Patent Application
20130081673
1. Technical Field
Embodiments of the subject matter described herein relate generally to solar collectors. More particularly, embodiments of the subject matter relate to photovoltaic panels designed to reduce soiling and methods for manufacturing the same.
2. Description of the Related Art
Solar power has long been viewed as an important alternative energy source. To this end, substantial efforts and investments have been made to develop and improve upon solar energy collection technology. Of particular interest are industrial- or commercial-type applications in which relatively significant amounts of solar energy can be collected and utilized in supplementing or satisfying power needs.
Solar photovoltaic systems (or simply “photovoltaic systems”) employ solar panels made of silicon or other materials (e.g., III-V cells such as GaAs) to convert sunlight into electricity. Photovoltaic systems typically include a plurality of photovoltaic (PV) modules (or “solar tiles”) interconnected with wiring to one or more appropriate electrical components (e.g., switches, inverters, junction boxes, etc.). The PV module conventionally consists of a PV laminate or panel generally forming an assembly of crystalline or amorphous semiconductor devices (“PV cells”) electrically interconnected and encapsulated within a weather-proof barrier. One or more electrical conductors are housed inside the PV laminate through which the solar-generated current is conducted.
Regardless of an exact construction of the PV laminate, most PV applications entail placing an array of PV modules at the installation site in a location where sunlight is readily present. This is especially true for commercial or industrial applications in which a relatively large number of PV modules are desirable for generating substantial amounts of energy, with the rooftop of the commercial building providing a convenient surface at which the PV modules can be placed.
As a point of reference, many commercial buildings have large, flat roofs that are inherently conducive to placement of a PV module array, and are the most efficient use of existing space. While rooftop installation is thus highly viable, certain environment constraints must be addressed.
For example, PV laminates are generally flat or planar. Thus, at some latitudes, it can be sufficiently efficient to install PV laminates in a precisely horizontal orientation. At other latitudes, it is more efficient to install PV laminates at a tilted angle, relative to a flat rooftop (i.e., toward the southern sky for northern hemisphere installation, or toward the northern sky for southern hemisphere installations). Additionally, PV laminates should be installed with frames that are sufficiently strong to withstand any environmental forces, such as wind or snow.
In light of the above, PV modules for commercial installations include robust frames for maintaining the PV laminate relative to the installation surface (e.g., penetrating-type mounting in which bolts are driven through the rooftop to attach the framework and/or auxiliary connectors to the rooftop; non-penetrating mounting in which auxiliary components interconnect PV modules to one another; etc.). Thus, some traditional PV modules employ an extruded aluminum frame that supports the entire perimeter of the corresponding PV laminate. A lip of the aluminum frame extends over and captures an upper surface of the PV laminate.
Airborne dust, dirt, and other debris are constantly being deposited onto the PV laminate, which reduces the output from the PV module. Rain and other moisture captures dust and debris, thereby leaving concentrated areas of dust and debris as the water evaporates, forming localized areas of “soiling” on the PV module. The frame lip impedes, to some extent, drainage of moisture from the PV laminate surface. As such, moisture will collect along the PV laminate, especially at the lowest point of the PV laminate. For example, where a flat PV panel is installed in a horizontal orientation, for example on a roof, the weight of the panel itself and/or additional water can cause the panel to bend into a concave shape, thereby causing water to accumulate in and around the center of the panel. Such accumulated water, as noted above, causes debris and dust to accumulate within the wetted area and thus cause a localized area of soiling, for example, after the water evaporates.
Similarly, with a tilted PV module, moisture (and entrained debris) will travel (via gravity) toward the lowermost edge of the PV laminate, effectively pooling against the frame lip. As the moisture subsequently evaporates, it leaves behind dirt and debris. This soiling has the effect of shading nearby PV cells, and can thus significantly decrease performance of the PV module. More specifically, localized areas of soiling on a PV panel can cause the photovoltaic cell shaded by such soiling to become an electrical load in the circuit connecting the various cells of the PV laminate together. Thus, while the unshaded cells in the PV panel are producing electricity, the shaded cells can dissipate some of that generated energy in the form of waste heat, thus reducing PV panel efficiency. Additionally, such shading can cause current mismatches damage the cells and possibly lead to premature failures.
To perhaps address the above concerns, it has been suggested to machine cut several channels into the aluminum frame at one or more corners thereof, with the channels providing a region for liquid to drain off of the PV module. Once such device is believed to be available from Kyocera Corp., Solar Energy Division, of Kyoto, Japan.
An aspect of at least one of the embodiments disclosed herein includes the realization that the upper surface of a PV module, such as the uppermost weather proof barrier, can be configured into a convex, upwardly bulging shape, without substantially affecting the overall solar collecting efficiency of a PV panel. As such, an upwardly bulged, convex shape of the outermost barrier of a PV panel can cause water droplets to flow away from the center of such a panel toward the edges thereby reducing localized areas of soiling which can negatively impact the electrical output of a PV panel.
Another aspect of at least one of the embodiments disclosed herein includes the realization that photovoltaic cells can be bent with a curvature sufficient to provide the above noted water flow effects without affecting the integrity of the photovoltaic cells. Thus, for example, where the photovoltaic cells are bent to match the curvature of a convex uppermost layer of the PV laminate, the cells and the uppermost layer can be bonded together, using the same techniques normally used for flat PV laminates, thereby eliminating optical aberrations that may result from using an upwardly convex outer layer over a flat layer of photovoltaic cells.
Thus, in accordance with at least one embodiment, a photovoltaic solar collector can comprise a photo electronic device configured to convert solar radiation into electrical power, the photo electronic device having a photo-sensitive surface arranged to be exposable to sunlight. An outer barrier member can be mounted relative to the photosensitive surface such that sunlight must pass through the outer barrier member to reach the photosensitive surface. The outer barrier member can comprise an outer surface arranged to be exposed to the environment and facing away from the photosensitive surface. The outer surface of the outer barrier member is convex.
In accordance with another embodiment, a method of making a photovoltaic solar collector can comprise bending an a photo electronic device configured to convert solar radiation into electrical power such that a photo sensitive surface of the photo electronic device is convex. The method can also comprise attaching a first member to the photo electronic device so as to hold the photo sensitive surface in the convex shape.
In accordance with yet another embodiment, a method of making a photovoltaic solar assembly can comprise mounting a photovoltaic solar collector such that a convex outer surface of the photovoltaic solar collector faces upwardly.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
A more complete understanding of the subject matter may be derived by referring to the detailed description and claims when considered in conjunction with the following figures, wherein like reference numbers refer to similar elements throughout the figures.
The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Any implementation described herein as exemplary is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.
“Coupled”—The following description refers to elements or nodes or features being “coupled” together. As used herein, unless expressly stated otherwise, “coupled” means that one element/node/feature is directly or indirectly joined to (or directly or indirectly communicates with) another element/node/feature.
“Locating connector”—The following description refers to devices or features being connected with a “locating connector”. As used herein, unless expressly stated otherwise, “locating connector” means that one element/node/feature is directly or indirectly joined to (or directly or indirectly communicates with) another element/node/feature with a mechanism that connects and also provides a locating function, such as for example but without limitation, alignment of elements/nodes/features or enhancing contact between two elements/nodes/features.
“Adjust”—Some elements, components, and/or features are described as being adjustable or adjusted. As used herein, unless expressly stated otherwise, “adjust” means to position, modify, alter, or dispose an element or component or portion thereof as suitable to the circumstance and embodiment. In certain cases, the element or component, or portion thereof, can remain in an unchanged position, state, and/or condition as a result of adjustment, if appropriate or desirable for the embodiment under the circumstances. In some cases, the element or component can be altered, changed, or modified to a new position, state, and/or condition as a result of adjustment, if appropriate or desired.
“Inhibit”—As used herein, inhibit is used to describe a reducing or minimizing effect. When a component or feature is described as inhibiting an action, motion, or condition it may completely prevent the result or outcome or future state completely. Additionally, “inhibit” can also refer to a reduction or lessening of the outcome, performance, and/or effect which might otherwise occur. Accordingly, when a component, element, or feature is referred to as inhibiting a result or state, it need not completely prevent or eliminate the result or state.
“Maximum Effective Slope”—As used herein, maximum effective slope is used to describe the average slope of an upper surface of a PV laminate from the highest point to the closest edge. More particularly, the maximum effective slope would be determined by dividing the difference in height between the highest point on the upper surface of a PV laminate and the closest edge by the lateral distance between the highest point and the closest edge. In some embodiments, the upper surface of the PV laminate may be continuously curved and thus only one point on the surface might have the same value as the maximum effective slope.
In addition, certain terminology may also be used in the following description for the purpose of reference only, and thus are not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, and “side” describe the orientation and/or location of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second”, and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context.
The inventions disclosed herein are described in the context of a photovoltaic module. However, these inventions can be used in other contexts as well.
A known photovoltaic (PV) known module 20 is shown in
The PV module 20 includes a PV device 22 (referenced generally) and a frame 24. Details on the various components are provided below. In general terms, however, the PV device 22 includes a PV laminate 26 that is encased by the frame 24.
The PV device 22 can assume a variety of forms that may or may not be implicated by
The PV laminate 26 includes a weather-proof barrier 32 that forms the uppermost surface of the PV laminate 26. The illustrated PV laminate 26 includes a glass member that provides a weather-proof barrier for the PV cells 30. The glass layer is bonded to the PV cells 30 in a well-known manner. The PV cells 30 comprise backside-contact cells, such as those of the type available from SunPower Corp., of San Jose, Calif. Backside-contact cells include wiring leading to external electrical circuits are coupled on the backside of the cell (i.e., the side facing away from the sun upon installation) for increased area for solar collection. Backside-contact cells are also disclosed in U.S. Pat. Nos. 5,053,083 and 4,927,770, which are both incorporated herein by reference in their entirety. Other types of PV cells may also be used without detracting from the merits of the present disclosure. For example, the photovoltaic cells 30 can incorporate thin film technology, such as silicon thin films, non-silicon devices (e.g., III-V cells including GaAs), etc. Thus, while not shown in the figures, in some embodiments the PV device 22 can include one or more components in addition to the PV laminate 26, such as wiring or other electrical components.
Regardless of an exact construction, the PV laminate 26 can be described as defining a outermost upwardly facing weather proof barrier 32 and a perimeter 34 (referenced generally in
The PV cells 30 are oriented so as to face toward the barrier 32 for receiving sunlight. With specific reference to
The PV cells 30 are identical in size and shape, and are uniformly distributed along the PV laminate. As a result, identical uniform spacings are defined between the PV cells 30.
With the above conventions in mind, the column spacings 60 and the row spacing 62 are uniform and identical in shape in some embodiments, with the particular shape being generated as a function of a shape of the PV individual cells 30. For example,
With continued reference to
With continued reference to
With reference to
Additionally, in order to reduce overall weight and raw material costs, the materials used to form the upper surface of the laminate 26 is thin and light. Thus, when such PV laminates 26 are subject to wind, the laminate can vibrate and flex up and down, thereby fluctuating between convex and concave shapes. This fluctuation is known as “oil-canning”. Such a fluctuation can accelerate fatigue failures of the PV laminate 26.
Similarly, even where the module 20 is mounted such that the laminate 26 is included relative to horizontal (5° to 10° from horizontal in the configuration of
As shown in
With reference to
The magnitude of the convexity of the upper surface of the barrier member 1032 can be measured in any known manner. For example, the curvature of the upper surface of the barrier member 1032 can be measured in terms of its maximum effective slope. The maximum effective slope can be determined by, first, determining the relative height 1206 of the highest point 1200 on the PV laminate and the height of the closest point 1204 on a lateral edge of the upper surface of the barrier 1032. This relative height represents the “rise” of the maximum effective slope.
Next, the lateral distance 1208 from the highest point 1200 to the position of the closest point 1204 can be determined. This distance represents the “run” of the maximum effective slope. Thus, the maximum effective slope can be determined by calculating the sine of the ratio of the “rise” 1206 over the “run” 1208. In some embodiments, the maximum effective slope can be at least about 2°. In some embodiments, the maximum effective slope can be 15° or less. In other embodiments, the maximum effective slope can be between about 5° and about 10°. In other embodiments, the maximum effective slope can be at least about 2.8°.
The magnitude of the convexity of the upper surface of the barrier member 1032 can also be expressed as the slope of the peripheral edge of the PV laminate 1026. For example, the actual slope of the upper surface of the barrier member 1032 can be directly measured against horizontal. As shown in
Additionally, in some embodiments, the upper surface of the barrier member 1032, in the area inward from the lateral edge 1050a, can be sloped at any of the angles □ noted above, with the terminal portion of the lateral edge 1050a being sloped at a lesser angle, such as 4° to 0°. As used herein, the term “terminal portion of the lateral edge 1050a” is intended to include the portion of the lateral edge connected to the frame 1024.
Other angles □ and maximum effective slopes can also be used. Additionally, the flow of water over the upper surface of the barrier member 1032 is different depending on the material used to form, the surface energy and electrical charge of the barrier member 1032. Thus, in some embodiments, the angle □ can be chosen to achieve the desired drainage and/or water flow characteristics.
Constructing the module 1020 with an upwardly convexly-shaped upper surface can provide additional advantages. For example, by providing the barrier member 1032 with a convex surface, the PV laminate 1026 can be stiffer, and thus better resist fluctuations such as “oil-canning” and the resulting fatigue failures.
As shown in
As noted above, the outer barrier member 1032 can be convexly curved in a single direction, as illustrated in
With continued reference to
With reference to
With reference to
As shown in
In the illustrated embodiment, the PV laminate 2026 is constructed or held in place such that the peripheral axis AP, is inclined relative to horizontal H by an angle theta Θ (when measured with the laminate 2026 laid in on a horizontal surface). In some embodiments, the angle theta Θ is at least about 1°. Other angles Θ can also be used, such as those noted above with reference to the non-limiting embodiments of
As shown in
With reference to
In some embodiments, with the barrier member 1032 shaped as such, the PV cells 1030 can then be bonded to the barrier member 1032. As noted above, typically, the photovoltaic cells 1030 can be bent by a reasonable amount allowing the cells to bend and follow the curvature of the barrier member 1032. The PV cells 1030 can be bonded to such a curved barrier member 1032 in any known manner. In some embodiments, adhesive can be spread over the outer surfaces of a flat member with PV cells 1030, then two flat barrier members 1032 can be applied to the outer surfaces of the cells 1030. With the adhesive still uncured, the cells 1030 and barriers members 1032 can be bent together in the desired shaped and allowed to cure in the desired bent shape. In some embodiments, the weight of the cells 1030 and barrier members 1032 is enough to cause sufficient bending. Optionally, additional weights can be placed on the cells 1030 and barrier members 1032 to cause additional bending to hold these members in the desired shape until sufficiently cured to retain the desired shape.
In some embodiments, with reference to
With reference to
Providing a PV module with an upper surface that has an upwardly convex shape can provide additional advantages. For example, when sunlight (at approximately “noon”) reaches the upper surface of a PV module having a convex upper surface, such as any of those described above with reference to
However, in a system including an array of PV modules, wherein two adjacent PV modules have upwardly convex upper surfaces, sunlight reflected by parts of the upper surface can be absorbed by the adjacent PV module having a convex upper surface. For example, because the upper surface of the PV module is upwardly convex, some of that surface can be oriented at an elevation and angle sufficient such that the sunlight laterally reflected from one PV module impacts the upper surface of the adjacent PV module and is thus absorbed and converted into electrical energy. As such, the total amount of absorbed sunlight can be increased. This benefit can be further enhanced where the photosensitive device of the PV laminate (i.e., the photovoltaic cells) are also convexly shaped along with the corresponding convex upper surface of the PV module.
Photovoltaic modules with flat upper surfaces can create lateral reflections. However, because such PV modules are normally mounted in orientations in which the upper surfaces are roughly coplanar and/or parallel, lateral reflections of sunlight from one PV module would not normally project along a path that would impact the upper surface of another adjacent PV module so that it could be absorbed.
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or embodiments described herein are not intended to limit the scope, applicability, or configuration of the claimed subject matter in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the described embodiment or embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope defined by the claims, which includes known equivalents and foreseeable equivalents at the time of filing this patent application.
