GB2403986A - Tidal energy system for power generation or storage - Google Patents

Abstract

Simpler 'Tidal Energy Cell' (TEC) systems have a flexible, air-tight discoidal vessel 10, fig.4, from which air is expelled to drive a turbine as the vessel is compressed by the rising tide and into which air is drawn from above the surface at low tide through pipe(s) as the compressed vessel recovers shape, also driving a turbine. Larger systems have a pair of generally rigid, shallow opposed domes, 12, fig.7a, separated by springs 3 and a flexible seal 2. They may exchange air/gases/fluids with pressure chambers 11 during rising/falling tides, driving turbines 8 via valves 9. Several TECs may be arranged in 'tidal stacks' (fig.8) at various levels on columns or cables rising from the seabed, and may exchange fluids with central chambers built around columns at various heights. Also disclosed are Inter Tidal Energy Reservoirs and Generators (ITERGs) (15, fig. 10) which are wide containers open from above so that water drives turbines as the containers fill and empty. TECs and ITERGs may be provided on platforms, fig. 10, combining multiple renewable systems, eg including wind turbines.

Description

l 2403986

NATURAL ENERGY SYSTEM FOR POWER GENERATION AND

STORAGE: Patent protection is sought for 'Tidal Energy Cell' (TEC) systems, and associated Intertidal Energy Reservoir and Generators' (ITERGs), for their arrangement arrayed in a tidal 'stack', in turn arranged into rig-like clusters offering opportunities to act as offshore 'Natural Energy Platforms' (NEPs) above and below the water column. Tidal stacks are generally vertical/near vertical structures arising from the seabed onto which large TECs/arrays of smaller TECs are fixed at various levels, but could also be a tensile cable connected to the seabed and pulled upward by a floating structure such as a buoy.

Conventional tidal barrages, tidal stream turbines and wave energy devices are only likely to be economic in a limited number of locations, often in areas of great environmental sensitivity such as the Severn or Rance Estuary, or relatively undisturbed, remote seascapes off the North West Highlands of Scotland where lateral currents or tidal ranges are maximised. TECs, ITERGs, tidal stacks and NEPs offer the opportunity to maximise power density per unit area, at least partially regulate power output and reduce environmental damage by concentration of units in smaller, often less sensitive areas.

TECs/tidal stacks could be efficiently combined with these wave/tidal stream energy and offshore wind facilities, solar arrays, among others, but because they derive tidal energy from vertical changes in height of the water column rather than strong horizontal currents they can also function efficiently in a much wider proportion of coastal waters where tidal ranges and currents are less, and where environmental and ecological sensitivity may also be less. T hey also afford the prospect of more regular electrical output than from wave or wind energy, reducing the need for other carbon- intensive or potentially hazardous sources such as fossil fuel and nuclear generation to guarantee security of supply.

Because a much higher proportion of the water column can be made to yield up its potential tidal energy leading to a much greater density of power generation, because horizontal currents are not greatly reduced, and because visual intrusion at the sea surface is minimised or avoided (unless wind/wave units are added), environmental impact is likely to be far less. Lack of exposure to strong currents and battering by waves in many locations also greatly reduces engineering challenges, likelihood of mechanical damage and of reduced operational life, reducing material usage and costs throughout fabrication, installation and maintenance relative to other coastal renewable options. Individual TECs can be removed for repair offsite/replaced easily without recourse to heavy engineering manoeuvres (ie not having to take the whole structure offsite for repair in distant coastal yards).

An additional benefit from TECs/tidal stacks is that they can be adapted to oxygenate coastal waters as well as generating tidal power, increasing biological productivity of fisheries and accelerating breakdown of organic pollutants.

TECs are designed to work in continual exhalation and inhalation cycles, during high tide and low tide respectively, offering opportunities for highly predictable electrical energy output from associated turbines. They can be constructed in a range of sizes, and since they depend on vertical water pressures rather than lateral currents, can be located closely together in tidal stacks at various heights in the same water column.

This maximises use of potential energy from tides in the column and facilitates economic collection of electrical output because large concentrations of TECs in stacks minimise length of undersea cable and therefore transmission losses to collection stations. Similarly, large numbers of tidal stacks can be arranged closely together in clusters to maximise efficiency of electrical transmission to collection stations for onward distribution to the National Grid or conversion into other forms of stored energy.

Gases/light fluids contained within TECs, normally air, are compressed as tides rise, forcing them out through a pipe, acting like bellows. In multiple arrangements, pipes from several adjacent TECs discharge into a larger pipe which creates a powerful current capable of more efficiently driving a turbine as the gases are forced into either a pressure chamber or allowed to drive upwards to the sea surface. As the tide recedes, falling pressure from the water column above permits TECs to regain their original shape, sucking in gases from the pressure chamber or from above the sea surface, affording another opportunity to drive turbines (the inhalation cycle). In addition, use of valves can regulate inhalation and exhalation rates to achieve a smoother generation cycle, and to prevent differential pressures between TECs at different heights in the water column from reducing flow in either direction by shutting them oMonce they reach a low point in either the inhalation or exhalation phase of the generation cycle.

Another embodiment of vertical tidal energy generation involves a container near the sea surface, open above, allowing waters to flow in from underneath through a pipe in which a turbine generator is fitted, and allowing outflow, again driving the turbine during low tide. The device, an Inter Tidal Energy Reservoir and Generator (ITERG), can be fitted onto/between tidal stacks, and can both generate tidal power from depths otherwise too shallow for TECs and store its own output and that of other devices on the stack. Flow and therefore generation output can be regulated as desired.

Figure I shows an embodiment of a simple version of the central section of a small- scale TEC system (side elevation) composed of a flexible, single/composite material moulded/fused/joined into one piece, designed for shallower waters when fully recharged at low tide Figure 2 shows an embodiment of the central section of a TEC system (side elevation), composed of a flexible, single or more often composite material with embedded spring reinforcements that can be built to a larger scale and can also be used in intermediate depths Figure 3 shows an embodiment of a side/oblique elevation of the central section of a large-scale, more robust TEC with upper and lower casing composed of rigid material/s, incorporating a flexible seal, springs, and retractable/extendable internal vertical supports, intended for deeper water and greater power output Figure 4 shows one embodiment of a TEC system inhaling/exhaling from/into the atmosphere above the sea surface Figure 5 shows a oncethrough embodiment of a TEC system in which air is drawn in from above the sea surface during low tide, and expelled into the open sea during high tide, both oxygenating waters and generating power Figure 6 shows a robust embodiment of a TEC designed for large-scale power generation in deeper waters in conjunction with a pressure chamber Figure 7a shows a toroidal embodiment of a large-scale, deepwater TEC in conjunction with a pressure chamber (with tubes connecting the TEC to the pressure chamber, turbines, valves and in some cases additional supports, present but not shown for clarity); 7b shows a comprehensive plan view, including tubes connecting to the pressure chamber; 7c shows a comprehensive plan view of a ring of separate TECs linked to a central pressure chamber Figure 8 shows an embodiment of a tidal stack arrangement in deep waters with sea floor cable for electricity export Figure 9 shows one embodiment of how several tidal stacks in a cluster offshore might appear if cross-linked for greater strength.

Figure 10 shows one embodiment of the use of tidal stacks as a Natural Energy Platform (NEP), combining TECs, ITERGs (operating between tidal extremes at the sea surface (7, 21), rotating/reversible tidal stream turbine generation, wind and wave generation facilities to achieve maximum power density by area to reduce grid connection unit costs and restrict environmental impact.

In the figures, it is understood that all embodiments may power turbines, whether shown or not, as well as generate heads of pressure for other uses, and that most use valves to regulate flow as desired, shown where helpful.

In cross-section, a TEC broadly resembles either a deep plate/shallow dome with another deep plate/shallow dome laid directly upon it upside down, fused together/joined/made in one single piece, from a single flexible material that recovers its shape after compression (Fig. I), or two such structures arranged in the same fashion joined together but strengthened by flexible ribbing in the form of a single durable spring (I) preferably embedded into the material of each half (Fig. 2), or rigid and separated by vertically collapsible but tough and flexible seals (Fig. 3) at their edges (2) and springs within (3). Addition of extendable/retractable vertical supports (4) to the versions shown in Figure 3 may be desirable in some cases to limit lateral misalignment of the two rigid halves (5) of the TEC in strong lateral current conditions and to prevent the seal from being stretched and pushed too far towards the interior of the TEC. In the latter case, the seal could become trapped, which could hamper proper functioning and possibly cause damage during inhalation and exhalation phases. External extendable/retractable vertical supports may also be added if outward pressures from the recharged TEC are likely to stretch the seal excessively.

In either case, a tube (6) emanates from the TEC, normally from the side, carrying gases/fluids out of it or into it to/from above the sea surface/pressure vessel, depending upon the tidal phase (see Figs. 4, 6), while another version sees air/other gas drawn in from above the sea surface (7) and expelled out the side of the TEC/tidal stack underwater in a once-through cycle (Fig. 5). A turbine/several turbines (8) is/are driven in both directions of flow, and in some embodiments regulating valves (9) may be used to control rate of flow/gencration to/from the TEC (10) (eg, Figures 4, 5, 6, 7b).

In larger structures, generally inhaling/exhaling into a pressure chamber (11), two rigid, lightweight, often metallic or composite domes (5) are more commonly used (Figures 3, 6), giving the structure strength against collapse or excessive outward pressures, while compression and extension is restricted to a gap between the edges of the domes where they are joined by a series of springs (3) around and just within the perimeter of the TEC, all of which are surrounded by a vertically collapsible seal, leaving the interior of the cell airtight/watertight. Extendable/retractable vertical supports (4) are often added internally to prevent misalignments of each half of the cell in strong lateral currents, and inward collapse of the seal, with equivalent vertical supports occasionally necessary externally to prevent excessive outward pressures damaging the seal.

An adapted form ofthis structure (Fig. 7a, b) envisages each halfofthe TEC (12) with a gap running through its centre, creating a torus-shaped TEC, which during rising tide alternately exhales and pressurizes a strong, rigid chamber (11) running through this central gap of the structure, and draws from it during falling tide. There could be one or several connections to the central pressure chamber. Turbines are driven during inhalation and exhalation cycles influenced by tidal phases, and flow rate can be regulated by valves (9), with internal vertical supports (4) if necessary.

Retractable/extendable external vertical supports may be added if necessary.

The torus-type TEC, or an annular deck ( 13) supporting a ring of separate TEC discs (10) as shown in Figure 7c, together with the central pressure chamber (11), could be supported by a single central column from the seabed (14), attached by radiating gaseous/light liquid supply tubes running into the chamber with additional supports if necessary, with several such arrangements stacked at different levels of the column, forming a tidal stack (Figure 8). Where there are not large differences between the tidal pressures in upper and lower levels, more than one torus/TEC array could be connected to a single central pressure chamber. It may also be desirable to construct the torus of multiple chambers, or use separate TECs which can be dismantled more easily for maintenance.

An example of a preferred horizontally layered tidal stack arrangement for large numbers of TECs that can be modular (see also Figure 9), and an ITERG (15) operating in the intertidal range between (7) and (21), the overall structure joined with neighbouring tidal stacks to increase both structural stability and power density, reducing cost of power cable connection to land (16), is shown in Figure 10. TECs could also be arranged sideways rather than horizontally, but the former is more likely to be efficient in terms of density of stacking possible.

TECs are likely to be most effective at midwater depths in the water column rather than in shallow depths, where pressures achievable are much less, or in greater depths, where much higher pressures exist but where the influence of tides is far less marked.

However, the smaller versions can be employed successfully in shallower waters near small communities for local use, for powering navigational buoys/weather stations, among other uses, and the more robust versions (Fig. 3, 6; 7a, b, c) for deeper sea use if there is necessity for this (for example, in underwater research/monitoring stations where smallscale, reliable generation may be needed in future). Use on offshore oil and gas structures is also feasible. In practice, a single tidal stack could, perhaps be joined (17) to an adjacent tidal stack for added strength, and employ more than one embodiment of a TEC and its outer shell at different heights and pressure regimes within the water column (5, 10, 12), combined with ITERGs and air tubes (6) arising above the sea surface for shallower water forms of TEC, to ensure optimal utilisation of the vertical tidal energy resource in the water column.

Tidal stacks/clusters can be adapted as Natural Energy Platforms (NEPs, Figure 10), with wind turbines ( 18), tidal stream turbines preferably able to turn into prevailing current direction as it changes ( 19), wave energy devices in the intertidal zone around offshore structures (7, 21), in addition to TECs and ITERGs.

Claims (9)

1. A submerged, compressible air/fluid-filled generally disc-shaped or flattened toroidal vessel (a Tidal Energy Cell, TEC generating electrical power from vertical changes in sea level from tidal phases) of a single flexible material such as rubber/plastic/composite which may be strengthened in the upper and lower halves by a spring in each case embedded into the material with wide base, tapering to the centre of each half, or of rigid material, with the TEC discharging through a pipe, generally at the side, under pressure as tides rise ('exhalation' phase) to drive a turbine generator/generators, and sucking in air from a pipe/pipes above the sea surface/other gases/light fluids during low pressure episodes when tides recede ('inhalation' phase), also generating electricity, with some forms exchanging gases/fluids exclusively within a closed circulation cycle with a pressure chamber.

2. A submerged, heavy duty, compressible generally disc-shaped cell or flattened toroidal cell (in cross section, side elevation) operating in a similar way to that in Claim I, but with upper and lower half of the cell of rigid material, not in direct contact, but separated by springs at the margins, and an outer air-tight flexible seal, often accompanied by retractable vertical supports to maintain both halves in position in strong tides and prevent inward collapse/outward stretching and rupture of the seal.

3. A submerged, compressible generally disc-shaped or flattened toroidal cell as in Claim 2, but attached by pipe/e to a pressure chamber, with air/other gases/light fluids maintained in a closed system for deeper waters, in which they are forced from the compressed TEC into the pressure chamber during rising tides ('exhalation' phase), and released to re-inflate the TEC during low tide ('inhalation' phase), driving an electrical turbine generator en-route between the two devices during both phases, often using valves to regulate flow rates and ensure a more even rate of electrical output.

4. A generally disc-shaped, compressible TEC as in Claims I and 2, but which inhales air from the sea surface through a pipe/pipes during low tide, driving an electrical turbine generator en-route, and during high tide exhales it directly through a pipe, generally at the side, into the surrounding sea providing oxygenation of waters as well as driving an electrical turbine generator as it does so, with a valve preventing intake of seawater from the outlet pipe during inhalation, while another prevents exhalation of air through the pipe/e back to the surface during compression at high tide.

5. An arrangement of a flattened toroidal TEC (Claim 2)/supported ring of individual TECs discharging air/other gases/light liquids via a pipe/pipes into a central pressure chamber during rising tide, driving an electrical turbine generator en-route, the TEC/s sucking back the air/other gases/fluids to replate at low tide, offering another opportunity to generate electricity, the rate of flow and thus generation of electricity regulated as necessary by valves, the central pressure chamber normally supported from the seabed by a central vertical column in this embodiment, with the column normally passing through the centre of the chamber, while the pipes are generally as spokes radiating outward from the column/pressure chamber to the surrounding toroidal TEC/ring of TECs, holding it/them firmly in position, in some cases, additional supports being added.

6. As in Claim 5, but at various levels up and down the normally central column, forming a modular 'tidal stack', with several adjacent stacks arranged in a cluster', often cross-linked for increased strength, and reducing lengths of undersea cable needed to bring electrical power generated to coastal collection stations.

7. Some embodiments of the tidal stack arrangement in Claim 5 and Claim 6 also include/exclusively consist of TECs described in Claims l, 2 and 4 linked to above the sea surface via a pipe/e, with non-heavy duty, shallower water TECs not necessarily employing pressure vessels, to optimise use of more marginal vertical tidal energy resources near the sea surface/in shallower coastal waters.

8. TECs and their various embodiments described in Claims 1-7, but supported by a tensed cable rather than column, normally arising nearvertically to the surface held by a buoy or other support.

9. Inter Tidal Energy Reservoirs and Generators (ITERGs), consisting of generally wide containers open above fixed into the inter-tidal zone in the upper extreme of the water column of a stack/cluster, allowing waters to fill the container from below as tides rise, driving a turbine in a pipe as they enter, and driving a turbine again as they flow out during low tide, acting as both generators and energy stores, with rate of flow/generation amenable to regulation as desired for grid supply.

l O. As in Claim 6 or 7, and in some cases 8, with additional renewable facilities added, such as ITERGs (Claim 9), offshore windmill structures rising from the column above the water level, wave energy devices around the stack/between stacks, and generally rotating tidal stream turbines, some embodiments with platforms added and held between stacks to support greater numbers of devices.