WO2013186796A1

WO2013186796A1 - Tracker for high concentration photovoltaic system.

Info

Publication number: WO2013186796A1
Application number: PCT/IT2012/000178
Authority: WO
Inventors: Alessandro Rossi
Original assignee: Alitec S.R.L.
Priority date: 2012-06-14
Filing date: 2012-06-14
Publication date: 2013-12-19

Abstract

An azimuth-altitude solar tracker for high concentration photovoltaic systems has a structure composed of an upright (10) and a main frame (30, 40a, 40b) supporting the photovoltaic panels (51) perfectly balanced irrespective of the angle of elevation. The above feature, together to a design of the assembly of PV panels in four distinct quadrants (50a, 50b, 50c, 50d) greatly reduces the stresses on the anchoring means for anchoring the system to the so that simple screw-type fastening means can be used without concrete foundations, also tank to the very rigid design of the tripod anchoring means (20).

Description

TRACKER FOR HIGH CONCENTRATION PHOTOVOLTAIC

SYSTEM.

TECHNICAL FIELD

The present invention concerns the structure of an azimuth-altitude tracking system for photovoltaic systems, in particular high concentration photovoltaic systems.

STATE OF THE ART

It is known that for high concentration photovoltaic systems a proper alignment to the sun in order to achieve maximum irradiation of the system is of fundamental importance and these systems are then mounted on trackers, usually trackers with two degrees of freedom. At relatively low latitudes, the most used trackers as they ensure the maximum radiation are azimuth-altitude trackers.

For high concentration photovoltaic systems, for which also misalignments of a few tenths of a degree produce significant reductions of efficiency, not only the electronics and the mechanics of the tracking devices have very stringent specifications, but also the structural elements which support and fasten the system. In fact, the structure of the tracker must be particularly rigid and the various parties must be coupled without clearance.

Conventionally, azimuth-altitude solar trackers for high concentration solar systems are constituted by an upright well anchored to concrete foundations so as to be perfectly perpendicular to the ground, while at the upper end of the upright a large frame is constrained for rotating about a horizontal axis, to which frame are anchored the photovoltaic panels, one adjacent to another, to form a sail.

In Figures 1 and 2 it is schematically shown the structure of a conventional solar tracker of this kind. An upright M is solidly anchored to the concrete foundations C in order to ensure the vertically respect to the ground. The upper portion of the upright M M1 is rotatable about the axis of the upright so as to achieve the azimuth degree of freedom. A frame T supporting the photovoltaic panels is constrained at the upper end of the upright so as to rotate about a horizontal axis A passing through the axis of the upright itself. A kinematic mechanism comprising a linear actuator L allows realizing the rotation around the axis A and therefore the elevation movement. The assembly of solar panels V covers an area very large which is usually of rectangular shape. To ensure the perfect co planarity of the surface of the panels the frame T must be properly designed in order to meet extremely stringent design parameters as regards the flexion of its various components. For example, the frame T shown in Fig.2 consists of a main transverse bar T1 to which are connected three longitudinal bars T2 which, together with a two further transverse bars T3 form the main frame. Additional secondary longitudinal bars T4 directly support the solar panels. The rigidity of the rectangular frame is increased by means of tie rods T5, while the rigidity of the main bar T1 is increased by means of reinforcing elements T6. With a structure of this kind to ensure the perfect flatness of an assembly of panels of large area is necessary to have considerable dimensions of the individual elements that then affect much on the weight of the structure. In fact, for large panels assemblies bending forces caused by wind become very important in the sizing of the structure. In addition, the possibility to insert reinforcement elements located externally to the plane of the frame T, such as the elements T6, is quite limited since these components might interfere and therefore restrict the movement of azimuth-altitude tracking. Another important problem affecting this type of structures consists in the fact that the frame T is fixed cantilever to the upright M, so that the plane parallel to the plane defined by the frame T where is located the center of gravity of the whole system constituted by the frame T and the assembly of photovoltaic panels V has an arm ' b' with respect to the axis of rotation A. This type of construction, which is necessary to allow the assembly V to rotate until it assumes a configuration almost vertical, entails considerable problems. In particular, the horizontal component of the arm between the axis of the upright M and the center of gravity of the system frame T plus assembly V produces a moment of the weight force that has two major negative consequences: generates stresses and loads on the locking elements of the upright M to the ground, and requires a greater power of the actuators that realize the movement of elevation. This factor affects the overall efficiency of the photovoltaic system that takes into account not only the power produced by the panels but also the power dissipated by the tracker. Regarding the latter, in fact, while the power dissipated by the electronic components can almost always be considered negligible, the same can not be said for the mechanical components.

SUMMARY OF THE INVENTION

It is therefore object of the present invention to propose a solar tracker with the structure optimized able to overcome the above described limitations of the prior art.

The above objects are achieved by means of an azimuth-altitude tracking system for high concentration photovoltaic systems as set forth and characterized in the independent claim.

The dependent claims describe other characteristics of the present invention or variants to the main inventive idea.

Conventionally, a azimuth-altitude tracking system for high concentration photovoltaic systems comprises an upright provided with anchoring means for anchoring to the ground, and at the upper portion of the upright is constrained rotatable around the axis of the upright a support element whose rotation determines the azimuth movement.

Still conventionally, a planar frame supporting the photovoltaic panels is bound to said support element so as to rotate about a horizontal axis passing through the axis of the upright and a kinematic system allows realizing the rotation about the said horizontal axis which is the elevation movement.

According to a characteristic feature of the present invention the group constituted by a main frame and the photovoltaic panels, has center of gravity at the point of intersection between said horizontal axis of rotation with the axis of the upright irrespective of the angle of elevation of the above group.

Thanks to this feature, the tracking system of the invention is perfectly balanced with respect to the weight force in any configuration of elevation and are thus reduced considerably the stresses on the fastening members for fastening the system to the ground.

Advantageously, the aforesaid main frame comprises a main cross member whose longitudinal barycentric axis coincides with the axis of rotation of the frame, and a planar frame supporting the photovoltaic panels fixed to said main cross member. The PV modules are installed on the side of said planar frame on which there is also the main cross member.

The planar frame consists of two half-frames identical to each other and fixed to the main member in a specular way with respect to the cross vertical plane XZ which is a centerplane of the solar tracker and orthogonal to the main cross member itself, and each half-frame is also symmetrical respect to a plane XY perpendicular to the plane of the half- frame itself, and passing through the axis of the main cross member.

Still advantageously, the photovoltaic panels are fixed to the planar frame in such a way as to form a total of four distinct photovoltaic assemblies, arranged in a symmetrical configuration with respect to both vertical plane XZ and XY plane. The division into four spaced away assemblies reduces the stresses generated by the wind as between the assemblies there are openings for the passage of wind.

The distance between the assemblies, which are located on one side of the XZ plane and the assemblies which are on the other side, is greater than the width of the upright so that the upright does not interfere with the rotation of the frame about the axis A. Thanks to the above feature the tracking system can assume, with a very simple structure, elevation angles much greater than the solar trackers of the prior art.

The main cross member is provided with a reinforcement truss lying in the XY plane that is included in the overall dimensions of the group formed by the frame and the photovoltaic panels.

The upright of the solar tracker is constituted by a single cylindrical tubular element and the means for anchoring to the ground are removable from the upright. This type of construction allows to considerably reducing the overall dimensions during the phases of transport of the solar tracker.

The anchoring means for anchoring to the ground are constituted by an element with a tripod structure provided with three anchoring elements spaced apart and at least two upright engaging members spaced in the direction of the axis of the upright, in which said elements are connected together in order to obtain a structure with high rigidity. The top constraining element of the upright includes tie fastening means. The perfect alignment and anchoring of the anchoring means to the upright and the structural rigidity of the anchoring means themselves allow to use, for fastening the solar tracker to the ground, screw means of small size and easy to install, without having to provide concrete foundations.

BRIEF DESCRIPTION OF DRAWINGS

These and more features of the invention will be more easily comprehensible from the following description of preferred embodiments, given as not limiting examples, with reference to the accompanying drawings in which:

Figure 1 shows a schematic side view of a conventional solar tracker for high concentration photovoltaic systems;

Figure 2 shows a top view of the solar tracker of fig. 1 with the frame arranged parallel to the ground;

Figure 3 shows a perspective view of a solar tracker according to the present invention;

Figure 4 shows a top view of the tracker of fig. 3 with the presence of the photovoltaic panels arranged parallel to the ground;

Figure 5 shows a side vie of the tracker of fig. 3 with the presence of the solar panels arranged perpendicular to the ground;

Figure 6 shows a top view of the tracker of fig. 3 with the presence of the solar panels arranged perpendicular to the ground;

Figure 7 shows a perspective view of a means for fastening to the ground the solar tracker of fig. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to Figures 3 to 7 a solar tracker, 100, according to a preferred embodiment of the present invention, comprises an upright, 10, anchored to the ground due to tripod anchoring means, 20. The upright 10 is constituted by a single tubular cylindrical element to the upper end of which there is a support fork, 11 , movable around the axis of the upright

10 to achieve the azimuth degree of freedom. In the fork-shaped support

1 1 is mounted an elongated main cross member, 30, which constitutes the main structural element of the supporting frame of the photovoltaic panels. The main cross member 30 is a cylindrical tubular rotatable about its own axis thanks to the way it is mounted in the support fork 1 1. Alternatively, the main cross member 30 may have cross-section of different shape, also variable, and still be bound to the support 11 so as to rotate around a longitudinal barycentric axis, A, horizontal and passing through the vertical axis of the upright 10 .

A planar frame supporting the photovoltaic panels is constituted by two half-frames, 40a, 40b identical to each other and fixed to the main cross member 30 in a specular way with respect to the vertical plane, XZ, which is a centerplane of the tracker 100 and orthogonal to the main cross member 30 itself. The half-frame 40a, 40b has a rectangular shape and comprises perimetral elements and internal reinforcing elements which are cross, longitudinal and diagonal elements. In addition, the half-frame 40a, 40b is symmetrical with respect to the plane, XY, which is orthogonal to the plane of the half-frame itself, and passing through the axis of the main cross member 30. Furthermore, the two half-frames 40a, 40b are spaced apart with respect to the vertical plane XZ. In particular, the distance between the two half-frames 40a, 40b is such to leave a gap between them at least equal to the diameter of the upright. In practice, in the embodiment depicted the distance between them is much greater because of the mode of assembly of photovoltaic panels on them. In fact, as clearly shown in Fig. 4, each half-frame supports twelve photovoltaic modules, 51 , six in the lower half with respect to the main cross member 30, and six in the upper half, in such a way that they form together four distinct photovoltaic assemblies, 50a, 50b, 50c, 50d, in a symmetrical configuration with respect to both vertical plane XZ and the XY plane. The system made by the main cross member 30 and the frame 40a, 40b constitutes the main frame supporting the photovoltaic panels 51. As can be seen, the panels extend transversely with respect to the half-frame 40a, 40b but the distance between them is always higher than the maximum width (diameter in this embodiment) of the upright 10. Thanks to this distance between the assemblies 50a, 50b that are located on one side of the XZ plane and the assemblies 50c, 50d that are located on the other side, the frame 40a, 40b, and the assemblies themselves can rotate virtually of 360 ⁰ around the axis of elevation or, in any case, they can also assume a perfectly vertical configuration (shown in Fig. 5), since the upright 10 does not interfere with their rotation.

The photovoltaic modules 51 are installed on the side of the planar frame 40a, 40b where there is also the main cross member 30. This makes it possible to design the system in such a way that the center of mass of the system made of the main cross member 30, the planar frame 40a, 40b, and the photovoltaic assemblies 50a, 50b, 50c, 50d, is located on the axis of the main cross member 30 exactly at the point of intersection with the axis of the upright 10. In this way, the system is perfectly balanced regardless of the elevation angle of the solar tracker 100 and are drastically reduced the stresses on the means of anchorage to the ground due to the weight force. Furthermore, the distribution of solar modules 51 in four separate assemblies reduces the stresses due to wind action by breaking the continuity of the surface, creating the walkways to the wind.

The main cross member 30 is provided with a reinforcing truss, 31 , lying in the XY plane. The reinforcing truss 31 allows to substantially stiffen the main cross member in said direction without creating extra bulk since the truss 31 remains substantially included in the volume of the group constituted by the frame 40a, 40b and the photovoltaic assemblies 50a, 50b, 50c, 50d.

In addition, for each half-frame 40a, 40b, there are provided two rods, 41 , symmetrically arranged with respect to the XY plane in the longitudinal direction, and are designed to further contain the bending of the half-frames. At the upper end, the two half-frames 40a, 40b are connected by a bar, 42, whose function is to further stiffen the structure. At the back side of the frame 40a, 40b there is a kinematic mechanism, 60 comprising a linear actuator 61 which, as in the prior art, allows to realize the rotation around the axis of the main cross member 30 and therefore the elevation movement.

With reference to Fig. 7, the anchoring means 20 of the upright 10 to the ground are designed as a removable component. Thanks to this arrangement it is possible to greatly reduce the overall dimensions of the solar tracker 100 during transport operations. The anchoring means 20 are arranged with a tripod shape, with three anchoring elements, 21 sufficiently spaced from each other and two upright engaging members: a baseline support element, 22, and a tie element, 23, which are also sufficiently spaced each other vertically so that, thanks to the presence in the baseline support 22 of diametric gripping means, you get a stable and free from clearance alignment of the upright 10 with the anchoring means 20. First structural elements, 24, for connecting the tie element 23 with the anchoring elements 21 , second structural elements, 25, for connecting the baseline support 22 with the anchoring elements 21 ; first reinforcing elements, 26 and second reinforcing elements, 27, between the aforesaid first and second structural elements 24 and 25, make the anchoring means 20 very rigid. The above high rigidity of the anchoring means 20 together to the perfect balance of the frame 40a, 40b relative to the axis of the upright 10 allow to use light screw-type fastening means, with low cost and quick installation features. Furthermore, the tie-type anchoring elements, together with the three screw-type fastening elements between the tripod and the upright, allows a strong coupling between the two components without damaging the galvanizing of the respective parts, a solution which lengthens the duration of protection.

However, the structure of the solar tracker described above may be subject to modifications and alternative embodiments, without departing from the scope of the present invention. For example, the upright 10 may have a different shape or could be constituted by a supporting structure made of multiple elements. The frame 40a, 40b may be constituted by a framework of even very different structural elements and connected to each other in a different way with respect to what shown in the figures, so, for example, to be able to install the photovoltaic modules other than those represented here. In the case that it is not necessary that the frame can reach the vertical configuration (Fig. 5) this could also be a single structure instead of being divided into two half-frames 40a, 40b.

Additional reinforcing elements, may be provided for the main cross member 30 or between the latter and the frame 40a, 40b.

Obviously, in addition to those described above, further variations or modifications may be made to a system according to the invention, while always remaining within the scope of protection defined by the following claims.

Claims

Azimuth-altitude solar tracker (100) for high concentration photovoltaic systems comprising:

un upright (10) provided with anchoring means (20) for anchoring it to the ground, at the upper portion of said upright (10) being constrained rotatable around the axis of the upright a support element ( 1) whose rotation determines the azimuth movement; a main frame (30, 40a, 40b) for supporting photovoltaic panels bound to said support element (11) so as to rotate about a horizontal axis (A) passing through the axis of the upright (10);

a kinematic system (60) which allows to realize the rotation about said horizontal axis (A) which is the elevation movement; characterized in that the group constituted by the main frame (30, 40a, 40b) and the photovoltaic panels (51) has center of gravity at the point of intersection between said horizontal axis (A) of rotation with the axis of the upright (10) irrespective of the angle of elevation of the above group (30, 40a, 40b, 51).

Solar tracker (100) according to claim 1 characterized in that said main frame comprises a main cross member (30) whose longitudinal barycentric axis coincides with said axis of rotation (A), and a planar frame (40a, 40b) supporting the photovoltaic panels (51), said planar frame being fixed to said main cross member (30), said PV modules (51) being installed on the side of said planar frame (40a, 40b) on which there is also the main cross member (30).

Solar tracker (100) according to the previous claim characterized in that said planar frame consists of two half-frames (40a, 40b) identical to each other and fixed to the main cross member (30) in a specular way with respect to the cross vertical plane XZ which is a centerplane of the solar tracker (100) and orthogonal to said main cross member (30), each half-frame (40a, 40b) being also symmetrical respect to a plane XY perpendicular to the plane of the half-frame (40a, 40b), and passing through the axis (A) of said main cross member (30).

Solar tracker (100) according to any preceding claim characterized in that said photovoltaic panels (51) are fixed to the planar frame(40a, 40b) in such a way as to form a total of four distinct photovoltaic assemblies(50a, 50b, 50c, 50d), arranged in a symmetrical configuration with respect to both vertical plane (XZ) and (XY).

Solar tracker (100) according to the previous claim characterized in that the distance between the assemblies (50a, 50b) which are located on one side of the (XZ) plane and the assemblies (50c, 50d) which are on the other side is greater than the width of said upright (10) so that the upright ( 0) does not interfere with the rotation of the main frame about the elevation axis (A).

Solar tracker (100) according to claim 2 or fallowings characterized in that said main cross member (30) is provided with a reinforcing truss (31) lying in the (XY) plane, said reinforcing truss being included in the overall dimensions of the group formed by said main frame (30, 40a, 40b) and said photovoltaic panels (51).

Solar tracker (100) according to any preceding claim characterized in that said upright (10) is composed of a single cylindrical tubular member, said anchoring means (20) being removable from said upright (10).

Solar tracker (100) according to the previous claim characterized in that said anchoring means (20) are constituted by an element with a tripod structure provided with three anchoring elements (21) spaced apart and at least two upright engaging members (22, 23) spaced in the direction of the axis of the upright (10), said elements (21 , 22, 23) being connected together in order to obtain a structure with high rigidity.

9. Solar tracker (100) according to claim 7 or 8 characterized in that at least one of said upright engaging elements (23) comprises tie-type fastening means.