Concentration and solar tracking device for photovoltaic cells

Technical Field

The present invention relates to the technology relating to photovoltaic power systems, to concentration photovoltaic modules, to systems of solar tracking and to the relative methods of manufacture. More particularly the invention relates to a concentration and solar tracking device for photovoltaic cells.

Background Art

It is well known how solar trackers are formed by mechanical structures, of different design and manufacture type, having the task of supporting a surface of reception of the solar radiation, orientating it and aligning it optically with the position of the sun throughout the day.

To date tracking systems are designed according to one of the two typical approaches which are distinguishing features of the technologies on the market. The first is that which provides for the presence of single elements, generally medium-large in size, having a central pillar on whose top a large capturing surface is placed.

The pillar is able to rotate around its main axis while the capturing surface can rotate around an axis perpendicular to the previous one, exploiting mechanisms of actuation and transmission of the motion of different types.

The second approach instead has a plurality of capturing elements reduced in size. They are installed on an articulated frame which moves them simultaneously, having the capacity to be able to regulate the slant of the receiving surfaces, placing them in rotation around one or two axes, according to the manufacture type. Both solutions suffer from considerable limitations, including low simplicity and flexibility of installation, limited precision of tracking and limitations of an economic type.

More particularly the first manufacture type anticipates the limitation of being suitable solely for housing receiving surfaces of high extension, with consequent considerable overall dimensions and masses in play, which entails difficulties linked to transport and installation, intense structural stresses caused by the wind and, in general, this type proves to be unsuitable for rooftop installations and architectural integrations.

Moreover special equipment (articulated means of transport, cranes, etc.) is often necessary for transport and installation as well as the presence of a considerable work force. This translates into correspondingly high costs which discourage the installation of this type in systems small in size.

The second type, featuring fewer difficulties of installation, is however less flexible and precise.

In fact the presence of an articulated frame, despite the fact that it leads to a reduction in the number of motors necessary for movement, implies a reduced precision of tracking, in that the rotating axes are not directly coupled to the motors, but are coupled indirectly with interposing of essential mechanisms of transmission of motion which inevitably introduce play and inaccuracy, which lead to a reduction in the precision of tracking.

Moreover the frame restrains the number of elements which can be installed, and their arrangement, not allowing in general the modification of the configuration of the array of modules during or after installation. All this is moreover in addition to the fact that, in general, the frames impose a physical limit on the angle which the capturing surfaces can sweep around the axes of rotation. As a result the frames, due to their very intrinsic presence, penalise the flexibility of installation, excluding for example the possibility of applications on vertical or sloping surfaces, unless preceded by a targeted design. The concentration photovoltaic solar technology, as is known, cannot depart from the use of tracking systems in that the precise optical alignment with the sun is the requirement for the concentration of the radiation on the converter element, constituted in general by a photovoltaic cell.

In this respect it is fundamental to specify how the quantity of electrical power produced increases proportionally with the capacity for concentrating with precision the radiation on the cell, maintaining a distribution which is as homogeneous as possible on the surface of the same and avoiding part of the radiation exiting from the cell and which is irremediably wasted. In particular this i latter aspect shows how the accuracy of the tracking system is fundamental, in the technology of concentration photovoltaic, in order to obtain an efficient system with high performances.

As regards the concentration optics, the first photovoltaic systems were orientated towards two different construction types.

; In the first case a vast orientable reflecting surface, or a series of articulated mirrors, is directed towards a single point, where the radiation is concentrated and converted.

In the second case, instead, use is made of groups of lenses, rigidly connected to form extended panels, which focus the solar radiation, each one on the reciprocal I underlying cell.

A new approach recently emerged which sets out to combine the concentration technology with the reduced dimension of the more classic silicon panels.

This third type of systems uses, like the previous one, groups of lenses which are however connected in groups of smaller number and extension, such as to allow i the formation of smaller and easier to handle modules, of size comparable to traditional photovoltaic panels.

However the solutions proposed to date are linked to the traditional systems of tracking described above, therefore they have the same limitations which were analysed previously, in particular the limited possibility of architectural » integration. Disclosure of the Invention

The object of the present invention is therefore that of avoiding these disadvantages by means of a system of tracking appropriately designed for the application to concentration photovoltaic.

More particularly the aim is to make a modular system which is extremely precise in tracking, which is at the same time economical, reduced in size and particularly suitable for architectural integrations which in other words allows a flexible installation on every surface, whether it is horizontal, vertical or in any case sloping.

Brief Description of the Drawings

According to the present invention this object is achieved by a concentration and solar tracking device whose features can clearly be found in any one of the appended claims, and the advantages whereof will be made clearer in the following detailed description, given with reference to the accompanying drawings which show an embodiment thereof by way of a non-limiting example of the invention, in which:

Figure 1 is an overall perspective view of the concentration and solar tracking device in accordance with the invention;

Figure 2 is a perspective view of a receiver module of the device of Figure l ;

Figure 3 is a perspective view of a module shown with some parts removed in order to highlight better others thereof;

Figure 4 is a plan view from above of the receiver module of Figure 3;

Figure 5 is a perspective view of a central plinth which equips the device of Figure 1 ;

Figure 6 is a perspective view of the plinth of Figure 5 shown with some parts removed in order to highlight better others thereof;

Figure 7 is a perspective view of a fork with an interconnected secondary shaft equipping the device of Figure 1 ; - Figure 8 is a side view of the fork of Figure 7 shown with some parts removed in order to highlight better others thereof;

Figure 9 is a perspective view of the fork of Figure 8;

- Figure 10 is a perspective view of an overall configuration of a plurality of devices mounted in pairs and combined in linear array form.

Detailed Description of the Preferred Embodiments of the Invention

In accordance with the accompanying drawings Figure 1 shows a concentration and solar tracking device for concentration photovoltaic cells which is denoted overall by reference numeral 100.

The concentration of the solar radiation by means of lenses, like the homogenisation of its distribution on the device 100, does not form an object of the present invention, therefore the detailed description of the same will not be dealt with here.

The same applies for the types of photovoltaic cells, used for the relative technologies of assembly and production. For the ones and the others use is made of technologies known in the field of multij unction photovoltaic cells which therefore depart from the object of the present invention.

The device 100 comprises a central articulated body, configured in such a way as to be able to house, peripherally and preferably, four modules 200 for capture and concentration of the solar radiation coupled two by two one with the other.

More particularly the following form part of the articulated body: a central plinth 300, which supports and moves a primary shaft 301 , and a pair of forks 400, positioned at the ends of the shaft 301 , which in turn support and move two secondary shafts 401 , transverse to the primary shaft 301.

Due to this configuration and arrangement the articulated body is able to rotate simultaneously all the modules 200 around a primary axis A, defined by the primary shaft 301 , while each fork 400 is able to rotate a pair of modules 200 around a secondary axis B, defined by each of the secondary shafts 401 , substantially perpendicular to the primary shaft 301. Due to this arrangement the modules 200 are arranged in such a way that, in each pair, each module 200 is symmetrical to the other one with respect to a plane passing through the axis A and perpendicular to each plane defined by one of the axes B and by the same axis A.

The two pairs of modules 200 also find themselves arranged in an equidistant manner with respect to the plane of symmetry of the primary shaft 301 , perpendicular to the axis A.

The embodiment described above allows a balanced spatial arrangement of the masses around the central plinth 300. This feature allows the possibility of using with considerable advantage stepper motors small in size and power, with a clear benefit in terms of reduction in the general costs of construction and components, and to the advantage of an improved overall energy balance of the device 100. Figure 2 shows the external structure of the concentration and capture module 200 presented according to a first configuration. At the base of the module 200 there is a metal plate 201 having the function of housing on its upper surface, inside the module 200 (Figure 3), the multijunction photovoltaic cells 205. At the top of the module 200 a lenses plane 206 is positioned, or more generally an equivalent capture member exposed directly to the solar radiation.

In the embodiment of the invention described here the capture member 206 is identified as a plane of shaped lenses which are formed on a surface of a plastic or vitreous type. The lower surface of the plane has particular grooves suitable for forming concentric annular sections whose purpose is that of concentrating the light radiation captured according to the well-known principle of Fresnel.

Between the metal base 201 and the lenses plane 206 a casing 204 in plastic material is interposed which defines a closed external surface preferably shaped complementarily with the contour geometry of the plate 201 and of the lenses plane 206. This casing 204 departs perpendicularly from the surface opposite the capturing one of the lenses plane 206, projecting itself in a cantilever towards the underlying metal plate 201. From the assembly of the three elements described previously a closed volume comes to be defined inside the module 200 which allows the multijunction cells

205 and the relative cables to be housed.

It can also be clearly seen in Figure 2 and even more clearly in Figure 3 how one of the two vertical surfaces corresponding to the larger side of the lenses plane

206 has a circular hole which allows the traversing of the secondary shaft 401 for coupling inside the module with a rigidly connected tubular sleeve 203; tubular sleeve 203 which is coaxial with the axis of rotation B and which allows one of the two movements, necessary for the orientation of the modules 200 in the space, to be performed (as will be explained in greater detail herein below).

The position of the hole in the casing 204, wherefrom departs the distance of the tubular sleeve 203 from the base plate 201, is preferably designed in such a way that the axis of rotation B passes through the centre of gravity of the module 200, which technique allows the driving torque of the rotation of a pair of modules 200 and of the relative tubular sleeve 203 to be minimised, reducing it substantially to the driving torque necessary for overcoming the mechanical frictions which oppose rotation.

This feature, together with what is described previously on the subject of the spatial arrangement of the modules 200, contributes to the obtaining of the considerable benefit of reduction of the size of the motors necessary, with the undoubted advantages described above.

It is to be noted however that said module 200 can also take on forms different from that given by way of an example, possibly provided for example with a plane 206 of conventional spherical lenses, in place of the plane 206 of Fresnel lenses, or possibly taking on different geometric forms without thereby departing from the technical scope of the present invention.

Figure 3 allows, in particular, the identification of the components housed entirely in the closed volume of the module 200, that is to say a pair of vertical uprights 202, placed close to the external casing 204, which connect structurally the lenses plane 206 and the underlying plate 201 and which are made preferably in material provided with high intrinsic rigidity.

Perpendicularly to the main dimension of the uprights 202, placed in a substantially intermediate position between the plate 201 and the lenses plane 206, there is, as mentioned, the tubular sleeve 203. The latter is preferably provided here with a cylindrical tubular form, flanged at the ends, which is very suitable for being firmly attached to the two uprights 202, contributing to conferring adequate rigidity to the module 200 as well as transmitting thereto the rigid rotation around the axis B received from the secondary shaft 401.

From Figure 3, and even better from Figure 4, it is noted that on the upper face of the plate 201 the sets of photovoltaic cells 205 are arranged.

The cells 205 are arranged preferably according to an array of two rows of four elements each, for a total of eight cells 205 per module 200.

This arrangement is congruent with the position of the overlying lenses of the lenses plane 206, so that the beam of light deviated by the lens hits with precision the corresponding cell 205.

It clearly emerges how this arrangement is wholly by way of a non-limiting example in that there are various possibilities relating both to the arrangement of the cells 205 and their number per module 200, according to the shape and size of the lenses plane 206.

The plinth 300 central to the concentration and capture modules 200, shown in Figure 5, is made up externally of a base plate 302, of two pairs of lateral walls 303 and 304 opposite two by two, and respectively transverse and longitudinal to the primary axis A; of an upper cover 305 and of two support elements 306 and 307 for the relative electric stepper motor 309.

The lateral walls 303 and 304 are manufactured in a rigid and resistant material, preferably metal, in that they have to support two drive shafts 301 and 308, whose axes are denoted by the letters A and C. More particularly the pair of lateral walls 303 have to support the shaft 301 , on the ends whereof the two forks 400 and the relative modules 200 are housed. Therefore the lateral walls 303 are called on to support the weight of the entire device 100.

The lateral walls 303 and 304 have holes 500a and 500b which allow the attachment of flanged ball bearings housed inside the plinth 300. In this example the holes 500a are smooth and through, that is to say they traverse the respective walls 303 and 304. The holes 500b, formed in the respective walls 303 and 304, are instead threaded for the insertion of screws for tightening of the bearings to the respective walls 303 and 304.

In this configuration, as can be seen clearly in Figure 6, the walls 303 and 304 have recesses which define in combination one with the other a seat 501 intended to house the upper cover 305. The support for the stepper motor 309 is formed by means of two of the aforementioned metal elements 306 and 307 appropriately coupled.

More particularly the element 306 is made up of an elongated lamina, bent into an elbow shape. Its shape allows, on one side, coupling with the small plate 307 for the attachment of the motor, and on the other side the insertion in an appropriate slot formed between the base plate 302 and the lateral wall 304 for the attachment with the rest of the plinth.

In fact, from the combined observation of Figures 5 and 6 it is possible to note that the rigid small plate 307 is shaped in such a way as to allow the housing of the stepper motor 309 and the coupling of the relative drive shaft pin 308 which is substantially perpendicular to the primary shaft 301. More particularly the drive shaft pin 308 penetrates inside the plinth 300 traversing the lateral wall 304; it is rotated around its axis C by the motor 309 and rotates around the axis A the shaft 301 by means of an interposed system of transmission of motion.

The system of transmission comprises, more particularly, an endless screw mechanism defined by a pair of elements: a screw 31 1 , integral with the shaft 309, and a screw wheel 3 12, restrained to the primary shaft 301. By means of the system of transmission of motion housed inside the plinth 300 and the components described above it is possible to use the stepper motor 309 in order to rotate the primary shaft 301 around its axis A.

Figure 6 also allows visualisation of the four ball bearings 310.

They are arranged in symmetrical pairs on the internal faces of the walls 303 and

304. The bearings 310, with their position, define univocally the axes A and C, allowing the shafts 301 and 308 to rotate freely around the same axes A and C.

An important aspect of the present configuration is that, not having any physical limit which constrains the possibility of rotation thereof, the shaft 301 is able to rotate through 360° around its own axis A, being able to take on all the orientations required without any limit on the resulting position of the modules

200 around the axis A.

It is to be noted however that said elements can also take on different forms from those given as an example, for example they can have geometries of various type or have different solutions forming part of the prior arts for the reciprocal attachment of the bearings, like for the transmission of motion.

Figure 7 shows the entire fork 400 coupled with the secondary shaft 401 which rotates around the axis B. The fork 400 is presented as a closed central body, below which an electric stepper motor 410 is installed, held by a support entirely similar to the one described in the plinth 300.

The central body of the fork 400 is composed of a first rigid member 402 which allows the connection with the primary shaft 301 and where to two further rigid members 403 and 404 are connected which make up the lateral faces of the actual fork 400.

An upper cover 406 and a lower one 407 close the central body. Both are appropriately shaped around the profile defined by the elements 402, 403 and 404. The combination of the three rigid members 402, 403 and 404 and of the two covers 406 and 407 defines a space closed around the central body and of adequate volume, wherein the components for the transmission of motion are housed. The stepper motor 410 is housed below the central body of the fork 400 in such a way that the motor pin 502 (Figure 8) of said motor 410 is orientated perpendicularly to the axis B and enters inside the central body of the fork 400 by means of two appropriate holes formed respectively in a relative small support plate 409 and in the lower cover 407.

The external structure of the fork 400 is completed by a pair of flanged ball bearings 405, mounted on the external faces of the members 403 and 404. They have the task of supporting the secondary shaft 401, together with the pair of associated modules 200, allowing the free rotation thereof around the axis B.

The three rigid members mentioned above, i.e. the rigid bodies 402, 403 and 404, are to be made preferably in metal material, or in any case in a rigid and resistant material, in that they have the task of supporting the weight of the shaft 401 and of the pair of modules 200 placed at the end of the same shaft 401 , discharging it onto the central shaft 301.

Contrarily the two covers 406 and 407, which have the sole function of protecting the components for the transmission of motion housed inside the fork 400, can be made in lower quality materials, such as plastics and polymers of various types. Housed inside the closed volume are the elements suitable for the transmission of motion from the motor 410 to the shaft 401. As can be seen clearly in Figure 8, this is a pair of cogged wheels 41 1 and 412 with perpendicular axes. In this representation cogged wheels 41 1 and 412, helicoidal, are preferably considered. However they could be replaced, for example, by a pair of conical wheels or equivalent components of another kind forming part of the prior arts for the transmission of rotary motion between two perpendicular axes.

The cogged wheel 412 smaller in size is rigidly connected to the pin 502 of the stepper motor 410. The coupling is formed at the upper end of its portion inside the body of the fork 400. The second cogged wheel 41 1 , which has larger dimensions, is coupled with the secondary shaft 401 , the orientation of its axis is therefore substantially perpendicular, both to the pin 502 of the motor 410 and to the main shaft 301. Figure 9 shows with greater efficacy of description the mechanism of retransmission of motion. The stepper motor 410 is provided with a pin 502 which, extending in the form of shaft entering the body of the fork 400 and rotating around the axis D, rotates the cogged wheel 412.

The cogged wheel 412, meshing with the cogged wheel 41 1 coupled thereto, rotates the latter wheel 41 1 around the axis B.

By means of the rigid connection of the latter wheel 411 with the shaft 401, the entire shaft 401 is therefore driven to rotate around its main axis B, substantially perpendicular to the axis D. From the configuration just described, like what is disclosed for the plinth 300 and the shaft 301, the significant advantage emerges whereby, thanks to the lack of physical constraints, the shaft 401 is also able to rotate through 360° around its own axis B, without any limitation on the resulting position of the modules around the same axis B.

The present configuration, wherein each receiver module 200 is placed at the end of a shaft 401, also allows the operations of assembly and maintenance to be facilitated, even allowing the replacement of possible damaged or malfunctioning modules 200, maintaining intact the rest of the structure.

As regards the embodiment of the motor reducers, stepper motors with 7.5° per step are preferably adopted, coupled with reducers with high reduction ratio, for example 1500: 1 , which, combined one with the other, allow extremely high angular resolutions to be obtained, of the order of 0.005° at each step.

The possibility of movement with such a high degree of angular resolution ensures the maximum precision of tracking, with evident benefits with respect to the production of electrical power. In fact, as mentioned previously, the electrical power produced is a direct consequence of the capacity of the concentrated light beam to strike with precision the cell 205 in its entirety and with homogeneous distribution, and in particular to avoidl part of the beam of light exiting from the cell 205, i.e. part of the radiation from being irremediably wasted. A further advantage of the present invention is in fact that of being able to use stepper motors as members of movement of the primary 301 and secondary 401 shafts which allow the spatial orientation of the modules 200, being able to manage them with command means with simple action. This allows, for example with respect to controls with feedback, the system of control to be greatly simplified, without

5 however sacrificing a high precision of tracking.

The embodiment of the device 100 just described is easy and economical to manufacture. This aspect, combined with the extremely limited overall dimensions and masses, makes it particularly suitable for the constitution of batteries of devices 1 10 (Figure 10). This means that a plurality of devices 100

) can be positioned together one with the other, according to the most adequate spatial arrangement, in order to adapt to the support surface effectively available and in order to minimise the reciprocal shading between the modules 200 of the different devices 100. In this way it is possible to create capture systems of various size and power, which can be scaled economically and which are also

> subject to relatively simple and reliable management of their control.

In this respect Figure 10 shows an installation of four devices 100 arranged in a linear array. In this arrangement, to be considered solely as an example and in no way binding, they are attached on a pair of standard metal section bars 500 housed parallel to the axis B, below the central plinth 300 of the various devices 100.

) The metal section bars 500 are standardised components available on the market in multiple sizes. They range over extremely variable lengths and dimensions of the section, and also have numerous solutions for the attachment on surfaces of any type and in any way orientated, aspects which enable them to adapt to every application and which make this technology the most widespread in the sector of

5 supports for standard solar panels.

The possibility of application of the device 100, the object of the present invention, on this type of section bars represents an undoubted advantage in terms of flexibility of installation and possibility of changes or substitutions, an aspect which makes it extremely suitable for architectural integrations with existing

) buildings or buildings under construction. This aspect also allows the use of the devices 100 in question in all cases wherein a photovoltaic system already present on the building yet close to the end of its life cycle is to be replaced with a more modern and efficient solution. In this case in fact it is possible to reuse the support structure already present, even re-adapting it to the geometry required, with a considerable saving in cost and reduction in times of return of the investment. A further advantage arising from this aspect, combined with the reduced dimensions and weight of the device 100, the appealing design as well as the possibility for the shafts 301 and 401 to rotate completely around their own axes, is that of allowing installations on surfaces that are vertical or in any way

I orientated. A further consequence of the possibility of the shafts 301 and 401 to rotate completely around their own axes is that, contrarily to most of the known technologies which have to be orientated in a prevalent direction (typically north- south), the device 100 does not need particular spatial orientations and can therefore be installed with the axes arranged in any direction. This aspect i underlines further the strong suitability thereof for architectural integrations, having the undeniable benefit of adapting also to those surfaces (such as for example vertical walls exposed to the south, edges and pylons with slim geometry) which could not house traditional photovoltaic systems nor concentration systems of a different nature.

I The invention thus conceived is subject to evident industrial application and may also be the object of numerous modifications and variations, all coming within the scope of the inventive concept; all the details can be modified, moreover, replacing them with technically equivalent elements.

The invention thus conceived is subject to evident industrial application and may i also be the object of numerous equivalent modifications and variations, all coming within the scope of the present invention. Moreover the materials used in order to manufacture the device according to the present invention, like the shapes and individual dimensions of the component parts, can be chosen in such a way as to fulfil appropriately every specific requirement of the invention without thereby I departing form the scope of the present invention.