WO2014027295A1

WO2014027295A1 - Wave energy converter

Info

Publication number: WO2014027295A1
Application number: PCT/IB2013/056574
Authority: WO
Inventors: Edmund Charles SWART
Original assignee: Swart Edmund Charles
Priority date: 2012-08-15
Filing date: 2013-08-12
Publication date: 2014-02-20

Abstract

A wave energy converter is provided for producing air under pressure from the movement of water waves. At least one elongate generally horizontal invested channel shaped chamber (2) extends from an outer end (5) to an inner end (7) in the general direction from which a succession of water waves moves. The chamber has a water inlet at its outer end (5) directed towards an oncoming succession of waves. One or more deflector walls (14) diverge from the outside of a sidewall in the direction of the outer end (5) of the chamber so as to act as a deflector for waves passing on the outside of the sidewalls towards one or more communication apertures ( 15) through the sidewall below the low tide water level towards the position where the deflector wall ( 14) meets the sidewall of the chamber. Preferably, the deflector walls (14) and co-operating communication apertures in the sidewalls are arranged in one or more pairs thereof.

Description

WAVE ENERGY CONVERTER

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.

Many wave energy convertors 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.

This led to the development of a shore based version of such an apparatus that formed the subject matter of my earlier international patent application published under number WO201 1098894.

Various improvements have now been made to that shore based version of such apparatus and those improvements form the subject matter of this application. 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 positioned to be located above the troughs of waves at high tide, a pair of opposite side walls and an outlet for air under pressure associated with an upper inner end region of the chamber wherein the chamber is fixed relative to the land and occupies at least a part of the surf region of the sea, the wave energy converter being characterized in that one or more deflector walls diverge from the outside of a sidewall in the direction of the outer end of the chamber so as to act as a deflector for waves passing on the outside of the sidewalls towards one or more communication apertures through the sidewall below the low tide water level towards the position where the deflector wall meets the sidewall of the chamber.

Further features of the invention provide for the deflector walls and cooperating communication apertures in the sidewalls to be arranged in one or more pairs thereof with the deflector walls being on opposite sides of the chamber; for deflector walls to be positioned at a single location along the length of the chamber that is preferably between a quarter and three quarters of the length of the chamber from the outer end thereof and preferably approximately midway along the length of the chamber; for the upper edges of the deflector walls to be provided with a top merging with the top of the chamber at least at an inner position where the divergent deflector walls are closer to the inverted channel shaped chamber; for the sidewalls of the chamber to diverge somewhat from the top of the chamber to the lower edges of thereof; 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, and preferably along the entire length thereof; for the top of the inverted channel shaped chamber to be inclined downwardly from the outer end to the inner end thereof; for the bottom of the chamber to be either closed by a floor or open to the sea in which instance the sidewalls preferably reach the sea bed and are supported thereby; and for upright divider walls to divide the outer end region of the chamber into two, three or more juxtaposed channels with such inlet end region extending up to a third to two thirds of the length of the chamber.

Still further features of the invention provide for lower regions of the sidewalls at least in an inner region of the length of the chamber to have spaced apertures below the low tide water level for assisting in water flowing from the chamber consequent on an 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 thence with a turbine for operatively creating rotational movement typically for the purpose of generating electricity but optionally for other purposes.

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.

One or more transverse baffles may 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 spaced downwards 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 features 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;

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 at different positions within the channel shaped chamber; Figure 4 is an end view of the outer end of the chamber taken in the direction of the inner end and illustrating the inlet to the channel shaped chamber;

Figure 5 is a view similar to Figure 3 showing a 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 is generally indicated by numeral (1 ) and 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.

The channel shaped member may be made of any suitable materials that are adequately corrosion resistant and suitable steel panels may be employed. However, it is envisaged that a suitable composition of concrete, either cast in situ or prefabricated in predetermined shapes of components, will be the most appropriate.

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 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 outer collection end of the chamber. 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 (9), a pair of opposite side walls (10), and a terminal inner end wall (1 1 ) with an outlet (12) 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 (13) thereof as will be apparent from Figure 4. In one planned application of the invention, a length of the chamber has been calculated to be about 63 metres as an appropriate length for certain coastal stretches along the South African coast in order to ensure that at least two waves be present within the chamber at all times. In this particular proposal, the chamber converges continuously from an open end having a width of about 10 metres to an inner end region having a width of about 1 .6 metres. The overall height of the top of the channel shaped chamber is about 6 metres above low tide water level at the outer end and is gently inclined downwards so as to be at a height of about 5 metres above low tide water level at the inner end.

As provided by this invention, a deflector wall (14) is provided on each side of the chamber about midway along the length thereof with the deflector wall diverging from the outside of the associated sidewall in the direction of the outer end of the chamber. The deflector wall therefore serves to direct wave water passing on the outside of the sidewalls and direct it towards one or more communication apertures (1 5) through the sidewall below the low tide water level that is indicated by numeral (1 6) and towards a position where the deflector wall meets the sidewall of the chamber. The upper edges of the deflector walls are provided with a top (1 7) merging with the top of the chamber, at least at an inner position where the divergent deflector walls are closer to the inverted channel shaped chamber.

At the inner end of the chamber there is an upwardly extending compartment serving as an accumulator (1 8) 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.

It will be understood that in the embodiment of the invention described above, the sidewalls are supported directly on the sea bed (21 ). Also, primarily for constructional stability, two upright divider walls (22) may be provided to divide the outer end region of the chamber into three equally sized juxtaposed channels (23) with the divider walls extending along the length of the chamber to a position approximately midway along its length. It is to be noted that the structural details of where the top, sidewalls and divider walls meet, they may well be chamfered as indicated by numeral (24) or constructed in any other suitably stable way. In use, air becomes trapped between the top of the chamber and 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 openings (25) in the lower regions of the sidewalls at least in the inner region of the chamber. Referring now to Figure 5 of the drawings, in the event that tidal variations are excessive, it is within the scope of this invention to install a secondary top wall (31 ) and that, together with the top (32) of the chamber (33), forms a compartment (34) having a valve closure (35) at the innermost end that is operated by a buoyant element (36). The arrangement is such that the compartment is closed when the water level drops to a level at which it is ineffective and the secondary top wall (31 ) then cooperates with the waves to compress air between successive waves in the manner described.

Figure 5 also shows a closed bottom (37) to the chamber in which instance a series of spaced cutouts (38) are provided along the length of the chamber to enable water to discharge itself from the chamber.

Figures 6 to 8 of the drawings illustrate a variation in which tidal variations can be combated, at least to some extent, utilizing a series of transverse baffles (41 ) 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 (42) spaced from the underside of the top to define an opening (43). 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 30° to 60°. It is to be noted that in this embodiment of the invention the chamber is also closed by a bottom (44) and the lower edges (45) of the sidewalls have spaced cut-outs (46) 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 metres; the height of the opening above the upper edge of the baffle plates may be 1 - 2 metres and the lower edges of the baffle plates are preferably positioned below the low tide water level. With a difference between high spring tide and low spring tide of about 1 .5 metres, it is envisaged that the height of the chamber will be about 3 - 5 metres.

Whilst an entire series of baffle plates has been described above, it is also within the scope of the invention to provide a single baffle or two spaced baffle plates towards the terminal onshore inner end of the chamber.

It will be understood that all of the dimensions given above are those that are presently envisaged in a particular application 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.

Claims

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 positioned to be located above the troughs of waves at high tide, a pair of opposite side walls and an outlet for air under pressure associated with an upper inner end region of the chamber wherein the chamber is fixed relative to the land and occupies at least a part of the surf region of the sea, the wave energy converter being characterized in that one or more deflector walls diverge from the outside of a sidewall in the direction of the outer end of the chamber so as to act as a deflector for waves passing on the outside of the sidewalls towards one or more communication apertures through the sidewall below the low tide water level towards the position where the deflector wall meets the sidewall of the chamber.

A wave energy converter as claimed in claim 1 in which the deflector walls and co-operating communication apertures in the sidewalls are arranged in one or more pairs thereof with the deflector walls being on opposite sides of the chamber.

A wave energy converter as claimed in either one of claims 1 or 2 in which the deflector walls are positioned at a single location along the length of the chamber that is between a quarter and three quarters of the length of the chamber from the outer end thereof.

A wave energy converter as claimed in claim 3 in which the deflector walls are positioned at a single location along the length of the chamber that is approximately midway along the length of the chamber.

A wave energy converter as claimed in any one of the preceding claims in which the upper edges of the deflector walls are provided with a top merging with the top of the chamber at least at an inner position where the divergent deflector walls are closer to the inverted channel shaped chamber.

A wave energy converter as claimed in any one of the preceding claims in which the sidewalls of the chamber diverge somewhat from the top of the chamber to the lower edges of thereof.

A wave energy converter as claimed in any one of the preceding claims in which the sidewalls 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.

A wave energy converter as claimed in any one of the preceding claims in which the top of the inverted channel shaped chamber is inclined downwardly from the outer end to the inner end thereof.

A wave energy converter as claimed in any one of the preceding claims in which the bottom of the chamber is open to the sea wherein the sidewalls reach the sea bed and are supported thereby.

A wave energy converter as claimed in any one of the preceding claims in which upright divider walls divide the outer end region of the chamber into two, three or more juxtaposed channels with such inlet end region extending along up to a third to two thirds of the length of the chamber. A wave energy converter as claimed in any one of the preceding claims in which lower regions of the sidewalls in an inner region of the length of the chamber have spaced apertures below the low tide water level for assisting in water flowing from the chamber consequent on an increase of pressure exerted by the waves on the top and air trapped beneath the top of the chamber.

A wave energy converter as claimed in any one of the preceding claims in which the channel has 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.

A wave energy converter as claimed in any one of the preceding claims in which 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.