Abstract:
A method and apparatus for soldering interconnectors to photovoltaic cells that, after soldering, prevents bending of the photovoltaic cells due to heat warping caused by heat contraction of the lead wires. The interconnectors are positioned at predetermined positions on the photovoltaic cell, the interconnectors and the photovoltaic cells are held tightly together, and the solder is melted as the photovoltaic cells are heated, after which the photovoltaic cells are sequentially cooled in the long direction of the interconnectors with cold blasts from the end of the photovoltaic cells in the long direction of the interconnector.

Description:
CLAIM FOR PRIORITY 
       [0001]    The present specification claims priority from Japanese Patent Application No. 2007-096530, filed on Apr. 2, 2007 in the Japan Patent Office, the entire contents of which are hereby incorporated by reference herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a method and an apparatus for soldering interconnectors onto photovoltaic cells (hereinafter also simply “cell” or “cells”) that form a photovoltaic module in the manufacture of such photovoltaic module. 
         [0004]    2. Description of the Related Art 
         [0005]    Interconnectors that attach to photovoltaic cells are comprised of a copper lead wire and a solder coating that coats the lead wire. 
         [0006]    Conventionally, when attaching the interconnectors to the photovoltaic cells, the interconnectors are pressed and supported against the cell by bar- or rod-shaped rigid press members and heated to melt the solder, after which the cells are cooled, thus soldering the interconnectors to the photovoltaic cells. In JP-H11-87756-A and JP-2003-168811-A, this type of technology is disclosed. 
         [0007]    When soldering the interconnectors to the photovoltaic cells, cooling of the photovoltaic cells after heating is accomplished by removing the cells from the heat source (a heater or the like), blowing ambient-temperature air over the entire photovoltaic cell or all areas of the interconnectors, or removing the photovoltaic cells from a heating oven to cool under ambient temperature conditions. 
         [0008]    With such cooling methods, the cell cools from the outer ends inward, with attachment of the interconnectors proceeding from both ends toward the center. 
         [0009]    Under such conditions, once the interconnectors are attached to the ends of the photovoltaic cell, the interconnectors try to shrink further as the temperature continues to drop after they are soldered in place, generating a compressive force that causes the cell to bend. 
         [0010]    In addition, when cooled gradually at room temperature, the solder that coats the copper lead wires hardens before the copper lead wires undergo adequate heat contraction, and a difference in thermal expansion coefficient between the lead wires and the cell sometimes causes the cell to bend. 
         [0011]    With current photovoltaic cells, in which the photovoltaic cells themselves are formed very thin, bending and other deformations often occur. In a square cell approximately 150 mm long on each side, bend of approximately 6 to 10 mm can occur, and a bend of that extent can cause the cell to crack. 
         [0012]    Further, when a bent or otherwise deformed photovoltaic cell is made part of a photovoltaic module, in the process of forming the photovoltaic module that deformation is mechanically corrected. Such mechanical correction places stress on the cell, causing the cell to crack, or to crack when conveyed to the next process. 
         [0013]    The photovoltaic cells account for a very high proportion of the cost of photovoltaic devices, and therefore defects due to cracks not only lower productivity but also increase production costs. 
         [0014]    Although a method for soldering is disclosed in JP-H11-87756-A and JP-2003-168811-A, no solution to the above-described problems is disclosed in either JP-H11-87756-A or JP-2003-168811-A. 
       SUMMARY OF THE INVENTION 
       [0015]    The present invention has as its object to provide a soldering method and an apparatus that prevent bending of photovoltaic cells due to a difference in heat contraction between a lead wire and the cell after soldering interconnectors to the photovoltaic cells. 
         [0016]    To achieve the above-described object, the present invention provides a method for soldering an interconnector to a photovoltaic cell, comprising positioning the interconnector at a predetermined position on the photovoltaic cell, holding the interconnector and the photovoltaic cell tightly together, melting the solder while heating the photovoltaic cell, and sequentially cooling the heated photovoltaic cell in a long direction of the interconnector with cold blasts from end of the photovoltaic cell in a long direction of the interconnector. 
         [0017]    In addition, preferably, the cold blasts with which the photovoltaic cell is cooled are simultaneously supplied across an entire width of the photovoltaic cell in a direction at a right angle to the interconnector soldered to the photovoltaic cell and locally in the long direction of the interconnector. 
         [0018]    Preferably, the cold blasts with which the photovoltaic cell is cooled are supplied from one or more nozzles. 
         [0019]    Preferably, the cold blasts with which the photovoltaic cell is cooled are a cooling gas comprising any one of chlorofluorocarbon, nitrogen, carbon dioxide, and inert gases, or any combination thereof. 
         [0020]    The above-described object of the present invention is also achieved by an apparatus for cooling a photovoltaic cell to which an interconnector is soldered, comprising a heating space to melt the solder while heating the photovoltaic cell to attach the interconnector to the cell, a transport conveyer to transport the photovoltaic cell to and from the heating space, and a plurality of supply ports. At least one supply port of the plurality of supply ports is disposed above an exit of the heating space and at least one other supply port of the plurality of supply ports is disposed below the exit of the heating space, with the plurality of supply ports sandwiching the photovoltaic cell on the transport conveyer therebetween to blow cold blasts to sequentially cool the heated photovoltaic cell in a long direction of the interconnector from end of the photovoltaic cell in a long direction of the interconnector. A tip portion of each supply port of the plurality of supply ports has a tapered section of reduced width in the long direction of the interconnector proximal to the transport conveyer. 
         [0021]    The method and apparatus for soldering an interconnector to a photovoltaic cell of the present invention provide at least one of the following effects. 
         [0022]    (1) Since the photovoltaic cell is cooled from the end inward, attachment of the solder is made to proceed from the cell end toward the other end, enabling interconnector compressive force after cooling to be reduced and as a result allowing soldering with little bending to be carried out. 
         [0023]    (2) Since the photovoltaic cell is cooled from the end inward, when the lead wire inside the interconnector positioned at the attachment part undergoes heat contraction, it can move within solder that has not yet hardened. Accordingly, interconnector compressive force after cooling can be reduced, enabling soldering with little bending to be carried out. 
         [0024]    (3) Since the photovoltaic cell is cooled from the end inward, the lead wire is made to undergo heat contraction before the solder hardens, thus enabling interconnector compressive force after cooling to be further reduced, enabling soldering with little bending to be carried out. 
         [0025]    (4) With little bending, soldering with very low rates of cracking can be achieved even with thin cells. 
         [0026]    (5) Since soldering with little bending can be achieved, rates of later-stage cracking are reduced. 
         [0027]    (6) With little bending, stable suctional transport can be achieved. 
         [0028]    (7) With little bending, there is little positional deviation in the spacing between cells during later-stage laminating, thus reducing the rate of occurrence of such defects as short-circuiting between cells and improving the external appearance (cell spacing is uniform). 
         [0029]    Other features and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings, in which like reference characters designate similar or identical parts throughout the several views thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  shows a plan view of photovoltaic cells to which interconnectors are to be soldered; 
           [0031]      FIG. 2  shows a sectional view of the photovoltaic cells shown in  FIG. 1 ; 
           [0032]      FIG. 3  shows a lateral sectional view showing schematically steps in implementing a soldering method according to the present invention; 
           [0033]      FIGS. 4A and 4B  show perspective views of one example of a photovoltaic cell holder used in the soldering method according to the present invention; 
           [0034]      FIG. 5  shows a first embodiment of a cooling unit  80  used in the soldering method according to the present invention; 
           [0035]      FIG. 6  shows a second embodiment of a cooling unit  80  used in the soldering method according to the present invention; 
           [0036]      FIG. 7  shows a third embodiment of a cooling unit used in the soldering method according to the present invention; and 
           [0037]      FIGS. 8A and 8B  show sectional views of a connecting portion between a photovoltaic cell and an interconnector. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0038]    A detailed description will now be given of illustrative embodiments of the present invention, with reference to the accompanying drawings. In so doing, specific terminology is employed solely for the sake of clarity, and the present disclosure is not to be limited to the specific terminology so selected. It is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve a similar result. 
         [0039]    The Photovoltaic Cell 
         [0040]      FIGS. 1 and 2  show photovoltaic cells  10  to which interconnectors  20  are to be soldered. 
         [0041]    As shown in  FIG. 1 , two parallel rows of electrodes  11  are provided on the surfaces of the photovoltaic cell  10 . 
         [0042]    As shown in  FIG. 2 , positive electrodes  11  are provided on the top surface of the photovoltaic cell  10  and negative electrodes  11  are provided on the bottom surface of the photovoltaic cell  10 . A plurality of photovoltaic cells  10  is aligned and the electrodes  11  on the top surfaces of adjacent photovoltaic cells  10  and the electrodes  11  on the bottom surfaces of adjacent photovoltaic cells  10  are connected in series by interconnectors  20 . 
         [0043]    Each interconnector  20  is comprised of a copper lead wire  21  and a solder coating  22  that coats the lead wire  21 . An attachment portion  12  is formed by soldering at a part that contacts the photovoltaic cell  10 , and through the attachment portion  12  the interconnector  20  is connected to the electrode  11  of the photovoltaic cell  10 . 
         [0044]    The Soldering Method 
         [0045]      FIG. 3  shows a sectional view of a soldering step using the soldering method of the present invention. 
         [0046]    The soldering step involves the use of a transport holder  30  comprised of an upper holder  40  and a lower holder  50 , one example of which is shown in  FIGS. 4A and 4B . The transport holder  30  positions and holds the photovoltaic cell  10  and the interconnectors  20 . When soldering a plurality of photovoltaic cells  10  and interconnectors  20  as shown in  FIGS. 1 and 2 , the required number of transport holders  30  is connected at constant intervals and used. For simplicity, a description is given of transporting only a single transport holder  30  to a heating space  70  using a transport conveyer  60 . 
         [0047]    In the soldering method of the present invention, the photovoltaic cell  10  and the interconnectors  20  are positioned and held using the photovoltaic cell transport holder  30 , with soldering carried out using a transport conveyer  60  that conveys the transport holder  30 , a heating space  70  and a cooling means  80 . The heating space  70  is a chamber-like space disposed so as to straddle the transport conveyer  60  from above and below, and formed in such a way that a transport surface of the transport conveyer  60  runs through an interior of the heating space  70 . A plurality of heating means  71  is positioned inside the heating space  70 , and cooling means  80  are disposed above and below an exit of the heating space  70 . 
         [0048]    Heating 
         [0049]    The transport holder  30  transports the photovoltaic cell  10  to the heating space  70  with the transport conveyer  60 , with the interconnectors  20  positioned and pressed against the electrodes  11  of the photovoltaic cell  10  and forming the attachment portions  12 . 
         [0050]    Inside the heating space  70 , the plurality of heating means  71 , such as a plurality of heaters, is disposed both above and below the transport conveyer  60  so as to sandwich the transport conveyer  60  therebetween. The photovoltaic cell  10 , having been brought to the heating space  70  by the transport holder  30 , is then heated on both top and bottom surfaces simultaneously by the heating means  71 , melting the solder  22 . 
         [0051]    The heated photovoltaic cell  10  on the transport holder  30  is then transported away from the heating space  70  by the transport conveyer  60 . 
       Method of Cooling after Melting the Solder (First Embodiment) 
       [0052]    A description is now given of cooling means used in cooling after heating the solder, in a first embodiment of the present invention. 
         [0053]    The photovoltaic cell  10  on the transport holder  30  transported away from the heating space  70  by the transport conveyer  60  is cooled by the cooling means  80  disposed above and below the exit of the heating space  70 , and the melted solder  22  on the interconnectors  20  starts to harden from the end of the photovoltaic cell  10  inward. The photovoltaic cell  10  thus transported on the transport holder  30  by the transport conveyer  60  is sequentially cooled by the cooling means  80  from the end. In the present embodiment, cold blasts  81  are used as the cooling means  80 . Cold blasts  81  are blown out of supply ports  82  such as nozzles or the like provided at the exit of the heating space  70  as shown in  FIG. 3 . In this case, cold blasts  81  are blown not only from above but also from below. 
         [0054]    The supply ports  82  provided above and below the exit of the heating space  70 , as one example as shown in  FIG. 5 , are aligned with the positions of the upper and lower interconnectors  20  that are to be soldered to the photovoltaic cell  10 . The width of the tips of the supply ports  82  is reduced in a long direction of the interconnectors  20 . 
       Second Embodiment 
       [0055]    A description is now given of the cooling means used in cooling after heating the solder, in a second embodiment of the present invention. 
         [0056]    In the second embodiment, as shown in  FIG. 6 , the supply ports  82  provided above and below the exit of the heating space  70  extend across the entire width of the photovoltaic cell  10 , and?the width of the tip of the supply ports is reduced in the long direction of the interconnectors  20 . 
       Third Embodiment 
       [0057]    A description is now given of cooling means used in cooling after heating the solder, in a third embodiment of the present invention. 
         [0058]    In the third embodiment, the supply ports  82  consist of a plurality of ports whose number and position may be varied according to a temperature distribution of the photovoltaic cell  10  as shown in  FIG. 7 . A flow adjustment valve  83  is provided on each one of the plurality of supply ports  82  to adjust the cold blast flow volume. 
         [0059]    Using  FIGS. 8A and 8B , a description is now given of how the interconnectors  20  on the photovoltaic cell  10  harden using the cooling means  80  described above. 
         [0060]      FIGS. 8A and 8B  show sectional views of the interconnector  20  during cooling, with  FIG. 8A  showing cooling conducted gradually under normal ambient conditions and  FIG. 8B  showing cooling sequentially from the end of the cell inward using the cooling means  80 . 
         [0061]    In  FIG. 8A  cooling is conducted gradually, and therefore the cooling of the interconnector  20  proceeds from both ends inward toward the center. In addition, since the cooling is gradual, the thermal contraction of the lead wire  21  and the hardening of the solder  22  take place simultaneously, unaffected by any difference in coefficient of thermal conductivity. As a result, the solder  22  hardens before the lead wire  21  undergoes adequate heat contraction, creating a compressive force on the interconnector that results in bending of the photovoltaic cell. 
         [0062]    By contrast, when the cell is cooled sequentially inward from the end by the cooling means  80 , as shown in  FIG. 3 , the photovoltaic cell  10  is cooled by the cooling means  80  while being transported by the transport conveyer  60 . 
         [0063]    Consequently, the interconnector  20  is cooled from the end in the long direction thereof (the end of the cell), along the long direction. As a result, as shown in  FIG. 8B , when the lead wire  21  undergoes heat contraction, it moves and contracts within melted solder  221 , and thus the heat contraction of the lead wire is not limited by the hardening of the solder  22  and the interconnector compressive force after cooling can be reduced. 
         [0064]    In addition, as shown in  FIG. 8B  the interconnector  20  is cooled by cold blasts  81 , and therefore the copper wire lead  21  with its higher coefficient of thermal conductivity, undergoes heat contraction before the solder  22  does. As a result, by the time the solder  22  has hardened the lead wire  21  has already undergone adequate heat contraction, and thus the interconnector compressive force after cooling can be reduced. 
         [0065]    Thus, as described above, using the cooling means  80  enables bending of a square soldered cell having a length of 150 mm on a side and having a thickness of 150 μm to be held to within±2 mm. 
       Fourth Embodiment 
       [0066]    A description is now given of a fourth embodiment of a cooling means  80  that is even more effective at preventing bending of a photovoltaic cell after melting solder. 
         [0067]    The fourth embodiment uses a cooling gas for the cold blasts  81  supplied to the photovoltaic cell by the cooling means  80 . The shape of the supply ports  82  is the same as that of the first embodiment, although since a cooling gas is used the bottom supply ports shown in  FIG. 3  can be eliminated. 
         [0068]    For the cooling gas, chlorofluorocarbon, nitrogen, carbon dioxide, and inert gases can be used, either singly or in some combination thereof. The cooling gas is cooled to a temperature of approximately −40 degrees Centigrade and blown onto the surface of the cell. In view of environmental concerns it is preferable to use an alternative chlorofluorocarbon as the cooling gas. 
         [0069]    In addition, since cooling can be conducted rapidly using cooling gas, the cell can be cooled in less time than in the first through third embodiments, and as described in  FIG. 8A  and  FIG. 8B , cooling sequentially from end of the cell inward enables the anti-bending effect to be enhanced. 
         [0070]    As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.