Abstract:
A photovoltaic (“PV”) array includes a plurality of interconnected PV modules. A PV array perimeter assembly may be positioned along the perimeter of the PV array to restrain horizontal movement of the array. For improved wind performance, the PV array perimeter assembly may include curbs that come with pre-attached flexible wind deflectors configured to prevent wind from penetrating underneath the PV array. The flexible wind deflectors may be made of a flexible membrane and may include water drainage holes to allow water to flow out of the PV array. The curbs do not necessarily have to be fixedly attached to a rooftop, and may include ballasts to prevent array movement. Embodiments of the invention may be employed on PV arrays installed on flat rooftops, and are especially advantageous when used on uneven roof surfaces.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to photovoltaic cells, and more particularly but not exclusively to method and apparatus for installing photovoltaic cells. 
         [0003]    2. Description of the Background Art 
         [0004]    Photovoltaic cells, also referred to as “solar cells,” are well known devices for converting solar radiation to electrical energy. Photovoltaic cells may be packaged together in a photovoltaic module (“PV module”), which comprises a plurality of interconnected photovoltaic cells. A photovoltaic installation may include a PV array, which includes a plurality of interconnected PV modules. The PV array may be installed on a rooftop, for example, with a surrounding perimeter assembly. 
         [0005]    Embodiments of the present invention pertain to a PV array perimeter assembly that can withstand relatively high wind loads. 
       SUMMARY 
       [0006]    In one embodiment, a photovoltaic (“PV”) array includes a plurality of interconnected PV modules. A PV array perimeter assembly may be positioned along the perimeter of the PV array to restrain horizontal movement of the array. For improved wind performance, the PV array perimeter assembly may include curbs that come with pre-attached flexible wind deflectors configured to prevent wind from penetrating underneath the PV array. The flexible wind deflectors may be made of a flexible membrane and may include water drainage holes to allow water to flow out of the PV array. The curbs do not necessarily have to be fixedly attached to a rooftop, and may include ballasts to prevent array movement. Embodiments of the invention may be employed on PV arrays installed on flat rooftops, and are especially advantageous when used on uneven roof surfaces. 
         [0007]    These and other features of the present invention will be readily apparent to persons of ordinary skill in the art upon reading the entirety of this disclosure, which includes the accompanying drawings and claims. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows a photovoltaic array in accordance with an embodiment of the present invention. 
           [0009]      FIG. 2  shows a curb and a photovoltaic module in the photovoltaic array of  FIG. 1 , in accordance with an embodiment of the present invention. 
           [0010]      FIG. 3  shows another view of the curb and photovoltaic module of  FIG. 2 . 
           [0011]      FIG. 4  is an exploded view of a curb assembly in accordance with an embodiment of the present invention. 
           [0012]      FIG. 5  is another view of the curb assembly of  FIG. 4 . 
           [0013]      FIGS. 6 and 7  show views of a flexible wind deflector, in accordance with an embodiment of the present invention. 
           [0014]      FIG. 8  shows a portion of a photovoltaic array in accordance with an embodiment of the present invention. 
           [0015]      FIG. 9  shows ballast positioned inside a curb of the curb assembly of  FIG. 8 , in accordance with an embodiment of the present invention. 
           [0016]      FIG. 10  shows results of wind tunnel testing of a photovoltaic perimeter assembly with different curb configurations. 
       
    
    
       [0017]    The use of the same reference label in different drawings indicates the same or like components. 
       DETAILED DESCRIPTION 
       [0018]    In the present disclosure, numerous specific details are provided, such as examples of apparatus, components, and methods, to provide a thorough understanding of embodiments of the invention. Persons of ordinary skill in the art will recognize, however, that the invention can be practiced without one or more of the specific details. In other instances, well-known details are not shown or described to avoid obscuring aspects of the invention. 
         [0019]    Wind loading is a major concern with some roof-installed PV modules. In particular, wind penetrating underneath PV modules results in a pressure differential above and below the PV modules. If the wind is strong enough, the pressure differential may lift up the PV modules, detaching them from the PV array. This could result in the PV modules flying off the roof, possibly damaging other PV modules or worse, result in bodily harm or even death. The present invention pertains to a novel PV array perimeter assembly that not only holds the PV modules together in the horizontal plane, but also provides a flexible wind deflector to prevent PV modules from lifting up. The novel PV array perimeter assembly may also advantageously include provisions for water drainage and come pre-attached to a curb for ease of installation in the field. 
         [0020]      FIG. 1  shows a PV array  100  in accordance with an embodiment of the present invention. The PV array  100  may include a plurality of PV modules  101  surrounded by a PV array perimeter assembly  110  and installed on a rooftop. The PV array perimeter assembly  110  does not necessarily have to be fastened or fixedly attached to the rooftop. For example, the PV array perimeter assembly  110  may simply be rested on the rooftop as installed for normal operation. 
         [0021]    Each PV module  101  may comprise a plurality of interconnected photovoltaic cells. The PV array perimeter assembly  110  restrains lateral movement of the modules  101 . In the example of  FIG. 1 , the PV array perimeter assembly  110  comprises a plurality of curbs  113  and curb corner pieces  112 . The curbs  113  provide a raised barrier around the perimeter of the modules  101 , preventing the modules  101  from separating horizontally while increasing the array&#39;s wind performance. The curb corner pieces  112  connect the curbs  113  together to form a rectangular perimeter assembly. Other curb pieces with varying shapes may also be used to form other perimeter assembly configurations and shapes. 
         [0022]      FIG. 2  shows a curb  113  and a PV module  101  in the PV array  100  in accordance with an embodiment of the present invention. A curb  113  may comprise a single-piece of material (e.g. aluminum-zinc coated steel), folded into four wall portions, namely a top portion  151 , a bottom portion  152 , a back portion  153 , and a front portion  154 . As installed in the field, the top portion  151  faces towards the sky, the bottom portion  152  faces towards the rooftop, the back portion  153  faces towards the modules  101 , and the front portion  154  faces away from the modules  101 . In one embodiment, the top portion  151  slopes down from the top edge of the back portion  153  to the top edge of the front portion  154  at an angle of approximately 5° to 10°, for example, relative to a horizontal plane parallel to the bottom portion  152 . Other curb shape configurations may also be used, including a triangular shape with a bottom, back, and outward facing diagonal slope. 
         [0023]    A plurality of water drainage holes  114  on the front portion  154  are aligned in-line with corresponding plurality of water drainage holes  114  on the back portion  153  (see  FIG. 4 ) and water drainage holes  121  on a flexible wind deflector  115  (see  FIG. 4 ). The water drainage holes  114  and  121  advantageously allow water to drain away from the center of the array. 
         [0024]    The flexible wind deflector  115  is so named because it may comprise a flexible membrane, such as a sheet of neoprene. In the example of  FIG. 2 , the wind deflector  115  is installed such that it extends past the front portion  154 , lays on the rooftop and contacts the bottom portion  152 , and folds to contact the back portion  153 . Having the wind deflector  115  extend past the front portion  154  advantageously allows for visual inspection that the installation was properly done and that the wind deflector  115  is in the correct position. 
         [0025]    A solar module  101  may be supported on standoffs  116 , which are supported by a solar tile  117 . The solar tile  117  may interlock with other solar tiles  117  supporting other solar modules  101  to hold the solar modules  101  together. The solar tiles  117  may be positioned against the back portion  153  of the curbs  113 . The solar tiles  117  and standoffs  116  may comprise commercially-available PV rooftop mounting components, such as the PowerGuard® interlocking roof tiles from Sunpower Corporation of San Jose, Calif. 
         [0026]      FIG. 3  shows another view of a curb  113  and a PV module  101  in the PV array  100 , in accordance with another embodiment of the present invention.  FIG. 3  also shows the solar tile  117  and standoff  116 . As shown in  FIG. 3 , the flexible wind deflector  115  folds from the bottom portion  152  and over to the back portion  153  around a corner  119  of the curb  113 . The flexible wind deflector  115  drapes over contours of the roof to fill in gaps between the curb  113  and the roof surface. The wind deflector  115  may bulge (see  118 ) on the back portion  115 . When the curb  113  is rested on the rooftop, wind penetrating between the bottom portion  153  and the wind deflector  115  is blocked by the portion of the wind deflector  115  on the back portion  153 . The curb  113  may be installed even on an uneven rooftop surface. The PV perimeter assembly may be rested on the rooftop without being fixedly attached to the rooftop. Ballast  131  (see  FIG. 8 ) may be installed inside curbs  113  to stabilize the PV perimeter assembly on the rooftop. 
         [0027]      FIG. 4  is an exploded view of a curb assembly  120  in accordance with an embodiment of the present invention. The curb assembly  120  may comprise a curb  113  and a flexible wind deflector  115 . In the example of  FIG. 4 , the wind deflector  115  is fixedly attached to the back portion  153  by rivets, screws, or other fastening means. This allows the curb  113  and the wind deflector  115  to be shipped as a single assembly for ease of shipping, inventory, and installation. The top portion  151  may be opened to allow a ballast or other components to be placed inside the curb  113 . The top portion  151  is folded closed onto the front portion  154  during normal operation. The wind deflector  115  is folded onto the back portion  152  and rested on the rooftop. 
         [0028]    The flexible wind deflector  115  includes a plurality of water drainage holes  121  that allow water to drain through corresponding water drainage holes  114  of the curb  113 . In the example of  FIG. 4 , the holes  123  and  122  on the wind deflector  115  are for foam screws (not shown) that attach the curb  113  to a solar tile. The foam screws go from inside the body of the curb  113  and into a foam backboard of the solar tile. 
         [0029]      FIG. 5  is another view of the curb assembly  120 , showing the water drainage holes  114  on the front portion  154  and the back portion  153 . As discussed, the flexible wind deflector  115  includes corresponding water drainage holes  121  (see  FIG. 4 ) to allow water to drain away from the PV array. 
         [0030]      FIGS. 6 and 7  show other views of the flexible wind deflector  115 , with the water drainage holes  121 , and holes  122  and  123 . In one embodiment, the water drainage holes  121  are shaped like quarter-ellipses for ease of manufacture, good drainage (wide cross-section lower to the ground where water will be), and low profile to prevent issues relating to wind penetrating the curb  113 . The water drainage holes  121 , and corresponding water drainage holes  114  on the curb  113 , may have other shapes without detracting from the merits of the present invention. 
         [0031]      FIG. 8  shows a portion of a PV array  100 A in accordance with an embodiment of the present invention. The PV array  100 A is a particular embodiment of the PV array  100  of  FIG. 1 . In practice, the curbs  113  would surround the perimeter of the modules  101 , but is not so drawn in  FIG. 8  to indicate that the PV array  100 A is not necessarily rectangular and may extend beyond what is shown in  FIG. 8 . For example, additional modules  101 , curbs  113 , and curb corner pieces  112  may be added to the PV array  100 A as depicted. 
         [0032]    In the example of  FIG. 8 , the curbs  113  may include ballasts  131 . The ballasts  131  stabilize the PV perimeter assembly and may comprise a heavy material, such as concrete/cinder block pavers.  FIG. 9  shows a ballast  131  positioned inside a curb  113  of the curb assembly  120 , which comprises the curb  113  and a flexible wind deflector  115 . 
         [0033]      FIG. 10  shows results of wind tunnel testing of a PV perimeter assembly with different curb configurations. The wind tunnel tests were conducted on full scale curbs rested (without being fixedly affixed) on a roof surface that is made of plywood and treated with a varnish surface to obtain the proper friction coefficient between the solar tiles supporting the PV modules and the roof surface. Although a roof surface may appear perfectly flat, imperfections in the plywood surface create gaps under the curb. 
         [0034]    The bar graphs  321  and  322  are for first and second trial runs, respectively, involving wind tunnel testing of a full scale curb that is taped onto the roof to create a perimeter seal without gaps under the curb. The resulting uplift force for the first trial run is 0.42 lb, while the resulting uplift force for the second trial run is −0.55 lb. These uplift forces were considered performance targets for a curb with gaps between the curb and the roof surface. 
         [0035]    The bar graph  323  is for a third trial run involving wind tunnel testing of a full scale curb with a flexible wind deflector (e.g., flexible wind deflector  115 ) underneath, with gaps underneath the curb. The uplift force for the third trial run is −0.13 lb, which falls within the target wind performance level. 
         [0036]    The bar graphs  324  and  325  are for fourth and fifth trial runs, respectively, involving wind tunnel testing of a full scale curb with gaps underneath the curb but without additional features, i.e., not taped onto the roof, without flexible wind deflector. The resulting uplift forces are 3.87 lb in the fourth trial run and 5.15 lb in the fifth trial run, which do not meet the target wind performance level. 
         [0037]    The results of the wind tunnel testing indicate that a curb with a flexible wind deflector provides improved wind performance level when placed over an uneven surface. This together with ease of installation and shipping make the use of the flexible wind deflector advantageous in PV perimeter assemblies. 
         [0038]    While specific embodiments of the present invention have been provided, it is to be understood that these embodiments are for illustration purposes and not limiting. Many additional embodiments will be apparent to persons of ordinary skill in the art reading this disclosure.