Photovoltaic cells are widely used for generation of electricity, with multiple photovoltaic cells interconnected in module assemblies. Such modules may in turn be arranged in arrays and integrated into building structures or otherwise assembled to convert solar energy into electricity by the photovoltaic effect. Individual modules are encapsulated to protect the module components from the environment. A module may be framed, with the frame configured for attachment to a support surface. Framing and encapsulating materials can contribute significantly to the weight and cost of a module.
Provided are novel solar modules including electrically isolated moisture barrier. According to various embodiments, the solar modules include two distinct seals: one to electrically isolate the moisture barrier and one to protect photovoltaic cells of the module. Also provided are novel back sheets for solar module encapsulation, and novel solar modules including such back sheets. According to various embodiments, the back sheets are ungrounded and flexible. In certain embodiments, the back sheets include an integrated flexible and electrically isolated moisture barrier. The electrically isolated moisture barrier may be a thin metallic sheet, e.g., an aluminum foil. The electrically isolated, flexible moisture barrier eliminates the need for grounding.
One aspect of the invention relates solar modules that include a transparent front layer; a flexible back sheet including an electrically isolated moisture barrier; a plurality of interconnected photovoltaic cells disposed between the transparent front layer and the flexible back sheet, a first seal isolating the plurality of interconnected photovoltaic cells; and a second seal isolating the moisture barrier, said second seal being distinct from said first seal.
In certain embodiments, the flexible back sheet is a multi-layer flexible back sheet that includes an insulation sheet, the electrically isolated moisture barrier, a back layer and the second seal, with the insulation sheet disposed between the plurality of photovoltaic cells and the moisture barrier, the moisture barrier disposed between the insulation sheet and the back layer, and wherein said second seal includes a bond between the insulation sheet and the back layer and extends around the moisture barrier such that the insulation sheet, back layer and second seal electrically isolate the moisture barrier. In certain embodiments the bond is a polymer adhesive bond.
In certain embodiments, the flexible back sheet is a multi-layer flexible back sheet including an insulation sheet, the electrically isolated moisture barrier and a back layer; with the insulation sheet disposed between the plurality of photovoltaic cells and the moisture barrier, the moisture barrier disposed between the insulation sheet and the back layer, and wherein the back layer has dimensions greater than the moisture barrier and extends past the moisture barrier to enclose an edge of the moisture barrier.
In certain embodiments, the flexible back sheet is a multi-layer flexible back sheet including an insulation sheet, the electrically isolated moisture barrier, a back layer and the second seal; with the insulation sheet disposed between the plurality of photovoltaic cells and the moisture barrier, the moisture barrier disposed between the insulation sheet and the back layer, and the second seal including the perimeter of the back layer.
According to various embodiments, the first seal includes a sealing material surrounding the interconnected photovoltaic cells. Examples of sealing materials include butyl-rubber containing moisture getters or desiccants. In certain embodiments, the first seal includes a bonding between the sealing material and the transparent front layer. In certain embodiments, the sealing material is adhesive. This may be a covalent bonding, an adhesive bonding or other type of bonding. The first seal may include a bonding between the sealing material and the flexible back sheet, e.g., a bonding to between the sealing material one or more layers of the flexible back sheet. This may be a covalent bonding, an adhesive bonding or other type of bonding. Also in certain embodiments, the second seal comprises a bond between the sealing material and the back layer. In certain embodiments, a back layer of the flexible back sheet extends past the insulation sheet to enclose an edge of the insulation sheet.
Other aspects of the invention relates to multi-layer flexible back sheets and solar modules incorporating multi-layer flexible back sheets. One aspect relates to solar modules that include a transparent front layer, a multi-layer flexible back sheet; and a plurality of interconnected photovoltaic cells disposed between the transparent front layer and the multi-layer flexible back sheet. The multi-layer flexible back sheet includes an insulation sheet, an electrically isolated moisture barrier, and a back layer; with the insulation sheet disposed between the plurality of photovoltaic cells and the moisture barrier and the moisture barrier disposed between the insulation sheet and the back layer. The back layer has dimensions greater than the moisture barrier and extends past the moisture barrier to enclose an edge of the moisture barrier.
In certain embodiments, the back layer also extends past the insulation sheet to enclose an edge of the insulation sheet. The back layer may enclose the entire perimeter edge of the moisture barrier and/or insulation sheet or a portion of the perimeter edge. All or part of a perimeter portion of the back layer may be sealed to another module component. In certain embodiments, an edge seal material surrounding the plurality of photovoltaic cells is sealed to the back layer. In certain embodiments, the insulation sheet and back layer are arranged to fully enclose the moisture barrier.
Another aspect of the invention relates to solar modules that include a transparent front layer; a multi-layer flexible back sheet; and a plurality of interconnected photovoltaic cells disposed between the transparent front layer and the multi-layer flexible back sheet. The multi-layer flexible back sheet includes an insulation sheet, an electrically isolated moisture barrier, a back layer and a seal; with the insulation sheet disposed between the plurality of photovoltaic cells and the moisture barrier, the moisture barrier disposed between the insulation sheet and the back layer, and the seal including the perimeter of the back layer and/or a bond to the perimeter of the back layer.
In certain embodiments, the seal includes a bond between the perimeter of the back layer and a second module component. The second module component may be an edge seal material that surrounds the photovoltaic cells, or may be another component. In certain embodiments, the back layer has dimensions greater than the moisture barrier and extends past the moisture barrier to cover the perimeter of the moisture barrier.
According to various embodiments, the transparent front layer may be a rigid material, e.g., a glass plate, or it may be flexible material. The photovoltaic cells may be any type of photovoltaic cells, including but not limited to CIS, CIGS, CdTe or silicon photovoltaic cells.
According to various embodiments, the moisture barrier is a pinhole free conductive material, e.g., pinhole free aluminum foil. The moisture barrier is typically thin, e.g., no more than about 50 microns thick, or no more than 25 microns thick. Other thicknesses may be used as appropriate to provide a flexible moisture barrier.
According to various embodiments, the insulation sheet is a dielectric material capable of withstanding at least a certain potential, e.g., a 600 V potential or 1000 V potential. In certain embodiments, a PET insulation sheet having a thickness of about 1-10 mils is used. The insulation sheet may be a single sheet or a multi-layer sheet, e.g., with different layers having different material properties or compositions.
The back layer may be a weatherable material capable of protecting the module from external conditions, for example polyvinyl fluoride or other fluoropolymers. In alternative embodiments, the back layer may be another material, and the module may include a weatherable material under the back layer. The back layer may be a single layer or may have multiple layers, e.g., with different layers having different material properties or compositions. If present, the bond between the back layer and another module component may be an adhesive bond, or any other type of bond sufficient to electrically isolate the moisture barrier.
One aspect of the invention relates to solar modules that include a transparent front layer, a multi-layer flexible back sheet; and a plurality of interconnected photovoltaic cells disposed between the transparent front layer and the multi-layer flexible back sheet. The multi-layer flexible back sheet includes an insulation sheet, an electrically isolated moisture barrier, a back layer and a seal; with the insulation sheet disposed between the plurality of photovoltaic cells and the moisture barrier and the moisture barrier disposed between the insulation sheet and the back layer. The seal includes a bond between the insulation sheet and the back layer and extends around the moisture barrier such that the insulation sheet, back layer and seal electrically isolate the moisture barrier.
Another aspect of the invention relates to solar modules including a transparent front layer, an ungrounded moisture barrier flexible back sheet, and a plurality of interconnected photovoltaic cells located between the transparent front layer and the ungrounded moisture barrier flexible back sheet, wherein the ungrounded moisture barrier flexible back sheet has a water vapor transmission rate (WVTR) of no more than about 10−2 g/m2/day. In certain embodiments, the WVTR no more than about 10−3 g/m2/day.
The transparent front layer may be a rigid material, e.g., a glass plate, or it may be flexible material. The photovoltaic cells may be any type of photovoltaic cells, including but not limited to CIS, CIGS, CdTe or silicon photovoltaic cells.
According to various embodiments, the moisture barrier is a pinhole free conductive material, e.g., pinhole free aluminum foil. The moisture barrier is typically thin, e.g., no more than about 50 microns thick, or no more than 25 microns thick. Other thicknesses may be used as appropriate to provide a flexible moisture barrier.
According to various embodiments, the insulation sheet is a dielectric material capable of withstanding at least a certain potential, e.g., a 600 V potential or 1000 V potential. In certain embodiments, a PET insulation sheet having a thickness of about 1-10 mils is used. The insulation sheet may be a single sheet or a multi-layer sheet, with different layers having different material properties or compositions.
The back layer may be a weatherable material capable of protecting the module from external conditions, for example polyvinyl fluoride or other fluoropolymers. In alternative embodiments, the back layer may be another material, and the module may include a weatherable material under the back layer. The back layer may be a single layer or may have multiple layers, e.g., with different layers having different material properties or compositions. The bond between the insulation sheet and back layer may be an adhesive bond, or any other type of bond sufficient to electrically isolate the edge of the moisture barrier.
In certain embodiments, the insulation sheet and/or back layer and the moisture barrier have substantially coextensive end portions along a first direction. For example, in a roll-to-roll process, a module-sized stack, including a moisture barrier as well as insulation sheet and/or back layer may be cut from a web, with the moisture barrier coextensive with the insulation sheet and/or back layer at the cut edges. A coextensive insulation sheet end portion and a moisture barrier end portion may be folded to together form an inwardly curved end portion, with the moisture barrier end portion on the interior of said inwardly curved end portion. In this manner, the edges of moisture barrier are electrically isolated from the rest of the module. In certain embodiments, the seal may include a folded over portion as described.
In certain embodiments, the seal extends at least about 1-2 mm past at least two edges or on all edges of the moisture barrier. In certain embodiments, the width of the seal on at least two edges or on all edges of the moisture barrier is at least about 1-2 mm. In certain embodiments, an edge seal material containing a moisture getter or desiccant material such as a butyl based material, surrounds the photovoltaic cells. The outer perimeter of the moisture barrier may be in between the inner and outer perimeters of the seal material in certain embodiments.
Another aspect of the invention relates to solar modules that include a transparent front layer, a multi-layer flexible back sheet; and a plurality of interconnected photovoltaic cells disposed between the transparent front layer and the multi-layer flexible back sheet. The multi-layer flexible back sheet includes an insulation sheet, an electrically isolated moisture barrier, a back layer and a seal; with the insulation sheet disposed between the plurality of photovoltaic cells and the moisture barrier and the moisture barrier disposed between the insulation sheet and the back layer. The seal includes a bond between the insulation sheet and the back layer and extends around the moisture barrier such that the insulation sheet, back layer and seal electrically isolate the moisture barrier.
Another aspect of the invention relates to solar modules including a transparent front layer, an ungrounded moisture barrier flexible back sheet, and a plurality of interconnected photovoltaic cells located between the transparent front layer and the ungrounded moisture barrier flexible back sheet, wherein the ungrounded moisture barrier flexible back sheet has a water vapor transmission rate (WVTR) of no more than about 10−2 g/m2/day. In certain embodiments, the WVTR is no more than about 10−3 g/m2/day.
The transparent front layer may be a rigid material, e.g., a glass plate, or it may be flexible material. The photovoltaic cells may be any type of photovoltaic cells, including but not limited to CIS, CIGS CdTe or silicon photovoltaic cells.
According to various embodiments, the moisture barrier is a pinhole free conductive material, e.g., pinhole free aluminum foil. The moisture barrier is typically thin, e.g., no more than about 50 microns thick, or no more than 25 microns thick. Other thicknesses may be used as appropriate to provide a flexible moisture barrier.
According to various embodiments, the insulation sheet is a dielectric material capable of withstanding at least a certain potential, e.g., a 600 V potential or 1000 V potential. In certain embodiments, a PET insulation sheet having a thickness of about 1-10 mils is used. The insulation sheet may be a single sheet or a multi-layer sheet, e.g., with different layers having different material properties or compositions.
The back layer may be a weatherable material capable of protecting the module from external conditions, for example polyvinyl fluoride or other fluoropolymers. In alternative embodiments, the back layer may be another material, and the module may include a weatherable material under the back layer. The back layer may be a single layer or may have multiple layers, e.g., with different layers having different material properties or compositions. The bond between the insulation sheet and back layer may be an adhesive bond, or any other type of bond sufficient to electrically isolate the edge of the moisture harrier.
In certain embodiments, the insulation sheet and/or back layer and the moisture barrier have substantially coextensive end portions along a first direction. For example, in a roll-to-roll process, a module-sized stack, including a moisture barrier as well as insulation sheet and/or back layer may be cut from a web, with the moisture barrier coextensive with the insulation sheet and/or back layer at the cut edges. A coextensive insulation sheet end portion and a moisture barrier end portion may be folded to together form an inwardly curved end portion, with the moisture barrier end portion on the interior of said inwardly curved end portion. In this manner, the edges of moisture barrier are electrically isolated from the rest of the module. In certain embodiments, the seal may include a folded over portion as described.
In certain embodiments, the seal extends at least about 1-2 mm past at least two edges or on all edges of the moisture barrier. In certain embodiments, the width of the seal on at least two edges or on all edges of the moisture barrier is at least about 1-2 mm. In certain embodiments, an edge seal material containing a moisture getter or desiccant material such as a butyl based material, surrounds the photovoltaic cells. The outer perimeter of the moisture barrier may be in between the inner and outer perimeters of the seal material in certain embodiments.
Also provided are flexible multi-layer back sheets and methods of fabricating the same, as well as pre- and post-laminate back sheet and solar module stack assemblies. These and other aspects of the invention are described further below with reference to the figures.
Reference will now be made in detail to specific embodiments of the invention. Examples of the specific embodiments are illustrated in the accompanying drawings. While the invention will be described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the invention to such specific embodiments. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be practiced without some or all of these specific details. In other instances, well known mechanical apparatuses and/or process operations have not been described in detail in order not to unnecessarily obscure the present invention.
Embodiments of the present invention relate to encapsulating solar modules for environmental protection and mechanical support.
Front and back encapsulating layers 104 and 106 can contribute significantly to the weight and transportation costs of a module. Rigid materials such as glass sheets, for example, provide good protection against environmental conditions but can add on the order of $2/sheet in transportation costs. While flexible materials such as aluminum foil are lighter and cheaper than glass, they present their own costs and issues. In particular, conventional metalized back sheets require grounding the metal in the back sheet or a grounded metal frame surrounding the module to prevent electrical shorting. Grounding a module, e.g., via a conductive frame also presents a major cost: the frame, conductors to ground, and installation costs of a grounded module are significant and present barriers to the competitive pricing of solar energy generation.
Provided herein are flexible encapsulating materials that do not require grounding or framing. The materials are considerably lighter and easier to handle than rigid encapsulation materials, and do not require the attendant issues of grounding and framing that conventional metalized encapsulation layers do. In certain embodiments, a flexible metallic back sheet is provided. Unlike current metalized back sheets for moisture impermeable solar module encapsulation, the metalized back sheets described herein do not require grounding to meet UL standards, and may be ungrounded in certain embodiments. Section 690.43 of the 2005 National Electrical Code (NEC) requires that: “Exposed non-current-carrying metal parts of module frames, equipment, and conductor enclosures shall be grounded in accordance with 250.134 or 250.136(A) regardless of voltage.” Because embodiments of the invention do not have exposed moisture barriers, or in certain embodiments, any exposed metal parts, they do not require grounding to be in compliance with the 2005 version of the US NEC. In particular embodiments, the solar modules or back sheets described herein meet the wet leakage current and/or high potential standards as defined in UL 1703. Article 690 of the 2005 NEC and UL 1703, edition 3, as revised April 2008, are incorporated by reference herein.
Moisture barrier 202 may be any material that is flexible and moisture impermeable. Moisture impermeability may be defined by the water vapor transmission rate (WVTR), the steady state rate at which water vapor permeates through a film at specified conditions of temperature and relative humidity. According to various embodiments, the moisture barrier has a WVTR of no more than 10−2 g/m2/day at 38° C. and 100% relative humidity. In certain embodiments, the moisture barrier has a WVTR of no more than 10−3 g/m2/day at 38° C. and 100% relative humidity.
The moisture barrier may be a pinhole-free metallic material, including, but not limited to pinhole-free aluminum foil. In addition to aluminum or alloys thereof, metallic moisture barriers may be copper, palladium, titanium, gold, silver, iron, molybdenum, stainless steel, steel, zinc, alloys thereof such as brass, or other combinations thereof. In certain embodiments, the moisture barrier may be a metallic or other conductive material in combination with another material. The moisture barrier should be thick enough to be pinhole-free, or to meet the desired WVTR. This varies according to the particular metal used. In one example, aluminum foil as thin as about 17 microns is used. In another example, pinhole-free aluminum foil as thin as about 25 microns, or about 50 microns is used. In certain embodiments, moisture barriers between about 5 and 500 microns may be used, though other thicknesses may be used as well.
In certain embodiments, insulation sheet 204 is sufficient to withstand a high electrical potential between a conductive moisture barrier 202 and the solar cells (not shown) to prevent arcing or shorting. The voltage withstand of the sheet is a function of the material properties of the insulation sheet material as well as the thickness of the sheet. In certain examples, thickness ranges from about 1 to 10 mils or higher, though other thicknesses may be used as appropriate. According to various embodiments, the voltage withstand of the insulation sheet is at least about 500 V, at least about 600 V, at least about 700 V, at least about 800 V, at least about 900 V, at least about 1000 V, at least about 1500 V, or at least about 2000 V. In certain embodiments, the insulation material is or contains a thermoplastic material. Non-limiting examples of insulation materials include thermal polymer olefins (TPO) and non-olefin thermoplastic polymers, including polyethylene, polypropylene, polybutylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene, polycarbonates, ethylene-vinyl acetate (EVA), fluoropolymers, acrylics, including poly(methyl methacrylate), or silicones, as well as multilayer laminates and co-extrusions, such as PET/EVA laminates or co-extrusions. In one example, the insulation sheet is PET. In other examples, the insulation sheet is a nylon, acylonitrile butadiene styrene ABS), polybutylene terephtalate (PBT), (polycarbonate (PC), PPS (polyphenylene sulfide (PPS), or potyphenylene oxide (PPO). Other suitable electrically insulating materials may be used, e.g., thin ceramic materials. Filled materials may also be used.
Back layer 206 may be a weatherable material that protects the cells and other module components from moisture, UV exposure, extreme temperatures, etc. The back layer may be a fluoropolymer, including but not limited to polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), ethylene-terafluoethylene (ETFE), fluorinated ethylene-propylene (FEP), perfluoroalkoxy (PFA) and polychlorotrifluoroethane (PCTFE). Other weatherable materials may be used in addition to or instead of a fluoropolymer, including silicone polyesters, chlorine-containing materials such as polyvinyl chloride (PVC), plastisols and acrylics. In certain embodiments, any material that meets UL 1703 requirements (incorporated by reference above) is used. In one example, the back layer is PVF. In certain examples, thickness range from about 1 to about 4 mils, although other thicknesses may be used as appropriate.
Seal 208 includes a bond between back layer 206 and insulation sheet 204 and is effective to prevent any electrical contact between the moisture barrier and the solar cells or any other component of the module at the edge of moisture barrier 202. It is typically a permanent or irreversible seal and prevents peeling at the edges that would expose the edge of moisture barrier 202. According to various embodiments, the seal is at least 0.5 mm, 1 mm or 2 mm wide and extends around the edge of the moisture barrier. The bond between back layer 206 and insulation sheet 204 may be an adhesive bonding, a fusion bonding, a welding, a solder bond, or a mechanical fastening. As used herein, the term “permanent seal” refers to a seal that has a resistance to rupture greater than a frangible seal. As used herein, “irreversible seal” refers to seal that is unbreakable by exposure to atmospheric heat and weather conditions, and generally must be deliberately tampered with to be broken. In certain embodiments, the seal includes covalent bonding, e.g., between an adhesive and the back layer and/or insulation sheet, or between the insulation sheet and back layer, etc.
If an adhesive material is used, it may be a thermoplastic adhesive, a liquid adhesive, a curable adhesive, or any other type of adhesive that creates an irreversible seal, is resistant to peeling and has good moisture resistance. Thermoplastic adhesives that may be used include acrylics, silicone resins, polyamines and polyurethanes. In certain embodiments, the adhesive may also be used to adhere the insulation sheet and back layer to the moisture barrier. In certain, embodiments, one of the layers may be formed by extrusion coating or casting, e.g., on a chemically primed surface. For example, moisture barrier 202 may be adhered to insulation sheet 204. Insulation sheet 204 or (insulation sheet 204 and moisture barrier 202) may then be chemically primed and back layer 206 formed by extrusion coating or casting onto the chemically primed surface.
Solar cells 318 are encapsulated by a material 310 that protects the solar cells and that may include one or more layers of a thermoplastic material, e.g., an acrylic or silicone material. A material 314 surrounds solar cells 318. The material 314 may be an organic or inorganic material that has a low inherent WVTR (typically less than 1-2 g/m2/day) and, in certain embodiments may absorb moisture, prevents its incursion through and along edges of material 310. In one example, a butyl-rubber containing moisture getter or desiccant is used. The encapsulated cells 318 are protected by a transparent front layer 312 and back sheet 322, including weatherable back layer 306, insulation sheet 304, moisture barrier 302 and seal 308.
In the figure, moisture barrier material 302 is disposed under solar cells 318, but extends at least a small distance past solar cells 318, such that it partially underlies material 314. In certain embodiments, the outer perimeter of the moisture barrier 302 is located between the inner and outer perimeters of the material 314.
In this example, perimeter portion 416 of back layer 406 is bonded to edge material 414 to form a seal at 408. Depending on the particular arrangement of the module components, the perimeter portion 416 of back layer 406 may be sealed to any suitable materials or layers that are disposed on the opposite side of moisture barrier 402 as the main portion of back layer 406. For example, the back layer may form a seal with an insulation sheet, an encapsulant material such as material 410, a transparent front layer 412, or any other suitable module component, or combination of these. According to various embodiments, the seal is at least 0.5 mm, 1 mm or 2 mm wide. It may extend around the module to fully isolate the moisture barrier.
Prior to being folded or bent toward the photovoltaic cells, the back layer 406 may have dimensions slightly larger than the front layer 412, i.e., to account for the perimeter portion 416 that is bent toward the edge material. According to various embodiments, the back layer extends up to 10 mm past each edge of the moisture barrier and/or insulation sheet. In certain embodiments, the insulation sheet and moisture barrier are about equally sized. In other embodiments, the insulation sheet may be larger than the moisture barrier.
As indicated above, in certain embodiments, the module includes a permanent and/or irreversible seal that includes bonding between the back layer and the edge material or other module component to which the back layer is sealed. This may be an adhesive bonding, a fusion bonding, a welding, a solder bond, or a mechanical fastening. In certain embodiments, the seal includes covalent bonding, e.g., between an adhesive and the back layer and/or edge material, or between the back layer and edge material, etc. Moisture barrier 402 is electrically isolated by insulation sheet 404 and sealed back layer 406.
In certain embodiments, the moisture barrier overlaps with an edge seal material surrounding the solar cells in a plane vertical to the module.
Plan view 552 shows the solar cell area 518 and surrounding material 514 (as depicted in view 550) overlying the metallic moisture barrier 502 and the back layer including the perimeter portion 516 (as depicted in view 551). Material 514 and metallic moisture barrier 502 overlap in region 536. This provides moisture protection over the entire solar cell area 518. All or a portion of the back layer that extends past the moisture barrier (perimeter area 516) may contact and/or be sealed to all or a portion of another module component, e.g., to an insulation sheet (as depicted in
Conventional back sheets that incorporate a metallic sheet, such as Tedlar®/Al foil/PET back sheets, require grounding the aluminum foil in the back sheet or a grounded metal frame surrounding the module to meet UL and other safety requirements. This is due to the exposure or possible exposure of the aluminum foil at the cut edge. According to various embodiments, the moisture barriers described herein are ungrounded. The overlying and underlying polymers layers (e.g., PET insulation sheet and PVF weatherable hack layer) together with the seal surrounding the moisture barrier electrically isolate the moisture barrier, obviating the need to ground the moisture barrier. Because the electrically isolated moisture barriers described herein do not need to be grounded, mechanical support considerations are decoupled from electrical considerations. Thus, according to various embodiments, the solar cell modules described herein included frameless as well as framed modules. In certain embodiments, the unframed modules may be configured to be attached an array frame or other support structure at an installation site.
Examples of multi-layer flexible back sheets and solar modules including these back sheets are described above. Another aspect of the invention provides modules that include two distinct seals: one seal that isolates the photovoltaic cells and another seal that isolates the moisture barrier. By providing two such seals, shorting between the moisture barrier and photovoltaic cells or connections thereto is avoided. Each of the two seals includes a permanent and/or irreversible connection between two layers or module components. In certain embodiments, the seal may include a sealing material, e.g., an adhesive, a desiccant, or other sealing material between the module components. In certain embodiments, the two layers or components connected together directly.
In certain embodiments, the seal surrounding the photovoltaic cells includes a desiccant-loaded low moisture vapor transmission polymer. Such polymers may be characterized by the time to moisture breakthrough. In certain embodiments, there is no moisture breakthrough for more than a thousand hours and more particularly more than two thousand hours.
A second seal 308 is depicted with box 370. Here, the seal 308 includes the connection between insulation sheet 304 and back layer 306. In the depicted embodiment, the seal includes a bond between these two layers. In other embodiments, another material may be present between the layers. With insulation sheet 304 and back layer 306, seal 308 completely electrically isolates moisture barrier 302. The seals depicted within boxes 360 and 370 are physically separate, having no common interface.
In another example,
Separate seals for isolating the photovoltaic cells and moisture barrier prevents shorting between the photovoltaic cells and the moisture barrier. Even in the event of a seal breach (e.g., because of physical disruption), shorting does not occur, with the other seal intact. The photovoltaic cell seals and moisture barrier seals described above with reference to
Also provided are processes of fabricating the multi-layer back sheets described herein.
Turning first to
In process 650, rather than inserting discrete sheets, the aluminum or other moisture barrier material is also provided as a web. The process begins in an operation 652 in which the polymer insulation sheet, adhesives (is used), backing layer and moisture barrier are provided on webs to form a pre-laminate stack assembly, e.g., insulation sheet/adhesive/moisture barrier/adhesive/back layer. In certain embodiments, the width of the moisture barrier web is less than the other webs to allow for formation of a seal. The pre-laminate stack assembly is laminated in an operation 654. The laminate stack is cut in an operation 656 to form module-sized laminate stacks. In certain embodiments, the resulting module-sized stack includes a moisture barrier material extending to the cut edges. This is depicted in
In a process 850, rather than positioning discrete stacks of insulation sheet and moisture barrier material on the back layer, the flexible back sheets may be assembled using a roll-to-roll process. The process begins in an operation 852 in which the polymer insulation sheet, adhesives (is used), backing layer and moisture barrier are provided on webs to form a pre-laminate stack assembly, e.g., insulation sheet/adhesive/moisture barrier/adhesive/back layer. In certain embodiments, the width of the back layer web is greater than the insulation sheet and moisture barrier webs to allow the perimeter of the hack layer to cover the edges of those layers. The pre-laminate stack assembly is laminated in an operation 854. The laminate stack is cut in an operation 856 to form module-sized laminate stacks. In this case, the laminate stacks may look like the laminate stack shown at view 702 in
As indicated above, the flexible back sheets and modules described herein include electrically isolated moisture barriers. In certain embodiments, the photovoltaic cells are electrically connected to the exterior of the module only by one or more connectors that safely connect to the exterior. An example is shown in
According to various embodiment, the flexible back sheet may include one or more additional layers. For example, in certain embodiments, additional layers may be between the moisture barrier layer and a weatherable material and/or between the moisture barrier layer and an insulation layer. The seal may include a bond between any of the layers, so long as a layer overlying the moisture barrier is bonded to an underlying barrier such to prevent any electrical connection to the edge of the moisture barrier.
While the description above refers chiefly to metallic moisture barriers, other types of flexible moisture barriers are within the scope of the invention, including moisture barriers made of non-metallic conductive materials, semiconductor materials, etc. As described above, in certain embodiments, the back sheets and methods described herein find particular application with conductive moisture barriers.
In addition to the specific examples of polymeric materials that may be used for the insulation sheet, back layer, adhesives, etc., examples of materials that may be used as appropriate for one of these layers or for other layers in the module include, silicone, silicone gel, epoxy, RTV silicone rubber, polydimethyl siloxane (PDMS), polyvinyl butyral (PVB), polycarbonates, acrylics, urethanes including thermoplastic polyurethanes (TPU), poly(vinyl acetal), polyolefin block elastomers, ethylene acrylate ester copolymers, acid copolymers, silicone elastomers, epoxy resins, polyolefin block elastomers, ethylene acrylate ester copolymers, rubber, thermoplastic elastomers, other materials with similar material properties, and mixtures thereof.
Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the invention. It should be noted that there are many alternative ways of implementing both the processes and apparatuses of the present invention. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein.
This application is a continuation of PCT Application No. PCT/US2010/034386, entitled “ISOLATED METALLIC FLEXIBLE BACK SHEET FOR SOLAR MODULE ENCAPSULATION,” filed 11 May 2010, which claims priority to U.S. patent application Ser. No. 12/464,721, entitled: “ISOLATED METALLIC FLEXIBLE BACK SHEET FOR SOLAR MODULE ENCAPSULATION” filed on 12 May 2009 (now issued as U.S. Pat. No. 7,829,783) and U.S. patent application Ser. No. 12/556,460, also entitled “ISOLATED METALLIC FLEXIBLE BACK SHEET FOR SOLAR MODULE ENCAPSULATION,” filed on 9 Sep. 2009, which are hereby incorporated by reference in their entireties and for all purposes.
Number | Date | Country | |
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Parent | PCT/US2010/034386 | May 2010 | US |
Child | 13107574 | US |
Number | Date | Country | |
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Parent | 12464721 | May 2009 | US |
Child | PCT/US2010/034386 | US | |
Parent | 12556460 | Sep 2009 | US |
Child | 12464721 | US |