Solar cell modules

Abstract

The present invention provides a solar cell module that can improve the bonding strength of the connecting members that connect the cells and busbars. [Solution] The solar cell module 1 comprises a solar cell string S in which a plurality of solar cells 10 are connected in series in a first direction, a bus bar 30 for drawing current from the solar cell string S, and an interconnector 20 for electrically connecting the solar cells 10 at the end of the solar cell string S and the bus bar 30. The interconnector 20 has a shape in which the longitudinal direction is in a second direction perpendicular to the first direction in a plan view. The bus bar 30 has a thermal expansion coefficient of 1 × 10 -6 / K~6×10 -6 A metallic material with a thermal expansion coefficient in the range of / K (a metallic material with a thermal expansion coefficient close to that of Si) is used, and it has an intermediate layer 32 extending in a second direction.

Description

[Technical Field]

[0001] This disclosure relates to solar cell modules. [Background technology]

[0002] Solar cell modules, which consist of multiple solar cells connected together, are commonly used. Patent Document 1 discloses a solar cell module in which back-electrode type solar cells are connected via connecting members. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Special Publication No. 2008-502149 [Overview of the project] [Problems that the invention aims to solve]

[0004] Back-electrode type solar cells allow for sufficient wiring area without worrying about light-shielding losses due to wiring, resulting in improved bonding strength with connecting materials compared to conventional double-electrode type cells. Meanwhile, in recent years, solar cells are not only required for installation on residential roofs but also for mobile applications such as those in vehicles. Solar cells for vehicles tend to require higher temperature resistance than conventional residential solar cells, thus necessitating further improvements in bonding strength.

[0005] In particular, in solar cell modules with back-electrode type solar cells connected in series, a tendency was observed for the bonding strength to be lower in the connecting members (interconnectors) that connect the cells at the end of the series connection to the busbars compared to the connecting members (interconnectors) that connect two adjacent cells. Therefore, improving the bonding strength of the connecting members that connect the cells to the busbars is expected to further extend the lifespan of the solar cell modules.

[0006] This disclosure has been made in view of the above-mentioned problems, and aims to provide a solar cell module that can improve the bonding strength of the connecting member that connects the cell and the busbar. [Means for solving the problem]

[0007] To solve the above problems, a solar cell module according to a first aspect of this disclosure comprises a solar cell string in which a plurality of solar cells are connected in series in a first direction, a bus bar for extracting current from the solar cell string, and a connecting member soldered to the solar cells at the end of the solar cell string and electrically connecting the solar cells at the end of the solar cell string and the bus bar, wherein the connecting member has a shape in which the longitudinal direction is in a second direction perpendicular to the first direction in a plan view, and the bus bar has a thermal expansion coefficient of 1 × 10 -6 / K~6×10 -6 It is characterized by being made of a metallic material in the range of / K and having a first metallic layer extending in the second direction.

[0008] In the above-described solar cell module, the metal material of the first metal layer can be Invar or Kovar.

[0009] In the solar cell module described above, the busbar can be configured as a clad material in which the first metal layer and the second metal layer, which is made of a metal material with a lower electrical resistivity than the first metal layer, are laminated together.

[0010] In the above-described solar cell module, the connecting member can be configured to be soldered to the busbar and the second metal layer.

[0011] In the above-described solar cell module, the busbar can be configured as a clad material with a three-layer structure in which the first metal layer is sandwiched between the second metal layer.

[0012] In the above solar cell module, the bus bar is divided into a first part to which the connection member is connected and a second part responsible for the connection from the first part to the terminal box, and the first metal layer can be formed only on the first part.

[0013] In the above solar cell module, the bus bar can be configured such that the second metal layers on both sides of the first metal layer are connected.

[0014] In the above solar cell module, the connection member can be configured to be soldered to the bus bar.

[0015] In the above solar cell module, the bus bar and the connection member can be configured as an integrated member.

Advantages of the Invention

[0016] In the solar cell module of the present disclosure, by using a metal material with a thermal expansion coefficient close to that of Si (in the range of 1×10 -6 / K to 6×10 -6 / K) in the bus bar, the thermal expansion and contraction amount of the bus bar can be made close to that of the solar cell, and both sides of the connection member are constrained by the solar cell and the bus bar, so that the expansion and contraction of the connection member during temperature cycling can be suppressed to a small extent, and thus the occurrence of solder breakage is less likely to occur.

Brief Description of the Drawings

[0017] [Figure 1A] It is a plan view of a back electrode type solar cell. [Figure 1B] It is a rear view of a back electrode type solar cell. [Figure 2] It is a rear view of a solar cell module. [Figure 3] It is an enlarged rear view showing a cell / cell connection part in a solar cell module. [Figure 4] It is an enlarged rear view showing a cell / bus bar connection part in a solar cell module. [Figure 5] It is a diagram showing a solder break location in the cell / bus bar connection part. [Figure 6] It is a cross-sectional view of the cell / bus bar connection part. [Figure 7] It is an enlarged back view of the vicinity of the end of the bus bar in the cell / bus bar connection part. [Figure 8] It is a partial back view of a solar cell module showing a modified example of an interconnector. [Figure 9] It is a cross-sectional view showing a modified example of a bus bar. [Figure 10] It shows a modified example of a bus bar and is an enlarged back view of the cell / bus bar connection part.

Mode for Carrying Out the Invention

[0018] 〔First Embodiment〕 Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. FIGS. 1A and 1B are a plan view and a back view of a solar cell 10 used in a solar cell module 1 according to an embodiment of the present disclosure. FIG. 2 is a back view of the solar cell module 1.

[0019] The solar cell 10 is a back electrode type solar cell, and as shown in FIG. 1B, it has a plurality of connection pads 11 on the back side (the side opposite to the light receiving surface). Note that on the back surface of the solar cell 10, the P electrode and the N electrode are formed to face each other in a comb shape, but in FIG. 1B, electrodes other than the connection pads 11 are not shown. The connection pads 11 include a negative electrode side connection pad 111 provided along one side (the lower side in the figure) of the solar cell 10, and a positive electrode side connection pad 112 provided along the side opposite to the negative electrode side connection pad 111 (the upper side in the figure). As a result, as shown in FIG. 1A, since the connection pads 11 are not provided on the light receiving surface which is the front side of the solar cell 10, the design property is enhanced. Note that the connection pads 11 are not limited to a configuration in which they are provided at three locations along one side of the solar cell 10 as in the example of FIG. 1B, and may be provided at a plurality of locations.

[0020] As shown in Figure 2, the solar cell module 1 has at least one row of solar cell strings S, in which multiple (five in Figure 2) solar cell cells 10 are connected in series. Alternatively, the solar cell module 1 may be a solar cell array in which multiple rows (four in Figure 2) of solar cell strings S are connected in series. The number of solar cell cells 10 connected in series in the solar cell string S and the number of rows of solar cell strings S in the solar cell array are not particularly limited. Note that in Figure 2 (and Figures 3 and 4), the connection pads 11 are omitted from the illustration for simplification. In the following description, the connection direction of the solar cell cells 10 in the solar cell string S is referred to as the first direction, and the direction perpendicular to the first direction in a plan view is referred to as the second direction.

[0021] In a solar cell string S, two adjacent solar cells 10 are connected using an interconnector (connecting member) 20. Furthermore, solar cells 10 located at the ends of the solar cell string S are connected to a busbar 30 via the interconnector 20. The busbar 30 is a conductive member that extracts current from the solar cell module 1 (i.e., from the solar cell string S) to the outside, and is formed as an elongated member (e.g., a rod-shaped member) with the second direction as its longitudinal direction.

[0022] Figure 3 is an enlarged rear view showing the connection point (cell / cell connection point) between two solar cells 10. In Figure 3, the upper solar cell 10 is designated as the first cell 10A, and the lower solar cell 10 is designated as the second cell 10B. At the cell / cell connection point between the first cell 10A and the second cell 10B, the side of the first cell 10A with the negative electrode connection pad 111 is designated as the connection side, and the side of the second cell 10B with the positive electrode connection pad 112 is designated as the connection side. At the cell / cell connection point, the connection sides of the first cell 10A and the second cell 10B are positioned facing each other, and the interconnector 20 electrically connects the negative electrode connection pad 111 of the first cell 10A and the positive electrode connection pad 112 of the second cell 10B.

[0023] The interconnector 20 is a thin, plate-like member made of a highly conductive metal (for example, copper). The interconnector 20 has an elongated shape with a longitudinal direction and a transverse direction (a direction perpendicular to the longitudinal direction) in a plan view, and has a main body portion 21 extending along the longitudinal direction and a plurality of connection tabs 22 protruding from the main body portion 21 on both sides in the transverse direction. The connection tabs 22 are provided in correspondence with the connection pads 11 of the solar cell 10, and in Figure 3, there are three on one side (upper side) and three on the other side (lower side) in the transverse direction relative to the main body portion 21.

[0024] Furthermore, the number of connection points for the interconnector 20 to a single solar cell 10 is not limited to three; it may be two, four or more, or any number of connection points. Also, the number of connection points for the first cell 10A and the second cell 10B to the interconnector 20 does not have to be the same.

[0025] The interconnector 20 is positioned so that its longitudinal direction is parallel to the second direction (parallel to the connection side of the solar cell 10), and the connection tabs 22 are soldered to the connection pads 11. Specifically, in Figure 3, the connection tab 22 located on the upper side of the main body 21 is soldered to the negative electrode side connection pad 111 of the first cell 10A, and the connection tab 22 located on the lower side is soldered to the positive electrode side connection pad 112 of the second cell 10B. As a result, at the cell / cell connection section, two adjacent solar cells 10 are connected in series via the interconnector 20.

[0026] Figure 4 is an enlarged rear view showing the connection between the solar cell 10 and the busbar 30 (cell / busbar connection). In the cell / busbar connection, the interconnector 20 is positioned so that its longitudinal direction is parallel to the second direction (parallel to the connection side of the solar cell 10 and the longitudinal direction of the busbar 30), and the connection tabs 22 are soldered to the connection pads 11 and the busbar 30. Specifically, in Figure 4, the connection tab 22 located on the upper side of the main body 21 is soldered to the busbar 30, and the connection tab 22 located on the lower side is soldered to the connection pad 11 of the solar cell 10.

[0027] A temperature cycling test was conducted on a conventional solar cell module having the same basic structure as shown in Figure 2. The conventional solar cell module referred to here is one that uses copper rod-shaped components for the busbars. The standard for the temperature cycling test, one of the certification tests, is to maintain 95% or more of the output after 200 cycles of temperature cycling from -40 to 85°C. However, the conventional solar cell module showed only a slight decrease in output of 1-2% even after more than 10 times that number of cycles (2000-3000 cycles), indicating it was a high-quality module. To further extend its lifespan, an investigation into the cause of the output decrease revealed an increase in resistance (increase in the resistive component) in some end cells (solar cells connected to the busbars) in the solar cell string. On the other hand, no output decrease was observed in solar cells other than the end cells.

[0028] For further analysis, a mini-module consisting of only two solar cells was fabricated, and after similar temperature cycling tests were conducted, a cross-sectional observation of the connection between the interconnector and the electrodes (connection pads) of the solar cells revealed partial solder fracture at the solder joints in the cell / busbar connection (see Figure 5). This is considered to be the cause of the increased resistance component in the end cells.

[0029] Solder fracture at cell / busbar connections is thought to be caused by the difference in thermal expansion between copper, which is commonly used in interconnects and busbars, and the Si (silicon) substrate that forms the solar cell (Coefficient of thermal expansion of Cu: 16.5 × 10⁻⁶). -6 Thermal expansion coefficient of Si: 3.5 × 10⁻⁶ / K -6(K). At the cell / cell connection, both sides of the interconnect are connected to and constrained by the solar cells, so the expansion and contraction of the interconnect during temperature cycling is kept to a minimum, which is thought to reduce the likelihood of solder fracture. On the other hand, at the cell / busbar connection, the side connected to the solar cell is constrained by the solar cell, but the side connected to the busbar can expand and contract freely in accordance with the thermal cycle because the busbar is made of the same copper as the interconnect. Also, because the interconnect is elongated in the second direction, the amount of expansion and contraction in the second direction is large. For this reason, the stress on the solder connection points is greater towards the ends in the longitudinal direction of the interconnect, and solder fracture is more likely to occur in these areas.

[0030] The solar cell module 1 in this disclosure aims to further extend its lifespan by suppressing solder fracture at the cell / busbar connection. Specifically, the solar cell module 1 uses a metal material with a thermal expansion coefficient close to that of Si in the busbar 30.

[0031] As a metallic material with a thermal expansion coefficient close to that of Si, for example, Invar (36Ni-Fe), which contains 36% nickel in iron, has a thermal expansion coefficient of 2 × 10⁻⁶. -6 There is a coefficient of thermal expansion of 4.5 × 10¹⁰ in some iron alloys. Alternatively, in other iron alloys, the coefficient of thermal expansion can be adjusted by adjusting nickel and other components, and Kovar (29Ni-17Co-Fe) has a coefficient of thermal expansion of 4.5 × 10¹⁰ -6 This will be closer to / K and Si.

[0032] However, since Invar and Kovar have higher electrical resistivity than copper, it is preferable that the busbar 30 have a configuration to suppress electrical resistance. For example, electrical resistance can be suppressed by using a clad material for the busbar 30, such as CIC (Cu / Invar / Cu). In addition, the thermal expansion coefficient and electrical resistivity of the busbar 30 as a whole can be appropriately adjusted by adjusting the thickness of the copper and Invar in the CIC.

[0033] FIG. 6 is a cross-sectional view of the cell / bus bar connection part (cross-sectional view taken along line VI-VI of FIG. 4). In the cell / bus bar connection part, the interconnector 20 is connected to the bus bar 30 and the solar cell 10 via solder 40. The bus bar 30 is a clad material in which a first surface layer (second metal layer) 31, an intermediate layer (first metal layer) 32, and a second surface layer (second metal layer) 33 are laminated in order from the back side (upper surface side in FIG. 6) of the solar cell module 1. A metal material having a thermal expansion coefficient close to that of Si is used for the intermediate layer 32 of the bus bar 30. Here, the "metal material having a thermal expansion coefficient close to that of Si" refers to a metal material in the range of 1×10 -6 / K to 6×10 -6 / K, and specific examples include Invar or Kovar. Materials having a lower electrical resistivity (at least lower than that of the intermediate layer 32) are used for the first surface layer 31 and the second surface layer 33. For example, when the bus bar 30 is CIC, the first surface layer 31 and the second surface layer 33 are copper, and the intermediate layer 32 is Invar. When forming a clad material with a metal having a small electrical resistance and a large thermal expansion coefficient such as copper, the thermal expansion coefficient of the "metal material having a thermal expansion coefficient close to that of Si" is preferably smaller than that of Si (1×10 -6 / K to 3.5×10 -6 / K).

[0034] In the solar cell module 1, by using the bus bar 30 which is a clad material, solder breakage at the cell / bus bar connection part can be suppressed. That is, a metal material having a thermal expansion coefficient close to that of Si is used for the intermediate layer 32 of the bus bar 30, and the intermediate layer 32 extends along the second direction within the bus bar 30. Thereby, the intermediate layer 32 can suppress the thermal expansion and contraction (thermal deformation) of the bus bar 30 in the second direction, and the amount of thermal expansion and contraction of the bus bar 30 can be made close to the amount of expansion and contraction of the solar cell 10. As a result, in the interconnector 20 used for the cell / bus bar connection part, similar to the cell / cell connection part, both sides of the interconnector 20 are restrained by the solar cell 10 and the bus bar 30, and the expansion and contraction of the interconnector 20 during temperature cycling are suppressed to a small extent, making it difficult for solder breakage to occur.

[0035] Furthermore, as shown in Figure 6, the interconnector 20 is soldered to the first surface layer 31 of the busbar 30. The first surface layer 31 is a layer with low electrical resistance and extends along the second direction. For example, the electrical resistivity of invar, which can be used for the intermediate layer 32, and copper, which can be used for the first surface layer 31 and the second surface layer, are 75 μΩcm and 1.7 μΩcm, respectively. By using a cladding material of invar and copper, the resistance loss can be significantly reduced compared to constructing the busbar 30 with invar alone.

[0036] Furthermore, from the viewpoint of achieving both a reduction in thermal expansion and a reduction in output loss in the busbar 30, the busbar 30 may have a two-layer structure consisting of a first surface layer 31 and an intermediate layer 32 (the second surface layer 33 may be omitted). However, in the example busbar 30 in Figure 6, the warping of the busbar 30 can be suppressed by forming the second surface layer 33 on the opposite side of the intermediate layer 32 from the first surface layer 31. That is, in a busbar 30 having a second surface layer 33, the warping due to the difference in thermal expansion between the first surface layer 31 and the intermediate layer 32 cancels out the warping due to the difference in thermal expansion between the second surface layer 33 and the intermediate layer 32, thereby suppressing the warping of the entire busbar 30, and thus it can be expected that solder fracture during temperature cycling will be less likely to occur. Furthermore, in the solar cell module 1, the busbars 30 are located at both ends of the module and, unlike the interconnector 20, do not overlap with the solar cells 10. This allows for greater design flexibility, and by increasing the width and thickness of the busbars 30, it is possible to reduce the impact of increased resistance due to the material of the intermediate layer 32.

[0037] [Second Embodiment] Figure 7 is an enlarged rear view of the area near the end of the busbar 30 in the cell / busbar connection section. Since the current output by the solar cell module 1 is input to a terminal box, the busbar 30 may be responsible for the connection to the terminal box. In this case, as shown in Figure 7, the busbar 30 is divided into a first part 34 to which the interconnector 20 is connected, and a second part 35 that is responsible for the connection from the first part 34 to the terminal box. A metal material with a coefficient of thermal expansion close to Si may be used only for the first part 34. That is, the second part 35 may be formed only of a metal material with low electrical resistance (for example, copper).

[0038] In this way, by dividing the busbar 30 into a first part 34 and a second part 35, and using a metal material with a thermal expansion coefficient close to Si only in the first part 34, the amount of metal used, which is generally more expensive than copper and has high electrical resistance and a low thermal expansion coefficient, can be reduced. This reduces the overall cost of the busbar 30, and also reduces output loss due to increased resistance of the busbar 30.

[0039] The embodiments disclosed herein are illustrative in all respects and are not intended to be restrictive. Therefore, the technical scope of this disclosure is not to be interpreted solely by the embodiments described above, but rather by the claims.

[0040] For example, the interconnector 20 is not limited to the shape having a main body 21 and connection tabs 22 as shown in Figures 2 to 4, but may also be a substantially rectangular shape with the second direction as the longitudinal direction, as shown in Figure 8. In this case, the connection pads 11 in the solar cell 10 do not need to be provided in multiples along the connection edge with the interconnector 20, but may be formed to be elongated along the connection edge.

[0041] Furthermore, when the busbar 30 has a first surface layer 31, an intermediate layer 32, and a second surface layer 33, it is not limited to the structure in which the first surface layer 31 and the second surface layer 33 are separated as shown in Figure 6, but may also be configured in which the first surface layer 31 and the second surface layer 33 are connected (i.e., the second metal layers on both sides of the first metal layer are connected to each other), as shown in Figure 9. In the configuration of Figure 9, the second metal layers (first surface layer 31 and second surface layer 33) with low electrical resistance are electrically connected, so that current flows efficiently to the second surface layer 33 which is not directly connected to the interconnector 20, thereby further reducing resistance loss.

[0042] Furthermore, in the cell / busbar connection section, although the busbar 30 and interconnector 20 are described as separate components in the above description, a busbar 36 may be used as an integrated component of the busbar and interconnector, as shown in Figure 10. The busbar 36 has a busbar portion 361 that has the same function as the busbar 30 described above, and a connector portion 362 that protrudes from the busbar portion 361 in a first direction. In the busbar 36, the connector portion 362 functions as an interconnector that is connected to the solar cell 10. That is, in the busbar 36, the busbar portion 361 corresponds to the busbar described in the claims, and the connector portion 362 corresponds to the connecting member. In the configuration of Figure 10, the use of the busbar 36 reduces the number of parts (connection points) and improves reliability. [Explanation of Symbols]

[0043] 1. Solar cell module 10 solar cells 11 connection pads 20 Interconnectors (connecting components) 30 Bus Bar 31 First surface layer (second metal layer) 32 Intermediate layer (first metal layer) 33 Second surface layer (second metal layer) 34 Part 1 35 Part 2 36 Bus Bar 361 Busbar section (busbar) 362 Connector part (connecting component) 40 Handa S Solar String

Claims

1. A solar cell string in which multiple solar cells are connected in series in the first direction, A busbar for extracting current from the aforementioned solar cell string, The solar cell string comprises a connecting member that is soldered to the solar cell at the end of the solar cell string and electrically connects the solar cell at the end of the solar cell string to the busbar, The connecting member has a shape in which the second direction perpendicular to the first direction in a plan view is its longitudinal direction, and is soldered to the busbar. The solar cell module is characterized in that the busbar is made of a metallic material having a thermal expansion coefficient in the range of 1 × 10⁻⁶ / K to 6 × 10⁻⁶ / K, and has a first metallic layer extending in the second direction.

2. A solar cell module according to claim 1, A solar cell module characterized in that the metal material of the first metal layer is Invar or Kovar.

3. A solar cell module according to claim 1, The solar cell module is characterized in that the busbar is a clad material in which the first metal layer and the second metal layer made of a metal material with a lower electrical resistivity than the first metal layer are laminated together.

4. A solar cell module according to claim 3, The solar cell module is characterized in that the connecting member is soldered to the busbar and to the second metal layer.

5. A solar cell module according to claim 3, The solar cell module is characterized in that the busbar is a clad material with a three-layer structure in which the first metal layer is sandwiched between the second metal layer.

6. A solar cell module according to claim 3, The solar cell module is characterized in that the busbar is divided into a first portion to which the connecting member is connected and a second portion responsible for the connection from the first portion to the terminal box, and the first metal layer is present only in the first portion.

7. A solar cell module according to claim 5, The aforementioned busbar is characterized in that the second metal layers on both sides of the first metal layer are connected to each other, in a solar cell module.

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