Abstract:
A photovoltaic connection system for maximum current output and heat dissipation properties. The connection system includes a connection box with improved heat transfer capability to permit higher current output capacity. Diodes are surface-mounted on a printed circuit board inside of the connection box. An optional metal plate may be mounted inside the cover plate of the connection box as a heat sink for dissipating heat from the diodes. The metal in the plate has good thermal transfer characteristics, e.g., copper or aluminum.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a connection system for photovoltaic arrays, and more particularly to a connection box in a PV connection system with improved thermal transfer properties for greater current carrying capacity. 
     BACKGROUND OF THE INVENTION 
     Photovoltaic (PV) modules or arrays produce electricity from solar energy. Electrical power produced by PV modules reduces the amount of energy required from non-renewable resources such as fossil fuels and nuclear energy. Significant environmental benefits are also realized from solar energy production, for example, reduction in air pollution from burning fossil fuels, reduction in water and land use from power generation plants, and reduction in the storage of waste byproducts. Solar energy produces no noise, and has few moving components. Because of their reliability, PV modules also reduce the cost of residential and commercial power to consumers. 
     PV cells are essentially large-area semiconductor diodes. Due to the photovoltaic effect, the energy of photons is converted into electrical power within a PV cell when the PV cell is irradiated by a light source such as sunlight. PV cells are typically interconnected into solar modules that have power ranges of up to 100 watts or greater. For large PV systems special PV modules are produced with typical power range of up to several 100 W. A photovoltaic module is the basic element of a photovoltaic power generation system. A PV module has many solar cells interconnected in series or parallel, according to the desired voltage and current parameters. PV cells are connected and placed between a polyvinyl plate on the bottom and a tempered glass on the top. PV cells are interconnected with thin contacts on the upper side of the semiconductor material. The typical crystalline modules power ranges from several W to up to 200 W/module. 
     In the case of facade or roof systems the photovoltaic system may be installed during construction, or added to the building after it is built. Roof systems are generally lower powered systems, e.g., 10 kW, to meet typical residential loads. Roof integrated photovoltaic systems may consist of different module types, such as crystalline and micro-perforated amorphous modules. Roof-integrated photovoltaic systems are integrated into the roof, such that the entire roof or a portion thereof is covered with photovoltaic modules, or they are added to the roof later. PV cells may be integrated with roof tiles or shingles. 
     PV modules/arrays require specially designed devices adapted for interconnecting the various PV modules/arrays with each other, and with electrical power distribution systems. PV connection systems are used to accommodate serial and parallel connection of PV arrays. In addition to connection boxes, a PV connection system includes connectors that allow for speedy field installation or high-speed manufacture of made-to-length cable assemblies. Connection or connection boxes may be required to receive specialized cable terminations from PV modules/arrays, with power diodes inside for controlling current flow to the load. Thus, certain connection box configurations may generate internal heat, which must be dissipated in order to protect the internal components and external structures adjacent to the connection box. In many cases, governmental regulations and industry standards establish the permissible temperature rise that must be maintained. 
     Therefore, there is a need for an improved connection box for dissipating heat expelled from electrical/electronic components inside of the box. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a junction box for interconnection of solar cell arrays in a power distribution system. The junction box includes a cover portion, a box portion and a printed circuit board (PCB). The cover portion includes a liner plate, mounting elements for mounting the PCB to the cover portion, and latch members for latching the cover portion to the box portion. The PCB has a first surface that includes diode elements. Each diode element has an associated heat sink element attached to the diode elements for dissipating heat generated by the diode elements. The second surface of the PCB has a plurality of foil elements and a plurality of clip elements. The box portion includes a hollow interior for receiving the PCB. A first opening receives the cover portion, and a second opening disposed opposite the first opening receives external power input wiring. A plurality of contact elements is disposed in the box portion for electrically connecting the PCB to the solar cell array. The box portion also includes receiving members to retentively engage the foil elements and recesses for retentively engaging the latch members. The heat sink elements are maintained in contact with the liner plate when the latch members are engaged with the recesses of the box portion, such that the heat sinks transfer heat to the liner plate, and the liner plate conducts heat to the cover portion for dissipation externally of the junction box. 
     An advantage of the present invention is improved current output capacity for PV junction boxes through novel heat dissipation techniques. 
     Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of the junction box assembly of the present invention. 
         FIGS. 2A-2C  show cross-sectional perspective views of the cover portion engaging the junction box. 
         FIG. 3  shows the component mounting side of the PCB. 
         FIGS. 4A-4C  are alternate embodiments of the PCB having a modified heat sink. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to a junction box for interconnection of solar cell arrays.  FIG. 1  is an exploded view of the present invention including the junction box  14 , printed circuit board (PCB)  12  and the cover portion  20 . Diodes  16  are part of the electric circuitry on the printed circuit board  12 . The J-Box ( 14 ) includes spring clips  10  mounted on the interior of the box  14  that receive contact members  23  that are mounted on PCB  12 . PCB  12  has push lock washers  17  that receive mounting posts  15 , so that the PCB  12  rests and is secured on mounting posts  15 . A separate cover portion  20  has latch members  13  that mate with a recess portion  37  on the box  14  to retain the cover portion  20  on the junction box  14 . The cover portion  20  also includes arm portions  11  opposite the latch members  13 , that slide beneath a flange  39  on the box  14  in cooperation with the latch members  13 , maintain the cover portion  20  in position. A gasket  40  preferably is used to provide a weatherproof seal. The gasket  40  is compressed between a lip  24  on the cover portion and a ridge  26  of the box  14  when the cover portion  20  is latched into position on the box  14 . A copper plate or lining  18  is adhesively or mechanically attached to the underside of the cover portion  20 . The copper plate  18  enhances thermal conduction of the internal components contained in the junction box  14 , as discussed in greater detail below. 
     The junction box  14  and associated cover portion  20  can be constructed of a substantially rigid, electrical insulating material suitable to receive the printed circuit board  12 , such as an ABS plastic or other suitable material. The junction box/cover material preferably has good thermal conductivity. The power interface termination contacts  21 , diodes  16  and other electrical components (not shown for simplicity of the drawing) are secured to the printed circuit board  12  with surface mount technology, solder connections, or any other suitable connection. The solder connection used can be a wave-solder connection or any other suitable solder connection.  FIG. 1  shows a four-position junction box  14  for receiving the cover portion  20 , and the PCB  12  which is mounted on the cover portion  20 . PCB  12  includes mounted components—e.g., diodes  16 , power interface contacts  21  and contact members  23 —however, it is to be understood that a junction box  14  and PCB  12  having one or more positions can be used for the present invention. The PCB  12  is modified with the number of contact members  23  and diodes  16  mounted thereon, depending upon the number of positions on the junction box  14 . For example, a junction box  14  with two positions would have a printed circuit board  12  with two contact members  23  mounted thereon. The printed circuit board  12  is coated with a sufficient amount, preferably a minimum of two ounces of copper or a copper alloy on both sides. However, any other type of conductive metal may be used. The system also includes the printed circuit board  12  having diodes  16  with integral heat sinks as part of the cathodes to help dissipate heat within the junction box. 
     The diode circuitry used with the present invention can be TO-220 packaged diodes  16 . The TO-220 packaged diodes  16  contain heat sinks that assist with dissipating heat and help to meet the temperature standard of IEC 61215 (Ed. 2) or other applicable industry standards. The present invention may also use ITO-220 diodes that have plastic covered heat sinks and help to dissipate any generated heat to meet the temperature standard. In addition to the TO-220 diode and ITO-220 diode, any other similar and suitable diode that can meet the temperature standard may be used with the present invention. 
       FIG. 1  also shows the posts  15  that secure the printed circuit board  12  to the cover portion  20  and latch members  13  that secure the cover portion  20  to the junction box  14  when closed. The printed circuit board  12  has apertures  17   a  and washers  17  that receive the cover portion  20  when lowered into place. As the printed circuit board  12  is lowered onto the cover portion  20 , the posts  15  slide through the circuit board apertures  17   a . The cover portion  20  is lowered onto the junction box  14  when terminating the foil strip  38  (see, e.g.,  FIGS. 2A-2C ). The posts  15  are configured to securely prevent movement of the printed circuit board  12  once it is in place secured to cover portion  20 . The latch members  13  are configured such that the cover portion  20  engages the junction box  14  with latch  13  as shown in  FIGS. 2A-2C . The latch  13  can be released by hand, i.e., without the aid of a tool or utensil, to detach the cover portion  20  from the junction box  14 , for convenience in installing and servicing a solar cell power distribution system. Alternately, the latch  13  can be designed such that the use of a tool or utensil is required for release to free the cover portion  20  from the junction box  14 , thereby restricting access. With either design, the posts  15  (in addition to securing the cover portion  20  to the junction box  14 ) prevent the circuit board  12  from moving substantially in any direction when disposed and secured in the junction box  14 . The posts  15  and latch members  13  may be constructed of the same material, such as ABS plastic or any other suitable material, as the junction box  14  and can be of unitary construction with the junction box  14  as well. In addition, a pair of fuse-style clips  21  attached to the PCB  12  clip onto mating posts  28  when the cover portion  20  is pressed into position on the junction box  14 . The power interface contacts  21  retentively engage the mating posts  28  to provide electrical engagement between the PCB  12  and the junction box  14 . 
     In addition to the posts  15  and latch members  13  that are disposed in the cover portion  20 , the junction box  14  contains supports  19  that provide support for the printed circuit board  12  when the cover portion  20  is secured in place in the junction box  14  by latch members  13  and arms  11 . The supports  19  may be constructed of the same material as the junction box  14 , the posts  15  and latch members  13 . The supports  19  can be of unitary construction with the junction box  14 . The supports  19  provide a guide to contain the foil strips  38  between the contact elements  23  and the clips  10 , and provides a stable foundation for the printed circuit board  12  to rest upon in the junction box  12  when secured in place on the posts  15 . 
     As previously indicated, the junction box  14  has a pair of sockets  30  for receiving external power connectors of a solar cell array (not shown). The sockets  30  are hollow cylindrical conduits that encompass mating posts  28 . The sockets may be configured for bayonet-type locking engagement, threaded engagement, or any other connections known in the art. Polarization features (not shown) may be incorporated into the sockets  30  to ensure proper polarity of the external connections with the PCB  12 . The mating posts  28  are preferably provided in pairs for each box, although boxes may be configured with a singular mating post, three posts, or other arrangements, as required by the PCB  12 . The mating posts  28  are electrical conductors for connecting the external power distribution (not shown) to the PCB  12 . The mating posts  28  are insert molded or otherwise formed or pressed within the box  14 , thereby maintaining the weatherproof seal inside of the box  14 . 
     An aperture  34  (shown in  FIG. 3 ) is provided in the bottom of the box  14 , for receiving incoming power conductors (e.g., the flexible foil strip  38  shown in  FIGS. 2A-2C ) from the solar cell array (not shown). The bottom of the box  14  is typically installed against a flat surface, such as a rooftop-mounted array, which is sealed to the outside elements around the periphery of the box  14  and the aperture  34 . 
     Referring to  FIGS. 2A-2C , a partial cross-sectional perspective view shows sequentially the placement of the cover portion  20  over the junction box  14 .  FIG. 2A  shows an open box  14 . Flexible foil strips  38  are connected at one end to the external phovoltaic array (not shown). The other end of the is flexible foil strips  38  are retained in the box  14  by loop  41 , and are positioned over the clip  10 , to allow dressing of the foil strip  38  until the cover portion  20  is set in place. Mating posts  28  are molded into the box  14  between the socket  30  and the box  14  interior. Contact elements  23  push the foil strips  38  into the clips  10  when the cover portion  20  is placed over the box  14 , as shown in  FIGS. 2B and 2C . The contact elements  23  and the foil strips  38  apply an outward force on the clip  10 . The clip  10  maintains the position of the contact elements  23  and the foil strips  38 , while providing electrical contact therebetween, and prevents any lateral movement. As the cover portion  20  is lowered over the box  14 , the foil strip  38  deforms under the contact element  23 , wedging into the gap of the clip  10 . The clip  10  is preferably metallic and conductive, and resilient so as to apply a retentive contact force to the contact element  23  and the foil strip  41 . When the cover portion  20  is fully engaged on top of the box  14 , each of the contact elements  23  is in electrical communication with the respective foil strip  38 , as illustrated in  FIG. 2C . Power interface contacts  21  retentively engage the mating posts  28 . 
       FIG. 3  shows an alternate embodiment of the junction box  14 , with the opposite side of the PCB  12  facing upward. In the configuration shown, the PCB  12  is fastened into the bottom of the box  14 , by sliding engagement with latch  36 . There are four termination contacts  45  arranged across one edge of the PCB  12 . The termination contacts  45  are preferably secured to the PCB  12  with a solderless connection, or alternately are soldered to the PCB  12 . Diodes  16  are attached to the PCB  12  adjacent to the termination contacts  45 , and are fastened to heat sinks  32  via rivets  44 . The heat sinks  32  and diodes are in thermal communication. The heat sinks  32  may be constructed of copper, aluminum, or other thermally conductive material. The heat sinks  32  have roots  43  extending downwardly to engage the bottom of the PCB  12  for support. When the cover portion  20  is engaged with junction box  14 , there is an air gap between the cover portion  20  and the heat sinks  32 . Heat is conducted from the PCB components—including termination contacts  45  and diodes  16 , and other electrical and electronic components through heat sinks  32 . Cover portion  20  dissipates the heat from the interior of the junction box  14  to the external environment. By contrast, in the embodiments of  FIGS. 1 and 1A , the diodes  16  are in thermal contact with the cover portion  20  or the liner plate  18 , to dissipate heat directly to the cover portion  20 . 
     The termination contacts  45  are preferably poke-in style contact assemblies that provide a secure connection for external wire tabbing from the PV array, and that do not require the use of tools or other utensils when inserting. The poke-in contact includes a lance (not shown) that displaces upon insertion of the wire tabbing The poke-in contact applies a force or retention when the tabbing is forced outward from the poke-in contact without the use of tools or other utensils. To effectively remove the tabbing from the contact, a tool or utensil is used to depress the lance and release the tabbing and the force applied to the tabbing by the lance. 
     Referring next to  FIGS. 4A ,  4 B and  4 C, one embodiment of the present invention includes modified heat sinks  32  having radiant fins  33  in thermal contact with the PCB  12 , the radiant fins  33  contact the PCB  12  and diodes  16 . The heat sinks  32  also have helically-coiled fins  35  extending downwardly towards the bottom of the junction box  14 . The helical fins  35  provide expanded heat transfer surface area for dissipating heat.  FIG. 4C  shows the PCB  12  mounted inside of the junction box  14  and adjacent to aperture  34 , with the heat sinks  32  mounted thereon. 
     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.