Patent Application
20130000689
This application relates generally to photovoltaic module installations and specifically to module mounting mechanisms for photovoltaic installations.
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. Arrays of modules are typically mounted on racking systems on the roof of buildings or on ground-based structures. The modules are required to pass load testing to ensure that they can safely withstand snow loading and other environmental conditions. This can be challenging for frameless photovoltaic modules.
SUMMARY OF SPECIFIC EMBODIMENTS
The invention relates generally to apparatus and techniques for mounting frameless photovoltaic modules to eliminate obstruction of corner and edge-mounted module components with longitudinally-oriented mounted modules. The invention further involves mounting clamps and rail/clamp spacing configured to relieve module stress by reducing or eliminating module sag.
In one aspect, the invention relates to a photovoltaic assembly. The photovoltaic assembly includes a frameless photovoltaic module comprising a frontside sheet and a backside sheet, a mounting structure comprising module mounting rails, and a plurality of standoff clamps mounted to at least two rails of the mounting structure and engaging the frontside sheet and the backside sheet of the frameless photovoltaic module at edge regions of the module, thereby securing the frameless photovoltaic module on the mounting structure, wherein the standoff clamps comprise a standoff portion.
Another aspect of the invention relates to a method of installing a frameless photovoltaic module comprising a frontside sheet and a backside sheet onto a mounting structure, the method comprising providing the mounting structure comprising module mounting rails, providing the frameless PV module, and securing the frameless photovoltaic module onto the mounting structure with a plurality of standoff clamps attached to at least two rails of the mounting structure and engaging the frontside of the frameless photovoltaic module at edge regions of the module overlying at least two rails, wherein the standoff clamps comprise a standoff portion.
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 order not to unnecessarily obscure the present invention.
Photovoltaic modules often comprise corner or edge-mounted components that can present mounting challenges when implemented with certain mounting systems and components. Furthermore, photovoltaic modules are required to meet load ratings specified by IEC 61646 and UL 1703, incorporated herein by reference for this purpose. In this regard, a module must be able to pass a 2400 MPa static load test for wind and 5400 MPa static loading test for snow/ice. This load testing requirement can be particularly challenging for a frameless photovoltaic module (a module without a metallic frame around its perimeter) to meet. Further, the structural stability and module integrity can be difficult to preserve in a racking system for frameless photovoltaic modules.
Embodiments of the present invention relate to mounting of frameless photovoltaic modules (also referred to as solar modules or solar panels or, in this application, simply as modules), and associated racking systems and methods.
The front and back layers may be any suitable material that provides the environmental protection and mechanical support required for reliable module operation. In some typical embodiments, the front and back layers are rigid plates, light transmitting in the case of the front layer, such as glass, although other materials, such as polymers, multi-layer laminates and metals that meet the functional requirements may also be used. In other embodiments the typical rigid back layer (e.g., back glass plate) can be replaced with a much lighter weight flexible material, thereby reducing handling costs associated with the module.
The front, light-incident layer 104 should transmit visible and near visible wavelengths of the solar spectrum 113 and be chemically and physically stable to anticipated environmental conditions, including solar radiation, temperature extremes, rain, snow, hail, dust, dirt and wind to provide protection for the module contents below. A glass plate comprising any suitable glass, including conventional and float glass, tempered or annealed glass, combinations thereof, or other glasses, is preferred in many embodiments. The total thickness of a suitable glass or multi-layer glass layer 104 may be in the range of about 2 mm to about 15 mm, optionally from about 2.5 mm to about 10 mm, for example about 3 mm or 4 mm. As noted above, it should be understood that in some embodiments, the front layer 104 may be made of a non-glass material that has the appropriate light transmission, stability and protective functional requirements. The front layer 104, whether glass or non-glass, transmits light in a spectral range from about 400 nm to about 1100 nm. The front layer 104 may not necessarily, and very often will not, transmit all incident light or all incident wavelengths in that spectral range equally. For example, a suitable front layer is a glass plate having greater than 50% transmission, or even greater than 80% or 90% transmission from about 400-1100 nm. In some embodiments, the front layer 104 may have surface treatments such as but not limited to filters, anti-reflective layers, surface roughness, protective layers, moisture barriers, or the like. Although not so limited, in particular embodiments the front layer 104 is a tempered glass plate about 3 mm thick.
The back layer 106 may be the same as or different than the front layer 104 and is also typically a glass plate as described above. However, since the back layer 106 does not have the same optical constraints as the front layer 104, it may also be composed of materials that are not optimized for light transmission, for example metals and/or polymers. And, while the present invention is applicable in more typical module configurations having both front and back glass plate layers, the invention finds particularly advantageous application in embodiments in which the back layer 104 is a lighter weight flexible material. Such lighter weight modules have manufacturing and transportation benefits, but can present additional challenges for module stability, including compliance with load testing requirements stresses induced by module mounting configurations. In such embodiments, the back layer 106 may be a flexible yet weatherable laminate that protects the photovoltaic cells and other module components from moisture, UV exposure, extreme temperatures, etc. The back layer laminate may include a weatherable back sheet exposed to the exterior of the module. The back sheet should be resistant to environmental conditions expected to be experienced by the module (e.g., temperatures of about −40 to 90° C.), so that it is stable throughout the range of temperate climate temperatures and conditions so as to retain its properties to perform its protective function.
The back sheet may be composed of a fluoropolymer, including but not limited to polyvinyl fluoride (PVF) (e.g., Tedlar® film available from DuPont), polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene (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, polyethylene terephthalate (PET), polypropylene, polybutylene, polybutylene terephthalate, and acrylics or combinations (laminated stacks) of the above. In certain embodiments, any material that meets UL 1703 requirements (incorporated by reference herein) can be used. In one example, the back layer includes PVF (e.g., Tedlar®). In certain examples, the thickness may range from about 2 to about 12 mils, although other thicknesses may be used as appropriate. A suitable flexible back layer laminate may also include a flexible moisture barrier sandwiched between an insulation sheet, for example a sheet of PET, and the weatherable back sheet. A suitable moisture barrier may be a metallic sheet, such as an aluminum foil. A suitable laminate back sheet in accordance with some embodiments of the invention is composed of a polyvinyl fluoride/Al foil/polyethylene terephthalate laminate (e.g., Tedlar®/Al foil/PET). Further description of suitable flexible back layers for photovoltaic cells that may be used in modules in accordance with the present invention is provided in U.S. Published Patent Application No. 2008/0289682 and U.S. Published Patent Application No. 2010-0071756, each of which is incorporated by reference herein for this purpose.
The edge material 108 may be an organic or inorganic material that has a low inherent water vapor transmission rate (WVTR) (typically less than 1-2 g/m2/day) and, in certain embodiments may absorb moisture and/or prevent its incursion. In one example, a butyl-rubber containing a moisture getter or desiccant is used.
The solar cells 102 may be any type of photovoltaic cell including crystalline and thin film cells such as, but not limited to, semiconductor-based solar cells including microcrystalline or amorphous silicon, cadmium telluride, copper indium gallium selenide or copper indium selenide, dye-sensitized solar cells, and organic polymer solar cells. In particular embodiments, the cells are copper indium gallium selenide (CIGS) cells. In other aspects of the invention, the cells can be deposited as thin films on the front, light-incident (e.g., glass) layer 104. Direct deposition of a solar cell on glass is described, for example, in U.S. Published Patent Application No. 2009/0272437, incorporated by reference herein for this purpose. In such an embodiment, element 110 of
Frameless photovoltaic modules are often rectangular in overall shape, as shown in
Reference is also made in this application to sagging of a frameless photovoltaic module. In some cases, a module will be described as experiencing sagging along a transverse or longitudinal direction. Sag along a transverse direction refers to sagging behavior which manifests as a non-linear displacement of the module from a line running in a transverse direction, as depicted in
Frameless photovoltaic modules are often mounted onto racking or mounting rail systems when installed at their installation locations. A plan view of an example mounting rail system is shown in
In one embodiment, the mounting rail system includes two or more rails 204 which support one or more frameless photovoltaic modules 208. The mounting rails 204 may be substantially longer than the mounting rails 204 are wide or deep. For example, a mounting rail 204 may have overall dimensions of 1″ wide by 3″ deep, but be 144″ long. Several sections of mounting rail 204 may also be connected end-to-end or be butted up to one another to form a much longer mounting rail. The mounting rails 204 may be mounted to a structure, such as roof 202, either directly or using standoffs 206. The mounting rails 204 may also be attached to a supplemental support structure; the supplemental support structure may elevate the rails or position the mounting rails 204 in a more optimum manner (e.g., position the mounting rails 204 such that attached frameless photovoltaic modules 208 will be oriented towards the sun to a greater extent).
The mounting rails 204 may be manufactured from extruded or rolled materials, such as aluminum or steel, or from other materials or using other manufacturing techniques. The mounting rails 204 may be hollow, solid, or filled with material, such as foam or honeycombs. The mounting rails 204 may include grooves, holes, t-slots, or other features which allow for hardware to be attached to the mounting rails 204; these features may provide pre-set hardware position points (e.g., pre-drilled holes) or allow for infinite positioning of hardware locations (e.g., grooves or t-slots).
For purposes of discussion, reference to the longitudinal direction or axis of a mounting rail refers to the direction or axis aligned with the substantially longer dimension of the mounting rail. As illustrated in
Frameless photovoltaic modules may be mounted to mounting rails 204 using one or more standoff clamps 210. Representative standoff clamps are discussed in greater detail below with reference to
Frameless photovoltaic modules mounted to rail mounting systems may experience sagging in areas not directly supported by a standoff clamp due to the modules' weight and geometry. In a two-rail mounting system, a frameless photovoltaic module will typically only be externally supported at the standoff clamp locations. In areas where the frameless photovoltaic module does not receive external support, the module must be self-supporting, i.e., the module must rely on the material properties and geometry of the module for support.
The standoff clamps may be spaced according to the L/4 rule, in which the midpoints standoff clamps are typically positioned at a distance of L/4 from the transverse edges of a module, where L refers to the length of the module. For example, for a 1611 mm×665 mm module, the L/4 distance would be 402.75 mm.
In one embodiment, the transverse midpoint of each standoff clamp in a two-row standoff clamp configuration is instead positioned approximately 22% of the length of the module from the transverse edges of the module. Thus, for a 1611 mm×665 mm module, the midpoints of the standoff clamps would be positioned about 354.4 mm from either transverse edge along the longitudinal axis.
More particularly, the midpoint of each standoff clamp in a two-row standoff clamp configuration may be positioned approximately 22.3% of the length of the module from a transverse edge of the module. 55.4% of the module would thus be located between the midpoints of the two rows of standoff clamps.
The orientation of the mounting rail system shown in
Many frameless photovoltaic modules comprise externally mounted components such as junction boxes, electronic equipment or other components mounted on corner or longitudinal edge regions of the modules. Such components may make it difficult to install the modules on longitudinally-eave-parallel mounting rail systems or ground-mounted mounting rails where the mounting rail runs directly under a module edge comprising an externally-mounted component, due to interference of the components with the mounting rails.
In order to clamp the frameless modules to the rail mounting system, a standoff clamp may be used to create a gap between the frameless module 408 and the mounting rail 404 wherein the gap provides sufficient space so that the components 402 on the corners or the longitudinal edges of the modules do not interfere with the mounting rails. After installation using standoff clamps, the gap between the frameless module and the mounting rail may be 0.5 to 5.0 inches, such as 1.0 to 3.0 inches.
Examples of certain embodiments of standoff clamps are shown in
Modeling was conducted in order to demonstrate the advantages provided by various aspects of this invention with regard to the positioning of the standoff clamps along the longitudinal edge of the module. The data presented here are intended to better illustrate the invention as described herein and are non-limiting.
An example installation process utilizing mounting rail systems in conjunction with standoff clamps is diagrammed in
Installation process 700 begins with the installation of mounting rails onto a support structure. This may include attaching one or more mounting rails to a roof, carport, or other support structure. Standoffs and mounting hardware may be used to implement the attachment. In the case of a pre-existing mounting rail installation, such as in a retrofit, reinstallation of the mounting rails may not be necessary.
In step 710, the mounting rails may be trued to remove any gross variation in mounting rail parallelity and levelness.
In step 715, module clamping hardware is mounted to the installed mounting rails. Of course, the clamping hardware may also be installed prior to truing 710 or prior to rail installation 705. In some cases, only the clamps which will engage one longitudinal side of a module will initially be installed. In other cases, all clamps for a module will be installed. The clamps may be securely attached to the mounting rails.
In step 725, a module is installed into the mounted clamps. Installing a module may involve sliding the module in a transverse direction into the gap between the clamp finger and the mounting rail. Alternatively, the module may be installed onto the mounting rails and any mounted clamps may then be slid into position to engage the frontside of the module.
In step 730, any remaining clamps, or clamp components, required to secure the module are installed.
In step 735, the clamps are adjusted to ensure uniformity in clamping force and position.
In step 540, the installation process returns to step 715 if any modules remain which will be installed on the installed mounting rails.
In step 545, the installation process returns to step 705 if there are any mounting rails remaining to be installed.
In step 550, electrical and control connections are made to the mounted modules, and any support electronics are installed and configured. In step 755, the mechanical installation is complete.
Of course, the above steps are merely examples of an installation process using the described technology. The ordering of the steps may be changed significantly—for example, it is not necessary to install the modules for one set of rails before installing a second set of rails. The order set forth in
Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modification 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.
