the closures only being opened at the first reservoir level to compress the residual medium and gas or vapour for transference to the remote storage containment. The remote gas or vapour container can be spatially stabilised by hanging it from a surface floating platform or pontoon using anchor lines so long as the mean density of the container is greater than water when fully charged with compressed gas or vapour. Alternatively a remote gas or vapour container can be spatially stabilised using anchor lines secured to the reservoir bed if its mean density remained less than that of water throughout its compressed air accumulated charging cycle.

Transfer of accumulated gas or vapour to a remote container may be facilitated through a compressed gas or vapour conduit or pipe-which may be flexible-leading to a compressed gas container on a surface vessel for transportation to a location for subsequent utilisation or remote storage.

As an alternative to transfer of accumulated gas from a submerged containment through a conduit or pipe to a surface vessel the submerged container could be temporarily secured to the reservoir bed by means of anchor lines secured to the reservoir bed but released when fully charged with compressed gas with its maximum buoyancy whereby it could rise to the reservoir surface under positive buoyancy preferably guided on a rail or stably secured line or the like. On reaching the reservoir surface the container could be transferred onto a surface compressed gas container vessel for transportation to a remote utilisation location. Advantageously the transportation vessel would carry and replace the charged containment vessel with an uncharged one whereby it can be flooded at the surface to create negative buoyancy to facilitate guided descent to the first reservoir level for subsequent accumulation of compressed gas derived from the submersible vessel. The aforesaid accumulated compressed gas or vapour container would preferably be streamlined to minimise viscous drag during transfer periods and may be equipped with on board hydraulic turbines energised from movement of the containment to or from the surface vessel.

Successive transfer of the submersible vessel between first and second reservoir levels for either on board power generation using hydraulic turbines or compressed gas or vapour storage using a submerged container secured at or close to the first reservoir level or at or close to the reservoir surface or using a mobile container for transferring accumulated compressed gas or vapour charges to a surface transportation vessel requires a means for both supporting and propelling it between the first and second reservoir levels. A preferred embodiment of the invention comprisesa chain or cable or the like from which the submersible vessel is suspended at one chain or cable end with the other end after passing over a chain or pulley wheel supporting a counter weight. An alternative means for supporting the submersible vessel and transferring it between first and second reservoir levels comprises a differential pulley with the chain or cable supporting the submersible vessel wound around the larger radial member of the differential pulley and a second chain or cable wound around the smaller member and supporting a counterweight such that the turning moments generated by the submersible vessel and counter weight are in opposite senses in order to create a balance between the two. For either chain wheel or pulley wheel with a single chain or cable respectively connecting both submersible vessel and counter weight or differential pulley securing separate chains or cables for the submersible vessel and counter weight facilities are deployed to accommodate changes in the counter weight's turning moment in response to changes in the submersible vessel's weight corresponding to its flooded or voided condition and thereby enabling balance conditions between the submersible vessel and counter weight to be effected. This will limit energy demands in transferring the submersible vessel between first and second reservoir levels to overcoming viscous drag forces with energy demands from forces from accelerations being potentially recoverable. Further the support of the submersible vessel from the larger radial member of the differential pulley rather than the smaller one will facilitate vessel transfer to relatively large depths compared to the corresponding range of movement of the counterweight vessel.

Specific embodiments of the invention will now be described by way of example only with reference to the accompanying drawing in which:-Fig. 1 shows a schematic illustration of a submersible vessel with a cylindrical main chamber and a piston for isolating a residual compressible medium from reservoir water.

Figs. 2a-c show a schematic illustrations of a weighted piston within a submersible vessel's cylindrical main chamber vented to atmosphere or to an external inverted chamber containing pressurised gas or vapour.

Figs. 3a-b show schematic illustrations of a submersible vessel at the second reservoir level Fig. 3a and the first reservoir level Fig 3b.

Figs. 4a-b show schematic illustrations of a bellows configuration for containment of residual gas or vapour within a submersible vessel's main chamber.

Figs. 5a-b show schematic illustrations of a compressible medium formed from a closed cell foam or sponge of natural or synthetic rubber or thermoplastics at the second Fig. Sa and first Fig. Sb reservoir levels.

Figs. 6a-b show schematic illustrations of a compressible medium formed from an impermeable bag for containing a resilient porous or open cell substance secured within a submersible vessel together with a gas or vapour source container Fig. 6a and a storage container for compressed gas or vapour Fig. Gb.

Figs. 7a-b show schematic illustrations of a compressible medium in the form of a spring within the main chamber of a submersible vessel.

Figs. 8a-b show schematic illustrations of a hydraulic turbine and inlet port located at the upper end of a submersible vessel.

Fig. 9 shows a schematic illustration of a submersible vessel shell with it's axis horizontal.

Figs. 1 Oa-b show schematic illustrations of a submersible vessel with a second chamber located within and towards the top of the main chamber. n j

Figs. 11 a-c show schematic illustrations of a system for compressing a gas or vapour transferable through a flexible extendible pipe from an external source.

Fig. 1 2 shows a schematic illustration of an arrangement for transferring compressed gas or vapour to an external container.

Figs. 1 3a-b show schematic illustrations of an inverted chamber local to a submersible vessel at the first reservoir level with a pump in the compressed gas or vapour transfer pipe.

Figs. 1 4a-b show schematic illustrations of a mechanical spring for depressurising the volume above the piston in a submersible vessel.

Figs. 1 5a-b show schematic illustrations of a bellows spring filled with a gas or vapour.

Figs. 1 6a-b show schematic illustrations of a method for compressing a gas or vapour from an external source using a piston and cylinder located on the outer surface of the closed end of a submersible vessel.

Figs. 1 7a-e show schematic illustrations of an energy conversion system deploying a beam pivoted at a position offset from its mid point and supporting a submersible and counterweight vessel connected by a cable.

Figs. 1 8a-e show schematic illustrations of an energy conversion system deploying a pivoted beam with a differential pulley at one end connected to which are individual cable's one supporting a submersible vessel and the other after passing over an idler pulley supporting a counterweight vessel Figs. 1 9a-e show schematic illustrations of an energy conversion system deploying two intersecting beams and supports with a differential pulley axial at the beam intersection point and supporting via separate cables a submersible and counterweight vessel.

Figs. 20a-e show schematic illustrations of an energy conversion system deploying submersible vessel transferable along a vertical guide rail and connected via a cable passing over a pulley to an adjustable floodable counterweight vessel transferable along an inclined guide rail.

Figs. 21 a-e show schematic illustrations of an energy conversion system deploying a differential pulley supporting via individual cables a submersible and adjustable floodable counterweight vessel both vertically transferable.

It has been stated herewith that the energy conversion system described may be supported on a floating pontoon. However alternative support facilities also exist including a floating vessel which as with a pontoon support would preferably deploy spatial stabilisation facilities by means of tension lines extending from the vessel or pontoon to the reservoir bed where they would be securely anchored. Alternatively a more rigid and spatially stable arrangement could be deployed in the form of steel support legs extending from the energy converter to the reservoir bed where they would be securely embedded as for standard oil rig designs.

Further as well as generating power using hydraulic turbines directly on an energy converter gas or vapour compressed at the first (deepest) reservoir level could be transferred to and stored in a local submerged containment or a remote surface or near surface containment for subsequent utilisation.

Referring to a drawing in Figs. 1 -1 6 these show different configurations of submersible vessel 1 submerged in a reservoir 2. The submersible vessel 1 geometries described are all cylindrical. However different geometries may be deployed (not shown) subject to the underlying operating principles described being applicable. Also shown in Figs. 1 -16 are different types of compressible media deployable. For reasons of clarity these figures exclude details of submersible vessel support and associated facilities such as counterbalancing but make reference to supporting cables or chains. Further as has been described herewith submersible vessels in operation for power generation or energy storage are transferred alternately between a first (lower) reservoir level 3 and a second (upper) reservoir level 4 within the reservoir 2 and because of the relative movement of the submersible vessel 1 suffer viscous drag forces hence increased energy demands on transfer processes. These can be significantly reduced by appropriate submersible vessel and associated equipment streamlining but again for reasons of clarity details of this streamlining are excluded from these figures.

Fig. 1 shows a submersible vessel 1 with a cylindrical main chamber 5 and piston 6 isolating the water 7 from a compressible medium which in this case is a gas or vapour 9. In this figure the submersible vessel 1 is shown submerged in the reservoir 2 at the second reservoir level 4 with the compressible medium 9 trapped in a compressed state between the upper face 1 0 of piston 6 and underside 11 of main chamber 5 uppermost closed end 12. For reasons of clarity the submersible vessel's support facility is not shown here. The piston 6 is latched in this position by a latching mechanism 1 3 to prevent expansion of the residual compressed gas or vapour 9 until required. The Fig. 1 shows the submersible vessel with its axis 14 vertical and with the base 1 5 of the main chamber 5 supporting a hydraulic turbine 16 with an associated closure valve 1 7 (shown open) and with an inlet port 18 with a closure valve 1 9 (shown closed) extending downwards from the base 1 5 of the main chamber. It will be noted that the inlet port 1 8 can also operate as an outlet port.

On releasing the piston 6 compressed gas or vapour 9 will expand forcing the piston 6 down and residual water 7 out of the submersible vessel 1 through the hydraulic turbine 16 which advantageously will be bi-directional thereby generating useful power irrespective of flow direction. As an alternative to deployment of a bi-directional hydraulic turbine two individual mono-directional hydraulic turbines (not shown) may be deployed one configured for power generation from flow in one direction and the other for flow in the opposite direction. During flow through the hydraulic turbine 16 the inlet port 18 closure valve 19 will be closed. It will be understood that for the bi-directional hydraulic turbine 16 at the second reservoir level 4 the outlet designated as 20 in references herewith involves water flow from within the submersible vessel 1 through the hydraulic turbine 16 inlet 21 within the submersible vessel's 1 base 1 5 and after hydraulic turbine 16 power generation discharge through the outlet 20 to the reservoir 2. For hydraulic turbine 1 6 power generation from water flow from the reservoir 2 at the first reservoir level 3 and into the submersible vessel 1 via the hydraulic turbine 1 6 the designated outlet 20 on the reservoir side of the hydraulic turbine 16 will operate as an inlet and the designated inlet 21 within the submersible vessel 1 will operate as an outlet. It will be noted that if the compressible medium is a gas then continued expansion from its compressed state at the second reservoir level 4 will generate a progressively lower pressure driving the piston 6 down and thereby a corresponding reduction in output power from the hydraulic turbine 1 6 this power being dependent upon the pressure difference between the expanding gas pressure and hydrostatic pressure at the outlet 20 of the hydraulic turbine 16. To maintain power generation from the hydraulic turbine 16 throughout the full stroke of the piston 6 the gas pressure at its fully expanded state with the piston 6 at or towards the base 1 5 of the main chamber 5 must exceed the hydrostatic pressure at the reservoir 2 side of the hydraulic turbine 16 i.e. its outlet 20 for this water 7 discharge condition. Instead of using a gas as a compressible medium a vapour may be used which, if unsaturated, would suffer a fall in vapour pressure with expansion. If however the vapour remained saturated throughout the expansion process its pressure for isothermal conditions would remain constant producing a constant force driving the piston 6 through its stroke and thereby discharging residual water 7 through the hydraulic turbine 16 with the generation of a more constant output power than would occur for an unsaturated vapour. For either saturated or unsaturated conditions for finite power generation the vapour pressure must exceed the hydrostatic pressure at the outlet 20 of the hydraulic turbine 16 when the latter is being energised from pressurised water 7 flow from the submersible vessel 1 at the second reservoir level.

A further alternative to a gas or vapour driving a piston 6 down at the second reservoir level 4 for discharge of residual water through the hydraulic turbine 16 for power generation would be to deploy a weighted piston 22 with the gas or vapour 9 above it or indeed with this volume above the piston 22 vented to atmosphere via a pipe 23 (see Fig. 2a) or to an external source of gas or vapour of constant pressure transferable through the pipe 23 or an alternative pipe (not shown) from an inverted chamber 25 (see Fig. 2b) located within a depth of the reservoir? such that the pressure applied to the piston 22 in combination with its weight and the weight of residual water 7 exceeded the hydrostatic pressure at the outlet 20 of the turbine 1 6.

The inverted chamber 25 support (not shown) could be from a floating vessel or pontoon or could remain buoyant and be spatially secured with anchor lines or supported on a rig secured to the reservoir bed. The inverted chamber 25 would trap a volume of gas or vapour 9 above the reservoir 2 free surface 24 under the chamber 25. If required the gas or vapour 9 could be isolated from the reservoir by means of a piston 26 as shown in Fig. 2c. This external gas or vapour source facility if at a depth to provide a higher gas or vapour pressure than the hydrostatic pressure at the outlet of the hydrostatic turbine 16 would in fact be suitable for use with either an unweighted piston 6 or a weighted piston 22 in the submersible vessel 1. In either case in order to charge the submersible vessel at the second reservoir level with gas or vapour for compression at the first reservoir level residual water 7 from the submersible vessel 1 must be driven out of the vessel 1 through the outlet port 1 8 or through the hydraulic turbine 16 (with relatively low level power generation). However in the case of an unweighted piston the pressure within the inverted chamber 25 hence it's depth would need to be greater than that when a weighted piston 22 was deployed. Following the discharge of water from the submersible vessel 1 there will be a resultant weight loss in the submersible vessel equal to the weight of water forced out but the submersible vessel will be configured to possess zero or negative buoyancy even when totally voided of water to provide corresponding zero or finite tension respectively in the supporting chain or cable (not shown). Figs. 3a-b show the submersible vessel 1 (voided of water) being transferred from the second reservoir level 4 (Fig. 3a) to the first level 3 (Fig. 3b) (shown flooded) using a supporting cable 27 and counter balancing mechanism -details not shown in Figs. 3a-b but to be described later.

The depth of the first reservoir level 3 will be chosen to have a hydrostatic pressure greater than the residual gas or vapour 9 pressure acting on the piston 6 together with the downward force of a weighted piston 22 (if deployed) and the weight of residual water 7 within the submersible vessel 1.

With the submersible vessel 1 at the first reservoir level 3 (Fig. 3b) for direct power generation from energisation of the hydraulic turbinel 6 the inlet port 18 closure valve 1 9 will be closed with reservoir water being forced through the hydraulic turbine 16 into the submersible vessel 1 with the resulting hydrostatically pressurised water acting on the underside of the piston 6.

The hydraulic power generated by the hydraulic turbine 16 during this process will increase with the pressure differential across it. It will be recalled that the hydraulic turbine 16 is bi-directional or is the one of a pair of mono-directional hydraulic turbines drivable from flow from the reservoir 2 into the submersible vessel 1 with the other mono-directional hydraulic turbine being drivable from flow in the opposite direction. For finite power generation the external reservoir 2 hydrostatic pressure at the first reservoir level must exceed the opposing residual gas or vapour 9 pressure by an amount greater than the pressure drop across associated flow passages and more significantly that across the hydraulic turbine 16 when energised from forcing water through it into the submersible vessel 1. For a gas or unsaturated vapour compressible medium 8 the opposing pressure will increase progressively with the level of compression or for an isothermal saturated vapour the opposing compressive pressure will be constant.

The compressible media and vessel configuration for direct power generation in the submersible vessel's main chamber S described herewith have been gas or vapour 9 acting on a piston & within the chamber 5 but alternative compressible media and configurations can be deployed. Figs. 4a-b show a configuration utilising a bellows 28 for containment of a gas or vapour 9 instead of a piston the bellows 28 being secured to the underside 11 of the upper end 12 of the submersible vessel's 1 main chamber S and with an end plate 29 latchable with a mechanism 1 3 located towards the upper end of the chamber S for retention of the gas or vapour 9 when compressed. The gas or vapour 9 within the bellows 28 would be isolated from external water and on release of the latching mechanism be fully expanded after power generation at the second reservoir level 4 (Fig. 4a) prior to transfer for compression at the first reservoir level 3 (Fig.4b). The hydraulic turbine 1 6 would be advantageously bi-directional as for the system deploying a piston 6 and located in the outlet port 20 of the submersible vessel's main chamber 5 below the base 1 5 of the chamber 5 adjacent to an inlet port 1 8. Apart from the means for isolating the contained gas or vapour from the water environment using a bellows 28 rather than a piston 6 the bellows 28 arrangement will operate in essentially the same manner as the piston 6 in generating clean hydraulic power from alternate transfer of the submersible vessel 1 between first 3 and second 4 reservoir 2 levels.

A second alternative to using a piston 6 or bellows 28 arrangement contained within a submersible vessel 1 for trapping a volume of gas or vapour for pressure cycling is shown in Figs. Sa-b and uses a closed cell foam or sponge of natural or synthetic rubber or thermoplastics 31 to provide a compressible medium which is contained in the main chamber 5.

Attached to the base of the closed cellular volume 31 would be a solid latchable end plate 33 for engagement with a latching facility 1 3 to facilitate retention of the compressed state of this closed cellular volume 31 induced at the first reservoir level 3 prior to release and expansion at the second reservoir level 4 with Fig. 5a showing the expanded state and Fig. 5b the compressed state. This closed cell compressible medium 31 would contain within its cellular structure a gas or vapour which when uncompressed would be at atmospheric pressure or at a higher pressure compatible with the strength of the cellular material and construction. The closed cellular configuration would provide inherent isolation of contained gas or vapour from residual water 7 derived from the reservoir 2 thereby avoiding any sealing limitations associated with the solid end plate 33. It will be appreciated that this closed cell form of compressible medium would only be suitable for power generation using hydraulic turbines on a submersible vessel but could not be deployed for gas or vapour compression then transfer to an external container for storage of compressed residual gas or vapour trapped within the closed cellular volume.

It will be noted that apart from gas or vapour based compressible media where isolation from reservoir 2 is permanent as for described for example with reference to Figs. 1-2 the pipe 23 deployed for transferring atmospheric air or relatively low pressure gas or vapour from an external source to the submersible vessel 1 at the second reservoir level for compression at the first reservoir level as herewith described can also be deployed for transferring gas or vapour compressed at the first reservoir level to an external container. For either application appropriate valving within the pipe 23 or its inlet or outlet would be necessary to facilitate conditions for flow of relatively low pressure gas or vapour into the submersible vessel at the second reservoir level or out flow of compressed gas or vapour at the first reservoir level to an external container. Advantageously the pipe 23 would be flexible and extendable to facilitate different separations of the submersible vessel from the external container.

A further alternative compressible medium contained within an impermeable bag 34 shown in Figs. 6a-b comprises a resilient compressible volume of a porous or open cell substance 35 secured within the main chamber 5 and with a solid latchable end plate 36 secured to its base to facilitate retention of compression induced at the first reservoir level 3 as for closed cell configurations described herewith. The resilient properties of the substance in combination with those of any gas or vapour contained within the impermeable bag 34 would be chosen to facilitate expansion and compression at the second reservoir level 4 (Fig. 6a) and the first reservoir level 3 (Fig. 6b) respectively with hydraulic power from the hydraulic turbine 16 generated as for configurations herewith described. Such an arrangement could also be used potentially to transfer, store and accumulate gas or vapour compressed at the first reservoir level 3 in a pressure container at or close to this level (to limit residual stresses in the container walls) but external to the submersible vessel 1. To implement this the impermeable bag 34 may be secured to the top end plate 12 in the main chamber 5 with relevant connections incorporated into this end plate 1 2 to facilitate transfer of compressed gas or vapour from the bag 34 through the pipe 23 to the external pressure container. Fig. 6b shows such a container in the form of an inverted chamber 37 which could be supported by a reservoir bed mounted rig or if remaining buoyant throughout its operational range by means of anchor lines Alternatively it could be suspended from a surface vessel or pontoon by cables or the like but in such cases would be vulnerable to currents if the reservoir was an ocean.However if the reservoir was a relatively deep lake or other natural or artificial water environment suspension of the container 37 or indeed container 25 from a surface vessel or pontoon would be feasible.

It will be recalled herewith and with reference to Fig. 2 and Fig. 6a that the pipe 23 could be used to transfer relatively low pressure gas or vapour from an external source including the atmosphere or contained in an inverted chamber 25 located at a relatively shallow depth in the reservoir 2 and supported by means described herewith with reference to Fig. 2b and Fig. 2c. However as mentioned herewith the pipe 23 could also be used to transfer compressed gas or vapour from the submersible vessel 1 to the external container 37 through connecting valves in the container and submersible vessel and possibly with the aid of a pump (not shown) and with the container 37 located at or close to the relatively deep first reservoir level 3. As an alternative to a deeply submerged inverted chamber 37 this compressed gas or vapour container could comprise of a local or remote pressure vessel (not shown in Fig. 6). It will be appreciated that this method for transferring and storing compressed gas or vapour in an external container can be deployed for other submersible vessel based energy conversion systems where the compressible medium 8 is a gas or vapour 9 and transferable to the submersible vessel 1 from an external source.

For all system configurations described herewith and to be described In order to maximise compression pressures in the main chamber S from hydrostatically pressurised water flow into the submersible vessel at the firstreservoir level for compressed gas or vapour storage in an external container and in the absence of power generation by on board hydraulic turbines 16 the turbine inlet port 20 may be closed with flow being redirected through the inlet port 19 thereby avoiding any pressure drop across the turbine 16. In Figs. Ga-b the port 20 is shown open for power generation but redirected flow through the inlet port 1 9 for greater compression levels can be implemented by closing the closure facility 1 7 to prevent flow through the port 20 and opening the closure facility 1 8 to permit flow through the inlet port 1 9.

Instead of deploying a gas or vapour compressible medium contained within the configurations described a cylinder and piston configuration deploying a spring could be used. Figs. 7a-b show a submersible vessel 1 with a spring 38 secured to the underside 11 of the top end 1 2 of the main chamber and acting on the upper surface 10 of a piston 6 below. The vessel 1 main chamber S may be vented via a pipe 23 to atmosphere or an alternative relatively low pressure gas or vapour source contained for example in an inverted chamber 25 (not shown) but as herewith described in order to draw gas or vapour into the main chamber S volume 30 defined by the piston 6 and underside 11 of the chamber 5 top 12. Alternatively this volume 30 can be sealed with a valve (not shown). The volume 30 containing the spring 38 may be evacuated at the second reservoir level 4 (Fig. 7a) by releasing the piston 6 previously latched in position by the latching mechanism 1 3 located towards the top of the main chamber 5 (Fig. 7a) hence allowing the spring 38 to expand thereby drawing in a gas or vapour 9 through the pipe 23 from an external source (not shown) but as defined herewith. The resultant residual gas or vapour 9 can then be compressed by transferring the submersible vessel to the first reservoir level 3 (Fig. 7b). Located in the outlet port 20 of the main chamber 5 below the base 1 5 is a bi-directional hydraulic turbine 16 and an adjacent inlet port 18 with the hydraulic turbine 16 energised from the expansion of the spring 38 at the second reservoir level 4 driving the piston down and residual water 7 out through the hydraulic turbine 16.

As described herewith the transfer of the submersible vessel 1 to the first reservoir deeper level 3 will induce inflow of hydrostatically pressurised water through the turbine 16 with a consequent pressure drop from hydraulic power generation or more directly through the inlet port 18 with either flow route generating hydrostatic pressure forces exceeding that from the opposing spring 38 and flooding the submersible vessel 1 prior to raising it back to the second reservoir level 4. The submersible vessel 1 configurations and compressible media described herewith have all deployed a cylindrical geometry with its axis 14 vertical and associated hydraulic turbine 16 located in the outlet port 20 below the base 1 5 of the submersible vessel's 1 main chamber 5 with the upper end of the main chamber 1 2 closed apart from a penetration for pipework 23 to facilitate transfer of compressed gas or vapour from the submersible vessel 1 to an external container 37 (see Fig. 6b) for storage. Alternatively the pipework 23 can operate as a vent pipe to draw into the volume 30 within the submersible vessel 1 atmospheric air or gas or vapour from an external container 25 (see Fig. 6a).

Alternative arrangements of a submersible vessel 1 can be deployed including one with the submersible vessel 1 axis 14 remaining vertical but with the hydraulic turbine 16 located at the upper end 12 of the main chamber 5 rather than the base 1 5. Figs. 8a and 8b show a piston and cylinder main chamber S with the hydraulic turbine 16 located at the upper end 12 of the main chamber 5. Fig. Ba shows the main chamber 5 void of water at the second reservoir level from expansion of compressed gas or vapour driving residual water 7 out through the power generating hydraulic turbine 16. Fig. Sb is shown flooded at the first reservoir level 3 through the hydraulic turbine 16 or through an adjacent inlet port 1 B from above the submersible vessel thereby compressing the relevant compressible media B -in this case a gas or vapour 9-within the main chamber 5. For power generation at the first reservoir level 3 the inlet port 1 8 would be closed via the closure valve 19 as shown in Fig. Sb with the turbine 16 closure valve 1 7 open. Alternatively to maximise compression of residual gas or vapour 9 at the first reservoir level for accumulation and storage in an external container 37 (see Fig. Sb for example) the turbine 16 closure valve 1 7 would be closed with the inlet port 18 closure valve open. For this configuration of submersible vessel the pipe work 23 may be deployed as for the alternative configuration discussed herewith but located on the underside of the submersible vessel rather than the top. Atmospheric air or a gas or vapour may be transferred from its source to the submersible vessel at the second reservoir level 4 by methods described herewith via the pipe 23 extending to the source. For a gas or vapour the source may be contained in an inverted submerged chamber 25 (see Figs. 2 or 6) with compression at the first reservoir level 3 for power generation at the first or second reservoir levels or transfer of compressed gas or vapour to an external container (for example, 37 Fig. 6b) for storage. However during the expansion process of the compressible medium 8 at the second reservoir level 4 (fig. 8a) the resultant flow rates of discharging water through the hydraulic turbine 16 when located at the upper end 12 of the main chamber 5 for a gas or vapour 9 based compressible medium 8 with progressively reducing pressure from expansion will be more constant than for a hydraulic turbine 1 6 located at the base of the submersible vessel 1 due to the progressively reducing hydrostatic pressure acting on an isolating piston 6 in the former case. For a constant pressure compressible medium 8 from a saturated vapour or an external constant pressure source the hydraulic power output from the hydraulic turbine 1 6 would increase as the opposing hydrostatic head reduced.

Instead of deploying a cylindrical vessel 1 with a vertically orientated axis as herewith discussed which would provide optimum conditions for streamlining for vertical transfer between the first 3 and second 4 reservoir levels a submersible vessel 1 could be orientated with its axis 14 horizontal 40. Fig. 9 shows the outer shell of the submersible vessel with this orientation but with a compressible medium 8 and other internal systems not shown. This configuration will enable location at the upper second reservoir level 4 closer to the reservoir 2 free surface with resultant minimal hydrostatic pressure forces opposing expansion of the compressible medium 8 hence water flow from the submersible vessel 1 through the hydraulic turbine 16 when located at either end of the submersible vessel I. However in such cases the submersible vessel support facilities (not shown in Fig. 9) would advantageously be required to orientate the submersible vessel 1 with its axis vertical prior to transfer between first and second reservoir levels 3 and 4 respectively in order to minimise viscous drag forces by optimising the effectiveness of vessel streamlining.

A method for retaining a compressible medium 8 in its compressed state after compression at the first reservoir level has involved the implementation of a latching facility 13 associated with a piston 6 or solid end plate 33 or 36 the latter two also being applicable to a bellows 28 based compressible medium or other non-gaseous or vapour based compressible media 8 thereby facilitating retention of the compressible medium in its compressed state induced at the first reservoir level 3 during transfer to the second reservoir level 4 prior to expansion at this level. However for a gas or vapour this could be stored under compression in a second chamber 41. Fig. 1 Oa shows the chamber 41 located within the main chamber 5 at or towards the upper end 1 2 and with the submersible vessel at the second reservoir level 4. Pressurised reservoir water flow at the first reservoir level 3 either through the inlet port 1 8 or through the power generating turbine 1 6 will drive the piston 6 up (Fig. 1 Ob) forcing residual gas or vapour above the piston 6 through a control valve 42 into the chamber 41 where on closing the valve 42 it will be stored under compression. On reaching the second reservoir level 4 the gas or vapour 9 will be released from the chamber 41 by opening the control valve 42 thus facilitating expansion of compressed gas or vapour driving the piston 6 down thereby discharging residual water within submersible vessel 1 through the power generating hydraulic turbine 16. It will be noted that in order to avoid any downward pressure force on the piston 6 from residual gas or vapour failing to enter the chamber 41 the piston 6 on reaching the top of its stroke will need to have forced all compressed gas or vapour above it into the chamber 41 before valve 42 closure. Subject to these conditions the provision of the second chamber 41 would render the requirement for a latching facility 1 3 discussed herewith unnecessary.

It has been described herewith how power may be generated directly from hydrostatic pressure at the first reservoir level 3 acting on a compressible medium 8 within a submersible vessel 1 or from expansion of the compressible medium 8 at the second reservoir level 4 driving residual water 7 out of the vessel through the hydraulic turbine 1 6. Alternatively a gas or vapour 9 compressible medium 8 from a relatively low pressure source 25 at the second reservoir level 4 external to the submersible vessel (Fig. 2) may be transferred to the vessel 1 at this level prior to compression within the submersible vessel 1 at the first reservoir level 3 with the compressed gas or vapour being transferred to an external containment facility 37 (Fig. 6b) where it may be accumulated and stored under compression for subsequent utilisation. The compressed gas or vapour containment facility 37 may be submerged and local to the submersible vessel 1 as shown in Fig. 6b.The gas or vapour source container 25 shown in Fig. 6a comprises an inverted open chamber with the pressure controlled by the local environmental reservoir hydrostatic pressure. However gas or vapour for compression may also be contained in a closed storage container with internal pressure regulation and could be located either close to or remote from the submersible vessel to which its contents are to be transferred. Figs.l la-c show schematic arrangements of a system for compressing a gas or vapour derived from an external source contained in a storage tank 43 with pressure regulation (details not shown) and located on a floating supply vessel 44 and fed to the submersible vessel 1 at the second reservoir level 4 through a pipe 23. For reasons of clarity the submersible vessel support facilities are not shown in Figs. 11 a-c. Fig. 11 a shows the submersible vessel 1 flooded but uncharged with low pressure gas or vapour 9. Fig.l lb shows the submersible vessel 1 charged with gas or vapour 9 by means of facilities herewith described transferred from the container 43 via pipe 23. Fig. 11 c shows the transfer of the vessel 1 from the second reservoir level 4 to the first reservoir level 3 where it is flooded from hydrostatically pressurised water thereby driving the piston 6 upwards and latching it (latching mechanism not shown for clarity) thereby compressing and retaining residual gas or vapour. The pipe 23 may be flexible or extendable to accommodate depth differences during the transfer of the submersible vessel 1 between first and second reservoir levels 3 and 4 respectively.

Alternatively for a flexible pipe 23 in order to accommodate large displacements between the first and second reservoir levels 3 and 4 respectively the pipe may be wound around a large drum 45 preferably supported on the supply vessel 44 as shown in Fig. 11 a.

If the gas or vapour 9 from the source in the container 25 or storage tank 43 has a pressure higher than the second reservoir level 4 hydrostatic pressure then it may be piped directly into the submersible vessel 1 located at the second reservoir level 4 prior to transfer to the first reservoir level 3 for compression at this level. The volume 30 within the submersible vessel 1 containing the gas or vapour 9 to be compressed would be bounded by the piston 6, the closed end 1 2 of the main chamber 5 and its cylindrical walls 46. As discussed herewith gas or vapour compression would result from hydrostatically induced forces acting on the piston 6 at the first reservoir level 3 thereby driving the piston 6 towards the end 1 2 of the main chamber until maximum compression is reached. Up to this point transfer of compressed gas or vapour to an external container would be prevented through an isolation valve (not shown in Figs.l la-c) associated with flexible or extendable pipe work 23 connecting the vessel 1 to the external container. The external container may comprise of an inverted chamber 37 located at the first reservoir level as discussed herewith or a receiver close to or remote from the submersible vessel 1. Fig. 1 2 shows a receiver vessel 48 which is buoyant but spatially stabilised by anchor lines 49 secured to the reservoir bed 39 and with the compressed gas or vapour transfer pipe 23 coupled to the receiver vessel via a valve 51. The other end of the transfer pipe 23 with an in line isolation valve 47 extends to and is coupled via a valve 52 into the submersible vessel 1. The receiver vessel would have an operating pressure controlled by an associated pressure regulator (not shown) equal to or compatible with the maximum gas or vapour pressure generated in the submersible vessel 1 with successive charging of the container 37 or receiver 48 taking place through valve 51 opening under the appropriate pressure conditions of the container 37 or receiver 48 and submersible vessel 1. Such pressure conditions would typically involve equal compressed gas or vapour pressures in the submersible vessel 1 and container 37 or receiver 48. However in some cases container 37 or receiver 48 pressures may require to be less than those in vessel 1 which can be facilitated through appropriate pressure regulation in container 37 or receiver 48 vessels. Figs. 1 3a and 1 3b show a compressed gas or vapour storage container in the form of an inverted chamber 37 local to the submersible vessel 1 at or close to the first reservoir level 3 (see also Fig. 6b). Air transferred into the submersible vessel from an external source at the second reservoir level as herewith described is compressed from hydrostatic pressure forces at the first reservoir level 3 acting on the piston 6 prior to the compressed air being transferred to the container 37. Figs.13a and b show water flow into the submersible vessel through the hydraulic turbine 16 through port 20 thereby generating power during compression processes albeit yielding a smaller level of compression due to the pressure drop across the turbine 16 than would have resulted from flow into the submersible vessel through inlet port 18. The chamber 37 would trap a volume of air above the lower water free surface 24 with a pressure equal to the hydrostatic pressure at the level of the water free surface 24 and with the compressed air pressure within the submersible vessel 1 possibly equal to or less than that in the chamber 37. In this case transfer of this compressed air from the submersible vessel 1 to the chamber 37 through the pipe 23 can be implemented through a pump 54 located at the inlet or along the pipe work 23 (Figs. 1 3a and b). If a gas other than air or a vapour is required to be accumulated and stored under pressure in the inverted chamber 37 and may be interactive with reservoir 2 water then isolation of the gas or vapour from reservoir water may be facilitated by means of a piston 55 (fig.1 3b) or flexible membrane (not shown) positioned within the chamber 37 at the level of and moveable with the water free surface 24. If the chamber 37 is located above the level of the submersible vessel 1 then compressed gas or vapour within the submersible vessel 1 may be transferred from the vessel 1 to the chamber 37 through the pipe work 23 through positive buoyancy but with the compressed gas or vapour pressure reduced in the chamber 37 and equal to the hydrostatic pressure prevailing at the chamber 37 level within the reservoir 2.

It has been described herewith how transfer of a gas or vapour to the submersible vessel 1 at the second reservoir level 4 can be carried out from a source in the chamber 25 external to the submersible vessel if the source pressure exceeds the internal pressure in the submersible vessel 1. However in circumstances where the source pressure does not exceed the submersible vessel 1 internal pressure alternative transfer means must be deployed including a pump 54 located in the connecting pipe work 23 as mentioned herewith but operating in a direction to draw gas or vapour from an external source container into the submersible vessel using appropriate valving in contrast to its operation to pump compressed gas or vapour from the submersible vessel into an external compressed gas or vapour container see figs 6 and 13. Alternatively the submersible vessel 1 may possess a weighted piston 22 (Fig. 2a) which at the first reservoir level 3 will be forced upwards by hydrostatic pressurised flow into the submersible vessel 1 as herewith described compressing residual gas or vapour prior to transfer, still at the first reservoir level 3 to an external compressed gas or vapour storage container which may be an inverted chamber 37 or an alternative configuration such as a compressed gas or vapour receiver 48 as herewith described. On transfer to the second reservoir level 4 the reduced hydrostatic pressure will allow the weighted piston 22 within the submersible vessel 1 to descend thereby creating a partial vacuum in the volume 30 above the piston 22 and with an isolation valve (not shown) open in the pipe work 23 gas or vapour 9 flow from the source in the container 25 or 43 (see Fig. 11) into the volume 30 above the weighted piston 22 will result. This procedure can only be deployed for a submersible vessel orientated with its axis vertical. An alternative method for creating a partial vacuum within the submersible vessel 1 for drawing a gas or vapour into the vessel 1 for subsequent compression prior to storage in an external containment 37 or 48 utilises a relatively lightweight piston 6 in contrast to a weighted piston 22 discussed herewith. To force the piston 6 down for creation of a partial vacuum the mechanical compression spring 38 (Figs. 7 and 14) may be used by trapping it within the compressible volume 30 between the upper surface 10 of the piston 6 and underside of the top closed end 12 of the main chamber 5. The spring 38 constant would be such that during gas or vapour compression at the first reservoir 3 level the spring 38 would be totally compressed with the piston 6 latched in the compressed position via the latching mechanism 1 3. By uncoupling the pipe 23 from the source container 25 or 43 and relocating it to a compressed gas or vapour container 37 or 48 for example at the first reservoir level 3 the compressed gas or vapour in the submersible vessel 1 can be transferred to the compressed gas or vapour container 37 or 48. On subsequent recoupling the pipe 23 to the source container 25 or 43 and transfer of the submersible vessel to the second reservoir level 4 the piston 6 will be released thereby allowing the spring 38 to expand and drive the piston down and residual water out through the hydraulic turbine 16 resulting in both power generation and depressurisation of the volume 30 in the submersible vessel with gas or vapour from the external source 25 or 43 being drawn into the de-pressurised volume 30. Fig. 1 4a shows the compressible vessel 1 with the spring 38 and residual gas or vapour 9 compressed at the second reservoir level and Fig. 1 4b shows the spring 38 residual gas or vapour 9 expanded.

Instead of using a mechanical spring 38 and piston for creating a de-pressurised volume 30 a bellows 56 formed from an elastic or springy (preferably metallic) material chargeable with gas or vapour could be deployed. Alternatively the bellows 56 could contain a spring (not shown) trapped between the latchable sealed base 29 and the underside of the vessel end 12 this latter possessing a valved inlet pipe leading to a gas or vapour source. Fig. 1 Sa shows this bellows based spring (excluding the internal spring option) compressed at the second reservoir level 4 following gas or vapour compression at the first reservoir level 3 (not shown) with Fig. 1 Sb showing the bellows expanded and charged with gas or vapour drawn from the external source container 25. The bellows based system will operate exactly as the mechanical spring system as described with reference to Figs. 1 4a and 1 4b herewith except that the piston 6 deployed for the latter in order to seal residual gas or vapour from environmental reservoir water would be rendered unnecessary sine the bellows would be sealed at the base or end plate 29. Gas or vapour for compression at the first reservoir level would be drawn into the submersible vessel through a valve 47 in the delivery pipe 23 leading to an external gas or vapour source container 25 or 43 (not shown). The use of a saturated vapour would provide a constant vapour flow from the source in containers 25 or 43 into the bellows 56 in the submersible vessel 1.

It will be appreciated that the methods described with reference to Figs. 14 and 1 5 can provide both on board power generation from compressed gas or vapour generated at the first reservoir level and also storage of compressed gas or vapour in a container external to the submersible vessel 1. In contrast methods deploying permanently sealed compressible gas or vapour containers within a submersible vessel 1 as for example described with reference to Figs. 1, 3, 4 and S are suitable only for on board power generation and cannot be deployed for storage of compressed gas or vapour in a container external to the submersible vessel.

Fig. 16 shows a further method for de-pressurising the volume 30 using a piston 57 in a second cylinder 58 smaller than the cylindrical main chamber and mounted on the outer surface of the submersible vessel 1 above the main chamber's 5 closed end 12. A rod 59 connects the piston 6 in the submersible vessel 1 through dynamic seals 60 in submersible vessel 1 to the piston 57 in the second cylinder 58. The cylinder 58 contains a gas or vapour 9 or a mechanical spring (not shown) trapped above the piston 57 which is compressed at the first reservoir level 3 from hydrostatic pressure forces acting on the lower piston 6 in the main chamber 5. The resultant compressed gas or vapour in the main chamber 5 when transferred at the first reservoir level 3 via the pipe 23 to an external container such as 37 or48 (see Fig. 6 and Fig. 12) will deplete the volume 30 in the main chamber of gas or vapour 9 whereby on transferring the submersible vessel 1 to the second reservoir level 4 (Fig. 1 6a) the compressed gas or vapour 9 or spring in the second cylinder 58 will expand driving pistons 6 and 57 down (Fig. 1 Sb) thereby depressurising the volume 30 in the main chamber 5 and drawing into this volume gas or vapour via pipe 23 or the like from an external source such as 25 or 43 (see Figs. 2 and 11) or air directly from the atmosphere for compression at the first reservoir level 3 prior to transfer to the external container 37 or 48.

Figs. 1 7a -e show schematic representations of an energy conversion system 61 employing a beam 62 supported by a heavy duty pivot 63 located at a position along its length displaced from the beam's midpoint 69 and with an optional additional beam section 64 parallel to and secured to the beam 62 and located in the region of the pivot 63. The beam 62 supports two pulley wheels, one at the left hand end 65 and one at the right hand end 66. Passing over pulley wheels 65 and 66 is a cable 67 from which is suspended from the left hand end pulley 65 a submersible vessel 1 and at the right hand end pulley 66 a counter weight 68. The submersible vessel 1 may possess one of several configurations as herewith described with reference to Figs. 1-16 but in all cases it possess a compressible medium 8 contained within the submersible vessel 1. A preferred configuration of the submersible vessel 1 has an inverted cylindrical geometry with a bi-directional hydraulic turbine 16 located at the base 1 5 of the vessel 1 which can be energised from water flow in either direction. Alternatively instead of a single bi-directional hydraulic turbine 1 6 two separate mono-directional hydraulic turbines may be deployed (not shown) each responsive to flow in an opposite directions.

The entire energy conversion system 61 is supported via the pivot 63 which in turn can be supported by one of a number of facilities including floating ones such as a pontoon or surface vessel or by a fixed sea bed mounted rig similar to a submerged crane or an oil rig or other facilities as herewith described. The system shown in Figs. 1 7 a-e deploys a crane type supporting facility 70 mounted and supported on the sea bed 39 and submerged over most of its length but with the upper section supporting the beam 62 and associated members as herewith described emergent above the reservoir 2 free surface 72. The submersible vessel 1 remains permanently submerged throughout the operating cycle to be described-but the counter weight is submerged for only part of the operating cycle.

The energy conversion system operates in five states. In state 1, Fig. 1 7a, the submersible vessel 1 is void of water and submerged just below the reservoir free surface 72 at the second reservoir level 4 and with the beam 62 horizontal and the counterweight 68 submerged at its descent limit i.e. the first reservoir level 3. The volumes and dry weights of the submersible vessel 1 and counterweight 68 are such that they are equal thereby producing equal but opposite tensions in the connecting cable 67 and are therefore balanced. Under this condition the off centre pivot 63 position of the beam 62 would create a turning moment in a clockwise direction for the system geometry shown in Fig. 1 7 a-e. However by locating a weighted member 71 on the beam 62 or parallel beam section 64 (as shown in Figs. 1 7a-e) on the submersible vessel 1 side of the pivot 63 position a balance condition for the beam 62 can be established by equalising clockwise and anticlockwise turning moments about the pivot 62. It will be noted that the addition of the weighted member 71 to the beam 62 or as shown in Figs. 1 7 a-e to beam section 64 will only affect the beam 62 balance condition but not affect the balance condition between the submersible vessel 1 and counter weight 68.

Transition to state 2 Fig. 1 7b involves lowering the submersible vessel 1 to the first reservoir level 3 and hence raising the counter weight 68 to the second reservoir level 4 i.e. just submerged below the reservoir 1 free surface 72 as shown in Fig. 1 7b. In state 2 the system remains balanced with the beam 62 remaining horizontal and submersible vessel 1 remaining void by preventing hydrostatically pressurised flow through the hydraulic turbine 16 by using a closure facility 17 (not shown in Figs.1 7 a-e for clarty) to isolate the hydraulic turbine 1 6 inlet port 20 (see for example Fig. 1). Note it will be recalled that the port 20 can operate as an inlet or outlet port when deploying a bi-directional hydraulic turbine. Transition to state 3 Fig. 1 7c involves opening the closure facility 17 in the inlet port 20 thereby permitting water under hydrostatic pressure to flow through the hydraulic turbine 16 into the vessel 1 and generate clean power. The resultant pressurised flooding of water into submersible vessel 1 will force the piston 6 upwards in the main chamber 5(see Fig. 1) thereby compressing the compressible medium 8 (in this example a gas or vapour) in the submersible vessel 1 and retaining it in its compressed condition by latching the piston 6 with the latching mechanism 1 3 as described herewith. The resultant water take up into the main chamber 5 will increase the weight of the submersible vessel 1 and hence the anticlockwise turning moment of the beam 62 about its pivot position 63. This will drive the beam 62 from its horizontal orientation anticlockwise with the resultant emergence of the counter weight 68 from the reservoir 2 to a suspended position above the reservoir 72 surface. With the counterweight 68 un-submerged its weight will have increased due to the loss of buoyancy such that with the appropriate mass and volume the system will regain its balanced condition following an adjustment to the magnitude of the beam's 62 counter clockwise turning moment. This adjustment can be effected by means of the weighted member 73 located on the guide beam member 64 close to the beam's 62 pivot 63 position when the beam is horizontal but on rotation anticlockwise of the beam 62 during transition from states 2 to 3 the weighted member 73 will slide or run along the member 64 on a track (not shown) towards the left hand pulley 65 in the Fig. 1 7c where it will remain for states 3, 4 and 5.

Transition from state 3 to 4 with the submersible vessel 1 and counter weight 68 balanced due to weight equality involves raising the submersible vessel 1 and thereby lowering the counterweight 68 resulting in the counterweight 68 being suspended just above the reservoir 2 free surface 72 with the submersible vessel 1 remaining submerged and flooded at a depth a little below its state 1 position see Fig. 1 7d. Transition from state 4 to state 5 involves releasing the piston 6 hence compressible medium 8 which remained locked in its compressed condition for states 3 and 4 whereby expansion of the compressible medium 8 on release will drive the piston 6 down and residual water in submersible vessel 1 out through the bi-directional hydraulic turbine 16 thereby generating useful power and with submersible vessel 1 losing weight with depletion of its water pay load see Fig. 1 7e. Although the weighted member 73 in state 5 is located close to the left hand pulley 65 in state 5 (Fig. 1 7e) the turning moment of the beam 63 about its pivot 63 will be clockwise under the assumptions of submersible vessel and counter weight 68 masses and volumes stated herewith thereby rotating the beam 62 back to its state 1 horizontal orientation whereby the counter weight 68 can be readily returned through sliding or running to the beam's 62 near pivot 63 position.

The Figures 1 7a-e show the submersible vessel 1 and counterweight 68 freely suspended from their respective pulleys 65 and 66 but alternatively either or both may run along vertical guide rails or the like (not shown) which may be secured to the system support facility for example 70 in Figs. 1 7a-e. Further instead of generating power from pressurised water flow through the hydraulic turbine 16 on board the submersible vessel 1 if the compressible medium is a gas or vapour this may be transferred to and stored and accumulated in its compressed state in an external submerged or surface storage container as described herewith.

The method described herewith with reference to Figs. 1 7a-e deploys a beam 62 supported by a pivot 63 at a position offset from its midpoint position 69 with a pulley 65 located at the left hand end of the beam 62 and a second pulley 66 at the right hand end with a separation from the pivot 63 significantly greater than that of the left hand pulley. However a potentially more compact energy conversion configuration 74 can be deployed as shown in Figs. 1 8a-e with a beam 75 potentially shorter than the beam 63.The beam 75 is supported by a heavy duty pivot 76 and has a pulley wheel 77 located to the left of the pivot 76 as for the method described with reference to Figs.1 7a-e but with a differential pulley wheel 79 located at the right hand end of the beam 75 and significantly closer to the pivot 76 than the separation of the pulley wheel 66 from the pivot 63 in the method described with reference to Figs.1 7a-e.

The energy conversion system 74 can be supported via the pivot 76 using a reservoir bed 39 mounted rig 70 or other support facilities as described with reference to Figs. 1 7a-e. In Figs. 1 8a-e a submersible vessel 1 is suspended from a cable 81 which passes over the pulley wheel 77 to the larger member 82 with radius R of the differential pulley wheel 79 to which it is secured and around which it can be wound. A counter weight 83 is suspended from a cable 85 secured to and windable around the smaller member 84 with radius r' of the differential pulley wheel 79 but in the opposite sense to cable 81 thereby generating an opposite turning moment about the differential pulley wheel 79 axis to than generated by the cable 81. As with the energy conversion facility described herewith with reference to Fig. 1 7 the method with reference to the schematics shown in Figs.1 8a-e operates in five states.

In statel (Fig. 1 8a) which is balanced with the beam 75 horizontal and the submersible vessel 1 void of water and submerged close to the surface of the reservoir 2 with the counter weight 83 also submerged at a depth deeper than that of the submersible vessel 1 as shown in Fig. 1 8a but significantly shallower than the depth of the counter weight 68 herewith described with reference to Fig. 1 7a. Transition to state 2 (Fig. 1 8b) with the beam 75 remaining horizontal involves lowering the submersible vessel 1 to the first reservoir level 3 but with flow into the submersible vessel 1 restricted by the hydraulic turbine 16 and inlet port 1 8 closures 1 7 and 19 respectively (1 7 and 19 not shown for clarity in Figs. 18a-e) (see Fig. 1). Fig.18b shows the submersible vessel 1 at its descent limit i.e. at the first reservoir level 3 with the counter weight 83 at its shallowest depth just below the reservoir 2 surface. Because of the differential pulley wheel's larger and smaller radii R and r respectively the vertical displacement of the counter weight 83 in transferring from state 1 to state 2 will be r/R times the corresponding vertical displacement of the submersible vessel 1. In order to generate high levels of compression of the compressible medium 8 hence hydraulic turbine 16 power output in the submersible vessel 1 or for energy storage in local or remote storage containers for gas or vapour compressible media 9 it is necessary that the submersible vessel 1 is lowered to as deep a reservoir 2 level as practical in order to achieve correspondingly high hydrostatic pressures in the reservoir 2 but at the same time limiting the vertical transfer range of the counter weight 83 again for practical reasons including those of structural integrity. Further in order to initiate a balance condition between the submersible vessel 1 and counter weight 83 their opposing torques generated in the differential pulley wheel 79 must be equal implying that the weight and volume of the counter weight 83 must be significantly greater than the weight and volume of the submersible vessel 1 by the ratio of R/r. Further in order to produce equal but opposite turning moments in the beam 75 about its pivot 76 to create a balance in the beam and also maintain a balance between the submersible vessel 1 and counterweight 83 an additional counterweight 80 may be located on the beam 75 or on a parallel beam section 78 (Figs. 1 8a-e) at a position to the left of the pivot 76 to generate an additional counter clockwise turning moment thereby creating balance conditions between both the submersible vessel 1 and counterweight 83 and the pivoted beam 75.Under balance conditions in state 2 with the submersible vessel remaining void but at the first reservoir level the system will be driven into state 3 (Fig. 1 8c) with the hydraulic turbine or inlet closure valves 1 7 or 19 (see Fig. 1) respectively opened thereby flooding the submersible vessel 1 either via the hydraulic turbine 16 for power generation or more directly through the inlet port 1 8 for potential storage of compressed gas or vapour in an external storage container.

Flooding the submersible vessel will increase its weight and drive the beam anticlockwise to an orientation inclined to the horizontal until the counterbalance 83 rise above the surface of the reservoir?. It will be noted from Fig. 1 8b that the state 2 balance condition implies that the submersible vessel 1 remains void during its transition from state 1 to state 2. If however it is flooded progressively during it's descent by opening either hydraulic turbine closure valve 1 7 or inlet closure valve 1 9 (see Fig. 1) then a progressively increasing anticlockwise turning moment in the differential pulley wheel 79 will result driving the system from state 2 to state 3.

However as stated herewith the state 3 condition will involve the counter weight 83 being lifted out of the reservoir 2 thereby removing buoyancy existing when submerged in states 1 and 2. With the appropriate relative magnitudes of the weights and volumes of submersible vessel 1 and counter weight 83 the increased weight of the submersible vessel 1 when flooded in state 3 can be partially offset by the corresponding increased weight of the counter weight 83 on removal of buoyancy. It will be noted however that in order that the beam 75 remains balanced for states 3 and 4 an additional anticlockwise turning moment must be generated for these two states by locating for example a mobile weight 86 (Figs. 1 8a-e) over or close to the pivot position 76 during states 1 and 2 which would run or slide under gravity along the beam 75 or beam section 78 (when inclined as described) towards the left hand end for the states 3 and 4 in a manner similar to that described with reference to Figs. 1 7a-e. Transition from state 3 to state 4 Fig. 1 8d with the beam 75 remaining inclined to the horizontal will facilitate the raising of the submersible vessel 1 and lowering of the counterweight 83 to a height just above the reservoir 2 surface to prevent buoyancy effects with balance conditions being retained. With the submersible vessel 1 at the state 4 shallower level, albeit a little deeper than the state 1 level and the closure valve 1 7 (see for example Fig. 7) open the compressible medium is able to expand against the reduced hydrostatic pressure of the surrounding reservoir thereby driving residual water out of the submersible vessel 1 and into state 5 (Fig. 1 Se) through the hydraulic power generating turbine 1 6.

This process will void hence reduce the weight of the submersible vessel 1 and thus generate a clockwise turning moment in the differential pulley wheel 79 to return the system back to state 1 with the beam 75 horizontal which will facilitate return of the counterweight 86 to its position in states 1 and 2 and thereby repeat the power generating or energy storage cycle this latter process being described herewith.

Figs. 1 9a-e show schematic illustrations of a further method for compressing a compressible medium for clean power generation or storage in a separate compressed gas or vapour containment for subsequent utilisation either locally or remotely as herewith discussed.

Figs. 1 9a-e show an energy conversion system 87 to be described deploying an assembly of interconnected beams supporting a submersible vessel 1 for containing a compressible medium 8 and two counter weights for creating balance conditions in the submersible vessel's support mechanism in order to minimise energy demands associated with successive transfer operations of the submersible vessel between first and second reservoir levels. As discussed herewith this will subject the compressible medium 8 to relatively high and low hydrostatic pressures respectively for power generation from on board hydraulic turbines or energy storage from compressed gas or vapour transferred to local or remote containers.

Figs. 1 9a-e shows the assembly of interconnected beams in the energy conversion system 87 including a pivoted beam 88 which is horizontal in Fig. 1 9a supporting a first pulley wheel 89 at its left hand end and a counter weight 90 at its right hand end and with a pivot 91 at a position lying between the pulley wheel 89 and counter weight 90. Located at the pivot 91 position on beam 87 is a differential pulley wheel 92 with a second beam 93 secured to the beam 88 at or close to the pivot 91 and inclined downwards at an angle e to the beam 88 with its lower most end supported by a further beam 94 forming a structural member which itself is secured to the beam 88 with the beams 88, 93 and 94 forming a rigid, high strength triangular configuration. A submersible vessel 1 is suspended from a cable 95 which passes over the first pulley wheel 89 to the larger member 96 with radius R of the differential pulley wheel 92 to which it is secured. Secured to the smaller member 97 of radius r of the differential pulley wheel 92 is a second cable 98 supporting a second counter weight 99 located upon and freely moveable along the inclined beam 93. The configuration illustrated in Fig. 19 is supported via the pivot 91 which has high strength and is supported itself by a rig 70 firmly secured to the reservoir bed 39 as illustrated in Figs. 1 9a-e. Alternatively the system 87 may be supported by a floating support vessel or pontoon or another supporting facility as described herewith. The method operates in five states with Fig. 1 9a showing state 1. In this state the submersible vessel 1 is void of water and is submerged just below the reservoir 2 surface with the beam 88 horizontal. The associated structural members i.e. beams 93 and member 94 remain located above the reservoir 2 surface. For state 1 the counter weight 99 is located at the lowermost position on the beam 93 and because the beam 93 is inclined at an angle 0 to the horizontal and not vertical the counter weight's 99 effective weight will be equal to its dry weight multiplied by sin e i.e. its resolved component in a vertical direction. Further it will be appreciated that because the submersible vessel 1 is secured to the larger member 96 of the differential pulley 92 it will be transferable to relatively larger depths than the corresponding range of movement along the supporting inclined beam 93 of the counterweight 99 which is secured to the smaller member 97 of the differential pulley 92 thereby facilitating relatively large hydrostatic pressure differentials between the first and second reservoir levels 3 and 4 respectively and hence greater power generating potential from an on board hydraulic turbine 1 6 than would be possible from lesser hydrostatic pressure differentials. Also in the case of energy storage where the compressible medium 8 is a gas or vapour 9 large hydrostatic pressure differentials will yield correspondingly large compression levels hence energy densities in external containers.

The system configuration as herewith described together with the weights and volumes of associated elements e.g. the submersible vessel 1 and counter weights 90 and 99 are such that for state 1 a balance condition exists between the submersible vessel 1 and counter weight 90 implying zero magnitude turning moment of the beam 88 about the pivot 91 with a further balance condition between the submersible vessel 1 and counter weight 99 supported on the inclined beam 93 this latter balance condition resulting from equal but opposite turning moments generated by the supporting cables 95 and 98. It will be appreciated that the submerged weight of the submersible vessel 1 when voided will be less than its dry weight or weight when flooded due to the buoyancy effect and the effective weight of the counter weight 99 on the beam 93 when inclined to the vertical will be less than its weight with the beam 93 vertical.

Transition to state 2, Fig. 1gb, involves lowering the submersible vessel 1 to the first reservoir level 3 where prevailing hydrostatic pressure forces acting on the compressible medium 8 in the main chamber 5 (Fig. 1) exceed the opposing compressible medium 8 pressure forces resulting in flooding of the main chamber 5 from inflow of hydrostatically pressurised water into the main chamber 5 either through the on board hydraulic turbine 16 for direct power generation or for a gas or vapour 9 based compressible medium 8 through the inlet port 18 (see Fig. 1) for energy storage or power generation at the second reservoir level but in either case the compression of the compressible medium 8 will increase of the weight of the submersible vessel 1. During the lowering of the submersible vessel 1 the counter weight 99 will be driven upwards along the inclined beam 93 until it reaches the uppermost position on the beam 93. During this process the support beam 88 will remain horizontal.

The increase in submersible vessel 1 weight will unbalance the system creating an anticlockwise turning moment in the beam 88 thus driving it in an anticlockwise direction into state 3 Fig. 1 9c. With the beam 93 assuming a vertical orientation and with the submersible vessel 1 lowered a little further due to the downward movement of the pulley wheel 89 at the left hand end of the supporting beam 88. In state 3 the flooded submersible vessel 1 and counter weight 99, now on the vertically orientated beam 93, will resume a balance condition whereby the lowering of the counter weight to the lowermost position on the beam 93 -state 4 Fig. 20d -will raise the submersible vessel 1 towards the surface of the reservoir 2 but to a depth greater than if the support beam 88 was horizontal. However this depth will be shallow enough for the compressible medium's 8 (shown as gas or vapour in figs.19a and d) expansive forces to exceed those from the environmental hydrostatic pressure at this depth thereby driving residual water 7 in the submersible vessel 1 out through the on board hydraulic turbine 16 with the generation of clean power. The resultant discharge of residual water 7 will lighten the submersible vessel 1 thereby creating an imbalance condition, state 5 Fig. 1 9e with a clockwise turning moment of the beam 88 about the pivot 91 position and driving the beam 88 back to its horizontal orientation and hence the beam 93 from its vertical orientation in states 3 and 4 to its orientation inclined by an angle 0 to the horizontal.

The energy conversion systems described with reference to Figs. 1 7, 18 and 19 all involved the use of constant mass counter balances but with system configurations designed to adjust the effective turning moments generated by the counter weight to compensate for submersible vessel weight changes resulting from voided to flooded conditions or vice versa in order to maintain balance conditions between the submersible vessel and counterweight.

However other methods can be deployed for accommodating said submersible vessel weight changes by using a variable weight counter balance the weight being automatically adjusted in response to submersible vessel weight changes such that balance conditions are maintained between counter weight and submersible vessel.

Figs. 20a-e and 21 a-e show schematic drawings of energy conversion systems with counterweights having weight adjustments through flooding or discharge of water in response to submersible vessel weight changes.

Figs. 20a-d show an energy conversion system 100 deploying a water based counterbalancing facility. In the arrangements shown in Figs. 20a-d a submersible vessel 1 and counterweight vessel 102 are connected via their respective pistons 103 and 104 by a chain or cablel 05 passing over an idler pulley 1 06.The submersible Vessel 1 can run freely up and down a submerged vertical guide rail 1 07 and counterweight vessel 102 can run freely along a guide rail 108 located above the reservoir 2 surface 72 and inclined downward to the horizontal at an angle 9 1 09. The vessels 1 and 102 may have main chambers 110 and 111 respectively of cylindrical and pistons geometry for containing compressible media 8 as shown in Figs. 20a-d or a bellows or the like geometry (not shown). For the submersible vessel 1 with a cylindrical and piston geometry the main chamber 110 will operate as a compression chamber for the submersible vessel 1 but with hydrostatically pressurised water acting on the upper side of the piston 103 in the submersible vessel 1 instead of the underside of pistons in main chambers 5 described herewith. If the compressible medium is a gas or vapour 9 chambers 110 and 111 may each have respective secondary chambers 112 and 11 3 which will have a smaller volume than their corresponding main chambers 110 and 111 but with valving (not shown) connecting associated chambers. The energy conversion system is supported by a floating pontoon or the like 114. Each of the vessels 1 and 102 has a bi-directional hydraulic turbine 16 for both the submersible vessel 1 and the counterweight vessel 102 which can be energised from inflow or outflow of water into or out of the compressible chambers within each vessel. The hydraulic turbine 1 6 associated with the submersible vessel 1 will be located above the piston 103 but adapted or positioned to facilitate unimpeded access for the cable 105 for connection to the piston 103. For reasons of clarity details of this are not shown. The counterweight vessel 102 also has a water delivery pipe 11 5 through which water can flow either into or out of the compressible chamber 111 through the hydraulic turbine 16 or through a bypass port (not shown). This latter would produce a lower impedance to water flow than would result from flow through the turbine 1 6 as herewith described.The water delivery pipe 11 5 extends from the base 116 of the counterweight vessel 102 down to and through the reservoir 2 surface 72.

To facilitate movement of the counterweight vessel 102 and hence the water delivery pipe 11 5 along the guide rail 108 the water delivery pipe may be routed over the side of the supporting vessel or through an elongated slot in the base of the vessel or pontoon with vertical sides where appropriate to prevent flooding of the supporting vessel.

The system operates in four states. In state 1 (Fig. 20a) the submersible vessel 1 is at the second reservoir level 4 on its guide rail 107 i.e. at its minimum depth with the compressible medium 8 in chamber 110 fully expanded and thereby with minimum pressure if this is a gas or vapour 9 and with the submersible vessel 1 void of water. Counterweight vessel 102 is at the its lowest position along it's guide rail 1 08 with the residual compressible medium 8 -again assuming gas or vapour 9 -fully expanded at its lowest pressure and with the vessel 1 02 void of water. Under these conditions each of the vessels 1 and 102 have minimum mean densities. The relative magnitudes of the submerged weight of the submersible vessel 1 and the weight of the counterweight vessel 102 are such that they are balanced in their voided state with the connecting cable 105 under a finite tension implying that the submersible vessel's mean density is greater than that of water. State 2 (Fig. 20b) involves lowering the submersible vessel 1 which will subject it to progressively increasing hydrostatic pressure and draw the counterweight vessel 102 upwards along it's guide rail 108. During this process the pistons 103 and 104 in vessels 1 and 102 respectively will be secured in position by a latching mechanism (not shown) to prevent inflow of reservoir water into the counterweight vessel 102 and submersible vessel 1 during the latter's descent. With the submersible vessel 1 reaching some prescribed depth at the lower (first) reservoir level 3 and with counterweight vessel 102 at its highest level along it's guide rail 108 the submersible vessel 1 and counterweight vessel 102 will each be latched onto their respective guide rails 107 and 1 08 with latching mechanisms (not shown) prior to the release of their respective pistons 1 03 in the submersible vessel 1 and 104 in the counterweight vessel 102 with the initiation of the transition into state 3 (Fig. 20c). This will induce downward movement of the piston 103 in the submersible vessel 101 from flow of hydrostatically pressurised reservoir water into the vessel advantageously though not essentially through a hydraulic power generating turbinel 6 located at the top of the submersible vessel 1 (see Fig. 8). By forcing the piston 103 downwards this process will compress the compressible medium 8 e.g. residual gas or vapour 9 in the submersible vessel 1 with a resultant increase in the submersible vessel 1 weight equal to the weight of water entering the vessel. The resultant downward movement of the piston 103 during the states 2-3 transition will increase the tension in the cable 1 05 connecting pistons 1 03 and 104 thereby drawing the piston 1 04 in the counterweight vessel 1 02-now also unlatched-inwards with the resultant inflow of water through the inlet pipe 11 5 and through the hydraulic turbine 16 if -deployed -in the counterweight vessel 1 02 and again compressing the compressible medium 8 e.g. gas or vapour 9 in this vessel as for the submersible vessel 1 and with a resultant increase in the flooded weight of the counterweight vessel 102. It will be noted that because of the inclination of the guide rail 108 to the horizontal in order to preserve a balance between submersible and counterweight vessels 1 and 102 under either voided or flooded conditions the dry weight and flooded weight of the vessel 102 must be significantly greater than the corresponding dry and flooded weights of the submersible vessel 1 by a factor of sec 0 = 1/sin 0.

The flooded condition of submersible vessel 1 and counterweight vessel 102 with each at their lowest and uppermost locations respectively (Fig. 20c) and with the compressible medium e.g. residual gas or vapour compressed in respective cylinders 110 and 111 or associated smaller cylinders 112 and 11 3 respectively and with their respective pistons 103 and 104 again latched in position constitute the completion of state 3. In state 3 these vessels will be under balance conditions albeit flooded which will persist during their transfer to state 4 (Fig. 20d) occupying their original (state 1) positions along their respective guide rails with submersible vessel 1 01 at the second reservoir level 4 and vessel 102 at the lower end of its rail 1 08.Energy required for this transfer operation will be limited to that to overcome viscous drag forces-only significant for the submersible vessel 101 -during the transfer operation with friction losses being minimised and inertial effects due to acceleration potentially recoverable. Viscous drag forces can of course be minimised by appropriate streamlining of submersible vessel 101.

To return to state 1 the pistons 103 and 104 are released and driven towards their respective chamber outlets by the resultant expansion of the residual compressed compressible medium 8 with water payloads in vessels 101 and 102 discharged through the hydraulic turbine 16 in the submersible vessel and the counterweight vessel 102 (if deployed) generating useful power. If the compressible medium is a gas or vapour 9 and previously valved under pressure into chambers 11 2 and 11 3 in compressible chambers 110 and 111 respectively this gas or vapour will be released by opening the valves connecting corresponding main and associated chambers prior to release of pistons 103 and 104.

Note it has been stated herewith that inflow of pressurised water into submersible vessel 1 will increase its weight and compress residual gas or vapour 9 in both vessels 1 and 102. However with submersible vessel 1 at its descent limit and vessel 102 at its highest level along it's guide rail 108 and locked in this position the force driving the piston 103 down in the submersible vessel 101 will be the hydraulic pressure force hpga where h is the head of water, a' the cross sectional area of the piston 103 in the submersible vessel 1, p' the density of water and g' the acceleration due to gravity.This hydrostatic pressure force will generally be significantly greater than the additional weight of the submersible vessel 1 from flooding alone thereby generating higher compressions in compressible media hence potentially higher power output or energy storage levels than would have been produced from just flooding of the submersible vessel 1.

The energy conversion method described herewith with reference to fig 20 deploys a hydraulic turbines 1 6 for the submersible vessel 1 and (if deployed) for the counterweight vessel 1 02. If the hydraulic turbine 16 in the counterweight vessel 102 was dispensed with or bypassed using a modified inlet pipe 115 or a separate inlet pipe (neither of which are shown) the level of compression of the residual compressible medium in the submersible vessel 1 would be increased due to the correspondingly reduced loading from the hydraulic turbine 16 in the counterweight vessel and hence reduced tension in the cable 1 05 connecting the pistons 1 03 and 104. To preserve the option for power generation directly from the counterweight vessel 1 02 orjust compression within this vessel for utilisation in a storage facility external to the vessel 102 in the absence of direct power generation appropriate closure facilities may be deployed to select either direct power generation via the hydraulic turbine 1 6 or by pass flow in the event that the hydraulic turbine 16 remained in place. In either case the resultant flooding of the counterweight vessel will facilitate provision of balance conditions between the submersible and counterweight vessels 101 and 102 respectively. Further it has been stated herewith that gas or vapour in the counterweight vessel 102 will be compressed from chain or cable 105 tension induced from hydrostatic pressure forces acting on the piston 103 in the submersible vessel 1 at the first reservoir level. However in the event of bypassing or not deploying the hydraulic turbine 1 6 in the counterweight vessel 1 02 the compressible medium in this vessel used to drive the piston 104 down in order to discharge residual water may be dispensed with together with the smaller chamber 11 3 by deploying a pipe 11 8 vented to atmosphere and preferably located at the top 11 9 of the chamber 111 in the counterweight vessel 102. In this case discharge of residual water from the counterweight vessel 102 from piston 1 04 movement would result from atmospheric pressure acting on this piston 104 rather than gas or vapour pressure. The atmospheric pressure forces acting on the piston 104 in the counterweight vessel 102 will generally be less than residual gas or vapour pressure forces acting on this piston. This atmospheric venting approach for discharging residual water from the counterweight vessel 102 rather than the use residual gas or vapour or indeed other compressible media as herewith discussed can facilitate balancing conditions between the submersible vessel 101 and counterweight vessel 102 by voiding each vessel of water. However the force (hence tension in the cable 1 05) from atmospheric pressure resisting hydrostatic pressure forces acting on the piston 103 in the submersible vessel 101 at the first reservoir level will be minimised thereby optimising higher gas or vapour compression levels hence potential output power levels in the submersible vessel's 1 chamber 111. Further for direct power generation from the turbine 16 -if deployed -in the counterbalance vessel 102 atmospheric venting as described herewith would create a lower resistance to flooding of this vessel thereby optimising potential power output levels from this vessel from inflow of reservoir water through an on board hydraulic turbine 16 Figs. 21 a-d shows an energy conversion system 120 deploying a water based variable weight counterweight vessel 121 but with an alternative system configuration to that described with reference to Figs. 20a-d. The Figs. 21a-d show a floating vessel 122 supporting a coaxial differential pulley 123 connected to which is a chain or cable 124 from which a submersible vessel 1 is suspended. The chain or cable 124 is secured to and windable around the larger member 1 26 (with radius R) of the differential pulley 1 23. A second chain or cable 127 supporting a weighted piston 128 in the counterweight vessel 121 passes over an idler pulley 129 to the smaller member 130 (with radius r) of the differential pulley 123 to which it is secured and around which it is windable. The weighted piston 128 has low friction seals (not shown) and can slide freely within the counterweight vessel 121 cylinder 131 with the cylinder 131 being relatively light compared to the weighted piston 128 unless counterbalanced as will be described in the following section. The chain or cables 124 and 127 are wound in opposite senses thereby generating opposing turning moments about the axis 1 32 of the differential pulley 123.

The weighted piston 128 and cylinder 1 31 assembly constitute the major components of the counterweight vessel 121. The cylinder 131 may be closed at the top 1 33 or vented to atmosphere or to an alternative relatively low pressure gas or vapour source. The base 1 34 will be closed except for a water delivery pipe 1 35 sealed to the base 1 34 and extending to and through the surface 72 of the reservoir 2 in which submersible vessel 1 is submerged. The submersible vessel 1 contains a compressible medium 8 (not shown) which typically though not essentially is a gas or vapour 9.The counterweight vessel's cylinder 131 may also contain a compressible medium 8 (not shown) above the weighted piston 128 albeit generating a relatively low constant pressure or force on the weighted piston 1 28 but sufficient to lift the cylinder 1 31 if this is lightweight and voided of water and is free to move. The compressible medium 8 in the submersible vessel 1 when in the form of a gas or vapour is sealed from the reservoir 2 by a piston 136 and when deployed in the counterweight vessel 121 by the piston 128. The submersible vessel 1 and weighted piston 128 -when free to move in its cylinder 131 when the cylinder 131 is latched in position -will each generate opposite turning moments on the larger (of radius R) and smaller (of radius r) members 1 26 and 1 30 respectively of the coaxial differential pulley wheel 1 23. Alternatively if the weighted piston 128 is latched in position and the cylinder 131 is unlatched then their combined weight which will be approximately equal to that of the counterweight vessel itself will again generate a turning moment on the differential pulley in opposition to that generated by the submersible vessel 1. The magnitudes of these aforementioned apposing turning moments will depend upon the individual weights or forces generated by the submersible vessel 1 and the weighted piston 128 alone when free to move in the cylinder 131.However with the weighted piston 128 latched in position within the cylinder 131 the turning moment of the entire counterweight vessel 121 itself will oppose that of the submersible vessel 1. These turning moments will of course also depend upon the radii R and r respectively of the differential pulley wheel members 126 and 1 30 supporting the submersible vessel 1 and weighted piston 128 or counterweight vessel 121 respectively. Under the appropriate magnitudes of the above weights or forces and pulley radii the net turning moment can be made zero implying a balance condition between the submersible vessel 1 and weighted piston 128 or entire counterweight vessel 121 as appropriate.

The ratio R/r of the differential pulley wheels should be made as large as practicable in order to facilitate large descent depths at the first reservoir level for the submersible vessel 1 compared to the corresponding vertical displacement of the counterweight vessel 121. This will subject the submersible vessel to correspondingly large hydrostatic pressures in the reservoir 2 hence large compression levels for generating correspondingly large power outputs at the second reservoir level or energy storage levels in a storage container external to the submersible vessel. However in order to implement balance conditions between the submersible vessel 1 and weighted piston 128 or counterweight vessel 121 the weight of the piston 128 or capacity of the counterweight vessel 121 must be significantly greater than weight or capacity respectively of the submersible vessel 1. It will be noted that under balance conditions the turning moment generated in the smaller of the two pulley wheels of radius r supporting the counterweight vessel 121 will be equal to that generated in the larger of the two pulley wheels of radius R supporting the submersible vessel 1 implying that the tension in the chain or cable 1 27 supporting the counterweight vessel 121 via the weighted piston 128 in this vessel 121 will be R/r times greater than that in chain or cable 1 24 supporting submersible vessel 1.

Transfer of the submersible vessel 1 (when void of water) from the second reservoir level 4 (statel, Fig.21a)to the first reservoir level 3 (state2, Fig.21 b) will subject the submersible vessel 1 to progressively increasing hydrostatic pressures from the reservoir 2. If the piston 1 36 in the cylinder 137 of the submersible vessel 1 is free to move in this cylinder from its position corresponding to the residual compressible medium 8 (advantageously a gas or vapour 9 shown in Figs. 21 a-d) being fully expanded this hydrostatic pressure will force the piston 1 36 down in the submersible vessel's cylinder 1 37. This will progressively compress the compressible medium e.g. residual gas or vapour 9, trapped by the piston 1 36 with the resultant increase in the weight of the submersible vessel 1 from the inflow of hydrostatically pressurised water.lf the volume above the weighted piston 128 in the counterweight vessel 121 is vented to atmosphere or another constant pressure source through a vent pipe 1 38 or alternatively contains a constant low pressure compressible medium such as a saturated vapour and the water delivery pipe 1 35 is closed by a valve (not shown) then irrespective of the position of the weighted piston 1 28 in its cylinder 131 the counterweight vessel's weight will remain constant However with the cylinder 131 prevented from upward movement by stops 139 or by a latching mechanism (not shown) any inward movement of the weighted piston 128 in the cylinderl 31 and with the water delivery pipe 135 closed will depressurise the volume in the cylinder 131 below the piston 128. If however the water delivery pipe 1 35 is open then a progressive increase in weight of the submersible vessel 1 will generate a corresponding increase in the tension of the chain or cable 1 27 supporting the weighted piston 128 thereby drawing it inwards in its cylinder 1 31 with the resultant inflow of water into this cylinder 131 and thus a corresponding progressive increase in the weight of the counterweight vessel 121. This will maintain a balance in the aforementioned flooded conditions between the counterweight and submersible vessels 121 and 1 respectively. It will be noted that If the piston 1 36 in the cylinder 1 37 in the submersible vessel is latched in position in statel (Fig. 21 a) with the compressible medium fully 5I expanded the latter will remain uncompressed during the descent of the submersible vessel 1 to the first reservoir level with its weight remaining constant until reaching the first reservoir level. If at this stage the piston 1 36 is released this will result in the compression of the compressible medium 8 in the cylinder 137 from inflow of hydrostatically pressurised water into the submersible vessel 1 with a resultant increase in its weight. This will unbalance the system and increase the tension in the chain or cable 1 24 supporting the submersible vessel 1 and with a corresponding increase in the tension in the chain or cable 127 supporting the weighted piston 128 in the counterweight vessel 121. If the water delivery pipe 135 is opened at this stage the weighted piston 1 28 will be drawn upwards towards the top of the cylinder 1 31 with an inflow of water from the reservoir 2 through the water delivery pipe 1 35 and a resultant increase in the weight of the counterweight vessel 121.

The volume hence weight of water drawn into the counterweight vessel 1 21 will be in proportion to the axial displacement of the weighted piston 1 28 but a balance between the submersible vessel 1 and counterweight vessel 121 can be re-established with each vessel flooded under the above stated vessel volumes and weights appropriate for balance when each vessel is voided of water.

During water take up periods of either or both vessels 1 and 121 the resultant flow of water into either vessel may be utilised to generate useful power by energising one or more hydraulic turbines 16 associated with the submersible vessel 1 and the counterweight vessel 121 this latter being incorporated into the water delivery pipe 135 but with the provision (not shown) to bypass the hydraulic turbine 16 in the counterweight vessel in order to preserve the option for power generation or gas or vapour 9 storage under compression in a storage facility external to the counterweight vessel 1 21 via transfer from the counterweight vessel 121 as hereby discussed with reference to Figs. 20a-d.

Because vessels 1 and 121 can remain balanced whilst in their flooded conditions the submersible vessel 1 may be raised from a relatively high hydrostatic pressure environment whilst at its descent limit at the first reservoir level 3 in state 2 (Fig. 21 b) to a relatively low one when at or close to the reservoir surface 72 at the second reservoir level in State 3 (Fig. 21 c) with minimum demands on the submersible vessel 1 transfer energy this being limited to overcoming viscous drag forces which can be minimised through vessel streamlining and with any opposing inertial forces being potentially recoverable.

With the submersible vessel 1 at its descent limit at the first reservoir level the weighted piston 128 in the counterweight vessel 121 will be at the limit of its stroke i.e. top dead centre (state 2, Fig. 21 b) and will be latched into position at this maximum weight condition. During the transition of the system from state 2 to state 3 with the submersible vessel 1 being raised to the second reservoir level 4 the counterweight vessel 121 will be lowered towards the reservoir 2 surface 72 (state 3, Fig. 21c). With the submersible vessel 1 at the second reservoir level 4 with a relatively low hydrostatic pressure and the base 134 of the counterweight vessel's cylinder 131 just above or in contact with the reservoir surface 72 the submersible vessel 1 and counterweight vessel 121 (if fitted with a hydraulic turbine) will discharge their water contents into the reservoir 2 through hydraulic turbines 16 for useful power generation. Discharge of water from the submersible vessel 1 will be from expansion of compressible medium driving the piston 1 36 axially downwards and water out through a hydraulic turbine 16. In the case of the counterweight vessel 121 being sealed at the top 133 and with a relatively low constant pressure compressible medium such as a saturated vapour the weighted piston 1 28 will be released from its latched condition whereby the counterweight vessel's 121 cylinder 131 if lightweight will be lifted upwards with relatively low energy demands. In the case of the counterweight vessel being vented to atmosphere or an alternative constant pressure source or if the cylinderl 31 is relatively heavy an associated counter balancing facility 140 can be deployed as shown in Figs. 21a-d.

These figures show a cable 141 connected to the cylinder 131 and passing over an idler pulley 142 and supporting a counterweight 143 at the other cable end. In both cases i.e. the cylinder 1 31 being sealed at the top 1 33 with a low pressure compressible medium or deployment of the cylinder being vented to atmosphere or an alternative low pressure source residual water will be discharged under gravity from the vessel 121 through the water delivery pipe 1 35 via a hydraulic turbine 16 (If Fitted) or through some alternative outlet (not shown) to transfer the system from state 3 (Fig. 21 c) to state 4 (Fig. 21d).

As an alternative or in addition to direct power generation through energisation from water flow through on board hydraulic turbines 16 with gas or vapour in the submersible vessel 1 at its descent limit and thus under maximum compression and weight and hence with the counterweight vessel 121 fully flooded the compressed gas or vapour in the submersible vessel 1 may be transferred to a submerged storage facility or to a surface pressure vessel for subsequent utilisation in power generation.

It will be recalled with reference to Figs. 1 7 and 20 that a submersible vessel and counterweight vessel or solid counterweight mass may run along guide rails which will provide lateral stabilisation for the vessels or counterweight mass as appropriate. It will be appreciated however that guide rails may also be deployed for the energy conversion configurations described with reference to figs. 18, 19, and 21 in order to provide lateral stabilisation for a submersible or counterweight vessel or solid mass these guide rails (though not shown in Figs. 18, 19, and 21) being supported from the relevant system support rig or vessel as appropriate.

In all cases of energy conversion configurations herewith described a submersible vessel is transferred alternately between first 3 and second 4 reservoir 2 levels for respective compression and expansion of a residual compressible medium within the submersible vessel for power generation or energy storage (for a gas or vapour compressible medium) in a local or remote containment. To minimise energy demands incurred in transfer operations the submersible vessel is connected by a cable either directly via one or more idler pulleys, for cable routing, to a counter weight or indirectly via a differential pulley to a counter weight in either case to facilitate balancing between the submersible vessel and counterweight. To initiate and maintain transfer mobility of the submersible vessel and counter weight the connecting cable must be driven in the appropriate direction from some power source. Such a power source could comprise of a motor energised for example from electricity or compressed gas or vapour derived from the energy conversion facility in operation and coupled directly or indirectly through gears to drive a pulley wheel. In the case of an idler pulley wheel to provide the necessary torque for cable tension the associated friction between cable and pulley can be increased by wrapping the cable at least once around the pulley rather than just over it. Instead of using a cable for connecting and transferring the submersible vessel and counter weight between first and second reservoir levels 3 and 4 respectively a chain may be used in conjunction with either pulley wheels or cog wheels. Other forms of cable or chain drive include a winch which may be of a single or differential drum design. Energisation of a motorised drive facility if from the energy conversion facility in operation will of course be parasitic but will under the appropriate operating conditions i.e. balancing, streamlining and submersible vessel transfer range between first and second reservoir levels demand significantly less energy than that derivable from gravity induced hydrostatic pressure gradients associated with the water reservoir within which the submersible vessel is submerged.

Different types of compressible media have been described herewith but a particularly suitable one would be a saturated vapour which would maintain its pressure for a given temperature throughout the extent of compression period even up to and including liquification as a saturated liquid. It will be noted that the method described with reference to Fig. 1 7 involves hydraulic turbine 16 energisation from flow of water at both first and second reservoir levels. However as has been mentioned herewith power generation at the first reservoir level involves a pressure drop across the hydraulic turbine 16 and thereby corresponding reduced compressive forces generated in the residual compressible medium and hence the hydraulic turbine 16 output power from subsequent discharge of water through the hydraulic turbine 1 6 at the second reservoir level 4.

It will be recalled with reference to Figs. 20 and 21 that the counterweight vessels 102 and 1 21 respectively are depressurised during their operation in order to facilitate flow of water into the vessels to maintain balance conditions with the corresponding flooded submersible vessels. However these depressurised conditions can also be deployed for water desalinisation and purification processes through the controlled introduction through for example spraying of salt or contaminated water into a depressurised volume within a counterweight vessel. The resultant clean, preferably saturated water vapour may then be drawn into a vapour collection volume which can be reduced in volume to induce vapour condensation Alternatively vapour condensation may be produced from cooling by deployment of an externally cooled heat exchanger located in the vapour collection volume.

Statements of invention

One aspect of the present invention provides a method for utilising gravitational potential energy associated with hydrostatic pressure gradients within a liquid reservoir and atmospheric pressure acting on said reservoir for the generation of useful power through the steps of alternately transferring a submersible vessel containing a compressible medium between a first and second level within said reservoirs said first level being deeper than said second level whereby said compressible medium is compressed at said first reservoir level through the inflow of hydrostatically pressurised liquid into said submersible vessel at this level with said compressible medium expanding at said second reservoir level from reduced environmental hydrostatic pressure at this level thereby driving residual liquid from said submersible vessel with useful power being generated from inflow or outflow of said liquid from said submersible vessel at said first or said second reservoir levels respectively through one or more hydraulic turbines associated with said submersible vessel and with energy to transfer said submersible vessel between said first and said second reservoir levels for direct power generation using said one or more hydraulic turbines minimised through the implementation of a counterbalancing mechanism associated with a support facility for said submersible vessel or as an alternative to said direct power generation using said associated hydraulic turbines and where said compressible medium is a gas or vapour this may be introduced into said submersible vessel at said second reservoir level prior to compression at said first reservoir level followed by transference to a compressed gas or vapour storage container external to said submersible vessel for subsequent utilisation.

A second aspect of the present invention provides an apparatus for utilising gravitational potential energy associated with hydrostatic pressure gradients within a liquid reservoir for the generating useful power said apparatus comprising a submersible vessel containing a compressible medium and alternately transferable between a first and second level within said reservoir said first level being deeper than said second level whereby said compressible medium is compressed at said first reservoir level from flow into said submersible vessel of hydrostatically pressurised liquid with said compressible medium expanding at said second reservoir level from reduced environmental hydrostatic pressure at this level thereby driving residual liquid from said submersible vessel with one or more hydraulic turbine means associated with said submersible vessel energised from flow of said liquid into or out of said submersible vessel at said first or second reservoir levels respectively or as an alternative to direct power generation using said one or more hydraulic turbine means and where said compressible medium is a gas or vapour this may be introduced into said submersible vessel at said second reservoir level prior to compression at said first reservoir level followed by transference to a compressed gas or vapour storage containment means external to said submersible vessel for subsequent utilisation and with means to support said submersible vessel and alternately transfer it between said first and second reservoir levels together with a counterbalancing means associated with said submersible vessel supporting means to minimise energy requirements for submersible vessel transfer operations between said first and second reservoir levels.

Either of the first or second of the present invention may include one or more of the following optional features, either singly, or in combination with any other.

Said liquid reservoir may be an ocean or lake or man made water containment facility.

Said second reservoir level may be close to said reservoir surface but for ocean reservoirs sufficiently deep to avoid damaging wave action to said submersible vessel.

Said first reservoir level may be as deep as practicable to provide a large hydrostatic pressure difference between said first and second reservoir levels.

Said hydrostatically pressurised water at said first reservoir level being forced into said submersible vessel may increase its weight.

Said submersible vessel may be transferred to said second reservoir level whereupon said compressible medium can expand from reduced hydrostatic pressure at this level driving residual water in said submersible vessel out with a resultant reduction in submersible vessel weight.

A bidirectional or two oppositely configured mono directional hydraulic turbines may be deployed to facilitate power generation from water flow into or out of said submersible vessel.

Said compressible medium may be a gas or a vapour.

Said gas or vapour compressed at said first reservoir level may be transferred to a container external to said submersible vessel for storage.

Said container may be located close to said submersible vessel when at said first reservoir level to minimise stresses across said container's walls.

Said container may comprise a pressure vessel located close to said reservoir's surface with compressed gas or vapour being transferred from said submersible vessel when at said first reservoir level through flexible or extendable pipework.

A gas or vapour based compressible medium which is potentially interactive with a submersible vessel's water payload isolation from said payload may be facilitated by means of a piston.

Energy to transfer said submersible vessel between said first and second reservoir levels may be minimised by a counter balancing mechanism with a facility to accommodate variations in the submerged weights of said submersible vessel corresponding to its flooded and voided conditions.

If only energy storage is required rather than direct power generation on board a submersible vessel a bellows or impermeable bag for containing a gas or vapour may be deployed in the absence of a rigid container.

Gas or vapour may be transferred through valving to said bellows or impermeable bag whilst at the second reservoir level from an external source with a pressure greater than said second reservoir level pressure.

Said bellows or impermeable bag may be provided with ballast to create neutral or negative buoyancy to facilitate transfer and compression at said first reservoir level prior to transfer to said external storage container.

For a gas or vapour source at pressure less than that of said second reservoir level, said bellows or impermeable bag may possess an open cell sponge or foam substance or spring with properties to expand at said second reservoir level but compress at said first reservoir level.

A securing mechanism may be provided to secure said compressible medium in its compressed condition when depleted of residual compressed gas or vapour.

Said securing mechanism may be contained within said bellows or impermeable bag but on transfer to said second reservoir level is releasable to depressurise said bellows or impermeable bag.

Said resilient member contained within said unrestrained bellows or impermeable bag may be contained instead within a piston and cylinder configuration or alternative rigid containment.

For circumstances where said residual gas or vapour is non-reactive with said reservoir water provision of an isolation bellows, impermeable bag or piston may be dispensed with by deploying a rigid vertically orientated gas or vapour containment volume within said submersible vessel with a closed end uppermost and lowermost end facilitating access for reservoir water to form a liquid piston from a water free surface within said submersible vessel.

Said access for reservoir water into said submersible vessel may be via a valved inlet port.

One or more hydraulic turbines may be located at the base of said submersible vessel with associated residual water outlet ports being contained to minimise flow impedance.

Said inlet port may be closed during periods of hydraulic turbine power generation.

A bidirectional hydraulic turbine may be deployed. Two mono directional hydraulic turbines may also deployed but configured for hydraulic flow energisation in opposite directions.

Said bidirectional hydraulic turbine may be energisable from flow at said first or said second reservoir levels.

One of said mono directional hydraulic turbines may energisable from flow into said submersible vessel at said first reservoir level and the second from flow at the second reservoir level.

Said hydraulic power generation levels at said first reservoir levels may be increased by venting residual gas or vapour to atmospheric air or to a relatively low pressure gas or vapour container external to said submersible vessel for gas or vapour.

Said low pressure gas or vapour containment may comprise an inverted chamber supported by anchor lines, or from a surface vessel or pontoon or on a reservoir bed mounted rig in all such cases located close to said reservoir surface.

Said low pressure gas or vapour containment may have a piston or impermeable bag or may be of bellows construction where transferred gas or vapour is potentially reactive with reservoir liquid.

Said compressed gas or vapour storage containment may be located at the reservoir One or more hydraulic turbines on said submersible vessel may be closed with valving at said first reservoir level when compressed gas or vapour is 6I required to be stored in a container external to said submersible vessel with hydrostatically pressurised water being routed through one or more flow inlet ports.

For power generation at said second reservoir level said one or more inlet ports may be closed and said one or more hydraulic turbines closure valves may be open.

For gas or vapour when compressed at said first reservoir level storage in a remote gas or vapour storage container may be carried out through an outlet pipe or conduit located at or towards the closed end of the gas or vapour containment volume within said submersible vessel when said closed end is uppermost.

To facilitate multiple charging of compressed gas or vapour when deploying a liquid piston in a remote storage containment all said turbine and inlet ports may be closed with said closure valves closed with said gas or vapour source being drawn into said submersible vessel at said second reservoir level.

Said gas or vapour containment source may be spatially stabilised by hanging it from a surface floating platform or pontoon if the mean density of said container exceeds that of water or if its density is less than that of water it may be spatially stabilised by anchor lines secured to the reservoir bed.

Transfer of accumulated compressed gas or vapour may be facilitated through a compressed gas or vapour conduit or pipe -which can be extendible or flexible -and lead to a compressed gas or vapour container on a surface vessel for transportation to a remote storage facility.

A submerged compressed gas or vapour containment may be deployed spatially secured through anchor lines with transfer of accumulated gas or vapour to a surface container facilitated through release of said submerged containment followed by ascent to said surface container with an option for guidance during ascent using guide rails.

Said surface gas or vapour containment may be transportable on a containment vessel to a remote location for utilisation.

Said gas or vapour container may be replaceable by a second empty gas or vapour container which on flooding at the surface will sink under negative buoyancy prior to charging with compressed gas or vapour at said first reservoir level as herein described for said other gas or vapour containment which may become positively buoyant on charging.

Said compressed gas or vapour container may be streamlined and may be optionally equipped with on board hydraulic turbines energisable from movement to and from said surface vessel.

Said piston may be weighted.

Said impermeable bag may contain a closed cell sponge or foam substance of natural or synthetic rubber or thermoplastics.

Said impermeable bag may be contained within said submersible vessel with said bag's contents comprising a compressible medium.

An energy conversion system may comprise a beam pivoted at a position displaced from its mid-point and with pulleys at either end over which are routed a chain or cable supporting a submersible vessel at the beam end closest to said pivot and a first counterweight at the other end.

Said beam may possess an additional beam section secured to said pivoted beam section on the submersible vessel side of said pivot with said additional beam section supporting a second counterweight transferable through sliding or running along said additional beam sections length.

Said pivoted beam horizontal said submersible vessel may be at its shallowest depth and void of water with said first counterweight submerged at its descent limit.

Said submerged vessel may be lowered to said first reservoir level and flooded from hydrostatic pressure forces with a resultant weight increase and with said first counterweight raised to said second reservoir level.

Said tensile forces generated in said submersible vessel and first counterweight may be equal but opposite together with equal but opposite turning moments about said pivot.

Said weight increase of said submersible vessel may cause said pivoted beam to rotate driving said first counterweight out of the reservoir thereby removing its buoyancy thus increasing its weight to preserve a weight equality between submersible vessel and said first counterweight together with equal turning moments about said pivot.

A beam may be pivoted at a mid-point position along its length and an idler pulley wheel may be located at one end of said beam and differential pulley wheel at the other end.

A submersible vessel may be supported from said idler pulley wheel from a chain or cable routed over this pulley wheel and secured to the larger of the two radial members of said differential pulley wheel.

A first counterweight may be secured to the smaller radial member of said differential pulley wheel.

An additional counterweight may be located at the end of said beam associated with said submersible vessel.

A beam section may be secured to said mid-point pivoted beam extending from the region of said pivot to the end associated with said submersible vessel.

Said beam section may support a further counterweight runnable along said beam section.

Said mid-point pivoted beam may be horizontal with said submersible vessel void of water when submerged at its shallowest reservoir level but with said first counterweight submerged at its descent limit.

Said submersible vessel may flood and gain weight when submerged to its descent limit with said first counterweight raised to just below said reservoir surface.

Said mid-point pivoted beam may be rotated by the increased flooded weight of said submersible vessel driving said counterweight out of said reservoir and thereby gaining weight through loss of buoyancy hence an equality between weights of said submersible vessel and counterweight.

Said rotation of said mid-point pivoted beam may induce mobility of said counterweight on said beam section to preserve equal but opposite turning moments of said chain or cables about said differential pulley axis.

A pivoted counter balanced first beam may support an idler pulley at one end and a differential pulley in the region of said pivot position.

A submersible vessel may be supported by a first chain or cable routed over said idler pulley and secured to the larger radial member of said differential pulley wheel together with a second chain or cable supporting a counterweight and secured to and supported by the smaller radial member of said differential pulley wheel.

Said second counterweight may be transferable along a second beam inclined to said first beam and secured at an upper end to said first beam.

Said inclined beam may be supported at its lower end and by a third beam connected to said first beam.

Said first beam may have a fixed counter balancing weight at the end opposite to said idler pulley position.

Said first beam may be horizontal with said second beam inclined to said vertical and with said submersible vessel void and at said second reservoir level and said second counterweight at its lowest position along said inclined beam such that said submersible vessel and said second counterweight are balanced.

On lowering said submersible vessel to said first reservoir level and thereby raising said second counterweight to said top of said second beam said submersible vessel may be flooded by increased hydrostatic pressure forces creating an imbalance between said submersible vessel and said second counterweight.

Said imbalance may cause said first beam to incline downwards and said second beam to orientate vertically thereby re-balancing said submersible vessel and said second counterweight.

Said submersible vessel may be raised towards said supporting idler pulley and said second counterweight lowered.

Said submersible vessel's residual water may be discharged through an on board hydraulic turbine with power generation and a reduction in the weight of said submersible vessel with the resulting imbalance condition of said submersible vessel and said counterweights returning said first beam to its horizontal orientation.

Said submersible vessel may be supported by a chain or cable routed over an idler pulley secured to the upper end of an inclined beam with the other end of said chain or cable being connected to a floodable counterweight transferable along said inclined beam.

Said floodable counterweight may have a lockable piston to which is connected said other end of said chain or cable.

Said floodable counterweight may have a water delivery pipe extending into said reservoir with said counterweight, inclined beam and idler pulley being supported on a floating vessel, pontoon or reservoir bed mounted rig but remaining above said reservoir surface.

Said submersible vessel may be flooded when lowered to said first reservoir level with said counterweight being drawn up said inclined beam via said lockable piston when locked in position.

Said lockable piston may be released on said counterweight reaching the top of its travel along said inclined beam thereby facilitating flooding of said counterweight through said water delivery pipe from said submersible vessel's flooding hence weight increase thereby pulling said counterweight piston upwards.

A balance between said submersible vessel and counterweight may exist when each are either void of water or flooded.

Lowering said submersible vessel from said second to first reservoir level may drive said floodable counterweight up said inclined beam with said lockable piston remaining locked in position.

Said lockable piston in said floodable counterweight may be released when said submersible vessel is flooded at said first reservoir level thereby drawing said lockable piston upward and drawing water into said floodable counterweight through said water delivery pipe with a resultant increase in the weight of said floodable counterweight.

A balance may exist between said submersible vessel and said floodable counterweight when they are either both void of water or both flooded.

Said energy conversion facility mat comprise a submersible vessel suspended from a first chain or cable connected to the larger radial member of a differential pulley wheel and windable around said member.

Said differential pulley wheel may support a second chain or cable connected to and windable around the smaller radial member of said differential pulley wheel but in the opposite sense to said first chain or cable.

Said second chain or cable may support a floodable counterweight through attachment to a lockable piston.

On lowering said submersible vessel said counterweight may be raised when said lockable piston is locked in position.

On releasing said lockable piston flooding of said counterweight via reservoir water inflow through a water delivery pipe may result due to the increased weight of said submersible vessel from flooding.