WO2012156734A1

WO2012156734A1 - A submersible structure adapted to host tidal energy converters

Info

Publication number: WO2012156734A1
Application number: PCT/GB2012/051095
Authority: WO
Inventors: Philip HEMSTED; Steven JERMY
Original assignee: Tidepod Limited
Priority date: 2011-05-16
Filing date: 2012-05-16
Publication date: 2012-11-22
Also published as: GB2491028A; GB201208630D0

Abstract

A submersible structure adapted to host one or more tidal energy converters, in which the structure includes one or more sea-towable, barge-shaped hulls. Each hull can host one or more TECs (tidal energy converters); these are typically installed onto the structure after the structure has been sunk to the sea-bed in its final deployment position. Sea-towable, barge shaped hulls can be rapidly and reliably towed to the deployment position using standard commercial tugs and can then be sunk to the seabed, where their barge-shaped (i.e. flat bottomed) design makes them inherently stable, when sufficiently ballasted. Hydro-dynamic streamlining may be used to minimise the downstream turbulence generated by the foundation, thus improving power generation.

Description

A SUBMERSIBLE STRUCTURE ADAPTED TO HOST TIDAL ENERGY CONVERTERS

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a submersible structure, designed and adapted to host tidal energy convertors, and related deployment and installation methods.

2. Description of the Prior Art

There are two generic ways to generate electricity from tidal resources. The first is to use tidal barrages across large estuaries, such as the Severn Estuary in the United Kingdom, working in a similar way to hydro-electric dams. The second is to place vanes or rotors on the sea floor to capture tidal energy in areas of high tidal streams. This invention, referred to as the 'Tidepod' system, is intended for use with the second of these approaches.

The UK has an unusually high percentage of the world's tidal stream resource, amounting to between 10% and 15% of the overall total. Around 80% of this resource is located in just 10 sites, mostly in the North of Scotland and the Channel Islands.

An important nuance is that all but 1 of the 10 high energy sites have water depths in excess of 40m, a depth which is difficult to access using current technologies. The remaining 20% of the UK's energy is in 47 other sites, spread throughout UK's territorial waters, generally in water depths of less than 40m.

The opportunities in tidal energy are significant when compared to other renewables. The resource is highly predictable, available 24/7 and, as will be shown, the environmental impact is significantly lower than all other renewable forms, because of the tide's high energy density. Current estimates suggest that nearly 30 TWh/ yr of tidal stream energy could be available from the combined sites, representing over 7% of the UK's overall energy requirement.

The challenges in the tidal resource are all associated with marine operation. High tidal streams are amongst the most challenging marine environments in which to work. As a rule of thumb, mariners compare the force imposed by tide and wind in the ratio 10:1 with 1 knot of tide having the force on a marine structure of 10 knots of wind. Thus, installing tidal energy devices at sea in 10 knot tidal streams is akin to installing wind turbines on land in 100 mph winds. Tidal stream energy is extracted by placing vanes or rotors on the sea floor, and two major types of tidal energy converters (TEC) are currently favoured by the industry:

• Horizontal Axis - the energy of the tidal stream flows past and rotates tidal vane propellers or turbine stators, and the rotational energy is then converted into electrical energy.

• Vertical Axis— the tide stream flows through a vertical drum comprised of a number of hydrodynamic 'wings'. The flow of water across each wing causes hydrodynamic lift that causes the drum to rotate, and the circular energy is converted into electrical energy.

So far, most industry R&D has focused on TEC design. Much less thought has been applied to the practical issue of deploying these devices to, and then securing and maintaining them on, the sea floor.

Deployment and installation of TECs is a key industry cost driver, but one that is only now beginning to attract appropriate levels of R&D investment. To fix TECs to the seabed, the industry uses two approaches:

• Pile foundations - are usually large column-shaped foundations, fabricated in steel, lowered into drilled recesses in the seafloor, and then secured by grouting.

• Gravity-base foundations - are stand-alone foundations, fabricated in steel or concrete, and secured on the sea bed by their inherent weight.

In both approaches, large seaborne cranes are required during the deployment. The cranes are deployed from jack-up barges or dynamic position (DP) vessels. The use of the cranes, and their host barges and DP vessels, is constrained by two factors, tidal stream speeds and local weather. The difficulty of working in high tidal streams means that operations on the sea bed are generally conducted in narrow 'slack-water' windows, which may be less than 2 hour in every 12.5 hour tidal period. The cranes are also unable to operate in high sea states, such as those routinely encountered during the UK's winters.

For all these reasons, the installation, station-keeping, and operations & maintenance (O&M) costs for 1^st generation tidal energy systems are around twice the capital cost of the individual TECs devices and account for around 60% of the overall tidal cost of energy (CoE). The industry is thus seeking significant cost reductions in the order to bring p/KWh figures down to target levels of 10 p/KWh. SUMMARY OF THE PRESENT INVENTION

The invention is a submersible structure adapted to host one or more tidal energy converters, in which the structure includes one or more sea-towable, barge-shaped hulls. Each hull can host one or more TECs (tidal energy converters); these are typically installed onto the structure after the structure has been sunk to the sea-bed in its final deployment position. Sea-towable, barge shaped hulls can be rapidly and reliably towed to the deployment position using standard commercial tugs and can then be sunk to the seabed, where their barge-shaped (i.e. flat bottomed) design makes them inherently stable, when sufficiently ballasted. Hydro-dynamic streamlining may be used to minimise the downstream turbulence generated by the foundation, thus improving power generation.

The structure may include multiple barge-shaped hulls, forming a catamaran or trimaran. Each sea- towable, barge-shaped hull may be made up of multiple standardised hull modules, at least one hull module adapted to host a tidal energy converter. Using standardised modules facilitates fast, cheap and reliable fabrication and enables hulls of different lengths to be readily fabricated using different numbers of modules. Simple and widely available fabrication techniques (plate steel welding etc) can be used. Multiple structures can be electrically connected in a large array on the sea bed.

Each barge-shaped hull may include one or more sockets or supports with standardized parameters, so that any tidal energy converter complying with those parameters can be used in the socket or on the support. This enables TECs to be deployed on a single submersible structure from several different manufacturers— a major advantage when testing of many different designs needs to be completed at a site.

The position of a TEC tidal energy converter on the structure can, e.g. to minimise wake turbulence, be adjusted laterally (e.g. by providing struts separating each hull of different lengths), longitudinally along the length of a hull and vertically using TEC supports of different heights. This can be readily achieved when the structure is being designed and built.

Each hull may be at least partly hollow for towing, but is then sufficiently ballasted (e.g. using site specific amounts of concrete) when to be sunk.

The submersible structure may host multiple tidal energy converters, but with a single power converter/ shaper serving each tidal energy converters.

The submersible structure may include navigation sensors that enable the structure to dynamically and stably control its descent to the sea bed and may include onboard rechargeable batteries that enable the structure to operate autonomously and without the need for remote controlled operation.

One implementation of this invention is called the system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the drawings, which show the Tidepod implementation of the invention.

Figure 1 shows the Tidepod modular, extensible hull design;

Figure 2 shows a Tidepod with trimaran hulls, including the vertical supports that each host a TEC;

Figure 3 shows a trimaran Tidepod with the TECs in position on the vertical supports;

Figure 4 shows a trimaran Tidepod with the TECs in position on the vertical supports; three different TEC designs are deployed on the Tidepod;

Figure 5 shows a trimaran Tidepod with the TECs in position on the vertical supports; the supports are each in different positions on their respective hulls;

Figure 6 shows a trimaran Tidepod with the TECs in position on the vertical supports; the supports all have different heights;

Figure 7 shows a a trimaran Tidepod with the TECs in position on the vertical supports; augmented hull profiles are shown; these optimise flow/ minimise wake turbulence;

Figure 8 shows three different Tidepod configurations: mono-hull, catamaran, trimaran;

Figure 9 shows a monohull Tidepod hull with a standardised flange interface on the top of the support tower; TECs from different manufacturers can be bolted to this flange so long as they use a matching flange. A standardised machine room space for electrical components is also shown.

DETAILED DESCRIPTION

The Tidepod system is based on the idea of a semi-buoyant gravity-based foundation of trimaran form, henceforth called a Tidepod, which is able to host multiple TECs. The structure would be modular in nature, based on a steel framework and steel or concrete hulls.

The trimaran hulls are hydro-dynamically streamlined, specifically to minimise their underwater drag and/or maximise the energy that may be harvested from individual sites. The spars that connect the individual hulls are hydro-dynamically designed so as to improve the stability of trimaran on the sea bed and may be adjusted in length to vary the size of the structure. Adjustment may be during fabrication or indeed once the structure has been assembled, e.g. is on the sea bed. Each individual hull has, on its underside, 'angry nibs', which are sharp structures, akin to racing shoe spikes, designed to penetrate the sea bed surface and adjustable in length to allow the Tidepods to be 'tuned' or otherwise customised to individual sea beds. Adjustment may be during fabrication or indeed once the structure has been assembled, e.g. is on the sea bed.

Each of the trimaran's three component hulls is host to, first, an upright support structure with a universal socket designed to accommodate an individual TEC and, second, a standardised power space for electrical power conversion and conditioning equipments:

• upright support structure— elliptical in cross-section, to minimise underwater drag and turning forces, and adjustable in height (e.g. can be manufactured in different lengths) to optimise the position of the TEC in the water column. Adjustment may be during fabrication or indeed once the structure has been assembled, e.g. is on the sea bed.

• electrical spaces - of standardised dimensions and with standardised connections, so as to host the electrical systems needed to meet the different power conditioning and conversion requirements of the different device manufacturers.

The concept of operation is based around a 6 phase build & install process:

• fabrication - mass-produce and assemble the trimaran hulls and structures in dockyards or coastal industrial facilities.

• deployment - tow the assembled Tidepod (or use float-on/float-off ship) to a forward shallow-water staging-location, close to the tidal site, for installation preparation.

• preparation - ballast the trimaran hulls according to the mass required for the specific tidal site, using concrete ballast and, in the process, sinking the Tidepod onto the shallow sea floor. Then recover the Tidepod to the surface, by winching it underneath a bespoke Tidepod installer vessel. The TECs may or may not be installed, at this stage, subject to the operational requirements of the tidal site.

• installation - tow the Tidepod installer and its under slung Tidepod to the installation site and lower the Tidepod, during a single slack water window, to the sea floor. Once on the sea floor, flood the Tidepod, so that it is fully ballasted for long-term sea bed stability.

• commissioning— if the TECs have not been shipped during preparation, these are then installed on the sea floor, using a surface crane. The Tidepod is then connected to underwater grid, via a single inter- array cable, and power generation may then begin.

• de-commissioning - air is pumped into the flooded spaces of the Tidepod, and it is then reconnected to the installer barge and winched back to the sea surface.

The Tidepod system thus allows the rapid deployment of TECs to a wide range of submerged locations, at a range of depths, without significant underwater engineering to fix tidal energy devices to the sea floor and minimising the use of large and expensive seaborne cranes during the installation and commissioning operation.

Tidepod System— Structural Design Factors

The base design is driven by five key factors:

• onshore build & local maintenance— the business economies of, first, a production line approach for Tidepod construction and, second, the desirability of preparing Tidepods in shallow-water forward-staging locations, close to tide farm locations.

• seaworthiness - the advantages of being able to tow Tidepods at reasonable speed behind a standard commercial tug, and minimising the extensive use of seaborne cranes and, thus, the high costs associated with current installation technologies.

• multiple designer device deployment - the likely business desirability of being able to deploy up to 3 TECs, from a wider range of manufacturers, per single Tidepod foundation, thus reducing, first, the number of foundation installations and, second, the number of underwater cable connections.

• array tailoring - the need to be able to design bespoke tidal arrays, so as to be able to optimise the power extraction and revenue generation of the different UK tidal sites. • depth - the likely strategic advantage of being able to place TECs at depths below 40 metres, where over 50% of the UK tidal resource exists, and ideally up to 100 metres, thus accessing over 90% of the UK's exploitable tidal energy.

The current engineering analysis points to a trimaran design, with a dry-weight of between 550 and 600 tons, and a ballasted weight of between 2500 and 3500 tons, subject to the operational demands of the specific tidal site.

Current designs demonstrate that the system is technologically capable of dealing with the most demanding tidal regimes in UK, which are amongst the most demanding in the world. It follows that the system should be deployable world wide, and have access to the world wide tidal energy market.

Tidepod System— Arr y Design Factors

The arrangement of TECs within tidal arrays shares some of the science of wind farm design, but is more complex. The two significant advantages of tidal arrays are, first, that water is around a 830 times denser than air and, second, the direction of tidal streams is highly predictable, unlike wind direction. As a result, the available energy per unit area is much higher. Outline calculations show that a 1 Km² tidal farm could generate at least a 100 times as much power as its wind farm equivalent, and very probably much more. Or, to put it another way, to generate the same power as a 1 Km² UK tide array, one would need to place wind turbines across either 100 Km² of UK's countryside or 100 Km² of UK's offshore waters.

Tidal array design science shows that a number of complexly related factors need to be taken into account to optimise tidal array power generation and thus maximise revenue. Key factors include: tidal steam speeds; water depths; TEC blade diameter in relation water depth; TEC height in the water column; cross-stream spacing between adjacent TECs; wake turbulence effects on downstream TECs. These factors vary hugely between sites, so there is no optimum generic array design. Instead, each array will need to be site tailored to maximise power extraction.

For this reason, and unlike other developer's approaches, Tidepod is designed to allow a high degree of site- specific array tailoring:

• TEC numbers - current designs allow Tidepod to host up to 3 TECs per structure (i.e. one TEC per trimaran hull) but extending the design to structures with more than one TEC per hull or to multi-hull designs (4 + hulls) is possible. • TEC blade diameter - Tidepod can host a range of TEC blade diameters, from 10m to 20m, on the same structure.

• TEC spacing - the capacity to vary the space between the Tidepod hulls allows the optimisation of X- flow spacing between adjacent TECs.

• flexible ballasting - because of its adjustable ballasting, Tidepod can accept the full range of different thrust and drag forces that result from different tidal speeds and TEC blade diameters.

• water column - the adjustable nature of the TEC upright support structure allows the TEC to be positioned at the optimum depth in the water column.

• wake turbulence - Tidepod's hydro-dynamic shape minimises downstream turbulence and thus helps maximise power generation in specific site arrays.

As well as helping optimise 1^st generation TEC array designs, the tuneability of the Tidepod system should allow it to cope with 2^nd and 3^rd generation approaches when these are introduced later in this decade and in the 2020s.

However, taking 1^st generation technologies as a yardstick, the calculations suggest that it should be possible to install 30-40 Tidepods per Km², giving nominal installed capacities of between 135MW and 180MW per Km² - comparative figures for wind turbines, of 2.2MW per Km², give a sense of the opportunity that results from the much higher energy density of tide over wind.

Market Potential

Around 70% of the UK's tidal resource is located in an area of just over 500 Km², of which:

• 29% is at depths of 30-40m and maximum Spring Tide velocities of between 2.5-4.5 ms⁴.

• 71% is at depths of 40m-100m maximum Spring Tide velocities greater than 3.5 ms⁴.

Assuming that 20% of the overall area - i.e. 100 Km² - is bathymetrically suitable for, and made available to, Tidepod arrays, and using the 30-40 Tidepods per Km², then the total market opportunity would be in the order of 3000 to 4000 Tidepods, with an overall capital value range of £6.6Bn to £10.4Bn. Similar calculations suggest an overall world market of up to 10 times that of UK. Conclusion

The purpose of this document is to describe the Tidepod System concept, and the calculations are designed to give an overall sense of the energy and expenditures involved.

The key potential advantages of the system are:

• Production line approach, with fabrication conducted ashore in UK dockyards.

• Economic and engineering benefits of being able to host a number of TECs in a single deployment vehicle and sea floor structure.

• Modularity, with potential for fitting a range of TECs, and replacing older with newer as technologies improve.

• Tuneability, with the potential to adjust TEC sizes and positioning - vertical, X-stream and down-stream— to maximise energy extraction and revenue generation from individual sites.

• Potential to deploy to significantly greater depths than many current deployment technologies, thus offering the possibility of gaining access to the 50% of UK tidal resource below 40m;

Tidepod - Key Advantage

Modularisation/Extensibility

Each Tidepod hull is made up of one or more standardised module-type hull sections, each capable of hosting a TEC system, in which different numbers of sections can be combined together to allow barges capable of retaining different numbers of tidal energy systems, to be readily constructed using widely available non-specialised techniques (see above section 'Fabrication')

Figure 1 shows this, with a Tidepod hull, shown at 1, has standardised fore 7 and aft 8 sections and a single section 4 that includes a standardised recess or socket 2 into which a column support can be fixed. A longer hull is shown at 2, with the same design of fore 7 and aft 8 sections, the same socket section 4 with standardised socket 2, a section 3 with a standardised bay to receive electrical equipment. This hull, with six sections of standardised modules is shown in exploded form at 9. A simpler hull, made up of four modules is shown at 10. At 11 is shown a catamaran design with two such hulls attached by struts 12. A column support (for supporting a TEC) is shown at 13.

Some environments may require single turbines, others multiple turbines, up to 3 and possibly more on a single structure. Tidepod can be implemented as a mono-hull, catamaran or trimaran design, as shown in Figure 8. The modular, extensible approach used in Tidepod means that a single design can be used across all configurations, saving costs and improving quality control.

Although a trimaran form provides best economies of scale, in the event that site conditions do not allow this, then catamaran structures, using the same structures and systems can be used as alternatives.

The modular/ extensible design give substantial fabrication advantages.

A simple design allows local manufacture & modular TEC fitment:

• fabrication in medium-to-large sized shipyards, with submerged testing completed close to the production facility.

• designed: on a modular basis, with standard 'sockets' for a range of devices, thus enabling different device manufacturers to employ the Tidepod for deployment.

• Use of a steel skeleton structure and steel-concrete trimaran hulls to reduce material costs.

• a modular design allowing 'future proofing', with 1^st Generation TECs replaced by 2^nd and 3^rd Generation devices, as these came into production.

The overall fabrication approach would be systemised, employing lean production techniques, minimising long-term maintenance and logistics support, and capable of sales worldwide.

Hydr odynamic form

Each hull of the Tidepod is a submersible barge-shaped structure, adapted to host one or more TECs. For comparison, current gravity-based foundations take three forms:

^■ heavy steel tripod

^■ heavy steel triangular base for single or multiple devices

^■ standard concrete offshore structures, multi-purpose for wind & wave

The barge shaped hull of the Tidepod has many advantages over the tripod/ triangular/ concrete support structures used in prior art systems:

• First, they are more streamlined for surface navigation, so they can be towed at greater speed behind a tug, thus getting them more quickly to the staging location. Figure 2 shows a typical trimaran form that would be towed at sea. Note that the TECs are not usually installed during sea-towing, but only once the structure has reached the deployment site. If the structure is gravity descending to the sea-bed, then the TECs are generally fitted once the structure is on the seabed; if they are fitted beforehand, then they can cause instability on descent. If the structure is winched down, then the TECs can be surface-fitted.

• Second, they are more buoyantly stable whilst being lowered/ descending to the sea bed.

• Third, they are more streamlined on the sea floor, and in particular better suited to meet the directional nature of tidal flows; tidal stream directions in high speed areas tend to tend to be bidirectional, e.g. East flowing on the flood tide, and West flowing on the ebb tide. Because Tidepod can be aligned longitudinally along the flood-ebb axis, it can always present a streamlined profile to the flood, with three inter-related advantages:

• less underwater drag, so greater stability for less ballast.

• less turning moment, so again greater stability for less ballast.

• less downstream turbulence, which means that rows of devices can be placed closer

together and, thus, more energy can be extracted from the same sea bend area.

• We may use the hull profiling to accentuate the flow over the turbines, again leading to a power increase.

• whereas a tripod or triangle can never be profiled so as to present a streamlined aspect to both flood and ebb tides.

• Fourth, possibility of including, within a hull's streamlined form, a standardised electrical compartment, without prejudicing foundation profile.

• Fifth, a flat bottom, for underwater stability once sunk onto the sea floor.

• Sixth, the deck of each hull can be augmented with hydrodynamically designed structures that increase flow rates through the TECs, as shown in Figure 7.

• Seventh, the hydrodynamic form of the Tidepod structure reduces the down stream turbulence, and increases the overall power generating capacity of the tidal array.

Note also that Tidepod is a submersible multi-hull structure, each hull adapted to host one or more TECs. This has advantages, even in an implementation where the hulls are not barge - shaped. Hosts different TEC design

Each hull of the Tidepod (e.g. the submersible trimaran) includes one or more sockets, (such as a bay or column structure or plate or flange on a column structure— the term 'socket' should be expansively construed to mean any structure against which another structure can be securely bolted or otherwise fixed) of standardised characteristics to host TEC systems from different designers/ manufacturers, to allow:

• many different designs of turbines from different manufacturers to be deployed - Tidepod could become the standard deployment solution. Figure 3 shows a Tidepod with identical TECs and Figure 4 by contrast shows a Tidepod with TECs of three different designs, from three different manufacturers. This is very advantageous, especially in the early years of the TEC industry since many different TECs need to be tried out and tested on the seabed. Each TEC fits onto the standard column with a standard flange, as shown in Figure 9. Hence, different TEC manufacturers need only ensure that they can fix their TECs securely to the specified socket - e.g. flange of defined radial thickness, bolt hole positions etc. and to ensure that their TECs meet the weight and torque (and any other applicable parameters) required for the Tidepod to be able to host that TEC.

• turbine systems to be removed and swapped-out with replacement systems for repair and maintenance.

• turbine systems to be removed and swapped-out with more up to date or different designs.

• the trimaran to be manufactured in any yard that is capable of building simple barges; fitting the TEC system is then a simple installation process.

The provision of a standardized electrical power space, to allow designers to install bespoke electrical power conditioning and conversion systems, according to their individual needs.

There is no complex interaction between TEC system and barge, so the design is more robust and is cheaper than systems that require bespoke integration of complex TEC. This also allows tidal energy system designers/ manufacturers to concentrate on doing what they do best, without having to worry about deployment.

Tuneability Tidepod can be optimised for the particular depth, tidal characteristics and seafloor topography, in particular:

• fitted with adjustable columns to allow the TEC to be placed in the optimum position in the water column. Figure 6 shows this. The reason for designing in adjustable elevation is twofold:

o first, to being able place the TEC in the optimum elevation for energy extraction in the water column - generally the higher the better,

o second, to adjust to ensure sufficient navigable water above the TEC.

• fitted with height adjustable 'angry nibs' to enable tuning for individual site sea-bed topography.

• able to adapt the configuration of the TECs ported, in order to optimise harvesting of the local tidal resource. Figure 5 shows this, with the two outer TECs positioned at different positions on the outer hulls compared with the inner TEC, to optimise energy extraction. The ability to adjust the location of the individual TECs on the structure so as to optimise tidal array design is important. Adjustment may be during fabrication or indeed once the structure has been assembled, e.g. is on the sea bed. The issue here is wake turbulence, and the very significant loss of power that can result from placing downstream TECs in the wake of those upstream. Tidepod should allow us to optimise for both tidal site and individual manufacturers devices, through:

o lateral adjustment between TECs - this is done by increasing or decreasing the width of the trimaran, through increasing or decreasing the lengths of the beams that connect the hulls.

o longitudinal adjustment between TECs - this is done by locating the supports for or aft on the hulls, and is important because there may be significant power advantages if we can place two TECs forward on the hull and one aft.

o elevation adjustment between TECs - there may be advantages for us to vary the height of the individual TECs on a Tidepod, so that a downstream TEC avoids the wake of an upstream TEC.

o we have designed in the capacity for lateral, longitudinal and elevational adjustment, giving Tidepod the ability to take advantage of the optimal locations, established through testing etc.

• Tidepod enables adjustable ballast to be used - the trimaran hulls are designed to be hollow, so that they may be towed easily to the preparation site, then ballasted using concrete. Because of this, we have the capacity to tune the ballast to suit the specific needs of the manufacturers and the site. Some high energy sites will require more ballast than others, and we can tune as needs be. For example, after site-specific ballasting, the dry weight of a Tidepod will be: 1915 tonnes, in a representative low energy site; 2984 tonnes, in a high energy site.

Electrical power conditioning, conversion & cabling

A single Tidepod (e.g. trimaran design):

• is able to host power conditioning and conversion equipment, fed by the three induction generators, thereby reducing costs when compared to single tide TEC deployments;

• hosts multiple TECs, reducing the need for underwater cabling in inverse proportion to the number of TECs hosted.

• has the capacity for standardised connection to underwater grid:

- first, between the grid and a Tidepod.

second, between individual Tidepods, so as to facilitate underwater electrical networks.

- third, between standard TEC Tidepods and an electrical hub Tidepod, designed to port electrical hub capacity within the standard Tidepod hull form.

• is a standardised structure able to be used as an underwater electrical hub.

Deployability

Tidepods deployment methods would depend on the distance between the production facility and the staging location:

• for strategic deployment to distant locations, the Tidepods would be embarked in batches in larger vessels or large semi- submersible ships, then sailed to the deployment location.

• once at site, or where the production facility was close to the tide site, local deployment would be by commercial tug. Depth

The ability to deploy at depths significantly in excess of many current technologies:

• 20% of UK tidal resource exists at depths in depths of between 30m and 40m, and 50% at depths between 40m and 100m.

• The majority of trials, however, have been conducted in shallower waters. Current technologies are secured to the sea floor by piles, facilitated by jack up and crane barges. However, at depths below 40metres, the use of piles to secure devices to the sea floor becomes increasingly impractical and, thus, uneconomic. Tidepod requires no such piles.

• Tidepod would be designed with an initial maximum operating depth of 60 metres, but with an early design intention to be able to operate down to 100m. A stretch target of 200m would enable deployment to any economic location on the continental shelf.

Appendix 1

MAIN INNOVATIONS IN THE TIDEPOD SYSTEM

To re-cap, there are 9 independent innovations in the TidePod system, summarised in this

Appendix 1. Tidepod is a:

A. Submersible barge-shaped structure, adapted to host one or more TECs

B. Submersible multi-hull structure, each hull adapted to host a TEC

C. Submersible structure made up of multiple standardised hull modules, at least one hull module adapted to host a TEC.

D. Submersible structure including one or more sockets or supports with standardized parameters, so that any TEC complying with those parameters can be used in the socket or fixed on or to the support.

E. Submersible structure with one or more hulls, in which the position of the or each TEC can be adjusted, e.g. to minimise wake turbulence and/ or optimise the design of an array of multiple submersible structures

F. Submersible structure with one or more hulls, each hull is at least partly hollow for towing, but is then sufficiently ballasted (e.g. using site specific amounts of concrete) when to be sunk.

G. Submersible structure hosting multiple TECs, but with a single power converter/ shaper serving each TEC

H. Submersible structure with navigation sensors that enable the structure to dynamically and stably control its descent to the sea bed.

I. Submersible structure with onboard rechargeable batteries that enable the structure to operate autonomously and without the need for remote controlled operation.

Each independent innovation can be combined with one or more of the other innovations. Appendix II

Fabrication

1. Capable of mass production in medium-to-large sized UK dockyards.

2. Able to host a range of TECs designs and technologies, possibly through the use of modular sockets in the hull.

Transportation

3. Of a buoyancy and seaworthy design such that it is capable of being routinely towed behind a commercial tug, at speeds of up to 10 knots, and on occasion within the highest envisaged sea states, without onboard enhancements to the tug.

4. Capable of being batch-transported worldwide in semi-submersible heavy-lift vessels.

Deployment.

5. Able to submerge to a depth of 100m within a single tidal windo of 1 hour.

6. Able to be connected, cost effectively, to undersea cable grid, possibly before submerging.

7. Able to position its TECs at the optimum height in the water column.

8. Capable of deployment and operation, minimizing the use of cranes, barges, divers or ROVs.

Operation

9. Able to act as a stable structure for multiple TECs, in depths of up to 100 meters across the full range of sea bed types, bathymetry, and tidal speeds, in particular:

able to resist horizontal sliding forces, through a combination of weight, friction, and hydro-dynamic design;

able to resist vertical turning moments, resulting from the highest local tides, through a combination of weight and design ;

able to have its TEC installations and positioning tuned so as to optimize overall array design for maximum power extraction and revenue generation.

10. Able to resist likely fatigue forces, resulting from tide, wave motion and vibration, and possible damage from underwater debris carried in high tidal streams, including on cable connections.

11. Able to resist undersea corrosion and fatigue, in order to achieve a design life of 50 years underwater operation. 12. Able to take bleed power from the TEC], so as to maintain battery capacity for onboard systems and controls.

13. Able to be communicate with, and be controlled from, a surface vessel.

14. Capable of environmentally monitoring the sea floor in its vicinity.

Repair & Maintenance

15. Of a size that allows scheduled maintenance and upkeep, in local dockyards in the vicinity of likely tide farms.

Capital and Operational Costs

16. To be able to do all of the above, with at an overall build, deploy, operate, and maintain cost of less that ΠΜ per M W .

Claims

1. A submersible structure adapted to host one or more tidal energy converters, in which the structure includes one or more sea-towable, barge-shaped hulls.

2. The submersible structure of Claim 1, in which the or each barge-shaped hull is hydro- dynamically streamlined, specifically to minimise their underwater drag and/or maximise the energy that may be harvested from individual sites.

3. The submersible structure of Claim 1 or 2 in which the or each hull is adapted to host a tidal energy converter on an upright support structure.

4. The submersible structure of Claim 3 in which the upright support is a pole that is elliptical in cross-section, to minimise underwater drag and turning forces, and can be provided in different heights to optimise the position of the TEC in the water column.

5. The submersible structure of any preceding Claim, further including spars to connect individual hulls (where a multi-hull design is used), and in which the spares are (i) hydro- dynamically designed so as to improve the stability of the structure on the sea bed and (ii) can be provided in different lengths to vary the size of the structure.

6. The submersible structure of any preceding Claim, in which each individual hull has, on its underside, sharp structures, designed to penetrate the sea bed surface and adjustable in length to allow the structure to be customised to individual sea beds.

7. The submersible structure as claimed in any preceding claim, in which the structure includes multiple barge-shaped hulls, each hull being adapted to host a tidal energy converter.

8. The submersible structure as claimed in Claim 7, in which the structure forms a catamaran.

9. The submersible structure as claimed in Claim 7, in which the structure forms a trimaran.

10. The submersible structure as claimed in any preceding Claim, in which multiple structures are electrically connected in a large array.

11. The submersible structure as claimed in any preceding Claim, in which each sea-towable barge-shaped hull is made up of multiple standardised hull modules, and at least one hull module is adapted to host a tidal energy converter.

12. The submersible structure as claimed in Claim 11, in which the standardised hull modules are defined by module parameters.

13. The submersible structure as claimed in Claim 12 in which the module parameters meet one or more of the following criteria:

a. module parameters include a set of width, length and/ or depth dimensions.

b. module parameters include multiple sets of different standardised parameters

c. module parameters are published parameters

d. module parameters apply to a number of different submersible energy generating structures e. module parameters include weight limits

f. module parameters include shape parameters, and the shape parameters define the shape of a portion of a hull

14. The submersible structure as claimed in Claim 11 - 13 in which multiple modules are welded together using conventional ship building techniques.

15. The submersible structure as claimed in Claim 11 - 14 in which each hull includes 2, 3, 4 or 5 or more modules.

16. The submersible structure as claimed in any preceding Claim in which at least one hull includes a standardised power space for electrical power conversion and conditioning equipment.

17. The submersible structure as claimed in Claim 16 in which the power spaces are of standardised dimensions and with standardised connections, so as to host the electrical systems needed to meet different power conditioning and conversion requirements of different device manufacturers .

18. The submersible structure of any preceding Claim, in which each hull includes one or more sockets or supports with standardized parameters, so that any tidal energy converter complying with those parameters can be used in or fixed on or to the socket or the support.

19. The submersible structure as claimed in Claim 18 in which at least one hull includes a socket with standardised parameters so that any tidal energy converter complying with those socket parameters can be used in the socket.

20. The submersible structure as claimed in Claim 19 in which the socket parameters meet one or more of the following criteria:

a. socket parameters include a set of width, length and/ or depth dimensions.

b. socket parameters include multiple sets of different standardised parameters c. socket parameters are published parameters

d. socket parameters apply to a number of different submersible energy generating structures

e. socket parameters include weight limits

f. socket parameters include turning moment limits

g. the or each TEC includes propellers or vanes plus a support structure that the propellers or vanes are mounted on or against

h. socket is a cavity or bay

i. socket is a flange

j. socket includes securing systems designed to secure the TEC in position in the socket, the securing systems enable the TEC to be removed from the structure k. socket includes an electrical power connector

1. socket enables TECs from different manufactures to be fitted to the structure so long as they comply with the standardised parameters m. socket enables the TECs to be removed from the socket for maintenance n. socket enables the TECs to be swapped out with replacement TECs

o. replacement TECs are different or more up to date than the TECs being replaced p. socket enables larger TECs to be used for deep water environments

q. structure includes multiple sockets, one for each TEC

r. TEC includes a generator that feeds electrical power to the electrical power connector in the socket

21. A submersible structure as claimed in any preceding Claim, in which the position of the or each tidal energy converter can be adjusted (for example during fabrication of the hull and support, or after the structure has been fabricated).

22. The submersible structure as claimed in Claim 21 in which adjustment is to minimise wake turbulence.

23. The submersible structure as claimed in Claim 21 or 22 in which adjustment is to optimise tidal array design.

24. The submersible structure as claimed in Claim 21— 23 in which the position of a TEC tidal energy converter on a hull is adjusted laterally (e.g. by altering the lengths of the struts separating each hull).

25. The submersible structure as claimed in Claim 21— 24 in which the position of a TEC tidal energy converter on a hull is adjusted longitudinally along the length of a hull.

26. The submersible structure as claimed in Claim 21— 25 in which the position of a TEC tidal energy converter on a hull is adjusted vertically using TEC supports of different heights.

27. The submersible structure as claimed in any preceding Claim, in which the structure is adapted to host a range of TEC blade diameters, from 10m to 20m, on the same structure.

28. The submersible structure of any preceding Claim, in which each hull is at least partly hollow for towing, but is then sufficiently ballasted (e.g. using site specific amounts of concrete) when to be sunk.

29. The submersible structure as claimed in Claim 28 in which, because of its adjustable ballasting, the structure can accept the full range of different thrust and drag forces that result from different tidal speeds and TEC blade diameters.

30. The submersible structure as claimed in any preceding Claim, being adapted to host multiple tidal energy converters, but with a single power converter/ shaper serving each tidal energy converter.

31. The submersible structure as claimed in Claim 30, in which the power converter converts the electrical power from the electrical generators to a form suitable for transmission along a power line to the shore.

32. The submersible structure as claimed in Claim 30— 31, in which the structure includes several power convertors, each serving multiple electrical generators.

33. The submersible structure as claimed in Claim 30 - 32 in which the power converter charges on-board electrical batteries that provide power to on-board systems.

34. The submersible structure as claimed in Claim 30— 33, in which the the structure includes at least one standardised section complying with predefined parameters, the section capable of retaining one or more TECs and the standardised section being designed so that multiple such sections can be combined together to allow different structures capable of retaining different numbers of TECs to be constructed, and the section includes at least one power converter serving multiple electrical generators.

35. The submersible structure of any preceding Claim including navigation sensors that enable the structure to dynamically and stably control its descent to the sea bed.

36. The submersible structure as claimed in Claim 35 in which the navigation sensors enable the structure to autonomously navigate itself down to the seabed.

37. The submersible structure as claimed in Claim 35 - 36 in which the navigation sensors are capable of providing information relating to the orientation of the structure during descent and/ or ascent.

38. The submersible structure as claimed in Claim 35 - 37 in which the navigation sensors are capable of providing information relating to the rate of descent and/ or ascent of the structure;

39. The submersible structure as claimed in Claim 35— 38 in which the navigation sensors are capable of providing information relating to the trajectory or descent and/or ascent of the structure.

40. The submersible structure as claimed in Claim 35— 39 in which the navigation sensors are capable of providing information relating to accurate surface positioning.

41. The submersible structure as claimed in Claim 35— 40 in which the navigation sensors provide control inputs to structure thrusters that enable or contribute to the control of one or more of:

o the orientation of the structure during descent and/ or ascent;

o the rate of descent and/ or ascent;

o the trajectory or descent and/ or ascent

o the accurate positioning of the device on the sea floor for optimal operation of the TECs

o the accurate surface positioning.

42. The submersible structure as claimed in Claim 35— 41 in which the navigation sensors provide data to a tug connected to the structure via a hawser line and a data connection.

43. The submersible structure as claimed in any preceding Claim, further including onboard rechargeable batteries that enable the structure to operate autonomously and without the need for remote controlled operation.

44. The submersible structure as claimed in Claim 43, in which the onboard rechargeable batteries provide power to thrusters to enable, or contribute to, the control of one or more of:

o the orientation of the structure during descent and/ or ascent;

o the rate of descent and/ or ascent;

o the trajectory of descent and/ or ascent.

o the actual position of the structure on the seabed.

45. The submersible structure as claimed in Claim 43 - 44, in which the onboard rechargeable batteries enable the structure to operate autonomously.

46. The submersible structure as claimed in Claim 43 - 45, in which the onboard rechargeable batteries enable the structure to operate autonomously, without the need for connection to an external power source.

47. The submersible structure as claimed in Claim 43 - 46, in which the onboard rechargeable batteries enable the structure to operate autonomously, without the need for connection to a remote control.

48. The submersible structure as claimed in Claim 43 - 47, in which the onboard rechargeable batteries provide power to thrusters that enable or contribute to accurate surface positioning.

49. The submersible structure as claimed in Claim 43 - 48, in which the onboard rechargeable batteries provide power to control a rudder and or a diving plane.

50. The submersible structure as claimed in Claim 43 - 49, in which the structure can be towed by a tug and the tug then provides power to the electrical batteries via an electrical cable.

51. The submersible structure as claimed in Claim 43— 50, in which the structure is connected to the tug by a hawser and the electrical cable whilst being towed.

52. The submersible structure as claimed in Claim 43— 41, in which the Structure is connected to the tug by a hawser and the electrical cable whilst descending.

53. The submersible structure as claimed in Claim 43— 52, in which the TECs provide, in operation under tidal power, electrical power to charge the batteries.

54. The submersible structure as claimed in Claim 43— 53, in which the electrical generator for a TEC is electrically connected to the onboard rechargeable batteries.

55. The submersible structure as claimed in Claim 54, in which the batteries enable the structure to be self-propelled.

56. The submersible structure as claimed in Claim 54, in which the rechargeable batteries provide power to pump water from ballast tanks.

57. The submersible structure as claimed in Claim 54 - 56, in which the rechargeable batteries power a system that controls the release of compressed air into the ballast tanks.

58. The submersible structure as claimed in Claim 54 - 57, in which the rechargeable batteries power on-board diagnostic or reporting systems.

59. The submersible structure as claimed in Claim 54 - 58, in which the rechargeable batteries power on-board control systems for the thrusters.

60. A submersible structure in which the structure includes multiple barge-shaped hulls, each hull adapted to host a tidal energy converter.

61. A submersible structure made up of multiple standardised hull modules, at least one hull module adapted to host a TEC.

62. A submersible structure including one or more sockets or supports with standardized parameters, so that any TEC complying with those parameters can be used in the socket or fixed on or to the support.

63. A submersible structure with one or more hulls, in which the position of the or each TEC can be adjusted, e.g. to minimise wake turbulence and/or optimise the design of an array of multiple submersible structures.

64. A submersible structure with one or more hulls, in which each hull is at least partly hollow for towing, but is then sufficiently ballasted (e.g. using site specific amounts of concrete) when to be sunk.

65. A submersible structure hosting multiple TECs, but with a single power converter/ shaper serving each TEC.

66. A submersible structure with navigation sensors that enable the structure to dynamically and stably control its descent to the sea bed.

67. A submersible structure with onboard rechargeable batteries that enable the structure to operate autonomously and without the need for remote controlled operation.

68. Method of manufacturing a submersible energy -genera ting structure; including the step of:

(a) constructing the structure using one or more standardised hull sections, the or each section complying with predefined parameters, the or each section capable of retaining one or more TECs and the or each standardised section being designed so that multiple such sections can be combined together to allow different structures capable of retaining different numbers of TECs to be constructed.

69. Method of deploying a submersible energy-generating structure; including the steps of: (a) constructing the structure using one or more standardised sections, the or each section complying with predefined parameters, the or each section capable of retaining one or more TECs and the or each standardised section being designed so that multiple such sections can be combined together to allow different structures capable of retaining different numbers of TECs to be constructed;

(b) towing the structure to a destination;

(d) causing the structure to submerge and settle on the seabed.

70. Method of manufacturing a submersible energy -generating structure; including the step of:

(a) manufacturing the structure with a socket with standardised parameters so that any TEC complying with those parameters and from any manufacturer can be used in the socket;

(b) fitting a TEC in the socket.

71. Method of deploying a submersible energy-generating structure; including the step of:

(c) towing the structure to a destination;

(d) causing the structure to submerge and settle on the seabed.

72. Method of deploying a submersible energy generating structure; including the steps of:

(a) manufacturing the structure with navigation sensors capable of providing information to enable the accurate positioning of the structure on the seabed for optimal operation of the TECs;

(b) towing the structure to a destination;

(c) causing the structure to submerge and settle on the seabed, with the navigation sensors enabling the accurate positioning of the structure onto the sea bed for optimal operation of the TECs.