"MULTIFUNCTIONAL PHOTOVOLTAIC STREETLAMP HAVING LOW
Field of application
The present invention relates to a photovoltaic device for residential and urban lighting, and in particular to a multifunctional street lamp with low visual impact.
Presentation of the known art
In an urban context, lighting assumes a very considerable importance both from the functional standpoint and from the aesthetic standpoint. According to the intended use of the place that is to be lit up, the attention of the designer can concentrate more on the former aspect, and hence give priority to achieving visual comfort, or else more on the latter aspect and valorize lighting as an element of decorative amenity. However, there are certain circumstances of application in which the two aspects are by no means easy to separate. This is the case of lighting of archaeological and cultural sites, or areas of interest from the point of view of landscape and natural scenery, in which, if on the one hand an asset which otherwise could not be appreciated during hours of darkness and in- conditions of poor visibility is to be valorized, on the other there is required the presence in situ of lighting systems that are extraneous to the context. In this connection, the material presence of lighting equipment in itself is not in actual fact the only element of environmental disturbance. Added to this are all the collateral systems to be provided for
guaranteeing operation of the lighting system, such as foundation works, cable ducts, inspection or junction wells, and so forth.
If said sites are then located in remote or impervious areas, where the supply of the electricity via the public distribution network proves impossible or excessively burdensome, said lighting systems must also be autonomous from the energy standpoint.
To solve the latter problem, photovoltaic street lamps are known that preserve the image of traditional street lamps, which associate to the usual mercury- vapour or sodium-vapour lamps a photovoltaic panel applied in an unrehearsed way on the lamp post for supporting the street lamp itself. A device of this type is illustrated in Figure 1 as last street lamp in the row and there designated as a whole by L.
However, the attempt to integrate the photovoltaic module in the structure of an already existing street lamp can lead to a considerable drop in the energy efficiency of the generator or a penalization of the aesthetic appearance of the ensemble. For example, a photovoltaic module connected for constructional reasons in a vertical position up against the lamp post leads to a loss of energy efficiency of approximately 70% of the yearly maximum obtainable with a reclined position according to the optimal angle of tilt, which, at Mediterranean latitudes, is approximately 30° with respect to the horizontal plane. The effort to provide the photovoltaic panel with the inclination and orientation suitable for optimization of the energy efficiency entails its installation on the street lamp
by means of a metal framework set in cantilever fashion or at the top of the lamp post, which is designed to receive said panel, with a consequent considerable increase in terms of overall dimensions, costs of construction, and visual impact. In particular, frequently the orientation of the panel does not coincide with that of the street lamp, with the result that the maximum overall dimensions of the lighting system increase, bestowing upon a decorative urban or residential element - which ought to be almost imperceptible to view - a visual impact that is by no means negligible.
On the basis of what has been set forth above, known photovoltaic devices - particularly for lighting in sensitive contexts - present the major drawback of not reconciling in a satisfactory way the need to use extensive solar panels with an overall structure that presents limited overall dimensions and costs, together with a low visual impact. Summary of the invention
Consequently, the technical problem tackled and solved by the present invention is to provide a lighting device capable of overcoming the drawbacks mentioned above with reference to the known art. Said problem is solved by a device according to Claim 1.
The preferred characteristics of the invention outlined above are specified in the subordinate claims depending upon Claim 1. The invention affords the advantage of an extremely low visual impact, as well as small
dimensions and low production costs.
The device according to the invention may be suitably obtained with a transparent structure that is able to sustain its own energy requirement by being supplied by photovoltaic modules or to produce an excess of electrical energy that can be fed back into the electrical distribution network or into purposely provided energy-accumulation means, such as electrical batteries . Non-limiting examples of spheres of application of the present invention are the lighting of protected archaeological or cultural sites, and areas of scenic or natural beauty without electrification, residential and urban areas with high energy efficiency (according to the European Directive 2002/91/CE) . Brief description of the figures
Further advantages, as well as characteristics and modalities of use of the present invention, will emerge clearly from the ensuing detailed description of a preferred embodiment thereof, presented by way of non- limiting example, with reference to the figures of the attached plates of drawings, in which:
Figure 1 shows a perspective view of a multifunctional photovoltaic street lamp with low visual impact according to a first embodiment of the invention, set alongside an example of embodiment of the known art;
- Figure 2 shows a perspective view from beneath of an illuminating body of the street lamp of Figure 1; - Figure 3 shows a perspective view from above of the illuminating body of Figure 2;
- Figure 4 shows in greater detail, in top plan view, the photovoltaic cover of the street lamp of Figure 1;
- Figure 5 shows, in exploded perspective view, the structure of the illuminating body of Figures 2 and
Figure 6A shows a partially cross-sectional perspective view of a light bulb present within of the illuminating body of Figures 2 and 3; - Figure 6B shows a perspective view of a lighting element adopted as light source in the light bulb of Figure 6A;
- Figure 7 shows a side view of the illuminating body of Figures 2 and 3 highlighted in which is the system for measuring the angle of inclination or tilt of said illuminating body with respect to the plane of the horizon;
Figure 8 shows a partially cross-sectional perspective view of a variant embodiment of the photovoltaic street lamp of Figure 1, in which the static voltage-conversion system and the accumulators are arranged in a housing on site;
Figure 9 represents in a partially cross- sectional perspective view a detail of the mechanical anchorage of the light bulb to the frame of the illuminating body of Figure 5;
Figure 10 shows a perspective view of a mechanized joint with two degrees of freedom designed to orient the illuminating body of the street lamp of Figure 1 according to a variant embodiment; and
- Figure 11 illustrates by way of example the
electrical diagram of a photovoltaic lighting system forming an "isolated" system or a "mains-connected" system of the street lamp of Figure 1.
Detailed description of preferred embodiments of the invention
With initial reference to Figures 1 and 2, a photovoltaic lighting device according to a first embodiment of the invention is designated as a whole by 1. The device 1 is in the form of street lamp, comprising an illuminating body 2 supported on a lamp post or stem 7 at a top end thereof.
As illustrated in greater detail in Figure 2, the illuminating body 2 is made up of two elements, each shaped substantially like a convex half-shell with polyhedral profile, and in particular a top .half-shell 3 and a bottom half-shell 5. Said half-shells 3 and 5 are set alongside one another and arranged with opposed convexities, in such a way as to define between them an internal compartment 35 of the illuminating body 2. The half-shells 3 and 5 thus define, respectively, the top outer surface and the bottom outer surface of the illuminating body 2.
In particular, in the present example the half- shells 3 and 5 each have five faces shaped substantially like an equilateral triangle or isosceles trapezium and a substantially pyramidal structure. The mutual arrangement is moreover such that the faces of the one are set staggered with respect to those of the other, and in particular that each vertex of the pentagonal base of the bottom half-shell 5 (see, for example, the vertex 50 in Figure 2) impinges upon an
intermediate portion of a base side of a respective face of the top half-shell 3 (in the example considered, the face 30) .
In addition, the base of the bottom half-shell 5 is inscribed in the base of the top half-shell 3 in such a way that - as has just been mentioned - the vertices of the base of the first impinge upon the sides of the base of the second.
With reference also to Figure 3, each of the two half-shells 3 and 5 has its faces formed by panels, designated by 11 for the top half-shell 3 and by 13 for the bottom one 5. The panels 11 of the top half-shell 3 are triangular in shape and consist of photovoltaic panels with a high degree of transparency. In a preferred embodiment, said photovoltaic panels are formed by means of a double triangular plate of glass, set at the centre of which are the photovoltaic cells 21 of a substantially square shape, with a maximum cover of the surface of the corresponding face that preferably does not exceed approximately 44% and that in any case is preferably comprised in a range of approximately 20-90%.
The panels 13 of the bottom half-shell 5 are substantially shaped like an isosceles trapezium and are made of thin plates of opalescent material, such as satin-finish glass or Plexiglas or translucent coloured plastic.
Figure 5 shows a framework 17 of the illuminating body 2, the framework 17 of which is common for the top half-shell 3 and for the bottom half-shell 5. Mounted on the framework 17 are the aforesaid panels 11 and 13
of the illuminating body 2.
The framework 17 is, for example, a metal structural framework and connects, by means of five first uprights 19 (these corresponding to the side edges of the pyramidal structure that forms the top half-shell 5) , a central flange 23 to a larger pentagonal frame 21, the lie of which is parallel to that of the flange 23. The uprights 19 branch off at equal distances apart from the flange 23 and intercept the frame 21 in the midpoint of its sides. Starting from the pentagonal frame 21, and in particular from the midpoint of its sides, there branch off, in a direction substantially opposite to that of the first uprights 19, another five uprights 25 that connect up again to a smaller pentagonal frame 20, the lie of which is on the opposite side to the flange 23 with respect to that of the first frame 21. The sides of the smaller frame 20 are moreover parallel to those of the larger frame 21. During installation, each photovoltaic panel 11 is inserted through the base in a groove purposely provided on the outer part of a respective side of the larger frame 21 and secured to the framework 17 by the proximal part of the panel bearing upon the side of the smaller frame 20. Two threaded elements 27, which engage through holes 26 close to the vertex of the panel 11, grip on corresponding threaded seats present on the side of the smaller frame 20.
The opalescent panels 13 are instead secured to the framework 17 along their oblique sides, through threaded elements that grip on contrast brackets 191 of
the first uprights 19.
Branching off from the central flange 23 are a further five third uprights 28, arranged on the inside of the uprights 19 and welded approximately in the middle to the profile 25. Said internal uprights 28 support, by means of L-shaped brackets 281 welded thereto, a light bulb 9 of the body 2 between the half- shells 3 and 5, as illustrated in detail in Figure 9.
With reference to Figure 6A, the light bulb 9 is made up of two pyramidal caps with pentagonal base 15 and 16, set alongside and opposite one another at the bases so as to define an inner compartment.
Preferably, the caps 15 and 16 are made of metal plate with mirror-finish surface, and, as mentioned previously, are coupled to one another at the respective mating base perimeters. Arranged on the bottom pyramidal cap 16, in a position corresponding to the triangular faces, are lighting elements 8, preferably at least one for each face. In a preferred embodiment, the lighting elements 8 are made up of LED sources .
Figure 6B shows a particular view of one of said lighting elements 8, in which arranged on a disk-shaped support 18 are three LEDs 14. To return to Figure 6A, housed inside the light bulb 9 is a static voltage converter 10, which is able to adapt the voltage of the photovoltaic panels 11 to the voltage of purposely provided accumulators, which can also be housed inside to the light bulb 9. In an preferred embodiment, represented in Figure 8, the static voltage-conversion circuit 10 is housed,
together with the aforementioned accumulators, in this case designated by 291, on the site of the lamp post 1, in a well 29.
The cable 12 of Figure 6A then functions as connection cable between the devices 10 and 28 of Figure 8 present in situ and the lighting elements 8.
In the case where all the electrical devices are confined within the light bulb 9, the cable 12 then makes the connection of the system to the public electrical network passing through the cavity of the lamp post 7, as illustrated in Figure 9.
As highlighted more clearly in Figure 7, the illuminating body 2 is mounted on the lamp post 7 in a position corresponding to the vertex of the bottom half-shell 5 in such a way as to present a predetermined angle of tilt with respect to the lamp post itself and hence to the line of the horizon.
On average, it is possible to provide the photovoltaic panels 11 of the element 3 with the preferential orientation to achieve maximum energy efficiency. At the latitude of central Italy, this is, for example, an orientation of the entire illuminating body 2 southwards with an angle of tilt of 30° with respect to the horizontal plane, as indicated in Figure 7. Consequently, it can never happen, in the embodiment according to the present invention, unlike the inventions according to the known art, that the illuminating body and the photovoltaic panel diverge having different orientations. Said inventive measure consequently prevents the possibility for the street lamp to assume, according to the different
installations, overall dimensions ranging between a minimum value and a maximum value .
The adoption then of a mechanized system of actuation of the angle of tilt and of azimuth, as illustrated for example in the variant of Figure 10, through a motor-driven joint 60 with two degrees of freedom, enables optimization of the energy efficiency of the system on a daily basis. Said application has a positive repercussion also as regards night-time lighting, enabling the use of a motor-driven system also for orienting the illuminating body 2 according to the direction that is 'most suitable for the need, which does not necessarily coincide with the daytime direction. In particular, the tilt angle of the lie of the base surfaces of the half-shells with respect to the horizon can be comprised between 20° and 40° and the angle of deviation of the projection on the horizontal plane of the normal to the lie of the base surfaces of the shells with respect to the north can be comprised between 135° and 225°.
The structure of the invention so far described highlights the high mechanical and functional integration of the different parts of the system, aimed at achieving both a low visual impact and reduced overall dimensions and low costs.
In particular, the integration of the photovoltaic panels 11 in the cover of the illuminating body 2 prevents the need to adopt additional structures, such as metal structural frameworks, designed to support the electrical-generating elements. This consequently
rationalizes the number of parts that make up the device, at the same time bestowing thereon simplicity and ease of production.
The adoption then of high-transparency photovoltaic panels 11 has the purpose of allowing filtration, in daylight hours, of a portion of the sunlight through the illuminating body 2, a portion that undergoes refraction on the opalescent panels 13 of Figure 2 and re-emerges from the bottom part of the street lamp. This phenomenon of transparency renders the illuminating body 2, which constitutes in principle the most voluminous part of the lighting device, almost as transparent as air to photopic vision.
Also in night-time use of the invention, the panels 13 perform a function of total refraction of the light emitted by the LED sources 8. The result is a diffused light, suitable for residential and urban lighting, which bestows upon the panels 13 a uniform luminance, such as to cause the overlying photovoltaic cover 3 to disappear by contrast. The scotopic visual result is consequently the sensation of an illuminating body 2 at the top of the lamp post that is much smaller than it really is.
Described hereinafter with reference to Figure 11 are the modalities of electrical operation of the multifunctional photovoltaic street lamp with low visual impact.
Exposure of the panels 11 to daylight causes in each of them generation of a d.c. electromotive force. According to the series-parallel connection of the electrical terminals of the panels 11, by arranging the
electromotive forces so that they present always the same direction, it is possible to generate a photovoltaic potential difference that is certainly not lower than the voltage of a single cell but in general is not adequate either for the load or for the accumulators. For this reason, in a static-conversion system 10, represented' schematically in Figure 8, with reference in the first place to operation of the system 1 isolated from the electrical distribution network, there may be noted downstream of the series-parallel of the photovoltaic panels a DC/DC voltage converter 30, which adapts the d.c. voltage Up to the level of the battery voltage UBatt present on the link. The voltage converter 30 contains, according to the type of accumulator used for the buffer function on the link and to the mode of charge, a regulator circuit with the function of battery charger. For a lead accumulator, for example, it is the circuit 30 that adapts the d.c. voltage Up to the level of the battery voltage UBatt present on the link. For a lead/gel accumulator, for example, the circuit 30 envisages a regulator circuit capable ' of carrying out initially charging of the battery with a current decreasing as a function of the voltage; subsequently, once a certain typical value of the battery charging voltage depending upon the temperature (typically 2.4 V per cell at 300C for lead/gel accumulators) is exceeded, the circuit proceeds with charging at a constant current for a preset time. Also the battery voltage ϋBatt may not be adequate for supplying the series-parallel connection of the lighting elements 8 of Figure 5. For this
reason, located downstream of the battery 35 is another DC/DC converter 40 that can function also as voltage stabilizer. If the photovoltaic system in question is, instead, connected to the public electrical distribution network, then the circuit of Figure 11 also contemplates the blocks 45 and 50. The first block represents a static DC/DC converter 45; the- second represents a static DC/AC inverter 50. The converter 45 basically raises the battery voltage UBatt to a level UL necessary on the link to produce at output from to the inverter 50 a three-phase system of voltages of a given effective value. Generally, for an effective value of the a. c. star-connection voltage of the three-phase system equal to URMS, it is necessary to establish a d.c. voltage UL on the link of the inverter 50 that is characteristic of the individual type of inverter. An electrical conversion system connected to the public distribution mains, as has just been described, enables the device according to the present invention not only to supply the lighting elements 8, but also to feed back a portion of the energy drawn from the solar radiation into the network in the form of electricity. In this perspective, the invention can perform two tasks in parallel: that of illuminating the area around it, thus performing its specific task, and that of producing electrical energy to be fed back into the mains network for other purposes different from that of lighting. The present invention is defined as "multifunctional" because it constitutes an effective functional element (street lamp) that provides a decorative amenity (with low visual impact) capable of
integrating or contributing to the supply of electrical energy in the site where it is used.
The present invention has so far been described with reference to preferred embodiments thereof. It is to be understood that there may exist other embodiments that come under the same inventive idea, all falling within the sphere of protection of the claims set forth hereinafter.