GB2241990A - Power generation from tides - Google Patents

Abstract

Power generation apparatus driven by the tides includes one or more floats 118 a b c d e or float assemblies which may comprise scrap containers sealed to make them buoyant. They are moored by running tackle 120 a b c or other selectively controlled restraining means in tidal waters e.g. by cables running in a continuous loop round guide pulleys between a supporting gantry 110 and a seabed anchorage 116, for controlled rising and falling motion on or submerged in the tidal waters and this motion is controlled and converted, e.g. by harnessing the runs of cable to energy conversion means, for generation of electricity or other power output. The vertical movement of the floats may be regulated by braking means acting on the running tackles. The floats could be fillable with water to assist their downward travel. Instead of running tackle 120, the floats could be connected to pivoted arms or guided within frames with the drive and braking being provided through a rack and pinion arrangement. <IMAGE>

Description

POWER GENERATION This invention relates to the generation of power utilising the tides. Typically, but not essentially, the power generated will be electricity e.g. for distribution through the National Grid though the application of the invention is not limited to generation of electricity and it may be applied to the production of other forms of secondary power or energy e.g. mechanical energy for local application or possibly hydraulic or pneumatic energy, maybe for wider distribution.

It is known to harness tidal forces for power generation but many known schemes involve the damming of a bay or inlet such as an estuary in tidal waters by a barrage so as to form a holding reservoir filled on a flow tide, the head of water so provided being utilised to drive hydro electric generators or other power conversion apparatus.

Such schemes involve large capital costs, can only be effective when built on a large scale, can only be installed at a very limited number of locations where conditions are suitable, and are objectionable on environmental and ecological grounds e.g. in giving rise to the destruction of wild life due to loss of salt marshes and the like, and loss of recreational and commercial facilities such as tidal beaches, harbours and anchorages, obstruction to navigation, and harmful side effects such as silting.

Tidal power generation using barrages is also inefficient in that operation is only possible when there is sufficient head of water on one or other side of the barrage to drive the generators. Even in locations having substantial tides power production may only be possible for at most approximately half of the time at spring tides and production may be even more restricted at times of neap tides. More4yer the productive periods will vary with the time of the tides throughout the year and will often be completely out of synchronization with periods of maximum demand for power. Thus it has been found that such tidal schemes as have been constructed have not generally been commercially viable or competitive with conventional power generation utilising non-renewable energy sources (e.g. coal or oil).

The object of the invention is to provide power generation apparatus harnessing tidal forces in a particularly efficient and economical manner and in a form which can be constructed and used on small or large scales at almost any location in tidal waters and without any substantial adverse ecological, environmental or commercial side effects. A further object of the invention is to utilise in an effective, profitable and desirable manner the vast quantities of waste containers of certain types whose disposal is itself causing or substantially contributing to environmental and ecological problems and wastage of energy and resources.

According to one aspect of the invention there is provided power generation apparatus including at least one buoyant body, restraining means for operatively mooring said body in tidal waters while permitting controlled rising and falling motion thereof, drive means for operatively harnessing primary energy of upward forces exerted on the restraining means in use due to flotation of the body on or submerged in a flow tide, and energy conversion means driven by the drive means for production of secondary energy to -be transmitted or -distributed from the apparatus in use.

Typically the power conversion means will include an alternator or other electric generator to produce secondary energy in the form of electric current.

Preferably the restraining means is arranged to selectively hold the buoyant body submersed substantially below water level during all or at least part of its operating cycle both to increase said upward forces thereon and to conserve said forces for their most efficient and economical controlled application according to requirements and to some extent independently of the timing of the tidal cycle, for example by holding the body at its lowest level so that it becomes submerged at the commencement of a flow tide its latent energy may be in effect stored for deferred release even at or after high tide or even during a substantial proportion of an ebb tide.

It is further contemplated that a power generating installation could comprise a plurality of buoyant bodies, or float assemblies each comprising a plurality of interconnected buoyant bodies; each said body or assembly having respective restraining means but with the primary energy harnessed through parallel or common drive means to act on the power conversion means, it being contemplated that they could be controlled for sequential operation e.g. as one submerged body or assembly nears or reaches the surface so that its primary energy is expended another submerged said body or assembly could be brought into operation by allowing it to commence rising, so providing substantially constant power output and/or enabling the power output to be adjusted according to demand.

For even greater efficiency and to provide continuous power output throughout the tidal cycle, i.e.

during both flow and ebb tides, the or each said apparatus or assembly preferably further includes at least one gravity drive body coupled to the or each said buoyant body or float assembly for rising and falling motion therewith and defining a water containing chamber disposed to be filled with water on submersion and to retain a substantial volume of water when above the water level, the weight of the contained water providing further primary energy to be harnessed by the associated drive means through the downward forces exerted on the restraining means in use due to gravity when said bodies or assemblies are above water level e.g. during all or part of the ebb tide.

The buoyant bodies may be formed of flexible or semi-rigid materials and may be internally pressurised to resist collapse at depth within the water.

According to a further aspect of the invention a method of disposal of waste products in the form of containers, of almost every size or type by utilising them non-destructively to produce power includes the steps of selecting those containers which can readily be rendered buoyant, closing or sealing them to prevent ingress of water, possibly with their internal pressurisation to resist collapse at depth within the water if they have non-rigid walls e.g. of plastics material, and utilising one or more said containers as a buoyant body or, in the case of a plurality thereof, as a float assembly in power generation apparatus or a power generating installation as above defined.

Said waste containers may range from scrap boats and ships e.g. tanker vessels through scrap industrial tanks, process vessels, and oil or similar barrels or drums, down to scrap plastics carbonated drinks bottles which could be collected in enormous quantities and gathered together e.g. by containment in nets or the like to form very cheap and simple highly buoyant float assemblies.

The method of said invention may also extend to utilisation of containers such as scrap tin cans, open drums and the like to provide gravity drive bodies disposed to contain and hold water in the power generating apparatus or installation as above defined.

Embodiments of the invention is now more particularly described with reference to and as shown in the accompanying drawings wherein : Figures la and Ib are diagrammatic elevations of a basic form of power generation apparatus, and Figure 2 is a like diagram of a power generating installation.

An example of a basic power generation apparatus embodying the invention is illustrated diagrammatically in Figures la, b. The apparatus can be installed at any convenient location in tidal waters, preferably just off shore for convenience of access and to reduce construction costs though it could be located in deeper water. Preferably the location chosen has a substantial tidal range.

In the example shown the apparatus comprises a fixed structure or gantry 10 planted securely in the seabed 12 and of sufficient height to carry its top including a pair of oppositely directed cantilever arms 14 clear of the water level at maximum high tides.

Aligned immediately below the outer end of each arm 14 is a fixed anchor 16 secured in or on the seabed.

The apparatus of this example further comprises a pair of float assemblies 18a, 18b which are moored for rising and falling movement by respective running tackle 20a,20b comprising wire rope, chain or other cable connected to the top and bottom of each assembly 18 and passing round pulleys on the respective arm 14, anchor 16, and on the gantry 10 to form an endless loop.

In this arrangement the cable of the tackle 20 serves not only as part of restraining means mooring the float assemblies 18 but also as part of drive means for transmitting vertical motion of said assemblies to energy conversion means referred to hereafter.

Each of the float assemblies 18 (whose construction is not detailed in the drawings) comprises one or more buoyant bodies so that the overall density of the assembly 18 is very substantially less than that of water, for example round half or less than water. While purpose built buoyant bodies might be used it is preferred that scrap or waste containers are utilised as referred to above.

In one example large quantities of plastics carbonated drinks bottles e.g. of one or two litre capacity are collected and corked or capped to seal them full of air. Preferably they are positively pressurised e.g. by charging them with pressurised air or other inert gas or possibly by using a small charge of a gas generating chemical or compound placed in each body immediately before capping. Said bottles are capable of withstanding substantial internal pressures and such pressurisation will resist any tendency of the containers to flatten or collapse when at depth within the water.

A large number of buoyant bodies so formed can be assembled together e.g. within a cage or net to make up each float assembly 18.

As well as having the advantages of cheapness and simplicity the use of large number of buoyant bodies such as said bottles makes the float assemblies more durable in that their performance will not be adversely effected if a few of the buoyant bodies leak or are subjected to damage e.g. by abrasion, and their maintenance by replacement with fresh bottles if and when need arises is cheap and speedy.

Each float assembly will further include, in this example, one or more gravity drive bodies. Again while purpose built bodies could be used it is preferred that these are also waste or scrap containers e.g. tins or drums but instead of being closed or sealed they will remain open so as to be filled with water and they will be so disposed in the assembly that they hold a substantial quantity, e.g. weight, of water when the respective assembly 18 is above water level.

It will be appreciated that when the gravity drive bodies are below the level of the water their overall density will be substantially equal to that of the water i.e. they will have minimal effect on the buoyancy of the float assembly as a whole apart from the density of the material making up the walls of said drive bodies.

The cables of each of the running tackles 20 are engaged around drums or driving pulleys of drive means of the apparatus which are indicated generally at 22 conveniently located on gantry 10 above the water level, said pulleys or drums being positively rotated by passage of the cables over or therearound and also being provided with braking means for selective control of each running tackle 20 either in unison or possibly independently so that the vertical movement of the float assemblies 18 is correspondingly regulated.

The drums or pulleys 22 are connected to appropriate drive transmission means which may take various forms and which may incorporate ratchet or similar devices to provide uni-directional rotary drive regardless of the direction of movement of the cables and which may also incorporate transmission gearing or torque conversion devices to give a higher speed and possibly constant velocity rotary output.

The latter output can be applied directly or indirectly to drive energy conversion means such as an electric alternator or other generator producing electric current which will be transmitted or distributed from the apparatus in known manner.

It will be appreciated that various forms of drive transmission could be employed, a further possibility is the use of hydraulic transmission, the movement of the cables driving a hydraulic pump (which could operate regardless of the direction of its drive input and which could also be controlled to serve as the braking device), the hydraulic power so provided being transmitted for use in driving an alternator or the like particularly where it may be more convenient to locate the latter remote from the gantry 10, e.g. in an on-shore power station.

In operation the float assemblies 18 could simply be allowed to rise buoyantly with each flow tide so that they would be floating at or near the water surface, and as the tide ebbed the weight of the water filled gravity drive bodies of the assemblies would be utilised in reverse downward motion. However, this form of operation would only provide intermittent power output as there would be little vertical movement during change of tide i.e. around low or high water so the operation would not be much more efficient than that provided by tidal barrages referred to above.

It is preferred that the braking means is selectively operated to hold the assemblies 18 below water level e.g. initially stationary at their lowest positions during a flow tide and to allow them to rise gradually or in stages in a controlled manner as represented in Figure la, the water level of the rising tide being indicated at 30a.

Not only does holding them at depth increase the buoyant forces acting thereon to provide the power output but it also permits effective operation over much longer periods if required, e.g. if either or both assemblies 18 have only reached or been held at a halfway position by the time of high tide their buoyant upward movement and hence production of power can continue even during the commencing portion of an ebb tide. Similarly if the assemblies have been raised to their highest level on a flow tide they can be braked and allowed to descend as represented in Figure ib (water level of ebbing tide indicated at 30b) utilising the weight of the gravity drive bodies independently of the rate of ebb subject only to the limitation that their rate of descent cannot exceed the ebb.

While apparatus incorporating a single float assembly is contemplated within the invention the use of at least a pair of assemblies acting on the opposite sides of the gantry 10 or other supporting structure is preferred because the forces on said structure are then better balanced and it can therefore be more lightly and economically constructed.

While an arrangement using cables and pulleys is convenient it will be appreciated that other forms of restraining and drive means could be employed, for example the or each assembly could be linked to fixed structure by pivoted swinging arms for rising and falling movement and the angular displacement of said arms could be applied to drive the generator or other energy conversion means directly or indirectly. In another arrangement envisaged the float assembly could be guided for rising and falling movement within a fixed frame with the drive and braking being provided through a vertical rack and pinion arrangement or similar mechanism.

The limitations of the simple form of apparatus described above will be apparent, there is very little flexibility of operation and power output and there will still be "dead periods when little or no power can be produced. If the assemblies 18 are not allowed to rise to the full extent possible by being carried up fully on a flow tide there will be corresponding reduction in their downward travel during an ebb tide and continuous power production at maximum rating will not be possible.

Thus a compound arrangement of a plurality of independently controlled float assemblies forming part of a power generating installation illustrated diagrammatically in Figure 2 is preferred.

In this arrangement a much large gantry 110 is provided to accommodate a large number of float assemblies 11era, b, c etc preferably disposed in pairs on opposite sides of the gantry to balance the forces thereon.

For clarity in Figure 2 three pairs of assemblies 118 have been shown disposed at varying distances laterally of the gantry 10 and connected by their respective running tackles 20 to common cantilever arms 114 thereof and to respective anchors 116. It is contemplated, however, that gantry 210 would be of substantial length (depending on requirements) so that many pairs of float assemblies could be accommodated in longitudinal rows.It will be appreciated that the simplicity of construction means that a gantry could be readily extended and further float assemblies added if power capacity was to be increased; and/or further power generating installations could be erected in close proximity to each other noting that they occupy a small area, that they can readily be positioned clear of navigation channels and that in any event the obstruction they present is small compared with many other kinds of power generating installations, and that they can also be located having due regard to visual and other amenities.

The multiple or compound arrangement incorporated in the Figure 2 installation enables continuous power output as the assemblies can be sequentially operated e.g. they can be released from their lowest submerged position in overlapping or other series and can be allowed to lower from their highest out of water positions again in overlapping or other series to provide continuous drive as a whole in one or other direction.

If the assemblies are allowed to rise or fall rapidly their impetus may provide a degree of over shoot contributing further to the continuous drive effect and the smoothness of drive may be further supplemented by use of power storage devices such as flywheels or hydraulic accumulators.

The desirability of utilising large quantities of scrap or waste containers in this way is readily apparent. Apparatus or installations can be constructed on small or large scales and/or can readily be added to as referred to above. Very large scale installations could utilise high volume buoyant bodies and gravity drive bodies, possibly even up to the scale of utilising scrap seagoing tanker vessels for this purpose.

Another type of scrap container whose use is contemplated is scrap motor vehicle tyres. The disposal of these is an increasing problem particularly as they do not degrade except by burning and their incineration produces a high level of pollution unless it is carried out under very carefully controlled conditions which make disposal troublesome and costly. Batches of tyres could be clamped together between suitable sealing plates to form buoyant bodies for use in the invention very cheaply and .simply and again the bodies so formed could be positively internally pressurised (which would add to the effective sealing).

As an example of the kind of power output contemplated as well within the capabilities of the invention a buoyant body or assembly of buoyant bodies having a cubic capacity of around 120 cu.m. (4,400 cu.

ft.) held at depth while a tide has risen by some 4 meters (13 1/2ft) above it and then allowed to rise buoyantly to the surface over a period of 2-3 minutes will provide over 100 hp over that period.

Further flexibility of operation could be provided by utilising the buoyant bodies to store power e.g. by absorbing surplus generating capacity for release at peak periods. With the embodiments shown this would be effected by winching the bodies up or down in opposition to the gravity or flotation forces acting thereon (depending on the state of the tide) for subsequent release as required.

It is contemplated that an installation occupying an area of some 1000 sq.m. will readily provide about 100hp output continuously.

Claims (13)

1. Power generation apparatus including at least one buoyant body, restraining means for operatively mooring said body in tidal waters while permitting controlled rising and falling motion thereof, drive means for operatively harnessing primary energy of upward forces exerted on the restraining means in use due to flotation of the body on or submerged in a flow tide, and energy conversion means driven by the drive means for production of secondary energy to be transmitted or distributed from the apparatus in use.

2. Apparatus as in claim 1 wherein the power conversion means includes an alternator or other electric generator to produce secondary energy in the form of electric current.

3. Apparatus as in claim 1 or 2 wherein the restraining means is arranged to selectively hold the buoyant body submersed substantially below water level during all or at least part if its operating cycle both to increase said upward forces thereon and to conserve said forces for their most efficient and economical controlled application according to requirements and to some extent independently of the timing of the tidal cycle.

4. Apparatus as in claim 1, 2 or 3 wherein said restraining means includes running tackle arranged in an endless loop mooring the buoyant body for vertical motion, said tackle also serving in said drive means to transfer said motion to the energy conversion means.

5. Apparatus as in any preceding claim comprising a plurality of said buoyant bodies or a plurality of float assemblies each comprising a plurality of interconnected buoyant bodies; each said body or assembly having respective restraining means but with the primary energy of all said bodies or assemblies harnessed through parallel or common drive means to act on common power conversion means.

6. Apparatus as in claim 5 including control means for regulated sequential operation of said bodies or assemblies to apply their primary energy successively to provide substantially constant power output and/or to enable the power output to be adjusted according to demand.

7. Apparatus as in any preceding claim wherein the or each said buoyant body or float assembly further includes at least one weighted gravity drive body incorporated therein or coupled thereto to provide a downward force whose primary energy can be harnessed by the drive means if and when the associated buoyant body or float assembly is not fully supported by the water.

8. Apparatus as in claim 7 wherein said gravity drive body comprises a water containing chamber disposed to be filled with water on submersion and to retain a substantial volume of water when above the water level.

9 Apparatus as in any preceding claim wherein the or each buoyant body is formed of flexible or semi rigid materials and is internally pressurised to resist collapse at depth within the water.

10. Power generation apparatus substantially as hereinbefore described with reference to and as shown in Figures Ia and 1b or in Figure 2 of the accompanying drawings.

11 A method of utilising waste products in the form of containers non-destructively to produce power including the steps of selecting those containers which can readily be rendered buoyant, closing or sealing them to prevent ingress of water, and incorporating one or more said containers as a buoyant body or, in the case of a plurality thereof, as a float assembly in power generation apparatus as defined in any preceding claim.

12 A method as in claim 11 utilising further containers to provide gravity drive bodies disposed to contain and hold water in power generating apparatus as in claim 8.

13. Electric power when generated by the apparatus or method of any preceding claim.