Abstract:
A photovoltaic system is disclosed having individual micro-inverters associated with each solar panel. The individual micro-inverters are easily installed without the aid of tools by snap locking a micro-inverter into place upon heat barriers mounted to and separated from the solar panels. When a micro-inverter is snapped into place it automatically electrically engages contacts from the solar panels mounted on the heat barriers. AC trunk cables pass through uni-strut channels along the backs of the solar panels. Flat jumper output cables from the micro-inverters fit adjacent the AC trunk cables within the uni-strut channels where a snap fit electrical connection is made, in a protected environment.

Description:
RELATED APPLICATION DATA 
     The present application claims priority of U.S. Provisional Patent Application Ser. No. 61/769,077 filed Feb. 25, 2013. 
    
    
     TECHNICAL FIELD 
     The present invention is directed to photovoltaic solar panels or modules which may be mounted on rooftops, racks or other places where sunlight is available to convert sunlight to electrical power. The output from photovoltaic solar panels is a DC voltage. Inverters convert the DC voltage to AC voltage. The present invention is directed to photovoltaic solar panels where each solar panel is provided with its own micro-inverter. 
     BACKGROUND OF THE INVENTION 
     Solar panels produce direct current (DC) which must be converted to alternating current (AC). Typically, useable outputs from solar panel installations are 240 volts AC at 60 Hz for North American installations. In some photovoltaic solar panel installations a single inverter may convert the DC outputs to AC from a string of solar panels. 
     Using a single inverter for a string of solar panels has some disadvantages. DC cables and attendant diodes are necessary to connect individual solar panels with the inverter. This adds a level of cost, complexity and associated installation labor. There are also inherent dangers. DC strings from solar panels can exceed 600 volts, which cannot be readily shut off. 
     An alternative approach is to use a single micro-inverter with each solar panel. As the name implies, micro-inverters are small inverters intended to handle the output of a single solar panel. Most are rated at about 260 watts. This enables one to isolate and tune the output of a solar panel. Large transformers for reducing cooling loads aren&#39;t needed nor are cooling fans. There is also evidence that overall efficiencies of solar installations are higher with the use of micro-inverters with each solar panel. 
     With micro-inverters, any solar panel that is under-performing will not have an adverse effect on the panels around it. Micro-inverters produce grid matching power directly at the back of a solar panel. Arrays of solar panels are connected in parallel to each other and then to the grid feed. Thus, a single failing panel or inverter will not take the entire solar panel string offline. 
     Although there are obvious advantages in employing micro-converters for the conversion of DC to AC emanating from solar panels, such products have experienced issues limiting their longevity. Specifically, it has been found that the high temperatures associated with the photovoltaic panels have resulted in micro-inverter failures. This situation has been somewhat addressed by component selection and the employment of UV glass surface treatment on the panels themselves which reduces heat buildup. 
     Other problems also exist. Since the solar panels create a warm environment animals such as rodents tend to migrate to these areas. In turn, they can chew or damage solar panel wire conductors. Theft of micro-inverters is also a problem. Finally, replacement of micro-inverters is often difficult and labor intensive. 
     It is therefore an object of the invention to provide an improved solar panel array utilizing a single micro-inverter for each solar panel. 
     Another object of the invention is to provide an improved mounting arrangement of a micro-inverter to a solar panel. 
     Another object of the invention is to mount a micro-inverter so as to be in direct contact with the outputs of a solar panel to thereby eliminate micro-inverter wire leads and diodes. 
     Still another object of the invention is to provide a system and method of mounting micro-inverters directly to solar panels in a manner that provides easy installation. 
     Yet another object of the invention is to provide a system whereby micro-inverters that are underperforming or not performing are easily replaced from a solar panel. 
     Another object of the invention is to mount a micro-inverter to a solar panel to minimize exposure of heat created by the solar panel. 
     Another object of the invention is to provide a method and structure to easily connect and disconnect the micro-inverter output cable to an AC trunk cable connected to a plurality of micro-inverters. 
     These and further objects will be readily apparent when considering the following disclosure and appended claims. 
     SUMMARY OF THE INVENTION 
     A solar photovoltaic system and method comprises a plurality of photovoltaic solar panels providing DC outputs, where each panel has an enclosure which encloses photovoltaic cells. Ribbon conductors conduct DC current from each of the photovoltaic cells. A heat barrier made of an insulating material is attached to the back of each solar panel. The ribbon conductors pass through the heat barriers and form exposed rigid contacts on insulator tabs formed in the heat barrier. A micro-inverter for converting the DC voltage from the ribbon conductors to AC voltage is releasably attached to each solar panel. Each micro-inverter directly engages and encloses the rigid contacts when the micro-inverter is releasably attached to the heat barrier. An O-ring seal in the heat barrier surround and seals the contacts. 
     A single AC trunk cable electrically connects all of the micro-inverter modules in the system or string. The AC trunk cable may be a flat cable with conductors. Each micro-inverter includes a flat jumper output cable with a corresponding number of conductors as the AC trunk cable. When a micro-inverter is installed, the jumper output cable is easily connected into the AC trunk cable. 
     In one embodiment, the flat jumper output cable has a distal end, where the distal end is enclosed in a molded housing. Piercing elements are formed within the molded housing. One set extends inwardly of the molded housing to electrically engage the jumper cable conductors. Other piercing elements extend outwardly of the molded housing. A snap-in housing or trough is provided to route the flat AC trunk cable. The molded housing of a flat jumper output cable to be attached is placed adjacent to the AC cable in the snap-in housing and the outwardly extending piercing elements engage and pierce the conductors of the AC trunk cable. This piercing action is facilitated by providing that the molded housing snap fits into the trough whereby the piercing elements are driven into the conductors of the AC trunk cable. An alignment mechanism insures proper registration of the output jumper cable conductors and the AC trunk cable conductors. 
     In accordance with another aspect of the invention, a method of releasably attaching individual micro-inverters to each of a plurality of photovoltaic solar panels is described. 
     The method includes the steps of attaching individual micro-inverters to each of a plurality of photovoltaic solar panels, each solar panel including photovoltaic cells, a back sheet, conductors attached to the photovoltaic cells and extending from the photovoltaic panel to conduct a DC voltage from the photovoltaic cells through a micro-inverter and a housing, including the steps of: forming rigid terminals on the heat barrier; passing the conductors through the heat barrier and forming contacts on the rigid terminals; attaching and connecting a single AC trunk cable between the individual micro-inverter modules; releasably attaching the micro-inverter housing to the heat barrier; and directly electrically engaging the micro-inverter with the contacts. 
     The method additionally includes the step of electrically connecting the outputs of each of the micro-inverters of the plurality of solar panels to a single AC trunk cable. Each micro-inverter has a jumper output cable, and the method includes the step of connecting each jumper output cable into the AC trunk line. 
     The method additionally includes the steps of releasably removing a micro-inverter if it fails to perform properly and replacing it with a new micro-inverter, disconnecting the jumper output cable from the AC trunk line, and releasably detaching the micro-inverter housing from the capture plate and attaching a new micro-inverter when necessary. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1A  is an exploded sectional view of a component of the solar panel rigid contact mount to a micro-inverter;  FIG. 1B  is a sectional view illustrating the micro-inverter quick mount feature; and  FIG. 1C  is a view of the micro-inverter housing as indicated by the view lines in  FIG. 1B , with a partial tunnel view. 
         FIG. 2  is an underside view of an array of three solar panels and micro-inverters according to the invention. 
         FIG. 3  is an enlarged view of  FIG. 1B . 
         FIG. 4  is a sectional view of the connector for the AC trunk line and micro-inverter output jumper cable prior to the “snap together” assembly. 
         FIG. 5  is a sectional view, taken along a plane indicated in  FIG. 8  of the AC trunk line and micro-inverter output jumper in a ‘snapped together” connection. 
         FIG. 6  is a perspective view of one of the contact plates having teeth-like piercing element. 
         FIG. 7  is a perspective view showing all four contact plates with four perpendicular teeth-like elements protruding from the contact plates. 
         FIG. 8  is a perspective view of the snap-in connector  52  showing the insert molding housing for plug-in cable housing in a closed position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Novel features which are characteristic of the invention, as to organization and method of operation, together with further objects and advantages thereof will be better understood from the following description considered in connection with the accompanying drawings, in which preferred embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for illustration description only and are not intended as definitions of the limits of the invention. The various features of novelty which characterize the invention are recited with particularity in the claims. 
     There has been broadly outlined more important features of the invention in the summary above and in order that the detailed description which follows may be better understood, and in order that the present contribution to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form additional subject matter of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based readily may be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important therefore, that claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
     Certain terminology and the derivations thereof may be used in the following description for convenience and reference only, and will not be limiting. For example, words such as “upward,” “downward,” “left,” and “right” refer to directions in the drawings to which reference is made unless otherwise stated. Similar words such as “inward” and “outward” refer to directions toward and away from, respectively, the geometric center of a device or area and designated parts thereof. Reference in the singular tense include the plural and vice versa, unless otherwise noted. 
       FIG. 1A  is an exploded sectional of the solar panel rigid contact mount  10  of the present invention. (See also  FIG. 1B ) A solar panel or module  12  includes a tempered glass  16  having an outer surface coated with a thin UV layer to reduce heat in the photovoltaic cell. A conductor  18  electrically connects individual cells which typically form photovoltaic cell  14 . Solar panel  12  includes an insulated back sheet or wall  20 . Flat ribbon DC conductors  22 , connected to conductor  18 , pass through back wall  20 . Mounted to the back wall  20  of solar panel  12  by any suitable adhesive is a heat barrier  24 , also an electrical insulator, which spaces a micro-inverter housing  26  ( FIG. 1B ) from the solar panel  12 . Heat barrier  24  can be a molded structural foam panel or other panel which has heat and electrical insulating properties. Solar panel  12  can be a standard solar panel which are readily available. One such solar panel is made by SunTech. Similarly, micro-inverters are standard items which are readily available. One such micro-inverter is sold by EnPhase. 
     Two flat ribbon DC conductors  22 , one positive and one negative, are fed through slots or orifices  28  in the heat barrier  24 . By wrapping the distal ends of the ribbon conductors around the heat barrier tabs or projections  30  in the heat barrier, rigid, fixed contacts are formed, one for the positive contact  32  and one for the negative contact  34  ( FIG. 1C ). This creates a direct electrical connections with exposed mating ribbon contacts  36  and  37  ( FIG. 1C ) on the micro-inverter housing  26  designed to receive the solar panel  12  DC output. Sealing is provided by an elliptical O-ring  38  surrounding the contacts  32  and  34 . 
     The micro-inverter is designed to be quickly mounted to the heat barrier  24 . Referring additionally to  FIG. 1B , a snap latch  40  is mounted to the back wall  20  of solar panel  12  by any suitable adhesive. To releasably attach the micro-converter housing  26  to the solar panel  12  the top of the inverter  26  is inserted into a hook  42  created in the heat barrier  24  ( FIG. 1A ) and then the bottom is pushed downwardly to engage the snap latch, for quick engagement and removal of the micro-inverter housing  26 . When engaged the mating contacts  36  and  37  of the micro-inverter are aligned with and in electrical contact with fixed DC terminals  32  and  34  to receive the DC output from solar panel  12 . 
     Micro-inverter housing  26  is provided with optional cooling fins  44 , which may be made from an aluminum extrusion. Cooling fins  44  can engage support rail  46  with an interference fit for direct conductive cooling. As will be described in greater detail later, each micro-inverter has an AC jumper or output cable  54  which is connected into an AC trunk cable  50  ( FIG. 2 ) inside of cable connecter  52 , which in turn is located inside of the uni-strut support rail  46 . With the micro-inverter  26  captured by the open side of support rail  46 , theft of the micro-inverter is discouraged. 
       FIG. 1C  is a view of the micro-inverter housing  26  as indicated by the view lines shown in  FIG. 1B  with DC contacts  32  and  34  on the heat barrier shown through a tunnel view in housing  26 . 
       FIG. 2  is a view of an array or module of three photovoltaic solar cells  12 ′,  12 ″ and  12 ′″. Micro-inverters  26 ′,  26 ″ and  26 ′″ are attached directly to the back or underside of solar modules  12 ′,  12 ″ and  12 ′″, respectively. The AC trunk cable  50  passes through the support rail  46  mounted to each of the micro-inverters. Each of the micro-inverter AC output jumper cables  54  are shown exiting the micro-inverters on the left as shown in  FIG. 2 . But they may exit from the right if desired. The jumper cables are spliced within connectors  52  in a manner which will be described in greater detail subsequently. Note that the jumper cables can be connected anywhere along the trunk cables and are not restricted to particular locations. Also shown is a sealed cap  56  closing the trunk cable at the end of the panel array. Of course the number of solar panels in a string is not limited to three, but can be up to 17 or more. 
       FIG. 3  is an enlarged edge view of  FIG. 1   b , better showing the placement of the micro-inverter  26  placement on the uni-strut  46  section and lower attachment including spring latch  40  with fixed stop  41 . Placement of the jumper cable is centered directly over the uni-strut for easy concealment to protect the cables from rodents and weather exposure. Also shown are the optional cooling fins  44  on micro-inverter  26  housing which capture the support rail providing added support and theft deterrence. 
       FIG. 4  is a section view of connector  52  prior to the “snap together” assembly. In the embodiment described, AC flat trunk cable and the AC output jumper cables are shown with four conductors each. But it should be understood that the invention may be used with 3, 5, 6 or more conductors. Four sets of teeth-like piercing elements  61 ,  62 ,  63  and  64  are shown poised to engage the 12 gauge, four conductor (12/4) flat trunk cable  50  and create a fixed contact. At opposite end of piercing elements  61 - 64  formed on contacts  66 ,  68 ,  70  and  72  (See  FIG. 7 ) are perpendicular piercing elements  73 ,  74 ,  75  and  76  which engage the wire strands of the individual conductors of the micro-inverter output jumper cable  54 . Each of the four separate sets of piercing teeth are shown in exact alignment with each other in this view, so that only the longitudinal side of the first sets of teeth are visible. The piercing elements  61 - 64  are embedded in an insert molded housing  78  at the distal end of the output jumper cable  54  which “snaps-in” to a snap-in cover  80 . The sharp hard plastic sealing ridge  103  engages the soft outer jacket of the trunk cable to provide a water tight seal. Keying feature  81  is provided at the interior bottom of the snap-in cover  80  which registers with a corresponding indent  83  in the trunk cable  50 , to prevent improper assembly. 
     Referring additionally to  FIG. 8  a protrusion  82  in jumper cable molded housing  78  registers with a slot  84  in snap-in cover  80  as keying features that prevent improper assembly. At the bottom of the snap-in cover  80  a double backed tape is attached to maintain the exact relationship and location with trunk cable  50  in order to allow reinsertion of a jumper cable. A screwdriver can be used to disconnect a locking shoulder at interior left or right side of snap cover  80 . 
       FIG. 5  is a sectional view, taken along the plane indicated in  FIG. 8 , through the AC trunk cable connector  52  of the micro-inverter plug-in cable connector  52  with the insert molded housing  78  in a closed, “snapped together” position with snap-in housing  80  showing the teeth-like piercing elements as they engage the four wires of the four conductor, twelve gauge (12/4) trunk cable  50  conductors L1 (black), L2 (red), Neutral (white) and Ground (green). Specifically, the four separate contacts are shown in exact alignment with each other in this view, so that only the longitudinal side of the first contact is visible. Also visible is one pair of perpendicular opposing piercing elements for each of the contact plates. Every contact plate has a total of four piercing elements, two facing up and two facing down, as shown in  FIGS. 6 and 7 . 
     Locking shoulders  90  and  92  formed in the molded housing are engaged by detents  94  and  96  of the snap-on housing  80 . This secures placement of the jumper cable  54  in the snap-in housing  80 . 
       FIG. 6  is a perspective view of one of the contact plates  66  with four teeth-like piercing elements  61 ,  73 ,  61 ′ and  73 ′ as they protrude from the sides of the plate. Referring additionally to  FIG. 5 , two alignment tabs  98  and  100  are provided which are formed at right angles, with the shorter supporting the keying feature  102  on the 18/4 flat jumper cable  54 . Pairs of piercing elements  61  and  61 ′ and  73  and  73 ′ extend in identical perpendicular alignment from the contact plate  66 . This provides dual piercing into the same conductor for improved electrical reliability. 
       FIG. 7  is a perspective view showing all four contact plates  66 ,  68 ,  70  and  72  each with the four perpendicular teeth-like piercing elements protruding from the plate. The orientation of the jumper cable and trunk cable may be seen by reference to  FIG. 5 . This view shows the spacing of the plates with their corresponding piercing elements within each of the connectors. As explained the piercing elements used to engage the conductors of the micro-inverter jumper cable  54  are set in an insert mold to create the housing mold  78 . During fabrication a breakaway carrier strip  102  is used to load the piercing elements into the insert mold. The strip is broken off after loading leaving the protruding perpendicular edge. 
     Contact plate  66  with corresponding piercing elements engages the L1 wire. 
     Contact plate  68  with corresponding piercing elements engages the ground wire G. Contact plate  70  with corresponding piercing element engages the L2 wire in  FIG. 5 . Contact plate  72  with corresponding piercing elements engages the neutral wire N 
       FIG. 8  is a perspective view of the snap-in connector  52 , showing the insert molded housing  78  for plug-in cable housing  80  showing a closed position, fixed contacts with piercing elements in a place, and with a 2″ length dimension. Shown are the trunk cable  50  and jumper cable  54  as they protrude from the housing. 
     The above disclosure is sufficient to enable one of ordinary skill in the art to practice the invention, and provides the best mode of practicing the invention presently contemplated by the inventor. While there is provided herein a full and complete disclosure of the preferred embodiments of the invention, it is not desired to limit the invention to the exact construction, dimensions, relationships, or operations as described. Various modifications, alternative constructions, changes and equivalents will readily occur to those skilled in the art and may be employed as suitable without departing from the true spirit and scope of the invention. Such changes might involve alternative materials, components, structural arrangements, sizes, shapes, forms, functions, operational features or the like. Therefore, the above description and illustration should not be considered as limiting the scope of the invention, which is defined by the appended claims.