Abstract:
Methods and systems for photovoltaic roofing systems are provided. The system includes a back sheet including a length, L, a width, W, and a thickness, T, the back sheet including an overlap portion extending along length L having a width, WO and an active portion extending along length L having a width, WA. The system also includes a photovoltaic cell formed on a surface of the active portion, the photovoltaic cell including a photovoltaic member electrically responsive to an absorption of photons, a negative electrode coupled to a surface of the photovoltaic member, and a positive electrode coupled to the surface of the photovoltaic member, wherein the thickness T is selected such that thickness T plus a thickness of the photoelectric cell substantially match a thickness of a proximate non-photovoltaic roofing member when the photovoltaic roofing system is installed.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to integrated photovoltaic roofing systems, and more specifically to methods and systems for roofing shingles having photovoltaic modules integrated into the shingle. 
     At least some known roofing systems with asphalt roofs mount directly on top of the existing shingles. Other known roofing systems replace the roofing tiles with an area that looks like a black or blue area covering a portion of the roof. Such products are often advertised as being photovoltaic cells “integrated” into a shingle roof but the photovoltaic cells are simply surrounded by standard asphalt roofing tiles. However, such roofing systems lack flexibility in design or construction methods to allow the various colors and shapes that are necessary to match the various product lines available in the asphalt roofing market to provide the aesthetic appeal needed for a residential rooftop photovoltaic solar system. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment, a photovoltaic roofing system includes a back sheet including a length, L, a width, W, and a thickness, T, the back sheet including an overlap portion extending along length L having a width, W O  and an active portion extending along length L having a width, W A . The system also includes a photovoltaic cell formed on a surface of the active portion, the photovoltaic cell including a photovoltaic member electrically responsive to an absorption of photons, a negative electrode coupled to a surface of the photovoltaic member, and a positive electrode coupled to the surface of the photovoltaic member, wherein the thickness T is selected such that thickness T plus a thickness of the photoelectric cell substantially match a thickness of a proximate non-photovoltaic roofing member when the photovoltaic roofing system is installed. 
     In another embodiment, a method of assembling a photovoltaic roofing system includes providing a substrate of roofing material including a top surface, a bottom surface and an edge extending therebetween about an outer periphery of the substrate, the substrate includes an overlay portion configured to be covered by at least one of an adjacent photovoltaic roofing system and an adjacent roofing shingle, the substrate further includes an active portion, forming a photovoltaic cell on the top surface of the active portion, the photovoltaic cell including a photovoltaic member electrically responsive to an absorption of photons, a negative electrode coupled to a surface of the photovoltaic member, and a positive electrode coupled to the surface of the photovoltaic member, and electrically coupling the negative electrode and the positive electrode to an electrical plug extending from the edge. 
     In yet another embodiment, a photovoltaic roofing system includes a back sheet including a first thickness, the back sheet including an overlap portion, a header portion configured to permit the roofing assembly to be coupled to a roof surface, and an adjacent active portion extending from the overlap portion, the active portion including a plurality of tab portions, a photovoltaic cell formed on a surface of each the tab portions, the photovoltaic cell including a second thickness, the photovoltaic cell further including a photovoltaic member, a negative electrode coupled to a surface of the photovoltaic member, and a positive electrode coupled to the surface of the photovoltaic member, wherein the first thickness plus the second thickness is substantially equal to a thickness of a proximate non-photovoltaic roofing member when the photovoltaic roofing system is installed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a roof including a plurality of exemplary photovoltaic roofing systems in accordance with an embodiment of the present invention; and 
         FIG. 2  is an exploded view of an exemplary photovoltaic cell that may be used with photovoltaic roofing systems shown in  FIG. 1 ; 
         FIG. 3  is a perspective view of the photovoltaic cell shown in  FIG. 2  after assembly; 
         FIG. 4  is an exploded view of the exemplary photovoltaic roofing system shown in  FIG. 1 ; 
         FIG. 5  is a perspective view of a photovoltaic roofing system in accordance with an embodiment of the present invention; 
         FIG. 6A  is an exploded perspective view of the photovoltaic roofing system in accordance with another embodiment of the present invention; 
         FIG. 6B  is a perspective view of the photovoltaic roofing system in accordance with another embodiment of the present invention; and 
         FIG. 7  is an exploded view of an exemplary embodiment of an electrically active shingle tab assembly shown in  FIGS. 6A and 6B . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a perspective view of a roof  100  including a plurality of exemplary photovoltaic roofing systems  102  in accordance with an embodiment of the present invention. A plurality of non-photovoltaic roofing shingles  104  are mixed in combination with the photovoltaic roofing systems  102  to form roof  100 . In  FIG. 1 , photovoltaic roofing systems  102  are shown darker than non-photovoltaic roofing shingles  104  for illustration only. In the exemplary embodiment, photovoltaic roofing systems  102  are colored to match non-photovoltaic roofing shingles  104 . Although non-photovoltaic roofing shingles are described herein as “shingles”, they may be more complex assemblies than typical roofing shingles, for example, non-photovoltaic roofing shingles may include a plurality of components and may lay flat on roof  100 , or may be textured or shaped to a particular feature. Photovoltaic roofing system  102  is configured to match a color, shape, and/or texture of non-photovoltaic roofing shingles  104  such that an aesthetic look is achieved. Additionally, a thickness of photovoltaic roofing systems  102  is selected to substantially match the thickness of non-photovoltaic roofing shingles  104  such that a profile difference between non-photovoltaic roofing shingles  104  and photovoltaic roofing systems  102  is essentially indiscernible. 
       FIG. 2  is an exploded view of an exemplary photovoltaic cell  200  that may be used with photovoltaic roofing systems  102  (shown in  FIG. 1 ). Photovoltaic cell  200  includes a waffle grid pattern  202  that is exposed to the sun when photovoltaic cell  200  is in operation. A molded wafer of photovoltaic material  204  is positioned on waffle grid pattern  202 . A first side  206  adjacent waffle grid pattern  202  is exposed to the sun during operation through opening  208  formed in waffle grid pattern  202 . A front contact wrap through layer  210  is applied to a second side  212  of photovoltaic material  204 . Front contact wrap through layer  210  is configured to provide a plurality of connection points  214  on second side  212  for connection to electrical bussing that will transmit the output of photovoltaic material  204  external to photovoltaic cell  200 . A back contact bussing  216  is coupled to a cathode portion of photovoltaic material  204 . A back field layer  218  and a dielectric layer  220  are applied over photovoltaic material  204  with openings  222 ,  224  that are complementary to front contact wrap through layer  210  and back contact bussing  216 , respectively such that front contact wrap through layer  210  and back contact bussing  216  are exposed through back field layer  218  and dielectric layer  220 . In the exemplary embodiment, back field layer  218  is fabricated from a metal ink, for example, but not limited to, aluminum or copper. A front contact bussing  226  is applied over dielectric layer  220  such that legs  228  of front contact bussing  226  are arranged to cover openings  222  and make connection to photovoltaic material  204  through connection points  214 . In the exemplary embodiment, connection points  214  are coupled to photovoltaic material  204  at cathode sites on photovoltaic material  204  such that front contact bussing is negatively charged during operation and back contact bussing  216  is coupled to photovoltaic material  204  at anode sites such that back contact bussing  216  is positively charged during operation. In an alternative embodiment, the polarity of back contact bussing  216  and front contact bussing  226  may be reversed during operation by coupling them to cathode sites and anode sites respectively. Both bus systems are coupled to a single side of photovoltaic material  204 , and in the exemplary embodiment, it is the side opposite of the side that receives the sunlight to provide the motive force for electron flow in photovoltaic material  204 . 
       FIG. 3  is a perspective view of photovoltaic cell  200  (shown in  FIG. 2 ) after assembly. Front contact bussing  226  is electrically connected to photovoltaic material  204  through connection points  214  coupled to side  212  of photovoltaic material  204 . Connection points  214  are exposed to front contact bussing  226  through openings  222  in dielectric layer  220  and back field layer  218 . Back contact bussing  216  is electrically connected to photovoltaic material and is exposed through openings  224  in dielectric layer  220  and back field layer  218 . In the exemplary embodiment, both front and back contact bussing  226 ,  216 , respectively are electrically coupled to the same side of photovoltaic material  204 . 
       FIG. 4  is an exploded view of an exemplary photovoltaic roofing system  102  (shown in  FIG. 1 ). Photovoltaic roofing system  102  includes a back sheet  402  comprising for example, a polyvinyl fluoride (PVF) film. An interconnection portion  404  permits a plurality of electrical wires to couple one or more photovoltaic cells to each other or to an electrical plug connection  406 . An encapsulation portion  408  permits the electrical wires and plug connection  406  to be sealed from ambient. In the exemplary embodiment, a header portion  410  is configured to receive one or more fasteners for affixing photovoltaic roofing system  102  to a roof. In the exemplary embodiment, photovoltaic roofing system  102  includes a first ethylene-vinyl acetate (EVA) layer  412  applied to an active portion  414  of back sheet  402 . One or more photovoltaic cells  200  are positioned on EVA layer  412  such that an edge of EVA layer  412  extends beyond an edge of photovoltaic cell  200  on all four sides. A second EVA layer  416  is applied to photovoltaic cell  200  such that the edges of second EVA layer  416  extend beyond the edges of photovoltaic cell  200  and substantially match the edges of first EVA layer  412 . In the exemplary embodiment, the edges of first EVA layer  412  and second EVA layer  416  are sealed to form a hermetic environment within first EVA layer  412  and second EVA layer  416  and surrounding photovoltaic cell  200 . Photovoltaic roofing system  102  includes a protective layer  418  such as solar glass. Production techniques used in the manufacture of photoelectric sensitive material  204  are selected such that the color of photovoltaic roofing system  102  as finally assembled is configured to match a non-photovoltaic roofing shingle or system that is positioned adjacent photovoltaic roofing system  102 . 
       FIG. 5  is a perspective view of a photovoltaic roofing system  102  in accordance with an embodiment of the present invention. Photovoltaic roofing system  102  includes back sheet  402  having a length and a width W O . In this embodiment, back sheet  402  includes one or more notches  501  defined by a slit or cutout through back sheet  402  and extending at least partially through a width W A  of active portion  414  to divide active portion  414  into a plurality of tabs  503 . In various other embodiments, back sheet  402  does not include notches  501 . Photovoltaic roofing system  102  also includes active portion  414 , and an overlay portion  502  on back sheet  402 . Overlay portion includes interconnection portion  404 , encapsulation portion  408 , header portion  410 , and plug connection  406 . Plug connection  406  extends from an upper edge  504  or lower edge  505  with respect to the pitch of the rrof such that electrical connections are made to other assemblies  200  above or below each assembly  200 . Waffle grid pattern  208  is exposed to the sun on an upper surface of back sheet  402 . Interconnection portion  404  includes a plurality of electrical traces or wires that carry electrical current from photovoltaic material  204  to plug connection  406 . 
       FIGS. 6A and 6B  are perspective views of photovoltaic roofing system  600  in accordance with another embodiment of the present invention.  FIG. 6A  is an exploded view with respect to  FIG. 6B . Photovoltaic roofing system  102  includes a roofing membrane  602  configured to extend under the entire photovoltaic roofing system  600  assembly and also includes a header portion  604 . In the exemplary embodiment, roofing membrane  602  does not include cutouts for separating shingle tabs. The tab “look” is achieved by spacing a plurality of electrically active shingle tab assemblies  606  with a gap  608  between assemblies  606  and along a roofing membrane edge  610 . Electrically active shingle tab assembly  606  is coupled to roofing membrane  602  such as by using an adhesive to affix tab assembly  606  to roofing membrane  602 . Interconnect wiring  612  connects electrically active shingle tabs  606  together in series with a plug assembly  614 . Interconnect wiring  612  is sandwiched between a stiffener  616  and roofing membrane  602  using an adhesive encapsulant. Stiffener  616  extends above interconnect wiring  612  and is used with header portion  604  as a nailing header for fastening photovoltaic roofing system  600  to a roof. Two rows of nails may be used, similar to standard roofing shingle installations. Plug assembly  614  includes a small wire extending downward from the middle of plug assembly  614 , which connects assembly  606  to the next row down on the roof. Once assembled on the roof, plug assembly  614  is completely covered by the shingle tab from the row above. 
       FIG. 7  is an exploded view of an exemplary embodiment of an electrically active shingle tab assembly  606  (shown in  FIGS. 6A and 6B ). In the exemplary embodiment, tab assembly  606  includes roofing membrane  602 , a first encapsulant layer  702  fabricated from for example, ethylene-vinyl acetate (EVA). An interconnection portion  704  permits a plurality of electrical wires to couple one or more photovoltaic cells to each other or to an electrical plug connection (not shown). A front contact bussing structure  706  is electrically coupled to interconnection portion  704 . A dielectric layer  708  is applied over front contact bussing structure  706  and a back field layer  710  is applied over dielectric layer  708 . Openings  712  in dielectric layer  708  and back field layer  710  facilitate electrical connection through dielectric layer  708  and back field layer  710 . Back contact bussing  714  and a front contact wrap through layer  716  is exposed to front contact bussing structure  706  through openings  712 . A molded wafer of photovoltaic material  718  is positioned over front contact wrap through layer  716  and an optional waffle grid pattern  720  is applied over photovoltaic material  718 . A first side  722  of waffle grid pattern  720  is exposed to the sun during operation through a plurality of openings  724  formed in waffle grid pattern  720 . A second encapsulant layer  726  fabricated from for example, ethylene-vinyl acetate (EVA) is applied over waffle grid pattern  720 , if used, and sealed to first encapsulant layer  702  to form a hermetic environment therebetween. A protective layer  728  such as solar glass is applied over second encapsulant layer  726 . 
     Exemplary embodiments of photovoltaic roofing systems and are described above in detail. The photovoltaic roofing system components illustrated are not limited to the specific embodiments described herein, but rather, components of each photovoltaic roofing system may be utilized independently and separately from other components described herein. For example, the photovoltaic roofing system components described above may also be used in combination with different photovoltaic roofing system components. 
     The above-described photovoltaic roofing systems and methods are cost-effective and highly reliable. The method permits maintaining the aesthetic appeal of a shingle type roof using both photovoltaic and non-photovoltaic roofing systems in adjacent position with respect to each other. A thickness of each roofing system is configured to match giving an even profile when viewed by a user. The appearance and profile permits using the above described photovoltaic roofing system with a variety of non-photovoltaic roofing systems with a minimum of obvious aesthetic differences between the two systems. Accordingly, the systems and methods described herein facilitate the operation of photovoltaic roofing systems in a cost-effective and reliable manner. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.