Patent Publication Number: US-9423775-B2

Title: Solar panel and timepiece including solar panel

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Divisional of U.S. Ser. No. 14/195,552, filed Mar. 3, 2014, which is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2013-041639, filed Mar. 4, 2013, the entire contents of both of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a solar panel that is used in a pointer-type timepiece such as a wristwatch or a pointer-type measuring instrument such as a meter, and a timepiece including the solar panel. 
     2. Description of the Related Art 
     For example, a solar panel for use in a wristwatch is known in which a plurality of solar cells each formed into a fan shape so as to have an equal area are circularly arranged and connected in series, as described in Japanese Patent Application Laid-Open (Kokai) Publication No. 10-039057. 
     This type of solar panel is structured to have a through hole provided in its center and a pointer shaft inserted in the through hole to protrude upward. On the upper end of the pointer shaft, a pointer is mounted, and moves above the plurality of solar cells. 
     In this type of solar panel, the value of output current obtained by the plurality of solar cells as a whole becomes equal to the value of the smallest output current obtained by one of the plurality of solar cells due to electrical characteristics of a diode or the like. 
     Accordingly, when the pointer is positioned over one of the plurality of solar cells, the light-receiving area of the solar cell over which the pointer has been positioned becomes smaller than the light-receiving areas of the other solar cells. 
     As a result, the output current of the solar cell over which the pointer has been positioned becomes smaller than the output currents of the other solar cells, and the value of the output current obtained by the plurality of solar cells as a whole becomes equal to this smallest output current of the solar cell. Thus, there is a problem in this solar panel in that a loss of the output current of the plurality of solar cells as a whole is disadvantageously large. 
     SUMMARY OF THE INVENTION 
     The present invention is to provide a solar panel capable of improving output current by dispersing a decrease of a light-receiving area due to a pointer by a plurality of solar cells, and a timepiece including the solar panel. 
     In order to achieve the above-described object, in accordance with one aspect of the present invention, there is provided a solar panel formed into a substantially circular shape and having a through hole which is provided in a center portion and into which a pointer shaft is inserted, and a pointer which is mounted on the pointer shaft and moves above the solar panel, comprising: a plurality of solar cells arranged in a substantially circular shape, wherein the plurality of solar cells are divisionally formed into a substantially spiral shape such that the pointer moving above the plurality of solar cells is always positioned over at least two of the plurality of solar cells. 
     In accordance with another aspect of the present invention, there is provided a timepiece comprising: a timepiece module having a timepiece movement, a solar panel, a dial plate, and a housing; and a timepiece case where the timepiece module is placed, wherein the solar panel is formed into a substantially circular shape, and has a through hole which is provided in a center portion and into which a pointer shaft is inserted, and a pointer which is mounted on the pointer shaft and moves above the solar panel, and wherein the solar panel includes a plurality of solar cells arranged in a substantially circular shape, and the plurality of solar cells are divisionally formed into a substantially spiral shape such that the pointer moving above the solar cells is always positioned over at least two of the plurality of solar cells. 
     The above and further objects and novel features of the present invention will more fully appear from the following detailed description when the same is read in conjunction with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an enlarged sectional view of a timepiece module in a first embodiment in which the present invention has been applied to a pointer-type wristwatch; 
         FIG. 2A ,  FIG. 2B  and  FIG. 2C  depict pointers of the timepiece module depicted in  FIG. 1 , of which  FIG. 2A  is an enlarged front view of a second hand,  FIG. 2B  is an enlarged front view of a minute hand, and  FIG. 2C  is an enlarged front view of an hour hand; 
         FIG. 3  is an enlarged front view of a solar panel of the timepiece module depicted in  FIG. 1 ; 
         FIG. 4  is an enlarged sectional view of a connecting section of the solar panel taken along line A-A in  FIG. 3 ; 
         FIG. 5  is an enlarged front view of a modification example of the solar panel of the first embodiment depicted in  FIG. 3 ; 
         FIG. 6  is an enlarged front view of a solar panel in a second embodiment in which the present invention has been applied to a pointer-type wristwatch; 
         FIG. 7  is an enlarged front view of a modification example of the solar panel of the second embodiment depicted in  FIG. 6 ; 
         FIG. 8  is an enlarged front view of a solar panel in a third embodiment in which the present invention has been applied to a pointer-type wristwatch; 
         FIG. 9  is an enlarged front view of a solar panel in a fourth embodiment in which the present invention has been applied to a pointer-type wristwatch; and 
         FIG. 10  is an enlarged front view of a modification example of the solar panel of the fourth embodiment depicted in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     A first embodiment in which the present invention has been applied to a pointer-type wristwatch will hereinafter be described with reference to  FIG. 1  to  FIG. 4 . 
     This pointer-type wristwatch includes a timepiece module  1  as depicted in  FIG. 1 . 
     The timepiece module  1 , which is arranged in a wristwatch case (not depicted in the drawing), has a housing  2 . 
     On the upper surface of the housing  2 , a solar panel  3  is arranged, and a dial plate  4  is arranged on the upper surface of this solar panel  3 , as depicted in  FIG. 1 . 
     Inside the housing  2 , a timepiece movement  5  is provided. 
     The timepiece movement  5  is structured to move pointers  7  such as an hour hand  7   a , a minute hand  7   b , and a second hand  7   c  by rotating a pointer shaft  6 . 
     In this case, the dial plate  4  is constituted by a transparent or translucent film, and formed into a substantially circular shape. 
     On peripheral portions on the upper surface of the dial plate  4 , time characters (not depicted in the drawing) are provided at predetermined spacing. 
     The pointer shaft  6  has a cylindrical hour-hand shaft  6   a , a cylindrical minute-hand shaft  6   b  rotatably arranged in the hour-hand shaft  6   a , and a second-hand shaft  6   c  rotatably arranged in the minute-hand shaft  6   b , and is structured to protrude above the dial plate  4  via a through hole  3   a  provided in the center of the solar panel  3  and a through hole  4   a  provided in the center of the dial plate  4 . 
     The pointers  7  are respectively mounted on an upper end portion of the pointer shaft  6  as depicted in  FIG. 1  and  FIG. 2A  to  FIG. 2C . 
     That is, the hour hand  7   a  is mounted on the upper end of the hour-hand shaft  6   a , the minute hand  7   b  is mounted on the upper end of the minute-hand shaft  6   b , and the second hand  7   c  is mounted on the upper end of the second-hand shaft  6   c.    
     As a result, the timepiece movement  5  is structured to move the pointers  7  including the hour hand  7   a , the minute hand  7   b , and the second hand  7   c  above the dial plate  4  by rotating the pointer shaft  6  including the hour-hand shaft  6   a , the minute-hand shaft  6   b , and the second-hand shaft  6   c.    
     In this case, among the hour hand  7   a , the minute hand  7   b , and the second hand  7   c , the minute hand  7   b  is formed to have the largest surface area as compared with the hour hand  7   a  and the second hand  7   c , as depicted in  FIG. 2A  to  FIG. 2C . 
     As a result, the area of the minute hand  7   b , which blocks external light applied to the solar panel  3 , is larger than those of the hour hand  7   a  and the second hand  7   c , and therefore the minute hand  7   b  has the largest influences on the light-receiving area of the solar panel  3 . 
     Thus, in the following descriptions, the minute hand  7   b  is mainly explained. 
     The solar panel  3  is formed into a circular shape, which is substantially equal in size to the dial plate  4 , as depicted in  FIG. 1  and  FIG. 3 . 
     This solar panel  3  includes a plurality of solar cells  11  to  16 . 
     The plurality of solar cells  11  to  16  are arranged in a circular shape centering on the through hole  3   a  on the upper surface of a film substrate  10 , as depicted in  FIG. 3  and  FIG. 4 . 
     In this case, each of the plurality of solar cells  11  to  16  is structured such that a lower electrode  17  made of metal such as aluminum is formed by patterning on the film substrate  10 , a power generation layer  18  constituted by a semiconductor layer made of amorphous silicon (a-Si) or the like is formed by patterning on the lower electrode  17 , a transparent upper electrode  19  made of ITO (Indium Tin Oxide) or the like is formed by patterning on the power generation layer  18 , and a protective film  20  made of transparent insulating synthetic resin covers the upper electrode  19 , as depicted in  FIG. 4 . 
     As a result, each of the plurality of solar cells  11  to  16  is structured such that, when external light is applied by passing through the dial plate  4 , this light is applied to the power generation layer  18  through the transparent upper electrode  19 , and the power generation layer  18  generates electromotive force by the applied light, as depicted in  FIG. 1  and  FIG. 4 . 
     These solar cells  11  to  16  are structured by the circle corresponding to the solar panel  3  being divided so as to have the same shape and area, as depicted in  FIG. 3 . 
     In this case, the plurality of solar cells  11  to  16  are divisionally formed into a substantially spiral shape so that the minute hand  7   b  moving there above is always positioned across two adjacent solar cells of the plurality of solar cells  11  to  16 . 
     Also, the plurality of solar cells  11  to  16  are formed into the substantially spiral shape such that areas where the minute hand  7   b  is positioned across two adjacent solar cells of the plurality of solar cells  11  to  16  are substantially equal to each other, as depicted in  FIG. 3 . 
     Moreover, the plurality of solar cells  11  to  16  are each formed into a shape where the length in the circumferential direction gradually elongates toward the radial direction centering on the through hole  3   a.    
     In this case, the plurality of solar cells  11  to  16  are each structured to have an outer circumferential area E 1  on the outer circumferential side of the solar panel  3  and an inner circumferential area E 2  on the through hole  3   a  side of the solar panel  3 , which are located at positions shifted from each other in the circumferential direction and coupled by a coupling section E 3 , as depicted in  FIG. 3 . 
     That is, the outer circumferential area E 1  and the inner circumferential area E 2  are each formed into a substantially fan shape having a different size, and the outer circumferential area E 1  is provided at a position shifted from the inner circumferential area E 2  in the clockwise direction. 
     As a result, the plurality of solar cells  11  to  16  are each formed into a shape where the inner circumferential area E 2  encroaches on the inner circumferential side (that is, on the center through hole  3   a  side) of a portion of the outer circumferential area E 1  positioned in the counterclockwise direction. 
     In the case of these plurality of solar cells  11  to  16 , for example, two solar cells  11  and  12  are formed such that a side portion positioned in the clockwise direction (right side portion in  FIG. 3 ) in the outer circumferential area E 1  of one solar cell  11  and a side portion positioned in the counterclockwise direction (left side portion in  FIG. 3 ) in the inner circumferential area E 2  of the other solar cell  12  are at positions slightly shifted from each other in the circumferential direction by the connection width of the coupling section E 3 , on the same straight line in the radial direction centering on the through hole  3   a , as depicted in  FIG. 3 . 
     Also, the outer circumferential area E 1  and the inner circumferential area E 2  are formed to have a different radial direction length in accordance with the shape of the minute hand  7   b  so that, when the minute hand  7   b  is positioned across two adjacent solar cells  11  and  12 , an area of the outer circumferential area E 1  of one solar cell  11  over which the minute hand  7   b  has been positioned and an area of the inner circumferential area E 2  of the other solar cell  12  over which the minute hand  7   b  has been positioned are substantially equal to each other, as depicted in  FIG. 3 . 
     For example, the outer circumferential area E 1  and the inner circumferential area E 2  are formed such that the radial direction length of the outer circumferential area E 1  is longer than the radial direction length of the inner circumferential area E 2 , as depicted in  FIG. 3 . 
     As a result, the outer circumferential area E 1  and the inner circumferential area E 2  are structured such that two areas in the outer circumferential area E 1  and the inner circumferential area E 2  where the minute hand  7   b  is positioned across two adjacent solar cells  11  and  12  are substantially equal to each other. 
     As such, among the plurality of solar cells  11  to  16 , not only two solar cells  11  and  12  over which the minute hand  7   b  is positioned as depicted in  FIG. 3 , but also other solar cells  13  to  16  are formed to have the above-described shape. 
     The coupling section E 3  coupling the outer circumferential area E 1  and the inner circumferential area E 2  together is preferably formed to have a sufficient connection width (for example, a width equal to or longer than 1 mm) in order to decrease an electrical resistance value. 
     The plurality of solar cells  11  to  16  are sequentially connected in series by a plurality of connecting sections  21  at the edge of the through hole  3   a  provided on the center portion of the solar panel  3 , as depicted in  FIG. 3  and  FIG. 4 . 
     That is, these connecting sections  21 , which are formed of conductive paste, are each structured to electrically connect the lower electrode  17  of one of adjacent solar cells  11 ,  13 , and  15  and the upper electrode  19  of the other one of the adjacent solar cells  12 ,  14 , and  16  together. 
     In this case, two solar cells  11  and  16  positioned at the last end among the plurality of solar cells  11  to  16  are not connected together by the connecting section  21 . 
     Accordingly, the upper electrode  19  of one solar cell  11  and the lower electrode  17  of the other solar cell  16  are connected to a pair of output electrodes (not depicted in the drawing). 
     As a result, the solar panel  3  is structured to supply generated electric power to a chargeable battery (not depicted in drawing) of the timepiece module  1 . 
     Next, the operation of this pointer-type wristwatch is described. 
     Normally, with electric power supplied to the timepiece movement  5 , the timepiece movement  5  operates to rotate the pointer shaft  6 , and the pointers  7  including the hour hand  7   a , the minute hand  7   b , and the second hand  7   c  move above the dial plate  4  with the rotation of the pointer shaft  6  so as to indicate the time. 
     Here, external light such as sunlight is applied to the dial plate  4 , and the applied external light passes through the dial plate  4  to be applied to the plurality of solar cells  11  to  16  of the solar panel  3 . 
     Then, the applied external light passes through the transparent protective film  20  and the transparent upper electrode  19  of each of the solar cells  11  to  16  to be applied to each power generation layer  18 . With this applied light, each power generation layer  18  generates electric power. 
     That is, when external light is applied, the power generation layer  18  of each of the plurality of solar cells  11  to  16  generates electromotive force in accordance with the application amount. 
     By the solar cells  11  to  16  being connected in series by the connecting sections  21 , the generated electromotive force is sent from the output electrode (not depicted in the drawing) of each of the solar cells  11  and  16  at the last end to the chargeable battery (not depicted in the drawing) of the timepiece module  1  for recharge. 
     As such, when the solar panel  3  generates electric power, the pointers  7  moving above the dial plate  4  block part of the external light applied to the solar panel  3 , as depicted in  FIG. 3 . Therefore, among the plurality of solar cells  11  to  16 , the light-receiving amounts of two of the solar cells  11  to  16  over which the minute hand  7   b  of the pointers  7  has been positioned are decreased. 
     In this case, for example, when the minute hand  7   b  is positioned across two adjacent solar cells  11  and  12  among the plurality of solar cells  11  to  16  as depicted in  FIG. 3 , an area of the outer circumferential area E 1  of one solar cell  11  over which the minute hand  7   b  has been positioned and an area of the inner circumferential area E 2  of the other solar cell  12  over which the minute hand  7   b  has been positioned are substantially equal to each other. 
     Therefore, even when the minute hand  7   b  is positioned across two solar cells  11  and  12 , both light-receiving areas are substantially equal to each other, and an area shaded by the minute hand  7   b  is substantially equally distributed between two solar cells  11  and  12 . 
     As a result, a current value that is outputted by the entire solar panel  3  is increased as compared with a structure where the minute hand  7   b  is positioned over only one of the plurality of solar cells  11  to  16 . 
     For example, when an average area of a half of the minute hand  7   b  in the longitudinal direction is approximately 5.85 mm 2  and the solar cells  11  to  16  each have an area of approximately 111.95 mm 2 , the light-receiving area of each of the solar cells  11  and  12  when the minute hand  7   b  is positioned across two solar cells  11  and  12  is approximately 106.11 mm 2 . 
     Thus, the light-receiving area of each of two solar cells  11  and  12  over which the minute hand  7   b  has been positioned is increased by approximately 5.1% as compared with a case where the light-receiving area of one of the solar cells  11  to  16  is approximately 95.26 mm 2  by the minute hand  7   b  being positioned over only one of the solar cells  11  to  16 . 
     As a result, the output current of the entire plurality of solar cells  11  to  16  is increased by approximately 5.1%. 
     As such, in this pointer-type wristwatch, the solar panel  3  above which the pointers  7  mounted on the pointer shaft  6  inserted in the through hole  3   a  in the center portion move has the plurality of solar cells  11  to  16  arranged in a substantially circular shape. These solar cells  11  to  16  have been divisionally formed to have a substantially spiral shape so that the minute hand  7   b  of the pointers  7  is always positioned across two of the plurality of solar cells  11  to  16 . Therefore, a decrease of light-receiving area due to the minute hand  7   b  is distributed between two of the plurality of solar cells  11  to  16 , and whereby the output current of the entire plurality of solar cells  11  to  16  can be improved. 
     That is, in the solar panel  3 , the minute hand  7   b  of the pointers  7  moving there above can always be positioned across two of the plurality of solar cells  11  to  16 , and therefore a decrease of light-receiving area due to the minute hand  7   b  can be distributed between two of the plurality of solar cells  11  to  16 . As a result, a decrease in the output current of two of the plurality of solar cells  11  to  16  over which the minute hand  7   b  is positioned can be suppressed, and whereby the output current of the entire plurality of solar cells  11  to  16  can be improved. 
     In this case, the plurality of solar cells  11  to  16  are formed to have the same shape and area size by equal division, and whereby the light-receiving area of each of two of the plurality of solar cells  11  to  16  over which the minute hand  7   b  of the pointers  7  is positioned can always be kept constant. As a result, fluctuations in the output current of the entire plurality of solar cells  11  to  16  by the movement of the minute hand  7   b  can be suppressed. Therefore, the output current of the entire plurality of solar cells  11  to  16  can be kept substantially constant. 
     Also, the plurality of solar cells  11  to  16  are formed into a shape in which areas where the minute hand  7   b  of the pointers  7  is positioned across two of the plurality of solar cells  11  to  16  are substantially equal to each other. Therefore, the light-receiving areas of two of the solar cells  11  to  16  over which the minute hand  7   b  is positioned can be equally distributed to have the same area. As a result, a decrease in the output current of two of the plurality of solar cells  11  to  16  over which the minute hand  7   b  is positioned can be efficiently and equally suppressed. Therefore, the output current of the entire plurality of solar cells  11  to  16  can be reliably improved. 
     Moreover, the plurality of solar cells  11  to  16  each having the outer circumferential area E 1  and the inner circumferential area E 2  are formed into a substantially spiral shape such that the inner circumferential area E 2  encroaches on the inner circumferential side of the outer circumferential area E 1  adjacent to the inner circumferential area E 2 . Therefore, the minute hand  7   b  of the pointers  7  moving above the plurality of solar cells  11  to  16  can always be reliably and favorably positioned across two adjacent ones of the plurality of solar cells  11  to  16 . 
     In this case, the plurality of solar cells  11  to  16  are each formed into a shape where the length in the circumferential direction gradually elongates toward the radial direction centering on the through hole  3   a  of the solar panel  3 . Therefore, the area of the outer circumferential area E 1  can be made sufficiently larger than the area of the inner circumferential area E 2 . As a result, areas of the plurality of solar cells  11  to  16  that are shaded by the minute hand  7   b  being positioned there over can be minimized. This can also improve the output current of the entire plurality of solar cells  11  to  16 . 
     Furthermore, the plurality of solar cells  11  to  16  are connected in series by the connecting sections  21  on the peripheral portion of the through hole  3   a  provide in the center portion of the solar panel  3 . This makes resistance to the influence of the pointers  7 , and a wide light-receiving area can be ensured for each of the plurality of solar cells  11  to  16 . 
     That is, at the peripheral portion of the through hole  3   a  of the solar panel  3 , a light blocking period by the pointers  7  is long and power generation efficiency is low. Thus, by the connecting sections  21  being provided to the peripheral portion of the through hole  3   a , a loss of power generation due to a change in the light-receiving area by the movement of the pointers  7  can be reduced, whereby the power generation efficiency can be enhanced. 
     In the above-described first embodiment, the outer circumferential area E 1  and the inner circumferential area E 2  of each of the plurality of solar cells  11  to  16  are formed into a substantially spiral shape by being coupled to each other and constricted by the coupling section E 3 . However, the present invention is not limited thereto. For example, as shown in a modification example in  FIG. 5 , a structure may be adopted in which a plurality of solar cells  23  to  28  are formed into a smoothly-curved spiral shape. 
     That is, it is only required that the plurality of solar cells  23  to  28  are formed into a spiral shape where the radius of curvature is gradually increased from the through hole  3   a  side of the solar panel  3  toward the outer circumferential side of the solar panel  3 . 
     In this case as well, it is only required that the plurality of solar cells  23  to  28  are formed into a spiral shape such that areas where the minute hand  7   b  of the pointers  7  is positioned across two adjacent ones of the solar cells  23  to  28  are substantially equal to each other. 
     Also, each of the plurality of solar cells  23  to  28  is only required to be formed into a shape where the length in the circumferential direction gradually elongates toward the radial direction centering on the through hole  3   a.    
     With this solar panel  3  as well, operations and effects similar to those of the first embodiment can be achieved. 
     Second Embodiment 
     Next, with reference to  FIG. 6 , a second embodiment in which the present invention has been applied to a pointer-type wristwatch is described. 
     Note that sections identical to those in the first embodiment depicted in  FIG. 1  to  FIG. 4  are provided with the same reference numerals for description. 
     This pointer-type wristwatch has a structure identical to that of the first embodiment except that a plurality of solar cells  31  to  36  of a solar panel  30  has a structure different from that of the first embodiment, as depicted in  FIG. 6 . 
     These solar cells  31  to  36  are structured by a circle corresponding to the solar panel  30  being divided into six portions such that they have the same shape and area, as depicted in  FIG. 6 . 
     In this case, the plurality of solar cells  31  to  36  are divisionally formed into a spiral shape so that the minute hand  7   b  of the pointers  7  is always positioned across four sequentially adjacent ones of the plurality of solar cells  31  to  36 . 
     Also, the plurality of solar cells  31  to  36  are formed into the spiral shape such that four areas where the minute hand  7   b  is positioned across four sequentially adjacent ones of the plurality of solar cells  31  to  36  are substantially equal to one another, as depicted in  FIG. 6 . 
     Moreover, the plurality of solar cells  31  to  36  are each formed into a shape where the length in the circumferential direction gradually elongates toward the radial direction centering on the through hole  3   a  of the solar panel  30 . 
     In this case, the plurality of solar cells  31  to  36  are each structured to have a first area F 1  located on the outer circumferential side of the solar panel  30 , a second area F 2  located on the inner circumferential side of the first area F 1 , a third area F 3  located on the inner circumferential side of the second area F 2 , and a fourth area F 4  located on the inner circumferential side of the third area F 3 , with these areas F 1  to F 4  being sequentially coupled by coupling sections F 5  and sequentially arranged at positions shifted from each other along the circumferential direction, as depicted in  FIG. 6 . 
     These first to fourth areas F 1  to F 4  are formed to have different sizes in accordance with the shape of the minute hand  7   b  and to be sequentially arranged at positions shifted from each other in the clockwise direction, as depicted in  FIG. 6 . 
     As a result, the first to fourth areas F 1  to F 4  are structured such that the entire shape obtained by combining these areas forms a fan shape having an opening angle of 60 degrees. 
     That is, the plurality of solar cells  31  to  36  are formed into a shape in which, with the first area F 1  positioned at the outermost perimeter as a reference point, the second area F 2  encroaches on the inner circumferential side of the first area F 1  positioned in the counterclockwise direction, the third area F 3  following the second area F 2  encroaches on the inner circumferential side of the second area F 2  positioned in the counterclockwise direction, and the fourth area F 4  following the third area F 3  encroaches on the inner circumferential side of the third area F 3  positioned in the counterclockwise direction, as depicted in  FIG. 6 . 
     In the case of these solar cells  31  to  36 , for example, two solar cells  31  and  32  are formed such that the coupling section F 5  coupling the first area F 1  and the second area F 2  together is provided between a side portion positioned in the counterclockwise direction (left side portion in  FIG. 6 ) in the first area F 1  of one solar cell  31  and a side portion positioned in the counterclockwise direction (left side portion in  FIG. 6 ) in the second area F 2  of the other solar cell  32 , as depicted in  FIG. 6 . 
     Also, for example, the two solar cells  31  and  32  of the plurality of solar cells  31  to  36  are formed such that the coupling section F 5  coupling the second area F 2  and the third area F 3  together is provided between a side portion positioned in the counterclockwise direction (left side portion in  FIG. 6 ) in the second area F 2  of one solar cell  31  and a side portion positioned in the counterclockwise direction (left side portion in  FIG. 6 ) in the third area F 3  of the other solar cell  32 , as depicted in  FIG. 6 . 
     Similarly, for example, the two solar cells  31  and  32  of the plurality of solar cells  31  to  36  are formed such that the coupling section F 5  coupling the third area F 3  and the fourth area F 4  together is provided between aside portion positioned in the counterclockwise direction (left side portion in  FIG. 6 ) in the third area F 3  of one solar cell  31  and a side portion positioned in the counterclockwise direction (left side portion in  FIG. 6 ) in the fourth area F 4  of the other solar cell  32 , as depicted in  FIG. 6 . 
     In the case of these solar cells  31  to  36 , the first to forth areas F 1  to F 4  and the coupling sections F 5  of the other solar cells  33  to  36  are formed similarly to the first to forth areas F 1  to F 4  and the coupling sections F 5  of the solar cells  31  and  32 , as depicted in  FIG. 6 . 
     Also, the first to fourth areas F 1  to F 4  are each formed to have a different length in the radial direction so that, when the minute hand  7   b  is positioned across four sequentially adjacent solar cells  31  to  34 , the first to fourth areas F 1  to F 4  of each of the solar cells  31  to  34  over which the minute hand  7   b  has been positioned are substantially equal to one another, as depicted in  FIG. 6 . 
     That is, the first to fourth areas F 1  to F 4  are each formed such that the length in the radial direction is gradually shortened from the outer circumferential side of the solar panel  30  toward the through hole  3   a  in the center portion, as depicted in  FIG. 6 . 
     As a result, the first to fourth areas F 1  to F 4  are structured such that areas where the minute hand  7   b  is positioned across four sequentially adjacent solar cells  31  to  34  are substantially equal to one another among the first to fourth areas F 1  to F 4 . 
     In the case of these solar cells  31  to  36 , not only the four solar cells  31  to  34  across which the minute hand  7   b  has been positioned but also the other solar cells  35  and  36  are formed into a shape similar to that described above, as depicted in  FIG. 6 . 
     Also, as with the first embodiment, the coupling sections F 5  coupling the first to fourth areas F 1  to F 4  are each preferably formed to have a sufficient connection width (for example, a width equal to or longer than 1 mm) in order to decrease the electrical resistance value. 
     As a result, in the plurality of solar cells  31  to  36 , in a case where an average area for each quarter of the minute hand  7   b  in the longitudinal direction is approximately 2.80 mm 2  and each area of the plurality of solar cells  31  to  36  is approximately 110.17 mm 2 , the light-receiving area of each of the solar cells  31  to  34  when the minute hand  7   b  is positioned across four solar cells  31  to  34  is 107.37 mm 2 , as depicted in  FIG. 6 . 
     Thus, the light-receiving area of each of four solar cells  31  to  34  over which the minute hand  7   b  has been positioned is increased by approximately 6.3% as compared with a case where the light-receiving area of one of the solar cells  31  to  36  is approximately 96.17 mm 2  by the minute hand  7   b  being positioned over only one of the solar cells  31  to  36 . 
     As a result, the output current of the plurality of solar cells  31  to  36  as a whole is increased by approximately 6.3%. 
     As described above, with this wristwatch solar panel  30 , the minute hand  7   b  of the pointers  7  moving there above can be always positioned across four of the plurality of solar cells  31  to  36 . Therefore, a decrease of light-receiving area due to the minute hand  7   b  can be distributed among four of the plurality of solar cells  31  to  36 . As a result, a decrease in the output current of four of the solar cells  31  to  36  over which the minute hand  7   b  has been positioned can be suppressed more than the case of the first embodiment, whereby the output current of the entire plurality of solar cells  31  to  36  can be significantly improved more than the case of the first embodiment. 
     In this case as well, the plurality of solar cells  31  to  36  are formed to have the same shape and area size by equal division, and whereby the light-receiving area of each of four of the plurality of solar cells  31  to  36  over which the minute hand  7   b  is positioned can be kept substantially constant. As a result, fluctuations in the output current of the entire plurality of solar cells  31  to  36  by the movement of the minute hand  7   b  can be suppressed. Therefore, the output current of the entire plurality of solar cells  31  to  36  can be kept substantially constant. 
     Also, the plurality of solar cells  31  to  36  are formed into a shape in which areas where the minute hand  7   b  of the pointers  7  is positioned across four of the plurality of solar cells  31  to  36  are substantially equal to each other. Therefore, the light-receiving areas of four of the solar cells  31  to  36  over which the minute hand  7   b  is positioned can be substantially equal to one another. As a result, a decrease in the output current of four of the plurality of solar cells  31  to  36  over which the minute hand  7   b  is positioned can be efficiently and equally suppressed. Therefore, the output current of the entire plurality of solar cells  31  to  36  can be improved more than the case of the first embodiment. 
     Moreover, the plurality of solar cells  31  to  36  each having the first to fourth areas F 1  to F 4  from the outer circumferential side toward the through hole  3   a  in the center portion are formed into a spiral shape such that the second area F 2  encroaches on the inner circumferential side of the first area F 1  that is an area on the outer circumferential side adjacent to the second area F 2 , the third area F 3  encroaches on the inner circumferential side of the second area F 2  that is an area adjacent to the second area F 3 , and the fourth area F 4  encroaches on the inner circumferential side of the third area F 3  that is an area adjacent to the fourth area F 4 . Therefore, the minute hand  7   b  of the pointers  7  moving above the solar panel  30  can always be reliably and favorably positioned across four of the plurality of solar cells  31  to  36 . 
     In this case as well, the plurality of solar cells  31  to  36  are each into a shape where the length in the circumferential direction gradually elongates toward the radial direction centering on the through hole  3   a  of the solar panel  30 . Therefore, the areas of the first and third areas F 1  to F 3  positioned on the outer circumferential side can be formed to be larger than the areas of the second to fourth areas F 2  and F 4  positioned on the inner circumferential side, respectively. As a result, areas of the plurality of solar cells  31  to  36  that are shaded by the minute hand  7   b  being positioned thereover can be minimized. This can also improve the output current of the entire plurality of solar cells  31  to  36 . 
     In the above-described second embodiment, the first to fourth areas F 1  to F 4  in each of the plurality of solar cells  31  to  36  are formed into a spiral shape by being coupled to one another and constricted by the coupling section F 5 . However, the present invention is not limited thereto. For example, as in a modification example in  FIG. 7 , a structure may be adopted in which the first to fourth areas F 1  to F 4  are formed into a smoothly-bent spiral shape. 
     That is, it is only required that the plurality of solar cells  31  to  36  are formed into a spiral shape where the bending angle is gradually decreased from the through hole  3   a  of the solar panel  30  toward the outer circumferential side of the solar panel  30 . 
     In this case as well, it is only required that the plurality of solar cells  31  to  36  are formed into a spiral shape such that areas where the minute hand  7   b  of the pointers  7  is positioned across four sequentially adjacent ones of the solar cells  31  to  36  are substantially equal to one another, as depicted in  FIG. 7 . 
     Also, each of the plurality of solar cells  31  to  36  is only required to be formed into a shape where the length in the circumferential direction gradually elongates toward the radial direction centering on the through hole  3   a.    
     With this solar panel  30  as well, operations and effects similar to those of the second embodiment can be achieved. 
     Third Embodiment 
     Next, with reference to  FIG. 8 , a third embodiment in which the present invention has been applied to a pointer-type wristwatch is described. In this case as well, sections identical to those in the first embodiment depicted in  FIG. 1  to  FIG. 4  are provided with the same reference numerals for description. 
     This pointer-type wristwatch has a structure identical to that of the first embodiment except that a plurality of solar cells  41  to  46  of a solar panel  40  has a structure different from that of the first embodiment, as depicted in  FIG. 8 . 
     These solar cells  41  to  46  are structured by a circle corresponding to the solar panel  40  being divided into six portions such that they have the same shape and area, as depicted in  FIG. 8 . 
     In this case, the plurality of solar cells  41  to  46  are divisionally formed into a spiral shape so that the minute hand  7   b  of the pointers  7  is always positioned across all of the plurality of solar cells  41  to  46 . 
     Also, the plurality of solar cells  41  to  46  are formed into the spiral shape such that areas where the minute hand  7   b  is positioned across all of the plurality of solar cells  41  to  46  are substantially equal to one another. 
     Moreover, the plurality of solar cells  41  to  46  are each formed to have a substantially equal length (width) in the radial direction, and are formed into the spiral shape such that the radius of curvature is gradually increased from the through hole  3   a  side of the solar panel  40  toward the outer circumferential side, as depicted in  FIG. 8 . 
     Furthermore, the plurality of solar cells  41  to  46  are formed into the spiral shape so as to be spirally curved from the perimeter of the through hole  3   a  of the solar panel  40  to the outer perimeter of the solar panel  40 . 
     With this wristwatch solar panel  40 , the minute hand  7   b  of the pointers  7  moving there above can be always positioned across all of the plurality of solar cells  41  to  46 , and therefore a decrease of light-receiving area due to the minute hand  7   b  can be distributed among all of the plurality of solar cells  41  to  46 , which is more than the first embodiment. 
     Accordingly, with this solar panel  40 , the light-receiving areas of all of the solar cells  41  to  46  over which the minute hand  7   b  is positioned can be increased more than those of the first embodiment, whereby a decrease in the output current of all of the solar cells  41  to  46  over which the minute hand  7   b  is positioned can be reliably and favorably suppressed. Therefore, the output current of the entire plurality of solar cells  41  to  46  can be significantly improved more than the case of the first embodiment. 
     In this case as well, the plurality of solar cells  41  to  46  are formed to have the same shape and area size by equal division, whereby the light-receiving areas of all of the plurality of solar cells  41  to  46  over which the minute hand  7   b  is positioned can be kept substantially constant. As a result, fluctuations in the output current of the entire plurality of solar cells  41  to  46  due to the movement of the minute hand  7   b  can be suppressed. Therefore, the output current of the entire plurality of solar cells  41  to  46  can be kept substantially constant. 
     Also, the plurality of solar cells  41  to  46  are formed into a spiral shape so that areas where the minute hand  7   b  of the pointers  7  is positioned over all of the plurality of solar cells  41  to  46  are substantially equal to each other. Therefore, the light-receiving areas of all of solar cells  41  to  46  over which the minute hand  7   b  is positioned can be made substantially equal to one another. As a result, the output current values of all of the solar cells  41  to  46  over which the minute hand  7   b  is positioned can be made substantially equal to one another. Therefore, the output current of the entire plurality of solar cells  41  to  46  can be significantly improved more than the case of the first embodiment. 
     Moreover, the plurality of solar cells  41  to  46  are each formed to have a substantially equal length (width) in the radial direction, and are formed into a spiral shape such that the radius of curvature is gradually increased from the through hole  3   a  of the solar panel  40  toward the outer circumferential side of the solar panel  40  and the solar cells are spirally curved from the perimeter of the through hole  3   a  to the outer perimeter of the solar panel  40 . Therefore, the minute hand  7   b  of the pointers  7  moving above the solar panel  40  can always be reliably and favorably positioned across all of the plurality of solar cells  41  to  46 . 
     In the above-described third embodiment, the plurality of solar cells  41  to  46  are formed such that all of the lengths (widths) in the radial direction are equal to one another. However, the present invention is not limited thereto. For example, the plurality of solar cells  41  to  46  of the solar panel  40  may be each formed such that the length (width) in the radial direction is gradually increased from the through hole  3   a  of the solar panel  40  toward the outer perimeter of the solar panel  40 . 
     In this case as well, it is only required that the plurality of solar cells  41  to  46  are divisionally formed into a spiral shape such that the minute hand  7   b  of the pointers  7  is always positioned across all of the plurality of solar cells  41  to  46 . 
     Also, the plurality of solar cells  41  to  46  are only required to be formed into a spiral shape such that areas where the minute hand  7   b  is positioned across all of the plurality of solar cells  41  to  46  are substantially equal to one another. 
     In this solar panel  40  as well, operations and effects substantially similar to those of the third embodiment can be achieved. 
     Fourth Embodiment 
     Next, with reference to  FIG. 9 , a fourth embodiment in which the present invention has been applied to a pointer-type wristwatch is described. 
     In this case as well, sections identical to those in the first embodiment depicted in  FIG. 1  to  FIG. 4  are provided with the same reference numerals for description. 
     This pointer-type wristwatch has a structure identical to that of the first embodiment except that a plurality of solar cells  51  to  56  of a solar panel  50  has a structure different from that of the first embodiment, as depicted in  FIG. 9 . 
     These solar cells  51  to  56  are structured by a circle corresponding to the solar panel  50  being divided into six portions such that they have the same shape and area, as depicted in  FIG. 9 . 
     In this case, the plurality of solar cells  51  to  56  are divisionally formed into a step-like spiral shape so that the minute hand  7   b  of the pointers  7  is always positioned across all of the plurality of solar cells  51  to  56 . 
     Also, the plurality of solar cells  51  to  56  are formed into the substantially step-like spiral shape such that areas where the minute hand  7   b  is positioned across all of the plurality of solar cells  51  to  56  are substantially equal to one another, as depicted in  FIG. 9 . 
     In this case, the plurality of solar cells  51  to  56  are each formed into a shape where the length in the circumferential direction gradually elongates toward the radial direction centering on the through hole  3   a  of the solar panel  50 . 
     Moreover, the plurality of solar cells  51  to  56  are each formed to have a substantially equal length (width) in the radial direction. 
     Furthermore, the plurality of solar cells  51  to  56  each have a first area G 1  located on the outer circumferential side of the solar panel  50 , a second area G 2  located on the inner circumferential side of the first area G 1 , a third area G 3  located on the inner circumferential side of the second area G 2 , a fourth area G 4  located on the inner circumferential side of the third area G 3 , a fifth area G 5  located on the inner circumferential side of the fourth area G 4 , and a sixth area G 6  located on the inner circumferential side of the firth area G 5 , as depicted in  FIG. 9 . 
     In this case, the plurality of solar cells  51  to  56  are each structured to have the first to sixth areas G 1  to G 6  sequentially formed in a staircase pattern at positions shifted from one another along the circumferential direction and sequentially coupled by coupling sections G 7 , as depicted in  FIG. 9 . 
     These first to sixth areas G 1  to G 6  are each formed to have a different size, and are sequentially formed at positions shifted from one another by 60 degrees in the counterclockwise direction. 
     As a result, the first to sixth areas G 1  to G 6  are structured such that the entire shape obtained by combining theses areas forms a fan shape having an opening angle of 60 degrees. 
     Still further, the plurality of solar cells  51  to  56  are formed into a shape in which, with the first area G 1  positioned at the outermost perimeter as a reference point, the second area G 2  encroaches on the inner circumferential side of the first area G 1  positioned in the counterclockwise direction thereof, the third area G 3  encroaches on the inner circumferential side of the second area G 2  positioned in the counterclockwise direction thereof, the fourth area G 4  encroaches on the inner circumferential side of the third area G 3  positioned in the counterclockwise direction thereof, the fifth area G 5  encroaches on the inner circumferential side of the fourth area G 4  positioned in the counterclockwise direction thereof, and the sixth area G 6  encroaches on the inner circumferential side of the fifth area G 5  positioned in the counterclockwise direction thereof, as depicted in  FIG. 9 . 
     In this case, the plurality of solar cells  51  to  56  are structured such that the coupling sections G 7 , which are sequentially coupling the first to sixth areas G 1  to G 6  so as to form a staircase pattern, are radially positioned at every 60 degrees centering on the through hole  3   a  of the solar panel  50 , as depicted in  FIG. 9 . 
     In this case, as with the first embodiment, each coupling section G 7  is preferably formed to have a connection width equal to or longer than 1 mm in order to decrease the electrical resistance value. 
     With this wristwatch solar panel  50 , the minute hand  7   b  of the pointers  7  moving there above can be always positioned across all of the plurality of solar cells  51  to  56 . Therefore, as with the third embodiment, a decrease of light-receiving area due to the minute hand  7   b  can be distributed among all of the plurality of solar cells  51  to  56 . 
     Thus, the light-receiving areas of all of the solar cells  51  to  56  over which the minute hand  7   b  is positioned can be increased more than the case of the first embodiment. As a result, a decrease in the output current of all of the solar cells  51  to  56  over which the minute hand  7   b  is positioned can be reliably and favorably suppressed, whereby the output current of the entire plurality of solar cells  51  to  56  can be significantly improved more than the case of the first embodiment. 
     In this case as well, the plurality of solar cells  51  to  56  are formed to have the same shape and area size by equal division, and whereby the light-receiving areas of all of the plurality of solar cells  51  to  56  over which the minute hand  7   b  of the pointers  7  is positioned can be kept substantially constant. As a result, fluctuations in the output current of the entire plurality of solar cells  51  to  56  due to the movement of the minute hand  7   b  can be suppressed. Therefore, the output current of the entire plurality of solar cells  51  to  56  can be kept substantially constant. 
     Also, the plurality of solar cells  51  to  56  are formed into a substantially step-like spiral shape such that areas where the minute hand  7   b  of the pointers  7  is positioned on all of the plurality of solar cells  51  to  56  are substantially equal to one another. Therefore, the light-receiving areas of all of the plurality of solar cells  51  to  56  over which the minute pointer  7   b  is positioned can be made substantially equal to one another. As a result, the output current values of all of the solar cells  51  to  56  over which the minute hand  7   b  is positioned can be made substantially equal to one another. Thus, as with the third embodiment, the output current of the entire plurality of solar cells  51  to  56  can be significantly improved. 
     Moreover, the plurality of solar cells  51  to  56  are each formed to have a substantially equal length (width) in the radial direction, and are formed into a substantially spiral shape such that the length in the circumferential direction is increased in steps from the through hole  3   a  of the solar panel  50  toward the outer circumferential side of the solar panel  50  at every 60 degrees and the first to sixth areas G 1  to G 6  are spirally curved in steps. Therefore, the pointers  7  moving above the plurality of solar cells  51  to  56  can always be reliably and favorably positioned across all of the plurality of solar cells  51  to  56 . 
     In the above-described fourth embodiment, the plurality of solar cells  51  to  56  are formed such that all of the lengths (widths) of the first to sixth areas G 1  to G 6  in the radial direction are equal to one another. However, the present invention is not limited thereto. For example, as in a modification example depicted in  FIG. 10 , a structure may be adopted in which a plurality of solar cells  61  to  66  of a solar panel  60  are each formed such that the length (width) of each of the first to sixth areas G 1  to G 6  in the radial direction is gradually increased from the through hole  3   a  of the solar panel  60  toward the outer perimeter of the solar panel  60 . 
     In this case as well, it is only required that the plurality of solar cells  61  to  66  are divisionally formed into a substantially step-like spiral shape where the minute hand  7   b  of the pointers  7  is always positioned across all of the plurality of solar cells  61  to  66 . 
     Also, the plurality of these solar cells  61  to  66  are only required to be formed into a substantially step-like spiral shape such that areas where the minute hand  7   b  is positioned across all of the plurality of solar cells  61  to  66  are substantially equal to one another. 
     With this solar panel  60 , operations and effects substantially similar to those of the fourth embodiment can be achieved. 
     In each of the above-described first to fourth embodiments and the modification examples thereof, the connecting sections  21  connecting the plurality of solar cells in series are sequentially provided along the perimeter of the through hole  3   a  of the solar panel. However, the present invention is not limited thereto. The connecting section  21  may be sequentially provided along the outer perimeter of the plurality of solar cells. 
     Also, in each of the above-described first to fourth embodiments and the modification examples thereof, the present invention has been applied to a pointer-type wristwatch. However, the present invention is not necessarily applied to a wristwatch. The present invention can be applied to various pointer-type timepieces, such as a travel watch, an alarm clock, a table clock, and a wall clock, and can also be widely applied to measuring instruments such as a pointer-type meter. 
     While the present invention has been described with reference to the preferred embodiments, it is intended that the invention be not limited by any of the details of the description therein but includes all the embodiments which fall within the scope of the appended claims.