Patent Publication Number: US-9893678-B2

Title: Photovoltaic system with improved AC connections and method of making same

Description:
GOVERNMENT LICENSE RIGHTS 
     This invention was made with Government support under contract number DE-EE0005344 awarded by the United States Department of Energy. The Government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     Embodiments of the invention relate generally to photovoltaic (PV) systems and more particularly to improved systems and methods for forming direct current (DC) electrical connections between a DC connector of a PV panel to a DC connector of a DC-to-alternating current (AC) micro-inverter and AC electrical connections between the micro-inverter and AC wiring harness of the PV system. 
     PV systems include PV modules arranged in arrays that generate direct current (DC) power, with the level of DC current being dependent on solar irradiation and the level of DC voltage dependent on temperature. PV systems may be constructed either as an inverter system or a micro-inverter system. A typical inverter system uses DC wiring to electrically couple multiple PV panels to a single inverter. The inverter then converts the DC energy from the PV panels into AC energy, such as AC energy suitable for transfer to a power grid. A typical micro-inverter system, on the other hand, uses DC wiring and a junction box to electrically connect a micro-inverter to each PV panel, forming an AC PV module  300  as shown in  FIG. 1 . In this AC PV module system, each micro-inverter  306  converts the DC energy from its respective PV panel into AC energy suitable for transfer to a power grid. The junction box  308  of each PV module  300  contains bypass diodes that allow each AC PV module  300  to maintain peak efficiency under partial shading conditions by bypassing sections of cells in the AC PV module  300  which are not receiving solar irradiation. By removing AC PV module cells that are not producing DC power from the electrical connection, the PV system ensures that these non-producing AC PV module cells do not draw DC power from the PV system, which may reduce power to the load and cause AC PV module overheating. 
     The construction of typical AC PV modules makes infield repairs time consuming. In the case of an internal wiring issue, a technician must diagnose the fault onsite in order to determine what component of the module to repair. An electrical fault may occur within the micro-inverter assembly itself  302 , which is secured to a PV panel  304 , the diodes within junction box  308 , or between the two (2) DC connections  310 ,  312  that contain respective DC connectors  314 ,  316  that connect the junction box  308  and the micro-inverter  306 . Since a unique key or tool must be used to the remove each of the junction box  308 , the micro-inverter  306 , and to disassemble the DC connectors  314 ,  316 , each component to determine which component of the AC PV module  300  is faulty, the onsite repair is time consuming and costly. Further, the wired connection between the PV panel  304  and the micro-inverter typically includes approximately one to two feet of DC cable and a junction box, which adds cost to the PV system. 
     To meet the national electrical code (NEC), special DC wiring and grounding specifications exist for DC module strings capable of producing voltages as high as 600 volts. Further, installers must properly manage the safety risks posed by the potentially lethal DC voltages when dealing with installation of DC wiring. As a result, a certified electrician is used for proper installation of the special DC wiring. Because all of the wiring is done on-site, the process for installing the DC wiring of the PV system accounts for a significant amount of the time and cost of the overall installation of the PV system. 
     AC PV modules are electrically connected together in groups to form multiple circuits within a PV system  322 , as shown in  FIG. 2 . The PV system  322  of  FIG. 2  includes a first row  324  of AC PV modules  326  and a second row  328  of AC PV modules  326 . An AC wire harness  334  is used to electrically couple AC PV modules  326  to a single AC power output. An AC wire harness  334  is used to electrically connect the AC PV modules within a given circuit to a single AC power output and includes a termination point  330  on one end and a connection point  338  on a second end to connect AC wire harness  334  to the another AC wire harness or the load panel. In installations where the AC PV modules of a given circuit are arranged in multiple rows  324 ,  328 , the AC wire harness is typically arranged to travel down a length of one of the rows of AC PV modules along a first side of a mounting rail, loop around the end of the mounting rail between the adjacent rows of AC PV modules, and then travel down the length of the next row of PV modules along a second side of the mounting rail. Therefore, AC wire harness  334  may be twice as long as rail  332  in order to fully track both sides of rail  332  and connect all AC PV modules  326 . Separate AC connections  336  are positioned along the length of the AC wire harness  334  to connect to each PV module  326 . Over the length of the AC wire harness  334 , power is lost due to cable resistance, which results in lower efficiencies for PV systems with long wire harnesses. This also results in a voltage drop along the length of the AC wire harness. If the AC wire harness  334  is too long, the resulting voltage drop will put the electrical circuit outside of its operating specifications and cause the micro-inverters to turn off, in order to comply with UL safety code. Further, resistance at each connection point along the length of the AC wire harness also results in power loss, and a decrease in efficiency for the PV system. 
     Therefore, it would be desirable to provide a PV system with DC connections that are easily field repairable, have a reliable and stable connection, and are less costly than the DC connections of known PV systems. It would likewise be desirable to provide an AC wire harness that improves the efficiency of the PV system while decreasing overall costs of the system. It would further be desirable for such a PV system to be manufactured in a manner that reduces the time, cost, and dangers of on-site installation of the PV system. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In accordance with one aspect of the invention, an alternating current (AC) harness for a photovoltaic (PV) system includes a wire assembly having a first end and a second end, the wire assembly having a plurality of lead wires. At least one AC connection module is positioned at a location along a length of the wire assembly between the first end and the second end. Further, the at least one AC connection module includes a first connection terminal electrically coupled to the plurality of lead wires of the wire assembly and constructed to electrically couple the wire assembly with an output of a first PV module of the PV system. The at least one AC connection module also includes a second connection terminal electrically coupled to the plurality of lead wires of the wire assembly and constructed to electrically couple the wire assembly with an output of a second PV module of the PV system. 
     In accordance with another aspect of the invention, a method of assembling a photovoltaic (PV) system includes providing a first row of PV modules and providing a second row of PV modules. The method also includes disposing an alternating current (AC) harness between the first row of PV modules and the second row of PV modules, the AC harness comprising a wire assembly and a plurality of AC connection modules positioned along a length of the wire assembly. Further, the method includes coupling a first PV module to a first terminal of a first AC connection module of the plurality of AC connection modules and coupling a second PV module to a second terminal of the first AC connection module, wherein the first PV module is positioned in the first row of PV modules and the second PV module is positioned in the second row of PV modules. 
     In accordance with yet another aspect of the invention, a photovoltaic (PV) connection system includes a plurality of PV modules arranged in a first row of PV modules and a second row of PV modules, wherein a first PV module of the plurality of PV modules is located in the first row and a second PV module of the plurality of PV modules is located in the second row. The PV connection system also includes an alternating current (AC) harness having a wire assembly having a first end and a second end. The AC harness further includes a first AC connection module coupled to the wire assembly at a first position between the first end and the second end of the wire assembly, the first AC connection module comprising a first terminal electrically coupling a micro-inverter of the first PV module to the wire assembly and a second terminal electrically coupling a micro-inverter of the second PV module to the wire assembly. 
     These and other advantages and features will be more readily understood from the following detailed description of preferred embodiments of the invention that is provided in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate embodiments presently contemplated for carrying out the invention. 
       In the drawings: 
         FIG. 1  is a perspective view of the inactive side of the inactive side of a prior art AC PV module. 
         FIG. 2  is a perspective view of a prior art PV system. 
         FIG. 3  is a front perspective view of a photovoltaic (PV) system, according to an embodiment of the invention. 
         FIG. 4  is an exploded perspective view of a portion of the PV system shown in  FIG. 3 . 
         FIG. 5A  is an exploded perspective view of the inactive side of an AC PV module suitable for use with the PV system shown in  FIG. 3  according to an embodiment of the invention. 
         FIG. 5B  is an enlarged version of portion  5 B of  FIG. 5A  showing a detailed view of a DC connector coupled to the PV panel of the AC PV module. 
         FIG. 6  is a perspective view of the bottom surface of the micro-inverter assembly in  FIG. 3 , according to an embodiment of the invention. 
         FIG. 7  is a schematic view of the components of the AC PV module of  FIG. 5A  illustrated in a first position during assembly of the AC PV module, according to an embodiment of the invention. 
         FIG. 8  is a schematic view of the components of the AC PV module of  FIG. 5A  illustrated in a second position during assembly of the AC PV module, according to an embodiment of the invention. 
         FIG. 9  is a cross-sectional view of a portion of the AC PV module of  FIG. 5A . 
         FIG. 10  is an exploded perspective view of the inactive side of an AC PV module suitable for use with the PV system shown in  FIG. 3  according to an embodiment of the invention. 
         FIG. 11  is a schematic view of the components of the AC PV module of  FIG. 10  illustrated in a first position during assembly of the AC PV module, according to an embodiment of the invention. 
         FIG. 12  is a schematic view of the components of the AC PV module of  FIG. 10  in a second position during assembly of the AC PV module, according to an embodiment of the invention. 
         FIG. 13A  is an exploded perspective view of the inactive or back side of the PV system of  FIG. 3 , according to an embodiment of the invention 
         FIG. 13B  is an enlarged view of portion  13 B in  FIG. 13A  showing wired connections between an AC connector of an AC wire harness of the PV system, a micro-inverter assembly of an AC PV module in one row of AC PV modules, and a micro-inverter assembly of an AC PV module in another row of AC PV modules, according to an embodiment of the invention. 
         FIGS. 14-16  are schematic views of electrical connections between the AC wire harness and micro-inverters of the PV system of  FIG. 3 , according to alternative embodiments of the invention. 
         FIG. 17  is a cross-sectional view of a portion of the central rail section of the PV system of  FIG. 3 , according to an embodiment of the invention. 
         FIG. 18  is a cross-sectional view of a portion of the central rail section of the PV system of  FIG. 3 , according to another embodiment of the invention. 
         FIG. 19  is a perspective view of a portion of the central rail section of the PV system of  FIG. 3 , according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 3 , a PV system  10  is illustrated according to an embodiment of the invention. PV system  10  includes a first row  12  containing at least one AC PV module  14  and a second row  16  containing at least one AC PV module  18 , and a rail system  20  that includes a number of support bars, as described in detail below. In the embodiment shown in  FIG. 3 , the first row  12  of PV system  10  includes five (5) AC PV modules  14 , and the second row  16  of PV system  10  includes five (5) AC PV modules  18 . However, one skilled it the art will appreciate that embodiments of the invention are not limited to rows  12 ,  16  having a particular number of AC PV modules  14 ,  18 . Thus, according to alternative embodiments, rows  12 ,  16  may include any desirable number of AC PV modules  14 ,  18  depending on design specifications and applicable limitations imposed by the National Electrical Code (NEC). Further, PV system  10  may have more or less than two (2) rows of AC PV modules, according to alterative embodiments. 
     Rail system  20  of PV system  10  has an asymmetric design that allows n rows of AC PV modules  14 ,  18  to be supported by n+1 horizontal rail sections. For example, a PV system  10  having two (2) rows of AC PV modules  14 ,  18  would be supported by three (3) rail sections. In one embodiment, rail system  20  includes five (5) support bars: a top rail section  24 , a central rail section  26 , a bottom rail section  28 , a first grounding bar  30 , and a second grounding bar  32 . As shown in  FIG. 3 , first and second grounding bars or support bars  30 ,  32  are positioned in a perpendicular arrangement to rail sections  24 ,  26 ,  28 . Fastener assemblies  34  mechanically and electrically couple first and second grounding bars  30 ,  32  to respective ends of rail sections  24 ,  26 ,  28 , as described in additional detail below. L-brackets  36  mount rail sections  24 ,  26 ,  28  to mounting stanchions  38 . 
     According to one embodiment, rail sections  24 ,  26 ,  28  and first and second grounding bars  30 ,  32  are constructed of an anodized metal, such as, for example, aluminum. In such an embodiment, fastener assemblies  34  include self-tapping screws or components constructed to break through the anodized surface of grounding bars  30 ,  32  during the assembly process in order to create an electrical connection between the base metal of grounding bars  30 ,  32  and the base metal of rail sections  24 ,  26 ,  28 . First and second grounding bars  30 ,  32  thus act to electrically bond together the rail sections  24 ,  26 ,  28  at equipotential. 
     According to one embodiment, first and second grounding bar  30 ,  32  and rail sections  24 ,  26 ,  28  include predrilled holes for fastener assemblies  34  to ensure correct physical spacing between rail sections  24 ,  26 ,  28  and reduce installation errors. 
     An exploded perspective view of a portion of PV system  10  associated with second row  16  of AC PV modules  18  is illustrated in  FIG. 4 . As shown, fastener assemblies  34  include respective pairs of fasteners  40  and star washers  42  that mechanically and electrically couple first and second grounding bars  30 ,  32  to top rail section  24  and bottom rail section  28  in one embodiment. 
     Central rail section  26  includes a rail cover  44 , which is secured to central rail section  26  using known fasteners such as, for example, retention clips as described in detail in  FIGS. 14-17 , and an AC harness  46  positioned within central rail section  26  beneath rail cover  44 . While AC harness  46  and rail cover  44  are illustrated as being associated with central rail section  26 , AC harness  46  and rail cover  44  may, alternatively, be positioned along multiple sections of rail system  20  according to alternative embodiments. 
     AC harness  46  includes a wire assembly  48  electrically coupled to the output of AC PV modules  14 ,  18  and an end connector  50  coupleable to a connector box  52  for delivery to a load panel  54 . The opposite end of AC harness  46  may include an end connector  198  (shown in  FIGS. 14-16 ). A number of AC connectors  56  are positioned at fixed intervals along the length of AC harness  46  to interface with respective AC PV modules  14 ,  18 , as described in more detail with respect to  FIG. 13A-16 . 
       FIG. 5A  is an exploded perspective view of the back or inactive side  58  of an AC PV module  60 , designed to be used with PV system  10  shown in  FIG. 3 . AC PV module  60  includes a PV panel  62  and a micro-inverter assembly  64 . The micro-inverter assembly  64  includes a circular DC connector  66  that is coupled or bonded to the inactive side  58  of PV panel  62  and is electrically coupled to a DC-to-AC micro-inverter  68 . Both the DC connector  66  and the micro-inverter  68  are positioned within a micro-inverter housing  70 . Housing  70  may include a housing cover  71  to allow access to the internal components of housing  70 . In one embodiment housing cover  71  is aluminum, however, housing cover  71  may be manufactured of alternative metals or plastics in alternative embodiments. A micro-inverter AC wiring harness  72  contains a pair of AC lead wires, a ground lead wire, and a neutral lead wire (not shown for clarity). One skilled in the art will recognize that lead wires of micro-inverter AC harness  72  may be arranged in a similar manner as like-named lead wires  200 ,  202 ,  204 ,  206  of AC harness  46  as shown in  FIG. 17 . Micro-inverter AC harness  72  is electrically coupled to micro-inverter  68  and extends through housing  70 . Fasteners  74  couple micro-inverter assembly  64  to PV panel frame  112  (shown in  FIG. 5A ). In one embodiment, fasteners  74  include a star washer that breaks through the anodized surface coating of PV panel frame  112  and electrically couples the frame  112  to the micro-inverter housing  70  to create a ground path therebetween. 
     DC connector  66  is positioned within an opening or recess  76  formed within a bottom surface  78  of housing  70 . A circular DC connector  80  is coupled or bonded to the back side  58  of PV panel  62  and is constructed to mate with circular DC connector  66  of micro-inverter  68  within recess  76 . DC connector  80  may be coupled to PV panel  62  using an adhesive such as silicon, as one example. In this embodiment, PV panel  62 , DC connector  66 , and micro-inverter  68  are electrically coupled together by way of electrical contacts and absent any wired connection between the components. Recess  76  is sized such that when housing  70  is coupled to AC PV module  60 , panel DC connector  80  and micro-inverter DC connector  66  are concealed within recess  76  and protected from exposure to the external environment. 
     In an alternative embodiment, panel DC connector  80  is attached to the back/inactive surface  58  of PV panel  62  via a flexible ribbon cable (not shown) that protrudes out of the back side  58  of the PV panel  62 . When housing  70  is coupled to AC PV module  60 , after DC connectors  66 ,  80  are mated, DC connectors  66 ,  80  and the flexible ribbon cable are concealed within the recess  76  of housing  70 , protected from exposure to the external environment, and are not accessible unless the micro-inverter assembly is disassembled from PV panel  62 . 
       FIG. 5B  provides a detailed view of panel DC connector  80 . Panel DC connector  80  contains four (4) leads  82  of the panel bus, which allow for electrical coupling with micro-inverter DC connector  66 . In an embodiment of the invention, leads  82  are made from copper or copper protected by a non-oxidizing coating; however, one having ordinary skill in the art would recognize that leads  82  could be made from other electrically conductive materials. Further, the number of leads  82  could be greater or less than four (4) in alternative embodiments. 
     DC connector  80  also contains a plurality of bypass diodes  84 . Each bypass diode  84  is located between two (2) adjacent leads  82 . When sections of panel  62  are not receiving a desired amount of solar irradiation, bypass diodes  84  effectively remove those sections from the overall circuit, thereby improving the overall system efficiency and reducing the possibility of shaded cells overheating. In an alternative embodiment of the invention, bypass diodes  84  are located between spring contacts  94  ( FIG. 6 ) of DC connector  66 . In yet another alternative embodiment of the invention, bypass diodes  84  are located within a circuit board  86  ( FIG. 6 ) of micro-inverter  68 . 
       FIG. 6  is a perspective view of the bottom surface of micro-inverter assembly  64  of  FIG. 5 . Micro-inverter  68  is disposed within the housing  70  at a position adjacent opening  76 . As shown, housing  70  includes optional threaded inserts  88  (shown in phantom) sized and positioned within a side surface  90  of housing  70  to receive fasteners  74  ( FIG. 5A ). Fasteners  74  may be a threaded screws or self-tapping screws that screw into the plastic housing  70 . Micro-inverter DC connector  66  includes a circular housing  92  that contains exposed electrical contacts  94  arranged to electrical couple with leads  82  in panel DC connector  80  ( FIG. 5B ). In one embodiment electrical contacts  94  are copper spring contacts, however, electrical contacts  94  may be constructed of differing materials and/or of a different configuration. As one example, electrical contacts  94  of micro-inverter DC connector  66  may be configured as flat contacts, while leads  82  of panel DC connector  80  are flexible or spring contacts. In one embodiment of the invention, the electrical contacts of micro-inverter DC connector  66  are electrically coupled to micro-inverter  68  via lead wires (not shown). 
     Micro-inverter DC connector  66  also includes recesses  96  that mate with corresponding alignment tabs  98  in panel DC connector  80  ( FIG. 5B ). In an alternative embodiment, panel DC connector  80  is configured with recesses and micro-inverter DC connector  66  is configured with alignment tabs. DC connector  66  also includes a gasket or o-ring  100  that fits within a groove  102  of panel DC connector  80  to create a waterproof seal when DC connectors  66 ,  80  are engaged. 
     Referring now to  FIGS. 7 and 8 , schematic views of a two-step process of connecting micro-inverter assembly  64  to PV panel  62  are illustrated. As shown in  FIG. 7 , micro-inverter assembly  64  is placed on the back/inactive surface  58  of PV panel  62  in a first position  104  during a first step of the assembly process. In first position  104 , micro-inverter DC connector  66  is aligned with panel DC connector  80  such that alignment tabs  98  of panel DC connector  80  are aligned with recesses  96  of micro-inverter DC connector  66 , however, micro-inverter DC connector  66  remains electrically disconnected with panel DC connector  80 . 
     In a second step of the assembly process, micro-inverter assembly  64  is moved in a rotational direction corresponding to arrow  106  to a second position  108 , as illustrated in  FIG. 8 . As micro-inverter assembly  64  is rotated, alignment tabs  98  of panel DC connector  80  travel along an alignment slot  110  ( FIG. 6 ) formed on the inside wall of micro-inverter DC connector  66 . In one embodiment, alignment tabs  98  reach an end of the alignment slot  110  when micro-inverter assembly  64  reaches the second position  108 . Alternatively, alignment slot  110  may be formed about the entire circumference of the micro-inverter DC connector  66 . The rotation of micro-inverter assembly  64  from first position  104  to second position  108  causes electrical connections  94  within micro-inverter DC connector  66  to engage with electrical connections  82  within panel DC connector  80 . Thus, in second position  108 , micro-inverter assembly  64  and PV panel  62  are electrically coupled. Further, the mating of o-ring  100  of micro-inverter DC connector  66  and groove  102  of panel DC connector  80  form a waterproof seal between connectors  66 ,  80  in the second position  108 . 
     In the embodiment illustrated in  FIG. 8 , micro-inverter assembly  64  is moved from the first position  104  to the second position  108  through a rotation of approximately  90  degrees in the counter-clockwise direction, however, alternative angles of rotation and directions of rotation are contemplated within the scope of the invention. Once micro-inverter assembly  64  is moved into second position  108 , fasteners  74  may be used to mechanically couple micro-inverter assembly  64  to PV panel frame  112 . In addition, fasteners  74  electrically ground micro-inverter assembly  64  to PV panel frame  112 . 
       FIG. 9  depicts a cross-sectional view of AC PV module  60 . As shown, micro-inverter assembly  64  is secured to PV panel frame  112  via fasteners  74  as to create an air gap  83  between micro-inverter assembly  64  and the inactive side  58  of PV panel  62 . Air gap  83  acts as a thermal barrier between PV panel  62  and micro-inverter assembly  64 , which in turn assists with micro-inverter assembly  64  not overheating PV panel  62 , and vice versa, and minimizes the thermal and mechanical stress put on PV panel  62  by micro-inverter assembly  64 . In an alternative embodiment, an optional thermal barrier  81  (shown in phantom) may be attached to the backside  58  of PV panel  62  adjacent to DC connector  80 . Thermal barrier  81  is positioned so as to have micro-inverter assembly  64  rest on thermal barrier  81 . As a result, thermal barrier  81  assists with preventing micro-inverter assembly  64  from overheating PV panel  62 , and vice versa. One having skill in the art would recognize that thermal barrier  81  could be made from an insulating material such as plastic. 
     Referring now to  FIG. 10 , an exploded perspective view of the back or inactive side  114  of an AC PV module  116  designed to be used with PV system  10  ( FIG. 3 ) is illustrated according to another embodiment of the invention. AC PV module  116  includes a PV panel  118  and a micro-inverter assembly  120 , which includes a micro-inverter  122 , a micro-inverter housing  124 , and a micro-inverter DC connector  126 . In one embodiment of the invention, micro-inverter housing  125  may include a housing cover  125 . A micro-inverter AC harness  128  containing AC, ground, and neutral lead wires is electrically coupled to micro-inverter  122  and extends through housing  124 . Micro-inverter  122  is positioned within housing  124  such that a DC connector  126  of micro-inverter  122  extends into an opening or recess  130  formed within housing  124 . In one embodiment, DC connector  126  and micro-inverter DC connector  126  are positioned entirely within housing  124  such that when housing  124  is coupled to AC PV module  116 , micro-inverter DC connector  126  and panel DC connector  126  are concealed within recess  130  housing  124  and protected from exposure to the external environment. DC connector  126  of micro-inverter  122  is constructed to interface with a DC connector  132  coupled to a back/inactive surface  114  of PV panel  118 , as described in more detail with respect to  FIGS. 11 and 12 . 
     In one embodiment of the invention, micro-inverter DC connector  126  and panel DC connector  132  include mating slot and pin or plug-and-play connectors  134 ,  136  that electrically couple micro-inverter DC connector  126  and panel DC connector  132  absent a wired cable connection therebetween. It is contemplated that micro-inverter DC connector  126  and panel DC connector  132  are constructed having a male end and a female end, respectively, or vice versa. In an alternative embodiment, panel DC connector  132  is attached to the back/inactive surface  114  of PV panel  118  via a flexible ribbon cable (not shown) such that when housing  124  is coupled to AC PV module  116 , after DC connectors  126 ,  132  are mated, DC connectors  126 ,  132  and the flexible ribbon cable are concealed within housing  124  and protected from exposure to the external environment. 
       FIGS. 11 and 12  illustrate schematic views of a two-step process of connecting micro-inverter assembly  120  of  FIG. 10  to PV panel  118 . As depicted in  FIG. 11 , micro-inverter assembly  120  is initially placed on the back/inactive surface  114  of the PV panel  118  in a first position  138  in which DC connector  126  of micro-inverter assembly  120  remains electrically disengaged from DC connector  132  of PV panel  118 . In one embodiment, micro-inverter assembly  120  is placed so as both panel DC connector  132  and micro-inverter DC connector  126  are located within recess  130  of housing  124 . 
     As shown in  FIG. 12 , micro-inverter assembly  120  is next linearly translated in the direction of arrow  140  from first position  138  of  FIG. 11  to a second position  142  during a second step of the assembly process. In second position  142 , the slot and pin connectors  134 ,  136  ( FIG. 10 ) of panel DC connector  132  and micro-inverter DC connector  126  are engaged, thereby electrically coupling micro-inverter assembly  120  and PV panel  62 . According to one embodiment, a portion of housing  124  is positioned beneath a lip  144  of PV panel frame  146  when the micro-inverter assembly  120  is in the second position  142 . Fasteners  74  mechanically couple micro-inverter assembly  120  and PV panel frame  146 . In addition, fasteners  74  electrically ground micro-inverter assembly  120  to PV panel frame  146 . 
     According to various embodiments of the invention, micro-inverter DC connector  126  is constructed in order to ensure a waterproof connection when electrically coupled with panel DC connector  132  in second position  142 . In one embodiment, housing  124  includes a gasket or similar device (not shown) that creates a waterproof seal between the electrical connections within recess  130  and the external environment. Alternatively, housing  124  may be coupled to PV panel  118  with an adhesive to form a watertight seal there between. 
     The schematic views illustrating the two-step process of connecting micro-inverter assembly  64  to PV panel  62 , as shown in  FIGS. 7 and 8 , and connecting micro-inverter assembly  120  to PV panel  118 , as shown in  FIGS. 11 and 12 , demonstrate a two-step process for creating the electrical connection between the respective DC connector of the micro-inverter and respective DC connector of the PV panel. This two-step assembly technique utilizes the mated plug connector configuration of the DC connectors  66 ,  80 ,  126 , and  132 , reduces stresses put on DC connectors  66 ,  80 ,  126 , and  132 , and greatly simplifies DC connection of the micro-inverter to the PV panel as compared to the typical technique of hard-wiring connections. Further, because micro-inverter assemblies  64 ,  120  are secured to PV panels  62 ,  118  via fasteners, micro-inverter assemblies  64 ,  120  may be removed for on-site repairs. 
     In an alternative embodiment of the invention, the electrical connection between respective DC connector of the micro-inverter and respective DC connector of the PV panel can be achieved with flexible ribbon cables. In this embodiment of the invention, the respective DC connectors would be engaged by coupling the flexible ribbon cable of one DC connector to the flexible ribbon cable of the other ribbon cable and the flexible ribbon cables would be able to be stored within the recess of the micro-inverter housing. 
       FIG. 13A  is a perspective view of the rear or inactive side of PV system  10  of  FIG. 3  that illustrates the wired connections between respective micro-inverter assemblies  64  of the first row  12  and second row  16  of AC PV modules  14 ,  18 , and AC harness  46 . As illustrated in  FIG. 13A , first row AC PV modules  14  and second row AC PV modules  18  are located on opposite sides along the length of central rail  26 . AC harness  46  runs along the length of central rail  26 . AC harness  46  includes AC connection modules  56 , which are located along the length of AC harness  46  in positions correlating to respective AC PV modules  14 ,  18 . Each AC connection module  56  is positioned to electrically couple AC harness  46  to a first row AC PV module  14  and a second row AC PV module  18 . 
     An enlarged view of portion  13 B of  FIG. 13A  is provided in  FIG. 13B  to illustrate the connections between AC harness  46  and AC PV modules  14 ,  18  in additional detail. In the embodiment shown in  FIG. 13B , AC connection module  56  is molded into the AC harness  46  at fixed intervals allowing two micro-inverters to connect to AC harness  46  at a single, fixed position. Each AC connection module  56  includes multiple AC terminals for electrically connecting wire assembly  48  of AC harness  46  to AC wiring harnesses of adjacent micro-inverters. In the embodiment shown, AC connection module  56  includes a first connection terminal  148  for coupling AC PV module  14  to AC harness  46  and a second connection terminal  150  for coupling AC PV module  18  to AC harness  46 . Either or both of first and second terminals  148 ,  150  may be capped depending on the location of AC connection module  56  within the PV system. A first AC junction wire assembly  152  is used to couple AC connection module  56  with micro-inverter assembly  64  of AC PV module  14  and a second AC junction wire assembly  154  is used to couple AC connection module  56  with micro-inverter assembly  64  of AC PV module  18 . In one embodiment, AC junction wire assemblies  152 ,  154  contain a pair of 120 V AC lead wires, a ground lead wire, and a neutral lead wire spliced to corresponding lead wires within wire assembly  48 . 
     In the embodiment illustrated in  FIG. 13B , AC connection module  56  is illustrated with connection terminals  148 ,  150  both being formed on the side of AC connection module  56  facing to AC PV module  18 . As one skilled in the art will appreciate, however, the location and configuration of connection terminals  148 ,  150 , may be varied in alternative embodiments based on various design specifications and system configurations. 
     In alternative embodiments, AC connection modules  56  may be designed as standalone components with multiple connection points for connections to individual sections of wire assembly  48  and micro-inverter AC harnesses  72 ,  128 . As one example, one such AC connection module might include four connection points, with two opposing connection points configured to connect the AC connection module between two sections of the wire assembly and two additional connection points for connection to two micro-inverter AC harnesses. The AC connection modules may be provided with end caps permitting any of the connection points of the AC connection module to be terminated. Each connection point on the AC connection module may be constructed with pin or slot connections to facilitate connections between respective slot or pin connections of the wire assembly and micro-inverter AC harnesses. The use of this type of design of AC connection modules permits multiple sections of the AC harness to be spliced or strung together with AC connection modules either at the manufacturing site or during field installation, allowing many potential system configurations. 
     The embodiments described with respect to  FIGS. 6-13B  illustrate the micro-inverter AC harness  72 ,  128  being a direct, hard-wired connection to respective micro-inverters  68 ,  122  that is provided as part of micro-inverter assemblies  64 ,  120  and coupled to the AC harness  46  after the micro-inverter  68 ,  122  is installed on PV panels  62 ,  118 . In alternative embodiments, the micro-inverter AC harness  72 ,  128  is provided as part of AC harness  46  and electrically coupled to micro-inverter  68 ,  122  following installation of micro-inverter assembly  64 ,  120  on PV panel  62 ,  118  and assembly of PV panel  62 ,  118  within rail system  20  ( FIG. 3 ). 
     In addition, while AC harness  46  and AC PV modules  14 ,  18  are illustrated in  FIG. 13B  as being connected via direct hard-wired connections between AC connection module  56  and micro-inverter assemblies  120 , AC electrical connections between AC harness  46  and respective AC outputs of micro-inverters  68 ,  122  may be made in a number of alternative manners. In addition, the AC connections may be made using various combinations of plug-and-play connectors and/or hard wired connections, as described with respect to the embodiments illustrated in  FIGS. 14-16 . 
     Referring first to  FIG. 14 , a schematic view of an alternative embodiment used to electrically connect micro-inverter assemblies  64  to wire assembly  48  is shown. In the embodiment shown, each AC connection module  56  includes a first AC connection wire assembly  156  and a second AC connection wire assembly  158  coupled thereto. First and second AC connection wire assemblies  156 ,  158  include a pair of AC lead wires, a ground lead wire, and a neutral lead wire, similar to that described with respect to AC junction wire assemblies  152 ,  154  of  FIG. 13B . A first end  160 ,  162  of each AC connection wire assembly  156 ,  158  is directly wired to corresponding lead wires of wire assembly  48  within AC connection module  56 . Second ends  164 ,  166  of each AC connection wire assembly  156 ,  158  are coupled to respective AC junction connectors  168 ,  170 , constructed to engage with corresponding module connectors  172  coupled to micro-inverter assemblies  64 . Module connectors  172  may be integrated within housing  70  ( FIG. 5 ) of micro-inverter assemblies  64  or coupled to housing  70  in alternative embodiments. While  FIG. 14  illustrates AC junction connectors  168 ,  170  as plug-and-play connectors having male connections and module connectors  172  as plug-and-play connectors having female connections, one having ordinary skill in the art will recognize that AC junction connectors  168 ,  170  and module connectors  172  may be constructed as plug-and-play connectors having male connections and female connections, respectively. 
       FIG. 15  depicts a schematic view of an alternative embodiment used to electrically connect micro-inverter assemblies  64  to wire assembly  48 . In this embodiment, first and second AC terminal connectors  174 ,  176  are integrated within each AC connection module  56  and are constructed to engage with AC connectors  178 , which are electrically coupled to a respective micro-inverter  64  via an AC wire harness  180 . AC wire harness  180  includes a pair of AC lead wires, a ground lead wire, and a neutral lead wire, similar to that described to AC junction wire assembly  152 ,  154  of  FIG. 13B . AC connectors  178  are coupled to first ends  182  of AC wire harnesses  180 . Second ends  184  of the AC wire assemblies  180  are directly hard wired to their respective micro-inverter assemblies  64 . While  FIG. 15  shows connectors  174 ,  176  as plug-and-play connectors having male connections and connectors  178  as plug-and-play connectors having female connections, connectors  174 ,  176  and connector  178  can be constructed as plug-and-play connectors having male connections and female connections, respectively. 
       FIG. 16  depicts a schematic view of yet another embodiment used to electrically connect micro-inverter assemblies  64  to wire assembly  48 . In the embodiment shown, first and second AC terminal connectors  174 ,  176  are integrated within each AC connection module  56  similar to  FIG. 15 . In this embodiment, module connectors  172  are integrated within or coupled to housing  124  of micro-inverter assemblies  64 . A dual-connector AC harness assembly  186  is provided to electrically connect module connectors  172  with AC terminal connectors  174 ,  176 . Each dual-connector AC harness assembly  186  includes a first harness connector  188  and a second harness connector  190 . First harness connector  188  is coupled to a first end  192  of an AC connection wire  194  of dual-connector AC harness assembly  186 , and second harness connector  190  is coupled to a second end  196  of AC connection wire  194 . One having ordinary skill in the art will recognize that connectors  172 ,  174 ,  176 ,  188 ,  190  may be constructed in alternative combinations of plug-and-play connectors having male connections and female connections than those illustrated in  FIG. 16  within the scope of the invention. 
     Referring to  FIGS. 14-16  together, according to some embodiments, AC wire harness  46  includes an optional end cap  198  (shown in phantom) that forms a termination point of AC harness  46  adjacent to the last AC connection module  56  located along the length of AC harness  46 . Alternatively, the end cap  198  may be integrated within the last AC connection module  56  located along AC harness  46  thereby forming a termination point of AC wiring harness  46  within AC connection module  56 . The use of optional end cap  198  permits AC harness  46  to be manufactured as a large continuous roll of wire with AC connection modules  56  positioned at fixed intervals along the length of the wire assembly  48 . During on-site installation or when preparing factory orders for shipment, the roll of wire would be cut to a desired length and an end cap  198  and end connector  50  could be installed on opposing ends of the cut wire to form an AC harness. 
     Although  FIGS. 13A, 13B, and 14-16  have been described as using micro-inverter assembly  64 , the embodiments described there in are equally applicable to micro-inverter assembly  120  of  FIG. 10 . 
       FIGS. 17-19  illustrate alternative embodiments for securing AC harness  46  to central rail section  26 . As shown in both Figures, AC harness  46  includes a pair of AC lead wires  200 ,  202 , a neutral lead wire  204 , and a ground lead wire  206 . As depicted in  FIG. 17 , according to one embodiment, AC harness  46  runs along a cavity  208  formed within rail  26 . 
     In an alternative embodiment shown in  FIG. 18 , AC harness  46  is secured to rail  26  by retention clips  210  positioned along the length of AC harness  46 . The retention clip  210  illustrated in  FIG. 18  includes an upper portion  212  and a lower portion  214  that clip together to secure AC harness  46  to the underside of rail  26 . In an alternative embodiment shown in  FIG. 19 , retention clips  216  may formed as a one piece mold part and positioned at fixed intervals along the length of one side of rail  26 , with adjacent clips  216  positioned on either side of each AC connection modules  56 . Retention clips  216  may be formed of a plastic or metal material. As shown in  FIG. 19 , AC connection modules  56  are positioned in recesses  218  formed within rail  26 . 
     In any of the embodiments described with respect to  FIGS. 17-19 , AC junction wire assemblies  152 ,  154  ( FIG. 13B ) may extend through optional openings or recesses, such as recesses  218  of  FIG. 19  formed in rail  26  or rail cover ( 44  of  FIG. 4 ) at locations corresponding to each AC connection module  56  to permit connection between AC connection modules  56  and micro-inverter assemblies  120  of each AC PV module  14 ,  18 . 
     In the embodiments set forth above, a single AC harness  46  is used to electrically connect the outputs of AC PV modules in the first row  12  and second row  16  of  FIG. 3 , with dual-input connectors positioned along the length of the AC harness to connect to pairs of opposing AC PV modules in the first and second row  12 ,  16 . 
     In summary, PV panel DC connectors, micro-inverter DC connectors, and various configurations of connectors between the AC harness and micro-inverters provide for improved DC and AC connections within individual AC PV modules and the overall PV system. The resulting system design facilitates on-site installation and repairs and reduces system costs. Further, the AC wire harness disclosed herein reduces the effective length of cable used to electrically connect the same amount of AC PV modules by approximately 50%, which results in the ability to increase the capacity of AC PV modules for a single AC wire harness. 
     Therefore, according to one embodiment of the invention, an alternating current (AC) harness for a photovoltaic (PV) system includes a wire assembly having a first end and a second end, the wire assembly having a plurality of lead wires. At least one AC connection module is positioned at a location along a length of the wire assembly between the first end and the second end. Further, the at least one AC connection module includes a first connection terminal electrically coupled to the plurality of lead wires of the wire assembly and constructed to electrically couple the wire assembly with an output of a first PV module of the PV system. The at least one AC connection module also includes a second connection terminal electrically coupled to the plurality of lead wires of the wire assembly and constructed to electrically couple the wire assembly with an output of a second PV module of the PV system. 
     According to another embodiment of the invention, a method of assembling a photovoltaic (PV) system includes providing a first row of PV modules and providing a second row of PV modules. The method also includes disposing an alternating current (AC) harness between the first row of PV modules and the second row of PV modules, the AC harness comprising a wire assembly and a plurality of AC connection modules positioned along a length of the wire assembly. Further, the method includes coupling a first PV module to a first terminal of a first AC connection module of the plurality of AC connection modules and coupling a second PV module to a second terminal of the first AC connection module, wherein the first PV module is positioned in the first row of PV modules and the second PV module is positioned in the second row of PV modules. 
     According to yet another embodiment of the invention, a photovoltaic (PV) connection system includes a plurality of PV modules arranged in a first row of PV modules and a second row of PV modules, wherein a first PV module of the plurality of PV modules is located in the first row and a second PV module of the plurality of PV modules is located in the second row. The PV connection system also includes an alternating current (AC) harness having a wire assembly having a first end and a second end. The AC harness further includes a first AC connection module coupled to the wire assembly at a first position between the first end and the second end of the wire assembly, the first AC connection module comprising a first terminal electrically coupling a micro-inverter of the first PV module to the wire assembly and a second terminal electrically coupling a micro-inverter of the second PV module to the wire assembly. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.