WO2019020968A1

WO2019020968A1 - Support structure for solar panels over water

Info

Publication number: WO2019020968A1
Application number: PCT/GB2018/000109
Authority: WO
Inventors: David James CAMPBELL
Original assignee: Semisub Systems Ltd
Priority date: 2017-07-26
Filing date: 2018-07-25
Publication date: 2019-01-31
Also published as: GB201712051D0

Abstract

An improved floating support structure for use with a solar PV array, particularly when sea waves are present. The structure comprises a floating semi-submersible support structure for a solar panel array which has at least one buoyant element positionable in a body of water below the surface. At least one surface piercing member which is attached to the buoyant element at or near its first end and a mounting structure connected to the surface piercing element at or near its second end wherein the surface piercing member is an elongate member positioned to interact with the surface of the body of water and shaped to minimise hydrodynamic drag associated with water waves at or near the surface of the body of water.

Description

Support Structure for Solar Panels Over Water

Introduction The present invention relates generally to a support structure and in particular to a support structure for photo-voltaic (PV) power systems over water.

Background to the Invention Photovoltaic solar panels convert electromagnetic radiation from the sun into electricity. This renewable energy source continues to attract a high level of interest in both research and commercial fields. Historically, solar panels were installed on land, typically in an area of ground or on a rooftop. Small scale solar arrays have been mounted on vehicles and boats.

Given the generally high cost of land and it's many other uses, rooftop solar arrays have been seen as a practical use of a space which would be

otherwise unused. However, they often require modification of the rooftop structure, can be dangerous and difficult to work on, and provide only a

limited footprint. Also, the amount of land required for a solar array that generates a significant amount of electrical power can be considerable.

More recently, there has been an increase in the creation and deployment of offshore solar panel arrays. One reason for considering offshore arrays as an alternative to onshore arrays is the cost of land. A structure on the water is also less likely to be affected by shading than a structure on land, where vegetation may otherwise have to be cleared to make way for solar panel arrays. In addition, in warm or hot weather, a body of water will have a

lower surface temperature which in turn will reduce the problem of

overheating in the solar array when compared with land based equivalent arrays. Several types of offshore solar arrays are known and may be installed on inland bodies of water such as lakes and reservoirs or in the sea, where, for convenience, they are located near the coast. Solar arrays located on inland bodies of water are subject to less wave action than is characteristic of open water where waves have a larger fetch and can have a larger size and energy. One example of a floating array is found on Thames Water's Queen Elizabeth II reservoir near Walton-On-Thames where 23,000 photovoltaic panels have been installed on a floating support structure in which the PV panels lie in the flat horizontal position but may be angled towards the sun.

In another example, the solar PV panels are mounted on fixed, vertically arranged piles or the like which are attached to the bed of the body of water. Floating offshore PV arrays are typically mounted upon a floating structure on the body of water.

US 2008/0029148 describes a modular floating support structure for a solar panel array having flotation elements and a support structure disposed above the flotation elements for adjustably and removably mounting at least one solar collector panel. Connectors joining flotation elements form a platform for gangways and catwalks providing access for installation, repair, and maintenance. Each solar PV panel has its own dedicated float and connectors for attachment to other support structures. WO 2011/094803 A describes a floatation device for supporting at least one photovoltaic solar panel above a body of water. The floatation device includes a base that is able to float on or in the body of water, and a support to position the photovoltaic solar panel at an angle to the base. A coupling member is used to couple the floatation device to an adjacent floatation device. The pitch angle of solar panels can be fixed or varied. WO2016/100995 A discloses a floating platform with a deck for photovoltaic elements, a base located below a smooth water surface during operation and at least one basic buoyancy member. This structure comprises a complex array of interconnected buoyancy members and stabilizers of varying displacement volumes which would cause significant wave interaction.

The Heliofloat™ system provides a platform for offshore solar power.

Buoyancy is provided by four supporting cylindrical membrane skirts which sit under the platform and have a diameter of about 25 meters on a 60x60 platform.

CN103523183 discloses a movable semi-submersible floating

multifunctional marine energy supply platform which comprises a senilsubmersible ship hull in which a main buoyancy tank is installed in the middle. WO2012/026883 discloses a platform with horizontally extending buoyancy elements and vertically extending buoyancy columns. The superstructure is an N-sided polygon. As with other prior art documents, the overall structure would experience significant wave interaction.

One problem which is of particular relevance to open water PV arrays is how to mitigate the action of waves. It is known that inland bodies of water such as reservoirs are not subject to wave action to the same extent as the sea, which may be a factor in the popularity of such inland floating PV arrays.

However, in locations such as islands where land is scarce and limited land may be subject to shading from vegetation, there is an obvious attraction to the use of offshore PV. However, offshore PV may require extensive building of breakwaters, jetties and a very careful selection of the location of the offshore PV array to avoid the damage that can be caused by wave motion in the sea. Summary of the Invention

It is an object of the present invention to provide an improved floating

support structure for use with a solar PV array, particularly when waves may be present.

In accordance with a first aspect of the invention there is floating semi-submersible support structure for a solar panel array, the support structure comprising:

at least one buoyant element positionable in a body of water below the surface; at least one surface piercing member which has a first and second end and which is attached to the buoyant element at or near a first end; and

a mounting structure connected to the at least one surface piercing element at or near second end of at least one surface piercing element, wherein

the surface piercing member is an elongate member positioned to interact with the surface of the body of water and shaped to minimise hydrodynamic drag associated with water waves at or near the surface of the body of water.

Preferably, the surface piercing members extend down from a lower surface of the mounting structure.

Preferably, a plurality of surface piercing elements are arranged at or near a first side and a second side sides of the mounting structure.

Preferably, a plurality of surface piercing elements are arranged at or near a front side and a rear side sides of the mounting structure.

Preferably, a plurality of surface piercing elements are distributed across the mounting structure underside. Preferably, a plurality of surface piercing elements are distributed across the mounting structure underside away from the sides of said structure such that the mounting structure extends beyond the position of the surface piercing member. Preferably, the surface piercing element is connected to a dedicated buoyant element.

Preferably, a plurality of surface piercing elements are connected to a single buoyant element.

Preferably, a support member extends between at least two buoyant elements.

Preferably, the buoyant element is of variable buoyancy such that the structure may be raised and lowered in the body of water.

Preferably, the floating support structure is of variable buoyancy such that parts of the structure may have their buoyancy adjusted individually so that the height across the structure may be varied. Preferably, a first end of the floating support structure is dropped lower in the water column and a second end remains afloat at a higher level wherein the first end is closer to the prevailing wind direction.

Optionally, wherein the floating support structure is of variable buoyancy such that different parts of the structure may be ballasted individually to different extents.

Optionally, wherein the buoyant element is integrally formed with at least one surface piercing member. Preferably, the buoyant element is shaped to reduce or minimise hydrodynamic drag. Preferably, the buoyant element is substantially cylindrical.

Optionally, the buoyancy element is substantially perpendicular to the surface piercing element.

Optionally, the buoyancy element is shaped to conform with the shape of the surface piercing element. Optionally, the buoyant element is substantially cylindrical and is connected to the surface piercing element by a frustoconical section.

Optionally, the buoyant element is substantially spheroid. Preferably, the mounting structure is adapted to receive solar photovoltaic panels which form a solar photovoltaic array.

Preferably, the mounting structure is a frame which defines the perimeter of the mounting structure.

Optionally, the frame is provided with a lattice structure which extends across at least part of the area defined by the perimeter.

Preferably, adjustment of buoyancy in the structure enables the height of the mounting structure above the water to be adjusted enabling access under the structure by boat for maintenance.

Preferably, wherein the surface piercing element's diameter is selected to reduce or minimise the drag forces Preferably, the surface piercing element's profile is selected to reduce or minimise the drag forces.

Preferably, wherein the surface piercing element has a small surface area with respect to the length of the surface piercing member.

Optionally, the frame comprises sections of aluminium, composite material and /or tubular steel. The present invention may provide a modular structure in which a structure made in accordance with the present invention is mechanically connected together with other identical or similar structures. The modules may also be electrically connected such that generated electricity is sent to shore from a single point. The present invention provides a floating support structure that is easy to assemble on site from its component parts and is designed to provide a very stable platform for solar PV by using an elongate surface piercing element which keeps wave related movement to a minimum. The distance between the float and the mounting structure allows the buoyant element to be sunk below the most energetic part of the wave and the mounting structure to be located above. The structure has some

characteristics of a sea vessel and may be easily towed to a safe place in the event of severe weather.

In view of its ease of construction, and novel solution to maintaining the stability of the platform, the present invention is particularly suitable for use on islands where land is too difficult or costly to use for solar power and other solutions are not economical. Brief Description of the Drawings

The present invention will now be described with reference to the accompanying drawings in which:

Figure 1 A is a side view of a first embodiment of a floating semi-submersible offshore support structure in accordance with the present invention, Figure 1B is a front view of the support structure of Figure 1 A and Figure 1 C is a view from below of the support structure of Figures 1A and 1B;

Figure 2 is a side view of the second embodiment of the present invention. Figure 3 is a perspective view of a third embodiment of the present invention; Figure 4 is a side view of a fourth embodiment of the present invention; Figure 5 is a side view of a fifth embodiment of the present invention; Figure 6 is a side view of a sixth embodiment of the present invention;

Figure 7 shows the embodiment of Figure 4 with the floating support structure connected to an anchor point and with buoyancy adjusted across the structure;

Figure 8 is a side view of a seventh embodiment of the present invention;

Figure 9 is a plan view of the seventh embodiment of the present invention;

Figure 10 is a side view of a lattice mounting structure used with the embodiment of Figures 8 and 9;

Figure 11 is a plan view of the eighth embodiment of the present invention; Figure 12 is a side view of a lattice mounting structure used with the embodiment of Figure 11 ; Figure 13 is a side view of the combined surface piercing member / buoyant element of Figures 8 and 12;

Figure 14 is a side view of another example of a surface piercing member and buoyant element;

Figure 15 is a side view of another example of a surface piercing member and buoyant element; and

Figure 16 is a plan view of another embodiment of a floating support structure in accordance with the present invention.

Detailed Description of the Drawings

Figure 1 A is a side view of a first embodiment of a floating offshore support structure in accordance with the present invention. Figure 1 shows a support structure comprising a semi-submersible buoyant element 3. The buoyant element 3 is configured to be buoyant and, in use, to be submerged in the body of water. In this example of the invention, the buoyant element 3 is substantially cylindrical with a circular cross section, as shown in Figure 1 B. The buoyant element 3 extends substantially along the length of the support structure 1 to provide buoyancy along its length. The water surface 6 and the seabed 8 are also shown. Tethers 4 connect the buoyant element 13 to the seabed 8.

The buoyant element 3 is connected to a mounting structure 7 by means of four elongate members 5 on each side of the structure which extend upwards from the buoyant element 3 and connect to the lower surface of the mounting structure 7. The elongate members are also referred to as surface piercing members 5 because they extend from the buoyant element 3 to the mounting structure 7 through the water surface. In use, the buoyant element 3 is below the surface of the water 6 and the mounting structure 7 is above the surface of the water 6. The diameter and profile of the surface piercing members 5 is selected to reduce or minimise the drag forces experienced by the support structure which would be caused by the waves. In particular, a small surface area with respect to the length of the surface piercing member 5 opposing the movement of the wave will reduce drag.

In addition, the length of the surface piercing member 5 is selected to ensure that the semi-submersible buoyant element 3 is positioned below the surface of the body of water such that it extends to a position substantially below the surface wave such that the buoyant element 3 experiences minimal drag forces from the surface wave.

In addition, the surface piercing member extends upwards at a length where the mounting structure is clear of the water surface. The length of the surface piercing member 5 is selected for this purpose, depending upon the sea conditions that are normally expected in a given location. In this embodiment of the present invention, the mounting structure 7 comprises a flat deck made of a suitable material and structure which is adopted to receive solar PV panels across its surface.

In use, the support structure is held in place with mooring attachments 4 to suit the seabed and wave conditions. In addition, the electricity collected by the solar panels is aggregated on the structure. The electricity would then be taken from the support structure to the point of use, either ashore or in another offshore structure by means of a power offtake cable 9. Figure 1 B is a front view of the support structure of Figure 1 A. It shows the semi- submersible flat 3, surface piercing members 5 which are arranged towards each side of the mounting structure 7. Figure 1C is a view from below of the support structure of Figures 1A and 1 B. Figures 1A and 1 C show the buoyant elements 3 as being substantially cylindrical but with an oval cross sectional shape which is shaped to reduce the hydrodynamic drag.

Figure 2 is a front view of the second embodiment of the present invention. Figure 2 shows a floating support structure 11 similar to the structure shown in Figure 1 which comprises a pair of semi-submersible buoyant elements 13, surface piercing members 15 and a mounting structure 17. In addition, a support member 19 extends between the semi-submersible buoyant elements 3 to provide additional rigidity and support the structure. The water surface 16 and seabed 18 are also shown. Tethers 14 connect the buoyant element 13 to the seabed 18. Further, a boat or platform 12 is shown under the mounting structure 17 in a position to carry out maintenance on the underside of the solar panels.

Figure 3 is a perspective view of a third embodiment of the present invention. Figure 3 shows a support structure 21 which comprises two semi-submersible buoyant elements 23 connected to eight surface piercing members 25 and to a number of coupling means 27 for connecting to a platform or the like. Four support members 29 are shown which connect the semi-submersible buoyant elements 23 to provide the structure 21 with additional rigidity.

Figure 4 is a side view of a fourth embodiment of the present invention. Figure 4 shows a support structure 31 which has been created for accommodating larger numbers of solar PV panels rather than the smaller examples of Figures 1 to 3, in this case an array of some 20x30 panels. It comprises a pair of semi-submersible buoyant elements 33 (one shown), eight surface piercing members 35 (four shown) and a mounting structure 37 upon which the solar PV panels will be located. The sea level 39 is shown and the platform is positioned above the water level 39 even accounting for a reasonable increase in wave height determined by site conditions. Figure 5 is a side view of a fifth embodiment of the present invention. Figure 5 shows a floating support structure 41 which comprises eight semi-submersible buoyant elements 43, four on each side of the structure, with four shown, surface piercing members 45, eight in total with four shown and a mounting structure 47. The water surface 49 and seabed 48 are also shown. In this embodiment, as with the embodiment shown in Figure 4, the overall size of the structure 41 is intended for use with larger scale solar PV arrays. In this embodiment, four floats 43 are positioned on either side of the structure 41 to reduce the effect of wave motion on the structure from the side. As shown in figure 5, the mounting structure overhangs the surface piercing elements and buoyancy elements.

Figure 6 is a side view of a sixth embodiment of the present invention with four buoyant elements 53, with two shown, connected to respective surface piercing members 55 and mounting structure 57, with the water surface shown as 59 and seabed as 58.

Figure 7 shows the embodiment of Figure 4 to deal with extreme wind. In this figure, the floating support structure 61 is connected to an anchor point 71 which could either be on the sea bed 68 or on the shore by means of a tether 73. Arrow 77 shows the wind direction. In this example of the invention, the structure 61 is deliberately dropped in height such that the structure 61 is lowered at the end of the structure 61 which is closest to the wind direction. This is achieved by having variable buoyancy along the length of the floats 63 such that one end of the structure may be dropped in height more than the other end. In extreme winds, the ability to angle the structure into the wind will reduce the risk of the wind getting under the structure 61 , thereby reducing the likelihood that the solar PV panels will be damaged. In addition, where extreme weather events are likely to arise, the entire floating support structure of the present invention can be towed to a sheltered location to further avoid extreme winds and the waves caused by that wind.

Optionally the windward end of the buoyant element 63 could be rested on the seabed 68 to give further protection. Figure 8 is a side view of a seventh embodiment of the present invention. Figure 9 is a plan view of the seventh embodiment of the present invention and Figure 10 is a side view of a lattice mounting structure used with the embodiment of Figures 8 and 9.

Figure 8 shows a floating support structure 81 , with a combined surface piercing member/buoyant element 83. In this example of the present invention, the internal chamber of the surface piercing element is used to control the buoyancy of the surface piercing member 83. In this example, the chamber is adapted to receive an air supply which will expel water from the chamber to create the required buoyancy. As is shown, the lower portions 85 of the surface piercing members 83 function as the semi-submersible buoyant elements. The mounting structure 89 is also shown in more detail in the plan view in Figure 9.

Of particular relevance to the present invention and shown in Figure 8 is the length 87 of the combined float/surface piercing member 83. The length 87 along with the selected buoyancy determines the distance below the water surface of the buoyancy element 85 with respect to the distance above the water surface of the mounting structure 89. The overall length is selected to cope with typical wave conditions of the location where the structure is to be positioned to allow the mounting structure to be above the water surface and the buoyant element to be below or substantially below all or most of the effect of a sea wave as it passes. Figure 9 shows a plan view of the floating support 8 . It comprises a mounting structure frame 91 optionally constructed in a lattice structure as shown in Figure 10. The frame 91 comprises sections of tubular steel, composite beams, aluminium sections or other suitable material joined together in situ to form the frame 91.

Reference numerals 93 show the position of the buoyant element/surface piercing elements shown in Figure 8. Tethers 95 are connected to the four corners of the substantially rectangular frame 91 to attach the structure to the seabed. The area enclosed by the frame 91 and which also forms part of the mounting structure 89 comprises a lattice of optionally thin steel beams, aluminium sections, composite beams or other suitable material 97 designed to provide a supporting frame for solar panels 99. The deck also supports a power take off device (PTO) 101 which aggregates and converts electricity for offtake from the structure. Electricity is taken from the structure 81 via an electrical cable 103 to a power grid, an energy storage facility or a substation for distribution to power users.

Figure 10 is a side view of the lattice 105 which shows a top member 107, a bottom member 109 and diagonal supports 111 which extend between top and bottom members adjacent to top member 107 and bottom member 109. This lattice has low weight and high strength and can be used within the mounting structure at the top of the support structure. As well as the two-dimensional form shown in Figure 10, this lattice structure could optionally be in three dimensions with a triangular or square cross section.

Figure 1 1 shows a plan view of the floating support structure 181 and Figure 12 is a side view of the same floating support structure 181. Figure 11 shows a mounting structure 191 which sits upon a series of surface piercing members / buoyant elements (shown as 185 in Figure 12), and where that mounting structure 191 overhangs the area framed by the surface piercing members. Tethers 195 are connected to the four corners of the substantially rectangular mounting structure 191. Solar panels 199 and power take off 201 are also shown. Electricity is taken from the structure 181 via an electrical cable 203 to a power grid, an energy storage facility or a substation for distribution to power users.

Figure 12 is a side view of the support structure 181 shown in Figure 1 1. This a lattice form 105 with a top member 107, a bottom member 109 and diagonal supports 111 which extend between top and bottom members adjacent to top member 107 and bottom member 109. This lattice has low weight and high strength and can be used within the mounting structure at the top of the support structure.

The buoyant element/surface piercing members 185 extend from the underside of the frame and are distributed across the underside. In addition, the deck 191 extends outwards from the lattice 105, overhanging the lattice 105 and surface piercing members 185 in both horizontal dimensions.

Figure 13 shows the combined surface piercing member/ buoyant element 113 as used in the embodiment of Figures 8, 9,11 and 12 which has an air chamber 1 16 which receives air from an inlet 115 via pipe 118. The water outlet 117 comprises a valve which ejects water from the chamber 116 when pressurised air enters and allows water back in when the air pressure drops. Figure 14 is another example of a buoyant element with a surface piercing member 121. In this example, the buoyant element 123 is shaped to reduce the

hydrodynamic drag which is created near the bottom of the wave and by other effects such as tides and currents. In this example, the buoyant element 123 is substantially ovoid and is connected to an air supply 127. Air inlet 129 allows air into the buoyant element and a valve 130 enables evacuation of ballast water when air is introduced.

Figure 15 is another example of a buoyant element with a surface piercing member 221. In this example, the buoyant element 223 is substantially cylindrical and is connected to the surface piercing element by a frustoconical section and is connected to an air supply 227. Air inlet 224 allows air into the buoyant element and a valve 230 enables evacuation of ballast water when air is introduced.

Figure 16 is a plan view of another embodiment of a floating support structure in accordance with the present invention. Figure 16 shows a buoyant element that is octagonal in shape 133 (and shown shaded) which would be below the water level as in other embodiments, linking through surface piercing elements 137 to a mounting structure following the same geometry. The mounting structure frame 135 comprising octagonally arranged lattice frame members responding to this basic geometry. It will be appreciated that the buoyancy element and the floating support structure of the present invention may be constructed in a suitable shape and is not restricted to the shapes shown herein. For example, triangular, square, pentagonal, hexagonal, decagonal, dodecagonal and circular structures could be used.

The support structure of the present invention may be provided as a number of modules which can be constructed separately. The modules may be connected together to create a larger structure with greater capacity.

Another advantage of the present invention is that variable buoyancy allows the structure to be raised to a height to enable a service boat to sail under the structure for maintenance of the panels. This is a useful improvement as the control parts which require maintenance are located on the back of the panel which would be presented on the underside of the support structure embodied in this invention. By maintaining from below, it also enables a higher density of panels on the surface of the mounting structure improving the efficiency of the space and structure costs.

Improvements and modifications may be incorporated herein without deviating from the scope of the invention.

Claims

1. A floating semi-submersible support structure for a solar panel array, the support structure comprising:

2. A floating support structure as claimed in claim 1 wherein, the surface piercing members extend down from a lower surface of the mounting structure..

3. A floating support structure as claimed in claim 1 wherein a plurality of surface piercing members are arranged at or near a first side and a second side of the mounting structure.

4. A floating support structure as claimed in any preceding claim wherein a plurality of surface piercing members are arranged at or near a front side and a rear side of the mounting structure.

5. A floating support structure as claimed in any preceding claim wherein, a plurality of surface piercing members are distributed across the mounting structure underside.

6. A floating support structure as claimed in any preceding claim wherein, a plurality of surface piercing elements are distributed across the mounting structure underside away from the sides of said structure such that the mounting structure extends beyond the position of the surface piercing member.

7. A floating support structure as claimed in any preceding claim wherein the length of the buoyancy element and surface piercing member is sufficient to allow access by a vessel underneath the mounting structure to carry out maintenance.

8. A floating support structure as claimed in any preceding claim wherein the surface piercing member is connected to a dedicated buoyant element.

9. A floating support structure as claimed in claims 1 to 4 wherein a plurality of surface piercing elements are connected to a single buoyant element.

10. A floating support structure wherein a support member, or support members, extend(s) between at least two buoyant elements.

11. A floating support structure as claimed in any preceding claim wherein the buoyant element is of variable buoyancy such that the structure may be raised and lowered in the body of water.

12. A floating support structure as claimed in any preceding claim wherein the floating support structure is of variable buoyancy such that different parts of the structure may be ballasted individually to different extents.

13. A floating support structure as claimed in claim 11 wherein a first end of the floating support structure is at more submerged and a second end more afloat wherein the first end is closer to the prevailing wind direction.

14. A floating support structure as claimed in any preceding claim wherein the buoyant element is integrally formed with at least one surface piercing member.

15. A buoyant element as claimed in any preceding claim wherein, the buoyant element is shaped to reduce or minimise hydrodynamic drag.

16. A floating support structure as claimed in any preceding claim wherein the buoyant element is substantially cylindrical.

17. A floating support structure as claimed in claims 1 to 15 wherein the buoyant element is substantially spheroid.

18. A floating support structure as claimed in claims 1 to 15 wherein, the buoyancy element is substantially perpendicular to the surface piercing member.

19. A floating support structure as claimed in claims 1 to 15 wherein, the buoyancy element is shaped to conform with the shape of the surface piercing member.

20. A floating support structure as claimed in claims 1 to 15 wherein, the buoyant element is substantially cylindrical and is connected to the surface piercing member by a frustoconical section.

21. A floating support structure as claimed in any preceding claim wherein the mounting structure is adapted to receive solar photovoltaic panels which form a solar photovoltaic array.

22. A floating support structure as claimed in any preceding claim wherein the mounting structure is a structure which defines the perimeter of the solar panel array.

23. A floating support structure as claimed in claim 22 wherein the frame is provided with a two dimensional or three dimensional lattice structure which extends across at least part of the area defined by the perimeter.

24. A floating support structure as claimed in any preceding claim wherein the height of the mounting structure above the water can be adjusted to allow for access by boat or floating maintenance platform for maintenance.

25. A floating support structure as claimed in any preceding claim wherein the surface piercing member's diameter is selected to reduce or minimise the drag forces

26. A floating support structure as claimed in any preceding claim wherein the surface piercing member's profile is selected to reduce or minimise the drag forces.

27. A floating support structure as claimed in any preceding claim wherein the surface piercing member has a small surface area at water level with respect to the length of the surface piercing member.

28. A floating support structure as claimed in claim 23 wherein the frame comprises sections of tubular steel, aluminium composite or other suitable structural material.