Patent Application
20140060622
Embodiments of the present invention are generally related to electrical attachment mechanisms and methods in thin film photovoltaic devices. In one particular embodiment, the present invention is generally related to photovoltaic devices having a direct electrical attachment of a solid lead through its back panel.
In photovoltaic modules, a robust electrical connection must be made from the buss lines or conductive ribbons, to the transmission lines. In many cases there is a barrier to making this connection. Historically, a relatively large hole is introduced to the back of the module in order to access the ribbon. For example, in most instances, the conductive ribbons is pulled up through this hole and cut, creating flat tabs or flaps, then the entire assembly is laminated together. The ribbon tabs are connected to the transmission line via a junction box (“J-Box”). The tabs are then soldered or brazed to the leads within the J-Box, and the entire J-Box, hole, ribbon assembly is then filled with a sealant, or potting mixture, to eliminate moisture intrusion. This method of making an electrical connection is commonly a manual process due to the difficulty in automating the ribbon handling steps. If the entire process is automated, it can be costly and unreliable.
Additionally, the hole in the back of the module is a mechanical defect that compromises the integrity of the back panel by introducing irregular geometry, as well as the front panel by creating an area with less than adequate support for impact, like from hail or dropping the panel during installation. Such a hole presents a weak spot in the module that is susceptible to hail impact, particularly when paired with a relatively thin (e.g., 2 mm or less) front glass. This issue can be corrected by mechanically reinforcing the hole. However, reinforcing the hole adds a process step and an additional part to the bill of materials.
Thus, a need exists to establish an electrical connection via a more manufacturing friendly process, as well as to eliminate the mechanical integrity issues inherent with the large hole.
Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
Thin film photovoltaic devices are generally provided that include a direct connection to at least one lead bar extending through a connection aperture defined in the encapsulation substrate to electrically connect to an underlying conductive ribbon. In one embodiment, the photovoltaic device includes: a transparent substrate; a plurality of photovoltaic cells on the transparent substrate; a conductive ribbon electrically connected to a photovoltaic cell; an encapsulation substrate laminated to the transparent substrate such that the plurality of photovoltaic cells and the conductive ribbon are positioned between the transparent substrate and the encapsulation substrate; and a lead bar extending through a connection aperture defined in the encapsulation substrate and electrically connected to the conductive ribbon. In a particular embodiment, the lead bar defines a lead tab that establishes a mechanical connection having a biasing force between the lead bar and the conductive ribbon.
Methods are also generally provided for electrically connecting at least one lead to a thin film photovoltaic device. For example, an encapsulation substrate can be attached to a transparent substrate such that a first connection aperture defined in the encapsulation substrate is positioned adjacent to a first conductive ribbon positioned between the encapsulation substrate and the transparent substrate. In one embodiment, a second connection aperture is also defined in the encapsulation substrate and is positioned adjacent to a second conductive ribbon positioned between the encapsulation substrate and the transparent substrate. A junction box can then be attached to an exposed surface of the encapsulation substrate opposite of the transparent substrate such that a first lead bar extending from the junction box is inserted into the first connection aperture and, if present, a second lead bar extending from the junction box is inserted into the second connection aperture. Each of the lead bars can include a lead tab that, upon application of pressure to the junction box, bends to establish a mechanical connection, respectively, to the first conductive ribbon and the optional second conductive ribbon via a biasing force. The lead bars can then be secured within the respective connection apertures.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:
Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention.
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
Thin film photovoltaic (“PV”) devices are generally provided having improved mechanical integrity at the point(s) of electrical connection from a conductive ribbon line(s) to a junction box(s) (“J-box), along with their methods of manufacture. In particular, a solid lead extending from the J-box is utilized to access and electrically connect to a connection ribbon below the surface of the back panel via insertion through a relatively small hole (e.g., having a diameter that is roughly equal to or less than the width of the ribbon) within the back panel. This electrical access can be achieved via direct contact between a given lead and corresponding ribbon and/or via an intermediary conductive material (e.g., adhesive, solder paste, etc.) deposited within the small hole. In the case of a mono-pole PV device design, the J-Box would have one lead that connects to one conductive ribbon. In the case of a bi-polar PV device design, the J-box would have two leads, each connected to a different connection ribbon. In other module designs, there could be many leads to connect to the many connection ribbons.
The resulting device is less susceptible to hail damage due to the small diameter of the connection aperture through the encapsulation substrate, as well as the fill of the connection aperture via by the lead bar, alone or in combination with an optional filling material (e.g., a meltable conductive material and/or a sealing material). In particular, the relatively small diameter of the connection aperture(s) results in higher shatter resistance due to the cavity being filled and reinforced with conductive material and because of the diameter relative to the size and shape of the potentially damaging hail.
Also, due to the design options, the J-box can easily be assembled to the back of the device in an automated fashion. For example, when used, preforms can be placed, or the solder (paste-form or molten) and/or adhesive can be injected into the holes, and the J-box housing can be adhered onto the back of the encapsulation substrate by lining up the lead bar(s) with the connection aperture(s) defined in the encapsulation substrate using a simple vision system and robotic arm.
As stated, the thin film stack 11 defines individual solar cells 28 (also referred to as photovoltaic cells) separated by scribes 26 to collectively form a plurality of serially connected solar cells. Specifically, the individual photovoltaic cells 28 are electrically connected together in series. In one particular embodiment, the thin film stack 11 includes a transparent conductive oxide layer on the inner surface 15 of the transparent substrate 12 (serving as a superstrate), an optional resistive transparent buffer layer on the transparent conductive oxide layer, an n-type window layer (e.g., comprising cadmium sulfide) on the transparent conductive oxide layer, an absorber layer (e.g., comprising cadmium telluride) on the n-type window layer, and a back contact on the absorber layer (e.g., a graphite layer and/or a metal contact layer). It is, however, to be understood that other material combinations could instead be used to form the back contact and that such combinations are considered to be within the scope of presently disclosed device. Other layers may also be present in the thin film stack 11. For example, index matching layers may be present between the transparent conductive oxide layer and the inner surface of the superstrate. Additionally, an oxygen getter layer may be present in the thin film stack, such as adjacent to the transparent conductive oxide layer (e.g., between the transparent conductive oxide layer and the optional resistive transparent buffer layer).
The plurality of serially connected solar cells 28 are between a dead cell 54 and a terminal cell 56. As shown, the dead cell 54 and the terminal cell 56 are positioned on opposite ends of the plurality of serially connected solar cells 28 in the y-direction of the device 10. The back contact of the dead cell 54 serves as an electrical connector for the device 10, while the TCO layer of the terminal cell 56 serves as the opposite electrical connector for the device 10. As such, the dead cell 54 does not produce a charge in the thin film stack 11, while the terminal cell 56 may.
An insulating layer 58 is on the thin film stack 11 to protect the back contact of the thin film stack 11. The insulating layer 58 generally includes an insulating material that can prevent electrical conductivity therethrough. Any suitable material can be used to produce the insulating layer 58. In one embodiment, the insulating layer 58 can be an insulating polymeric film coated on both surfaces with an adhesive coating. The adhesive coating can allow for adhesion of the insulating layer 58 to the underlying thin film stack 11 and for the adhesion of the conductive strip 60, 62 to the insulating layer 58. For example, the insulating layer 58 can include a polymeric film of polyethylene terephthalate (PET) having an adhesive coating on either surface. The adhesive coating can be, for example, an acrylic adhesive, such as a thermosetting acrylic adhesive.
In one particular embodiment, the insulating layer 58 is a strip of insulating material generally oriented in a direction substantially perpendicular to the orientation of the scribes 26. For example, the insulating layer 58 can be generally oriented in the y-direction that is substantially perpendicular to the orientation of the scribes 26 in the x-direction.
The insulating layer 58 can have a thickness in the z-direction suitable to prevent electrical conductivity from the underlying thin film layers, particularly the back contact, to any subsequently applied layers. In one particular embodiment, the insulating layer 58 can prevent electrically conductivity between the thin film stack 11 and the conductive strips 60, 62.
The conductive strips 60, 62, in one embodiment, can be applied as a continuous strip over the insulating layer 58, and then severed to produce a first conducting ribbon 60 and a second conducting ribbon 62, as shown in
Bus bars 64, 66 can then be attached over the terminal cell 56 and the dead cell 54, respectively, of the photovoltaic device 10 to serve as an opposite electrical connections. The encapsulating substrate 70 can be adhered to the photovoltaic device 10 via an adhesive layer 72. The adhesive layer 72 is generally positioned over the conductive strips 60, 62, the insulating layer 58, and any remaining exposed areas of the thin film stack 11. For example, the adhesive layer 72 can define adhesive gaps that generally corresponds to the connection apertures 74, 76 defined by the encapsulating substrate 70. As such, the first conducting ribbon 60 and a second conducting ribbon 62 can be accessible through the adhesive gaps and the connection apertures 74, 76. The adhesive layer 72 can generally provide mechanical stability within the connection apertures 74, 76 and can also protect the thin film stack 11 and attach the encapsulating substrate 70 to the device 10. The adhesive layer 72 can be constructed from ethylene vinyl acetate (EVA), polyvinyl butyral (PVB), silicone based adhesives, or other adhesives which are configured to prevent moisture from penetrating the device.
A junction box 80 can also be included in the device and can be configured to electrically connect the photovoltaic device 10 by completing the DC circuit via a pair of lead bars 84, 86 that are electrically connected to a pair of wires 94, 96, respectively, for collection of the current generated by the device 10. In particular, the first lead bar 84 and a second lead bar 86 extend from the junction box 80 and, respectively, through the first connection aperture 74 and the second connection aperture 76. As shown in
In one embodiment, the connection apertures 74, 76 can have a maximum diameter that is substantially equal to or less than the width of their respective conductive ribbons 60, 62. For example, the connection apertures 74, 76 can have a maximum diameter that is about 50% to about 100% of the width of their respective conductive ribbons 60, 62 (e.g., about 55% to about 90%). As such, the size of the connection apertures 60, 62 can be minimized, while still allowing for an adequate electrical connection to be made for current collection from the device 10.
Although described with respect to the embodiment of
As shown, a pair of preforms 104, 106 are inserted into the connection apertures 74, 76 either before, during, or after lamination of the encapsulation substrate 70 onto the transparent substrate 12. Each of the preform 104, 106 includes a meltable conductive material. Thus, the meltable conductive material of the preforms 104, 106 can electrically connect to the lead bars 84, 86 to the respective conductive ribbon 60, 62. Suitable meltable conducive materials can include, but are not limited to metallic materials and alloys, solder materials, etc.
In addition to the preforms, or in the alternative to the preforms, a solder paste (as a liquid) can be inserted into the connection apertures 74, 76 either before, during, or after lamination of the encapsulation substrate 70 onto the transparent substrate 12.
For example, the meltable conductive material can generally include any suitable solder material, including but not limited to, tin, lead, antimony, bismuth, indium, silver, copper, cadmium, or alloys thereof, or mixtures thereof. Generally, the solder material may be configured to melt at a solder temperature of about 150° C. to about 250° C. (e.g., a soft solder) to ensure that melting the solder can occur without significantly affecting the other components of the device 10. Both lead-based solders and non-lead-based solders may prove useful for this application.
As illustrated in
The lead tab 302 extends from the lead body 304 and is generally configured to establish a mechanical connection having a biasing force between the lead bar 300 and the conductive ribbon 60, such as shown in
The stamp form 300 also defines a crimp section 308 that is configured to be electrically connected to a wire 94 (e.g,. crimped by surrounding the wire 94, either circumscribing the entire or a portion of the wire 94). A shank bar 306 is also defined by the stamped form 300 between the crimp section 308 and the lead body 304. In use, the shank bar 306 is configured and sized to extend out of the connection aperture 74 and bridge (mechanically and electrically) the lead tab 302 and lead body 304 to the crimp section 308. Thus, the wire 94 can be electrically connected to the conductive ribbon 60 via the stamped form 300 serving as the lead bar 84.
Due to is relatively small width when stamped (i.e., less than the diameter of the lead body 304 and/or the crimp section 308), the shank bar 306 can be positioned and/or bent as desired. For example, bending the form 300 as the shank bar 306 extends out of the connection aperture 74 allows for the insertion of a heating element through the lead aperture 900 defined by the curved lead body 304. Additionally, the shank bar 306 can serve as a shock absorber and/or flexible pivot that allows the connected wire 94 to move without transferring significant force to the device 10, particularly the encapsulating substrate 70 via the connection aperture 74. As such, the shank bar 306 can substantially avoid transferring stress from to the solder joint.
Alternatively or additionally, the lead body 304 can be shaped around a preform 104 and then inserted together into the connection aperture 74. The meltable conductive material can then be melted (e.g., via a heating element inserted into the lead aperture 305 defined by the lead body 304) to electrically secure the conductive ribbon 60 to the lead bar 84 formed by the stamped form 300.
As shown in
In one embodiment, the sealing material can include a synthetic polymeric material, such as a butyl rubber or other rubber material. Though the exact chemistry of the butyl rubber can be tweaked as desired, most butyl rubbers are a copolymer of isobutylene with isoprene (e.g. produced by polymerization of about 98% of isobutylene with about 2% of isoprene). One particularly suitable synthetic polymeric material for use in the sealing layer 22 is available commercially under the name HelioSeal® PVS 101 from ADCO Products, Inc. (Michigan Center, Mich.).
The synthetic polymeric material can, in one embodiment, melt at the lamination temperature, reached when the encapsulating substrate 70 is laminated to the substrate 12, such that the synthetic polymeric material melts and/or otherwise conforms and adheres to form a protected area on the thin film layers 11 where the connection aperture(s) is located on the device 10. For instance, the synthetic polymeric material can melt at laminations temperatures of about 120° C. to about 160° C.
As shown in
Although described with reference to the embodiment shown in
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
