GB2481365A

GB2481365A - Harnessing energy from a tidal or wave energy source

Info

Publication number: GB2481365A
Application number: GB1004287.7A
Authority: GB
Inventors: William Mackay Sinclair
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-03-16
Filing date: 2010-03-16
Publication date: 2011-12-28
Also published as: GB201004287D0

Abstract

A method for harnessing energy from a tidal or wave energy source comprises excavating a portion of the geological formation between two shore locations on the same island or land headway to provide a manmade water flow path, eg channel J, between the locations; providing an energy extraction device, eg turbines G, in the manmade path; using the energy extraction device to extract energy from water flowing through said path eg by driving generators situated on land. Normally tidal energy may be extracted by the energy extraction device as the tide moves water in a first direction between the two shore locations and also as the water moves in the opposite direction between the two shore locations. The channel J may have transversely spaced piers (14, fig.1) providing slots (13) in which turbines cassette modules (50) are fitted; a service bridge (16) may extend over the piers.

Description

Methods and System This invention relates to a tidal and wave energy extraction method, system and method of making the system.

Given the environmental concerns over global warming, the finite resource of fossil fuels and the increasing cost of extracting these fuels, much focus has turned to alternative and sustainable energy sources to meet the world's energy demand.

One such source is tidal and wave energy. Current systems are varied but typically involve provision of a turbine or other energy extraction device offshore with a connection onshore to transport the energy.

From the early 1990's interest has gathered in the production of power from tidal flows in a manner similar to wind turbines. To this end large investments have been made to investigate the possibility of deploying machines on the seabed to harness tidal power and use this as an alternative to fossil fuels.

Tidal power is more predictable than wind power and as such can be more easily linked into the demand cycles of daily life.

The inventor of the present invention has noted that whilst several competing designs of open tidal flow turbines show promise, certain mechanical weaknesses and a high cost of maintenance may still mean that they are not suitable for the long term energy generation on a commercial scale.

Several different turbines have been constructed and used to conduct experiments in the long term viability of the designs and the possible power that could be contributed to the national grid. Each machine represents new technology and is a high risk venture for those providing the funds.

Hitherto, the approach is to construct machines large enough to provide a measurable electrical output and place it on a test site on the sea bed with a wire leading to the shore where the output can be monitored. For each machine the circumstances at the site have been carefully investigated and the situation with regard to currents, seabed conditions together with probable freak incidences carefully assessed top minimise risk. Whilst improvements in the designs have been made there is presently little sign of a machine that can be mass produced and placed on the seabed in arrays to provide for the country's thirst for energy.

Moreover the knowledge of seabed currents and turbulence at all states of the tide is not well known. The shape of a local area of seabed may provide eddies that move at different states of the tide affecting the efficiency of nearby apparatus.

The inventor of the present invention has noted a number of problems that contribute to the difficulty in providing a commercially viable turbine. For example, it is difficult to predict maximum flow rates during tidal surges and storms and to secure apparatus against these economically. Peak flows may be significantly greater than normal tidal predictions and massive structures to retain a turbine may not be cost effective.

According to a first aspect of the present invention there is provided a method of harnessing energy from a tidal or wave energy source, the method comprising: providing an energy extraction device in a manmade path between two shore locations typically on the same island or land headway; using the energy extraction device to extract energy from water flowing through said path.

A manmade path is a path that is not a natural geographical feature but has been created by human intervention.

Preferably the manmade path is a path that has been created from the natural geological formation, for example by excavation. Preferably therefore the manmade path has not been created through a manmade barrier, for example a manmade dam. The method may include excavating a portion of the geological formation between the two shore locations to provide the manmade water path therebetween.

Preferably the two shore locations are provided on the same island or land headway.

Thus the present invention is fundamentally different from known tidal or wave energy methods in that the water is directed to the energy extraction device in the manmade path rather than positioning the energy extraction device in the natural water flow.

Thus embodiments of the invention have significant benefits in manufacturing and especially maintaining the systems required to extract energy in such a way, since they are essentially based on land and not in remote offshore locations which are much more difficult to access and maintain.

The manmade path between the shore locations is typically a more direct water path than is presently provided by the natural land and waterscape. In any case water preferably flows preferentially through the (preferably smooth) manmade path than by any other route.

Preferably the energy extraction device is adapted to extract tidal energy.

Preferably the tidal energy is extracted by the energy extraction device as the tide moves water in a first direction between the first and second shore and also in the opposite direction between the first and second shore. Thus as the tide ebbs and flows energy may be extracted from the energy extraction device in accordance with certain embodiments of the present invention.

Pipes, however will cause large friction losses and so discourage the flow therethrough and so are less preferred especially when also considering the slowed flow rate through the water path due to the energy extraction device.

Preferably therefore the path is an open channel, especially at least partially open opposite its bottom, the bottom being defined by the portion of the path which water naturally flows over due to gravity/tidal/weather effects and conditions.

The energy extraction device may drive a hydraulic system or a transmission system which is connected to generators which may be on land. In this way subsea generators need not be provided.

Water' as used herein typically refers to sea water or may be any flowing water.

According to a second aspect of the invention there is provided a method of manufacturing a system to generate energy from wave and/or tidal resources, the method comprising: excavating a portion of the geological formation between two shore locations to provide a manmade water path therebetween.

Preferably the invention according to the second aspect of the invention is then used to harness energy according to the first aspect of the invention.

Geological formation' as used herein relates to the natural landscape as opposed to manmade structures.

Preferably the portion of the geological formation excavated is on the same landmass, that is, the path is not provided between two islands.

Preferably the path is excavated to the extent necessary to cause water flow from one shore location to the other via the manmade water path. Thus one preferred aspect to the invention is to provide a preferential route for the flowing tide to that in the natural land and water scape.

Normally before excavation there is no body of water flowing in the geological formation which will be excavated to form the water path.

Preferably a portion of land which is ultimately excavated is left at an earlier stage in the method, in order to form a barrier to water flow; said portion of land being referred to as a dam'. Especially two such dams are initially left to maintain a barrier to the water between the dams. In this way work can proceed on excavating the portion of dry land therebetween without the water flowing therethrough. At a later stage in the method according to the invention the dams are typically removed.

Preferably at least one, spacer is provided in the water path in order to define at least one slot to receive the energy extraction device; the slot may be defined between two spacers or between a spacer and one bank of the water path.

According to a further aspect of the invention there is provided a system, comprising at least one spacer provided in a manmade water path, the spacer at least in part-defining at least one slot shaped to receive an energy extraction device.

Typically the system according to the third aspect of the invention comprises the energy extraction device.

Typically the system is manufactured using the method according to the second aspect of the invention. Preferably the system is used to recover energy according to the first aspect of the invention.

Various preferred and other optional features of the system will now be described and it will be understood that these are, each taken independently, also preferred and optional features of the system manufactured according to the second aspect of the invention, and are each, taken independently, preferred and other optional features to be used in accordance with the first aspect of the invention.

The spacers may be pillars or piers, and typically extend vertically. The spacers are typically manufactured from a concrete.

Preferably a plurality of spacers, and a plurality of slots are provided.

Preferably the arrangement of the spacers extends from one bank to an opposite bank, normally in a straight line. In one embodiment, there are six spacers and seven slots.

Multiple groups or banks' of spacers may be provided at different parts of the water path. For example a first line of six spacers defining slots for receiving the energy extraction devices may be provided at one location, and a second, often identical, series of six spacers provided on the water path I OOm away.

The energy extraction device is preferably shaped to locate in said at least one slot. The energy extraction device may comprise a housing with an external face shaped to locate in said at least one slot and an energy extraction component, such as a turbine.

Normally one energy extraction device is provided for each slot.

An alignment mechanism may be provided in order to aid alignment and location of the energy extraction device in the slot. The alignment mechanism may comprise a groove on one of the energy extraction device and a slot on the other; preferably the groove is on the energy extraction device and the slot is on the spacer. A shock absorber may also be provided between the spacer and the energy extraction device; for example an

inflatable packer.

A screen may be provided in the water path in order to resist flow of objects above a certain size; especially to prevent larger fish from entering the water path. Typically a screen is provided at each end of the water path proximate to each shore location.

A retractable door may also be provided in the water path. Where there are two energy extraction devices spaced apart in the water path in the longitudinal direction as defined by the water path, preferably the retractable door is provided between the one of the shore locations and the closest energy extraction device. Preferably such a retractable door is provided between each shore location and the nearest energy extraction device and normally a retractable door is provided proximate to each shore location.

The retractable door may also comprise said screen.

The retractable door may comprise a spacer, referred to as a retractable door spacer'. Whilst the retractable door spacer functions for a different purpose than the spacer(s) used for defining slots to receive the energy extraction device, preferably the retractable door spacers are the same as the extraction device spacers.

Preferably therefore a plurality of retractable door spacers, and a plurality of slots are provided. Preferably the arrangement of the retractable door spacers extends from one bank to an opposite bank, normally in a straight line. In one embodiment, there are six retractable door spacers and seven slots.

Multiple groups or banks' of retractable door spacers may be provided at different parts of the water path. For example a first line of six retractable door spacers defining slots for receiving the energy extraction devices may be provided at one location, and a second, often identical, series of six retractable door spacers provided on the water path 200m away.

Typically the retractable door comprises a plug which may be moved into the slot defined by the retractable door spacer(s) thus resisting flow of fluid therepast. The retractable door thus functions to provide the option of blocking the water path and so essentially removing water thereform, for maintenance or for other purposes.

The retractable door may be a cofferdam door.

Optionally a bridge is provided over the channel. The bridge may be used to deliver equipment, such as a turbine, to the channel. The bridge may have moveable panels in order to access voids for the equipment. For certain preferred embodiments, the bridge has rails provided thereon.

Preferably link roads from a workshop to the turbine slots are of sufficient width and gradient to allow for the largest pieces of machinery to be transported for repair and maintenance.

Preferably the channel is kept clear of weed by using the alternating flow in the channel to power a scraper, with an underwater sail, the length of the channel at each change of tide.

The size of the path will depend on the site, its potential hydraulic head and the geology of the surroundings. Preferably the water path is at least 5m deep, more preferably at least I 5m deep but greater depths will reduce head losses in the channel, and so ideally about 30m deep would be practicable.

Preferably the water path is at least 1 5m wide, preferably at least 30m wide.

In one embodiment, the water path is 15m deep and 40m wide. Such an embodiment may have three lOm turbines.

The path may be up to 200m wide (but may also be wider). Preferably the path is less than 150m more preferably about lOOm.

The sizing of channel and depth may vary with turbines and piers to suit.

The natural tidal flows of the location where the method of the invention is put into practice are important. Preferably there is a deep fast flowing tidal channel close to the shore, that is preferably at least at least 5m deep, preferably at least 15m, ideally about 30m deep and the flow preferably being at a speed of at least 2 knots more preferably at least 6 knots ideally about 12 knot Preferably the location has some natural resistance to the natural flow of the tide, that is the water and landscape directs the tide naturally more towards the shore rather than along the shore. This can provide a usable hydraulic head. Preferably the shore line lends itself to civil engineering and quarrying techniques to construct an alternative channel, that is preferably rock at high water level and below high water level, preferably for the whole extent of the path.

For certain embodiments, a rock promontory could provide sufficient hydraulic head although these often push the deeper channels seaward which is less preferred. The presence of sandy beaches in the more sheltered sides to the promontory will cause problems as this will require significant shoring and pumping due to ingress of water during excavations and so is less preferred.

Where two islands cause fast tidal flows (ie above 2 knots) therebetween there is often suitable sites on one of the islands, provided the channels are sufficiently deep near the shore that is at least 5m deep preferably at least 15m deep ideally about 30m deep.

One suitable location is Duncansby head in Caithness, Scotland, United Kingdom.

Embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying figures in which: Fig. I a is an end view of one embodiment of a channel and tidal power generating system in accordance with the present invention; Fig. lb is a plan view of the Fig. 1 a channel and tidal power generating system; Fig. 2a is a plan view of one embodiment of a tidal power generating system in accordance with the present invention; Fig. 2b is a side sectional view of the Fig. 2a tidal power generating system; Fig. 3a is a front view of an elevation of one embodiment of a tidal power generating system in accordance with the present invention; Fig. 3b is a plan view of the concrete piers; Fig. 3c is a plan view of a pier showing a portion of a module interlocking therewith; Fig. 4a is a plan view of a cassette module used in tidal power generating system of Fig. 1; Fig. 4b is a front view of the Fig. 4a cassette module; Fig. 4c is an end view of the Fig. 4a cassette module; Fig. 5 is a perspective view of a crane used in the Fig. 1 tidal power generating system; Fig. 6 is a side view of a pier used in the tidal power generating system of Fig. 1; Fig. 7a is a plan view of another embodiment of a tidal power generating system; Fig. 7b is an end sectional view of the Fig. 7a tidal power generating system in accordance with the present invention; Fig. 7c is a side sectional view of the Fig. 7a tidal power generating system; and Fig. 8a is a plan view of a cassette module having a mesh screen therein used in accordance with one embodiment of the invention; Fig. 8b is a front view of the Fig. 8a cassette module and screen; Fig. 8c is a side view of the Fig. 8a cassette and screen; Fig. 9a is a plan view of a cassette module having a cofferdam door therein used in accordance with one embodiment of the invention; Fig. 9b is a front view of the Fig. 9a cassette module and door; Fig. 9c is a side view of the Fig. 9a cassette and door; and Fig. 10 is map of Duncansby Head, Caithness, Scotland, showing a tidal power generating system of the present invention provided proximate thereto.

An end and plan view of a tidal power generating system 100 are shown in Figs. Ia and lb comprising a longitudinally extending channel 10 which has been excavated from the land 12. The channel 10 defines a void into which a plurality of transversely spaced apart, vertically extending piers 14 are provided. The piers allow a cassette module 50 comprising a turbine 52 to be added to slots 13 therebetween. In use, water flows through the turbines 52 due to tidal currents and recovers energy therefrom.

A bridge 16 is provided over the piers 14 in order to allow access for cranes 60 (not shown in Fig. 1) or the like to install and remove the modules 50 or for other purposes.

A suitable crane may be a rubber tired gantry crane rated to 40,000 kg or 50,000kg and may be obtained from Kalmar Shropshire, UK.

In use tidal currents cause water to flow through the turbines 52 in the channel 10 which recovers a portion of the tidal energy. The tidal currents will of course ebb and flow and the turbines 50 can recover energy regardless of the direction of the tidal flow.

Fig. 2a shows a plan view of the system according to one embodiment of the present invention with guide rails 17a, 17b on the bridge 16. Although not shown in Fig. 2a, the guide rails I 7a, I 7b will normally extend away from the bridge 16 to a workshop or other loading location.

Fig. 2b is an end view showing a series of modules 50 comprising turbines 52 provided in the spaces between the piers 14, with a first module 50a in the process of being raised for maintenance.

The provision of piers, such as the piers 14, allow for easy installation, removal and maintenance of the modules 50 comprising the turbines 52. In one embodiment, the piers 14 are approximately 40m high x lOm long x 4m thick.

Fig. 3a shows another embodiment of a tidal power generating system comprising piers 114 and a bridge 116. A plan view is shown in Fig. 3b where bridge beams 16a -16d support vehicles (not shown) thereover. Fig. 3c is a plan view of a pier 114 showing grooves 122 which receive V-shaped key steel guides 124 welded to the sides of the module 150 which together align the modules 150 in slots 113 of the piers 114. Hardwood guides 125 are bolted to the key guides 124 as wear plates. Whilst not essential, it is preferred that other embodiments also incorporate a similar aligning mechanism.

A plan and front view of the module 50 and turbine 52 are shown in Fig. 4a and Fig. 4b. A variety of different energy extraction devices may be used within the scope of the invention. Indeed the provision of a body of fast flowing sea water on land lends itself to the provision of a cheap research facility into deep sea tidal energy structures. Currently, testing the efficiency of new energy extraction devices such as turbines for extracting tidal power is extremely expensive since limited experiments can be conducted in a laboratory tank and then upscaled in the open sea, which is extremely expensive. Embodiments of the present invention allow large scale turbines to be placed in tidal stream at a fraction of the cost to launch them in the open sea.

Thus their efficiency can be determined and if need be, optimised without offshore installation and maintenance. After trials this cassette module can easily be removed and taken to workshops for inspection and maintenance.

Moreover this removes the need to provide artificial anchorage for the new turbine.

In one embodiment, the cassette modules 50 are approximately lOm x4m long x 17m high, weighing between 30-50 tonnes and are of a steel cage construction with slightly wedge V-shaped key steel guide welded to the sides.

In use, the cassette module 50 sits approximately Im high above the invert of the concrete channel 10. This allows for better water flow and also for marine wildlife such as fish to pass thereunder. To achieve this, cassette module footings (not shown) are provided approximately Im below the cassette. The footings also have hardwood guide beams as wear plates.

Referring to Fig. 6, the service bridge 16 is situated on the concrete piers 14 is preferably constructed from galvanised steel and beams bolted together and fixed to the individual concrete piers 14. Two of these beams iSa, 15b are shown in Fig. 6. The bridge 16 carries service ducts, cables and a pipe manifold (not shown). In one embodiment, there are four steel beams placed and bolted to each pier to carry a 6m wide roadway over the 101 m wide channel. The two outer steel beams may carry a bridge with guide rails I 7a, 1 7b thereover which travels the gantry crane 60 and cradle 62. For the purpose of raising and lowering of the cassette modules 50 into the slots 13 and therefore the tidal stream, the middle bridge beams may be removed, as shown in Fig. 1 a where the central portion of the bridge between two central piers has been removed.

The recovery of cassette modules 50 is the reverse procedure to the installation of same. To accomplish this the middle two steel beams between the concrete piers 14 over which the bridge travels are unbolted and lifted out to reveal the slots 13 for the cassette modules 50. After recovery the steel beams are placed and bolted to the concrete piers 14 thus reinstating access bridge 16.

In Fig. 5, a gantry crane 60 is shown which is designed to run on the rail tracks 17a, 17b of the bridge 16 but can equally be adapted to run on a road.

The crane 60 can pick up a cassette module 50 including a turbine 52 from a workshop by manoeuvring the crane 60 on rails (not shown in Fig. 5), over the cassette module 50, lift the cassette module into a cradle carrier 62 provided on the crane 60 and transport to it the bridge 16. The gantry crane and cradle carrier 62 are manoeuvred above the piers 14 and lined up with a slot 13. All hydraulic connection of pipes to manifold or transmission connections or electric cabling (not shown), through ducting are completed prior to lowering cassette modules 50 into the slot 13 and therefore the tidal stream. The cassette module 50 is then lowered down into the slot 13 between the piers 14 and into the tidal stream flowing through the channel 10.

Thus energy is recovered from the tidal stream moving through the channel 10 by activating the turbines 52 provided in this tidal stream. Preferably the turbines drive a generator (not shown) housed away from the water which allows for easier maintenance thereof. In one embodiment the hydraulic pumps (not shown) connect to a manifold (not shown) on the service bridge 14 where the manifold extends on to the west bank of the channel 10 next to a transformer substation (not shown). Here oil pressure drives hydraulic motors on generators (not shown).

Thus such embodiments incorporate built in' machinery to enable straightforward removal and replacement of cassette modules. Preferably all maintenance is designed and provided for in order that the work is part of a routine.

Utilising such system for installation and removal of turbines in a cassette module operation makes maintenance procedures much more cost effective compared to offshore systems, or and are preferred over embodiments of the present invention which do not include such a facility.

Fig. 7a shows one embodiment where two such systems 100, referred to as two banks', are provided in a channel 90. At either end of the channel 90 are cassettes 70 comprising cofferdam doors or gate screens.

Whilst various configurations would suffice, banks containing the cofferdam doors/gate screens, described in more detail below, are preferably constructed on the same principle as the turbine banks 100, thus utilizing six reinforced concrete piers and a maintenance bridge.

A cassette module 70 comprising a gate screen 72 is shown in Figs 8a -8c.

In use the gate screen mesh 72 is provided in the cassette 70 in the channel to prevent ingress of larger fish or large objects from the water 80 into the channel 90 at each end thereof and so avoiding such marine life or debris contacting the turbines in use.

A cassette module 70 comprising a cofferdam door 74 is shown in Figs 9a - 9c. The cofferdam door is a solid plug' having a rubber seal 78 at its bottom and valves 76 provided thereon. It can be added in place or in addition to the gate screen 72. In the event of maintenance being required in the channel 90, a cofferdam door is dropped into slots between the slots of each pier to resist all water ingress into the channel 90 at each end thereof. The channel can then be drained of water and maintenance conducted in largely dry conditions.

Maintenance which may occasionally be required to the screens 72 and cofferdam doors 74 can safely be carried out between tides or onshore by lifting out the cassette modules 70.

The cofferdam doors and mesh gate screens 70 are operated using the same crane system on the turbines lifted and lowered for ease of maintenance.

In a preferred embodiment two banks of turbines are provided each bank having seven approximately lOm diameter turbines housed in a removable cassette module driving hydraulic pumps or electric generators.

In a modification to the Fig. 7a embodiment, a further bank of piers and a service bridge is constructed between the two banks 100; thus further bank may be employed as a research and development tidal power test facility. On a tidal power test facility there is a separate transformer substation for monitoring turbine output at different tidal conditions.

One suitable location for the installation of a system in accordance with the present invention is at Duncansby head near John o'Groats in the North of Scotland. Here the flood tide travels east past Stroma and is near to the shore at Sannick Bay. The ebb tide flows close to Duncansby Stacks where the rock shelves to deep water. Between these two locations is a valley starting at the beach of Sannick Bay and rising to the lowest point on the cliff on the east coast, this valley is caused by a fault line which has broken the rocks allowing greater erosion.

This site is particularly suitable because of the low sea cliff face in the east together with the close proximity of a deep and fast flowing channel just offshore. Whilst there is sand in Sannick Bay it is not deep and are removed as part of the excavation for the works, rock is expected to be encountered here at the level of low tide.

Observations indicate a hydraulic head of 400mm at most states of the tide, both flood and ebb, between the two ends of the valley.

In accordance with the present invention there is now described one embodiment of manufacturing a system to generate energy from wave and/or tidal resources. The embodiment described hereinafter is with reference to a system at Duncansby Head but the invention is not limited to this location.

A ground, tidal and water depth survey is first performed to ascertain potential and best sizing and location of channel. One suitable channel is shown in Fig. 8. An open cut channel is then constructed in the dry by leaving rock plug dams at each end of the channel close to the shore -these are approximately 6m higher than the high spring tide level as a safety barrier in storm conditions. Pumps (not shown) are utilised to cope with any ground water leakage encountered during excavations.

The open cut excavation in rock is carried out and excavated to reduced levels of approximately 6m above the high water spring tide. Thereafter a channel of approximately lOim wide x 18m below sea level (allowing for 17m depth and I m concrete) x 800m long is constructed. The topsoil and subsoil are excavated over the entire site and re-used for landscaping where possible.

Further excavation in rock is carried out to reduced levels to suit the final depth, length and width of the proposed channel leaving the rock plug 70 dams at each end of the channel. A further 4m excavation is carried out locally to allow for concrete thickening at location for turbines and cofferdam footings. Water pumps (not shown) are provided where required with pumps to pump out any water leakage throughout works. The depths given for this embodiment refer to depths below sea level. The surrounding rock formations makes the channel in this embodiment greater in overall depth -about 40m. It is preferred that the piers etc, described below, extend up to this latter height so that they are level with the surrounding rock formations and the bridge is level therewith.

A reinforced concrete lining is constructed over the entire channel floor with walls approximately I m thick. The concrete is thickened locally where the turbine piers and cofferdam door piers are to be located for example concrete depths may be 5m thick reinforced concrete at these specific locations.

Constructed across the channel are six vertically extending and spaced apart concrete piers between which cassette modules may be inserted and removed. A maintenance bridge 16 is constructed above the channel and a gantry crane 60 on bridges with guide rails I 7a, I 7b provided thereover.

Units with cofferdam doors are also constructed at each end of the channel.

On completion of the concrete works on the tidal channel, piers and bridges the rock dams are excavated at either end of the channel utilising quarry plant. This is achieved by firstly closing the cofferdam doors and gate screens at either end of the channel, then excavating the rock plugs to a minus 8m level utilising the rock excavated for profiling the approach entrance to tidal channel. Thereafter the excavation works are carried out utilising a floating barge and dredger (not shown) to give a channel depth of approximately 17 metres below high tide level.

As described in exemplary fashion above, such system can be constructed resulting in a tidal power generating system shown in the figures.

Thus as embodiments of the invention involves excavating land, the maintenance associated with sustaining such an onshore facility is significantly less than maintaining an offshore facility. Ease of access for maintenance is normally a paramount consideration for renewable technologies.

Whilst embodiments of the invention require capital outlay medium to long term savings in maintenance costs are expected to be enjoyed to justify such an outlay.

A number of other benefits results from one or more embodiments of the present invention.

For example, in offshore turbines, marine growth will reduce efficiency of the blades or worse destroy bearing seals. Whilst anti-fouling paints can be used these are short lived and cause pollution. However embodiments of the present invention allows access for maintenance 24/7; turbines may be lifted out, pressure washed and lowered back into tidal streams at relatively low cost.

Abrasions of turbine blades, caused by suspended solids, will reduce efficiency. Embodiments of the present invention mitigate this problem by the provision of screens at ends of channel which prevent any suspended solids, nets or creels causing any damage to turbines.

The smallest quantity of sea water can destroy a generator and the watertight seals are costly to replace regularly and so providing these turbines offshore rather than onshore results in difficulties and expenses.

To maximise their load, offshore turbines are sited in areas exposed to extreme weather conditions and/or fast moving currents. Such conditions however make maintenance more difficult and storms or the like can delay access for repair of these relatively remote structures resulting in periodic downtime of the turbine.

Embodiments of the invention provide a safe haven' for turbines during tidal storms and access for repair or maintenance is much easier. There is no requirement for costly tug boats, barges, sea cranes and harbour facilities -all of which present safety issues.

Health and safety considerations during deployment and maintenance will often increase the costs. Maintenance on turbines used in accordance with certain embodiments of the present invention, will be possible at virtually any time, as they are much more accessible. Thus for preferred embodiments of the invention, once constructed, all operations will be carried out away from the perils of the sea and as such will be inherently safer than maintenance of offshore structures.

Similarly there is a relatively high cost of construction and deployment for each turbine offshore compared to embodiments of the present invention where they can be situated onshore.

For offshore turbines, connections to the grid will need to be made underwater and will be very expensive. However for embodiments of the invention there is no requirement to connect power cables to turbines in a subsea tidal environment.

The risk for the deployment of turbines in open tidal waters is reflected in insurance premiums whereas embodiments of the present invention will significantly reduce the risk and associated premium.

For offshore facilities, there is a risk of collision in areas with fast tidal currents near shipping lanes. Large vessels do not compete well against the strong currents and are especially a danger to any apparatus that relies on a mast for its support and access for maintenance. Similarly shipping will be endangered if a turbine should slip its mooring or foundation and insurance claims will be huge. At some locations there will be interference to small boats and local creel or other fishing. Conversely turbines could possibly be snagged by pots and buoys if the become loose in a storm. Thus avoiding such problems is another clear benefit of the present invention.

Improvements and modifications may be made without departing from the scope of the invention.

For certain embodiments, rock from the excavations may be used on site for access roads, car parking, workshops, transformer station & office foundations as well as profiling the tidal channel on the seaward approaches.

In addition to or instead of turbines, wave energy capture device may be used, although preferred embodiments extract tidal energy.

Claims

Claims 1. A method of harnessing energy from a tidal or wave energy source, the method comprising: providing an energy extraction device in a manmade path between two shore locations on the same island or land headway; using the energy extraction device to extract energy from water flowing through said path.
2. A method as claimed in claim 1, wherein water flows preferentially through the manmade path than by any other route.
3. A method as claimed in any preceding claim, wherein the energy extraction device extracts tidal energy.
4. A method as claimed in claim 3, wherein the tidal energy is extracted by the energy extraction device as the tide moves water in a first direction between the two shore locations and also in the opposite direction between the two shore locations.
5. A method as claimed in any preceding claim, wherein the path is an open channel, at least partially open opposite its bottom, the bottom being defined by the portion of the path which water naturally flows over due to gravity/tidal/weather effects and conditions.
6. A method as claimed in any preceding claim, wherein the energy extraction device drives a hydraulic system or a transmission system which is connected to generators which are on land.
7. A method as claimed in any preceding claim, wherein the path is at least 5m deep, preferably at least 15m deep.
8. A method as claimed in any preceding claim, wherein the path is at least 15m wide, preferably at least 30m wide.
9. A method as claimed in any preceding claim, wherein the path is up to 200m wide, preferably less than 150m.
10. A method as claimed in any preceding claim, wherein at least one spacer is provided in the path in order to define at least one slot to receive the energy extraction device; the slot is defined between two spacers or between a spacer and one bank of the path.
11. A method as claimed in any preceding claim, comprising excavating a portion of the geological formation between the two shore locations to provide the manmade path therebetween.
12. A method as claimed in claim 11, wherein the path is excavated to the extent necessary to cause water flow from one shore location to the other via the manmade path.
13. A method as claimed in claim 11 or claim 12, wherein before excavation, there is no body of water flowing in the geological formation which will be excavated to form the path.
14. A method as claimed in any one of claims 11 to 13, wherein first, leaving a portion of land which is ultimately excavated to form a barrier to water flow; then, excavating the portion of dry land; then said portion of land forming the barrier is excavated.
15. A system for harnessing energy from a tidal or wave energy source, the system comprising: an energy extraction device in a manmade path between two shore locations on the same island or land headway; the energy extraction device configured to extract energy from water flowing through said path.
16. The system as claimed in claim 15, comprising at least one spacer provided in the manmade path, the spacer at least in part-defining at least one slot, shaped to receive the energy extraction device.
17. The system as claimed in claim 16, wherein the spacers are manufactured from a concrete.
18. The system as claimed in claim 16 or claim 17, wherein a plurality of spacers extend from one bank to an opposite bank.
19. The system as claimed in any one of claims 15 to 18, wherein a screen is provided in the path in order to resist flow of objects above a certain size.
20. The system as claimed in any one of claims 15 to 19, wherein a retractable door is provided in the path.
21. The system as claimed in claim 20, wherein the retractable door is a cofferdam door.
22. The system as claimed in claim 20 or claim 21, wherein the retractable door comprises a plug which is moveable into the slot defined by retractable door spacer(s) thus actuable to resist flow of fluid therepast.
23. The system as claimed in any one of claims 15 to 22, wherein where there is a second energy extraction devices spaced apart from the first energy extraction devices in the path in the longitudinal direction (0 15 as defined by the path, the retractable door is provided between one of the shore locations and the closest energy extraction device.*::r: INTELLECTUAL . ... PROPERTY OFFICE Application No: GB 1004287.7 Examiner: John Twin Claims searched: ito 23 Date of search: 12 July 2011 Patents Act 1977: Search Report under Section 17 Documents considered to be relevant: Category Relevant Identity of document and passage or figure of particular relevance to claims X 1-6,11-JP05263413A 13,15 at see abstract and drawings least X 1-3,5,11-JP2000018146A 13,15 at (Ueda) -see eg abstract, drawings least X,E 1-4,6,11-W02011/005100A 13,15 at (Eriksen) -note manmade water path is made through landmass neck S; least see eg figures 1B,9,i0,15 X 1,3-JP60219469A 5,11,12,1 (Urata) -note eg the manmade channels 3A,3B at least X 1-5,11-FR2309671A 13,15 at (Schwetzoff) -note the ring canal across isthmus least X 1,6,lSat JP58119972A least (Monma) -see eg abstract, drawings Categories: X Document indicating lack of novelty or inventive A Document indicating technological background and/or state step of the art.Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of before the filing date of this invention.same category.& Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:Search of GB, EP, WO & US patent docuirients classified in the following areas of the UKCX: Worldwide search of patent dociiments classified in the following areas of the IPC EO2B; FO3B The following online and other databases have been used in the preparation of this search report EPODOC, TXTE, WPI Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk *.:r: INTELLECTUAL . ... PROPERTY OFFICE 30 International Classification: Subclass Subgroup Valid From FO3B 00 13/26 01/01/2006 EO2B 0009/08 01/01/2006 FO3B 00 13/22 01/01/2006 Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk