US 20080283118 A1
A replaceable photovoltaic inverter is mounted on each of a plurality of photovoltaic module for the conversion of direct current, produced by the photovoltaic cells, to alternating current. The inverter is coupled to a mounting bracket on the photovoltaic module such that is can be easily replaced. Replacement of an individual photovoltaic module inverter can occur during continuous operation of the photovoltaic module system with minimal impact on overall power production. The inverter is also mounted apart from the photovoltaic module to facilitate heat transfer generated by operation of the inverter.
1. A system for mounting a photovoltaic power element, the system comprising;
a bracket affixed to a photovoltaic module having a plurality of photovoltaic cells wherein the bracket includes a first mounting interface wherein direct current leads from the plurality of photovoltaic cells conveying direct current are coupled to the first mounting interface; and
a replaceable power element casing housing the photovoltaic power element having a second mounting interface mated with the first interface such that power conveyed from the plurality of photovoltaic cells is modified by the photovoltaic power element and conveyed back to the bracket via the first and second mounting interface.
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15. A mounting fixture for a attaching a photovoltaic power element to a bracket fixed to a photovoltaic module, the mounting fixture comprising;
a first interface housed in the bracket and coupled to direct current leads from photovoltaic cells of the photovoltaic module and to multi-wire cables linking the photovoltaic module to other photovoltaic modules; and
a second interface housed in a replaceable photovoltaic power element casing and coupled to the photovoltaic power element configured to mate with the first interface so as to mount the photovoltaic inverter to the bracket.
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21. A method for removing a photovoltaic power element in a photovoltaic system, the method comprising;
identifying from among a plurality of operational photovoltaic modules within the photovoltaic system at least one photovoltaic module having an power element bracket wherein the bracket includes a mounting interface coupling the photovoltaic power element to the power element bracket and herein the mounting interface includes a plurality of connectors for conveyance of electrical power between the photovoltaic module and the photovoltaic power element;
releasing the photovoltaic power element from the power element bracket; and
extracting the photovoltaic power element from the power element bracket wherein prior to the plurality of connectors breaking contact, a connector pin connection is broken, and responsive to the connector pin connection being broken the photovoltaic power element ceases operation.
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The present application relates to and claims the benefit of priority to U.S. Provisional Patent Application No. 60/938,663 filed May 17, 2007, which is hereby incorporated by reference in its entirety for all purposes as if fully set forth herein. The present application is further related to co-pending U.S. Patent Application Ser. No. LAR003 entitled, “Photovoltaic Module-Mounted AC Inverter” and U.S. Patent Application Ser. No. LAR002 entitled “Distributed Inverter and Intelligent Gateway”, both of which are hereby incorporated by this reference in their entirety.
1. Field of the Invention
The invention relates to electrical current power conversion and, more particularly, to a mount for an inverter configured to convert photovoltaic module output power into alternating current.
2. Relevant Background
An inverter is a device that converts direct current (“DC”) into alternating current (“AC”). Inverters can be designed to supply power from photovoltaic (“PV”) modules to a utility power grid, also referred to herein as the “grid.” This process places several special constraints on the power conversion process. Existing photovoltaic inverters generally fall into the category of centralized inverters wherein a single inverter performs power conversion of the DC supplied by a group of PV modules into the desired AC grid.
Another category of inverters is known as distributed inverters. A distributed inverter uses multiple inverters to generate the desired AC power from a number of PV modules. When the inverter is mounted on the PV module, the assembly comprising the PV module and inverter is termed an AC module. Previous attempts at development and marketing of AC modules have met with little success. One reason for this failure has been that the sales volume was too low to achieve any kind of economies of scale. Additionally, the components used in the distributed inverters associated with AC modules were off-the-shelf and, in many cases, were not optimized for the rigors of supplying AC power to the grid. The reliability levels of existing off-the-shelf components used in the inverters limits their lifetime to between five and ten years. Additionally, there can be up to 1000 components in an inverter resulting in significant cost per unit of energy. Furthermore, the complexity and system requirements of such an inverter result in a cumbersome package that is difficult to attach to a PV module.
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Additionally, existing designs of PV module-mounted inverters present significant reliability problems. Inverters occasionally fail. When such an event occurs the PV module to which it is attached is no longer contributing in the production of electricity for the system. The identification of that singular PV module failure, however, is extremely difficult as there is no outright indication that a PV module has failed. Generally the only indication of a PV module failure is a decrease in power production. This is compounded with the fact that each PV module and its installation in a system represents a significant capital outlay. A failure of an inverter, should it be identified, results in the replacement of the entire PV module. To do such a repair, under the systems and inverters currently used in the prior art, the entire PV system must be taken off line. Not only is the replacement of the entire PV system costly, but the loss in power production of at least a significant portion of the entire PV system while a single module is replaced is inefficient.
The weight, size, metallic enclosure and relatively low efficiency of the existing inverter designs result in a more complex mounting arrangement and a considerable increase in cost over a centralized inverter approach. But a centralized inverter is also not an optimal solution. Yet, the benefits of maximum power-point tracking optimization normally achieved by having an inverter at each PV module easily can be lost by a lack of power efficiency. Also the lifetime of an inverter is less than that of a PV module; therefore, any inverter mounted onto a PV module in a distributed model will need replacement at some point during the life of the PV module. Finally, existing inverters are difficult to replace due to their weight, anchoring schemes and wiring.
An efficient inverter that creates little heat, is lightweight in construction, is easily replaced and minimizes exposed wiring remains a challenge. Compounding this challenge is that such an invention should also minimize system cost and easily fit within the depth of the PV module frame. These and other deficiencies of the prior art are addressed by embodiments of the present invention.
According to one embodiment of the present invention, a replaceable PV module-mounted AC inverter is designed to be inserted into an inverter mounting bracket. The inverter mounting bracket is attached to the back of a PV module via adhesive of some other means. The inverter and inverter mounting bracket are made of non-conducting materials to remove electrical code requirements for equipment grounding conductors. The inverter is coupled to the bracket via locking mounting clips on the inverter mounting bracket that lock into inverter mounting recesses. No tools are required to insert the inverter into the bracket and only a simple blade screwdriver is required to release the clips for removal and replacement of the inverter.
According to one embodiment of the present invention, the inverter is spaced from the back surface of the PV module to minimize heating of the PV module by the inverter and to provide for convective air flow surrounding the inverter to dissipate heat generation. Furthermore, the inverter can be replaced while the PV module and indeed the entire PV module system remains operational. According to one embodiment of the present invention, by virtue of the joining mechanism of the inverter to the PV module bracket, an inverter can safely be removed from the bracket/interconnect with minimal fear of an arc and without disrupting the production of power from the remaining PV modules.
There are, according to one embodiment, two inverter mounting bracket AC connections to support daisy-chain connections between multiple AC modules. The AC connections can be made using bracket mounted connectors or by using cables affixed to the bracket. Finally, AC connections can be a combination of one affixed cable and one bracket-mounted connector.
The inverter mounting bracket DC connections, according to one embodiment of the present invention, can be implemented inside the bracket by mounting the bracket on top of the DC connections of a PV module. Additional external single-wire cables can be added to accommodate connection to an existing junction box mounted on a PV module.
For applications requiring permanent inverter installation without the capability of field replacement of the inverter, the inverter can be completely enclosed by the bracket to result in a very reliable and low-cost bracket implementation. By removing the interface between the bracket and the inverter, the reliability of the PV module is enhanced at the cost of the flexibility to replace an inverter in the field.
The features and advantages described in this disclosure and in the following detailed description are not all-inclusive. Many additional features and advantages will be apparent to one of ordinary skill in the relevant art in view of the drawings, specification, and claims hereof Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes and may not have been selected to delineate or circumscribe the inventive subject matter; reference to the claims is necessary to determine such inventive subject matter.
The aforementioned and other features and objects of the present invention and the manner of attaining them will become more apparent, and the invention itself will be best understood, by reference to the following description of a preferred embodiment taken in conjunction with the accompanying drawings, wherein:
The Figures depict embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention described herein.
Specific embodiments of the present invention are hereafter described in detail with reference to the accompanying Figures. Like elements in the various Figures are identified by like reference numerals for consistency. Although the invention has been described and illustrated with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the combination and arrangement of parts can be resorted to by those skilled in the art without departing from the spirit and scope of the invention.
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PV modules operate as current sources derived from a photoexcited semiconductor junction. The maximum available power from the PV cell is defined by the product of its output voltage and current. The current is due to generated photocarriers and, at low output voltages, will be proportional to the incident illumination on the PV cell and is termed the photocurrent. The PV cell behaves as if it has a photocurrent source in parallel with a non-illuminated junction diode. The output voltage is defined by the diode circuit effects implicit in the semiconductor junction and ultimately limits the maximum useful output voltage to a point where the diode current begins to increase significantly. Diode current is a strong function of operating temperature and results in a reduced PV cell voltage for a given output current as temperature rises. PV module output power therefore decreases with temperature. This effect requires that the PV module temperature be kept as low as possible by mitigating any related heat sources as much as possible.
Previous designs neglect to consider this important aspect of power production. According to one embodiment of the present invention, a replaceable inverter 602 is mounted physically apart from the PV module. By maximizing surface area of the inverter open to surrounding air currents the heat produced by each inverter can be dissipated away from the inverter by way of convection to the atmosphere and not to the PV module.
No tools are required to insert the inverter and only a simple blade screwdriver is required to release the clips for removal and replacement.
According to another embodiment of the present invention and as shown in
Similarly the connector pin 425 upon replacement of the inverter prevents operations of the inverter prior to the connection of the receptacles 1420, 1421, 1422, 1423, 1424. As the inverter is mated with the inverter bracket, each receptacle of the inverter mates with a corresponding connection of the inverter bracket. Subsequent to the connections being made the connection pin 1425 establishes contact with a corresponding component of the inverter bracket signifying that operation of the inverter can safely begin. In one embodiment the connection pin is a recessed pin/receptacle combination over which a simple continuity circuit can be attached while in another the pin is a telescoping pin coupled to a switch that signifies whether a complete connection or extraction of the inverter.
Accordingly, blocks of the flowchart illustrations support combinations of means for performing the specified functions and combinations of steps for performing the specified functions. It will also be understood that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, can be implemented by various means including a computer, robotics, or via human implementation. Indeed many of the steps illustrated in
As the PV inverter is removed from the inverter bracket but prior to the connectors mating the PV module to the PV inverter from breaking contact, a connector pin indicates 1540 to the inverter that a secure connection between the inverter bracket and the PV inverter has been compromised. Responsive to the connector pin breaking contact, the PV inverter ceases operation 1550. As one skilled in art will recognize the termination of operation of the PV inverter can be accomplished by a number of methodologies. According to one embodiment a detection circuit is included in the PV inverter to ensure that a positive connection exists between the PV module (inverter bracket) and the PV inverter prior to converting the DC power to AC power. The process ends 1595 with the inverter being safely removed 1560 from an operation PV module without any electrical arc or danger to the technician.
While there have been described above the principles of the present invention in conjunction with a PV module AC inverter mount and interconnect, it is to be clearly understood that the foregoing description is made only by way of example and not as a limitation to the scope of the invention. Particularly, it is recognized that the teachings of the foregoing disclosure will suggest other modifications to those persons skilled in the relevant art. Such modifications may involve other features that are already known per se and which may be used instead of or in addition to features already described herein. Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure herein also includes any novel feature or any novel combination of features disclosed either explicitly or implicitly or any generalization or modification thereof which would be apparent to persons skilled in the relevant art, whether or not such relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as confronted by the present invention. The Applicant hereby reserves the right to formulate new claims to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.