GB2546562A

GB2546562A - Underwater power generation system

Info

Publication number: GB2546562A
Application number: GB1604380.4A
Authority: GB
Inventors: Hayman Jason; Burden Christopher
Original assignee: Sustainable Marine Energy Ltd
Current assignee: Sustainable Marine Energy Ltd
Priority date: 2016-01-21
Filing date: 2016-03-15
Publication date: 2017-07-26
Anticipated expiration: 2036-03-15
Also published as: GB201601162D0; GB2546562B; GB201604380D0

Abstract

A submersible turbine assembly 200 for location in river or sea locations with unidirectional or bidirectional flow. The assembly has: a support structure 224, 226, and a first turbine system 216, supported by the support structure. The first turbine system 216 is pivotally connected to the support structure so that the first turbine system is rotatable, about a centre of rotation. The turbine 216 has an operational axis, and is designed for optimum power output when local water flow is aligned with the operational axis. The centre of mass of the turbine 216 is spaced from the centre of rotation in a direction parallel to the operational axis of the turbine. The turbine assembly is arranged to rotate due to local currents, thereby bringing the operational axis towards alignment with local water flow.

Description

Underwater power generation system

The present invention relates to underwater or submersible systems for generating power from flowing water.

Turbine-based power generation systems can be submerged in order to extract power from flowing water. The water flow in a given location may be unidirectional, such as in a river, or bidirectional, for example where local flow is dominated by tidal effects.

According to a first aspect, there is provided a submersible turbine assembly having: a support structure; and a first turbine system, supported by the support structure, the first turbine system having a centre of mass and being pivotally connected to the support structure so that the first turbine system is rotatable, relative to the support structure, about a centre of rotation; wherein the first turbine system includes a first flowing-water driveable turbine for generating power from water flow, the first turbine having an operational axis, and being designed for optimum power output when local water flow is aligned with the operational axis; and wherein the centre of rotation is spaced away from the centre of mass of the first turbine system in a direction parallel to the operational axis of the turbine.

This arrangement allows turbines to be mounted on the submersible assembly and to passively flip to maximise their power output. Passive flipping means that no external input is required to rotate the turbines to achieve this effect. Instead, the water flow itself causes the turbines to come closer to alignment with the water flow. This arrangement does not require complex actuator systems to implement the flipping, and the device is therefore simpler, and less prone to mechanical failures. Such a passive flipping system will result in the turbine system operating in a downstream flow mode in which the part of the turbine which produces the greatest hydrodynamic drag, usually the turbine blades, is the most downstream part of the system, meaning that the water flow hits this part of the system last. This is because the flow of water past the turbine forces the turbine blades to swing away from the direction from which the flow is coming, in order to settle into a position of stable equilibrium.

In this context, the first turbine system being supported by the support structure means that the support structure constrains the turbine system to the same general location, relative to the support structure, although the turbine system is still able to rotate, as described above. Put another way, this means that the support structure is arranged to withstand any mechanical forces caused by the weight of the turbine system, or drag forces acting on the submersible assembly as a whole, while providing a stable location for mounting the turbine system, and allowing it to rotate, as described above.

When a turbine is described as being designed for optimum power output when local water flow is aligned with the operational axis, this means that the turbine will operate to most efficiently convert kinetic energy from water flowing past it into other, more useful forms of energy, typically electricity, when local water flows is along a particular axis relative to the turbine. In particular, it should be noted that turbines are able to generate useful energy from local water flow even if the local water flow is not exactly aligned with the operations axis. Often turbines have blades which rotate, tracing out a cone or a disc. The operational axis in these cases usually extends through the centre of the disc or the apex of the cone, as appropriate.

In this context, local water flow simply means the direction in which the water around the turbine is moving. Typically for both rivers and tidally dominated systems, water flow will be predominantly in either a single direction or two opposite directions in a cycle which varies with time. In these examples, the absolute direction in which water flows does not change greatly with position, or in other words, the flow in adjacent regions is usually in approximately parallel directions.

In particular, this arrangement means that in the absence of external forces acting on it (e.g. from local current flow), the turbine system will align its operational axis with the local gravitational field, that is to say, vertically. This provides a stable position when there is no current flow. In addition, since current flow is typically substantially horizontal, that is to say it is dominated by a component perpendicular to the local gravitational field, the stable, vertical, position does not naturally favour any particular direction of current flow, and therefore allows the turbine system to rotate to align itself with local water flow when this changes, unimpeded by its orientation prior to the change in water flow. This effect may be particularly advantageous when the submersible assembly extracts power from water flow driven primarily by tidal flow patterns, as the local flow will cycle between strong flow in a first direction; no flow; strong flow in a second direction opposite to the first direction; no flow; and then the cycle repeats, starting again with strong flow in the first direction. In these conditions, the turbine system will rotate towards aligning its operational axis with the water flow in the first direction, then when the local flow drops to zero, its operational axis will point vertically, then as flow increases in the second direction, the turbine system will rotate towards aligning its operational axis with the water flow in the second direction, before rotating back to vertical when flow drops to zero.

In this context, the turbines do not necessarily align themselves fully with the local water flow. As noted above, it is not necessary that exact alignment between the operational axis and the local water flow is achieved in order for useful power to be extracted. Therefore, while exact alignment is the optimal position, even a partial alignment allows the system to function to extract energy from flowing water. Putting this another way, the operational axis of the turbine may be changed so that the angle between it and the local water flow is reduced, or that the operational axis rotates towards becoming parallel with the local fluid flow.

According to a second aspect, there is provided a submersible turbine assembly having: a support structure; and a first turbine system, supported by the support structure, the first turbine system being rotatable relative to the support structure; wherein the first turbine system includes a first flowing-water driveable turbine for generating power from water flow, the first turbine having an operational axis, and being designed for optimum power output when local water flow is aligned with the operational axis; and wherein the first turbine system is mounted so as to rotate about a horizontal axis relative to the support structure in response to local water flow so that it brings the operational axis of the first turbine towards alignment with the direction of local water flow.

This arrangement also allows turbines to be mounted on the submersible assembly and to passively flip to maximise their power output. Passive flipping means that no external input is required to rotate the turbines to achieve this effect. Instead, the water flow itself causes the turbines to come closer to alignment with the water flow. This arrangement does not require complex actuator systems to implement the flipping, and the device is therefore simpler, and less prone to mechanical failures. Such a passive flipping system will result in the turbine system operating in a downstream flow mode in which the part of the turbine which produces the greatest hydrodynamic drag, usually the turbine blades, is the most downstream part of the system, meaning that the water flow hits this part of the system last. This is because the flow of water past the turbine forces the turbine blades to swing away from the direction from which the flow is coming, in order to settle into a position of stable equilibrium.

Optionally, the submersible turbine assembly of the second aspect further includes the first turbine system having a centre of mass and being pivotally connected to the support structure so that the first turbine system is rotatable about a centre of rotation; and wherein the centre of rotation is spaced away from the centre of mass of the first turbine system in a direction parallel to the operational axis of the turbine.

Optional features applicable to either the first aspect, or the second aspect or both are now described.

The first turbine system may be rotatable independently of the parts of the support structure to which the first turbine system is directly connected. This allows fewer parts of the submersible assembly to rotate, consequently simplifying the design.

Optionally, the first turbine system has a centre of mass and is pivotally connected to the support structure so that the first turbine system is rotatable about a centre of rotation; and wherein the centre of rotation is spaced away from the centre of mass of the first turbine system in a direction parallel to the operational axis of the turbine. In this arrangement, in the absence of external forces acting on it (e.g. from local current flow), the turbine system will align its operational axis with the local gravitational field, that is to say, vertically. This provides a stable position when there is no current flow. In addition, since current flow is typically horizontal, that is to say it is dominated by a component perpendicular to the local gravitational field, the stable, vertical, position does not naturally favour any particular direction of current flow, and therefore allows the turbine system to rotate to align itself with local water flow when this changes, unimpeded by its orientation prior to the change in water flow. This effect may be particularly advantageous when the submersible assembly extracts power from water flow driven primarily by tidal flow patterns, as the local flow will cycle between strong flow in a first direction; no flow; strong flow in a second direction opposite to the first direction; no flow; and then the cycle repeats, starting again with strong flow in the first direction. In these conditions, the turbine system of the present invention will rotate towards aligning its operational axis with the water flow in the first direction, then when the local flow drops to zero, its operational axis will point vertically, then as flow increases in the second direction, the turbine system will rotate towards aligning its operational axis with the water flow in the second direction, before rotating back to vertical when flow drops to zero.

The turbine system may further include a second flowing-water driveable turbine for generating power from water flow, the second turbine having an operational axis, and being designed for optimum power output when local water flow is aligned with the operational axis; and wherein the operational axes of the first and second turbines are parallel with one another. By placing two turbines on the same assembly, more power may be generated per platform, thereby increasing efficiency.

Moreover, the turbine system may include a beam connecting the first turbine and the second turbine. The use of a beam to connect the two turbines forces the two turbines to rotate together. This means that they can both contribute to the rotational motion, and thereby rotate in a more efficient manner.

Optionally, the first turbine may be mounted on one surface of the beam, and the second turbine may be mounted on a second, opposing surface of the beam. For example, the turbines may be mounted above and below the beam when the turbines are aligned with a substantially horizontal flow of water. This allows the torque generated by each turbine rotating to cancel, and thus reduces stresses on the support structure.

The beam may further comprise a hydrodynamic foil having a drag coefficient which varies with orientation, and wherein the turbines are mounted on the hydrodynamic foil so that their operational axes are aligned with the orientation in which the drag coefficient of the hydrodynamic foil is at a minimum. This arrangement allows the beam to contribute to the passive flipping, as the beam will naturally find its lowest drag arrangement in flowing water, and thereby assist the turbine system in rotating. The beam or foil may also be shaped to provide lift to encourage the turbine system to rotate into an operational orientation.

Optionally, the or each turbine may have a fairing to reduce hydrodynamic drag. Reduction of drag on submersible assemblies allows their anchoring systems to be simpler, and the design of the system less complex, since the overall stresses will be lower.

Moreover, the or each turbine may have a fairing having a drag coefficient which varies with orientation, and is lowest in the orientation which is aligned with the operational axis of the turbine. This arrangement provides a boost to the inherent passive flipping effect of the turbines, in much the same way that a hydrodynamic foil does.

The support structure may comprise a platform, and the turbine system may be spaced away from the platform by supports around which the turbine system can rotate about an axis generally parallel to the plane of the platform. This arrangement separates the structural support requirements of the assembly from the moveable portions of the assembly. This allows the moveable portions to be designed without requiring them to also perform a structural role.

The turbine system may be supported above the platform. This arrangement means that the entire assembly can rest on dry land prior to installation, or during repair operations, using the platform as a base, and keeping the turbines away from the ground, to prevent damage.

The turbine system may further be arranged to rotate in response to changes of local water flow so that the turbine blades rotate away from the platform. By rotating the turbines in the direction which takes them away from the platform (i.e. rotating them up, when the platform is below the turbines, and rotating them down in the event that the platform is above the turbines), there is no requirement for there to be enough space between the platform and the rotational axis of the turbine to fit the full length of the turbine. This allows a more compact structure, and saves on materials and building costs. It also reduces the chance that the turbine blades and the structure will collide, damaging one or both of them in the process.

The submersible assembly may further comprise an actuator to rotate the turbine system. This may be beneficial in the event that the alignment between the operational axis of the turbine system is not exact, and a slight adjustment must be made. In this case, exact alignment can be achieved by using the actuator, and more power can be extracted from the flowing water.

The submersible assembly may further comprise a brake to resist the rotation of the turbine system. It may be necessary at times to restrict or entirely stop the rotation of the turbine system, for example to prevent damage to the turbine or the submersible assembly. In particular, it may be necessary to lock the turbine system with its operational axis vertical to inhibit power generation, in the event of rough seas.

The submersible turbine assembly may further comprise a second turbine system, supported by the support structure, the second turbine system having a centre of mass and being pivotally connected to the support structure so that the second turbine system is rotatable, relative to the support structure, about a centre of rotation; wherein the second turbine system is of the same design, and is connected to the support structure in the same way, as the first turbine system. In particular, the second turbine system may include third and fourth turbines, preferably mounted on opposing sides of a second beam. By providing two complete turbine systems of the same design, the power output of the assembly can be doubled.

The submersible assembly may be positively buoyant in water, and may be anchored to a water bed, so that the assembly is held in a state of floating equilibrium. In this state, the submersible assembly may be situated high up in the water column, which has a larger amount of energy available for extraction than lower parts of the water column. The state of floating equilibrium, in which the upward buoyant force is cancelled by the downward component of tension in the anchoring means holds the assembly rigidly. Rigidly holding the assembly in this way allows the directions in which the turbines can rotate to face, to be set at installation. Since the design is rigid, this direction will not change with time. This may be particularly advantageous when applied to systems for extracting tidal energy, in which the water flow is typically always along one of two opposite directions.

The submersible assembly may be variably buoyant. This may be advantageous when installing the submersible assembly, as the buoyancy can be made low while the system is being lowered to its operational depth, thus requiring smaller forces to lower it, and then once it is in position, and the anchoring system in place, the buoyancy can be increased to hold the submersible assembly rigidly in floating equilibrium.

According to a second aspect, there is provided a submersible turbine assembly for generating power from water flow, having: a centralised onboard control module for providing control signals to the submersible turbine assembly, wherein the control module comprises a watertight dry space containing electronic control systems. Centralising the control systems allows a reduction in the number and size of dry spaces, and thereby simplifies the design of the submersible assembly.

The onboard control module of the submersible turbine assembly may be removably coupled to the assembly. In such an embodiment, the control module is detachable from the assembly. For example, the module may be cold swappable, so that the module can be removed from the assembly while the assembly is surfaced (on a surface vessel, or even a dockside). In combination with the centralised nature of the module, this allows a quick and simple repair of the workings of the assembly. Since the control systems often comprise moving parts and/or electronic systems, they are the most likely parts to develop a fault. In the worst case scenario, the assembly can be quickly repaired by simply swapping a damaged or faulty module with a new one. Additionally, the assembly may be upgraded in a simple manner, for example with new control systems, by swapping an existing module with an updated one.

The submersible turbine assembly may have an onboard control module which further contains hydraulic actuation systems. This provides a further centralisation of features so that the design of the submersible assembly may be further simplified.

The onboard control module may further contain mechanical actuators for providing mechanical motive power to the submersible turbine assembly. Once again, this provides a further centralisation of features so that the design of the submersible assembly may be further simplified.

The onboard control module may further contain power transfer systems for transferring power generated by the turbine assembly to an external location. Once again, this provides a further centralisation of features so that the design of the submersible assembly may be further simplified.

According to a third aspect, there is provided a submersible turbine assembly for generating power from water flow, the submersible turbine assembly being positively buoyant in water, and arranged to be anchored to a water bed, the submersible turbine assembly having: a support structure for mounting turbines, comprising a plurality of hollow, watertight trusses. This arrangement allows the support structure to fulfil dual roles of mechanical support and buoyancy, thus resulting in a simpler and lighter design.

The hollow trusses may have a variable buoyancy. This assists with installing the submersible assembly, as the buoyancy can be made low while the system is being lowered to its operational depth, thus requiring smaller forces to lower it, and then once it is in position, and the anchoring system in place, the buoyancy can be increased to hold the submersible assembly rigidly in floating equilibrium.

The buoyancy of the hollow trusses may be varied by selectively flooding their hollow spaces. This further allows the trusses to perform a dual role, and thus reduces the complexity of the system.

The hollow trusses may have a fairing to reduce hydrodynamic drag. Since lower drag forces mean lower stresses on the structure, the whole system can be made simpler and lighter, thus reducing building costs.

The submersible turbine assembly of the first aspect may further include the centralised onboard control module of the second aspect and/or the support structure of the third aspect, which may be provided in conjunction with any of the further features set out above.

Embodiments will now be described with reference to the drawings, in which:

Figure 1 is a perspective view of an embodiment of a submersible assembly of the present invention;

Figure 2 is a perspective view of another embodiment of a submersible assembly of the present invention;

Figure 3 is a detailed perspective view of a portion of the submersible assembly of Figure 2, showing a turbine;

Figure 4 is a side view of an embodiment of a submersible assembly of the present invention.

Figure 5 is a perspective view of an onboard control module according to an embodiment of the present invention;

Figure 6 is a sectional view of the onboard control module of Figure 5 shown mounted on an embodiment of a submersible assembly according to the present invention;

Figure 7 shows equivalent features to those presented in Figure 1;

Figure 8 shows equivalent features to those presented in Figure 2;

Figure 9 shows equivalent features to those presented in Figure 3;

Figure 10 shows equivalent features to those presented in Figure 4;

Figure 11 shows equivalent features to those presented in Figure 5; and

Figure 12 shows equivalent features to those presented in Figure 6.

Figure 1 shows a perspective view of a submersible assembly 100 according to an embodiment. A series of anchoring points 102 are provided on the water bed to which primary anchoring lines 106 are attached. The anchoring lines bifurcate into upper 108 and lower 110 anchoring lines, each of which attaches to the submersible assembly 100 at a different location. It is not necessary for the anchoring system of the present invention to bifurcate in this way, and a single anchoring line is possible.

The submersible assembly 100 is buoyant in water, with the buoyancy being provided by buoyancy devices 126. These may simply be fixed buoyancy devices such as air-filled tanks, or foam based buoyancy devices. Or they may be variable buoyancy devices which can be selectively flooded with water to reduce their buoyancy or filled with air and sealed to increase their buoyancy. The submersible assembly 100 is held in a state of floating equilibrium by the combination of the upward buoyant force from the buoyancy devices 126 and the downward component of tension in the anchoring lines 106, 108, 110. It is not necessary for the present invention to be anchored in this way. It is possible, for example, for the whole assembly to be a rigid structure permanently affixed to the water bed.

The submersible assembly 100 has a support structure 112 in the form of a series of beams linking the buoyancy devices together. These beams provide support to a turbine system 114, which comprises a turbine 116 rotatably mounted to the support structure 112. The turbines 116 are arranged to rotate in response to external forces from a local water flow. This is discussed in more detail below.

Turning now to Figure 2, another submersible assembly 200 according to an embodiment of the present invention is shown. The anchoring system is omitted from this figure, but the anchoring systems discussed above in relation to Figure 1 could be used in this embodiment too.

Submersible assembly 200 has a set of four buoyancy devices 226, two at each end. Each of these may be fixed or variable, as described above. Each pair of buoyancy devices is spaced apart from one another by a pair of vertical support members 230. The support structure further includes a plurality of horizontal trusses 228 spanning the width of the assembly and connecting the lower buoyancy device 226 at one end of the assembly 200 to the lower buoyancy device 226 at the other end. These trusses 228 may be simple trusses, or they may be hollow and selectively floodable to alter the buoyancy of the assembly. Rising from the trusses 228 are a pair of intermediate vertical supports 232. Between the vertical supports 232, and also rising from the trusses 228 is a central pontoon 234. The central pontoon 234 may be hollow, and may further be air-filled, water filled, or selectively floodable to achieve variable buoyancy, depending on the buoyancy requirements of the system. A beam 224 spans between the upper buoyancy device 226 at one end of the assembly 200 to central pontoon 234, and a second beam spans between the upper buoyancy device 226 at the other end of the assembly and the central pontoon 234. Each of these beams is supported approximately at its midpoint by one of the intermediate vertical supports 232.

Four turbines 216 are mounted on the beam 224 in pairs (collectively referred to in this embodiment as a turbine system) with one turbine 216 from each pair being located between an intermediate support 232 and a buoyancy device 226, and the other turbine of the pair being located between the intermediate support 232 and the central pontoon 234. Both turbines 216 have their blades facing in the same direction, as explained in more detail below. In this case, the turbine systems are each arranged to rotate independently of the parts of the support structure 226, 232, 234 to which they are directly connected. That is, the turbine system is able to rotate, but the parts of the support structure which it connects to do not rotate.

One turbine 216 of the pair is mounted on top of the beam 224, and the other turbine 216 is mounted below the beam. When the direction of water flow changes, the turbines 216 and the beam 224 rotate together. Once the direction of water flow has completely reversed, for example when the tide is no longer ebbing, but is flowing instead, the turbines will have rotated so that their turbine blades will be facing in the opposite direction. Moreover, the turbine 216 which was previously situated on top of the beam 224 will then be located below the beam 224, while the turbine 216 which was previously underneath the beam 224 will now be located on top of the beam 224.

The beam 224 is shaped to act as a hydrodynamic foil, and has a coefficient of drag which changes depending on its orientation relative to local water flow. In particular, it has an orientation of minimum coefficient of drag, and it will rotate to align this with local water flow. This example of a beam has a plane of symmetry, which is beneficial in the present system as it means that it will work equally well when the turbines 216 (and thus the beam 224 as well) are oriented in a first direction as when they are oriented in a second direction opposite to the first direction. It is not necessary that the beam 224 have these hydrodynamic properties, and instead it may simply have the function of connecting the turbines 216 together so that they rotate as a single unit. In fact, in some embodiments the beam 224 may not even be arranged to connect the turbines 216 in this way. It may simply serve as an axis around which the turbines 216 rotate, while remaining static relative to the rest of the support structure. A turbine 316, mounted on a beam 324 (once more shaped to act as a hydrodynamic foil) is shown in more detail in Figure 3. This figure shows a turbine 316 mounted as described in relation to the embodiment shown in Figure 2. It will, however, be clear to the skilled person that the detailed description of the turbine 316 may be applied to other embodiments, in particular those with a larger or smaller number of turbines than the four shown in Figure 2.

The turbine 316 has a generally elongate body, contained in nacelle 320 located at the front (upstream) end of the turbine 316. The nacelle 320 provides a streamlined enclosure within which generators are housed, as well as optionally other equipment, for example AC/DC converters, transformers, sensing equipment, or actuators and/or brakes for controlling the rotation of the turbine 216. The streamlined shape helps to reduce drag on the structure as a whole. Although the nacelle 320 is shown as smooth in this embodiment, fins, foils or other hydrodynamic shapes can be included to assist the turbines 316 in interacting with local water flows to cause them to rotate.

Any suitable generator for the anticipated water current and turbine characteristics can be provided. However, in one particular embodiment, the generator is arranged to receive rotational motive power and convert it into a more useful form of energy, typically electrical energy. The machinery of the generator is often relatively heavy compared with the rest of the turbine 316, and tends to result in the centre of mass of the turbine 316 being located towards the middle, or even towards the front (upstream end) of the nacelle 320.

Mounted at the rear (downstream end) of the nacelle 320 are turbine blades 318. Typically these are mounted on a driveshaft which feeds into the generator. The blades 318 are shaped and mounted so that water flow from the nacelle 320 to the blades 318 will cause them to rotate. A dashed line 322 represents the operational axis of the turbine 316. The turbine 316 is designed so that when the operational axis 322 is aligned parallel to the direction of local water flow, the turbine 316 achieves optimum power generation for a given local water flow rate. Primarily this is achieved by altering the shape and mounting angle of the turbine blades 318.

As shown, the turbine is mounted on the beam 324 towards the rear (downstream end) of the nacelle 320. Since in this embodiment the turbine 316 rotates along with the beam 324 and the centre of mass of the turbine 316 is inside the nacelle 320, this means that the point of rotation and the centre of mass of the turbine are not at the same place. In other words, they are spaced apart from one another.

This arrangement causes a torque due to gravity on the turbine 316, tending to rotate the turbine 316 (and the beam 324 in this embodiment) so that its rear end points downwards (i.e. its operational axis 322 tends towards the vertical). When there is a water current, this torque can be counteracted, at least in part, and a position of stable equilibrium can be attained, in which the front end of the nacelle 318 receives the water current first, which flows over the nacelle 320 and the beam 324, before reaching the turbine blades 318.

When the water flow hits the turbine blades 318, they rotate, and cause the driveshaft to rotate too, thereby feeding rotational power to the generator and causing useful power, e.g. electrical power, to be generated. This process results in the turbine blades 318 generating a large drag force which provides a countertorque to the torque due to gravity acting on the centre of mass of the turbine 316, thus stabilising the turbine 316 in the water flow, with its operational axis 322 dragged away from the vertical, and closer to alignment with the water flow.

Since the position of equilibrium attained in this way depends on the water flow, the turbine 316 responds dynamically to changes in water flow. In particular, water flow in a first direction will hold the turbine aligned with the water flow in a first direction, for example in the direction shown Figure 3. Then, as the flow rate drops, the drag force reduces causing the torque due to gravity to be opposed less and less strongly, and the turbine 316 rotates until the turbine blades are at the top. This is because, absent any external forces, the centre of mass (located at the middle or front of the nacelle 320) will tend to move to place itself directly below (as determined by the local gravitational field) the centre of rotation. As the water flow increases again, for example in a second direction opposite to the first direction as would be seen in a tidally dominated system, the drag forces on the turbine 316 increase, and oppose the gravitational torque. This time, the drag forces cause the turbine 316 and beam 324 to rotate to align with the second direction of water flow, that is to say, the turbine 316 faces in the opposite direction to that shown in Figure 3.

The hydrodynamic shape of the beam 324 may assist the turbine 316 in rotating from the orientation in which the operational axis 322 is vertical, by presenting a large drag coefficient while the turbine operational axis 322 is vertical, and a progressively lower drag coefficient as the orientation of the operational axis approaches alignment with the local direction of water flow. In addition, water flowing over the foil 324 first, and the turbine 316 later helps to smooth the flow, and improve power generation from the turbine 316.

Figure 3 shows a single turbine 316 mounted on a beam 324, along with a second, adjacent beam. The adjacent beam may also have a turbine mounted on it, and both turbines may be arranged to rotate in a pair, along with their respective beams. This may be achieved, for example, by forming the hydrodynamic foil as a covering on a generally cylindrical beam. The fairing may then extend up to the intermediate support 332 which separates the two portions of fairing from one another. The intermediate support 332 may further have an aperture comprising bearings to allow the cylindrical beam to pass through and rotate. The second portion of fairing and second turbine may then be provided on the other side of the intermediate support 332 in a similar manner.

The turbine 316 in Figure 3 is shown mounted on top of the beam 324, although clearly when the turbine 316 rotates to adapt to a change in current flow direction, this may change, and the turbine 316 may later located below the beam.

It is entirely possible to mount the turbine 316 in such a way that the nacelle 320 extends as equally as far above and below the beam 324. This arrangement may be preferred for systems in which turbines 316 may rotate independently of any other turbines on the submersible assembly, including single turbine assemblies. This is because a turbine 316 can only align its operational axis 322 vertically by using gravity alone, if the centre of mass is spaced apart from the centre of rotation along a line parallel to the operational axis 322. Clearly this requires that the axis about which the turbine 316 rotates must intersect the operational axis 322, which further requires that the beam 324 supports the turbine 316 in such a way that it intersects the nacelle 320, rather than passing above or below it. Allowing the operational axis 322 to self-orient vertically in the absence of external forces means that the turbine 316 is not biased towards a particular direction of current flow.

As described above, turbine 316 may be arranged to rotate together with a second turbine, by virtue of sharing a common beam 324. In this arrangement, both turbines 316 and the beam 324 are collectively known as a turbine system. The turbine 316 shown in Figure 3 is mounted above the beam. In order to reduce torques on the support structure, and also to allow the turbine system to orient the operational axes of the two turbines vertically, the second turbine should be mounted below the beam with its operational axis parallel to that of the first turbine, and separated from the common axis of rotation (as defined by the beam 324 with which both turbines collectively rotate) by the same distance as the first turbine 316 is separated from this axis, when the two turbines are of identical design. This is equivalent to saying that the centre of mass is the same height for rotational deflections or equal magnitude in either direction relative vertically oriented operational axes 322, so there is no inherent preferred direction for the turbines to rotate towards.

This detailed description has proposed mounting the turbines 316 with the beam 324 providing a centre of rotation for the turbines 316 located between the centre of mass and the turbine blades, so that in the absence of external forces the turbine 316 rotates to vertically orient its operational axis 322 with its blades 318 uppermost. However, it is entirely possible to arrange the mounting location of the turbine 316 on the beam 324 so that the centre of mass of the turbine 316 is located between the beam 324 and the turbine blades 318. In this case, the turbine 316 may still rotate to align its operational axis 322 vertically, but in this configuration, the blades 318 represent the lowest point of the turbine 316.

While the foregoing has described how turbines 316 may use forces generated by interacting with local water streams to bring their operational axes 322 towards alignment with local water flow, even with assistance from the beam 324 and its hydrodynamic properties, it may not be possible to exactly align the turbine operational axis 322 with the local water flow. It is therefore contemplated that an actuator may be provided to rotate the turbine 316 or the beam 324 to make small corrections, and thereby improve power generation.

Additionally, the turbine 316 or beam 324 may be supplied with a brake to resist rotation. This may allow the turbine to be locked in a particular position, for example it may be used to lock a turbine 316 with its operational axis 322 aligned with local current flow, even as the strength of the flow drops. This ensures that the turbine 316 keeps its operational axis 322 aligned with the flow, even when the flow is not strong enough to fully counteract the gravitational torque.

Finally, a brake may also be useful in retaining the turbine 316 in the orientation in which its operational axis 322 is vertical, to inhibit power generation, for example if repairs are being carried out to the submersible assembly, or if the flow rate is outside safe limits.

Turning now to Figure 4, the mounting of turbines 416 in pairs is clearly shown. This figure shows a side view of the embodiment of Figure 3. In addition to the buoyancy devices 426; trusses 428; central pontoon 434; end 430, and intermediate 432, vertical supports already described in detail in reference to Figure 2, it can clearly be seen that each pair of turbines 316, situated either side of the central pontoon 434, comprise a turbine 416 mounted above the beam 424 and a turbine 416 mounted below the beam 424. It is also clear that each turbine is spaced away from the central plane of the beam by the same distance, whether above it or below it.

The view in Figure 4 shows the importance of carefully selecting the direction in which the turbine blades should point when there is no current flow. If the turbines 416 were arranged to rotate so that their blades are the lowest point of the turbine in the absence of externa forces (i.e. the centres of mass of the turbines 416 are located between the beam 424 and the turbine blades), then there is a danger that the blades could collide with the trusses 428 or other parts of the support structure, damaging the device. Therefore, the turbines 416 are mounted with the beam 424 between their centres of mass and their blades in this embodiment.

Of course designs are contemplated where the support structure forms a platform similar to that shown in Figure 4, but where the turbines are mounted vertically below the platform, instead of above it, as shown in Figure 4. In this case, the arrangement in which the centres of mass of the turbines 416 are located between the beam 424 and the turbine blades would be appropriate to ensure that the blades rotate to the bottom of the turbines 416 in the absence of external forces. In general, this feature is that the turbines rotate in such a way as to cause the blades to rotate away from the platform.

Finally, it should be noted that the support structure could also be designed in such a way that there was sufficient clearance for the blades to rotate in any direction, in which case the above considerations are less important.

Turning now to Figure 5, there is shown an embodiment of a centralised onboard control module 536 according to a second aspect of the present invention. This design comprises an upper torispherical dome portion 338 and a lower generally cylindrical portion 540. These are joined together by a watertight seal 542.

The control module 536 contains electronic control systems for the submersible assembly, for example to control actuators or brakes on the turbines of the assembly to change their rotational status. In principle, this allows these water-sensitive components to be sealed on dry land, to protect them from water damage, and subsequently the module 536 can be attached to the submersible assembly and submerged. In the event of accidental damage, the centralised nature of these control systems allows them to be easily removed and repaired.

The control module 536 is provided with a mounting bracket 544 or similar means so that it can be simply mounted and/or detached as the need arises. In particular, the control module 536 may be removable in its entirety form the assembly. For example, in the event that the module develops a fault, or needs an upgrade, the assembly may be raised to the surface, the module removed, and repairs or replacement of the module can be made, as appropriate.

In addition, other systems such as hydraulic actuators, mechanical actuators, pneumatic systems, and high power electrical equipment may also be housed in the module 536. This allows easy and centralised access to these key systems, while keeping them safe in a dry space. Centralising in this way means that fewer spaces need be sealed, and monitored to ensure safe working of the apparatus.

Externally, the module is provided with cable feedthroughs 546 for outputting control signals (in the form of electronic, or other suitable, e.g. fibre optic, signals) or electrical power as required, or for receiving electrical power e.g. from the turbines, for processing with high power electrical equipment prior to transferring to an external location, e.g. for feeding into a local electricity grid.

There may further be provided mechanical, hydraulic or pneumatic feedthroughs (not shown) for transferring mechanical power from corresponding mechanical, pneumatic or hydraulic actuators located inside the module 536 to the rest of the submersible assembly. These may be used, for example to adjust the anchoring system of the submersible assembly, or to control the variable buoyancy.

Figure 6 shows a sectional view through the central pontoon of the embodiment of a submersible assembly 600, as shown in Figures 2 and 4. The buoyancy devices 628 and vertical end supports are visible 630, as is a turbine 616. The central pontoon 634 is shown with the centralised onboard control module 636 mounted in a recess. As discussed above, the mounting of the module may be permanent, or it may be removable for repair or replacement purposes. This arrangement is purely exemplary, and the control module 636 may be recessed in a different location, or even to the exterior of the assembly, depending on the desired outcome.

Claims

1. A submersible turbine assembly having: a support structure; and a first turbine system, supported by the support structure, the first turbine system having a centre of mass and being pivotally connected to the support structure so that the first turbine system is rotatable, relative to the support structure, about a centre of rotation; wherein the first turbine system includes a first flowing-water driveable turbine for generating power from water flow, the first turbine having an operational axis, and being designed for optimum power output when local water flow is aligned with the operational axis; and wherein the centre of rotation is spaced away from the centre of mass of the first turbine system in a direction parallel to the operational axis of the turbine.

2. A submersible turbine assembly having: a support structure; and a first turbine system, supported by the support structure, the first turbine system being rotatable relative to the support structure; wherein the first turbine system includes a first flowing-water driveable turbine for generating power from water flow, the first turbine having an operational axis, and being designed for optimum power output when local water flow is aligned with the operational axis; and wherein the first turbine system is mounted so as to rotate about a horizontal axis relative to the support structure in response to local water flow so that it brings the operational axis of the first turbine towards alignment with the direction of local water flow.

3. A submersible turbine assembly according to claim 2, wherein: the first turbine system has a centre of mass and is pivotally connected to the support structure so that the first turbine system is rotatable about a centre of rotation; and wherein the centre of rotation is spaced away from the centre of mass of the first turbine system in a direction parallel to the operational axis of the turbine.

4. The submersible turbine assembly of any preceding claim, wherein the first turbine system is rotatable independently of the parts of the support structure to which the first turbine system is directly connected.

5. A submersible turbine assembly according to any preceding claim, wherein the first turbine system includes a second flowing-water driveable turbine for generating power from water flow, the second turbine having an operational axis, and being designed for optimum power output when local water flow is aligned with the operational axis; and wherein the operational axes of the first and second turbines are parallel with one another.

6. A submersible turbine assembly according to claim 5, wherein the first turbine system includes a beam connecting the first turbine and the second turbine.

7. A submersible assembly according to claim 6, wherein the first turbine is mounted on one surface of the beam, and the second turbine is mounted on a second, opposing surface of the beam.

8. A submersible turbine assembly according to claim 6 or 7, wherein the beam comprises a hydrodynamic foil having a drag coefficient which varies with orientation, and wherein the turbines are mounted on the hydrodynamic foil so that their operational axes are aligned with the orientation in which the drag coefficient of the hydrodynamic foil is at a minimum.

9. A submersible turbine assembly according to any preceding claim, wherein each turbine has a fairing to reduce hydrodynamic drag.

10. A submersible turbine assembly according to any preceding claim, wherein each turbine has a fairing having a drag coefficient which varies with orientation, and is lowest in the orientation which is aligned with the operational axis of the turbine.

11. A submersible turbine assembly according to any preceding claim, wherein the support structure comprises a platform, and the first turbine system is spaced away from the platform by supports around which the first turbine system can rotate about an axis generally parallel to the plane of the platform.

12. A submersible turbine assembly according to claim 11, wherein the first turbine system is supported above the platform.

13. A submersible assembly according to claim 11 or 12, wherein the first turbine system is arranged to rotate in response to changes of local water flow so that the turbine blades rotate away from the platform.

14. A submersible assembly according to any preceding claim, further comprising an actuator to rotate the first turbine system.

15. A submersible assembly according to any preceding claim, further comprising a brake to resist the rotation of the first turbine system.

16. A submersible turbine assembly according to any preceding claim, further comprising a second turbine system, supported by the support structure, the second turbine system having a centre of mass and being pivotally connected to the support structure so that the second turbine system is rotatable, relative to the support structure, about a centre of rotation; wherein the second turbine system is of the same design, and is connected to the support structure in the same way, as the first turbine system.

17. A submersible assembly according to any preceding claim, wherein the submersible assembly is positively buoyant in water, and is anchored to a water bed, so that the assembly is held in a state of floating equilibrium.

18. A submersible assembly according to any preceding claim, wherein the submersible assembly is variably buoyant in water.

19. A submersible turbine assembly for generating power from water flow, having: a centralised onboard control module for providing control signals to the submersible turbine assembly, wherein the control module comprises a watertight dry space containing electronic control systems.

20. The submersible turbine assembly of claim 19, wherein the onboard control module is removably coupled to the assembly.

21. The submersible turbine assembly of claim 19 or 20, wherein the onboard control module further contains hydraulic actuation systems.

22. The submersible turbine assembly of any of claims 19 to 21, wherein the onboard control module further contains mechanical actuators for providing mechanical motive power to the submersible turbine assembly.

23. The submersible turbine assembly of any one of claims 19 to 22, wherein the onboard control module further contains power transfer systems for transferring power generated by the turbine assembly to an external location.

24. A submersible turbine assembly for generating power from water flow, the submersible turbine assembly being positively buoyant in water, and arranged to be anchored to a water bed, the submersible turbine assembly having: a support structure for mounting turbines, comprising a plurality of hollow, watertight trusses.

25. A submersible turbine assembly according to claim 24, wherein the hollow trusses have a variable buoyancy.

26. A submersible turbine assembly according to claim 25, wherein the buoyancy of the hollow trusses is variable by selectively flooding their hollow spaces.

27. A submersible turbine assembly according to any of claims 24 to 26, wherein the hollow trusses have a fairing to reduce hydrodynamic drag.

28. A submersible turbine assembly according to any of claims 1 to 18, further having the centralised onboard control module of claims 19 to 23 and/or the support structure of claims 24 to 27.

29. A submersible turbine assembly substantially as herein described, and as illustrated in the accompanying figures.