Technical Field

The invention relates to a floating photovoltaic plant as well as to a method for operating such a photovoltaic plant in a body of water.

Background Art

US 2008/0169203 Al and US 2007/0283999A1 describe photovoltaic plants to be operated in a body of water. The plants float in the water, with the panels at least partially submerged.

Disclosure of the Invention

It is an object of the present invention to provide an economic, efficient solution for a floating photovoltaic plant of this type as well as for its operation.

This object is achieved by the method and plant of the independent claims.

Accordingly, in a first aspect, the invention relates to a method for operating a floating photovoltaic plant, wherein said photovoltaic plant comprises at least one module having at least the following elements:

- A frame structure: This is a structure to which various elements of the module are mounted, directly or indirectly.

- A plurality of solar panels: These panels are the parts converting light into electrical energy. Each panel may comprise one or more photovoltaic cells.

- A plurality of sub-modules: Each sub-module comprises one or more of the solar panels. At least some of the sub-modules are “pivotal sub-modules” that are pivotal in respect to the frame structure.

The method comprises at least the following steps:

- Operating the module at a first vertical position in a body of water. In this first vertical position, at least a subset of the pivotal sub-modules are located at a first tilt position in respect to the surface of said body of water. The subset advantageously corresponds to all the sub-modules of the module, but it may also be a true subset of the sub-modules, i.e. some of the sub-modules may also be non-pivotal. Advantageously, the subset includes at least a major part, i.e. at least 50%, of the submodules of the module.

- Moving the module to a second vertical position in the body of water. The second vertical position is different from the first vertical position, i.e. the module is lowered or raised within the body of water. While moving the module to the second vertical position, at least some of the pivotal sub-modules are brought into a second tilt position. In this second tilt position, the inclination of the pivotal submodules in respect to the surface of the body of water is larger than in the first tilt position.

In this context, the inclination is defined as the smallest angle between the normal of the surface of the body of water and the normal of the surface of the panels of the sub-module. Hence, in other words, the sub-modules with their panels are brought into a “steeper” position while moving the module to the second vertical position. This reduces the flow resistance of the water through the module, thereby decreasing the forces acting on the module while lowering or raising it. This, in turn, allows to use a more lightweight, simpler design for the module and/or to move the module more quickly through the water.

Advantageously, the module comprises actuators for individually pivoting at least some of the pivotal sub-modules. In this case, the method may comprise the step of actuating said actuators while or before moving the module to the second vertical position, thereby moving the given sub-modules from the first to the second tilt position. In this context, an actuator comprises an active drive component (e.g. a motor or a pneumatic or hydraulic piston) and actuating the actuator comprises controlling the actuator to change the tilt angle. This aspect of the invention allows to actively change the tilt angle of the pivotal sub-modules.

In addition or alternatively thereto, at least some of the pivotal submodules may comprise restorative mounts adapted and structured to allow a reversible tilting of the sub-modules or of panels of the sub-modules against a restorative force of the restorative mounts by at least 5°, in particular by at least 15°, i.e. their tilt angle can be changed by at least 5°, in particular by at least 15°, against the restorative force. In this case, the method may comprise the step of using dynamic pressure exerted by the body of water to change the tilt angle of the sub-modules or panels while moving the module to the second vertical position. In this case, the tilting to the second tilt position can be achieved by means of the water pressure, without the need to provide active actuators for all the pivotal sub-modules or panels. Advantageously, at said “first vertical position”, at least some of the modules are submerged in the body of water. In particular, all of the modules are submerged in the body of water and electricity is generated. This allows operating the module with the panels under water, which provides better cooling and allows to keep the panels cleaner, thereby improving operating efficiency.

The module may further comprise a rigid gas tank, at least one inflatable float, and a gas tank. For raising the module, gas may be moved from the tank to the float(s). For lowering the module, gas may be moved from the float(s) to the tank.

The gas used in this steps is advantageously air, but it may also be another type of gas.

The method may further comprise the step of generating, by means of a propulsion, a horizontal force to move or keep the module to/at a desired horizontal location. This allows to actively control the horizontal position of the module.

In another aspect, the invention also relates to a photovoltaic plant comprising at least one module, with the module comprising at least the following elements:

- A frame structure: This is the structure to which various elements of the module are mounted, directly or indirectly.

- A plurality of solar panels: These panels are the parts converting light to electrical energy. Each panel may comprise one or more photovoltaic cells.

- A plurality of sub-modules: Each sub-module comprises one or more of the solar panels. At least some of the sub-modules are “pivotal sub-modules” that are pivotal in respect to the frame structure.

Advantageously, this module is adapted to carry out the above method, for example by means of a control unit adapted to carry out the method and/or e.g. by comprising sub-modules that are restoratively mounted to be tilted by the water flow when lowering/raising the module.

The module may comprise at least one inflatable float. In this case, the module can be structured to change the volume of gas in the float in order to control the attitude and/or vertical position of the module in the body of water.

The module may further comprise at least one rigid gas tank and a gas pump adapted to pump gas into the gas tank. In this case the gas tank can be used to store gas, which allows to move gas between the tank and the float in order to control the buoyancy of the float.

Advantageously, in this case, the module further comprises a gas duct between the gas tank and the float as well as an electrically controllable valve controlling a passage of gas through the duct. By opening the valve, as described above, pressurized gas can be moved quickly, and with little energy, from the tank to the float.

The module advantageously comprises several such floats arranged along a circumference thereof. These floats allow to change the attitude of the module.

Advantageously, the module comprises a pump system adapted and structured to move gas between said floats. This allows to change the attitude without the intake or loss of gas. This pump system may be implemented by the pump mentioned above, which e.g. transfers the gas from one float to another float via the tank. Or it may be implemented by one or more other pumps that directly convey gas between the tanks.

In a structurally robust, light-weight embodiment, the frame structure comprises a lattice with openings, with one sub-module arranged in each opening. Advantageously, the openings are arranged in a two-dimensional array, such as in an array having an angle of 60° or 90° between its rows and columns.

In a particularly advantageous embodiment, the sub-modules are hexagonal, and the lattice forms a honeycomb with hexagonal openings to receive the sub-modules. This kind of lattice has good rigidity at low weight, with the hexagonal sub-modules efficiently using the available space in the openings.

Brief Description of the Drawings

The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the schematic drawings, wherein:

Fig. 1 shows a top view of a first embodiment of a module, Fig. 2 shows a vertical sectional view along line A-A of Fig. 1, Fig. 3 shows the embodiment of Fig. 2 with tilted sub-modules, Fig. 4 shows a top view of a second embodiment of a sub-module, Fig. 5 shows a vertical sectional view along line B-B of Fig. 4, Fig. 6 shows the embodiment of Fig. 5 in a tilted position,

Fig. 7 shows a top view of a third embodiment of a sub-module, Fig. 8 shows a top view of a second embodiment of a module, Fig. 9 shows a vertical sectional view along line C-C of Fig. 8, Fig. 10 shows a top view of a third embodiment of a module,

Fig. 11 shows a vertical sectional view along line D-D of Fig. 10, Fig. 12 shows the embodiment of Fig. 11 in a tilted position, Fig. 13 shows a top view of another embodiment of a sub-module, Fig. 14 shows a vertical sectional view along line E-E of Fig. 13, Fig. 15 shows a top view of another embodiment of a sub-module, Fig. 16 shows a top view of another embodiment of a sub-module, Fig. 17 shows a top view of a first embodiment of a plant comprising several modules,

Fig. 18 shows a top view of a second embodiment of a plant comprising several modules,

Fig. 19 shows a side view of two neighboring modules of the plant ofFig. 18,

Fig. 20 shows a block diagram of some components of a module.

Modes for Carrying Out the Invention

Overview

Figs. 1 - 6 show a first embodiment of the solar plant, but the features described in this overview section can be readily applied to all embodiments.

As mentioned, the present solar plant comprises one or more modules 2, with an example of one such module 2 shown in Figs. 1 - 6. Module 2 is adapted to be floating in a body of water. It comprises a plurality of sub-modules 4 mounted to a frame structure 6.

Each sub-module 4 comprises a plate-shaped carrier and forms one or more solar panels 8, with the solar sub-modules 4 being pivotal. In the embodiment of Figs. 1 - 6, each sub-module 4 forms two solar panels 8a, 8b, see Fig. 4, with each solar panel 8a, 8b carrying one or more photovoltaic cells. Fig. 4 shows, by way of example, a plurality of such photovoltaic cells 10 having triangular shape.

Alternatively, a sub-module 4 may form a single solar panel 8, or it may form more than two solar panels.

In the embodiment of Figs. 1 - 6, all sub-modules 4 are pivotal. Alternatively, and as mentioned above, only a subset of the sub-modules 4 may be pivotal.

Frame structure 6 of module 2 e.g. comprises an outer frame 12 and a plurality of bars 14. The bars 14 form, optionally together with outer frame 12, a lattice with openings 16 (see Figs. 1, 4), wherein one sub-module 4 is arranged in each opening 16.

(Note that the bars 14 are shown in Fig. 1 but, for simplicity, they have been omitted in the top view of the further embodiments of the module, such as in Figs. 8 and 10.)

The openings 16 form a two-dimensional array with rows and columns. The angle between the rows and columns is, in the shown embodiments, 60°. Alternatively, it may e.g. be 90°, e.g. in combination with square sub-modules 4.

Advantageously, and as shown, the lattice forms a honeycomb, and the openings 16 are hexagonal. Such a honeycomb structure combines good rigidity and low weight.

Similarly, the sub-modules 4 are hexagonal in order to efficiently use the space provided by the hexagonal openings 16.

As shown in Figs. 5 and 6, the bars 14 are hollow, forming gas-tight interior chamber 16 for providing buoyancy. They may e.g. be of metal or plastics. This design allows to better distribute the forces through the structure, which again is expedient for a light-weight design.

Frame structure 6 together with the panels 8 forms a panel assembly 30. This panel assembly 30 defines a plane 18, with the solar panels 8 being arranged in said plane. In operation, plane 18 is advantageously arranged substantially parallel to the surface 20 of the body of water.

Plane 18 is advantageously defined by the plane extending through the geometrical centers of the panels 8 when the panels are in their horizontal position.

As further shown in Fig. 2, module 2 advantageously comprises a control assembly 22 and a control mount 24 connecting control assembly 22 to panel assembly 30 and holding control assembly 22 at a non-zero distance from plane 18 and from panel assembly 30. In operation of the module 2, control assembly 22 is located beneath panel assembly 30.

In the embodiment of Figs. 1 and 2, control mount 24 is formed by several girders 26 extending between outer frame 12 and control assembly 22.

Advantageously, control assembly 22 is held, by control mount 24, in a central axis 28 of module 2, which extends perpendicularly to plane 18 through the center of mass of module 2. This allows to balance the module 2 more easily.

Control assembly 22 advantageously comprises a gas pump 32 and/or a rigid gas tank 34, in particular both, the function of which will be described in more detail below. Module 2 further comprises a control unit 36, which is e.g. located in control assembly 22, and which is programmed to control the operation of module 2.

In the following sections, advantageous aspects of the module as well as of its control are described in reference to the first embodiment, but these aspects can also be used in combination with the other embodiments of the solar plant.

Panel tilting

As mentioned, at least some of the sub-modules 4, and therefore of the panels 8, are “pivotal” panels that can be tilted in respect to frame structure 6. In order to implement this, each pivotal sub-module 4 is connected to frame structure 6 by means of a tilt mount 36, which allows to tilt sub-module 4 in respect to frame structure 6 about a tilt axis 38 as shown in Figs. 4 - 6.

Advantageously, tilt axis 38 is parallel to plane 18.

In one variant, when seen from above, e.g. as shown in Fig. 4, tilt axis 38 extends through the center of sub-module 4, which allows to balance submodule 4 around tilt axis 38, which reduces the forces required for tilting it. Alternatively, as shown in other embodiments below, tilt axis 38 may be offset to the center of sub-module 4 and/or to the center of a given panel 8.

In the embodiment of Figs. 4 and 5, tilt axis 38 extends through opposite corners 40a, 40b of the sub-module 4. In another embodiment, as later shown in Fig. 7, it extends through the centers of opposite, flat sides 42a, 42b of sub-module 4.

Advantageously, all tilt axes 38 of the sub-modules 4 of module 2 are parallel to each other, which allows to tilt all sub-modules 4 in the same way, e.g. in order to catch sunlight coming in from an oblique direction, as illustrated in Fig. 3. This design also allows to efficiently generate horizontal force components while raising or lower module 2 as described in the section “Horizontal Position Control” below.

Figs. 5 and 6 show an example for actively tilting a sub-module 4 or panel 8. Even though these figures are shown for the embodiment of Fig. 4, the same mechanism can also be employed for the embodiment of Fig. 7.

Here, a tilt actuator 44 extends between the lattice, advantageously one of the bars 14, of frame structure 6 and an edge of sub-module 4, and it is adapted to exert a force having a component perpendicular to plane 18 onto sub-module 4, thereby generating a torque about tilt axis 38. In the shown embodiment, for example, tilt actuator 44 may comprise a pneumatic or hydraulic piston 46 pivotally connected to the lattice as well as to the sub-module.

Advantageously, at least one tilt actuator 44 is provided for each pivotal sub-module 4 for individually tilting it. However, tilt actuator 44 may also be common to several sub-modules 4.

Figs. 4 - 6 illustrate a further possibility of tilting a panel 8, which can e.g. also be applied to the embodiment of Fig. 7 or other embodiments of the invention.

Namely, here, sub-module 4 comprises two or more panels 8a, 8b, with each panel 8a, 8b comprising one or more photovoltaic cells 10, and with the two panels 8a, 8b being pivotal in respect to each other. In Figs. 4 - 6, this is shown for a pivotal sub-module 4, but it may also be used for a non-pivotal sub-module 4.

For example, the panels 8a, 8b may be pivotal in respect to each other about the same tilt axis 38 as the whole sub-module 4.

Advantageously, the panels 8a, 8b are interconnected by an elastic mount 48, which e.g. comprises a leaf spring 49, and which is adapted to generate a restoring force and to move the two panels 8a, 8b into a common plane in the absence of an external force. In the presence of an external force, the two panels 8a, 8b can be elastically tilted in respect to each other, at least by 5°, without damaging the module.

Such an external force for tilting can e.g. be exerted by waves of the body of water and/or by a vertical movement of module 2 relative to the body of water, in which case, at least one of the panels 8a, 8b can yield to the force, thereby letting water pass more easily and reducing the strain on frame structure 6.

Figs. 5 and 6 further show a stop member 50 between the panels 8a, 8b, which allows a relative tilting, starting from a position where the two panels 8a, 8b are in a common plane, into a first direction XI, but not into an opposite, second direction X2. This, in combination with tilt actuator 44, allows to tilt the whole submodule 4, but it also allows panel 8a, which is not connected to tilt actuator 44, to move upwards in respect to the other panel 8b.

As shown in Figs. 5 and 6, stop member 50 may be a rigid element mounted beneath the two panels 8a, 8b while elastic mount 48 is arranged above the two panels 8a, 8b.

Hence, in more general terms, sub-module 4 comprises a first panel 8a, a second panel 8b, and a stop member 50 between the panels 8a, 8b. Tilt actuator 44 is adapted to apply its force to second panel 8b, and stop member 50 is adapted to allow first panel 8a to tilt in first direction XI in respect to second panel 8b but not in respect to opposite second direction X2. Instead of using elastic mount 48, gravitational forces can be used to keep panel 8a urged against stop member 50 in the absence of hydrodynamic forces exerted by the body of water. This type of gravitationally restorative mount can be used instead of an elastic mount for any applications described herein.

Elastic mounts or gravitationally restorative mounts both form restorative mounts adapted to bring a panel or sub-module into a predefined position in the absence of hydrodynamic forces generated by the body of water.

Controlling Attitude and Vertical Position

The module 2 is advantageously adapted to control its attitude and/or vertical position.

In this respect, “attitude” is understood to be the angle between plane 18 of the solar panels and the surface 20 of the body of water, and “vertical position” is understood to be the distance between surface 20 and the intersection of central axis 28 and plane 18.

Both, attitude and vertical position, may be controlled by inflatable floats and/or by one or more propulsion units provided on module 2. Both these means are shown in Figs. 1 - 6, but there may also be only one of these means. They can also be used, alone or in combination, with the other embodiments of the module.

In particular, module 2 advantageously comprises one or more inflatable floats 52a, 52b...

At least some of the floats 52a, 52b... may be arranged on panel assembly 30.

Advantageously, and as e.g. seen in Fig. 1, module 2 comprises several floats 52a - 52f in order to control its attitude and/or vertical position. In particular, module 2 comprises several floats 52a - 52f arranged along its circumference. These floats 52a - 52f can be positioned to form the outmost parts of the module 2 in order to act as bumpers, thereby reducing impact forces if the module collides with other modules or with obstacles. This is particularly important when the plant comprises several modules 2 that might come into contact with each other (see below for an example).

The floats 52a, 52b... form closed chambers the volume of which can be changed by moving gas into or from the floats. They may e.g. comprise an outer body which is, at least in part, repeatedly deformable, in elastic or non-elastic manner, to inflate and deflate the volume of the chamber by at least 10%, in particular by at least 50%. Module 2 may comprise at least a first and a second float, e.g. floats 52a and 52d in Fig. 1, arranged at different radial directions, in particular two opposing radial directions, in respect to central axis 28. To control the attitude of module 2, the relative amount R of gas of the first and the second float can be changed, with R = V1/V2, with VI being the amount of gas in the first float and V2 being the amount of gas in the second float. For example, the amount of gas in the first float can be increased or decreased, and/or the amount of gas in the second float can be decreased or increased.

In a particularly efficient embodiment, the relative amount R can be changed by directly moving gas between the first and second float, thereby reducing or eliminating the need to aspire/discard/store gas elsewhere.

Alternatively, however, attitude can be controlled by moving gas between one or more floats and tank 34 and/or by aspiring gas (air) from above the body of water or by releasing gas into the body of water or the air above it.

To control the vertical position of module 2, the volume of gas in at least some of the floats can be increased or decreased, respectively, thereby changing the buoyance of the floats.

This can be implemented by moving between tank 34 and the floats and/or by aspiring gas (air) from above the body of water or by releasing gas into the body of water or the air above it. In particular:

- For raising the module, gas may be moved from tank 34 to the floats 52a, 52b...

- For lowering the module, gas may be moved from the floats 52a, 52b... to tank 34.

Module 2 may be operated to maintain a desired vertical position and/or attitude by means of a control loop. This involves the steps of

- Measuring the current vertical position and/or attitude of module 2 in the body of water. This can e.g. be achieved by using several vertical position sensors at different locations of the module.

- Controlling the vertical position and/or attitude of module 2 in order to maintain the module at the desired vertical position and/or attitude.

This allows e.g. to maintain module 2 at an ideal operating position in respect to the surface and/or the sun.

These steps for controlling vertical position and/or attitude are advantageously performed repetitively to maintain the position/attitude.

As mentioned, the module can be moved at least between a first and second vertical position (i.e. depth) in the body of water. The first position is typically the operating position for harvesting solar energy while the second position is a “dive position” further below surface 20 of the body of water as explained in the section “Operation” below.

For example, at the first position, at least some of the panels are submerged in the body of water, in particular all of the panels are submerged in the body of water. As mentioned, this location is advantageous because the panels cooled by the water and therefore have higher efficiency. Also, the panels are more likely to stay clean.

At the first position, the distance between the panels 8 (in their nontilted position) and surface 20 is advantageously between 2 and 20 cm, in particular around 5 cm.

As mentioned, to move gas between the floats 52a, 52b..., between the floats 52a, 52b... and tank 34, or between the environment and the tank or floats, pump 32 may be used.

There may be one central pump 32, e.g. in control assembly 22, or there may be several pumps distributed over the module.

In addition, valves 90 may be used to release gas from tank 34 and/or the floats 52a, 52b.

In particular, pump 32 can advantageously be used to fill tank 34 with pressurized gas of at least 2 bar, in particular of at least 10 bar, either by moving gas from the float(s) to tank 34 or by aspiring gas (air) from above the surface of the body of water.

For this to work well, tank 34 is advantageously “rigid” in the sense that, when increasing the pressure of the gas therein from 1 bar to 2 bar, relative to the pressure of the water around it, its volume does not change by more than 5%, in particular not by more than 1%.

Advantageously, for raising the module, a valve 90 between tank 34 and one or more of the floats is opened for letting the pressurized gas expand through one or more ducts 94 into the float. This allows, quickly and with little expense of energy, to fill the float(s) without the need of getting gas from above the body of water or operating the pump.

As already explained, when lowering or raising module 2, the water resistance can be decreased by moving the pivotal sub-modules to the second, steeper tilt position as described above.

Advantageously, for a given pivotal sub-module 4, in said second tilt position, the distance between said sub-module 4 and a next neighbor of said sub- module 4 is larger than in the first tilt position. This provides larger gaps 96 (see Fig. 3) for the passage of water when lowering/raising module 4.

In addition or alternatively to controlling the attitude and/or vertical position of module 2 by means of the floats, the attitude and/or vertical position can be controlled by means of active propulsion units, such as the depth control propellers 54 shown in Fig. 2 or by means of flaps operated by actuators.

Horizontal Position Control

As mentioned above, module 2 may also be adapted to move itself to a desired horizontal location or to maintain a desired horizontal location even if e.g. placed in a flowing body of water. In this context, the horizontal location is the location of the module in a two-dimensional coordinate system parallel to surface 20 when seen from above.

For this purpose, the module may be adapted to generate, by means of some kind of propulsion, a horizontal force component to move or keep the module to/at the desired horizontal location.

Such a horizontal force can e.g. be generated by means of a horizontal control propeller 56 as shown in Fig. 2. Propeller 56 rotates about a propeller rotation axis 58 that is e.g. parallel to plane 20, and this rotation axis can be rotated about a steering axis 60 by means of a steering unit 62. Steering axis is advantageously perpendicular to plane 20 and may e.g. coincide with central axis 28 or be parallel thereto.

Alternatively or in addition to propeller 56, horizontal propulsion may be generated by means of lowering and/or raising module 2 with at least some of the sub-modules 4 tilted into a non-horizontal, non-vertical position, e.g. as shown in Fig. 3. In this case, a vertical movement of the module will generate a horizontal force component because water is deflected at the oblique surfaces of the tilted submodules 4. Advantageously, for generating such a horizontal force, the angle between the normal to plane 18 and the normal of surfaces of the panels of the sub-module is between 15° and 75°, in particular between 30° and 60°.

Advantageously, for generating such propulsion, the tilt axis 38 of the tilted sub-modules 4 are parallel to each other, such that the horizontal force components generated by the individual sub-modules 4 are added to each other. Rotation

Advantageously, the module as a whole or at least its panel assembly 30 is adapted to rotate within the body of water. In this context, a rotation is understood to be the rotation about central axis 28 of the module, with the central axis advantageously being parallel to the normal of surface 20 or being inclined in respect to the normal of surface 20 by no more than 30°.

Rotation can e.g. be used to better align the tilted sub-modules 4 with the incoming sunlight, as shown in Fig. 3.

Rotation can also be used to select the direction of horizontal displacement, e.g. when generating horizontal displacement by lowering/raising the module with tilted sub-modules as described in the previous section.

A rotation of module 2 can e.g. implemented by means of propellers similarly to the depth control propellers 54 but with their rotation axes arranged e.g. parallel to surface 20.

In one embodiment, panel assembly 30 can be rotated in respect to control assembly 22. Such a mutual rotation between the two assemblies 30, 22 will result in a rotation of panel assembly 30 in respect to the body of water.

An embodiment implementing this is shown in Figs. 8 and 9, where control mount 24 connecting control assembly 22 to panel assembly 30 comprises an annular rail 64 and rollers 66, with the rollers 66 running along annular rail 64. Annular rail advantageously extends parallel to plane 18 and/or is concentric with central axis 28.

In the shown embodiment, annular rail 64 is fixedly connected to control assembly 22 while the rollers 66 are fixedly connected to panel assembly 30, but these parts may also be swapped.

In another embodiment, as shown in Figs. 10 and 11, control mount 24 comprises a socket 68 and a shaft 70, with shaft 70 being rotatable, in respect to rotational socket 68, e.g. by means of a bearing arranged between them. In the shown embodiment, socket 68 is mounted to panel assembly 30 and shaft is mounted to control assembly 22, but these parts may also be swapped.

Advantageously, 70 extends along central axis 28 and is rotatable, in respect to socket 68, around central axis 28.

To rotate panel assembly 30 in respect to control assembly 22 in e.g. the embodiments of Figs. 8 - 11, active direct driving means can be provided, such as propellers arranged to either one or both assemblies or by means of motors directly generating a torque between the assemblies. Said motors may e.g. drive the rollers 66 or generate a torque between socket 68 and shaft 70, e.g. by means of a gear or belt.

Alternatively to, or in addition to, propellers or direct driving means, imbalances in the assemblies 22 and 30 can be used for generating a rotation. This is illustrated, by way of example, for the embodiment of Figs. 10 and 11, even though it can also e.g. be implemented for the embodiment of Figs. 8 and 9.

For this scheme to work, it must be possible to provide in both the panel assembly 30 as well as the control assembly 22, an asymmetry of buoyancy in respect to the desired rotation axis, e.g. in respect to central axis 28. In this context, such an asymmetry of buoyancy is present, by definition, if the buoyancy of the respective assembly 22, 30 in the body of water is unevenly distributed around said axis such that the respective assembly 22, 30 has a tendency to tilt about a tilt axis perpendicular to the rotation axis.

Such an asymmetry of buoyancy may be generated by permanent means, e.g. by affixing a weight 72 to e.g. one side of panel assembly 30 (and/or of control assembly 22) but not to the other side, e.g. as shown in dotted lines in Fig. 12. Alternatively or in addition thereto, the asymmetry of buoyancy may be generated by asymmetrically inflating the floats 52a - 52f of the panel assembly 30 and/or, if control assembly 22 is provided with floats 52g, 52h... as shown in Figs. 11 and 12, by asymmetrically inflating the inflatable floats 52a - 52f of control assembly 22.

In the following, we assume the direction of minimum buoyancy of panel assembly 30 is located along a first direction Al and the direction of minimum buoyancy of control assembly 22 is located along a second direction A2, as shown in Fig. 10.

If the first and second directions Al and A2 are non-parallel, a torque will be generated within module 2 that strives to make the directions Al and A2 parallel in order to minimize the overall potential energy of the module. Hence, panel assembly 30 will rotate in respect to control assembly 22. This will, in general, make both parts rotate in relation to the body of water, in opposite directions, which allows to rotate panel assembly 30 towards a desired position.

Advantageously, for an efficient rotation of panel assembly 30, control assembly 22 may be rotationally locked, e.g. by mooring it to the ground or connecting it to neighboring modules 2 of the same plant, as shown below.

Once the desired rotational direction is reached, the imbalances in the two assemblies 22, 30 may be removed, or it may be maintained. The procedure of adding imbalances into different directions and then removing them again may be repeated to rotate panel assembly 30 by larger angles.

Figs. 8 - 11 show another aspect that can also be advantageously combined with other embodiments of module 2. As can be seen, outer frame 12 of panel frame structure 6 may be circular while the sub-modules 4 cover a substantially hexagonal area, which provides space to locate at least some of the floats 52a - 52f at six locations between this hexagonal area and outer frame 12.

Submodules and Panels

In the embodiment of Figs. 4 - 6, sub-module 4 comprises two solar panels 8a, 8b, with sub-module 4 being tiltable in respect to frame structure 6 and the two solar panels 8a, 8b being tiltable (i.e. pivotal) in respect to each other.

However, the two panels 8a, 8b of sub-module 4 of Figs. 4 - 6 may also be rigidly connected to each other, or sub-module 4 may comprise but a single, hexagonal solar panel.

Fig. 13 illustrates some alternative approaches that can be used individually or in combination:

A) Sub-module 4 may comprise several individually tiltable solar panels 8a - 8f, e.g. three, four, or (as shown) six such panels. Each panel may be directly mounted to the bars 14 or other parts of frame structure 6 by means of one or more hinge mechanisms 74, and at least some of the tilt axes 38a, 38b... may be nonparallel (note: in Fig. 13, only two of these tilt axes are shown). This is a simple design, and it can e.g. be used to tilt the panels 8a - 8f and therefore the sub-module 4 from the first to the second tilt position when raising or lowering the module.

B) The design of Fig. 13 does not comprise a tilt actuator. Rather, the panels 8a - 8f, are passively pivoted by the flow of the water against the restoring force of an elastic member 48, which is e.g. part of hinge mechanism 74 as shown in Fig. 14. In another embodiment, sub-module 4 may be pivotal as a whole (and not its individual panels) may be pivotal against the restoring force of such an elastic member 48. The restoring force moves the sub-module and/or the panels into a position parallel to plane 18 if no water is flowing through the module.

C) The design of Fig. 13 further illustrates how a hexagonal submodule may consist of six triangular solar panels, which may or may not be individually tiltable. Such a design combines low weight and good mechanical stability. Fig. 15 shows another embodiment of a sub-module 4. This submodule again has six triangular solar panels 8a - 8f. Two panels 8a, 8d, which are arranged on opposite sides of sub-module 4, are mounted to the bars 14 or other parts of frame structure 6 by means of a common tilt mount 36. Tilt mount 36 is adapted to allow the panels 8a, 8d to be tilted about tilt axis 38.

Tilt mount 36 may be passive in the sense that it comprises an elastic member generating a restoring force to move the panels 8a, 8d into a position parallel to plane 18 in the absence of water flow, but it allows the sub-module to yield to asymmetric flow patterns of the water, e.g. as generated by small waves. Alternatively or in addition thereto, tilt mount 36 may comprise a tilt actuator (not shown) for actively tilting the panels 8a, 8d.

The other panels 8b, 8c, 8e, 8f may be connected to the panels 8a, 8d by means of connector members 76.

One or more of these connector members 76 may be rigid connector members, which keep the respective panel 8b, 8c, 8e, 8f in the same plane as the panel 8a, 8d they are connected to.

In addition or alternatively thereof, or more of these connector members 76 may, however, also be flexible connector members, which allow the respective panel 8b, 8c, 8e, 8f to tilt in respect to the panel 8a, 8d it is connected to while keeping the panels in the same plane in the absence of a water flow.

In the embodiment of Fig. 15, the connector members 76 are flexible connector members that allow the panels 8b, 8c, 8e, 8f to tilt about tilt exes 38a and 38b, respectively, in relation to the panels 8a, 8d.

In yet another embodiment, as shown in Fig. 16, sub-module 4 may comprise a rigid sub-frame 78, which in turn holds the panels 8a - 8f of the sub-module.

In this embodiment, tilt mount 36 pivotally connects sub-frame 78 to the bars 14 or another part of frame structure 6 and allows sub-frame 78 to pivot about tilt axis 38. Further, sub-module 4 is advantageously provided with a tilt actuator 44, e.g. of the type shown in Figs. 5 and 6, for actively tilting sub-frame 78 in respect to frame structure 6 about axis 38.

Further, at least some, advantageously all, of the panels 8a - 8f of the sub-module 4 are pivotally mounted to sub-frame 78 by means of elastic connector members 76. These elastic connector members 76 generate restoring forces that move the panels 8a - 8f into a common plane in the absence of water flow.

Fig. 16 illustrates two types of connector members 76, even though a specific implementation may only use of them: (A) The connector members 76 of the panels 8a, 8d e.g. allow to pivot the panels, in respect to sub-frame 78, around tilt axes 38a, 38d, which extend along side edges of sub-module 4.

(B) The connector members 76 of the panels 8b, 8c, 8e, and 8f e.g. allow to pivot the panels, in respect to sub-frame 78, around tilt axes 38b, 38c, 38e, and 38f, respectively, with these tilt axes intersecting the center of sub-module 4 and extending perpendicularly to its side edges.

Hence, in an advantageous embodiment, at least some of the submodules 4 may comprise a sub-frame 78 that is tiltable in respect to the frame structure 6, in particular by means of a tilt actuator 44. The sub-modules further comprise several panels 8a - 8f mounted to the sub-frame 78 as well as restorative mounts, such as the connector members 76, pivotally connecting the panels 8a - 8f to the subframe 78 and structured to allow the panels to tilt, in respect to the sub-frame 78, against restorative forces. The restorative forces will keep the panels 8a - 8f in the same plane in the absence of a flow of water through the module

Plant

In the embodiments shown so far, the plant comprises a single module 2. However, advantageously, the plant comprises several such modules 2, located over a larger area of the body of water. Such an embodiment is shown in Fig. 17.

In this case, the modules 2 should be provided with an interconnect structure 80 for interconnecting them.

Interconnect structure 80 may have one or more of the following functions:

- It may provide a mechanical interconnection between the modules 2 for restricting relative horizontal movements of the modules 2, at least within certain limits.

- It may provide an electrical interconnection that e.g. allows to route power and/or control signals through the plant to/from the individual modules 2.

However, interconnect structure 80 should be structured to allow the modules 2 to tilt in respect to their neighbors by at least 5°, in particular at least 15°, in order to avoid excessive strain on the structure in the presence of waves.

For example, and as shown in Fig. 17, interconnect structure 80 may comprise links 82 interconnecting the panel assembly 30 of at least one given module 2, in particular of any given module 2, to the panel assembly of to at least some of the modules 2 next to the given module. Such links may e.g. be formed by rigid bars pivotally connected to the panel assemblies 30 of both modules 2 they connect, or they may be formed by chains or ropes, in particular by elastic ropes.

In an alternative embodiment, shown in Fig. 18 and 19, interconnect structure 80 may comprise links 82 interconnecting the control assembly 22 of at least one given module 2, in particular of any given module 2, to the control assembly 22 of to at least some of the modules 2 next to the given module. Such links may e.g. again be formed by rigid bars pivotally connected to the control assemblies 22 of both modules 2 they connect, or they may be formed by chains or ropes, in particular flexible robes. In this case, advantageously, the links 82 are structured to rotationally lock the control assemblies 22 to each other, at least within a certain degree, to support the rotation procedure described above. This can e.g. be achieved by connecting several links 82 to different locations of a given control assembly 22, with these locations being at a non-zero distance from the central axis 28 of the given module 2.

In this context, a flexible rope is a bungee-type rope that can be elastically extending by at least 50%.

Fig. 18 shows a further aspect of the plant, which may also be present e.g. in the embodiment of Fig. 17, namely a mooring 84, which moors the plant to the ground or the shore of the body of water.

Such mooring 84 may be adapted and structured to pull the modules 2 of the plant apart, against the force of the links 82, which allows to define, within limits, the distance between neighboring modules 2 even if the links 82 are adapted to generate attractive forces between neighboring modules 2 only (i.e. if they are not able to generate repulsive forces).

Such a mooring 84 that pulls the modules 2 of the plant apart is advantageously combined with links 82 of flexible ropes that pull neighboring modules 2 together. This combination supports a spontaneous but flexible alignment of the modules.

Control Unit

As mentioned above, module 2 comprises a control unit 36 for controlling its operation. Such a control unit 36, and some of the component it is connected to, is shown in Fig. 20.

In particular, control unit 36 may be connected to an attitude and depth sensor 86, which may e.g. comprise several sub-sensors. One of these sub-sensors may be an acceleration sensor structured to measure a tilt of frame structure 6 in respect to the force of gravity, which is equivalent to measuring the angle between frame structure 6 and surface 20 of the body of water.

One or more other of these sub-sensors may be distance sensors, e.g. based on optical or sonic echo measurements, which are adapted to measure the distance between one or more parts of frame structure 6 and the surface 20 or the ground of the body of water.

Attitude and depth sensor 86 can be used for controlling the attitude and/or depth of the module 2 as described in the section “Controlling Attitude and Vertical Position”.

Control unit 36 may also be connected to a horizontal position sensor 88, which is adapted to measure the horizontal position of the module. It may e.g. comprise a satellite navigation receiver, e.g. a GPS receiver. Or it may comprise another triangulation system based on triangulation measurements, in particular based on radio triangulation using satellite-born and/or stationary radio beacons.

Horizontal position sensor 88 may be used to control the horizontal position of the module 2 as described in the section “Horizontal Position Control”, e.g. when module 2 is deployed in a body of flowing water.

Control unit 36 may further be connected to the tilt actuators 44 as described above for tilting sub-modules 4 and/or individual panels 8.

Control unit 36 may further be connected to pump 32 and/or one or more of the gas valves 90 for conveying gas through the ducts 94 (see also Fig. 2, where one valve 90 and gas duct 94 are shown in dotted lines) to and from the inflatable floats 52 and/or tank 34 in order to control attitude and/or vertical position and/or the imbalance of panel assembly 30 and/or of control assembly 22 as described above.

Control unit 36 may also be connected to the horizontal control propeller 56, steering unit 62, and/or the depth control propellers 54, as well as to any other active propulsion units.

Control unit 36 may also be connected to a power management unit 92 controlling the electricity generation by the panels 8 and/or comprising batteries for temporarily storing energy at night or when module has been lowered to a deeper region of the body of water. Operation

Various aspects of the operation of the plant have been described above. The following illustrates some further advantageous points of operating the plant, which can typically be applied to all the embodiments of module 2.

As mentioned, module 2 may be displaced vertically, i.e. it may be raised or lowered in the body of water.

Such vertical displacement may be combined with a horizontal displacement as described above, in particular if the sub-modules 4 and/or panels 8 are tilted in respect to the vertical axis. If the horizontal displacement is undesired but the sub-modules 4 and/or panels 8 are tilted in such a way that a horizontal force is generated while changing the vertical position of the module, module 2 may be rotated while raising or lowering it as described in the section “Rotation” above in order to convert the linear displacement into a helical displacement.

In operation, i.e. when used for converting sunlight to electrical energy, module 2 is advantageously placed with its panels 8 slightly below surface 20 for the reasons mentioned above, but it may also be operated with its panels 8 above surface 8.

In operation, panels 8 can be aligned parallel to surface 20, or they may be tilted, as e.g. shown in Fig. 3, to optimize the angle of incidence of the light onto the panels. Note that tilting the panels individually, as shown in Fig. 3, is preferable to tilting the whole module 2 into the sunlight because, in the latter case, some of the panels 8 will be at a much deeper position in the body of water, and the amount of light available for energy conversion decreases quickly with increasing distance from the surface.

Module 2 may be lowered to a deeper position in the body of water for e.g. any of the following reasons:

- In stormy weather conditions, lowering the module 2 may protect it from damage.

- Lowering the module 2 may clear the body of water, i.e. provide space in the body of water near the surface, e.g. for the passage of a ship.

Notes

In the above examples, the floating photovoltaic plant comprises at least one module 2 having a frame structure 6. A plurality of solar panels 8 are mounted to a plurality of sub-modules 4 of the module 2. At least some of the submodules 4 are pivotal in respect to the frame structure 6, and such pivoting can be used for one or more diverse purposes, such as for optimizing light capture, reducing water resistance while vertically moving the module, and/or generating horizontal force components while vertically moving the module.

The frame structure 6 and the sub-modules 4 form a panel assembly 30. The control assembly 22 is mounted beneath the panel assembly 30, which prevents it from casting shadows over the panels while it is still easy to balance the panel.

Control assembly 22 may be rotatable in respect to the panel assembly 30, which can be used to rotate the panel assembly 30.

The module 2 can be operated at a first vertical position in with the sub-modules 4 located at a first tilt position. While the module 2 is being moved to a second vertical position, the sub-modules 4 are tilted to a second tilt position to reduce water resistance and/or to generate horizontal forces.

The module 2 is suitable for light-weight construction.

In the above embodiments, the sub-modules 4 are hexagonal, providing a structure that is well adapted to handle forces of compression, expansion, and shearing. Alternatively, though, the sub-modules and/or the lattice holding them may have other types of symmetry. For example, the sub-modules may be rectangular or triangular.

The module 2 is advantageously operated to produce electricity with its panels 8 submerged in the body of water. However, as mentioned, the module can also be operated to produce electricity with its panels 8 above the surface 20 of the body of water.

While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

List of Reference Numbers

2: module

4: sub-module

6: frame structure

8: solar panel

10: photovoltaic cell

12: outer frame

14: bars

16: openings

18: plane

20: surface of the body of water

22: control assembly

24: control mount

26: girders

28: central axis of module

30: panel assembly

32: pump

34: tank

36: tilt mount

38: tilt axis

40a, 40b: corners of a sub-module

42a, 42b: sides of a sub-module

44: tilt actuator

46: piston

48: elastic member

49: leaf spring

50: stop member

52: floats

54: depth control propellers

56: horizontal control propeller

58: propeller rotation axis

60: steering axis : steering unit : annular rail : rollers : socket : shaft : weight : hinge mechanism : connector members : sub-frame : interconnect structure: links : mooring : attitude and depth sensor: horizontal position sensor: gas valves : power management unit: gas duct : gap