Zenithal solar tracker

Abstract

A zenithal single-axis solar tracker comprising a plurality of modules, each module formed by two symmetrical photovoltaic panels (1) that are in opposite positions with respect to a central tube (2) and attached to said tube by means of two pairs of arms (3), characterised in that each arm (3) is joined to the central tube (2) and to each of the two panels (1) forming each module, in such a way that the arms (3) are identical to each other, are mounted opposite the central tube (2) and are offset from the corresponding arms on the opposite side; and where the solar tracking movement in the east-west direction is provided by means of three drives.

Description

[0001] DESCRIPTION

[0002] ZENITHAL SOLAR TRACKER

[0003] Technical sector

[0004] The present invention relates to a single-axis zenith solar tracker whose structure is composed of a central tube on which the photovoltaic panels are placed and, by means of three drives, it is given the solar tracking movement, in the east-west direction.

[0005] State of the art

[0006] As is well known, for a solar panel to perform optimally, solar radiation must strike the panel perpendicularly. As is also known, the sun's position varies throughout the day, just as its position relative to any point on Earth varies throughout the year.

[0007] For this reason, solar trackers are known as those that allow the collecting elements, i.e. the photovoltaic panels, to adapt their own position to that of the sun at any given time, i.e., to progressively vary their own position in parallel with how the sun changes its position.

[0008] However, the size of photovoltaic panels in the last decade was less than two square meters. With the improvement in photovoltaic cell efficiency, yields of 20% or slightly higher had been achieved. In an effort to increase the unitary power of the panel (which until then was 450 Wp), the trend was to increase the area of ​​photovoltaic panels, reaching up to 3.1 square meters. With this increase in area, power outputs of 650 Wp were achieved.

[0009] That is, over the past few years, the useful surface area of ​​photovoltaic panels has grown by up to 50%. This represents a disadvantage for the mechanical strength of the array, since the same number of panels per tracker unit corresponds to a larger area exposed to the wind, with structures with sails of up to four meters. Due to a lack of understanding of concepts such as fluttering and torsional stability, the same solutions used for smaller panels continued to be used in the design of solar trackers. Fluttering is a self-induced vibration that occurs when a supporting surface bends under an aerodynamic load. Specifically, it is a phenomenon that occurs when the aerodynamic force of the wind causes a natural periodic motion, i.e., causes high-amplitude oscillations in the tracker structures.If these vibrations persist, and the structure does not have any modes higher than those of the wind, that is, higher than 2 Hz, the structure enters into resonance, which causes an exponential increase in vibration that can cause failures in the structure and ultimately collapse.

[0010] This failure to adapt to the new panel dimensions has caused damage to photovoltaic parks, resulting in structural failures in a large number of the installed trackers.

[0011] As a result, the sector, instead of using the 2V type (solar tracker with two rows of panels placed vertically), is using shorter structures with a shorter chord, such as the 1V type (solar tracker with one row of panels placed vertically). Returning to this configuration results in a loss of land utilization rate (LUR), reduced adaptability, and higher costs when acquiring the land needed to achieve the same installed capacity as with the 2V type.

[0012] The present invention aims to take advantage of the benefits offered by the 2V typology through a structure that takes into account the large dimensions of current panels with the aim of achieving maximum use of the land per installed power.

[0013] Many structural suppliers have attempted to solve these problems by adding damping or locking systems to the external part of the solar trackers or by retrospectively incorporating new piles to increase the number of fixed points. However, these systems are not integrated into the design from the outset, resulting in a lack of optimization and associated costs. Incorporating new piles requires dismantling the solar trackers, causing them to be disconnected and, therefore, affecting plant production. Additionally, it can cause damage to adjacent solar trackers as it requires the introduction of large machinery for installation. These drawbacks highlight why these are not optimal solutions.

[0014] Additionally, cracking problems are appearing in the elements that support the photovoltaic panels, namely, in the purlins. Conventional W-type or C-type purlins are attached to the central axis of the solar tracker through a truss, generating significant stress and fatigue. The solutions proposed to date are based on increasing the thickness of these purlins and even adding brackets to the purlins. If these are replaced after the fact, that is, once the photovoltaic plant is operational, the plant again incurs downtime, resulting in a loss of productivity. If this solution is incorporated from the outset, it entails a lack of material optimization and an increase in the weight of these supports, which may result in the need to reinforce the pillars of the solar tracker structure.

[0015] Document ES2274710B1 describes a support arm for a parabolic trough collector configured to be coupled to a central body of the collector as a bracket, in a direction substantially perpendicular to a focal line of the collector, said arm having a wedge shape that has: a first side provided with support devices to support at least one mirror; a second side; a third side provided with support devices so that the arm is supported by the central body. The arm is formed by at least one stamped sheet metal shaped to obtain a resistant structure to provide rigidity and load-bearing capacity by means of a plurality of ribs that form a lattice that has a plurality of laminar portions between said ribs. The manufacture of these lattice-type belts, hereinafter stamped arms, is achieved by means of a die system.Large tooling facilities are required, as the die required for its manufacture is approximately 5 meters long, and presses weighing more than 1,200 tons.

[0016] In summary, the state of the art has detected problems related to the aeroelasticity of solar trackers (such as the flapping effect and torsional stability) when using the same structures for larger panels. Traditional structures are unable to support the new photovoltaic panels that have appeared on the market under aerodynamic loads, resulting in the use of smaller panels, resulting in a loss of GCR and an increase in the required installation area for the same plant capacity.

[0017] To achieve natural frequencies far removed from the natural frequencies of the wind, and thus eliminate the flutter effect of structures, structural solutions must be sought that optimize the design with greater efficiency. Increasing the thickness would help stiffen the solar tracker, but would require more steel, reduce the usability of the assembly, and complicate installation. Finally, the appearance of cracks in the straps has prompted the search for a solution that minimizes the stress and fatigue generated in the support elements of the photovoltaic panels.

[0018] These technical problems are solved with the zenith solar tracker of claim 1.

[0019] Explanation of the invention

[0020] The present invention relates to a single-axis overhead solar tracker. As indicated, its structure consists of a central tube on which the photovoltaic panels are placed. It is driven by three drives to track the sun on one axis. The motors are the zero reference points of the assembly. Furthermore, the overhead solar tracker comprises a series of jacks distributed on each side of the drive. Torsion tubes and arms configured as supports for the photovoltaic panels are placed on the jacks. This object is achieved with the solar tracker of claim 1, which accompanies this specification. Particular solutions of the invention are described in the dependent claims.

[0021] The structure of the solar tracker of the invention allows that, at the beginning of the day, the drives rotate and place the assembly at the inclination limit of 55 eto the east. The drive varies the tilt angle according to a solar tracking control algorithm, aligning the modules and ending at the end of the day at its tilt limit of 55°. e westward.

[0022] An object of the invention is to increase the torsional rigidity of the solar tracker structure. To this end, the present invention reduces torsional moments, the flutter effect, and angular deformation at the tracker's ends by reducing the distance between the fixed point (motor drive) and the tracker's free end. For this reason, a tracker with a triple actuator is proposed, compared to the conventional design with a single actuator. In this way, three synchronized actuators have been integrated, reducing the spans to 10 meters compared to the 30-35 meter spans found in conventional trackers. This proposal, in addition to improving the tracker's performance, has made it possible to dispense with the dampers used in state-of-the-art trackers.

[0023] The central follower tube has a geometry that modifies the moment of inertia, since it depends solely on the geometry of the body and the position of the axis of rotation. This modification has had a beneficial effect on the central tube by reducing angular deformations. Therefore, one objective of the invention is a central tube with improved inertia, which simultaneously uses the least amount of material possible, to reduce costs and weight, while allowing for machining. The optimal cross-section of the central tube is a rectangular hollow profile with rounded corners, as opposed to the commonly used square hollow profile.

[0024] The arms are designed to optimize the amount of material used by reducing the arm sections required to support the panel at points where it is not necessary, favoring material optimization compared to a conventional belt system. Furthermore, thanks to the use of these arms, the center of gravity of the assembly has been shifted, resulting in lower consumption and, therefore, greater energy efficiency for the tracker.

[0025] Finally, the solar tracker's structure allows for standardized field assembly. Thus, it is possible to industrialize the process. To this end, an in-plant assembly line is proposed, which, through templates, standardizes the assembly process using "poka-yoke" systems that ensure the operator meets the engineering standards required during the assembly process. This will prevent deviations and possible future repairs.

[0026] Brief explanation of the drawings

[0027] To complement the description being made, and in order to help better understand the characteristics of the invention, a set of drawings is attached as an integral part of said description, in which, for illustrative and non-limiting purposes, the following has been represented:

[0028] Figure 1 shows a general view of the zenith solar tracker according to the invention.

[0029] Figure 2 shows an illustrative view of the operation of the solar tracker of the invention.

[0030] Figure 3 shows a detailed view of the arm assembly together with the photovoltaic panels.

[0031] Preferred embodiment of the invention

[0032] As can be seen in the drawings accompanying this specification, the single-axis overhead solar tracker comprises a plurality of photovoltaic panels (1 ) - hereinafter simply the panels - which are supported by a central tube (2) to which a plurality of arms (3) are attached. The purpose of the arms (3) is to support the weight of the panels (1 ) that make up the surface of the solar tracker. Each section of the tracker is made up of two symmetrical halves, each of which is in turn formed by a panel (1 ).

[0033] The arm (3) is attached to the central tube (2) and to the panels (1 ) by means of joining means. Each panel (1 ) requires a pair of arms (3) to support a pair of panels. The arms (3) mounted on the right and left of the central tube (2) are identical, with the difference that they are rotated 180 eand offset from the corresponding panels on the opposite side, so that the panels are perfectly symmetrical.

[0034] The function of the arms (3) is to provide a structural connection that transmits loads from the panels (1 ), such as weight, wind, snow and earthquakes, to the central tube (2). In addition, they make it possible to guarantee a support area that forms a flat surface with great precision so that the two panels (1 ) that are supported on each arm (3) are positioned relative to each other with a certain tolerance. To this end, the arms (3) consist - essentially - of at least one rolled steel sheet with a thickness greater than 1 mm and less than 2 mm, suitable for cold stamping with a guaranteed minimum yield strength of 350 N / mm2. This simplified structure of the solar tracker also allows it to be installed more easily in the same location where the tracker of the invention will operate, such that assembly costs and times are reduced.

[0035] The complex where the solar tracker of the invention is assembled is preferably located in the central area of ​​the work zone, so as to minimize the transport time of each solar tracker from this location (the assembly plant) to its final position at the solar generation plant. The assembly plant consists of three areas:

[0036] The main area or assembly area, where all the elements that make up the assembly line are located and which will be explained in detail later.

[0037] One or more secondary areas or storage areas, located on both sides of the line, where the materials required for the daily production are stored, so that workers can easily access the necessary components and place them on the line. The central beams (2), arms (3), solar modules (panels (1)) and connecting elements will be located in these areas.

[0038] In the third area, or departure area, are the trailers responsible for transporting each solar tracker to its installation point in the field.

[0039] The assembly line or plant can even be installed in an area where the solar trackers will later be located. This allows the required structures to be driven into the ground and installed in the space used once the assembly process for the rest of the work area has been completed and the line itself has been dismantled. In a particular embodiment of the invention, the required area for the installation is estimated to be approximately 50x25 meters, ensuring a comfortable and ample space for work and loading and unloading materials.

[0040] The assembly of the solar tracker that is the object of the present invention comprises, firstly, the placement of the central tube (2) and the joints for the rest of the elements. The central tube (2) is placed on a mobile support on the support beam of the line, to facilitate its advancement, since it allows the assembly to be moved to the different positions easily by a single operator. Once the tubes (2) are fixed, T-joints are fixed on them. These T-joints will be the elements that allow the union with the arms (3) in the next assembly or assembly station of the solar tracker of the invention. As has been commented, the arms (3) are installed in the T-joints fixed on the tubes (2).To do this, firstly, the arm (3) is placed on a mounting template and the joining element is fixed to the panel (1) -in a particular embodiment, a plurality of clips- after which the assembly process of the tracker continues, at a rate of four arms (3) for each column of two modules (PV panels) one on each side of the central tube (2). The placement of the modules is carried out by placing the panels (1) on the arms (3) and using the clips to partially fix the module, so that they are ready for their final placement in the next position.

[0041] The final assembly phase of the solar tracker of the invention will be carried out in an area with a pit, allowing the operators to work at a comfortable height below the modules. At this station, an operator will adjust the photovoltaic modules (1) on the arms (3) to ensure they meet the positioning tolerances. Once completed and inspected, the assembly, secured at both ends of the central tube (2), will be lifted and placed on a trailer. This trailer is provided with guides to which the assemblies are secured at the ends of the central tubes (2), preventing any type of rotation or movement during transport.

[0042] Once the solar tracker of the invention reaches the corresponding location in the field, the assembly will be placed on pillars fixed or cemented in the field. Positioning is much simpler using bearings, since this device allows the pillars to be opened and closed with the central tube (2) in its final position. This allows, if necessary, the disassembly of a section of the central tube (2) without having to disassemble the entire tracker from the motor to the section in question.

Claims

CLAIMS 1 A zenith solar tracker on an axis comprising a plurality of modules, each formed by two symmetrical photovoltaic panels (1) in opposite positions with respect to a central tube (2) and fixed to it by means of two pairs of arms (3), characterized in that each arm (3) is connected to the central tube (2) and to each of the two panels (1) that form each module, such that the arms (3) are identical to each other, are mounted in an opposite manner with respect to the central tube (2) and are offset with respect to the corresponding ones on the opposite side. 2.- The zenith solar tracker according to claim 1, where each arm (3) consists of at least one rolled steel sheet with a thickness greater than 1 mm and less than 2 mm, suitable for cold stamping with a guaranteed minimum yield strength of 350 N / mm. 2 . 3.- The zenith solar tracker according to claim 1 or 2 comprising more than one actuator, synchronized with each other, to reduce the span of the tracker to approximately 10 meters. 4.- The zenith solar tracker according to any one of the preceding claims, where the central tube (2) is a rectangular hollow profile with a radius of curvature at its vertices.

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