Abstract:
An integrated solar power collector system for direct installation on an upholding structure includes a plurality of first array of photovoltaic modules. Each array comprises a substrate, defining a module support area, an anchoring zone, a first interlocking zone and a second interlocking zone on an opposite side of the first substrate from the first interlocking zone. A array also comprises collecting surface with a plurality of photovoltaic modules arranged proximal to each other on the module support area so as to leave a minimal residual space between the modules. The substrates are made of a corrugated material so as to present an increased support for the modules and to provide channels for channels for removing the heat dissipated by the modules. Each array is fixed to an upholding structure along the anchoring zone and the first interlocking zone and is fixed to a neighboring module along the second interlocking zone.

Description:
This appln. claims benefit of provisional appln. 60/060,797, Oct. 3, 1997 and Provisional Appln. 60/063,070 Oct. 27, 1997 and provisional appln. 60/067,378 Dec. 3, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention is directed to a solar collector system and in particular to an array of photovoltaic modules for an integrated solar power collector system. 
     2. Background and Related Art 
     Photovoltaic devices made of Selenium have been known since the 19 th  century. The silicon solar cell was the first known photovoltaic device that could convert a sufficient amount of sun&#39;s energy to power complex electronic circuits. 
     A photovoltaic cell is a solid-state device in which a junction is formed between adjacent layers of semiconductor materials doped with specific atoms, in order to create an n-type region and a p-type region. The photons incident on the semiconductor dislodge electrons from the valence band. These electrons, collected by the electric field at the junction, create a voltage which can be put at work in an external circuit. 
     A basic limit on the performance of these devices is that light photons lacking the energy needed to lift electrons from the valence to the conduction bands can not contribute to photovoltaic current, and also the energy transferred to electrons which exceeds the minimum excitation threshold, can not be recovered as useful electric current. Most of the photon energy not recovered as electricity, is converted to thermal energy in the cell. The overall effect is that the efficiency of solar cells does not exceed 16% in commercial devices. 
     As the energy collected is proportional with the surface exposed to solar radiation, and also in order to accommodate the electrical characteristics of the solar cells, in most application 36 (4×9) photovoltaic cells are grouped in a module, the cells being connected in series. The wires between the cells are arranged inside the module and not accessible. The only accessible connections are the “+” terminal of the first cell in the series and the “−” terminal of the last cell. 
     A module usually has an area of 1.5′×3′ or 4′×2′. Larger modules with an area of  16  square feet are also commercially available. A cell generates approximately 0.5 volts, and as a result, a module generates approximately 20 volts open circuit, giving a short-circuit current of 4 to 6 amperes. Still, the power generated by a module is rather low, a fill factor of only 0.5-0.8 can be obtained, depending on the quality of the cells. 
     Therefore, many applications use arrays of modules which are connected to each other in accordance with current and voltage requirements of the application. There are also various ways for electrically connecting the modules; in general, the positive and negative poles of all modules are wired to two bus-bars, or are wired with conductors placed in channels specifically provided on the back of the modules. 
     It is known practice to mount solar modules on rooftops where they are most likely to receive a maximum amount of sunlight without interference from trees or nearby constructions. One method for mounting an array of solar modules on a roof is to first assemble the modules on a base, to form the array, and then to secure the array on the existing rooftop. Special consideration should be given to the wind load, the weight of the snow, and the extra weight of the modules, when designing such a roof-over roof assembly. 
     Another method for mounting an array on the roof is to mount the solar modules individually directly on the roof. In this case, there are a number of operations which must be performed on the roof, such as installing the modules, interlocking the modules to each other, wiring the modules and treating the surface thus obtained to obtain a weather—resistant roof. The modules are fragile and may break if stepped on. As such, walkways must be provided on the roof, which reduce the surface dedicated to the modules. 
     A photovoltaic roofing assembly is disclosed in U.S. Pat. No. 5,505,788 (issued to Dinwoodie on Apr. 9, 1996), where the modules are disposed as a layer on top of the roof, and separated therefrom by pre-formed spacers, pedestals or supports. Use of spacers enables heat exchange with a convecting fluid flowing between the modules and the roof. Preferably, the cooling fluid is air or other gaseous fluid, or could also be a liquid. Besides the disadvantages listed above, it is difficult to mount the spacers on the roof and then the modules on the spacers as in the system disclosed by this patent. 
     There is a need to provide a method for installing an array of photovoltaic modules directly on the roof, which is simple, cost-effective and easy to install. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a solar power collector system which alleviates totally or in part the drawbacks of the prior art photovoltaic systems. 
     It is another object of the present invention to provide an integrated solar power collector system which uses arrays of photovoltaic modules interlocked to form an integrated collecting surface of a desired size. 
     Still another object of the present invention is to provide a solar power collector system comprising a plurality of photovoltaic modules installed on a corrugated substrate. The substrate provides enhanced resistance to stress and facilitates temperature control of the modules. As such, the solar power collector system according to the invention acts as a combined electrical current generator and hot air collector. 
     Still another object of the invention is to provide an integrated solar power collector system which is weather resistant and offers improved resistance to water leakage. 
     Accordingly, the invention provides an integrated solar power collector system comprising a first array of photovoltaic modules including: a first substrate, defining a module support area, an anchoring zone, a first interlocking zone and a second interlocking zone on an opposite side of the first substrate from the first interlocking zone; and a first collecting surface comprising a plurality of photovoltaic modules arranged proximal to each other on the module support area so as to leave a minimal residual space between the modules. 
     A second corrugated substrate, supports a second collecting surface comprising a plurality of photovoltaic modules arranged proximal to each other so as to leave a minimal residual space between the modules. Means for interlocking the second interlocking zone of the first array and the first interlocking zone of the second array to each other provide an integral collecting area. The solar power collector system may be installed directly on an upholding structure, such as the roof of a building. 
     The invention also provides for a method for collecting solar power comprising providing a first array of photovoltaic modules on a first substrate so as to leave a minimal residual space between the modules, the first substrate defining a first collecting surface, an anchoring zone, a first interlocking zone and a second interlocking zone on an opposite side of the first substrate from the first interlocking zone, and fixing the first substrate to an upholding structure along the anchoring zone and the first interlocking zone. 
     A second array of photovoltaic modules is provided on a second substrate, the second substrate defining a second collecting surface, an anchoring zone, a first interlocking zone and a second interlocking zone on an opposite side of the second substrate from the first interlocking zone. The second substrate is fixed to the upholding structure along the anchoring zone, and the first substrate is fixed to the second substrate and to the upholding structure along the second interlocking zone of the first substrate and the second interlocking zone of the second substrate, to provide an integral collecting area. 
     Advantageously, the solar power collector system of the invention alleviates the need for individual framing of the modules, resulting in a system that is lighter and less expensive than systems of the prior art. 
     Another advantage of this invention is that the modules are assembled in arrays at the factory, which results again in cost savings and reduced installation time. The modules may support heavy loads, such as ice and snow, since each is supported along a large portion of its area. 
     Still another advantage is that the electrical connections between the modules are made on the back of the collecting surface, which is in the attic of the building when the system is installed on the roof. In this way, not only the installation is easier to perform, but also the electrical leads are weather protected. 
     The collector system according to an embodiment of the invention has the advantage that it can be used to keep in place the roof tresses using simple/common installation methods. The system is advantageously used in areas where wood is the construction material of choice. 
     Other advantages of the collector system of the invention are that it has a sturdy structure, does not require provision of walkways, it enables temperature regulation under the cells, and the hot air resulting in the process of cooling the cells can be used for heating. 
     All these advantages result in a longer life of the solar cells and of the system according to the invention, and in a higher collection efficiency. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages, features and details of the invention will be apparent from the following description of the preferred embodiments with reference to the drawings, in which: 
     FIG. 1A shows a perspective view of a solar power collector system according to the invention; 
     FIG. 1B shows how the photovoltaic cells are arranged in a module; 
     FIG. 1C shows the support area for the modules; 
     FIG. 2A illustrates a transversal cross-section in the solar system of FIG. 1A, along line S—S; 
     FIG. 2B shows a detail (A) of FIG. 2A, illustrating how two adjacent arrays are assembled to each other; 
     FIG. 2C shows a detail (B) of FIG. 2A, illustrating the electrical connection of the modules; 
     FIG. 3 shows the electrical connections between the arrays; 
     FIG. 4 shows a transversal cross-section in the solar system of FIG. 1A, along line S—S according to another embodiment of the invention; 
     FIG. 5 shows a partially perspective, partially open view of a solar energy collecting surface according to another embodiment of the invention; 
     FIG. 6A is a cross-section along lines A—A in FIG. 5; 
     FIG. 6B shows a cross-section along lines B—B in FIG. 5; and 
     FIG. 7 illustrates the electrical and air circuits for the solar system used as a collector roof. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1A shows a perspective view of a solar power collector system  100  comprising two arrays  10  and  20  of photovoltaic modules according to the invention. Each array  10 ,  20  of solar power collector system  100  comprises a plurality of photvoltaic modules arranged in rows and columns, and fixed on a respective substrate  30 ,  40 . A column of modules of system  100 , such as column C 1  comprises modules  1 ,  3 ,  5  and  7 , whereas a row, such as row R 1  comprises modules  1 ,  2 ,  1 ′, and  2 ′. A module is characterized by a length (l) and a width (w); these definitions will be used in the following also for designating sides “/”, and respectively “w” of a module. 
     While solar system  100  illustrated in FIG. 1A has 4×4 modules, it is to be understood that the number of modules of collector system  100  is selected in accordance with the size of the upholding structure to be covered, and on the power necessary for the respective application. The modules and the substrate are selected so as to obtain a maximum area of exposition to sun for the size of the upholding structure on which it is installed. 
     Array  10  comprises modules  1 - 8  arranged in rows and columns on substrate  30 , while array  20  comprises modules  1 ′- 8 ′ arranged on substrate  40 . The corrugations, or ribs,  11  to  19  are illustrated with a trapezoidal profile on FIG. 1A, however other profiles are acceptable, as long as the upper sides of the ribs form a flat surface for providing an as large as possible area of support for the modules. The top face of a rib is denoted here with “i” (see FIG.  2 A), which will also be used to define the width of the rib. Channels  21  to  28  are formed between the modules and the respective substrates  30  and  40 . The arrays are interlocked to each other in a simple manner, to form the unitary solar power collector system  100 . 
     A plurality of substrates  30 ,  40  may be fixed to each other to form a base  50  of a desired width H and length “L”. Base  50  has a plurality of functions: it supports the modules, it offers a larger cooling surface for the modules than a flat substrate, and also acts as a heat collector. 
     In the example of FIG. 1A, the modules are arranged with side “w” oriented along ribs  11 - 19  of base  50 . The distance between two adjacent ribs, denoted herein with λ, is in a 2:1 relationship with side “/” of the modules, such that each module is supported by three ribs. 
     As also shown in FIGS. 1C and 2A, module  2  is supported in its middle by rib  14  on an area  14 ′ defined by the width “/” of the top face of this rib and the width “w” of the module. As well, module  2  is supported along sides “w” by ribs  13  and  15 , on areas  13 ′ and respectively  15 ′, defined by less than ½ of the width of the upper side rib and the width of the module. 
     For a general case, the ratio “R” between “/” and “λ” should be an integer selected such that a module can be arranged on the substrate with sides “w” supported by half of a rib. 
     This arrangement results in a sturdy structure, since the modules are supported in the middle, where they may broke easily if not supported. They are also supported along two edges. As such, a person may walk on the roof system without damaging the modules. 
     FIG. 1C also illustrates channels  21 - 28  formed under the modules. These channels are used according to this invention for providing a heat exchange between the modules and a flow of cool air that removes the heat generated by the cells and uses the air so heated as need be. 
     FIG. 1B illustrates a module  1  without the upper cover for showing the photovoltaic cells, designated with reference numeral  115 . As indicated above, the modules are off-shelf components. For example, a module that is currently available on the market and can be used for this invention is CANROM-60™ which generates 20.5 V open circuit, has a short-circuit current of 4.6 A, and a rated power of 60 W. The voltage and current at the maximum power point are 16.0 V, and respectively 3.9 A. The size of this module is  21 ′/ 46 ′ (53.3/116.8 cm). It is to be understood that other types of modules may be used for this invention, as required by the application. 
     System  100  is attached to the upholding structure, such as for example to the roof truss of a building, along sides  110 ,  120  and  130  of base  50 . While the attachment along side  130  of the substrate may or may be not always necessary, the upper side  110  should always be used for fixing the system to the upholding structure. 
     To this end, each substrate  30 ,  40  is provided with an anchoring zone at the upper side  110 . This means that the substrates are cut longer with a distance “d” than the cumulated width of the modules forming a column. For example, width “H” of substrates  30  and  40  in FIG. 1A is 4×(w)+(d) and plus three times the residual distance between the modules. Holes  105  are perforated in the channels between the ribs, and the arrays  10  and  20  are fixed with screws to the upholding structure. 
     Base  50  is shown in the appended drawing as comprised of two substrates of corrugated material, namely substrates  30  and  40 , but it is to be understood that the number of substrates depends on the size of the modules available, the size of the roof, the electrical power necessary for the respective application, and other design parameters, as it is well known to a person of ordinary skill in the art of solar power collectors. 
     The arrays are interlocked to each other such that the modules from a continuous collecting surface, with minimal residual space in-between. To this end, each substrate is provided with a first and a second interlocking zone on two opposed sides of the respective substrate. Each interlocking zone has the length “H”, and a width of approximately λ. As such, width “L1” of corrugated substrate  30  is minimum 4+1 ribs in the example of FIG. 1A, or is minimum “R” times the number of columns of the array plus one rib, in the general case. 
     Two adjacent substrates are arranged so that the second interlocking zone of the first substrate overlaps with the first interlocking zone of the second substrate. The second interlocking zone of corrugated substrate  30  comprises the portion from the rib  15  to the right, while the first interlocking zone of the second substrate  40  comprises the portion from rib  15  to the left. The substrates are fixed to each other as it will be explained later in further detail. 
     The first array  10  is also fixed to the upholding structure along the first interlocking zone of substrate  30 , which comprises the portion from the rib  11  to the left. To this end, holes  106  are perforated in the first interlocking zone of substrate  30  and array  10  is fixed to the upholding structure with screws. 
     It is to be understood that other fixing means may be used for fixing the solar power collector system to the upholding structure. 
     FIG. 1A also illustrates that corrugated substrate  40  extends outwardly from under the modules by half of rib  19 , showing a case when an additional array may be attached to the right of array  20 . If array  20  is the last, a zone with a length H and a minimum additional width of λ/2+r/2 is provided along side  130 . Thus, the last array may also be fixed to the upholding structure on the right side, in a similar manner as is array  10  at its left. 
     The first and second interlocking zones may be wider that the dimensions suggested above, it is important that they comprise at least a channel, for allowing easy attachment to the upholding structure. 
     Modules  7 ,  8 ,  7 ′ and  8 ′ are flush to substrates  30  and respectively  40  along side  140 . 
     FIG. 2A illustrates a transversal cross-section in the system  100  of FIG. 1A along lines S-S′, showing ribs  13  and  14  of substrate  30 , rib  15  made by both substrates  30  and  40 , and rib  16  of substrate  40 . Module  2 , supported by ribs  13 ,  14 , and  15 , forms with base  50  channels  23  and  24 . Module  1 ′, supported by ribs  15 ,  16  and  17 , forms with base  50  channels  25 ,  26  and  27 . Rib  17  and channels  26  and  27  are not illustrated on FIG. 2A, but they are apparent on e.g. FIG.  1 C. 
     The modules are fixed to the respective substrates using a means for fixing, which can be for example a water resistant glue shown at  31 . Any other suitable means for fixing may be used, as long as it provides a reliable attachment of modules to the upper side r of the ribs of base  50 . 
     FIG. 2B shows how substrates  30  and  40  of the respective arrays  10  and  20  are interlocked to each-other (detail A), namely how substrates  30  and  40  are assembled to form base  50 . Thus, the second interlocking zone  32  of substrate  30  is arranged to overlap on the first interlocking zone  33  of substrate  40 , such that the resulting rib  15  has a cross-section approximately equal to the cross-section of the other ribs. The interlocking zones  32  and  33  are fixed to each other and to the upholding structure  300  using, for example, screws  34  placed through in holes  107  and secured with growers  35  and nuts  36 . Holes  107  are provided in zones  32  and  33  at intervals determined by the size and weight of the modules and substrate. 
     Also seen on FIG. 2A are the J-boxes  62 , and  63  used for connecting the positive and negative poles of modules  2  and respectively  1 ′, while FIG. 2C shows in detail the electrical connections between a module and a corresponding J-box (detail B). 
     FIG. 2C shows a J-box  62  is fixed under rib  14 , that supports the middle section of module  2 . Rib  14  has two holes  36 , to pass a respective negative terminal  41  and the positive terminal  42  of module  1 ′ to J-box  63 . As it is readily understood, the J-box can be accessed from other side of the upholding structure, such as from the attic of the building when system  100  is used as a roof. In this way, the positive and negative terminals from all modules can be connected in series or in parallel, as needed. 
     By placing the J-boxes inside the building, they are easy accessible for electrical connection and maintenance. In addition, being under the roof, the J-boxes are protected against humidity, penetration of water, wind, etc. 
     Holes  36  are properly sealed to avoid penetration of the water using any suitable sealant. As well, the space between the modules is sealed with adhesive tape  37  (FIG.  2 B), or any other sealing means. 
     FIG. 3 illustrates the electrical connection between the J-boxes. For example, all positive poles  42  of J-boxes of column C 3  may be connected to each other, to obtain a single positive terminal for column C 3 . Similarly, all negative poles  41  of J-boxes of column C 3  may be connected to each other to obtain a single negative terminal for column C 3 . Next, all negative and positive terminal of columns C 1 -C 4  may be connected in parallel. However, the columns may be connected in series, as need be. This arrangement results in important economies in wires. 
     Substrates  30 ,  40  of base  50  are preferably made of a suitable thermoplastic material such as PVC, for reducing condensation of the moisture inherently present in the air inside the building. The substrates can be vacuum formed with the ribs, channels and interlocking features in place. 
     In this case, the EVA (Ethylene-Vinyl-Acetate) material which is used for the lamination of the solar panel can be considered as an adhesive for fixing the modules to the substrates. The process of manufacture of a module, such as modules  1 - 8 , comprises applying EVA material on a sheet of glass, then placing the solar cells  115  on the glass with the EVA. The cells are electrically interconnected at the time when they are applied on the glass. Another layer of EVA is laid thereafter on the cells, and the sandwich so formed is covered with a foil of Tedlar®, which is a moisture resistant plastic sheet. 
     The sandwich is heated up at maximum 100° C. in a laminator, in vacuum, and compressed to eliminate trapped air. Thereafter, the module is maintained for approximately twenty minutes at 100° C., with or without pressure. This cycle cures the EVA material so that it looses its thermoplastic characteristics. 
     According to the present invention, solar modules  1 - 8  and  1 ′- 8 ′ are placed on the vacuum formed corrugated substrates  30 ,  40 , before the curing cycle is completed. The modules adhere firmly to the sheet as the curing cycle is completed outside the laminator. 
     Curing is thus achieved in a simple way, without the need of a laminator. In addition, the operation of adhering the panels to the substrate as a separate step is practically eliminated by this method. 
     Base  50  may be reinforced with wood ribs placed as necessary. The ribs may be used to additionally facilitate fastening of the panels on the roof. 
     FIG. 4 illustrates a cross-section along line S—S of FIG. 1 for another embodiment of the invention. This solution was provided for reducing condensation when the system of the invention is used as a solar power collector roof in countries where the temperature drops significantly during winter. Condensation may occur on the underside of the array, as shown at  47 , due to the difference between the outside temperature and the temperature inside the building, and also to the rather high level of humidity inside the building. 
     In this embodiment, the width “r” of the ribs is smaller than the width of the channels. A preferred ratio could be 3:1. A layer of insulating foam  44  is provided in all channels, the foam being attached to the sheets using an adhesive  43 . The foam will thermally insulate the sheet for lowering the temperature gradient between the outside and inside faces. A spacer  45  is also provided in all channels for maintaining a space between foam  44  and the respective module for air flow. 
     It is also to be noted that proper ventilation of the attic may in addition address condensation problem problem. 
     For houses to be retrofitted with photovoltaic modules on both slopes of the roof, a dome-shaped support  50  may be provided for system  100  to end at the roof level to reduce leakage. The array will appear as part of the roof. 
     FIG. 5 illustrates a perspective view of another embodiment of a solar system used as a collector roof. As indicated above, it is to be understood that the invention may also have other applications. FIG. 5 shows two arrays, array  10 ′ comprising modules  1 - 6 , and array  20 ′ comprising modules  1 ′- 6 ′. As indicated above, the number of solar modules forming an array can be selected according to the application. 
     Solar modules  1 - 6 , of array  10 ′ are supported by a wood rafter  30 ′. Rafter  30 ′ comprises rails  11 ′- 15 ′, arranged parallel to each other at a distance λ on a substrate  90 . Support beams of a desired length “L”  92 ,  94 ,  96 ,  98  are mounted on same substrate  90  transversal w to the rails. Distance λ between the rails is selected in accordance with the width “/” of a solar module, and should not necessarily be constant. The only constraint in connection with the distance between the rails is that rails supporting the lateral side of a module must be arranged at distance “/” from each other and a rail should be placed approximatelyin the middle portion of a module. 
     It is to be understood that more than one rail may be provided under a module, when larger modules are used. As such, “/” can be a higher multiple of λ than shown in FIG.  5 . Beams  92 ,  94 ,  96 ,  98 , are preferably arranged at a distance “w” from each other, where “w” represents the width of a module. Each beam supports two adjacent modules are supported along the edges by one beam. For example, beam  96  supports modules  1  and  3  along their adjacent sides “/”. 
     The substrate  90 , as better seen in FIG. 6B, is formed by a sheet, which can be made of plastic or plywood. The rafters are fixed to the substrate  90  with any suitable adhesive material  31 . The material used to encapsulate the solar cells  115  could be used to fix rails  11 ′- 15 ′ to substrate  90  and also to fix the modules  1 - 6  to the rafters. 
     As seen in FIG. 6B, module  3  extends outwardly form rail  11 ′ to the left; this enables to extend the collecting surface to the left by adding another array. For the same reason, module  4 , for example, is supported along side w by half the width of rail  15 ′; the other half of rail  15 ′ supports module  3 ′ of array  20 . 
     Similarly, modules  1 ′- 6 ′ of array  20  are supported by a wood rafter made of rails  15 ′,  16 ′ to  19 ′ arranged in parallel to each other at a distance λ on a substrate  91 . Support beams  91 ,  93 ,  95  and  97  are also mounted on substrate  90 ′ transversal to the rails. 
     The modules are cooled with an air flow that circulates in the channels formed between the module and the rafters, and through holes  101  in the rails  11 - 19 . Holes w  101  are equally disposed in transverse beams  91 - 98 . Holes  101  create passageways for the cooling air to circulate under the solar modules and is subsequently used for heating. 
     The electrical leads from each panel are passed to the backside of the collecting surface through slots provided in substrate  90 , and respectively  90 ′ and connected to terminal strips corresponding to each module. 
     Channels  21  to  28  formed between base  50  and the modules are conveniently used for cooling the modules, and the heat collected in these channels may be used for heating. FIG. 7 schematically illustrates the electrical and air circuits for the solar system  100  used as a collector roof. The arrays are generally arranged on one side  46  of the roof, namely the side that has southern exposure. 
     The modules are connected in general in parallel, and to poles  51  and  52  of the entire system are provided in a convenient place in attic  70 . The dc current obtained between poles  51  and  52  may be used in any convenient way. 
     A first air deflector  53  is installed on the top of the roof to direct the hot air exiting channels  21 - 28  of the solar power collector system  100  towards attic  70 . A fan  80  collects the hot air and directs it through conduit  54  to any place of interest, e.g. the heating system of the building. A second air deflector  55  directs the cold air received from conduit  56  into channels  21 - 28  of the solar power collector system  100 . 
     While the invention has been described with reference to particular example embodiments, further modifications and improvements which will occur to those skilled in the art, may be made within the purview of the appended claims, without departing from the scope of the invention in its broader aspect.