Completely submerged wave energy converter

A wave energy converter apparatus comprising at least two members joined by a connector movable so as to allow displacement of the members relative to one another in response to waves in water where the apparatus is located. The apparatus also includes an energy converter for converting motion of the connector to electrical energy, and a device for storing and/or transporting elsewhere the energy produced. The members, when in use and located in a body of water, are non-floating and completely submerged, the apparatus, as a whole, being neutrally buoyant. A member is additionally provided for maintaining each of the submerged members substantially at rest relative to the surrounding water with which they are in contact, such that the submerged members move under wave-induced action substantially in the same manner as a water particle would move under wave-induced action if located in the same region as the respective submerged member.

FIELD OF THE INVENTION

This disclosure relates generally to energy and, more particularly, to arrangements for power generation and the like.

BACKGROUND OF THE INVENTION

Conventional wave energy converters have experienced considerable problems including low efficiency, complex design, and/or high cost of maintenance resulting in considerable limitations in their use.

Firstly, known WECs use mainly the vertical component of the wave motion. Since the wave motion is generally circular, a significant component of the motion is wasted, see for example the devices in U.S. Pat. No. 4,453,894, U.S. Pat. No. 6,857,266, WO2004065785, U.S. Pat. No. 4,232,230, U.S. Pat. No. 4,672,222, U.S. Pat. No. 5,411,377, and the devices Pelamis, AWS WEC and AquaBuOY marketed respectively by the companies OPD Ltd (www.oceanpd.com), AWS Ocean Energy Ltd (www.waveswing.com) and AquaEnergy Group Ltd (www.aquaenergygroup.com).

In some cases, e.g. the devices shown in U.S. Pat. No. 4,453,894 and U.S. Pat. No. 6,857,266, the installation has a natural frequency of oscillation, and therefore is capable of using efficiently only waves with certain frequencies, or a latching mechanism is needed to overcome this limitation.

On the other hand, in order to seek the highest possible efficiency, known WECs using floating or near surface elements need to be oriented depending on the direction of the wave system which is to be harvested for energy. In any case, the efficiency is satisfactory only when harvesting monochromatic waves, or in any case waves moving all in the same general direction, as in the device of US2005167988A1, and in the device Pelamis and WavePlane (by the company WavePlane Production A/S, www.waveplane.com).

Furthermore, many known devices must be linked to the ground or placed in the surf zone, like for example in US2005167988A1, U.S. Pat. No. 5,411,377, and in the above mentioned devices AWS WEC, Pelamis and AquaBuOY. Therefore, they cannot be positioned where the waves are biggest and with the highest energy potential. Moreover, the on-shore or near-shore ones are bulky and hardly compatible with environmental protection.

Finally, as mentioned, the majority of the known devices use a surface float to extract energy from the wave motion or in any case they have a substantial part of their volume above the surface of the water at least during some part of the wave cycle, which can expose them excessively to severe weather and to drag due to wind and small waves. This is the case of the installations shown in U.S. Pat. No. 4,453,894, U.S. Pat. No. 6,857,266, WO2004065785, U.S. Pat. No. 4,232,230, U.S. Pat. No. 4,672,222, U.S. Pat. No. 5,411,377, and the Pelamis, AquaBuOY, WavePlane and Wave Dragon (by the company Wave Dragon ApS, www.wavedragon.net). Due to the presence of surface elements which have necessarily a limited size, there is also a structural limitation to the amount of energy which a single device can harvest.

OBJECTS AND SUMMARY OF THE INVENTION

Summary of the Invention

Accordingly, it is an object of the disclosure to provide an apparatus for wave energy conversion that achieves higher efficiency by using all the components of the wave motion.

Another object of the disclosure is to provide a wave energy converter having working efficiency both with a monochromatic wave system and a non monochromatic wave system, without being affected significantly by wave direction and waves of relatively smaller wavelength.

A further object of the disclosure is to provide a wave energy converter having a simple design that is easy to implement and maintain.

Yet an other object of the disclosure is to provide an apparatus for wave energy conversion that yields negligible motion due to natural oscillations.

Still another object of the disclosure is to provide a wave energy converter that may be positioned offshore, in very deep water.

Another object of the disclosure is to provide an apparatus for wave energy conversion that provides satisfactory resistance to severe weather.

This object is achieved with the improved wave energy converter according to the present invention, the essential characteristics of which are defined in the first of the accompanying claims.

The same numerals are used throughout the drawing figures to designate similar elements. Still other objects and advantages of the disclosure will become apparent from the following description of the preferred embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings and, more particularly, toFIGS. 1-4, there is shown generally a specific, illustrative wave energy converter, according to various aspects of the disclosure. In one embodiment, shown inFIG. 1, the wave energy converter comprises: an upper submerged member1(e.g., a cylindrical tank containing mostly water and air, with an inertial mass as low as possible); a lower submerged member2, e.g., having six smaller cylindrical tanks3of mostly water and air, linked together relatively rigidly in a circular configuration about a generally cylindrical, central linking piece5; a pole4extending between upper member1and lower member2along a common axis thereof, projecting beyond the lower member and provided internally with an appropriate counterweight system (not shown), at a selected point along its length corresponding to the average position of lower submerged member2; and a plurality of turbines6mounted to respective ends of a transversal rod7, integrally and orthogonally crossing pole4correspondingly with the lower, free end thereof.

The pole can also take the shape of a latticed steel structure, with a bigger section than that appearing in the drawings, or in any case a structure assuring enough rigidity and resistance to the stresses at play. The linking piece5will be scaled up and modified accordingly. To assist in keeping the position of the submerged members1and2fixed with respect to the water intimately surrounding them, one can also provide them with virtual mass means, in the shape of partially enclosed water and/or fins.

Pole4is desirably mounted to a lower, flat surface1aof upper submerged tank1via a joint8, such that the orientation of the pole may change relative to the tank. In one embodiment, joint8can, for example, be of a ball-and-socket type. A plurality of buoyancy elements9, e.g., small cylindrical tanks filled with air, are attached to a top flat face1bof upper submerged member1via cables10. Under the wave action buoyancy elements9assist in maintaining upper tank1at a relatively constant distance from the water surface and with its top face1bparallel thereto. The buoyancy elements are alternatively submerged or exposed by waves of shorter wavelength, such that a stabilizing action will result from their average buoyancy force.

The connection between the same pole and the lower submerged member2is realized, as mentioned, via the linking piece5. In further detail, the linking piece comprises a disc-shaped body11on an outer side surface lib of which the smaller tanks9are mounted. A spherical housing11ais formed inside the body11for rotatably accommodating a ball member12with a through hole12afor the slidable insertion of the pole4.

Therefore, there is assured the relative movement of the lower submerged member2along the axial direction of the pole4, thanks to the sliding engagement of the latter with the hole12aof the ball member12of the linking piece5. Furthermore, the lower member2can tilt around the pole via the rotatable engagement of the ball member within the housing11aof the body11. Both the sliding and the rotation can be assisted by the provision of balls and/or rollers as in roller or ball bearing configurations or other means to assist the relative movement between the parts so that the lower member can displace and tilt freely with respect to the pole.

For the sake of simplicity, in the drawings the lower member2is positioned generally in the middle of pole4. In practice, however, the portion of the pole4between the members1and2will be on average longer than the portion below and beyond the element2, in order to impress a greater motion on the turbines6in response to the movement of the upper member1.

The transversal rod7is linked to a revolving end segment4aof the pole4, so that the rod can rotate around the axis of the same pole4, while keeping its center on the same axis. The turbines6are connected to the ends of the rod7with their front side facing the rod, and with a mounting that allows them to rotate around the central axis of the same rod.

An engine system to accumulate and/or transform the energy produced by the motion of the turbines6, as explained hereafter, is neither shown nor described, having characteristics that, as such, can be learned or derived from the prior art. The engine system can be located inside the lower submerged member2and can be for example a device for electrolysis of water and generation of hydrogen, which can then be easily stored and retrieved periodically by ships. If appropriate, one can also use a cable to transfer the generated electricity to a floating or submerged engine room, or directly to the electricity grid.

In use, the apparatus as a whole has neutral buoyancy under normal operation and under rest. During normal operation, the lower member2will move much less than the upper member1which is under the direct influence of the wave action, as the wave influence decreases rapidly with depth. In particular, in a limit situation in which the biggest wavelength of incident waves is lower than, or equal to, the distance between the members1and2, the lower member2will remain approximately unmoved under a wave cycle. In a real deployment, in which for practical reasons the above mentioned average distance between members1and2will in general be shorter than a full wavelength, the motion of the lower member can be further reduced by increasing its inertial mass (and correspondingly its buoyancy, to leave it with total neutral buoyancy).

On the other hand, the upper member1would tend to move in a circular path under the influence of a monochromatic wave with wavelength comparable to the above mentioned distance (as it is usual for the motion of water particles under the influence of a monochromatic wave). If the wave system is not monochromatic, the movement of the upper member1will be a superposition of the various circular paths determined by the various monochromatic waves which are the dominant components of the wave system.

The buoyancy of the upper member1and the buoyancy elements9is precisely balanced by the counterweight inside the pole4, and by the weight of the same pole along with the transversal rod7and the turbines6, to keep the water level at about half the height of the buoyancy elements9on average. Due to the presence of the lower submerged member2and the inertia of the counterweight inside the pole4, the circular motion of the upper member1is transformed in a closed trajectory of the lower end of the pole4. This trajectory is only very roughly circular, as the motion would be circular only if the lower member2were always exactly at the midpoint of the pole4, which cannot happen under normal operation.

Under the wave action, the lower end of the pole4then moves with respect to the surrounding water and therefore the whole assembly of transversal rod7and turbines6moves setting the turbines into motion. Using fins and/or motors the turbines6can be kept always pointed in the direction of motion with respect to the surrounding water, so as to obtain a better efficiency. During the whole wave cycle of a monochromatic wave system the turbines make a turn of 360° around the axis of the transversal rod7. With a monochromatic wave system the rod7does not rotate with respect to the pole4. If the wave system is a superposition of different monochromatic wave systems, the turbines6will always be kept pointed in the direction of motion with little effort due to the fact that they describe a closed trajectory with respect to the surrounding water and hence the redirection can be incremental.

Depending on the efficiency of the turbines6in extracting energy from their motion through the water and to the position of the linking piece5along the pole4during a wave cycle, the trajectory of the lower end of the pole will tend to become roughly elliptical instead of circular. To a smaller extent also the trajectory of the upper member1will tend to become roughly elliptical. By varying the position of the lower member2with respect to the two ends of the pole4, one can modify the shape and size of this trajectory. In particular it may be useful to adapt at least slightly this position dynamically, depending on the wave regime, by raising or lowering the lower member2via variable buoyancy devices and/or propellers, to optimize the speed and therefore the efficiency of the turbines6.

Under a complete wave cycle, the resultant of the forces exerted on the lower submerged member2will be approximately vertical and will depend only on the energy and shape of the waves affecting the apparatus. Therefore, in order to keep the lower member2at a constant average position, it will be sufficient to have a control system which considers its average position after many wave cycles, and the interventions will be incremental and small compared to the energy of the waves acting on the apparatus. In particular, if the shape and energy of the waves remain constant for a while, the apparatus will reach equilibrium and no further interventions will be needed to stabilize the lower member2. The control system may be a static device of the kind of the buoyancy elements9(see the second embodiment described further on) or even simply consisting of variable buoyancy devices driven by a computerized control device.

The length of the pole4for an oceanic apparatus could be in excess of 50 meters to have the lower member2in a region much less affected by the dominant waves than the upper member1, but could be shorter to reduce costs. In fact, even with a shorter pole the apparatus works in a satisfactory manner, as the wave action decreases rapidly with depth, and moreover the horizontal component of the motion of the lower end of the pole4would be in a roughly opposite direction to that of the surrounding water. The dimensions will in any case be optimized to obtain a highly efficient device, also taking into account the dominant wave regimes of the area of deployment.

The upper member1will remain above the lower member2even after many wave cycles, due to the nature of the wave motion which, in a good approximation, does not involve an overall displacement of the water. In order to compensate for the possible action of the wind, friction, of water currents with different speed and/or direction at the different depths of the members1and2, and also for possible unforeseen extraordinary events, the buoyancy of the upper member1and the weight of the pole4and the turbines6will be optimized to provide a sufficiently strong righting moment. As an alternative, or to be able to compensate more rapidly the effect of exceptional events, small propellers can be placed on the members1and2and/or along the pole4, controlled by a computerized control system.

The buoyancy elements9can be replaced by variable buoyancy devices attached to the upper member1and driven by a computerized control system. The upper member1will in any case tend to remain at a constant average distance from the surface of the water, and on average with its upper face parallel to it, and therefore the interventions of this control system will be of a small scale compared to the energy of the wave action on the apparatus. In this way one can achieve total submersion, possibly many meters below the sea surface, which can be useful to minimize wear and tear and the possibility of hazard to ships.

In a typical oceanic configuration, the upper tank1will have a volume in the range of 1000 m3, while the smaller lower tanks3will have a volume in the range of 200 m3. The volume of the lower submerged member2, which can easily exceed 1000 m3in an oceanic deployment, leaves ample room for the various configurations of the energy conversion system which one might want to utilize.

In a simplified version, the junction between the pole4and the upper member1can be rigid, keeping the pole always perpendicular to the lower surface1aof the tank1, which in this case can more efficiently take spherical shape with only one buoyancy element9attached with a cable to its upper pole. The linking piece5can take the shape of a simple ball-and-socket type of joint, especially in smaller scale deployments, or make use of a cardan joint.

In another simplified version, the function of the lower submerged member2may be taken by the sole linking piece5, placed at a fixed position along the pole4and containing the counterweight. This simplification, together with the previously mentioned one regarding the junction between the pole and the upper member, although causing a certain decay in the efficiency of the apparatus, allows for the quick construction of very simple and cheap implementations, which is useful among other things for testing and prototyping purposes. If the apparatus is connected directly to the electricity grid or to an external engine room via a cable system, there is also no need for an engine room embodied in the apparatus, thus reducing further its complexity.

Referring now toFIGS. 5 to 7, in a second embodiment of the apparatus according to the invention, parts corresponding to those of the first embodiment are indicated with corresponding reference numerals and will not be described again. Also the general behavior of this apparatus under the wave action is the same as that of the first embodiment, with a lower submerged member102remaining mainly at rest and an upper submerged member101following the water motion due to the wave passage and keeping its orientation so that its upper face101bis always substantially parallel to the water surface. Also in this case, the use of virtual mass means (enclosed water and/or fins) can be contemplated.

However, in this embodiment the lower end of the pole104is free, that is to say lacking of the assembly of transversal rod and turbines. The extraction of energy from the motion of the apparatus is carried out via hydraulic and/or electric devices housed within a joint108connecting the lower face101bof the upper tank101with the pole104, and also within the linking piece105between the pole104and the lower member102. The joint108, in the same manner as the previous embodiment, allows for the change of orientation between the pole and the upper tank, and this relative movement, driven by the wave motion, is exploited by the above cited devices to extract energy. The devices embodied in the linking piece105extract energy from the reciprocating motion of the pole104through the hole112a. This type of devices are already known as such, and will not described in detail. For instance, inside the element105one can have a linear electric generator (see e.g. the linear generator device inside the WEC buoy proposed by the MRSF of the School of Electrical Engineering and Computer Science, Oregon State University http://eecs.oregonstate.edu/msrf/), while inside the element108one can have one or more pulleys or rollers driven by the relative movement and linked to dynamos.

In this embodiment one can also notice a plurality of further buoyancy elements113attached to the lower submerged member102via radial beams114projecting from the smaller tanks103, and cables115connected to the free ends of the beams114. The elements113contribute to the preservation of the orientation and position of the apparatus with respect to the average water surface. Also, the average resultant of the forces exerted on the lower member102will change from the rest position to normal operation, and the elements113will compensate for this. The hole112ain the ball member112is in this case a bore of a sleeve112bprojecting axially from opposite sides of the ball member.

In a simplified version of this embodiment, the pole104may be replaced by a cable with the counterweight attached to its lower end. In this case, it may be practical to place the lower member102at a much greater distance from the upper member1than in the configuration with a pole. Then, the lower member102may end up in the proximity of the sea bottom, and if appropriate may even be moored to it to simplify its design. This very last version of the apparatus would be however more difficult to deploy and maintain, and more exposed to severe weather.

A further alternative is to connect the upper and lower submerged members via an extensible pole, of the type described further on for a third embodiment, provided with energy extraction systems that exploit the reciprocating extension and contraction movement of the pole. In this way, one can get rid of the energy extraction devices in the linking piece105itself, and the pole104can end in the linking piece instead of passing through and beyond it. This makes the apparatus more compact, though with the drawback of a more complex structure of the pole. Under exceptionally big waves the whole apparatus will move, as in this case also the lower member will be interested by the wave action. This reduces the possibility of a motion capable of disassembling the apparatus.

In any case, a possible separation of the two parts will not be destructive, and the apparatus can afterwards be reassembled by letting the pole go back through its housing in the linking piece (or connecting back to each other the two parts of the pole if a design as in the third embodiment is adopted). This operation can be also made automatic, with a computerized control system on both parts and small propellers, plus the possibility of changing the distance of the lower member from the water surface (for example by lengthening the cables keeping the elements113into place).

With reference toFIGS. 8 and 9, in a third embodiment of the apparatus according to the invention, the full wave motion is captured using only linear electric generators. In this embodiment the apparatus comprises a plurality of submerged members201, e.g. four members having the shape of spherical tanks containing mainly water and air, mutually joined by connecting poles204so as to define a 3D structure, generally tetrahedral in the example.

Each pole204(FIG. 9) consists of a stick204acoaxially and telescopically engaging in a slidable manner within a tubular sleeve204b. The ends of the assembly so obtained are connected to respective submerged members201. A linear electric power generator205, fed by the mutual reciprocating movement of the stick204aand sleeve204b, is connected to the inner end of the same sleeve. Also this kind of power generation device is known as such, represented schematically and not described in detail. Reference can however be made to what already mentioned for the second embodiment.

Both a single member201and a single pole204(with the relevant generator205) are neutrally buoyant when immersed in water at their average operating depth. Under the influence of the waves the different tanks201will find themselves in different water motion regimes, either because spaced by a distance not multiple of the wavelength or because at different depths. The relative movement between them will create tension or pressure on the connecting poles204. As a consequence, the inner stick204awill move with respect to the outer sleeve204b, and this linear reciprocating motion is exploited to generate electricity. Power is therefore extracted from the relative motion of different parts of the connecting means among themselves. The geometry of the structure, also in this case, is such that all (circular) movement of water particles due to the wave action is harvested for energy.

On average, all the members201will tend to remain in the same position, remaining substantially at rest with respect to the surrounding water whose average position does not move even after many cycles of the wave motion. Virtual mass means can be used also in this case. However, to keep the submerged members201, on average, in their nominal tetrahedral configuration, it will be necessary from time to time to give back some of the energy, to move the average position of the tanks and poles so as to counteract any displacement due to drift, different buoyancy at different depths, currents or unbalanced operation of the various parts. This can be carried out by using the linear generators as linear electric motors and/or by attaching small propellers to the structure and/or by putting springs inside the poles and/or using variable buoyancy devices.

If one of the tanks201is heavier than the other three identical ones (though displacing the same amount of water), the system, designed to have in any case neutral total buoyancy, will tend to orient itself with three upper submerged tanks and one lower one. In this case these lighter members with the poles that connect them to each other could be replaced by a single submerged member as the upper member1,101of the previous embodiments, so that the whole apparatus can be kept at a substantially fixed depth below the water surface. The other connecting poles to the lower tank could as well be replaced with a single pole, so as to generate the variant envisaged above when referring to the second embodiment. Analogous degenerations of the structure of this third embodiment may be envisaged if one tank is lighter than the other three identical ones. As in the previous embodiments, the apparatus may be kept on average at a fixed depth below the surface by the use of variable buoyancy devices attached to the tanks and controlled by a computerized control system.

The engine room can be positioned inside one or more of the tanks201which in a typical oceanic deployment may have a volume of 1000 m3(the actual volume will depend from the optimization chosen, which in turn will depend, among other factors, from the typical wave regime of the region of deployment).

As in the previous embodiment, under extremely big waves the apparatus will tend to move as a whole, and therefore there will not be excessive relative movements between its parts. By positioning variable buoyancy devices on the tanks and/or on the poles, linked to a computerized control system, one can also arrange for the whole apparatus to sink deeper in response to bigger waves, and to rise when the waves are smaller, thus protecting it from severe weather and optimizing its efficiency.

The tetrahedral structure shown in the example is the simplest 3D rigid structure that may be adopted; but many other 3D configurations are possible with the same simple basic design. For example, a plurality of tetrahedral modules as the one described above can be interconnected to form a whole structural layer, extending for many square kilometers. Such a structure can be kept at a fixed depth of a few tens of meters below the average sea surface, to avoid interference with ships and minimize hazard due to storms and very big waves. Such a structure would be modular with respect to power generation and maintenance, considering that the failure of single modules will not prevent a satisfactory work of the whole system.

With reference toFIGS. 10 and 11, in a fourth embodiment of the apparatus according to the invention, the full wave motion is captured using only dynamos coupled to cables via pulleys. Also in this embodiment, however, power is extracted from the relative motion between an upper submerged member and a lower submerged member, and from the consequent displacement of a system connecting the members. In fact, this embodiment shares many features with the first and second embodiments described above, and corresponding parts are denoted at corresponding reference numerals. In this embodiment a lower submerged member302consists of a plurality of tanks303, rigidly connected to each other in sequence via a central ring305and around it.

Instead of a pole connecting the upper submerged member301(with buoyancy elements309) with the lower submerged member302, cables304are attached with a first end to the upper member301and with the other end to weights316, passing through deviation pulleys317supported by frames318mounted on the outside of respective submerged tanks303. The pulleys317drive respective dynamos for the generation of electricity, not shown, located inside the support frames318or in the tanks303. Under the action of a monochromatic wave (considered here for simplicity), the upper member301tends to describe a generally circular trajectory. This determines alternatively traction or release on the cables, which will make the pulleys317move and therefore generate electricity.

The presence of the weights316guarantees power generation during both traction and release, and also that on average the upper member301will be positioned above the center of mass of the lower member302. The lower tanks303tend to remain on average at their position, due to the water that they displace, to their inertial mass and to their virtual mass due to partially enclosed water and/or fins. To compensate for exceptional events and for small drift due to unbalanced frictions or currents, small propellers and/or variable buoyancy devices should be associated to tanks303or ring305, controlled by a computerized control system. In a variant of this embodiment the lower submerged tanks303can be kept in position also by additional buoyancy elements as in the second embodiment.

Referring now toFIGS. from 12 to 16, a fifth embodiment of the apparatus according to the invention is similar to the first embodiment, as made clear also by the use of corresponding numerals for identical or analogous parts. An upper submerged member401, with buoyancy elements409, and a lower submerged member402have the same general structure as in the first embodiment. The same applies to a linking piece405with an outer disc-shaped body411and rotatable ball member412with a hole412a(FIG. 13). As in the previous embodiments, use can be made also of virtual mass means (partially enclosed water and/or fins).

The hole412a, much wider than in the previous embodiments, accommodates a central cylindrical block404dof a pole404, represented schematically, enclosing a counterweight and an engine room for the production of electric energy, as explained hereafter. The pole404further comprises a central core404bextending axially from both flat basis of the block404d. Around the core404ba reinforcing cage404cprojects axially from the periphery of the block404d.

The upper end of the pole404is connected to the upper submerged member401via a joint408, again in an analogous fashion to the embodiments already described. The lower end of the pole404pivotally supports a couple of water collectors406, each with an inlet front mouth406aand a tail with fins406b. The assembly of the two collectors can rotate freely around the central axis of the pole404, like the transversal rod with the turbines of the first embodiment. Moreover, each collector can swing around a transversal axle (orthogonal to the central axis of the pole), indicated at407inFIG. 14. The collectors are hydraulically connected to a water circuit, not shown, formed in the core404bof the pole404. The water circuit is communicated with the engine room inside the block404dwhich houses a generation system, e.g. a Francis turbine, for converting the water flow into electric energy.

The upper submerged member401is a completely submerged tank full of air, whose buoyancy is balanced by the weight of the pole404(including the central block404dwith the counterweight) and the water collectors406. Under the action of the waves, the pole404will move in a vertical reciprocating motion with respect to the linking piece405, and together with the ball member412will move in an oscillating tilting motion with respect to the lower submerged member402. The block404dmay slip outside the hole412awithout affecting the working of the apparatus, as the cage structure404cwill in this case enter into in contact with the ball member412and provide the required resistance. The consequent motion of the lower end of the pole404will result in an inflow of pressurized water to the internal circuit of the pole, via the collectors406, and consequently in a water flow that drives the turbine in the engine room. Also in this embodiment, therefore, power is extracted from the relative motion of the submerged members, causing the motion of one end of the connecting pole with respect to its surrounding water.

As in the first embodiment, a number of variants are possible in which either the function of the lower submerged member402is carried out simply by the linking piece405and the block404d, and/or the upper joint408is rigid, or both this simplifications at the same time. It is also possible to consider a variant in which the collectors406are replaced by a plurality of collectors placed rigidly on the lower end of the pole and facing, above and beyond a number of different horizontal directions, various angled directions upwards and downwards with respect to the axis of the pole. In this case it might be necessary to place valves on the inner part of the collectors, to block the flow of water for those which do not face the direction of motion of the lower end of the pole. Such a variant (with all three simplifications at the same time) would be less efficient than the embodiment as shown in the figures, but would have the important advantage of not having any external moving part.

It will be appreciated from the above that the apparatus according to the invention is capable of circumventing all the limitations of the wave energy converters of the prior art, and that it uses a conceptually different system to extract energy from the waves.

The apparatus according to the invention can be placed completely under water, so that it can be protected from severe weather and if desired also isolated from shorter wavelength waves, which are contributors to wear and tear of offshore structures. Two or more submerged members are used, kept at rest with respect to the surrounding water by means of any combination of the following: partially enclosed water (virtual mass), fins, inertial mass, propellers.

Some of the submerged members (possibly one as in the first, second, fourth and fifth embodiments) have inertial mass as low as possible, and a size small with respect to the smallest of the main wavelengths which one wants to harvest for energy, but big enough to intercept enough water motion. Other submerged members or connection means have correspondingly very large inertial mass (in the first, second, fourth and fifth embodiments), to compensate for the buoyancy of the previous ones. In the third embodiment, instead, all the submerged members have the inertial mass to compensate for the buoyancy inside them.

The members tend to follow the motion of the water which intimately surrounds them, which is approximately circular for a single monochromatic wave. When the members are placed in different motion regimes with respect to the main wavelengths (e.g. at different depths), they move with respect to each other. By linking them with connecting means, it is possible to extract energy from this relative motion or from the induced relative motion of the connection means with respect to some submerged members or to the surrounding water.

Thus, the advantages of the present apparatus can be summarized as follows.It is more efficient because it uses all the components of the wave motion, its members being kept as much as possible at rest with respect to the surrounding water, contrary to a traditional apparatus using one or more floats as surface element.It can have a simple design, very easy to implement and maintain, especially in some of the simplified variants described. As mentioned, this can be useful also for prototyping purposes.Having only submerged elements with very low, or very large inertial mass it has a negligible motion due to natural oscillations.It can be positioned offshore, in very deep water. Its average geographic position can be kept constant with the use of thrust means, or can in any case be signaled by means of the GPS system coupled to radio transmitters and/or light emitters and/or sonar buoys.It can be designed in such a manner as to be largely unaffected, or only slightly affected, by extremely severe weather. The whole apparatus will move due to very big waves, so that the relative distance between the members will exceed the limit point only under a very unlikely combination of factors. In any case, if the motion does exceed the maximum limit, the apparatus can be designed to simply disassemble, and one can arrange for the system to reassemble itself once the storm is over (possibly in an automated way, if the members are provided with propellers.It works as efficiently with a monochromatic wave system as with a non monochromatic one, and is not sensible to the wave direction;The size of the apparatus and the energy which it can harvest from the waves is limited only by the wavelength. A simplified computation shows that it should be possible to construct apparatuses producing more than 10 MW of power (as an average) from 5 m high (or higher) monochromatic deep water waves.

All the embodiments have been described referring to their oceanic configuration; embodiments destined for deployment in areas with smaller wavelength waves will be accordingly scaled down.

Various modifications and alterations may be appreciated based on a review of this disclosure. These changes and additions are intended to be within the scope and spirit of the disclosure as defined by the following claims.