US20120174982A1 - Photovoltaic module and method for manufacturing photovoltaic module - Google Patents
Photovoltaic module and method for manufacturing photovoltaic module Download PDFInfo
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- US20120174982A1 US20120174982A1 US13/426,558 US201213426558A US2012174982A1 US 20120174982 A1 US20120174982 A1 US 20120174982A1 US 201213426558 A US201213426558 A US 201213426558A US 2012174982 A1 US2012174982 A1 US 2012174982A1
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- sealing material
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- light receiving
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- solar cell
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Images
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
- H01L31/042—PV modules or arrays of single PV cells
- H01L31/048—Encapsulation of modules
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
- H01L31/042—PV modules or arrays of single PV cells
- H01L31/048—Encapsulation of modules
- H01L31/0481—Encapsulation of modules characterised by the composition of the encapsulation material
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
Abstract
An object of the present invention is to provide a photovoltaic module that achieves a reduction in adverse influence of damage accumulated in a collector electrode provided on the light receiving surface side, and a method for manufacturing the photovoltaic module. To this end, in a photovoltaic module of the present invention, the degree of cross-linkage of the second region of the sealing material that is in contact with the back surface of the solar cell is smaller than that of the first region of the sealing material that is in contact with the light receiving surface of the solar cell.
Description
- This application is a continuation application of U.S. application Ser. No. 11/723,849, filed on Mar. 22, 2007, which is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-095647, filed on Mar. 30, 2006; and prior Japanese Patent Application No. 2007-029661, filed on Feb. 8, 2007. The entire disclosure of each of the referenced applications is herewith incorporated by reference.
- 1. Technical Field of the Invention
- The present invention relates to a photovoltaic module and a method for manufacturing the photovoltaic module. In particular, the present invention relates to a photovoltaic module that brings improved reliability, and a method for manufacturing the photovoltaic module.
- 2. Description of the Related Art
- A photovoltaic system directly converts the solar light, which is clean and inexhaustibly supplied, into electricity. For this reason, the photovoltaic system is expected as a new energy source.
- Here, in a case of a solar cell constituting the photovoltaic system, an output power per unit is in the order of several watts. For this reason, when a photovoltaic system is used as an electric power source for a house, a building or the like, a photovoltaic module including a plurality of solar cells that are electrically connected to one another in series or in parallel is used. With this module, the output power of the photovoltaic system can be increased up to the order of several hundred watts.
- To be more precise, as shown in
FIG. 1 , aphotovoltaic module 100 includes asolar cell 101, a light receiving surfaceside supporting member 102, a back surfaceside supporting member 103 and asealing material 104. The light receiving surfaceside supporting member 102 is provided along a light receiving surface of thesolar cell 101. The back surfaceside supporting member 103 is provided along a back surface of thesolar cell 101. The sealingmaterial 104 seals thesolar cell 101 between the light receiving surfaceside supporting member 102 and the back surfaceside supporting member 103. - In order to accelerate curing of the sealing
material 104 in thephotovoltaic module 100, proposed is a technique of adding cross-linking agent to the sealing material 104 (For example, Japanese Patent Application Laid-open Publication No. Hei 11-61055). - When the
photovoltaic module 100 does not receive the solar light, a stress a on the light receiving surface side of thesolar cell 101 is substantially equal to a stress b on the back surface side of thesolar cell 101, as shown inFIG. 1 . - In contrast, when the
photovoltaic module 100 receives the solar light, the temperature on the light receiving surface side of thesolar cell 101 becomes higher than the temperature on the back surface side of thesolar cell 101. With this phenomenon, the sealingmaterial 104 is thermally expanded more on the light receiving surface side of thesolar cell 101 than on the back surface side of thesolar cell 101. Since a coefficient of thermal expansion of the sealingmaterial 104 is greater than that of thesolar cell 101, the stress a on the light receiving surface side of thesolar cell 101 becomes smaller than the stress b on the back surface side thereof, as shown inFIG. 2 . - In this way, when the
solar cell 101 receives the solar light, the balance between the stress a and the stress b is disrupted. As a result, thesolar cell 101 is warped as shown inFIG. 2 . - Here, as shown in
FIG. 3 , in order to collect photogenerated carriers generated in aphotovoltaic body 105, thesolar cell 101 is provided with acollector electrode 106 on the light receiving surface of thephotovoltaic body 105, and acollector electrode 107 on the back surface of thephotovoltaic body 105. Since thecollector electrode 106 is provided on the light receiving surface side of thephotovoltaic body 105, it is preferable to form thecollector electrode 106 as narrow as possible in order not to block the reception of the solar light. - However, when the
solar cell 101 is warped due to the reception of the solar light, a stress is applied to thecollector electrode 106. In addition, since thephotovoltaic module 100 is used in the open air, and repeats receiving and not receiving the solar light, damage in thecollector electrode 106 is accumulated. For this reason, the electron collection performance of thecollector electrode 106 is likely to be lowered. Moreover, the thinner the thickness of a substrate constituting thephotovoltaic body 105 is, the more heavily thesolar cell 101 is warped. Accordingly, heretofore, the thickness of the substrate cannot be made extremely thin. - The present invention has been made in consideration of the aforementioned problem. An object of the present invention is to provide a photovoltaic module that achieves a reduction in adverse influence of damage accumulated in a collector electrode provided on a light receiving surface side, and a method for manufacturing the photovoltaic module.
- In summary, a photovoltaic module according to a first aspect of the present invention includes a solar cell, a light receiving surface side supporting member, a back surface side supporting member and a sealing material, and also has the following features. The solar cell has a light receiving surface allowing light to enter therein, and a back surface provided on the opposite side of the light receiving surface. The light receiving surface side supporting member is provided at the light receiving surface side of the solar cell. The back surface side supporting member is provided at the back surface side of the solar cell. The sealing material seals the solar cell between the light receiving surface side supporting member and the back surface side supporting member. The sealing material includes a first region that is in contact with the light receiving surface, and a second region that is in contact with the back surface. A degree of cross-linkage of the second region is smaller than that of the first region.
- In this photovoltaic module, by making the degree of cross-linkage of the second region smaller than that of the first region, the second region of the sealing material that is in contact with the back surface of the solar cell is thermally expanded easily at a lower temperature than the first region of the sealing material that is in contact with the light receiving surface of the solar cell. Accordingly, when the photovoltaic module is subjected to the solar light during daytime, the second region whose temperature is less likely to rise can also be thermally expanded. This makes it possible to reduce the stress applied to the solar cell on the back surface side as well, and thereby to reduce the difference between the stresses of the light receiving surface side and the back surface side of the solar cell. This results in a relaxation of a force that acts to warp the solar cell so as to be convex toward the light receiving side. Hence, the stress applied to a collector electrode adhering to the light receiving surface is lowered.
- A second aspect of the present invention is summarized in that a gel fraction of the second region is smaller than that of the first region in the photovoltaic module according to the first aspect of the present invention.
- A third aspect of the present invention is related to the first or second aspect of the present invention, and is summarized in that a amount of a cross-liking agent used for forming crosslinks in the second region is smaller than that used for forming crosslinks in the first region.
- A fourth aspect of the present invention is related to the first aspect of the present invention, and is summarized in that the solar cell has a photovoltaic body for generating photogenerated carriers by receiving light, and a collector electrode which adheres onto the light receiving surface and the back surface of the photovoltaic body, and which collects the photogenerated carriers from the photovoltaic body. In addition, in the solar cell, an adhesion area where the collector electrode adheres onto the light receiving surface of the photovoltaic body is smaller than that where the collector electrode adheres onto the back surface of the photovoltaic body.
- In summary, a photovoltaic module according to a fifth aspect of the present invention includes a solar cell, a light receiving surface side supporting member, a back surface side supporting member and a sealing material, and also has the following features. The solar cell has a light receiving surface allowing light to enter therein, and a back surface provided on the opposite side of the light receiving surface. The light receiving surface side supporting member is provided at the light receiving surface side of the solar cell. The back surface side supporting member is provided at the back surface side of the solar cell. The sealing material seals the solar cell between the light receiving surface side supporting member and the back surface side supporting member. The sealing material includes a first region that is in contact with the light receiving surface, and a second region that is in contact with the back surface. The gel fraction of the second region is smaller than that of the first region.
- In summary, a sixth aspect of the present invention is a method for manufacturing a photovoltaic module including: a solar cell having a light receiving surface allowing light to enter therein, and a back surface provided on the opposite side of the light receiving surface; a light receiving surface side supporting member provided at the light receiving surface side of the solar cell; a back surface side supporting member provided at the back surface side of the solar cell; and a sealing material for sealing the solar cell between the light receiving surface side supporting member and the back surface side supporting member. The method includes steps A and B. In step A, a layered product is obtained by laminating the light receiving surface side supporting member, a first sealing material sheet constituting the sealing material, the solar cell, a second sealing material sheet constituting the sealing material, and the back surface side supporting member on one another in this order. In step B, a crosslinking reaction in the sealing material is promoted by heating the layered product. In addition, in step B, a condition for heating the second sealing material sheet is less favorable for the crosslinking reaction in the sealing material than a condition for heating the first sealing material sheet.
- According to the present invention, it is possible to provide a photovoltaic module that achieves a reduction in adverse influence of damage accumulated in a collector electrode provided on a light receiving surface side, and a method for manufacturing the photovoltaic module.
-
FIG. 1 is a diagram for explaining stresses applied to a conventional solar cell. -
FIG. 2 is a diagram for explaining the stresses applied to the conventional solar cell. -
FIG. 3 is a diagram for explaining the stresses applied to the conventional solar cell. -
FIG. 4 is a diagram for explaining a photovoltaic module according to an embodiment. -
FIG. 5 is a diagram for explaining a solar cell according to the embodiment. -
FIG. 6 is a diagram for explaining the photovoltaic module according to the embodiment. -
FIG. 7 is a diagram for explaining a vacuum lamination apparatus used in a laminating process. -
FIG. 8 is a diagram for explaining a heater used in a curing process. -
FIG. 9 is a diagram for explaining stresses applied to a solar cell according to the embodiment. -
FIG. 10 is a graph of a temperature condition in a temperature cycle test. - Hereinafter, a embodiment of the present invention will be described by using the drawings. In the following description of the drawings, the same or similar reference numerals are given to the same or similar components. It should be noted that the drawings are schematic ones, each dimensional ratio or the like shown in the drawings are different from those of actual ones. For this reason, specific dimensions or the like should be determined with reference to the following description. Moreover, as a matter of course, the drawings include part where there are differences among the drawings in terms of dimensional relationships and ratios.
-
FIGS. 4A and 4B show cross sectional diagrams of aphotovoltaic module 10 according to this embodiment.FIG. 4A is a diagram for illustrating a cross sectional structure of thephotovoltaic module 10 that has been integrated through a module forming process.FIG. 4B is an exploded diagram for illustrating thephotovoltaic module 10 before the module forming process. - The
photovoltaic module 10 includes asolar cell string 1, a sealingmaterial 2, a light receiving surfaceside supporting member 3 and a back surfaceside supporting member 4. - The
solar cell string 1 is formed of a plurality ofsolar cells 1 a which are electrically connected to one another withwiring materials 5. - The
solar cell 1 a includes aphotovoltaic body 6 and a collector electrode 7. - The
photovoltaic body 6 can be formed of a general solar cell material which includes a semiconductor junction such as a pn junction or a pin junction therein, including: a crystal type semiconductor material such as single-crystalline silicon (Si) and poly-crystalline Si; a compound type semiconductor material such as GaAs and CuInSe; a thin-film silicon type material; a organic type material such as dye sensitization type material; or the like. - The collector electrode 7 adheres onto the light receiving surface and the back surface of the
photovoltaic body 6, and collects photogenerated carriers generated in thephotovoltaic body 6. For this purpose, the collector electrode 7 includes a light receivingsurface side electrode 7 a and a backsurface side electrode 7 b. - The light receiving
surface side electrode 7 a and the backsurface side electrode 7 b are formed of a conductive material including silver, aluminum, copper, nickel, tin, gold or the like, or alloy of any of these. Note that the collector electrode 7 may have a monolayer structure or a multilayer structure including the conductive material. In addition to the foregoing layer including the conductive material, the electrode may have a layer including a translucent conductive oxide such as SnO2, ITO, IWO or ZnO. - The light receiving
surface side electrode 7 a is provided so as to occupy an area as small as possible for the purpose of securing a large light receiving area on the light receiving surface side of thephotovoltaic body 6, that is, for securing the large exposed area on the light receiving surface side of thephotovoltaic body 6. For example, the light receivingsurface side electrode 7 a is formed in a comb-like shape with the width of the light receivingsurface side electrode 7 a made narrow, as shown in a top view of thesolar cell 1 a (seeFIG. 5 ). On the other hand, the backsurface side electrode 7 b may be formed in a comb-like shape, or may be formed over an entire area of the back surface of thephotovoltaic body 6. In this embodiment, as described above, the adhesion area where the light receivingsurface side electrode 7 a adheres onto the light receiving surface of thephotovoltaic body 6 is smaller than the adhesion area where the backsurface side electrode 7 b adheres onto the back surface of thephotovoltaic body 6. - The sealing
material 2 seals thesolar cell string 1. Specifically, as shown inFIG. 4B , the light receiving surface of thesolar cell 1 a is in contact with afirst region 2 a of the sealingmaterial 2, and the back surface of thesolar cell 1 a is in contact with asecond region 2 b of the sealingmaterial 2. - The sealing
material 2 can be formed of a resin material such as EVA (ethylene vinyl acetate), PVB (polyvinyl butyral), silicone resin, urethane resin, acrylic resin, fluorocarbon-based resin, ionomer resin, silane denatured resin, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, polyethylene-based resin, polypropylene-based resin, acid-denatured polyolefin based resin, or epoxy-based resin. More than one type of the above resin materials may be used and compounded to form the sealingmaterial 2. - Here, in this embodiment, the degree of cross-linkage in the
second region 2 b of the sealingmaterial 2 that is in contact with the back surface of thesolar cell 1 a is smaller than that of thefirst region 2 a of the sealingmaterial 2 that is in contact with the light receiving surface of thesolar cell 1 a. Such a structure of the sealingmaterial 2 will be described later in detail, since it relates to a feature of the present invention. Incidentally, the degree of cross-linkage means a crosslinking rate in the sealingmaterial 2, and a smaller degree of cross-linkage means that a larger region containing non-crosslinked resin component exists. - The light receiving surface
side supporting member 3 is joined to the light receiving side of thesolar cell 1 a on contact with thefirst region 2 a of the sealingmaterial 2 interposed in between. The light receiving surfaceside supporting member 3 may be formed of a material, such as glass or plastic, allowing greater part of light with a wavelength which thesolar cell 1 a can absorb to pass therethrough. - The back surface
side supporting member 4 is joined to the back surface of thesolar cell 1 a on contact with thesecond region 2 b of the sealingmaterial 2 interposed in between. The back surfaceside supporting member 4 can be formed of a material such as a resin film including a PET (polyethylene terephthalate) film, a fluorine resin film, or the like; a resin film in which a vapor-deposited film of metal oxide such as silica or alumina is formed; a metal film such as an aluminum foil; or a lamination film including some of these films. - As described above, in this embodiment, the light receiving surface of the
solar cell 1 a is in contact with thefirst region 2 a of the sealingmaterial 2, and the back surface of thesolar cell 1 a is in contact with thesecond region 2 b of the sealingmaterial 2. - This embodiment is characterized in that the degree of cross-linkage of the
second region 2 b of the sealingmaterial 2 which is in contact with the back surface of thesolar cell 1 a is smaller than that of thefirst region 2 a of the sealingmaterial 2 which is in contact with the light receiving surface of thesolar cell 1 a. Any of the following methods can be used to make the degree of cross-linkage of thesecond region 2 b smaller than that of thefirst region 2 a like the above. - In a first method, the same sealing material to which a cross-linking agent of the same type and the same amount is added is used as a sealing material to form the
first region 2 a and thesecond region 2 b. Then, different crosslinking conditions are employed to form therespective regions second region 2 b can be made smaller than that of thefirst region 2 a. Specifically, a temperature that causes crosslinks to be formed in the sealing material used for forming thesecond region 2 b is set lower than a temperature that causes crosslinks to be formed in the sealing material used for forming thesecond region 2 a. Thereby, the degree of cross-linkage of thesecond region 2 b can be made smaller than that of thefirst region 2 a. - In a second method, the degree of cross-linkage of the
second region 2 b can be made smaller than that of thefirst region 2 a by using the smaller amount of cross-linking agent added to the sealing material for forming thesecond region 2 b, than that of cross-linking agent added to the sealing material for forming thesecond region 2 a. In this case, the degree of cross-linkage of the sealing material mainly depends on the amount of cross-linking agent added to the sealing material, and depends on the type of the sealing material only to a slight degree. For this reason, any one of or a combination of the foregoing resin materials such as the EVA and the PVB can be used as the sealing material for forming thefirst region 2 a and thesecond region 2 b. - Note that an organic peroxide is used as a cross-linking agent, in general. For example, as the organic peroxide for causing crosslinks to be formed in the EVA, it is possible to use 2,5-dimethylhexane, 2,5-dihydroperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 3-di-t-butylperoxide, t-dicumylperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, dicumylperoxide, α,α-bis(t-butylperoxyisopropyl)benzene, n-butyl-4,4-bis(t-butylperoxy)butane, 2,2-bis(t-butylperoxy)butane, 1,1-bis(t-butylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, t-butylperoxybenzoate, benzoylperoxide or the like.
- The present invention is characterized in that the above-described relationship is satisfied between the degrees of cross-linkage of the
first region 2 a and thesecond region 2 b of the sealingmaterial 2 which are in contact with the light receiving surface and the back surface of thesolar cell 1 a, respectively. Accordingly, the sealingmaterial 2 may further include another sealing material as long as it includes thefirst region 2 a and thesecond region 2 b that satisfy the above-described relationship. - For example, the sealing
material 2 may include thefirst region 2 a that is in contact with the light receiving surface of thesolar cell 1 a, and may further include one or more sealing material layers on the light receiving surface side of thefirst region 2 a. Similarly, the sealingmaterial 2 may include thesecond region 2 b that is in contact with the back surface of thesolar cell 1 a, and may further include one or more sealing material layers on the back surface side of thesecond region 2 b. Alternatively, the sealingmaterial 2 may have a structure formed by combining these two. -
FIG. 6 is an exploded cross sectional diagram of thephotovoltaic module 10 including athird region 2 c on the light receiving surface of thefirst region 2 a, and also afourth region 2 d on the back surface of thesecond region 2 b. In thephotovoltaic module 10 shown inFIG. 6 , the degree of cross-linkage of thesecond region 2 b of the sealingmaterial 2 that is in contact with the back surface of thesolar cell 1 a is smaller than that of thefirst region 2 a of the sealingmaterial 2 that is in contact with the light receiving surface of thesolar cell 1 a. In addition, as sealing materials for forming the third region and the fourth region, it is possible to select any one of or a combination of the foregoing materials such as the EVA and the PVB. - In this way, the sealing
material 2 may have a multi-layered structure including three layers or more. - By using
FIGS. 7 and 8 , descriptions will be given of a method for manufacturing thephotovoltaic module 10 according to the present invention, that is, a module forming process for thephotovoltaic module 10. The descriptions will be given of a case where the same sealing material is used for thefirst region 2 a and thesecond region 2 b firstly, and then a case where the amount of cross-linking agent added to a sealing material for thesecond region 2 b is made smaller than that for thefirst region 2 a. - (1) Case where the same sealing material is used for the
first region 2 a and thesecond region 2 b - In this case, by changing a condition of a heating temperature and a heating duration, the degree of cross-linkage of the
second region 2 b of the sealingmaterial 2 that is in contact with the back surface of thesolar cell 1 a is made smaller than that of thefirst region 2 a of the sealingmaterial 2 that is in contact with the light receiving surface of thesolar cell 1 a. The following three processes are used for changing the condition. - Laminating process: In this process, internal materials are made to temporarily adhere to each other by using a
vacuum lamination apparatus 20 shown inFIG. 7 while an air bubble is prevented from forming between each pair of the internal materials. The interior of thevacuum lamination apparatus 20 is divided into two chambers, that is, upper and lower chambers with adiaphragm 30, and thereby it is possible to decompress each of the chambers independently. Firstly, the light receiving surfaceside supporting member 3, the light receiving side sealing material sheet (first region) 2 a, thesolar cell string 1, the back surface side sealing material sheet (second region) 2 b and the back surfaceside supporting member 4 are mounted in this order on a mounting table 40 which can be heated. Secondly, the air is discharged from each of the upper and lower chambers, while the mounting table 40 is being heated up to a predetermined temperature. In this way, the formation of an air bubble is prevented. Here, the predetermined temperature is lower than a temperature causing crosslinks to be formed in the sealingmaterial 2. Then, thephotovoltaic module 10 is pressed with thediaphragm 30 for a predetermined duration by causing the air to flow into the upper chamber. Hence, the temporary adhesion is completed. - First curing process: In this process, the sealing
material 2 is cured crosslinks are formed in the sealingmaterial 2 by using aheater 50 shown inFIG. 8A . Theheater 50 is capable of uniformly heating thephotovoltaic module 10 by high-temperature bast thereto. Firstly, thephotovoltaic module 10 including the temporarily adhering internal materials is placed inside theheater 50. Then, thephotovoltaic module 10 is heated at a predetermined temperature for a predetermined duration. Here, the predetermined temperature is set to be higher than the temperature causing crosslinks to be formed in the sealingmaterial 2. By using such a temperature, crosslinking reaction occurs in thefirst region 2 a of the sealingmaterial 2 that is in contact with the light receiving surface of thesolar cell 1 a, and in thesecond region 2 b of the sealingmaterial 2 that is in contact with the back surface of thesolar cell 1 a. - Second curing process: In this process, the crosslinking reaction is more advanced in the
first region 2 a of the sealingmaterial 2 that is in contact with the light receiving surface of thesolar cell 1 a, by using aheater 60 shown inFIG. 8B or 8C. Theheater 60 shown inFIG. 8B or 8C heats the light receiving surface side by using the hot air, while cooling the back surface side by using a cooling medium or a cool air. Alternatively, theheater 60 heats only the sealing material on the light receiving surface side at the temperature higher than the crosslinking temperature, while heating the sealing material on the back surface side at the temperature lower than the crosslinking temperature. In this manner, the crosslinking reaction is advanced only in thefirst region 2 a of the sealingmaterial 2 that is in contact with the light receiving surface of thesolar cell 1 a. - While being processed through the foregoing processes, the crosslinks are formed in the sealing material on the light receiving surface side during the first curing process and the second curing process. On the other hand, the crosslinks are formed in the sealing material on the back surface side during only the first curing process.
- (2) Case where the amount of cross-linking agent added to the sealing material for the
second region 2 b is made smaller than that added to the sealing material for thefirst region 2 a. - In this case, it is not necessary to separately adjust the heating durations in the curing processes for the
first region 2 a and thesecond region 2 b, unlike the case where the same sealing material is used for thefirst region 2 a and thesecond region 2 b. This is because the degree of cross-linkage depends on the amount of cross-linking agent. Accordingly, it is not necessary to change the condition of the heating temperature and the heating duration between the light receiving surface side and the back surface side of thephotovoltaic module 10. For this reason, only two processes of the laminating process and the first curing process are used. - After being processed in the foregoing laminating process, the
photovoltaic module 10 is heated at the temperature higher than the crosslinking temperature of the sealingmaterial 2 for a predetermined duration. Here, the predetermined duration is one during which the crosslink formation in the sealingmaterial 2 is completed. There is no need to perform the second curing process. - In the foregoing manner, the
photovoltaic module 10 of this embodiment is manufactured. - According to this embodiment, by applying such a structure to a photovoltaic module, it is possible to provide the photovoltaic module that brings improved reliability by preventing damage to a collector electrode from accumulating, the damage caused by a difference in the way that the light receiving and back surfaces of the photovoltaic module are subjected to the solar light. The reason for this will be described in detail below.
- Table 1 is a property table showing the linear expansion coefficients of main materials constituting a photovoltaic module. As the sealing material, shown is the value of EVA resin, which is a typically used material. As the solar cell, shown is the value of silicon, which is a generally used material. In addition, as the back surface side supporting member, shown is the value of a PET film. As shown in Table 1, the linear expansion coefficients have a relationship of the sealing material>the PET film>copper>glass≈the silicon. Moreover, a difference between the linear expansion coefficients of the sealing material and the silicon is the largest among those between any pair of the components constituting the photovoltaic module.
-
TABLE 1 LINER EXPANSION COEFFICIENTS OF MAIN MATERIALS FOR PHOTOVOLTAIC MODULE (UNIT: ° C.−1) SEALING MATERIAL ~4 × 10−4(TYPICAL EXAMPLE) PET ~0.7 × 10−4 COPPER ~0.17 × 10−4 GLASS ~0.05 × 10−4 SILICON ~0.03 × 10−4 - Accordingly, in terms of the contraction degrees of the components that have been thermally expanded in the module forming processing, the sealing material with the largest linear expansion coefficient has the largest contraction degree, and the solar cell formed of a silicon material with the smallest linear expansion coefficient has the smallest contraction degree.
- For this reason, when the conventional
photovoltaic module 100 receives the solar light, the stress a applied to the light receiving surface of thesolar cell 101, and the stress b applied to the back surface of thesolar cell 101 are unbalanced, and thereby thesolar cell 101 is warped, as shown inFIGS. 2 and 3 . As a result, damage to thecollector electrode 106 is accumulated therein, and this deteriorates the electron collection performance of thecollector electrode 106. - Incidentally, the thinner the thickness of a silicon wafer becomes, the more frequently, the above-described deterioration of the power of the photovoltaic module happens.
- In contrast to this, in a case of the
photovoltaic module 10 according to this embodiment, thesecond region 2 b of the sealingmaterial 2 that is in contact with the back surface of thesolar cell 1 a is thermally expanded easily at a lower temperature than thefirst region 2 a of the sealingmaterial 2 that is in contact with the light receiving surface of thesolar cell 1 a, by making the degree of cross-linkage of thesecond region 2 b smaller than that of thefirst region 2 a. Accordingly, when thephotovoltaic module 10 is subjected to the solar light during daytime, thesecond region 2 b whose temperature is less likely to rise can also be thermally expanded. This makes it possible to reduce the stress applied to thesolar cell 1 a on the back surface side as well, and thereby to reduce the difference between the stresses on the light receiving surface side and the back surface side of thesolar cell 1 a. This results in a relaxation of a force that acts to warp thesolar cell 1 a so as to be convex toward the light receiving side. Hence, the stress applied to the light receivingsurface side electrode 7 a is lowered. - To be more precise, in a case where the solar light enters the
photovoltaic module 10 of this embodiment as shown inFIGS. 9A and 9B , the stress applied to the light receiving surface of thesolar cell 1 a is equal in magnitude to the stress applied to the back surface (seeFIG. 9A ), or the stress applied to the back surface is greater than that applied to the light receiving surface (seeFIG. 9B ). Note that, in comparison with the light receivingsurface side electrode 7 a, the adhesion strength of the backsurface side electrode 7 b can be made larger by enlarging an adhesion area where theelectrode 7 b adheres onto thephotovoltaic body 6. Accordingly, even when thesolar cell 1 a is warped to be convex toward the back surface side as shown inFIG. 9B , damage to the backsurface side electrode 7 b is small. - As described above, according to the
photovoltaic module 10 of this embodiment, it is possible to provide a photovoltaic module that allows the reliability to be improved by suppressing the damage accumulated in the collector electrode provided on the light receiving surface side, and the method for manufacturing such a photovoltaic module. - Although the present invention has been described by using the foregoing embodiment, it should not be understood that the descriptions and the drawings constituting part of this disclosure limit the present invention. From this disclosure, it is obvious to one skilled in the art that various alternative embodiments, examples and applied techniques can be made.
- For example, although the back
surface side electrode 7 b is made to adhere to the entire back surface of thephotovoltaic body 6 in the foregoing embodiment, the backsurface side electrode 7 b may adhere to thephotovoltaic body 6 so as to expose a part of thephotovoltaic body 6, or the backsurface side electrode 7 b may be formed in a comb-like shape similar to that of the light receivingsurface side electrode 7 a. - As such, needless to say, the present invention includes various embodiments and the like that are not described in this disclosure. Accordingly, the technical scope of the present invention should be limited only by the scope of the invention as defined by the appended claims appropriate for the foregoing description.
- Hereinafter, the photovoltaic module of the present invention will be described specifically by taking examples. The present invention is not limited to the below-described examples, and any appropriate modification can be made as long as the spirit and scope of the invention are not changed.
- In the first place, a relationship between a temperature in the crosslinking process and the degree of cross-linkage was examined by using an EVA sheet as a sealing material sheet. Firstly, a glass plate, an EVA sheet with the thickness of 0.6 mm and a PET film were placed in this order on a mounting table of a lamination apparatus. Secondly, these materials are heated under reduced pressure at a temperature of approximately 120° C. for 10 minutes. In this way, the air was released, and the temporary adhesion was completed. Note that the temperature of approximately 120° C. is lower than the crosslinking temperature of the EVA. Thirdly, the sample in a temporary adhering state was placed in a heating furnace, and the crosslinking process was performed at a heating temperature of approximately 150° C. At this time, the crosslinking processes were performed with the heating duration changed within a range of 5 minutes to 45 minutes, since the degree of cross-linkage of the sealing material(EVA) also depends on the heating duration. Fourthly, only the sealing material was taken off from the glass plate of each of the samples thus manufactured, and then the gel fraction was measured in the following manner. Thereby, the degree of cross-linkage of each of sealing materials was evaluated.
- Firstly, the weight of each sealing material taken off from the glass plate was measured. Secondly, each sealing material was immersed in a xylene solvent, and thereby a region in a sol state where crosslinks were not formed was dissolved into the solvent. Thirdly, the crosslinked gel region was extracted by evaporating the xylene solution. Fourthly, the weight of the extracted gel region was measured, and the gel fraction was figured out by calculating a ratio of the weight of the gel region, to the weight of the sealing material before the immersion into the solvent. The following shows the equation for this calculation.
-
Gel fraction (%)=(the weight of an undissolved region/the weight of a sample before the immersion)×100 - Table 2 is a property table showing the thus figured-out gel fractions of the respective samples.
-
TABLE 2 HEATING DURATION AT 150° C. GEL FRACTION(%) 0 0 5 13 10 27 15 35 20 53 30 71 45 87 - As shown in Table 2, it was found that the gel fraction of an obtained sealing material can be changed within a range of 13% to 87% by adjusting the heating duration within a range of 5 minutes to 45 minutes when the crosslinking process is performed at the temperature of approximately 150° C.
- In the second place, photovoltaic modules according to the present invention were manufactured on the basis of the result shown in Table 2, in the following manner. In these examples, the same sealing material sheet was used as a sealing material of the light receiving side and a sealing material of the back surface side. For this reason, the photovoltaic modules of the present invention were each manufactured by performing the second curing process using the lower heating temperature for the sealing material sheet of the back surface side than that for the sealing material sheet of the light receiving side.
- Note that an EVA sheet with the thickness of approximately 0.6 mm was used as each of the sealing material sheets of the light receiving side and the back surface side in the following examples. Moreover, as each of the solar cells, used was a solar cell with the thickness of 100 to 140 μm having a HIT (registered trademark) structure that includes a pn junction consisting of n-type single-crystal silicon and p-type amorphous silicon with a thin i-type amorphous silicon layer interposed in between. In addition, a glass plate with the thickness of approximately 3.2 mm was used as each of the light receiving surface side supporting members, and a lamination film consisting of a tedra film with the thickness of approximately 38 μm, an aluminum film with the thickness of approximately 30 μm, and a tedra film with the thickness of approximately 38 μm was used as each of the back surface side supporting members.
- A sample of an example 1 was fabricated by performing the laminating process for 10 minutes, the first curing process for 0 minute, and the second curing process for 45 minutes.
- In other words, in the sample of the example 1, the sealing material on the light receiving surface side was heated at the temperature of 150° C. for 45 minutes, while the sealing material on the back surface side was heated at the temperature of 150° C. for 0 minute. Hence, from the foregoing result shown in Table 2, it can be assumed that the gel fraction of the sealing material on the light receiving surface side is approximately 87%, and that the gel fraction of the sealing material on the back surface side is approximately 0%.
- A sample of an example 2 was fabricated by performing the laminating process for 10 minutes, the first curing process for 5 minutes, and the second curing process for 40 minutes.
- In other words, in the sample of the example 2, the sealing material on the light receiving surface side was heated at the temperature of 150° C. for 45 minutes, while the sealing material on the back surface side was heated at the temperature of 150° C. for 5 minutes. Hence, from the foregoing result shown in Table 2, it can be assumed that the gel fraction of the sealing material on the light receiving surface side is approximately 87%, and that the gel fraction of the sealing material on the back surface side is approximately 13%.
- A sample of an example 3 was fabricated by performing the laminating process for 10 minutes, the first curing process for 10 minutes, and the second curing process for 35 minutes.
- In other words, in the sample of the example 3, the sealing material on the light receiving surface side was heated at the temperature of 150° C. for 45 minutes, while the sealing material on the back surface side was heated at the temperature of 150° C. for 10 minutes. Hence, from the foregoing result shown in Table 2, it can be assumed that the gel fraction of the sealing material on the light receiving surface side is approximately 87%, and that the gel fraction of the sealing material on the back surface side is approximately 27%.
- A sample of an example 4 was fabricated by performing the laminating process for 10 minutes, the first curing process for 20 minutes, and the second curing process for 25 minutes.
- In other words, in the sample of the example 4, the sealing material on the light receiving surface side was heated at the temperature of 150° C. for 45 minutes, while the sealing material on the back surface side was heated at the temperature of 150° C. for 20 minutes. Hence, from the foregoing result shown in Table 2, it can be assumed that the gel fraction of the sealing material on the light receiving surface side is approximately 87%, and that the gel fraction of the sealing material on the back surface side is approximately 53%.
- A sample of an example 5 was fabricated by performing the laminating process for 10 minutes, the first curing process for 30 minutes, and the second curing process for 15 minutes.
- In other words, in the sample of the example 5, the sealing material on the light receiving surface side was heated at the temperature of 150° C. for 45 minutes, while the sealing material on the back surface side was heated at the temperature of 150° C. for 15 minutes. Hence, from the foregoing result shown in Table 2, it can be assumed that the gel fraction of the sealing material on the light receiving surface side is approximately 87%, and that the gel fraction of the sealing material on the back surface side is approximately 71%.
- A sample of a comparative example 1 was fabricated by performing the laminating process for 10 minutes, the first curing process for 45 minutes, and the second curing process for 0 minute
- In other words, in the sample of the comparative example 1, the sealing material on both of the light receiving side and of the back surface side was heated at the temperature of 150° C. for 45 minutes. Hence, from the foregoing result shown in Table 2, it can be assumed that the gel fraction of the sealing material on both of the light receiving surface and of the back surface side is approximately 87%.
- Each of the photovoltaic modules of the examples 1 to 5 and the comparative example 1 was examined by performing the below-described temperature cycle test with a temperature-controlled bath, and the output power of the photovoltaic module before and after the cycle test were compared.
- The cycle test was performed a method in conformity with the temperature cycle test of JIS C 8917.
FIG. 10 is a graph showing a change of the temperature condition that was programmed in a controller of the temperature-controlled bath. As shown inFIG. 10 , firstly the temperature was increased from 25° C. to 90° C. by taking 45 minutes, secondly the upper limit temperature was maintained for 90 minutes, thirdly the temperature was decreased up to −40° C. by taking 90 minutes, fourthly the lower limit temperature was maintained for 90 minutes, and fifthly the temperature was increased up to 25° C. by taking 45 minutes. One cycle (6 hours) consists of these five time periods. - In the temperature cycle test, in addition to the temperature cycle test method of JIS C 8917, the inventors of the present invention irradiated the photovoltaic module with light of AM1.5, 100 mW/cm2 from the light receiving surface side for the first 180 minutes, in order to make the test environment closer to an environment under exposure to the solar rays. Incidentally, assuming that a half of the time period in one cycle is a daytime, and that the other half is a nighttime, the irradiating duration was set to 180 minutes, the period of which is half of one cycle.
- With this light irradiation, the temperature of the test-target photovoltaic module on the light receiving surface side can be made higher than that on the back surface side. In other words, it can be assumed that this light irradiation caused the temperature of the sealing material on the light receiving surface side to be higher than 90° C., when the temperature inside the temperature-controlled bath was kept at 90° C.
- Then, each of the cycle tests was performed by repeating this cycle up to 400 cycles. As the result of the cycle tests, the power properties of the respective samples were checked. Table 3 shows this result.
- Note that Table 3 shows each measurement result by using a normalized power reduction ratio. Here, the power reduction ratio is calculated by using the following equation:
-
power reduction ratio (%)={(pretest power−posttest power)/pretest power}×100. - Accordingly, the smaller power reduction ratio means that the power reduction is smaller, and thereby that the photovoltaic module brings the superior reliability. Moreover, the normalized power reduction ratio is a normalized value by using the power reduction ratio of the comparative example as 1.00.
-
TABLE 3 GEL GEL NORMALIZED FRACTION FRACTION POWER ON FRONT ON BACK REDUCTION SURFACE (%) SURFACE (%) RATIO COMPARATIVE 1 87 87 1.00 EXAMPLE 1 87 0 0.50 EXAMPLE 2 87 13 0.50 EXAMPLE 3 87 27 0.53 EXAMPLE 4 87 53 0.70 EXAMPLE 5 87 71 0.73 - By referring to Table 3, it is found that the normalized power reduction ratios of the examples 1 to 5 are lower than the normalized power reduction ratio of the comparative example. By taking the samples of the examples 1 to 5 into consideration, it may be concluded that this resulted from a phenomenon that the property deterioration after long-time use was suppressed by making the degree of cross-linkage of the sealing material on the back surface side smaller than that of the sealing material on the light receiving surface. Incidentally, the property deterioration was attributable to the difference in the way that the light receiving and back surfaces of each of the photovoltaic module are subjected to light.
- Additionally, it can be seen that, in a case where the gel fraction on the back surface side is smaller than that on the light receiving side by 50% or more as in the cases of the examples 1 to 3, the power reduction ratio is decreased by approximately half as compared with that of the comparative example. As such, according to this embodiment, obtained were the photovoltaic modules whose power reduction ratios are low in comparison with the conventional ones, and each of which brings the superior reliability.
- As described above, according to the present invention, it is possible to provide a photovoltaic module that brings superior reliability by suppressing the property deterioration after long-time use attributable to the difference in the way that the light receiving and back surfaces of the collector electrode are subjected to the solar light. Moreover, the present invention is particularly suitable for a photovoltaic module including solar cells each using a thin substrate that is more likely to be warped because of stresses.
- Note that, it should be understood that the embodiment disclosed here is just an example in all respects, and is not a restrictive one. The embodiment of the present invention can be appropriately modified in various manners without departing from the technical sprit described in the scope of claims.
Claims (7)
1. A photovoltaic module comprising:
a solar cell having a receiving surface allowing light to enter therein, and a back surface provided on the opposite side of the light receiving surface;
a light receiving surface side supporting member provided at the light receiving surface side of the solar cell;
a back surface side supporting member provided at the back surface side of the solar cell; and
a sealing material for sealing the solar cell between the light receiving surface side supporting member and the back surface side supporting member; wherein
the sealing material includes a first region that is in contact with the light receiving surface, and a second region that is disposed between the back surface of the solar cell and the back surface side supporting member, and
a gel fraction of the second region is smaller than a gel fraction of the first region by at least 50%.
2. The photovoltaic module of claim 1 , wherein the gel fraction of the second region is 13% or less.
3. The photovoltaic module of claim 1 , wherein the gel fraction of the second region is 0%.
4. The photovoltaic module of claim 2 , wherein the gel fraction of the second region is more than 0%.
5. The photovoltaic module of claim 1 , wherein the gel fraction of the first region is 87% or more.
6. The photovoltaic module of claim 4 , wherein the gel fraction of the second region is 87% or more.
7. A photovoltaic module comprising:
a solar cell having a light receiving surface allowing light to enter therein, and a back surface provided on the opposite side of the light receiving surface;
a light receiving surface side supporting member provided at the light receiving surface side of the solar cell;
a back surface side supporting member provided at the back surface side of the solar cell;
and
a sealing material for sealing the solar cell between the light receiving surface side supporting member and the back surface side supporting member;
wherein the sealing material includes a first region that is in contact with the light receiving surface of the solar cell and a second region that is in contact with the back surface of the solar cell, with the sealing material of the first region and the sealing material of the second region each being cross-linked; and wherein the degree of cross-linkage of the second region is smaller than the degree of cross linkage of the first region.
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US11/723,849 US8178776B2 (en) | 2006-03-30 | 2007-03-22 | Photovoltaic module and method for manufacturing photovoltaic module |
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Also Published As
Publication number | Publication date |
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JP2007294868A (en) | 2007-11-08 |
TW200742104A (en) | 2007-11-01 |
TWI396290B (en) | 2013-05-11 |
EP1840974B1 (en) | 2015-11-11 |
US20070227584A1 (en) | 2007-10-04 |
JP4667406B2 (en) | 2011-04-13 |
EP1840974A3 (en) | 2009-12-30 |
EP1840974A2 (en) | 2007-10-03 |
KR20070098637A (en) | 2007-10-05 |
KR101215694B1 (en) | 2012-12-26 |
CN101047212B (en) | 2010-12-08 |
US8178776B2 (en) | 2012-05-15 |
CN101047212A (en) | 2007-10-03 |
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