Patent Description:
Global warming, depletion of fossil fuels and other factors have increased the need for renewable energy sources and, while various means have been developed to harvest energy from flowing fluids such as wind and rivers, using turbines, there are still enormous sources of renewable energy that are not being harvested commercially.

The present invention seeks to provide means for harvesting such energy sources, particularly including harvesting energy from fluids that move vertically in relation to gravity. By such vertical movement of fluids is not only meant vertical flows, but also movement in which the boundaries between fluids move vertically, e.g. tides and waves, where the elevation of a surface between two fluids with different densities (e.g. water and air), changes.

<CIT> discloses apparatus for the conversion of wave energy comprising a series of circumferential on a central drum that can rotate as water levels vary with waves action, with a rotational axis that is aligned with the waves' direction of travel.

The present invention further seeks to combine multiple modes of harvesting energy from moving fluids, simultaneously and/or consecutively.

According to a first aspect of the present invention there is provided apparatus for harvesting energy from fluids, said apparatus comprising;.

According to another aspect of the present invention there is provided a method of harvesting energy from fluids, said method comprising:.

For a better understanding of the present invention, and to show how it may be put into effect, the invention will now be described by way of non-limiting example, with reference to the accompanying drawings in which:.

Referring to the drawings, apparatus for harvesting energy from fluids according to the present invention is identified, generally, by reference numeral <NUM>. Features that are common between different embodiments of the invention are identified by like reference numerals. Where reference is made to a particular embodiment of the invention, the embodiment is identified with a suffix to the reference numeral.

Referring to <FIG>, the apparatus <NUM> includes a rotor <NUM> that is supported to rotate about a generally horizontal rotational axis <NUM> in a rotation direction. The rotor <NUM> is supported by a support structure (not shown in <FIG>) and it can rotate about a shaft that extends along the rotational axis <NUM>, on bosses or bearings or the like. The rotor <NUM> is mechanically connectable to an unlimited number of driven devices, which can receive rotational energy from the rotor to perform useful functions. Persons skilled in the art would appreciate how varied the uses are, for rotational power from the rotor <NUM>, but by way of non-exhaustive example, it includes driving mechanical machines such as winches, pumps, etc. and includes driving generators or like machines, for converting rotational power from the rotor into electricity. The output from such machines can be applied immediately (e.g. when a machine is driven to perform a mechanical task), can be converted to different forms of energy (e.g. by generating electricity), and/or can be accumulated or stored, e.g. by pumping a fluid to a higher elevation from where it's potential energy can be harvested in future (e.g. with turbines).

The rotor <NUM> includes thirty hollow elements in the form of tubes <NUM> that are arranged to rotate along with the rest of the rotor, the tubes being mounted between two spoked wheels <NUM> and having their ends closed off with caps <NUM>. Each tube <NUM> has a cylindrical outer wall <NUM> and defines a cavity on its inside.

The shape and configuration of the rotor <NUM> and its means for defining cavities, can vary greatly, e.g. the cavities can be formed in a unitary body, there can be any number of cavities from two, different shaped hollow elements can be used to form the cavities, etc. However, at least some of the cavities must be defined at different radial rotations relative to the rotational axis <NUM> in the rotation direction <NUM>, and preferably at least two of the cavities should be defined on opposing sides of the axis - preferably, but not essentially, diametrically opposed. Preferably, the rotor should define a large number of cavities and they should be evenly distributed (circumferentially spaced) about the rotational axis <NUM>.

Each tube <NUM> (and thus each cavity inside the tube) is spaced from the rotational axis <NUM>, although some tubes are spaced further from the axis - at a greater radius.

Even though the parts of the rotor <NUM> that define the cavities, can have various configurations, using tubes <NUM> for this purpose is preferable because of the low cost of manufacturing the rotor, using commercially available tubing, the longitudinal scalability of the tubes, the avoidance of "dead spaces" between the tubes (see below), and the ease of operating longitudinally spaced valves on each tube (see below).

Each of the tubes <NUM> has a longitudinal row of trailing apertures <NUM> that extend from the cavity inside the tube in a direction opposite to the rotation direction <NUM>, to the outside of the rotor <NUM>. Each tube <NUM> need only have a single trailing aperture <NUM>, but depending on operational parameters, it may be preferable to provide a plurality of trailing apertures.

The size of the trailing apertures <NUM> is relatively small in relation to the volume of the cavity inside the tube <NUM>. The relative sizes of the trailing apertures <NUM> and tubes depend on the fluids for which they are intended and depend on the actual dimensions and operational parameters of the apparatus <NUM>. Suffice it to say that the cross-sectional dimensions of the trailing apertures <NUM> are substantially less than the cross-sectional dimensions of the cavities inside the tubes <NUM>.

The tubes <NUM> are configured to form six vanes <NUM>, with five tubes in each vane. Each of the vanes <NUM> extends in a radial direction from the rotational axis <NUM> and the tubes <NUM> in each vane are attached to common spokes <NUM> on each of the wheels <NUM>. The configuration of the vanes <NUM> can be varied in number of tubes <NUM>, size, orientation, etc., as long as the vanes form surfaces that can receive an impingement load from a flowing fluid, to drive the rotor <NUM> to rotate about the rotational axis <NUM> (see below).

The tubes <NUM> are preferably spaced apart, to allow fluids to pass between them and to avoid dead spaces. The spaces between the tubes <NUM> potentially reduce the efficacy of the vanes <NUM>, because some of a fluid impinging upon a vane will pass between the tubes <NUM> and not exert its full impinging potential on the vane. However, in the absence of spaces between the tubes <NUM>, fluids vented from the trailing apertures <NUM> can get trapped between vanes, and inhibit rotation of the rotor.

The size of the rotor <NUM> and the relative sizes of its components, can be varied, depending on operational parameters when using the rotor.

Referring to <FIG>, the apparatus <NUM> includes a rotor <NUM> is shown with a rotational direction <NUM> that is opposite from that shown in <FIG>. The tubes <NUM> are supported in spokes <NUM>, but the spokes do not form part of wheels and the diameters of the tubes are smaller closer to the rotational axis <NUM>, than the tubes at greater radii. The variation in tube diameter is merely intended to ensure adequate free space around the tubes <NUM> closer to the rotational axis <NUM>, to prevent dead space.

Referring to <FIG>, the support structure supporting each rotor <NUM> is configured to support the rotor so that is selectively above and below a boundary formed between two fluids of different density. The invention is not limited to any fluids (not even to compressible or incompressible fluids), but in most scenarios, it is likely to be implemented for use with water as the higher density fluid, air as the lower density fluid and the water surface as the boundary between the two fluids. Without limiting the scope of the invention, reference will be made herein below to water <NUM> and air <NUM> as representative examples of high and low density fluids.

The support structure should preferably be configured to support the rotor <NUM> so that it is selectively, preferably sequentially, completely submerged in the water <NUM> and completely elevated in the air <NUM> above the water surface. However, in some embodiments, it may be preferable that the rotor <NUM> remain partially submerged for part or all of its use. However, it is still essential for purposes of the present invention that the rotational axis <NUM> is at least occasionally above and below the water surface <NUM>.

Supporting the rotor <NUM> to be sequentially above and below the water surface <NUM> can be achieved in various ways: it can be the result of varying water levels, e.g. as a result of tidal variations in water levels or variations in water levels resulting from wave action. However, it can also result from adjustment of the support structure (i.e. a support structure configured to lift and lower the rotor <NUM>), or from other relative motion between the support structure and the water surface - e.g. the rotor can be supported stationary relative to the hull of a water borne vessel, which rocks while afloat in waves.

The rotor <NUM> can operate in various modes, including: a submerged mode in which it is in a submerged position in which preferably the entire rotor is submerged under the water surface <NUM>, as shown in <FIG>; an elevated mode in which it is in an elevated position in which preferably the entire rotor is elevated above the water surface, as shown in <FIG>; and a part-submerged mode in which substantial parts of the rotor are above and below the water surface, respectively. There are also other variations on these modes of operation, in which the water surface <NUM> can be anywhere in relation to the rotor <NUM>, but operation of the rotor by mass displacement (as will be described below) requires submersion and elevation of the rotor, at least to some degree and as a minimum, its rotational axis <NUM> should be sequentially submerged below and elevated above the water surface.

Referring to <FIG>, For purposes of explanation, one of the cavities <NUM> will be regarded as a "first cavity" of the rotor <NUM> and a cavity <NUM> that is diametrically opposed to the first cavity, will be regarded as the "second" cavity. However, depending on the positions of any of the other cavities of the rotor <NUM> - to the left or to the right of the rotational axis <NUM>, those cavities would operate the same way as the first and second cavities.

When the rotor <NUM> is initially submerged from above the water surface <NUM>, each of the cavities <NUM>,<NUM> is filled to some extent, preferably entirely with air and for purposes of explanation, it will be assumed that they are all completely filled with air. For simplicity of explanation, it is assumed that the first and second cavities <NUM>,<NUM> are of equal shape and size and they are spaced equally far from the rotational axis <NUM> - that is the case in the illustrated example, but it need not be the case in other embodiments of the invention.

The trailing aperture <NUM> of the second cavity <NUM> is directed downwards, so that the air inside the second cavity is held captive inside the second cavity. The air in the second cavity <NUM> is lighter than the water <NUM> surrounding the rotor <NUM> and as a result, the air inside the second cavity exerts an upward buoyant force <NUM>.

The trailing aperture <NUM> of the first cavity <NUM> is directed upwards, so that air can escape from the first cavity, through the trailing aperture and some of the surrounding water <NUM> can enter the first cavity <NUM> via its trailing aperture. The inflow of water <NUM> into and venting of air from the first cavity <NUM> increases the overall density of contents inside the first cavity. The contents inside the first cavity <NUM> could change from being made up entirely of air to being made up entirely of water, or could be a mixture of air and water. The increase in density of the contents inside the first cavity reduces the buoyancy of the first cavity in the surrounding water <NUM> and reduces an upward buoyant force <NUM> exerted by the contents of the first cavity.

Initially, when the first cavity <NUM> is filled with air, the density of its contents is the same as that of the second cavity <NUM> and the upward buoyant forces <NUM>,<NUM> exerted by the air inside each of these cavities <NUM>,<NUM>, are in balance. However, as the density of the contents of the first cavity <NUM> increases, so its buoyant force <NUM> will be reduced and the stronger buoyant force <NUM> from the second cavity <NUM> will dominate so that the resultant difference between the buoyant forces will exert a moment on the rotor <NUM>, causing it to rotate in the rotation direction <NUM>.

Depending on the exact physical configurations of the cavities and their trailing apertures <NUM>, the cavities inside each of the tubes <NUM> on the right of the rotational axis <NUM>, as shown in <FIG>, could have an upwardly extending trailing aperture and could function like the first cavity <NUM>. Similarly each of the cavities in tubes <NUM> to the left of the rotational axis <NUM> could function like the second cavity <NUM>.

The rotation of the rotor <NUM> in the rotational direction <NUM> could continue for more than one rotation, while air escapes from cavities in tubes <NUM> to the right of the rotational axis, until all air has escaped and the tubes are filled with water, or until only a small volume of air remains in each tube. In some embodiments, the rotation could end when some tubes <NUM> contain substantially more air than others and the tubes with more air are at the top of the rotor <NUM>, but preferably, the tubes and trailing apertures <NUM> are configured to maximise rotation of the rotor and venting of air from the cavities over several revolutions of the rotor <NUM>.

Air escaping from the trailing apertures <NUM> of the tubes <NUM> to the right of the rotational axis (including the first cavity <NUM>) forms bubbles that travel upwards to the water surface <NUM> by virtue of their buoyancy. However, if dead spaces are formed in the rotor <NUM> where these bubbles could get trapped, the buoyant forces of these bubbles would drive the vanes <NUM> and/or tubes <NUM> on the right, upwards, against the rotation direction <NUM> and would thus reduce the efficiency of the rotor <NUM>. This is why it is preferable that the tubes <NUM> should be spaced apart, leaving spaces between them through which air bubbles can travel to the water surface <NUM>.

For the purposes of explanation and as illustrated in the drawings, the tubes <NUM> and their cavities are geometrically mirrored about the rotational axis <NUM>. However, in other embodiments, the sizes of cavities, their radial orientation in the rotation direction <NUM> and their spacing from the rotational axis, may vary - as long as the combined moment about the rotational axis <NUM>, of all the volumes of the cavities, respectively to the left and the right of the rotational axis, are balanced, irrespective of the rotation of the rotor <NUM>.

Referring to <FIG>, when the rotor <NUM> operates in its elevated mode, above the water surface <NUM>, it can for ease of explanation be presumed to have the same orientation as that shown in <FIG> and when the rotor is initially elevated from below the water surface, each of the cavities <NUM>,<NUM> is filled to some extent, preferably entirely, with water and for purposes of explanation, it will be assumed that they are all completely filled with water.

The trailing aperture <NUM> of the first cavity <NUM> is directed upwards, so that the water inside the first cavity is held captive inside the first cavity. The water in the first cavity <NUM> is heavier than the air <NUM> surrounding the rotor <NUM> and as a result, the water inside the first cavity exerts a downward gravitational force or weight <NUM>.

The trailing aperture <NUM> of the second cavity <NUM> is directed downwards, so that water can escape from the second cavity, through the trailing aperture and some of the surrounding air <NUM> can enter the second cavity <NUM> via its trailing aperture. The inflow of air <NUM> into and draining of water from the second cavity <NUM> reduces the overall density of contents inside the second cavity. The contents inside the second cavity <NUM> could change from being made up entirely of water to being made up entirely of air, or could be a mixture of air and water. The decrease in density of the contents inside the second cavity reduces the downward gravitational force or weight <NUM> exerted by the contents of the second cavity.

Initially, when the second cavity <NUM> is filled with water, the density of its contents is the same as that of the first cavity <NUM> and the weights <NUM>,<NUM> exerted by the water inside each of these cavities <NUM>,<NUM>, are in balance. However, as the density of the contents of the second cavity <NUM> decreases, so its weight <NUM> will be reduced and the stronger weight <NUM> from the second cavity <NUM> will dominate so that the resultant difference between the weights will exert a moment on the rotor <NUM>, causing it to rotate in the rotation direction <NUM>.

The rotation of the rotor <NUM> in the rotational direction <NUM> could continue for more than one rotation, while water drains from cavities in tubes <NUM> to the left of the rotational axis <NUM>, until all water has drained and the tubes are filled with air, or until only a small volume of water remains in each tube. In some embodiments, the rotation could end when some tubes <NUM> contain substantially more water than others and the tubes with more water are at the bottom of the rotor <NUM>, but preferably, the tubes and trailing apertures <NUM> are configured to maximise rotation of the rotor <NUM> and draining of water from the cavities.

Water escaping from the trailing apertures <NUM> of the tubes <NUM> to the left of the rotational axis (including the second cavity <NUM>) travel downwards under gravity to the water surface <NUM> and like the air bubbles mentioned with reference to <FIG>, the drained water would drive the vanes <NUM> and/or tubes <NUM> on the left downwards, against the rotation direction <NUM> if it were trapped in dead spaces in the rotor <NUM> and would thus reduce the efficiency of the rotor. However, the drained water can pass through spaces between adjacent tubes <NUM>, without significantly affecting rotation of the rotor.

The submerged and elevated modes of operation of the rotor <NUM>, described with reference to <FIG>, rely on mass displacement from cavities in the rotor, to drive its rotation, but the mass displacement requires simultaneous out-flow and inflow of fluids through the trailing apertures <NUM>. If the trailing apertures <NUM> are too small, this counter-flow of fluids would cause either or both of the fluid flows to become throttled and insufficient mass displacement would take place. If the trailing apertures <NUM> are too large in relation to the volumes of the cavities inside the tubes <NUM>, then the mass displacement would be too rapid and rotation of the rotor <NUM> would cease prematurely (before venting sufficient air or before draining sufficient water).

Referring to <FIG>, the rotor <NUM> is shown submerged about one third of its height, in the water <NUM>, with its upper two thirds protruding above the water surface <NUM> in the air <NUM>. The rotor <NUM> may be driven as described with reference to <FIG> (in elevated mode), may have rotational momentum as a result of being driven previously in submerged or elevated mode (as shown in <FIG>), may be in a transition between being driven in elevated or submerged mode, or the like.

The water <NUM> could flow in a direction from right to left, as shown in <FIG> as a result of gravitational flow (e.g. a river), flow from wave action, and/or tidal flow and the flowing water would impinge on the tubes <NUM> that are submerged, to drive the rotor <NUM> to rotate in the rotation direction <NUM>. This impingement of the flowing water <NUM> on the rotor <NUM> is made more effective by the arrangement of the tubes <NUM> in vanes <NUM>.

Similarly, the air <NUM> could be moving as wind <NUM> from left to right, above the water surface <NUM> an would impinge on the tubes <NUM> and vanes <NUM> above the water level, driving the rotor <NUM> to rotate in the rotational direction <NUM>. However, to use impingement from the wind <NUM> on the vanes <NUM> more efficiently, it would be preferable if the wind only impinges on the tubes <NUM> above the water surface <NUM>.

Impingement on the tubes <NUM> and vanes <NUM> by water flow <NUM> below the water surface <NUM> and the impingement on the tubes and vanes by wind <NUM> above the water surface, could take place simultaneously, in opposing directions (as shown in <FIG>), or only one of these two fluids could be flowing at a time - the two fluid flows have merely been illustrated in a single drawing, for the sake of brevity.

The modes of driving the rotor <NUM> to rotate in the rotation direction <NUM> by impingement of fluids, described with reference to <FIG>, operate independently of the submerged and elevated modes of operation (which rely on mass displacement) and the impingement and mass transfer modes of operation can operate separately or simultaneously. Ideally, the support structure is configured so that different modes of operation of the rotor <NUM> would drive it in the same rotational direction and for this purpose, water flows <NUM> and/or wind <NUM> can be redirected to drive the rotor in the same rotation direction <NUM> as the mass transfer modes of operation.

Referring to <FIG>, in addition to trailing apertures <NUM>, each tube <NUM> can also have leading apertures <NUM> on its opposite side and the leading apertures or all apertures can be configured to be opened and closed, e.g. with valves. Various configurations of valves can be used and they can be operated in manual, semi-automated or fully automated manners. Preferably, the operation of the valves is fully automated and is controlled remotely, with mechanical actuation affected on the rotor <NUM>, e.g. with solenoids (not shown) that are on the rotor <NUM>.

The rotor <NUM> shown in <FIG> includes a shaft <NUM> with a pulley <NUM> at its end, from which rotational power can be transferred with a belt or the like.

<FIG> shows a tube <NUM> to which a gate element <NUM> has been strapped, that can slide longitudinally along the tube to operate as a common slot valve for a row of apertures <NUM>,<NUM>. A row of gate apertures <NUM> are defined in the gate element <NUM>, which can be in register with the apertures <NUM>,<NUM> when the valves are open, or the gate element can be slid longitudinally so that the gate apertures <NUM> and apertures <NUM>,<NUM> of the tube <NUM> are not aligned and the valves are closed. The simplicity of construction and operation of this slot valve mechanism and the ease with which the single gate element <NUM> can be operated by a single solenoid to open and close all the apertures <NUM>,<NUM>, make the slot valve ideally suited for the present invention.

<FIG> shows a tube <NUM> with butterfly valves <NUM> on each of its leading and trailing apertures <NUM>,<NUM> and a row of the butterfly valves on one side of the tube are operated together with a common push-rod <NUM> that is connected to individual crank arms <NUM> of each butterfly valve.

The valves <NUM>,<NUM> allows the trailing apertures <NUM> to be closed selectively and the leading apertures <NUM> to be opened, so that the rotor can operate in the mass transfer modes as described above with reference to <FIG>, except that the rotation direction <NUM> will have been inverted and the leading apertures <NUM> will act as trailing apertures. Accordingly, the selective opening and closing of the leading and trailing apertures <NUM>,<NUM>, respectively, allows the operation of the rotor <NUM> to be inverted in mass transfer mode. This can be used if a flow of water <NUM> or a wind direction <NUM> has changed, e.g. if the impingement of the water <NUM> and/or wind <NUM> on the vanes <NUM> drives the rotor <NUM> in the opposite rotation direction <NUM>, then this inversion can be used so that the rotor will also be driven in the opposite direction in the mass displacement modes of operation.

The valves <NUM>,<NUM> also allows both the leading and trailing apertures <NUM>,<NUM> to be opened on the tubes that are venting air in the submerged mode or that are draining water in the elevated mode, so that fluids can flow into each cavity from one side and out the other side, simultaneously, thus increasing the rate at which air is vented or water is drained from the cavity, as the case may be. This would only be done temporarily, while a tube <NUM> is on the side of the rotor <NUM> where mass displacement takes place, and the trailing apertures <NUM> would be closed again while the tube is on the side of the rotor where no mass displacement takes place. The leading apertures <NUM> would thus be opened and closed cyclically with rotation of the rotor <NUM> and this cyclical operation of the leading apertures can be affected by simple mechanical means, such as a cam adjacent the rotor.

The ability to open the leading apertures <NUM> thus overcomes the difficulties caused by counter-flow of fluids that can throttle flow through the trailing apertures <NUM>, as described above. In addition, the ability to open and close the leading apertures <NUM> selectively, means that this can be done when more rapid mass transfer is required, but the leading apertures and/or trailing apertures <NUM> can be closed completely or partially when slower mass transfer is required.

Referring to <FIG>, apparatus <NUM> is shown in each of these drawings, which includes a rotor <NUM>, substantially as shown in <FIG>, with a support structure that includes a stand <NUM>. Each rotor <NUM> is supported on a shaft along its rotational axis <NUM> and the opposing ends of each shaft are supported by the stand <NUM>, but each stand defines vertical slots <NUM> in which the ends of the shaft can slide vertically, to move the rotor <NUM> up and down.

The configurations of support structures that can be used to support the rotors <NUM> in use, are unlimited and the structures can be geo-stationary (such as the stands <NUM>), could be supported from other objects, could float, or the like. Further, the stands <NUM> shown in the drawings, each allow for vertical displacement of the rotor <NUM> along the slots <NUM>, but in other embodiments, the rotors can be moved vertically in various other ways or their height could be fixed.

None of the rotors <NUM> shown in <FIG> have leading apertures in their tubes <NUM>, but this is mere co-incidence and rotors with leading apertures could be used in any of these embodiments. Further, only the rotor <NUM> in <FIG> has valves on its trailing apertures <NUM>, but this is also mere coincidence and the rotors shown in <FIG> could also have valves.

Referring to <FIG>, a sealed alternator <NUM> is provided on one end of the rotor's shaft <NUM> and is configured to generate electricity from rotation of the rotor - thus avoiding the need to transfer motive power from the apparatus <NUM>. Floats <NUM> are provided to provide buoyancy to control the elevation of the rotor <NUM> (see below) and the floats include; floats at either end of the rotor and two floats on opposing sides of the alternator <NUM> to compensate for the weight of the alternator.

Referring to <FIG>, the rotor <NUM> includes wheels <NUM> and each wheel has a groove in its outer circumference in which a belt or other flexible transfer element is receivable, to transfer motive power from the wheel to driven equipment. The rotor <NUM> has floats <NUM> at each end.

Referring to <FIG>, apart from having valves, the rotor <NUM> and stand <NUM> are identical to those shown in <FIG>, but in addition, the apparatus <NUM> includes an alternator <NUM> supported on an alternator stand <NUM>, which is driven from one wheel <NUM> of the rotor <NUM> with a belt <NUM>. Tension on the belt <NUM> is maintained by way of an idle pulley <NUM>, which can slide horizontally in the alternator stand <NUM>. However, in other embodiments, actuated horizontal sliding of the idle pulley <NUM> can be used to raise and lower the rotor <NUM>, instead of or in addition to the floats <NUM>.

Referring to <FIG>, the vertical position (elevation) of each rotor <NUM> can be controlled by actuation (e.g. by movement of the idle pulley <NUM>), or by controlling the buoyancy of the floats <NUM>. In a preferred embodiment, the buoyancy of the floats <NUM> is controlled by timing the opening and closing of valves on the floats to vent air and allow water into the float, to drain water and allow air into the float, or to maintain the contents and thus the density of the float.

When the predominant mode of operation of the rotor <NUM> is impinging flow, whether from water flow <NUM>, or wind <NUM>, it would be desirable to maintain the rotor at an optimal elevation in relation to the water surface <NUM>, irrespective of varying water levels from tides and/or waves. In particular, when impingement from water flow <NUM> is the predominant motive power for the rotor <NUM>, then it is preferable to keep the rotor submerged about one third of its height (as shown in <FIG>). Accordingly, in these circumstances, it would be preferable to allow the rotor <NUM> to move up and down along the slots <NUM> as the water level changes and this can be achieved if the floats <NUM> have the correct buoyancy to maintain the rotor <NUM> at the optimal depth.

Operation of the rotor <NUM> by mass displacement can only last for a finite period after each change between submerged and elevated positions and the rotor performs optimally in mass displacement mode when it is completely elevated or completely submerged, sequentially. Complete submersion of the rotor <NUM> can be achieved by venting air from the floats <NUM> so that they lose buoyancy and the rotor "sinks", but complete elevation of the rotor cannot be achieved by controlling the buoyancy of the floats alone. Instead, or in addition, submersion or elevation of the rotor <NUM> can be achieved by allowing the rotor to raise and fall with changes in water level <NUM> and to lock the vertical position of the rotor selectively, while allowing the water level to raise over the rotor or to drop below the rotor.

The operation of the apparatus <NUM> is preferably controlled remotely by a computer, but this need not be the case. Further, the operation of the apparatus <NUM> can be optimised for each location and can be adapted to make optimal use of the energy available - which will change over time in most instances. In particular, some forms of energy that can be harvested by the apparatus <NUM> is relatively predictable, such as tidal flows. Other sources of energy may be less predictable, but can be moderated, e.g. the flowrate of a river may not be predictable, but a predetermined portion of the flow can be channelled to provide a predetermined flowrate, or wind of which the direction is unpredictable, can be channelled to impinge on the rotor <NUM> in a preferred direction. However, some sources of energy are more difficult to predict, e.g. wave height and wind strength and to make optimal use of these energy sources, operation of the apparatus <NUM> may need to be adapted on demand. One of the benefits of the present invention is the versatility of the apparatus <NUM> to harvest energy from moving fluids in various modes.

By way of example, the apparatus <NUM> can be installed in a location where the rotor is exposed to waves and tides - which can be supplemented with wind action, but wind action is omitted from this example, for brevity. If there is no significant wave action, but there are significant tidal flows of water, then air can be partly vented from the floats <NUM> to support the rotor <NUM> submerged one third of its height (irrespective of the water level) and it will be rotated by impingement of the tidal flow <NUM> on the vanes <NUM>.

As the tide approaches low tide, the rotor <NUM> can be locked against downward sliding in the slots <NUM> while the water level drops further as the tide recedes to low tide. This would allow water from the floats to be drained under gravity if their buoyancy needs to be increased. In addition, locking the rotor <NUM> against downward sliding will allow it to become elevated above the water level <NUM> as the tide recedes, so that it can operate in elevated mode (as shown in <FIG>). The operation in elevated mode can thus take place around low tide, when the tidal flow is relatively small.

Once the water has drained from the cavities in the tubes <NUM> in the elevated mode, the rotor <NUM> can be released to slide downward along the slots <NUM> under gravity and air can be vented from the floats <NUM> (if required) so that the rotor is again supported by buoyancy of the floats, at a suitable level to harvest energy from the tidal flow <NUM>, which would become stronger about midway between low tide and high tide.

As the tide approaches high tide, the rotor <NUM> can be locked against upward sliding in the slots <NUM> while the water level continues to rise to high tide and the water submerges the rotor. While submerged, the rotor <NUM> can operate in submerged mode (as shown in <FIG>) - which will take place around high tide, when the tidal flow is relatively small.

Once the air has been vented from the cavities in the tubes <NUM> in the submerged mode, the rotor can be released to slide upwards along the slots <NUM> under buoyancy of the floats <NUM>, to resume its elevation relative to the water level <NUM> where it can harvest the receding tidal flow.

Claim 1:
Apparatus (<NUM>) for harvesting energy from fluids, said apparatus (<NUM>) comprising;
a rotor (<NUM>); and
a support structure (<NUM>) supporting said rotor (<NUM>) to rotate about a generally horizontal rotational axis (<NUM>) in a rotation direction (<NUM>), said support structure (<NUM>) being configured such that said rotational axis (<NUM>) is selectively above and below a boundary (<NUM>) between two fluids (<NUM>,<NUM>) of different density;
said rotor (<NUM>) defining at least a first cavity (<NUM>) at a first radial orientation relative to the rotational axis (<NUM>) and a second cavity (<NUM>) at a second radial orientation relative to the rotational axis (<NUM>), each of said first cavity (<NUM>) and said second cavity (<NUM>) being spaced from the rotational axis (<NUM>), and said first radial orientation being spaced from said second radial orientation in the rotation direction (<NUM>);
wherein said rotor (<NUM>) defines a first trailing aperture (<NUM>) extending from the first cavity (<NUM>) in a direction opposite to the rotation direction (<NUM>), to an outside of the rotor (<NUM>), and a second trailing aperture (<NUM>) extending from the second cavity (<NUM>) in a direction opposite to the rotation direction (<NUM>), to the outside of the rotor (<NUM>);
wherein the rotor (<NUM>) includes a plurality of hollow elements (<NUM>) and each of said cavities (<NUM>,<NUM>) is defined inside one of said hollow elements (<NUM>);
characterised in that a plurality of said hollow elements (<NUM>) are arranged within the rotor (<NUM>), to form vanes (<NUM>), each vane (<NUM>) extending in a radial direction and comprising a plurality of said hollow elements (<NUM>) that are spaced apart.