WO2017178989A1

WO2017178989A1 - Holographic film of particular application in photovoltaic panels, in solar thermal panels and in solar light diffusion panels

Info

Publication number: WO2017178989A1
Application number: PCT/IB2017/052118
Authority: WO
Inventors: Raul Maria Orlandi; Mario Vismara; Maurizio RUBINO
Original assignee: Goal S.R.L.
Priority date: 2016-04-13
Filing date: 2017-04-12
Publication date: 2017-10-19
Also published as: ITUA20162561A1

Abstract

The holographic film is made of transparent material such as polyester material and is characterized in that it implements at its interior one or more holographic lenses, each consisting of a myriad of holographic microlenses of infinitesimal size, of the order of a few microns, each microlens being adapted to converge the light rays of the same wavelength refracted thereby in a predetermined focus common to all microlenses.

Description

HOLOGRAPHIC FILM OF PARTICULAR APPLICATION IN PHOTOVOLTAIC PANELS, IN SOLAR THERMAL PANELS AND IN SOLAR LIGHT DIFFUSION PANELS The present invention relates to a holographic film, of particular application in photovoltaic panels, in solar thermal panels and in solar light diffusion panels.

Holographic technology has long been used also in the field of photovoltaic panels and solar thermal panels. In fact, this technology has the characteristic to create, through the interference of laser light, lenses, prisms, mirrors and optical units without having to "shape" the traditional materials used to produce these optical components. In particular, it allows reproducing on a plastic film, such as a polyester film, holographic lenses whose thickness can reach a minimum size of a few microns. This film can be applied on any kind of organic and inorganic photovoltaic cells, on photovoltaic panels, on solar thermal panels, on lighting sources, on reflective material of the type used in road signs. Holographic technology in fact allows a large number of options in the guiding of light rays, performances that are often not otherwise obtainable. Holographic technology also provides the designer and the researcher with the ability to perform and simultaneously combine several particular performances in an infinite number of combinations. This is made possible by the fact that a hologram is not only able to perform different tasks and carry them out simultaneously but, as a result of a specific design, the same hologram is even able to differentiate its action, in the guide imparted to the rays, selectively on the basis of their characteristics such as their direction and/or their wavelength.

Among the purposes of holographic technology applied to the construction of panels of the type mentioned above there is also to create more efficient and less bulky structures to reduce the ecological impact on the planet .

The object of the present invention is the implementation of holographic films of particular application in the field of photovoltaic panels, solar thermal panels and solar light diffusion panels, having improved features as regards the overall dimensions of the related equipment, increased energetic efficiency and concentration ratios of light thereof.

To this end, the holographic film according to the invention is made of transparent material such as polyester material, and in its essential features, is characterized in that it implements at its interior one or more holographic lenses (lenses that hereinafter are also referred to as "AHPL lenses" [Absolute Holographic Planar Lens] for the sake of brevity), each consisting of a myriad of holographic microlenses of infinitesimal size, of the order of a few microns, each microlens being adapted to converge the light rays of the same wavelength refracted thereby in a predetermined focus common to all microlenses.

The holographic film according to the present invention increases efficiency in environmentally friendly energy sources and minimizes, through its application on thermal and photovoltaic panels, the space and bulks on the ground, maintaining and increasing its energy production power. In fact, using this invention it is possible to make energy conversion modules with high efficiency features while exponentially reducing the overall dimensions. The combination of the holographic film with the volumetric geometry of energy transformation receptors (photovoltaic, solar thermal panels and others) allows creating structures of the planar type with reduced dimensions, while keeping the energy production unchanged and reducing bulk and volume by up to 50%. Moreover, the efficiency of existing photovoltaic plants can be increased up to a production of 30% more with the application of the holographic film alone on photovoltaic panels, generating the static tracker function.

Another fundamental innovative aspect is that with the application of the holographic film according to the present invention on the photovoltaic panel, the need to place the photovoltaic panels facing southwards and with inclination of the inclined modules having inclination bound to latitude no longer exists, but photovoltaic plants can be created in any conditions and any inclination, horizontal, vertical, oblique, on roofs facing Northwards, Southwards, Eastwards, Westwards, as the sun rays are conveyed in the right direction and even tracking the sun statically using the holographic film applied on the module.

A further advantage is the possibility to make the concentrating holographic lenses with electronic E-BEAM lithography, which from the mathematical model allows incising the interferential optical structure to create focusing lenses and light deflectors.

Moreover, the solutions object of the present patent allow guiding and/or concentrating the light beams of light in paths and with concentration ratios of particular utility and interest which were not so far allowed by the prior art.

The present invention allows combining standard photovoltaic panels with photovoltaic panels with partially transparent photovoltaic panels, i.e. glass- glass panels, in a combined structure to create energy volumes in the form of solid geometry of the "TESSERACT" type, having the feature of conveying and trapping solar energy through the application and combination of the holographic film, which by its nature is able to deflect the sun rays concentrating, expanding and compressing them, so as to make them bounce into the photovoltaic panel and the structure that incorporates them, in the form of solid geometry, to create energetic modules which by occupying a surface, for example, of a standard photovoltaic panel, can develop on three dimensions, thereby developing a volume such that with the same surface of the photovoltaic panel positioned either on the ground or on the roof of a building, it creates a solid structure that generates an energy-efficient power 10 times higher than the surface area occupied by the module, as photovoltaic panels can be mounted in a battery, in a vertical position, distant from each other by just 10 centimeters and can receive sunlight by conveying the holographic film applied on the surface of the panels and at the sides of the volumetric solid formed by vertical photovoltaic panels (see examples in Figures 15, 16 and 17) .

The holographic film, as mentioned above, has more functions being able to act as light diverter, light concentrator, light guide, light trap, all these features transferred on the holographic films applied to the single photovoltaic panels, to glass-glass photovoltaic panels, to thermal panels, allow it to be used both in classic configurations of photovoltaic and solar thermal plants and in modular systems in the form of solid geometry as described above.

These and other features of the invention will become more apparent from the following description of non- limiting embodiment examples, made with reference to the accompanying drawings whose figures schematically show :

Fig. 1: an example of elementary module of a holographic lens according to the present invention, showing how the solar rays incident on the respective area converge, whatever their direction, in a fixed focus common to all microlenses belonging to such an area .

Fig. 2: an example of holographic lens according to the present invention obtained by aggregation of multiple elementary modules concentrating their rays in the same focus .

Fig. 3: several possible embodiments of elementary modules and their aggregations making all converge their rays in the same focus.

Figs. 4, 5, 6, and 7: various possibilities of use of AHPL lenses.

Fig. 8: an "AHPL" lens designed into two smaller areas diversified both based on the different wavelengths and on the shape and size of the area.

Fig. 9: an "AHPL" focal lens applied to reflective mirrors to create an "Energy" light concentration, which has the power to act as a solar light stove.

Fig. 10: a section of a window or a glass wall consisting of a double glass and a photovoltaic panel of the "glass to glass" type, in the outer wall of which is placed the holographic film.

Fig. 11: the positioning of photovoltaic cells at the outer edges of the sheet of fig. 10.

Fig. 12: the possibility to reduce the space occupied by photovoltaic cells and how this allows acceptable compromises with aesthetics, in the case of windows and glass walls.

Figures 13 to 17: examples of use of TIR holographic films .

An example of a holographic film which implements a holographic lens therein according to the present invention (lens which, as already mentioned, is also referred to herein as "AHPL lens" also for the sake of brevity), is schematically shown in Fig. 1. The example shows a film M of a transparent material, such as polyester, square in shape (with long side of, for example, 1 cm) , in which a myriad of holographic microlenses were microincised, designed each to converge light rays of a same wavelength, refracted thereby, in a preset focus common to all microlenses. The example shows how light rays RIA1, RIA2, RIA3 having different source direction and incident on a same point E, and light rays RIB1, RIB2, RIB3 having different source direction and incident on another point G converge all after refraction toward the common focus F located at a distance FC (e.g. equal to 0.8 cm) from panel M.

The example in Fig. 1 refers to an elementary form module of an AHPL holographic lens of small size (1 cm²) . However, the holographic lenses according to the present invention may also be very large in size and may even consist of multiple modules. In the case of multiple modules, depending on the desired function, the modules may be designed to have a single common focus when it is desired to converge the rays in one focus, or the modules may be designed to convey the rays in different directions according to particular projects.

Figure 2 shows an example of AHPL lens obtained by the aggregation of a series of elementary modules such as those in Fig. 1, in which the incident rays are all directed to a single focus regardless of their origin and the module on which the ray incides.

The holographic lens modules according to the present invention and their aggregation modality do not necessarily have the shapes of Fig. 1 and Fig. 2. In fact, they may be made in other shapes, as shown in Figure 3, which shows various possible shapes of elementary modules (in the shape of a square, rectangle, hexagon, triangle, rhombus ... ) and their aggregations .

Fig. 4 shows an example of use of the infinity focus holographic film as a lighting means to deviate the sunlight in architectural structures such as halls, hotels, etc. that have skylights for natural lighting. Fig. 5 shows a solution of the following invention in which a transparent sheet with an infinity focus holographic film applied thereon is used to send the rays belonging to two wavelength bands in different directions .

Fig. 6 shows a preferred use of the following invention in which a sheet having an infinity focus holographic planar holographic lens is used to increase the amount of light that is sent to a traditional solar panel.

Fig. 7 shows a possible use of "AHPL" holographic lenses, in particular situations, such as porches and greenhouses, and shows possible positions of the optical focuses generated by the holographic lenses, even different for light frequencies that are separated by the holographic film affected by the sun rays.

Fig. 8 shows the case of an AHPL lens designed to concentrate sun rays into two smaller areas differentiated both by the different wavelength, and by the shape and size of the area; in this example, the rays are concentrated by the modules in specific directions differentiated both by direction and by belonging to different wavelength bands; it is noted that as the areas have non-infinitesimal size, it is not necessary that the focuses lie on the same plane of the areas to be reached, and that they can be relatively indifferently spaced in excess or defect of distance from the plane itself.

It is noted that it is also possible to make a deflection of the cone of rays produced by the AHPL lens simply with a mirror; in this case, the focus will clearly be in specular position to the natural focus: this useful preferred application is exemplified in Figure 9, which shows the possibility of using a sheet with AHPL lens and a mirror to converge the refracted rays from the bottom upwards on a fire/stove and thus cook thanks to the sole sun rays. In other applications, the concentration of rays achieved with the AHPL lenses allows the miniaturization of the thermal and photovoltaic receptors .

All this is achieved with the aid of a simple sheet of glass (or other transparent material) which incorporates an AHPL hologram.

A limit to using large AHPL lenses as such as sun rays concentrators may be to have to accept distances commensurate with the size of the lens between the focus and the lens plane and have to keep the cone of space between focus and lens clear of any interference, a situation that is not always acceptable and/or feasible. For use in photovoltaics , a non-intuitive solution to this limitation was found by us in the combination of AHPL lenses with the TIR (Total Internal Reflection) technology.

In fact, the phenomenon of TIR is especially valuable when ones want to direct the light beam with high efficiency and/or concentrate light; in fact, unlike with mirrors where at each reflection, a non- insignificant portion of the incident light is absorbed by the metal that makes up the mirror, in the case of TIR the totality of light radiation is reflected and the number of possible reflections/rebounds is almost unlimited. This is shown for example in the transmission of light beam in optical fibers, which takes place for several kilometers and where the reduction of the intensity of the light beams transmitted is a phenomenon exclusively related to the absorption index of medium in which light propagates. It is clear then how very interesting is, with reference to applications in the photovoltaic sector, to have the possibility to take advantage of this phenomenon .

In fact, the photovoltaic panel in its structure is composed of the protective glass or other transparent material that acts as a trap of light when the holographic film that contains the holographic lenses incised therein is applied on its surface and/or within it.

As regards the combination of the AHPL lenses with the TIR technology, we observed that the ability to concentrate the light radiation in small well delimited areas, corresponding to the focuses of the AHPL planar holographic lenses, it can be highly advantageously used to make the use of the TIR technique in the photovoltaic field much more efficient.

In fact, the fact that the hologram for the introduction in TIR of the rays concentrated by the AHPL planar lenses may have very small dimensions entails a consequent corresponding reduction of the probabilities offered to the ray, once introduced in its path in TIR, to encounter another area bearing the hologram that, in accordance with the law of reversibility of optical phenomena, would constitute an escape window. Transmissions in TIR are thus possible with much higher light ray concentration ratios than those allowed by the actual prior art, and this also paves the way for further new TIR technology insights in photovoltaics and new ways of using the same as illustrated hereinafter.

The possibility to have higher concentration ratios of light in TIR translates into a first general and important option, always usable in all of the possible applications of the invention, that is, to significantly reduce the size of photovoltaic cells. This can be exploited and valued for various purposes and reasons, for example for the resulting reduction in the costs of the cells, or to improve the efficiency of photovoltaic cells with increasing concentration of the incident rays, or for the economic affordability of better performing but more expensive cells, or for the simplification and the lower cost of electrical connections, or for better accessibility that it can provide to the so-called "roll to roll" technology, or to reduce the visual and/or architectural impact, etc. Moreover, having noted that working as described above greatly reduces the possibility/probability of escape and that indeed the rays entered may travel in TIR without significant loss/leakage along the paths, the following additional opportunities are allowed:

a)

The opportunity to place the photovoltaic cells at the edges of the sheet (see Fig. 10) . It is in fact advantageous to gather the light rays at the edges of the sheet exposed to solar radiation for a variety of reasons including for instance: the surface of the photovoltaic cell is smaller and therefore less expensive, and thus cells built with high efficient but expensive materials become more accessible; in this situation, the rays are focused and the photovoltaic cells have an efficiency that increases with increasing concentration of light; the positioning of the cells on the edge is also advantageous from the aesthetic viewpoint. In fact, the support sheet (glass or other material) remains free from the presence of unsightly opaque cells and the holographic films can be made with materials that allow considerable transparency; therefore, the proposed solution allows creating solar panels that have no architectural impact and that can be used for example for glass panels and windows;

Figure 10 shows a preferred solution of the present invention, i.e. it shows the section of a window or a glass wall or a covering sheet of the outer surface of a building consisting of a double glazing, or of a photovoltaic panel; on the inner wall of the outer glass is placed the film with the AHPL lenses (or the AHPL holography is reproduced by any other means described) ; on the inner side of the second glass are centered at the focuses produced by the AHPL lenses the small areas in which the holograms are for the introduction in TIR of the rays concentrated by the AHPL lenses; these second holograms will be arranged on a second film or alternatively printed on the inner sheet itself or, as a third alternative if one opts for a reflective hologram, the hologram will be placed on the outer side of the second sheet and will have an aesthetically pleasing shape and design; the size of the areas covered by the second hologram will be according to the concentration desired and the accuracy capacity achievable with the assembly technology. It is noted that it is not necessary to place the second holography exactly at the focal distance, but it is preferable to be a little out of focus by defect or excess of axial distance from the focus.

Figure 11 shows the positioning of the photovoltaic cells at the outer edges of the sheet; in case of rectangular sheets, the cells may be on a unique edge, and in this case the opposite edge will be mirror- treated or will bear glued a high-reflectance surface while the sides alongside that containing the cell will have a mirror edge or will bear glued a high- reflectance surface, preferably with very light undulations. Likewise, the cells may be placed on two side by side or opposite edges, or on three edges or even on all four edges.

If holograms have been selected that have the ability to enter in TIR the rays in different directions depending on the ray wavelength beam, the cells at the edges will be selected to optimize the conversion efficiency into electric energy of the incident photons on each edge.

Because of the partial transparency of the holograms which never reflect the totality of the incident light, the sheets thus constructed will maintain a moderate residual transparency value that will be appreciated for glass walls and windows.

In cases, instead, of use in photovoltaic panels in which one is looking for the optimization of energy recovery, the device described above may be used simply as outer sheet of traditional photovoltaic panels: the cells of the latter will provide a further energy recovery. Or the surface opposite to that exposed to the sun will be provided with a second reflective TIR hologram or anyway a possibly irregular reflective surface .

b)

If one does not choose to place the cells at the outer edges of the sheet, there is still the advantage that one no longer needs to enter the rays in TIR with a few degree angle to reduce the number of bounces/reflections as provided by the previous technology; therefore, the use of metal-based cells in crystalline phase, e.g. mono or pluricrystalline silicon, which are very efficient but reflecting most of the incident rays when they incide with small angles of incidence in relation to their surface, is not penalized any more. It is noted how also in this case (see Fig. 12), the space occupied by the cells can be reduced to very modest dimensions and how this allows acceptable compromises with aesthetics in the case of glass panels and windows.

Figure 12 shows an example of the application of the present invention on a window (or a glass wall or a wall panel of the outer surface of a building consisting of a double glass, or a photovoltaic panel) with the arrangement of the photovoltaic cells in the so-called glass-glass position, i.e. arranged between two sheets of glass and between them completely buried with a sealing material, usually consisting of EVA.

In this case, the small areas bearing the holograms for entering in TIR the rays concentrated by the outermost hologram will be centered and preferably positioned on the inner part of the second glass, or between glass and glass, also buried in the sealing material, on the inner surface of the third glass (still at the focuses produced by the lenses of the outer hologram; these second holograms will be arranged on a second film or alternatively printed on the sheet themselves; the size of the areas covered by the second hologram will be a function of the desired concentration and accuracy capacity reachable by the assembly technology. It is noted that it is not necessary to place holography for entering in TIR exactly at the focal distance, but it is preferable to be a little out of focus by defect or excess of axial distance from the focus.

It is noted that unlike what happens in the prior art, it is no longer necessary for the cells to cover at least 40% of the surface of the sheet, allowing a sort of transparency, but creating insurmountable aesthetic problems when it comes to windows or glass wall.

Due to the much greater possibility of concentration obtainable with the devices made according to the present invention, the cell surface may be significantly reduced, allowing solutions to the problem of aesthetic impact.

Moreover, a much longer path being allowed according to the present invention without risk of escape of the ray entered into TIR, it will be possible to use greater angles that allow the use of materials such as microcrystalline silicon cells that reflect the incident rays with angles smaller than their surface; moreover, double-sided cells can also advantageously be used since light equally reaches the cells on both sides and finally, in view of the reduced surface, using more expensive but more efficient materials for the cells becomes more accessible. Finally, it is noted that reducing the cell size automatically leads to an increase in the concentration of the incident light per surface unit thereof and that this has a positive effect on the efficiency of photovoltaic cells. What said in the previous paragraph also applies as regards the treatment of the edges and the possible energy recovery in case this solution is adopted for the production of photovoltaic panels:

Figure 13 shows how, with the precautions described in the present description, by positioning a small portion of holographic lenses to produce the TIR effect, it is possible to obtain the further concentration of incident solar radiations.

Fig. 14 shows how the incident radiation of the sun, which is guided and recovered on the more or less square end edge of the profile, can further increase the concentration of the solar radiation. In particular, the photovoltaic cells can be accommodated in a component in which the double-sided cell is positioned at 45° with respect to the two sides of the main sheet, so as to interact with the light coming from the sides of the sheet.

Fig. 15 schematically shows the volumetric structure of the module consisting of a battery of photovoltaic panels of the glass-to-glass type with the "TIR" holographic film encapsulated therein.

Fig. 16 shows a single photovoltaic panel module of the glass-to-glass type containing the cells of double- sided monocrystalline silicon and the holographic film that generates the "TIR" effect therein.

Fig. 17 shows a side view of the battery of photovoltaic panels of the glass-to-glass type with "TIR" functions, placed within the photovoltaic volumetric module combined with the panel placed horizontally on the volumetric structure that focuses the sun rays within the volumetric structure by directing the sun rays on the inner walls of the volumetric module, by means of the multichannel holographic film that serves as a multi directional sunlight roof.

The following advantages of the holographic film according to the present invention are apparent from the above description:

a) The AHPL holographic lenses have the ability to concentrate the incident rays into focuses, with the particularity of being able to always maintain, throughout the day and regardless of the changing seasons (except the tiny variations permitted by the hologram) the position of such focuses fixed and unchanged. In other words, the focuses of such holographic lenses do not undergo the displacements that the effect of the Earth's rotation causes, nor those related to the changing seasons, displacements that, on the contrary, are inevitably observed when using ordinary lenses. Not only that, but unlike ordinary lenses, the holographic lenses object of the present patent preferably have the features of being designed to capture and concentrate in the same focus not only directed and coaxial solar rays but also diffused radiation which, especially on cloudy days or with smog, is very significant and sometimes prevalent. b) Another property of the AHPL lenses is be designed with focuses also completely misaligned (even by more than 85°) with respect to the perpendicular of the plane on which the hologram lies.

c) A further property of these lenses is that to refract the incident rays in various different focuses also having different distances from the plane on which the hologram lies and/or placed along axes with mutually different orientations with respect to the perpendicular of the center of gravity of the surface of the hologram, and to send the refracted rays to each focus selectively based on their own wavelength; in other words, they may be designed to generate various focuses in different positions for different wave frequency ranges (see for example figs. 7/9) .

d) Another property of these lenses is that to have the infinity focus; in this case, all the myriad of microscopic holographic lenses that make up the AHPL lens refract the incident rays all with the same inclination with respect to the plane of the lens, irrespective of the angle of incidence of the rays that incide thereon; also in this case, the direction of the refracted rays may also differ by many degrees (even by more than 85°) with respect to the perpendicular of the plane on which the hologram lies, and the refracted rays may be selectively directed with different angles depending on their belonging to different wavelength ranges .

e) The holographic film according to the invention, due to the light concentration ability, allows the miniaturization and standardization of the photovoltaic cells and electrical connections. This feature is particularly effective when the photovoltaic cell is double sided and positioned at 45° with respect to the two sides of the main sheet.

Claims

1. Holographic film, of particular application in photovoltaic panels, thermal-solar panels and solar light diffusion panels, made of transparent material such as polyester material, characterized in that it implements at its interior one or more holographic lenses, each consisting of a myriad of holographic microlenses of infinitesimal size, of the order of a few microns, each microlens being adapted to converge the light rays of the same wavelength refracted thereby in a predetermined focus common to all microlenses.

2. Holographic film according to claim 1, characterized in that the holographic lenses are designed with focuses that are also fully offset, with respect to the perpendicular of the plane where the lenticular hologram lies.

3. Holographic film according to claim 1, characterized in that the holographic lenses are designed to refract the incident rays in multiple different focuses also having different distances from the plane where the hologram lies, and placed along axes having mutually different orientations, with respect to the perpendicular to the center of gravity of the surface of the hologram, and to selectively send the refracted rays to each focus based on their own wavelength.

4. Holographic film according to claim 1, characterized in that the holographic lenses are designed so that, according to the sensitivity of the films used to make the hologram and/or of the type of dichroic metallization combined with the holographic film, the percentage of incident rays refracted according to the interference structure provided by the hologram itself and the percentage that is transmitted unaltered are determined .

5. Holographic film according to claim 1, characterized in that the holographic lenses direct the refracted rays having a different frequency of light wave in different focuses and directions, even opposite each other .

6. Holographic film according to claim 1, characterized in that it entirely or partially covers panels for converting solar energy into other forms of energy, such as photovoltaic panels or solar thermal panels or solar light diffusion panels.

7. Holographic film according to claim 6, characterized in that it is applied in integrated systems for the volumetric construction of thermal and photovoltaic modules powered by solar energy in order to increase the thermal or electric energy produced.

8. Holographic film according to claim 6, characterized in that it is combined with photovoltaic modules in order to collect the light at the edges of holographic film for transferring the energy power of the sun directly to the edges of the transparent photovoltaic panel, which has silicon cells placed on the sides of the panel itself.

9. Holographic film according to claim 1, characterized in that the holographic lenses are generated by means of ELECTRON-BEAM lithography, by calculating with a mathematical model the optical parameters necessary to generate the multichannel holograms for the composition of the different combinations of holographic lenses, to be applied on the volumetric module composed from the assembly of photovoltaic and/or thermal panels.