Patent Application
20080142071
The present invention relates generally to a photovoltaic device and more particularly to reconfigurable photovoltaic modules.
Most of the photovoltaic (PV) modules (which are also known as solar cell modules) are passive devices that are configured with a fixed arrangement of PV cells (which are also known as solar cells), interconnections and output characteristics. In the vast majority of these module products, the cell to cell interconnections are made using a tab and string method by soldering copper strips between adjacent cells.
The prior art module products have many limitations relating to their manufacture, installation and operation. These include the complexity of forming the interconnection and configuring multiple products for multiple customer demands; the performance degradation from shading, hotspots, and low light; and the complexity of installing modules in a variety of locations each with characteristic constraints on the placement of modules.
An embodiment of the invention provides a PV module, comprising a plurality of PV cells and a plurality of reconfigurable interconnects which electrically interconnect the plurality of PV cells.
The embodiments of the invention provide improved manufacture, installation, and operation of photovoltaic modules utilizing an integrated and internal flexible circuit. The circuit serves as a means of collection of current from PV cells and as the electrical interconnection of two or more PV cells for the purpose of transferring the current generated in one PV cell to adjacent cells and/or out of the PV module to the output connectors.
A PV module includes a plurality of PV cells and a plurality of reconfigurable interconnects which electrically interconnect the plurality of PV cells. In the first embodiment, the plurality of interconnects comprise a reconfigurable circuit which in operation collects current from the plurality of PV cells. The interconnection between the plurality of PV cells may be reconfigured after fabrication of the PV module is completed. For example, the reconfiguration may take place after an insulating laminating material is formed over the cells to complete the module and/or after the initial interconnection of the cells is completed.
The interconnection between the cells in the module may be reconfigured to optimize one or more of the following properties. For example, the interconnection may be reconfigured to optimize at least one of module output current, voltage, frequency and/or power. Alternatively, the interconnection can be reconfigured to maximize module output power by accommodating underperforming or overperforming PV cells or isolating non-functioning PV cells. For example, the interconnection can be optimized to maximize power by accommodating hotspots, damaged, shaded, or otherwise underperforming cells, by isolating these underperforming cells from the other cells and/or from the output leads (which may also be referred to as output contacts, connectors or terminals). Alternatively, cells that are performing better than others in its string may be connected to a different string and/or connected separately to the output leads. Alternatively, the interconnection can be reconfigured such that the output characteristics of the module are made to more efficiently match inverter requirements across varied light conditions. Such a module could also divert power to one or more secondary paths, such as providing some power to charge a battery and the remaining power to an inverter as a function of the environment. Cell connectivity could also be modified to disconnect all cells as a safety feature.
As used herein, the term “module” includes an assembly of at least two, and preferably three or more, such as 3 to 10,000 electrically interconnected PV cells. Each PV cell includes a photovoltaic material, such as a semiconductor material. For example, the photovoltaic semiconductor material may comprise a p-n or p-i-n junction in a Group IV semiconductor material, such as amorphous or crystalline silicon, a Group II-VI semiconductor material, such as CdTe or CdS, a Group I-III-VI semiconductor material, such as CuInSe2 (CIS) or Cu(In,Ga)Se2 (CIGS), and/or a Group III-V semiconductor material, such as GaAs or InGaP. The p-n junctions may comprise heterojunctions of different materials, such as a CIGS/CdS heterojunction, for example. Each cell also contains front and back side electrodes. These electrodes can be designated as first and second polarity electrodes since electrodes have an opposite polarity. For example, the front side electrode may be electrically connected to an n-side of a p-n junction and the back side electrode may be electrically connected to a p-side of a p-n junction. The front side electrode on the front surface of the cells may be an optically transparent electrode which is adapted to face the Sun, and may comprise a transparent conductive material, such as indium tin oxide or aluminum doped zinc oxide. The back side electrode on the back surface of the cells is adapted to face away from the Sun, and may comprise one or more conductive materials, such as copper, molybdenum, aluminum, stainless steel and/or alloys thereof. If the module is formed on an electrically conductive substrate, such as a flexible stainless steel sheet or other material, then the back side electrode may be electrically connected to the substrate. For example, the module formed on a flexible substrate may comprise a mechanically flexible, large area module.
The module also contains the interconnects that form a grid-like contact to the cell electrodes, such as the front side electrodes. The interconnect may include thin traces or gridlines as well as optional thick bus bars or bus lines, as will be described in more detail below. If bus bars or bus lines are present, then the gridlines may be arranged as thin “fingers” which extend from the bus bars or bus lines. The interconnects may be formed directly over the front side electrodes of the cells. Alternatively, the interconnects may be first formed on an insulating carrier sheet, which is then attached to the exposed front side electrodes of the cells, as described in more detail in U.S. application Ser. No. 11/451,604, filed on Jun. 13, 2006 and incorporated herein by reference in its entirety.
The module may also include an optional detector, which in operation, monitors performance of the plurality of the PV cells. The detector may comprise a photodetector array which is dispersed throughout the module and which monitors the light conditions in different portions of the module. Alternatively, the detector may comprise one or more voltmeters or ammeters which measure voltage or current, respectively, at different cells in the module.
Modules with active, automatic reconfigurations of the interconnections may also include a control device, such as a computer, an operator control panel, a microcontroller, a logic chip or a logic circuit. The control device controls reconfiguration of the interconnection between the plurality of PV cells based on information provided by the detector regarding performance of the plurality of PV cells. Thus, the control device may be electrically connected to the detector and automatically reconfigure the interconnection of the cells. Alternatively, for a control panel type control device, a human operator operates the control panel based on observed information displayed or otherwise provided by the detector.
In one aspect of the first embodiment, the reconfiguration discussed above can be made actively such that the interconnections can be automatically reconfigured by switching devices. Non-limiting examples of such switching devices include electromechanical or mechanical switches, transistors or other solid state devices, such as fuses and/or antifuses, relays or other devices for making or breaking electrical contact. The switching devices electrically connect or disconnect the plurality of PV cells to or from each other. The switching devices can also electrically connect or disconnect the plurality of PV cells to or from one or more interconnects, such as conductive bus lines or traces. The switching devices may be switched manually or automatically by the control device.
In another aspect of the first embodiment shown in
In the second and third embodiments of the invention, the interconnections can be optimized or customized in a fixed configuration in the factory or in the field. This may be done by selectively making a connection or a series of connections between the traces or bus lines on the circuit, or by breaking a connection or series of connections in the traces or bus line in the circuit. The interconnects can configured so that they remain fixed in that configuration for the life of the module. Alternatively, the interconnects can be reconfigured multiple times throughout the life of the module.
In the second embodiment, instead of using switching devices, such as electromechanical switches, transistors, or relays of the first embodiment, conductive bridges are placed between the traces or bus lines to reconfigure the interconnections. Alternatively, individual traces (or in some cases individual bus lines) may be selectively broken to reconfigure the interconnections.
As shown in
As shown in
In an alternative configuration shown in
Alternatively, as shown in
In another configuration shown in
In an alternative configuration, the conductive bridges 15 discussed above may be replaced by other connectors, such as screw terminals, mini junction boxes, or universal connectors, which are used to connect the traces to each other. The universal connectors may be used for interconnection within the module, interconnection between modules, or ports for test probes in the factory or in the field.
In a third embodiment, the module comprises at least one interconnect containing a break formed after the fabrication of the module is completed. As used herein, a break means a discontinuity in the interconnect such that the interconnect cannot conduct current across the discontinuity. For example, the traces 5 can be selectively broken by punching, slicing, slitting, or cutting through the trace and laminating layer and then adding a sealant or additional layers of protective laminating material to preserve the integrity of the laminated module. The traces may be broken by mechanical means, such as a hole punch, drill or a saw, or by ultrasonic or optical means, such as by a focused ultrasonic or laser cutting instrument, for example.
The traces could also be selectively broken by pumping sufficient current to destroy the trace selectively in the area where the trace should be removed. In other words, the traces 5 act as antifuses which are blown by passing a current above a critical current through the selected traces. In addition, traces may selectively broken by stretching, tearing, or deforming the trace where the connection should be broken.
In addition, the shorting of underperforming cells through the flexible configuration may be a planned part of the module manufacturing process to simplify or eliminate the cell sorting process allowing the planned removal of the worst performing cells in each module.
In a fourth embodiment, the modules are customized during manufacturing, such as at a factory, by using a custom trace layout for each module. This mass customization may be achieved by utilizing flexible printing methods, such as ink-jet printing, to define the layout of conductive traces. Customers could order their desired configuration from a list of feasible configurations in a catalog or on a website.
In another aspect of the fourth embodiment, a custom interconnect configuration is achieved in the factory by selectively placing an insulating layer or sheet between two layers of mating material that contain the conductive traces 5. As shown in
In a fifth embodiment, the modules are separated from a continuous sheet or roll (i.e., a rolled up sheet) of strings of cells. The modules are made by providing a sheet (such as a rolled up or unrolled sheet) of repeating, interconnected PV cells. One or more PV modules are separated from the sheet. The module is configured to have a plurality of output locations, as will be discussed in more detail below. The output leads or a junction box are then attached in some but not all of the plurality of output locations, such as the desired output locations based on the module installation location, to allow more freedom during the installation of the module. A shown in
Once the desired length of string is cut or torn, the cell interconnections and final electrical termination can be made. For example, in a simplest case shown in
If desired, both output leads 55 are placed on the same end of the string (i.e., the same end of the module) by connecting one of the polarities (i.e., the bottom set of traces) with an interconnect 57 to a bus line 7 that runs the length of the module, as shown in
In an alternative configuration shown in
Alternatively, as shown in
If desired, the laminated module may contain at least one open edge 63, as shown in
In another embodiment shown in
In another embodiment, the interconnection is part of a collector-connector described in U.S. patent application Ser. No. 11/451,616, filed on Jun. 13, 2006, which is incorporated herein by reference in its entirety. The “collector-connector” is a device that acts as both a current collector to collect current from at least one photovoltaic cell of the module, and as an interconnect which electrically interconnects the at least one photovoltaic cell with at least one other photovoltaic cell of the module. In general, the collector-connector takes the current collected from each cell of the module and combines it to provide a useful current and voltage at the output connectors of the module. This collector-connector 111 (which can also be referred to as a “decal”) preferably comprises an electrically insulating carrier 113 and at least one electrical conductor 5 which electrically connects one photovoltaic cell 3a to at least one other photovoltaic cell 3b of the module, as shown in
The collector-connector 111 electrically contacts the first polarity electrode of the first photovoltaic cell 3a in such a way as to collect current from the first photovoltaic cell. For example, the electrical conductor 5 electrically contacts a major portion of a surface of the first polarity electrode of the first photovoltaic cell 3a to collect current from cell 3a. The conductor 5 portion of the collector-connector 111 also directly or indirectly electrically contacts the second polarity electrode of the second photovoltaic cell 3b to electrically connect the first polarity electrode of the first photovoltaic cell 3a to the second polarity electrode of the second photovoltaic cell 3b.
Preferably, the carrier 113 comprises a flexible, electrically insulating polymer film having a sheet or ribbon shape, supporting at least one electrical conductor 5. Examples of suitable polymer materials include thermal polymer olefin (TPO). TPO includes any olefins which have thermoplastic properties, such as polyethylene, polypropylene, polybutylene, etc. Other polymer materials which are not significantly degraded by sunlight, such as EVA, other non-olefin thermoplastic polymers, such as fluoropolymers, acrylics or silicones, as well as multilayer laminates and co-extrusions, such as PET/EVA laminates or co-extrusions, may also be used. The insulating carrier 113 may also comprise any other electrically insulating material, such as glass or ceramic materials. The carrier 113 may be a sheet or ribbon which is unrolled from a roll or spool and which is used to support conductor(s) 5 which interconnect three or more cells 3 in a module. The carrier 113 may also have other suitable shapes besides sheet or ribbon shape.
The conductor 5 may comprise any electrically conductive trace or wire. Preferably, the conductor 5 is applied to an insulating carrier 113 which acts as a substrate during deposition of the conductor. The collector-connector 111 is then applied in contact with the cells 3 such that the conductor 5 contacts one or more electrodes of the cells 3. For example, the conductor 5 may comprise a trace, such as silver paste, for example a polymer-silver powder mixture paste, which is spread, such as screen printed, onto the carrier 113 to form a plurality of conductive traces on the carrier 113. The conductor 5 may also comprise a multilayer trace. For example, the multilayer trace may comprise a seed layer and a plated layer. The seed layer may comprise any conductive material, such as a silver filled ink or a carbon filled ink which is printed on the carrier 113 in a desired pattern. The seed layer may be formed by high speed printing, such as rotary screen printing, flat bed printing, rotary gravure printing, etc. The plated layer may comprise any conductive material which can by formed by plating, such as copper, nickel, cobalt or their alloys. The plated layer may be formed by electroplating by selectively forming the plated layer on the seed layer which is used as one of the electrodes in a plating bath. Alternatively, the plated layer may be formed by electroless plating. Alternatively, the conductor 5 may comprise a plurality of metal wires, such as copper, aluminum, and/or their alloy wires, which are supported by or attached to the carrier 113.
In another embodiment, the location of the junction box or output leads on the module can be customized in the field using the interconnection techniques described above. As shown in
In another configuration shown in
In a sixth embodiment, the conductive traces can be used to make interconnections between modules rather than within a single module. For example, as shown in
Thus, in summary, the reconfigurable flexible circuit enables multiple configurations of interconnection between the cells, as well as multiple configurations of current and voltage flow and output. The reconfigurable module is less expensive, more durable, and allows more light to strike the active area of the photovoltaic module. In addition, a reconfigurable module provides additional value, flexibility and cost savings to the manufacturers, installers, and users of PV modules.
Although the foregoing refers to particular preferred embodiments, it will be understood that the present invention is not so limited. It will occur to those of ordinary skill in the art that various modifications may be made to the disclosed embodiments and that such modifications are intended to be within the scope of the present invention. All of the publications, patent applications and patents cited herein are incorporated herein by reference in their entirety.
