Patent Application
20130180575
This invention relates generally to photovoltaic devices, and more specifically, to improved building-integrated photovoltaic devices.
Building-integrated photovoltaic (BIPV) roof tiles currently represent a small portion of the overall photovoltaic market, in spite of the seemingly compelling proposition of integrating an energy source into a roofing component. Market adoption has been slow due in part to the relatively high cost of roofing tiles integrated with PV modules. High cost is currently incurred since solar modules are not designed to serve as a bulk construction material, but rather integrated into a home as a custom electrical installation. There are several barriers within the current residential rooftop BIPV market that have kept the overall market small and limited product adoption.
One of these barriers comprises costly manufacturing processes whereby relatively expensive silicon wafers are interconnected with the often mismatched framework of a roofing tile. The solar cells are inherently costly, and their interconnection process takes time and incurs additional cost, increasing the total system cost.
Conventional BIPV roofing tile product has substantial dead space where the wafers do not fully occupy the area within the tile frame (the “open area”). This spatial inefficiency reduces the power density of the roofing tile, and requires additional tiles to be installed to achieve a particular power output for a given solar system.
Additionally, time-consuming installation processes for BIPV products such as roofing tiles, including extensive electrical wiring and mechanical interconnection between tiles, results in high system installation costs and makes operation and maintenance of installed systems cost-prohibitive.
Drawbacks associated with traditional photovoltaic solar tiles have limited the ability and financial rationale to install large numbers of BIPV roofing in a cost-effective manner. These traditional solar tile configurations are also constrained by conventional design methodology that limits the modules to certain materials and inherits a large number of legacy parts.
A roofing element includes a solar cell array positioned in an opening in a top surface of a roofing material. The solar cell array has a plurality of low series resistance solar cells, where the low series resistance is based on a metallization-wrap-through (MWT) solar cell architecture. Each solar cell has a cell aspect ratio, and the solar cells are electrically connected in an electrical string configuration by a low resistance cell-to-cell bonding method.
The opening of the roofing material has an aperture area, and the amount of aperture area covered by the solar cell array defines an aperture fill. The cell aspect ratio and the electrical string configuration are tailored to achieve a specified total current and total voltage for the solar cell array while optimizing the aperture fill.
A further understanding of the nature and advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. It may be noted that, as used in the specification and the appended claims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a material” may include mixtures of materials, reference to “a compound” may include multiple compounds, and the like. References cited herein are hereby incorporated by reference in their entirety, except to the extent that they conflict with teachings explicitly set forth in this specification.
In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings:
“Optional” or “optionally” means that the subsequently described circumstance may or may not occur, so that the description includes instances where the circumstance occurs and instances where it does not. For example, if a device optionally contains a feature for an anti-reflective film, this means that the anti-reflective film feature may or may not be present, and, thus, the description includes both structures wherein a device possesses the anti-reflective film feature and structures wherein the anti-reflective film feature is not present.
The present invention provides for low series resistance solar cells which are integrated into roofing materials. The solar cells are flexible in size and aspect ratio, and thus the surface area of the inlays can be almost completely be covered by active cells for all existing conventional tile geometries. In comparison with silicon wafer cells that in most roof tile sized modules might only fill part of the available area, similar overall efficiency can therefore be achieved with the customizable solar cells of the present disclosure, at substantially lower per watt cost. The output current of the tile can be tuned for optimal system efficiency by varying cell size, with the system voltage being decided by the amount of tiles in series. Overall, this results in lower material cost and a flexible design allowing installers to rapidly and cost-efficiently deploy solar roofing at a large scale.
In one embodiment of the present invention, a photovoltaic roofing structure is provided comprising a roofing tile having a top surface, and an opening—such as a recessed portion—in the top surface. A photovoltaic module made of an array low resistance series solar cells may be tailored in size to fit within the recessed portion of the tile. Optionally, instead of a tile, other roofing material may be used. Optionally, in other embodiments, instead of a roof, the module is integrated with other non-roof building material.
The present invention also provides for an improved BIPV roofing tile design that simplifies the configuration and reduces the materials costs associated with such photovoltaic roofing elements. Although not limited to the following, these improved roofing element designs are well suited for installation at dedicated sites where redundant elements can be eliminated and where some common elements or features may be shared by many modules. Embodiments of the present invention may be adaptable for roll-to-roll and/or batch manufacturing processes. At least some of these and other objectives described herein will be met by various embodiments of the present invention.
Large scale solar panels distribute the cost of one set of electrical connectors and mounting over a larger quantity of cells. This has led to solar module sizes that, optimized for commercial rooftops and green field installations, are significantly larger than a standard roof tile format, which over decades has been fine-tuned for optimum balance between installation effort and flexibility. As multi-faceted residential roofs have gables, chimneys and partial shading, which all restrict the area where solar modules can be mounted, a smaller form factor is desirable to maximize the flexibility of installation. The present design is a foil substrate which can be cut into a wide range of cell formats, increasing the format options to fit into a single tile.
As the solar tiles replace the existing conventional roof tiles and mount onto the existing roof battens, no additional on-roof mounting infrastructure is required. Given the ease of use, the same roofers that install regular tiles can install the solar roof tiles, as the installation follows the same rules, on the same level of care. Additional installation cost is limited to an electrician connecting the start and end tiles of a row to the inverter or to each other. Sales and distribution channels are equivalent to existing roofing product channels.
Traditional solar cell manufacturing typically creates a solar cell of a specific current and voltage. Tailoring of these parameters is usually done at the device level. Solar modules, if they are created from cells rather than monolithically integrated, have specific size and connectivity and inherently do not lend themselves to variations in size and architecture. An example of this is the silicon solar cell that is formed from a specific size silicon ingot. In theory the size can be varied, but the cost associated with the wafer makes variations away from the maximum optimal configuration uneconomic. Silicon solar found in consumable electronics devices (watches, calculators, etc.) are typically formed from wafers of high defects or broken wafers. Another example is a thin film solar cell on a stainless steel substrate. This type of product is able to be formed into varying dimensions but the range of dimensions that is electrically relevant is severely limited by the lower conductivity of stainless steel compared to aluminum.
Referring now to
As seen in
As seen in
Advantageously in one embodiment of the present invention, the ratio of the weight of the module 20 to the weight of the tile 30 may be equal to, less than, or more than that of the tile. The overall weight of the combination is less than that of a roofing tile of the same size but providing coverage without the photovoltaic module. Optionally, the overall weight is less than that of a roofing tile of the same size made of a Class A fire rated material but providing roofing coverage without the photovoltaic module. In one embodiment, the ratio of the weight of the tile to the weight of the photovoltaic module is in the range of about 3:1 to 1:1. In one embodiment, the ratio of the weight of the tile to the module is in the range of about 5:1 to 1:1. In another embodiment, the range is about 10:1 to 1:1. These ratios allow for the photovoltaic module to contribute relatively less to the overall weight of the combined BIPV tile. The tile remains first and foremost a Class A fire-rated material. Even if the inlaid solar module is itself damaged in some way, the present embodiment of tile 30 will continue to retain is inherent weatherproofing and fireproofing capability. In this manner, the bulk of the weight still comes from the tile material itself and not from the module.
Referring now to
It should be understood that after the module is inserted into the tile 44, the slot 46 may be filled or sealed with material to close the slot 46. In some embodiments, only enough sealing material is provided to prevent the module from sliding out of the tile 44, without actually completely sealing the slot 46. In alternative embodiments, a mechanical stopper, mechanical attachment, or other device such as a set screw may be used to secure the tile in position.
Optionally, in some embodiments, there is no slot 46. In such embodiments, the module 42 is integrally molded with the tile during tile fabrication and there is no need for a slot to insert the module 42 at a later time. Although not limited to the following, the module may be loosely held therein to allow for coefficient of thermal expansion (CTE) differences between the module 42 and the tile 44.
In other embodiments, a shingle or other modular roofing construct may be used instead of a tile as a roofing material. The roofing material may be rigid or flexible as needed to meet the requirements of the roof on which the material is to be installed.
While the appearance of most solar roof modules stands in stark contrast with the surrounding roof surface, the solar tiles may use frames of the material, color and texture identical to that of the surrounding tiles. The solar inlays have no frame, visible electrical contacts or mounting hardware. Shape and style match the conventional tile, and given the flexible cell substrate, an arced glass top on the solar insert is possible to harmonically ‘weave’ solar inlays into S-shaped tiles. A uniform layout of grids and rows of solar tiles becomes feasible on a roof by offering matching dummy cells that look like solar tiles for shaded areas. The juxtaposition of the traditional material and solar glass inserts creates an aesthetic tension that does not try to hide the solar panels, but frames them into a bold statement.
Referring now to
This thermal issue may be of particular concern for BIPV devices. Most conventional solar modules are ground mounted or roof mounted in a manner sufficiently spaced above the ground or roof surface such that the underside of the module is not in such close proximity to a thermal mass. This distance allows for decreased operating temperature as various factors such as wind and distance from radiant heat sources allow the modules to be at a lower temperature. With a building integrated photovoltaic material, the design constraints are such that the module is necessarily in relatively close proximity to a radiant heat source or thermal mass such as the tile itself
Also shown in
The metal-wrap-through architecture described in
The metallization-wrap-through type solar cells described herein facilitate relatively low cost manufacture of large-scale arrays of series-connected optoelectronic devices. Larger devices may be connected in series due to the reduced sheet resistance as a result of the connection between back planes and the transparent conducting layers through the contacts that penetrate the layers of the device modules. The conductive traces can further reduce sheet resistance. Larger devices can be arrayed with fewer connections.
It should also be understood that some embodiments may include diodes in the cells or optionally, only diodes are used to protect strings not cells. Diodes may include those described in PCT patent application No. PCT/US10/46877, which is fully incorporated herein by reference for all purposes.
Although glass is the layer most often described as the top layer for the module in the present disclosure, it should be understood that other material may be used and some multi-laminate materials may be used in place of or in combination with the glass. Some embodiments may use flexible top layers or coversheets. There may be anti-reflective or other surface treatments of the top layer. By way of nonlimiting example, the backsheet is not limited to rigid modules and may be adapted for use with flexible solar modules and flexible photovoltaic building materials. Embodiments of the present invention may be adapted for use with superstrate or substrate designs.
Details of modules with thermally conductive backplanes and heat sinks can be found in commonly assigned U.S. Pat. No. 7,985,919 entitled “Thermal Management for Photovoltaic Devices,” which is fully incorporated herein by reference for all purposes. Pottant materials which are used may be made more thermally conductive based on techniques shown in U.S. Pat. No. 7,985,919. The use of a conductive foil also provides a module back layer with sufficiently high thermally conductivity to improve heat transfer out of the module. Other backsheet materials may also be used and is not limited to glass only embodiments.
Furthermore, those of skill in the art will recognize that variations to the type of solar cell material and/or architecture are possible. For example, an absorber layer in the solar cell may be an absorber layer comprised of silicon, amorphous silicon, organic oligomers or polymers (for organic solar cells), bi-layers or interpenetrating layers or inorganic and organic materials (for hybrid organic/inorganic solar cells), dye-sensitized titania nanoparticles in a liquid or gel-based electrolyte (for Graetzel cells in which an optically transparent film comprised of titanium dioxide particles a few nanometers in size is coated with a monolayer of charge transfer dye to sensitize the film for light harvesting), copper-indium-gallium-selenium (for CIGS solar cells), CdSe, CdTe, Cu(In,Ga)(S,Se)2, Cu(In,Ga,Al)(S,Se,Te)2, and/or combinations of the above, where the active materials are present in any of several forms including but not limited to bulk materials, micro-particles, nano-particles, or quantum dots. The CIGS cells may be formed by vacuum or non-vacuum processes. The processes may be one stage, two stage, or multi-stage CIGS processing techniques. Additionally, other possible absorber layers may be based on amorphous silicon (doped or undoped), a nanostructured layer having an inorganic porous semiconductor template with pores filled by an organic semiconductor material (see e.g., U.S. Pat. No. 6,946,597 entitled “Photovoltaic Devices Fabricated By Growth from Porous Template” which is incorporated herein by reference), a polymer/blend cell architecture, organic dyes, and/or C60 molecules, and/or other small molecules, micro-crystalline silicon cell architecture, randomly placed nanorods and/or tetrapods of inorganic materials dispersed in an organic matrix, quantum dot-based cells, or combinations of the above. Many of these types of cells can be fabricated on flexible substrates, including other non-CIGS thin-film solar cells.
Although the cells as shown as being planar in shape, those of round, tubular, rod or other shapes are not excluded. Some embodiments may also use internal reflectors positioned between cells to improve light collection. Some embodiments may have the cells formed directly on a glass surface of the module without an encapsulant layer between one layer of the glass and the cell.
The sizes of cell 900 and aperture 910 in
Thus, the various arrangements of
Variations of the connectors described herein are possible. For example, the housing of a connector could be made of any material by any method. The connector could be designed for hand assembly or automated assembly, with or without locating features. The connector could be designed without the channel and holes to allow potting. The connector could be designed to allow two or more connectors to exit the solar module, and could include a diode linked between the exiting conductors. In one embodiment, both electrical leads or edge connectors are on the same side of module. In another embodiment, they are on different sides. In a still further embodiment, they are diagonal from each other. In yet another embodiment, they are on opposing sides. Optionally, in such a configuration, the top sheet may be a flexible top sheet such as that set forth in U.S. patent application Ser. No. 60/806,096 (Attorney Docket No. NSL-085P) entitled “Improved Encapsulant Layer for Photovoltaic Devices,” filed Jun. 28, 2006 and fully incorporated herein by reference for all purposes. It should also be understood that embodiments of the present invention may also be used with a central junction box and are not limited to only edge exiting electrical connectors. The modules may be mounted in either landscape or portrait orientation, with edge connectors located as appropriate to minimize distance to the closes adjacent module. It should also be understood that some embodiments of the module may have no pottant layers.
While the invention has been described and illustrated with reference to certain particular embodiments thereof, those skilled in the art will appreciate that various adaptations, changes, modifications, substitutions, deletions, or additions of procedures and protocols may be made without departing from the spirit and scope of the invention.
Additionally, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a thickness range of about 1 nm to about 200 nm should be interpreted to include not only the explicitly recited limits of about 1 nm and about 200 nm, but also to include individual sizes such as but not limited to 2 nm, 3 nm, 4 nm, and sub-ranges such as 10 nm to 50 nm, 20 nm to 100 nm, etc.
The publications discussed or cited herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed. All publications mentioned herein are incorporated herein by reference to disclose and describe the structures and/or methods in connection with which the publications are cited.
While the above is a complete description of the preferred embodiment of the present invention, it is possible to use various alternatives, modifications and equivalents. Therefore, the scope of the present invention should be determined not with reference to the above description but should, instead, be determined with reference to the appended claims, along with their full scope of equivalents. Any feature, whether preferred or not, may be combined with any other feature, whether preferred or not. In the claims that follow, the indefinite article “A”, or “An” refers to a quantity of one or more of the item following the article, except where expressly stated otherwise. The appended claims are not to be interpreted as including means-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase “means for.”
This application: 1) claims priority to U.S. Provisional Patent Application No. 61/509,785 filed Jul. 20, 2011, entitled “Structures For Low Cost, Reliable Solar Roofing”; and 2) is a continuation-in-part of U.S. patent application Ser. No. 12/116,932 filed May 7, 2008, entitled “Structures For Low Cost, Reliable Solar Roofing,” which claims priority to U.S. Provisional Patent Application No. 60/916,551 filed May 7, 2007, entitled “Structures For Low Cost, Reliable Solar Roofing”; all of which are hereby incorporated by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 61509785 | Jul 2011 | US | |
| 60916551 | May 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12116932 | May 2008 | US |
| Child | 13555033 | US |
