FIELD OF THE INVENTION

This invention relates to a wave energy converter for extracting energy from water waves [more properly known as wind waves] in a large body of water, typically the sea, whether it be part of one of the oceans or an inland sea.

BACKGROUND TO THE INVENTION

There is an ongoing and growing interest in extracting energy from water waves for the primary purpose of generating electricity; pumping water, desalinating sea water or utilizing extracted energy for any other purpose.

Most wave energy converters utilize the vertical movement of water between the crests and troughs of a succession of waves to create a type of pumping action that is typically utilized to compress air or pressurize hydraulic fluid, or even seawater, that can be then used for its designed purpose such as to drive a turbine for generating electricity or pumping water. There have been numerous attempts at utilizing the rising and falling of the surface of water as waves pass a particular position to mechanically generate movement that can be utilized to generate electricity or for any other purpose.

It is, however, generally undesirable to employ apparatus that has moving parts in contact with seawater as maintenance becomes a major issue and a major cost. One proposal to substantially eliminate moving parts in the energy conversion step is set out in patent publication no WO 01/651 12 that has apparently devolved upon the company OFFSHORE WAVE ENERGY LIMITED of Australia. That publication describes apparatus for converting wave energy in which an offshore floating apparatus utilizes the forward movement of successive crest regions of waves to compress air that becomes trapped in the troughs between successive wave crest regions.

That apparatus comprises a plurality of generally parallel horizontally elongate floating chambers having a water plane area such that the vertical oscillating movement of the apparatus is substantially damped relative to the height of waves in the water in which it is floating. Each chamber has an inlet port at one end adapted to face into a wave train, and vertical side plates that serve to deliver air trapped between successive wave crest regions to a manifold. An outlet port and a baffle arrangement at the other end direct the water of the waves downwards and out of the apparatus. Applicant perceives a number of disadvantages with this apparatus. It is generally inconvenient and costly to operate any type of offshore apparatus. It is difficult to effectively anchor the floating apparatus and to ensure that it floats at a suitable level to result in proper operation of the apparatus. Also, it is at least inconvenient and generally costly to provide communications media with the land where the energy is generally to be ultimately used.

It has now surprisingly been found that apparatus of this general nature that is especially configured for the purpose, can be used along the shoreline. It has also been found that compression of air between successive waves can be enhanced.

OBJECT OF THE INVENTION It is, accordingly, one object of this invention to provide a wave energy converter of this general nature on a shoreline. It is another object of the invention to provide a wave energy converter of this general nature in which the action of successive waves is enhanced, especially as regards tidal fluctuations of wave height. SUMMARY OF THE INVENTION

In accordance with this invention there is provided a wave energy converter for producing air under pressure from the movement of water waves, the wave energy converter comprising at least one elongate generally horizontal inverted channel shaped chamber extending from an outer end to an inner end in the general direction from which a succession of water waves moves, the chamber having a water inlet at its outer end directed towards an oncoming succession of waves, a top, a pair of opposite side walls and an outlet for air under pressure associated with an upper inner end region of the chamber, the wave energy converter being characterized in that the chamber is fixed relative to the land and occupies at least a part of the surf region of the sea.

Further features of the invention provide for the sidewalls of the chamber to diverge somewhat from the top of the chamber to the lower edges of the sidewalls; for the sidewalls to converge towards each other from their outer ends to their inner ends over at least predetermined zones of the length of the inverted channel shaped chamber; for the inlet to the chamber to be associated with more sharply divergent outer end regions of the sidewalls that form a type of funnel at the outer end region of the chamber; for the bottom of the chamber to be either closed by a floor or open to the sea; for lower edges of the sidewalls to have spaced cut-outs for assisting in water flowing from the chamber consequent on increase of pressure exerted by the waves on the top and air trapped beneath the top of the chamber; for the inner end of the chamber to have a terminal end wall arranged to ensure that air trapped by wave movement is channelled to the outlet; and for the outlet to communicate with an accumulator for smoothing air pressure and separating out entrained water and a turbine for operatively creating rotational movement typically for the purpose of generating electricity but optionally for other purposes. It is a particular feature of the invention that the channel may have one or more secondary top walls generally parallel to, and spaced downwardly from, the top of the channel shaped chamber to form one or more sub-chambers between such generally parallel top wall and the adjacent secondary top wall, or between adjacent secondary top walls in the event that there are more than one, with appropriate water level operated valves for closing the inner ends of empty sub chambers according to tide dependent water levels.

It is another particular feature of the invention that one or more transverse baffles extend between the sidewalls at one or more selected positions commencing towards the inner end of the chamber with the or each baffle being inclined upwardly in the direction of the inner end of the chamber and having an upper edge that is spaced from the underside of the top or secondary top wall to define an opening. It will be understood that the wave energy converter will generally need to be designed, or at least selected, specifically for a particular geographical location and in the light of typical wave heights that are associated with such location and further taking into consideration tidal fluctuations of the sea level. Obviously, the wave energy converter provided by this invention will be less effective, and possibly not viable, if the average wave height in a particular geographical location is less than a calculated minimum. In such an event the wave energy converter of this invention may be inappropriate for use at such a geographical location. Of course, tidal variations in sea level must also be taken into account and in some geographical locations may be too great to implement a single wave energy converter according to the invention that is fixed relative to the land, although the provision of one or more secondary top walls motif from the top of the channel shaped chamber may solve the problem in respect of many geographical locations. The tidal situation must be taken into consideration at the planning stage. Of course, there is nothing to stop the installation of a series of different wave energy converters operating at different heights relative to a mean sea level so that different wave energy converters according to the invention will operate at different times during the tidal cycle.

In order that the above and other variations of the invention may be more fully understood, different embodiments thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:-

Figure 1 is a schematic plan view illustrating the general concept of the invention illustrating the general concept of the invention;

Figure 2 is a schematic side elevation illustrating the general concept of the invention;

Figure 3 is an enlarged sectional side view illustrating schematically a succession of waves illustrated in dotted lines within the channel shaped chamber;

Figure 4 is an end view of the outer end of the chamber illustrating the inlet to the channel shaped will chamber;

Figure 5 is a view similar to Figure 3 showing a single secondary top wall to the channel shaped chamber; Figure 6 is a view similar to Figure 3 but showing a series of inclined baffles in position within the channel shaped chamber;

Figure 7 is a schematic plan view of a wave energy converter as illustrated in Figure 6; and,

Figure 8 is a schematic inverted plan view of the wave energy converter illustrated in Figures 6 and 7.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

In one simple embodiment of the invention a wave energy converter for producing air under pressure from the movement of water waves, generally indicated by numeral [1], comprises at least one elongate generally horizontal inverted channel shaped chamber [2] that is fixed relative to the land [3] and occupies at least a part of the surf region [4] of the sea.

As regards geographical location of the wave energy converter, the general guidelines indicated above are applied and respected in the event that a wave energy converter according to the present invention is inappropriate for a particular location. Depending on the general wave configuration attributable to a particular geographical location, it is envisaged that it may well be appropriate to construct the inverted channel shaped chamber within the surf region of the sea that may be associated with the larger waves that are generally termed breakers or it may be more appropriate to construct the wave energy converter in a somewhat sheltered area to protect it from excessively severe breakers.

The selection of site is to be made based on historic and observed wave patterns and characteristics and the design and dimensions of the channel shaped chamber will depend, at least to some extent, on the expected average wave height, the wavelength between successive wave crests; and the tidal variation in height of average water level in the particular geographical location, particularly the variation at spring tide. As indicated above, it may also be inappropriate to employ a wave energy converter according to this invention in view of the tidal variations in water level especially variations associated with spring tides although one or more secondary top walls that will be more fully described below may be employed to solve this problem if it is appropriate.

In general, it is intended that the wave energy converter will be built in the surf zone, and will stretch seaward far enough so that only unbroken waves enter the open collection end. In any event, the elongate chamber has a length that is in excess of a wavelength and preferably in excess of two or three wavelengths to ensure that multiple waves are present at all times within the chamber. The elongate chamber extends in the general median historic direction from which a succession of water waves may be expected to move with an outer end [5] forming a water inlet directed towards an oncoming succession of waves [6] and an inner end [7] located closer to the shore [8].

The chamber is defined by a continuous top [1 1], a pair of opposite side walls [12], and a terminal inner end wall [13] with an outlet [14] being provided for air under pressure associated with an upper inner end region of the chamber. The sidewalls of the chamber may diverge somewhat from the top of the chamber towards the lower edges [15] thereof.

In this particular embodiment of the invention, the sidewalls converge fairly sharply for about one quarter of the overall length of the chamber followed by an intermediate section [16] of constant cross-sectional shape that extends for about 45% of the overall length of the chamber followed in turn by a terminal converging section [17] for the remainder of the length of the chamber.

In one application the overall length of the chamber has been calculated to be 63 metres as an appropriate length for certain coastal stretches in South Africa in order to ensure that at least two waves be present within the chamber at all times. In this particular proposal, the convergent end section extends a distance of 15 metres from the open outer end and converges from an open end having a width of 20 m to the constant cross-sectional intermediate section that has a width of 6 m. The terminal converging section [17] then converges from the width of 6 m to a width of 4 m at the innermost end. The overall height of the channel shaped chamber is about 5 m. At the inner end of the chamber has an upwardly extending compartment serving as an accumulator [18] for smoothing air pressure and a turbine [19] associated with an outlet from the accumulator for creating rotational movement, typically for the purpose of generating electricity using a generator [20], but optionally for any other purpose.

In use, air becomes trapped between successive waves by the natural wave movement that is channelled from the inlet at the outer end of the chamber to the inner end, and thus to the accumulator and air outlet. As a consequence of the diminishing cross-sectional shape of the chamber, the pressure exerted on pockets of air that become trapped between successive waves increases and incompressible water that is surplus escapes through the open bottom.

Initial tests conducted using a small-scale prototype in a water wave situation in which small waves of short wavelength were present have been conducted and indicate that the wave energy converter of the invention should operate highly effectively in use. Referring now to Figure 5 of the drawings, in the event that tidal variations are excessive, it is in the scope of this invention to install a second secondary top wall [25] and that forms, together with the top [26] of the chamber [27], forms a compartment [28] having a valve closure [29] at the innermost end that is operated by a buoyant element [30]. The arrangement is such that the compartment is closed when the water level drops to a level in which it is ineffective and the secondary top wall [25] then cooperates with the waves to compress the air between successive waves in the manner described.

Figure 5 also shows the bottom [31 ] of the chamber closed in which instance a series of spaced cutouts [32] are provided along the length of the chamber to enable spent water to discharge itself from the chamber. Figures 6 to 8 of the drawings illustrate a variation in which tidal variations can be combated utilizing a series of transverse baffles [35] extending between the sidewalls at evenly spaced positions between the outer and inner ends of the chamber. Each baffle is in the form of a flat plate that is inclined upwardly in the direction of the inner end of the chamber with an upper edge [36] spaced from the underside of the top to define an opening [37]. Typically, the angle of inclination could be about 45° although further research may indicate that a different angle is preferable. It is, however, expected that the angle of inclination will be in the range of from 50° to 60°. It is to be noted that in this embodiment of the invention the chamber is also closed by a bottom [38] and the lower edges [39] of the sidewalls have spaced cut-outs [40] for assisting in water flowing from the chamber consequent on an increase of pressure exerted by the waves on the top of the chamber and air trapped beneath the top of the chamber and also consequent on the diminishing cross-sectional size of the chamber. It is also possible that the bottom may be open to the sea in which instance the cutouts will most likely become unnecessary. The planned spacing between the baffle plates may be 10 - 13 m; the height of the opening above the upper edge of the baffle plates may be 1 - 2 m and the lower edges of the baffle plates are to be positioned below the low water spring tide water level. With a difference between high spring tide and low spring tide of about 1.5 m, it is envisaged that the height of the chamber will be about 3 - 5 m.

Whilst an entire series of battles have been described above, it is also within the scope of the invention to provide a single baffle or to spaced baffles towards the terminal onshore end.

It will be understood that all of the dimensions given above are those that are presently envisaged and are by no means to be interpreted as being in any way limiting on the scope of the invention.

It will be understood that numerous variations may be made to the embodiments of the invention described above without departing from the scope hereof.