Patent Application
20090014049
The present invention relates generally to a photovoltaic device and more particularly to photovoltaic modules having an integrated energy storage device.
Many current collection methods in photovoltaic (“PV”) devices (which are also known as solar cell devices) use conductive inks that are screen printed on the surface of the PV cell. Alternative current collection methods involve conductive wires that are placed in contact with the cell.
A large portion of prior art PV cells are interconnected by using the so-called “tab and string” technique of soldering two or three conductive ribbons between the front and back surfaces of adjacent cells. Alternative interconnect configurations include shingled interconnects with conductive adhesives. Some prior art PV devices also include embossing of an adhesive backed metal foil to enhance conductivity of the substrate of the device.
However, the “tab and string” interconnection configuration suffers from poor yield and reliability due to solder joints that fail from thermal coefficient of expansion mismatches and defects, requires significant labor or capital equipment to assemble, and does not pack the cells in a PV module very closely. In addition, previous attempts at shingled interconnects have been plagued by reliability problems from degradation of the conductive adhesives used.
Most of the module products in the PV industry are solely passive devices that are configured with a fixed arrangement of 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. Energy demands do not always synchronize with energy as it is generated by a PV array resulting in wasted energy or insufficient supply when there is demand. Batteries are commonly used in PV applications as separate ancillary devices, but not as an integrated component of the module.
One embodiment of the invention includes a photovoltaic module comprising a first photovoltaic cell, a second photovoltaic cell, and an energy storage device integrated into the module.
The dimensions of the components in the Figures are not necessarily to scale.
An embodiment of the invention includes a photovoltaic module which includes a plurality of PV cells and an energy storage device integrated into the module. The integrated energy storage device stores electrical energy generated by the PV cells and delivers the stored energy to the energy consumer on demand.
Preferably, the energy storage device is physically integrated into the module by being located between the encapsulating layers which encapsulate the PV cells, such as between the front and the back encapsulating layers. The front encapsulating layer may be an optically transparent polymer or glass layer which allows the sunlight to be transmitted to the PV cells. The back encapsulating layer may be a polymer or metal layer which is located below the PV cells. For PV cells manufactured on a flexible metal substrate, the metal substrate may be used as the back encapsulating layer.
For example, the energy storage device may comprise a thin film device which is electrically connected to one or more PV cells and is located together with the PV cells between the insulating encapsulating layers (which are also known as laminating layers) of the module. Thus, one or more energy storage devices are encapsulated together with the PV cells into the module.
The energy storage device may comprise a rechargeable, solid state, thin film battery such as a lithium battery, or a thin film capacitor, such as a supercapacitor or other type of capacitor, or any other energy storage device that can be laminated into the module stack. For example, flexible, thin film batteries, such as Flexion brand lithium polymer batteries, are available from Solicore of Lakeland, Fla.
Preferably but not necessarily, the energy storage device is integrated into a flexible PV module 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. This photovoltaic module includes at least two photovoltaic cells and a collector-connector. As used herein, the term “module” includes an assembly of at least two, and preferably three or more electrically interconnected photovoltaic cells, which may also be referred to as “solar cells”. 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 (which can also be referred to as a flexible circuit or “decal”) preferably comprises an electrically insulating carrier and at least one electrical conductor which electrically connects one photovoltaic cell to at least one other photovoltaic cell of the module.
Each cell 3a, 3b includes a photovoltaic material 5, such as a semiconductor material. For example, the photovoltaic semiconductor material may comprise a p-i-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 CIGS/CdS heterojunction, for example. Each cell 3a, 3b also contains front and back side electrodes 7, 9. These electrodes 7, 9 can be designated as first and second polarity electrodes since electrodes have an opposite polarity. For example, the front side electrode 7 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 electrode 7 on the front surface of the cells may be an optically transparent front side 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 electrode 9 on the back surface of the cells may be a back side electrode which 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. This electrode 9 may also comprise the substrate upon which the photovoltaic material 5 and the front electrode 7 are deposited during fabrication of the cells.
The module 1 also contains the collector-connector 11, which comprises an electrically insulating carrier 13 and at least one electrical conductor 15. The collector-connector 11 electrically contacts the first polarity electrode 7 of the first photovoltaic cell 3a in such a way as to collect current from the first photovoltaic cell. For example, the electrical conductor 15 electrically contacts a major portion of a surface of the first polarity electrode 7 of the first photovoltaic cell 3a to collect current from cell 3a. The conductor 15 portion of the collector-connector 11 also directly or indirectly electrically contacts the second polarity electrode 9 of the second photovoltaic cell 3b to electrically connect the first polarity electrode 7 of the first photovoltaic cell 3a to the second polarity electrode 9 of the second photovoltaic cell 3b.
Preferably, the carrier 13 comprises a flexible, electrically insulating polymer film having a sheet or ribbon shape, supporting at least one electrical conductor 15. 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 13 may also comprise any other electrically insulating material, such as glass or ceramic materials. The carrier 13 may be a sheet or ribbon which is unrolled from a roll or spool and which is used to support conductor(s) 15 which interconnect three or more cells 3 in a module 1. The carrier 13 may also have other suitable shapes besides sheet or ribbon shape.
The conductor 15 may comprise any electrically conductive trace or wire. Preferably, the conductor 15 is applied to an insulating carrier 13 which acts as a substrate during deposition of the conductor. The collector-connector 11 is then applied in contact with the cells 3 such that the conductor 15 contacts one or more electrodes 7, 9 of the cells 3. For example, the conductor 15 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 13 to form a plurality of conductive traces on the carrier 13. The conductor 15 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 13 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 15 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 13. The wires or the traces 15 electrically contact a major portion of a surface of the first polarity electrode 7 of the first photovoltaic cell 3a to collect current from this cell 3a. The wires or the traces 15 also directly or indirectly electrically contact at least a portion of the second polarity electrode 9 of the second photovoltaic cell 3b to electrically connect this electrode 9 of cell 3b to the first polarity electrode 7 of the first photovoltaic cell 3a. The wires or traces 15 may form a grid-like contact to the electrode 7. The wires or traces 15 may include thin gridlines as well as optional thick busbars or buslines. If busbars or buslines are present, then the gridlines may be arranged as thin “fingers” which extend from the busbars or buslines.
In summary, in the module configuration of
Each carrier 13a, 13b is selectively printed with conductors 15a, 15b, respectively, such as conductive traces and/or wires, thus forming a flexible circuit or “decal”. The conductors 15a on carrier 13a contact the front (i.e., the front electrode 7) of the PV cells 3 collecting current generated on the cells and the front of the energy storage devices 103, and the conductors 15b on carrier 13b contact the back side electrodes of the PV cells and the devices 103. Each pair of adjacent conductors 15a, 15b contact each other in region 17 between the PV cells. The front side electrode of each PV cell 3 and each energy storage device 103 is electrically connected to the back side electrode of each respective PV cell to complete the circuit.
The connection in region 17 connects the conductors 15a, 15b both electrically and mechanically to achieve serialization of the module (i.e., the connection of the components in series). The connection methods include direct physical contact (i.e., pressing the conductor traces together), solder (such as SnBi or SnPb), conductive adhesive, embossing, mechanical connection means, solvent bonding or ultrasonic bonding. If desired, the sidewalls of the cells 3 and/or devices 103 may be covered with an insulating spacer to prevent the conductors 15 from short circuiting or shunting the opposite polarity electrodes of the same cell 3 or device 103 to each other.
If desired, the energy storage device 103 may be used to replace the bypass diode used in prior art PV modules for hot spot protection and to save the power loss in the bypass diode.
In summary, the module includes a first flexible sheet or ribbon shaped, electrically insulating carrier 13a supporting a first conductor 15a, and a second flexible sheet or ribbon shaped, electrically insulating carrier 13b supporting a second conductor 15b. The first conductor 15a electrically contacts a major portion of a surface of the first polarity electrode 7 of the first photovoltaic cell 3a. The second conductor 15b electrically contacts the first conductor 15a and at least a portion of the back side electrode of the second photovoltaic cell 3b.
In another embodiment of the invention, the first carrier 13a comprises a passivation material of the module and the second carrier 13b comprises a back support material of the module. In other words, the top carrier film 13a is the upper layer of the module which acts as the passivation and protection film of the module. The bottom carrier film 13b is the back support film which supports the module over the installation location support, such as a roof of a building, vehicle roof (including wings of plane or tops of blimps) or other structure or a solar cell stand or platform (i.e., for free standing photovoltaic modules supported on a dedicated stand or platform). The bottom carrier film may also support auxiliary electronics for connection to junction boxes.
While all PV cells 3 are electrically connected to the charge storage devices 103 in the modules described above, it should be noted that only a portion of the PV cells in the module may coupled with energy storage devices 103.
In another embodiment, the modules described above may additionally contain a universal DC port that enables external DC devices, such as charge storage devices, for example batteries, across a range of current or voltage characteristics to be powered or charged. In this embodiment, the external battery or batteries may be plugged into the module through the port to be charged. Once charged, the batteries are disconnected and used for any desired application.
In another embodiment, the module comprises a completely integrated one-piece system that can be used for off-grid or battery back-up applications. This fully integrated module consists the PV cells 3, energy storage devices 103, charge control device 113, as well as an inverter, output connectors and other components needed for the generation, storage, and delivery of usable energy.
In another embodiment, one or more charge storage devices are integrated into the junction box of the PV module 1.
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.
