JP6471501B2 - Back surface protection sheet for solar cell module and solar cell module using the same - Google Patents

Description

  The present invention relates to a back protective sheet for a solar cell module having excellent light reflectivity and a solar cell module using the same.

In recent years, solar cells as a clean energy source have attracted attention due to the growing awareness of environmental issues. In general, a solar cell module constituting a solar cell has a structure in which each member of a transparent front substrate, a front surface side sealing material, a solar cell element, a back surface side sealing material, and a back surface protection sheet is laminated in order from the light receiving surface side. And has a function of generating electric power when sunlight enters the solar cell element.
The back protection sheet for solar cell modules requires adhesion to the sealing material to prevent moisture from entering from the back protection sheet side, and durability that can withstand outdoor use for long periods of harsh environments. Has been. At present, in addition to this physical property, light that has passed through the gaps between solar cell elements without contributing to power generation out of incident light to the solar cell module is reflected by the solar cell elements, and power is generated using the reflected light. The effect of increasing the efficiency is also expected for the back surface protection sheet. As such a back protective sheet having light reflectivity, a sheet having a white resin layer is generally known (Patent Document 1).

  Moreover, the structure of the back surface protection sheet for using an incident solar ray efficiently is proposed for the further power generation efficiency improvement. In Patent Documents 2 and 3, a layer containing white particles having a particle size relatively larger than that of general general-purpose white particles is laminated on a layer containing general general-purpose white particles, so that it is close to visible light. The back surface protection sheet which reflects the light of the wavelength between infrared lights and improves the power generation efficiency of a solar cell is disclosed.

JP 2006-270025 A JP 2011-173241 A JP 2014-160810 A

However, in order to direct more passing light to the surface of the solar cell element and improve the power generation efficiency of the solar cell module, it is not sufficient to simply increase the light reflectance of the back surface protection sheet, It is necessary to diffuse the incident light and increase the light reflectivity in the high angle region with respect to the back surface protection sheet, and the back surface protection sheets described in Patent Documents 2 and 3 are based on such knowledge. Nothing is given.
The subject of this invention is providing the back surface protection sheet for solar cells which has a light reflection layer which optimized the diffusion angle distribution, and can contribute to the improvement of power generation efficiency.

As a result of intensive studies to solve the above problems, the inventors of the present invention have a multilayer structure having a first reflective layer and a second reflective layer in a solar cell back surface protective sheet having light reflectivity, It has been found that the above problem can be solved by setting the sum of the reflected light intensities in the high angle region to a specified value or more, and the present invention has been completed. More specifically, the present invention provides the following.

(1) A back surface protection sheet for a solar cell module including a multilayer sheet laminated in the order of at least a base material layer, a second reflective layer, and a first reflective layer, wherein the first reflective layer has an average particle diameter. The second reflective layer contains white particles having an average particle size of 0.40 μm or less, and is obtained by measurement of the following diffusion angle distribution. A back surface protective sheet having a total sum of reflected light intensities of 43 ° or more when receiving light is 5.4 or more.
The diffusion angle distribution is measured according to JIS Z 8722 “Measurement Method of Color-Reflection and Transmission Object Color” 5.3.3 “Measurement of Spectral Reflectance” Method a (when using a two-pass spectrophotometer and a substitution method) ).
(2) The back surface protection according to (1), wherein the thickness of the first reflective layer is 1.0 μm or more and 20.0 μm or less, and the white particles contained in the first reflective layer have a Mohs hardness of 3.0 or less. Sheet.
(3) The white particles contained in the first reflective layer are formed between the major axis direction of the white particles and the planar direction of the base material layer on the first reflective layer side in the first reflective layer. The back surface protective sheet according to (1) or (2), which is oriented in such a manner that the angle is 10 degrees or more and 60 degrees or less.
(4) A solar cell module provided with the back surface protection sheet in any one of (1) to (3).

ADVANTAGE OF THE INVENTION According to this invention, it can provide the back surface protection sheet for solar cells which contributes to the improvement of electric power generation efficiency by having the light reflection layer which was excellent in the reflectance of light, and optimized the light diffusion angle distribution. .

It is a schematic diagram of the cross section which illustrates an example of the laminated constitution of the solar cell module using the back surface protection sheet of this invention. It is the partial expansion schematic diagram of the cross section of the solar cell module using the back surface protection sheet of this invention. It is drawing which uses for description about the correlation with the reflection angle of the diffuse reflection in a solar cell module, and the amount of light collection of a solar cell element. It is a schematic diagram of the cross section which illustrates an example of the layer structure of the back surface protection sheet which concerns on 1st Embodiment of this invention. It is a schematic diagram of the cross section which illustrates an example of the layer structure of the back surface protection sheet which concerns on 2nd Embodiment of this invention.

Hereinafter, the back surface protection sheet of this invention and the detail of a solar cell module using the same are demonstrated. The present invention is not limited to the embodiments described below.

<Basic configuration of solar cell module>
First, the basic structure of the solar cell module using the back surface protective sheet of the present invention will be described. FIG. 1 is a schematic cross-sectional view showing an example of a layer structure of a solar cell module. As shown in FIG. 1, the solar cell module 10 includes a transparent front substrate 5, a light receiving surface side sealing material sheet 4, a solar cell element 3, a non-light receiving surface side sealing material sheet 2, from the light receiving surface side of the incident light 6. It is the structure by which the back surface protection sheet 1 of this invention was laminated | stacked in order. The solar cell module 10 is manufactured by sequentially laminating these layers and then using a conventional molding method such as a lamination method in which the layers are integrated by vacuum suction or the like and thermocompression bonded. can do.

  FIG. 2 is an enlarged schematic view showing a part of the cross section of the solar cell module 10. As shown in FIG. 2, in the solar cell module 10 provided with the back surface protection sheet 1, the incident light 6 </ b> A that has passed through the back surface protection sheet 1 and does not contribute to power generation is reflected by the back surface protection sheet 1. Thus, the light-receiving surface of the solar cell element 3 can be reached. The back surface protective sheet 1 is a material that significantly improves the contribution to the improvement of power generation efficiency by optimizing the diffusion angle distribution while increasing the light reflectance.

  Here, the diffusion angle distribution is an index value indicating the distribution of the angle (optical path) after reflection of light reflected by the surface of the base material used as the light reflection layer. The angle distribution of the reflected light is determined according to JIS Z 8722 “Color measurement method-reflective and transmissive object color” 5.3.3 “Spectral reflectance measurement” method a (substitution method using a two-path spectrophotometer. Measure in accordance with In the present invention, focusing on this diffusion angle distribution as an evaluation index of the reflection performance of various light reflecting materials such as the back surface protection sheet, in particular, the integrated total value of the reflected light intensity at a light receiving angle of 43 ° or more is used as the light reflection. It was used as an evaluation index for performance.

  A method for obtaining the evaluation index will be described. First, the incident angle of the incident light on the surface of the reflective base material to be evaluated is fixed at 0 ° (normal angle with respect to the base material surface). Next, the light receiving angle that receives the reflected light to be measured is varied in the range of 30 ° to 75 ° C. with respect to 0 °, and the intensity of the reflected light is measured for each angle. Then, the total sum of the reflected light intensities having a light receiving angle of 43 ° or more was calculated, and this value was used as an evaluation index for the light reflection performance of the back surface protection sheet.

  The reason why the total sum of the reflected light intensities at a light receiving angle of 43 ° or more is used as an evaluation index for the light reflection performance of the back surface protection sheet is as follows. As shown in FIG. 3, for example, as a reference value for evaluation in a standard solar cell module, the refractive index of the light-receiving surface side sealing material sheet 4 is 1.4 (n = 1.4), and the transparent front surface made of glass Assume that the refractive index of the substrate 5 is 1.51 (n = 1.51), and the refractive index of air is 1 (n = 1). As described above, with respect to the reflected light of 0 ° incident light, the behavior of the reflected light at the interface between the transparent front substrate 5 and the air is calculated based on Snell's law. Then, as shown in FIG. 3, the reflected light having a light receiving angle of 43 ° (θ2 = 43 °) or more out of the reflected light reflected on the back surface protective sheet 1 is totally reflected on the transparent front substrate 5 to be solar cell element 3. It will reach the light receiving surface again.

Here, the value of 43 ° as the critical value is a numerical value that causes a slight variation depending on the layer configuration of the solar cell module. However, the correlation between the light receiving angle and the power generation efficiency that the rate of improvement in power generation efficiency changes discontinuously in the preferred direction when the above light receiving angle value exceeds a certain critical value near 43 ° is Since the solar cell module having a general configuration is generally universally recognized, the critical value as an index for evaluating the performance of the back surface protection sheet is set to 43 °. This value is considered to be extremely appropriate as a general-purpose evaluation index of the light reflection performance of the back surface protection sheet for solar cell modules.
As the solar cell element 3, various conventionally known solar cell elements can be used without particular limitation. Here, the solar cell element generally has a high spectral sensitivity with respect to light of 300 nm to 1500 nm. More specifically, the amorphous silicon type solar cell element is 300 nm to 1500 nm, the crystalline silicon type solar cell element is 300 nm to 1200 nm, the CdTe type solar cell element is 400 nm to 900 nm, and the CIS type solar cell. The element has a spectral sensitivity to light of 300 nm to 1500 nm, and the GaAs solar cell element has a spectral sensitivity to light of 300 nm to 900 nm. Although the back surface protective sheet of the present invention can be used for a solar cell module using any of the above solar cell elements, as will be described later, particularly for light in a high wavelength region of 1000 nm or more, such as a crystalline silicon solar cell element. On the other hand, it can be very preferably used for a solar cell module using a solar cell element having high spectral sensitivity. Moreover, it can use preferably also for a solar cell module provided with not only a single-sided light reception type solar cell element but a double-sided light reception type solar cell element.

  The non-light-receiving surface side sealing material sheet 2 and the light-receiving surface side sealing material sheet 4 are both surfaces of the solar cell element 3 in the solar cell module 10 mainly for protecting the solar cell element 3 from external impact. It is the resin sheet arrange | positioned covering. As a resin base material forming these encapsulant sheets, various thermoplastic resins such as polyolefin resins such as ethylene-vinyl acetate copolymer resin (EVA), ionomer, polyvinyl butyral (PVB), and polyethylene are appropriately used. Although it can be used, the non-light-receiving surface side sealing material sheet 2 preferably has a high light transmittance because light can be efficiently taken into the back surface protection sheet. Here, the light transmittance is the transmittance of light having a wavelength of 300 nm to 1500 nm in which the solar cell element has high spectral sensitivity, and the light transmittance of the non-light-receiving surface side sealing material sheet 2 of the present invention is: It is preferable that it is 80% or more.

  The transparent front substrate 5 is generally a glass substrate. The transparent front substrate 5 may also be another member as long as it maintains the weather resistance, impact resistance, and durability of the solar cell module 10 and transmits sunlight with high transmittance. .

<Back protection sheet>
[First Embodiment]
As shown in FIG. 4, the back surface protective sheet 1 according to the first embodiment of the present invention is a resin sheet having a multilayer structure in which at least a base material layer 11, a second reflective layer 12, and a first reflective layer 13 are sequentially laminated. It is. Although the thickness of the back surface protection sheet 1 is not specifically limited, The thickness of the range of 20 micrometers or more and 500 micrometers or less can be mentioned as a general example. And as shown in FIG. 1, the back surface protection sheet 1 is arrange | positioned and used in the solar cell module 10 in the aspect from which this 1st reflective layer 13 becomes a light-receiving surface side. In addition, the thickness of each layer and sheet | seat in this invention measures the thickness of the arbitrary 5 places of the said layer or sheet | seat, respectively, and is given as the arithmetic mean value.

  The back surface protective sheet 1 of the present invention has an essential requirement that the total sum of reflected light intensities at a light receiving angle of 43 ° or more when 0 ° light enters is 5.4 or more. By setting the total sum of the reflected light intensities of the back surface protection sheet 1 to 5.4 or more, the power generation efficiency of the solar cell module 10 can be significantly improved.

  Moreover, although it is not an essential constituent requirement of the back surface protection sheet of the present invention, the back surface protection sheet 1 has a weather resistant layer (not shown) on the surface of the base material layer 11 opposite to the surface on which the second reflective layer 12 is formed. ) May be further provided. As the weather resistant layer, a layer excellent in weather resistance, heat resistance, light resistance and the like is used. Preferred examples of such a resin sheet include polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene perfluoroalkyl vinyl ester copolymer (PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene A resin sheet such as an ethylene copolymer (ETFE) or a fluororesin such as polyvinylidene fluoride (PVDF) can be given.

(Base material layer)
The base material layer 11 is a resin layer disposed as a base material of the back surface protection sheet 1. As a material of the base material layer 11, what molded the following resin material in the sheet form can be used. For example, polyethylene resin, cyclic polyolefin resin, polystyrene resin, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, polyvinyl chloride resin, poly (meth) acrylic resin, polycarbonate resin, polyethylene Polyester resins such as terephthalate (PET) and polyethylene naphthalate, polyamide resins such as various nylons, polyimide resins, polyamideimide resins, polyarylphthalate resins, silicone resins, polysulfone resins, polyphenylene sulfide resins Various resin sheets such as polyethersulfone resin, polyurethane resin, acetal resin, and cellulose resin can be used as the base material layer 11. Among these, polyethylene terephthalate (PET) can be preferably used as the material of the base material layer 11 from the viewpoints of physical properties such as insulation performance, mechanical strength, cost, transparency, and economy. Further, from the viewpoint of further improving mechanical strength and water vapor barrier property, a multilayer sheet obtained by further laminating hydrolysis-resistant PET in addition to the above PET as the outermost layer can be particularly preferably used as the base material layer 11. .

  The thickness of the base material layer 11 is not particularly limited. As described above, the thickness may be appropriately determined in consideration of the total thickness of the back surface protective sheet 1 generally in the range of 20 to 500 μm, but it is preferably 10 μm or more and 250 μm or less. When the thickness of the base material layer 11 is 10 μm or more, preferable durability and weather resistance can be imparted to the back surface protection sheet 1, and when the thickness of the base material layer 11 is 250 μm or less, lamination processing is performed. It is possible to impart sheet transportability at the time.

(Second reflection layer)
The second reflective layer 12 is a layer disposed between the base material layer 11 and the first reflective layer 13, and is a layer having light reflectivity together with the first reflective layer 13. As the material of the second reflective layer 12, various resin sheets can be used, but an olefin resin, specifically, a polypropylene (PP) or polyethylene (PE) resin is preferably used as the base resin. Can do. In particular, by using a polypropylene (PP) resin as the base resin of the second reflective layer 12, appropriate heat resistance can be imparted to the back surface protective sheet 1.

In addition, the back surface protection sheet 1 should be preferable for improving the barrier property and durability of the solar cell module by using a polyethylene (PE) resin as the base resin of the second reflective layer 12. Can do. This is because polyethylene (PE) -based resin has a low melting point, and adhesion between layers is increased by melting at the time of lamination, and chemical stability is high and durability of the resin is high. Specific examples of such a polyethylene (PE) resin include linear low density polyethylene (LLDPE) of about 0.890 g / cm ^{3 to} 0.910 g / cm ³ or less.

  The thickness of the second reflective layer 12 may be determined as appropriate in consideration of the thickness required for the back surface protective sheet 1. As an example, the thickness of the second reflective layer 12 is 3 to 200 μm, and is not particularly limited. When the thickness of the 2nd reflective layer 12 is 3 micrometers or more, sufficient adhesiveness between the other layers of the back surface protection sheet 1 can be provided.

  The second reflective layer 12 contains white particles having an average particle diameter of 0.40 μm or less, whereby the same layer exhibits a function as a white light reflective layer. The type of white particles contained in the second reflective layer 12 is not particularly limited, and calcium carbonate, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate, calcium sulfate, zinc oxide, magnesium oxide, calcium oxide, titanium oxide, and alumina. Various white particles such as aluminum hydroxide, hydroxyapatite, silica, mica, talc, kaolin, clay, glass powder, asbestos powder, zeolite, silicate clay, etc. can be used. In particular, it is preferable to use white particles having a large refractive index from the viewpoint that a large difference in refractive index from the base resin is obtained and an excellent reflection performance is obtained. Specific examples include calcium carbonate, barium sulfate, titanium oxide, and zinc oxide having a refractive index of 1.6 or more.

  Above all, titanium oxide with a refractive index of 2.5 or more can remarkably increase the difference in refractive index from the base resin, so it has a high reflection performance with a smaller blending amount than when other fillers are used. And heat shielding performance can be imparted to the second reflective layer 12. Titanium oxide is excellent in weather resistance, can be easily made into a paint, and is widely used. Therefore, titanium oxide having various average particle diameters is available at low cost.

  Further, the content of the white particles contained in the second reflective layer 12 is particularly as long as the total sum of the reflected light intensities of the light receiving angle of 43 ° or more when entering 0 ° as the back surface protective sheet is 5.4 or more. Although not limited, 10 mass% or less and 30 mass% or less are preferable, and, as for content in the resin component which forms a layer, 15 to 25 mass% is more preferable. When the content of the white particles is less than 10% by mass, the reflection performance is lowered and the power generation efficiency is lowered, which is not preferable. When the content of the white particles exceeds 30% by mass, the resin is hard and brittle. This is not preferable because the mechanical strength is lowered.

The white particles contained in the second reflective layer 12 have an average particle size of 0.40 μm or less, more preferably 0.30 μm or less. The back surface protection sheet 1 has optimized the reflection performance of the back surface protection sheet 1, that is, the above-described diffusion angle distribution, by making the particles contained in the second reflection layer 12 and the first reflection layer 13 into a unique combination. It is characteristic in that it is a thing.
Here, the average particle diameter in the present invention indicates a volume average particle diameter measured by a laser diffraction method, and the measurement is performed according to ISO 13320.

(First reflective layer)
The first reflective layer 13 is a layer disposed on the surface of the second reflective layer 12 opposite to the base material layer 11, and is a layer having light reflectivity together with the second reflective layer 12. The material of the first reflective layer 13 is selected in the same manner as the second reflective layer 12 described above. Here, the first reflective layer 13 and the second reflective layer 12 are preferably coextruded layers made of the same kind of thermoplastic resin. By forming the two layers with the same kind of thermoplastic resin, the adhesion between the two layers is improved, so that the barrier property and durability of the back surface protective sheet 1 can be made preferable.

The first reflective layer 13 contains plate-shaped white particles having an average particle diameter of 0.75 μm or more. The kind of white particle is not particularly limited, and various white particles satisfying the above average particle diameter and shape can be used. In particular, when the white particles having an average particle diameter of 0.75 μm or more are hard particles, the extrusion machine and the sheet are cut, the burden on the manufacturing machine increases, and film formation may be impossible. It is preferable to use white particles having a low Mohs hardness. Specific examples include calcium carbonate, calcium sulfate, and talc having a Mohs hardness of 3.0 or less.
Here, the long axis of the particle means a line segment indicating the maximum length of the particle, and the short axis of the particle is a line segment indicating the maximum length of the particle in a direction perpendicular to the long axis direction. The thickness of the particle means a line segment indicating the maximum length of the particle in a direction perpendicular to the horizontal plane when the particle is stably placed on the horizontal plane. Further, the plate-like shape in the present invention refers to a plate having a minor axis / thickness length ratio (minor axis length / thickness length) of 2 or more. In the plate-like particles contained in the first reflective layer, the ratio is preferably 5 to 1000, more preferably 10 to 1000. By using the plate-like particles for the first reflective layer 13, it is possible to obtain the back surface protective sheet 1 that is more excellent in light reflectivity and optimized in the light diffusion angle distribution.

  The first reflective layer 13 optimizes the diffusion angle distribution of the back surface protective sheet 1 in combination with the second reflective layer 12. The second reflective layer 12 of the present invention contains general general-purpose white particles having an average particle diameter of 0.40 μm or less, and has excellent light reflectivity. When incident light is considered, the incident light is almost regularly reflected. On the other hand, the first reflective layer has an average particle diameter of 0.75 μm or more, has an average particle size larger than that of the second reflective layer 12, and contains plate-shaped white particles. Excellent diffusion effect in various directions. By providing the first reflective layer 13 and the second reflective layer 12, the back surface protective sheet 1 of the present invention increases the light reflectance in the high angle region, and can contribute to the improvement of power generation efficiency.

Moreover, the combination of the 1st reflective layer 13 and the 2nd reflective layer 12 in this invention brings about the following effects. As described above, the solar cell element generally has a high spectral sensitivity with respect to light of 300 nm to 1500 nm. When only the layer containing general general-purpose white particles having an average particle diameter of 0.4 μm or less is used on the light-receiving surface side of the back protective sheet, the reflectance at a wavelength of 350 nm is as high as 90 to 100%, but the long wavelength As it becomes, the reflectance decreases, and the reflectance near 1500 nm, which is the limit of absorption sensitivity of the solar cell element, decreases to 30 to 40%. That is, the general-purpose white particles that reflect light in the wavelength range with the highest sensitivity for the human eye cannot effectively use wavelengths in the near-infrared region. Therefore, by using a white pigment having an average particle size larger than that of general general-purpose white particles, light in the near infrared region can be reflected to improve the power generation efficiency of the solar cell element.
In the first reflective layer 13, the major axis direction of the plate-like white particles forms a certain angle with the plane direction of the base layer 11 on the first reflective layer side, so that the first reflective layer 13 The effect of diffusing light is further increased, and the power generation efficiency of the solar cell module can be further improved. The angle is preferably 10 degrees or more and 60 degrees or less, and more preferably 15 degrees or more and 50 degrees or less. If the angle is less than 10 degrees, the light diffusion effect is not increased, and if the angle exceeds 60 degrees, it is difficult for light to hit the plate-shaped white particles contained in the first reflective layer 13, resulting in As a result, the power generation efficiency cannot be sufficiently improved. The light diffusion effect becomes significant when 80% by mass or more, more preferably 90% by mass or more, of all the white particles in the first reflective layer 13 form the above angle. Further, in the first reflective layer 13, even if the minor axis direction of the plate-shaped white particles forms the above angle with the plane direction of the base layer 11 on the first reflective layer side, Can be increased, and the power generation efficiency of the solar cell module can be improved.
The white particles contained in the first reflective layer 13 have an average particle diameter of 0.75 μm or more, more preferably 1.0 μm or more, and further preferably 1.5 μm or more. It is known that if the particle size of the white particles is at least λ / 2 which is half the wavelength λ to be reflected, it is known that the wavelength can be reflected. If it is a back surface protection sheet provided with a layer containing white particles having a diameter of 750 nm = 0.75 μm, light having a wavelength of 1500 nm can be reflected with high efficiency.

  The content of the white particles contained in the first reflective layer 13 is not particularly limited as long as the total sum of reflected light intensities at a light receiving angle of 43 ° or more when entering 0 ° as a back protective sheet is 5.4 or more. However, the content in the resin component forming the layer is preferably 3% by mass or less and 25% by mass or less, and more preferably 5% by mass or more and 20% by mass or less. When the content of the white particles is less than 3% by mass, the reflection performance is lowered and power generation efficiency is lowered, which is not preferable. When the content of the white particles exceeds 25% by mass, the reflection performance is decreased. In addition, since the resin is hard and brittle, a decrease in mechanical strength is not preferable.

  The thickness of the first reflective layer 13 may be appropriately determined in consideration of the thickness required for the back surface protective sheet 1. As an example, 1-200 micrometers is mentioned as thickness of the 1st reflective layer 13, and it does not specifically limit. When the thickness of the 1st reflection layer 12 is 1 micrometer or more, sufficient adhesiveness between the back surface protection sheet 1 and the other layer of the solar cell module 10 can be provided.

  In addition, when the other layer is not disposed on the surface of the first reflective layer 13 opposite to the second reflective layer 12, the back surface protective sheet 1 includes the first reflective layer 13 and the non-light-receiving surface side sealing material sheet 2. It arrange | positions and uses in the solar cell module 10 in the aspect which touches. Here, in addition to light reflectivity, the back surface protection sheet for solar cell modules needs to have strong adhesion to the sealing material for the purpose of preventing moisture from entering from the back surface protection sheet side. In the case of using a general resin constituting an adhesive layer having adhesiveness with this sealing material, if the thickness is thick, positional displacement occurs at the time of lamination at the time of module creation. The adhesion layer is preferably formed with an average thickness of 1.0 μm or more and 20.0 μm or less because it causes problems such as contamination of manufacturing equipment and curling easily. However, if a layer having white particles having a relatively large particle size and high Mohs hardness is formed with a thickness equal to or less than a certain film thickness relative to the particle size, the film is formed. There was a problem that the adhesion layer was torn. Accordingly, when the first reflective layer 13 is in contact with the non-light-receiving surface side sealing material sheet 2 in the back surface protective sheet 1, the average thickness of the first reflective layer 13 is 1.0 μm or more and 20.0 μm or less, and The plate-like white particles having an average particle diameter of 0.75 μm or more contained in the first reflective layer 13 preferably have a Mohs hardness of 3.0 or less.

(Other ingredients)
The second reflective layer 12 and the first reflective layer 13 can further contain other components. For example, components such as various weather resistance master batches, various fillers, light stabilizers, ultraviolet absorbers, and heat stabilizers for imparting weather resistance to the back protective sheet 1 are exemplified. By containing these additives, the back surface protective sheet 1 can be provided with a long-term stable improvement in mechanical strength, an effect of preventing yellowing, cracking, and the like.

[Second Embodiment]
FIG. 5 is a schematic cross-sectional view showing the layer structure of the back surface protective sheet according to the second embodiment of the present invention. In addition to being able to give an angle to the plate-shaped white particles of the first reflective layer 13 by shaping the first reflective layer 13 and the second reflective layer 12 as in the present embodiment, the shape of the first reflective layer 13 and the second reflective layer 12 is given. By improving the light diffusibility due to the shape, the change in power generation efficiency due to the change in the incident angle of sunlight over time can be reduced, for example, the total power generation amount per day under the same weather conditions can be increased.

  Moreover, the back surface protection sheet 1 may include the sealing material adhesion layer 14 on the outermost surface of the first reflective layer 13 opposite to the second reflective layer 12 as in the present embodiment. As the sealing material adhesion layer, a material having excellent adhesion to the non-light-receiving surface side sealing material sheet is used. Preferable examples of the sealing material adhesion layer include olefin resins, specifically polyethylene (PE) resins having a low melting point and excellent adhesion, or polypropylene (PP) capable of imparting rigidity and heat resistance. Based resins. Further, by forming the first reflective layer 13 and the sealing material adhesion layer 14 with the same kind of thermoplastic resin, the adhesion between both layers is improved, and the barrier property and durability of the back surface protective sheet 1 are more preferable. can do.

Here, in the case of the back surface protective sheet having a concavo-convex shape on the surface, heat resistance sufficient to hold the concavo-convex shape is also required during the thermocompression treatment in the integration step of the solar cell module. Therefore, the second reflective layer 12 preferably uses a polypropylene (PP) resin having a melting point of 160 ° C. or higher as the base resin. By using the second reflective layer 12 as the resin, the second reflective layer 12 itself is hard to be softened by the laminate and can maintain the shape of the entire surface on the light receiving surface side. Therefore, the laminating temperature is preferably in the range of 110 ° C. or higher and 160 ° C. or lower, more preferably in the range of 135 ° C. or higher and 155 ° C. or lower. It is preferable because it becomes possible to maintain <a manufacturing method of a back surface protection sheet>
The manufacturing method of the back surface protection sheet of this invention is demonstrated. The back surface protection sheet 1 includes a base resin sheet forming step for forming a base resin sheet constituting the base layer 11 and a reflective resin sheet for forming the first reflective layer 13 and the second reflective layer 12. It can manufacture by passing through the resin resin sheet formation process and the integration process of laminating and integrating the reflective resin sheet on the base resin sheet.

(Base resin sheet forming process)
The base resin sheet for forming the base layer 11 is made of the resin material such as PET described above by an extrusion method, a cast molding method, a T-die method, a cutting method, an inflation method, other film forming methods, or the like. It can be formed by forming a film. The base resin sheet may contain other additives such as pigments in addition to the resin material as long as the effects of the present invention are not impaired.

(Reflective resin sheet forming process)
The reflective resin sheet includes an olefin resin, preferably polypropylene (PP) or polyethylene (PE) as a main component, a resin composition for the first reflective layer 13 containing predetermined white particles, and predetermined white particles. The resin composition for the second reflective layer 12 that is contained can be obtained by integral molding by a known coextrusion method.

(Integration process)
The back surface protective sheet of the present invention is formed by laminating and further integrating the base resin sheet, the reflective resin sheet described above, and a sheet for forming other layers formed by the same method as necessary. 1 can be obtained. The integration of the sheets can be performed by a conventionally known dry laminating method. Conventionally known laminating adhesives can be used and are not particularly limited. A two-component curable dry laminating adhesive composed of a main agent such as urethane or epoxy and a curing agent can be used as appropriate.

<Method for manufacturing solar cell module>
For example, the solar cell module 10 sequentially stacks the members including the transparent front substrate 5, the light receiving surface side sealing material sheet 4, the solar cell element 3, the non-light receiving surface side sealing material sheet 2, and the back surface protection sheet 1. Then, they can be integrated by vacuum suction or the like, and then manufactured by thermocompression-bonding the above-mentioned member as an integral molded body by a molding method such as a lamination method. For example, in the case of vacuum heat laminating, the laminating temperature is preferably in the range of 110 ° C to 160 ° C. The laminating time is preferably in the range of 5 to 20 minutes, particularly preferably in the range of 8 to 15 minutes. In this way, the solar cell module 10 can be manufactured by thermocompression-bonding each of the above layers as an integral molded body.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example.

<Manufacture of backside protection sheet>
In accordance with the above-mentioned “Production method of the back surface protection sheet”, the resin sheet materials described below are integrated by dry laminating to produce the back surface protection sheet having the layer structure shown in FIG. And it was set as the back surface protection sheet of a comparative example.

[Reflective resin sheet]
The following composition for each layer was formed as a multilayer film by coextrusion to form a resin sheet having a thickness of 60 μm (first reflective layer 6.0 μm / second reflective layer 54.0 μm), and the back surface of each example and comparative example A reflective resin sheet constituting the first reflective layer and the second reflective layer of the protective sheet was used.

(Second reflection layer composition)
Base resin: Homo PP (melting point 164 ° C.), random PP resin (melting point 140 ° C., ethylene content 3% by mass) containing ethylene, and elastomer PP resin (melting point 125 ° C., ethylene content 7% by mass), A PP resin kneaded at a ratio of 8: 1: 1 was used.

    White particles: The following titanium oxide was selectively used as shown in Table 1, and kneaded into the base resin so that the content in the base resin was 20% by mass.

Titanium oxide 1: “Ti-pure R105 (manufactured by Dupont)” Average particle size 0.23 μm
Titanium oxide 2: "Infrared shielding titanium oxide (manufactured by Teica)" Average particle diameter 1.0 μm
(First reflective layer composition)
Base resin: Homo PP (melting point 164 ° C.), random PP resin (melting point 140 ° C., ethylene content 3% by mass) containing ethylene, and elastomer PP resin (melting point 125 ° C., ethylene content 7% by mass), A PP resin kneaded at a ratio of 8: 1: 1 was used.

    White particles: The following talc was selectively used as shown in Table 1, and kneaded into the base resin so that the content in the base resin was 20% by mass.

Talc 1: “Nanoace (Nippon Talc)” Average particle size 0.8μm
Talc 2: “Microace (manufactured by Nippon Talc)”, plate shape, average particle size 2.5 μm
Talc 3: “Nanoace (made by Nippon Talc)” Average particle size 0.6μm
[Base resin sheet]
The following PET film and HR-PET film were used as the base resin sheet. And these were laminated | stacked by the dry lamination method, and it was set as the base-material resin sheet.

Polyethylene terephthalate (PET) film: thickness 188 μm (trade name “Lumirror S10”, manufactured by Toray Industries, Inc.)
Hydrolysis-resistant polyethylene terephthalate (HR-PET) film: thickness 50 μm (trade name “Lumirror X10S”, manufactured by Toray Industries, Inc.)
[Total sum of reflected light intensities with a light receiving angle of 43 ° or more at 0 ° incident light]
This was performed in accordance with JIS Z 8722 “Color measurement method—reflection and transmission object color” 5.3.3 “Spectral reflectance measurement” method a (in the case of a substitution method using a two-pass spectrophotometer).

  The diffusion angle distribution was measured according to the following procedure. First, about the back surface protection sheet of the said Example and the comparative example, the angle was changed 1 degree in the range of light reception angle 30 degrees-75 degrees, and the reflected light intensity of the light of wavelength 700nm was measured. Next, the total sum of reflected light intensities at a light receiving angle of 43 ° or more, that is, an integral value in a range of 43 ° to 75 ° was calculated.

<Evaluation of optical characteristics and PV characteristics>
About the back surface protection sheet of an Example and the comparative example 1, the diffuse reflectance and the short circuit current value were calculated | required. Evaluation was performed based on the numerical value measured by the following method. The results are shown in Table 2.

(Measurement of diffuse reflectance)
The diffuse reflectance for light having a wavelength of 700 μm was measured by the following method.

  The diffuse reflectance is measured by measuring the diffuse reflectance (%) of light having a wavelength of 700 nm when light is incident from the adhesion reinforcing layer side of each back protective sheet using a spectrophotometer (manufactured by Shimadzu Corporation, UV-3100). ), And the relative value of the diffuse reflectance, with the diffuse reflectance of the white plate solidified with fine barium sulfate powder being 100%.

(Measurement of short circuit current value)
The solar cell module of an Example and a comparative example was created using the back surface protection sheet of an Example and a comparative example, and PV characteristic as a solar cell module was evaluated. Specifically, the following sealing material sheets are laminated on the upper and lower sides of a single crystal cell (ASG-180A) manufactured by Asden Co., Ltd., and the respective back surface protective sheets of Examples or Comparative Examples are formed on the outermost layer on the non-light-receiving surface side. Then, blue plate glass was laminated on the outermost layer on the light receiving surface side and integrated by a thermal lamination method to obtain module samples for evaluation of examples of solar cell modules and comparative examples. The test is performed by measuring a short-circuit current value for each evaluation module sample using a solar simulator (EWXS-300S-50 manufactured by Eihiro Seiki Co., Ltd.) at a cell back surface temperature of 25 ° C. and an illuminance of 100 mW / cm ^2. It was. The value of the short circuit current value obtained by this measurement was used as an index of the power generation efficiency of the solar cell module, that is, the PV characteristic.

  From the results shown in Tables 1 and 2, the back protective sheet of the present invention has a light reflection layer with an optimized light diffusion angle distribution, and reflects light with a wavelength of about 700 nm that contributes to the power generation efficiency of the solar cell module. It can be seen that by optimizing the sum of the intensity and the intensity of the reflected light having a light receiving angle of 43 ° or more, it can greatly contribute to the improvement of the power generation efficiency of the solar cell module.

  In addition, it can be seen from Table 2 that simply increasing the diffuse reflectance does not always directly improve the power generation efficiency of the solar cell module. The back surface protective sheet of the present invention has been created based on a unique finding that power generation efficiency is improved by maximizing the sum of reflected light intensities above a critical angle.

DESCRIPTION OF SYMBOLS 1 Back surface protection sheet 11 Base material layer 12 2nd reflection layer 13 1st reflection layer 14 Sealing material adhesion layer 2 Non-light-receiving surface side sealing material sheet 3 Solar cell element 4 Light-receiving surface side sealing material sheet 5 Transparent front substrate 6 Incident light 6A Passing light 10 Solar cell module

Claims (4)

A solar cell module back surface protection sheet comprising a multilayer sheet laminated in the order of at least a base material layer, a second reflective layer, and a first reflective layer,
When a volume average particle size based on a spherical equivalent particle size distribution obtained by assuming spherical particles, measured by a laser diffraction method according to ISO 13320, is an average particle size,
The first reflective layer contains plate-shaped white particles having an average particle diameter of 0.75 μm or more,
The second reflective layer contains white particles having an average particle size of 0.40 μm or less,
A back surface protective sheet obtained by measurement of the following diffusion angle distribution, wherein the total sum of reflected light intensities at a light receiving angle of 43 ° or more at 0 ° incident light is 5.4 or more.
The diffusion angle distribution is measured according to JIS Z 8722 “Measurement Method of Color-Reflection and Transmission Object Color” 5.3.3 “Measurement of Spectral Reflectance” Method a (when using a two-pass spectrophotometer and a substitution method) ). 2. The back protective sheet according to claim 1, wherein the thickness of the first reflective layer is 1.0 μm or more and 20.0 μm or less, and the white particles contained in the first reflective layer have a Mohs hardness of 3.0 or less. In the first reflective layer, the white particles contained in the first reflective layer have an angle formed by a major axis direction of the white particles and a plane direction on the first reflective layer side of the base material layer of 10 The back surface protective sheet according to claim 1 or 2, wherein the back surface protective sheet is oriented in a manner of at least 60 degrees and not more than 60 degrees. A solar cell module provided with the back surface protection sheet in any one of Claim 1 to 3.