Patent Application
20140216530
The invention relates generally to photovoltaic (PV) systems and more particularly to a system and method for grounding PV mounting system and rail sections.
Nearly all electrical systems in the U.S. are grounded to mitigate the impacts of lightning, line surges, or unintentional contact with high voltage lines. Most PV systems include modules with metal frames and metal mounting racks that are in exposed locations, e.g. rooftops where they are subject to lightning strikes, or are located near high voltage transmission lines that in the event of high winds, etc., can come into contact with PV arrays.
The modules in a typical PV array have aluminum frames that are often anodized. The 2008-NEC code that has the same requirements as the draft 2010-NEC code and governs installation of PV systems requires exposed metal surfaces be grounded. There are special dc wiring and grounding requirements that must be met specifically for dc module strings that can produce voltages at high as 600 volts. A failure in the insulating material of the PV laminate could allow the frame to be energized up to 600V dc.
The installer of a PV system is required to ground each module frame per the NEC code and UL standard 1703. This inter-module grounding must be met using a heavy, e.g. at least #10 gauge) copper wire and a 10-32 screw that can cut into the frame. Additional assurances are required even for frames having anodized surfaces. Washer/connectors in such cases are used to cut into the metal frame and provide the best electrical contact. Because the modules in a typical PV array have aluminum frames that are often anodized, providing continuity of frame grounding does not ensure rail grounding and at least #10 gauge copper ground leads are required to be attached to each separate rail section and brought to a common point.
Traditional installation of a PV mounting system requires layout of the rail system prior to physical attachment, usually necessitating measurement and snapping of chalk lines for alignment. This is usually sufficient for most applications. However, some applications require a well-controlled spacing between rails in order to ensure proper alignment of modules so a more consistent method for assuring alignment of parallel rails is desired.
The inventors of the present application have solved the problem of assuring proper alignment of PV modules, while providing adequate grounding of the metal rail segments of the PV mounting system and a connector box that is attached to an end of an individual rail segment.
Briefly, in accordance with one embodiment, a system for grounding photovoltaic (PV) modules comprising at least one building block (30) including at least one PV module (12), a pair of metallic rail sections (14), and a metallic grounding bar (16) connected to each end of the metallic rail sections (14) for grounding the metallic rail sections (14).
In another aspect, a method for grounding a photovoltaic system (10) comprises inserting a PV module (12) into a first metallic rail section (14) and into a second, opposite metallic rail section (14) to hold the PV module (12) in place; and connecting a grounding bar (16) to each end of the first and second metallic rail sections (14) for grounding the metallic rail sections (14).
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
a) and 5(b) are schematic views of a standard connector box and a pass-through connector box, respectively, according to an embodiment of the invention.
While the above-identified drawing figures set forth alternative embodiments, other embodiments of the present invention are also contemplated, as noted in the discussion. In all cases, this disclosure presents illustrated embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.
Referring now to
As shown in
Presently, all commercial systems that employ micro-inverters 32 still require an equipment ground, meaning that all modules with metallic frames 40 and metal mounting systems have to be connected to a common earth ground through a low resistance path. Such inter-module ground connections are still made using processes that require the use of metallic splices, lugs, penetrating washers, and wires. All of these methods require hands-on grounding connections be made at the time of installation and usually requires the presence of an experience electrician.
Each micro-inverter 32 may be connected to the PV module 12 through a corresponding junction box 48. Each junction box 48 houses the normal +/−dc wiring/connectors of a PV module 12 and the corresponding micro-inverter 32. Because each micro-inverter case 36 is also electrically coupled to the metallic frame 40 of its corresponding PV module 12, the ground pin in each of the connectors 19, 42 automatically grounds all of the module frames 40 that are interconnected through the connectors 19, 42.
The connectors 19, 42 carry a ground connection from PV module 12 to PV module 12 of the basic building block 30 of the PV mounting system 10. Because each micro-inverter case 36 is electrically coupled to the metallic frame 40 of its corresponding PV module 12, the ground pins in the power connectors 19, 42 automatically ground all of the module frames 40 when all of the PV modules 12 are installed into the metallic rail sections 14. Further, the metallic grounding bars 16 connected to each end of the metallic rail sections 14 serve to provide a continuous grounding path between the metallic rail sections 14. Further, pre-drilled holes in the ends of the rail sections 14 for mounting the metallic grounding bars 16 ensure the correct spacing between the pair of rail sections 14 of the basic building block 30, as shown in
The number of basic building blocks 30 that form a single circuit of the PV mounting system 10 depends on the amount of electrical power generated by each PV module 12. To this end, the invention can be practiced with any desirable number of basic building blocks 30 and PV modules 12, depending on the amount of electrical power generated by each PV module 12, the limitation of the electrical load panel according to NEC limitations, and the rating of the protection circuit breaker in the load panel. It is noted that each micro-inverter 34 produces ˜1 A of current and the circuit breaker rating is 15-20 A, which constitutes a single circuit. More power can be accommodated by the load panel, but will require an additional breaker, circuit and home run cable 24. In one example, a basic building block 30 comprising a single row, R1, of five (5) PV modules 12 forms a single circuit, C1, as shown in
One end of the wire harness 18 is connected to a connector box 22. The home run cable 24 from the connector box 22 produces a single circuit, C1, with about 5 A of electrical current (for five (5) PV modules), which can be fed to a conventional 15 A circuit breaker panel (not shown). Because each PV module 12 generates about 1 A of electrical current, a total of about 10-13 PV modules 12 on a single circuit, C1, can be fed to a conventional 15 A circuit breaker panel, depending on the amount of electrical current that is generated by each PV module 12. It will be appreciated that the connector 56 can be fed to another row of PV modules, and so on, until the last row of PV modules are fed to the circuit breaker panel. A system having more than about 10-13 PV modules 12 will need an additional home run cable 24 and circuit breaker. It is noted that the ground pin from the connectors 19, 42 (not visible in
Because the PV mounting system 10 requires the capture of the top and bottom of each PV module 12 in the rail sections 14, the spacing between the metallic rail sections 14 is important. One aspect of the invention is that the rails sections 14 include a plurality of pre-drilled holes for mounting the metallic grounding bars 16 at the proper location and ensuring the correct spacing between the pair of rail sections 14, thereby reducing installation errors. Therefore, the metallic grounding bars 16 serve a dual purpose: 1) to ensure correct physical spacing between the metallic rail sections 14; and 2) to automatically ground the metallic rail sections 14 and connectors 19, 42.
As shown in
One end of the wire harness 18 is connected to a standard connector box 22. A connector 54 from the standard connector box 22 is, in turn, connected to a pass-through connector box 22′. In the illustrated example, a connector 56 from the pass-through connector box 22′ produces a single circuit, C1, with about 10 amps of electrical power, which can be fed to a conventional 15 amp circuit breaker panel (not shown). It will be appreciated that the connector 54 can be directly fed to the circuit breaker panel if there is only one row of up to about 10-13 PV modules 12, similar to the example of
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
The present application is a continuation of and claims priority to U.S. patent application Ser. No. 13/079,900, filed Apr. 5, 2011, the disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13079900 | Apr 2011 | US |
| Child | 14250982 | US |
