GB2550692A

GB2550692A - Subsea energy generation assembly utilising wind energy

Info

Publication number: GB2550692A
Application number: GB1708095.3A
Authority: GB
Inventors: King Lee
Original assignee: Hydro Energy And Tech Ltd
Current assignee: Hydro Energy And Tech Ltd
Priority date: 2016-05-23
Filing date: 2017-05-19
Publication date: 2017-11-29
Anticipated expiration: 2037-05-19
Also published as: GB201708095D0; GB201609047D0; GB2550692B

Abstract

A subsea energy generation assembly 1 comprises a subsea pressure vessel 20 with a storage chamber 25 for receiving and releasing fluid, and a hydroelectric turbine 28, disposed in an inlet 22, that generates electrical power when water 27b flows through the turbine 28. The subsea pressure vessel 20 is connected to a sail 50 that harnesses wind energy and converts it to mechanical energy by raising the pressure vessel 20 from a first lower operating depth, where the inlet 22 is opened and energy is generated as the storage chamber 25 fills at least partially with water, to a second higher operating depth, where the storage chamber 25 is at least partially emptied of water. The pressure vessel 20 can then, with the inlet 22 closed, be lowered to the first operating depth again to restart the energy generation cycle.

Description

SUBSEA ENERGY GENERATION ASSEMBLY UTILISING WIND ENERGY

Renewable energy generation presently fails to achieve levels of power density, energy density, economy, and scalability comparable to that produced by fossil fuels. Current designs of wind turbines both on and offshore have reached a plateau in terms of structural and efficiency limitations, and the energy generation from said turbines suffers from intermittency and variability in power output.

Offshore wind turbines are limited to sites with a maximum water depth of 60m, preventing exploitation of deep water sites. For any wind turbine, tower height is an important factor in the design of the turbine and can have a significant effect on the power output and capacity factor of the apparatus, as wind strength and persistence increases with altitude. However, due to structural and cost limitations, the largest offshore turbines deployed to date are unable to exceed heights of 150m. For deep water deployment especially, the additional investment required to provide foundations or mooring platforms that are sufficient to anchor and support the turbines can be prohibitive.

Turbine blade portions contribute predominantly to power production, while the remaining structure is used to mechanically support the blades. The larger the diameter of the swept area of the turbine, the greater the power output - however, this is offset by the increased cost of the correspondingly larger rotor and supporting structures. Additionally, any increase in blade size requires increased spacing between turbines.

Wind energy is an intermittent, unpredictable and non-dispatchable energy source, with no direct control of the power output of the turbines, and hence no guarantee of levels of energy generation. Wind forecasts provide some general predictions of output, and long-term analysis of output data provides further information for the grid operators as to the overall energy contribution a turbine, or a wind farm, can make. In the short term, however, electrical output is dependent on factors such as, for example, wind speed and air density (determined to an extent by the geographical location of the turbine), and turbine characteristics. Wind turbines operate optimally above wind speeds of 3.5 m/s, as lower speeds result in negligible energy generation, and below 25 m/s to avoid damage to the turbine.

Due to the intermittency and non-dispatchability of wind energy, increased demand for energy do not necessarily correspond to rises in renewable energy generation. Although wind is fairly consistent in the long run, short term capacity fluctuations prohibit wind from replacing dependable fossil fuel-based energy systems. This limitation could be overcome if the energy harvested from wind could be temporarily stored in a cost-effective manner and released when needed. It is therefore useful to be able to store energy produced above grid requirements, and use the stored energy to offset periods of low production, or to satisfy periods of increased demand. Any energy storage system must take into account power rating, storage duration, frequency of charge and discharge, efficiency and response time, and site constraints that determine power and energy density requirements.

SUMMARY OF THE INVENTION A subsea energy generation assembly adapted to generate electrical power, the assembly comprising a subsea pressure vessel, the subsea pressure vessel having a storage chamber adapted to receive and release fluid; wherein the subsea pressure vessel comprises a hydroelectric turbine adapted to generate electrical power as water flows through the hydroelectric turbine; wherein the subsea pressure vessel is connected to a sail, wherein the sail is adapted to convert wind energy into mechanical energy by transforming the subsea pressure vessel between at least two configurations:- a first configuration wherein the subsea pressure vessel is at least prepared to be at least partially filled with said water; a second configuration wherein the subsea pressure vessel is at least partially filled with said water; and wherein the turbine generates electrical power when said water flows through the hydroelectric turbine as it enters the storage chamber, thereby generating electrical power.

For the purposes of this application, the skilled person will understand that the term “sail” also includes kites.

The storage chamber of the subsea pressure vessel is adapted to receive fluid in the form of water or gas, for example air.

Optionally the subsea pressure vessel is connected to one end of a pulley system, and the pulley system is optionally connected at another end to a buoyant device, for example a buoy. Optionally the sail is adapted to raise the subsea pressure vessel by actuating the pulley system. Optionally the buoyant device and the sail together act on the pulley system to actuate it, such that lifting of the sail whilst the pulley system is in tension will raise the subsea pressure vessel. Optionally the sail is connected to the pulley system by a control line that passes over or through the pulley system. The subsea pressure vessel is lowered under gravity, typically when an operator arranges for the sail to lower and/or arranges for the sail to no longer remain in tension with respect to the pulley system and more preferably, when the operator additionally or alternatively arranges for the subsea pressure vessel to be lowered with respect to the buoyant device. This can be achieved by, for example, unlocking a brake acting on the pulley system and/or the control line connecting the buoyant device to the subsea pressure vessel and permitting the subsea pressure vessel to sink with respect to the buoyant device, whereby the distance between the buoyant device and the subsea pressure vessel increases until a desired lower operating depth of the subsea pressure vessel has been reached. As the pressure vessel is negatively buoyant at its operating depth, optionally said brake is locked to thereby lock the pulley system and/or the control line and thereby prevent any further sinking of the subsea pressure vessel.

Optionally the pulley system and/or control line holds the pressure vessel at its lower operating depth by virtue of a predetermined length of control line that passes through the pulley system, and is connected at one end to the buoyant device at surface. Optionally the negative buoyancy and the weight of the pressure vessel at its lower operating depth leads to a slight increase in the draft line of the buoyant device as it is weighed down.

Optionally a gearing system may be used in place of the pulley system.

Optionally the control line is a cable, or optionally a chain or rope, optionally formed from nylon rope, nylon webbing, wire cable, carbon nanotube fibre or another suitable material. Optionally the sail may be connected to more than one control line that passes over and around the pulley system. Optionally one pulley is disposed on or within a floating buoy. Optionally one pulley is disposed on or within the subsea pressure vessel. Optionally the control line passes over and/or around one or both of the pulleys.

Optionally the sail is connected to or through the buoy. Optionally as the water surface changes in height through swells and troughs, the buoy changes vertical position relative to the subsea pressure vessel.

Optionally, as the sail rises, it exerts a pulling force on the pulley system by means of exerting tension upon the control line. The pulley system, and more particularly the control line, then optionally lifts the subsea pressure vessel in a substantially vertical direction to, or near to or toward, the surface of the water. The force or tension on the pulley system may be relatively smooth and constant. Optionally, the pulley system is a block and tackle system, or optionally any other kind of mechanical advantage or gearing system.

Optionally the subsea pressure vessel is connected to the sail via a roller system, for example a gearing system. Optionally the control line connecting the sail to the subsea pressure vessel passes over or through the rollers or gears.

Optionally the subsea pressure vessel is manufactured from metal, optionally steel, carbon steel, or steel composites, but any material with good tensile properties that is chemically and physically stable in the operation environment and conditions could be used. Optionally the mass of the subsea pressure vessel is calculated so that when fully submerged, the pressure vessel is negatively buoyant, optionally by around 500-600kg. Optionally the storage chamber is filled with air at atmospheric pressure. More preferably, the storage chamber is filled with air at a pressure of approximately 200 kPa. Filling the storage chamber with air at 200 kPa offers the advantage that the pressure vessel can be kept below the surface of the water during the lifting process (i.e. the pressure vessel doesn’t need to be completely removed form the water during the lifting process) at a highest depth of approximately 10 metres, as the water pressure at that depth is also 200kPa, and therefore there is no pressure differential at that highest in-use depth. The pressure vessel can then be prepared for lowering through the water column, by sealing the storage chamber and lowering the pressure vessel to a depth of, for example 100m below the waterline, where the ambient hydrostatic pressure is around 1100kPa.

Optionally the subsea pressure vessel is submerged at a selected deployment site and depth. Optionally once the subsea pressure vessel is submerged to its operational depth, an inlet aperture or passage is opened in the subsea pressure vessel by for example opening a valve therein and water is flowed into the storage chamber. The water flows through the hydroelectric turbine preferably through the now open valve. The passage of water through the hydroelectric turbine generates electrical power, which can optionally then be transferred to, for example, an onshore substation for further transfer to the national grid. Optionally, the electrical power may be transferred to an offshore structure, optionally to power the structure, or optionally for storage.

Optionally the diameter of the aperture through which seawater passes determines the maximum power output, and optionally the duration of power generation. For example, a larger diameter results in a greater maximum power output but a shorter duration of generation.

Optionally the subsea pressure vessel is flooded with water at a depth of 100m, corresponding to a water pressure of approximately 1100kPa. At this depth, the pressure differential between the water outside the pressure vessel and the air inside the pressure vessel, which is at a pressure of 200 kPa, is approximately 900kPa. The pressure differential creates a transient kinetic water flow into the storage chamber, resulting in the air contained therein being compressed into a small volume or pocket. The skilled person will realise that substantially filling the storage chamber with water (except for the pocket of air) increases the negative buoyancy of the pressure vessel, for example, depending on the size of the pressure vessel, to approximately 450-500 metric tonnes. The skilled person will understand that if they choose a pressure vessel with a larger volume, the negative buoyancy of that vessel will be correspondingly larger than a vessel with a smaller volume. The skilled person can of course select greater or lesser volume and/or sizes of pressure vessels to be used, which result in respectively greater or lesser negative buoyancies. The skilled person will understand that if a larger pressure vessel is used the energy storage capacity is greater.

Optionally, the sail is adapted to be flown at high altitudes, for example a high-altitude kite. The sail comprises a cover consisting of a sheet of material, optionally affixed to structural components such as spurs, struts, or similar parts. Optionally the cover is made of a polymer material, such as polypropylene, nylon, cotton, carbon laminated or another suitable material.

Optionally the sail is free flying. Optionally the sail is connected to the energy generation assembly by control lines, wherein the length of the control lines is optionally selected so that the kite flies at an altitude of up to 1000m, but more usually at an altitude of between 100-300m. This altitude has increased wind speeds that are approximately 50% more than the wind speed at an altitude of 10m above sea level. Optionally the sail is adapted to take advantage of the increased wind speed at this altitude by flying downwind, or optionally by following a suitable flight pattern that increases the apparent wind speed experienced by the sail, a figure of eight. Flying downwind and/or following these flight patterns increases the aerodynamic forces, lift, and drag, as these forces are dependent on the square of the relative wind velocity experienced by the sail.

Optionally a tethered sail can be used, optionally at lower altitudes of around 100-600 metres. At these altitudes, the winds are stronger and more stable in comparison to wind at sea level. Optionally the sail is tethered such that it follows a figure-of-eight. Optionally the sail comprises at least one bridle line, and the length, or lengths, of bridle line of the sail are selected to encourage a specific flight path.

As the pressure vessel is lifted, the outlet aperture is opened and water flows out of the storage chamber into the sea. As the water flows out, the weight of the pressure vessel of course decreases. The compressed air pocket expands back to substantially 200 kPa as the volume of water within the storage chamber decreases.

Alternatively, or in addition, a small amount of electrical power may be generated by the turbine as water flows out of the storage chamber. For example, the outlet aperture may remain closed by for example keeping said valve therein closed during the lifting process and may be opened once the subsea pressure vessel has been raised to a suitable depth, e.g. 10m below the sea surface. The aperture can then be opened by for example opening said valve therein and, due to the pressure differential between the air and the water within the storage chamber (which are both at approximately 1100 kPa) and the surrounding water (at approximately 200 kPa), the water flows out of the storage chamber through the hydroelectrical turbine, generating electrical power. Thus, electrical energy may be produced by the system by water entering and/or exiting the storage chamber of the subsea pressure vessel. Preferably, the outlet aperture is located toward the vertically lowest in use portion of the storage chamber and more preferably is located at the vertically lowest in use portion of the storage chamber which has the advantage that no air will escape the storage chamber when the outlet aperture is opened. This is due to the difference in the densities of air and water.

As the air within the storage chamber reaches 200 kPa, the outlet aperture is closed, and the subsea pressure vessel is optionally allowed to sink back to a depth of around 100m.

This depth may be altered according to the requirements of the operator, and the subsea pressure vessel may be operated at any depth, which will translate into greater power and energy density. The capacity of the system to store energy with a given volume increases linearly with the depth of the water. That is, for every 100m increase in depth, the system described herein doubles its energy storage capacity. The discharge time also increases proportionally. For example, for a pressure vessel with a 500m3 storage chamber, and a 1MW power output, at a water depth of 100m, the system discharges 100kWh in 5 minutes. For the same system at 200m, the system discharges 220 kWh in 10 minutes, and at 300m depth, the system discharges 330 kWh in 15 minutes.

The sail is flown out of the wind to permit retraction of the control line, reeling the sail in to a threshold altitude, allowing the power generation process to recommence the conversion of wind energy harnessed by the sail into mechanical energy in the subsequent lifting of the subsea pressure vessel. Optionally, the sail can use wind power to return to its original altitude. With proper orientation and control of the sail, movement in any direction can be achieved relative to the direction of the wind by using the principles of aerodynamic lift and drag, and the reeling in of the sail thus requires very little energy. By using known kite and/or sail control mechanisms and flight manoeuvres, the sail can be maintained at a certain altitude indefinitely, until it is required for lifting of the pressure vessel.

The cycle of energy transformation that the system undergoes can be described as follows. Upon initial submergence of the system to the first (highest) operating depth, the subsea pressure vessel has potential energy by virtue of being suspended by the buoy device at height in the water against the gravitational force. Once the pressure vessel is released gravity causes it to sink to the operating depth (since the pressure vessel is negatively buoyant). Submergence of the subsea pressure vessel to the operating depth creates a pressure differential between the water outside the vessel and the air inside the storage chamber. When the valve provided in the outlet aperture is opened the pressure differential between the air contained therein and the higher pressure water outside of the pressure vessel is converted to kinetic energy of the water flowing through the valve and thus the turbine, which is then transferred to the hydroelectric turbine. More specifically, the potential energy stored in water under hydrostatic pressure due to height is converted into kinetic energy due to the flow of water and pressure difference. The turbine converts the mechanical energy of its rotation to electrical energy. Once the storage chamber has been sufficiently filled with water, and the pressure inside is equalised with the pressure outside of the pressure vessel (such that the air stored within the chamber is compressed to e.g. approximately 1100 kPa), wind energy is harnessed by the kite and converted to kinetic or mechanical energy to lift the subsea pressure vessel against the gravitational force.

Any feature described in connection with another aspect of the invention is also applicable to the present aspect of the invention where appropriate.

Optionally, a semi-rigid sail may be used to harness wind energy and convert it to potential (mechanical) energy to lift the pressure vessel.

In a second example of the invention, the storage chamber is filled as before with water, compressing the air therein into a small volume or pocket. The subsea pressure vessel comprises an inlet aperture with a hydroelectric turbine as before, however in this example the aperture is located at the end of the pressure vessel that is nearest the buoy. The pressure vessel further comprises a conduit that extends from the storage chamber to the air above sea level. The sail is used to power a water pump, or optionally a power take-off system, or the like, to expunge water from the storage chamber within the pressure vessel. In this example, the storage chamber comprises a piston that is lifted as the buoyant device and/or sail is raised, forcing the water out of the aperture. As the water is removed, the air pocket expands, eventually reaching substantially atmospheric pressure.

Once the water has been removed, the inlet/outlet aperture is closed, and the conduit is opened. Air flows through the conduit into the storage chamber as the piston returns to its original configuration. The sail is reeled in to a certain altitude until required to lift the piston again.

Optionally the subsea pressure vessel can be extended and operated at any depth. As pressure is arbitrarily considered to be synonymous with energy density per volume, the deeper the pressure vessel is submerged the greater the pressure, and therefore the higher the capacity of the pressure vessel to store energy for the same volume. The table below outlines some examples of energy storage capacity with increasing subsea depth, using an exemplary pressure vessel volume of 500m3. Energy storage is dependent on the volume of the pressure vessel and submerged depth. The amount of energy generated remains constant with a fixed volume. The inlet diameter and pressure difference determines both the power output and discharge time. A larger pipe diameter increases the flow rate and power output permitting the process to finish more quickly.

Table 1

According to the present invention there is also provided a method for generating electrical power, the method comprising the steps of deploying a subsea energy generation assembly comprising a subsea pressure vessel in a body of water, the subsea pressure vessel comprising a storage chamber adapted to receive and release water and a hydroelectric turbine adapted to generate electrical power as water flows through the hydroelectric turbine; connecting the subsea pressure vessel to a sail, wherein the sail is adapted to convert wind energy to mechanical energy by transforming the subsea pressure vessel between at least two configurations, including a first configuration wherein the subsea pressure vessel is at least prepared to be at least partially filled with said water, and a second configuration wherein the subsea pressure vessel is at least partially filled with said water; submerging the subsea pressure vessel to a suitable depth providing a desired ambient pressure level; transforming the configuration of the subsea pressure vessel from the first configuration to the second configuration thereby generating electrical power via the hydroelectric turbine by flowing water through the hydroelectric turbine as it enters the storage chamber, thereby generating said electrical power; and arranging for the sail to be raised in the wind such that the subsea pressure vessel is raised in the body of water, thereby converting wind energy into mechanical energy and transforming the subsea pressure vessel from the second configuration to the first configuration.

Optionally, the method includes connecting the subsea pressure vessel to one end of a pulley system optionally mounted on or in the subsea pressure vessel. Optionally the other end of the pulley system is mounted on or in a floating buoy. Optionally a control line is passed over, through, or around the pulley system and connects to the sail. Optionally the subsea pressure vessel is raised and lowered as the sail rises and falls, as the movement of the sail optionally actuates the pulley system.

Optionally the sail actuates a roller or gearing system, and the control line passes over, through, or around the rollers or gears.

The various aspects of the present invention can be practiced alone or in combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects of the invention can optionally be provided in combination with one or more of the optional features of the other aspects of the invention. Also, optional features described in relation to one example can optionally be combined alone or together with other features in different examples of the invention. Any subject matter described in the specification can be combined with any other subject matter in the specification to form a novel combination.

Various examples and aspects of the invention will now be described in detail with reference to the accompanying figures. Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrate a number of exemplary aspects and implementations. The invention is also capable of other and different aspects and implementations, and its several details can be modified in various respects, all without departing from the scope of the present invention as defined by the claims. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as "including," "comprising," "having," "containing," or "involving," and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes.

Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention.

In this disclosure, whenever a composition, an element or a group of elements is preceded with the transitional phrase "comprising", it is understood that we also contemplate the same composition, element or group of elements with transitional phrases "consisting essentially of”, "consisting", "selected from the group of consisting of, “including”, or "is" preceding the recitation of the composition, element or group of elements and vice versa.

All numerical values in this disclosure are understood as being modified by "about". All singular forms of elements, or any other components described herein are understood to include plural forms thereof and vice versa. References to directional and positional descriptions such as upper and lower and directions such as “up”, “down” etc. in relation to the assembly are to be interpreted by a skilled reader in the context of the examples described and are not to be interpreted as limiting the invention to the literal interpretation of the term, but instead should be as understood by the skilled addressee. In particular, positional references to the assembly such as “up” will be interpreted to refer to a direction toward the surface of the water, and “down” will be interpreted to refer to a direction away from the surface of the water.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

Figure 1 shows a schematic view of a first example of the invention, with the subsea pressure vessel submerged at 100m and filled with air, and the pulley system illustrated in a fully extended configuration;

Figure 2 shows a schematic view of the assembly of Figure 1, with the aperture in the pressure vessel open and water inflowing to the storage chamber and with the fully-extended pulley system illustrated;

Figure 3 shows a schematic view of the assembly of Figures 1 and 2, with the pressure vessel being lifted and water flowing out of the storage chamber and with the pulley system illustrated in a retracted configuration;

Figure 4 shows a schematic view of the assembly of Figures 1-3, with the subsea pressure vessel returned to its original, air-filled configuration and with the fully-extended pulley system illustrated;

Figure 5 shows another schematic illustration of the first example of the invention, illustrating the sail in the form of a kite, buoy, pulley system, pressure vessel and turbine, and the electrical conduit connecting the assembly to an onshore substation; Figure 6 shows the assembly of Figure 5 with water flooding the storage chamber of the pressure vessel, flowing through the hydroelectric turbine and generating electricity;

Figure 7 shows the assembly of Figures 5 and 6, the pressure vessel having been lifted under the force of the kite, releasing water from the storage chamber;

Figure 8 shows the assembly of Figures 5-7, with the kite being reeled in and the system returned to its original configuration for a new generation cycle;

Figure 9 shows a schematic view of a second aspect of the invention, where the pressure vessel comprises a piston within the storage chamber;

Figure 10 shows the assembly of Figure 9, with water flowing into the storage chamber creating an air pocket under the piston;

Figure 11 shows the assembly of Figures 9 and 10, with the piston being raised under the force of the kite and the pocket of air expanding accordingly, pushing water out of the pressure vessel;

Figure 12 shows the assembly of Figures 9-11 with the storage chamber of the pressure vessel filled with air and the kite being reeled in.

DETAILED DESCRIPTION OF EXAMPLES OF THE INVENTION

Referring now to the figures, a first example of the invention shown in Figures 1-8 comprises a subsea energy generation assembly 1 that generates electrical power and transfers the electrical power, for example, to an onshore substation or offshore structure. The subsea energy generation assembly 1 includes a subsea pressure vessel 20 with a storage chamber 25 that receives and releases water 27b in a manner that generates electricity on demand as will be subsequently described in detail. In general though, the subsea pressure vessel 20 has a hydroelectric turbine 28 that turns and generates electrical power as water 27b flows through the hydroelectric turbine 28.

The subsea pressure vessel 20 is connected to one (in use lower) end of a pulley system 30, which is in turn connected at its other (in use upper) end to a kite 50 by means of a control line 53. In general terms, the kite 50 raises the subsea pressure vessel 20 by actuating/via the pulley system 30 and the control line 53 as the kite 50 rises and falls in response to air speed and air flow. As the subsea pressure vessel 20 changes position, the storage chamber 25 fills with and empties of water 27b; in particular, the water 27b flows through the hydroelectric turbine 28 as the water 27b enters the storage chamber 25, and thereby generates electrical power.

The subsea energy generation assembly 1 also includes a buoy 60 that can be moored or tethered, typically to the seabed 12, by a weight 10 and/or anchor 10 and tether line 11 to stabilise and/or moor the assembly 1. The control line 53 passes through the buoy 60 and connects to bridle lines 55 of the kite 50, where the kite 50 typically comprises at least one bridle line 55 at each of it’s ends and where an in use uppermost end of the respective bridle line 55 is secured to a respective end of the kite 50 and the in use lower most end of each bridle line 55 is secured to the in use upper most end of the control line 53.

The subsea pressure vessel 20 can be manufactured from metal, optionally steel. The mass of the subsea pressure vessel 20 is calculated so that when fully submerged, with the storage chamber 25 filled only with air 26 at 200 kPa, the pressure vessel 20 is negatively buoyant by, for example, 500-600kg or less.

As shown in Figure 1, a deployment site is selected and the subsea pressure vessel 20 is submerged and the buoy 60 tethered to the chosen location, typically on the seabed 12, via the tether line 11. The subsea pressure vessel 20 is initially submerged with the storage chamber 25 filled with air 26 at 200 kPa, and a control line 20 braking mechanism (not shown) provided on or in association with the buoy 60 initially brakes or locks the control line 53 with respect to the buoy when the pressure vessel 20 is in the configuration shown in Fig. 1 such that the buoy 60 initially supports the weight of the negatively buoyant pressure vessel 20 at initial (higher) operating depth.

When the operator wishes to start the energy transfer process, the operator releases the said braking mechanism and also arranges for the kite 50 to no longer remain or to not be in tension with respect to the control line 53 such that the subsea pressure vessel 20 will naturally sink with respect to the buoy 60 under the influence of gravity whereby the distance between the buoy 60 and the subsea pressure vessel 20 increases until a desired (lower) operating depth of the subsea pressure vessel 20 has been reached. Optionally the braking mechanism is then actuated again to thereby lock the control line 53, preventing any further sinking of the subsea pressure vessel 20 beyond the lower operating depth.

Alternatively, in place of a braking mechanism, the control line 53 can be paid out until there is no additional line available and the control line 53 thus becomes taut, and the subsea pressure vessel 20 is prevented from sinking below its lower operating depth.

The storage chamber 25 has an inlet 22 located toward or at it’s lowermost end and which remains closed as the subsea pressure vessel 20 is lowered to its desired depth.

As shown in Figure 2, after the subsea pressure vessel 20 is submerged, the inlet 22 is opened and water 27b flows into the storage chamber 25, passing through the hydroelectric turbine 28. Importantly, the hydroelectric turbine 28 is located within the inlet 22 (or at least in sealed fluid communication with the inlet 22) in such a manner that when the inlet is opened whilst the vessel 20 is submerged, water 27a can flow from the outer marine environment (i.e. that water 27a outside of the vessel 20) into the storage chamber 25 but can only do so by flowing through the inlet and in so doing flowing through the hydroelectric turbine 28. In other words, the vessel 20 has maximum energy generation capacity by ensuring that all such water 27b flowing into the chamber 25 drives the turbine 28, with no means of such flowing water 27b bypassing the turbine 28. The passage of water 27b through the hydroelectric turbine 28 drives the turbine to rotate and said rotation generates electrical power, which can then be transferred to, for example, an onshore substation for further transfer to the national grid. Alternatively, the electrical power may be transferred to an offshore structure, optionally to power the structure, or optionally for storage.

The diameter of the inlet 22 determines the maximum power output and the duration of power generation. For example, a larger diameter of inlet 22 results in a greater maximum power output but a shorter duration of generation.

In the example shown in Fig. 2, the inlet 22 is opened when the subsea pressure vessel 20 is at a water 27a depth of 100m such that the subsea pressure vessel 20 is flooded with water 27b at a depth of 100m, corresponding to a water pressure of approximately 1100kPa. At the moment the inlet 22 is opened, this produces a pressure differential between the water 27a outside the pressure vessel 20 and the air 26 inside the storage chamber 25 of the pressure vessel 20 of approximately 1100kPa. The pressure differential creates a transient kinetic water flow into the storage chamber 25, resulting in the air 26 contained within the storage chamber 25 being compressed into a small volume until the pressure of the air 26 contained within the storage chamber 25 reaches 1100kPa (i.e. the pressure of the water 27a at that depth of 100m), at which point the pressure of said air 26 and said water 27a equalises and thus the transient kinetic water flow stops. Filling the storage chamber 25 with water 27b (except for the relatively small volume occupied by the compressed air 26) increases the negative buoyancy of the pressure vessel to approximately 450-500 metric tonnes.

The subsea pressure vessel 20 is connected to the kite 50, which in this example is a high-altitude kite. The kite 50 comprises a covering sail, which is optionally made of a polymer material, such as polypropylene or nylon.

The kite 50 is controlled and maintained at altitude through a kite control mechanism which preferably comprises at least one control line 53. The kite 50 shown in the present example is connected to the energy generation assembly 1 by a single control line 53, and in the present example is not further connected to the energy generation assembly 1 by additional tether lines, and so in this example can be considered to be free flying. However, in other embodiments (not shown), the kite control mechanism may comprise additional tether lines (not shown)_to provide additional control over the kite for example to permit the user to steer the kite in one or more desired directions and/or to provide additional control and or maintenance of the kite 50 at altitude including increasing or decreasing the altitude of the kite 50.

The kite 50 alternatively may have more than one control line 53. Optionally the control lines may be carbon fibre, or alternatively they may be cotton or other materials. The length of the control line(s) can be selected so that the kite flies at an altitude of up to 1000m, but usually between 100-300m. At an altitude of 300m, the wind speeds are approximately 50% more than at an altitude of 10m above sea level.

The kite 50 takes advantage of increased wind speed at high altitude by flying downwind, or by following a suitable flight pattern that increases the apparent wind speed experienced by the kite 50, for example a figure of eight. Flying downwind and/or following these flight patterns increases the aerodynamic forces, lift, and drag, as these forces are dependent on the square of the relative wind velocity experienced by the kite 50.

Optionally a tethered kite can be used, optionally at lower altitudes of around 100-600 metres. At these altitudes, the winds are stronger and more stable in comparison to wind speeds at sea level. Optionally the kite is tethered such that it follows a figure-of-eight flight path. Optionally the length, or lengths, of bridle line 55 of the kite 50 are selected to encourage a specific flight path.

The control line 53 passes over and around the pulley system 30. The pulley system 30 has an upper sheave 30t and a lower sheave 30b over which the control line 53 passes, and the upper sheave 30t is fixed onto or in the buoy 60. The lower sheave of the pulley system 30t is fixed onto or within the subsea pressure vessel 20. The control line 53 passes over and/or around one or both of the sheaves 30t, 30b.

As the kite 50 rises, typically after being controlled by the operator to do so, it exerts a pulling force on the pulley system 30. The pulley system 30 then lifts the subsea pressure vessel 20 in a substantially vertical direction to, or near to, the surface of the water W. The force on the pulley system 30 exerted by the kite 50 is relatively smooth and constant.

As the pressure vessel 20 is lifted, an outlet 23 is opened and water 27b flows out of the storage chamber 25 into the sea (best seen in Figure 3). Optionally the inlet and outlet can be the same, so that as the water flows out of the storage chamber 25. In a less preferred embodiment (not shown), the inlet 22 and outlet 23 are separate like this present embodiment shown in Figs 1 to 4. In any event, as the vessel 20 is raised through the water column 27b by the kite 50, the surrounding water pressure 27b reduces, which results in the pressure of the water 27b within the storage chamber 25 reducing (due to the open outlet 23, through which a transient water outflow occurs). The reduction in water pressure allows the compressed air pocket 26 within the storage chamber 25 to expand back toward it’s original volume as the pressure of the air 26 within the storage chamber 25 also reduces (because it follows or matches the pressure of the water 27b in the chamber 25) towards or equal to 200 kPa as the volume of water 27b within the storage chamber 25 decreases.

As the air 26 within the storage chamber 25 reaches (or at least once it has reached or is reasonably close to reaching) 200 kPa the outlet 23 is closed, the kite 50 is flown out of the wind to permit retraction of the control line 53, reeling the kite 50 in to a threshold altitude, allowing the power generation process to start again. Because the kite 50 is no longer lifting or supporting the subsea pressure vessel 20, the vessel 20 sinks back to a depth of around 100m due to being negatively buoyant. This depth may be altered according to the requirements of the operator.

The kite 50 can use wind power to return to its original altitude (the threshold altitude mentioned above). With proper orientation and control of the kite 50, movement in any direction can be achieved relative to the direction of the wind by using the principles of aerodynamic lift and drag, and the reeling in of the kite 50 requires very little energy. By using the right control mechanisms and flight manoeuvres, the kite 50 can be maintained at a given altitude indefinitely, until it is required for lifting of the pressure vessel 20 again.

The subsea pressure vessel 20 can be extended and operated at any suitable desired depth.

Figures 5-8 show a further example of the invention substantially in line with the first example of the energy generation assembly.

As shown in Fig. 5, an empty subsea pressure vessel 20 filled with air is submerged against buoyancy force to a depth of approximately 100m, with a hydroelectric turbine 28 connected to a water inlet 22 of the subsea pressure vessel 20.

Referring now to Fig. 6, the inlet 22 is opened and a storage chamber 25 within the pressure vessel 22 is flooded with water at 100m depth, flowing through the hydroelectric turbine 28. The hydroelectric turbine 28 converts the flow of water into electricity. Underwater cables C carry the electricity to an onshore substation S, which then transfers the electricity to the national grid.

Referring now to Fig. 7, once the subsea pressure vessel 20 has filled with water, it is lifted vertically by a pulley system 30 connected to, in this example, at least one low-altitude kite 50. The line 53 of the kite 50 is paid out until the kite 50 is flying in the wind, thereby providing the lifting force to lift the subsea pressure vessel 20. Prior to lifting of the vessel 20 occurring, an outlet 22 in the subsea pressure vessel 20 is opened so that during lifting of the vessel 20, the water 27b in the storage chamber 25 is gradually released, so that the pressure within the storage chamber 25 is equalising with the ambient water 27a pressure at every depth.

As shown in Fig. 8, after the subsea pressure vessel 20 has emptied, the kite 50 or kites are flown out of the wind and returned to their retracted starting position, and optionally, the tether for the kite 50 is reeled back in. The pressure vessel 20, again filled with air, is returned to its starting depth and the vessel will then be back in the position and configuration as first shown in Fig. 5, ready for the cycle shown in Figs. 5 to 6 to 7 to 8 to be repeated whenever electricity generation is required.

Any feature described in connection with another example of the invention is also applicable to the first example of the invention where appropriate.

In a further example of the invention, shown in Figures 9-12, the storage chamber 125 is submerged while filled with air at atmospheric pressure. The storage chamber 125 comprises a large volume 126b that is separated into a volume that is located above a piston 170, and a smaller volume 126a that is located below the piston 170. Both volumes are initially at atmospheric pressure.

The subsea pressure vessel 120 comprises an inlet 122 with a hydroelectric turbine 128 as before, however in this example the inlet 122 is located at or toward the uppermost end of the pressure vessel 120 that is nearest the buoy 160. The inlet 122 is opened to fill the storage chamber 125 with water 127b in a similar manner to the first example described above, compressing the air pocket 126a therein into a smaller volume. As there is a pressure differential between the air inside the storage chamber 125 and the surrounding water, a transient kinetic water flow is set up into the pressure vessel 120. The pressure vessel 120 further comprises a conduit in the form of a breathing pipe 175 that extends from the storage chamber 125 to the air A above sea level. Importantly, the breathing pipe 175 is connected to the interior of the storage chamber 125 at a location above the upper face of the piston 170 (regardless of the stroke position the piston 170 is at). As water flows into the storage chamber 125, air within volume 126b exits the chamber 125 through the breathing pipe 175.

As water flows into the inlet 122, it passes through the hydroelectric turbine 128, driving the turbine 128 to rotate. Said rotation generates electrical power, which can then be transferred to, for example, an onshore substation for further transfer to the national grid. Alternatively, the electrical power may be transferred to an offshore structure, optionally to power the structure, or optionally for storage.

The kite 150 is used to power a water pump, or optionally a power take-off system, or the like, to expunge water from the storage chamber 125 within the pressure vessel 120 through an open outlet 123 (the breathing pipe 175 is closed during the expulsion of the water). In this example, the storage chamber 125 comprises a water pump in the form of piston 170 that is lifted as the kite 150 rises, forcing the water out of the outlet 123. As the piston 170 is lifted, it forces the water 127b located above it to exit the storage chamber 125 via the outlet 123, and as a result of the piston 170 being lifted, the air pocket 126a located below the piston 170 within the storage chamber 125 expands in volume. Due to the decompression of the storage chamber 125, the pressure of the air within the air pocket 126a reduces until the piston 170 is at maximum (extended) upward stroke, at which point the air pressure in the pocket 126a is below atmospheric pressure.

Once the water 127b has been removed, the outlet 123 is closed, and the breathing pipe 175 is opened. Air flows through the breathing pipe 175 into the storage chamber 125 as the piston 170 returns to its original configuration. As the pressure of the volume of air within the air pocket 127a has reduced to less than atmospheric pressure, there is a pressure differential between the air flowing through the breathing pipe 175 and the air pocket 126a. Accordingly, air flows into the storage chamber 125, pushing down on the piston 170, and therefore compressing the air pocket 126a until the air within the air pocket 126a again reaches substantially atmospheric pressure, such that the air in volume 126b is in equilibrium with the air in volume 126a.

The kite 150 is then reeled in to the required altitude until required to lift the piston 170 again.

Modifications and improvements may be made to the embodiments hereinbefore described without departing from the scope of the invention.

Claims

1. A subsea energy generation assembly adapted to generate electrical power, the assembly comprising a subsea pressure vessel, the subsea pressure vessel having a storage chamber adapted to receive and release fluid; wherein the subsea pressure vessel comprises a hydroelectric turbine adapted to generate electrical power as water flows through the hydroelectric turbine; wherein the subsea pressure vessel is connected to a sail, wherein the sail is adapted to convert wind energy into mechanical energy by transforming the subsea pressure vessel between at least two configurations:- a first configuration wherein the subsea pressure vessel is at least prepared to be at least partially filled with said water; a second configuration wherein the subsea pressure vessel is at least partially filled with said water; and wherein the turbine generates electrical power when said water flows through the hydroelectric turbine as it enters the storage chamber, thereby generating electrical power.

2. A subsea energy generation assembly as claimed in claim 1, wherein the subsea pressure vessel is connected to one end of a pulley system and the sail is connected to another end of the pulley system.

3. A subsea energy generation assembly as claimed in claim 2, wherein the sail is adapted to raise the subsea pressure vessel by actuating the pulley system.

4. A subsea energy generation assembly as claimed in claim 2 or claim 3, wherein the buoyant device and the sail together act on the pulley system to actuate it and raise the subsea pressure vessel.

5. A subsea energy generation assembly as claimed in claims 2-4, wherein the sail is connected to the pulley system by a control line that passes over or through the pulley system.

6. A subsea energy generation assembly as claimed in claims 2-5, wherein at least one pulley is disposed on or within a floating buoy.

7. A subsea energy generation assembly as claimed in claim 6, wherein the sail is connected to or through the floating buoy.

8. A subsea energy generation assembly as claimed in claim 7, wherein as the water surface changes in height through swells and troughs, the floating buoy changes vertical position relative to the subsea pressure vessel.

9. A subsea energy generation assembly as claimed in claims 2-8, wherein at least one pulley is disposed on or within the subsea pressure vessel.

10. A subsea energy generation assembly as claimed in claims 2-9, wherein the sail exerts a pulling force on the pulley system as said sail rises under the influence of air flow.

11. A subsea energy generation assembly as claimed in claim 10, wherein the pulley system lifts the subsea pressure vessel in a substantially vertical direction towards the surface of the water.

12. A subsea energy generation assembly as claimed in claims 2-11, wherein the pulley system is a block and tackle system.

13. A subsea energy generation assembly as claimed in claim 1, wherein the subsea pressure vessel is connected to the sail via a gearing system comprising at least two gears.

14. A subsea energy generation assembly as claimed in claim 13, wherein the control line connecting the sail to the subsea pressure vessel passes over or through the at least two gears.

15. A subsea energy generation assembly as claimed in claim 1, wherein the subsea pressure vessel is connected to the sail via a roller system comprising at least one roller.

16. A subsea energy generation assembly as claimed in claim 15, wherein the control line connection the sail to the subsea pressure vessel passes over, around, or through the at least one roller.

17. A subsea energy generation assembly as claimed in claims 1-16, wherein the subsea pressure vessel is adapted to be submerged, and an aperture is adapted to be opened in the subsea pressure vessel following submergence of said subsea pressure vessel to permit flow of seawater into the storage chamber.

18. A subsea energy generation assembly as claimed in claim 17, wherein the diameter of the aperture through which seawater passes determines the maximum power output.

19. A subsea energy generation assembly as claimed in claim 17 or claim 18, wherein the diameter of the aperture through which seawater passes determines the duration of power generation.

20. A subsea energy generation assembly as claimed in claims 17-19, wherein the subsea pressure vessel is flooded with water at a depth of 100m, corresponding to a water pressure of approximately 1100kPa.

21. A subsea energy generation assembly as claimed in claim 20, wherein a pressure differential is created between the water outside the pressure vessel and the air inside the pressure vessel.

22. A subsea energy generation assembly as claimed in claim 21, wherein the pressure differential creates a transient kinetic water flow into the storage chamber, resulting in the air contained therein being compressed into a small volume.

23. A subsea energy generation assembly as claimed in claim 22, wherein as the sail lifts under air flow, the pulley system actuates and raises the subsea pressure vessel towards the surface of the sea, and the outlet aperture is opened such that water flows out of the storage chamber into the sea.

24. A subsea energy generation assembly as claimed in claim 23, wherein the compressed air volume expands back to substantially 200 kPa as the volume of water within the storage chamber decreases; wherein the expansion of the air volume closes the outlet aperture; and wherein the subsea pressure vessel returns to its original submerged depth.

25. A subsea energy generation assembly as claimed in claims 1-24, wherein the sail is a high-altitude kite.

26. A subsea energy generation assembly as claimed in claims 1-25, wherein the cover of the sail is made of a polymer material.

27. A subsea energy generation assembly as claimed in claims 1-26, wherein the sail is free flying.

28. A subsea energy generation assembly as claimed in claims 1-26, wherein the sail is tethered.

29. A subsea energy generation assembly as claimed in claims 1-28, wherein the sail is connected to the energy generation assembly by control lines, wherein the length of the control lines is optionally selected so that the sail flies at an altitude of up to 1000m.

30. A subsea energy generation assembly as claimed in claims 1-29, wherein the sail is reeled in to a threshold altitude by flying the sail out of the wind to permit retraction of the control line.

31. A subsea energy generation assembly as claimed in claim 1, wherein the sail powers a water pump that is adapted to expunge water from the storage chamber within the subsea pressure vessel.

32. A subsea energy generation assembly as claimed in claim 31, wherein the storage chamber comprises a piston that is lifted as the sail is raised, forcing the water out of the aperture.

33. Method for generating electrical power, the method comprising the steps of deploying a subsea energy generation assembly comprising a subsea pressure vessel in a body of water, the subsea pressure vessel comprising a storage chamber adapted to receive and release fluid and a hydroelectric turbine adapted to generate electrical power as water flows through the hydroelectric turbine; connecting the subsea pressure vessel to a sail, wherein the sail is adapted to convert wind energy to potential energy by transforming the subsea pressure vessel between at least two configurations, including a first configuration wherein the subsea pressure vessel is at least prepared to be at least partially filled with said water, and a second configuration wherein the subsea pressure vessel is at least partially filled with said water; submerging the subsea pressure vessel to a suitable depth providing a desired ambient pressure level; transforming the configuration of the subsea pressure vessel between at least the first and second configurations; and generating electrical power via the hydroelectric turbine by flowing water through the hydroelectric turbine as it enters the storage chamber, thereby generating electrical power; and arranging for the sail to be raised in the wind such that the subsea pressure vessel is raised in the body of water, thereby converting wind energy into potential energy stored within the subsea pressure vessel.

34. Method as claimed in claim 33, including the steps of transferring the electrical power generated by water flowing through the hydroelectric turbine to an onshore substation for further transfer to the national grid.

35. Method as claimed in claim 33, including the steps of transferring the electrical power generate by water flowing through the hydroelectric turbine to an offshore structure.

36. Method as claimed in claim 35, including utilising at least a portion of the transferred electrical power to power the offshore structure.

37. Method as claimed in claim 35 or claim 36, including storing at least a portion of the transferred electrical power.

38. Method as claimed in claims 33-37, including connecting the subsea pressure vessel to one end of a pulley system mounted on or in the subsea pressure vessel.

39. Method as claimed in claims 33-38, including mounting one end of a pulley system on or in a floating buoy.

40. Method as claimed in claim 38 or claim 39, including passing a control line over, through, or around the pulley system and connecting said control line to the sail.

41. Method as claimed in claims 38-40, including actuating the pulley system as the sail moves, and thereby raising and lowering the subsea pressure vessel as the sail rises and falls in response to air flow.

42. Method as claimed in claims 33-37, wherein the sail actuates a roller system and the control line passes over, through, or around the rollers.

43. Method as claimed in claims 33-37, wherein the sail actuates a gearing system, and the control line passes over, through, or around the gears.

44. Method as claimed in claims 33-43, including flying the sail by following a suitable flight pattern that increases the apparent wind speed experienced by the sail.