JP5603434B2 - Organic material optical sheet for concentrating solar cells - Google Patents

Description

  The present invention relates to an optical sheet for a concentrating solar cell.

  As a method for a photovoltaic power generation panel, a flat plate method in which solar cells called commonly called cells are spread all over the light receiving surface of sunlight is often used. However, it is difficult to reduce the cost of the photovoltaic power generation panel because the photovoltaic cells spread according to the light receiving area are expensive.

  From such a background, the development of a concentrating solar power generation panel that condenses light on a light receiving surface of sunlight on a small-diameter solar cell using a condensing lens has been performed (Patent Document 1). This concentrating solar power generation panel condenses light several hundred times, so that the amount of solar cells used can be greatly reduced as compared to the flat plate method. However, in a concentrating solar power generation panel that condenses light several hundred times, it is necessary to track the sunlight receiving surface in two directions in the direction of sunlight. Furthermore, since the tracking platform is also required to be sturdy in consideration of the outdoor use environment, the amount of use of the original expensive solar cell has been greatly reduced when its installation cost is included. Cost benefits are offset.

  At present, simple and lightweight concentrating solar power generation using a resin Fresnel lens as a condensing lens, with the aim of simplifying solar tracking and reducing costs. Panel development is underway. Resin is required to have high light transmittance, but recently, a silicone rubber composition having high transparency has been reported as an optical waveguide plate for a backlight device for keypad illumination such as a cellular phone even if it contains silica. (Patent Document 2).

  As a mechanism that does not track the sunlight receiving surface in the direction of sunlight, a mechanism has been proposed in which a prism or a trapezoidal member is arranged on the light receiving surface to collect light. However, the material as the light condensing part forming material used in these is a liquid type or a thermoplastic material, and there is a problem that the process when manufacturing the solar cell panel becomes complicated and the cost is increased (Patent Document) 3-4). In addition, a Fresnel lens is used as a condensing lens on the sunlight receiving surface, the focal point is positioned between the condensing lens and the solar cell, and the light receiving surface of the cell is curved concavely toward the condensing lens. A structure has been proposed (Patent Document 5). Furthermore, a prism type sheet is arranged on the sunlight receiving surface, and the incident light from the outside is condensed in the normal direction with respect to the light receiving surface, and then the light is distributed in a predetermined direction by reflection or refraction, and the light is further distributed. It is proposed to guide the light by total reflection and finally increase the energy density of incident light (Patent Document 6).

  On the other hand, as a double-sided light receiving solar cell module, both sides of the double-sided light receiving solar cell are sealed with a light-transmissive sealing glass plate via a light-transmissive adhesive and fixed to a frame. Double-sided light-receiving solar cell module (Patent Document 7), a method using a cell of a double-sided light-receiving solar cell as a road marking device that is easy to handle without much consideration of the position and installation angle of sunlight (Patent Document 8) A method of providing glass sandwich type panels on both the front and back surfaces (Patent Document 9) has been proposed, but both are configured to spread according to the light receiving area, reducing the cost of the photovoltaic power generation panel Can be difficult.

JP 2003-258291 A JP 2010-83978 A Special table 2008-543111 gazette US2009 / 0314329A1 JP 2007-48910 A JP 2009-229581 A JP 2004-259928 A JP 2004-60637 A JP 11-31834 A

In order for the photovoltaic power generation panel to be widely spread as a solution to the problem of global warming, it is necessary to achieve a cost reduction that is competitive with the power cost of the grid commercial power system. The cost of the photovoltaic power generation panel is said to be 100 yen / Wp, and it is required to have excellent durability and low material costs and processing costs for the Fresnel lens shape.
In the resin Fresnel lens, acrylic resin, polymethyl methacrylate resin, and polycarbonate resin are generally used as the material. However, in a concentrating solar cell panel that is required to have a long-term durability of more than 20 years under sunlight, a silicone resin having higher ultraviolet resistance than these general-purpose resins is suitable.
When processing silicone resin into a Fresnel lens or prism lens shape, in order to produce it with a low-productivity processing process, injecting the resin into the mold by injection molding and taking out the product after molding, like acrylic resin used for general purposes As a result, the manufacturing cost was high.
For these reasons, it has been difficult to put a simple and lightweight concentrating solar power generation panel using a resin Fresnel lens or prism lens into practical use.
The present invention has been made in view of such points, and is excellent in durability against sunlight irradiation. For example, a Fresnel sheet having a Fresnel lens shape, for aligning sunlight in the normal direction of the Fresnel lens sheet. An object of the present invention is to provide an organic material optical sheet that can be used as a microlens sheet or a prism lens sheet that aligns the incidence of sunlight in the normal direction before entering the prism sheet. In addition, the present invention is an organic material optical sheet of a double-sided concentrating solar cell that can collect light without performing tracking or tracking on a single axis, and is excellent in durability against sunlight irradiation, and also in a liquid type. In comparison, the purpose is to provide an organic material optical sheet for a double-sided concentrating solar cell using a silicone resin material that is excellent in calendar molding and extrusion moldability and can easily process the shape of the sunlight condensing part. To do. This organic material optical sheet can be used for, for example, a concentrating solar cell panel including a double-sided concentrating solar cell panel.

In the present invention, two or more light-transmitting quadrangular prisms having an isosceles trapezoidal cross section are arranged in parallel so that the incident side surfaces of the quadrangular prism having a long side of two parallel sides of the isosceles trapezoid are in the same plane. The solar light is incident on the incident side surface, passes through the inside of the quadrangular prism, and exits from the exit side surface of the quadrangular column having a short side of the two parallel sides of the isosceles trapezoid. Provided is an organic material optical sheet for a concentrating solar cell in which a part or all of an incident side surface is curved so as to be condensed on a cell disposed on the side surface. Further, the present invention is a double-sided condensing type that combines the second organic material optical sheets joined in such a manner that each of the emission side surfaces is a joining surface, and a surface including the joining surface is a symmetry surface, and the surfaces are symmetrical. And the sunlight enters from the incident side surface, passes through the inside of the quadrangular column, and exits from the exit side surface of the quadrangular column having a short side out of the two parallel sides of the isosceles trapezoid. Incident into the quadrangular prism, passes through the inside of the second quadrangular prism, and exits from the exit side surface of the second quadrangular prism having the long side of the two parallel sides of the isosceles trapezoid that is the cross section of the second quadrangular prism. Thus, the above-described concentrating solar cell of the double-sided concentrating type in which a part or all of the second emitting side surface is curved so as to be condensed on the cell disposed on the emitting side surface of the second quadrangular prism. An organic material optical sheet is provided.

  Since the organic material optical sheet of the concentrating solar cell including the double-sided concentrating solar cell of the present invention can condense sunlight twice or more, the cell cost can be reduced. Excellent rubber processability by containing a large amount. Moreover, since it has high transparency with respect to sunlight and is excellent in durability against sunlight irradiation, it is optimal as an organic material optical sheet for a concentrating solar cell.

Sectional drawing of an example of the concentrating solar cell using an optical sheet is shown. The perspective view of an example of the concentrating solar cell using an optical sheet is shown. Sectional drawing of an example of a structure of the module using an optical sheet is shown. An example is shown in which sunlight enters the incident side surface perpendicularly and the focal point of the incident light is formed behind the emission side surface. (A) and (C) show an example in which sunlight enters perpendicularly to the incident side surface, and the focal point of incident light is formed inside an isosceles trapezoid inside the emission side surface, and (B) An example is shown in which light is incident perpendicular to the incident side surface and the focal point of the incident light is formed outside the isosceles trapezoid. An example is shown in which sunlight enters the incident side surface at 23 degrees, and the incident light is totally reflected in the optical sheet and reaches the exit side surface. Sectional drawing of an example of the concentrating solar cell using the optical sheet which made a part of sunlight incident side surface into a plane is shown. In the optical sheet in which a part of the sunlight incident side surface is flat, sunlight is incident on the incident side surface at 23 degrees, and the incident light is totally reflected in the optical sheet and reaches the emission side surface. Sectional drawing of an example of the double-sided concentrating solar cell using an optical sheet is shown. The perspective view of an example of the double-sided concentrating solar cell using an optical sheet is shown.

The optical sheet is preferably
(A) The following average composition formula (I)
R ¹ _a SiO _{(4-a) / 2} (I)
(In the formula, R ¹ represents the same or different unsubstituted or substituted monovalent hydrocarbon group, and at least two in the molecule are alkenyl groups, and a is a positive number of 1.95 to 2.05. is there.)
100 parts by weight of an organopolysiloxane having a degree of polymerization represented by
(B) 70-150 parts by mass of fumed silica having a specific surface area exceeding 200 m ² / g,
(C) 0.1-30 parts by mass of an organohydrogenpolysiloxane containing hydrogen atoms bonded to at least two silicon atoms in one molecule, and (D) a catalytic amount of hydrosilylation reaction catalyst (preferably 0 .1-10 parts by mass)
It is obtained by curing a silicone rubber composition comprising at least.
This silicone rubber composition is a millable type material that can be extruded, calendered, etc., and its cured product has high transparency even if it contains silica, and includes a double-sided concentrating solar cell. It is most suitable as an optical sheet for optical solar cells.

The component (A) is an organopolysiloxane having a degree of polymerization represented by the average composition formula (I) of 100 or more. In the average composition formula (I), R ¹ represents the same or different unsubstituted or substituted monovalent hydrocarbon group, and usually one having 1 to 12 carbon atoms, particularly preferably 1 to 8 carbon atoms. Specifically, alkyl groups such as methyl group, ethyl group, propyl group, butyl group, hexyl group and octyl group, cycloalkyl groups such as cyclopentyl group and cyclohexyl group, alkenyl groups such as vinyl group, allyl group and propenyl group Aryl groups such as cycloalkenyl group, phenyl group and tolyl group, aralkyl groups such as benzyl group and 2-phenylethyl group, or part or all of hydrogen atoms of these groups are substituted with halogen atoms or cyano groups A methyl group, a vinyl group, a phenyl group, and a trifluoropropyl group are preferable, and a methyl group and a vinyl group are particularly preferable.

As the component (A), specifically, a part of the dimethylpolysiloxane structure in which the main chain of the organopolysiloxane is composed of repeating dimethylsiloxane units or the dimethylsiloxane unit constituting the main chain is repeated. Introduce diphenylsiloxane unit, methylphenylsiloxane unit, methylvinylsiloxane unit, or methyl-3,3,3-trifluoropropylsiloxane unit having phenyl group, vinyl group, 3,3,3-trifluoropropyl group, etc. The thing etc. which were made are suitable.
In particular, the organopolysiloxane preferably has two or more aliphatic unsaturated groups such as alkenyl groups and cycloalkenyl groups in one molecule, and particularly preferably a vinyl group. In this case, it is preferable that 0.01 to 20 mol%, particularly 0.02 to 10 mol%, of all R ¹ are aliphatic unsaturated groups. The aliphatic unsaturated group may be bonded to a silicon atom at the molecular chain end, or may be bonded to a silicon atom in the middle of the molecular chain, or both. It is preferably bonded to the silicon atom. Moreover, a is a positive number of 1.95 to 2.05, preferably 1.98 to 2.02, more preferably 1.99 to 2.01.
More preferably, as the organopolysiloxane of component (A), R ¹ in the average composition formula (I) is a monovalent hydrocarbon group having 1 to 6 carbon atoms, and at least two in one molecule are alkenyl groups. is there.

The organopolysiloxane of component (A) is blocked with a triorganosiloxy group such as a trimethylsiloxy group, a dimethylphenylsiloxy group, a dimethylhydroxysiloxy group, a dimethylvinylsiloxy group, a methyldivinylsiloxy group, or a trivinylsiloxy group. Preferred examples can be given.
Particularly preferred are methyl vinyl polysiloxane, methyl phenyl vinyl polysiloxane, methyl trifluoropropyl vinyl polysiloxane and the like.

  Such an organopolysiloxane can be obtained by, for example, hydrolyzing and condensing one or more types of organohalogenosilanes, or by converting cyclic polysiloxanes (siloxane trimers, tetramers, etc.) to alkaline or acidic. It can obtain by ring-opening polymerization using the catalyst of. These are basically linear diorganopolysiloxanes, but the component (A) may be a mixture of two or more different molecular weights (degree of polymerization) and molecular structures.

  The degree of polymerization of the organopolysiloxane is 100 or more, preferably 100 to 100,000, particularly preferably 3,000 to 20,000. This degree of polymerization can be measured as a weight average degree of polymerization in terms of polystyrene by gel permeation chromatography (GPC) analysis.

The component (B) is fumed silica having a BET specific surface area of more than 200 m ² / g. This reinforcing silica is added to obtain a rubber composition having excellent transparency and excellent mechanical strength. Further, in order to improve the transparency of the silicone rubber composition, the BET specific surface area needs to exceed 200 m ² / g, preferably 250 m ² / g or more. When the BET specific surface area is 200 m ² / g or less, the transparency of the cured product is lowered.
The silica usually used in the silicone rubber composition includes fumed silica, precipitated silica, and the like. However, when precipitated silica is used, fumed silica is used because transparency decreases. The fumed silica can be used as it is, but the surface-treated one is preferred. A material obtained by hydrophobizing the surface of fumed silica with chlorosilane, alkoxysilane, hexamethyldisilazane, or the like is also preferably used. In particular, treatment with hexamethylsilazane is preferable because of its high transparency.

  The addition amount of the fumed silica of the component (B) is 70 to 150 parts by mass with respect to 100 parts by mass of the organopolysiloxane of the component (A). If it is less than 70 parts by mass, the transparency of the sheet obtained by curing the silicone rubber compound is lowered. If it exceeds 150 parts by mass, it will be difficult to disperse the silica in the silicone polymer.

Component (C) is an organohydrogenpolysiloxane containing hydrogen atoms bonded to at least two silicon atoms in one molecule. This organohydrogenpolysiloxane contains hydrogen atoms (SiH groups) bonded to at least two silicon atoms in one molecule, and preferably has the following average composition formula (II)
R ² _b H _c SiO _{(4-b-c) / 2} (II)
(In the above formula, R ² is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms, b is a number of 0.7 to 2.1, and c is 0.18 to 1.0. And b + c satisfies 0.8 to 3.0.)
A conventionally known organohydrogenpolysiloxane represented by the formula is applicable.
R ² is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably having no aliphatic unsaturated bond, for example, a methyl group, an ethyl group, a propyl group, a butyl group , An alkyl group such as a pentyl group and a hexyl group, an unsubstituted monovalent hydrocarbon group such as a cyclohexyl group, a cyclohexenyl group and a phenyl group, or the above monovalent group such as a 3,3,3-trifluoropropyl group and a cyanomethyl group A substituted monovalent hydrocarbon group such as a substituted alkyl group in which at least a part of the hydrogen atoms of the hydrocarbon group is substituted with a halogen atom or a cyano group.
With respect to b and c, preferably, b is a number from 0.8 to 2.0, c is a number from 0.2 to 1.0, and b + c satisfies 1.0 to 2.5.

  The molecular structure of the organohydrogenpolysiloxane of component (C) may be any of linear, cyclic, branched, and three-dimensional network structures. In this case, the number of silicon atoms in one molecule (or the degree of polymerization) is preferably 2 to 300, particularly about 4 to 200 at room temperature. In addition, the hydrogen atom (SiH group) bonded to the silicon atom may be at the end of the molecular chain, at the side chain, or both, and at least two (usually 2 to 300) per molecule. Preferably, those containing 3 or more (for example, 3 to 200), more preferably about 4 to 150 are used.

Specific examples of the component (C) organohydrogenpolysiloxane include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, and methylhydrogencyclopolysiloxane. , Methylhydrogensiloxane / dimethylsiloxane cyclic copolymer, tris (dimethylhydrogensiloxy) methylsilane, tris (dimethylhydrogensiloxy) phenylsilane, trimethylsiloxy group-blocked methylhydrogenpolysiloxane, trimethylsiloxy group-blocked at both ends Dimethylsiloxane / methylhydrogensiloxane copolymer, both ends dimethylhydrogensiloxy-blocked dimethylpolysiloxane, both ends dimethylhydrogensiloxy-blocked dimethylsiloxane / methyl Hydrogensiloxane copolymer, trimethylsiloxy group-capped methylhydrogensiloxane / diphenylsiloxane copolymer, trimethylsiloxy group-capped methylhydrogensiloxane / diphenylsiloxane / dimethylsiloxane copolymer, cyclic methylhydrogenpolysiloxane , Cyclic methylhydrogensiloxane / dimethylsiloxane copolymer, cyclic methylhydrogensiloxane / diphenylsiloxane / dimethylsiloxane copolymer, a copolymer comprising (CH ₃ ) ₂ HSiO _1/2 units and SiO _4/2 units , (CH ₃ ) ₂ HSiO _1/2 unit, SiO _4/2 unit and (C ₆ H ₅ ) SiO _3/2 unit copolymer, etc. Is an ethyl group And those substituted with other alkyl groups such as a propyl group and aryl groups such as a phenyl group.

The compounding amount of the organohydrogenpolysiloxane of component (C) is preferably 0.1 to 30 parts by mass, more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the organopolysiloxane of component (A). More preferably, it is 0.3 to 10 parts by mass.
The organohydrogenpolysiloxane of component (C) is a molar ratio of hydrogen atoms bonded to silicon atoms in component (C) (ie, SiH groups) to alkenyl groups bonded to silicon atoms in component (A). However, the amount is preferably 0.5 to 5 mol / mol, more preferably 0.8 to 4 mol / mol, and still more preferably 1 to 3 mol / mol.

As the hydrosilylation reaction catalyst of component (D), known ones can be applied, such as platinum black, platinous chloride, chloroplatinic acid, a reaction product of chloroplatinic acid and a monohydric alcohol, chloroplatinic acid and olefin. And platinum-based catalysts such as platinum bisacetoacetate, palladium-based catalysts, rhodium-based catalysts, and the like.
The compounding amount of the component (D) hydrosilylation reaction catalyst can be a catalytic amount, and is usually 0.1 to 10 parts by mass with respect to 100 parts by mass of the component (A) as a platinum group metal.

  In addition to the above components, the silicone rubber composition comprising at least components (A) to (D) may contain a flame retardant or a colorant as long as the object of the present invention is not impaired. .

The silicone rubber composition can be obtained by kneading a predetermined amount of the above-described components with a two roll, kneader, Banbury mixer or the like.
When the silicone rubber composition is molded, the molding method is not particularly limited, but press molding, extrusion molding, calendar molding, and the like are possible.
The curing conditions for the silicone rubber composition are not particularly limited. Generally, a keypad or the like can be obtained by heating and curing at 80 to 300 ° C., particularly 100 to 250 ° C. for 5 seconds to 1 hour, particularly 30 seconds to 30 minutes. Moreover, you may post-cure about 10 minutes-10 hours at 100-200 degreeC.

The silicone rubber composition is molded and cured by a method such as press molding to obtain a highly transparent silicone rubber optical sheet.
In this optical sheet, the total light transmittance of a cured sheet having a thickness of 2 mm is preferably 90% or more at a wavelength of 0.35 to 1.15 microns which is a spectral sensitivity region of crystalline silicon. Specifically, it is preferably 90% or more as measured by a direct reading haze computer HGM-2 manufactured by Suga Test Instruments. If the total light transmittance is less than 90%, light diffusion is too large, and incident light may not reach the farthest part of the optical sheet. This optical sheet preferably has a haze value (cloudiness value) of a cured sheet having a thickness of 2 mm of 10 or less, particularly 8 or less, as measured by a direct reading haze computer HGM-2 manufactured by Suga Test Instruments Co., Ltd. When the haze value (cloudiness value) exceeds 10, the light diffusion is too large and the incident light may not reach the farthest part of the optical sheet.

  An organic material optical sheet of a concentrating solar cell including a double-sided concentrating solar cell has a transmittance of 90% or more for a wavelength of sunlight irradiation spectrum of 0.35 to 1.15 microns (when the thickness is 2 mm). A case where the rubber composition is made of a sheet obtained by curing the rubber composition will be described. In a concentrating solar cell, in order to efficiently capture direct sunlight, it is necessary to consider that the altitude in the south and middle fluctuates from season to season.In the present invention, the shape of the present invention in the uniaxial direction (drawing) An optical sheet formed with a reference) is prepared. Although it is necessary to consider that the south-central altitude changes from +23 degrees at the summer solstice and −23 degrees at the winter solstice starting from the spring equinox and autumn equinox, according to the shape of the optical sheet of the present invention, Then, it was confirmed by using geometric optical software (Light Tools) that the light can be incident on the light receiving surface of the solar cell on the emission side. And it confirmed that the total incident area to a solar cell was 2.7 to 1.0 with respect to the sunlight total incident area of an optical sheet. In the implementation of the present invention, a tracking system toward the sun on the light receiving surface is not essential. With one linear optical sheet having a simple and repeating linear structure according to the present invention, it was possible to achieve 2.7 times condensing. According to the present invention, it is possible to provide an optical sheet capable of concentrating more than twice as much as direct light having a deviation of ± 23 degrees in south-medium luminous intensity.

A sectional view of an example of a concentrating solar cell using an optical sheet is shown in FIG. 1, and a perspective view is shown in FIG. The optical sheet 1 includes two or more light-transmitting rectangular columns having an isosceles trapezoidal section in parallel so that incident surfaces of the rectangular columns having long sides of two parallel sides of the isosceles trapezoid are in the same plane. The solar light is incident from the incident side surface, passes through the inside of the quadrangular column (isosceles trapezoid), and is emitted from the exit side surface of the quadrangular column having a short side of the two parallel sides of the isosceles trapezoid. A part or all of the incident side surface 3 has a curved surface so as to be focused on the cell 2 arranged on the emission side surface. The curved surface normally protrudes toward the incident light.
Sunlight incident from the incident side surface is transmitted through the optical sheet 1 or reflected within the optical sheet, and is collected on the solar cells 2 installed on the output side surface.

  When specifically configuring as a module, for example, as shown in FIG. 3, in order to fix the cell 2 to the optical sheet 1, a cell sheet fixing jig 5 made of resin such as polycarbonate or acrylic is used. The cell used here is preferably made of polycrystalline or single crystal silicon. In addition, this cell has a strip shape, for example, Sliver Cell (registered trademark) manufactured by Origin Energy of Australia. On the other hand, this strip-shaped cell can process a general solar battery by methods, such as dicing. Each cell is connected in series or in parallel with at least one other cell by a tab line to form an electric circuit for supplying power (Patent Document 3). Moreover, preferably, silicone oil or silicone gel having the same refractive index as that of the optical sheet 1 can be added to the gap between the optical sheet 1 and the cell 2 to prevent irregular reflection or birefringence of sunlight. Further, preferably, a white plate tempered glass 4 or the like can be disposed on the light incident side in order to prevent contamination of the optical sheet 1. On the other hand, a back sheet or tempered glass 6 can be preferably arranged on the opposite side of the cell sheet fixing jig 5 from the light incident surface.

The focal point of sunlight incident from the incident side surface is preferably formed in the isosceles trapezoid or behind the emission side surface. In FIG. 1, the focal point of sunlight is formed on the emission side surface of the isosceles trapezoid, and the cell 2 is arranged on the emission side surface.
When sunlight is incident on the incident side surface perpendicularly, as shown in the optical sheet 11 of FIG. 4, the curved surface of the sunlight incident side surface (for example, a shape of a part of a circle or a part of an ellipse) is more preferable. Is a curved surface in which the focal point of sunlight when incident is formed behind the emission side surface (the side surface including the short side of the two parallel sides of the isosceles trapezoid).
When the focal point of the incident sunlight is formed in the isosceles trapezoid, that is, on the entrance side surface from the exit side surface including the longer side of two parallel sides of the isosceles trapezoid shape, The incident angle when incident on (an isosceles trapezoidal side surface having two sides other than two parallel sides) becomes smaller than the critical angle, exits the optical sheet without being totally reflected, and reaches the solar cell. This is because light may be reduced and may not contribute to effective power generation. As an aspect of the focal point generated in the isosceles trapezoid, when one focal point is generated in the isosceles trapezoid as shown in the optical sheet 21 in FIG. 5A, the optical in FIGS. As shown in the sheets 31 and 41, a plurality of focal points may be shifted.

The sunlight incident from the incident side is preferably emitted directly through the isosceles trapezoid or is emitted after being totally reflected once in the isosceles trapezoid.
FIG. 4 shows that when incident light is incident on the incident side surface perpendicularly, the incident light directly reaches the emission side surface without being reflected in the optical sheet. Moreover, FIG. 6 shows that the sunlight when incident at 23 degrees from the incident side surface is emitted after being totally reflected once in the isosceles trapezoid of the optical sheet 51.

The curved surface of part or all of the sunlight incident side surface is preferably formed such that the focal point of sunlight when incident is on the rear side of the emission side surface (a side surface including a short side of two parallel sides of the isosceles trapezoid). It is a curved surface. The sunlight incident side surface may be all curved surfaces having a part of a circular shape or a part of an elliptical shape, for example. Preferably, the protruding portion of the curved surface is a quadrangular prism section. It is a partially curved surface that is a combination of a flat surface portion and a curved surface portion, replaced by a flat (flat) portion that is parallel to two parallel sides of the trapezoid. FIG. 7 shows an example in which the sunlight incident side surface is a combination of a curved surface and a flat surface portion. 7 is a combination of a curved surface portion 63c and a flat surface portion 63f that is parallel to two parallel sides of an isosceles trapezoid. When the white tempered glass or the like is arranged on the light incident side, the white plate tempered glass is supported by dots or lines only on the curved surface, so that the sheet may be deformed by the weight of the white tempered glass. However, by combining the curved surface portion and the flat surface portion, the white plate tempered glass can be supported by the flat surface portion, and the possibility that the sheet is deformed by the weight of the white plate tempered glass can be reduced.
FIG. 8 shows an optical sheet in which a part of the sunlight incident side surface is flat. Similarly to FIG. 6, sunlight is incident on the incident side surface at 23 degrees, and the incident light is totally reflected in the optical sheet and is emitted. An example of reaching is shown.

An example of a double-sided concentrating solar cell using an optical sheet is shown in FIG. 9, and a perspective view is shown in FIG. This optical sheet is completely symmetrical so that a surface having a short side of two parallel sides of the isosceles trapezoid that is a cross section of the optical sheet described above is a bonding surface, and a surface including the bonding surface is a plane of symmetry. It is a double-sided condensing type that combines the same second optical sheets, and sunlight enters from the incident side surface, passes through the inside of the first quadrangular prism, and is short of the two parallel sides of the first isosceles trapezoid. The two parallel sides of the isosceles trapezoid that is the cross section of the second quadrangular prism enter the second quadrangular prism and enter the second quadrangular prism at the same time as the light exits from the exit side of the quadrangular prism having sides. A part or all of the second emission side surface is emitted from the emission side surface of the second quadrangular column having a long side and is collected on the cell disposed on the emission side surface of the second square column. A double-sided condensing type with a curved surface.
Sunlight incident from the incident side surface is transmitted through the combined optical sheet or reflected within the combined optical sheet, and is collected on the solar cells installed on the output side surface.
The focal point of sunlight when entering from the incident side surface is preferably formed in the second isosceles trapezoid or behind the exit surface side. In FIG. 9, the focal point of sunlight is formed on the emission side surface of the isosceles trapezoid, and cells are arranged on the emission surface.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to the following examples. In addition, a weight average molecular weight and a weight average polymerization degree are the polystyrene conversion values in a gel permeation chromatography (GPC) analysis.

Example 1
100 parts by mass of an organopolysiloxane comprising 99.425 mol% of dimethylsiloxane units, 0.50 mol% of methylvinylsiloxane units and 0.025 mol% of dimethylvinylsiloxane units and having an average degree of polymerization of about 6,000, BET ratio 70 parts by mass of silica having a surface area of 300 m ² / g (trade name Aerosil 300, manufactured by Nippon Aerosil Co., Ltd.), 16 parts by mass of hexamethyldisilazane and 4 parts by mass of water were added as a dispersant, and kneaded with a kneader at 170 ° C. A compound was prepared by heating for 2 hours.
0.5 parts by mass / 2.0 C-25A (platinum catalyst) / C-25B (organohydrogenpolysiloxane) (both manufactured by Shin-Etsu Chemical Co., Ltd.) as an addition crosslinking curing agent for 100 parts by mass of the compound. After kneading the mass part with two rolls and adding and mixing uniformly, press curing was performed for 10 minutes under the conditions of 120 ° C. and 70 kgf / cm ² , followed by post curing at 200 ° C. for 4 hours to prepare a test sheet. .

Example 2
Example except that the addition amount of silica (trade name Aerosil 300, manufactured by Nippon Aerosil Co., Ltd.) having a BET specific surface area of 300 m ² / g was 80 parts by mass, 18.5 parts by mass of hexamethyldisilazane, and 4.6 parts by mass of water. A sheet was molded by the same method as in 1.

Example 3
Example 1 except that the addition amount of silica having a BET specific surface area of 300 m ² / g (trade name Aerosil 300, manufactured by Nippon Aerosil Co., Ltd.) was 100 parts by mass, 23 parts by mass of hexamethyldisilazane, and 5.7 parts by mass of water. A sheet was molded by the same method.

Example 4
Except that the addition amount of silica having a BET specific surface area of 380 m ² / g (trade name Aerosil 380, manufactured by Nippon Aerosil Co., Ltd.) was 70 parts by mass, hexamethyldisilazane 20.3 parts by mass, and water 5.1 parts by mass. A sheet was molded by the same method as in 1.

Example 5
Example 1 except that the addition amount of silica having a BET specific surface area of 300 m ² / g (trade name Aerosil 380, manufactured by Nippon Aerosil Co., Ltd.) was 70 parts by mass, 22 parts by mass of hexamethyldisilazane, and 5.4 parts by mass of water. A sheet was molded by the same method. However, a mold in which a part of the incident surface becomes a flat surface after molding was used as a mold for molding the sheet.

Example 6
Example 5 except that the addition amount of silica (trade name Aerosil 300, manufactured by Nippon Aerosil Co., Ltd.) having a BET specific surface area of 300 m ² / g was 100 parts by mass, 21 parts by mass of hexamethyldisilazane, and 5.0 parts by mass of water. Similarly, it shape | molded using the metal mold | die with which a part of entrance plane becomes a plane after shaping | molding.

Comparative Example 1
Except that the addition amount of silica (trade name Aerosil 300, manufactured by Nippon Aerosil Co., Ltd.) having a BET specific surface area of 300 m ² / g was 50 parts by mass, 11.4 parts by mass of hexamethyldisilazane, and 2.9 parts by mass of water. A sheet was molded by the same method as in 1.

Comparative Example 2
Example 1 except that the addition amount of silica (trade name Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) having a BET specific surface area of 200 m ² / g was 70 parts by mass, 16 parts by mass of hexamethyldisilazane, and 4 parts by mass of water. A sheet was formed by the method.

<Sheet evaluation method>
About the sheet | seat obtained in Examples 1-6 and Comparative Examples 1-2, the total light transmittance and haze value (haze value) of a 2 mm sheet | seat were measured as plasticity, hardness (durometer A), and transparency evaluation. . The plasticity is measured according to JIS K6249, and the hardness (durometer A) is measured according to JIS K6249 after curing the rubber composition at 120 ° C./10 minutes, and the total light transmittance and haze value (cloudiness). Was measured with a direct reading haze computer HGM-2 manufactured by Suga Test Instruments Co., Ltd. The results are shown in Table 1.

The sheets obtained in Examples 1 to 6 are excellent in plasticity and hardness. The sheets obtained in Examples 1 to 6 have a total light transmittance of 90% or more, a haze value (cloudiness value) of 8 or less, high transparency, and concentrated sunlight. It is suitable for the optical sheet. The sheet obtained from Comparative Example 1 in which the amount of fumed silica added is insufficient and the sheet obtained from Comparative Example 2 using silica having a BET specific surface area of 200 m ² / g are low in transparency. It cannot be used for optical solar light sheets.
Moreover, about the sheet | seat obtained in Examples 1-5, it measured using the solar cell IV measurement system (made by Opt Research). As shown in FIG. 7, strip-shaped cells were bonded to the sheets obtained in Examples 1 to 5 using a silicone resin. In addition, in order to compare the characteristics, the same area as the total area of the strip-shaped cells used for each sheet was made the same as the flat silicone sheet having the same thickness as the sheet obtained in Examples 1 to 5. To create a flat plate model. The measurement is performed under a solar simulator, irradiated pseudo-sunlight is irradiated at an angle of ± 30 degrees from directly above at 100 mW / cm ² and AM1.5, and the optical condensing magnification defined as the short-circuit current and the ratio thereof. As a result, it was confirmed that the light could be condensed by 2.4 to 2.6 times compared with the flat plate model.
Furthermore, the sheet | seat obtained in Examples 1-6 was irradiated for 500 hours using the UV irradiation apparatus which can irradiate the light of the wavelength of 300 nm vicinity. For comparison, acrylic resin boards and polycarbonate resin boards with the same thickness as the silicone sheet were irradiated in the same way, but acrylic resin boards and polycarbonate resin boards had discoloration cracks, etc. It was confirmed that the silicone sheet was excellent in durability with almost no change.

1, 11, 21, 31, 41, 51, 61 Optical sheet 2, 62 Cell 3, 63 Incident side surface 4 White plate tempered glass 5 Cell sheet fixing jig 6 Back sheet or tempered glass 63c Curved portion 63f Plane portion L Sunlight

Claims (6)

Two or more light-transmitting quadrangular prisms whose cross-sections are isosceles trapezoids are connected in parallel so that the incident sides of the quadrangular prisms having long sides out of two parallel sides of the isosceles trapezoids are coplanar, Sunlight enters from the incident side surface, passes through the inside of the quadrangular prism, exits from the exit side surface of the quadrangular column having a short side of the two parallel sides of the isosceles trapezoid, and is disposed on the exit side surface. An organic material optical sheet for a concentrating solar cell having a curved surface on a part or all of the incident side surface ,
Focus sunlight entering from the incident side surface is formed at the rear in or above the exit side of the isosceles trapezoid, sunlight entering from the top fill morphism law surface, through the inside of an isosceles trapezoid the , Emitted directly or after being totally reflected once ,
Upper Symbol organic material optical sheet, at least,
(A) The following average composition formula (I)
R ¹ _a SiO _{(4-a) / 2} (I)
(In the above formula, R ¹ represents the same or different unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number of 1.95 to 2.05.)
100 parts by weight of an organopolysiloxane having a degree of polymerization represented by
(B) 70-150 parts by mass of fumed silica having a specific surface area exceeding 200 m ² / g,
(C) 0.1-30 parts by mass of an organohydrogenpolysiloxane containing hydrogen atoms bonded to at least two silicon atoms in one molecule, and (D) a silicone comprising a catalytic amount of a hydrosilylation reaction catalyst An organic material optical sheet for a concentrating solar cell , obtained by curing a rubber composition. The organic material optical sheet for a concentrating solar cell according to claim 1 , wherein the fumed silica is surface-treated silica. The organic material optical sheet for a concentrating solar cell according to claim 2 , wherein the surface-treated silica is treated with hexamethyldisilazane. The concentrating type according to any one of claims 1 to 3 , wherein a spectral radiation transmittance of a cured sheet having a thickness of 2 mm of the silicone rubber composition is 90% or more at a wavelength of 0.35 to 1.15 microns. Organic material optical sheet for solar cells. The haze value of the cured product sheet having a thickness of 2mm of the silicone rubber composition (haze) is an organic material optical sheet for concentrating solar battery according to any one of claims 1 to 4, 10 or less. Each of the emission side surfaces is a double-sided condensing type that combines the second organic material optical sheet bonded to be plane-symmetrical with a plane including the bonding surface as a plane of symmetry, and the sunlight is , Incident from the incident side surface, exits from the exit side surface of the quadrangular column having a short side out of the two parallel sides of the isosceles trapezoid through the inside of the quadrangular column, and simultaneously enters the second quadrangular column, Outgoing from the exit side of the second quadrangular column having the long side of the two parallel sides of the isosceles trapezoid that is the cross section of the second quadrangular column through the inside of the second quadrangular column, The condensing according to any one of claims 1 to 5 , which is a double-sided condensing type in which a part or all of the second emission side surface is curved so as to be condensed on a cell disposed on the emission side surface of the quadrangular prism. Type organic material optical sheet for solar cell.

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