Patent application title: Hybrid Solar Thermal and Photovoltaic Collector
Dale N. Skillman (Rapid City, SD, US)
IPC8 Class: AF24J250FI
Class name: Collector housing cover glass
Publication date: 2012-02-02
Patent application number: 20120024283
A single air or liquid type flat-plate solar collector assembly with a
variable area proportion of the hybrid and solar thermal functions,
having: a channel having a front, a back, opposite sides, a bottom inlet
opening and a top outlet opening; a photovoltaic collector cover disposed
across a hybrid portion of the front of the channel; and a transparent
glazing covering disposed across a solar thermal portion of the front of
the channel. Preferably, the body of the collector utilizes a standard
standing seam metal panel with associated mounting expansion clips, and
the photovoltaic collector cover and transparent glazing are both held
onto the panel by a glazing mounting channel affixed to the standing seam
of the metal panel.
1. A combined hybrid/solar thermal solar collector, comprising: a
contiguous channel having, a front, a back, opposite sides, a bottom
inlet opening and a top outlet opening; a photovoltaic collector disposed
across a lower portion of the front of the channel; and a transparent
glazing cover disposed across an upper thermal portion of the front of
2. The combined hybrid/solar thermal solar collector of claim 1, wherein a working fluid passes through the channel, and the working fluid is a gas.
3. The combined hybrid/solar thermal solar collector of claim 1, including an additional third layer of internal film glazing and wherein a working fluid passes internally through the heat exchanger, and the working fluid is a liquid.
4. The combined hybrid/solar thermal solar collector of claim 1, further comprising: a solar thermal absorber disposed in the upper portion of the channel behind the transparent glazing covering.
5. The combined hybrid/solar thermal solar collector of claim 4, wherein the solar thermal absorber is a flat panel that is spaced apart and insulated from the back of the channel.
6. The combined hybrid/solar thermal solar collector of claim 4, wherein the solar thermal absorber is mounted at the top of the channel and is free to expand and contract along a length of the interior of the channel.
7. The combined hybrid/solar thermal solar collector of claim 1, wherein the photovoltaic collector covers a proportion, determined by design, of the front of the channel and the transparent glazing covering covers the remaining thermal proportion of the front of the channel.
8. The combined hybrid/solar thermal collector of claim 1, wherein the channel is closed across its front, back and opposite sides to permit air or a fluid to enter the channel at the bottom inlet opening and to exit the channel at the top outlet opening.
9. The combined hybrid/solar thermal collector of claim 1, wherein the front of the channel is closed by relative proportions of the photovoltaic collector cover and the transparent glazing cover.
10. The combined hybrid/solar thermal collector of claim 1, wherein the back and opposite sides of the chamber are formed from a single modular metal standing seam metal roofing or siding section.
11. The combined hybrid/solar thermal solar collector of claim 10, wherein the single modular standing seam metal roofing section is a Butler Manufacturing MR-24.TM. roofing section.
12. The combined hybrid/solar thermal collector of claim 1, wherein the photovoltaic collector cover is made of either a thin film amorphous silicon or a rigid crystalline silicon photovoltaic module.
13. The combined hybrid/solar thermal solar collector of claim 1, wherein the transparent glazing is made of a pair of transparent or translucent glass, fiberglass or polycarbonate films separated by an insulating air gap.
14. The combined hybrid/solar thermal solar collector of claim 1, wherein the glazing is made of at least one pane of glass.
15. The combined hybrid/solar thermal collector of claim 4, wherein the solar absorber panel is made of a thin gauge metal with a selective absorber finish on the front side.
16. The combined hybrid/solar thermal collector of claim 4, wherein the solar absorber panel is made of a liquid heat exchanger with a selective absorber finish on the front side.
17. The combined hybrid/solar thermal solar collector of claim 10, wherein the photovoltaic collector cover is mounted onto the front of the air channel by way of a contiguous extruded architectural glazing channel that is affixed to the standing seam portion of the metal panel.
18. The combined hybrid/solar thermal solar collector of claim 17, wherein the transparent glazing is mounted onto the front of the channel by a contiguous extruded glazing channel that is affixed to a standing seam portion of a standing seam metal roofing panel.
19. The combined hybrid/solar thermal solar collector of claim 1, further comprising: a bulkhead attached to a building, wherein the combined hybrid/solar thermal collector is suspended from the bulkhead.
20. The combined hybrid/solar thermal solar collector assembly of claim 17, wherein the collector comprises a solar thermal absorber disposed in the upper portion of the channel, and wherein an architectural glazing support framework transfer the combined weight of the photovoltaic and transparent glazing channel cover to the bulkhead.
TECHNICAL FIELD AND BRIEF DESCRIPTION
 The present invention relates to utilization of standing seam metal panels as the platform for constructing building integrated or retrofitting combined function solar collectors in a single assembly and with variable area proportions of the hybrid solar collector type and the flat plate solar thermal collector type.
BACKGROUND AND ADVANTAGES OF THE INVENTION
 Various designs of either hybrid or solar thermal collectors have been around for years. Typically solar collectors are centrally manufactured as modules with a single dedicated function, either hybrid, which is a combination of photovoltaic and solar thermal, or photovoltaic only or solar thermal only. The present invention provides unique advantages by combining both the hybrid and solar thermal functions into a single, site fabricated assembly with variable proportions of collector area dedicated to the hybrid function and the balance of the area dedicated to the solar thermal function depending on the nature of the energy load to be met.
 Also, single function solar collectors of both types (thermal and photovoltaic) are typically centrally manufactured modules which are designed to be mounted onto a structure rather than being integrated into the structure. Solar collectors that are integrated into a building are collectors which perform as a functional element in the building envelope in addition to their energy conversion function. The present invention provides a cost effective solution to the problem of integrating a collector into the building by utilizing a standing seam metal panel, which typically serves as the weather membrane element of the building envelope, and may additionally serve as the platform for integrating both hybrid and/or solar thermal collector assemblies into the building envelope. Although particularly cost effective in new construction, the present invention is suitable for retrofit onto existing structures as well.
 A common problem in photovoltaic modules used in all collector configurations has to do with the decrease in solar/electric conversion efficiency with an increase in temperature. This is particularly true for crystalline silicone photovoltaic collectors where the efficiency may drop by a half percent/degree C increase in temperature. The increase in temperature experienced by the photovoltaic module in any collector assembly is a result of the fact that as solar energy is absorbed only about 10% is converted to electricity. Most of the balance of the solar energy absorbed actually raises the temperature of the photovoltaic module. This increase in temperature creates the opportunity to recover thermal energy from the photovoltaic module itself in addition to the electricity it generates. Both thermal energy and electricity are produced by a typical hybrid collector. The problem encountered when combining the photovoltaic and thermal functions into a single assembly is this, high temperatures that are good for the thermal function are bad for the photovoltaic function. This present invention solves this problem by creating the hybrid function and the solar thermal function sharing a common air channel and with the hybrid section of the assembly receiving the coolest air available. This cool air will assist in keeping the operating temperature of the photovoltaic module as low as possible. Additionally, while the underside of the photovoltaic module is cooled by the forced convection of a cool thermal fluid, the top side is exposed to the environment and is cooled by natural convection. This cooling arrangement with natural convection on the top side and forced convection on the bottom side of the photovoltaic module should provide better overall cooling of the module than would occur in a typical photovoltaic installation with natural convection cooling only on both sides of the photovoltaic module.
 Another common problem with building integrated solar collector systems is the expansion and contraction of the involved building envelope elements with temperature changes. One must accommodate the differential thermal expansion between the involved building envelope elements and the supporting structure. No involved element may be rigidly attached to the supporting structure in multiple locations. The present invention solves this problem in three distinct ways. First, the entire standing seam metal panel system that is utilized is of a design that may be mounted to a wall or roof or inclined support structure. In addition, it preferably utilizes differential expansion clips which are designed to accommodate some relative expansion between the metal panel and the supporting structure without tearing holes in the metal panel. Secondly, the metal panel finish over its entire length is of the "cool roof" type, with a high reflectivity and a high emmisivity. This "anti-absorption" finish keeps the standing seam metal roof panel itself as cool as possible thus mitigating the differential expansion problem. Thirdly, a separate flat plate absorber, dedicated to either air or liquid heating, complete with a high performance selective absorber finish, may be installed above the standing seam panel face. This selective absorber has a finish with a very high absorptivity and a very low emmisivity and when heated by the sun, may attain temperatures around 300F. Excessive thermal expansion would result if the standing seam metal roof itself got this hot. However, the present flat plate absorber both shades the standing seam panel and through the use of a high performance insulating blanket is thermally decoupled from the standing seam metal panel. This allows for a much cooler standing seam metal panel and thus much less differential thermal expansion to be accommodated by the metal panel mounting system. Preferably as well, the flat plate absorber is supported longitudinally from a bulkhead at the top of the collector and is free to expand and contract without compromising the metal panel weather membrane function.
 Another problem with utilizing standing seam metal panel systems which, by design, include an expansion clip mounting system is that these expansion systems are typically functional only on relatively low pitches. At a steep pitch the weight of the metal panel assembly alone will cause the expansion clips to travel to the bottom of their throw thereby compromising their expansion capability. In solar applications it is desirable that the standing seam metal panels to be used as the platform for a solar collector assembly that may be installed at orientations ranging continuously from horizontal roofs to vertical walls. The present invention solves this problem in steep pitch installations by providing an external support for the entire assembly including; the standing seam metal panel, the flat plate absorber and the glazing and photovoltaic module system. The present mounting system supports the longitudinal load of these elements rather than depending upon the expansion clips to support any of the longitudinal loads which include the combined weight of the standing seam metal panel, the flat plate absorber, the photovoltaic module and the clear glazing. The attachment point is typically located at the top of the pitch and is affixed rigidly to the underlying building structure. The element which supports the entire longitudinal load of the assembly is referred to herein as a bulkhead and is the only rigid longitudinal affixment to the supporting structure along the full length of the collector.
 Another problem of combining the hybrid solar function and the solar thermal function into a single contiguous assembly is the creation of a channel or duct to carry the working fluid. This problem is solved by the current invention. Specifically, a channel is created by installing a cover disposed above the standing seam metal panel. When air is used as the working fluid, the air is circulated by forced convection within this duct or channel (which is disposed behind the front cover of the device and above its rear panel). A first (lower) section of the present collector assembly comprises a hybrid collector with the cover being an opaque photovoltaic module. This photovoltaic module has the structural integrity to be used as the front portion of the collector cover exposed to the environment. The collector cover then transitions into a second (upper) portion comprising a clear glazing to accommodate the solar thermal function. As air enters the inlet/hybrid section of the channel, it is heated initially by convectively cooling the back side of the photovoltaic module (which acts as an opaque channel cover). Exiting the hybrid section, the air in the common channel then enters the solar thermal section (which has a clear channel cover or glazing). The air flowing in the channel is now heated by forced convection from the absorber flat plate.
 Another problem of adding a cover to a collector installed at high pitch is the support of the weight of the covers and absorber flat plate. The present invention solves this problem by supporting the weight longitudinally along the length of the collector assembly by hanging the covers and the absorber flat plate from the bulkhead.
 Another problem of adding a cover to a collector to create a channel is the sealing of the air channel. The channel must be weather tight from the outside and air tight from the inside continuously from its inlet to its outlet. This problem may be solved by utilizing a glazing channel that runs the full length of the collector (which preferably has a channel within which to mount the covers). In addition to maintaining an air tight seal, the present mounting system also accommodates the differential expansion between the cover and the supporting structure. Also, while the weight of the cover is longitudinally supported from the bulkhead, the present cover mounting system holds the covers on to the face of the panel in the normal direction. This advantageously prevents the collector covers from being pulled off the face of the assembly by low pressures caused by the wind. The glazing channel also allows one, during the assembly of the collectors, to insert the covers, both photovoltaic and clear glass, from either the top or the bottom end. This ability simplifies the assembly process. A horizontal glazing channel seals the joint between individual cover sections.
 Another problem experienced with modular photovoltaic, solar thermal and hybrid units is their high cost. This is due partially to the modular construction which must be robust enough to withstand the rigors of shipping and handling. The present invention solves this problem by creating a jobsite-fabricated, building-integrated assembly. First, solar system costs are reduced by the dual-function, building-integrated system. Secondly, shipping costs are reduced by having all components ship in very dense, i.e. in a coiled or nested and stacked, form.
 Another problem experienced in the field is the relatively low temperature range achievable with air-type flat plate solar thermal collectors. Even when using a selective absorber on the absorber plate and a low iron glass cover with a matt finish on the surface, the attainable temperature range is only from approximately 140-180 degrees F. The present invention solves this problem when higher discharge temperatures are required. First, the air-type flat plate solar absorber is replaced with a liquid/radiation heat exchanger with a selective absorber finish applied to the front face. This liquid heat exchanger is located in the same relative position as that occupied by air-type flat plate absorber. To further enhance the thermal performance of this assembly, a single transparent film of high temperature material such as Teflon is secured across and above the heat exchanger. This thin film creates a third layer of collector cover. This triple glazed liquid-type flat plate collector is expected to produce discharge temperatures up to 250° F. This is an example where flat plate technology may perform as well as some of the concentrating collectors available.
SUMMARY OF THE INVENTION
 The present invention combines, in a single solar collector assembly, a hybrid (photovoltaic and thermal) section and a straight thermal section. The relative proportions of the hybrid section and the thermal section are variable by design. Specifically, prior to fabricating the present collector, the designer determines the optimal dimensions of each the hybrid and the thermal sections. This proportion is based on the demand for electricity vs thermal output. Thus, the present collector can be made 1/3 hybrid, and 2/3 straight thermal, or 1/2 hybrid and 1/2 straight thermal, or any other relative dimensions selected. In fact, in optional embodiments, all of the present collector can be made to be hybrid collector, or all of the collector can be made to be a thermal collector. The hybrid section simultaneously generates electricity photovoltaically and heats the working fluid convectively. In one preferred embodiment, the working fluid is air (or any other suitable gas). In another preferred embodiment, the working fluid is a liquid (such as water or any other suitable liquid). The solar thermal section heats the working fluid, either air or liquid, convectively only. The present collector preferably comprises: a channel having a front, a back, opposite sides, a bottom inlet and a top outlet; with a photovoltaic collector disposed across the hybrid bottom portion of the front of the channel; and a transparent glazing with an exterior matt finish covering disposed across the upper thermal portion of the front of the channel. Note: as defined herein, transparent also includes translucent, or any other light permissible material.
 In the solar thermal section of the collector, a solar thermal absorber is disposed within the upper portion of the channel behind the transparent glazing covering. When air (or other gas) is the working fluid, this solar thermal absorber is preferably a panel that is spaced apart from the back of the channel via insulation, and is suspended in the channel being affixed to an affixment point at the top of the channel. Preferably, the absorber, being a flat plate (for air) or a heat exchanger (for liquid) is affixed to a bulkhead. This solar thermal absorber, supported from its upper end, is therefore free to expand and contract relative to and along the length of the interior of the channel. When water (or any other liquid) is the working fluid, the solar thermal absorber may be a plate-type heat exchanger with internal passages for liquid flow.
 In preferred embodiments, the back and opposite sides of the channel are formed from an existing single modular standing seam steel roofing or siding section (such as a Butler Manufacturing MR-24® roofing section). In this exemplary embodiment, both the photovoltaic cover of the lower hybrid section and the transparent glazing thermal of the upper solar thermal section are easily mounted onto the MR-24 roofing system using a custom architectural glazing system. Similar to the thermal absorber panel, the glazing cover(s) and the glazing channels may be suspended in combination from a mount at the top of the assembly (for example, from a bulkhead).
 The present invention has many advantages. Most importantly, this invention affords the opportunity to integrate, in variable area proportions by design, both the hybrid function and the solar thermal functions, air or liquid type, into a single contiguous assembly. For the air heating configuration (where air is the working fluid), the air flow channel begins at the inlet end and extends uninterrupted to the outlet end. The hybrid collector cover, however, located near the inlet end of the air channel is comprised of photovoltaic modules. At some point along the assembly length (as determined by design), the cover material transitions to a clear glazing facilitating the solar thermal function. The solar thermal function extends from the glazing transition upwards to the air channel outlet. The relative area proportions of the hybrid vs solar thermal is determined by design as a function of the actual electrical and thermal load the system is designed to meet.
 Another advantage of the present invention in its air heating configuration is that air is heated within the collector by forced convection, however, this heated air does not heat the photovoltaic panel. Instead, relatively cool air entering at the bottom of the device actually cools the back of the photovoltaic panel thereby heating the air flowing in the air channel. Keeping the photovoltaic panel cool increases its electrical conversion efficiency. This overcomes the major drawback of existing photovoltaic collectors (which are cooled by natural convection only on the front and back surfaces). Therefore, whereas existing systems must compromise between solar electric and solar thermal optimization, the present invention permits both to be optimized in a single combined function collector assembly.
 Moreover, the present collector preferably uses an interior solar absorption panel to heat the working fluid. This solar absorber panel is preferably mounted in the collector in a way to shade the sides and back of the air channel from radiation while a space behind the absorber filled with insulation separates the absorber panel from the back of the collector, thereby providing an effective thermal break between the absorber and the metal roof panel itself. Such a design has the advantage of reducing the temperature of the sides and back of the metal roof panel itself (such that the roof itself doesn't overheat and over-expand). Moreover, this solar thermal panel may be mounted such that it is free to expand (while heating) and contract (while cooling) within the collector channel. This effect lowers the temperature of the metal roof panel and thereby reduces its thermal expansion and contraction and associated strains on the metal roof mounting system itself. Moreover, this solar absorber panel will have a selective absorber finish on its front side. This surface heats due to radiation and in turn heats the working fluid that flows over or within due to forced convection.
 Third, the present collector body can be formed out of (and/or mounted to) a standard metal roofing system including, but not limited to, a Butler Manufacturing MR-24® Standing Seam Metal Panel. As a result, the present system is relatively inexpensive to make and to install as compared to single function collector assemblies installed "onto a structure" rather than integrated "into the structure", i.e. "building integrated".
BRIEF DESCRIPTION OF THE DRAWINGS
 FIG. 1 is a perspective schematic sectional view of the present combined function hybrid/solar thermal collector (showing a plurality of collectors mounted together side-by-side).
 FIG. 2A is a sectional side elevation view through the present hybrid/solar thermal collector when the working fluid is air.
 FIG. 2B is a sectional side elevation view through the present hybrid/solar thermal collector when the working fluid is a liquid.
 FIG. 3A is a view taken along line 3-3 in FIG. 2A.
 FIG. 3B is a view taken along line 3-3 in FIG. 2B.
 FIG. 4A is a view taken along line 4-4 in FIG. 2A.
 FIG. 4B is a view taken along line 4-4 in FIG. 2B.
 FIG. 5 is a sectional elevation view illustrating the glazing channel which is dimensioned to receive either a photovoltaic panel or a clear glazing section.
 FIG. 6 is an illustration of the present invention being placed onto the roof of a building.
DETAILED DESCRIPTION OF THE DRAWINGS
 As seen in the attached Figs, the present invention provides a novel hybrid solar thermal and photovoltaic collector 20. As illustrated, a plurality of these collectors 20 are positioned side-by-side. Each collector 20 comprises: a channel 30 having a front 32, a back 34, opposite sides 36, a bottom channel inlet 38 and a top channel outlet 39; a photovoltaic collector 40 disposed across a lower portion L of the front 32 of the channel 30; and a transparent glazing covering 50 disposed across an upper portion U of the front 32 of the channel 30. As seen in FIG. 1, horizontal glazing mounting elements 35 separate and seal adjacent cover modules, photovoltaic or clear glazing, along the longitudinal length of the collector assembly.
 FIGS. 2A, 3A and 4A illustrate an embodiment of the invention in which the working fluid is air (or other gas). FIGS. 2B, 3B and 4B illustrate an embodiment of the invention in which the working fluid is water (or other liquid).
 Referring first to FIGS. 2A, 3A and 4A a solar thermal absorber panel 60A (which may comprise a flat plate) may be disposed in the upper portion U of the channel 30 behind translucent or transparent glazing 50. Preferably, solar thermal absorber panel 60A is a panel that is spaced apart from the back 34 of channel 30, leaving an insulation filled gap 61, thereby creating a "thermal break".
 In operation, light from the sun S will be incident directly on photovoltaic panel 40 and on glazing 50. The light on photovoltaic panel 40 is used to produce electricity. In preferred embodiments, photovoltaic collector 40 may be made of thin film amorphous silicon or of a rigid crystalline silicon. It is to be understood, that the present invention is not so limited, and that any suitable photovoltaic panel or system may be used.
 The light incident on transparent glazing 50 passes through and reaches solar absorber panel 60A. Glazing 50 may optionally be made from a pair of transparent or translucent glass, fiberglass or polycarbonate sheets or PVDF or Teflon films separated by an insulating air gap(s). Solar absorber panel 60A is preferably made of a thin gauge metal with a selective absorber finish on its front side. In one embodiment, the selective absorber finish is a black chrome anodized finish. (However, any other suitable material or finish with high absorptivity and low emissivity may be used). The selective absorber finish may be baked on similar to the finish applied to metal siding and heavy architectural trim. When light hits panel 60A, it the solar energy is absorbed and the panel will heat up, thus warming the air in channel 30 convectively. The channel 30 is closed across its front 32, back 34 and opposite sides 36 to permit air to enter the air channel at the bottom air inlet 38 and to exit the air chamber at the top air outlet 39.
 Referring next to FIGS. 2B, 3B and 4B, an embodiment of the invention in which the working fluid is water (or other liquid) is described. In this embodiment, the solar absorber 60B comprises a plate-type heat exchanger with a selective absorber finish on its front side. When light hits heat exchanger 60B, the solar energy is absorbed and the panel will heat up, thus warming the liquid in channel 30 (which passes within the heat exchanger). In this liquid collector configuration, water flows from the inlet at the bottom, thru internal passages in heat exchanger 60B and out the top. This heat exchanger 60B is preferably covered by a thin high-temperature film 55, such as Teflon, which creates a third layer of glazing and an additional air gap insulating the heat exchanger from the environment and thus producing relatively high water temperatures at the outlet.
 As seen in the mounting orientations of FIGS. 2A and 2B, channel 30 is preferably angled to the ground to optimize the incident sun angle and overall energy conversion efficiency. The collector assembly may, however, function from a vertical to a horizontal orientation. In the air embodiment of FIGS. 2A, 3A and 4A, forced air flow in channel 30 rises, heated air will exit at top air outlet 39. Cooler air is introduced by forced convection into channel 30 through bottom air inlet 38. This cooler air entering the bottom of the system will have the advantage of cooling the back side of photovoltaic panel 40. This cooling has the beneficial effect of raising the electrical conversion efficiency of photovoltaic panel 40.
 When the working fluid is a gas, it is also to be understood that the solar thermal panel 60A is merely exemplary and that the present invention is not limited to embodiments having such a separate solar thermal absorber panel. For example, the present invention also encompasses designs in which there is no separate solar thermal absorber panel. For example, the back 34 and opposite sides 36 of the collector 30 may instead be finished with a suitable dark coloring or covered with a suitable coating such that light incident thereon will heat the back 34 and/or sides 36 is absorber and thereby convectively warming the air flowing in the collector channel.
 In optional preferred embodiments, solar thermal absorber panel 60A is preferably mounted at its top end 62 to the bulkhead anchor 80. The opposite lower end 64 of panel 60 is not attached to the interior of channel 30. As a result, panel 60 is free to expand and contract along a length of the interior of the air chamber. Specifically, as light passes through glazing 50, and reaches the thermal absorber panel 60, the panel will heat up and thus expand in length. Conversely, at night or during cloudy weather, less light will pass through transparent glazing 50, and panel 60 will not be heated as much. At that time, panel 60 would contract in length. This design has the advantage that the expansion and contraction caused by the sun primarily borne by panel 60 rather than being borne by the metal roof system itself.
 As can be seen, channel 30 has the unique advantage that the lower portion L generates both electrical and thermal energy while the upper portion U generates thermal energy in the form of a heated working fluid. In the air type configuration (FIGS. 2A, 3A, 4A) forced convection introduces cooler air into the bottom inlet of the system to boost the efficiency of the electrical energy generation. It is to be understood that the relative dimensions of the upper and lower portions (U and L respectively) may be varied when constructing different designs. Thus, different channels 30's can be designed and manufactured with different percentages of their face 32 being covered by photovoltaic collector 40 and transparent glazing 50. In one exemplary embodiment, photovoltaic collector 40 covers approximately one third of the front 32 of air channel 30 and transparent glazing covering 50 covers approximately two thirds of the front 32 of air channel 30. It is to be understood however, that any relative dimensions are contemplated within the scope of the present invention. In addition, the present invention may be designed to be fully hybrid or fully solar thermal. Moreover, as seen in FIG. 1, horizontal glazing mounting elements 35 can be used to separate the photovoltaic and glazing sections (40 and 50) from one another. When the photovoltaic panel 40 is a rigid crystalline silicon, these photovoltaic sections are short, and more horizontal glazing mounting elements 35 may be used between adjacent photovoltaic sections. Conversely, when the photovoltaic panel 40 is made of thin film amorphous silicon, the photovoltaic sections are longer, and horizontal glazing mounting elements 35 therebetween may not be required.
 As seen in FIGS. 3A, 3B, 4A and 4B, the back 34 and opposite sides 36 of channel 30 may optionally be formed from a single modular steel roofing or siding section. As a result, the present system is easy to retrofit on existing structures, or build in a stand-alone device. Additionally, in its least expensive configuration, the present collector assembly is integrated into new construction and serves the function of the weather membrane. In one preferred embodiment, a standing seam steel roofing section (such as a Butler Manufacturing MR-24® roof panel) may be used. As can be appreciated, a unique benefit of the present system is that it can use an existing metal sheet roof to form most of the collector. As will be shown, photovoltaic panel 40 and transparent glazing 50 can be quickly and easily attached onto the new or existing roof by using architectural glazing framework secured to the seam of each panel in such a way to allow differential expansion between the panel and the glazing system.
 As seen in FIG. 5, a glazing channel 90 forming a continuous channel, metal or extruded EPDM, UV resistant rubber, is affixed to the standing seam and used to both hold sides 36 of two different adjacent collectors 20 together. A batten 70 may preferably mechanically attach to trim and seal the joint. The glazing channel 90 which is affixed to the standing seam secures the glazing system to the body of the collector in a direction normal to the panel surface. Such an affixment provides for relative thermal expansion between the glazing channel and the standing seam roofing system. For example, the left side of glazing channel 90 shows a photovoltaic panel 40 received into a mount 92 which is inserted into glazing channel 90. The right side of glazing channel 90 shows a glear glazing section 50 also received into a mount 92 which is inserted into the opposite side of glazing channel 90. (Glazing channel 90 is first received downwardly onto the standing lock seam 100 formed as a "Pittsburgh Standing Lock Seam" by crimping together the edges of expansion clip 71.
 As can be seen in FIG. 5, glazing channel 90 is dimensioned such that the edges of photovoltaic panel 40 (or glazing 50) can be positioned thereunder. This fastens photovoltaic panel 40 (or glazing 50) across the surface 32 of channel 30. In optional preferred aspects, both the photovoltaic cover (panel 40) and the clear glazing cover (50) are made to be of identical dimensions and detail in order to slideably insert into the glazing channel under batten 70. (Note: batten 70 may either be integrally formed into glazing channel 90, or it may be a separate piece that is later attached on top of the body of glazing channel 90). The individual sections of glazing (either PV panel 40 or glazing 50) may be inserted into the glazing channel one at a time in succession from either the top or bottom end of the glazing channel. The entire glazing system, covers and glazing channel can be indirectly affixed to and suspended from the bulkhead anchor 80.
 In preferred embodiments, transparent glazing 50 may comprise a pair of thin films 52, 54 separated by an air gap 53. Air gap 53 has the benefit of providing thermal insulation such that the heat from channel 30 does not simply pass out of the front of the system through the glazing. Thus, air gap 53 helps to keep the heat in the chamber such that the heated air can be extracted for use at top air outlet 39. In the embodiment in which the working fluid is a liquid, a high temperature Teflon film 55 is a third glazing layer and provides an additional insulating air gap to further reduce heat loss out the face of the panel.
 It is to be understood, however, that the present invention is not limited to dual or triple pane/film glazing. Alternatively, other materials (including low iron glass panes or a combination of glass and film layers) can be used. Moreover, the present invention encompasses embodiments with any number of glazing layers, including single layer glass panes, double layer glass panes and one or more layers of film glazing.
 In installations of steep pitch, the weight of the glazing channels 90, collector covers (40 and 50), the thermal absorber panel (60A or 60B) and the metal roofing panel is preferably supported from its upper end and hung in a curtain-wall fashion from a support element which is rigidly affixed to the supporting structure. This support element is referred to as "bulkhead" 80. In turn, each individual element of the assembly is, in turn, attached to bulkhead 80 at the top of the pitch. This method of affixment and support allows the entire assembly 20 to expand and contract with temperature changes independently from the supporting structure. While the metal panel expansion clips provide attachment of the assembly to the surface of the support structure in a direction normal to the collector surface, the assembly preferably hangs from the bulkhead and is free to expand and contract freely in the longitudinal direction.
 In accordance with the present invention, assembly of a building integrated collector assembly proceeds thusly. First, the metal roofing panel expansion clips 71 are rigidly affixed to the supporting structure. Secondly, the bulkhead 80 is rigidly affixed to the supporting structure at the top of the pitch. Thirdly, the metal roofing panel section 34/36 is placed and typically attached to the expansion clip 71 by way of the standing lock seam which also adjoins adjacent panels 20 together. Fourth, a top end of metal panel 34/36 is clamped into bulkhead 80. Fifth, the thermal absorber panel 60A with back insulation 61 is nested in channel 30 and clamped at its top into bulkhead 80 just above the back 34 of the metal panel. Sixth, the glazing channel 72 is affixed to the standing seam. And Finally the glazing sections, being either photovoltaic modules 40 or clear glazing 50, are slideably inserted into glazing channel 72. Optionally, a batten strip may be affixed longitudinally along glazing channel as asthetic trim.
 Lastly, FIG. 6 illustrates the present invention being placed onto the roof of a building. The vertical lines illustrate the battens 70 covering glazing channels 90 (which run from the top to the bottom of the roof). The horizontal lines 35 represent the glazing mounting elements 35 that separate sections of photovoltaic panel 40 or clear glazing sections 50 from one another.