Abstract:
A solar cell module that has a back protective sheet and a front transparent protective sheet and edge sealant members that seal an inner portion of the solar cell module so as to define a cavity that receives a plurality of solar cells. A portion of the back protective sheet extends beyond the sealant members so as to define a mounting region that can receive mounting structures such as holes, connectors, rails or the like. By providing the mounting region, the mounting structures can be spaced from the sealant members which limits the damage to the sealant members during the mounting process and preserves the moisture sealed state of the solar cell cavity.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 12/945,759 entitled Flexible Solar Shell and Support Structure for Use with Rooftops which was filed Nov. 12, 2010 and is hereby incorporated by reference in it&#39;s entirety. This application is also related to U.S. Application No. ______(Atty Docket No. SPOW.013A2) entitled INTEGRATED STRUCTURAL SOLAR MODULE AND CHASSIS and U.S. Application No. (Atty Docket No. SPOW.011A) entitled JUNCTION BOX ATTACHMENT FOR PHOTOVOLTAIC THIN FILM DEVICES. 
     
    
     BACKGROUND 
       [0002]    1. FIELD OF THE INVENTIONS 
         [0003]    The aspects and advantages of the present inventions generally relate to apparatus and methods of photovoltaic or solar module design and fabrication and, more particularly, to roll-to-roll or continuous packaging techniques for flexible modules employing thin film solar cells. 
         [0004]    2. DESCRIPTION OF THE RELATED ART 
         [0005]    Solar cells are photovoltaic (PV) devices that convert sunlight directly into electrical energy. Solar cells can be based on crystalline silicon or thin films of various semiconductor materials, that are usually deposited on low-cost substrates, such as glass, plastic, or stainless steel. 
         [0006]    Thin film based photovoltaic cells, such as amorphous silicon, cadmium telluride, copper indium diselenide or copper indium gallium diselenide based solar cells, offer improved cost advantages by employing deposition techniques widely used in the thin film industry. Group IBIIIAVIA compound photovoltaic cells including copper indium gallium diselenide (CIGS) based solar cells have demonstrated the greatest potential for high performance, high efficiency, and low cost thin film PV products. 
         [0007]    As illustrated in  FIG. 1 , a conventional Group IBIIIAVIA compound solar cell  10  can be built on a substrate  11  that can be a sheet of glass, a sheet of metal, an insulating foil or web, or a conductive foil or web. A contact layer  12  such as a molybdenum (Mo) film is deposited on the substrate as the back electrode of the solar cell. An absorber thin film  14  including a material in the family of Cu(In,Ga)(S,Se) 2 , is formed on the conductive Mo film. The substrate  11  and the contact layer  12  form a base layer  13 . Although there are other methods, Cu(In,Ga)(S,Se) 2  type compound thin films are typically formed by a two-stage process where the components (components being Cu, In, Ga, Se and S) of the Cu(In,Ga)(S,Se) 2  material are first deposited onto the substrate or the contact layer formed on the substrate as an absorber precursor, and are then reacted with S and/or Se in a high temperature annealing process. 
         [0008]    After the absorber film  14  is formed, a transparent layer  15 , for example, a CdS film, a ZnO film or a CdS/ZnO film-stack is formed on the absorber film  14 . Light enters the solar cell  10  through the transparent layer  15  in the direction of the arrows  16 . The preferred electrical type of the absorber film is p-type, and the preferred electrical type of the transparent layer is n-type. However, an n-type absorber and a p-type window layer can also be formed. The above described conventional device structure is called a substrate-type structure. In the substrate-type structure light enters the device from the transparent layer side as shown in  FIG. 1 . A so called superstrate-type structure can also be formed by depositing a transparent conductive layer on a transparent superstrate such as glass or transparent polymeric foil, and then depositing the Cu(In,Ga)(S,Se) 2  absorber film, and finally forming an ohmic contact to the device by a conductive layer. In the superstrate-type structure light enters the device from the transparent superstrate side. 
         [0009]    Standard silicon, CIGS and amorphous silicon cells can be fabricated on conductive substrates such as aluminum or stainless steel foils. Such solar cells are separately manufactured, and the manufactured solar cells are electrically interconnected by a stringing or shingling process to form solar cell circuits. In the stringing or shingling process, the (+) terminal of one cell is typically electrically connected to the (−) terminal of the adjacent solar cell. For the Group IBIIIAVIA compound solar cell shown in  FIG. 1 , if the substrate  11  is a conductive material such as a metallic foil, the substrate, which forms the bottom contact of the cell, becomes the (+) terminal of the solar cell. The metallic grid (not shown) deposited on the transparent layer  15  is the top contact of the device and becomes the (−) terminal of the cell. When interconnected by a shingling process, individual solar cells are placed in a staggered manner so that a bottom surface of one cell, i.e. the (+) terminal, makes direct physical and electrical contact to a top surface, i.e. the (−) terminal, of an adjacent cell. Therefore, there is no gap between two shingled cells. Stringing is typically done by placing the cells side by side with a small gap between them and using conductive wires or ribbons that connect the (+) terminal of one cell to the (−) terminal of an adjacent cell. Solar cell strings obtained by stringing or shingling individual solar cells are interconnected to form circuits. Circuits can then be packaged in protective packages to form modules. Each module typically includes a plurality of solar cells which are electrically connected to one another. Many modules can also be combined to form large solar panels. The solar modules are constructed using various packaging materials to mechanically support and protect the solar cells contained in the packaging against mechanical damage. 
         [0010]    In general, solar panels are placed on rooftops, often on roof shingles or other varieties of rooftop structures, to directly expose them to unobstructed sunlight. The modules are either directly secured onto the rooftops or onto a rack secured onto the rooftops. However considering most solar panels are installed on rooftops in large numbers, installers often attach the panels to underlying roof support structures using various fasteners, for example, adhesives or conventional fasteners. During the installation such fasteners physically contact the moisture sealed body of a conventional module. As a result, they can potentially damage the module during the installation. Such installation approaches also further complicates replacements and maintenance of the solar panels that are, in some cases, permanently anchored to the roof support structures. Since the solar panels are permanently attached to the rooftop, any maintenance work can result in damaging the module and the rooftop. 
         [0011]    From the foregoing, there is a need in the solar cell industry, especially in thin film photovoltaics, for improved solar module designs that result in easy to maintain solar modules so that replacements and repairs can be performed in short time and reduced cost. Such techniques should not require alterations in the existing rooftop structure. 
       SUMMARY 
       [0012]    The aforementioned needs are addressed by the present invention which in one aspect comprises a solar module, comprising a back protective sheet including an inner section surrounded by an edge section, wherein the edge section extends between the edge of the back protective sheet and the inner section. The solar module further comprises a transparent front protective sheet disposed above a top surface of the inner section of the back protective sheet, wherein the front protective sheet having the size and shape of the top surface of the inner section. In this aspect the solar module further comprises a peripheral sealant wall surrounding the inner section and extending between the edge of the front protective sheet and the edge of the inner section of the back protective sheet so as to form a module cavity on the inner section of the back protective sheet and a plurality of interconnected solar cells disposed within the module cavity so that a light receiving side of each solar cell faces the front protective sheet and a back side of each solar cell faces the back protective sheet. The solar module in this aspect further comprises a transparent support material that fills a remainder of the module cavity and surrounds the plurality of solar cells. 
         [0013]    In another aspect the present invention comprises a method of manufacturing a solar module, comprising the steps of providing a back protective sheet including an inner section surrounded by an edge section, wherein the edge section has a predetermined width extending between the perimeter of the back protective sheet and the inner section and forming a module stack on a top surface of the inner section. Forming a module stack in this aspect comprises the steps of forming a peripheral sealant wall on the top surface of the inner section, which surrounds the inner section; disposing a plurality of interconnected solar cells over the top surface of the inner section that is surrounded by the peripheral sealant wall, each solar cell including a front light receiving side and a back substrate side; covering the plurality of solar cells with a transparent support material on both the front light receiving side and the back substrate side that faces the top surface of the inner section; placing a transparent protective sheet over the peripheral sealant wall and the support material covering the plurality of interconnected solar cells to form a module stack, wherein the transparent protective sheet has the same shape and size as the top surface of the inner section; and heating the module stack to form the solar module on the back protective sheet. 
         [0014]    In another aspect, the present invention comprises a solar module comprising a back protective sheet having a first peripheral dimension and an inner portion and a transparent front protective sheet disposed above a top surface of the inner portion, wherein the transparent front protective sheet defines a second peripheral dimension that is less than the first peripheral dimension so that at least a portion of the back protective sheets extends outward from the transparent front protective sheet so as to define a mounting region of the back protective sheet. In this aspect the solar module further includes a peripheral sealant wall surrounding the inner portion of the back protective sheet, wherein the peripheral sealant wall is interposed between the mounting region and the inner portion and wherein the peripheral walls interconnect the back protective sheet and the transparent front protective sheet so as to define a module cavity in the inner potion of the back protective sheet and a plurality of interconnected solar cells positioned within the module cavity. 
         [0015]    These and other aspects and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic view a thin film solar cell; 
           [0017]      FIG. 2A  is a schematic top view of an embodiment of a solar module including an edge section; 
           [0018]      FIG. 2B  is a schematic side view of a back protective sheet of the solar module shown in  FIG. 2A ; 
           [0019]      FIG. 2C  is a schematic side view of the solar module shown in  FIG. 2A ; 
           [0020]      FIG. 3  is a schematic top view of the solar module shown in  FIG. 2A  including a treatment zone at the edge section; 
           [0021]      FIG. 4A  is a schematic view of a method of constructing a solar module structure in a lay-up station; 
           [0022]      FIG. 4B  is a schematic view of a method of laminating the module structure in a laminator to form a solar module; 
           [0023]      FIG. 4C  is a schematic view of a method of edge treating the module in a module edge treatment station; and 
           [0024]      FIGS. 5A-5C  are schematic illustrations of various edge treatment embodiments; 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    The preferred embodiments described herein provide solar cells and methods of manufacturing a photovoltaic module including one or more thin film solar cells, preferably including Group IBIIIAVIA compound solar cells. Preferably, a flexible polymer sheet, or a flat and flexible polymer sheet, or a flat and flexible polymer sheet including a moisture barrier layer such as a metallic layer or an insulator layer, is used to as a back protective sheet of the solar module. Specifically, the module including a plurality of interconnected thin film solar cells is built over an inner section of the back protective sheet that is surrounded by an edge section of the back protective sheet. The module is built by: applying a module edge sealant along the borders of the inner section and thereby forming a module cavity on the inner section that excludes the edge section of the back protective sheet; placing a plurality of interconnected solar cells within the module cavity and covering the interconnected solar cells with a support material such as an encapsulant material; finally, sealing the module cavity by placing a transparent front protective sheet on the module edge sealant. The transparent front protective sheet may have the size and shape of the top surface of the inner section. The edge section surrounding the module forms a shelf or extension of the solar module and is used to mount the solar module or panel on a surface by applying various fastening or capturing means to the edge section but not the sealed module itself or its sealed perimeter. The edge section may be mechanically or chemically treated or modified to include holes, fasteners or rails, or the like, or a combination of them, to assist mounting the solar module on a support structure such as rooftops or support racks. In one implementation one or more additional layers having the same size and shape of, or larger than, the back protective sheet may be attached to at least a portion of a back surface of the back protective sheet to further support it. 
         [0026]      FIGS. 2A and 2C  show an embodiment of a module  100  of the present invention in schematic plan view and in side view, respectively. As will be described more fully below, the module  100 , shown in  FIGS. 2A and 2C , is a laminated module. The module  100  includes solar cells  102  in a sealed module shell  104  that is formed by a back protective sheet  106 , a transparent front protective sheet  108  and a peripheral edge sealant  110  extending between the back protective sheet and the front protective sheet. As also specifically illustrated in  FIG. 2B  in side view, the back protective sheet  106 , having a top surface  106 A and a bottom surface  106 B, includes an inner section  107 A and an edge section  107 B. The edge section  107 B may fully or partially surround the inner section  107 A and may have a width in the range of 0.5 cm to 10 cm, preferably 1-4 cm extending between the border of the inner section and the edge of the back protective sheet. Depending on the application needs, the width of the edge section  107 B may or may not be uniform around the inner section  107 A. In this embodiment, the inner section  107 A and the edge section  107 B are integral parts of the back protective sheet  106 ; however, they may be made of different materials, which may be subsequently combined to form a single back protective sheet piece. 
         [0027]    As shown in  FIG. 2C , the peripheral edge sealant  110  is applied onto the top surface  106 A to form a module cavity  112 , or an inner space, over the inner section  107 A on the top surface  106 A. The peripheral edge sealant  110  is applied along the border between the inner section  107 A and the edge section  107 B excluding the edge section  107 B. Solar cells  106  in the module cavity  112  may be covered or coated with a transparent support material  114  such as an encapsulant which fully or partially covers or coats the solar cells  102 . The transparent front protective sheet  108  of the module is placed on the peripheral edge sealant  110  and the support material  114 . Each solar cell  102  may be a thin film solar cell such as CIGS compound solar cells, silicon based solar cell or any other solar cell. In the preferred embodiment, the solar cells  102  are CIGS solar cells that are examplified in  FIG. 1  described in the background section. In this embodiment, the solar cells are interconnected as an electrical circuit or string by interconnecting the solar cells  102  in series using conductive wires  116 A by a process referred to as stringing. However, the solar cells  102  may be interconnected using a shingling process as described above in the background section. In the module  100 , a light receiving side  118  of the solar cells  102  face towards the transparent front protective sheet  108  and a substrate side  120  facing towards the back protective sheet  106 . The light receiving side  118  of the solar cells  102  includes a conductive grid  122  or terminal to collect current from the light receiving side  118 . One more output wires  116 B connect the circuit including the solar cells  102  to an outside junction box (not shown) which can in turn be used to connect the solar module to a power circuitry. A junction box may be attached on an edge section portion that may preferably be adjacent the location of the output wires  116 B. As shown in  FIG. 2C , optionally, one or more sheet support materials  124  may be attached or adhered to bottom surface  106 B of the back protective sheet  106  to provide additional strength to the back protective sheet. The sheet support material  124  may have the same size and shape as the back protective sheet or larger than the back protective sheet  106 . 
         [0028]    An examplary material for the back protective sheet  106  may be a sheet of glass or a flexible polymeric sheet including for example polyvinyl fluoride (PVF) under TEDLAR® commercial name. The back protective sheet  106  may also comprise stacked sheets comprising polymeric sheets with various material combinations such as metallic films as moisture barrier. The transparent front protective sheet  108  may also include glass or a flexible polymeric sheet such as ethylene tetrafluoroethylene (ETFE) under TEFZEL® commercial name or fluorinated ethylene propylene (FEP). The transparent support material  114  or the encapsulant may include ethylene vinyl acetate copolymer (EVA) or thermoplastic polyurethanes (TPU). The peripheral sealant wall  110  may include butyl rubber with desiccants. The water vapor transmission rate of the module of the present invention may be 10 −3 gram/m 2 /day or less. 
         [0029]    As shown in  FIG. 3 , the module  100  may have a treated zone  125  surrounding the edge section  107 B. The treated zone  125  may extend along both the top surface and the bottom surface of the edge section  107 B as in the manner shown in  FIG. 3 . The module  100  is held or captured using the treated zone  125  when placed on a support structure such as rooftops or support racks. Since the treated zone  125  is located away from the peripheral module sealant  110 , the sealed shell  104  of the module  100  ( FIG. 2C ) is less likely to be accidentally damaged during the installation and operation of the module. The treated zone  125  may be formed by mechanically or chemically treating or modifying the edge section  107 B to form various openings or structures to assist mounting the solar module on a support structure such as rooftops or support racks. The treated zone  125  may include one or more fasteners attached to the treated zone, such as clamps or the like to assist mounting the solar module on a support to capture the support. The treated zone  125  may also include one more auxiliary structures to assist mounting the solar module on a support structure, such as rails or the like protruding structures that can be held by a support structure. Various conventional fastening members such as nails, screws or adhesives may also be applied to top or back surface in the treated zone  125 . 
         [0030]      FIGS. 4A-4C  illustrate an examplary method of manufacturing the module  100  of the present invention. As shown in  FIG. 4A , in a lay-up station  200 A, a module structure  100 A or stack is first formed by applying the peripheral module sealant  110  on the inner section  107 A of the back protective sheet  106  and forming a module cavity  112 . Between the layers of support material  114 , the solar cells  102 , which are interconnected, are disposed within the module cavity  112 , and in the following step the transparent front protective sheet  108  of the module is placed on the peripheral edge sealant  110  and the support material  114 . As shown  FIG. 4B , the module structure  100 A formed on the back protective sheet  106  is then placed into a chamber of a laminator  200 B, preferably a vacuum laminator. The module structure  100 A is processed in the vacuum laminator by application of heat. During the lamination process, the support material  114  of the module structure  200 A adheres to the interconnected solar cells and to the back and front protective sheets  106  and  108 . The peripheral edge sealant  110  also adheres to the back and front protective sheets  106  and  108  sealing the module. 
         [0031]    As shown in  FIG. 4C , after the lamination process, the treated zone  125  at the edge section  107 B of the module  100  may be formed at a module edge preparation station  200 C. As shown in  FIG. 5A  in one embodiment, a number of holes  130 A formed through the treated zone  125 . As shown in  FIG. 5B , The treated zone  125  may include one or more fasteners  130 B attached to the treated zone  125 , such as clamps or the like to assist mounting the solar module on a support. As shown in  FIG. 5C , the treated zone  125  may include rails  130 C or the like protruding structures that can be held by a support structure or support structure components. 
         [0032]    Although aspects and advantages of the present inventions are described herein with respect to certain preferred embodiments, modifications of the preferred embodiments will be apparent to those skilled in the art. The scope of the present invention should not be limited to the foregoing discussion but should be defined by the appended claims.