GB2439643A

GB2439643A - Tidal energy system with compressible vessel and open circulation

Info

Publication number: GB2439643A
Application number: GB0712423A
Authority: GB
Inventors: Paul Kristian Hatchwell
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-07-15
Filing date: 2003-07-15
Publication date: 2008-01-02
Anticipated expiration: 2023-07-15
Also published as: GB2439643B; GB0712423D0

Abstract

An Open Circulation Tidal Energy Cell (OCTEC) comprises a sealed compressible vessel 3 formed by two plates of a flexible material that recovers its shape after compression, one inverted on the other and joined together. The vessel is located at depth in tidal waters and communicates with the atmosphere above water level 4 by at least one pipe 2. During lower tides air is inhaled from the atmosphere and during higher tides air is exhaled either back into the atmosphere, fig.3, or underwater, fig.4, driving one or more turbines 5 in each direction. The flow of air is regulated by valve(s) 6. OCTEC systems may generate electrical power, store energy and compress air for oxygenation of waters. An Inter Tidal Energy Reservoir and Generator (ITERG) sub-system may be integrated to provide pumped storage during slack demand and additional power through turbines from rising tide and gravity-fed discharge at low tide, enhancing amount and regularity of useful output. OCTECs may be arranged in 'tidal stacks' on columns or cables arising from the seabed to maximise power density and reduce environmental impact and costs of power supply.

Description

* 2439643 NATURAL ENERGY SYSTEM FOR POWER, PRESSURISED GAS/FLUID

GENERATION AND STORAGE: Patent protection is sought for an Open Circulation Tidal Energy Cell' (OCTEC) system, combined in many cases with an Inter Tidal Reservoir Generator (ITERG) for enhanced storage, generation and output regulation, several of which systems may be arranged 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 OCTECs/arrays of smaller OCTECs 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. Closed circulation forms of TEC (CTECs) provide many similar benefits, but are the subject of another patent (GB 0316518.0) and so are not detailed further here.

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. OCTECs, 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.

OCTECs/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. They 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 to 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 OCTECs 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 OCTECs/tidal stacks is that they can oxygenate waters, for example to increase biological productivity of fisheries and accelerate breakdown of organic pollutants, generate compressed fluids for various uses, as well as generating tidal power in electrical or other stored forms.

OCTECs 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 OCTECs 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, normally air, or light fluids contained within OCTECs, are compressed as tides rise, forcing them out through a pipe, acting like bellows. In multiple arrangements, pipes from several adjacent OCTECs discharge into a larger pipe, which creates a powerful current capable of more efficiently driving a turbine as the gases/fluids are forced back upwards to the atmosphere. As the tide recedes, falling pressure from the water column above permits OCTECs to regain their original shape, sucking in gases/fluids from the atmosphere above, 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 OCTECs at different heights in the water column from reducing flow in either direction by shutting them off once they reach a low point in either the inhalation or exhalation phase of the generation cycle.

Figure 1 shows an embodiment of the compressible vessel of a small-scale OCTEC system (side elevation) composed of two plates of flexible, single/composite material moulded/fused/joined together, when fully recharged at low tide Figure 2 shows an embodiment of the compressible vessel of an OCTEC 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 greater depths Figure 3 shows one embodiment of a complete OCTEC system as submerged in tidal waters, inhaling/exhaling from/into the atmosphere above the surface of the waters, generating power in each direction of flow, or pressurised gases/fluids for various uses at the surface Figure 4 shows a once-through embodiment of an OCTEC system in which gases, generally air, or fluids are drawn in from the atmosphere above during lower tides, and expelled into the open sea during higher tides, oxygenating waters, generating power, or yielding compressed fluids as desired 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.

T

In cross-section, an OCTEC compressible vessel broadly resembles either a deep plate/shallow dome with another deep plate/shallow dome laid directly upon it upside down, fused together/joined/made into one single piece, from a single or composite, flexible material that recovers its shape after compression (Fig. 1), in some embodiments (Figure 2) strengthened by flexible ribbing in the form of a durable spring (1) preferably embedded into the material of each half (Fig. 2).

In many embodiments (Figure 3), one or more conduits (2) emanate from the OCTEC compressible vessel (3), normally from the side, carrying gases, generally air, or fluids out of it or into it to/from the atmosphere above water level (4), depending upon the tidal phase. A turbine/several turbines (5) is/are driven in both directions of flow, generally with valves (6) used to control rate of flow and thus generation to/from the compressible vessel (3).

In other embodiments (eg, Figure 4), air/other gas/fluid is drawn in from the atmosphere above water level (4) and expelled out the side of the compressible vessel/tidal stack underwater in a once-through cycle.

OCTEC systems are likely to be most effective at mid-water 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 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 more robust versions for deeper estuarine and sea use if there is necessity for this (for example, in underwater research/monitoring stations where small-scale, 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 to an adjacent tidal stack for added strength, and employ more than one embodiment of an OCTEC system at different heights and pressure regimes within the water column, combined with ITERG sub-systems as appropriate, to ensure optimal utilisation of vertical tidal energy in the water column.

Tidal stacks/clusters can be adapted as Natural Energy Platforms (NEPs), with various other forms of renewable generation such as wind turbines, tidal stream turbines preferably able to turn into prevailing current direction as it changes, and wave energy devices in the intertidal zone around offshore structures, in addition to OCTEC/ITERG systems.

On and between OCTEC stacks reaching upwards to near the sea surface containers are fitted within the intertidal zone, allowing waters to flow in from underneath by conduit means in which a turbine generator is fitted, and allowing outflow, again passing over a turbine during low tide. This subsystem, an Inter Tidal Energy Reservoir and Generator (ITERG), can both generate tidal power from depths otherwise too shallow for OCTECs below and store its own output and that of other devices on the stack. Output of the overall OCTEC system/stack/cluster can thus be further regulated and enhanced.

Claims

CLAIMS

1. An Open Circulation Tidal Energy Cell (OCTEC) comprised of a sealed compressible vessel bounded by two plates of a flexible material, one inverted on the other, fused or otherwise joined, located at depth in tidal waters linked to the atmosphere above by one or more conduits, differential pressures alternately compressing and allowing recovery of the shape of the vessel, forcing pressurised fluid through conduits to the atmosphere above or below water level as desired for useful output of power or fluids in an exhalation phase during higher tide, and sucking fluid through conduits in an inhalation phase during lower tide, regulated by one or more valves, for useful output of power or fluids.

2. Arrangement as in Claim I, in which OCTECs, combined with associated Inter-Tidal Energy Reservoir Generators (ITERGs) to enhance useful output and storage are stacked horizontally on a robust supporting vertical column arising from the floor of the sea or estuary, connected by cable to the local or national grid as desired.

3. Arrangement as in Claim I, in which OCTECs, combined with associated Inter-Tidal Energy Reservoir Generators (ITERGs) to enhance useful output and storage are stacked horizontally on a supporting cable arising upwards from the floor of the sea or estuary, connected by cable to the local or national grid as desired.

4. Arrangement as in Claim I, in which OCTECs are stacked horizontally on a robust supporting vertical column arising from the floor of the sea or estuary, connected by cable to the local or national grid as desired, in the absence of an ITERG.

5. Arrangement as in Claim I, in which OCTECs are stacked horizontally on a supporting cable arising upwards from the floor of the sea or estuary, connected by cable to the local or national grid as desired, in the absence of an ITERG. *

Amended claims have been files as follows:-

CLAIMS

I. An Open Circulation Tidal Energy Cell (OCTEC) comprised of a compressible vessel bounded by two plates of a flexible material, one inverted on the other, fused or otherwise joined, located at depth in tidal waters linked to the atmosphere above by one or more conduits, differential pressures alternately compressing and allowing recovery of the shape of the vessel, forcing pressurised air through conduits to the atmosphere above or below water level as desired for useful output of power or air in an exhalation phase during higher tide, and sucking air through conduits in an inhalation phase during lower tide, regulated by one or more valves, for useful output of power or air.

2. Arrangement as in Claim I, in which OCTECs, combined with associated Inter-Tidal Energy Reservoir Generators (!TERGs) to enhance useful output and storage are stacked on a robust supporting vertical column arising from the floor of the sea or estuary, connected by cable to the local or national grid as desired.

3. Arrangement as in Claim 1, in which OCTECs, combined with associated Inter-Tidal Energy Reservoir Generators (ITERGs) to enhance useful output and storage are stacked on a supporting cable arising upwards from the floor of the sea or estuary, connected by cable to the local or national grid as desired.

4. Arrangement as in Claim 1, in which OCTECs are stacked on a robust supporting vertical column arising from the floor of the sea or estuary, connected by cable to the local or national grid as desired, in the absence of an ITERG.

5. Arrangement as in Claim I, in which OCTECs are stacked on a supporting cable arising upwards from the floor of the sea or estuary, connected by cable to the local or national grid as desired, in the absence of an ITERG. * S *** S... * . S... * S * .. * S * *S..

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