Field of the Invention

The present invention relates to generators that can be used to extract energy from waves in a body of water, by converting the wave energy to more readily usable energy.

Background to the Invention

In recent years, there has been increased emphasis on the need to exploit renewable energy so that it significantly contributes to global energy production. A combination of government targets, media representation of the issues associated with non-renewable energy sources, and ever increasing energy costs have all created a powerful driving force for the development of renewable energy systems.

Negative impacts of fossil fuels on our environment are well known, as are the problems and high costs associated with nuclear energy. Harnessing of the huge natural abundance of renewable energy on the other hand is constrained merely by our capability of capturing and supplying it at an economically viable price.

One potential renewable energy source is wave power - an abundant and consistent energy resource available in all of the world's large oceans and seas. Various wave devices for generating energy from wave power have been proposed, but such devices have many limitations with no one device having the proven ability to reliably exploit the available wave power resource over the long term. We have disclosed in WO2010007418, WO2011 158006 and WO2013068748 successively improved generators for converting wave motion to useful energy. The generators disclosed use a submersible reaction body to solve many of the difficulties associated with existing wave energy converters. However, the wave energy converters disclosed in WO2010007418, WO2011 158006 and WO2013068748 still have potential for further improvement.

Summary of the invention In accordance with the invention, a generator is provided as outlined in the accompanying claims. The generator of the present invention is for converting wave motion in a body of water to useful energy, the generator comprising: at least one energy capturing float which is movable in response to said wave motion; a reaction member to be positioned below the energy capturing float; connection means for connecting said at least one energy capturing float to said reaction member; energy conversion means for converting relative movement between said reaction member and said at least one respective energy capturing float to the useful energy; wherein the generator includes adaptable depth setting means for setting, over a predetermined range, the depth of the reaction member in the body of water and the height of the reaction member from a bed of the body of water; characterised in that both the float and the reaction member have a positive buoyancy.

With reference to the prior art, the apparatus described and illustrated in WO2010007418 has an energy capturing float that remains on the sea surface continuously, all the time. This means that in highly energetic sea conditions, such as storms, the float will be subject to high loads. These high loads must be managed by the structure and the power take-off system, resulting in costly over-engineering of the apparatus.

The apparatus described and illustrated in WO201 1158006 and WO2013068748 provide improvements over this, however the stability of the submerged reaction member is limited by the mass and therefore size of the reaction member, and therefore is significantly variable across the range of conformations disclosed in WO201 1158006 and WO2013068748.

We have now devised a generator for converting wave motion in a body of water to useful energy, the generator having positive buoyancy in both the reaction member and the energy capturing float to increase the stability of the reaction member in response to forces exerted on it both directly by the waves and indirectly through forces transferred to it by the power capturing float. Our simulation work has shown that by increasing the buoyancy of the reaction member it is possible to transfer more of the reaction forces to the seabed and therefore increase the stability of the reaction member, particularly in energetic sea states. A further advantage of increasing the utilisation of the seabed for reaction purposes is that the size and mass of the reaction member can be reduced at the same time as the stability is improved.

The known generator described in the abovementioned WO2013068748 comprises: at least one energy capturing float which is movable in response to said wave motion; a reaction member to be positioned below the energy capturing float; connection means for connecting said at least one energy capturing float to said reaction member and defining a distance between said energy capturing float and said reaction member; energy conversion means for converting relative movement between said reaction member and said at least one respective energy capturing float to the useful energy; wherein the generator includes adaptable depth setting means for setting, over a predetermined range, the depth of the reaction member in the body of water and the height of the reaction member from a bed of the body of water, and in that the connection means are of adjustable length for independently adjusting the distance between the energy capturing float and the reaction member.

Any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates, at the priority date of this application. Preferably the connecting means defines a distance between said energy capturing float and said reaction member. Most preferably, the connection means are of adjustable length for independently adjusting the distance between the energy capturing float and the reaction member. The generator preferably includes adaptable setting means for setting, over a predetermined range, the depth of the reaction member in the body of water. The setting means further is arranged to set the height of the reaction member from the bed of the body of water.

By "setting the depth" we mean controlling in a manner whereby the precise depth can be chosen and fixed in a modifiable manner. In otherwords, if it is wished to change the set depth, the setting means may be adapted, modified and controlled such that a further precise depth can be chosen and fixed.

In a first embodiment of the invention, the depth setting means comprise at least one flexible mooring line of adjustable length to adjustably secure the reaction member to a bed of the body of water. In this embodiment, the generator has a net positive buoyancy that is resisted by tension of the flexible mooring line(s).

The angle at which the mooring lines are positioned relative to the bed of the body of water can be changed to optimise the stability of the reaction body. A desirable angular configuration of the mooring lines is vertical in the water column, i.e. straight down from the reaction body to the bed of the body of water. In the above-mentioned embodiment, the depth setting means is preferably coupled to the reaction member by one or more winches. Preferably, the connectors in the generator according to the invention include at least one flexible line, which is of adjustable length, the length adjustment being typically achieved by winding the or each line around a respective drum. Thus the distance between the reaction member and the energy capturing float can be adjusted by winding the connector lines on or off the respective drums.

In preferred embodiments of the invention the connectors are of adjustable length so as to permit independent adjustment of the distance (or spacing in a vertical direction) between the energy capturing float and the reaction member, and therefore the depth of the energy capturing float in the body of water.

Furthermore, it is preferred that the reaction member has adjustable buoyancy and a plurality of buoyancy modes, including at least one submerged operating mode in which the reaction member and buoyancy float are submerged using the depth setting means, and a maximum buoyancy mode in which the reaction member floats on the surface of the body of water. In any of these plurality of buoyancy modes, the reaction member should have inertia and drag to resist potential movement of the energy capturing float caused by the wave motion.

Reaction member width and/or can be selected to provide maximum stability and may relate proportionally to float diameter, width and/or length. In preferred embodiments, the reaction member length and/or width is selected from the range 30 to 50 metres, where a float diameter, width and/or length is selected from between 10 metres and 20 metres. Most preferably, the reaction member width and/or length is 40 metres and the float diameter, width and/or length is 15 metres. At this approximate ratio, optimum stability is provided for the reaction member within the water. Positive buoyancy of both the reaction member and the float provide adequate tension on the mooring lines of the depth setting means, which in turn also confers an optimum level of stability upon the generator within the water.

The separation between the float and the reaction member is also critical to the stability of the generator, particularly in highly energetic sea conditions wherein the generator is subjected to powerful wave forces. An optimum separation distance between the reaction member and the float is preferably selected from the range 20 to 40 metres. Most preferable embodiments comprise a separation between the float and the reaction member of 30 metres. Preferred embodiments of the invention will now be described in more detail, with reference to the accompanying drawings, in which like parts are denoted by like reference numerals throughout. In order to avoid detracting from the clarity of the drawings, not all parts are labelled in all drawings.

Detailed Description

Specific embodiments will now be described by way of example only, and with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a preferred embodiment of wave generator according to the invention when on the surface of a body of water (generally, the sea); FIG. 2 is a perspective view of the wave generator of FIG. 1 when submerged beneath the surface of that body of water; and

FIG. 3 is an orthogonal view showing the energy convertor of FIG. 2 moored to the bed of the body of water.

Referring first to FIG. 1 and FIG. 2, there is shown an exemplary wave powered generator according to the invention which comprises a submersible subsea reaction member 1 ; an energy capturing float 2 that moves in response to the waves; a series of energy converters 6a, 6b, 6c, 6d mounted on the reaction member 1 ; and respective connecting lines 5a, 5b, 5c, 5d of adjustable length that connect the energy capturing float 2 to the respective energy converter 6a, 6b, 6c, 6d.

In FIG. 1 , each of the connecting lines 5a, 5b, 5c, 5d is wound around a drum on the respective energy converter 6a, 6b, 6c, 6d to the fullest or maximum extent such that the spacing between the energy capturing float 2 and the reaction member 1 is at a minimum. In this case the reaction member 1 and the energy capturing float 2 are together floating on the surface S of a body of water.

Conversely, in the arrangement shown in FIG. 2, each of the connecting lines 5a, 5b, 5c, 5d is let out (wound around the respective drum) such that the spacing between the energy capturing float 2 and the reaction member 1 is at a maximum. In this case, the energy capturing float 2 is shown just below the surface S of the body of water. FIG. 2 and FIG. 3 show the wave energy generator with mooring lines 3a, 3b, 3c, 3d which tether the generator to the seabed SB, thereby keeping the generator on station. The mooring lines 3a, 3b, 3c, 3d may be connected to the reaction body 1 via corresponding length adjusting means 4a, 4b, 4c, 4d to enable the depth of submersion of the reaction member 1 to be varied.

It should be noted that in the first embodiment of the invention the mooring lines 3a, 3b, 3c, 3d remain tensioned at all times so that the generator cannot move freely up and down in the water column. The positive buoyancy of the reaction member 1 and the float 2, B2 and B1 respectively, enables the reaction member 1 to place upon the mooring lines 3a, 3b, 3c, 3d a tension Ta, Tb, Tc, Td, providing stability to the reaction member 1 and the float 2 in highly energetic sea conditions.

In the embodiment shown, the float has a radius R of 7.5 metres (diameter of 15 metres) and the reaction member has a length and width L of 40 metres. The separation from the float 1 and the reaction member 2 is a distance D2 of 30 metres. In this configuration the generator is arranged to perform optimally in an open sea environment.

The reaction member 1 is generally of a hollow construction and is adapted to be selectively filled with air or water to adjust its buoyancy. The wave powered generator according to the invention has a positive net buoyancy comprising the buoyancy of the reaction member 1 , B2 and the buoyancy of the energy capturing float 2, B1. The generator has a permanent positive buoyancy, but may comprise a surface configuration as shown in FIG. 1 and a submerged configuration as shown in FIG. 2 and FIG. 3. The submerged configuration is the result of the mooring lines 3a, 3b, 3c, 3d used as a depth setting means.

When in the surface configuration (FIG. 1), the reaction member 1 floats on the surface S of the body of water (such as the sea) with sufficient buoyancy for it to carry all other components of the apparatus. In this condition the generator according to the invention can be readily disconnected from the mooring lines 3a, 3b, 3c, 3d and transported across the surface S of the body of water. The wave powered generator can sit sufficiently high in the water that all connections to mooring lines 3a, 3b, 3c, 3d and power umbilical 7 can be clear of the water and be easily accessible. The wave powered generator can also create its own stable service platform with all serviceable components clear of the water to enable easy access for maintenance. With reference to FIG. 2, when the wave generator is in the submersed operating configuration, the buoyant reaction member 1 is held suspended by the combination of the energy capturing float 2 and the mooring lines 3a, 3b, 3c, 3d. The net buoyancy of the generator is defined by the sum of the buoyancy values of the reaction member 1 and the energy capturing float 2 (B1 + B2).

The reaction member 1 has a large mass that resists movements caused to it by the forces applied by the float 2 via the connecting lines 5a, 5b, 5c, 5d, and by the forces applied to it directly by the waves. The reaction member 1 also has a large surface area perpendicular to the direction of the heave force, which thereby provides further resistance to movement by way of a large drag and added mass.

The reaction member 1 may be held suspended between the energy capturing float 2 and the seabed SB using the mooring lines 3a, 3b, 3c, 3d at a depth D1 sufficient to ensure that the reaction member 1 is generally below the influence of waves on the sea surface. Therefore movement of the energy capturing float 2 caused by waves results in relative motion between the energy capturing float 2 and the reaction member 1. This movement is taken up by respective working strokes of the energy converters 6a, 6b, 6c, 6d and thus exploited to produce power.

In the illustrated embodiment, a single float 2 is shown, but it will be understood that more than one such float can be provided if appropriate, each with its own series of energy converters mounted on the reaction member 1 , together with respective connecting lines.

In the described embodiments, the float radius is shown as 7.5 metres (diameter 15 meters) and the length and width of the reaction member are shown as 40 metres. Alternative embodiments may comprise a float which can be of any shape with a diameter, or width and/or length, of between 10 metres and 20 metres. Alternative embodiments may also comprise a reaction member of any shape, with length and/or width, or diameter (where spherical), of between 20 metres and 40 metres.