WO2023223019A1

WO2023223019A1 - Tidal energy system

Info

Publication number: WO2023223019A1
Application number: PCT/GB2023/051286
Authority: WO
Inventors: Stuart Frank MURPHY
Original assignee: Murphy Stuart Frank
Priority date: 2022-05-16
Filing date: 2023-05-16
Publication date: 2023-11-23
Also published as: GB202207103D0

Abstract

A tidal energy system comprising: a seaward and a landward storage basin and an intermediate storage basin between the seaward and landward storage basins; and a bypass storage basin. A turbine is provided between the sea and the seaward storage basin, a turbine is provided between the seaward and the intermediate storage basins, a turbine is provided between the intermediate and the landward storage basins, a turbine is provided between the bypass storage basin and the sea; and a turbine is provided between the bypass and the landward storage basins. In a first operation phase, rising tidal water received at the seaward storage basin charges the tidal energy system by movement of water from the sea, to seaward to intermediate then to landward storage basins.

Description

Tidal Energy System

FIELD

[01] The present invention relates to tidal energy systems, and to related methods.

BACKGROUND

[02] Tidal energy systems offer the potential to generate electricity while avoiding disadvantages associated with using fossil fuels in generation. In order to increase the efficiency of tidal energy systems it is desirable to maximise the amount of water that flows through the turbines, so for systems that employ tidal storage a location that that has a large tidal range is preferred. Use of a single basin for tidal storage leads to significant periods of time during which electricity is not being generated. These periods are typically while the tide is incoming before water is accumulated in the basin, and while waiting for the outgoing tide to cause a reduction in water level outside the basin. Furthermore, in systems that use the head of accumulated water in a storage basin to drive turbines it may be difficult to ensure that the turbines are working at maximum efficiency as the basin empties and the head of accumulated water drops.

[03] Example embodiments aim to address issues associated with the prior art, whether identified herein or otherwise.

SUMMARY

[04] In one example, there is provided a tidal energy system comprising: a seaward storage basin; a landward storage basin; an intermediate storage basin between the seaward and landward storage basins; and a bypass storage basin; wherein: the seaward storage basin is in use operable: to receive and store incoming tidal water; to deliver water therefrom to the intermediate storage basin; to receive and store outgoing tidal water from the intermediate storage basin; and to deliver water therefrom out of the tidal energy system to sea; the landward storage basin is in use operable to: receive and store water from the intermediate storage basin; to deliver water therefrom to the intermediate storage basin; and to deliver water therefrom to the bypass storage basin; the intermediate storage basin is in use operable: to receive and store water from the seaward storage basin; to deliver water therefrom to the landward storage basin; to receive and store water from the landward storage basin; and to deliver water therefrom into the seaward storage basin; and the bypass storage basin is in use operable: to receive and store incoming tidal water; to receive and store outgoing tidal water from the landward storage basin; and to deliver water therefrom out of the tidal energy system to sea; wherein a turbine is provided between the sea and the seaward storage basin, a turbine is provided between the seaward storage basin and the intermediate storage basin, a turbine is provided between the intermediate storage basin and the landward storage basin, a turbine is provided between the bypass storage basin and the sea; and a turbine is provided between the bypass storage basin and the landward storage basin, wherein the turbines are arranged such that during cyclical operation phases corresponding to a tidal cycle: in a first operation phase, rising tidal water received at the seaward storage basin charges the tidal energy system by movement of water from the sea, to seaward to intermediate then to landward storage basins; in a second operation phase, incoming tidal water reaches a maximum tidal depth in the seaward, intermediate and landward storage basins, and is delivered to the bypass storage basin at a depth above the maximum tidal depth; in a third operation phase, as the tide falls water is discharged from the tidal energy system to sea by movement of water from landward to intermediate to seaward storage basins and to sea, driving the turbines there-between, out of the seaward storage basin and thus out of the tidal energy system; and in a fourth operation phase, water is discharged from the bypass storage basin; wherein, in the third operation phase, water is delivered to the bypass storage basin to ensure sufficient water is present to operate the fourth operation phase until such time as the tide has turned and risen to allow commencement of the first operation phase for a following tidal cycle.

[05] In one example, in the fourth operation phase, water is discharged from the tidal energy system by movement of water from the bypass storage basin to sea, and thus out of the tidal energy system, and/or is discharged from the bypass storage basin to the landward storage basin.

[06] In one example, the bypass storage basin is in use operable to receive and store water from the landward storage basin in the second operation phase. In one example the bypass storage basin is in use operable to receive and store water from the sea in the second operation phase. In one example the bypass storage basin is in use operable to receive and store water from the landward storage basin and from the sea in the second operation phase.

[07] In one example, the landward storage basin is in use operable to receive and store water from the bypass storage basin; and in the third operation phase, water is delivered to the bypass storage basin from the landward storage basin to ensure sufficient water is present to operate the fourth operation phase until such time as the tide has turned and risen to allow commencement of the first operation phase in the following tidal cycle.

[08] In one example, a plurality of bypass storage basins are provided; the bypass storage basins interconnected with one another. In one example, the plurality of bypass storage basins are operable: to receive and store incoming tidal water; to deliver water therefrom to the landward storage basin; to receive and store outgoing tidal water from the landward storage basin; and to deliver water therefrom out of the tidal energy system to sea, with turbines provided at the interconnects, and between the bypass storage basins and the sea. [09] In one example, the turbine provided between the sea and the seaward storage basin is arranged such that movement of water into the seaward storage basin from the sea is arranged to drive said turbine. In one example, the turbine provided between the sea and the seaward storage basin is arranged such that movement of water out of the tidal energy system from the seaward storage basin is arranged to drive said turbine. In one example, flow is controlled through said turbine such that relative water levels in are maintained at a predetermined water level difference between inlet and outlet sides of the turbine as water moves into the seaward storage basin during the first operation phase. In one example, flow is controlled through said turbine such that relative water levels in are maintained at a predetermined water level difference between inlet and outlet sides of the turbine as water moves into the seaward storage basin during the first operation phase.

[10] In one example, the turbine provided between the seaward storage basin and intermediate storage basin is arranged such that movement of water into the intermediate storage basin from the seaward storage basin, and movement of water out of the intermediate storage basin to the seaward storage basin is arranged to drive said turbine, and wherein flow is controlled through said turbine such that relative water levels are maintained at a predetermined water level difference between inlet and outlet sides of the turbine as water moves into or out of the intermediate storage basin during the first and third operation phases respectively.

[11] In one example, the turbine provided between the intermediate storage basin and landward storage basin is arranged such that movement of water into the landward storage basin from the intermediate storage basin is arranged to drive said turbine. In one example, the turbine provided between the intermediate storage basin and landward storage basin is arranged such that movement of water out of the landward storage basin to the intermediate storage basin is arranged to drive said turbine. In one example, flow is controlled through said turbine such that relative water levels are maintained at a predetermined water level difference between inlet and outlet sides of the turbine as water moves into or out of the landward storage basin during the first and third operation phases respectively.

[12] In one example, wherein one or more of said turbines is provided as a turbine assembly comprising an inlet/outlet on each side, operable so that in use movement of water through the turbine assembly in either direction drives the turbine. In one example, all of said turbines are provided as a turbine assembly comprising an inlet/outlet on each side, operable so that in use movement of water through the turbine assembly in either direction drives the turbine.

[13] In one example, one or more of said turbines is provided as a turbine assembly comprising sluice gates operable to in use control movement of water there-through. In one example, all of said turbines are provided as a turbine assembly comprising sluice gates operable to in use control movement of water there-through [14] In one example, one or more of said turbines is provided as a turbine assembly that is mounted for movement relative to the water levels in the storage basins. In one example, all of said turbines is provided as a turbine assembly that is mounted for movement relative to the water levels in the storage basins.

[15] In one example, one of more of said turbines, such as all of said turbines, is provided as a turbine assembly comprising a plurality of turbine elements and an associated plurality of inlets/outlets arranged vertically distanced from one another such that flow is controlled through said turbine assembly such that relative water levels are maintained within a predetermined water level difference between inlet and outlet sides of the turbine, by opening and closing the inlets/outlets as the water levels on both sides of the turbine change.

[16] In one example, one or more of said turbines is operable as a pump to drive movement of water between the respective storage basins. In one example, one or more of said turbines is operable as a pump to drive movement of water the sea and the respective storage basins. In one example, all of said turbines are operable as pumps. In one example, one or more of said turbines is operable to drive an associated generator to thereby produce electrical energy as the turbine is driven. In one example, all of said turbines are operable to drive associated generators to thereby produce electrical energy as the turbines are driven.

[17] In one example, the turbines described may be a distributed array of turbine elements, operable together to generate or to pump as described.

[18] In one example, the tidal energy system further comprises a forward guide structure arranged to shelter the seaward storage basin from the sea while still allowing tidal flow to and from the seaward storage basin. In one example, the forward guide structure comprises a narrowing channel or plurality of narrowing channels, to provide a local increase in depth as the incoming tide impinges thereon.

[19] In one example, reference to a predetermined water level difference means that the water level difference does not exceed a predetermined threshold for maximum water level difference. In one example, reference to a predetermined water level difference means that the water level difference does not vary by more than a set percentage from a target water level difference during the passage of water from one basin to another and/or between the sea and a basin and/or the basin and the sea. In one example, the predetermined water level difference is maintained during a set percentage of the respective operation phase, for example, for 50%, or more than 50% thereof, such as 60%, 70%, 80%, 90% or more thereof. In one example, the predetermined water level difference is maintained during a set percentage of the respective operation phase, centred around the midpoint of the operation phase. [20] In one example, the storage volume of the seaward storage basin is larger than the storage volume of the intermediate storage basin. In one example, the ratio of storage volumes between the seaward storage basin and the intermediate storage basin is in the range 1 .5:1 and 1.1 :1 , for example 1 .2:1 . In one example, the storage volume of the intermediate storage basin is larger than the storage volume of the landward storage basin. In one example, the ratio of storage volumes between the intermediate storage basin and the landward storage basin is in the range 1.5:1 and 1.1 :1 , for example 1.25:1. In one example, the storage volume of the bypass storage basin is larger than the storage volume of the landward storage basin. In one example, the ratio of storage volumes between the bypass storage basin and the landward storage basin and the is in the range 2:1 and 1 .5:1 , for example 1 .9:1 .

[21] In one example, a method of tidal energy generation is provided, comprising (a) in a first operation phase, receiving tidal water at the seaward storage basin to charge the tidal energy system by movement of water from the sea, to the seaward to an intermediate then to a landward storage basin; (b) in a second operation phase, as the incoming tidal water reaches a maximum tidal depth in the seaward, intermediate and landward storage basins, delivering water to a bypass storage basin at a depth above the maximum tidal depth; (c) in a third operation phase, as the tide falls discharging water from the tidal energy system to sea by movement of water from landward to intermediate to seaward storage basins and to sea, driving the turbines there-between, out of the seaward storage basin and thus out of the tidal energy system; and (d) in a fourth operation phase, discharging water from the bypass storage basin; wherein, in the third operation phase, water is delivered to the bypass storage basin to ensure sufficient water is present to operate the fourth operation phase until such time as the tide has turned and risen to allow commencement of the first operation phase for a following tidal cycle.

[22] In one example, the height of the turbine between the sea and the seaward storage basin is the same as that of the turbine between the seaward storage basin and the intermediate storage basin. In one example, the height of the turbine between the seaward storage basin and the intermediate storage basin is the same as that of the turbine between the intermediate storage basin and the landward storage basin. In one example, the height of the turbine between the intermediate storage basin and the landward storage basin is the same as the height of the turbine between the landward storage basin and bypass storage basin. In one example, the height of the turbine between the landward storage basin and the bypass storage basin is the same as the height the turbine between the bypass storage basin and the sea. In one example the height of the turbine between the bypass storage basin and the sea is the same as the height of the turbine between the sea and the seaward storage basin.

[23] In one example, the method is performed with a tidal energy system as described herein. [24] According to the present invention there is provided a system as set forth in the accompanying independent claim. Other features of the invention will be apparent from the dependent claims, and the description which follows.

BRIEF DESCRIPTION OF DRAWINGS

[25] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which:

[26] FIG. 1 shows a schematic plan view of a tidal energy system according to an example embodiment of the present invention;

[27] FIG.s 2-5 shows a schematic side sectional views of the storage basins and schematically the turbines of the tidal energy system of FIG. 1 ;

[28] FIG.s 6-27 show schematic water levels during operation of the tidal energy system of FIG. 1 during a tidal cycle; and

[29] FIG. 28 shows steps in a method of tidal energy generation according to an example embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

[30] FIG. 1 shows a schematic plan view of a tidal energy system 1 according to an example embodiment of the present invention. The tidal energy system 1 is for generating electrical energy from the tidal movement of sea water. Water is allowed to flow from the sea S into storage basins 10, 20, 30, 40 which are also referred to as lagoons, as the tide rises, and allowed to flow from the tidal energy system 1 as the tide goes out. Movement of water into and out of some of the storage basins 10, 20, 30, 40 is used to drive turbines that are coupled to electrical generators, as described in detail further below.

[31] The tidal energy system 1 comprises a seaward storage basin 10, a landward storage basin 30, and an intermediate storage basin 20. The intermediate storage basin 20 is located between the seaward storage basin 10 and the landward storage basin 30. The boundaries between the sea S and the seaward storage basin 10, between the seaward storage basin 10 and the intermediate storage basin 20 and between the intermediate storage basin 20 and the landward storage basin 30 are provided by first, second and third dams 11 , 12, 13 respectively.

[32] Coupled between the sea and the landward storage basin 30 is a bypass storage basin 40. In this example tidal energy system 1 the bypass storage basin is divided into six component bypass storage basins 41-46, grouped in pairs as a first pair of component bypass storage basins 41 ,44, a second pair of component bypass storage basins 42,45 and a third pair of component bypass storage basins 43, 46.

[33] FIG.s 2-5 shows schematic side views of the storage basins 10, 20, 30 ,40 of the tidal energy system 1 , the section being along the centreline. In the example shown, the storage basins operate to a maximum depth of 10m above a zero datum, and down to -6m below the zero datum. The zero datum at 0m coincides with the low point of the tidal range. The width of the seaward, intermediate, and landward storage basins 10, 20, 30 is in this example 6km. In this example the width of the components of the bypass storage basins is 0.5km each, so an overall width of six times 0.5km, that is 3km. In this example, the length in the seaward - landward direction of the seaward storage basin is 6km, of the intermediate storage basin is 5km and the landward storage basin is 4km.

[34] During an incoming tide the seaward storage basin 10 receives and stores incoming tidal water 10. This connection is via turbine T1 , which as described below may be provided as an array of turbines spread across the height of the wall of dam 11 , and/across the width of the wall of dam 11. For example, in the tidal energy system 1 , T1 may be provided as seventy five different turbine elements are provided across the width of the dam 11..

[35] Water from the seaward storage basin 10 may be delivered to the intermediate storage basin 20 via a turbine T2 in the wall of dam 12, which as described below may be provided as an array of turbines spread across the width of the wall of dam 12. The turbine T2 may be an array, as per T1. The seaward storage basin 10 may receive and store outgoing tidal water from the intermediate storage basin 20 during operation of the tidal energy system 1 with the. In addition, the seaward storage basin 10 may deliver water therefrom and out of the tidal energy system 1 to sea S, such as during an outgoing tide.

[36] The landward storage basin 30 is in use operable to receive and store water from the intermediate storage basin 20, and to deliver water to the intermediate storage basin 20 during operation of the tidal energy system 1 . This connection is via a turbine T3 in the wall of dam 13, which as described below may be provided as an array of turbines spread across the width of the wall of dam 13 in a manner similar to T1 and T2.

[37] The intermediate storage basin 20 is, as already indicated, operable to receive and store water from the seaward storage basin 10, to deliver water therefrom to the landward storage basin 30, to receive and store water from the landward storage basin 30, and to deliver water therefrom into the seaward storage basin 10 during operation of the tidal energy system 1 . The Turbines T2 and T3 are driven by such operations.

[38] The bypass storage basin 40 is in use operable to receive and store incoming tidal water from the sea S via turbine T5, which may be provided as an array of turbines as per T1 , T2 and T3. Further, bypass storage basin 40 is in use operable to receive and store outgoing water from the landward storage basin 30 via a turbine T4. T4 may be provided as an array of turbines as per the other turbines.

[39] Turbines T1 are provided between the sea S and the seaward storage basin 10. Turbines T2 are provided between the seaward storage basin 10 and the intermediate storage basin 20. Furthermore, turbines T3 are provided between the intermediate storage basin 20 and the landward storage basin 30 and as turbines T4 between the landward storage basin and the bypass storage basin 40. The turbines are arranged such that movement of water from one storage basin 10, 20, 30, 40 to the next drives the turbine between the respective storage basins 10, 20, 30, 40. By regulating movement of water within the system, the turbines that sit at the boundaries of the storage basins can used to generate electricity during both incoming and outgoing tides during different phases of operation, including by operating in reverse to pump water to the bypass storage basins for use in a manner that does no coincide with the cyclical pattern of the rise and fall of the tide. In this way, increasing the flexibility to smooth output of the tidal energy system 1 is achieved.

[40] It will be appreciated that in order for the system to drain completely under gravity, the seaward storage basin may be provided with an outflow that is lower than that of the intermediate storage basin, and in turn the intermediate storage basin may be provided with an outflow that is lower than that of the landward storage basin, However, this need not necessarily be achieved by a general downward slope from landward to seaward, as there may be drainage flues, pumps, or cambered or other surface features provided at the bottom of the storage basins. Furthermore, although a generally linear arrangement from seaward to landward is preferred in order that the bulk flows water may move in the system may take place also in a generally linear manner, it is to be understood that other geometries may be used, and "seaward" and "landward" ought to be interpreted herein in relation to their functions in receiving and delivering water. Similar considerations apply to the bypass storage basins, described in more detail below.

[41] The turbines are mounted arranged to operate within a predetermined water level difference between input and output sides thereof as water moves from one storage basin 10, 20, 30, 40 to the next. In this way demand matching is facilitated because the output of the turbines when operational is relatively constant, and the turbines can be optimised to work at peak efficiency at the predetermined head difference, rather than being exposed to a wide range different heads. In the example shown, the predetermined head difference may be in the region of 1 m to 2m.

[42] The turbines at the boundary between the sea S and the seaward storage basin 10 are arranged such that movement of water into the tidal energy system 1 from the sea S, or movement of water out of the tidal energy system 1 from the seaward storage basin 10 is arranged to drive said turbines. The turbines at the boundary between the sea S and the seaward storage basin 10 are mounted and provide sufficient flow capacity to maintain a predetermined water level difference between input and output sides thereof as water moves into or out of the seaward storage basin 10.

[43] In the tidal energy system 1 the landward storage basin 30 is associated with the bypass storage basin 40. The bypass storage basin 40 is arranged so that water may in use move between the bypass storage basin 40 and the landward storage basin 30, and in the reverse direction. The bypass storage basins 40 as shown in the tidal energy system of FIG. 1 are provided in three pairs of components, one of each pair being provided on either side of the associated seaward, intermediate, and landward storage basins. The three-part bypass storage basins arranged in this manner provide a degree of symmetry for the tidal energy system 1 and increase the flexibility for by manipulation of water levels during the third operational phase of the tidal energy system 1 .

[44] Further turbines T' are provided between each of the parts of the bypass storage basins. The turbines T' may be provided as an array as with the other turbines described herein. These turbines T' are arranged such that movement of water between components of the bypass storage basin 40 drives said turbines. As described in relation to the turbines between the storage basins 10, 20, 30, the turbines for the bypass storage basin components are arranged to maintain a predetermined water level difference between input and output sides thereof as water moves from one side to the other during operation of the tidal energy system 1 .

[45] In the tidal energy system 1 a forward lagoon 50 is provided. The forward lagoon 50 is arranged seaward of the seaward storage basin 10 and serves to shelter the seaward storage basin 10. A permeable breakwater 51 and pontoons 52 provide protection from storms etc. while still allowing tidal flow to and from the seaward storage basin 10. Similar provisions may be made for the bypass storage basins 40. To increase the available maximum head of water available, including beyond that of nominal high tide, the forward lagoon 50 channels I shoals the incoming tide, for example through a narrowing that funnels the tide inwards and upwards toward the top of the dam 11 .

[46] The turbines as described herein are provided in a turbine assembly comprising an inlet/outlet on each side, and are operable so that in use movement of water through the turbine assembly in either direction drives the turbine. The turbine assemblies further comprise sluice gates operable to open and close to thereby control movement of water through the turbines.

[47] The turbine assemblies may comprise first, second, third and optionally fourth turbines, each turbine having individually operable sluice gates that open to allow water to flow through inlets to the turbine or to close to interrupt the flow of water through the inlets to the turbine. In this arrangement, the turbines may be distributed vertically. Thus, head matching across the turbines can be controlled by opening and closing the sluice gates as the water level rises and falls.

[48] FIG.s 6-27 show schematic side sectional views of the tidal energy system of FIG. 1 during a complete cycle, starting from the point where the tide has turned and is incoming. In these views the movement of water between storage basins is illustrated according to the interconnections thereof, and the accompanying generation of electrical energy or pumping of water is inferred based on the described connections between the basins and the positions of the turbines. The distribution around high tide at FIG.s 15-17 and low tide at FIG.s 25-27 are shown, with the cyclical pattern repeating to FIG. 6 to restart. These drawings represent the changes in level of water in the storage basins at approximately half-hourly intervals over a twice-daily tidal cycle.

[49] The method of operation is shown in FIG. 7 and comprises a first operation phase S101 receiving tidal water at the seaward storage basin to charge the tidal energy system by movement of water from the sea, to seaward to intermediate then to landward storage basins, driving the turbines there-between. This corresponds to the operations shown in FIG.s 6-15. In FIG. 14 and FIG. 15 water in the seaward and intermediate storage basins may rise above the nominal 8m high tide mark by operation of the shoaling I channelling effect from the inflow at the forward lagoon.

[50] In a second operation phase S102, as the incoming tidal water reaches a maximum tidal depth in the seaward, intermediate, and landward storage basins, water is delivered to the bypass storage basin at a depth above the maximum tidal depth. This corresponds to the operations shown in FIG. 16. In FIG.s 16-21 , water which has been pumped into the bypass storage basins is shown in the uppermost shaded sections.

[51] In a third operation phase S103, as the tide falls water is discharged water from the tidal energy system to sea by movement of water from landward to intermediate to seaward storage basins and to sea, driving the turbines there-between, out of the seaward storage basin and thus out of the tidal energy system. This corresponds to the operations shown in FIG.s 17-26.

[52] In a fourth operation phase S104 water is discharged from the bypass storage basin to sea, driving the turbines there-between. This corresponds to the operations shown in FIG. 27.

[53] Also shown in FIG.s 17-26 in the third operation phase, water is delivered to the bypass storage basin to ensure sufficient water is present to operate the fourth operation phase until such time as the tide has turned and risen to allow commencement of the first operation phase for a following tidal cycle. [54] As is illustrated in FIG.s 6-27, operation of the tidal energy systems as described, during a complete, repeatable tidal cycle can smooth the electrical output of the system over time. Only a minor amount of energy is used by the system in smoothing the peak supply over the whole cycle, making the tidal energy systems described suitable for delivering the sort of baseload generation capacity that is difficult to achieve with other forms of renewable generation such as wind or solar, or indeed with a traditional tidal barrage. The methods and apparatus described herein thus enhance the environmental and other benefits associated with generation of electrical energy by capturing energy from tidal sources.

[55] Although a few example embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

[56] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[57] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[58] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[59] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1 . A tidal energy system comprising: a seaward storage basin; a landward storage basin; an intermediate storage basin between the seaward and landward storage basins; and a bypass storage basin; wherein: the seaward storage basin is in use operable: to receive and store incoming tidal water; to deliver water therefrom to the intermediate storage basin; to receive and store outgoing tidal water from the intermediate storage basin; and to deliver water therefrom out of the tidal energy system to sea; the landward storage basin is in use operable to: receive and store water from the intermediate storage basin; to deliver water therefrom to the intermediate storage basin; and to deliver water therefrom to the bypass storage basin; the intermediate storage basin is in use operable: to receive and store water from the seaward storage basin; to deliver water therefrom to the landward storage basin; to receive and store water from the landward storage basin; and to deliver water therefrom into the seaward storage basin; and the bypass storage basin is in use operable: to receive and store incoming tidal water; to receive and store outgoing tidal water from the landward storage basin; and to deliver water therefrom out of the tidal energy system to sea; wherein a turbine is provided between the sea and the seaward storage basin, a turbine is provided between the seaward storage basin and the intermediate storage basin, a turbine is provided between the intermediate storage basin and the landward storage basin, a turbine is provided between the bypass storage basin and the sea; and a turbine is provided between the bypass storage basin and the landward storage basin, wherein the turbines are arranged such that during cyclical operation phases corresponding to a tidal cycle: in a first operation phase, rising tidal water received at the seaward storage basin charges the tidal energy system by movement of water from the sea, to seaward to intermediate then to landward storage basins; in a second operation phase, incoming tidal water reaches a maximum tidal depth in the seaward, intermediate, and landward storage basins, and is delivered to the bypass storage basin at a depth above the maximum tidal depth; in a third operation phase, as the tide falls water is discharged from the tidal energy system to sea by movement of water from landward to intermediate to seaward storage basins and to sea, driving the turbines there-between, out of the seaward storage basin and thus out of the tidal energy system; and in a fourth operation phase, water is discharged from the bypass storage basin; wherein, in the third operation phase, water is delivered to the bypass storage basin to ensure sufficient water is present to operate the fourth operation phase until such time as the tide has turned and risen to allow commencement of the first operation phase for a following tidal cycle.

2. The tidal energy system of claim 1 , wherein in the fourth operation phase, water is discharged from the tidal energy system by movement of water from the bypass storage basin to sea, and thus out of the tidal energy system, and/or is discharged from the bypass storage basin to the landward storage basin.

3. The tidal energy system of claim 1 or 2, wherein the bypass storage basin is in use operable to receive and store water from the landward storage basin and/or from the sea in the second operation phase.

4. The tidal energy system of claim 1 , 2 or 3, wherein the landward storage basin is in use operable to receive and store water from the bypass storage basin; and in the third operation phase, water is delivered to the bypass storage basin from the landward storage basin to ensure sufficient water is present to operate the fourth operation phase until such time as the tide has turned and risen to allow commencement of the first operation phase in the following tidal cycle.

5. The tidal energy system of any preceding claim, wherein a plurality of bypass storage basins are provided; the bypass storage basins interconnected with one another, and in use are operable: to receive and store incoming tidal water; to deliver water therefrom to the landward storage basin; to receive and store outgoing tidal water from the landward storage basin; and to deliver water therefrom out of the tidal energy system to sea, with turbines provided at the interconnects and between the bypass storage basins and the sea.

6. The tidal energy system of any preceding claim, wherein the turbine provided between the sea and the seaward storage basin is arranged such that movement of water into the seaward storage basin from the sea, and movement of water out of the tidal energy system from the seaward storage basin is arranged to drive said turbine, and wherein flow is controlled through said turbine such that relative water levels in are maintained at a predetermined water level difference between inlet and outlet sides of the turbine as water moves into or out of the seaward storage basin during the first and third operation phases respectively.

7. The tidal energy system of any preceding claim, wherein the turbine provided between the seaward storage basin and intermediate storage basin is arranged such that movement of water into the intermediate storage basin from the seaward storage basin, and movement of water out of the intermediate storage basin to the seaward storage basin is arranged to drive said turbine, and wherein flow is controlled through said turbine such that relative water levels are maintained at a predetermined water level difference between inlet and outlet sides of the turbine as water moves into or out of the intermediate storage basin during the first and third operation phases respectively.

8. The tidal energy system of any preceding claim, wherein the turbine provided between the intermediate storage basin and landward storage basin is arranged such that movement of water into the landward storage basin from the intermediate storage basin, and movement of water out of the landward storage basin to the intermediate storage basin is arranged to drive said turbine, and wherein flow is controlled through said turbine such that relative water levels are maintained at a predetermined water level difference between inlet and outlet sides of the turbine as water moves into or out of the landward storage basin during the first and third operation phases respectively.

9. The tidal energy system of any preceding claim, wherein one or more of said turbines is provided as a turbine assembly comprising an inlet/outlet on each side, operable so that in use movement of water through the turbine assembly in either direction drives the turbine.

10. The tidal energy system of any preceding claim, wherein one or more of said turbines is provided as a turbine assembly comprising sluice gates operable to in use control movement of water there-th rough.

11 . The tidal energy system of any preceding claim, wherein one or more of said turbines is provided as a turbine assembly that is mounted for movement relative to the water levels in the storage basins.

12. The tidal energy system of any preceding claim, wherein one of more of said turbines is provided as a turbine assembly comprising a plurality of turbine elements and an associated plurality of inlets/outlets arranged vertically distanced from one another such that flow is controlled through said turbine assembly such that relative water levels are maintained within a predetermined water level difference between inlet and outlet sides of the turbine, by opening and closing the inlets/outlets as the water levels on both sides of the turbine change.

13. The tidal energy system of any preceding claim, wherein one or more of said turbines is operable as a pump to enable powered movement of water between the respective storage basins and/or between the respective storage basins and the sea.

14. The tidal energy system of any preceding claim, wherein all of said turbines are operable as pumps.

15. A method of tidal energy generation using the tidal energy system of any preceding claim, the method comprising: (a) in a first operation phase, receiving tidal water at the seaward storage basin to charge the tidal energy system by movement of water from the sea, to seaward to intermediate then to landward storage basins;

(b) in a second operation phase, as the incoming tidal water reaches a maximum tidal depth in the seaward, intermediate, and landward storage basins, delivering water to the bypass storage basin at a depth above the maximum tidal depth;

(c) in a third operation phase, as the tide falls discharging water from the tidal energy system to sea by movement of water from landward to intermediate to seaward storage basins and to sea, driving the turbines there-between, out of the seaward storage basin and thus out of the tidal energy system; and

(d) in a fourth operation phase, discharging water from the bypass storage basin; wherein, in the third operation phase, water is delivered to the bypass storage basin to ensure sufficient water is present to operate the fourth operation phase until such time as the tide has turned and risen to allow commencement of the first operation phase for a following tidal cycle.