Reflective sheet for solar cells and solar power generation system

Abstract

To provide a reflective sheet for solar cells that exhibits superior reflectivity and can prevent warpage.SOLUTION: Provided is a reflective sheet 10 for solar cells that comprises a first resin film 1, which is a reflective film, a fabric base material 2, and a second resin film 3, in the stated order.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a reflective sheet for solar cells and a photovoltaic power generation system using the same.

Background Art

[0002] In a ground-mounted photovoltaic power generation system, in order to increase the power generation amount, a reflective sheet is laid on the site. Further, in a ground-mounted photovoltaic power generation system, when weeds grow thickly, there is a problem that the power generation efficiency decreases due to the shadow of the weeds. Therefore, in order to prevent the growth of weeds, it is known to lay a weed control sheet on the site. Furthermore, a weed control sheet having reflectivity has also been proposed. (See Patent Document 1)

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As the reflective weed control sheet, a white non-woven fabric and a white woven fabric are known. However, the white non-woven fabric and the white woven fabric have a problem of poor stain resistance. When dirt adheres to the sheet, the reflectivity of the sheet decreases. Further, since the white non-woven fabric and the white woven fabric need to be thickened to increase the strength, there is also a problem of poor workability.

[0005] In addition, as a reflective weed control sheet, a sheet in which a metal foil or a metal vapor deposition film is laminated with a non-woven fabric or a woven fabric is known. However, since the linear expansion coefficients of the metal foil or the metal vapor deposition film and the non-woven fabric or the woven fabric are significantly different, there is a problem that the sheet warps. When the sheet warps, the workability decreases when the sheet is laid on a large site. In addition, in the case of a metal foil or a metal vapor deposition film, since specular reflection becomes strong, depending on the installation angle of the solar cell module, it may be difficult to contribute to the power generation efficiency. In addition, since specular reflection becomes strong, glare occurs, and there is a risk of light damage.

[0006] The present disclosure has been made in view of the above circumstances, and the main object thereof is to provide a reflective sheet for solar cells that has good reflectivity and can suppress warping.

Means for Solving the Problems

[0007] One embodiment of the present disclosure provides a reflective sheet for solar cells having, in this order, a first resin film that is a reflective film, a cloth base material, and a second resin film.

[0008] Another embodiment of the present disclosure provides a photovoltaic power generation system including a solar cell module and a reflective sheet for solar cells laid on a site where the solar cell module is installed, the reflective sheet for solar cells having, in this order from the solar cell module side, a first resin film that is a reflective film, a cloth base material, and a second resin film.

Advantages of the Invention

[0009] The reflective sheet for solar cells of the present disclosure has an effect of having good reflectivity and being able to suppress warping.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0011] Embodiments of the present disclosure will be described below with reference to the drawings and the like. However, the present disclosure can be implemented in many different aspects and is not construed as being limited to the description content of the embodiments exemplified below. Also, for the purpose of making the description clearer, the drawings may schematically represent the width, thickness, shape, etc. of each part compared to the actual form, but this is merely an example and does not limit the interpretation of the present disclosure. Further, in this specification and each drawing, elements that are the same as those described above with respect to the previously presented drawings may be denoted by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0012] In this specification, when expressing the aspect of arranging one member on another member, if simply expressed as "on" or "under", unless otherwise specified, it includes both the case of arranging another member directly on or under so as to be in contact with a certain member, and the case of arranging another member above or below a certain member via yet another member. Also, in this specification, when expressing the aspect of arranging one member on the surface of another member, if simply expressed as "on the surface", unless otherwise specified, it includes both the case of arranging another member directly on or under so as to be in contact with a certain member, and the case of arranging another member above or below a certain member via yet another member.

[0013] Also, in this specification, "sheet" includes a member called "film". Also, "film" includes a member called "sheet".

[0014] Hereinafter, the reflective sheet for a solar cell and the solar power generation system in the present disclosure will be described in detail.

[0015] A. Reflective Sheet for Solar Cells The reflective sheet for solar cells in the present disclosure has, in this order, a first resin film which is a reflective film, a cloth base material, and a second resin film.

[0016] FIG. 1 is a schematic cross-sectional view illustrating the reflective sheet for solar cells in the present disclosure. As shown in FIG. 1, the reflective sheet 10 for solar cells has, in this order, a first resin film 1 which is a reflective film, a cloth base material 2, and a second resin film 3.

[0017] The reflective sheet for solar cells in the present disclosure has the first resin film, the cloth base material, and the second resin film in order, and has a symmetric layer structure, so that the occurrence of warpage can be suppressed. Therefore, even when the reflective sheet for solar cells is laid on a vast site, the workability is good. Further, the reflective sheet for solar cells in the present disclosure has the first resin film, the cloth base material, and the second resin film in order, so that high strength can be obtained even when the overall thickness of the reflective sheet for solar cells is relatively thin. Therefore, the overall thickness of the reflective sheet for solar cells can be reduced, and the workability can be improved.

[0018] When the reflective sheet for solar cells in the present disclosure is used in a solar power generation system, the first resin film is arranged to face the solar cell module side, and the second resin film is arranged to face the ground. Since the surface of the first resin film is usually smooth, the antifouling property is good. Therefore, a decrease in the reflectivity of the reflective sheet for solar cells due to dirt can be suppressed. Further, since the surface of the first resin film is usually smooth, dirt is easily removed by wind and rain. Therefore, the reflectivity of the reflective sheet for solar cells can be maintained over a long period of time, and the durability can be enhanced.

[0019] Further, in the present disclosure, in the first resin film, unlike a metal foil or a metal vapor deposition film, diffuse reflection increases. Therefore, the power generation efficiency can be increased regardless of the installation angle of the solar cell module. Further, glare can be suppressed and light pollution can be suppressed.

[0020] Furthermore, the reflective sheet for solar cells in the present disclosure also functions as a weed control sheet because it reflects sunlight.

[0021] Hereinafter, the reflective sheet for solar cells in the present disclosure will be described for each configuration.

[0022] 1. First resin film The first resin film in the present disclosure is a reflective film. When the reflective sheet for solar cells in the present disclosure is used in a solar power generation system, the first resin film is arranged to face the solar cell module side.

[0023] The first resin film may be any reflective film. For example, it may be a resin film containing a resin component and a colorant, or a resin film having voids inside. Among them, the first resin film is preferably a resin film containing a resin component and a colorant. Hereinafter, a first aspect in which the first resin film contains a resin component and a colorant, and a second aspect in which the first resin film has voids inside will be described.

[0024] (1) First aspect of the first resin film The first aspect of the first resin film in the present disclosure contains a resin component and a colorant.

[0025] (a) Material of the first resin film (i) Resin component The resin component contained in the first resin film is not particularly limited. For example, it includes polyolefin resins, polyurethane resins, polyester resins, acrylic resins, styrene resins, vinyl fluoride resins, and polyamide resins. Among them, polyolefin resins are preferred because of their excellent heat resistance, water resistance, chemical resistance, and cost performance.

[0026] Examples of polyolefin resins include homopolymers of olefins, copolymers of two or more olefins, and copolymers of one or more olefins and one or more polymerizable monomers copolymerizable with olefins. Examples of olefin monomers include ethylene, propylene, butene, and hexene. The copolymer may be a binary copolymer, a ternary copolymer, or a quaternary copolymer. The copolymer may be a random copolymer or a block copolymer.

[0027] Examples of polyolefin resins include polyethylene resins and polypropylene resins. Examples of polyethylene resins include high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), and very-low-density polyethylene (VLDPE). These may be used alone or in combination of two or more.

[0028] As described later, when the first resin film is heat-sealed to the fabric substrate without using the first adhesive layer, the first resin film preferably contains at least one of linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE).

[0029] The first resin film preferably contains a polyolefin resin as the main component of the resin component, and more preferably contains a polyethylene resin. The "main component of the resin component" refers to a resin component having a ratio of 50% by mass or more based on 100% by mass of all the resin components in the first resin film. The ratio of the polyolefin resin is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more based on 100% by mass of all the resin components in the first resin film.

[0030] In addition, it is preferable that the first resin film, the cloth base material, and the second resin film contain the same type of resin. By the first resin film, the cloth base material, and the second resin film containing the same type of resin, the recyclability is improved and the environmental load at the time of disposal is reduced. Further, as will be described later, when the first resin film and the cloth base material are adhered by the first adhesive layer and the second resin film and the cloth base material are adhered by the second adhesive layer, the first resin film, the cloth base material, and the second resin film contain the same type of resin, so that the interlayer adhesiveness is increased, and thus interlayer peeling can be suppressed. Further, since the degree of expansion or contraction due to heat, moisture, etc. becomes close when the first resin film, the cloth base material, and the second resin film contain the same type of resin, the occurrence of warpage and interlayer peeling can be suppressed. Therefore, the durability can be improved.

[0031] The "same type of resin" refers to resins having a common main chain structure, such as polyolefin resins, polyurethane resins, polyester resins, and acrylic resins.

[0032] In particular, from the viewpoints of productivity and recyclability, it is preferable that the first resin film, the cloth base material, and the second resin film contain a polyolefin resin, and more preferably contain a polyethylene resin.

[0033] (ii) Colorant The colorant is not particularly limited as long as it has reflectivity, and examples thereof include white pigments, extender pigments, metal powder pigments, and pearl pigments. Examples of the white pigment include titanium oxide and zinc oxide. Examples of the extender pigment include calcium carbonate, barium sulfate, silica, clay, and talc. The colorant may be used alone or in combination of two or more. Among them, white pigments and extender pigments are preferable from the viewpoint of cost.

[0034] The content of the colorant in the first resin film is not particularly limited as long as the desired reflectivity can be obtained, and is appropriately selected according to the type of the colorant and the like. The content of the colorant in the first resin film is, for example, 5% by mass or more, and may be 10% by mass or more. If the content of the colorant is too small, the reflectivity of the first resin film may be low. On the other hand, the content of the colorant in the first resin film is, for example, 40% by mass or less, and may be 30% by mass or less. If the content of the colorant is too large, the processability of the first resin film may be low. Specifically, the content of the colorant in the first resin film is 5% by mass or more and 40% by mass or less, and may be 10% by mass or more and 30% by mass or less.

[0035] (iii) Other components The first resin film may further contain an additive. Examples of the additive include a light stabilizer, an antioxidant, an ultraviolet absorber, a lubricant, a heat stabilizer, a pigment, a modifier, a flame retardant, an antistatic agent, a reinforcing agent, a filler, a dispersant, a plasticizer, a fungicide, and the like.

[0036] Among them, the first resin film preferably contains a light stabilizer. The weather resistance can be improved. Examples of the light stabilizer include hindered amine light stabilizers (HALS).

[0037] (b) Thickness and forming method of the first resin film The thickness of the first resin film is not particularly limited as long as the desired reflectivity can be obtained. The thickness of the first resin film is, for example, 20 μm or more, and may be 40 μm or more. If the thickness of the first resin film is too thin, the strength may be low. On the other hand, the thickness of the first resin film is, for example, 200 μm or less, and may be 100 μm or less. If the thickness of the first resin film is too thick, the handleability may decrease. Specifically, the thickness of the first resin film is 20 μm or more and 200 μm or less, and may be 40 μm or more and 100 μm or less.

[0038] Also, the difference between the thickness of the first resin film and the thickness of the second resin film is preferably small. Thereby, the occurrence of warping can be suppressed. The difference between the thickness of the first resin film and the thickness of the second resin film is, for example, within 100 μm, may be within 50 μm, or may be within 20 μm.

[0039] Examples of the method for forming the first resin film include a method of molding a resin composition containing the above resin component, colorant, and additive. Examples of the molding method include extrusion molding and calender molding.

[0040] The first resin film may be a stretched film or an unstretched film. Further, the first resin film may have voids inside or may not have voids inside.

[0041] (2) Second aspect of the first resin film The second aspect of the first resin film in the present disclosure has voids inside. The first resin film is preferably a porous film having voids inside.

[0042] The first resin film having voids inside is obtained by molding a resin composition containing a resin component and a filler to obtain an unstretched film, and then stretching the unstretched film. When the unstretched film is stretched, peeling occurs at the interface between the resin component and the filler, and the peeling generated at this interface propagates and expands by further stretching. Thereby, a first resin film having voids inside is obtained.

[0043] (a) Materials of the first resin film The first resin film preferably contains a resin component and a filler.

[0044] (i) Resin component Since the resin component contained in the first resin film is the same as the resin component in the above first aspect, the description here is omitted.

[0045] (ii) Filler Examples of the filler include inorganic fillers and organic fillers. The filler may be used alone or in combination of two or more kinds.

[0046] Examples of the inorganic filler include calcium carbonate, clay, talc, silica, diatomaceous earth, titanium oxide, magnesium oxide, zinc oxide, and barium sulfate.

[0047] Examples of the organic filler include polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polyamide, polyethylene naphthalate, polystyrene, melamine, polyethylene sulfite, polyimide, polyether ether ketone, polyphenylene sulfite, poly-4-methyl-1-pentene, and polymethyl methacrylate. Further, as the organic filler, a homopolymer of cyclic olefin or a copolymer of cyclic olefin and ethylene, having a melting point of 120°C or higher and 300°C or lower, or a glass transition temperature of 120°C or higher and 280°C or lower, can also be used. It is preferable that the organic filler and the resin component are different materials.

[0048] The content of the filler in the first resin film is not particularly limited as long as the desired reflectivity can be obtained, and is appropriately selected depending on the type of the filler and the like. The content of the filler in the first resin film is, for example, 5% by mass or more, and may be 10% by mass or more. If the content of the filler is too small, the reflectivity of the first resin film may be low. On the other hand, the content of the filler in the first resin film is, for example, 40% by mass or less, and may be 30% by mass or less. If the content of the filler is too large, the processability of the first resin film may be low. Specifically, the content of the filler in the first resin film is 5% by mass or more and 40% by mass or less, and may be 10% by mass or more and 30% by mass or less.

[0049] (iii) Other components The first resin film may further contain an additive. The additive is the same as the additive in the first aspect described above.

[0050] (b) Thickness and forming method of the first resin film The thickness of the first resin film is not particularly limited as long as the desired reflectivity can be obtained. The thickness of the first resin film is, for example, 20 μm or more, and may be 40 μm or more. If the thickness of the first resin film is too thin, the strength may be low. On the other hand, the thickness of the first resin film is, for example, 200 μm or less, and may be 100 μm or less. If the thickness of the first resin film is too thick, the handleability may decrease. Specifically, the thickness of the first resin film may be 20 μm or more and 200 μm or less, or may be 40 μm or more and 100 μm or less.

[0051] As a method for forming the first resin film, for example, a method of forming an unstretched film by molding a resin composition containing the above resin components, filler, and additive, and then stretching the unstretched film can be mentioned. Examples of the molding method include extrusion molding and calender molding. As the stretching method, a general stretching method can be applied, and examples include uniaxial stretching in the longitudinal direction, multi-stage uniaxial stretching in the longitudinal direction, uniaxial stretching in the transverse direction, sequential biaxial stretching in the longitudinal and transverse directions, simultaneous biaxial stretching in the longitudinal and transverse directions, and combinations thereof.

[0052] In addition, in the method for forming the first resin film, after removing the filler from the unstretched film, the unstretched film may be stretched. The method for removing the filler is appropriately selected according to the type of the filler, and examples include a method using an acidic aqueous solution or an alkaline aqueous solution.

[0053] 2. The second resin film When the reflection sheet for solar cells in the present disclosure is used in a solar power generation system, the second resin film is arranged to face the ground.

[0054] The optical properties of the second resin film are not particularly limited. For example, when not only the first resin film but also the second resin film has reflectivity, the reflectivity of the reflection sheet for solar cells can be increased.

[0055] When the second resin film is a reflective film, since the second resin film is the same as the first resin film described above, the description here is omitted.

[0056] As described above, it is preferable that the first resin film, the cloth base material, and the second resin film contain the same kind of resin, more preferably contain a polyolefin resin, and even more preferably contain a polyethylene resin.

[0057] As described above, when the reflective sheet for a solar cell in the present disclosure is used in a solar power generation system, the second resin film is arranged to face the ground. Therefore, the second resin film may or may not contain a light stabilizer.

[0058] 3. Cloth base material The cloth base material in the present disclosure is arranged between the above-mentioned first resin film and the second resin film. By arranging the cloth base material between the first resin film and the second resin film, the strength of the reflective sheet for a solar cell can be increased.

[0059] (1) Structure of the cloth base material Examples of the cloth base material include non-woven fabric, woven fabric, and knitted fabric.

[0060] Examples of the non-woven fabric include fiber cross non-woven fabric, long fiber non-woven fabric, short fiber non-woven fabric, wet non-woven fabric, dry non-woven fabric, airlaid non-woven fabric, carded non-woven fabric, parallel non-woven fabric, cross non-woven fabric, random non-woven fabric, spunbond non-woven fabric, meltblown non-woven fabric, flash spun non-woven fabric, chemical bonded non-woven fabric, hydroentangled non-woven fabric, needle punched non-woven fabric, stitch bonded non-woven fabric, thermal bonded non-woven fabric, burst fiber non-woven fabric, tow opened fiber non-woven fabric, split fiber non-woven fabric, composite non-woven fabric, laminated non-woven fabric, coated non-woven fabric, and laminated non-woven fabric.

[0061] Examples of the fiber orthogonal nonwoven fabric include, for example, a nonwoven fabric in which a plurality of uniaxially stretched net-like films are laminated so that the stretching directions are orthogonal, and a nonwoven fabric in which a plurality of webs in which the fibers are oriented in one direction are laminated so that the fiber directions are orthogonal.

[0062] Examples of the uniaxially stretched net-like film include, for example, a uniaxially stretched net-like film obtained by uniaxially stretching a resin film, intermittently making slits in the stretching direction, and further widening it, and a uniaxially stretched net-like film obtained by intermittently making cuts in a resin film and then uniaxially stretching it in the direction of the cuts. In the uniaxially stretched net-like film, a plurality of the former uniaxially stretched net-like films may be laminated, a plurality of the latter uniaxially stretched net-like films may be laminated, or the former uniaxially stretched net-like film and the latter uniaxially stretched net-like film may be laminated.

[0063] Also, the uniaxially stretched net-like film may be single-layer or multilayer. In the case of multilayer, a plurality of resin layers may be laminated via an adhesive layer, or a plurality of resin layers may be laminated without an adhesive layer.

[0064] Examples of the fiber orthogonal nonwoven fabric in which a plurality of uniaxially stretched net-like films are laminated so that the stretching directions are orthogonal include, for example, "WALIF (registered trademark)" and "CLAF (registered trademark)" manufactured by ENEOS Techno Materials Co., Ltd. Also, an example of the fiber orthogonal nonwoven fabric in which a plurality of webs in which the fibers are oriented in one direction are laminated so that the fiber directions are orthogonal is "MIRAI-F (registered trademark)" manufactured by ENEOS Techno Materials Co., Ltd.

[0065] Among them, the cloth base material is preferably a fiber cross nonwoven fabric, a woven fabric, or a knitted fabric. The woven fabric is composed of warp and weft threads, has gaps in the weave pattern, and has a height at the intersection of the warp and weft threads. Also, the fiber cross nonwoven fabric is a net-like nonwoven fabric, and since the directions of the fibers intersect, it can be regarded as being composed of warp and weft threads like a woven fabric. Also, the knitted fabric has gaps in the knitting pattern and has a height at the part where the loops are connected. Therefore, in the case of a fiber cross nonwoven fabric, a woven fabric, or a knitted fabric, as will be described later, in the cross section in the thickness direction of the reflective sheet for solar cells, a gap is likely to be formed between the first resin film and the second resin film. Thus, the reflectivity and strength of the reflective sheet for solar cells can be improved.

[0066] The weaving method of the woven fabric is not particularly limited. Also, the knitting method of the knitted fabric is not particularly limited.

[0067] In the woven fabric, the warp and weft threads may each be a monofilament or a multifilament.

[0068] In the woven fabric, the diameter of the warp thread and the diameter of the weft thread are not particularly limited as long as the desired strength can be obtained. As will be described later, when a first adhesive layer is disposed between the first resin film and the cloth base material and a second adhesive layer is disposed between the second resin film and the cloth base material, it is preferable that at least one of the diameter of the warp thread and the diameter of the weft thread is larger than the thickness of the first adhesive layer and larger than the thickness of the second adhesive layer. In particular, it is preferable that both the diameter of the warp thread and the diameter of the weft thread are larger than the thickness of the first adhesive layer and larger than the thickness of the second adhesive layer. In this case, as will be described later, in the cross section in the thickness direction of the reflective sheet for solar cells, a gap is likely to be formed between the first resin film and the second resin film. Thus, the reflectivity and strength of the reflective sheet for solar cells can be improved.

[0069] In the fabric, the diameter of the warp yarns is preferably larger than the thickness of the first adhesive layer and larger than the thickness of the second adhesive layer as described above. For example, it is 20 μm or more, and may be 40 μm or more, or may be 60 μm or more. When the diameter of the warp yarns is large as in the above range, the strength of the reflective sheet for solar cells can be increased. Also, when the diameter of the warp yarns is large as in the above range, voids are likely to be formed between the first resin film and the second resin film, and the reflectivity and strength of the reflective sheet for solar cells can be increased. On the other hand, the diameter of the warp yarns is, for example, 200 μm or less, and may be 160 μm or less, or may be 120 μm or less. If the diameter of the warp yarns is too large, the thickness of the fabric increases, and the thickness of the entire reflective sheet for solar cells increases, so the handleability and workability may decrease. Specifically, the diameter of the warp yarns is 20 μm or more and 200 μm or less, and may be 40 μm or more and 160 μm or less, or may be 60 μm or more and 120 μm or less.

[0070] In the fabric, the diameter of the weft yarns is the same as that of the above warp yarns. The diameter of the warp yarns and the diameter of the weft yarns may be the same or different.

[0071] The diameter of the warp yarns refers to the diameter of the warp yarns in the thickness direction of the reflective sheet for solar cells. Also, the diameter of the weft yarns refers to the diameter of the weft yarns in the thickness direction of the reflective sheet for solar cells. Fig. 2(a) shows an example where the cloth base material is the fabric 2a. For example, in Fig. 2(a), the diameter of the warp yarns 11a is indicated by d1, and the diameter of the weft yarns 11b is indicated by d2. When the warp yarns and the weft yarns are multifilaments, the diameter of the warp yarns and the diameter of the weft yarns refer to the diameter of the multifilaments. The diameter of the warp yarns is the arithmetic mean value of the diameters of 10 randomly selected warp yarns. The diameter of the weft yarns is the arithmetic mean value of the diameters of 10 randomly selected weft yarns. The diameter of the warp yarns and the diameter of the weft yarns are measured by preparing a section of the cross-section in the thickness direction of the reflective sheet for solar cells using a microtome and observing the cross-section of the reflective sheet for solar cells with a laser microscope. As the laser microscope, "VK-9710" manufactured by Keyence Corporation is used.

[0072] The thickness of the fabric is not particularly limited as long as the desired strength can be obtained. The thickness of the fabric may be, for example, 40 μm or more, may be 80 μm or more, and may be 120 μm or more. On the other hand, the thickness of the fabric may be, for example, 400 μm or less, may be 320 μm or less, and may be 240 μm or less. If the thickness of the fabric is too thick, the thickness of the entire reflective sheet for solar cells will become thick, so the handleability and workability may decrease. Specifically, the thickness of the fabric may be 40 μm or more and 400 μm or less, may be 80 μm or more and 320 μm or less, and may be 120 μm or more and 240 μm or less.

[0073] The thickness of the fabric refers to the maximum thickness of the intersection portion of the warp and weft in the cross-section in the thickness direction of the reflective sheet for solar cells. For example, in FIG. 2(a), the thickness of the fabric 2a is indicated by the maximum thickness d3 of the intersection portion of the warp 11a and the weft 11b. The thickness of the fabric is taken as the arithmetic mean value of the thicknesses at 10 randomly selected locations. The thickness of the fabric is measured by preparing a section of the cross-section in the thickness direction of the reflective sheet for solar cells using a microtome and observing the cross-section of the reflective sheet for solar cells with a laser microscope. As the laser microscope, "VK-9710" manufactured by Keyence Corporation is used.

[0074] In the fiber cross nonwoven fabric, the thickness of the uniaxially stretched net-like film is not particularly limited as long as the desired strength can be obtained. As described later, when a first adhesive layer is disposed between the first resin film and the fabric substrate, and a second adhesive layer is disposed between the second resin film and the fabric substrate, among the plurality of uniaxially stretched net-like films constituting the fiber cross nonwoven fabric, it is preferable that the thickness of the uniaxially stretched net-like film located on the first resin film side is larger than the thickness of the first adhesive layer. Further, among the plurality of uniaxially stretched net-like films constituting the fiber cross nonwoven fabric, it is preferable that the thickness of the uniaxially stretched net-like film located on the second resin film side is larger than the thickness of the second adhesive layer. In particular, it is preferable that the thickness of all the uniaxially stretched net-like films constituting the fiber cross nonwoven fabric is larger than the thickness of the first adhesive layer and larger than the thickness of the second adhesive layer. In this case, as described later, in the cross section in the thickness direction of the reflective sheet for solar cells, a gap is likely to be formed between the first resin film and the second resin film. Therefore, the reflectivity and strength of the reflective sheet for solar cells can be improved.

[0075] In the fiber cross nonwoven fabric, as described above, it is preferable that the thickness of the uniaxially stretched net-like film is larger than the thickness of the first adhesive layer and larger than the thickness of the second adhesive layer. For example, it may be 20 μm or more, may be 40 μm or more, or may be 60 μm or more. By making the thickness of the uniaxially stretched net-like film large as in the above range, the strength of the reflective sheet for solar cells can be increased. Further, when the thickness of the uniaxially stretched net-like film is large as in the above range, a gap is likely to be formed between the first resin film and the second resin film, and the reflectivity and strength of the reflective sheet for solar cells can be increased. On the other hand, the thickness of the uniaxially stretched net-like film is, for example, 200 μm or less, may be 160 μm or less, or may be 120 μm or less. If the thickness of the uniaxially stretched net-like film is too large, the thickness of the fiber cross nonwoven fabric will increase, and the thickness of the entire reflective sheet for solar cells will increase, so the handleability and workability may decrease. Specifically, the thickness of the uniaxially stretched net-like film is 20 μm or more and 200 μm or less, may be 40 μm or more and 160 μm or less, or may be 60 μm or more and 120 μm or less.

[0076] Fig. 2(b) shows an example in which the cloth base material is the fiber cross nonwoven fabric 2b. For example, in Fig. 2(b), the thicknesses of the uniaxially stretched mesh films 12a and 12b are represented by t1 and t2, respectively. The thickness of the uniaxially stretched mesh film is the arithmetic average value of the thicknesses at 10 randomly selected locations. The thickness of the uniaxially stretched mesh film is measured by preparing a section of the cross-section in the thickness direction of the reflective sheet for solar cells using a microtome and observing the cross-section of the reflective sheet for solar cells with a laser microscope. As the laser microscope, “VK-9710” manufactured by Keyence Corporation is used.

[0077] Also, in the fiber cross nonwoven fabric, the fiber diameter of the web in which the fibers are oriented in one direction is not particularly limited as long as the desired strength can be obtained. As will be described later, when a first adhesive layer is disposed between the first resin film and the cloth base material and a second adhesive layer is disposed between the second resin film and the cloth base material, among the plurality of webs constituting the fiber cross nonwoven fabric, it is preferable that the fiber diameter of the web located on the first resin film side is larger than the thickness of the first adhesive layer. Further, among the plurality of webs constituting the fiber cross nonwoven fabric, it is preferable that the fiber diameter of the web located on the second resin film side is larger than the thickness of the second adhesive layer. In particular, it is preferable that the fiber diameter of all the webs constituting the fiber cross nonwoven fabric is larger than the thickness of the first adhesive layer and larger than the thickness of the second adhesive layer. In this case, as will be described later, in the cross-section in the thickness direction of the reflective sheet for solar cells, a gap is likely to be formed between the first resin film and the second resin film. Therefore, the reflectivity and strength of the reflective sheet for solar cells can be improved.

[0078] In the fiber cross nonwoven fabric, the fiber diameter of the web is preferably larger than the thickness of the first adhesive layer and larger than the thickness of the second adhesive layer as described above. For example, it is 20 μm or more, and may be 40 μm or more, or may be 60 μm or more. By the fiber diameter of the web being large as in the above range, the strength of the reflective sheet for solar cells can be increased. Further, when the fiber diameter of the web is large as in the above range, voids are likely to be formed between the first resin film and the second resin film, and the reflectivity and strength of the reflective sheet for solar cells can be increased. On the other hand, the fiber diameter of the web is, for example, 200 μm or less, and may be 160 μm or less, or may be 120 μm or less. If the fiber diameter of the web is too large, the thickness of the fiber cross nonwoven fabric becomes thick, and the thickness of the entire reflective sheet for solar cells becomes thick, so that the handleability and workability may be reduced. Specifically, the fiber diameter of the web is 20 μm or more and 200 μm or less, and may be 40 μm or more and 160 μm or less, or may be 60 μm or more and 120 μm or less.

[0079] Fig. 2(c) shows an example in which the cloth base material is the fiber cross nonwoven fabric 2c. The fiber diameter of the web means the fiber diameter in the thickness direction of the reflective sheet for solar cells. For example, in Fig. 2(c), the fiber diameters of the webs 13a and 13b are indicated by d4 and d5, respectively. The fiber diameter of the web is taken as the arithmetic mean value of 10 randomly selected fiber diameters. The fiber diameter of the web is measured by preparing a section of the cross section in the thickness direction of the reflective sheet for solar cells using a microtome and observing the cross section of the reflective sheet for solar cells with a laser microscope. As the laser microscope, "VK-9710" manufactured by Keyence Corporation is used.

[0080] The thickness of the cross-laid nonwoven fabric is not particularly limited as long as the desired strength can be obtained. The thickness of the cross-laid nonwoven fabric is, for example, 40 μm or more, and may be 80 μm or more, or may be 120 μm or more. On the other hand, the thickness of the cross-laid nonwoven fabric is, for example, 400 μm or less, and may be 320 μm or less, or may be 240 μm or less. If the thickness of the cross-laid nonwoven fabric is too thick, the thickness of the entire reflective sheet for solar cells will increase, which may reduce the handleability and workability. Specifically, the thickness of the cross-laid nonwoven fabric is 40 μm or more and 400 μm or less, and may be 80 μm or more and 320 μm or less, or may be 120 μm or more and 240 μm or less.

[0081] When the cross-laid nonwoven fabric is a nonwoven fabric in which a plurality of uniaxially stretched net-like films are laminated so that the stretching directions are orthogonal, the thickness of the cross-laid nonwoven fabric refers to the maximum thickness of the portion where the plurality of uniaxially stretched net-like films overlap. For example, in FIG. 2(b), the thickness of the cross-laid nonwoven fabric 2b is indicated by the maximum thickness t3 of the portion where the plurality of uniaxially stretched net-like films 12a and 12b overlap. On the other hand, when the cross-laid nonwoven fabric is a nonwoven fabric in which a plurality of webs in which fibers are oriented in one direction are laminated so that the fiber directions are orthogonal, the thickness of the cross-laid nonwoven fabric refers to the maximum thickness of the portion where the plurality of webs overlap. For example, in FIG. 2(c), the thickness of the cross-laid nonwoven fabric 2c is indicated by the maximum thickness d6 of the portion where the plurality of webs 13a and 13b overlap. The thickness of the cross-laid nonwoven fabric is the arithmetic mean value of the thicknesses at 10 randomly selected locations. The thickness of the cross-laid nonwoven fabric is measured by preparing a section of the cross-sectional slice in the thickness direction of the reflective sheet for solar cells using a microtome and observing the cross-section of the reflective sheet for solar cells with a laser microscope. As the laser microscope, "VK-9710" manufactured by Keyence Corporation is used.

[0082] In the knitted fabric, the yarn diameter is not particularly limited as long as the desired strength can be obtained. As will be described later, when a first adhesive layer is disposed between the first resin film and the cloth substrate, and a second adhesive layer is disposed between the second resin film and the cloth substrate, it is preferable that the yarn diameter is larger than the thickness of the first adhesive layer and larger than the thickness of the second adhesive layer. In this case, as will be described later, in the cross-section in the thickness direction of the reflective sheet for solar cells, a gap is likely to be formed between the first resin film and the second resin film. Therefore, the reflectivity and strength of the reflective sheet for solar cells can be improved.

[0083] In the knitted fabric, as described above, it is preferable that the yarn diameter is larger than the thickness of the first adhesive layer and larger than the thickness of the second adhesive layer. For example, it is 20 μm or more, and may be 40 μm or more, or may be 60 μm or more. By making the yarn diameter large as in the above range, the strength of the reflective sheet for solar cells can be increased. Further, when the yarn diameter is large as in the above range, a gap is likely to be formed between the first resin film and the second resin film, and the reflectivity and strength of the reflective sheet for solar cells can be increased. On the other hand, the yarn diameter is, for example, 200 μm or less, and may be 160 μm or less, or may be 120 μm or less. If the yarn diameter is too large, the thickness of the knitted fabric increases and the thickness of the entire reflective sheet for solar cells increases, so the handleability and workability may decrease. Specifically, the yarn diameter is 20 μm or more and 200 μm or less, and may be 40 μm or more and 160 μm or less, or may be 60 μm or more and 120 μm or less.

[0084] Fig. 2(d) shows an example in which the cloth substrate is the knitted fabric 2d. The yarn diameter refers to the diameter in the thickness direction of the reflective sheet for solar cells. For example, in Fig. 2(d), the yarn diameter is indicated by d7. The yarn diameter is the arithmetic mean value of the diameters at 10 randomly selected locations. The yarn diameter is measured by preparing a section of the cross-section in the thickness direction of the reflective sheet for solar cells using a microtome and observing the cross-section of the reflective sheet for solar cells with a laser microscope. As the laser microscope, "VK-9710" manufactured by Keyence Corporation is used.

[0085] The thickness of the knitted fabric is not particularly limited as long as the desired strength can be obtained. The thickness of the knitted fabric is, for example, 40 μm or more, may be 80 μm or more, and may be 120 μm or more. On the other hand, the thickness of the knitted fabric is, for example, 400 μm or less, may be 320 μm or less, and may be 240 μm or less. If the thickness of the knitted fabric is too thick, the thickness of the entire reflective sheet for solar cells will increase, which may reduce the handleability and workability. Specifically, the thickness of the knitted fabric is 40 μm or more and 400 μm or less, may be 80 μm or more and 320 μm or less, and may be 120 μm or more and 240 μm or less.

[0086] The thickness of the knitted fabric refers to the maximum thickness of the portion where the yarns cross. For example, in FIG. 2(d), the thickness of the knitted fabric 2d is indicated by the maximum thickness d8 of the portion where the yarns cross. The thickness of the knitted fabric is taken as the arithmetic mean value of the thicknesses at 10 randomly selected locations. The thickness of the knitted fabric is measured by preparing a section of the cross-section in the thickness direction of the reflective sheet for solar cells using a microtome and observing the cross-section of the reflective sheet for solar cells with a laser microscope. As the laser microscope, "VK-9710" manufactured by Keyence Corporation is used.

[0087] (2) Material of the fabric substrate Examples of the material of the fabric substrate include inorganic fibers and organic fibers. Examples of the inorganic fibers include glass fibers, metal fibers, ceramic fibers, carbon fibers, etc. Examples of the organic fibers include natural fibers and chemical fibers. Examples of the chemical fibers include synthetic fibers, semi-synthetic fibers, and regenerated fibers.

[0088] Among them, synthetic fibers are preferred. As described above, the same kind of resin can be contained in the first resin film, the fabric substrate, and the second resin film. Examples of the resin constituting the synthetic fiber include polyester resins, acrylic resins, polyamide resins, polyolefin resins, polyurethane resins, fluorine resins, polyvinyl chloride, polyvinylidene chloride, and polyvinyl alcohol. Examples of the polyamide resins include nylon and aramid. Examples of the polyolefin resins include polyethylene resins and polypropylene resins.

[0089] Further, when the cloth base material is an orthogonal nonwoven fabric and is composed of a uniaxially stretched net-like film, examples of the material of the uniaxially stretched net-like film include resins. Examples of the resin include thermoplastic resins and thermosetting resins. Among them, thermoplastic resins are preferred. Examples of the thermoplastic resin include polyolefin resins, acrylic resins, styrene resins, vinyl fluoride resins, polyamide resins, and polyester resins. Examples of the polyolefin resin include polyethylene resins and polypropylene resins. Examples of the acrylic resin include polymethyl acrylate, polymethyl methacrylate, and ethylene-ethyl acrylate copolymers. Examples of the styrene resin include butadiene-styrene copolymers, acrylonitrile-styrene copolymers, polystyrene, styrene-butadiene-styrene copolymers, styrene-isoprene-styrene copolymers, and styrene-acrylic acid copolymers. Examples of the vinyl fluoride resin include polyvinyl fluoride and polyvinylidene fluoride. Examples of the polyamide resin include nylon. Examples of the polyester resin include polyethylene terephthalate and polybutylene terephthalate. Further, as the thermoplastic resin, polycarbonate, polyphenylene oxide, polyacetal, polyphenylene sulfide, silicone resin, thermoplastic urethane resin, polyether ether ketone, polyether imide, thermoplastic elastomer, etc. may be used.

[0090] Among them, polyolefin resins are preferred because of their excellent heat resistance, water resistance, chemical resistance, and cost performance.

[0091] In the case of a uniaxially stretched net-like film, a polyethylene-based resin is more preferable. Examples of the polyethylene-based resin include high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), and very low-density polyethylene (VLDPE). These may be used alone or in combination of two or more. Among them, in the case of a uniaxially stretched net-like film, high-density polyethylene and linear low-density polyethylene are preferable, and high-density polyethylene is more preferable. High-density polyethylene is excellent in weather resistance and tensile strength. Furthermore, a uniaxially stretched net-like film containing high-density polyethylene has no slack even when formed into a long roll, and is less likely to cause poor appearance due to whitening during bending processing. In particular, when the uniaxially stretched net-like film contains only a polyethylene-based resin as a resin component, it is preferable to use at least one of high-density polyethylene and linear low-density polyethylene.

[0092] As described above, it is preferable that the first resin film, the cloth base material, and the second resin film contain the same kind of resin, more preferably contain a polyolefin-based resin, and even more preferably contain a polyethylene-based resin.

[0093] (3) Void The reflective sheet for solar cells in the present disclosure may have a void between the first resin film and the second resin film in the cross-section in the thickness direction of the reflective sheet for solar cells. For example, in FIGS. 2(a) to 2(d), there is a void V between the first resin film 1 and the second resin film 2. The void can improve the reflectivity of the reflective sheet for solar cells. Further, when a force is applied to the reflective sheet for solar cells, if there is a void, the yarns constituting the cloth base material can shift, so that the stress can be dispersed. Therefore, it is possible to suppress the reflective sheet for solar cells from being broken due to stress concentration. Therefore, it is considered that the strength of the reflective sheet for solar cells is increased. In addition, due to the presence of the void, the weight of the reflective sheet for solar cells can be reduced. Therefore, when the reflective sheet for solar cells is in a roll shape, the handleability is improved.

[0094] In the present disclosure, since a cloth base material is disposed between the first resin film and the second resin film, by appropriately selecting the structure of the cloth base material, a void can be formed between the first resin film and the second resin film. The structure of the cloth base material is as described above.

[0095] That the reflective sheet for solar cells has a void between the first resin film and the second resin film in the cross-section in the thickness direction of the reflective sheet for solar cells is confirmed by preparing a section of the cross-section in the thickness direction of the reflective sheet for solar cells using a microtome and observing the cross-section of the reflective sheet for solar cells with a laser microscope. As the laser microscope, “VK-9710” manufactured by Keyence Corporation is used.

[0096] 4. The first adhesive layer and the second adhesive layer In the present disclosure, a first adhesive layer may be disposed between the first resin film and the cloth base material, or the first resin film and the cloth base material may be directly laminated. Also, in the present disclosure, a second adhesive layer may be disposed between the second resin film and the cloth base material, or the second resin film and the cloth base material may be directly laminated. For example, in FIG. 3, a first adhesive layer 4 is disposed between the first resin film 1 and the cloth base material 2, and a second adhesive layer 5 is disposed between the second resin film 3 and the cloth base material 2.

[0097] The first adhesive layer and the second adhesive layer contain an adhesive or an extruded coating resin. The first adhesive layer and the second adhesive layer are preferably extruded coating layers.

[0098] As the extrusion coating resin, a resin capable of heat welding can be used. For example, polyolefin resins, acid-modified polyolefin resins, polyvinyl acetate resins, acrylic resins, and polyvinyl chloride resins can be mentioned. Examples of polyolefin resins include low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ionomer resin, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl methacrylate copolymer, ethylene-propylene copolymer, polymethylpentene, polybutene, etc. The acid-modified polyethylene resin is obtained by modifying a polyolefin resin such as polyethylene or polypropylene with an unsaturated carboxylic acid. Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, etc. These may be used alone or in combination of two or more.

[0099] The first resin film, the first adhesive layer, the cloth base material, the second adhesive layer, and the second resin film preferably contain the same kind of resin, more preferably contain a polyolefin resin, and even more preferably contain a polyethylene resin. In particular, low-density polyethylene and linear low-density polyethylene are preferred, and low-density polyethylene is more preferred. Low-density polyethylene is excellent in processability, has excellent adhesiveness to a cloth base material containing a polyethylene resin, and is inexpensive.

[0100] The thickness of the first adhesive layer and the thickness of the second adhesive layer are not particularly limited, but from the viewpoint of the handleability of the reflective sheet for solar cells, it is preferably thin. The thickness of the first adhesive layer and the thickness of the second adhesive layer are preferably, for example, 10 μm or more and 20 μm or less.

[0101] 5. The first anchor layer and the second anchor layer In the present disclosure, for improving adhesiveness, a first anchor layer may be disposed between the first resin film and the first adhesive layer. Similarly, a second anchor layer may be disposed between the second resin film and the second adhesive layer.

[0102] Examples of the anchor coating agent used for the anchor layer include organic titanium-based anchor coating agents such as alkyl titanate, isocyanate-based anchor coating agents, polyethyleneimine-based anchor coating agents, polybutadiene-based anchor coating agents, and polyurethane-based anchor coating agents.

[0103] 6. Physical Properties of the Reflective Sheet for Solar Cells The reflective sheet for solar cells in the present disclosure has high reflectivity of sunlight. Specifically, the average reflectance at wavelengths of 400 nm or more and 1200 nm or less is 40% or more, may be 60% or more, or may be 80% or more.

[0104] The average reflectance at wavelengths of 400 nm or more and 1200 nm or less is obtained by measuring the reflectance at wavelengths of 400 nm or more and 1200 nm or less in accordance with the method for obtaining the total light reflectance specified in JIS K7375:2008 and calculating the average reflectance. As the ultraviolet-visible near-infrared spectrophotometer, “V-670” manufactured by JASCO Corporation is used, and as the integrating sphere unit, “INL-725 type” manufactured by JASCO Corporation is used. The incident angle is 5°, and the measurement wavelength range is 400 nm or more and 1200 nm or less. As the standard white plate, “095G” manufactured by JASCO Corporation is used.

[0105] 7. Use of the Reflective Sheet for Solar Cells The reflective sheet for solar cells in the present disclosure is laid on the site where the solar cell module is installed in a solar power generation system. The solar power generation system will be described later.

[0106] The reflective sheet for solar cells in the present disclosure is preferably used for a double-sided lighting type solar cell. By using the reflective sheet for solar cells, the power generation efficiency can be improved even in the case of a single-sided lighting type solar cell, but the power generation efficiency can be further improved in the case of a double-sided lighting type solar cell.

[0107] B. Solar Power Generation Device The photovoltaic power generation system in the present disclosure includes a solar cell module and a reflective sheet for solar cells laid on a site where the solar cell module is installed. The reflective sheet for solar cells has, in order from the solar cell module side, a first resin film which is a reflective film, a cloth base material, and a second resin film, in this order.

[0108] FIG. 4 is a schematic diagram illustrating the photovoltaic power generation system in the present disclosure. As shown in FIG. 4, the photovoltaic power generation system 20 includes a solar cell module 21, a pedestal 22 on which the solar cell module 21 is installed, and a reflective sheet 10 for solar cells laid on a site 23 where the solar cell module 21 is installed.

[0109] In the photovoltaic power generation system in the present disclosure, by using the above-described reflective sheet for solar cells, the power generation efficiency can be increased.

[0110] Hereinafter, the photovoltaic power generation system in the present disclosure will be described for each component.

[0111] 1. Reflective Sheet for Solar Cells In the present disclosure, the reflective sheet for solar cells is the same as the above-described reflective sheet for solar cells, so the description here is omitted. The reflective sheet for solar cells is arranged such that the first resin film faces the solar cell module side and the second resin film faces the ground.

[0112] The reflective sheet for solar cells is laid on a site where the solar cell module is installed. The reflective sheet for solar cells may be laid over the entire site where the solar cell module is installed, may be laid under the solar cell module in the site where the solar cell module is installed, or may be laid around the solar cell module in the site where the solar cell module is installed. Since the angle at which sunlight can be efficiently reflected varies depending on the installation height and angle of the solar cell module, the latitude of the location of the photovoltaic power generation system, etc., the position of the reflective sheet for solar cells is set as appropriate.

[0113] 2. Solar Cell Module As the solar cell module in the present disclosure, a general solar cell module can be used. The installation angle of the solar cell module is not particularly limited.

[0114] 3. Other Configurations The solar power generation system in the present disclosure usually has a pedestal for installing the solar cell module. As the pedestal, a general pedestal can be used.

[0115] Other configurations of the solar power generation system are the same as those of a general solar power generation system.

[0116] Note that the present disclosure is not limited to the above embodiments. The above embodiments are examples, and those having a configuration substantially the same as the technical idea described in the claims of the present disclosure and exhibiting the same operational effects are included in the technical scope of the present disclosure regardless of what they are.

Example

[0117] Hereinafter, examples and comparative examples are shown to further explain the present disclosure.

[0118] [Example 1] As the first resin film, a linear low-density polyethylene (density 0.93 g / cm 3 , melting point 115 °C, MFR 2 g / 10 min), titanium oxide, and HALS ("XJ100H" manufactured by Nippon Polyethylene Co., Ltd.) were contained, and a white polyethylene film (manufactured by Tamapoly Co., Ltd., "RSW100") with a thickness of 40 μm was used. Also, as the second resin film, a linear low-density polyethylene (density 0.93 g / m 3 , melting point 118 °C, MFR 2 g / 10 min) and titanium oxide were contained, and a white polyethylene film (manufactured by Tamapoly Co., Ltd., "SE625NWT02") with a thickness of 30 μm was used. Also, as the cloth substrate, a polyethylene non-woven fabric (manufactured by ENEOS Techno Materials Co., Ltd., "WALIF EX(T)", basis weight 45 g / m 2) was used. As the extrusion coating resin, low-density polyethylene (Sumika Sei L420 manufactured by Sumitomo Chemical Co., density 0.924 g / cm 3 , melting point 106 °C, MFR 3.5 g / 10 min) was used.

[0119] The first resin film, the cloth substrate, and the second resin film were laminated by an extrusion lamination method via the extrusion coating resin. As a result, a reflective sheet for solar cells having a first resin film, a first adhesive layer, a cloth substrate, a second adhesive layer, and a second resin film was obtained.

[0120] [Comparative Example 1] An aluminum reflective and weed-proof sheet manufactured by DMM Energy Co., Ltd. was used. This aluminum reflective and weed-proof sheet has an aluminum foil, an adhesive layer, a glass cloth, and a polyethylene resin layer.

[0121] [Comparative Example 2] "Rurun Sheet White Pikachu" manufactured by Koizumi Seima Co., Ltd. was used. Rurun Sheet White Pikachu is a white polypropylene fabric.

[0122] [Comparative Example 3] "Tyvek 1000AG" manufactured by DuPont was used. Tyvek is a white high-density polyethylene non-woven fabric.

[0123] [Comparative Example 4] "Mighty Sheet 150" manufactured by IQg Co., Ltd. was used. Mighty Sheet 150 has a white polyethylene terephthalate non-woven fabric and a black polyethylene terephthalate non-woven fabric.

[0124] [Comparative Example 5] "TS Up Sheet" manufactured by Taniguchi Sangyo Co., Ltd. was used. TS Up Sheet is a white polyethylene non-woven fabric.

[0125] [Comparative Example 6] "Hybrid Up Sheet" manufactured by Taniguchi Sangyo Co., Ltd. was used. Hybrid Up Sheet has a white polyethylene cloth, an adhesive layer, and an aluminum vapor-deposited film.

[0126] [Evaluation] (1) Tensile strength (1-1) Initial Test pieces with a width of 10 mm and a length of 150 mm were cut out from the reflective sheet for solar cells in the MD direction and TD direction respectively. Using a precision universal testing machine (Autograph), a tensile test was conducted at a gauge length of 100 mm and a tensile speed of 100 mm / min to measure the tensile strength. The tensile strength was measured for 10 test pieces, and the arithmetic mean value was adopted.

[0127] (1-2) Pressure cooker test Using a pressure cooker tester (「HASTTEST」manufactured by Hirayama Seisakusho Co., Ltd.), the conditions were set to 120 °C, 85% RH, and 1.6 atm, and the reflective sheet for solar cells was inserted for a predetermined time. After each elapsed time, it was left at room temperature for several hours. Then, in the same manner as above, the tensile strength was measured. And the retention rate of the tensile strength before and after the pressure cooker test was obtained from the following formula. Retention rate of tensile strength (%) = (Tensile strength after test / Tensile strength before test) × 100

[0128] (1-3) Super UV test Using a super UV tester (「Eye Super UV Tester」manufactured by Iwasaki Electric Co., Ltd.), light source: metal halide lamp, illuminance: 1000 W / m 2 (wavelength from 300 nm to 400 nm), black panel temperature: 63 °C, the reflective sheet for solar cells was inserted for a predetermined time. Then, in the same manner as above, the tensile strength was measured. And in the same manner as the above pressure cooker test, the retention rate of the tensile strength before and after the super UV test was obtained from the above formula.

[0129] (1-4) Chemical resistance The reflective sheet for solar cells was immersed in a 0.5% sodium hydroxide aqueous solution (alkaline solution) with a pH of 13 for 48 hours and then air-dried. Then, in the same manner as above, the tensile strength and the retention rate of the tensile strength before and after the pressure cooker test, as well as the tensile strength and the retention rate of the tensile strength before and after the super UV test were obtained.

[0130] Also, the reflective sheet for solar cells was immersed in a 5% sulfurous acid aqueous solution (acidic solution) with a pH of 1.5 for 48 hours and then air-dried. Thereafter, in the same manner as above, the breaking strength and the breaking strength retention rate before and after the pressure cooker test, and the breaking strength and the breaking strength retention rate before and after the super UV test were determined.

[0131] The results are shown in Tables 1 and 2. It was confirmed that the breaking strength retention rate was high and the durability was excellent both after immersion in the alkaline solution and after immersion in the acidic solution.

[0132]

Table 1

[0133]

Table 2

[0134] (1-5) Damp heat test The damp heat test was conducted under the conditions of 85°C and 85% RH. Then, in the same manner as the above pressure cooker test, the breaking strength retention rate before and after the damp heat test was determined from the above formula. The results are shown in Table 3. In Comparative Example 1, the decrease in the breaking strength after the damp heat test was significant and the durability was low. On the other hand, in Example 1, it was confirmed that the breaking strength retention rate was high and the durability was excellent.

[0135]

Table 3

[0136] (2) Elongation at break (2-1) Initial Test pieces with a width of 10 mm and a length of 150 mm were cut out from the reflective sheet for solar cells. Using a precision universal testing machine (Autograph), a tensile test was conducted at a gauge length of 100 mm and a tensile speed of 100 mm / min to measure the elongation at break. The elongation at break was measured for 10 test pieces, and the arithmetic mean value was adopted.

[0137] (2-2) Pressure Cooker Test In the same manner as above, a pressure cooker test was conducted on the reflective sheet for solar cells. After that, in the same manner as above, the elongation at break was measured. Then, the retention rate of elongation at break before and after the pressure cooker test was determined from the following formula. Retention rate of elongation at break (%) = (Elongation at break after test / Elongation at break before test) × 100

[0138] (2-3) Super UV Test In the same manner as above, a super UV test was conducted on the reflective sheet for solar cells. After that, in the same manner as above, the elongation at break was measured. Then, in the same manner as the above pressure cooker test, the retention rate of elongation at break before and after the super UV test was determined from the above formula.

[0139] (2-4) Chemical Resistance The reflective sheet for solar cells was immersed in a 0.5% sodium hydroxide aqueous solution (alkaline solution) at pH 13 for 48 hours and then air-dried. After that, in the same manner as above, the elongation at break and the retention rate of elongation at break before and after the pressure cooker test, as well as the elongation at break and the retention rate of elongation at break before and after the super UV test, were determined.

[0140] Also, the reflective sheet for solar cells was immersed in a 5% sulfurous acid aqueous solution (acidic solution) at pH 1.5 for 48 hours and then air-dried. After that, in the same manner as above, the elongation at break and the retention rate of elongation at break before and after the pressure cooker test, as well as the elongation at break and the retention rate of elongation at break before and after the super UV test, were determined.

[0141] The results are shown in Tables 4 and 5. It was confirmed that in both cases after immersion in the alkaline solution and after immersion in the acidic solution, the retention rate of elongation at break was high and the durability was excellent.

[0142]

Table 4

[0143]

Table 5

[0144] (2-5) Damp heat test The damp heat test was carried out under the conditions of 85 °C and 85% RH. Then, in the same manner as the above pressure cooker test, the elongation at break retention rate before and after the damp heat test was determined from the above formula. The results are shown in Table 6. In Comparative Example 1, the decrease in the elongation at break after the damp heat test was remarkable, and the durability was low. On the other hand, in Example 1, it was confirmed that the elongation at break retention rate was high and the durability was excellent.

[0145]

Table 6

[0146] (3) Degree of yellowing (ΔYI) In the same manner as above, a super UV test was performed on the reflective sheet for solar cells. Using a spectrophotometer "CM-2500c" manufactured by Konica Minolta, the yellowness index (YI) of the reflective sheet for solar cells before and after ultraviolet irradiation was determined under the conditions of a D65 light source and an observation field of view of 2°. Then, the degree of yellowing (ΔYI) was calculated from the following formula. ΔYI was calculated for 10 test pieces, and the arithmetic mean value was adopted. ΔYI = YI after ultraviolet irradiation - YI before ultraviolet irradiation

[0147] The reflective sheet for solar cells was immersed in a 0.5% sodium hydroxide aqueous solution (alkaline solution) with a pH of 13 for 48 hours and then naturally dried. Then, in the same manner as above, the degree of yellowing before and after ultraviolet irradiation was determined.

[0148] Also, the reflective sheet for solar cells was immersed in a 5% sulfurous acid aqueous solution (acidic solution) with a pH of 1.5 for 48 hours and then naturally dried. Then, in the same manner as above, the degree of yellowing before and after ultraviolet irradiation was determined.

[0149] The results are shown in Table 7. It was confirmed that there was no discoloration due to ultraviolet rays and the reflectance could be maintained, that is, the light resistance was excellent.

[0150]

Table 7

[0151] (4) Antifouling property First, 5 g of sand was freely dropped from a height of 10 cm onto the φ70 mm range on the sample using a funnel. For Example 1, the sand was dropped onto the surface of the first film side of the reflective sheet for solar cells. After the sample was set vertically and the sand was dropped, the degree of sand adhesion was observed visually. Next, the sample after the sand was dropped was washed away with water at a constant flow rate for 30 seconds, allowed to stand and dry, and then the degree of sand adhesion was observed visually again. Furthermore, for the initial stage, after the sand was dropped, and after the water washing, the total light reflectance of the φ70 mm area where the sand was freely dropped was measured. Specifically, the sample was cut into a 5 cm square, and in accordance with JIS K7375:2008, using a UV-visible near-infrared spectrophotometer "V-670" manufactured by JASCO Corporation and an integrating sphere unit "INL-725 type" manufactured by JASCO Corporation, with a standard white plate "095G" manufactured by JASCO Corporation, the total light transmittance in the range of a wavelength of 400 nm or more and 1200 nm or less at an incident angle of 5° was measured. Then, the reflectance retention rate was calculated. The results are shown in Table 8.

[0152]

Table 8

[0153] Since the reflective sheet for solar cells of Example 1 has the first resin film on the outermost surface, the surface is smooth, so it is difficult to get dirty and easy to remove dirt. As a result, it was confirmed that the reflectance could be maintained even after the antifouling test, and it has excellent antifouling properties.

[0154] (5) Total light reflectance The sample was cut into a 5 cm square, and in accordance with JIS K7375:2008, using a UV-visible near-infrared spectrophotometer "V-670" manufactured by JASCO Corporation and an integrating sphere unit "INL-725 type" manufactured by JASCO Corporation, with a standard white plate "095G" manufactured by JASCO Corporation, the total light transmittance in the range of 400 nm or more and 1200 nm or less at an incident angle of 5° was measured. For Example 1, the total light transmittance of the surface on the first film side of the reflective sheet for solar cells was measured.

[0155]

Table 9

[0156] (6) Interlayer strength In the reflective sheet for solar cells of Example 1, the interlayer strength between the first resin film and the cloth base material, and the interlayer strength between the cloth base material and the second resin film were measured. Also, in the sheet of Comparative Example 1, the interlayer strength between the aluminum foil and the adhesive layer, the interlayer strength between the adhesive layer and the glass cloth, and the interlayer strength between the glass cloth and the polyethylene resin layer were measured. Further, in the sheet of Comparative Example 6, the interlayer strength between the white polyethylene fabric and the adhesive layer, and the interlayer strength between the adhesive layer and the aluminum vapor-deposited film were measured. The interlayer strength was measured in accordance with JIS K6854-2:1999, using a tensile testing machine ("Tensilon RTE-1210" manufactured by A&D Company), and a test piece cut out to a width of 15 mm from the sheet was peeled off under the conditions of a temperature of 25 ± 5°C, a humidity of 50 ± 10% RH, a tensile speed of 300 mm / min, and a peel angle of 180°. The interlayer strength was measured for 3 test pieces, and the arithmetic mean value was adopted.

[0157]

Table 10

[0158] In Example 1, since the first resin film, the first adhesive layer, the cloth base material, the second adhesive layer, and the second resin film all contained a polyethylene-based resin, the interlayer adhesiveness was excellent.

[0159] The present disclosure provides the following inventions. [1] A reflection sheet for a solar cell, having a first resin film which is a reflection film, a cloth base material, and a second resin film in this order. [2] The reflection sheet for a solar cell according to [1], wherein the first resin film, the cloth base material, and the second resin film contain a polyolefin resin. [3] The reflection sheet for a solar cell according to [1] or [2], having a void between the first resin film and the second resin film in a cross-section in the thickness direction of the reflection sheet for a solar cell. [4] The reflection sheet for a solar cell according to any one of [1] to [3], which is used for a double-sided lighting type solar cell. [5] A solar cell module, A reflection sheet for a solar cell laid on a site where the solar cell module is installed, and a solar power generation system comprising the same, wherein the reflection sheet for a solar cell has a first resin film which is a reflection film, a cloth base material, and a second resin film in this order from the solar cell module side. [6] The solar power generation system according to [5], wherein the solar cell module is a double-sided lighting type solar cell module.

Explanation of symbols

[0160] 1... First resin film 2... Cloth base material 3... Second resin film 10... Reflection sheet for a solar cell

Claims

1. A reflection sheet for a solar cell, comprising a first resin film which is a reflection film, a cloth substrate, and a second resin film, in this order.

2. The reflection sheet for a solar cell according to Claim 1, wherein the first resin film, the cloth substrate, and the second resin film contain a polyolefin-based resin.

3. The reflection sheet for a solar cell according to Claim 1 or Claim 2, having a void between the first resin film and the second resin film in a cross-section in the thickness direction of the reflection sheet for a solar cell.

4. The reflection sheet for a solar cell according to Claim 1 or Claim 2, which is used for a double-sided sunlight collection type solar cell.

5. A solar power generation system, comprising: a solar cell module; and a reflection sheet for a solar cell laid on a site where the solar cell module is installed, the reflection sheet for a solar cell having, in order from the solar cell module side, a first resin film which is a reflection film, a cloth substrate, and a second resin film, in this order.

6. The solar power generation system according to Claim 5, wherein the solar cell module is a double-sided sunlight collection type solar cell module.

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