EP3204632A1

EP3204632A1 - Wave energy device

Info

Publication number: EP3204632A1
Application number: EP15775714.7A
Authority: EP
Inventors: Alejandro GONZÁLEZ ANDREU; Alberto PIZÁ SEÑAS; Enrique MUÑOZ ARJONA; Remy Pascal; Ángel MARTÍN-BEJARANO; Cristina RODRÍGUEZ BORDALLO; Alejandro Torres Molina; Antonio CAMPOS MARÍN; Antonio Luis RUIZ MONTERO
Original assignee: Abengoa Seapower SA
Current assignee: Abengoa Seapower SA
Priority date: 2014-10-09
Filing date: 2015-10-08
Publication date: 2017-08-16
Also published as: WO2016055559A1

Abstract

The wave energy device comprises at least three nodes (1A, 1B, 1C, 1D, 1E), each node being connected to at least another one of the nodes, each node comprising at least one enclosure (11) for housing a water column (100) in an internal space (12) of the enclosure (11). The wave energy device comprises at least one buoyancy chamber (15, 25) associated with means (16, 26) for controlling an amount of water in the buoyancy chamber (15) by pumping water out of and by admitting water into the buoyancy chamber (15, 25), respectively, so as to allow for the adaptation of the mass of the wave energy device to the state of the sea, for enhancing efficiency of energy capture.

Description

WAVE ENERGY DEVICE

TECHNICAL FIELD

The invention relates to the field of wave energy conversion based on oscillating water columns.

STATE OF THE ART

In view of the increased global energy consumption and the drawbacks involved with nuclear energy and the combustion of fossil fuels such as primarily coal, fuel oil or natural gas, during the last decades a substantial development of so-called renewable energies has taken place. Renewable energies include solar power, wind power, and also the so-called wave power, where the waves on the surface of water, such as in large seas or oceans, are used to drive different energy conversion devices, such as turbines for producing electrical energy. Some wave energy converters are based on floats that move vertically with the waves, this movement being transmitted, for example, by pumps driving hydraulic fluid, to some kind of generator of electrical energy. Another type of wave energy converters are based on the so-called oscillating water column (OWC) technology. Generally, OWC converters comprise at least one enclosure for housing a water column which is in fluid communication with the water outside the enclosure, for example, due to an open bottom portion of the enclosure. Thereby, the waves in the water outside the enclosure cause the water column inside the enclosure to rise and to sink, that is, to oscillate. This oscillation can be used to drive one or more energy converters, for example, for converting the oscillating movement into electrical energy by driving a turbine. For example, the turbine can be driven by an air flow caused by the variation in the pressure in a fluid, such as air, above the water column in the enclosure, when the water column rises and sinks within the enclosure, due to the waves outside the enclosure. That is, OWC systems can operate based on the cyclical compression of air above the water column, the compressed air being used to drive a generator of electrical energy, for example, via a pneumatically driven turbine.

WO-201 1 /162615-A2 teaches an ocean wave energy system based on an array of enclosures, in this case, hollow columns whose respective lower ends are in fluid communication with ocean waves and whose respective upper ends are in air communication with a turbine arrangement such that wave motion occurring at the lower ends causes air movement within the columns for propelling the turbine arrangement to generate power output. The document includes a discussion of the theory of energy production from waves, including a discussion of the need to tune the arrangement to the frequency of the waves, and the difficulties involved therewith. Position-adjustable and/or angle-adjustable submerged structures are used to improve coupling of the waves into the hollow columns in a controllable manner. The hollow columns are arranged in a structure or platform that is supported on the seabed, or in an unspecified floating structure. It appears that a relatively substantial number of hollow tubes are arranged on or within a very substantial frame structure, such as a floating platform that is seabed-supported or coastal- supported. The document teaches the use of an optional sensing arrangement for determining one or more characteristics of ocean waves, and a control arrangement for providing a dynamically responsive control of submerged structures for tuning the arrangement. The control can be based on numerical models or neural networks. The document mentions the option of sensing a prevailing direction of propagation of the waves, and rotating the array of columns accordingly. The document also mentions the use of baffles to stabilize the platform.

GB-A-2504682-A discloses an OWC wave energy converter with a plurality of columns in fluid communication with ocean waves via ports, arranged in a specific manner. In one embodiment the system comprises a buoyant platform having a plurality of peripheral outwardly-projecting lobes. This arrangement is said to be robust and difficult to flip over. Other embodiments are described in which the columns are arranged around a central cylindrical base with a heavy ballast mass at a lower portion thereof, or within a buoyant framework comprising buoyant cylindrical towers. The document teaches that port channels and air columns can be arranged to operate in a resonant mode, for example by carefully controlling an amount of energy pickoff at the energy pickoff devices, so as to obtain a desired degree of damping, namely resonant Q-factor. The document also teaches that a natural period of resonance of water depends on water mass and thus on water height in the converter, and that the converter can be tuned to a frequency characteristic of ocean waves to be received at the converter by height adjustment, conveniently achieved by a suitable ballasting system onto which the converter is mounted. Also, it is suggested that in the case of very severe storm conditions, the port channels can beneficially be submerged more deeply into the ocean.

CA-2785428-A1 relates to a system involving ducts for receiving oscillating water columns. A support structure involving rigid columns or pylons is disclosed, and ballast elements can be provided to stabilize the support structure.

GB-2460553-A teaches an OWC system with a plurality of chambers or enclosures, and more than two turbines per chamber. Tension mooring systems and systems requiring heave are discussed. Resonance of the mass of water within the chambers is discussed. It is explained that the turbine acts as a restriction to the entry and exit of water from the surrounding sea into the air chamber, that is, the enclosure in which the oscillating water column is housed, and that the extent of this restriction is known as the damping level. For optimum power transfer from wave to turbine, there exists an optimum damping or restriction level. For an impulse turbine, the damping level the turbine applies increases as the air mass flow rate and the differential air pressure increase. As the applied damping level increases, there comes some point when the damping level will exceed the optimum value. The use of more than two turbines per enclosure can be used to divide mass flow between several turbines so as to lower the applied damping level back towards the optimum level. However, this implies the use of a large number of turbines, some of which will remain idle for a substantial amount of time when the system is in use.

WO-2010/022474- A1 discloses OWC system with a duct having two segments arranged transversally to each other. A buoyancy element can be laterally mounted to the duct. An energy conversion unit preferably includes a turbine being hydraulically driven by the oscillating water column.

US-2007/0180823-A1 discloses a system comprising flow paths which can have different lengths so that the flow paths can have different frequencies, in order to allow the system to extract energy from waves of different periodicity in an efficient manner. The system can be based on a heave-resistant vessel.

WO-87/03045-A1 discloses an OWC system with an inclined column.

GB-2325964-A is a further example of a document discussing tuning of an OWC system to enhance efficiency. Pressure adjustment means are used for controlling the mean pressure of the fluid within the tube.

It is clear from the state in the art that a substantial attention has been paid to the tuning of the OWC systems to the state of the sea or ocean, basically, to the frequency of the waves. This can involve damping. Whereas it appears to be known in the art that damping can be achieved, at least to a certain extent, by the operation of the means (such as turbine/generator) for converting the oscillations into electrical energy (as the energy capture has a damping effect), for efficient energy conversion turbines and generators have to operate under certain conditions or ranges of conditions. Thus, and whereas the operation of the energy conversion means may be useful to accommodate for minor changes of the behavior of the waves, such as for short-time adaptation to minor variations, it may not be appropriate or sufficient to accommodate, on its own, for the more substantial variations that often take place over longer periods of time.

DE-10200900821 1 -A1 discloses an OWC system with a plurality of tubular members. It is stated that in some embodiments, the level of the system in the water can be adjusted by adding or removing air under pressure from the tubular members.

US-201 1/0308244-A1 and JP-H01 -102483-U disclose further examples of wave energy transformation devices.

DESCRIPTION OF THE INVENTION A first aspect of the invention relates to a wave energy device comprising at least three nodes, each one of said nodes being connected to at least another one of said nodes. In some embodiments, each node is connected to at least two other nodes. Each node comprises at least one enclosure for housing a water column in an internal space of said enclosure, said enclosure comprising at least one opening, such as an open lower end of the enclosure, for establishing fluid communication between said internal space and a surrounding space, that is, to the sea or ocean water in which the wave energy device is placed, so that when the device is placed in water, the water column in said internal space is in fluid communication with water surrounding the enclosure, so that waves in the water outside the enclosure produce oscillation of said water column.

The wave energy device further comprises energy conversion means including, for example, a pneumatically driven turbine and generator. The energy conversion means are arranged to be driven by the oscillation of the water column to produce electrical energy. Due to the oscillation of the level of the water column, the air pressure varies within the enclosure, above the water column, and this variation in the air pressure drives the turbine.

Placing the enclosures at nodes makes it possible to implement a nodal system in which major components, including the enclosures for housing the oscillating water columns, are located at specific nodes, which can be substantially spaced from each other, thereby distributing the system over a substantial area and reducing the risk for any overturning of the system. The nodes can be connected to each other using beams or similar, for example, establishing a mesh-like structure or lattice of beams interconnecting nodes. This nodal structure makes it easy to implement a distributed system, with a high diameter or width to height ratio, thereby enhancing stability and reducing the risk for the system being overturned in the case of extreme waves.

In accordance with this aspect of the invention, the device additionally comprises at least one buoyancy chamber or ballast chamber associated with means for controlling an amount of water in the buoyancy chamber by pumping water out of and by admitting water into said buoyancy chamber, respectively, so as to allow for the adaptation of the mass of the wave energy device to the state of the sea, for enhancing efficiency of energy capture. Thereby, tuning of the device to the characteristics of the sea can be made by letting ballast, namely water, into or out of one or more of the buoyancy chambers, thereby increasing/decreasing the mass of the device. For example, this can be used to adapt the device to substantial and/or long-term variations (for example, in terms of days) of the frequency of the waves, in addition to the fine-tuning or short-term adaptation (for example, in terms of hours or even shorter) that can be achieved by controlling the damping provided by the energy conversion means.

Due to buoyancy chambers and other buoyancy means, the wave energy device can float in the water, partly submerged to an extent that is determined, at least to a certain extent, by the amount of water that has been admitted into the buoyancy chambers.

In some embodiments of the invention, the wave energy device comprises a plurality of said buoyancy chambers, at least one of said buoyancy chambers being associated to each one of a plurality of the nodes. Distributing the buoyancy chambers between a plurality of nodes makes it possible to further enhance the nodal character of the system.

In some embodiments of the invention, in each of a plurality of said nodes at least one of said enclosures for housing a water column comprises a double wall, with a space between an inner wall and an outer wall making up one of said buoyancy chambers. This is advantageous as the structure of the enclosures needed to establish the oscillating water column is further used to establish at least part of the buoyancy chambers. This implies an efficient use of material and a cost reduction, and a simple implementation of a distributed system with water columns and buoyancy/ballast chambers distributed among the different nodes. Further, the use of a double wall for establishing the enclosure for the oscillating water column benefits the rigidity of the enclosure. Thus, the double wall serves a double purpose: it enhances rigidity with a limited use of material (that is, it provides for an advantageous rigidity/cost ratio), and at the same time it serves to establish a space that makes up a buoyancy chamber that can be used to adapt the mass of the wave energy device to the state of the sea. Thus, the enclosures will feature a substantial resistance against the forces exerted by the waves, and at the same time serve as buoyancy chambers.

In some embodiments of the invention, one or more buoyancy chambers are not associated directly to any node, but are placed elsewhere in the wave energy device. For example, in some embodiments of the invention, the nodes are spaced from each other and interconnected by beams, for example, by a lattice structure comprising some kind of beams, and at least one of the buoyancy chambers is associated to one of the beams. This can be in addition to or as an alternative to buoyancy chambers at the nodes. For example, in some of the embodiments, one or more of the buoyancy chambers are arranged within the corresponding beam or beams. In some embodiments of the invention, at least one of the beams is subdivided into a plurality of compartments, each of said compartments forming a buoyancy chamber. This kind of arrangement has been found practical and economical, as it uses part of the structure used to interconnect the nodes to implement the buoyancy chambers, thus making efficient use of the material used for manufacturing the device.

In some embodiments of the invention, the wave energy device further comprises a plurality of heave plates, at least some of said heave plates being mounted in correspondence with at least some of the enclosures. The heave plates serve to increase stability of the device, reducing a balancing movement of the device that can reduce the efficiency with which energy is extracted from the waves. They can also serve to enhance the rigidity of the enclosures. In some embodiments of the invention, at least one of the heave plates is attached to one of the enclosures. It has been found that for example the walls of the enclosures can be an appropriate place for attaching the heave plates. For example, heave plates can be attached in correspondence to a lower portion of said walls. The heave plates can for example be placed to surround all or a substantial portion of the enclosure. In some embodiments of the invention, the heave plates have a polygonal shape when viewed from above, such as an octagonal shape. In some embodiments of the invention, one or more of the heave plates, such as all of the heave plates, surround the entire enclosure. In other embodiments of the invention, one or more of the heave plates, such as all of the heave plates, only partially surround the corresponding enclosure, for example, extending around less than 290° of the enclosure, such as around 90 ° of the enclosure.

In some embodiments of the invention, the nodes are spaced from each other and interconnected by beams, such as by a lattice structure of beams. For example, each node can be placed several meters from the adjacent notes, and each node can be connected by beams to other nodes. A substantial separation, such as a spacing by 5, 10, 15 or 20 meters or more between nodes reduces the extent to which nodes affect the waves reaching other nodes, such as shadowing effects. Thus, a very extensive and stable structure can be achieved, with distributed but interconnected nodes, wherein the stability does not depend on the mooring lines but on the substantial width to height ratio of the device.

In some embodiments of the invention, each node has a maximum width, and the distance between adjacent nodes is at least 50%, more preferably at least 100%, of said maximum width. As indicated above, this distribution reduces the risk for shadow effects and enhances stability of the system.

In some embodiments of the invention, the wave energy device comprises at least four nodes, said at least four nodes comprising at least three nodes forming the corners of a polygon, each of said at least three nodes being connected to two adjacent nodes forming corners of said polygon, and at least one node not forming a corner of the polygon and being connected to at least three other nodes. This nodal or reticular arrangement provides for a distributed system, with stability in different directions. For example, the wave energy device may comprise at least five nodes, at least four nodes forming the corners of a polygon, and at least one node not forming a corner of the polygon and being connected to at least some of the nodes forming the corners of the polygon.

In some embodiments of the invention, the wave energy device has exactly three nodes, so that the wave energy device has a substantially triangular shape when viewed from above. Each node can be placed in correspondence with an apex of a triangle. In some embodiments, the wave energy device is substantially shaped as an isosceles triangle when viewed from above, that is, with two identically long sides and one side having a different length. For example, one of the sides can be longer than the other sides. The use of a triangular layout, with three nodes, has been found to enhance efficiency in terms of produced power in relation to the weight of the system.

It has been found that when using for example a structure with five nodes wherein four nodes are arranged in correspondence with the corners of a square and the fifth one in the center, the amount of energy produced by the nodes at the downstream end (considering the direction in which the waves travel) of the device was rather low. It is believed that the reason for this may be that these downstream nodes follow the movement of the waves, thereby reducing the amplitude of oscillation of the water column. It has been found that a triangular layout can provide for enhanced efficiency in terms of energy production versus weight. The device can be arranged with one of the sides facing the waves, for example, in the case of an isosceles triangle having two shorter sides and one longer side, the larger side can be chosen to face the waves.

In some embodiments of the invention using the triangular or three-node layout, a first node is connected to a second node by at least one first beam, the first node is connected to a third node by at least one second beam, and the second node is connected to the third node by at least a third beam. The beams can form part of a lattice structure.

In other embodiments of the invention using the triangular layout, a first node is connected to a second node by at least one first beam, and the first node is connected to a third node by at least one second beam, but the second node is not directly connected to the third node by any beam. The side comprising the second and the third node can, for example, be arranged to face the waves, whereby the absence of beams or lattice structure minimizes the influence of the structure on the incoming waves. This may serve to further enhance efficiency. In some embodiments, the distance between the second node and the third node is larger than the distance between the first node and the second node, and also larger than the distance between the first node and the third node.

In some embodiments of the invention, the first node is connected to the second node by a first lattice structure, and the first node is connected to the third node by a second lattice structure, and the second node is connected to the third node by a third lattice structure, the third lattice structure being different (such as by having a different structure as such, and/or by being placed differently, for example, on a different height) from the first lattice structure and the second lattice structure, to minimize interference of the third lattice structure with waves when the wave energy device is arranged with the third lattice structure facing the waves. For example, the third lattice structure can be less bulky and/or be positioned lower than the first and second lattice structures. For example, the most substantial part of the resistance of the structure interconnecting the nodes can be provided by the first and second lattice structures, whereas the third lattice structure can simply be there to provide some additional support, for example, so as to maintain the separation between the second and third nodes.

In some embodiments of the invention, in at least one of the enclosures the internal space includes a water column division means extending through part of the internal space and arranged so that when the device is in use, the water column division means will separate at least one part of the water column from another part of the water column at least in correspondence with an upper surface of the water column. For example, the water column division means can include at least one panel extending vertically within the internal space, preferably without reaching the top of the internal space. The water column division means can serve to divide the surface of the water column into several smaller surface portions, thereby reducing the waves or swell on the surface of the oscillating water column. These waves or swell consume energy and thus reduce the efficiency of the system. One easy way of implementing this is by using one or more separating walls or panels extending vertically within the internal space. Preferably, they do not reach the top of the internal space, so that the fluid air communication between the internal space and the energy conversion means (such as the turbine) can be established via one single outlet, for example, in a top closure of the enclosure. This solution allows for the use of rather large enclosures, such as enclosures having an inner space with a major dimension in the horizontal direction, such as a diameter, of five meters or more. Also, the panels or other division means can be used to reinforce the structure of the enclosures, for example, acting as reinforcing structures or beams that prevent the walls of the enclosure from being deformed by the waves, for example, from bulging inwards due to the impacts produced by waves when the device is used in rough conditions.

In some embodiments of the invention, the wave energy device further comprises a control system arranged for modifying the characteristics of the device depending on the frequency of the waves, by adapting the damping provided by the energy conversion means and by adapting the amount of water in the buoyancy chambers. As indicated above, major and long-term variations are preferably accommodated by adapting the amount of water in the buoyancy chambers, and short-term variations by adapting the damping provided by the energy conversion means, such as pneumatic turbines.

In some embodiments of the invention, the energy conversion means comprise at least one turbine, preferably a pneumatically driven turbine arranged to be driven by air movement or air pressure oscillations caused by the oscillating water column. In some embodiments, at least one of the turbines is mounted in each node. Although it may sometimes be preferred to have one turbine being feed by several nodes, or all of the turbines grouped together in one portion of the device, due to the often preferred substantial separation of the nodes, it can be preferred to have at least one turbine mounted on each node.

Another aspect of the invention relates to a method of adapting or tuning a wave energy device as the one described above to the state of the sea. The adaptation or tuning is carried out by adapting the damping provided by the energy conversion means and by adapting the mass of the device by adapting the amount of water in the at least one buoyancy chamber. The adaptation of the damping provided by the energy conversion means can be used for rapid fine-tuning of the device to the state of the see, whereas larger variations in the state of the sea that take place over longer time periods are accommodated by the adaptation of the amount of water in one or more of the buoyancy chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the invention, which should not be interpreted as restricting the scope of the invention, but just as examples of how the invention can be carried out. The drawings comprise the following figures:

Figure 1 is a schematic perspective view of a wave energy device in accordance with an embodiment of the invention.

Figure 2 is a schematic cross sectional side view of one of the nodes of the wave energy device of figure 1 .

Figure 3 is a schematic perspective view of this node.

Figure 4 is a schematic perspective view of a wave energy device in accordance with another embodiment of the invention.

Figures 5A-5H schematically illustrate the general layouts of the wave energy device in accordance with different embodiments of the invention.

Figures 6A and 6B are a top view and a side view, respectively, of a wave energy device in accordance with an embodiment of the invention.

Figure 6C is a top view of a variant of the embodiment of figures 6A and 6B.

Figure 7 is an exploded view showing some of the components of a node in accordance with an embodiment of the invention.

Figures 8A and 8B schematically illustrate how a heave plate can be attached to the cylinder forming the outer wall of the enclosure.

Figure 9A and 9B schematically illustrate how a support for components can be attached to the top portion of the enclosure.

Figure 10 schematically illustrates a portion of a lattice structure for interconnection of nodes in an embodiment of the invention. Figure 1 1 shows the result of a comparative analysis of efficiency of a wave energy device with five nodes and a wave energy device with three nodes.

Figure 12 is a schematic perspective view of a wave energy device according to an alternative embodiment of the invention.

DESCRIPTION OF WAYS OF CARRYING OUT THE INVENTION

Figure 1 illustrates an embodiment of the device, comprising five nodes, namely, four nodes (1 B, 1 C, 1 D, 1 E) placed in correspondence with the four corners of a polygon -in this case a square- corresponding to the general outline of the device, and one node (1 A) placed at the center of the device. The nodes are interconnected by a lattice structure comprising beams 2. The nodes are separated from each other by these beams, and the shortest distance d between two adjacent nodes is preferably substantial, for example, similar to or larger than the width of each node. The spacing between adjacent nodes amounts to several meters, such as more than 10 meters, and provides for a distributed system, wherein the nodes are spread over a substantial area, thereby increasing the general stability of the system and reducing the risk for the device being overturned in the case of bad weather or rough conditions of the sea. The spacing between the nodes (1 B, 1 C, 1 D, 1 E) placed in correspondence with the corners of the polygon is larger than the width of each node.

Each node comprises an enclosure 1 1 for housing a water column 100, as schematically illustrated in figure 2. The enclosure is open 13 at its bottom, thereby establishing fluid communication with the water surrounding the enclosure, so that the water can enter the internal space 12 of the enclosure. The waves outside the enclosure 1 1 will give rise to an oscillation of the water column. On the other hand, the enclosure has an upper end which is closed except for one or more openings communicating with a pneumatic turbine 14. The oscillation of the water column produces corresponding changes in the air pressure above the water column 100 in the enclosure, and these pressure changes are used to drive the pneumatic turbine, as known per se in the art.

Figures 2 and 3 show how the enclosure 1 1 comprises a double wall comprising an outer wall (1 1 a) and an inner wall (1 1 b), these two walls delimiting (together with closures at the top and at the bottom) a buoyancy chamber 15. Water can enter and exit the buoyancy chamber 15 through an inlet/outlet system including pumps 16 and valves (not illustrated in the drawings). Thus, the pumps 16 allow for an active control of the amount and level of water in the buoyancy chamber 15, and thereby of the total mass of the wave energy device. By letting water into the buoyancy chambers and by pumping water out of the buoyancy chambers of the nodes, the mass of the system can be adapted or tuned to the state of the sea, thereby enhancing efficiency of the system. On the other hand, the double wall of the enclosure 1 1 additionally provides for rigidity and resistance. Thus, this embodiment allows for a stable and distributed nodal system, with a double wall structure that provides for rigidity and at the same time serves to establish buoyancy chambers that contribute to the floatability of the device and to the adaptability of the mass of the device to the state of the sea. Additional rigidity and stability of the device can be provided by the use of horizontal heave plates 17, as schematically illustrated in figure 3. The heave plates serve to reduce the movement up and down of the nodes, thereby enhancing the efficiency.

Figure 2 schematically illustrates how the device includes a control system 20 that controls operation of the pneumatic turbine 14 and operation of the pumps 16, whereby the control system 20 can control the adaptation of the device to the state of the sea, by controlling and adapting the damping of the pneumatic turbines of the device and by controlling the mass of the device by controlling the amount of water in the ballast chambers, that is, the amount of water within the double walls of the enclosure 1 1 . The adaptation of the damping of the turbines can be carried out rapidly, that is, it allows for a rapid fine-tuning to rapid and minor changes in the state of the sea, whereas larger long-term changes are accommodated by adapting the mass of the device by pumping water out of or into the ballast chambers of the enclosures 1 1 .

Figure 3 schematically shows how the enclosure 1 1 includes a panel 18 extending vertically within said internal space, but without reaching the top of the internal space. This panel 18 divides the surface of the water column into two smaller surface portions, thereby reducing the waves or swell on the surface of the oscillating water column. This enhances the efficiency of the device, as this kind of waves or swell consumes energy and thus reduces the efficiency of the system. As the panel 18 does not reach the top of the internal space, full air communication between the internal space at the top of the enclosure and the pneumatic turbine or turbines can be established via one single outlet, for example, in the top closure of the enclosure. This solution allows for the use of rather large enclosures, such as enclosures having an inner space with a major dimension in the horizontal direction, such as a diameter, of five meters or more, without losing too much efficiency due to waves or swell at the top of the oscillating water columns. Also, the panel 18 can further enhance the rigidity of the system.

Instead of one flat panel as shown in figure 3, the enclosure 1 1 can house a structure with two or more panels connected (such as welded) together forming a vertical and reinforcing X beam. Instead of one panel 18 extending between two of the inner walls 1 1 b, a structure interconnecting the four inner side walls 1 1 b can be used.

Figure 4 schematically illustrates a variant using enclosures having a circular cross section, instead of the substantially square cross sections of the enclosures of the embodiment of figures 1 -3. Figures 5A-5H show the general layout of some embodiments of the invention. Figures 5A and 5B illustrate two embodiments with five enclosures for establishing water columns, figures 5C and 5D illustrate two embodiments with six enclosures, figure 5E illustrates an embodiment with seven enclosures, figure 5F illustrates an embodiment with eight enclosures, and figures 5G and 5H illustrate two embodiments with nine enclosures.

Figures 6A and 6B show a wave energy device with three nodes, featuring a triangular layout and, more specifically, a layout where the nodes 1 A, 1 B and 1 C are arranged at the apices of an isosceles triangle, that is, a triangle with two identically long sides and one side of different length. In the illustrated embodiment, nodes 1 A and 1 B are placed at the ends of the longer side, and both are connected to node 1 C. In this embodiment, the enclosures 1 1 are cylindrical and provided with polygonal -in this case, octagonal- heave plates 17 to improve stability. The nodes 1 A, 1 B and 1 C are interconnected by beams 2 and 2', forming a lattice structure. In some embodiments of the invention, the nodes have diameters in the order of 0.7-1 .2 meters, and the centers of the enclosures are separated from each other by a distance at least 30% larger than the diameter of each enclosure. As explained above, some of the beams can, in some embodiments, incorporate one or more buoyancy chambers.

In the embodiment shown in figure 6A, the side corresponding to the longest beam 2' can be arranged facing the waves; in figure 6A, the arrow shows the direction of the waves in relation to the wave energy device, when the wave energy device has been placed in this way. The lattice structure comprising the beam 2' can be different, such as placed differently, compared to the other lattice structures. For example, it can be placed at a level minimizing the impact it will have on the waves, thereby allowing the waves to reach also the downstream node 1 C with full power.

Figure 6C shows a similar embodiment, but with the lattice structure joining node 1 A and 1 B removed, thereby preventing any interaction between such a lattice structure and the incoming waves.

Figure 7 schematically illustrates some of the components of one of the nodes. The main component is the enclosure, with an outer cylindrical wall 104. A truncated cone shaped closure element 103 is placed on top of the cylinder 104, and a circular support 101 for attaching components, such as for example a valve or a generator, is attached to the closure element 103, with the use of a plurality of triangular intermediate elements 102.

A heave plate is provided at the bottom of the cylinder 104, and comprises an upper portion 105 and a bottom portion 109, as well as some additional elements 106-108. These elements are shown more in detail in figures 8A and 8B. Figure 8A shows how the bottom portion 109 of the heave plate is attached to the cylinder 104 by an interconnection member 107 having cross section in the vertical place featuring a curvature. This kind of partly toroidal surface at the interface between heave plate and cylinder is considered to provide for enhanced stability. However, for even further enhanced stability, a further component 106 in the shape of a truncated cone is provided covering the external surface of the interconnection member 107, and the beams 108A of the rib structure 108 can be welded to this further component. The upper portion 105 can then be placed on top of these beams 108A. This layout of the heave plate is considered to provide for high stability at a reasonable cost.

Figures 9A and 9B show how the support 101 can be attached to the cover 103 using simple triangular attachment members 102.

Figure 10 schematically illustrates how, in an embodiment of the invention, the nodes can be interconnected using a lattice structure made up of beams 2A, 2B of different sizes, welded to each other.

Figure 1 1 illustrates the result of a simulation comparing the efficiency, in terms of kW/tonnes, between a device with three nodes and a device with five nodes, during different conditions in terms of power on site expressed as kW/m².

Figure 12 illustrates an embodiment in which a plurality of buoyancy chambers 25 have been arranged within at least some of the beams 2, 2' used for interconnecting the nodes. In this embodiment, all of the lowermost beams are arranged to house such buoyancy chambers 25, which are enclosed within the beams and separated from each other by walls 27. Means 26 for controlling the amount of water in the buoyancy chambers include conduits 26A extending out of the corresponding beam so as to interconnect the space within the beam with the water outside the beam, main valves 26B, manifolds 26C and valves 26D placed in the individual buoyancy chambers. Pumps (not shown) are connected to the conduits 26A. Thus, this embodiment makes use of the beams or lattice structure interconnecting the nodes to implement the buoyancy chambers.

In this text, the term "comprises" and its derivations (such as "comprising", etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.

On the other hand, the invention is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the invention as defined in the claims.

Claims

1 . - A wave energy device, comprising at least three nodes (1 A, 1 B, 1 C, 1 D, 1 E), each one of the nodes being connected to at least another one of the nodes, each node comprising at least one enclosure (1 1 ) for housing a water column (100) in an internal space (12) of the enclosure (1 1 ), the enclosure comprising at least one opening (13) for establishing fluid communication between the internal space and a surrounding space so that when the device is placed in water, the water column (100) in the internal space is in fluid communication with water surrounding the enclosure, so that waves in the water outside the enclosure produce oscillation of the water column, the wave energy device further comprising energy conversion means arranged to be driven by the oscillation of the water column to produce electrical energy,

wherein

the device additionally comprises at least one buoyancy chamber (15, 25) associated with means (16, 26) for controlling an amount of water in the buoyancy chamber (15, 25) by pumping water out of and by admitting water into the buoyancy chamber (15, 25), respectively.

2. - The wave energy device according to claim 1 , comprising a plurality of the buoyancy chambers (15), at least one of the buoyancy chambers being associated to each one of a plurality of the nodes (1 A, 1 B, 1 C, 1 D, 1 E).

3. - The wave energy device according to claim 2, wherein in each of a plurality of the nodes, at least one of the enclosures for housing a water column comprises a double wall, with a space between an inner wall (1 1 b) and an outer wall (1 1 a, 104) making up one of the buoyancy chambers (15).

4. - The wave energy device according to any of the preceding claims, further comprising a plurality of heave plates, at least some of the heave plates (17) being mounted in correspondence with at least some of the enclosures (1 1 ).

5. - The wave energy device according to claim 4, wherein at least one of the heave plates (17) is attached to one of the enclosures (1 1 ).

6. - The wave energy device according to any of the preceding claims, wherein the nodes (1 A, 1 B, 1 C, 1 D, 1 E) are spaced from each other and interconnected by beams (2, 2').

7. - The wave energy device according to claim 1 , wherein the nodes (1 A, 1 B, 1 C, 1 D, 1 E) are spaced from each other and interconnected by beams (2, 2'), and wherein at least one of the buoyancy chambers (25) is associated to one of the beams.

8. - The wave energy device according to claim 7, wherein said at least one buoyancy chamber (25) is arranged within the corresponding beam (2, 2').

9. - The wave energy device according to claim 8, wherein at least one of the beams (2, 2') is subdivided into a plurality of compartments, each of said compartments forming a buoyancy chamber (25).

10. - The wave energy device according to any of the preceding claims, wherein each node has a maximum width (W), and wherein the distance (d) between adjacent nodes is at least 50%, more preferably at least 100%, of the maximum width (W).

1 1 .- The wave energy device according to any of the preceding claims, comprising at least four nodes (1 A, 1 B, 1 C, 1 D, 1 E), the at least four nodes comprising

at least three nodes (1 B, 1 C, 1 D, 1 E) forming the corners of a polygon, each of said at least three nodes being connected to two adjacent nodes forming corners of said polygon, and at least one node (1 A) not forming a corner of the polygon and being connected to at least three other nodes.

12. - The wave energy device according to any of claims 1 -10, said wave energy device having exactly three nodes (1 A, 1 B, 1 C), whereby said wave energy device has a substantially triangular shape, each node of said plurality of nodes being placed in correspondence with an apex of a triangle.

13. - The wave energy device according to claim 12, wherein said wave energy device is substantially shaped as an isosceles triangle.

14.- The wave energy device according to claim 12 or 13, wherein a first node (1 C) is connected to a second node (1 A) by at least one first beam (2), and wherein the first node (1 C) is connected to a third node (1 B) by at least one second beam (2), and wherein the second node (1 A) is connected to the third node (1 C) by at least one third beam (2').

15.- The wave energy device according to claim 12 or 13, wherein a first node (1 C) is connected to a second node (1 A) by at least one first beam (2), and wherein the first node (1 C) is connected to a third node (1 B) by at least one second beam (2), and wherein the second node (1 A) is not directly connected to the third node (1 C) by any beam.

16. - The wave energy device according to claim 12 or 13, wherein a first node (1 C) is connected to a second node (1 A) by a first lattice structure, and wherein the first node is connected to a third node (1 C) by a second lattice structure, and wherein the second node (1 A) is connected to the third node (1 C) by a third lattice structure, the third lattice structure being different from the first lattice structure and the second lattice structure to minimize interference of the third lattice structure with waves when the wave energy device is arranged with the third lattice structure facing the waves.

17. - The wave energy device according to any of the preceding claims, wherein in at least one of the enclosures the internal space includes a water column division means extending through part of the internal space and arranged so that when the device is in use, the water column division means will separate at least one part of the water column from another part of the water column at least in correspondence with an upper surface of the water column.

18. - The wave energy device according to claim 17, wherein the water column division means includes at least one panel (18) extending vertically within the internal space, preferably without reaching the top of the internal space.

19. - The wave energy device according to any of the preceding claims, further comprising a control system (20) arranged for modifying the characteristics of the device depending on the frequency of the waves, by adapting the damping provided by the energy conversion means and by adapting the amount of water in the buoyancy chambers (15, 25).

20. - The wave energy device according to claim 19, wherein the control system is arranged to adapt the device to long-term variations in the frequency of the waves by adapting the amount of water in the buoyancy chambers, and to adapt the device to short-term variations in the frequency of the waves by adapting the damping provided by the energy conversion means.

21 . - The wave energy device according to any of the preceding claims, wherein the energy conversion means comprise at least one turbine (14), preferably a pneumatically driven turbine arranged to be driven by air pressure oscillations caused by the oscillating water column.

22. - The wave energy device according to claim 21 , wherein at least one of the turbines (14) is mounted in each node.

23. - A method of adapting a wave energy device according to any of the preceding claims to the state of the sea, by adapting the damping provided by the energy conversion means and by adapting the mass of the device by adapting an amount of water in the at least one buoyancy chamber (15, 25).

24. - The method according to claim 23, wherein the method comprises adapting the device to long-term variations in the frequency of the waves by adapting the amount of water in the buoyancy chambers, and adapting the device to short-term variations in the frequency of the waves by adapting the damping provided by the energy conversion means.