WO2019041028A1

WO2019041028A1 - Sunlight forwarding system and use thereof

Info

Publication number: WO2019041028A1
Application number: PCT/CA2018/051027
Authority: WO
Inventors: Elton SOARES DE LIMA FILHO; Steeve Morency; Younès MESSADDEQ
Original assignee: UNIVERSITé LAVAL
Priority date: 2017-08-29
Filing date: 2018-08-27
Publication date: 2019-03-07
Also published as: MA48427B1; MA48427A1

Abstract

There is described a sunlight forwarding system generally having a sunlight concentrator; a plurality of optical fibers extending between a receiving end and a transmitting end, the receiving end being optically coupled to the sunlight concentrator, the plurality of optical fibers having end facets being bundled to one another at the receiving end in a manner that the end facets of the plurality of optical fibers collectively form a surface; a lens optically coupled to the surface formed by the end facets of the plurality of optical fibers at the receiving end; and a structure supporting the lens with respect to the plurality of optical fibers.

Description

SUNLIGHT FORWARDING SYSTEM AND USE THEREOF

FIELD

[0001 ] The improvements generally relate to the field of light concentrators and more particularly to the field of sunlight concentrators. BACKGROUND

[0002] It is known that the sun projects an important amount of solar power, in the form of sunlight, towards earth. As the portion of the solar power that reaches earth's surface is substantial, harnessing only a little amount of that solar power in day-to-day activities would yield not only environmental but also economic benefits. For instance, converting some of the solar power into electricity, e.g., using photovoltaic cells, could reduce the society's dependence on petroleum products. Although existing ways of harnessing sunlight are satisfactory to a certain degree, there remains room for improvement.

SUMMARY

[0003] Some types of photovoltaic cells can require sunlight concentrators to focus the sunlight onto them to increase their conversion efficiency. However, the amount of sunlight that is focussed onto the photovoltaic cells should generally be limited in optical power since electrical components of the photovoltaic cells could suffer from too much sunlight. Consequently, the inventors found that there was a need in providing a sunlight forwarding system configured to transmit a sunlight beam for higher power applications.

[0004] In accordance with one aspect, there is provided a sunlight forwarding system comprising: a sunlight concentrator; a plurality of optical fibers extending between a receiving end and a transmitting end, the receiving end being optically coupled to the sunlight concentrator, the plurality of optical fibers having end facets being bundled to one another at the receiving end in a manner that the end facets of the plurality of optical fibers collectively form a surface; a lens optically coupled to the surface formed by the end facets of the plurality of optical fibers at the receiving end; and a structure supporting the lens with respect to the plurality of optical fibers. In this way, when the sunlight concentrator is oriented towards sunlight, the lens can receive sunlight from the sunlight concentrator and focus the received sunlight onto the surface thereby injecting sunlight in at least some of the plurality of optical fibers via corresponding end facets, allowing the at least some of the plurality of optical fibers to guide the injected sunlight from the receiving end to the transmitting end, for transmitting a sunlight beam.

[0005] In accordance with another aspect, there is provided a sunlight forwarding system comprising: a sunlight concentrator; a plurality of optical fibers extending between a receiving end and a transmitting end, the receiving end being optically coupled to the sunlight concentrator, the plurality of optical fibers having end facets being bundled to one another at the receiving end in a manner that the end facets of the plurality of optical fibers collectively form a surface; a lens optically coupled to the surface formed by the end facets of the plurality of optical fibers at the receiving end; and a structure supporting the lens with respect to the plurality of optical fibers.

[0006] Accordingly, the inventors found that the sunlight forwarding system described herein can be used to provide a sunlight beam having a sufficient power for high power applications and/or any other suitable applications.

[0007] Many further features and combinations thereof concerning the present improvements will appear to those skilled in the art following a reading of the instant disclosure.

DESCRIPTION OF THE FIGURES

[0008] In the figures,

[0009] Fig. 1 is a schematic view of an example of a sunlight forwarding system having three sunlight forwarding units, in accordance with an embodiment;

[0010] Fig. 2 is a sectional view of one of the sunlight forwarding units of Fig. 1 ;

[001 1] Fig. 3 is an enlarged view of the sunlight forwarding unit of Fig. 2;

[0012] Fig. 4 is an oblique view of another example of a sunlight forwarding unit having a structure with a structural sleeve having no corrugation, in accordance with another embodiment;

[0013] Fig. 4A is a graph showing an intensity profile of a sunlight beam transmitted by the sunlight forwarding unit of Fig. 4; [0014] Fig. 5 is an oblique view of another example of a sunlight forwarding unit having a structure with a corrugated structural sleeve, in accordance with another embodiment;

[0015] Fig. 5A is a graph showing an intensity profile of a sunlight beam transmitted by the sunlight forwarding unit of Fig. 5; and [0016] Fig. 6 is an enlarged view of an alternate embodiment of a structural sleeve for a sunlight forwarding unit.

DETAILED DESCRIPTION

[0017] Fig. 1 shows an example of such a sunlight forwarding system 10, in accordance with an embodiment. [0018] As depicted in this example, the sunlight forwarding system 10 has a frame 12 supporting three sunlight forwarding units 14. However, it will be understood that the sunlight forwarding system 10 can have only one, two, and even more than three sunlight forwarding units 14, depending on the embodiment.

[0019] Each sunlight forwarding unit 14 has a sunlight concentrator 16 for concentrating sunlight radiated by the sun where desired, a bundle of optical fibers 18 (hereinafter "the optical fibers 18") extending between a receiving end 20 and a transmitting end 22, and a lens 24.

[0020] More specifically, the receiving end 20 of the plurality of optical fibers 18 is optically coupled to the sunlight concentrator 16 for concentrating and receiving sunlight whereas the transmitting end 22 can be provided where desired to provide a high power sunlight beam 26 for use in high power applications which would have otherwise required a significant amount of costly electricity.

[0021] In this example, the optical fibers 18 of the three sunlight forwarding units 14 are merged and packaged into a single cable 28. In an alternate embodiment, the sunlight forwarding units can have independent cables which are merged only near the transmitting end 22.

[0022] In the illustrated embodiment, the transmitting end 22 is coupled to a processing device 30, in which material can be processed by the high power sunlight beam 26 transmitted at the transmitting end 22. For example, the processing device 30 can be used for disinfecting liquids such as water via distributed photocatalysis, disinfecting animal waste, drying minerals such as phosphate for fertilizers, heating materials such as heating water for destroying copper cyanide contaminants, for 3D manufacturing, for material cutting, for material marking and/or any other suitable material processing application.

[0023] It is envisaged that, in some other embodiments, the sunlight beam 26 can also be used for illuminating buildings, pumping a laser, storing energy via reduction- oxidation reaction or any other suitable high power demanding applications.

[0024] As will be understood, the transmitting end 22 of the optical fibers 18 can be customized for the high power demanding application for which it will be used.

[0025] Fig. 2 shows one of the sunlight forwarding units 14 of Fig. 1. As can be seen, the sunlight concentrator 16 is provided in the form of a reflecting telescope having a primary mirror 32 and a secondary mirror 34. In the illustrated embodiment, the primary mirror 32 and the secondary mirror 34 are configured in a Cassegrain telescope, in which the secondary mirror 34 redirects sunlight along an axis 36 parallel to incoming sunlight 38.

[0026] However, in some other embodiments, the sunlight concentrator 16 can be provided in the form of a reflecting telescope configured in a Newtonian telescope, a Gregorian telescope and the like. In alternate embodiments, the sunlight concentrator 16 can be provided in the form of one or more Fresnel lenses. In alternate embodiments, the sunlight concentrator 16 can have a magnification factor greater than 4000X, preferably greater than 5000X, most preferably greater than 10000X and ideally of 44000X.

[0027] As can be seen in the illustrated embodiment, the optical fibers 18 have end facets 40 which are bundled to one another at the receiving end 20 in a manner that the end facets 40 of the optical fibers 18 collectively form a surface 42.

[0028] In this example, the surface 42 so formed is a planar surface (hereinafter "the planar surface 42"), as the end facets 40 of the optical fibers 18 are cleaved at right angle and aligned in a common plane 44. As illustrated, the planar surface 42 is perpendicular to both an optical axis 46 of the lens 24 and the incoming sunlight 38. Providing the end facets 40 of the optical fibers 18 in the planar surface 42 may simplify the design of the lens 24, which is designed to focus the incoming sunlight 38 onto the end facets 40 of the optical fibers 18.

[0029] However, the surface 42 need not to be planar. For example, the surface 42 formed by the end facets 40 can be positioned so as to form either a concave surface or a convex surface, in which case the lens 24 is designed to focus the incoming sunlight 38 onto the end facets 40 so positioned.

[0030] In this embodiment, the bundle of optical fibers 18 include 470 optical fibers. However, in some other embodiments, the bundle of optical fibers 18 can include more or less than 470 optical fibers. Also, each of the optical fibers 18 is multimode with a diameter of 600 μηι in this example. The diameter of the optical fibers 18 can be larger or smaller than 600 μηι, depending on the number N of optical fibers 18 in the bundle, and on the desired power of the sunlight beam. It is noted that for a given desired power, the larger the diameter of the optical fibers 18, the lesser the number N of optical fibers 18 in the bundle, and the lesser the resulting bundle is flexible, and vice versa. It is also noted that the time required for assembling the sunlight forwarding unit 14 strongly depends on the number N of optical fibers 18 in the bundle.

[0031] In this embodiment, the optical fibers 18 can be made from pure silica. In alternate embodiments, the optical fibers 18 can be microstructured optical fiber or any other suitable type of optical fiber. [0032] In this embodiment, each optical fiber 18 has a low refractive index coating along at least a length thereof providing satisfactory mechanical properties as well as guiding properties for guiding the injected sunlight satisfactorily therealong. Examples of material of such coating can include acrylic, for instance. Such coating is preferably removed along the receiving end 20, thus avoiding the coating to be melted by stray light, i.e., sunlight which is focussed by the lens 24 but not injected into one of the optical fibers 18, if any.

[0033] The lens 24 is optically coupled to the planar surface 42 formed by the end facets 40 of the optical fibers 18 at the receiving end 20. Accordingly, during use, e.g., when the sunlight concentrator 16 is oriented towards the sun, the lens 24 receives the incoming sunlight 38 from the sunlight concentrator 16 and focusses the received sunlight onto the planar surface 42 thereby injecting sunlight in at least some of the optical fibers 18 via corresponding end facets 40. This allows the optical fibers 18 to guide the injected sunlight from the receiving end 20 to the transmitting end 22, for transmitting a sunlight beam elsewhere.

[0034] In this embodiment, the end facets 40 of the optical fibers 18 are fused to one another which can help reduce, or even avoid, the presence of dead zones, i.e., interstices resulting from the bundling of circularly shaped end facets 40. Fusing the end facets 40 of the optical fibers 18 to one another can be performed by rotating the optical fibers 18 about an axis of the bundle while simultaneously heating the end facets 40 using a flame. This can be performed with a glassworking lathe at angular speeds in the order of 10RPM, for instance. The fused end of the optical fibers can then be cut and the fused end facets 40 can be polished so as to form the planar surface 42. Any other suitable process for fusing the end facets 40 to one another can be used.

[0035] Still referring to Fig. 2, the sunlight forwarding unit 14 has a structure 50 which mechanically supports the lens 24 with respect to the sunlight concentrator 16 and/or to the optical fibers 18.

[0036] As shown in the illustrated embodiment, the structure 50 has a structural tube 52 mechanically coupled to the primary mirror 32 and/or to the frame 12 (shown in Fig. 1), and a structural sleeve 54 mechanically coupled inside the structural tube 52. In this example, the structural sleeve 54 has a longitudinally extending cavity 56, inside which the optical fibers 18 of the receiving end 20 run towards the planar surface 42. More specifically, the structural sleeve 54 can enclose, protect and space the optical fibers 18 of the receiving end 20 from one another, especially along their uncoated regions 58.

[0037] As shown, the structural sleeve 54 has a first extremity 60 lying inside the structural tube 52 and a second extremity 62 protruding from the structural tube 52. The lens 24 can be fused to the end facets 40. In this embodiment, the lens 24 is further fused to the second extremity 62 to provide greater structure. As shown, the structural sleeve 54 has a spacer disc 64 mechanically coupled inside the structural sleeve 54. In this embodiment, the spacer disc 64 has a plurality of spaced-apart holes receiving corresponding ones of the optical fibers 18, spacing the optical fibers 18 from one another. The spacer disc 64 may be used to decouple the portion of the optical fibers 18 extending on a first side of the spacer disc 64, between the spacer disc 64 and the second extremity 62, from any mechanical stress imparted to the optical fibers 18 on the other side of the spacer disc 64. Each one of the independent optical fibers 18 can be glued to the spacer disc 64 in a predetermined configuration.

[0038] In this example, there is only one spacer disc 64 positioned in the middle of the structural sleeve 54, although it may be positioned elsewhere, e.g., closer to the first extremity 60 of the structural sleeve 54. In alternate embodiments, there may be more than one spacer disc 64.

[0039] As best seen in Fig. 3, the lens 24 has a face 70 which is in contact with the end facets 40. In this embodiment, the face 70 of the lens 24 can be fused to the end facets 40 of the optical fibers 18 and to the second extremity 62 of the structural sleeve 54 for greater structure. Such construction may seal the second extremity 62 of the structural sleeve 54 and help avoid undesirable particles such as sand to reach the cavity 56 of the structural sleeve 54. Moreover, a portion 72 of the optical fibers 18 adjacent to the end facets 40 may be fused to the interior of the second extremity 62 of the structural sleeve 54 for greater structure. In some embodiments, the lens 24 may have an anti- reflective coating 74, if found suitable in the specific context.

[0040] In some other embodiments, however, the face 70 of the lens 24 can be adhered to the end facets 40 of the optical fibers 18 and to the second extremity 62 of the structural sleeve 54 using an appropriate adhesive. Examples of appropriate adhesive include adhesives which are optically transparent to sunlight and/or resistant to high optical power. In some other embodiments, the lens 24 may be spaced apart from the end facets 40 of the optical fibers 18.

[0041] As illustrated in this embodiment, the structural sleeve 54 is made of an optically guiding material (e.g., glass) and has an end portion 76 tapering towards the second extremity 62. In this way, stray light can be guided inside a thickness 80 of the structural sleeve 54 and away from the optical fibers 18, thus avoiding the stray light to damage the optical fibers 18.

[0042] In this particular example, the end portion 76 has a longitudinal succession of annular corrugations 82 around the end portion 76, causing stray light guided in the thickness 80 to be refracted out of the structural sleeve 54, away from the optical fibers 18, as shown by arrows A. In this embodiment, a succession of three annular corrugations 82 was used. As can be understood, there can be more or less than the three corrugations 82 in some other embodiments.

[0043] Fig. 4 shows an example of a sunlight forwarding unit 1 14 with a structural sleeve 154 having no such corrugation. Fig. 4A shows an example of an intensity profile of the sunlight beam transmitted by the sunlight forwarding unit 1 14. As it can be seen, the intensity profile shows a high intensity region 190 resulting from the sunlight transmitted by the optical fibers 18 at the transmitting end 22, and a low intensity annular region 192 resulting from stray light guided into the thickness 80 of the structural sleeve 154. [0044] In contrast, Fig. 5 shows another example of a sunlight forwarding unit 214 with a structural sleeve 254 having corrugations 282. Fig. 5A shows an example of an intensity profile of the sunlight beam transmitted by the sunlight forwarding unit 214. As can be seen, the intensity profile shows only a high intensity region 290 resulting from the sunlight transmitted by the optical fibers 18 at the transmitting end 22. Accordingly, providing the corrugations 282 can help avoid the low intensity annular region 192 shown in Fig. 4A, which can be beneficial for at least some high power applications.

[0045] Fig. 6 shows an alternate example of a structural sleeve. In this embodiment, the structural sleeve 154 has a short, non-tapering end portion 176 leading to the second extremity 162. Stray light in the thickness of the structural sleeve 154 was found to be suitably extracted by the action of the corrugations 182. The structural sleeve has a broad section 178 extending from the first extremity 160, a tapering section 180, and a narrow section 182 leading to the corrugations 182. In this embodiment, it was preferred to use a spacer disc in the broad section 178, and to maintain an unstripped portion of the optical fibers between the spacer disc and a first portion 184 of the narrow section 182. The diameter of the narrow section 182 can be designed to snugly receive the unstripped portion of the optical fibers in the first portion 184. The optical fibers can be stripped from their acrylic coating between the first portion 184 and the second extremity 162 (and the fused portion/lens). The narrow section 182 can extend along a given length selected in a manner for the solid angle occupied by the optical fibers in the first portion 184 relatively to the second extremity to be sufficiently small for the amount of power stemming from stray light remaining in the first portion to be insufficient to cause damage to the acrylic coating. Moreover, it was found that in a configuration such as shown in Fig. 3, if the length of the stripped portion of the optical fibers was sufficiently long to avoid damage of the acrylic coating (the unstripped portion could extend on roughly 40 mm on a total distance of between 250 and 300 mm between the spacer disc 64 and the second extremity 62 for instance), fusing the end of the optical fibers on a horizontal lathe at about 10 RPM could cause some torsion and warping of the stripped length of the optical fibers, which lead to a manageable, but undesired amount of power loss. It was found that this inconvenience could be alleviated with the configuration shown in Fig. 6. In particular, it was found that having the unstripped portion of the optical fibers held tightly in the first portion 184 of the neck section and having an stripped portion of the optical fibers extending along a length in the order of 150 mm, allowed to lower the amount of torsion in the stripped length, and the acrylic coating in the first portion 184 was found sufficiently durable, likely because the amount of power concentration of stray light in the first portion was below a damaging threshold. It will be understood by persons having ordinary skill in the art that still other alternate embodiments of structural sleeves are possible. As can be understood, the examples described above and illustrated are intended to be exemplary only. For instance, it is envisaged that the structural sleeve can have reinforcing struts longitudinally extending between two or more spacer discs for providing greater structure to the sunlight forwarding unit. In some other embodiments, the stray light can be absorbed or diffused away from the optical fibers using a corresponding absorbent or diffuse material positioned against the exterior surface of the structural sleeve. In alternate embodiments, the structure can include an adhesive adhering the optical fibers to one another along a given portion of the receiving end. Accordingly, the structural tube and the structural sleeve can be omitted. The scope is indicated by the appended claims.

Claims

WHAT IS CLAIMED IS:

1 . A sunlight forwarding system comprising: a sunlight concentrator; a plurality of optical fibers extending between a receiving end and a transmitting end, the receiving end being optically coupled to the sunlight concentrator, the plurality of optical fibers having end facets being bundled to one another at the receiving end in a manner that the end facets of the plurality of optical fibers collectively form a surface; a lens optically coupled to the surface formed by the end facets of the plurality of optical fibers at the receiving end; and a structure supporting the lens with respect to the plurality of optical fibers.

2. The sunlight forwarding system of claim 1 , wherein the structure has a structural sleeve having a longitudinally extending cavity, inside which the plurality of optical fibers runs towards the surface.

3. The sunlight forwarding system of claim 2, wherein the lens is mechanically coupled to an extremity of the structural sleeve.

4. The sunlight forwarding system of claim 2, wherein the structural sleeve has an end portion adjacent the lens, the structural sleeve being made of an optically guiding material, the end portion having a thickness allowing stray light to be guided along the structural sleeve and inside the thickness.

5. The sunlight forwarding system of claim 4, wherein the end portion has at least one corrugations around the end portion, allowing the stray light guided in the thickness to be refracted out of the structural sleeve, away from the plurality of optical fibers.

6. The sunlight forwarding system of claim 2, wherein the structural sleeve has at least one spacer disc mechanically coupled inside the structural sleeve, the spacer disc having a plurality of spaced-apart holes receiving corresponding ones of the plurality of optical fibers, spacing the plurality of optical fibers from one another.

7. The sunlight forwarding system of claim 1 wherein the plurality of optical fibers are packaged in a cable along at least a length of the plurality of optical fibers.

8. The sunlight forwarding system of claim 1 wherein the end facets of the plurality of optical fibers are fused to one another.

9. The sunlight forwarding system of claim 1 wherein the surface formed by the end facets of the plurality of optical fibers is a planar surface, and the planar surface is perpendicular to an optical axis of the lens.

10. The sunlight forwarding system of claim 1 wherein the lens has a face in contact with the end facets.

1 1. The sunlight forwarding system of claim 1 wherein the lens has a face which is fused to the end facets of the plurality of optical fibers.

12. The sunlight forwarding system of claim 1 wherein the sunlight concentrator is configured to provide a magnification factor greater than 4000x.

13. The sunlight forwarding system of claim 1 wherein the plurality of optical fibers are made of pure silica.

14. The sunlight forwarding system of claim 1 wherein the plurality of optical fibers includes more than 400 optical fibers, each optical fiber having a diameter of 600 μηι and being multimode.

15. Use of the sunlight forwarding system of claim 1 in at least one of for processing material, illuminating a building, pumping a laser, and storing energy via reduction- oxidation reaction.