A wave power plant and a rotor for use in a wave power plant

Abstract

Disclosed is a wave power plant comprising a frame construction extending in a longitudinal direction and having a rotor shaft extending in the longitudinal direction of the frame construction, a plurality of rocking rotors, the plurality of rocking rotors being arranged rotatably with respect to the frame construction around the rotor shaft each rocking rotor comprising a buoyant body, the buoyant body having a shell, a bearing arranged at the rotor shaft, an interface construction configured to interconnect the buoyant body with the bearing, such that the rocking rotor is rotatably connected to the rotor shaft, wherein, the shell of the buoyant body has a triangular shape having a first side and a second side being first and second convex shaped sides and a third side being a third concave shaped side, the third concave shaped side facing the rotor shaft.

Description

[0001] A WAVE POWER PLANT AND A ROTOR FOR USE IN A WAVE POWER PLANT

[0002] TECHNICAL FIELD

[0003] The invention relates to the field of wave power plants for extracting power from the wave movement of a water surface area, and particularly to wave power plants having a plurality of rotors, such as rocking rotors, and a rotor, such as a rocking rotor for use with a wave power plant.

[0004] BACKGROUND

[0005] Extracting the energy of waves continue to be a field with much development as waves are more predictable and reliable than solar or wind energy, and they could power hard-to-reach locations, like coastal communities and remote islands. Wave power plants are realized in various ways, with some wave power plants utilizing rocking rotors as the method of energy extraction. Rocking rotors provide an alternating movement substantially in a vertical direction as a response to impacting waves. The vertical movement is transformed into a rotational movement when the rocking rotor is mounted to a frame places in a location horizontally displaced with respect to the centre of gravity of the rocking rotor.

[0006] Wave power plants intended for off-shore use face the problem that they need to be able to cope with very harsh marine conditions, i.e. a salty environment, that will increase corrosion, and weather conditions that challenges engineering solutions, through extreme temperature differences and extreme mechanical stress on the construction. Further, the off-shore location may make regular service and maintenance difficult and costly. Yet further, in order to obtain an acceptable energy harvest, relative to the investment of locating and maintain the wave power plant in such hostile environments, wave power plants will need to be rather large structures. The forces acting on such large structures will stress the need for reliable mechanical solutions. Thus there is need for very sturdy, stable solutions for any moving parts on such wave energy plants in order to be placed at off-shore locations. Additionally, the energy harvesting mechanism needs to be as efficient as possible to ensure as high yield as possible for the wave power plant. SUMMARY

[0007] In a first aspect of the present invention, a wave power plant is provided, the wave power plant comprising a frame construction extending in a longitudinal direction and having a rotor shaft extending in the longitudinal direction of the frame construction and a plurality of rocking rotors. The plurality of rocking rotors are arranged rotatably with respect to the frame construction around the rotor shaft. Each rocking rotor comprises a buoyant body. The buoyant body has a shell, a bearing arranged at the rotor shaft, and an interface construction configured to interconnect the buoyant body with the bearing, such that the rocking rotor is rotatably connected to the rotor shaft.

[0008] In a second aspect of the present invention, a rocking rotor for use in a wave power plant is provided, the rocking rotor comprising a buoyant body having a shell, a bearing configured to be arranged at a rotor shaft, and an interface construction configured to interconnect the buoyant body with the bearing.

[0009] In some embodiments, the shell of the buoyant body has a triangular shape, such as a substantially triangular shape, having a first side and a second side being first and second convex shaped sides and a third side being a third concave shaped side, the third concave shaped side facing the rotor shaft. The shell of the buoyant body may have two convex sides and one concave side.

[0010] In some embodiments, the shell of the buoyant body has an opening around the rotor shaft, wherein the opening may be configured to tangentially touch the water surface, when the rocking rotor is placed in the operational position in the water, and wherein the shell with the opening does not enclose the rotor shaft.

[0011] In some embodiments, a cross-section of the shell of the buoyant body may have a perimeter P, which does not enclose the rotor shaft.

[0012] The shell of the buoyant body may have two end faces.

[0013] In some embodiments, the third side of the triangular shaped shell is configured to be submerged in water when the rocking rotor is positioned in the intended operational position in the wave power plant. In some embodiments, the concave shaped third side is shaped as an arc of a circle, such as shaped as a part of a circumference of a circle. The concave shaped third side may be configured to tangentially touch the water surface when the rocking rotor is placed in the intended operational position in the water.

[0014] In some embodiments, at least a cross section of the shell of the buoyant body has a triangular shape.

[0015] It is an advantage of providing a rocking rotor as described herein, in that the mass or weight of the part of the rocking rotor configured to be submerged in water when the rocking rotor is positioned in the intended operational position in the wave power plant may be minimized. By the rocking rotor according to the present disclosure, the weight of the rocking rotor is optimized so that a buoyancy index of the rocking rotor may be significantly decreased over conventional rocking rotors having a larger mass configured to be submerged. Decreasing the buoyance index of the rocking rotor may lead to an increased overall efficiency of the rocking rotor which in turn may lead to a higher nominal power output of the wave energy plant. This is particularly relevant for a rocking rotor configured to be positioned in an area of the ocean in which the wave behaviour is characterized by shorter wave periods, and / or where the wave behaviour is characterized by having a shifting or dynamic wave behaviour. The wave period being the time between arrival of consecutive crests at a stationary point.

[0016] Having a reduced buoyant mass configured to be submerged may improve the efficiency of the energy yield of the rocking rotor in that the inertia, i.e. the mass inertia, is reduced. Hereby, the rocking rotor will provide a faster response to the force of an incoming wave, or in other words, the inertia that an incoming wave needs to overcome for setting the rocking rotor in motion is smaller, and the responsiveness of the rocking rotor may hereby be increased. Thus, having a more dynamic and more responsive rocking rotor, may ultimately result in a higher energy yield of incoming waves. This is particularly relevant in areas where the wave period is fairly short, such as below 10 seconds, such as below 15 seconds. Such wave periods are often found in e.g. the North Sea. The wave power plant comprising a frame construction extending in a longitudinal direction and having a rotor shaft extending in the longitudinal direction of the frame construction provides a scalable wave power plant design which is capable of operation during strong wind and tall waves. The rotor shaft in the frame construction may create a foundation for the rocking rotors to be installed while ensuring a common axis of rotation. In some embodiments, the shaft is uniform and parallel to the frame construction in the longitudinal direction, but may alternatively be non-parallel.

[0017] In some embodiments, the plurality of rocking rotors are arranged rotatably with respect to the frame construction around the rotor shaft. In some embodiments, the frame construction may comprise a mounting point for a rocking rotor comprising an individual shaft.

[0018] The wave power plant may be arranged so that the frame construction is parallel to the direction of impacting waves, the wave power plant may also be arranged so that the frame construction is perpendicular to the direction of impacting waves.

[0019] The wave power plant may be arranged at an angle of between 0° - 90° with respect to the impacting waves.

[0020] It is an advantage, that the rotor shaft provides a common centre of rotation, as it ensures that each rocking rotor of the plurality of rocking rotors arranged rotatably around the rotor shaft experience little to no stress due to impacting sea waves, when the rotor shaft is arranged in parallel to the direction of the waves, and little to no wake effect from adjacent rocking rotors, when the rotor shaft is arranged perpendicular to the impacting waves.

[0021] Each rocking rotor comprises a buoyant body. The buoyant body has a shell. In some embodiments, the shell of the buoyant body corresponds to a surface part of the buoyant body. The buoyant body, and / or the shell of the buoyant body, may be made of any material capable of withstanding the rough environment of the open sea and saline water conditions. The buoyant body, and / or the shell of the buoyant body may comprise metal, such as in steel, such as in stainless steel, the buoyant body, and / or the shell of the buoyant body, may comprise concrete, such as reinforced concrete, the buoyant body, and / or the shell of the buoyant body, may comprise a composite material, such as in a reinforced composite material, the buoyant body, and / or the shell of the buoyant body, may comprise carbon fibre, glass fibre, polymeric material, thermoplastics, etc. In some embodiments, the buoyant body comprises a buoyant material, such as a foam, such as a polystyrene foam, such as Styrofoam, enclosed air, etc. In some embodiments a foam core may be coated with coating, such a polyurethane, an epoxy, etc.

[0022] The plurality of rocking rotors are via the bearing arranged rotatably with respect to the frame construction around the rotor shaft, such that the rocking rotor is rotatably connected to the rotor shaft. The buoyant body preferably enables the rocking rotor to float independently, so that the rocking rotor may rock with the waves.

[0023] In some embodiments, the shell of the buoyant body has a smooth surface, so as to minimize the resistance of the shell when the buoyant body rocks with the waves.

[0024] The shell of the buoyant body may comprise an outer layer such as a layer for antifouling purposes e.g. anti-fouling paint, biocides, or alternatively coatings such as Teflon coatings or silicone coating. The outer layer may alternatively be a surface of the shell which has anti-fouling capabilities.

[0025] Hereby, growth of marine life, such as e.g. barnacles, may be reduced or inhibited, allowing an improved performance of the rocking rotor over time, as any growth of marine life would impact the hydrodynamic performance of the rocking rotor. For example, growth of marine life could alter the surface of the shell, so that the surface of the shell of the buoyant body could become more rough increasing the resistance when moving through water. For example, growth of marine life could alter the weight of the shell and thereby alter how deep the rocking rotor would sit in the water, that is the draft of the rocking rotor could be altered.

[0026] The buoyant body has a bearing arranged at or configured to be arranged at the rotor shaft, and an interface construction configured to interconnect the buoyant body with the bearing such that the rocking rotor is rotatably connected to the rotor shaft. The bearing ensures that the rocking rotor can rotate with respect to the frame construction around the rotor shaft. The bearing may be any type of bearing, e.g. journal bearings, sleeve bearings, ball bearings, roller bearings, plain bearings, fluid film bearing, magnetic bearings, etc. Typically, bearings capable of withstanding the harsh open sea environment are preferred. Each rocking rotor may have a single bearing. In some embodiments, each rocking rotor has a plurality of bearings, such as two bearings, such as four bearings.

[0027] The interface construction interconnects the buoyant body, such as in some examples the shell of the buoyant body, with the bearing, whereby the rocking rotor may rotate about the rotor shaft.

[0028] In some embodiments, the interface construction comprises one or more spokes, the spokes may have any thickness sufficient to withstand the forces likely to be impressed on the interface construction during operation. In some embodiments, the interface construction comprises one or more sheets, such as sheets in the form a full disc, such as in the form of a part of a disc.

[0029] In some embodiments, the interface construction may be made with a combination of sheets and spokes. The interface construction may be a part fixated to the shell and bearing, but may also be formed as a part of the shell, e.g. as an extension of the shell.

[0030] In some embodiments, the shell of the buoyant body has triangular shape, such as a substantially triangular shape, having two convex sides and one concave side. The concave side may be configured to face the rotor shaft. The interface construction may extend between the concave side and the rotor shaft with the bearing in the first aspect. The interface construction may extend between the concave side and the bearing configured to be mounted at the rotor shaft in the second aspect.

[0031] In some embodiments, the rocking rotor is configured so that the concave side of the shell of the buoyant body may tangentially touch the water surface, when the rocking rotor is placed in the operational position in the water.

[0032] Typically, rocking rotors have been more or less egg shaped with a pointed top and a through hole to accommodate a rotor shaft. Such prior rocking rotors had a quite significant mass being provided below the water surface when such rocking rotors were place in the operational position in the water.

[0033] It is an advantage of providing rocking rotors with two convex sides and a concave side, such as a concave side facing the rotor shaft that a mass of the rocking rotor below the water surface when the rocking rotor is place in the operational position in the water, may be significantly reduced.

[0034] Hereby, the buoyant body have a reduced buoyant mass under the water surface, thereby reducing an inertia, such as a mass inertia, of the rocking rotor, effectively increasing the responsiveness of the buoyant body with respect to the incoming waves and the variations in sea conditions, waves and wave behaviour. Thus, an efficiency of the rocking rotor may be improved.

[0035] In some embodiments, the shell of the buoyant body is configured so as not to enclose the rotor shaft. The shell of the buoyant body may be configured so as to enclose less than 180 degrees of a circumference of the rotor shaft, such as less than 120 degrees of a circumference of the rotor shaft.

[0036] In some embodiments, the width of the rocking rotor is at least 2 meters, such as at least 3 meters, such as 4.5 meters in diameter. The width may be equal to the overall width of the concave side of the triangular shaped buoyant body.

[0037] The length of the rocking rotor in the longitudinal direction of frame construction may be at least 2 meters, such as at least 3.5 meters, such as 5.3 meters.

[0038] The present inventor has found that even when the shape of the shell of the buoyant body is not egg formed, as for the prior art rocking rotors, but has a triangular shape with two convex sides and a concave side of the shell facing the center of rotation of the rocking rotor, the rocking rotor may experience less friction during rotation due to decreased water resistance below the water surface. In that the mass of the buoyant body below the surface is reduced also a torque in the opposite direction than the direction of rotation of the rocking rotor may be reduced, while at the same time maintaining buoyant mass generating a torque in the direction of rotation. In some embodiments, the two convex sides, first and second sides, of the shell are joined at a top vertex of the triangle. The bottom end of the convex sides may be tapered, accommodating the concave third side of the triangle. In some embodiments, the bottom end of the first and or second convex side of the shell may be arranged to be in line with the centre of the rotor shaft.

[0039] In some embodiments, the first and second sides of the triangular shaped shell may be symmetrical. The first and second sides of the triangular shaped shell may be symmetrical about a first axis of the rocking rotor, the first axis extending through the top vertex of the triangle and a center point of the third concave side of the triangle.

[0040] In some embodiments the rocking rotor is configured so as to obtain a specified resonance frequency of the rocking rotor . The rocking rotor may also be configured so that the eigenfrequency of the rocking rotor matches the wave period of approaching waves.

[0041] It is an advantage that the eigenfrequency of the rocking rotor matches the wave period of impacting waves. A rocking rotor with an eigenfrequency matching the wave period of incoming waves will have an improved response , as the rocking rotor will be impacted with constructive interference. For example, if the eigenfrequency of the rocking rotor matches the wave period of the incoming waves then the rocking rotor may have rocked back, such as rocked substantially back, to the resting position after having been impacted by a first wave, at the time when a second wave arrives and impacts the rocking rotor, allowing for a maximized range of motion for the rocking rotor.

[0042] Additionally, it is advantageous if the rocking rotor is configured so as the eigenfrequency of the rocking rotor is located at the shaft of the rocking rotor.

[0043] In one or more embodiments of the invention, each rocking rotor is configured to have a floating rest position, in which the first axis of the rocking rotor forms an angle in the range of 25° to 70°, such as in the range of such as 30 to 60°, such as between 40° to 50°, such as about 45°, with respect to a vertical plane, such as a calm-water surface of the water, when the rocking rotor is provided in the intended operation position in the water. By assuming such an asymmetric rest position, the range of motion of the rocking rotor in one direction from the floating rest position upon being impacted by a wave may be optimized.

[0044] The rocking rotor may be angled, so that the angle of the first axis relative to a vertical surface, e.g. relative to a calm-water surface of the water, the rocking rotor may be angled vertically upwards to minimize waves passing over the rocking rotor, but also angled sufficiently in the horizontal direction to have an optimal range of motion.

[0045] In one or more embodiments of the invention, each rocking rotor comprises driving elements for harvesting the power generated by the rocking motion of the rocking rotor. The driving element may comprise a rotor wheel driving element, such as a rotor drive wheel, a rack and pinion type driving element, a magnetic type driving element, etc.

[0046] In some embodiments, each rocking rotor comprises a rotor drive wheel, the rotor drive wheel being fixedly connected to buoyant body.

[0047] The rotor drive wheel may transfer the mechanical energy generated by the buoyant body of the rocking rotor, for example to a drive shaft. The rotor drive wheel is preferably of a circular shape with a centre placed in the centre of rotation of the rocking rotor. The rotor drive wheel may alternatively be a half circle or a sector with two radii and a corresponding arc, preferably arranged so that the centre of the arc corresponds to the centre of the circumference of an arc of the concave shaped third side of the shell of the buoyant body. The length of the arc may be arranged to be of a similar size as the third side of the shell, , but may alternatively be larger or smaller.

[0048] The rotor drive wheel may be arranged at either end of the buoyant body of the rocking rotor, one or more rotor drive wheels may be connected to the buoyant body. In some embodiments, one or more rotor drive wheels may be distributed along the longitudinal axis of the rocking rotor.

[0049] In one or more embodiments of the invention, the drive wheel is rotatably interconnected to the rotor shaft via the bearing. The drive wheel interconnected to the rotor shaft via the bearing may reduce the stress of the buoyant body of the rocking rotor. The rotor shaft may aid the buoyant body in supporting the rotor drive wheel, which may result in a more buoyant and lightweight rocking rotor. The bearing may be the bearing that interconnects the buoyant body of the rocking rotor with the shaft, but may also be a separate bearing, such separate bearing may be of the same type or a different type of the bearing that interconnects the buoyant body of the rocking rotor with the shaft.

[0050] In some embodiments, the rotor drive wheel is interconnected to the frame construction via a drive shaft.

[0051] The rotor drive wheel may drive a drive shaft using e.g. wires, chains or preferably belts. The drive shaft functions as a common point for collection of mechanical energy generated by each rocking rotor so that the energy can be transformed into electrical energy simultaneously for a plurality of rocking rotors. The frame construction may have a single shaft, but may also have a plurality of shafts, each covering an individual number of rocking rotors that may and may not be identical.

[0052] In some embodiments , one or more of the plurality of rocking rotors comprises one or more ballast(s).

[0053] Providing a ballast within the rocking rotor may move the centre of gravity of the rocking rotor so that the rocking rotor is hereby configured to obtain a preferred angle with respect to a horizontal plane when placed in water. The ballast may comprise sand, concrete, metal, such as steel, such as stainless steel, such as iron or lead, the ballast may be in the form of liquid tanks, such as sea-water tanks, fresh-water tanks or oil tanks, or any combination of all of the above mentioned ballasts. The one or more ballast(s) may have a fixed mass, or a variable mass e.g. a liquid tank which may deposit and receive liquid. A ballast with a variable mass may be advantageous as the eigenfrequency, or natural frequency, of the rocking rotor may be modified by varying the mass of the ballast to match the requirements in locations with varying weather and sea conditions. In some embodiments , the one or more ballast(s) are arranged in the buoyant body of one or more of the plurality of rocking rotors.

[0054] The one or more ballast(s) may be arranged in the buoyant body. The one or more ballast(s) in the buoyant body may form a part of the shell, the one or more ballast(s) may be provided within the shell of the buoyant body, or the one or more ballast(s) may be provided as a combination. Having the ballasts as a part of the buoyant body ensures a steady mass of each means of ballast. The ballast within the shell of the buoyant body may be fixed at specified locations within or at the shell of the buoyant body. In some embodiments, the ballast forms part of the shell of the buoyant body.

[0055] In some embodiments, the one or more ballast(s) arranged in the buoyant body are arranged opposite of the top part.

[0056] One or more ballast(s) may be arranged opposite of the top part. The one or more ballast(s) may be arranged at the lower end of the shell of the buoyant body, such as closer to the third concave shaped side of the shell than to the top part, such as at one tapered end or both tapered ends of the buoyant body. A ballast in a tapered end of the buoyant body, such as tapered end adjacent to the third concave shaped side of the shell, may move the centre of gravity of the rocking rotor towards the tapered end in question. Such a ballast may be combined with a ballast positioned at an opposite tapered end adjacent to the third concave shaped side of the shell in order to move the centre of gravity in a desired direction between the two tapered ends. One tapered end of the shell may comprise a larger ballast than the opposing tapered end of the shell in order to primarily move the centre of gravity in a direction aimed at the tapered end of the shell comprising the heavier ballast.

[0057] In some embodiments, one or more ballast(s) arranged in the buoyant body are arranged substantially along one of the two convex sides of the body.

[0058] The ballast may be arranged as close to the top part of the rocking rotor as possible, providing a maximized torque generated by the ballast on the shaft with a minimized weight. In one or more embodiments of the invention, the wave power plant comprises one or more generator(s) arranged in the frame construction, and at least one drive shaft interconnected with the rocking rotor and one or more of the generator(s).

[0059] The wave power plant may comprise one or more generators configured to transfer the mechanical energy generated by one or more rocking rotors of the wave power plant to another energy form. The generators may be any type of generator e.g. an induction generator, a synchronous generator or a permanent magnet generator. The synchronous generator may have a voltage supply connected to the rotor windings of the synchronous generator to excite the rotor of the synchronous generator. The voltage supply may be variable. A variable excitation of the rotor windings is advantageous for controlling the rotor angle of the synchronous generator wheel

[0060] In some embodiments , at least one drive shaft is interconnected with the rocking rotor via a free-running mechanism.

[0061] By interconnecting the driver shaft with the rocking rotor via a free-running mechanism, the drive shaft may absorb torque in one direction only so that the drive shaft only rotates in one direction. The direction may be clockwise or counterclockwise. The free-running mechanism may interconnect the drive shaft with the driving elements, such as with the rotor drive wheel. The free-running mechanism may be arranged above the surface of the water, providing a simpler and more robust mechanism.

[0062] In some embodiments, a unidirectional gearbox may be implemented as an alternative to the free-running mechanism. Hereby energy may be harvested from the rocking rotor in both directions of rotation with a single rotor drive wheel.

[0063] In one or more embodiments of the invention, the free-running mechanism may be active when the rocking rotor is in an upwards movement or downwards movement, or in a combination of both. The free running-mechanism may be configured to provide a torque to the drive shaft during upwards rotation the rocking rotor due to the buoyancy of the rocking rotor, or the free running-mechanism may be configured to provide a torque to the drive shaft during downwards rotation of the rocking rotor due to gravity.

[0064] The free-running mechanism may alternatively provide a torque to the drive shaft for both the upwards and downwards rotation of the rocking rotor, e.g., when at least two or more means for transferring torque from the rotation of the rocking rotor is present. At least one of the means for transferring torque from the rotation of the rocking rotor may provide a torque with an opposite direction than the other means for transferring torque.

[0065] In some embodiments, the frame construction comprises a first frame construction and a second frame construction adjourned in a rotating joint, and an actuating means for arranging the first frame construction and second frame construction in an angle 0 in a horizontal direction, wherein the actuating means is arranged to modify the angle 0 between an angle of 0° - 180°, such as 45° - 135°.

[0066] A wave power plant having a frame construction with two arms and a variable angle O between the arms provides a flexible wave power plant. The angle between the arms may be lowered during harsh sea conditions. Lowering the angle of the two arms may reduce the stress on the wave power plant, and especially on an anchoring point or grid connection on the wave power plant. The wave power plant may also increase the angle to a maximum angle of 180° for a maximized power generation.

[0067] In some embodiments, the wave power plant comprises a first frame construction extending in a longitudinal direction a first set of rocking rotors provided along a first rotor shaft extending in the longitudinal direction along a first side of the frame construction, a second set of rocking rotors provided along a second rotor shaft extending in the longitudinal direction along a second side of the frame construction.

[0068] Providing a frame construction having two sets of rocking rotors provided at each side of the frame construction extending in the longitudinal direction, allows for a more compact design of the wave power plan, which again allows for re-use, or common use of further components for both sets of rocking rotors. Additionally, one service bridge provided at the frame construction may service both the first set of rocking rotors and the second set of rocking rotors.

[0069] In a second aspect the present invention is a method of generating electrical power using a wave power plant according to the first aspect of the invention.

[0070] The present invention relates to different aspects including the wave power plant and the rocking rotor described above and in the following, and corresponding system parts, methods, devices, systems, kits, uses and / or product means, each yielding one or more of the benefits and advantages described in connection with the first mentioned aspect, and each having one or more embodiments corresponding to the embodiments described in connection with the first mentioned aspect and / or disclosed in the appended claims.

[0071] BRIEF DESCRIPTION OF THE DRAWINGS

[0072] The above and other features and advantages will become readily apparent to those skilled in the art by the following detailed description of exemplary embodiments thereof with reference to the attached drawings, in which:

[0073] Fig. 1 shows a rocking rotor according to an aspect of the present invention.

[0074] Fig. 2a-b show a rocking rotor with tapered ends,

[0075] Fig. 3 in a perspective view, shows a rocking rotor comprising a rotor drive wheel, Fig. 4 shows a rocking rotor according to an aspect of the present invention comprising a rotor drive wheel interconnected with a drive shaft with a belt,

[0076] Fig. 5 shows a rocking rotor comprising a rotor drive wheel and a ballast in each tapered end,

[0077] Figs. 6a-k show different views of a rocking rotor comprising a rotor drive wheel, Fig. 7 shows a rocking rotor with plates configured as the interface construction, Fig. 8 shows a perspective view of a wave power plant comprising two arms in two different configurations,

[0078] Figs. 9a-b show a rocking rotor with and without ballast. DETAILED DESCRIPTION

[0079] Various embodiments are described hereinafter with reference to the figures. Like reference numerals refer to like elements throughout. Like elements will, thus, not be described in detail with respect to the description of each figure. It should also be noted that the figures are only intended to facilitate the description of the embodiments. They are not intended as an exhaustive description of the claimed invention or as a limitation on the scope of the claimed invention. In addition, an illustrated embodiment needs not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments even if not so illustrated, or if not so explicitly described.

[0080] Fig. 1 illustrates an exemplary rocking rotor 1. The rocking rotor 1 comprises a buoyant body 12, the buoyant body 12 having a shell 3, a bearing 7 arranged at the rotor shaft 5 and an interface construction 9 configured to interconnect the buoyant body 12 with the bearing 7, such that the rocking rotor 1 is rotatably connected to the rotor shaft 5. The shell 12 of the buoyant body has a triangular shape having a first side 4 and a second side 4’ being first and second convex shaped sides 4, 4’ and a third side 6 being a third concave shaped side 6, the third concave shaped side 6 facing the rotor shaft 5.

[0081] As is seen, an opening in the shell 3, or the concave shape third side, is configured with a distance d from the centre of the rotor shaft 5 to tangentially touch the water surface 17 (not shown) when the rocking rotor 1 is placed in the operational position in the water. The shell 3 enclose no more than 180 degrees of the circumference of the rotor shaft 5, such as 120 degrees of the circumference of the rotor shaft 5.

[0082] The rocking rotor 1 is configured to maintain an asymmetric operation point, which is described in Fig. 4, facing incoming waves in off-shore locations.

[0083] The asymmetric operation point enables that the rocking rotor 1 to react with a vertical rotating movement around the shaft 5 as incoming waves reaches the rocking rotor 1. The concave shaped third side 6 of the shell 1 will during the rotation of the rocking rotor 1 , be submerged under the water surface and being tangent to the water surface 17. The opening of the shell 3 may be said to be partly enclosed by the shell 3, as two tapered ends 33 are formed in the shell 3 on either side of the opening.

[0084] Preferably, the tapered ends 33 at each side of the opening of the shell 3 only generate a torque in the direction of the rotation of the rocking rotor 3. The tapered ends 33 are preferably formed to have a streamlined hydrodynamic form, so as the water resistance while rotating through the water is minimized.

[0085] The mechanical energy may be harvested with methods such as wires, cylinders, pumps or belts, etc.

[0086] Fig. 2a illustrates a shell 3, wherein a tapered end 33 is formed on each side of the opening of the shell 3, that is the bottom of the convex shaped first and second sides are tapered. The end may be rounded or straight, and it is envisaged that even when a straight or rectangular end face is shown, a rounded end face is preferred to decrease resistance when moving through water. The thickness of the end 33 is preferably kept as small as possible, as a small thickness of the tapered end 33 results in a lower hydrodynamic resistance during rotation of the rocking rotor 1.

[0087] Fig. 2b illustrates a shell 3, wherein the tapered end 33 formed on each side of the opening of the shell 3 has an increased thickness. The thickness of the tapered end 33 illustrated in Fig. 2b provides an increased hydrodynamic resistance, when compared to the example illustrated in Fig. 2a. The face of the tapered end 33 that is placed orthogonally to the direction of rotation of the rocking rotor 1 may be have a rounded shape, but may also be flattened.

[0088] Fig. 3 illustrates an exemplary rocking rotor 1 according to some of the embodiments of the disclosure. The rocking rotor 1 comprises a shell 3, a bearing 7 which is interconnected to a shaft 5 of the frame construction 25 (not shown) with an interface construction 9, and an opening in the shell 3 configured with a distance d from the centre of the shaft 5 to tangentially touch the water surface 17 (not shown) when the rocking rotor 1 is placed in the operational position in the water. The shell 3 of the rocking rotor 1 further comprises a tapered end 33 on each side of the opening.

[0089] Fig. 3 further shows a rotor drive wheel 11 fixated to the shell 3 of the rocking rotor 1 with fixation means 13 and a second interface construction 15 to interconnect the rotor drive wheel 11 to a second bearing 7’ arranged at the shaft 5. The first bearing 7 and the second bearing 7’ can alternatively be the same bearing.

[0090] The rotor drive wheel 11 functions as a means for transferring torque generated by the rocking rotor 1 to a drive shaft 23 connected to a generator 29 by the use of a means for transferring rotational movement, such as a belt 21 .

[0091] Fig. 4 illustrates a rocking rotor 1 comprising a rotor drive wheel 11. The rocking rotor 1 is placed in the operational position in the water, with the buoyant body 3 partly rising above the water surface 17. The rocking rotor 1 is interconnected with the drive shaft 23 via a free running mechanism (not shown) with a belt 21 .

[0092] The operational position of the rocking rotor 1 is configured by altering the centre of gravity 19 of the rocking rotor 1. The asymmetric centre of gravity 19 may be achieved by the use of ballast(s) (not shown) provided in the buoyant body12.

[0093] Preferably, the operational position of the rocking rotor 1 is configured so that at least a part of the shell 3 of the rocking rotor 1 is above the water surface 17 when subjected to an incoming wave, while at the same time having a volume of the shell 3 below the water surface 17. Having the shell 3 as submerged below the water surface 17 as possible, while at the same time configured to be at least partly above the water surface 17, enables the rocking rotor 1 to have a large range-of-motion during rotation while still generating a torque from the total mass of an incoming wave.

[0094] The buoyant body 12 of the rocking rotor 1 may also be configured to provide a desired eigenfrequency, or natural frequency, for the rocking rotor 1 . Fig. 5 illustrates a rocking rotor 1 according to some of the embodiments. The rocking rotor 1 comprises a shell 3 with an opening around the shaft 5. The shell 3 is interconnected with the shaft 5 through an interface construction 9 arranged between the shell 3 and bearing 7. The rocking rotor 1 further comprises two ballasts 31. The two ballasts 31 are shown as being part of the buoyant body12. Preferably, the ballasts are enclosed by the shell, but are for illustrative purposes seen in the open. The ballasts 31 are in this embodiment made of concrete, but may alternative be made of any known material for ballast purposes. A rotor drive wheel 11 is fixated to the shell 3 of the rocking rotor 1 with fixation means 13. The rotor drive wheel 11 is further interconnected to a second bearing 7’ arranged at the shaft 5 with second interface construction 15. The second 7’ may be the same as the bearing 7.

[0095] Figs. 6a-k illustrate a rocking rotor 1 comprising a rotor wheel drive 11 in perspective views.

[0096] Fig. 7 illustrates a rocking rotor 1 comprising a shell 3 and two interface constructions 9. Each interface construction 9 comprises a circular or disc formed plate 9 with a radius according to the distance d between the rotor shaft 5 and the concave shape third side, the plates 9 are configured to interconnect the shell 3 of the rocking rotor 1 with a bearing 7 (not shown). The interface connection 9 may be a part of the shell 3.

[0097] Fig. 8 illustrates two wave power plants 2, wherein one wave power plant 2 comprises a frame construction 25 in two parts that are adjourned in a rotating joint 27, and one wave power plant 2 comprises a frame construction 25 in one part. The wave power plants 2 both comprises a plurality of rocking rotors 1. The wave power plant 2 with a frame construction 25 in two parts comprises a plurality of rocking rotors 1 on one side of the frame construction 25, where the wave power plant 2 comprising a frame construction 25 in one part comprises a plurality of rocking rotors 1 on both sides of the frame construction 25. The wave power plants 2 comprises a generator 29 arranged in each part of the frame construction 25 of the corresponding wave power plants 2. The wave power plants 2 further comprises a drive shaft 23 arranged in each part of the frame construction 25 and connected to the respective generators 29 of the corresponding wave power plants 2. Each rocking rotor 1 further comprises a ballast 31 arranged in the shell 3 of the buoyant body.

[0098] The wave power plant 2 comprising a two-part frame construction 25, such as including a first frame construction and a second frame construction, may preferably comprising an actuating means (not shown) for modifying the angle between the two parts of the frame construction 25. An increased angle of the frame construction 25 may result in a larger area covered by the plurality of rocking rotors 1 of the wave power plant 2. An increased area covered by the plurality of rocking rotors 1 may consequently improve power generation of the wave power plant 2. The angle between the two parts of the frame construction 25 may be decreased during harsh off-shore conditions, such as high wind and / or tall waves. A decreased angle between the two parts of the two-part frame construction 25 may reduce the impact of the waves on the wave power plant 2. A decreased impact of waves may reduce power generation, but may also reduce mechanical tear on the wave power plant 2.

[0099] The wave power plant comprising a one-part frame construction, such as including a first frame construction extending in a longitudinal direction has a first set of rocking rotors 1 provided along a first rotor shaft extending in the longitudinal direction along a first side of the frame construction, and a second set of rocking rotors 31 provided along a second rotor shaft extending in the longitudinal direction along a second side of the frame construction.

[0100] Providing a frame construction having two sets of rocking rotors provided at each side of the frame construction extending in the longitudinal direction, allows for a more compact design of the wave power plan, which again allows for re-use, or common use of further components for both sets of rocking rotors. Additionally, one service bridge provided at the frame construction may service both the first set of rocking rotors and the second set of rocking rotors.

[0101] The wave power plant 2 comprising a one-part frame construction 25 has the advantage of increased durability towards harsh off-shore conditions, such as high wind and / or tall waves. The one-part frame construction 25 enables the wave power plant 2 to have a durably design, while at the same time reducing number of components needed for power generation.

[0102] Fig. 9a, shows a rocking rotor 1 according to prior art with and without ballast 31. The figure illustrates effect of the ballast 31 on the operational resting position of the rocking rotor 1 when placed in water 17. The rocking rotor 1 according to the invention differs from the prior art, in that the shell 3 has an opening around the shaft 5 (not shown), wherein the shell 3 does not enclose the circumference of the shaft 5 (not shown). The opening of the shell 3 introduces two tapered ends 33 to the shell 3. The effect of the open-back design of the shell 3 with two tapered ends 33, is that the torque generated by the rocking rotor 1 during rotation is increased, when compared the rocking rotor 1 of Fig. 9a and 9b. The torque generated by the rocking rotor 1 is increased, at least partly due to reduced hydrodynamic resistance and friction, and at least partly due to an at least reduced or completely remove amount of buoyant mass generating torque in an opposite direction than the rotation of the rocking rotor 1. A rocking rotor 1 according to Fig. 9a and 9b, will during rotation, be impacted by friction, resistance, and counter-acting torque due to a part of the shell 3 being arranged in a location that does not contribute to torque generation during rotation of the rocking rotor 1.

[0103] Fig. 9b, illustrates the effect of the centre of gravity 19 and range of motion due to the ballast 31 of the rocking rotor 1. The rocking rotor 1 depicted in Fig. 9b is not according to the invention, but is described to illustrate the change of range of motion due to a ballast 31 being incorporated in a rocking rotor 1. The ballast 31 ensures a balanced asymmetric operational position of the rocking rotor 1 when placed in water (not shown). The asymmetric operational position ensures a range of motion of the rocking rotor 1 , that enables the rocking rotor 1 to alternate between a vertical and horizontal position when impacted by waves. The range of motion of the rocking rotor 1 is illustrated by dashed lines for illustrative purposes.

[0104] The buoyancy of the shell 3 generates a torque while rotating the rocking rotor 1 to a vertical position. The rocking rotor 1 will then, as an impacting wave has passed, rotate to a horizontal position. The rocking rotor may also rotate even further below the water surface 17 (not shown) than the horizontal position due to inertia provided by the mass of the ballast 31.

[0105] List of references

[0106] 1 rocking rotor

[0107] 2 wave power plant d. distance

[0108] 3 shell

[0109] 4, 4’ convex side

[0110] 5 rotor shaft

[0111] 6 concave side

[0112] 7 bearing

[0113] 7’ second bearing

[0114] 8 center of rotation

[0115] 9 interface construction

[0116] 10 top vertex

[0117] 11 rotor drive wheel

[0118] 12 buoyant body

[0119] 13 fixation means

[0120] 15 second interface construction

[0121] 17 water surface

[0122] 19 centre of gravity (cog)

[0123] 21 belt

[0124] 23 drive shaft

[0125] 25 frame construction

[0126] 27 rotating joint

[0127] 29 generator

[0128] 31 ballast

[0129] 33 tapered end

Claims

CLAIMS1 . A wave power plant comprising a frame construction extending in a longitudinal direction and having a rotor shaft extending in the longitudinal direction of the frame construction, a plurality of rocking rotors, the plurality of rocking rotors being arranged rotatably with respect to the frame construction around the rotor shaft each rocking rotor comprising a buoyant body, the buoyant body having a shell, a bearing arranged at the rotor shaft, an interface construction configured to interconnect the buoyant body with the bearing, such that the rocking rotor is rotatably connected to the rotor shaft, wherein the shell of the buoyant body has a triangular shape having a first side and a second side being first and second convex shaped sides and a third side being a third concave shaped side, the third concave shaped side facing the rotor shaft.

2. The wave power plant according to claim 1 , wherein the third side of the triangular shaped shell is configured to be submerged in water when the rocking rotor is positioned in the operational position in a wave power plant.

3. The wave power plant according to any of the preceding claims, wherein the concave side is shaped as an arc of a circle, such as shaped as a part of a circumference of a circle.

4. The wave power plant according to claim 3, wherein the concave shaped third side is configured to tangentially touch the water surface when the rocking rotor is placed in the intended operational position in the water.RECTIFIED SHEET (RULE 91) ISA / EP5. The wave power plant according to any of the preceding claims, wherein the interface construction extend between the concave shaped third side and the rotor shaft with the bearing.

6. The wave power plant according to any of the preceding claims, wherein each of the rocking rotors are configured so that each rocking rotor in a floating rest position will assume an asymmetric resting position, wherein a top vertex of the shell extends upwards with an angle in the range of 25° to 70° to vertical direction, such as 30° to 60°.

7. The wave power plant according to any of the preceding claims, wherein each rocking rotor comprises a rotor drive wheel, the rotor drive wheel being fixedly connected to buoyant body.

8. The wave power plant according to claim 7, wherein the drive wheel is rotatably interconnected to the rotor shaft via the bearing.

9. The wave power plant according to any of claims 7 or 8, wherein the rotor drive wheel is interconnected to the frame construction via a drive shaft.

10. The wave power plant according to any of the preceding claims, wherein one or more of the plurality of rocking rotors comprises one or more ballast(s).

11. The wave power plant according to claim 10, wherein the one or more ballast(s) are arranged in the buoyant body of one or more of the plurality of rocking rotors.

12. The wave power plant according to claim 11 , wherein the one or more ballast(s) arranged in the buoyant body are arranged opposite of a top vertex formed by the first and second convex sides.

13. The wave power plant according to claims 10-11 , wherein the one or more ballast(s) arranged in the buoyant body are arranged substantially in one of the two convex sides of the body.RECTIFIED SHEET (RULE 91) ISA / EP14. The wave power plant according to any of the preceding claims, wherein the wave power plant comprises: one or more generator(s) arranged in the frame construction, and at least one drive shaft interconnected with the rocking rotor and one or more of the generator(s).

15. The wave power plant according to any of the preceding claims, wherein the at least one drive shaft is interconnected with the rocking rotor via a free-running mechanism.

16. The wave power plant according to claim 15, wherein the free-running mechanism may be active when the rocking rotor is in an upwards movement or downwards movement.

17. The wave power plant according to any of the preceding claims, wherein the frame construction comprises: a first frame construction and a second frame construction adjourned in a rotating joint, and an actuating means for arranging the first frame construction and second frame construction in an angle 0 in a horizontal direction, wherein the actuating means is arranged to modify the angle 0 between an angle of 0° - 180°, such as 45° - 135°.

18. A method of generating electrical power using a wave power plant according to any of the claims 1-17.

19. A rocking rotor for use in a wave power plant, the rocking rotor comprising a buoyant body having a shell, a bearing configured to be arranged at a rotor shaft, and an interface construction configured to interconnect the buoyant body with the bearing,RECTIFIED SHEET (RULE 91) ISA / EPwherein, the shell of the buoyant body has a triangular shape having a first side and a second side being first and second convex shaped sides and a third side being a third concave shaped side, the third concave shaped side facing the rotor shaft.

20. The rocking rotor according to claim 19, wherein the interface construction extends between the concave shaped third side and the bearing configured to be arranged at the rotor shaft.RECTIFIED SHEET (RULE 91) ISA / EP

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