Abstract:
A thin film photovoltaic module that is connectable to a terminal includes a first glass sheet defining a sun facing surface and a second glass sheet defining a back facing surface opposite the front side surface. The second glass sheet includes a feed-though opening extending through the second glass sheet. A photovoltaic material is between the first glass sheet and the second glass sheet. An encapsulant material is between the first glass sheet and the second glass sheet that bonds the first glass sheet and the second glass sheet together and seals the photovoltaic material from moisture. A conductor is electrically connected to the photovoltaic material at one end. The conductor passes through the feed-though opening. A reinforcing member is disposed on the sun facing surface of the first glass sheet. The reinforcing member has a footprint hanging over at least a portion of the feed-through opening.

Description:
FIELD 
       [0001]    The present specification generally relates to photovoltaic modules, and more particularly to photovoltaic modules that include reinforcing members for reducing stresses in the photovoltaic modules. 
       BACKGROUND 
       [0002]    Photovoltaic modules often use light energy (photons) from the sun to generate electricity through a photovoltaic effect. A thin film photovoltaic module typically consists of two pieces of glass that are laminated together using a thin sheet of polymeric material. One of the glass members has photovoltaic materials deposited onto its surface. Photovoltaic modules should be constructed to endure various environmental conditions that cause stresses in the glass members. Accordingly, reinforcing structures are needed for reducing stresses in the glass members. 
       SUMMARY 
       [0003]    In one embodiment, a thin film photovoltaic module that is connectable to a terminal includes a first glass sheet defining a sun facing surface and a second glass sheet defining a back facing surface opposite the front side surface. The second glass sheet includes a feed-though opening extending through the second glass sheet. A photovoltaic material is between the first glass sheet and the second glass sheet. An encapsulant material is between the first glass sheet and the second glass sheet that bonds the first glass sheet and the second glass sheet together and seals the photovoltaic material from moisture. A conductor is electrically connected to the photovoltaic material at one end. The conductor passes through the feed-though opening. A reinforcing member is disposed on the sun facing surface of the first glass sheet. The reinforcing member has a footprint hanging over at least a portion of the feed-through opening. 
         [0004]    In another embodiment, a thin film photovoltaic module that is connectable to a terminal includes a first glass sheet defining a sun facing surface and a second glass sheet defining a back facing surface opposite the front side surface. The second glass sheet includes a feed-though opening extending through the second glass sheet. A photovoltaic material is between the first glass sheet and the second glass sheet. An encapsulant material is between the first glass sheet and the second glass sheet that bonds the first glass sheet and the second glass sheet together and seals the photovoltaic material from moisture. The feed-through opening defining an unbonded region between the first glass sheet and the second glass sheet. A conductor is electrically connected to the photovoltaic material at one end. The conductor passes through the feed-though opening. A reinforcing member is disposed on the sun facing surface and extends into the unbonded region of the first glass sheet. 
         [0005]    In another embodiment, a method of reducing bending stresses in a thin film photovoltaic module comprising a first glass sheet defining a sun facing surface, a second glass sheet defining a back facing surface opposite the front side surface and a photovoltaic material between the first glass sheet and the second glass sheet is provided. The method includes providing the second glass sheet with a feed-though opening extending through the second glass sheet through which a conductor passes. The first glass sheet and the second glass sheet are bonded together with an encapsulant material between the first glass sheet and the second glass sheet thereby sealing the photovoltaic material from moisture. A reinforcing member is disposed on the sun facing surface of the first glass sheet such that the reinforcing member has a footprint hanging over at least a portion of the feed-through opening. 
         [0006]    Additional features and advantages of the claimed subject matter will be set forth in the detailed description which follows, and in part, will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings. 
         [0007]    It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a side section view of an embodiment of a photovoltaic module; 
           [0009]      FIG. 2  is a quarter section perspective view of the photovoltaic module of  FIG. 1 ; 
           [0010]      FIG. 3  is a quarter section perspective view of the photovoltaic module of  FIG. 1 ; 
           [0011]      FIG. 4  is a quarter section perspective view of the photovoltaic module of  FIG. 1  with an embodiment of a reinforcing member; and 
           [0012]      FIG. 5  illustrates an exemplary reinforcing member footprint of the reinforcing member of  FIG. 4  on a sun facing surface laid over an opening footprint of a feed-through opening on the sun facing surface. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Embodiments described herein generally relate to thin film photovoltaic modules including reinforcing features that serve to reduce stresses that occur in glass sheets, for example, due to an impact. For example, International Electrotechnical Commission (IEC) document 61646, “Thin-Film Terrestrial Photovoltaic (PV) Modules—Design Qualification and Type Approval,” incorporated herein by reference, states that a thin film photovoltaic module must withstand impacts by one-inch diameter ice balls projected in a direction perpendicular to the photovoltaic module face at a speed of 23 m/s (51 mph). The reinforcing features help reduce the stresses in the glass sheets due to such an impact to prevent any breakage. 
         [0014]    Referring to  FIG. 1 , a section view of a photovoltaic module  10  includes a relatively thin glass sheet  12  (e.g., less than about one mm, such as 0.7 mm) forming a sun facing surface  14 . The glass sheet  12  may be a specialty glass commercially available from Corning Incorporated. The photovoltaic module  10  further includes a thicker glass sheet  16  (e.g., greater than one mm, such as 3.2 mm) forming a back facing surface  18  that faces opposite the sun facing surface  14 . The glass sheet  16  may be a soda lime glass that may or may not be heat strengthened. In another embodiment, the glass sheet  16  may be replaced with a specialty glass also commercially available from Corning Incorporated, which may be thinner than 3.2 mm. For example, the glass sheet  12  and the glass sheet  16  may have about the same thicknesses. Photovoltaic materials (represented by element  20 ) are located between the glass sheet  12  and the glass sheet  16 . In some embodiments, the photovoltaic materials are deposited on an internal side  22  of the glass sheet  12 . A central polymeric layer  24 , called the encapsulant or interlayer, may be provided between the glass sheets  12  and  16 . The encapsulant layer  24  may serve two purposes: First, it can bond the two glass sheets  12  and  16  together into one structural member. Second, the encapsulant layer  24  can seal the photovoltaic materials  20  that are sandwiched between the two glass sheets  12  and  16  from moisture ingress over the expected life of the photovoltaic module  10 , which can be 30 years or more. 
         [0015]    The encapsulant material used for thin film photovoltaic modules  10  may be ethylene vinyl acetate (EVA) or polyvinyl butyral (PVB), as examples. These materials may be in solid sheet form with a thickness of approximately 0.4 mm to 0.76 mm. The three components (glass with PV/encapsulant/cover glass) may be stacked and placed into an autoclave oven during formation of the photovoltaic module  10 . The assembly may be first heated to sufficient temperature to melt the encapsulant layer  24  and evacuated to remove air and moisture. A press force may be applied to the stacked assembly so that the melted encapsulant material fills void regions between the glass sheets  12  and  16 . The encapsulant layer  24  solidifies as the assembly is cooled. 
         [0016]    Referring to  FIG. 2 , a quarter section of the photovoltaic module  10  is shown and may include conductors  26  and  28  (e.g., wires) are in contact with the photovoltaic materials  20  and are used to carry the power generated by the photovoltaic materials  20  to devices that process the power into a useable form. A feed-through opening  30  may be provided in a centralized region of the glass sheet  16  (as opposed to an edge of the glass sheet  16 ) so that the conductors  26  and  28  may pass out of the photovoltaic module  10  (e.g., to be connected to a terminal). The feed-through opening  30  may be provided in the centralized region of the glass sheet  16  such that the relatively delicate conductors  26  and  28  can be protected with a junction box or other protective cover. 
         [0017]    Providing a feed-through opening  30  through the glass sheet  16  provides an unbonded region  32  between the glass sheet  12  and the glass sheet  16 . For example, for a radiused opening sidewall  34 , the unbonded region  32  begins at an inner opening edge  36  where the glass sheet  16  is bonded to the glass sheet  12 . Referring briefly to  FIG. 3 , a potting material  38  may be used to fill the feed through opening  30  through the glass sheet  16 . The potting material  38  may have material properties selected to support and stiffen the glass sheet  12  in the unbonded region  32  defined by the feed-through opening  30  to improve the reliability of the photovoltaic module  10 . 
         [0018]    As can be appreciated, presence of the unbonded region  32  and absence of the glass sheet  16  in this unbonded region  32  can leave the glass sheet  12  providing the sun facing surface  14  vulnerable to stresses, particularly impact stresses since the glass sheet  12  may take the brunt of the impact and bending loads at the unbonded region  32 . Referring now to  FIG. 4 , a reinforcing member  40  is disposed on the sun facing surface  14  of the glass sheet  12 . The reinforcing member  40  covers at least a portion of the feed-through opening  30 , extending into the unbonded region  32  between the glass sheet  12  and the glass sheet  16 . The reinforcing member  40  may be a flat glass sheet material, for example, of specialty glass commercially available from Corning Incorporated. The thickness of both the glass sheet  12  and the reinforcing member  40  may be determined by economics and product reliability requirements. The thickness of the reinforcing member  40  may chosen to significantly increase the rigidity of the photovoltaic module  10  while keeping the reinforcing member thickness to a reasonably small value and therefore low cost and low profile height above the sun facing surface  14  of the glass sheet  12 . The thickness of the glass sheet  12  and that of the reinforcing member  40  may be about the same, such as about 0.7 mm. 
         [0019]    An adhesive layer  42  may be used to attach the reinforcing member  40  to the sun facing surface  14  of the glass sheet  12 . The adhesive material of the adhesive layer  42  may have a small thickness as well as a modulus of elasticity large enough that there is a relatively low amount of shear deformation occurring within the cross-section of the adhesive layer  42 . The large modulus of elasticity for the adhesive layer  42  may be selected such that the glass sheet  12  and the reinforcing member  42  act nearly as if they were one single piece of glass with a thickness equal to the sum of the glass sheet  12  and the reinforcing member  40  plus the thickness of the adhesive layer  42 . Even if the adhesive material selected has a relatively low modulus of elasticity, the assembly can behave as if it were two pieces of glass allowed to slide relative to each other, and the reinforcing member  40  can still act to stiffen the assembly and reduce the bending that occurs in the glass sheet due to an impact force, thereby improving reliability. 
         [0020]      FIG. 5  illustrates an exemplary reinforcing member footprint  50  of the reinforcing member  40  on the sun facing surface  14  laid over an opening footprint  52  of the feed-through opening  30  on the sun facing surface  14 . The reinforcing member footprint  50  should significantly overlap the opening footprint  52  over the entire area of the opening footprint  52  in order to adequately limit bending distortion of the glass sheet  12  upon an impact force applied at a location corresponding to a center C of the feed-through opening  30 . For example, the overlap distance may be at least  3  times the thickness of the reinforcing member  40 . In some embodiments, the reinforcing member footprint  50  may have an area that is larger than an area of the opening footprint  52 . In these embodiments, the reinforcing member footprint  50  may overlie the entire opening footprint  52 . 
         [0021]    When selecting the reinforcing member  40  and the adhesive layer  42 , various attributes may be considered. The resulting modulus of elasticity (Young&#39;s modulus) of the adhesive material after the material has cured may be considered. A high modulus of elasticity (e.g., of at least about 3 MPa) may be desired. The thicknesses of the reinforcing member  40  and the adhesive layer  42  may be kept small in order to keep the height of the reinforcement member  40  as compact as possible. Higher profiles of the reinforcing member  40  are more likely to be impacted during module installation, for example. Higher profiles of the reinforcing member  40  also tend to more readily collect debris when the photovoltaic module  10  is in use, thereby blocking sun exposure and reducing module efficiency. The adhesive strength may be as high as possible. The optical transmittance of the adhesive layer  42  (and the reinforcing member  40 ) should be as high as possible (e.g., a hemispherical transmittance of at least about 85 percent over an optical wavelength range of 400 nanometers to 1100 nanometers) in order to minimize loss of sun energy exposing the PV material. The photovoltaic module  10  may be mounted outdoors and can experience a variety of environmental conditions, and the potting material must withstand these conditions and still serves its functions for the life of the photovoltaic module  10 . The adhesive material may be selected to resist yellowing when exposed to UV light over long durations. As one example, the adhesive used to attach the reinforcing member  40  to the photovoltaic module  10  may be Dow Corning model PV-6100 which has excellent adhesive, durability, and energy transmission properties. The thickness of this adhesive layer  42  may be for example, 0.1 to 0.5 mm thick. 
         [0022]    The above-described thin film photovoltaic (PV) modules  10  include a feed-through opening  30  that serves the purpose of allowing electrical conductors to pass from the photovoltaic material layer externally to a point outside the module, in which an additional reinforcing member  40  (e.g., formed of glass) that is significantly larger than the diameter of the feed-through opening  30  is attached with an adhesive to the sun facing surface  14  of the glass sheet  12 . This reinforcing member  40  can serve to stiffen the sun side glass sheet  12  in the unbonded region of the feed-through opening, thereby reducing bending stresses that occur in the sun side glass when impacted with an ice ball (or hail) and subsequently improving the reliability of the module. The additional reinforcing member  40  and the adhesive layer  42  which is used to attach it to the glass sheet  12  both have optical transmitting properties such that a negligible reduction in sun power is delivered to the thin film PV materials. The tensile stress levels in the glass sheet  12  can be reduced by a factor of  10 . 
         [0023]    It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein, provided such modification and variations come within the scope of the appended claims and their equivalents.