WO2015001284A1

WO2015001284A1 - A wave energy extraction device

Info

Publication number: WO2015001284A1
Application number: PCT/GB2014/000251
Authority: WO
Inventors: Nicholas James ADKINS
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-07-04
Filing date: 2014-06-25
Publication date: 2015-01-08
Anticipated expiration: 2016-01-04

Abstract

A wave energy extraction device comprises a hull and at least one driving mass, supported on the hull by a horizontal pivot, such that the driving mass has no significant tendency to harmonic motion, and at least one energy conversion device, operatively associated with the hull and the driving mass. The vertical velocity of a wave produces a vertical velocity of the hull, this vertical velocity passing to the driving mass via the energy conversion device, the energy conversion means further extracting energy from periodic differences in the velocity of the hull and the velocity of the driving mass, at different phases of the wave cycle.

Description

A WAVE ENERGY EXTRACTION DEVICE

Field of the Invention

The present invention relates to a wave energy extraction device.

Background of the Invention

Decades of research into wave energy extraction and the application of much ingenuity has yielded valuable data, knowledge and experience, but has not resulted in the extraction of useful energy on a scale anywhere near the potential of the resource.

Examination of published material shows that problems common to many proposed wave energy extraction devices are mechanical complexity and lack of regard for the harshness of the marine environment in which the devices must operate. Mechanical complexity also obscures the simplicity of the underlying physical principles that are necessarily common to all WOM (wave operated member) / REM (reaction member) wave energy extraction devices.

Design for seaworthiness should be informed by the existing maritime industry with its wealth of knowledge, experience and expertise. A brief study of marine vessels is sufficient to show that wherever possible mechanisms with, for example, pivots, rotary joints or sliding linear joints should be kept out of the water and preferably further protected from the elements. As the design, construction and operation of large wave energy extraction devices will be almost certainly undertaken by the existing maritime construction industry, it is clearly advantageous if proposals are formulated with existing maritime practices in mind.

Some known wave energy extraction devices aim to capture waves arriving from any direction, using a circular wave operated member. While this achieves the desired omni-directional effect, it imposes a severe limit on the total wave energy available to a device, since at any one time waves tend towards uni- directionality.

Other proposed devices describe the use of a submerged reaction member (REM) or body, the motion of which is resisted by the surrounding water. However, the submerged REM suffers a reduction in effective mass due to the buoyancy effect of the water that it displaces, and the requirement that the REM must be submerged to a significant depth means that construction of such a device must depart significantly from conventional ship building, together rendering any net benefit of a submerged reaction member or body doubtful.

Some proposed devices describe the use of an REM in the manner of a pendulum. Whilst the periodic motion of a pendulum may intuitively suggest it as a method of capturing wave energy, it transpires that problems arise associated with the characteristic periodicity or harmonic motion of a pendulum, and published proposals show these problems being addressed by methods of varying degrees of complexity.

It is hence an object of the present invention to provide an alternative to existing wave energy extraction devices that obviates the above problems, and provides a robust, effective, efficient and cost-effective means of extracting useful amounts of energy from wave motion.

Summary of the Invention

According to a first aspect of the present invention, there is provided a wave energy extraction device comprising:

hull means to support the device buoyantly on a body of water traversed by waves;

at least one driving mass means, pivotably supported on the hull means and so balanced as to have no significant tendency to harmonic motion;

- at least one energy conversion means mounted to the hull means and operatively associated with the driving mass means at a point remote from a pivot axis of the driving mass means;

wherein, when the hull means is so aligned that a direction of travel of said waves is transverse to the pivot axis of the driving mass means, vertical motion of the waves is transmitted to the driving mass means, causing it to move pivotingly; and energy is extracted from said pivoting motion of the driving mass means by said associated energy conversion means.

The hull means thus acts as a wave operated member (WOM) and the or each driving mass means acts as a reaction member (REM).

Preferably, the or each driving mass means comprises a pair of driving bodies, mounted adjacent respective remote ends of a support structure. The driving bodies of the or each driving mass means may have substantially the same mass.

The driving bodies may be disposed symmetrically about the pivot axis of the or each driving mass means.

Preferably, each driving body has an elongate form.

Advantageously, each said elongate driving body extends substantially parallelly to the pivot axis of the or each respective driving mass means.

Preferably, the pivot axis of the or each driving mass means extends through its respective centre of mass.

Advantageously, the pivot axis of the driving mass means extends substantially horizontally.

In a preferred embodiment, the wave energy extraction device comprises a plurality of driving mass means.

The respective pivot axes of each said driving mass means may then extend substantially parallelly. The respective pivot axes of each said driving mass means may then extend substantially collinearly.

The plurality of driving mass means may ideally be pivotably mounted along the same pivot axis.

Preferably, the hull means comprises a pair of hull elements spaced apart, each from the other, and each extending generally parallelly to the pivot axis of the or each driving mass means.

Advantageously, each hull body is aligned with a respective driving body.

Each hull element may have at least one said energy conversion means mounted thereto.

Preferably, the energy conversion means comprises a hydraulic pump providing hydraulic energy.

Alternatively or additionally, the energy conversion means may comprise a heat pump.

Alternatively or additionally, the energy conversion means may comprise a reverse osmosis mechanism. Preferably, the motion of the driving mass means relative to the hull means is controlled by the energy conversion means.

Advantageously, the operative length of the driving mass means extends beyond the hull means.

Preferably, the wave energy extraction device comprises motor and propeller means for propulsion and/or station keeping, powered by one of: energy extracted by the energy conversion means; a stored energy source; a combination of energy sources.

The wave energy extraction device may be further provided with tether means for the purpose of position keeping.

The wave energy extraction device may be further provided with tether means adapted for transmission of energy therethrough. Said driving mass means may at least partly comprise one of: operative equipment; raw materials; processed materials.

Preferably, the hydraulic energy is used to drive a hydraulic motor which in turn drives electrical energy generator means, producing electrical energy.

Said hydraulic energy may be used to process materials.

Said hydraulic energy may be used to operate a reverse osmosis mechanism.

The heat pump may be used to liquefy air.

Preferably, the electrical energy is conditioned for transmission via the tether.

Advantageously, the extracted energy is chemically stored. The extracted energy may be used in electro-chemical processing. Preferably, the extracted energy is used to produce ammonia. The wave energy extraction device may comprise a means for storing ammonia.

According to a second aspect of the present invention, there is provided a method of extracting energy from waves, comprising the steps of: receiving a wave energy device as described in the first aspect above, and deploying said device in a body of water in which surface waves are present.

Brief Description of the Drawings

For a better understanding of the invention and to show how the same may be carried into effect, there will now be described by way of example only, specific embodiments, methods and processes according to the present invention with reference to the accompanying drawings in which:

Figure 1 is a perspective view of a first wave energy extraction device embodying the present invention;

Figure 2 is a perspective view of a second wave energy extraction device embodying the present invention;

Figure 3 is a side elevation of the wave energy extraction device of Figure

2;

Figure 4a is a diagrammatic view of a first example of an operating cycle of the wave energy extraction device of Figure 2;

Figure 4b is a diagrammatic view of a second example of an operating cycle of the wave energy extraction device of Figure 2;

Figure 5 is a perspective view of a third wave energy extraction device embodying the present invention, similar to that of Figure 1 but having a plurality of energy conversion devices and reaction members;

Figure 6 is a graph of a representative deep sea wave used in calculations herein; Figure 7 is a perspective view of a fourth wave energy extraction device embodying the present invention, in which the buoyant body is shown separated from the reaction member;

Figure 8 is a perspective view of the wave energy extraction device of Figure 7 in assembled form;

Figure 9 is a side elevation of a fifth wave energy extraction device embodying the present invention, having a lengthened reaction member; and

Figure 10 is a perspective view of a sixth wave energy extraction device embodying the present invention.

Detailed Description of the Embodiments

There will now be described by way of example a specific mode contemplated by the inventor. In the following description numerous specific details are set forth in order to provide a thorough understanding. It will be apparent however, to one skiljed in the art, that the present invention may be practiced without limitation to these specific details. In other instances well known methods and structures are not described in detail, so as not to unnecessarily obscure the description.

Figure 1

Figure 1 is a perspective view of a first wave energy extraction device (WEED), comprising a buoyant body or hull (1) (the wave operated member, or WOM), and a reaction member or driving mass (2) (REM), supported at its centre of gravity upon the buoyant body (1) by a horizontal pivot (4), such that the reaction member (2) has no significant tendency to harmonic or pendular motion. The longitudinal axis of the horizontal pivot (4) is substantially parallel to the wave front. The device also comprises an energy conversion device (5), operatively connected between the buoyant body (1) and the reaction member (2), spaced at a distance away from the pivot (4) This energy conversion device (5) allows the energy of a rising wave acting through the buoyancy of the wave operated member (buoyant body) (1) to impart angular momentum to the reaction member (2), and further extracts energy from the periodic positive or negative acceleration given to the reaction member (2) by the buoyant body (1) at different phases of the wave cycle.

In this example, the buoyant body (1) consists of two buoyant sections, spaced apart, each from the other, connected by supports (3), and each extending parallelly to the pivot axis of the reaction member (2).

Since the reaction member of a free-floating WOM/REM device is effectively a substitute for the inertia of the Earth, as used by non-reaction member devices which are fixed to the sea bed or shore, then the Earth can be regarded as the ideal reaction member and the practical reaction member of a WOM/REM device should seek to approach the relevant characteristics of the Earth, these being very large mass and no relevant periodicity or harmonic motion. The mass of the reaction member (2) is limited to that which can be supported by the buoyancy of its associated buoyant body (1), which fact leads to a general principle that the reaction member (2) should comprise the greatest practicable proportion of the total mass of the wave energy extraction device.

The desired non-pendular motion of the reaction member (2) is achieved by pivoting the reaction member (2) on the buoyant body (1) in such a way that the reaction member (2) has no significant tendency towards pendular or harmonic motion or, in other words, has no single position of equilibrium, its angular momentum determined by the alternate forces applied to it at either side of the pivot (4) by the buoyant body (1). The reaction member (2) will tend to rotate in the manner of a wheel such that when given angular momentum by force from the buoyant body (1), the reaction member (2) will continue to rotate until given an opposing force from the other end of the buoyant body (1), or until it is otherwise constrained.

The reaction member (2) comprises a mass at each end, so that its mass is concentrated at its ends, at the furthest practicable distance from the pivot (4); the reaction member (2) is therefore able to possess the maximum momentum or kinetic energy for a given total mass of the reaction member (2), which in turn means that a wave energy extraction device of a given displacement can extract a greater amount of wave energy. Note that the word 'displacement' is used here in its maritime sense of the mass of water displaced by a floating body.

Figure 2 and Figure 3

Figure 2 is a perspective view of a second wave energy extraction device, in which the device has a width W and a length L. The buoyant body (1) is of a form and size such that under the action of waves there are two portions of the body that are supported in the water, periodically at different heights. In practice, this means that the buoyant body (1) (WOM) length L, measured in the direction of wave propagation, might be from a few metres up to two thirds of the wavelength of a common oceanic wave, or approximately 150 metres. Although the wave energy extraction device of the present invention will be able to operate in a wide range of sea conditions, for the purpose of analysis it is possible to assume a single sinusoidal wave of a single wave length, wave height and wave period, for example, a wave of 4 metres in height, 12 seconds period and 224 metres in length. In this example, the buoyant body (1) has a length L of 74.7 metres (one third of a wavelength). The operative length L of the wave energy extraction device is measured in the direction of wave propagation, the operative width W being measured parallel to the wave front, as indicated by the dimension lines L and W respectively in Figure 2.

In this example, the wave energy extraction device comprises two energy conversion elements (5a and 5b), each operatively connected between the buoyant body (1) and the reaction member (2), and distal to the horizontal pivot (4). The energy conversion elements (5a, 5b) in this embodiment comprise hydraulic pumps, providing hydraulic energy. This hydraulic energy is used to drive an electrical energy generator of substantially conventional form (not shown here), producing electrical energy. In other embodiments of the present invention, the hydraulic energy may be used to process materials, or to operate a reverse osmosis mechanism. In further embodiments, the energy conversion elements may comprise heat pumps, which may be used to liquefy air, or reverse osmosis mechanisms. Figure 3 is a side elevation of the wave energy extraction device of Figure 2, comprising a buoyant body (1), a reaction member (2), supported on a horizontal pivot (4), and two energy conversion elements (5a, 5b). Figures 4a and 4b

Figures 4a and 4b are diagrammatic views of two examples of operating cycles of the wave energy extraction device of Figure 2, through one cycle of a wave, this device having a length of one-third of a wavelength of the wave. From top to bottom, Figures 4a and 4b show eight positions at 45 degree intervals of wave phase. The direction of wave propagation is from right to left, and the curved arrows represent the direction of rotation of the buoyant body or reaction member.

Figure 4a shows a simplified sequence which operationally is not ideal but by isolating the essential events of the energy extraction process renders the principles more apparent.

Starting at 0 degrees, the reaction member (REM) (2) has completed its clockwise rotation and has transferred its energy to the second energy conversion element (ECD) (5b). The first ECD (5a) is moving to its maximum extension by using a small amount of extracted energy.

At 45 degrees, the front of the buoyant body (WOM) (1) rises with the rising wave front. This force is transmitted through the now locked second ECD (5b) to the REM (2). The REM (2) is thus given an anti-clockwise rotation about its pivot (4). Shortly after 45 degrees, the wave will reach its maximum vertical velocity and via the locked second ECD (5b) rotate the REM (2) at this maximum velocity.

At 90 degrees, the REM (2) rotates under its own momentum and possesses the kinetic energy given to it by the rising wave. It should be noted that at this stage of the cycle the rise and fall of the pivot (4) has no significant effect on the angular momentum of the REM (2). The first ECD (5a) is fully extended in readiness to receive energy from REM (2).

At 135 degrees, the REM (2) has made contact with the first energy extraction element (5a) and the kinetic energy of the REM (2) is being transferred to it (5a). Between 135 degrees and 180 degrees, the REM (2) transfers its energy to the first ECD (5a), the rising wave under the back of the WOM (1) transfers energy via the now locked first ECD (5a) to the REM (2) and the REM (2) begins to rotate clockwise.

At 180 degrees, the rising wave under the back of the WOM (1) continues to transfer energy via the locked first ECD (5a) to the REM (2) and the REM (2) gains kinetic energy until it achieves practically the maximum vertical velocity of the wave.

At 225 degrees, the REM (2) rotates under its own momentum and possesses the kinetic energy given to it by the rising wave.

At 270 degrees, the REM (2) continues to rotate under its own momentum, and the second ECD (5b) is fully extended in readiness to receive energy from the REM (2).

At 315 degrees, the REM (2) has made contact with the second ECD (5b) and the kinetic energy of the REM (2) is being transferred to the second ECD (5b).

The cycle then returns to 0 degrees.

Figure 4a clearly shows the fundamental importance of the mass of the REM (2) in determining the wave energy extraction ability of the WEED; at 90 degrees and 270 degrees, the REM (2) is freely rotating through a small angle and its angular momentum, or kinetic energy, is clearly identifiable. The equation of kinetic energy (ke = ½ MV²⁾ involves only two terms, mass and velocity; the velocity of the REM (2) is practically that of the maximum vertical velocity of the wave; the mass of the REM (2) is known or is measurable, therefore the energy extraction potential of a WEED as described above can be calculated.

A wave energy extraction device embodying the present invention, of, for example, 50 metres width, 75 metres length, having the approximate form as shown in Figure 2 above, operating in 4 metre high waves of 12 seconds period and 224 metres wavelength, as shown in Figure 6 below, is able to extract 833kW of energy. Figure 6 also shows a diagonal straight line representing the maximum vertical velocity of the wave of 1.048 metres per second and shows that, to a reasonable approximation, this maximum vertical velocity is maintained for three seconds or 90 degrees of the wave cycle.

The wave operated member (WOM) of Figure 2 comprises two buoyant vessels, each with a displacement volume of 10 metres x 10 metres x 50 metres = 5,000 cubic metres, the total for the two vessels forming the WOM being 10,000 cubic metres. Rounding down the density of seawater to 1,000kg per cubic metre for simplicity in calculation, this gives a total displacement equivalent to 10,000,000kg or 10,000 metric tons, which will be the approximate mass of the reaction member (REM).

The maximum vertical velocity of a sinusoidal wave of four metres height and twelve seconds period is 1.048 metres per second, which for simplicity can be rounded down to 1.0. Referring to Figure 4a, the sequence around 45 degrees shows this velocity being given to the REM. The small angle of rotation of the REM and the concentration of mass at the ends of the REM, as described in Figure 1 above, allows the use of the linear equation of kinetic energy to achieve results of sufficient accuracy for the present purpose: ke = ½ MV² = ½ x 1 x 10⁷ x 1² = 5x10⁶ joules. Figure 4a at 135 degrees shows the kinetic energy of the REM (2) being transfered to the first energy conversion device (ECD) (5a). A similar energy exchange takes place during the second half cycle shown in the sequence of Figure 4a at around 180 degrees, when wave energy gives kinetic energy to the REM (2) and at 315 degrees, when the REM (2) gives this kinetic energy to the second energy conversion device (ECD) (5b).

Thus, 5x10⁶ joules of wave energy are extracted by each of the first and second energy conversion devices (5a and 5b), in every twelve second cycle of the wave, giving a power rating of: 10x10⁶ joules divided by 12 seconds = 833,000 Watts or 833kW or

16.67kW per metre of WOM width. 2,

From MOLLISON, Heriot-Watt, "P is approximately ½ H_s xT in kW per metre" (of wave front), where P = power of wave, H_s = significant wave height, T = wave period.

P= y₂ x 4² x 12= 96kW

This gives an efficiency of conversion of:

16.67/94= 0.174 or 17.4% The accuracy of the foregoing figures must be considered in the context of the complex nature of ocean waves and the simplifications and approximations made in these calculations. However, the application of existing wave energy extraction knowledge and expertise to the present invention might realistically be expected to improve performance making an efficiency in the region of 17.4% achievable.

Figure 4b shows a cyclic sequence more likely to be of use in a practical implementation of the present invention. The sequence is representative of similar sequences which may be used to suit varying sea conditions, the progress of the sequence being controlled by the first and second energy conversion devices (5a, 5b). It should be noted that although the rotation of the reaction member (2) (REM) is less than that shown in Figure 4a, rotation remains an essential feature of the present invention. In this sequence, the first and second energy conversion elements (ECDs) (5a and 5b) remain in contact with the reaction member (2). The motion of the reaction member (2) is therefore controlled by the first and second energy conversion means (5a, 5b), and particularly their locking and unlocking.

At 0 degrees, the buoyant body or wave operated member (WOM) (1) is falling at the back and rising at the front. The force of the rising wave is used in part to rotate the reaction member (REM) (2) anti-clockwise and in part to give energy to the second energy conversion device (ECD) (5b). At 45 degrees, the buoyant body (1) continues to rotate the reaction member (2) anti-clockwise, and the second energy conversion device (ECD) (5b) has reached its minimum extension.

At 90 degrees, the reaction member (REM) (2) rotates anti-clockwise under its own momentum and shortly after 90 degrees begins to transfer energy to the first energy conversion device (ECD) (5a).

At 135 degrees, the reaction member (REM) (2) continues to rotate anticlockwise under its own momentum and the buoyant body (1) is rotating clockwise as the wave rises under the back of the buoyant body (1), and the first energy conversion device (ECD) (5a) extracts energy from the rising wave and the rotating reaction member (REM) (2).

At 180 degrees, the energy of the rising wave is extracted by the first energy conversion device (ECD) (5a) and also transmitted to the reaction member (REM) (2) starting the clockwise rotation of the reaction member (REM) (2).

At 225 degrees, further clockwise rotation of the buoyant body (1) transmits energy through the now locked first energy conversion device (5a) to the reaction member (REM) (2), increasing the clockwise rate of rotation and therefore the kinetic energy of the reaction member (REM) (2).

At 270 degrees, the reaction member (REM) (2) is rotating clockwise under its own momentum and shortly after 270 degrees begins to transfer energy to the second energy conversion device (ECD) (5b).

At 315 degrees, the buoyant body (1) and the reaction member (REM) (2) rotate in opposite directions and the second energy conversion device (ECD) (5b) extracts energy from the relative motion of the buoyant body (1) and the reaction member (REM) (2).

The cycle then returns to 0 degrees.

Figure 5

Figure 5 is a perspective view of a third wave energy extraction device similar to that shown in Figure 1, but being provided with a plurality of energy conversion devices (5). The reaction member (REM) (2) periodically possesses a large amount of kinetic energy, with the potential to cause severe damage to the wave energy extraction device (WEED) if, for instance, there is a failure of the normal system of energy conversion, and it will be considered prudent to provide a robust emergency system. Such an emergency system must be capable of deployment while the reaction member (REM) (2) is in motion relative to the buoyant body or wave operated member (WOM) (1), deployment in extreme weather conditions and may consist of ropes, stays, jacks, dashpots, shock absorbers or other such means that are well known in the maritime and allied industries.

A useful feature of the wave energy device would be to remain partially functional during maintenance or breakdown, and an embodiment of the present invention with this ability is shown in Figure 5; an arrangement of three sets, each composed of one reaction member REM (2) and two energy conversion devices (ECDs) (5), one or two of which sets might cease to function, while the remaining two sets or one set continues to function. The reaction member (2) might be prevented from rotating about the pivot (4) by fixing the energy conversion devices (5) in one position or extension and thereby locking the reaction member (2) to the buoyant body (1). This might also be accomplished by introducing an additional device or devices. Such devices might operate at each remote end of the reaction member (2) in compression as a jack or in tension as a rope.

In the case of a wave energy extraction device using hydraulic energy conversion devices (5), consisting of, for instance, a cylinder and piston, under normal operative conditions the reaction member (2) is easily controlled by regulating the flow of hydraulic fluid from the cylinder. It would then be a simple matter to bring the reaction member (2) to rest, relative to the buoyant body (1).

Under normal operating conditions, the reaction member (2) may be controlled by methods of varying degrees of sophistication, ranging from a simple mechanical system of progressive restriction of the outflow of the hydraulic cylinders of the energy conversion devices (5), to a computer-controlled system. Such a computer-controlled system may receive input data from on-board wave energy extraction device (WEED) equipment and facilities, external wave data and meteorological data, and provide an output of control signals to, primarily, the energy conversion devices (5) in order to achieve optimised energy extraction and safe operation. Other considerations in the control of the reaction member (2) may be the stability of equipment and facilities within the reaction member (2) and the comfort of any personnel housed within the reaction member (2).

In such a system having multiple energy conversion devices (5), hydraulic pressure may be maintained in low wave conditions (low reaction member (2) velocity) by rendering one or more of the energy conversion devices (5) inoperative by, for example, not extending the piston, thereby reducing the effective hydraulic area. Figure 6

Figure 6 is a graph of a representative deep sea wave used in calculations herein. For the purposes of simplification, it can be assumed that, since it is desirable for the mass of the reaction member of the wave energy extraction device to constitute as much of the total device mass as practicable, the reaction mass actually constitutes the whole mass of the WEED. It can further be assumed that there is insignificant change in the volume of water displaced by the device throughout the wave cycle. This can be justified as follows:

Turning now to the sinusoidal wave, shown in Figure 6, of 4 metres height, 12 seconds period, having a maximum vertical velocity component represented by the diagonal straight line of 1.048 metres per second, assuming this velocity is reached in one quarter of a wave period, which is three seconds, then the vertical velocity component undergoes an acceleration of 1.048 metres per second divided by 3 seconds = 0.349 metres per second squared. Further dividing this acceleration by gravitational acceleration of 9.8 metres per second squared gives 0.0365. Given that displacement is proportional to the weight and therefore the vertical acceleration given to a buoyant body, the maximum increase in displacement above the displacement caused by gravity is 0.0356 or 3.56%.

Considering that upward force is given to the REM (reaction member) by only half the WOM (buoyant body) at one time, then this increase in displacement of that half of the WOM (buoyant body) must be doubled to 0.071 or 7.1%. If the horizontal cross sectional area of the WOM (buoyant body) about the waterline is approximately constant, then the 7.1% increase in displacement will result in a similar amount of increase in submerged depth. If, as is common marine design practice, the horizontal cross sectional area above the waterline increases with height, then the already small figure of 7.1% increase in submerged depth will be significantly reduced. The significance of this is that the WOM (buoyant body) is able to accelerate the REM (reaction member) to practically the full value of the wave's vertical velocity component.

This fact that the submerged depth of the buoyant body (1) is little affected by even quite severe wave action is contrary to the dramatic behavior of ships pitching in a heavy sea, when their bows rise out of and plunge under the water. This difference is due to three significant factors:

The bows of a ship are pointed and have little buoyancy in proportion to their length, whereas the buoyant body of the present invention presents a broadside to the wave; the bows are streamlined to aid horizontal movement through the water, which also aids vertical movement, whereas the buoyant body is not streamlined in the direction of wave propagation; and finally the pitching of a ship is due in part to its harmonic motion about its centre of gravity, whereas the reaction member of the present invention has no significant tendency to harmonic motion, and the device tends to ride the wave, as shown in Figure 4a, 4b.

The wave shown in the graph of Figure 6 has zero vertical velocity at zero seconds, from which time the wave gains vertical velocity until by 1.5 seconds the vertical velocity of the wave has practically reached that of the diagonal maximum vertical velocity line. The wave continues with practically this vertical velocity of 1.048 metres per second until approximately 4.5 seconds by which time the wave, through the buoyant body (WOM) and locked energy conversion element, will have accelerated the reaction member (REM) to 1.048 metres per second. The wave, WOM and REM will be rising with the same vertical velocity, therefore there is no acceleration, no increased displacement and no loss of vertical velocity due to increased displacement. Figure 7

Figure 7 is a perspective view of a fourth wave energy extraction device, in which the buoyant body means (1) is shown separated from the reaction member means (2) for clarity. This illustrates how the mass of the wave energy extraction device (WEED) is concentrated in the reaction member (REM) (2). One reaction member (2) is represented in cut-away form, to show a representation of the equipment, facilities and storage which may be contained therein. The mass of the reaction member (2) may therefore at least partly comprise one or more of: operative equipment, raw materials, processed materials.

The buoyant body (1) is shown reduced to the minimum required to provide buoyancy and support for the reaction member (2). Pivot supports (3) form that part of the buoyant body (1) which connects; the two buoyant vessels.

Figure 8

Figure 8 is a perspective view of the wave energy extraction device of

Figure 7 in assembled form, and shows a number of the equipments and facilities of an embodiment of the present invention that might be tethered or otherwise fixed to the sea bed or shore, or un-tethered and able to move to areas of high wave activity, produce and store ammonia for later shipment, as described with respect to Figure 10 below, and provided with means of self-propulsion and steering and/or attachments for towing by another vessel. Such systems, for example, a motor and propeller (marine screw), may be powered by any one of: energy extracted by the energy conversion means (5); a stored energy source; a combination of energy sources.

Where the wave energy extraction device is provided with a tether, this may be for the purposes of position keeping, and/or for the purposes of energy transmission. Any electrical energy produced by the WEED may be conditioned for transmission via the tether. This electrical energy may also be chemically stored.

Any embodiment might be operated as a single wave energy extraction device (WEED), or in company with other WEEDs or terminal facilities. The cutaway part of reaction member (REM) (2) shown in Figure 7 above reveals example modules and equipment which might be duplicated in the other part of the reaction member (REM) (2), this being one way to the maintain the centre of gravity at the pivot (4) and to facilitate maintenance and repair.

A hydraulic energy conversion device (ECD) (5) has its cylinder operatively connected to the reaction member REM (2) and its piston (not visible here) operatively connected to the buoyant body (WOM) (1). Hydraulic energy is stored in the accumulators (10) from which it is available to a hydraulic motor ( 2), or to other processes. The hydraulic motor (12) here drives an electrical generator (11), which sends its energy to an electrical energy conditioner (7) from which the electrical energy might be transmitted off the wave energy extraction device (WEED) or used within the wave energy extraction device (WEED). Storage batteries (13) receive energy from the electrical energy conditioner (7), the stored energy being available for use on the WEED.

An electrochemical facility (14) uses the electrical energy produced by the wave energy extraction device (WEED) for, as one example, the production of hydrogen and oxygen by the electrolysis of water. Mass bodies (8) might be simple weights or, more usefully, storage tanks for raw materials or storage tanks for ammonia (see below). These mass bodies (8) are shown positioned at maximum distance from the pivot (4) so as maximally to increase the moment of inertia of the reaction member (REM) (2). Secondary mass bodies (9) are positioned substantially above the horizontal centre line of the reaction member (REM) (2) and provide a means of balancing the masses of equipment and facilities which might be located substantially below the horizontal centre line. Therefore secondary mass bodies (9) maintain the centre of gravity of the reaction member (REM) (2) at the longitudinal centre of the pivot (4). Secondary mass bodies (9) might usefully be used for storage in a similar manner to mass bodies (8).

To further illustrate the requirement to maintain balance, the electrochemical facility (14) is shown positioned in the upper part of the reaction member (REM) (2) to counter balance equipment and facilities located lower down. For purposes of maintenance and repair, it might be required to limit or to stop the rotation of the reaction member (REM) (2) relative to the buoyant body (WOM) (1). One method would be to restrict the flow of fluid into and out of the energy conversion devices (ECD) (5), to the point that the desired limit or complete cessation of rotation is achieved, at which point substantial members may be temporarily fixed between the reaction member (2) and the buoyant body

(1) , these members acting in tension in the manner of a cable or in compression in the manner of a jack.

With no movement of the reaction member (2) (REM) relative to the buoyant body (1) (WOM), maintenance and repair can be undertaken on equipment that is inaccessible while the WEED is in operation. An individual energy conversion device (5) might be rendered inoperative by disconnecting it from the buoyant body (1) (WOM) and then securing it to the reaction member

(2) , all parts of the inoperative energy conversion device (5) would have no motion relative to the reaction member (2) and that energy conversion device (5) and its associated equipment could be worked on while the rest of the WEED continued to operate.

In a further embodiment of the present invention, the hydraulic power produced by the energy conversion devices is used as the pressure source required for desalination of seawater by reverse osmosis, the equipment and facilities depicted within the reaction member (2) in Figure 8 being interpreted as appropriate for that purpose, with filled water tanks constituting a large proportion of the mass of the reaction member (2). The seawater to be desalinated may be used as the hydraulic fluid in the energy conversion devices (5), the pressure between the reaction member (2) and buoyant body (1) (WOM) bearing directly upon the seawater. Alternatively, an intermediate hydraulic system may be used. In the former case it would be of benefit to provide a sufficient number of energy extraction devices (5) to allow for regular cleaning of individual energy extraction device (5) without interrupting the operation of the entire WEED. Figure 9

Figure 9 is a side elevation of a fifth wave energy extraction device with a lengthened reaction member. The effectiveness of a reaction member (REM) (2) of a given mass can be improved by increasing its moment of inertia about its pivot. Increasing the length of the reaction member (2) beyond the perimeter of the buoyant body (1) (WOM), so that the attachment point of the energy conversion device (5a, 5b) to the reaction member (REM) (2) is moved relatively nearer to the pivot (4), as shown in Figure 9, will increase the vertical velocity of the reaction member REM (2) relative to the vertical velocity of a rising wave by the ratio of D:d, where D is the horizontal distance between the centre of the pivot (4) and the midpoint of the mass at one end of the reaction member (2), and d is the horizontal distance between the centre of the pivot (4) and the midpoint of either of the energy conversion devices (5a or 5b). The increased kinetic energy of the reaction member REM (2) will indicate the increase in energy extracted from the wave. This improvement is achieved with little increase in static displacement of the wave energy extraction device (WEED). This can also be viewed as increasing the leverage exerted on the ECDs (5a, 5b).

Figure 10

Figure 10 is a perspective view of a sixth wave energy extraction device, which shows the buoyant vessels of the buoyant body (1) fully enclosed and watertight with the energy conversion device (5) bearing on the top, or deck, of the enclosed buoyant vessels, in which case the energy conversion device (5) may be extended under gravity at the appropriate phase of the wave cycle. A wave energy extraction device (WEED) having a buoyant body (WOM) (1) comprising fully enclosed buoyant vessels divided into watertight compartments, and a reaction member (REM) (2) able to be secured to the buoyant body (WOM) (1), will be very robust and able to withstand very severe sea conditions.

Ammonia synthesis using energy from a wave energy extraction device might be achieved by using systems including (but not limited to) systems based on the Haber-Bosch process or systems based on Solid State Ammonia Synthesis (SSAS). Small scale, renewable energy powered, land based ammonia production facilities have been operated and these could be adapted for use with a wave energy extraction device (WEED). The equipment necessary for any given ammonia synthesis system will, where possible, for the reasons given above, be housed in the reaction member (REM).

A WEED operating independently from the shore must have some means of storing extracted energy. Ammonia, NH₃, has much to recommend it as a carbon free energy storage medium. Effectively, ammonia is a convenient store of hydrogen able to store hydrogen at a density greater than that of liquid hydrogen itself and under far less exacting pressures and cryogenic temperatures. Storage of ammonia by absorption in a solid matrix has been shown to offer ammonia storage density per unit volume comparable to that of liquid ammonia.

A WEED can provide energy in the forms appropriate for the production of ammonia, these forms being; pressure, heat and electricity. The constituent elements of ammonia are readily available to a WEED: nitrogen from the atmosphere and hydrogen from electrolysing seawater or from atmospheric moisture.

The current states of the arts of ammonia synthesis, storage and transportation enable these processes to be carried out in connection with WEEDs.

As the proportion of electricity generated by renewables grows, the need for large capacity energy storage becomes more urgent. Ammonia has already been studied as a potential energy storage medium for other renewables, particularly wind energy. An ammonia energy storage facility serving a coastal wind power site would be well situated also to receive ammonia transported from offshore WEEDs.

Figure 10 shows an embodiment of the present invention which includes a number of preferred features: the buoyant vessels of the buoyant body or wave operated member (WOM) (1) are watertight; energy conversion devices (ECDs) (5) bear upon the top of the WOM; and the greater part of the mass of the reaction member (REM) (2) is located at a substantial distance from the pivot (4). Figure 10 also shows central sections of the reaction member (2a) forming passageways between the ends of the reaction member (REM) (2), allowing the transfer of materials and energy, and the passage of personnel. Mass bodies (8) are shown attached to the extremities of the reaction member (REM) (2), where their mass is of maximum benefit in energy extraction and, when they are containers of ammonia, from where they might be lowered into the sea to enable their eventual transfer to the shore. Such a transfer might, for example, be accomplished by firstly transferring said containers under the control of cables to a ship that could either take the containers on board or take them in-tow. A cable previously connected to the container at the buoyant body (WOM) (1) might then be removed from the transferred container and connected to a second container brought by the ship for transfer to the WEED. Such a second container might be an empty ammonia container or hold various materials and provisions. It might, for example, be preferable to supply the WEED with pure water where this is plentiful on shore and if on-board desalination is insufficiently effective. Transfers of any fluid materials to and from the WEED might also be accomplished with one or more pipes. Some or all of the mass bodies (8) might contain seawater, either as a raw material for the ammonia production process or as a simple mass or ballast; this seawater would conveniently be taken into the mass bodies (8) after the WEED has arrived at its operational location.

A group of WEEDs might operate so that an individual WEED has a specific function. For example, a number of WEEDs in a group might specialize in the production of electricity, while other WEEDs in the group receive the electricity and produce ammonia.

The different forms of energy which rnay easily be made available, on a

WEED embodying the present invention, are sufficient for the production of ammonia using a number of processes and variations of processes, with potentially significantly more energy efficiency than if the same processes were carried out on land with electrical energy supplied by a distant WEED. A WEED having the dimensions: 50 metres width, 75 metres length, might be constructed with dimensions sufficient to accommodate a crew for operation and maintenance of the WEED or a group of WEEDs.

The twin hull construction of the buoyant body (1) enables it to present a broad buoyant body to a wave front when in operation, while when being geographically located or relocated, it can travel in the direction of the long axes of the hulls, in the manner of a conventional twin hulled vessel. Locating and relocating the WEED might be achieved by towing with another vessel, or by providing the WEED with at least one motor and propeller powered by stored energy, or by a combination of both methods. A motor and propeller pod, such as are now common in modern ships, might be operatively fixed below the middle of the buoyant body (WOM) and be rotatable for the purpose of steering and position keeping. Energy for the motor and propeller could be hydraulic or electrical energy from currently converted wave energy, or from stored energy, or a combination of both. Travel in a direction parallel to the wave fronts might be accomplished with a maximum amount of currently converted energy and a minimum amount of stored energy.

In operation, the WEED might be expected passively to adopt an orientation approaching the optimum by the natural tendency of a buoyant body to present its broadest side to the wave fronts.

When travelling to a location, and when in operation at a location, a WEED embodying the present invention might be operated using techniques, skills, knowledge and practices within the scope of current maritime practices and in accordance with national and international regulations. Similarly, a WEED embodying the present invention might be constructed with current widely available ship building facilities.

WEEDs embodying the present invention may well form part of a holistic approach to the use of renewable energy, as a means of competing with persistently cheap fossil fuel energy sources, around which the present electrical distribution systems and much of industry were constructed.

Claims

1. A wave energy extraction device comprising:

at least one energy conversion means mounted to the hull means and operatively associated with the driving mass means at a point remote from a pivot axis of the driving mass means;

wherein, when the hull means is so aligned that a direction of travel of said waves is transverse to the pivot axis of the driving mass means, vertical motion of the waves is transmitted to the driving mass means, causing it to move pivotingly; and

energy is extracted from said pivoting motion of the driving mass means by said associated energy conversion means.

2. A wave energy extraction device as claimed in claim 1 , wherein the or each driving mass means comprises a pair of driving bodies, mounted adjacent respective remote ends of a support element.

3. A wave energy extraction device as claimed in claim 2, wherein the driving bodies of the or each driving mass means have substantially the same mass.

4. A wave energy extraction device as claimed in either claim 2 or claim 3, wherein the driving bodies are disposed symmetrically about the pivot axis of the or each driving mass means.

5. A wave energy extraction device as claimed in any one of claims 2 to 4, wherein each driving body has an elongate form.

6. A wave energy extraction device as claimed in claim 5, wherein each said elongate driving body extends substantially parallelly to the pivot axis of the or each respective driving mass means.

7. A wave energy extraction device as claimed in any of the preceding claims, wherein the pivot axis of the or each driving mass means extends through its respective centre of mass.

8. A wave energy extraction device as claimed in any one of the preceding claims, wherein the pivot axis of the driving mass means extends substantially horizontally.

9. A wave energy extraction device as claimed in any one of the preceding claims comprising a plurality of said driving mass means.

10. A wave energy extraction device as claimed in claim 9, wherein the respective pivot axes of each said driving mass means extend substantially parallelly.

11.A wave energy extraction device as claimed in either claim 9 or claim 10, wherein the respective pivot axes of each said driving mass means extend substantially collinearly.

12. A wave energy extraction device as claimed in any one of claims 9 to 11 , wherein the plurality of driving mass means are pivotably mounted along the same pivot axis.

13. A wave energy extraction device as claimed in any one of the preceding claims, wherein the hull means comprises a pair of hull elements spaced apart, each from the other, and each extending generally parallelly to the pivot axis of the or each driving mass means.

14. A wave energy extraction device as claimed in claim 13, wherein each hull element is aligned with a respective driving body.

15. A wave energy extraction device as claimed in either claim 13 or claim 14, wherein each hull element has at least one said energy conversion means mounted thereto.

16. A wave energy extraction device as claimed in any one of the preceding claims, wherein the energy conversion means comprises a hydraulic pump providing hydraulic energy.

17. A wave energy extraction device as claimed in any one of the preceding claims, wherein the energy conversion means comprises a heat pump.

18. A wave energy extraction device as claimed in any one of the preceding claims, wherein the energy conversion means comprises a reverse osmosis mechanism.

19. A wave energy extraction device as claimed in any one of the preceding claims, wherein the motion of the driving mass means relative to the hull means is controlled by the energy conversion means.

20. A wave energy extraction device as claimed in any one of the preceding claims, wherein an operative length of the driving mass means extends outwardly beyond the hull means.

21. A wave energy extraction device as claimed in any one of the preceding claims, further comprising motor and propeller means for propulsion and/or station-keeping, powered by one of: energy extracted by the energy conversion means; a stored energy source; a combination of energy sources.

22. A wave energy extraction device as claimed in any one of the preceding claims, wherein the device is further provided with tether means for the purpose of position keeping.

23. A wave energy extraction device as claimed in any one of the preceding claims, wherein the device is further provided with tether means adapted for energy transmission therethrough.

24. A wave energy extraction device as claimed in any one of the preceding claims wherein said driving mass means at least partly comprises one of: operative equipment, raw materials, processed materials.

25. A wave energy extraction device as claimed in claim 16, wherein said hydraulic energy drives hydraulic motor means which in turn drives electrical energy generator means, producing electrical energy.

26. A wave energy extraction device as claimed in claim 16, wherein said hydraulic energy is used to process materials.

27. A wave energy extraction device as claimed in claim 16, wherein said hydraulic energy is used to operate a reverse osmosis mechanism.

28. A wave energy extraction device as claimed in claim 17, wherein said heat pump is used to liquefy air.

29. A wave energy extraction device as claimed in claim 23, wherein said electrical energy is conditioned for transmission via said tether.

30. A wave energy extraction device as claimed in any one of the preceding claims, wherein said extracted energy stored in chemical storage means.

31. A wave energy extraction device as claimed in any one of the preceding claims, wherein said extracted energy is used in electro-chemical processing.

32. A wave energy extraction device as claimed in any one of the preceding claims, wherein said extracted energy is used to produce ammonia.

33. A wave energy extraction device as claimed in claim 32, further comprising means for storing said ammonia.

34. A method of extracting energy from waves, comprising the steps of: a) receiving a wave energy extraction device as claimed in any one of the preceding claims; and

b) deploying said device in a body of water traversed by waves.