WO2009064237A1

WO2009064237A1 - Wave energy conversion system

Info

Publication number: WO2009064237A1
Application number: PCT/SE2008/000642
Authority: WO
Inventors: Per-Arne Nordlander
Original assignee: FRAME ENERGY AB
Current assignee: FRAME ENERGY AB
Priority date: 2007-11-14
Filing date: 2008-11-14
Publication date: 2009-05-22
Anticipated expiration: 2010-05-14
Also published as: SE532254C2; SE0702508L

Abstract

The present invention relates to a system for conversion of wave energy from liquid waves. The system includes a first buoyant support member, which is elongated so as to establish a reference liquid level, and at least one considerably shorter buoyant working member connected to the said first buoyant support member, and being arranged to rise and fall when influenced by waves. The said buoyant working member is arranged to be connected to the said elongated support member by means of at least one arm so as to allow energy transfer by means of the said arm to the said support member by movement, caused by the influence of waves on the said buoyant working member, of the said buoyant working member in relation to the said reference liquid level.

Description

WAVE ENERGY CONVERSION SYSTEM Field of the invention

The present invention relates to a system for converting the energy of liquid waves, such as ocean waves, to electrical energy. More particularly, the system is of the kind defined in the preamble of claim 1.

Background of the invention

The increasing interest in alternative power sources has, among other, lead to an increasing interest in ocean wave energy conversion systems, e.g. since the theoretical potential of converting ocean wave energy into electrical energy is considerable.

Already, there exist various kinds of ocean wave energy conversion systems. These systems can be categorized with regard to location, i.e. if the system is intended for offshore usage, on-shore usage and/or near- shore usage. The wave energy conversion systems can also be categorized based on the specific technology that is used to capture the energy of the waves, and also the various methods of converting the energy into electric energy.

Most, if not all, wave energy conversion systems, however, have in common that they aim to overcome one or more of the specific challenges that are associated with ocean wave energy conversion systems. Such challenges include, for example, finding a manner of efficiently converting the energy of the motion of the waves into electricity, a task that is complicated by the fact that wave power is usually available as waves providing high forces at low- speed in varying directions . Further, the environment in which wave energy conversion systems are installed is often very exposed and literally attacked by the elements of nature and must, for example, be constructed in a manner that is capable of surviving regular storms and salt water collusion. In addition, it is highly desirable that the production of electricity can be carried out at a low cost in order to be competitive when comparing with other energy conversion systems, not only other ocean wave energy conversion systems, but also conventional energy conversion systems.

Consequently, wave energy conversion systems face a plurality of problems and there exists a need for an improved wave energy conversion system that solves or at least mitigates one or more of the above mentioned problems.

Summary of the invention

According to the present invention, it is provided a wave energy conversion system that solves or at least mitigates one or more of the above-mentioned problems. This is accomplished by a wave energy conversion system according to claim 1.

According to the invention, a system for conversion of wave energy from liquid waves is provided, the system including a first buoyant support member, which is elongated so as to establish a reference liquid level, and at least one considerably shorter buoyant working member connected to the said first buoyant support member, and being arranged to rise and fall when influenced by waves. The said buoyant working member is arranged to be connected to the said elongated support member by means of a mechanical linkage such as at least one arm so as to allow energy transfer by means of the said arm to the said support member by movement, caused by the influence of waves on the said buoyant working member, of the said buoyant working member in relation to the said reference liquid level. This has the advantage that the present invention provides a simple yet robust wave energy conversion system having few components, and which in a simple manner is capable of absorbing energy from waves passing the system. Further, the elongated structure allows use of a plurality of buoyant working members aligned in one or more rows. This has the advantage that, in particular when the buoyant working members are arranged in a row in the direction of motion of the waves, more energy can be extracted from the passing waves.

Further, the elongated support member or members has the advantage that they define an "artificial" reference level, that is, no anchoring of the system is required to establish a level in relation to which the working members are working, but instead the reference level is established by the elongated support member, allowing operation at locations in the ocean where anchoring would be impossible or impractical due to the depths of the ocean. Consequently, since the energy conversion of the present invention does not require a fixed reference point the invention allows use at the locations of the oceans where the wave powers are high.

In one embodiment, the system according to the invention is provided with at least one anchoring point closer to one end of the system, so as to allow the system to, thanks to its elongated structure, strive to align itself with the direction of motion of the waves, thereby improving energy conversion in changing wave direction conditions. This also has the advantage that the stress on the system, caused by the ocean waves, can be kept at a minimum. However, alignment of the system according to the invention can also be accomplished by means of propellers controlled by a "wind/direction" control system. Consequently, according to the present invention anchoring is not necessary for the production of energy. However, it can often be advantageous to anchor the system in order to maximise energy output and to achieve an easier alignment to the incoming waves. Anchoring also facilitate the arrangement of cable or cables for transporting the generated electric energy, to shore and energy consumer (s) .

In one embodiment, the system comprises a second elongated buoyant support member, said first buoyant working member being arranged to be connected to at least one of the said first and second elongated support members. In one embodiment, the system is provided with more than two elongated buoyant support members, having one or more buoyant working members arranged between each pair of support members. Brief description of the drawings

Fig. IA discloses an exemplary embodiment of a wave energy conversion system according to the present invention, seen from above.

Fig. IB discloses a side elevation view of the embodiment of fig. IA.

Fig. 2 discloses exemplary cross-sectional embodiments of the elongated support members according to the invention.

Figs. 3A-B discloses an alternative exemplary embodiment of a wave energy conversion system according to the present invention.

Fig. 4 discloses a further alternative exemplary embodiment of a wave energy conversion system according to the present invention.

Fig. 5 discloses another alternative exemplary embodiment of a wave energy conversion system according to the present invention. Fig. 6 discloses a further alternative exemplary embodiment of a wave energy conversion system according to the present invention.

Detailed description of exemplary embodiments Figs. IA and IB disclose a first exemplary embodiment of a wave energy conversion system according to the present invention. The system 100 consists of a frame, which is made up from two elongated buoyant support members 101, 102. The two support members 101, 102 are connected to each other by means of connecting rods 103, 104, 105, e.g. consisting of steel bars or any other suitable material having sufficient strength. The elongated buoyant members 101, 102 can, for example consist of hollow cylinders made from steel or any other suitable material, or be composed of a light weight massive buoyant material, which is preferably armoured on the surface, e.g. using armoured plastic, composite or metal in order to be capable of withstanding the forces acting thereupon by the elements, such as ocean waves and occasional storms. In one embodiment, the elongated support members are made up from steel cylinders filled with a buoyant material so as to prevent the system from sinking in situations such as if the support members start to leek.

The energy conversion system further comprises buoyant working members 108, 109, which, due to their considerably shorter length when compared to the buoyant support members, will rise and fall with respect to the support members 101, 102 when waves are passing between the support members 101, 102. The length of the elongated support members 101, 102 is a plurality of times the length of the waves the system is designed for. The buoyant working members 108, 109 are connected to the support members 101, 102 by means of mechanical linkages in the form of arms 110, 111 and 112, 113, respectively, the function of which will be described more in detail below. The relative movements of the buoyant working members are illustrated in fig IB, which shows a side elevation view of the system seen from above in fig IA. As can be seen in fig IB, the buoyant support members 101, 102 (of which only support member 102 is shown) is shown as resting substantially at a mean wave height level β. The considerable shorter buoyant working members 108, 109, however, move with the passing waves (indicated by arrows) and consequently exhibit a lateral movement with respect to the support members 101, 102.

The elongated support members 101, 102 can, for example, be of lengths from 10 - 2000 meters. Due to the length of the elongated support members 101, 102, which can exceed a plurality of times the wavelength of the waves at the location at which the system is installed, the elongated support members 101, 102 will define an "artificial" reference level, which can be seen as a mean wave height level, where the longer the length of the buoyant support members, the greater the correlation of this artificial reference level and the actual mean wave height level will be.

In this description and claims, the term "reference water (or liquid) level" is to be interpreted as the level that is defined by the relatively smaller/slower motion the elongated support member will exhibit in waves when compared to the considerably shorter buoyant working member. Consequently, the elongated support member, although still being affected by passing waves, and thereby not defining a fixed reference level, still will provide a (although possibly shifting) reference level that in the short term (e.g. a passing wave) can be considered as substantially fixed or slowly changing when comparing with the relatively faster motion of a considerably shorter buoyant working member.

Preferably, the length of the elongated support members 101, 102 exceeds the length of, e.g., two or more waves, whereby the elongated support members will substantially rest at a mean water level (with respect to wave height) .

The above is exemplified further in the following. If the support members have a length equalling a plurality of wave lengths, the buoyant support members will rest in water substantially as shown in fig IB. If, however, the wave length of the waves is rather long when compared to the length of the support members, it is quite possible that the support members will not rest substantially horizontally as shown in fig IB but with a (varying) angle with respect to a horizontal plane. As was explained above, however, this does not affect the operation of the system according to the invention, since the movement of the support members will be much slower when compared to the movement of the working members, which therefore will rise and fall with respect to the support members, and thereby absorb energy from the waves for conversion to electrical energy by the energy conversion system 100.

In use, the system is preferably anchored in a manner such that the longitudinal axis A is substantially aligned with the direction of movement of the wave front (waves) , indicated by arrows B. This alignment can, for example, be accomplished by arranging the anchorage point of the system closer to one end of the elongated support members than to the other, for example at a point 106 on connection rod 105 or a pair of anchorage points 106' at each of the elongated support members, respectively. The arms 110, 111, and 112, 113, respectively, by which the buoyant working members 108, 109 are connected to the support members are connected to "energy conversion means", 114, 115, 116, 117, such as generators or hydraulic pumps, which are used to convert energy taken up from the waves by the buoyant working members when following, or substantially following, the amplitude motions of the waves and thereby rotating (back and forth) a shaft (or shafts, such as shafts 121-122 and 123- 124, respectively) of the energy conversion means. Consequently, the arms have the function of levers, and energy absorbed by the buoyant working members is transferred to the support members by a lever action caused by the rise and fall of the buoyant working members in relation to the support members when influenced by the passing waves, wherein the said axes act as lever shafts. The movement pattern of the working members, at least when the length of the arms are constant, is thus a movement along the periphery of an arc of a circle. However, it is also contemplated that the lengths of the arms can be adjustable, e.g. to allow adaption to variations in wave height. It is also contemplated that the lengths of the arms of consecutive working members may individually vary. Further, said arms may be arranged such that the length of the arms can be varied during operation, i.e. the length of the arms can be varied e.g. during a single wave cycle. The movement will then follow the periphery of an arc of an ellipse or some other geometric shape.

The energy conversion means 114 - 117 can, for example, consist of electrical generators wherein the work produced by the working members 108, 109 when performing lateral movements with respect to the support members 101, 102 are converted to electrical energy by the rotation of the respective shaft of the generators . In another example, the energy conversion means 114 - 117 can, instead, consist of hydraulic pumps for converting the mechanical work produced by the working members 108, 109 to hydraulic power, where the hydraulic pumps 114 - 117, in turn, are connected to one or more electrical generators, e.g., one generator for each support member, or a generator central for the energy conversion system 100. The connection arms 110 - 113 of the working members 108, 109 can be connected directly to shafts of the electrical generators/hydraulic pumps or via a gear mechanism allowing the generators/pumps to work at higher speeds .

Further, instead of having generators/pumps in both of the support members, the generators/pumps can be located in only one of the support members, e.g. support member 102. Even further, the number of buoyant working members used in connection with a pair of support members can be any suitable number of working members, and consequently need not be two, but a single working member, or three, four or more working members can be used, e.g., according to what is appropriate for the length of the particular support members. The use of a plurality of consecutive working members have the advantage that a greater portion of the energy contained in a single wave can be absorbed.

The support members can, in principle, take on any suitable cross sectional appearance, such as cylindrical, square or hexagonal. However, if, for example, the support members are cylindrical, they can be provided with vertical side portions toward the wave capturing area between the support members (see 203, 204 in fig. 2 where support members 201, 202 have been provided with such vertical side portions. The use of square cross sections (see 205, 206 in fig. 2), or vertical members 203, 204, can be used to "capture" the waves. The support members can also be arranged in a manner so as to amplify the wave amplitude. This is illustrated in figs. 3A-B. The principles of the system 300 disclosed in fig. 3A are similar to the system disclosed in fig. IA-B, however, with the difference that instead of having two parallel elongated support members, the support members 301, 302 of fig. 3A are arranged such that their ends 310, 311 pointing away from the direction from which waves are entering the system are relatively closer to each other than the ends 312, 313 receiving the waves. In this way, the waves entering the system are compressed as the passage gets narrower and narrower, thereby increasing the energy per meter of the wave as the wave progresses between the elongated support members 301, 302. The power (energy) of the wave can be measured in W (or kW) per meter wave front. If, for example, the average power contained in consecutive waves is 50 kW/meter wave front, an energy capturing system with elongated support members being located 10 metres apart will "capture" a mean power of 500 kW. If, however, converging elongated support members are used, a larger portion of the wave front can be captured and the relative energy of the wave front can be increased. If the buoyant working members are concentrated to the end of the system facing away from the incident wave front, the buoyant working members can be subject to considerable larger powers.

For example, with the above prerequisites, if the elongated support members are located 100 meters apart at the end facing the incident waves while being located e.g. 10 meters away from each other at the opposite end, with the buoyant working members being located at the narrower end with 20 meters between the support members at the working members closest to the incident wave and approx. 10 meters between the last set of working members, the energy per meter wave front when the concentrated wave front reaches the first set of buoyant working members will be in the order of 25OkW. This has the advantage that the working members can be designed for higher powers to thereby allow use of fewer working members when compared to the system with parallel support members.

Also, the continued concentration of the wave power of the remainder of the wave after the first set of working members allows for higher power absorption also by the subsequent working members, since the converging support members at least partly compensate for the reduction in energy, and thereby height (or even amplifies the wave height between consecutive working members) of the waves caused by energy absorption from working members. It is in general favourable to absorb energy from a narrower but higher amplitude wave front rather than from a wider wave front having lower amplitude.

Consequently, more rational energy absorption can be obtained, while at the same time allowing cost effectiveness due to a reduced consumption of material. Similar to the above, the converging support members can take on any suitable cross sectional appearance and, e.g. be provided with vertical sides.

This is illustrated in fig. 3B where the amplitude of a wave passing the system is illustrated for the length of the system, and as can be seen the amplitude A₀ at a point P₀, i.e. a point where the waves enter the energy conversion system 300 is smaller than the amplitude Ai at a point Pi, i.e. the position of the last working member 307 of the system. The solution according to fig. 3A has the advantage that the increase in amplitude obtained by converging support members counteracts the decrease in wave height that a passing wave otherwise is subjected to when passing through the system, the decrease in wave height being due to energy loss in interaction with the working members.

With regard to the buoyant working members these can, similar to the support members, consist of hollow steel formations such as steel cylinders or be made up from a light weight massive buoyant material, preferably having an armoured surface, e.g. using armoured plastic, composite or metal in order to withstand the impact of the elements. The buoyant working members have the only task to impose movements in the linkage (arms) with the support members by being pushed upwards by the forces of the waves and follow the movements of the waves downwards by means of gravity. It is also contemplated that the support and/or working members wholly or partly are made from natural materials such as bamboo. The buoyant working members can transfer the accumulated energy either in the gravitation motion i.e. when they "fall" from the wave top to the wave bottom or in the uplift motion, i.e. when they are lifted from the wave bottom to the wave top, or by using a combination of the two. To transfer the energy in the gravitation motion, the working members should have a high mass in order to produce as much work as possible given the prevailing wave height. This can, for example, be accomplished by partially filling the working members with a heavy material, or alternatively filling the working members with water to such extent that the working members just barely float in order to maximize their weight and thereby the power that can be output from the system. Consequently, the work produced by the working members can be controlled by the volume of the working members, since larger volumes allow higher weights. By altering the weight of one or more buoyant working member the system can be optimized so that maximum efficiency of all involved buoyant working member can be achieved.

On the other hand, if the energy is to be transferred during the uplift motion, the working members should have as little mass as possible. In this working mode, the lifting of the working members by the waves is subjected to a counter-acting force, e.g. by means of hydraulic pumps, so that high power is required to lift the buoyant working member, thereby absorbing the energy from the passing waves. That is, the hydraulic pumps or other suitable means applies a counter-acting force to the shaft or shafts being rotated by the arm(s), thereby applying a counter-acting force to the uplifting motion of the working member caused by a passing wave. The energy that can be absorbed is to a large extent dependent on the volume of the working members and can also be dependent on the shape of the working member.

Lightweight working members of the system working according to the uplift principle have the advantage that less material is required, thereby making the construction more cost-efficient . In fig. 4 the system according to the invention is shown in its most simple form. Instead of having two parallel elongated buoyant support members, the system according to fig. 4 only includes a single elongated buoyant support member 401. The elongated support member 401 includes an anchoring point 402 located towards one end of the support member so as to allow anchoring in such a manner that the energy conversion system will substantially be aligned with the direction of movement of the waves as has been described above.

In the system shown in fig. 4, pairs 403, 404 and 405, 406, respectively, of buoyant working members are used. The buoyant working members 403 - 406 are similar to the ones described above and work in a similar manner, since a water reference level will be defined in the same manner as described above by a single support member as when using two support members. The reason for having pairs of buoyant working members is that if working members were only used to the one side of the elongated support members, the system would most likely, unless stabilizers are used, exhibit a rotational movement of the support member, with reduced efficiency as a result. The use of pairs of working members balances the system. Naturally, it is also possible to use working members on each side of the support members of figs. Ia and 3.

Fig. 5 shows a further alternative exemplary embodiment of the present invention. The invention is not limited to the use of one or two elongated support members, but a suitable number of elongated support members can be used. This is illustrated in fig. 5, wherein four elongated buoyant support members 501-

504 are used. Similar to the above, a plurality of electrical generators can be used, or, alternatively, a central electrical generator can be used, e.g. powered by hydraulic pumps receiving the work performed by the working members. If hydraulic power is to be transferred between support members, this can, for example, be accomplished by using channels in the connecting rods. It is also contemplated that working members are used on both sides of the outer support members 501, 504 of fig. 5. While the present invention has been described with reference to several embodiments above, a person skilled in the art will recognize that various changes of the above embodiments can be made without departing from the spirit and scope of the claimed invention. For example, in the above examples the working members are disclosed as being connected to shafts extending through the sides of the buoyant support members. However, it is also contemplated that the working members can be attached to the support members via shafts that extend on top of or below the support members. Moreover, an example of a further embodiment of the present invention is disclosed in fig. 6, in which even further features are disclosed. As can be seen in fig. 6, the elongated buoyant support members are arranged such that the distance between respective ends of the two elongated buoyant support members 601, 604 at the end of the system from which waves enter the system is greater than the distance between the support members 601, 604 at the positions of the buoyant working members being arranged in between the support members, i.e., the system follows the principle of the system disclosed in fig. 3A. In the disclosed example, the outermost support members 601, 604 are formed as straight bars, but it is also contemplated that they can be of any suitable shape, e.g. arc- shaped.

One feature of the system shown in fig. 6, is that instead of using a single buoyant working member between two laterally displaced support members, i.e. similar to the working members 108, 109 in fig. IA, a plurality of buoyant working members can be used instead. This is exemplified by the buoyant working members 610-621 working in parallel, four between each pair of support members, respectively, in a direction transversal to the wave propagation. The buoyant working members 610-621 are, instead of being connected to shafts extending through the sides of the elongated buoyant support members 601-604, connected to individual shafts (not shown) arranged on a shaft support structure 622 connecting the elongated buoyant support members 601-604. The use of a plurality of working members connected to individual shafts (which, for example, can be arranged to operate associated hydraulic pumps, respectively) has the advantage that effects owing e.g. the concentration of the wave power can be taken accounted for. For example, in systems such as the ones in fig. 3A and fig. 6 where the wave power is concentrated using converging support members, the concentration gives rise to turbulence and variations in wave height also in the direction transversal to the direction of wave propagation.

For example, the wave height near the support members can be considerable higher than at a position halfway between the support members. The use of a plurality of buoyant working members working in parallel as shown in fig. 6 has the advantage that such variations can be accounted for, with increased efficiency as result.

A further feature, which can also be seen from the figure, is that the support members can vary in length and, for example, be arranged such that support members 602, 603 in between the outermost support members 601, 604 of the system are shorter and only provided at the portion of the system where buoyant working members are provided.

Even further, as is exemplified by the buoyant working members 610-621, the working members can be arranged not only "downstream" of the shaft (s) to which they are connected, but also upstream of the shaft (s) to which they are connected.

Accordingly, this invention is not limited to what is shown in the drawings and what is described above, but only of the scope indicated in the following claims.

Claims

1. A system for conversion of wave energy from liquid waves, the system including a first buoyant support member, and at least one buoyant working member connected to the said first support member, and being arranged to rise and fall when influenced by waves, characterised in that

- the said buoyant support member is elongated so as to establish a reference liquid level, and

- said buoyant working member is arranged to be connected to the said elongated support member by means of a first mechanical linkage so as to allow energy transfer to the said support member by lateral movement, caused by the influence of waves on the said buoyant working member, of the said buoyant working member in relation to the said reference liquid level.

2. A system according to claim 1, characterised in that it comprises a second buoyant working member, arranged to be connected to the said elongated support member by means of a second mechanical linkage, the said first and second buoyant working members being arranged on opposite sides of the longitudinal axis of the said first elongated support member.

3. A system according to claim 2, characterised in that the support member connection points of the said mechanical linkages are arranged substantially along a common axis.

4. A system according to any of the preceding claims, characterised in that movement of the said mechanical linkage or linkages, caused by rises and falls of the said buoyant working member with respect to the elongated support member when influenced by passing waves, is arranged to actuate a shaft of, or a shaft that is connected to, energy conversion means.

5. A system according to claim 4, characterised in that the said energy conversion means consists of any from the group: electric generator, hydraulic pump.

6. A system according to claim 4, characterised in that the said movement of the said mechanical linkage or linkages is arranged to actuate energy conversion means via one or more gear mechanisms.

7. A system according to claim 1, characterised in that it comprises a second elongated buoyant support member, being laterally displaced from said first elongated buoyant support member, said first buoyant working member being arranged to be connected to at least one of the said first and second elongated support members.

8. A system according to claim 7, characterised in that the said first buoyant working member is arranged to be connected to the said first support member by means of the said first mechanical linkage and to the said second support member by means of a second mechanical linkage.

9. A system according to any of the preceding claims, characterised in that it comprises a plurality of buoyant working members arranged substantially along one or more rows substantially parallel to the intended direction of motion of passing waves, each of said plurality of buoyant working members being arranged to be connected to at least one support member.

10. A system according to any of the claims 7-9, characterised in that the elongated buoyant support members are arranged such that the distance between respective ends of the two elongated buoyant support members at the end of the system from which waves are to enter the system is greater than the distance between the support members at the position of at least one buoyant working member being arranged in between the said support members .

11.A system according to claim 1, characterised in that it comprises a plurality of elongated buoyant support members, wherein at least one buoyant working member is being arranged between each pair of elongated support members .

12. A system according to any of the preceding claims, characterised in that the length of said support member or members is a plurality of times the mean wavelength of the waves for which the system is designed.

13. A system according to any of the preceding claims, characterised in that the length of said support member or members is 10-2000 meters.

14. A system according to any of the preceding claims, characterised in that it comprises at least one anchoring point, located closer to one end of the said elongated support member or members, so as to, in use, allow the support member or members to be substantially aligned along the travelling direction of the waves passing the system.

15. A system according to any of the preceding claims, characterised in that the said mechanical linkage is arranged to function as a lever means, so as to allow energy to be absorbed by rotating a lever shaft affixed to the said buoyant support member by movement of the lever means, the said movement of the lever means being caused by lateral movement of the said buoyant working member with respect to the said support member or members, caused by a passing wave.

16. A system according to claim 15, characterised in that rotation of the said lever shaft is arranged to rotate a shaft of an electric generator and/or hydraulic pump.

17. A system according to any of the claims 15-16, characterised in that the length of the said lever means is adjustable so as to allow adjustment of the length between the said lever shaft and the said buoyant working member.

18. A system according to any of the claims 15-17, characterised in that, at least when the length of the said level means is constant, the movement of the said buoyant working member about the said lever shaft is a motion along the arc of a circle.

19. A system according to any of the claims 15-18, characterised in that, in use, the length of the said lever means, and thereby radius of the arc of a circle along which the buoyant working member is arranged to move, is adjustable.

20. A system according to any of the claims 15-19, characterised in that at least two buoyant working members are connected to a single shaft affixed to an elongated buoyant support member by means of respective mechanical linkages.

21. A system according to any of the preceding claims, characterised in that energy transfer to the said support member by lateral movement of the buoyant working member is substantially effected by a gravitational motion of the buoyant working member following a rise caused by a passing wave.

22.A system according to any of the preceding claims, characterised in that the energy transfer to the said support member by lateral movement of the buoyant working member energy is substantially effected by applying a counter-acting force to the said mechanical linkage when the buoyant working member is being risen by a passing wave .

23.A system according to claim 22, characterised in that said mechanical linkage is arranged to function as a lever means, and that said counter-acting force is arranged to be applied by a shaft to which the lever means is connected, and which is rotated by the lever means when the buoyant working member is being risen by a passing wave.