Patent Publication Number: US-2009229655-A1

Title: Solar Cell

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a solar cell. More particularly, the present invention relates to a solar cell with a transparent cover plate which includes a base plate and a structured plate. 
     2. Description of the Prior Art 
     In the recent years, the greenhouse effect caused by the mass generation of greenhouse gas and the price upswing of petroleum result in the fact that people are giving more and more weight to the renewable energy. In the present, the renewable energy includes: solar energy, wind power, geothermal energy, hydro power, tide energy, ocean thermal energy conversion and biomass energy, wherein the solar energy is the most generally used among the renewable energy. 
     Please refer to  FIG. 1  for a prior solar cell. The solar cell  10  defines a receiving room  14 , which includes an encapsulant material  17  and pluralities of polysilicon solar cells  16 . The polysilicon solar cells  16  are connected in series by wire  18 , and the encapsulant material  17  is ethylene-vinyl acetate copolymer for example. A glass cover plate  12  is placed over the solar cell  10 . The sun light can transmit the glass cover plate  12 , irradiating the polysilicon solar cells  16 . However, when the angle of incident sun light to the normal of the incident surface  121  of the glass cover plate  12  is greater than the critical angle, the total reflection occurs, which means the sun light will stop crossing the glass cover plate  12 , with the result that the efficiency of the solar cell  10  decreases. 
     Therefore, some prior articles disclosed patterns disposed on the incident surface of the glass cover plate to prevent total reflection. For example, some concave patterns are formed on the incident surface to prevent total reflection. However, the concave patterns are apt to accumulate dust and/or water, especially in the desert. Therefore, the glass cover plate needs cleaning frequently, increasing the cost of maintenance. Moreover, the concave patterns are formed on fused glass in the industry. As the glass cools down, the patterns thereof shrink due to the larger expansion coefficient of glass, with the result that the dimensions of patterns are often undesirable. 
     It would, therefore, be desirable to prevent the incident surface of glass cover plate from accumulating dust and water more effectively and to form patterns on the incident surface more precisely. 
     SUMMARY OF THE INVENTION 
     The present invention provides a solar cell, wherein the incident surface of a transparent cover plate thereof can present the accumulation of dust and/or water more effectively, and patterns on the incident surface can be more precisely formed. 
     To achieve the foregoing and other subjects, the invention provides a solar cell. The solar cell defines a receiving room in where at least a cell unit is located. A transparent cover plate is placed over the cell unit. The solar cell is further characterized in that: the transparent cover plate includes a base plate and a structured plate which are adhered to each other, wherein the base plate is made from inflexible material, the structured plate is made from a photo resin and pluralities of convex first patterns are disposed on the incident surface of the structured plate. 
     In the present solar cell, a transparent waterproof material is spread over the incident surface of the structured plate. 
     In the present solar cell, the waterproof material is polytetrafluoro ethylene. 
     In the present solar cell, the first patterns are bar-shaped, and the sections thereof are triangular for example. Wherein, the height is half the width. Or, the sections of the first patterns are arc-shaped, for example. Wherein, the height and the width can be related by the following formula: 
       Height/Width=0.05˜0.25 
     In the present solar cell, there are arc-shaped grooves between the first patterns. 
     In the present solar cell, the base is made from glass. Moreover, if the cell unit is a singlesilicon solar cell, the thickness of the base plate is between 3 mm to 12 mm. 
     Due to the convex first patterns disposed on the transparent cover plate, the transparent cover plate can prevent the accumulation of dust and water more effectively. Moreover, the structured plate is made from a photo resin, which shrinks slightly during curing. Therefore, the precision of the dimensions of the first patterns is more easily controlled and the transparent cover plate can reach the requirement for the optic effect as well. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a prior solar cell. 
         FIG. 2A  is a solar cell of the first embodiment; 
         FIG. 2B  is an arc-shaped groove. 
         FIG. 3A  to  FIG. 3D  shows a manufacturing process of a transparent cover plate of the first embodiment. 
         FIG. 4  is a comparative drawing, which shows luminous flux of transparent cover plates of the first embodiment and a comparative embodiment when the incident angle of light varies. 
         FIG. 5  is a transparent cover plate of the solar cell of the second embodiment. 
         FIG. 6  is a top view of a transparent cover plate of a solar cell of the third embodiment. 
         FIG. 7  is a transparent cover plate of the solar cell of the fourth embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     Please refer to  FIG. 2A  for a solar cell of a first embodiment. The solar cell  20  defines a receiving room  24 , which includes an encapsulant material  27  and pluralities of cell units  26 . The encapsulant material  27  is ethylene-vinyl acetate copolymer for example and the cell units  26  are singlesilicon solar cells in the present embodiment. However, the cell units  26  can be dye sensitized solar cells, polysilicon solar cells or other apparatus which can transform light energy into electric energy. Moreover, a transparent cover plate  22  is placed over the cell units  26 . The transparent cover plate  22  includes a base plate  221  and a structured plate  222 . The base plate  221  is made from glass, wherein the thickness thereof is between 3 mm to 12 mm. The structured plate  222  is made from a photo resin, such as a UV-curable resin. However, those skilled in the art can also select other inflexible material as the material of the base plate  221 , such as polymethyl methacrylate (PMMA), polycarbonate (PC), polystyrene (PS), polypropene (PP), polyethylene (PE) or polyethylene terephthalate (PET). 
     Please refer to  FIG. 2A  again. Pluralities of first patterns  222   b  are disposed on the incident surface of the structured plate  222 . The first patterns  222   b  are bar-shaped, and the sections thereof are triangular. Because the first patterns  222   b  are convex bar-shaped and the solar cell  20  is disposed at an angle with horizontal, the water along with the dust can flow down the structured plate  222  from the grooves  222   a  between the first patterns  222   b,  which makes the transparent cover plate  22  more easily to clean. In the present embodiment, the height H 1  of first patterns  222   b  is generally half the width W 1  of the first patterns  222   b.  Wherein, the height H 1  is 0.025 mm and the width W 1  is 0.05 mm, for example. Besides, the grooves  222   a ′ between the first patterns  222   b,  as depicted in  FIG. 2B , can also be arc-shaped, so as to reduce the accumulation of dust on the grooves  222   a′.    
     Then, please refer to  FIG. 3A  to  FIG. 3D  for a manufacturing process of a transparent cover plate of the first embodiment. First, please refer to  FIG. 3A . A base plate  221  is prepared. Then, please refer to  FIG. 3B . A photo resin  61  is applied on the base plate  221 . Next, the base plate  221  is placed on a transport band (not depicted) to be transported forward, and then the photo resin  61  is over-rolled by a roller  70 . The second patterns (not depicted) on a surface  71  of the roller  70  are corresponding to the first patterns  222   b  depicted in  FIG. 2 . In the present embodiment, the sections of the first patterns  222   b  are convex triangular, which means the sections of the second patterns on the roller  70  are concave triangular. 
     Moreover, there is a UV lamp  80  located under the roller  70 . As the roller  70  rolls over the photo resin  61 , the UV lamp  80  irradiates the over-rolled photo resin  61  to harden it, forming the first patterns  222   b.  Then, please refer to  FIG. 3D . After the whole photo resin  61  is over-rolled by the roller  70  and irradiated by the UV lamp  80 , a structured plate  222  is formed, which means the manufacture of the transparent cover plate  22  is complete. A point for attention, the view of  FIG. 3D  is perpendicular to the views of  FIG. 3B  and  FIG. 3C . That is to say,  FIG. 3B  and  FIG. 3C  are front views, and yet  FIG. 3D  is a side view. 
     In the present embodiment, the first patterns  222   b  are formed on the structured plate  222 , which is made from a photo resin. Wherein, the photo resin shrinks slightly during curing. Therefore, the precision of the dimensions of the first patterns  222   b  is more easily controlled and the transparent cover plate  22  can reach the requirement for the optic effect as well. 
     Please refer to  FIG. 4  for a comparative drawing, which shows luminous flux of transparent cover plates of the first embodiment and a comparative embodiment when the incident angle of light varies. Moreover,  FIG. 4  is a drawing based on the result of a computer optic simulation, wherein the luminous flux of incident light is 1000 lumen and the incident angle of light varies from 0° to 90°. In the comparative embodiment, the transparent cover plate is a pattern glass made by Taiwan Glass Corporation located in Taiwan. Wherein, the patterns of the pattern glass are directly-formed on the glass. As shown in  FIG. 4 , it is obvious that the transparent cover plate of the first embodiment, comparing to the pattern glass of the comparative embodiment, has higher luminous flux no matter how the incident angle of light varies. 
     In the first embodiment, the sections of first patterns  222   b  are triangular. However, those skilled in the art can also vary the section of first patterns  222   b  into other shape. Please refer to  FIG. 5  for a transparent cover plate of the solar cell of the second embodiment. The transparent cover plate  22 ′ includes a base plate  221 ′ and a structured plate  222 ′. The function and formation of the present base plate  221 ′ are similar to those of base plate  221  of the first embodiment. Wherein, the first patterns  222   b ′ on the structured plate  222 ′ are arc-shaped. The height H 2  and the width W 2  of the first patterns  222   b ′ can be related by the following formula: 
         H 2/ W 2=0.05˜0.25 
     Wherein, the height H 2  is 0.03 mm and the width W 2  is 0.4 mm, for example. 
     Moreover, those skilled in the art can also vary the first patterns into structures other than bar-shaped structure. Please refer to  FIG. 6  for a top view of a transparent cover plate of a solar cell of the third embodiment. The bases of the first patterns  222   b ″ on the transparent cover plate  222  are circular. 
     Then, please refer to  FIG. 7  for a transparent cover plate of the solar cell of the fourth embodiment. The difference between the present transparent cover plate  22 ′″ and the transparent cover plate  22 ″ of the second embodiment is that there is a transparent waterproof material  223 ′″ applied on the structured plate  222 ′ of the transparent cover plate  22 ′″. The waterproof material  223 ′″ is polytetrafluoro ethylene, for example. In the present embodiment, it is not easy for water to adhere on the transparent cover plate  22 ′″ due to the waterproof material  223 ′″. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.