HK1096445B - A wave power apparatus comprising a plurality of arms arranged to pivot with a mutual phase shift - Google Patents

Description

Wave power apparatus comprising a plurality of arms arranged to pivot with a mutual phase shift

Technical Field

The present invention relates to a wave power apparatus for converting sea or ocean wave energy into useful energy such as electricity. The device according to the invention has the particular object of providing a system in which a uniform power output can be obtained.

Background

As is well known, sea waves seem to constitute an almost unlimited energy resource that, if exploited efficiently, may be able to solve a considerable part of the world's energy problems. However, despite many efforts to develop and utilize ocean wave energy, no commercially successful system has been devised to date for converting ocean wave energy into electrical energy.

Generally, in the prior art, three different types of wave power generation devices have been proposed. One such apparatus is disclosed in US patent 6,476,511, the apparatus comprising a plurality of buoyant cylindrical body members connected together at their ends to form an articulated chain-like structure. Each pair of adjacent cylindrical members are interconnected by a coupling which allows relative rotational movement of the cylindrical members about a transverse axis. Adjacent links are relatively rotationally movable about mutually orthogonal transverse axes. Each coupling has elements, such as a set of hydraulic rams, which resist and extract energy in the relative rotational movement of the cylinder members. The equipment floats freely on the surface of the sea and is fixed to the sea floor.

A second type of wave power apparatus comprises one or more surface floats which are able to move along the surface of the ocean under the action of ocean waves and a reference member which is completely submerged at a certain depth in the ocean and is substantially unaffected by ocean waves, see for example US 4,453,894. The movement of the float on the surface of the ocean causes the hydraulic fluid in a hydraulic system comprising hydraulic means interconnecting a surface float or floats to a reference member, whereby useful energy can be extracted from the hydraulic system. It will be appreciated that such equipment is also fixed to the seabed.

Finally, a third type of wave power apparatus is a wave power apparatus having one or more arms supported by a support structure, said one or more arms carrying one or more floats which are moved by waves. The moving wave energy is transmitted to the arm and can be fed into a hydraulic system, as in the system of US 4,013,382, or into a mechanical system of shafts which drive one or more generators through a mechanical transmission system for the production of electricity, as in the system of WO 01/92644.

The present invention relates generally to a wave power apparatus of the third type described above. It is an aim of some preferred embodiments of the present invention to provide an apparatus which can be used for uniform power output, i.e. a substantially constant power output over time, of an apparatus energy conversion device. It is a further object of the preferred embodiments to provide a system that reduces or eliminates the need for a frequency converter. It is a further object of a preferred embodiment to provide a wave power apparatus which can be conveniently taken out of operation, for example in order to prevent ice from forming on various components of the apparatus during operation. It is yet another object of a preferred embodiment of the present invention to provide an apparatus that can be used for convenient maintenance access to arms and floats, and most preferably to individual arms and floats in a system comprising a plurality of arms, each arm having a float. It is yet another object of the preferred embodiments to provide an apparatus that can be conveniently transported from an onshore production facility to an onshore job site at an open sea location.

Disclosure of Invention

The invention provides a wave power apparatus comprising a plurality of arms, each arm being rotatably supported at one end by a shaft, wherein each arm carries a float at its other end, which is opposite to the support end, such that a translational movement of the float caused by a wave causes the arm to rotate about the shaft, the apparatus comprising power conversion means for converting power transmitted by the wave to the arm into electrical power, the plurality of arms being arranged in a row such that the arms are successively pivoted about the shaft by the waves of the row of arms, the arms being arranged at a distance from each other such that the passage of the waves causes the arms to pivot with a mutual phase shift, the power conversion means comprising a hydraulic drive system having a hydraulic drive motor, wherein each arm is connected to the hydraulic drive system by at least one hydraulic cylinder which causes hydraulic medium of the hydraulic drive system to be displaced into the motor, the hydraulic cylinders are arranged to discharge hydraulic medium to the motor via a common hydraulic conduit, each hydraulic cylinder being provided with a sensor for determining the position and/or rate of movement of the cylinder piston, which sensor is arranged to transmit a signal to a control unit of the hydraulic cylinder and associated valve, so that the transmission of energy from each hydraulic cylinder to the remaining components of the hydraulic drive system can be individually controlled in response to a signal representing the position and/or rate of movement of the respective cylinder piston.

The arms are preferably arranged at a distance from one another such that at least two arms always deliver a power portion to the power conversion means simultaneously. The energy transforming device preferably comprises a hydraulic actuator associated with each arm, which hydraulic actuators feed hydraulic medium to at least one hydraulic motor via a common hydraulic conduit. Thus, a uniform power output of the energy conversion device can be obtained. This is particularly the case in embodiments where the apparatus comprises a plurality of, say 60, arms, floats and actuators, since the sum of the energy shares of the individual actuators is substantially constant over time. Possible pressure fluctuations on the pressure side of the hydraulic motor can be substantially eliminated by means of a per se known wave crest suppression device which is arranged in fluid communication with the common hydraulic conduit. Preferably, the sum of all energy contributions is substantially constant in a certain wave climate, i.e. wave height and wave frequency. The hydraulic motor is preferably a variable displacement per revolution hydraulic motor. The change in wave climate can be compensated by a control circuit which controls the displacement per revolution of the motor in order to keep the motor rpm substantially constant. In order to generate an alternating current at a specified frequency without the use of a frequency converter, the motor rpm should be controlled within +/-0.1-0.2%. In case different types of motors are used or in case the rpm cannot be controlled precisely, a frequency converter may be applied to fine-tune the frequency of the generated AC current.

In some preferred embodiments, the apparatus of the invention comprises at least 5 arms, such as at least 20 arms, preferably at least 40 arms, preferably 50-80 arms, such as 55-65 arms, for example 60 arms. The arms of the apparatus are preferably distributed such that at least 5 arms, preferably at least 10 arms, are provided for each ocean wave wavelength. In open sea, the wave length of sea waves is typically 50-300m, such as 50-200 m. In protected waters, the wave length of a sea wave is typically 5-50 m.

In some preferred embodiments, the device spans at least two wavelengths. This makes it possible to arrange the arm and the row of floats at a relatively large angle, such as +/-60 deg., with respect to the wave direction, since the wavelength projecting into the orientation of the row of floats spans at least a wavelength of 2 x cos (60 deg.), i.e. at least one wavelength, thus ensuring that the energy share is always delivered.

The plurality of arms are preferably arranged in one or more rows, such as in a star, V or hexagon as disclosed in WO 01/92644. In order to efficiently exploit the wave energy, the row of arms is preferably oriented with respect to the wave direction such that the row of arms forms an angle with the wave direction within +/-60 °.

It has been found that the efficiency of the apparatus according to the invention increases as the buoyancy of the float increases in terms of its dry weight. Thus, in some preferred embodiments of the invention, the buoyancy of the float is at least 10 times, such as at least 20, 30 or 50 times, preferably 20-40 times its dry weight. For example, the dry weight of the float is typically 100kg or less per cubic meter of buoyancy, and the buoyancy of salt water is typically about 1050kg/m³. Floats are typically made of rigid lightweight cellular plastic materials or balsa wood coated with a composite material, such as a reinforced fiberglass composite or fiberglass and carbonA combination of fiber composites. Alternatively, the float may be made of a sandwich of reinforced fibre material with rigid foam being provided in the middle of the sandwich and at the bottom and top of the float, with the foam layers being separated by a honeycomb structure of reinforced fibre material.

Efficiency also increases with increasing the ratio of the diameter of the float to its height. Preferably, the diameter of the float is at least 5 times, such as at least 7 times, such as at least 10 times, or 5-20 times its height. In a preferred embodiment, the float has a substantially circular cross-section and, in order to improve the hydrodynamic performance of the float, it may have a rounded edge portion which acts as a streamline.

The energy transforming device preferably comprises a hydraulic drive system with a hydraulic drive motor. For example, each arm may be connected to the hydraulic drive system by at least one actuator which causes the hydraulic medium of the hydraulic drive system to be discharged into the hydraulic motor, the actuator being arranged to discharge the hydraulic medium to the motor via a hydraulic conduit. In the case of a plurality of arms and a plurality of actuators, the hydraulic medium is preferably discharged to the motor via a common hydraulic line. In other words, a plurality of hydraulic actuators can feed hydraulic medium into one hydraulic motor via a system common to the hydraulic lines. Most preferably, the hydraulic medium is not accumulated in a hydraulic tank for accumulating the hydraulic medium under pressure, from which the pressure is released to the motor. The actuator thus feeds the hydraulic medium directly into the motor. However, as will be described below, it is advantageous to be able to use the hydraulic accumulator bank for a completely different purpose, namely for forcing the float into the wave near the wave trough. As in the preferred embodiment, the multiple actuators simultaneously deliver electrical power to the motor, eliminating the need for a hydraulic reservoir, as the motor can be operated at a substantially constant speed and a substantially constant energy input, due to the delivery of energy from the multiple actuators at a time in a common hydraulic system.

It should be understood that more than one hydraulic motor may be foreseen. Preferably, two, three or more motors may be arranged in parallel at the end of the common hydraulic conduit. Thus, the energy delivered through the common hydraulic conduit may drive multiple motors. For example, if the hydraulic drive system produces 4MW, eight motors each delivering 500KW may be coupled in parallel at a common hydraulic conduit. The motors may deliver the same rated power output, or they may deliver different rated power outputs. For example, one motor may deliver 400KW, one may deliver 500KW, etc.

All hydraulic motors may also be connected by the same through-shaft driving at least one common generator, or all hydraulic motors may drive one cog wheel driving at least one common generator.

In order for the hydraulic system to force the one or more arms and the float in any desired direction, each actuator may comprise a double acting cylinder which may be used to extract energy in the arm into the hydraulic system and to input energy in the hydraulic system into the arm, such as to force the float into a wave near a wave trough, as will be described in detail below with respect to the hydraulic accumulator.

In a preferred embodiment the apparatus comprises means to force one or more floats into the wave at the trough of the wave in order to increase the vertical distance travelled by the floats to increase the energy output in one wave cycle. Such means may for example comprise one or more hydraulic accumulators for intermittently storing energy in the hydraulic drive system. Advantageously, the energy stored in the hydraulic accumulator may be derived from releasing potential energy when the float is lifted out of the water surface of the wave crest. In other words, the potential energy is released when the float moves from a position submerged in a wave near the crest of the wave to a position above the water surface. This energy can be stored in a hydraulic accumulator or in a group of hydraulic accumulators, wherein different hydraulic accumulators can be charged at different pressures, for example at pressure levels according to the number of hydraulic accumulators. In embodiments including these hydraulic accumulators, the hydraulic drive system is controllable to release energy stored in the hydraulic accumulators as the troughs pass the floats so as to force the floats carried by the arms into the waves. In order to improve the efficiency of the hydraulic accumulator system, a plurality of hydraulic accumulators, e.g. at least 2, such as 3-20, such as usually 6-12, may be used, which preferably store hydraulic medium at different pressure levels. In a preferred embodiment, the float is forced a certain distance into the wave near the trough, then allowed to move upwards in the wave, but still submerged in the wave, and released at the crest, i.e. moved out of the water. As mentioned above, the energy released by the float at the wave crest is utilized to charge one or more hydraulic accumulators where the energy is stored for forcing the float into the wave. Thus, the potential energy released when the float moves out of the wave near the crest is not lost. Instead, the float is forced into the wave at the trough of the wave by the above-mentioned released potential energy, whereby the total vertical distance traveled by the float increases. Thus, the energy output of one wave cycle increases. It is estimated that at a wave height of 1.5m, the vertical distance traveled by the float can be increased from about 0.75m to about 1.5m, thus doubling the energy output. The energy used to force the float into the wave at the trough is essentially not lost in the drive system, as the energy is provided by the float released at the crest.

In order to enable accurate control of the system, each hydraulic cylinder, or at least a selected one of the hydraulic cylinders, may be provided with a sensor for determining the position and/or rate of movement of the cylinder piston, the sensor being arranged to transmit a signal to a control unit of the hydraulic cylinder and associated valve, so that the transmission of energy from the respective hydraulic cylinder to the remaining components of the hydraulic drive system can be controlled individually in response to the signal indicative of the position and/or rate of movement of the respective cylinder piston. Thus, the cylinders can be controlled individually and one cylinder can be pulled out of operation for maintenance while the remaining cylinder remains operational so that the entire system is substantially unaffected by pulling out one cylinder. The pressing of the float into the water, i.e. the release of pressure from the hydraulic accumulator bank, is preferably also controlled by means of a sensor. The sensor can also be used to charge the accumulator, i.e. to determine the passage of the wave peak. In addition, the sensor is useful for controlling the release of the float at the wave crest, i.e. preventing the float from popping up like a projectile. The sensors may also be used to monitor the energy output of each actuator in the hydraulic drive system so that the energy output of the individual actuators and the overall apparatus can be so optimized.

While some prior art systems rely on submerged datums to support devices that convert ocean wave energy into useful energy or on shore supports, it has been found that wave energy is most efficiently exploited in open seas. The apparatus of the invention therefore preferably comprises a support structure secured to the seabed. In a presently preferred embodiment, the support structure is fixed to the sea floor by means of suction anchors, or alternatively by means of a gravity base, or to the rock seabed by means of short columns. Advantageously the support structure may comprise a truss structure with the suction anchor being located at a first node of the structure. At least one arm and preferably all arms of the apparatus are supported at a second node of the truss structure, most preferably at the apex of the triangular substructure of the truss structure. The triangular substructure may define two vertices at the sea floor by means for securing the structure to the sea floor at each corner. Preferably, the means for securing is at least partially embedded in the sea floor, such as by a gravity base or suction anchor. When the means for securing are provided at the nodes of the truss structure, vertical forces in the truss structure caused by buoyancy of the floats can be effectively counteracted. The truss structure as described above ensures maximum stability of the system while allowing for a low overall weight support structure.

It has been found that a general problem in prior art systems is to prevent the extreme impacts that occur during storms and hurricanes from damaging the floats, arms and other components of the wave power apparatus. Embodiments of the present invention therefore have features that enable a wave power apparatus to withstand extreme wave conditions. This embodiment comprises a hydraulic lifting system for lifting the float out of the sea and for locking the float in an upper position above the sea surface.

The hydraulic lifting system preferably comprises one or more pumps for pumping hydraulic medium into the hydraulic cylinders to lift them out of the sea.

Thanks to the hydraulic lifting system, the float can be pulled out of the sea surface and kept in a locked position above the surface, for example when a storm occurs or before icing occurs. Thus, the only effect on the float when it is pulled out of the sea surface is that of wind, which is significantly less than the wave force. In one embodiment the arm can be lifted out of the water by creating hydraulic pressure in the hydraulic lifting system, which can move the arm out of the sea and by closing a valve appropriately, preferably by means of a conical locking pin, in order to maintain the lifting pressure. The hydraulic lifting system may be controlled from a remote onshore location or by a control system constituting part of the wave power generator and acting in response to a signal indicative of a storm condition, such as in response to a signal from an electronic device for continuously determining wind speed. The control system may be programmed to pull the float and arm out of the water at a predetermined wave height. This wave height may, for example, relate to a certain proportion, for example 30%, of the largest forecast waves at the site of operation of the installation, so-called "one hundred year waves". At an ocean depth of 20m this height is about 18m, so the control system pulls the buoy and arm out of the ocean at a wave height of about 6 m. The wave height can be determined by mechanical, optical, electromagnetic or acoustic systems, such as a pressure sensing system with pressure sensors arranged on the sea floor, an echo detection system arranged at the float, an echo detection system arranged on the fixed structure of the apparatus and directed upwards towards the surface of the wave or operated in air down towards the water surface, or a sensor system with light emitting or light receiving means, such as lasers, arranged on the float and/or on the fixed support structure. Alternatively, a radar system may be provided on the structure. The pressure of the hydraulic medium in the lifting system may be generated by a pump forming part of the hydraulic lifting system. Alternatively, the pressure may be generated by releasing pressurized hydraulic medium from a hydraulic accumulator. The hydraulic accumulator may for instance be charged by a hydraulic drive system, which in one embodiment of the invention is included in the energy conversion means. For example, the hydraulic accumulator for transmitting the hydraulic lifting pressure may be one hydraulic accumulator or a plurality of hydraulic accumulators in a so-called hydraulic accumulator bank for forcing the float into the wave at the wave trough, as will be explained in detail below.

The hydraulic lifting system is preferably adapted to lift each float out of the sea individually. For example, the lifting system may comprise a plurality of hydraulic circuits, each associated with one arm, and each comprising valve and/or pump means for pressurising the hydraulic circuit for lifting the arm and the float out of the sea. In one embodiment, the hydraulic lifting system comprises fewer pumps than circuits, so the or each pump is connected to a plurality of circuits, each circuit having an associated valve being assigned to one arm. In a preferred embodiment of the invention, the energy transforming device and the arms are arranged such that those arms remaining in the sea can transfer energy to the energy transforming device while one or more other arms remain lifted out of the sea. The embodiment of the energy transforming device of WO01/92644, hereby included as reference in this document, is freely rotatable around the drive shaft of the energy transforming device for lifting the drive shaft of the arm out of the ocean. Some embodiments relying on hydraulic energy conversion devices may include means for deactivating those energy conversion devices, such as those hydraulic actuators associated with an arm that has been lifted out of the sea, wherein movement of the arm generates pressure in a hydraulic drive system. In the presently preferred embodiment, the sea surface can be lifted and locked in the raised position by means of an arm actuator, such as a double acting hydraulic cylinder, which can be used to lift and lock the arm.

Some preferred embodiments of the invention also provide a solution to the problem of providing a stable rotating support of one or more arms that has less effect on the horizontal force component. It has been found that the structure of US 4013382 is likely to become unstable due to the horizontal force component generated by the waves. More specifically, the bearings of the connecting rod consist of simple pins, and any slight loosening of these bearings may cause irreparable damage to the connecting rod and its support. The device of US 4013382 is therefore not suitable for installation at open sea, i.e. at relatively high wave forces. The structure disclosed in WO 01/02644 also has the disadvantage that even the slightest loosening in the one-way bearing(s) supporting the rocker arm and connecting the rocker arm tube and the force shaft may damage the bearing. In addition, the device of WO 01/02644 requires a very strong force shaft, in which a total of 40 rocker arms are supported with one force shaft, which is difficult to achieve due to the size required for it to be able to transfer the required energy due to its weight caused by its large size, which is necessary due to the transfer of momentum from the arms to the force shaft. A preferred embodiment of the apparatus according to the invention provides an improved support of the arm which makes the apparatus less influential on horizontal force components. Thus, in a preferred embodiment, the apparatus of the present invention comprises a pair of pre-stressed and substantially non-loose bearings. In this way the bearings are able to effectively counteract radial and axial forces and are therefore able to withstand the horizontal force components provided by the waves. The term "play-free bearing" is understood to include any bearing that is play-free both in the horizontal and in the axial direction. For example, the bearing pair may comprise two conical bearings whose conical surfaces are opposite to each other. In one embodiment, the bearing is a pressure lubricated bearing.

In another embodiment, the bearing comprises an inner ring fixed to the rotational axis of the arm and an outer ring or cylinder fixed to a fixed support, the bearing further comprising a flexible material between the inner and outer rings. During operation, the inner ring rotates relative to the outer ring, thereby twisting the flexible material. In order to adjust the stiffness of the flexible material, at least one cavity or perforation may be provided in the material. The flexible material may for example comprise a spring member such as a flat spring. By suitable positioning of the perforations or by suitable design of the spring members, the bearing support can be designed to have a greater capacity to bear forces in one direction than in the other.

The arm is preferably supported by bearings on two mounting points offset from the central axis of the arm, the central axis of the bearings coinciding with the axis of rotation of the arm. Since each arm is connected to and supported by a single bearing, stable rotational support of the arm can be achieved. In particular, since the two bearings are preferably arranged at a mutual distance along the rotational axis of the arm, the influence on the float on the axis caused by the horizontal force component can be counteracted.

It will therefore be appreciated that the structure of the present invention is more stable than that of the prior art devices. Since the present apparatus is primarily intended as an offshore building, stability is a major concern due to maintenance costs at the offshore site. The maintenance costs at an offshore site are typically 10 times higher than at an onshore site.

Drawings

Some preferred embodiments of the invention will now be further described with reference to the accompanying drawings, in which:

figures 1 and 2 are cross-sectional views of a wave power apparatus according to the invention;

3-5 show three embodiments of truss structures of embodiments of a wave power apparatus according to the invention;

FIG. 6 shows a honeycomb structure of the float;

figure 7 shows a support structure for the arm of the apparatus of figures 1 and 2;

8-13 illustrate various bearing assemblies for an arm of an apparatus;

FIGS. 14-17 show hydraulic drive system diagrams of embodiments of the apparatus according to the invention;

FIG. 18 shows a diagram of a hydraulic lifting system for lifting a float out of the sea;

figure 19 shows a wave power apparatus having an array of floats spanning two wave crests;

FIG. 20 shows the hydraulic pressure as a function of time in the supply line of the hydraulic drive system of a prior art wave power plant and in an embodiment of the plant according to the invention, respectively;

figure 21 shows two different travel paths of the float across the wave;

FIG. 22 shows a diagram of a hydraulic drive system with accumulators for forcing the float into the wave at the trough;

FIG. 23 illustrates multi-stage accumulation of energy in a hydraulic storage system;

fig. 24 and 25 are schematic views of waves and float motion.

Detailed Description

The following description of the figures discloses various features and options included in various embodiments of a wave power apparatus according to the invention. The principle of operation of the broadest aspects of the invention is best understood from the description of the embodiment of fig. 1 and 14-20.

Fig. 1 and 2 show a cross-sectional view of a wave power apparatus 102, said wave power apparatus 102 comprising a truss structure 104, which truss structure 104 may for instance have a so-called space truss structure. The truss structure, also shown in fig. 3-5, includes a substantially triangular lower portion having first, second and third force members 106, 108, 110 and a substantially rectangular upper portion 111. The upper part of the rectangle can be used to house hydraulic and electrical equipment, including hydraulic drive and lifting systems, and it can also be used as a narrow walkway or walking bridge for maintenance personnel. As shown in fig. 3-5, the rectangular upper part extends a distance perpendicular to the plane of fig. 1 and 2, while a number of significantly lower triangular lower parts are provided. The truss structure defines first, second, third, fourth, fifth, and sixth nodes 112, 114, 116, 117, 118, and 120. Preferably, the force members are substantially rigid so that they can withstand tension and compression, the first and second nodes 112, 114 being disposed at the seafloor and held at the seafloor by a suction anchor 121 such as that shown in fig. 3-5. Alternatively, the first and second nodes 112, 114 may be supported by a concrete foundation at the seafloor. An arm 122 carrying a float 124 is rotatably supported at or near the third and fourth nodes 116, 117. Fig. 3-5 show perspective views of truss structures for supporting a plurality of arms on either side of the structure. It will be appreciated that the truss structure of figures 3-5 may have a wider width than that actually shown in figures 3-5, so that it includes, for example, twenty or thirty triangular segments, and thus the arms may extend away from the truss structure at each node 116, 117. A plurality of truss structures such as those of fig. 3-5, e.g. three, six or more truss structures, may be arranged in a star, V or hexagonal configuration in order to increase the total number of arms and buoys included in a facility comprising the apparatus of the invention or a plurality of apparatus according to the invention.

The third, fourth, fifth and sixth nodes 116, 117, 118, 120 are located at a height above the surface of the sea that is sufficient to ensure that they are also above the surface of the sea when the waves are high in storm conditions. For example, nodes 116, 117, 118, and 120 may be located 20 meters above the sea surface when the sea is calm. To convert wave energy into hydraulic energy, the wave power apparatus 102 comprises a plurality of arms 122, each arm 122 comprising a float 124 at one end and being connected to a shaft 126 at the opposite end. Each arm is adapted to rotate about an axis 126. Each arm 122 is attached to a hydraulic actuator, such as a hydraulic cylinder 128 that includes a piston 130. The hydraulic cylinder 128 is pivotally connected to the arm in a first attachment point 132 and to the truss structure 104 in a second attachment point 134. The second attachment point is preferably located at a node, i.e. along an edge portion of a substantially rectangular structure provided on top of the triangular main structure of the truss structure. The float 124 moves the arm up and down under the influence of wave motion. As the arm moves up and down, the piston 130 is caused to move, thus converting wave energy into hydraulic energy which can be converted into useful electrical energy as described below with respect to fig. 14-18 and 22.

As shown in fig. 2, the hydraulic cylinder 128 is adapted to lock the arm 122 in a raised position in which a wave cannot reach the arm 122 and the float 124, the arm 122 being pulled to its raised position by the hydraulic cylinder 128. Thus protecting the arm 122 and float 124 during a storm or risking being exposed to icing on the float when the ambient temperature is near or below the freezing point of sea water. The hydraulic cylinder 128 is connected to a hydraulic lift system for locking the hydraulic cylinder in the raised position, which is discussed in more detail below with respect to fig. 18. The float 124 is pivotally connected to the arm 122. Thus, when the arm is raised during a storm, the floats can rotate to a position where they are substantially parallel to the direction of the wind. Thereby limiting the surface upon which the wind acts and thus reducing the forces acting on the floats 124 and reducing the moment transferred to the truss structure 104 by the arms 122. Furthermore, the float is designed to have an aerodynamic shape with rounded edges (not shown) in order to reduce wind forces on the device.

As shown in fig. 3-5, the truss structure 104 may include diagonal force members 113, 115 (not shown in fig. 1 and 2) for providing additional support at the nodes 116, 117.

In fig. 4 and 5, the truss structure is loaded with a downward acting weight to reduce the upward force at the anchor point 121. The weight is generated by a longitudinally extending weight such as a water tank 123 (fig. 4) or by a plurality of different weights such as a plurality of water tanks 125 (fig. 5).

Fig. 6 shows the structure of a substantially hollow float 124, said hollow float 124 comprising a honeycomb structure 127, said honeycomb structure 127 supporting the outer wall of the float.

Fig. 7 shows one of the arms 122, the arm 122 being pivotally attached to a float 124 and adapted to rotate about an axis 126. The arm is connected to the shaft at first and second attachment points 136, 138, which first and second attachment points 136, 138 are offset from a central axis 140 of the arm. The shaft 126 is rotatably supported by a fixed support structure 142. the fixed support structure 142 includes two bearings 144 configured to counteract radial and axial forces.

To provide a substantially maintenance-free bearing support for rotation of the arm 122, the present inventors propose bearings such as those shown in fig. 8-13. The bearing of fig. 8 to 13 can be incorporated in the bearing arrangement shown in fig. 7 as bearing 144 and is particularly suitable for supporting a shaft whose rotation amplitude during normal operation is equal to or less than 30 °, i.e. equal to or less than ± 15 °, such as equal to or less than 20 °, i.e. equal to or less than ± 10 °. When the arms are pivoted to the fastening position of fig. 2, the securing means of the outer ring 147 can be loosened to allow a greater rotation range, such as ± 40 °. Conventional roller or ball bearings have a short service life at such small rotational amplitudes, because their lubricating medium only achieves its use to the desired extent when continuously rotating at a rotational speed higher than that provided by the arms 122. The bearing of fig. 8 includes an inner ring or cylinder 145 and an outer ring or cylinder 147 between which is disposed a flexible material 149, such as a rubber material. The inner ring 145 is fixed to the rotating shaft and the outer ring 147 is fixed to the fixed support of the shaft. Due to the elasticity of the flexible material 149, the inner ring can rotate relative to the outer ring to enable the supported shaft to rotate relative to its support. Axial and radial support of the shaft is provided because the outer ring 147 is supported by or fitted into a fixed structure, such as by press fitting along its outer circumference. The stiffness of the flexible material 149 may be adjusted by providing cavities 151 in the material, such as drilled holes or perforations. The maximum load that the bearing can support can be increased by increasing the length of the bearing (i.e., across the plane of fig. 8). The number and size of the cavities 151 may be selected to suit a particular application, such as to minimize notch sensitivity and maximize the forces that the bearing counteracts. The same bearing 344 is shown in fig. 9, said bearing 344 having fewer cavities 151 in order to increase the bearing's ability to carry forces in one direction.

Similar torsion bearings (while bearings) 346, 348 and 354 are shown in fig. 10, 11 and 12, respectively. These bearings include inner and outer rings 145, 147 with one or more flat springs interposed between the inner and outer rings. In fig. 10, two flat springs 147 are provided, and each flat spring 147 is shaped in the shape of the numeral 3. Arrows 345 and 347 indicate that the capacity to carry forces is greater in the vertical direction (arrow 345) than in the horizontal direction (arrow 347). In the bearing 348 of fig. 11, a flat spring element 352 is provided, the flat spring element 352 defining a plurality of cavities 353. Arrows 349 and 350 indicate that the bearing capacity to carry forces is greater in the vertical and horizontal directions than in the non-horizontal and non-vertical directions (arrow 350). The bearing 354 of fig. 12 includes two H-shaped flat spring elements 362, each flat spring element 362 defining outer and inner portions 364 and 365 and an interconnecting portion 368. The stiffness of the bearing may be selected by appropriately selecting the geometry of the spring element 362. For example, the interconnecting portion 368 may be shaped as an S-shape. Arrows 355 and 357 indicate that the capacity to carry forces is greater in the vertical direction than in the horizontal direction.

The inner and outer rings 145, 147 of fig. 8-12 may be made of steel or of carbon fiber material. The flat springs 342, 352 and 362 may likewise be made of steel or carbon fiber material.

The bearing principles of fig. 8-12 may also be used to provide support for hydraulic cylinder 128.

Fig. 13 shows a bearing support for the arm 122, which support comprises two flat springs 372 and 374. The first flat spring 372 increases torsional stiffness and lateral stiffness of the bearing. The flat spring may be made of a carbon fiber material.

In the hydraulic diagram of fig. 14, a plurality of hydraulic cylinders 128 are shown with respective pistons 130, each piston 130 being movable up and down as 122 and floats 124 move in the waves, see the description of fig. 1 above. Although three hydraulic cylinders are shown in the diagram of fig. 14, it should be understood that the apparatus according to the invention typically includes a relatively large number of hydraulic cylinders, for example, 60 hydraulic cylinders. Hydraulic pressureThe cylinders 128 are shown as double acting hydraulic cylinders connected at their upper ends to a supply conduit 176 for system hydraulic medium. In each supply conduit 176, a pressure valve 178 is provided. The supply conduits 176 all merge into a common main conduit 180, which main conduit 180 flows into a hydraulic motor 182 at a variable volume displacement per revolution. In the supply line 176 and the common main line 180, a working pressure p is maintained₀. Pressure p₀It may also be advantageous to have a threshold pressure of the valve 178 at which the valve is switched between its open and closed states. The hydraulic motor drives a generator 184 and at the outlet of the hydraulic motor, the hydraulic medium is led to a reservoir 186. From the reservoir 186, the hydraulic medium flows back into the hydraulic cylinder 128 via a common return conduit 188 and a branch return conduit 190.

In each cylinder 128, a piston 130 divides the cylinder into upper and lower chambers 192, 194, which chambers 192, 194 are interconnected by conduits 196 and 198. In each conduit 196, a two-way valve 200 is provided, and in conduit 198, a pressure valve 202 and a flow control valve 204 in series are provided in parallel with two-way valve 200. Finally, each hydraulic cylinder is equipped with a control element 206 for determining the position and/or the rate of movement of the piston 130 of the hydraulic cylinder 128.

When two-way valve 200 is open, piston 130 may move freely as arm 122 (see fig. 1) moves in the wave. When the control element 206 determines a certain position and/or rate of movement of the piston 130, a control signal is transmitted to the valve 200 causing the valve 200 to close. When the pressure valve 178 is closed, the piston 130 will lock and the wave will continue to rise until the buoyancy of the float is sufficiently great to overcome the working pressure p in the supply and main conduits 176, 180₀Thereby opening the pressure valve 178. It should therefore be appreciated that when the valve 178 is open (see also the discussion of fig. 21 below), the float 124 (see fig. 1) is at least partially submerged in the wave. Once the pressure valve 178 is opened, hydraulic medium is sent to the motor 182. When the float passes a wave crest, the float is still submerged, but the pressure in upper portion 192 of hydraulic cylinder 128 drops, and pressure valve 178 closes. Then as the float moves from wave crest to wave downwards in the waveThe valley, the two-way valve 200 is open and hydraulic medium is drained from the lower cylinder portion 194 to the upper cylinder portion 192.

It is clear that due to the large number of hydraulic cylinders 128 it is ensured at all times that at least two and preferably several of them deliver a flow of hydraulic medium to the motor 182. Thus, a uniform power output of the generator 184 can be ensured, preferably without any frequency converter.

The above description of fig. 14 also applies to fig. 15, however, in the embodiment of fig. 15, a plurality of hydraulic motors 182, 208, 210 are provided. Each hydraulic motor 182, 208, 210 is connected to a respective electrical generator 184, 212, 214. In the embodiment of fig. 15, only three motors and generators are provided, but in other embodiments the wave power apparatus comprises a greater number of motors and generators. For example, five, ten or twenty motors and generators may be provided. The capacity of each hydraulic motor and its respective generator may be selected so that it can produce different energy levels. In one example, three generators may be capable of generating 0.5MW, and 2MW, respectively. Thus, to produce 1MW, the hydraulic motors of two 0.5MW generators may be connected to a common main conduit 180, while the third generator would be separate from main conduit 180. Where wave energy is always substantially constant, each generator and its respective electric machine capacity may each be selected to its maximum possible rating in order to reduce the total number of hydraulic motors and generators. Where the wave height and the wave frequency fluctuate significantly, the capacity of the generator can be chosen according to the binary principle (binary principle), such as 1MW, 2MW and 4 MW. By selecting the generator according to the binary principle, the generator can be switched in and out in the following pattern in order to make the best use of the wave energy.

Generator 1(1MW)	Generator 2(2MW)	Generator 3(4MW)	Total output (MW)
				Is connected to	Disconnect	Disconnect	1
Disconnect	Is connected to	Disconnect	2
				Is connected to	Is connected to	Disconnect	3
Disconnect	Disconnect	Is connected to	4
				Is connected to	Disconnect	Is connected to	5
Is connected to	Is connected to	Is connected to	6

The system of fig. 16 is similar to the system of fig. 15, however in the system of fig. 16, only a single generator 184 is provided, which generator 184 is driven by hydraulic motors 182, 208 and 210 through a gearbox 185. The hydraulic motors may for example drive a toothed rim of a planetary gear. Alternatively, as shown in fig. 17, the hydraulic motors 182, 208, and 210 may drive a common generator 184 through a common through shaft 187.

Fig. 18 shows a hydraulic lifting system for lifting the floats 124 out of the sea and keeping them in a raised position where waves cannot reach the floats. Fig. 18 also includes a hydraulic drive system similar to the drive system described above in fig. 14-17. If the same or similar elements to those shown in fig. 14-17 are included in the drive system shown in fig. 18, the reference numerals of fig. 6 are used in fig. 8 and the description of these elements and their functions are described with reference to fig. 14-17 above. The hydraulic lift system of fig. 18 is adapted to lift one or more floats 124 out of the water individually and to separate the lifted float cylinders from the hydraulic drive system. The system of fig. 18, in addition to the common return line 188, includes a line 266 that connects the reservoir 186 to a pump 268 driven by a motor 270. A conduit 272 connects the downstream side of the pump 268 to a plurality of check valves 274, the number of check valves 274 being equal to the number of floats and hydraulic cylinders 128. A conduit 276 connects a respective downstream side of valve 274 to a respective two-way valve 278 and a check valve 280, conduit 276 merging into a common conduit 282 downstream of check valve 280 as described above. Conduit 276 communicates with the lower cylinder chamber 194 and conduit 198 via conduit 284. In addition, the conduit 276 communicates with the upper cylinder chamber 192 and the supply conduit 176 via conduit 196. Finally, a two-way valve 286 is provided in branch return conduit 190 and a two-way valve 288 is provided in conduit 198.

When the arm is lifted out of the water, valve 278, valve 286, and valve 288 are closed. Valves 274 and 280 are opened and pump 268 can force hydraulic medium into the lower cylinder chamber 194 and raise the arm associated with the cylinder. The hydraulic medium in the upper cylinder chamber 192 is led to the reservoir 186 via a valve 280. The control element 206 senses the arm and, via the arm, causes the piston 130 to reach its desired position, such as its uppermost position, and transmits a signal to the valves 274 and 280 to cause them to close. The piston 130 is then locked and the arm is secured in a position where the float 124 is lifted out of the water. The arm 122 may additionally be supported by a pawl (not shown) that engages the arm.

Fig. 19 is a schematic diagram showing multiple floats 124 and 164, the multiple floats 124 and 164 being coupled to a hydraulic drive system by hydraulic cylinders as described above in fig. 14-18. In fig. 19, those floats located at the peaks 146, 148 are indicated by reference numeral 164, while all other floats are indicated by reference numeral 124. However, there is no structural difference between the float 124 and the float 164. The first, second and third peaks 146, 148, 150 are indicated by double lines in fig. 19, while the first and second valleys 152, 154 are indicated by single lines in fig. 19. The direction of wave front movement is indicated by a first arrow 156, the wavelength by a second arrow 158 and the rising and falling parts of the wave by third and fourth arrows 160, 162 respectively. As shown in fig. 19, those floats 164 at the wave crests 146 and 148 have their upward motion caused by the waves just finished. Those floats 124 between the first crest 146 and the first trough 152 are on their way up in the wave, while those floats between the second crest 148 and the first trough 152 move down the downstream side of the wave. Because the array of floats 124, 164 spans the entire wavelength, many floats are on their way up in the wave at any time, thus ensuring that multiple floats deliver a share of energy to the hydraulic drive system at any time. As described above with reference to fig. 14-17, each float drives a hydraulic cylinder and generates hydraulic pressure in main conduit 180 (see fig. 14-17). As the plurality of floats are moved upward at the same time, the plurality of hydraulic cylinders simultaneously supply hydraulic pressure. Thus, due to the configuration of the common main conduit 180 being connected to a plurality of hydraulic cylinders having respective floats, and due to the length of the float array spanning at least one full wavelength, pressure fluctuations in the common conduit 180 and at the inlet of the hydraulic motor 182 or motors 182, 208, 210 may be kept low. Because the hydraulic motors 182, 208, and 210 are motors having a variable displacement per revolution, the rpm of each motor may be maintained substantially constant. This also has the effect that the frequency of the Alternating Current (AC) current produced by the generator 184 or generators 184, 212 and 214 is substantially constant, thus achieving that in a preferred embodiment of the invention, the AC current can be produced without the need for a frequency converter.

In fig. 19, the wave direction defines an angle e relative to the row of floats. When θ is 0 °, the wave direction is parallel to the row of floats. It will be appreciated that the larger the angle e, up to 0 deg., the longer the row of floats must be in order to ensure that at least one float is moved upwards by a wave at any given moment, delivering a distribution of pressure in a common main conduit 180 (see figures 14-17) of the hydraulic drive system.

Representative wavelengths and orientations of locations should be considered in designing the system to ensure substantially constant hydraulic pressure in the system. In a preferred embodiment of the invention, the relationship between the wave direction (angle θ) and the length of the wave power apparatus, i.e. the length spanned by the floats 124, 164, may be determined by the following equation:

fig. 20 shows hydraulic pressure as a function of time 240 in the common main conduit 180 (see fig. 14-17). The first curve 244 is the hydraulic pressure in the supply line of a typical prior art wave power plant having a hydraulic cylinder supplied with an accumulator by a hydraulic motor. As shown in fig. 20, the hydraulic pressure fluctuates with the wave period 246. In an embodiment of the wave power apparatus of the invention, in which the hydraulic pressure 248 fluctuates with a low amplitude, the above-described wave power apparatus of the invention comprises a plurality of arms, floats and hydraulic cylinders, and is free of accumulators.

Fig. 21 shows two different travel paths of the float across a wave moving in the direction of arrow 171. The upper portion of fig. 21 shows a flow path where no measures are taken to increase the vertical travel distance of the float 124 as a wave passes through it. The flow path shown in the lower portion of fig. 21, where the travel distance of the float is increased by actively forcing the float 124 into the water at the trough 152.

In the upper part of fig. 21, at position 172a, the float 124 moves down with the wave until it reaches the trough 152 at position 172 b. At this point, as pressure valve 178 closes (see fig. 14-17), two-way valve 200 also closes, locking the hydraulic cylinder and thus the float moves horizontally into the wave via position 172c to position 172 d. As the wave rises, pressure builds in chamber 192 in hydraulic cylinder 128 and in the conduit upstream of pressure valve 178 (see fig. 14-17). At position 172d, the pressure is sufficient to overcome the threshold pressure of the pressure valve 178, the pressure valve 178 opens, and the float 124 can move upward in the wave via position 172e to position 172 f. During this movement, the hydraulic cylinders 128 of the floats 124 feed hydraulic medium into the common hydraulic line 180, thus delivering a power contribution to the hydraulic motor 182 or motors 182, 208, 210. At position 172f, when the passing wave is about to fall, the pressure in the supply line 176 drops below the closing threshold of the pressure valve 178, which pressure valve 178 is closed. Once pressure valve 178 is closed and two-way valve 200 is open, float 124 is disconnected from common hydraulic conduit 180 and the buoyancy of float 124 enables it to move substantially vertically out of the water to position 172 g. As the wave falls, the float 124 moves down with the wave to position 172h and the float begins a new cycle in the next wave. The float 124 travels a vertical distance 168. From the above description of fig. 21, it will be appreciated that the energy share of each individual float 124 and associated hydraulic cylinder 128 is imparted to the hydraulic drive system during vertical movement of the float.

In order to increase the power output of the wave power apparatus, it is therefore desirable to increase the vertical travel distance of the float 124. The lower portion of fig. 21 shows an alternative travel path for the float 124 across the wave, where measures are taken to increase the vertical distance traveled by the float 124. At position 174a, the float 124 drops to the downstream side of the wave. At position 174b, float 124 reaches trough 152. At this point, the float is forced downward under water to position 174c and pressure valve 178 and two-way valve 200 are closed (see fig. 14-17). When the pressure upstream of the pressure valve 178 exceeds the pressure valve's critical closing pressure, the valve 178 opens and the float 124 moves to the position 174g via the positions 174d, 174e, and 174 f. At position 174f, pressure valve 178 is closed and two-way valve 202 is open, and the buoyancy of float 124 causes the float to move substantially vertically out of the water to position 174h, from position 174h the float drops on the downstream side of the wave to position 174i, and the cycle repeats. Since the float is forced into the water at the wave crest 152, i.e., from position 174b to position 174c, the vertical distance 170 traveled by the float is significantly greater than the vertical distance 168 traveled in an embodiment where the float is not forced down into the wave at or near the trough, see the upper portion of fig. 21. The energy share of the hydraulic cylinder 128 of the float 124 is also significantly greater in the path of the lower part of fig. 21 than in the path of the upper part of fig. 21.

Clearly, the net gain in the overall power output of the wave power apparatus is increased only when the energy used to force the float 124 into the wave at the trough 152 is not subtracted from the power output of the apparatus. Fig. 22 shows a modified embodiment of the hydraulic drive system of fig. 14 that can accumulate the potential energy released when the float 124 moves vertically out of the water at or near the crest of a wave, i.e., from position 174g to 174h in the lower portion of fig. 21. This energy is lost in the embodiment of fig. 14-17, and is used to force the float 124 into the wave.

More specifically, fig. 22 shows a hydraulic diagram with first, second, third and fourth hydraulic accumulators 216, 218, 220, 222, which hydraulic accumulators 216, 218, 220, 222 are used to force the float downward below the wave at the trough. In addition to the system of fig. 14, the hydraulic system of fig. 22 includes hydraulic accumulators 216, 218, 220, 222 disposed at one end of hydraulic accumulator conduits 224, 226, 228, 230, the hydraulic accumulator conduits 224, 226, 228, 230 being connected to the supply conduit 176 via first, second, third and fourth two-way valves 232, 234, 236, 238. Once the float passes the wave crest, the pressure valve 178 closes as described above with respect to fig. 14, and the float 124 displaces the wave from its submerged position in the wave. The hydraulic medium thus removed from the upper cylinder part 192 is conducted via the valves 232, 234, 236, 238 and the hydraulic accumulator conduits 224, 226, 228, 230 to the hydraulic accumulators 216, 218, 220, 222. In one embodiment, the valves 232, 234, 236, 238 are arranged and controlled such that the first valve 232 is closed at a first pressure p1, said p1 being lower than the working pressure p0 in the main conduit 180. The second valve 234 opens at a first pressure p1 and closes again at a lower second pressure p 2. The third valve 236 is open at the second pressure p2 and closed at the lower third pressure p 3. The fourth valve 238 opens at a third pressure p3 and closes again at a lower fourth pressure p 4. At still lower pressure p5, two-way valve 200 is opened.

At the trough, valve 200 is open, fourth two-way valve 238 is open, and the pressure in fourth hydraulic accumulator 222 is used to force the float under water. With fourth two-way valve 238 closed, third two-way valve 236 opens and uses the pressure in third hydraulic accumulator 220 to force the float further subsea. Thereafter the third two-way valve 236 is closed and the second two-way valve 234 is opened and the pressure in the second accumulator 218 is used to force the float further subsea. Subsequently, the second two-way valve 234 is closed, and the first two-way valve 232 is opened so that the pressure in the first accumulator 216 is used to force the float further below the surface of the water. Finally, the first two-way valve 232 is closed and the pressure valve 178 is opened.

It will be appreciated that when the float 124 moves from position 174g to position 174h (see the lower part of figure 21) vertically out of the wave, at least a portion of the released potential energy may be utilised to force the float into the water at the trough 152 in order to increase the power output of the wave power apparatus. Thus, forcing the float downward in the manner described above can be considered as a way of exploiting the potential energy released at the wave crest, which would otherwise be lost.

More than four hydraulic accumulators 216, 218, 220, 222 may be provided. For example, six, eight, ten, twelve, twenty or more hydraulic accumulators may be provided.

Fig. 23 generally shows a graphical representation of energy accumulation in N stages, i.e., in N hydraulic accumulators corresponding to the hydraulic accumulators 216, 218, 220, and 222 of fig. 22. The first axis represents the vertical displacement d of the float in the water₀250, while the second axis represents the force F₀252. The area of the shaded triangle covering half of the graph in fig. 23 represents the ideal maximum energy available. However, in order to utilize this energy, the system should include an indefinite number of stages, i.e. an indefinite number of hydraulic accumulators. In other words, the greater the pressure differential between the two stages, the greater the energy loss of each stage. In fig. 23, the energy loss is represented by shaded triangle 254. Each triangle represents the float moving a vertical distance ad. The area of each small triangle is the height multiplied by half the length. Thus, the loss at each stage can be determined using the following equation:

in the formula:

F₀the float is forced under water by a distance d₀The force of the offset in time of the operation,

Δd＝d₀n, and

n is the number of stages.

The total loss of energy, i.e. the sum of the small triangles, is defined by the following equation:

therefore, the larger the number of stages N, the smaller the total loss of energy.

The effect of the hydraulic accumulator in fig. 22 and 23 described above is illustrated in fig. 24, where curve 256 shows the movement of the float in the wave as a function of time, and curve 258 the shape of the wave as a function of time. Downstream of the wave, i.e. on the falling side, the curves 256 and 258 partly overlap. At 260, two-way valve 200 is closed (see fig. 22), while pressure valve 178 is also closed and locks the float. At 262, the float moves away from the wave and delivers energy to the hydraulic accumulators 216, 218, 220, and 222. In fig. 25, curve 264 shows the actual amount of descent of the float in the wave.

Claims (26)

1. A wave power apparatus comprising:

a plurality of arms, each arm being rotatably supported at one end by a shaft, and wherein each arm carries a float at its other end, said other end being opposite the supported end, such that translational movement of the float caused by a wave causes the arm to rotate about said shaft; energy transforming means for transforming energy transmitted from the waves to the arms into electric power, said arms being arranged in a row such that waves passing through said row cause the arms to pivot in turn about said axis, the arms being arranged at a distance from each other such that passage of the waves causes the arms to pivot with a mutual phase shift, the energy transforming means comprising a hydraulic drive system with a hydraulic drive motor,

wherein each arm is connected to the hydraulic drive system by at least one hydraulic cylinder which discharges hydraulic medium of the hydraulic drive system into the motor, the hydraulic cylinders being arranged to discharge hydraulic medium to the motor via a common hydraulic conduit,

it is characterized in that the preparation method is characterized in that,

each hydraulic cylinder is provided with a sensor for determining the position and/or rate of movement of the cylinder piston, which sensor is arranged to transmit a signal to a control unit of the hydraulic cylinder and the associated valve, so that the transmission of energy from each hydraulic cylinder to the remaining components of the hydraulic drive system can be individually controlled in response to a signal representing the position and/or rate of movement of the respective cylinder piston.

2. A wave power apparatus according to claim 1, wherein the row of arms is oriented such with respect to the wave direction that the row of arms forms an angle with the wave direction within +/-60 °.

3. A wave power apparatus according to claim 1 or 2, wherein each arm intermittently transmits power to the power conversion means when a wave passes the float of the arm, the arms and floats being arranged with such mutual distances that at all times at least two arms and floats simultaneously transmit a power contribution to the power conversion means.

4. A wave power apparatus according to claim 1 or 2, wherein the buoyancy of the float is at least 10 times its dry weight.

5. A wave power apparatus according to claim 1 or 2, wherein the diameter of the float is at least 5 times its height.

6. A wave power apparatus according to claim 1 or 2, wherein the plurality of arms comprises at least 5 arms per wave of wavelength.

7. A wave power apparatus according to claim 1 or 2, wherein the plurality of arms comprises at least 5 arms spanning an overall length of 50-200 m.

8. A wave power apparatus according to claim 1 or 2, wherein the arm and the float have a density of at most 1000kg/m³Is manufactured by the material of (1).

9. A wave power apparatus according to claim 1, wherein the at least one hydraulic cylinder of each arm comprises a double-acting cylinder.

10. A wave power apparatus according to claim 9, wherein the hydraulic drive system comprises at least one hydraulic accumulator for intermittently storing energy in the hydraulic drive system, and wherein the hydraulic drive system is controllable to release the energy stored in the accumulator when a float is passed by a wave trough, thereby forcing the float carried by the arm into the wave.

11. A wave power apparatus according to claim 10, wherein the hydraulic medium is supplied to the hydraulic accumulator via a common hydraulic conduit.

12. A wave power apparatus according to claim 1 or 2, wherein the shaft and the power conversion means are supported by a support structure, which is anchored to the sea floor by means of a suction anchor or a gravity support.

13. A wave power apparatus according to claim 12, wherein the support structure comprises a truss structure, and wherein the suction anchor is arranged at a first node of the truss structure.

14. A wave power apparatus according to claim 13, wherein at least one arm is supported by the truss structure at its second node.

15. A wave power apparatus according to claim 14, wherein the second node is arranged at the highest point of a triangular substructure of the truss structure, and wherein the triangular substructure defines two vertices at the sea bottom with anchors in each corner.

16. A wave power apparatus according to claim 15, wherein the truss structure comprises a polygonal substructure arranged above the triangular substructure.

17. A wave power apparatus according to claim 12, wherein the support structure comprises a ballast for providing a downward force on the support structure, the ballast being arranged above sea level.

18. A wave power apparatus according to claim 17, wherein the ballast comprises at least one ballast tank or ballast container.

19. A wave power apparatus according to claim 12, wherein the arm is connected to the shaft at least two points along the shaft, which points are offset from a centre axis of the arm, and wherein the shaft is rotatably supported by a fixed support structure comprising two bearings arranged to counteract radial and axial forces.

20. A wave power apparatus according to claim 19, wherein the bearing is pre-stressed in the axial direction.

21. A wave power apparatus according to claim 19, comprising a plurality of arms and a plurality of shafts, such that each arm is supported by its own shaft, each arm being connected to its own shaft at two points along the shaft, the at least two points being offset from a central axis of the arm, wherein each shaft is rotatably supported by the fixed support structure by two bearings arranged to counteract radial and axial forces.

22. A wave power apparatus according to claim 19, wherein each bearing comprises an inner ring and an outer ring, the inner ring being fixed to the rotational axis of the arm and the outer ring being fixed to a fixed support, the bearing further comprising a flexible material between the inner ring and the outer ring.

23. A wave power apparatus according to claim 22, wherein the flexible material comprises at least one cavity or perforation.

24. A wave power apparatus according to claim 22, wherein the flexible material comprises at least one spring element.

25. A wave power apparatus according to claim 1 or 2, further comprising a hydraulic lifting system for lifting the float out of the sea and for locking the float in an upper position above the sea surface.

26. A wave power apparatus according to claim 25, wherein the double-acting cylinder forms part of a hydraulic lifting system, whereby the cylinder is controllable to lift the float out of the sea.