Roof mounting bracket for photovoltaic power generation system

[0035]Referring to the drawings, wherein like reference numerals represent like parts throughout the various drawing figures, reference numeral 10 is directed to a bracket (FIGS. 1 and 2) for a roof mounted photovoltaic power generation system. The brackets 10 are provided in pairs 12 (FIG. 3) which together support a photovoltaic cell 102 stack assembly to form a panel 100 (FIG. 9). The panel 100 can act similar to a shingle S (FIG. 13) upon the roof R to shed water and protect structural portions of the roof. The brackets 10 interlock together laterally and vertically while accommodating airflow therebeneath for cooling. The brackets also accommodate thermal expansion and have edge details to facilitate airflow and to provide water preclusion. The brackets are also configured to facilitate interconnection of an electric subsystem 110 for combining adjacent panels 100 together as part of the overall photovoltaic power generation system.

[0036]In essence, and with particular reference to FIGS. 1-3, basic details of the bracket 10 are described. The bracket 10 is typically utilized in pairs 12 (FIG. 3) as a structural portion of a panel 100 (FIG. 9) also supporting photovoltaic cell 102 stack assemblies thereon. The brackets 10 each include a mounting rail 20 at an upper side and a bottom rail 50 at a lower side. A cell support structure 30 is interposed between the mounting rail 20 and bottom rail 50. A lateral joint 40 defines lateral sides of each bracket 10. The lateral joint 40 is configured so that it can interface with lateral edges of adjacent brackets 10 for lateral interconnection of multiple brackets 10, either of a common panel 100 (where the joint 40 is an expansion joint 14 (FIGS. 3 and 9) in the middle of the panel 100) or lateral interconnection of adjacent panels 100.

[0037]An air circulation system 60 routes air beneath the brackets 10 so that by natural convection air can be circulated beneath the brackets 10 and cool the brackets 10 and associated photovoltaic cell stack assemblies 102. An end piece 70 (FIGS. 3, 4, 9-11 and 13) is provided adjacent the bottom rail of a lowest bracket in a series of vertically spaced brackets 10. The end piece 70 holds up this lower side of the lowermost bracket so that air can pass beneath the bracket 10 and be routed beneath the series of brackets 10 for cooling. Edge flashing 80 (FIGS. 12 and 13) is provided so that water is prevented from migrating around the brackets 10 or panels 100 laterally. A J-box 90 (FIG. 8) is provided for each panel 100 to combine power from photovoltaic cells 102 of each panel 100 and allow the power from each panel 100 to be combined together into strings which can then be routed to a combiner box before being passed on to an inverter 140 and subpanel 130 for effective utilization of the electric power from the system. An electric subsystem 110 (FIG. 14) is described which utilizes the panels 100 formed of brackets 10 according to this system.

[0038]More specifically, and with particular reference to FIGS. 1-3, specific details of the bracket 10 are described, according to a preferred embodiment. Each bracket 10 is preferably similar in form and in this preferred embodiment is comprised of a mounting rail 20 (FIGS. 1 and 2), a cell support structure (FIGS. 1 and 2), a lateral joint (FIG. 5) and a bottom rail 50 (FIGS. 1, 2 and 7). Each bracket 10 most preferably provides only half of the structural under support for a panel 100 (FIG. 9). Thus, a pair 12 of brackets 10 are provided together along with the photovoltaic cells 102 within a stack assembly to complete the panel 100 (FIG. 3). In this way, an expansion joint 14 (FIG. 3) is provided between the two brackets 10 within each pair 12. Note that the expansion joint 14 is the same as the lateral joint 40 with different terminology used depending on whether the brackets 10 are coming together at a midpoint within a panel 100 or at a lateral edge of a panel 100 where adjacent panels 100 are joined together laterally.

[0039]An upper side of each bracket 10 is defined by the mounting rail 20. The mounting rail 20 provides a preferred form of mounting portion for the bracket 10. This mounting rail 20 preferably includes a planar surface 22 with holes 24 passing therethrough for fasteners to pass and then penetrate the roof R. Preferably, a recess 26 surrounds each hole 24 to provide relief into which a head of the fastener can reside, such as the head of a roofing nail, or the head of a fastening screw.

[0040]A perimeter skirt 28 preferably surrounds at least an upper edge of the planar surface 22 of the mounting rail 20. The perimeter skirt 28 preferably extends perpendicularly down from the planar surface 22. Gussets 29 are preferably formed beneath the planar surface 22 to provide structural support and rigidity to the mounting rail 20 (FIG. 2). The perimeter skirt 28 also helps to rigidify the bracket 10.

[0041]The mounting rail 20 is typically covered by a bottom rail 50 of a higher adjacent similar bracket 10 of a separate higher adjacent panel 100 (FIGS. 7 and I1). However, a highest panel 100 will be formed of brackets 10 which have mounting rails 20 which are not covered by adjacent brackets 10 or panels 100. Instead, the highest panels 100 will have their mounting rails 20 typically covered by shingles placed on the roof R and allowed to have lower shingle edges overlap the mounting rail 20 portion of the bracket 10. If desired, a tapering piece of filler material can be provided directly above this highest bracket so that rather than having a somewhat abrupt transition in thickness at the perimeter skirt 28 of the mounting rail 20, a more gradual transition to greater thickness can be provided.

[0042]Most preferably, this perimeter skirt 28 is kept ventilated so that air circulating beneath the brackets 10 can escape out of the perimeter skirt 28, such as through gaps 58 (FIG. 2). In a preferred form of the invention, this highest row of brackets 10 are near a ridge of the roof and a ridge vent is provided which overlaps the mounting rail 20 portion of the bracket 10 and allows air circulating beneath the brackets 10 to escape. Such ridge vents are known in the composition shingle roofing construction trades.

[0043]The cell support structure 30 is provided below the mounting rail 20 and extending down to the bottom rail 50. This cell support structure 30 is generally formed of a series of vertical ribs 32 and at least one lateral rib 34 extending substantially perpendicular to the vertical ribs 32. A perimeter deck 36 surrounds a perimeter of this cell support structure space with the perimeter deck 36 generally planar with upper sides of the vertical ribs 32 and lateral rib 34. A trough 38 (FIG. 5) preferably is formed in the perimeter deck 36 and defines a slightly recessed depression in the perimeter deck 36. This trough 38 can accommodate adhesive to hold the photovoltaic cell 102 stack assembly within the cell support structure 30 space and against the perimeter deck 36 (FIG. 7). A lip 39 defines a lowermost edge of the cell support structure 30 and acts as a barrier to keep the photovoltaic cell 102 stack assembly from migrating downward out of the cell support structure 30 space.

[0044]The cell support structure 30 of the bracket 10 adds some rigidity to the overall panel 100 when two brackets 10 are provided laterally together along with a photovoltaic cell 102 stack assembly. However, the photovoltaic cell 102 stack assembly also adds rigidity and strength to the resulting panel 100. Windows between adjacent vertical ribs 32 and lateral rib 34 are open until covered by the photovoltaic cell 102 stack assembly. With such a rib cell support structure 30, the overall bracket 10 has a minimum of material and thus maintains light weight while still providing strength where required to keep the panel 100 sufficiently strong to resist weight loads, such as from snow loading or from maintenance personnel walking on the panels 00.

[0045]The lateral joint 40 (FIG. 5) is formed of an over tab 42 on one lateral side of the bracket 10 and an under tab 46 on the other lateral side of the bracket 10. The over tab 42 and under tab 46 fit together with the over tab 42 over the under tab 46. A cell support plane 41 is defined above the lateral joint 40 formed of the photovoltaic cell 102 stack assembly which rests upon this cell support plane 41.

[0046]The over tab 41 extends to a tip 43. The tip 43 extends primarily upward from the trough 38, but also extends slightly downward to a heel 44. The heel 44 rests within an expansion slot 49 formed on a shelf 48 of the under tab 46. A perimeter wall 47 is located beneath the shelf 48 and helps support the shelf 48. The heel 44 can ride within this expansion slot 49 some distance to allow for lateral motion therebetween (along arrow B of FIGS. 3 and 5), such as to decrease spacing when temperatures increase and increase spacing when temperatures decrease. Such lateral expansion and contraction across the lateral joints 40 and expansion joint 14 (FIG. 3) allows the brackets 10 to accommodate temperature changes without damaging the panels 100 or causing the system to fail. In one embodiment the lateral joint 40 is formed with the heel 44 in a middle of the expansion slot 49 with the brackets 10 and other portions of the panel 100 substantially at room temperature. In this way, the bracket 10 and panel 100 can undergo thermal expansion or contraction away from room temperature either in a cooling direction or a heating direction and the heel 44 will have room to move in either direction within the expansion slot 49 before damage will occur to the brackets 10 or the panel 100.

[0047]Preferably, the lateral joint 40 (and expansion joint 14) are not fitted with any adhesive, but rather are allowed to float relative to each other. Both the over tab 42 and under tab 46 are able to shed water in a downward direction while overlapping each other, such that water is prevented from migrating beneath the bracket 10 around or through this lateral joint 40. When configured as the expansion joint 14, the photovoltaic cell 102 stack assembly further covers the expansion joint 14 to resist water migration therethrough except at the mounting rail 40 (FIGS. 3 and 9).

[0048]The bottom rail 50 defines a lowermost portion of each bracket 10 (see particularly FIG. 2). The bottom rail 50 includes an edge wall 52 defining an extreme lower side of each bracket 10. Feet 53 (FIG. 7) define an underside of the bottom rail 50 which are configured to rest upon the mounting rail 20 of an adjacent lower bracket 10 and most particularly just below the mounting rail 20 and over the cell support structure 30 as well as over the photovoltaic cells 102 of the stack assembly of the next lower panel 100 (FIG. 7). In such an arrangement, thermal expansion and contraction can be accommodated (along arrow C of FIG. 7) by sliding of the feet 53 up or down along the pitch of the roof R (horizontally in FIG. 7).

[0049]The bottom rails 50 are configured not to rest on the roof R directly, but rather to rest upon an adjacent lower bracket 10. A wind clip 55 defines a portion of the underside of each bracket 10 adjacent the bottom rail 50. These wind clips 55 are preferably in the form of elongate rigid structures extending downwardly as a portion of an underside of each vertical rib 32. These wind clips 55 are configured so that they can rest on the roof R and fit within the gaps 58 of the perimeter skirt 28 in the mounting rail 20 of the next lower bracket 10. In this way, the bottom rail 50 of each bracket 10 is held down by the mounting rail 20 of the next lower bracket 10.

[0050]The wind clip 55 includes a clearance space 56 above each wind clip 55. A step 57 defines an abutment which can be provided on every other rib 32, rather than a wind clip 55, and help to keep the brackets 10 aligned adjacent each other. Preferably, the brackets 10 are not placed with the steps 57 abutting the mounting rails 20 when installed, but rather with a small gap therebetween to accommodate some thermal expansion that would tend to drive adjacent brackets 10 against each other. The bottom rail 50 also preferably includes stiffeners 59 in the form of horizontal and vertical ribs adjacent the bottom rail 50 to help strengthen the bottom rail 50 and also supporting the feet 53 of the bottom rail 50. The gaps 58 (FIG. 2) in the perimeter skirt 28 of the mounting rail 20 are sized to receive the wind clips 55 therein, while also providing openings for air circulation therethrough.

[0051]With particular reference to FIGS. 3, 6, 10 and 11, details of the air circulation system 60 of this invention are described, according to a preferred embodiment. The brackets 10 are configured to interconnect together in a way that preserves an air circulation system 60 driven by natural convection to help cool the brackets 10 and the overall photovoltaic power generation system. This air circulation system 60 begins with end pieces such as the undulating end piece 70 (FIG. 4) which are fitted beneath the bottom rail 50 of a lowermost bracket 10 of an overall power generation system (FIG. 11).

[0052]The bottom rail 50 is not configured to have the feet 53 rest upon the roof R. Rather, the feet 53 are configured to rest upon an adjacent lower mounting rail 20 or the cell support structure 30 just below the mounting rail 20. Thus, the end piece 70 is provided to hold up the bottom rail 50 of the bracket 10 defining a lowermost portion of the overall system.

[0053]This end piece 70 is preferably in the form of an undulating end piece with lateral ends 72 spaced from each other and with troughs 74 and crests 76 alternating between the ends 72. Airflow is thus easily accommodated through the end piece 70 and beneath the brackets 10. While the end piece 70 is shown relatively shallow in extent toward the mounting rail 20, most preferably the end piece is deep enough toward the mounting rail 20 to abut the steps 57 (FIG. 2). In this way the lowest brackets 10 in the series of panels 100 is fully supported beneath the bottom rail 40 by the end piece 70. The deeper end piece can be captured by the wind clip 55 to further secure the end piece to the bracket 10.

[0054]Airflow (along arrow A) passes through the troughs 74 and crests 76 in the undulating end piece 70. This air is then located beneath the bracket 10. Heat within the bracket 10 or within other portions of the panel 100 or roof R is allowed to transfer to the air in this space beneath the bracket 10. With the air having been heated, natural convection causes the air to rise. While the photovoltaic cell 102 stack assembly keeps the air from rising purely vertically, passages 62 are preferably formed in the lateral rib 34 which allow the air to pass beneath the cell support structure 70 from the bottom rail 50 up to the mounting rail 20.

[0055]The gaps 58 in the perimeter skirt 28 allow the air to continue from beneath the mounting rail 20 and to under the next bracket 10 (arrow A of FIGS. 3 and 11). This airflow can continue beneath each of the brackets 10 until the highest bracket 10 is reached. The air can then escape out the gaps 58 in the highest brackets 10. With such airflow, a maximum temperature of the panels 100 is minimized. Different patterns of gaps 58 and passages 62 can be provided to route the air where desired for maximum cooling heat transfer, to optimize performance of the power generation system.

[0056]With particular reference to FIGS. 12 and 13, details of the edge flashing 80 are described, according to a preferred embodiment. The edge flashing 80 is provided to keep water from migrating beneath the brackets 10 and panels 100 along lateral edges of the overall system. While the lateral joints 40 preclude water from getting beneath the panels 100 where panels 100 are spaced laterally from each other, eventually the panels 100 at a perimeter edge of the overall system are reached. The edge flashing 80 is then utilized to transition from the panels 100 to shingles S upon the roof R.

[0057]With particular reference to FIG. 13, a series of three panels 100′, 100″, 100′″ are shown stacked adjacent each other with an undulating end piece 70 at a lower side of the lowermost panel 100′. The edge flashing 80 is configured with upper ends 82 opposite lower ends 84 and with a top plate 86 spaced from a bottom plate 88 by a web 85, with the plates 86, 88 generally parallel with each other. The top plate 86 is configured to rest upon an upper surface of the panel 100. The bottom plate 88 is configured to rest adjacent the roof R with shingles S resting on top of the bottom plate 88. The web 85 joints the two plates 86, 88 together and precludes water from migrating laterally beneath the panels 100. The edge flashing 88 overlaps somewhat at the ends 82, 84 to further preclude water migration at seams between adjacent pieces of edge flashing 80.

[0058]Because each of the brackets 10 and associated photovoltaic cell 102 stack assemblies taper somewhat in thickness with a thinnest edge adjacent the mounting rail 20 and a thickest edge adjacent the bottom rail 50, the web 85 preferably tapers from being shorter at the upper ends 82 to being longer at the lower ends 84. In this way, such tapering of the brackets 10 and overall panels 100 can be accommodated. Typically, the edge flashing 80 is formed by cutting rigid planar material, such as galvanized steel, and bending it to have the shape depicted in FIG. 12.

[0059]With particular reference to FIG. 8, particular details of a J-box 90 and associated electrical interconnection for the photovoltaic cells 102 within each panel 100 are described, according to a preferred embodiment. The J-box 90 is preferably an electronic device embedded within a waterproof resin to make it entirely waterproof.

[0060]Each photovoltaic cell 102 stack assembly is preferably formed of a series of separate cells 102 (most typically fourteen in two rows of seven a piece). In a simplest form of the invention, as few as one photovoltaic cell could be provided on each panel 100 of two brackets 10. Photovoltaic cells 102 are shown in this embodiment as a preferred form of photovoltaic element. Other photovoltaic elements could be substituted, such as thin film photovoltaic materials or structures, either now known or later developed. These separate cells 102 are joined together in series electrically. They are then laminated together between layers of waterproof materials.

[0061]Particularly, this layering preferably involves a low iron glass as a top layer, followed by a low melt temperature plastic layer such as EVA, followed by the photovoltaic cells themselves, followed by another low melt temperature plastic layer such as EVA, followed by a layer of Tedlar. This layering stack is laminated to further preclude water penetration. This stack is followed by an adhesive for mounting to the perimeter deck 36 of the cell support structure 30 of the bracket 10. One adhesive that can be utilized is known as adhesive 804 Dow Flexible Adhesive provided by the Dow Chemical Company of Midland, Mich.

[0062]Because the photovoltaic cells 102 are encased within this sandwich, electrical connections between adjacent photovoltaic cells are kept from shorting out, such as due to the presence of water when rain is falling on the roof. At the J-box 90, separate conductors from the series of photovoltaic cells 102 are routed into the J-box 90 so that all of the power from the series of photovoltaic cells 102 within the panel 100 are received at the J-box 90. This power is then routed through leads 94, 96. The leads 94, 96 allow adjacent panels 100 to be coupled together, typically in series.

[0063]Support clips 98 preferably extend from the perimeter skirt 28 of the mounting rail 20. These support clips 98 can hold the leads 94, 96 therein to prevent them from experiencing damage. The leads 94, 96 are preferably insulated to allow direct exposure to the elements. Slots 95 are provided at strategic locations in the perimeter skirt 28 of the mounting rail 20 to allow the leads 94, 96 to extend through the perimeter skirt 28 before bending 90° and extending along the perimeter skirt 28 and over the support clips 98. Couplers 97 allow the leads 94, 96 to be interconnected together to connect a series of such panels 100 together in series.

[0064]Each series connection of such panels 100 can be combined together through an end lead 112 extending into a combiner box 120 to further combine power from individual panels 100 and to configure the overall power from the series of panels 100 into power having the desired voltage and current. Inverters 140 can be utilized downstream from a combiner box 120 if it desired to generate AC power. Transformers can be utilized if a different current and voltage is desired.

[0065]The inverter 140 is typically coupled to a subpanel 130 where the power can be effectively utilized as AC power service within a residential structure or sold to a power company, or put to other beneficial use. The converter box 120, inverter 140 and subpanel 130 together form an electrical subsystem 110 which receives end leads 112 from separate strings of panels 100 through function of the leads 94, 96 and J-box 90.

[0066]Each panel 100 (also referred to as a “tile” or “solar tile”) is typically provided in an array including N columns and M rows. Typically, each row is coupled in series and routed to a common combiner box 120 through end leads 112. In one form of the invention, panels 100 are coupled together in series until the desired voltage for the system is achieved. Then multiple such strings of series connections of panels are joined together in the combiner box 120 to increase the current provided by the overall system.

[0067]This disclosure is provided to reveal a preferred embodiment of the invention and a best mode for practicing the invention. Having thus described the invention in this way, it should be apparent that various different modifications can be made to the preferred embodiment without departing from the scope and spirit of this invention disclosure. When structures are identified as a means to perform a function, the identification is intended to include all structures which can perform the function specified. When structures of this invention are identified as being coupled together, such language should be interpreted broadly to include the structures being coupled directly together or coupled together through intervening structures. Such coupling could be permanent or temporary and either in a rigid fashion or in a fashion which allows pivoting, sliding or other relative motion while still providing some form of attachment, unless specifically restricted.