FIELD OF THE INVENTION This invention is in the general field of solar power generation .

More specifically, one particularly important, although nonexclusive, application of the invention is in the field of floating photovoltaic solar tracker systems capable of tracking the sun during the course of the day to maximize the energy output of photovoltaic modules.

PRIOR ART DISCUSSION Photovoltaic solar tracker systems provide means for rotating an array of photovoltaic solar modules around one or multiple axis in order to orientate these solar modules toward the sun.

In the specific case of floating photovoltaic solar systems which are designed to be installed on the surface of water bodies, there is to date a very limited number of tracker systems which have been installed. Most of the floating solar system which have been deployed rely on the use of simple floaters which are designed to support one or multiple solar modules at a fixed inclination angle.

There are few examples which have been reported in the literature of single axis floating solar tracking systems which provide a mean for rotating an array of floats around a vertical axis. The patent applications US4771764, US4786795, US20160087573A1, W02014/005626AI, WO2016/185267A1,

KR101028944B1, US20170040926A1 present different variants of vertical axis floating solar tracking systems.

For utility scale solar farm installations comprising thousands of solar modules, these types of vertical axis tracker systems typically comprise several tracker units rotating around separate vertical axis.

As several tracker units rotate multiple arrays of solar modules around different fixed points separated by a horizontal distance, this configuration induces challenging constraints for anchoring each block individually and extra lengths of underwater electrical cables are required for interconnecting multiple arrays of rotating solar modules blocks .

In addition, vertical axis floating tracker systems are more complex to install and their geometrical configuration does not permit simple access paths for performing maintenance operations on solar modules or on the mechanical components of the tracker units.

Furthermore, as the tracking trajectory of vertical axis tracker systems is far from being ideal, the extra energy production gain achieved by this class of tracking system is typically lower than 10%. Higher energy gain may be achieved by vertical single axis trackers if the solar modules are inclined at a steep inclination angle (i.e. >30°), but this configuration is highly undesirable as wind drag coefficients increase considerably and large separation distances between rows of modules are then required in order to avoid cross shading losses. In fact, the prior art fails to propose an easy to install product sufficiently cost effective to make utility scale floating tracking solar systems more competitive than floating solar installations installed on basic floats supporting solar modules at a fixed angle.

It is therefore an object of the present invention to further reduce manufacturing, shipping, installation and maintenance costs of floating photovoltaic solar installations, via an exemplary floating tracker design which addresses many of the limitations of prior-art designs.

To this end the present invention mainly proposes a floating photovoltaic solar tracker system which minimizes material usage, reduces shipping volume, simplifies field assembly, provide a geometrical configuration with simple access paths for performing maintenance operations on the solar modules, and capable of orienting the solar modules along a more optimal tracking trajectory in order to improve energy production and improve the competitiveness of floating solar plants .

According to theses aims one object of the invention is mainly to propose a floating solar tracker assembly, also called hereafter a solar tracker float assembly, extending along a principal longitudinal rotational axis and comprising at least one floating tube element extending along and/or parallel to said principal axis and having at least one internal cavity, at least one array of photovoltaic solar modules oriented at an angle with regard to said principal longitudinal axis and rigidly connected to said support tracker assembly, and a control system comprising pumping means and an electronic controller arranged to control said pumping means to inject or withdraw water and/or air inside said internal cavity in order to rotate the floating tracker assembly about said principal axis between a maximum right directed position and a maximum left directed position.

By maximum right directed position or maximum left directed position, it should be understood a direction into which the top periphery of said array of photovoltaic solar module is higher than the horizontal plane including said principal axis on the right or on the left of said directed position, also referred to as a maximum cardinal point directed position (i.e. for instance East/West or North/South) .

In other words the control system (including the activator of the movement) is arranged to rotate the array of the floating tracker assembly along its principal axis and adjust the angle of said array of photovoltaic solar modules between a low inclination angle position near or below the horizontal plane and a high angle position above the horizontal plane.

In some advantageous embodiments, it is also and/or further proposed a solar tracker float assembly including one or more of the following features:

- the principal axis is oriented along an East/West direction;

- the principal axis is oriented along a South/North direction;

- the angle of said photovoltaic solar modules with regard to said principal axis is < 20°; - the angle of said voltaic solar modules with regards to said principal axis is equal to 0°;

- it comprises a plurality of tubes elements symmetrically and longitudinally disposed along said principal axis;

- it comprises two parallel plans of two parallel tube elements, said plans being rigidly connected together and said parallel tube elements being symmetrically disposed along the principal axis and in bias with regard to the tube elements of the other plan;

- it comprises one lower tube element and two upper parallel tube elements symmetrically disposed with regard to said principal axis;

- said lower tube element is rigidly connected to said upper parallel tube elements via two dissymmetric traverse parts, said traverse parts being supporting the array on their respective upper periphery with an inclined angle with regard to the horizontal plane;

- the tube elements are partially or completely hollow tubes having at least one internal cavity to be filled or emptied by water and/or air for rotation about said principal axis between said maximum positions;

- the floating tube element comprises multiple (for instance three) cavities radially (and/or regularly) disposed around said principal axis to be filled or emptied by water and/or air for rotation about said principal axis between said maximum positions;

- the arrays of photovoltaic solar modules comprise four photovoltaic solar modules in series; - the tube elements are partially or completely hollow tubes having at least one internal cavity to be filled or emptied by water and/or air and comprising additional floating structure for rendering the floating tracker assembly un- submersible;

- the additional floating structure comprises floating elements provided in an internal ring shaped core of said corresponding tube element;

- the additional floating structure comprises a plurality of hollow floating containers having a spherical shape or equivalent, for instance twenty to thirty containers for a tube element, for example with a length of 4 or 5 meters;

- each floating tube element is partially filled with one or a plurality of air filled containers or with other buoyant material;

- in position of floating on the water, the assembly is configured for having some of its cavities to be normally located under the water surface, wherein they are filled naturally with water by gravity;

- it comprises air pumps for pushing the water out of at least some of the cavities;

- the principal axis is oriented along an East/West direction, and said control system inject or withdraw water inside said internal cavities in order to rotate the floating tracker assembly along its principal axis and adjust the inclination angle of said array of photovoltaic solar modules between a minimum inclination angle position and a maximum inclination angle position, directed towards South or North; - it further comprises a heating system for preheating the water to fill the cavities;

- the control system is arranged to compute the position of the sun during the course of the day and adjust the volume of water injected or withdrawn inside of each cavity of the tube elements, in order to orientate the solar modules toward the sun;

- each floating tube element comprises an external surface, a ring shape core and an internal surface, said ring shape core being in lightweight material such as polystyrene or polyurethane foam, and/or filled with air filled cylindrical cans or spheres or other buoyant material.

Advantageously another object of the invention is to provide a floating tracker system comprising a plurality of solar tracker float assembly as described hereabove.

Advantageously the system comprises the following elements: a linear array of parallel columns of elongated float assemblies rotating along their principal axis which is oriented along a North-South direction parallel to the water surface,

each float assembly supports an array of photovoltaic solar modules oriented at a small (i.e. < 20°) inclined angle,

each float assembly comprises one or multiple tube elements having one or multiple internal cavities,

a control system comprising a set of pumps and an electronic controller which controls the volume of water and/or air injected inside the different internal cavities of the float tubes in order to adjust the rotation angle of each column of float assemblies along their respective principal axis .

In advantageous embodiments the system is according to any of the following features: - the system comprises a plurality of solar tracker float assemblies as described above, wherein it comprises anchoring means to be anchored on the ground;

- each of said solar tracker float assemblies are longitudinally connected to an adjacent one;

- it further comprises a security system for filling or emptying automatically the tube elements in order to provide a rotation angle of 45 ° or more toward East or West in case of snow, and/or back to an horizontal position (0°) in case of high wind;

- it further comprises a security system for filling automatically the cavities of the tube elements in a symmetrical manner in order to partially sink into water the float assemblies and reduce their wind-drag coefficients in case of high wind;

- each floating tube is connected to a waterline in series with a least one other floating tube, in their lower parts;

- each floating tube is connected to an air line in series with the other floating tubes, for example in their upper parts . BRIEF DESCRIPTION OF THE DRAWINGS The above and other features and advantages of the present invention will become apparent upon review of the following summarized and detailed descriptions taken into conjunction with the accompanying drawings in which:

Figures 1A & IB show 3D view diagrams of a floating solar tracker float assembly according to one embodiment of the invention which is arranged for supporting an array of 4 solar modules .

Figures 2A and 2B shows maximum right directed position or maximum left directed position, on the right or on the left of said principal axis, also referred to as a maximum cardinal point directed position, i.e. East/West for Figure 2A and North/South for Figure 2B.

Figures 3A, 3B and 3C show 2D cross section view diagrams of elongated tubular shaped float elements, also designated hereafter by floating tube elements, of different embodiments of a solar tracker float assembly of the invention which are partially filled with water.

Figure 3D shows a 2D side view diagram of an endcap of an elongated tubular shaped float element of a solar tracker float assembly of the invention.

Figures 4A, 4B and 4C show 2D cross view diagrams of an array of another embodiment of solar tracker float assemblies of the invention which are rotated at different angles around their principal axis. Figure 5 shows 3D view rows of solar tracker float assemblies, according to an embodiment of the invention which are rotated at different angles around their principal axis.

Figures 6A and 6B shows top and side view diagrams of an embodiment of a foundation solution for anchoring an array of solar tracker float assemblies according to the invention in a water body.

Figure 7 shows a schematic diagram of an embodiment of a control system of the floating solar tracker system of the invention.

Figure 8 shows a lateral view of another embodiment of the invention, with two upper tube elements and one entirely immersed lower tube element.

DETAILED DESCRIPTION OF THE INVENTION

The invention essentially provides a floating photovoltaic solar tracker system which minimizes material usage, reduces shipping volume, simplifies field assembly, provide a geometrical configuration with simple access paths for performing maintenance operations and capable of orienting the solar modules along a more optimal tracking trajectory in order to achieve higher energy production and improve the competitiveness of floating solar plants. Figure 1A & IB show 3D view diagrams of a floating solar tracker float assembly according to one embodiment of the invention which is arranged for supporting an array of 4 solar modules. This embodiment of solar tracker float assembly 1000 comprises 4 hollow tube elements 101-104 which are operably connected together with 5 frame assemblies 200.

In this preferred embodiment of the invention, an array of 4 photovoltaic solar modules 300 are operably connected to the frame assemblies using module support brackets 210 which are designed to hold the solar modules 300 at an inclined angle toward South or North. In the Northern hemisphere, the solar modules are inclined toward South and toward North in the Southern hemisphere.

In a preferred embodiment of the invention, the inclination angle of the solar modules is lower than 20° in order to minimize wind drag coefficients. In alternative embodiments of the invention, each floating solar tracker float assembly may be equipped with a different number (N) of solar modules 300. In these alternative embodiments, N+l frame assemblies 200 are used for supporting N solar modules 300. The tracker float assembly 1000 and hollow tube elements 101-104 have their principal axis oriented along a North-South direction.

In a preferred embodiment of the invention the hollow tube elements 101-104 have a cylindrically shape. In other embodiments of the invention the hollow tubes may have a different cross section shape such as a square, rectangle, hexagonal, or any closed shape polygon profile. The hollow tube elements 101-104 are operably connected to the frame assemblies 200 using structural glue or standard mechanical fasteners such as bolts, rivets, screws or straps. The module support brackets 210 are operably connected to each frame assembly 200 using structural glue or standard mechanical fasteners such as bolts, rivets or screws. Figures 2A and 2B show in perspective the rotation of the floating tracker assembly along its principal axis, and more precisely the rotation of the general plan P formed by the two superior floating tube elements 101 and 104 (in the case of the embodiment of figure 1) toward East or toward West, in case of a principal axis orientated South/North (Figure 2A) or toward South or toward North, in case of a principal axis orientated West/East (Figure 2B) .

Figures 3A , 3B and 3C show cross section view diagrams of elongated cylindrically shaped tube float elements of an embodiment of a solar tracker float assembly of the invention comprising internal cavities which are partially filled with water 140. The remaining volume of the internal cavity 113 not filled by water 140 is filled by air injected directly or ejected by filling with water the cavity of the tube element.

In one embodiment of the invention, each tube float element comprises an external 110 surface, a ring shaped core 111 and an internal surface 112.

The ring shaped core 111 may be fabricated using a lightweight material such as expanded polystyrene or polyurethane foam.

In another embodiment of the invention, air filled cylindrical cans or spheres 114 may be used to partially or completely fill the ring shaped core 111. The outer surface 110 of the ring shaped core 111 may be reinforced with a scratch resistant layer such as a rubber layer, hard plastic shell or a thin metal sheet. The inner surface 112 of the ring shaped core 111 may be protected with a water proof layer such as a rubber, a plastic film or a thin metal sheet. Figure 3C is a cross section of another embodiment of a floating cylindrical tube element with an external surface 110 having an internal cavity 113 containing a plurality of containers 115, for instance spherical cans, floating on internal water 140, present in the interior of said tube element, each of said cans having a cross section for example of a dimension comprised between 1/2 and 9/10 of the cross section of the tube element.

More precisely the floating containers may have a spherical shape, an oblong shape or equivalent.

In a preferred embodiment of the invention, twenty to thirty floating containers 115 may be inserted inside a tube element with a length of 5 meters in order to insure that a minimum buoyancy will be preserved if some of the floating containers 115 get perforated. The remaining volume of the internal cavity 113 not filled with water 140 is filled by air injected directly or ejected by filling with water the cavity of the tube element .

Another embodiment uses (also and/or in substitution) air lines for interconnecting in series multiple floating tube elements from different float assemblies through their endcaps airline connector, for instance in the upper part of said endcaps .

Both ends of each float tube are closed by an endcap 120 which is illustrated on Figure 3D. Each endcap 120 may comprise a vent hole or an air-line connector 121 located on the upper side of the endcap.

If the tube element comprises a ring shape core, the air line 121 and water-line 122 connectors are respectively located immediately bellow and immediately above the perimeter of the internal surface 112 of the ring shape core of the float tube element. Short water lines are used for interconnecting in series multiple float tubes (or floating tube elements) from different float assemblies through their endcap water line connectors 122.

An other embodiment uses (also and/or in substitution) air lines for interconnecting in series multiple floating tube elements from different float assemblies through their endcaps air-line connectors 121, for instance in the upper part of said end caps .

The preferred embodiment of a solar tracker float assembly 1000 of the invention illustrated in Figure 1A comprises 4 hollow tube elements 101-104. In other embodiments of the invention the solar tracker float assembly may comprise a different number of tubes with a minimum of 2 hollow tube elements or 1 hollow tube element having a minimum of 2 internal cavities (see also Figure 8 hereafter) .

Figure 4 shows 2D side view diagrams of an array of another embodiment of solar tracker float assemblies of the invention which are rotated at different angles around their respective principal axis. In this alternative embodiment of the invention, each solar tracker float assembly comprises one hollow tube element 100 having 3 internal cavities 115, 116 & 117.

Figure 5 shows 3D view diagrams of an array of solar tracker float assemblies of one embodiment of the invention which are rotated at different angles around their principal axis (here a South/North axis) . The hollow tube elements which are located on the West side of each tracker float assembly are evacuated (filled with air) and the hollow tube elements located on the East side of each tracker float assembly are partially filled with water in order to orientate the solar modules toward the East direction .

In an opposite manner, the hollow tube elements which are located on the East side of each tracker float assembly are evacuated (filled with air) and the hollow tube elements located on the West side of each tracker float assembly are partially filled with water in order to orient the solar modules toward the West direction. The volume of water injected in each hollow tube element is adjusted continuously during the course of a day in order to orient the solar modules toward the sun.

In a preferred embodiment of the invention, the tracker float assemblies are designed to track the sun with an angular rotation range of -45° to +45°. In other embodiments of the invention the angular rotation range may be extended to a range of -60° to +60°, or in a less preferred embodiment of the invention reduced to a range of -30° to +30°.

Figures 6A and 6B show top and side view diagrams of an embodiment of a foundation solution for anchoring an array of solar tracker float assemblies 1000 of the invention in a water body. In a preferred embodiment of the invention, the float assemblies 1000 are mechanically connected to a linear array of horizontal cables 510 .

In a preferred embodiment of the invention, the horizontal cables 510 are positioned at a depth of at least 0.5m under the water surface in order to provide clear service paths between the columns of float assemblies. In this configuration, short vertical cables or chains 511 are used for mechanically connecting the float assemblies 1000 to the horizontal cables 510. With this configuration, maintenance operations such as replacement of defective solar modules can be easily performed using a small motorized service boat. In order to reduce the number of horizontal cables required for a large solar plant, one or multiple float assemblies may be mechanically connected together in a series manner along the North-South direction and only their upper and lower ends are then mechanically connected to the horizontal cables 510. The East and West side of each horizontal cable 510 are mechanically connected to vertical cables 520.

A pair of horizontal 510 and vertical cables 520 forms a block of tracker float assemblies which are secured with anchoring cables 540 attached to one of multiple fixed foundations 550 which are installed on the shore or at the bottom of the water body 700. Ground anchors driven into the soil 710 or ballast blocks may be used as fixed foundations 550. Buoys 530 may be added at the end of the horizontal cables 510 in order to compensate vertical forces induced by the anchoring cables 540 connecting the horizontal 510 and vertical 520 cables to the foundations 550. The anchoring cables 540 may be equipped with tensioner devices in order to accommodate water height variations.

Figure 7 shows a schematic diagram of an embodiment of a control system 600 of the floating solar tracker system of the invention. The control system comprises a set of primary pumps 610 and valves 621 & 622, 631 & 632 which are connected through water lines 602 to the different tubes of the float assemblies 1000.

The control system 600 may be installed on shore to facilitate maintenance operations. The water lines 603 connected to the tubes of the float assemblies should be thermally insulated and preferably routed inside a trench on the ground and then under the water surface in order to protect them from freezing. In order to improve the system's overall reliability, multiple primary water pumps 610 may be connected in parallel in order to provide some redundancy.

The water flow direction may be inverted using a pair of 4- ways valves 621 & 622 or in an alternative embodiment using 2 water pumps connected in opposite directions. In this last configuration, one-way valves should be added in series with each water pump to prevent backflow through the other pump connected in opposite direction.

The filling with water or emptying of the water may be obtained also by injection or withdrawing air via an adequate circuit, for instance a set of air pumps, the water being introduced by gravity or pushed out by air pressure.

For installations on sites which are exposed to long periods of ice, the control system may be equipped with an optional heating system which may be used to pre-heat the water injected inside the tubes of the float assemblies. Water located at a depth of few meters under the surface of large bodies of water never freeze and thus the calories contained in deep water may be recovered to pre-heat the water injected inside the tubes of the float assemblies. In a preferred embodiment of the invention, the system comprises a primary water injection loop which is hydraulically isolated from a secondary pre-heating loop.

In this configuration, one or multiple secondary water pumps 640 are configured to pump deep water from the water body. The calories of the deep water are transferred to the primary injection loop through a heat exchanger 642. For very cold sites subject to long periods of ice, the heat exchanger 642 may be replaced by a water-to-water heat pump system in order to further increase the temperature of the water injected inside the tubes of the float assemblies.

The deep water supply port may be equipped with a coarse filter 644 and finer filters may be installed on the input side of the water pumps. In another embodiment of the invention, the primary injection loop may be configured as a close loop system with the primary pump(s) connected directly to the deep water supply port . In yet another embodiment of the invention, a water reservoir 642 may be used to partially isolate the primary injection loop from the secondary pre- heating loop.

In this last configuration, no heat exchanger is required as the water reservoir act a mixing bottle and sediment tank. In all embodiments of the invention, the control system comprises an electronic control system 601 which controls the water pumps and valves in an automated manner.

The electronic control system 601 computes the position of the sun during the course of the day and adjust the volume of water injected inside each tube of the float assemblies in order to orientate the solar modules toward the sun. In a preferred embodiment of the invention, the control system 601 uses an open loop algorithm to adjust the volume of water injected inside the tubes of the float assemblies according to the system kinetic transfer function.

Flow sensors may be installed on the water lines to measure the volume of water injected or evacuated from each tube. In another embodiment of the invention, a tilt sensor may be mounted onto a float assembly in order to measure the rotation angle and operate the electronic control system 601 in a close loop control configuration.

In yet another embodiment of the invention, the internal cavities of the tubes of the float assemblies may be configured to be normally located under the water surface and thus filled naturally with water by gravity forces.

Figure 8 shows an example of such embodiment of the invention. In this example, the two upper tube elements 101 & 104 are floating above the water body 700 and the lower tube element 102 is entirely immersed in water.

For this embodiment of the invention, the control system may be equipped with air pumps instead of water pumps in order to fill the tubes of the float assemblies with air and push out water.

In the example illustrated in Figure 8, the float assembly rotates toward the South direction as the buoyancy of the lower tube element 102 increases when it is partially or fully filled with air. In such embodiment of the invention, short open-ended tubes may be connected to the water-line connectors 122 which are located at the bottom of the tube endcaps of the float tubes. These open-ended tubes enable water to go in and out of the float tubes when the control system adjusts the pressure of the air inside the tube internal cavity.

In a preferred embodiment of the invention, the control system is connected to temperature sensors to monitor external air temperature and the surface temperature of water. When these measured temperatures fall under pre-defined thresholds, the control system activates a special ice mitigation operating mode in order to prevent ice formation in the water lines and in the internal cavities of the tubes of the float assemblies.

In the specific case of the exemplary float design illustrated in Figure 1A, the following ice mitigation operating mode may be used: step 1) empty the top 2 tubes, step 2) activate the pre-heating system, step 3) pump continuously pre-heated water into the bottom 2 tubes of the float assemblies. This ice mitigation operating mode can be easily adapted depending on the number of tubes used in each float assembly using a similar approach.

In yet another embodiment of the invention, the control system may also activate a different operating mode in order to mechanically evacuate snow from the surface of the solar modules. The control system may be equipped with a snow sensor or it can receive a command from an operator or an external server to activate this special snow management mode.

When this special snow management mode is active, the control system can quickly rotate the float assemblies to their extreme (Left or Right) angular rotation limit. Thick layers of snow typically naturally fall under gravity force when solar modules are inclined at an angle exceeding ~30°. This special snow management mode uniquely enable safe installation of the floating solar system of the invention on water bodies which are exposed to snow falls .

In a preferred embodiment of the invention, the control system is connected to a wind sensor instrument and when the measured wind speed exceeds a defined threshold the float assemblies are moved into a 0 degree rotation angle position (horizontal along the East-West direction) .

In order to further improve the system resistance to extreme winds, some or all of the tubes of the float assemblies may be partially or fully filled with water in a symmetrical manner. In this specific configuration, the float assemblies are maintained into a 0 degree rotation angle position and partially sunk into water which induces a reduction of their wind-drag coefficients and limit the forces transferred by the system anchoring lines to the foundations.

In yet another embodiment of the invention, the control system may be equipped with another special operating mode to fill completely all the tubes of the float assemblies and then stop the pumps. This special operating mode may be used for installations on sites such as water retention reservoir. When the water retention reservoir is empty, this special operating mode may be activated to ballast on the ground the float assemblies and continue to operate the plant in a fixed position.

Figure 8 shows a lateral view of a floating tracker float assembly according to another embodiment of the invention arranged to support an array of photovoltaic solar modules 300 . It comprises three hollow tube elements, i.e. two upper tube elements 101 and 104 (forming the general plan P), and one lower tube element 102. The tube elements 101, 102 and 104 are connected together by N+l frames assemblies 200 having a dissymmetric (with regard to the principal axis) form in order to hold the solar modules with an inclined angle OC, for instance with a substantially "V" angle shape, the upper tubes being fixed to said branches for example, for one (101) at an intermediate external part of a first branch of the "V" and for the other (104) at the extremity part of the second branch of the "V" . Due to the dissymmetry with regard to the central point M, and when the lower tube is filled with air for instance, the pressure of the force F generates the rotation (arrow on the figure) and therefore the variation of the inclination of the photovoltaic panel 300.

The invention has been described with reference to various specific and preferred embodiments and techniques. However, it should be understood that variations and modifications may be made while remaining within the spirit and the scope of the invention. This invention is not to be limited by the embodiments disclosed, including any shown in the drawings or exemplified in the specification, which are given by way of example or illustration and not of limitation. The scope of the invention shall only be limited by the claims .