The entire disclosure of Japanese Patent Application No. 2015-194696 filed on Sep. 30, 2015 including specification, claims, drawings and abstract is incorporated herein by reference in its entirety.
The present disclosure relates to a solar cell module.
There has hitherto been proposed a solar cell module provided with metal foils covering, over wiring members, the collector electrodes formed on the rear surfaces of photoelectric conversion parts (see Patent Literature 1). Patent Literature 1 describes reduction of the serial resistance in modularization through the same effect achieved by the provision of the metal foils as the effect due to the increase of the thickness of the wiring members. In Patent Literature 1, the dimensions of the metal foils are described to be preferably the larger the better; Patent Literature 1 discloses a structure provided with metal foils so as to cover almost the whole area of the rear surfaces of the photoelectric conversion parts.
However, as in the solar cell module disclosed in Patent Literature 1, when metal foils are provided on almost the whole area of the rear surfaces of the photoelectric conversion parts, light is not incident from the rear surface side of the cells, for example, in such a way that the light incident from the rear surface side of the solar cell module cannot be utilized for power generation. Even when the light incident from the light receiving surface side of the solar cell module is reflected by a back sheet or the like, the metal foils shield the reflected light and hence the reflected light is not incident on the rear surface side of the cells. In other words, it is an important technical problem to reduce the amount of the electrode material used in a solar cell module while the shadow loss is being suppressed.
The solar cell module as an aspect of the present disclosure includes a first protection member, having transparency, disposed on the light receiving surface side of the solar cell module, a second protection member disposed on the rear surface side of the solar cell module, and a string disposed between the first protection member and the second protection member, wherein the string includes a plurality of solar cells respectively having a plurality of finger electrodes formed on the rear surface of a photoelectric conversion part so as to be approximately parallel to each other, a plurality of wiring members fitted respectively to the solar cells in directions intersecting the plurality of finger electrodes and connecting adjacent solar cells to each other, and a plurality of metal foils provided at intervals from each other on the rear surface side of the photoelectric conversion part, at positions not overlapping the wiring members in directions intersecting the plurality of finger electrodes and electrically connected to the plurality of finger electrodes.
According to an aspect of the present disclosure, it is possible to provide a solar cell module having a high efficiency of light utilization and being capable of reducing the amount of electrode materials used.
Embodiments of the present invention will be described based on the following figures, wherein:
Hereinafter, an example of the embodiments will be described in detail.
The drawings referred to in the description of the embodiments are schematically drawn, and the dimensional proportions or the like of the constituent elements depicted in the drawings are sometimes different from those of the actual constituent elements or the like. Specific dimensional proportions or the like should be determined in consideration of the following descriptions. In the present description, the term “approximately **” is intended to mean, for example, in the case of “approximately the same,” of course the case of being exactly the same and also the case of being regarded as substantially the same. Additionally, the term “edge” means the edge of an object and the vicinity thereof.
Hereinafter, with reference to
As shown in
The metal foils 17 are not provided on the light receiving surface side of each of the solar cells 11, but are provided on the rear surface side of each of the solar cells 11, in consideration of the shadow loss. The metal foils 17 are provided on the rear surface side of each of the solar cells 11, and the metal foils 17 can be said to be constituent elements of the solar cell 11. In the present description, a solar cell 11 provided with the metal foils 17 is sometimes referred to as a solar cell 11 with metal foils. In the present description, the “light receiving surface” of each of the photoelectric conversion part, the solar cell and the solar cell module means the surface on which sunlight is mainly incident (exceeding 50%), and the “rear surface” means the surface opposite to the light receiving surface.
The solar cell module 10 includes a first protection member 12 provided on the light receiving surface side of the solar cells 11, a second protection member 13 provided on the rear surface side of the solar cells 11, and a sealing material 14 filled between the protection members. The plurality of the solar cells 11 are sealed with the sealing material 14 between the first protection member 12 and the second protection member 13. The sealing material 14 includes, for example, a first sealing material 14a provided between the solar cells 11 and the first protection member 12, and a second sealing material 14b provided between the solar cells 11 and the second protection member 13. The solar cell module 10 is generally produced by laminating the thin plate-like or film-like constituent members.
For the first protection member 12, a member having transparency such as a glass substrate, a resin substrate, or a resin sheet can be used. Among these, from the viewpoint of fire resistance, durability or the like, it is preferable to use a glass substrate. For the second protection member 13, the same transparent member as the first protection member 12 or an opaque member may be used. For example, a glass substrate is used for the first protection member 12, and a resin film is used for the second protection member 13. For the sealing material 14, for example, an olefin resin or a copolymer between α-olefin and a carboxylic acid vinyl ester such as ethylene-vinyl acetate copolymer (EVA) is used.
The solar cell module 10 has a string formed by connecting the adjacent solar cells 11 to each other with wiring members 15. The string is a unit formed of a plurality of solar cells 11 arranged so as to form a line and electrically connected to each other with wiring members 15. In the present embodiment, the plurality of solar cells 11 are serially connected to each other with the wiring members 15. The wiring members 15 are bent between the adjacent solar cells 11 in the thickness direction of the solar cell module 10, in such a way that the wiring members are fitted to the light receiving surface of one of the adjacent solar cells 11 and the rear surface of the other of the adjacent solar cells 11. A plurality of the wiring members 15 are fitted to each of the solar cells 11 (see
The wiring member 15 is a belt-like conductive metal wire constituted by a metal such as copper, aluminum, silver, or an alloy including at least one of these metals. For example, the width of the wiring member 15 is 10 mm to 30 mm, and the thickness of the wiring member 15 is 20 mm to 40 mm. The wiring member 15 may be fitted to the light receiving surface and the rear surface of the solar cell 11 with solder, and is preferably fitted with an adhesive (not shown). The adhesive may be either a conductive adhesive including conductive particles or an insulating adhesive constituted only by a resin component, but at least the adhesive applied to the light receiving surface is preferably a transparent insulating adhesive. Examples of the conductive particles may include metal particles such as silver particles, copper particles and nickel particles, carbon particles, and mixtures of these particles. Preferable among these are silver particles.
As shown in
The photoelectric conversion part 20 preferably has a semiconductor substrate 20a, and amorphous semiconductor layers 20b and 20c formed on the substrate. Examples of the semiconductor substrate 20a may include semiconductor wafers made of crystalline silicon (c-Si), gallium arsenide (GaAs) and indium phosphide (InP). The crystalline silicon wafer is preferable among these, and an n-type single crystalline silicon wafer is particularly preferable. As an example of a preferable photoelectric conversion part 20, there may be quoted a photoelectric conversion part having a structure in which on the light receiving surface of an n-type single crystalline silicon wafer, an i-type amorphous silicon layer and a p-type amorphous silicon layer are sequentially formed, and on the rear surface, an i-type amorphous silicon layer and an n-type amorphous silicon layer are sequentially formed.
The photoelectric conversion part 20 preferably has transparent conductive layers 21 and 24 respectively formed on the amorphous semiconductor layers 20b and 20c. The transparent conductive layers 21 and 24 are each constituted with a transparent conductive oxide formed by doping, for example, tin (Sn) or antimony (Sb) in a metal oxide such as indium oxide (In2O3) or zinc oxide (ZnO). The transparent conductive layers 21 and 24 are preferably formed on the light receiving surface and the rear surface of the photoelectric conversion part 20, respectively in such a way that the transparent conductive layers are each formed on almost the whole area of the surface involved except for the edges of the surface involved.
In the present embodiment, on the light receiving surface of the photoelectric conversion part 20, a plurality of finger electrodes 22 are formed as the collector electrodes. On the rear surface of the photoelectric conversion part 20, a plurality of finger electrodes 25 are formed as the collector electrodes. The pluralities of the finger electrodes 22 and 25 are formed respectively in the wide ranges on the transparent conductive layers 21 and 24. In each of the pluralities of the finger electrodes, the finger electrodes all extend in the same direction, and are formed so as to be approximately parallel to each other at approximately equal intervals from each other. The collector electrode may have a bus bar electrode (not shown) arranged to be approximately perpendicular to the finger electrodes. A plurality of bus bar electrodes are formed, for example, to be approximately parallel to each other at approximately equal intervals from each other. In the case where bus bar electrodes are formed on the transparent conductive layers 21 and 24, the wiring members 15 are disposed on the bus bar electrodes in the lengthwise direction of the bus bar electrodes.
The finger electrodes 25 are preferably formed in larger areas than the finger electrodes 22. For example, the finger electrodes 25 are formed wider in width than the finger electrodes 22, and additionally, larger in number than the finger electrodes 22. In order to enhance the current collectability while the shadow loss is being suppressed, the finger electrodes 22 are formed thicker than the finger electrodes 25.
The collector electrodes each have, for example, a structure in which the conductive particles are dispersed in a binder resin, and can be formed by printing a conductive paste on the photoelectric conversion part 20. For example, when the conductive particles are silver particles, a preferable content of the conductive particles is 60% by mass to 90% by mass in relation to the total weight of the collector electrodes. Examples of the binder resin may include thermosetting resins such as an epoxy resin, a urethane resin, a urea resin, an acrylic resin, an imide resin and a phenolic resin. The collector electrodes can be formed by a plating method, but are preferably formed by a printing method using a conductive paste from the viewpoint of productivity.
As described above, the solar cell module 10 includes the first protection member 12 having transparency, disposed on the light receiving surface side, the second protection member 13 disposed on the rear surface side, and the string 19 provided between the first protection member 12 and the second protection member 13. The string 19 includes a plurality of the solar cells 11 each having a plurality of finger electrodes 25 formed so as to be approximately parallel to each other on the rear surface of the photoelectric conversion part 20, a plurality of the wiring members 15, and a plurality of the metal foils 17. The wiring members 15 are fitted to each of the solar cells 11 in the direction intersecting the plurality of the finger electrodes 25 and connect the adjacent solar cells 11 to each other. The metal foils 17 are provided on the rear surface side of the photoelectric conversion part 20, at intervals from each other, at positions not overlapping the wiring members 15 and in a direction intersecting the plurality of the finger electrodes 25, and are electrically connected to the plurality of the finger electrodes 25.
Hereinafter, with further reference to
As shown in
For the purpose of reducing the serial resistance of the solar cell module 10, the provision of the metal foils 17 at positions overlapping the wiring members 15 can also be considered. However, when the metal foils 17 are provided so as to cover the wiring members 15, because the thickness of the wiring members 15 is larger than the thickness of the collector electrodes, large cavities (air bubbles) tend to be present between the rear surface of the photoelectric conversion part 20 and the metal foils 17. When cavities are present, for example, exterior appearance faults such as expansion of the back sheet or detachment of the sealing material 14 are sometimes caused in the laminating step or the subsequent curing step. Additionally, when the metal foils 17 are disposed on the wiring members 15, pressure is applied to the wiring members 15 and the solar cells 11 are sometimes damaged. Moreover, in the part of the collector electrodes, overlapping the wiring members 15 and in the vicinity of the overlapping part, a large amount of the carriers gather, and hence when the collector electrodes are reduced, it becomes difficult to sufficiently achieve the reduction of the serial resistance. In other words, the collector electrodes cannot be reduced to a high degree, which results in only a small reduction of the material cost. When the metal foils 17 are provided between the rear surface of the photoelectric conversion part 20 and the wiring members 15, problems such as the occurrence of the cavities or damage to the solar cells 11 are hardly caused, but significant reduction of the material cost is difficult, and problems such as the tendency for the metal foils 17 to be damaged when force is exerted one the wiring members 15 may be assumed to occur.
Accordingly, as described above, the metal foils 17 are provided on the rear surface side of the photoelectric conversion part 20, at positions not overlapping the wiring members 15. The metal foils 17 are disposed at intervals from each other, and on the rear surface of the solar cell 11, the rear surface (the transparent conductive layer 24) of the photoelectric conversion part 20 is exposed between the collector electrodes in the regions free from the metal foils 17. Thus, light can be incident from the rear surface side of the solar cell 11, and the reduction of the serial resistance and the reduction of the material cost can be achieved while the shadow loss is being suppressed.
The metal foils 17 are preferably provided in such a way that at least one metal foil 17 is provided between every pair of adjacent wiring members 15. In the example shown in
In the present embodiment, the metal foils 17 formed in a belt-like form are provided in a state of being approximately perpendicular to the finger electrodes 25. The metal foils 17 extend long in the Y-direction along the lengthwise direction of the wiring members 15, cover all the finger electrodes 25 arranged in the Y-direction, and are electrically connected to the aforementioned electrodes. The metal foils 17 are preferably provided so as not to traverse the edges of the rear surface of the photoelectric conversion part 20, in consideration of the prevention of short circuiting. The metal foils 17 each have, for example, a long and thin rectangular form having an approximately constant width W17. However, the shape of the metal foils is not limited to this (see
The metal foils 17 may have approximately the same shapes and approximately the same dimensions, or alternatively respectively different shapes and respectively different dimensions. In the example shown in
The metal foils 17 are metal thin films constituted by, for example, aluminum, copper, silver or nickel, or alloys mainly composed of these metals. In consideration of the material cost and conductivity, it is preferable to use metal foils 17 made of aluminum or an aluminum alloy. The thickness of the metal foils 17 is not particularly limited, but is preferably 30 μm or less and more preferably 15 μm to 30 μm.
The metal foils 17 are preferably made to adhere to the finger electrodes 25 (see
Examples of the preferable resin component of the adhesive 18 include an olefin resin and a copolymer of an α-olefin and a carboxylic acid such as an ethylene-vinyl acetate copolymer (EVA). In the adhesive 18, a resin of the same type as the sealing material 14 may also be used. The adhesive 18 may include a white pigment such as titanium oxide for the purpose of reflecting the light transmitting the photoelectric conversion part 20 so as to be again made incident on the photoelectric conversion part 20.
When an insulating adhesive is used as the adhesive 18, between the finger electrode 25 and the metal foil 17, a thin film of the adhesive 18 is formed to such an extent that the electrical connection between the finger electrode 25 and the metal foil 17 is not disturbed. When a conductive adhesive is used as the adhesive 18, the adhesive 18 interposed between the finger electrode 25 and the metal foil 17 may be thicker than when the insulating adhesive is used. The adhesive 18 is extruded, for example, between the finger electrode 25 and the metal foil 17, part of the finger electrode 25 is brought into contact with the metal foil 17 without intermediary of the adhesive 18, and a large amount of the adhesive 18 is present between the transparent conductive layer 24 and the metal foil 17. The adhesive 18 is preferably filled between the transparent conductive layer 24 and the metal foil 17, without forming a gap, in the gaps between the finger electrodes 25.
The finger electrodes 25 are formed respectively in first regions Z1 covered with the metal foil 17 on the rear surface of the photoelectric conversion part 20 and in second regions Z2 other than the first regions Z1. The area density of the finger electrodes 25 in the first region Z1 and the area density of the finger electrodes 25 in the second region Z2 may be approximately the same as each other. In this case, for example, all the finger electrodes 25 formed in the second region Z2 are formed so as to cross the first region Z1 widthwise. The area density of the finger electrodes 25 (collector electrodes) means the total weight of the collector electrodes formed in the object region (such as the first region Z1) per total area of the object region.
The area density (hereinafter, sometimes referred to as the “first area density”) of the finger electrodes 25 in the first region Z1 is preferably smaller than the area density (hereinafter, sometimes referred to as the “second area density”) of the finger electrodes 25 in the second region Z2. By reducing the first area density, for example, the amount of the conductive paste used is reduced, and the material cost can be reduced. By reducing the amount of the conductive paste used in the first region Z1, there is a possibility that the continuity of the finger electrodes 25 in the first region Z1 will be impaired. However, the metal foils 17 are provided in the present embodiment, and hence even when the continuity of the finger electrodes 25 is impaired in the first region Z1, the electrical connection to the bus bar electrodes is maintained by the metal foils 17.
In the example shown in
If all the finger electrodes 25 are continuously formed from the one edge in the X-direction to the other edge in the X-direction on the transparent conductive layer 24, when the finger electrodes 25 contract in the production process or the like, the solar cell 11 tends to warp toward the rear surface side having a larger electrode area. The structure allowing at least some of the finger electrodes 25 to be divided in the first region Z1 allows the material cost to be reduced while the occurrence of warping of the solar cell 11 is suppressed.
The finger electrodes 25a are formed over from the second region Z2 on one side in the X-direction to one widthwise edge of the first region Z1, and the finger electrodes 25b are formed over from the second region Z2 on the other side in the X-direction to the other widthwise edge of the first region Z1. Pluralities of the lengthwise ends of the finger electrodes 25a and 25b are connected to both widthwise edges of the metal foil 17. In other words, the metal foil 17 is provided in a state of overlapping the lengthwise ends of the finger electrodes 25a and 25b, and the finger electrodes 25a and 25b are electrically connected to each other through the intermediary of the metal foil 17.
The finger electrodes 25 formed in the second region Z2 are formed so that only 1 in 3 of the finger electrodes 25 cross the first region Z1 widthwise. The first region Z1 is a region most distant from the bus bar electrodes, and accordingly, the collection efficiency of the carriers generated in this region is lower than the collection efficiency of the carriers in the second region Z2. When the amount of the finger electrodes 25 widthwise crossing the first region Z1 is set to be 1 in 2 or less, and the first area density is set to be approximately ½ of the second area density, although the conversion efficiency of the solar cell 11 is degraded, the material used for formation of the finger electrodes 25 can be reduced. Accordingly, the production cost of the solar cells 11 per unit output power can be decreased. In particular, this effect is manifested when a silver-containing conductive paste is used in the formation of the finger electrodes 25. In the finger electrodes 25 of the first region Z1, the divided regions are formed, but by providing the metal foil 17, the electrical connection of the finger electrodes 25 in the first region Z1 is also maintained.
According to the solar cell module 10 provided with the above-described constitution, by forming a conductive path by providing the metal foils 17 electrically connected to the plurality of the collector electrodes at positions not overlapping the wiring members 15, it is possible to decrease the production cost of the solar cells 11 per unit output power. Additionally, in the solar cell module 10, the following problems can be made more unlikely occur: problems including exterior appearance faults such as expansion of the back sheet or detachment of the sealing material 14, in the lamination step or the subsequent curing step.
In the solar cell module 10, by providing the plurality of the metal foils 17 at intervals from each other on the rear surface side of the photoelectric conversion part 20, the light receiving from the rear surface side of the solar cells 11 is made possible, and thus the production cost of the solar cells 11 per unit output power can be reduced while the shadow loss is being suppressed. According to the solar cell module 10, for example, the light incident from the rear surface side of the module or the light incident from the light receiving surface side of the module and reflected by the back sheet or the like can be utilized for power generation.
As shown in
The finger electrode 25A includes thicker sections 26a and 26b, and a thinner section 26c. The thicker section 26a is formed over from the second region Z2 on one side in the X-direction to one widthwise edge of the first region Z1, and the thicker section 26b is formed over from the second region Z2 on the other side in the X-direction to the other widthwise edge of the first region Z1. The thinner section 26c is connected to the thicker sections 26a and 26b in the first region Z1. The Y-direction widths of the thicker sections 26a and 26b are bigger than the Y-direction width of the thinner section 26c. To both widthwise edges of the metal foil 17, a plurality of the lengthwise ends of the thicker sections 26a and 26b are connected, and the thinner sections 26c are also electrically connected to the metal foil 17. For example, some of the carriers move from the thicker sections 26a to the thicker sections 26b through the intermediary of the metal foil 17, and the rest of the carriers move from the thicker sections 26a to the thicker sections 26b through the intermediary of the thinner sections 26c.
In the case where the finger electrodes 25A are formed by screen printing, when the Y-direction width is made small, the cross-sectional areas of part of the finger electrodes 25A sometimes becomes small to form high-resistance regions, or some of the finger electrodes 25A sometimes undergo the formation of divided regions. In the case where the metal foil 17 is not provided, when the high resistance regions or the divided regions are formed in the finger electrodes 25A, the collection efficiency of the carriers generated in the photoelectric conversion part 20 is degraded. In the example shown in
In the example shown in
As shown in
In the example shown in
As shown in
In the metal foil 17C, pluralities of approximately circular through holes 30 are formed on both widthwise sides. The pluralities of the through holes 30 are formed at approximately equal intervals in the lengthwise direction and in a zigzag pattern without being aligned in the widthwise direction of the metal foil 17C. The through holes 30 may be disposed in such a way that the through holes each have a diameter smaller than the spacing between the finger electrodes 25 and the through holes do not overlap the finger electrodes 25. For example, the shape and the disposition of the through holes 30 are not limited to the shape and the disposition shown in
In the example shown in
As shown in
Number | Date | Country | Kind |
---|---|---|---|
2015-194696 | Sep 2015 | JP | national |