SUBMERSIBLE POWER PLANT FOR PRODUCING ELECTRICAL POWER

Abstract

A submersible power plant and a method for providing a submersible power plant. The submersible power plant includes an anchoring provided at a minimum depth and a vehicle including at least one wing. The vehicle is arranged to be secured to the anchoring of at least one tether rotatably attached to the anchoring by an anchoring coupling and attached to the vehicle by at least one vehicle coupling. The submersible power plant is completely submerged in a body of fluid both during operation and non-operation of the submersible power plant and the tether has an unextended tether length between 2-20 times a wingspan of the wing, specifically between 3-12 times the wingspan of the wing, more specifically between 5-10 times the wingspan of the wing.

Claims

1.-15. (canceled)

16. Submersible power plant for producing electrical power, the submersible power plant comprising an anchoring provided at a minimum depth Dmin and a vehicle comprising at least one wing, the vehicle being arranged to be secured to the anchoring by means of at least one tether rotatably attached to the anchoring by means of an anchoring coupling and attached to the vehicle by means of at least one vehicle coupling, the vehicle being arranged to move in a predetermined trajectory by means of a fluid stream passing the wing during operation of the submersible power plant, the vehicle being arranged to stay in a position essentially above the anchoring during non-operation of the submersible power plant, wherein the submersible power plant is completely submerged in a body of fluid both during operation and non-operation of the submersible power plant and wherein the tether has an unextended tether length between 2-20 times a wingspan of the wing, specifically between 3-12 times the wingspan of the wing, more specifically between 5-10 times the wingspan of the wing, characterized in that the tether is releasably attached to an anchoring coupling arranged to be releasable from the anchoring, wherein the anchoring coupling is movably attached to an anchor line running from the anchoring to a surface of the body of fluid, such that the anchoring coupling and tether can be brought to and from the surface, and in that the anchoring coupling is buoyant.

17. Submersible power plant according to claim 16, wherein the anchoring is a foundation arranged on a seabed, lake bed or stream bed.

18. Submersible power plant according to claim 16, wherein a part of the tether comprises an element that is arranged to change or arranged to allow change of the distance between the anchoring and the vehicle during operation of the submersible power plant.

19. Submersible power plant according to claim 18, wherein the element makes up between 5-15% of the tether length.

20. Submersible power plant according to claim 18, wherein the element comprises one or more of: a spiral or coil spring, a disk spring stack, an elastomer spring or a gas spring.

21. Submersible power plant according to claim 16, wherein at least one turbine connected to a generator is attached to the wing of the submersible power plant for power generation during operation of the submersible power plant.

22. Submersible power plant according to claim 16, wherein the vehicle is arranged to move with a varying speed or essentially the same speed over the predetermined trajectory during operation of the submersible power plant.

23. Method for providing a submersible power plant for producing electrical power, the submersible power plant comprising an anchoring and a vehicle comprising at least one wing, the vehicle being arranged to be secured to the anchoring by means of at least one tether rotatably attached to the anchoring by means of an anchoring coupling and attached to the vehicle by means of at least one vehicle coupling, the vehicle being arranged to move in a predetermined trajectory by means of a fluid stream passing the wing during operation of the submersible power plant, the vehicle being arranged to stay in position essentially above the anchoring during non-operation of the submersible power plant, wherein the method comprises: providing an anchoring at a minimum depth Dmin in a body of fluid, attaching a tether to the anchoring, the tether being connected to the vehicle, providing the tether with a buoyant anchoring coupling releasably attached to the anchoring. providing the anchoring with an anchor line to which the anchoring coupling is movably attached, wherein tether has an unextended tether length such that the submersible power plant is completely submerged in the body of fluid during operation and non-operation of the submersible power plant and the unextended tether length is between 2-20 times the wingspan of the wing, specifically between 3-12 times the wingspan of the wing, more specifically between 5-10 times the wingspan of the wing.

24. Method according to claim 23, wherein the method further comprises: providing an anchoring by providing a foundation on a seabed, lake bed or stream bed.

25. Method according to claim 23, wherein the method further comprises: providing a tether having a part that comprises an element that is arranged to change or arranged to allow change of the distance between the anchoring and the vehicle during operation of the submersible power plant.

26. Method according to claim 23, wherein the method further comprises: providing the vehicle with at least one turbine attached to the wing of the vehicle connected to a generator for power generation during operation of the submersible power plant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 schematically shows a submersible power plant according to the invention during operation,

[0039] FIG. 2 schematically shows a submersible power plant according to the invention, during non-operation,

[0040] FIG. 3 schematically shows the relation between tether length and the wingspan of the wing.

DETAILED DESCRIPTION

[0041] One reason behind selecting tether length depending on the wingspan of the wing is as follows. A deeper installation depth allows for larger vehicles, i.e. larger wingspans of the wing. When planning for an installation of an array of submersible power plants, water depths suitable for a given rated submersible power plant is first looked for. For an Island Mode installation (or islanding) of say a 200 kW unit, the flow characteristics at an installation site first determine the wingspan of the wing. An area in this site with sufficient water depth is then located. The anchoring can be installed at a suitable depth and can be for instance installed in a foundation placed directly in the seabed, an elevated foundation, at a local underwater peak or to an intermediate mooring in the water column somewhere for the vehicle to attach to.

[0042] Smaller vehicles can be installed also at deeper depths, but it is preferable to have the vehicle operating as close to the surface as allowed by local or global regulations, as the flow velocity is often higher in this part of the water column.

[0043] FIG. 1 schematically shows a submersible power plant 1 according to the invention during operation. The submersible power plant 1 comprises an anchoring 2 and a vehicle 3 comprising at least one wing 4. The vehicle is arranged to be secured to the anchoring 2 by means of at least one tether 5. The vehicle 3 is arranged to move in a predetermined trajectory 6 by means of a fluid stream 7 passing the wing 4 during operation of the submersible power plant.

[0044] When the vehicle 3 of the submersible power plant 1 is placed in a fluid stream 7, the fluid stream 7 moves over the wing 4 and creates lift. This causes the wing 4 to move due to the pressure differences between the different sides of the wing 4. The fluid stream 7 can for instance be a tidal stream or an underwater ocean current. By using one or more control surfaces 8, the wing 4 can be made to move along the predetermined trajectory 6. The control surfaces 8 can for instance be a rudder, ailerons, elevators, spoilers or any combination of ailerons, elevators, spoilers and rudders. In FIG. 1, the predetermined trajectory 6 is a figure-8 trajectory. The predetermined trajectory 6 can also be round, oval or other closed trajectories.

[0045] As can be seen from FIG. 1, the submersible power plant 1 is completely submerged in a body of fluid 9 during operation. With operation is meant that the vehicle 3 moves along the predetermined trajectory 6. In FIG. 1, a tether length L is shorter than a depth Dmin of the body of fluid 9 at an installation site. Both the depth Dmin and the tether length L are measured from a point where the tether 5 is attached to the anchoring 2. Dmin is determined by for instance license requirements (if any) for distance to surface (shipping lanes, diving birds or any other requirements) and other site parameters, such as wave conditions for example.

[0046] FIG. 1 is not necessarily to scale and is intended to illustrate the principle behind the disclosure. That the submersible power plant 1 is completely submerged means that there is always a minimum clearance depth d between the vehicle 3 and a surface 10 of the body of fluid. The condition of being completely submerged is fulfilled also during non-operation and at low tide. Non-operation means that the vehicle 3 is not moving along the predetermined trajectory 6. Non-operation can arise from a too low stream velocity, for instance when the direction of the tide changes or due to other conditions that prevents the vehicle from moving along the predetermined trajectory. The vehicle 3 may still move during non-operation as it can turn during rising and falling tides and vice versa. The clearance depth d varies and are is in some cases determined by national or international regulations. Present examples vary from between 5 meters for installation sites without shipping lanes passing overhead to 20 to installation sites with shipping lanes passing overhead.

[0047] The wing 4 of the vehicle 3 may in one aspect be equipped with at least one turbine 11 connected to a generator 12. The movement of the vehicle 3 through the fluid, powered by the fluid stream 7, causes the turbine 11 and generator 12 to rotate, thereby generating power during operation of the submersible power plant 1. The wing 4 of the vehicle 3 may be equipped with more than one turbine 11/generator 12 configuration. A turbine 11/generator 12 configuration may be attached to an upper side 13 of the wing 4 or a lower side 14 of the wing 4. The wing 4 of the vehicle 3 may comprise at least one nacelle 15 in which the turbine 11 and generator 12 can be housed. Parts of the systems can alternatively be built into the wing while a keel pod houses the turbine/generator only. Also the turbine/generator can be built into the wing.

[0048] The vehicle 3 also comprises struts 16 attaching the tether 5 to the anchoring 2. The anchoring can be positioned at a depth Dmin with the anchoring being attached to the seabed by means of for instance a chain, a second tether or similar. The anchoring 2 can also be a foundation positioned on a bottom surface 17 such as a sea bed, lakebed or stream bed. The foundation is in such case preferably fixed or secured in place.

[0049] The vehicle 3 may further be arranged to move with a varying speed or essentially the same speed over the predetermined trajectory 6 during operation. This enables control of dynamic forces acting on the various parts of the submersible power plant 1. This is controlled by operating the one or more control surfaces 8. Alternatively, adjusting the position of one or more of the struts or adjusting the turbine speed can be used to control the speed of the vehicle.

[0050] A part of the tether 5 may comprise an element 18 that is arranged to change or arranged to allow change of the distance between the anchoring 2 and the vehicle 3. In tethers without an element, the distance between the vehicle 3 and the anchoring 2 changes due to that the tether 5 is exposed to various tensile loads over the predetermined trajectory 6. The variation in tensile loads has a quadratic relation to the speed of the wing 4 and thereby of the vehicle 3. This leads to that the tether 5 exhibits elastic lengthening and contraction over the predetermined trajectory 6 thereby changing the distance between the vehicle 3 and the anchoring 2 in an undesirable way as the tether 5 is continuously exposed to stress. The element 18 may be arranged to change or to allow change of the distance between the vehicle 3 and the anchoring 2 continuously over the entire predetermined trajectory 6 or during parts of the predetermined trajectory 6. With to change means that the element 18 is passive but has predetermined features, such as a spring constant which may be dependent on the properties of the submersible power plant 1, the site of the submersible power plant 1 and other design features. To allow change means that the element 18 can be actively controlled so that the distance can be regulated within certain parameters. Both options lead to smoothening of the speed over and/or between different parts of the predetermined trajectory 6. Speed is defined as the magnitude of the velocity of the vehicle 3 as it covers the predetermined trajectory 6.

[0051] Structural limitations set on the vehicle 3 are results of optimizations of product cost and total power output over time. The wing 4 may need to be large and efficient enough to extract/convert appropriate energy amounts during times with low flow speeds. The speed of such a relatively large and efficient wing 4 may then need limitations during times with higher speed flows in order not to exceed such optimized structural limitations.

[0052] A reduction of the amplitude of the variation of the forces acting on the various parts of the submersible power plant 1 is advantageous for e.g. material fatigue reasons. For power production reasons, the cubic relationship between speed and produced power needs to be considered. The power production is largely proportional to the integral of the cube of the speed, i.e. the area under the power curve. By lowering speed when high forces are acting on the vehicle 3 towards a certain average speed, the power production would be lowered to the power of three at those parts of the predetermined trajectory. This would in turn cause a quite significant power production loss. Correspondingly, if the speed dips are elevated towards the same certain average speed, the power production increase at those dips would be much less than the power production lost during the lowered peaks. A constant average speed with lowered amplitude of the speed variation would lead to a lowered power production.

[0053] With an increased average speed, which may be obtainable if the amplitude of the speed variation is decreased and the speed peaks are kept on the same level, an increased power output could be achieved. This would mean no loss of power at the peaks, but increased power production during all other parts of the speed curve. This is valid for spring tides, when peaks may need to be cut. During neap tides when peaks may not need to be cut power output increase would occur during the entire predetermined trajectory 6.

[0054] The speed or force curve may be raised to a higher mean value by means of e.g. a larger wing 4 or by the use of an installation site with higher flow speeds.

[0055] A decrease of the speed variation amplitude by using the element 18 to allow a change in the distance between the vehicle 3 and the anchoring 2 may also facilitate for economically feasible installation on sites with greater variations between neap tides and spring tides than otherwise would be possible if the speed of the vehicle 3 during neap tides can be raised without the peak speeds during spring tides becoming too high.

[0056] The element 18 may make up between 5-15% of the tether length. The element 18 may comprise one or more of: a spiral or coil spring, a disk spring stack, an elastomer spring or a gas spring.

[0057] Further, by connecting a transducer (not shown) to the element 18, electrical energy can be generated from the variation in distance between the vehicle 3 and the anchoring 2 by converting mechanical energy generated by the variation in distance to electrical energy.

[0058] FIG. 2 schematically shows a submersible power plant 1 according to the invention, during non-operation when the anchoring 2 is a foundation provided on a seabed. As mentioned, non-operation means that the vehicle 3 does not move along the predetermined trajectory 6. The vehicle 3 may still move due to movement in the surrounding water, but no power will be produced. The vehicle 3 will be set up with a net buoyant force enabling the submersible power plant 1 to position the tether 5 vertically in slack water conditions when the submersible power plant 1 is installed in a tidal area. The buoyancy is achieved by designing and balancing the weight of the vehicle 3 and tether 5 against available total buoyancy of the entire submersible power plant 1. Alternatively, the submersible power plant 1 can be installed in or near an ocean current. Due to the permanency of motion in the ocean current, the buoyancy of the vehicle 3 can be the same or lower than when installed for tidal power generation.

[0059] The tether 5 and vehicle 3 are in one aspect one assembly which can be installed and recovered as one unit. In another aspect, the tether 5 and the vehicle 3 can also be connected by a joint, coupling or similar located somewhere between the vehicle 3 and the anchoring 2.

[0060] The tether 5 may be equipped with swivelling tether elements (not shown) over parts of or over the entire tether 5 in order to lower drag, protect the cable and/or introduce a net zero lift value on the tether 5 enabling the movement of the vehicle 3 of the submersible power plant 1 to be predictable in no-flow or low flow conditions.

[0061] As seen in FIG. 2, the tether 5 is releasably attached to an anchoring coupling 19. The tether is also rotatably attached to the anchoring 2 by means of the anchoring coupling 19 and attached to the vehicle 3 by means of at least one vehicle coupling (not shown). Alternatives are e.g. connecting the tether to a top joint where the vehicle has two front struts and one rear strut, connecting the tether to a top joint where the vehicle has front struts only, or the tether is connected directly to the nacelle. The anchoring coupling 19 is itself arranged to be releasable from the anchoring 2. The anchoring coupling 19 is temporarily or permanently movably attached to an anchor line 20 running from the anchoring 2 to the surface 10 of the body of fluid 9 in which the submersible power plant 1 is installed. The anchor line 20 runs to the surface 10 by first being run parallel to the bottom surface 17 to a weight 21 that secures or weighs down the part of the anchor line 20 running parallel to the bottom surface 17. From the weight 21, the anchor line 20 runs to the surface such that the anchoring coupling 19 and tether 5 can be brought to and from the surface 10. This ensures that the anchor line 20 does not interfere with the predetermined trajectory 6 during operation of the submersible power plant. Alternatively, the entire anchor line 20 can be kept at or near the bottom surface 17. The anchor line 20 can be released when the vehicle 3 and tether 5 needs to be recovered. Alternatively, a winch on the anchoring 2 or the anchoring coupling 19 can be used to move the tether 5 and/or vehicle 3 to and from the surface 10. Other systems not requiring a permanent line system are also conceivable.

[0062] In the example when the anchoring is at a depth Dmin which is not a seabed, lake bed or stream bed but instead is attached to the seabed far below the anchoring, the anchor line can be kept essentially horizontal and run a distance from the anchoring by means of an anchor line attachment (not shown) that is neutrally buoyant at essentially the same depth as the anchoring or also attached to the seabed far below the anchoring.

[0063] A surface end of the anchor line may be buoyant and may in one aspect comprise a floating marking means 22 in order to locate the anchor line 20 when the tether 5 and vehicle 3 is to be installed or re-installed after maintenance. The floating marking means 22 can for instance be a buoy, a radio transmitter, a visible light transmitter, a GPS marker or similar. A combination of marking means can be used to further simplify the location of the anchor line 20. The anchoring coupling 19 may be connected to the anchoring 2 by means of a winch or line extension to shore.

[0064] The anchoring coupling 19 is in one aspect buoyant. In one aspect, the anchoring coupling 19 comprises a marking means.

[0065] FIG. 3 schematically shows the relation between tether length L and a wingspan W of the wing 4. A tether length L is between approximately 2-20 times the wingspan W of the wing 4, specifically between approximately 3-12 times the wingspan W of the wing 4, more specifically between approximately 5-10 times the wingspan W of the wing 4.

[0066] The tether length L is measured as the distance of the tether 5 between the anchoring coupling 19 and the at least one vehicle coupling on the vehicle 3. The tether 5 normally comprises an attachment point such as a joint, coupling or similar between the tether 5 and the wing 4 of the vehicle 3. The tether length L includes the distance between the attachment point and the lowest point on the lower side 14 of the wing 4 of the vehicle 3.

[0067] The wingspan W of the wing 4 is measured from one wingtip to the other wingtip of the wing 4, i.e. the points of the wing 4 that are furthest from each other when viewing the wing 4 from above. As can be seen in FIG. 3, the wing 4 may comprise winglets 23 in order to reduce drag. The winglets 23 are not included in the measurement of the wingspan W.

[0068] Reference signs mentioned in the claims should not be seen as limiting the extent of the matter protected by the claims, and their sole function is to make claims easier to understand.

[0069] As will be realised, the invention is capable of modification in various obvious respects, all without departing from the scope of the appended claims. Accordingly, the drawings and the description are to be regarded as illustrative in nature, and not restrictive. For instance the vehicle 3 does not necessarily need to be equipped with a turbine 11 for producing electrical energy. Electrical energy can be produced only by means of the transducer attached to the element 18.