Patent Publication Number: US-2007095388-A1

Title: Photovoltaic roof-top components, a photovoltaic IRMA roofing system, and a photovoltaic roofing system

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      This Application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/732,501 that was filed Nov. 2, 2005, entitled “Photovoltaic Roof-Top Components, Photovoltaic Roof-Top Assemblies, and Photovoltaic Roofing Systems”. 
    
    
     TECHNICAL FIELD  
      The present invention relates to photovoltaic roof-top components, photovoltaic roof-top assemblies, and photovoltaic systems that convert solar energy directly into electricity.  
      BACKGROUND ART  
      Roof-top assemblies that utilize solar energy are well known, and photovoltaic roof-top components that convert solar energy directly into electrical energy are increasingly common, especially on large commercial, essentially flat roofs. Such photovoltaic roof-top assemblies generally include photovoltaic panels on top of a roofing membrane that overlies a top surface of a roof deck.  
      A well known roofing system includes use of a roofing membrane, and then a loosely laid insulation layer above the roofing membrane, and then a layer of ballast material, such as stone or concrete layers on the insulation layer to secure the insulation against wind disruption, etc. Such roofing systems are often referred to as “inverted roofing membrane assemblies”, or by the acronym IRMA or PMR. By having the insulation on top of the roofing membrane, instead of under the membrane, IRMA systems protect the membrane from deterioration due to exposure to ultraviolet light and thermal stress. However, the ballast materials add a substantial weight load to the roof, and also require substantial cost and effort in applying the ballast materials to the roof. Each IRMA roofing system requires a predetermined minimum weight per unit area to adequately secure against disruption by wind or other weather events. The minimum weight per unit area cannot exceed a maximum design weight load for the underlying roof structure.  
      For example, a common predetermined weight per unit area for an IRMA roofing system could be about five to about twelve pounds per square foot. Consequently, such newly constructed buildings must design for the additional loads and existing IRMA roofs may present weight limitation challenges if it is desired to add a photovoltaic roofing system to the IRMA roof. In addition the buildings underlying roof structure must be analyzed for reserve load capability when it is desired to replace an existing conventional membrane over insulation roofing system with an IRMA roofing system or a photovoltaic IRMA roofing system.  
      Other problems associated with roof-top assemblies using photovoltaic roofing components include efforts to minimize penetration and related possible leakage through the roofing membrane by apparatus used to secure the panels to the roof membrane; resistance to wind forces that may rip photovoltaic panels off of a roof deck; stabilizing temperatures experienced during operation of the photovoltaic panels; drainage of rain and melt water under such photovoltaic components; and a number of related challenges.  
      For example, U.S. Pat. No. 4,886,554 to Woodring et al. shows a solar roofing system that uses tapered insulation blocks to generate flow of rain water off of surfaces of the photovoltaic cells and then between the insulation blocks and adjacent pavers to direct rain water over the roofing membrane and away from the system. U.S. Pat. No. 5,316,592 to Dinwoodie discloses use of a plurality of insulation blocks between a roofing membrane and a photovoltaic module wherein rainwater flows off of the module surfaces and between insulation blocks of adjacent modules to then flow onto the roofing membrane away from the photovoltaic modules. These patents indicate that the types of flat roofs appropriate for use of such photovoltaic modules include modest slopes for drainage of rain water, which is well understood.  
      As a further example of problems addressed in the field of photovoltaic roofing modules, U.S. Pat. No. 5,505,788 to Dinwoodie shows elaborate means for regulating temperature of the photovoltaic modules, including use of phase change materials and fluid flow conduits adjacent back sides of the modules. This patent also points out that rain water will drain between joints between the modules. Additionally, U.S. Pat. No. 5,746,839 to Dinwoodie discloses use of pre-formed spacers supporting photovoltaic modules above a roofing membrane, or above an insulation block, to support photovoltaic modules, wherein geometry of the spacers is configured to reduce the force of wind uplift on the overall system.  
      These and other known patents endeavor to resolve a number of beguiling issues related to installation of photovoltaic modules on essentially flat roofs. However, no known patent or known photovoltaic roofing system efficiently resolves major challenges that have become more pressing with the development of modern, stringent building codes. In particular, new “IBC” codes call for at least a one-quarter inch per foot of run slope for positive drainage on all commercial flat roofs. By requiring such significant drainage slope, known photovoltaic modules are essentially incapable of effectively dealing with a substantial flow of water from upstream of the module in all types of flat or moderately sloped roof conditions. In some circumstances, a sudden, high rain-fall rate may lead to such a flow of water from areas upstream of the modules and then onto the modules, so that the modules may be damaged dislodged from their positions on the roof and also causing damage to the membrane.  
      Additionally, it has been determined that standardized insulation layers beneath photovoltaic modules may give rise to unacceptable dew points below roofing membranes in certain roofing structures, thereby leading to unacceptable condensation of moisture below a roofing membrane upon a roofing deck. Such condensation may lead to corrosion of metal roofing decks and/or rotting of wooden deck materials &amp; membrane.  
      Other problems associated with such roofing systems using photovoltaic roof-top components include excessive weight of such known systems, and difficulties associated with repair or upgrading of the photovoltaic panel components of the roofing assemblies. Some older flat roofs are only capable of supporting between four to five pounds per square foot, and most known photovoltaic roofing systems weigh substantially more. Hence, there is a need for a lightweight photovoltaic roofing system.  
      Moreover, typical and known solar roofing assemblies, such as those disclosed in the aforesaid U.S. Pat. Nos. 5,316,592 and 5,505,788 to Dinwoodie, show that for convenience of manufacture and installation, photovoltaic panels are manufactured to be integral with insulation layers and/or with spacers between the panels and insulation layers below the photovoltaic panels. While that may facilitate manufacture and installation, it is know that frequently only one photovoltaic panel may fail or be damaged by accidental impact by debris resulting from severe weather, falling installation tools, and/or misuse etc.  
      It is also known that large, flat roofs may have photovoltaic roofing systems with literally hundreds of photovoltaic panels. To remove and replace one or only several photovoltaic panels of such a system is extremely difficult where the photovoltaic panels are integral with spacers and/or an insulation layers below the panels. Removal and disruption of a section of the insulation layer raises risks of damage to the underlying roofing membrane, and adjacent panels. Additionally, environmentally friendly technology such as photovoltaics is developing rapidly, and the quality of photovoltaic panels is changing and is expected to continually change as the panels become more efficient. However, to upgrade known photovoltaic roofing systems may require removal of the entire system because the photovoltaic panels are known to be integral with insulation layers and spacers below the panels.  
      Accordingly, there is a need for a photovoltaic roofing system that may be easily manufactured and applied to essentially flat roofs that provides for efficient and effective drainage of rain water and/or snow-melt water, and that also allows for variable insulation of a photovoltaic roof panel to prevent deterioration of the roof deck or membrane. There is also a need for a photovoltaic roofing system that facilitates removal of system components for repair and/or upgrading, and that also provides flexibility in weight of system components so that the photovoltaic roofing system may be installed on roofs capable of supporting modest loads.  
     SUMMARY OF THE INVENTION  
      The invention includes improved photovoltaic roof-top components that may be used alone or as part of photovoltaic roofing assemblies or systems. An improved photovoltaic insulation layer includes a top surface and an opposed bottom surface, wherein the bottom surface defines a predetermined number of drainage channels, and includes a predetermined insulation layer thickness between a top surface and the opposed bottom surface. The photovoltaic roofing system includes a roofing membrane overlying a top surface of a roof deck; the improved photovoltaic insulation layer above the roofing membrane; and a photovoltaic panel above the insulation layer. The predetermined number of drainage channels between the insulation layer and the roofing membrane is a function of variable drainage requirements of the roofing system that are appropriate for a specific roof deck to which the system is installed. Additionally, the predetermined insulation layer thickness between opposed top and bottom surfaces is a function of variable insulation requirements of the insulation layer to address dew point and thermal design issues.  
      The invention also includes a photovoltaic IRMA roofing system for application to a traditional inverted roofing membrane assembly (“IRMA”) roof system. The photovoltaic IRMA roofing system includes a roofing membrane overlying a top surface of a roof deck; an insulation layer above the roofing membrane; ballast material installed above the insulation layer; and a photovoltaic panel secured above the ballast material. The combined weight of the ballast material and the photovoltaic panel are equal to or greater than a predetermined minimum weight per unit area for the roofing system. The preferred ballast material in the photovoltaic IRMA roofing system is a concrete topping secured to the top of the insulation layer.  
      By replacing a traditional layer of ballast material in an IRMA roofing system with the photovoltaic panel and concrete topping on the insulation layer, the photovoltaic IRMA roofing system efficiently satisfies the predetermined minimum weight per unit area requirement of any specific roofing system while minimizing any risk of exceeding a maximum weight load of the roof. This is particularly valuable when improving an existing IRMA roof by removing existing ballast materials and replacing them with the combined weight of the concrete layer and the photovoltaic panels. This also adds insulation to enhance the energy efficiency of the building. The photovoltaic IRMA roofing system also minimizes a weight load, cost of materials and assembly for any new roof that is to include photovoltaic panels.  
      (For purposes herein, use of the word “above” with respect to adjacent components is to mean with respect to a direction of gravity. In other words, where an “insulation layer is secured above a roofing membrane”, that is to means the roofing membrane is closer the center of the earth than is the insulation layer.)  
      An alternative embodiment of the photovoltaic roofing system of the present invention is referred to for convenience as a “dew-point sensitive roofing system”, and includes the above described roofing membrane, insulation layer and photovoltaic panel above the insulation layer, and also includes a sub-membrane insulation layer secured between the top surface of the roof deck and the roofing membrane such as would occur in an installation of photovoltaic panels over an existing roof or as part of an engineered combination of photovoltaic panels and a new roofing system having a membrane above insulation and decking. The sub-membrane insulation layer defines a predetermined sub-membrane insulation layer thickness between the top surface of the roof deck and the roofing membrane. The above membrane insulation layer in this dew-point sensitive roofing system must define a predetermined thickness that is a function of the sub-membrane insulation layer thickness so that the above membrane insulation layer has a greater “R” (resistance to movement of heat) value than the sub-membrane insulation layer. This dew-point sensitive roofing system alternative embodiment of the invention provides advantages of a protected membrane (“inverted roofing membrane assemblies”, or by the acronym “IRMA”, or “PMR”) roofing system in all applications by combining the dew point sensitive system insulation with a ballast layer consisting of the weight of the photovoltaic glass panel and the weight of a cementitious face of an uppermost layer of insulation. The advantages include longer membrane life due to a more constant membrane temperature and preventing damaging ultraviolet rays from reaching the membrane.  
      In use of the improved photovoltaic roofing components and system, the area of the roof deck covered by the system would be measured, and the particular position of the system with respect to potential upstream to downstream flow would also be determined so that potential upstream flow through the system could then be measured. With at least these two variables, a user could then determine the variable drainage requirements of the roofing system for a particular installation, including direction and volume of flow. Measurement of the total volume of water that must be moved from the top surface of the photovoltaic system through the system, as well as through the system from flow of water on the roof deck upstream of the system, determines the total flow capacity of the drainage channels defined within the insulation layer above the roofing membrane. The insulation layer would then be selected and/or manufactured to have defined drainage channels that provide adequate flow and directionality for the measured drainage requirements of that particular installation of the present photovoltaic roofing system.  
      Additionally, prior to installation, the thickness of the insulation layer of the photovoltaic panel would be selected based upon the insulation layer of a particular existing or new roofing system upon which the photovoltaic panels are being installed. The thickness of the insulation layer would be selected based upon variable insulation requirements of a particular roofing system being installed on a particular roof. Determination of a predetermined thickness of the insulation layer would include measurement of the “R” factor of the particular existing or new roof deck or roofing system to which the photovoltaic roofing system is being installed.  
      Perhaps more importantly, for certain roof decks, such as metal roofs that employ an insulation layer (the “sub-membrane insulation layer” referred to above) under the roofing membrane over metal ribs of a metal deck, it is critically important that the R factor of the sub-membrane insulation layer, and therefore the thickness of the sub-membrane insulation layer, be selected to make sure that the “R” value above the roofing membrane is greater than the “R” factor below the roofing membrane so that condensation between the roofing membrane and the roof deck is avoided. This involves not only a measurement of the R factor and hence thickness of the sub-membrane insulation layer, but also a measurement of the R factor of the roof deck itself, as well as the R factor of the insulation layer between the roofing membrane and the photovoltaic cell. It is to be understood that the “dew point sensitive” embodiment of the roofing system may include retrofitting an existing roof-top system that employs sub-membrane insulation layers and is not limited to newly applied photovoltaic roofing system. In such existing roof-top assemblies having sub-membrane insulation layers, the “R” value of the sub-membrane insulation may simply be measured by taking a core sample by drilling, etc. That sub-membrane “R” factor is then one of the variables used to determine the thickness of the insulation layer above the roofing membrane. Therefore, the present photovoltaic roofing components and roofing systems provide for application of insulation layers of predetermined thicknesses that are appropriate for the specific insulation requirements of the roof deck to which the roofing system is to be installed.  
      Preferred embodiments of the improved photovoltaic roofing components and photovoltaic roofing system and improved photovoltaic insulation layer also include drainage channels that are both parallel to an axis of gravity flow of water draining through the system, and that are also not parallel to the axis of gravity of flow and that intersect with the channels parallel to the gravity axis of flow. This may appear as the insulation layer having an approximately checked appearance on a surface closest to the roofing membrane including gravity flow drainage channels and channels perpendicular to and intersecting with the gravity flow channels. Such various drainage channels enhance lateral movement of water to thereby provide for even more rapid movement of water through the system, so that, for example, snow-melt water, or water backed up above a temporary snow damn may readily move through the photovoltaic roofing system.  
      The photovoltaic roofing system invention also includes a photovoltaic roofing system with quick-disconnect photovoltaic panels. The system includes an insulation layer positioned above a roofing membrane of a roof deck. Two or more spacers are positioned above the insulation layer so that the spacers define cooling voids between the spacers and above the insulation layer. A quick-disconnect photovoltaic panel is positioned above the spacers, and the quick-disconnect photovoltaic panel defines a plurality of quick-disconnect throughbores adjacent the cooling voids between the spacers. A quick-disconnect fastener-receiving sleeve is secured to the insulation layer and is also dimensioned to pass through one of the cooling voids and to also pass through a quick-disconnect throughbore of the photovoltaic panel.  
      A fastener having a flared end and a stem secured to the flared end is dimensioned so that the stem passes through the panel throughbore and into the quick-disconnect fastener-receiving sleeve to be secured within the sleeve by standard mechanical methods, such as a threaded sleeve and screw, etc. The flared end of the fastener is dimensioned to have a diameter greater than any diameter of the throughbore defined within the photovoltaic panel. Therefore, the flared end secures the photovoltaic panel to the insulation layer whenever the fastener is secured within the quick-disconnect fastener-receiving sleeve and the fastener permits disconnection of the photovoltaic panel from the insulation layer whenever the fastener is removed from the fastener-receiving sleeve.  
      Any quick-disconnect photovoltaic panels may therefore be readily removed from a photovoltaic roofing system without disrupting the insulation layer below the photovoltaic panels, and without risk of damage to adjacent photovoltaic panels, to repair or to replace the removed panel, etc. Additionally, all of the quick-disconnect panels may be removed to be replaced with upgraded photovoltaic panels without disrupting the insulation layer thereby minimizing any risk of damage to the roof membrane, and further minimizing cost of such repairs or upgrades.  
      The invention also includes a lightweight photovoltaic roofing system. The system includes a plurality of photovoltaic panels secured adjacent each other to define a photovoltaic region. Each photovoltaic panel is secured above a lightweight insulation panel so that each photovoltaic panel and insulation panel have a combined weight of between about 4 and about 5 pounds per square foot. The photovoltaic region defines an exterior perimeter extending around the entire photovoltaic region. A plurality of the lightweight insulation panels completely surrounds and interlocks with the exterior perimeter of the photovoltaic region and interlocks with each other to define a lightweight insulation panel ballast region. At least one insulation panel extends between the exterior perimeter of the photovoltaic region and an exterior perimeter of the lightweight insulation panel ballast region.  
      Each lightweight insulation panel weighs between about 4 and about 5 pounds per square foot. The lightweight system also includes a paver ballast perimeter that overlies lightweight insulation panel ballast region. The paver ballast perimeter weighs between about 12 and about 17 pounds per square foot, and the width of the paver ballast perimeter is less than half of a width of a photovoltaic panel, or preferably about 16 inches. (For purposes herein, the word “about” is to mean plus or minus 20 percent.)  
      Accordingly, it is a general purpose of the present invention to provide improved photovoltaic roofing components and a photovoltaic roofing system that overcomes deficiencies of the prior art.  
      It is a more specific purpose to provide improved photovoltaic roofing components and a photovoltaic roofing system that may be customized for particular conditions of a specific roof deck to thereby enhance performance, service and longevity of the photovoltaic roofing system.  
      These and other purposes and advantages of the present photovoltaic roof-top components, photovoltaic IRMA roofing system, and photovoltaic roofing system will become more readily apparent when the following description is read in conjunction with the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a fragmentary sectional view of a photovoltaic roofing system constructed in accordance with the present invention showing a limited number of drainage channels.  
       FIG. 2  is a fragmentary sectional view of a section of the  FIG. 1  insulation layer of a photovoltaic roofing system showing a drainage channel.  
       FIG. 3  is a fragmentary sectional view of a second embodiment of a photovoltaic roofing system constructed in accordance with the present invention showing a substantial number of drainage channels.  
       FIG. 4  is a bottom view of an improved photovoltaic insulation layer showing a plurality of intersecting drainage channels.  
       FIG. 5  is a fragmentary sectional view of a dew point sensitive embodiment of a photovoltaic roofing system of the present invention on a metal roof deck and having a modest number of drainage channels.  
       FIG. 6  is a fragmentary sectional view of a dew point sensitive embodiment of a photovoltaic roofing system of the present invention on a metal roof deck and having a substantial number of drainage channels.  
       FIG. 7  is a fragmentary sectional view of an alternative embodiment of the present invention showing a photovoltaic IRMA (“inverted roofing membrane assembly”) system, and showing the system on a concrete roof deck and having a modest number of drainage channels defined within the insulation layer.  
       FIG. 8  is a fragmentary sectional view of the  FIG. 7  alternative embodiment of the present invention showing the  FIG. 7  photovoltaic IRMA system on a concrete roof deck and having a substantial number of drainage channels defined within the insulation layer.  
       FIG. 9  is a top schematic view of a photovoltaic roofing system on roof deck A in showing an upstream drainage area A.  
       FIG. 10  is a top schematic view of a photovoltaic roofing system on roof deck B showing an upstream drainage area B.  
       FIG. 11  is a top schematic view of a photovoltaic IRMA roofing system of the present invention showing a perimeter and internal areas not covered by photovoltaic panels.  
       FIG. 12  is a top plan, simplified schematic view of a quick-disconnect photovoltaic panel constructed in accordance with the present invention.  
       FIG. 13  is a fragmentary cross-sectional view taken along view lines  2 - 2  of  FIG. 12 , showing a quick-disconnect photovoltaic panel having a quick-disconnect fastener-receiving sleeve extending between an insulation layer and the panel.  
       FIG. 14  is an expanded sectional view of the  FIG. 13  quick-disconnect fastener-receiving sleeve.  
       FIG. 15  is a fragmentary top plan view of a lightweight photovoltaic roofing system constructed in accordance with the present invention.  
       FIG. 16  is a fragmentary cross-sectional view of a segment of the  FIG. 15  lightweight photovoltaic roofing system. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Referring to the drawings in detail, an improved photovoltaic roofing system is shown in  FIG. 1 , and is generally designated by the reference numeral  10 . The system  10  includes a roofing membrane  12  overlying a top surface  14  of a roofing deck  16 . An improved photovoltaic insulation layer  18  is above the roofing membrane  12 . A photovoltaic panel  20  is above the insulation layer  18  and supported typically by way of insulation blocks or spacers  22 ,  24  that may provide an air space  26 . (For purposes herein, the word “above” is to mean opposed to the direction of gravity. Additionally, hereinafter the phrase “secured to” is to mean either, “overlying”, “above” or “adjacent”, and does not mean that any securing apparatus or force is necessarily applied to adhere adjacent components to each other.) The improved insulation layer  18  may be secured to the photovoltaic panel  20  by being laminated to the panel  20 , or to the panel spacers  22 ,  24 , by lamination securing means known in the art. Alternatively, the panel  20  may simply be placed adjacent the insulation layer  18  if the panel  20  includes active thermal management, or in certain circumstances, the photovoltaic panel  20  may be located on top of ballast stone  66  above the insulation layer  18 , as discussed in more detail below with respect to  FIGS. 5, 6 .  
      The photovoltaic insulation layer  18  may, and typically does, include a concrete topping  28  that provides ballast weight for the assembly or system  10  and other benefits well known in the art. This provides for “securing” described components to the roofing membrane  12 . The insulation layer  18  defines a predetermined number of drainage channels  30 , wherein only one drainage channel  30  is shown in  FIG. 1 .  FIG. 2  shows an expanded view of the  FIG. 1  drainage channel  30  defined in the insulation layer  18 .  
       FIG. 3  shows a second embodiment of the photovoltaic roofing system  10 ′ (virtually identical elements of the  FIG. 1  system  10  are shown with prime reference numerals (e.g.,  10 ′) of the  FIG. 1  reference numerals), wherein a much larger number of drainage channels  32  are shown defined in the insulation layer  18 ′ adjacent or above the roofing deck  16 ′.  FIG. 4  shows a bottom plan view of a bottom surface  34  of an alternative insulation layer  36  wherein a plurality of drainage channels  38  intersect with each other to provide a checked appearance of the bottom surface  34 . As described above, this provides for drainage in a direction parallel to a gravity flow axis, as well as in directions that are not parallel to the gravity flow axis to thereby provide for lateral movement to enhance overall flow rates for the drainage channels  38 .  
       FIG. 5  shows a second alternative, or dew-point sensitive photovoltaic roofing system  40  that includes a roofing membrane  42  secured to a sub-membrane insulation layer  54  that is secured above the metal deck  44 , and a photovoltaic panel  48  secured adjacent to or above an insulation layer  46  secured above the-roofing membrane  42 . (As shown in  FIG. 5 , the insulation layer  46  may consist of one solid insulation substance, or a plurality of stacked insulation sheets  50 ,  52  below an air space  53 .) The sub-membrane insulation layer  54  is secured between the roof deck  44  (such as the metal deck  44  having sub-membrane insulation panels  56 A,  56 B,  56 C) and the roofing membrane  42 . As described above, the sub-membrane insulation layer  54  may be of a predetermined thickness, and, based upon measurements to determine the predetermined thickness of the sub-membrane insulation layer  54 , the insulation layer  46  above the roofing membrane  42  has a predetermined thickness wherein its predetermined thickness is a function of the thickness of the sub-membrane insulation layer  54  so that the “R” value of the insulation layer  46  above the roofing membrane  42  is greater than the “R” value of the insulation layer  54  below the membrane  42 . This dew-point sensitive embodiment of the improved photovoltaic roofing system thereby eliminates any condensation of moisture between the sub-membrane insulation layer  54  and the roofing membrane  42  and/or the roofing deck  44 .  
       FIG. 6  shows the  FIG. 5  or dew-point sensitive photovoltaic roofing system  40 , but with the insulation layer  46  defining a substantial number of drainage channels  60  to facilitate drainage of a much greater flow of water.  
      The photovoltaic roofing system  40  of  FIGS. 5 and 6  also includes components that would be adjacent an edge of the system  40 , between the photovoltaic panel  48  and an exterior edge  62  of the system  40 . Included are a concrete block  64 , and a plurality of ballast stones  66  and a filter fabric  68  to permit movement of only filtered rain water through the ballast stones  66  and down into an exterior drainage channel  70  for movement of such rain water through and out of the roofing system  40 .  
       FIGS. 7 and 8  show a third alternative or photovoltaic IRMA roofing system  72  that has very similar components as the roofing system  40  shown in  FIGS. 5 and 6 . A section of a traditional IRMA (“inverted roofing membrane assembly”) roof system  73  is shown in  FIG. 7  as part of the photovoltaic IRMA system  72 . It includes the roofing membrane  76  above and adjacent to a standard roof deck  74 ; an insulation layer  78  that may be one or more layers secured above the roofing membrane  76 ; and ballast material  79  that may consist of stone, concrete layers, or anything known in roofing technology utilized for adding ballast to insulation layers  78 , and secured above the insulation layer  78 . The traditional IRMA system  73  may also include a filter fabric  68 ′ for restricting passage of large particles passing through the insulation layer with rain water to restrict clogging insulation drainage channels. The photovoltaic IRMA roofing system  72  shown in  FIGS. 7 and 8  to the left of the traditional IRMA roofing system  73  includes the roofing membrane  76  above and immediately adjacent to the roof deck  74 ; the insulation layer  78  secured above the roofing membrane  76 ; ballast material such as a concrete topping  83  secured adjacent the insulation layer  78 ; and a photovoltaic panel  80  secured above the concrete topping  83  of the insulation layer  78 . The photovoltaic panel  80  may be secured above the concrete topping  83  of the insulation layer  78  on a plurality of spacers  85 A,  85 B to define an air space  53  between the panel  80  and insulation layer  78  that facilitates removal of heat from the panel  80 . The insulation layer  78  may also consist of a plurality of insulation layers  77 A,  77 B to provide enhanced insulation, or to utilize thinner layers  77 A,  77 B stacked together.  
      As is apparent in  FIGS. 7 and 8 , the photovoltaic IRMA roofing system  72  provides for replacement of the traditional ballast material  79  with the combination of the weight of the photovoltaic panel  80  and concrete topping  83  ballast material on the insulation layer  78 . As is known, traditional IRMA roofing systems require a predetermined minimum weight per unit area requirement to prevent disruption of the system by prevailing winds or other related weather phenomenon. By using the combination of the weight of the photovoltaic panel  80  and the concrete topping  83  or any similar ballast material adjacent the insulation layer  78  between the photovoltaic panel  80  and the roofing membrane  76 , the photovoltaic IRMA roofing system  73  efficiently satisfies the predetermined minimum weight per unit area requirement of any specific roof while minimizing any risk of exceeding a maximum weight load of the underlying roof deck  74 . As recited above, this is particularly valuable when improving an existing IRMA roof system by adding photovoltaic panels  80  to enhance the energy efficiency of a building supporting the roof deck  74 . The same benefit may be realized when totally removing an existing “membrane-over-insulation” roofing system and replacing it with the above referenced photovoltaic IRMA roofing system  72  provided the existing underlying roof deck  74  is analyzed for its ability to carry the additional load. The photovoltaic IRMA roofing system  72  also minimizes a weight load, cost of materials and assembly for any new roof system that is to include photovoltaic panels  80 .  
      As shown in  FIGS. 7 and 8 , it is common that a photovoltaic IRMA roofing system  72  includes photovoltaic panels  80  that extend only to a photovoltaic panel perimeter  87 . Between the photovoltaic panel perimeter  87  and a roofing system exterior perimeter  89  there may be a section of a traditional IRMA roofing system  73 , such as shown in  FIGS. 7 and 8 . There may be similar excluded areas that are internal to the photovoltaic panel perimeter  87 . The photovoltaic panel perimeter  87  is defined by requirements of rooftop mechanical system such as stairs, related walk areas and other penetrations of the roofing membrane  76 . For example and as shown in  FIG. 11  such internal areas having no overlying photovoltaic panels  80  include access aisles  86 , stair bulkheads  87 , elevator mechanical rooms  88 , HVAC systems  89 , and vent stack and exhaust fan areas  91 . The traditional IRMA roofing system section  73  together with the photovoltaic IRMA system  72  ensures that the entire roofing systems functions as an IRMA roofing system  72 , so that the system  72  satisfies the predetermined minimum weight per unit area requirement specific to the roof deck  74 .  
      It is also pointed out that, the third alternative photovoltaic IRMA roofing system  72  may be secured to a metal or a non-metal roof deck  74 . The third alternative photovoltaic IRMA roofing system  72  shows, similarly to the second embodiment in  FIGS. 5 and 6 , a distinction between only one drainage channel  80  in  FIG. 7  and a plurality of channels  82  in  FIG. 8 . Additionally, this third embodiment shown in FIGS. and  8  of the system  72  may not include the sub-membrane insulation layer  54  of the second embodiment of  FIGS. 5 and 6 .  
      An additional advantage of the present photovoltaic assemblies or system  10  and its individual components is shown in  FIGS. 9 and 10 , wherein a first photovoltaic panel A  90  is shown in  FIG. 9  secured to a roofing deck  92 . Direction of flow by gravity arrows  94  identify a gravity flow direction to a drain  96  for rain water or accumulated snow-melt water (not shown). The photovoltaic panel A  90  is positioned in close proximity to an edge  98  of the roofing deck  92  so that an upstream drainage area A  100  is defined between the panel A  90  and the edge  98  of the roofing deck.  FIG. 10  shows a photovoltaic panel B  102  secured to a roof deck B  104  a further distance from an edge  104 , wherein flow arrows  106  show gravity flow directions to a drain  108 . As is apparent, an upstream drainage area B  110  is significantly larger than the upstream drainage area A of  FIG. 9 . Therefore, the photovoltaic roofing system  102  of  FIG. 10  requires a significantly larger water drainage flow capacity than the photovoltaic roofing system  90  of  FIG. 9  to deal with the varying sizes of the upstream drainage areas A  100  and B  110 .  
      The present invention also includes the described insulation panel  18  as an improved photovoltaic insulation layer  18  for a photovoltaic roofing system  10 .  40 ,  72 . The improved photovoltaic insulation layer  18  has a top surface  19  and an opposed bottom surface  21  (see  FIGS. 1 and 2 ) wherein the bottom surface  21  defines a predetermined number of drainage channels  30 . The predetermined number of drainage channels  30  is a function of variable drainage requirements, as described above. Additionally, the improved photovoltaic insulation layer  18  has a predetermined insulation layer thickness between its opposed top surface  19  and bottom surfaces  21 , wherein the predetermined insulation layer thickness is a function of variable insulation requirements of the roofing system  10 ,  40 ,  72 , as described above.  
      As is well known in the art, the schematics of  FIGS. 9 and 10  show simplified, demonstrative systems  90 ,  102  only. In actual installation of photovoltaic roof-top assemblies or systems  10 ,  40 ,  72 , many photovoltaic panels  20  are combined with multiple insulation sheets  18  to cover large, often irregular areas of essentially flat roofs. Therefore, by the present photovoltaic roofing assembly or system  10 ,  40 ,  72 , sensitive adjustments of both the drainage capacity and insulation capacity may be made to customize the roofing system  10 ,  40 ,  72  to meet varying, specific drainage and insulation requirements of large photovoltaic roof system installations, such as are now common on the roofs of increasingly large “big box” stores of contemporary malls, schools, large manufacturing and similar facilities, etc.  
      While the vast majority of photovoltaic roof-top assemblies or systems  10 ,  40 ,  72  applies to use of panels  20  that directly convert solar energy into electrical energy, it is to be understood that for purposes herein, the phrases “photovoltaic roofing system”, “photovoltaic roof-top assemblies” or “roofing systems” are to include systems that convert solar energy directly to electrical energy, as well as any roofing system that captures solar energy for any purposes, including for capture of heat energy, etc. Additionally, the phrase “insulation layer defines drainage channels” means that the drainage channels permit flow of liquids from opposed edges of the insulation layer so that the liquids flowing through the photovoltaic roofing system  10  flow from an upstream end of the system through to and out of a downstream end of the system, or out of sides of the system  10 . The phrase “insulation layer defines drainage channels” may also mean that drainage channels simply lie between insulation sheets of the insulation layer  18  and the roofing membrane  12 , such as by application of fluid conduits (e.g., pipes, hoses, lines, carved tunnels, carved channels, etc.) to or in the insulation sheets  50 ,  52 .  
      The photovoltaic roofing system of the present invention also includes a quick-disconnect photovoltaic roofing system  100  with a quick-disconnect photovoltaic panel  102  that is shown in  FIGS. 12 and 13  and is generally designated by the reference numeral  100 . The system  100  includes an insulation layer  104  positioned above a roofing membrane  105  above a roof deck  106 . Two or more spacers  108 A,  108 B,  108 C,  108 D and  122  are positioned above the insulation layer  104  so that the spacers define cooling voids  120 A,  120 B between the spacers  108 A- 108 D, and above the insulation layer  104 . An insulation spacer may take the form of an insulation spacer-support block  122  in variable positions and in variable heights, as shown in  FIG. 12 , which may also be used to provide further support, and that may also divide the cooling voids  120 A,  120 B.  
      A quick disconnect photovoltaic panel  102  is positioned above the spacers  108 A- 108 D, and the quick-disconnect photovoltaic panel  102  defines a plurality of quick-disconnect throughbores  126 A,  126 B,  126 C,  126 D,  126 E,  126 F adjacent the cooling voids  120 A,  120 B between the spacers  108 A- 108 D. A plurality of quick-disconnect fastener-receiving sleeves  128 A,  128 B,  128 C (shown best in  FIGS. 13 and 14 ) are secured to the insulation layer  104  and are also dimensioned and positioned to pass through one of the cooling voids  120 A,  120 B or through the spacers  108 A- 108 D and to also pass through corresponding quick-disconnect throughbores  126 A,  126 B,  126 C of the quick-disconnect photovoltaic panel  102 . It is pointed out that in the  FIG. 14  expanded view of the quick-disconnect fastener-receiving sleeve  128 C, a layer of concrete  130  or “concrete topping” is shown secured to the insulation layer  104 .  
      For purposes of clarity in explanation, this description will describe one fastener  132 , while it will be understood by those skilled in the art that virtually identical fasteners are deployed within each of the quick-disconnect throughbores  126 A- 126 F and fastener-receiving sleeves  128 A- 128 D. The fastener  132  has a flared end  134  and a stem  136  that is secured to the flared end  134 , and the fastener  132  is dimensioned so that the stem  136  passes through the panel throughbore  126 C and into the quick-disconnect fastener-receiving sleeve  128 C to be secured within the sleeve by standard mechanical methods, such as a threaded sleeve and screw, etc. The flared end  134  of the fastener  132  is dimensioned to have a diameter greater than any diameter of the throughbore  126 C defined within the photovoltaic panel  102 . Therefore, the flared end  134  secures the photovoltaic panel  102  to the insulation layer  104  whenever the fastener  132  is secured within the quick-disconnect fastener-receiving sleeve  128 C and the fastener  132  permits disconnection of the photovoltaic panel  102  from the insulation layer  104  whenever the fastener  132  is removed from the fastener-receiving sleeve  128 C. The insulation layer  104  may be secured to an adjacent roof membrane  105  by any means known in the art.  
      While the fastener  132  and corresponding receiving sleeve  128 C have been described as a conventional threaded sleeve and threaded bolt, it is to be understood that any quick-disconnect fastening means may be utilized that is known in the art and that is capable of securing the photovoltaic panel  102  to the insulation layer  104  above the cooling voids  120 A,  120 B, such as bolts and nuts, instead of sleeves, washer-defined sleeves, securing rods with pivot latches at terminal ends, etc. As shown in  FIG. 14 , the quick-disconnect fastening means  132  may also include a panel grommet  138  surrounding the photovoltaic panel throughbore  128 C, and an insulation layer grommet  140  as part of a mechanism to secure the fastener-receiving sleeve  128 C to the insulation layer  104 . In addition, a panel washer  142  may be utilized between the flared end  134  of the fastener  132  and the photovoltaic panel  124  to diffuse compressive forces against the panel  102 . Additionally, the panel washer  142  may be made of a hard translucent material to facilitate transmission of light into the panel  102 .  
      As described above, the quick-disconnect photovoltaic panel  102  may therefore be readily removed from the quick-disconnect photovoltaic roofing system  100  without disrupting the insulation layer  104  below the photovoltaic panel  102 , and without risk of damage to any adjacent photovoltaic panels (not shown), to repair or to replace the removed panel  102 , etc.  
      As shown best in  FIGS. 15 and 16 , the invention also includes a lightweight photovoltaic roofing system  150 . The system  150  includes a plurality of photovoltaic panels  152  secured adjacent each other to define a photovoltaic region  154 . Each photovoltaic panel  152  is secured above a lightweight insulation panel  156  (shown best in  FIG. 16 ) having a concrete topping  158 , and having a top surface  170  below the concrete layer  158  and an opposed bottom surface  172 , wherein the bottom surface  172  may also define a predetermined number of drainage channels  174 . The light weight insulation panels  156  are secured adjacent a roofing membrane  105 ′ above a roofing deck  106 ′, and the lightweight insulation panels  156  typically support insulation spacers  108 ′ as described above and known in the art. Each photovoltaic panel  152  and adjacent insulation panel  156  with its concrete topping  158  have a combined weight of between about four and about five pounds per square foot.  
      The photovoltaic region  154  defines an exterior perimeter  160  extending around the entire photovoltaic region  154 . A plurality of the lightweight insulation panels  156  completely surrounds and interlocks with the exterior perimeter  160  of the photovoltaic region  154  and interlocks with each other  156  to define a lightweight insulation panel ballast region  162 . At least one insulation panel  156  extends between the exterior perimeter  160  of the photovoltaic region  154  and an exterior perimeter  164  of the lightweight insulation panel ballast region  164 . Additional insulation panels  156  may extend between the exterior perimeter  160  of the photovoltaic region and the exterior perimeter  164  of the lightweight insulation panel ballast region  164  if the area of the roof permits, and if additional ballast is needed.  
      Each lightweight insulation panel  156  weighs between about four and about five pounds per square foot. The lightweight photovoltaic system  150  also includes a paver ballast perimeter  166  that overlies the lightweight insulation panel ballast region  162 . In varying embodiments, the paver ballast perimeter  166  may overlie the exterior perimeter  160  of the photovoltaic region  154  and simultaneously overlie an interior perimeter  168  of the lightweight insulation panel ballast region  164  (as shown in  FIGS. 15 and 16 ). Alternatively, the paver ballast perimeter  166  may overlie and exterior perimeter  164  of the lightweight insulation panel ballast region  162  (as shown in  FIG. 15 ). Or, if circumstances permit, the paver ballast perimeter  166  may simply overlie the lightweight panel ballast region  164  wherever convenient. The paver ballast perimeter  166  weighs between about twelve and about seventeen pounds per square foot, and the width of the paver ballast perimeter  166  may be less than half of a width of a photovoltaic panel  152 , or preferably about sixteen inches. (For purposes herein, the word “about” is to mean plus or minus 20 percent.)  
      Use of the word “interlocks” in the above description: “A plurality of the lightweight insulation panels  156  completely surrounds and interlocks with the exterior perimeter  160  of the photovoltaic region  154  and interlocks with each other  156  to define . . . ” will now be described. By stating that a plurality of the insulation panels  156  . . . “interlocks”, it is meant to include the type of “tongue and groove” mechanical interlocking shown in  FIG. 16  at the interface of reference numerals  160  and  168 . However, the word “interlocks” is also meant to include any other known mechanical, adhesive, gravity-based (e.g., overlapping edges), bonding, fusing, etc., known in the art that can achieve the described function of the plurality of lightweight insulation panels  156  adding to the ballast necessary to hold down the lightweight photovoltaic roofing system  150  from movement or other damage from wind forces acting upon the system  150 . The lightweight photovoltaic roofing system  150  and/or the quick-disconnect photovoltaic panels  102  may also include the improved photovoltaic insulation layer  18  described above.  
      Use of the lightweight photovoltaic roofing system  150  provides a more efficient system  150  that may be used on roofs that would prohibit use of known systems because of weight restrictions of the roof  106 ′. Use of the quick-disconnect photovoltaic panels  102  provides for rapid removal of damaged panels, or of outdated panels with minimal risk of damage to the roof membrane  105 ,  105 ′, roof deck  106 ,  106 ′ and/or adjacent panels, and minimizes cost of such replacement by retaining an existing insulation layer  104  and any ballast components  156 ,  166 . The quick-disconnect photovoltaic panels  102  may be used in known photovoltaic systems, or the photovoltaic systems  10 ,  40 ,  72 ,  150  of the present invention described above.  
      While the present invention has been disclosed with respect to the described and illustrated embodiments, it is to be understood that the invention is not to be limited to those embodiments. Accordingly, reference should be made primarily to the following claims rather than the foregoing description to determine the scope of the invention.