Terminal assembly including a junction box for a photovoltaic module and method of forming

A terminal assembly and a junction box for a photovoltaic module are provided. The terminal assembly includes a terminal connector, a power cable, and a gasket. The junction box is positioned over the terminal connector and attached to a first surface of the photovoltaic module. The terminal connector extends through the first surface of a photovoltaic module. The power cable is attached to the terminal connector and extends through the junction box. The gasket is housed between the first surface of the photovoltaic module and the junction box. The gasket comprises a first material and a second material and provides a seal about an end portion of the power cable. A method for forming the terminal assembly is also provided.

BACKGROUND OF THE INVENTION

This invention relates generally to photovoltaic (PV) modules, and more specifically to an improved terminal assembly for use with a flexible PV module.

Flexible PV modules utilizing thin-film PV semiconductor materials, such as thin-film silicon based amorphous silicon (a-Si), can be formed to generate electricity. Thin-film PV semiconductor materials can be deposited from a variety of methods to form PV cells. Generally, a PV module has a plurality of PV cells electrically connected in series to form a string of cells. The PV module may include a plurality of PV cell strings. Typically, at the beginning of the first string of PV cells and at the end of the last string of PV cells is a terminal assembly. A terminal assembly allows the PV module to be electrically connected to a power grid or used as a local power source.

Each terminal assembly has at least one power cable attached to a terminal connector. To protect the connection point between the terminal cable and the terminal connector, a junction box is also typically provided. The junction box may be filled with a rigid potting material to provide support to the junction box. The potting material also may help to prevent moisture from entering the junction box by forming a seal around attachment point of the power cable and the terminal connector as well as the area between the power cable and the junction box.

However, since traditional potting materials are rigid, flexing of the PV module or power cable movement may separate the interfaces between the terminal assembly components, the junction box, and the potting material. Thus, leak points for moisture ingress may be created. Therefore, a need exists for a terminal assembly which prevents moisture from penetrating the junction box, is simple and robust in design, and inexpensive to manufacture.

BRIEF SUMMARY OF THE INVENTION

A terminal assembly including a junction box for a photovoltaic module is provided. A method of forming a terminal assembly for a photovoltaic module is also provided.

In an embodiment, the terminal assembly comprises a terminal connector, a power cable, and a gasket. The terminal connector extends through a first surface of the photovoltaic module. The junction box is positioned over the terminal connector and is attached to the first surface of the photovoltaic module. The power cable is attached to the terminal connector and extends through the junction box. The gasket comprises a first material and a second material. The gasket is housed between the first surface of the photovoltaic module and the junction box and provides a seal about an end portion of the power cable.

In another embodiment, the terminal assembly comprises a terminal connector, a power cable, and a gasket. The terminal connector extends through a first surface of a photovoltaic module. The junction box comprises a first portion and a second portion and is attached to the first surface of a photovoltaic module with an adhesive. The first portion of the junction box is positioned over the terminal connector and the second portion of the junction box has an aperture. The power cable is attached to the terminal connector and extends from the junction box first portion through the second portion aperture. Further, the power cable comprises an inner conductive core and an outer insulating sheath. The gasket is attached to the power cable outer sheath and is located between the first surface of the photovoltaic module and the junction box. The gasket comprises an epoxy and butyl rubber.

The method of forming the terminal assembly for a photovoltaic module comprises providing a terminal connector and attaching a power cable to the terminal connector. The method also comprises attaching a second gasket material to the terminal cable. A junction box is attached to the photovoltaic module and a portion of the terminal connector, a portion of the terminal cable and the second gasket material are housed within a cavity of the junction box. Further, the method comprises filling the junction box cavity with a first gasket material and curing the first gasket material to form a seal about an end portion of the power cable.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly stated to the contrary. It should also be appreciated that the specific embodiments and methods illustrated in and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. For example, although the present invention will be described in connection with a-Si PV cells the present invention is not so limited. As such, the present invention may also be utilized with PV cells having at least one single junction (SJ) of cadmium telluride (CdTe), amorphous silicon germanium (a-SiGe), crystalline silicon (c-Si), microcrystalline silicon (mc-Si), nanocrystalline silicon (nc-Si), CIS2, or CIGS.

A PV module10is provided inFIG. 1. In an embodiment, the PV module10is a flexible PV module. For example, the flexible PV module could be an XR-12 sold by the Xunlight Corporation. However, while the present invention will be described for use with a flexible PV module, the present invention is not so limited. Thus, it is within the scope of the present invention that rigid PV modules, i.e. PV modules utilizing glass substrates, may also be utilized to practice the present invention.

The PV module10has a first surface (facing the sun) protective layer12and a second surface protective layer14. In an embodiment, the first surface protective layer12is composed of a fluoropolymer material. A preferred fluoropolymer is a fluorinated polyethylene such as ethylene tetrafluoroethylene. The PV module10also has at least one PV cell16encapsulated between the protective layers12,14. When a plurality of PV cells16are provided, the PV cells16are electrically connected in series to form at least one PV cell string. The PV module10may comprise a single PV cell string or multiple PV cell strings. The PV module10depicted inFIG. 1has two PV cell strings.

To connect the PV module10to other PV modules (not depicted) or to use the PV module10as a single module power source, a pair of terminal assemblies18are provided. As would be appreciated by those skilled in the art, each terminal assembly18has either a positive or a negative electrical polarity. Additionally, at least one junction box22is provided to cover and protect the terminal assemblies18. It is advantageous to separate the terminal assemblies18. Thus, as shown inFIG. 1, two junction boxes22are provided. It should be appreciate that, although it is advantageous to provide a separate junction box22for each terminal assembly18, the present invention is not so limited.

Referring now toFIGS. 2-4, each terminal assembly18comprises a terminal connector24, a power cable26, and a gasket28.

The terminal connector24is composed of a conductive material, preferably copper or an alloy thereof. The terminal connector24has a first end portion30and a second end portion32. The first end portion30is attached to the second end portion32. In an embodiment, the end portions30,32may be configured such that the terminal connector24is L-shaped. The first end portion30extends through one of the protective layers12,14and is attached to a header34. As shown inFIG. 4, the first end portion30extends through the first surface protective layer12. However, it should be appreciated that the present invention could be utilized on and over the second surface protective layer14. The second end portion32is attached to the power cable26. The second end portion32may have an aperture36to facilitate attaching the terminal connector24to the power cable26.

Although a PV cell16is not depicted inFIGS. 2-4, the header34is in electrical communication with at least one PV cell16and the terminal connector24. Thus, the terminal connector24is in electrical communication with at least one PV cell16and/or a PV cell string. The header34and the terminal connector24may be attached by soldering, welding, or a conductive adhesive. Additional methods for attaching the terminal connector24to the header34may also be utilized.

As stated, the power cable26is attached to the terminal connector24. The power cable26is in electrical communication with the terminal connector24. The power cable26may be attached to the terminal connector24mechanically, by welding, or by soldering at a connection point84.

In an embodiment, the power cable26comprises a first end portion67and a second end portion68. The power cable first end portion67is attached to the terminal connector24and is positioned within the junction box22. The power cable first end portion67extends through a majority of the junction box22. The power cable second end portion68may be attached to other PV modules or to a device (not depicted) if the PV module10is being used as a single module power source.

In an embodiment, the power cable26further comprises an outer sheath69and an inner core71. The outer sheath69is composed of an insulating material and may comprise a polyolefin. The inner core71is composed of a conductive material. The inner core71may be a braided wire and composed of a metal or a metal alloy. The outer insulating sheath69covers and electrically insulates the inner conductive core71. However, a portion73of the inner conductive core71adjacent the connection point84between the power cable26and the terminal connector24may not be covered by the outer insulating sheath69. This embodiment allows the power cable26to be in electrical communication with the terminal connector24and allows it to be touch safe outside the junction box22.

The gasket28is composed of electrically insulating materials. The gasket28contacts the first surface12of the PV module10, the junction box22, the terminal connector24, and the power cable26. In an embodiment, the gasket28is housed between the first surface12of the PV module10and the junction box22. In this embodiment, the gasket28is located substantially within the junction box22and provides support for the junction box22. The gasket28also provides a seal about the second end portion32of the terminal connector24, the first end portion67of the power cable26, and their connection point84. Preferably, the seal is watertight.

The gasket28comprises a first material70and a second material72. The first gasket material70is different than the second gasket material72. As an example, the first gasket material70has a different composition than the second gasket material72. Additionally, the first gasket material70may have different physical properties than the second gasket material72. For example, the first gasket material70may be more rigid than the second gasket material72. Also, in an embodiment, the first and second gasket materials70,72have a different composition than the material of the outer sheath69of the power cable26.

The first gasket material70may be an epoxy. In an embodiment, the first gasket material70may be a curable liquid epoxy. A suitable curable epoxy may be DP190 sold by 3M. Additionally, in certain embodiments, the first gasket material70may be a thermoset material. In these embodiments, the first gasket material70may be a thermoset resin epoxy.

In an embodiment, the second gasket material72is flexible. In another embodiment, the second gasket material72is elastomeric. In yet a further embodiment, the second gasket material72is heat treatable so that after being attached to the power cable26it can be formed into a desired shape or thickness. For example, the second gasket material72may be heated to a temperature equal to or above 100° F. and formed to have a substantially uniform diameter.

The second gasket material72may be an adhesive. In an embodiment, the second gasket material72is butyl rubber adhesive. In another embodiment, the second gasket material72is an adhesive selected from the group consisting of polyolefin, ethyl vinyl acetate, VHB™, acrylic, styrene-butadiene-styrene, styrene-isoprene-styrene, styrene-ethylene/butylene-styrene, and ethylene propylene diene monomer (EPDM). In these embodiments, the second gasket material72may be in the form of an adhesive tape. For example, a butyl rubber tape having adhesive on both sides of the tape or an EPDM seam tape could be utilized. A VHB™ foam tape sold by 3M could also be utilized. When the second gasket material72is a tape, the second gasket material72may be cut to a specific length and width so that when it is attached to the power cable26the second gasket material72can be formed to have a substantially uniform diameter.

The second gasket material72is sealingly attached to the power cable26and the first gasket material70to provide a watertight seal. More specifically, the second gasket material72is sealingly attached to the power cable first end portion67and aids in providing a watertight seal about the first end portion67. Additionally, the second gasket material72may be formed so that it does not contact the PV module first surface12or the junction box22, i.e. the first gasket material70is disposed between the PV module10, the junction box22, and the second gasket material72. In these embodiments, the first gasket material70surrounds the second gasket material72and the first end portion67of the power cable26.

In an embodiment, the gasket28further comprises a third gasket material78. The third gasket material78is positioned between the first gasket material70and the second gasket material72. In an embodiment, the third gasket material78is attached to the second gasket material72such that the second gasket material72remains sealingly attached with the power cable26and the first gasket material70. Further, in this embodiment, the third gasket material78may be a heat shrink material which compresses a portion of the second gasket material72. For example, the third gasket material78may be polyvinyl chloride.

In another embodiment, the gasket28further comprises a fourth gasket material80attached to the terminal connector24and the first surface protective layer12of the PV module10. In this embodiment, the fourth gasket material80may be embedded in the first surface protective layer12. The fourth gasket material80may be composed of the same material as the first gasket material70, the second gasket72, or the third gasket material78. For example, the fourth gasket material80may be a strip of butyl rubber adhesive tape.

The junction box22is preferably composed of an electrically insulating material. In an embodiment, the junction box22may be composed of a polyester material. To provide additional strength the polyester material may be filled with fiberglass. The junction box22is attached to the PV module first surface protective layer12and is positioned over at least one terminal assembly18. As such, the junction box22covers at least one terminal assembly18and a portion20of the first surface protective layer12. Additionally, portions38of the junction box22are attached to the PV module10to form a substantially watertight seal40around each terminal assembly18. The junction box22is preferably attached to the PV module first surface protective layer12with an adhesive layer42. The adhesive layer42may be a pressure sensitive adhesive tape. A primer may be utilized to promote adhesion between the adhesive layer42and the first surface protective layer12.

The junction box22comprises a first portion44and a second portion46. The first portion44is attached to the second portion46. Preferably, the first portion44and second portion46form a unitary body.

The junction box first portion44includes a wall48. The first portion wall48has an outer surface50and an inner surface52. An aperture54may be formed in the first portion wall48. The aperture54extends from the outer surface50to the inner surface52. A cap56may be disposed within the aperture54to maintain the integrity of the seal40around each terminal assembly18.

The first portion wall inner surface52substantially defines a cavity58which is positioned over portions of the terminal assembly18. In an embodiment, the terminal connector second end portion32is located within the cavity58. Additionally, the power cable26is attached to the terminal connector24within the cavity58. As depicted, the first portion wall48may be generally configured to have a partially rectangular shape. However, the shape of the first portion wall48is not limited to being a partial rectangle. In practice, the first portion wall48may be of any shape or configuration including a partial ellipse, square, or circle. As such, the cavity58may have a partial rectangle shape or may be configured to include another shape.

In an embodiment, the junction box second portion46includes a wall60. The second portion wall60has an outer surface62and an inner surface64. The second portion wall inner surface64defines an aperture66. In an embodiment, the aperture66has a uniform diameter. The power cable26extends from the junction box first portion44, where it is attached to the terminal connector24, and through the second portion aperture66.

The gasket28is housed between the first surface protective layer12of the photovoltaic module10and the junction box22. In an embodiment, the gasket28is housed substantially within the junction box cavity58and second portion aperture66. In this embodiment, a first portion74of the first gasket material70is located within the cavity58and a second portion76of the first gasket material70is located in a space77between the power cable26and the second portion wall inner surface64. The first portion74of the first gasket material70is sealingly attached to the first surface protective layer12of the photovoltaic module10, the junction box22, the terminal connector24, and the first end portion67of the power cable26to provide a watertight seal. The second portion76of the first gasket material70is also sealingly attached to the power cable26and the inner surface64of the junction box second portion46to provide a watertight seal.

The terminal assembly18allows power to be transferred from the PV module10. Flexible PV modules are susceptible to damage adjacent the terminal assembly18and junction box22from moisture ingress. Specifically, moisture adjacent the connection point84of the terminal connector24and the power cable26can reduce the amount of power transferred from the PV module10and prevent the PV module10from being touch safe.

Moisture ingress into the junction box22is difficult to prevent for several reasons. First, flexing of the PV module10may occur during the manufacturing, shipping, or installation of the PV module10. Flexing may create separation between the components of the terminal assembly18or between the components of the terminal assembly18and the junction box22. Additionally, the terminal assembly18and the junction box22may be composed of materials which are not compatible to form a watertight seal. Thus, paths for moisture ingress may develop at the interfaces of the PV module first surface protective layer12, the terminal assembly18, and/or the junction box22.

However, the present invention provides for the safe and repeatable transfer of power from the PV module10by forming a watertight seal about the first end portion67of the power cable26. The present invention also provides that the connection point84between the terminal connector24and the power cable26is electrically insulated and isolated. Further, the present invention is mechanically strong and protects the terminal connector24and the power cable26from damage and is weatherable such that it will maintain performance for the functional life of the PV module10.

The present invention also provides a method of forming the terminal assembly18for the PV module10.

In an embodiment, the method comprises providing the terminal connector24, attaching the power cable26to the terminal connector24, attaching the second gasket material72to the power cable26, and attaching the junction box22to the PV module10. In this embodiment a portion82of the terminal connector24, a portion86of the power cable26, and the second gasket material72are housed within the junction box cavity58.

In an embodiment, the second gasket material72may be formed into a seamless body. Preferably, the second gasket material72is formed so that the second gasket material72and the power cable26are in a concentric relationship. As noted above, in an embodiment the second gasket material72is heat treatable. Thus, in these embodiments, the method may further comprise forming the second gasket material72by applying heat to the second gasket material72. Additionally, while the second gasket material72may be formed using heat, it may also be formed in combination with other forming methods, i.e. mechanical or roll forming.

In certain embodiments the first gasket material70may at a certain time be a liquid. Therefore, the method of the present invention may further comprise filling the junction box cavity58with the first gasket material70and curing the first gasket material70. Thus, after a pre-determined cure time, the PV module10will be ready for use. Since, in certain embodiments the gasket materials70,72are insulating, electrical isolation and insulation around the connection point84between the terminal connector22and the power cable26is provided.

The method may further comprise filling the junction box second portion aperture66with the first gasket material70. In this embodiment, a ring gasket (not depicted) may be selectively positioned adjacent the power cable26and the aperture66. After the aperture66is filled with the first gasket material70and the first gasket material70is cured, the ring gasket may be removed. Utilizing a ring gasket in this manner helps to prevent the first gasket material70from escaping out the aperture66before it is cured.

EXAMPLE

The following example and comparative example is for illustrative purposes only and is not to be construed as a limitation on the invention.

A pair of XR-12 PV modules made by the Xunlight Corporation were separately tested for insulation resistance. Each PV module had substantially the same construction. For instance, each PV module had 12 PV cells arranged into two PV cell strings and electrically connected in series. Each PV module had a pair of terminal assemblies. Each terminal assembly had either a positive or a negative electrical polarity and was in electrical communication with the PV cells via a header. A junction box was provided for each terminal assembly. Also, each PV module had the same protective layer composition. However, the first PV module utilized terminal assemblies and junction boxes formed as described for the present invention and the second PV module, the comparative example, utilized terminal assemblies and junction boxes known in the art.

The insulation resistance of each PV module was recorded during a wet insulation resistance test. The wet insulation test was conducted by submerging the PV modules in water and applying a voltage of 500 volts to the modules. Insulation resistance was measured using a dielectric analyzer made by Associated Research, Inc. and was measured in millions of ohms (M ohms). The insulation resistance was calculated based in part on the area of PV module being tested. The area of each PV module was 1.6 m2.

The degree of wet insulation resistance for the first PV module was ≧21,416 M ohms and was ≦2.34 M ohms for the second PV module. Thus, the present invention increased the wet insulation resistance of the first PV module by almost a factor of 10,000. Therefore, it should be appreciated that the terminal assembly including the junction box and method of forming the terminal assembly as described, above, is an improvement over those known in the art. Additionally, it should be appreciated that utilizing and forming the terminal assembly18as described, above, allows a seal to be formed about the first end portion67of the power cable26and, specifically, around the connection point84between the terminal connector24and the power cable26.

The above detailed description of the present invention is given for explanatory purposes. Thus, it will be apparent to those skilled in the art that numerous changes and modifications can be made without departing from the scope of the invention. Accordingly, the whole of the foregoing description is to be construed in an illustrative and not in a limitative sense.