The invention relates generally to solar energy collection and conversion, and specifically to solar photovoltaic concentrators.
Much of current solar photovoltaic concentrator technology involves use of large, cumbersome, heavy, and, because of their size and bulk, relatively expensive solar panels. Most photovoltaic concentrators use either flat Fresnel lenses and/or parabolic mirrors to focus sunlight onto silicon or multi-junction photovoltaic cells.
A better optical approach is to use Fresnel lenses, which can be arched or domed, to focus sunlight onto the photovoltaic cells, since the optical advantages of arched or domed lenses over flat Fresnel lenses or mirrors are many and are well known to those of ordinary skill in the art of photovoltaic concentrator technology. However, current solar panels using large, arched Fresnel lenses are nonetheless bulky, heavy, and require large heat sinks. If the arched lens comprises an acrylic plastic, which is the presently preferred material, these acrylic lenses are flammable and can be damaged due to exposure to weather and environmental elements such as hail, wind, blowing sand, and the like. Furthermore, acrylic lens material allows water vapor to diffuse through the lens into the interior of the concentrator panel, where condensation can cause optical (condensation on the lens) and electrical (condensation on the cell circuit) problems.
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Container 10 comprises top 12, sides 15-18, and bottom 14. Sides 15 and 17 (
In certain contemplated embodiments, bottom 14 comprises an aluminum radiator sheet. However, the container material is in no way restricted to aluminum, since many other materials such as galvanized steel, plastics, glass, or the like, or a combination thereof could be used.
As typically configured, container 10 comprises a weatherproof enclosure, with water-tight joints or seals between the exterior components, including top 12, sides 16 and 18, bottom 14, and end plates 15 and 17 (
In certain contemplated embodiments, container 10 may also include one or more breathing ports 11, which provides a fluid conduit between the interior of container 10 and the outside environment and is dimensioned to help prevent a pressure differential between an interior portion of container 10 and the outside air.
In preferred embodiments, top 12 comprises a transparent material which defines window 20. Typically, window 20 comprises a glass with typical dimensions of around 1 meter wide by around 1.5 meters long. In currently contemplated embodiments, window 20 may comprise a glass coated with an anti-reflection (AR) coating on one or both of its surfaces, minimizing the optical transmittance loss for solar rays passing through the glass. For example, an inexpensive sol-gel coating on both glass surfaces can achieve 96% net transmittance for low-iron, tempered float glass with a thickness of around 3 mm. The window material is in no way restricted to glass, since any transparent material, such as plastic sheet or film, could serve the same function. For example, in alternative, lighter weight embodiments, window 20 may comprise a polymer sheet, such as acrylic plastic, a polymer film such as ETFE or FEP fluoropolymer material, a laminated combination of glass and polymer materials, or the like, or a combination thereof.
Window 20 may be coextensive with all of top 12 or comprise a predetermined portion of top 12 such as being disposed within a glass mounting frame (not shown in the figures) that is at least coextensive with top 12.
In currently preferred embodiments, window 20 is not a lens and does not contain any lens features, serving instead to allow incident light into container 10 and to protect Fresnel lens concentrator 30, receiver 40, and other interior components from exposure to weather elements such as rain, hail, blowing sand, dirt, and wind.
End plates 15 and 17 (
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Using an array of small Fresnel lens concentrators 30 allows photovoltaic concentrator panel 1 to have a depth of only a few inches versus a conventional concentrating photovoltaic module depth of 2-3 feet. This can save costs such as for enclosure materials, packaging/shipping cost, and/or installation cost.
A further important feature of Fresnel lens concentrator 30 is that it is mounted within container 10 independently of window 20. Thus, in typical installations, Fresnel lens concentrators 30 and receivers 40 are configured as independent pairs with self-aligning supports which are not connected to window 20, i.e. one Fresnel lens concentrator 30 is paired with one specific receiver 40. It is understood that there can be a plurality of paired Fresnel lens concentrators 30 and corresponding photovoltaic cell circuits 49 within container 10.
If photovoltaic concentrator panel 1 uses dome lens concentrators 30 and multi-junction photovoltaic cells 41, the dome lens design may further include color-mixing features as are known in the art. Container 10, including window 20 and bottom 14 dimensioned and configured to act as a heat rejection structure, can be adapted to a number of different photovoltaic concentrator configurations using free-standing lens concentrators 30 of various geometries focusing onto photovoltaic cells 41 of various types. The lens concentrator material is in no way restricted to acrylic or other polymeric plastic, since lens concentrators 30 could be made of any transparent moldable material, such as clear silicone materials.
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Typically, receivers 40 are fully encapsulated and dielectrically isolated and capable of high-voltage operation for decades with no ground faults (shorts to the heat rejection structures). Carrier 42 may act as a substrate and may comprise a flex circuit or printed circuit board or other electronic circuit element, as is well known to those of ordinary skill in the art of assembling photovoltaic cell circuits or other types of electronic circuits. In one preferred embodiment, carrier 42, acting as an electrical insulator, may include one or more independent dielectric film layers 46, each made of a high-voltage insulation material such as polyimide, disposed below photovoltaic concentrator cell circuit 49. Two or more independent dielectric film layers 46 are preferred to prevent insulation breakdown due to a pinhole or other defect in one dielectric film layer 46.
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Carrier 42, typically a strip of aluminum, is used to support photovoltaic cell circuit 49. Photovoltaic concentrator cell circuit 49 is typically adhesively bonded to first adhesive layer 45. Dielectric film layer 46 may be present and adhesively bonded to second adhesive layer 47 which is then bonded to carrier 42. Carrier 42 may be attached to bottom 14 of container 10 using any suitable means such as by a further adhesive layer.
In a preferred embodiment, the layers beneath photovoltaic cell circuit 49 comprise thermally loaded adhesive layer 45, further comprising a silicone material such as alumina-loaded Dow Corning Sylgard® 184; dielectric film layer 46, further comprising one or more laminated layers of polyimide material such as DuPont Kapton® CR, where two such layers are preferred; and adhesive layer 47, further comprising a thermally loaded silicone such as alumina-loaded Dow Corning Sylgard® 184. Where dielectric layer 46 comprises redundant layers of polyimide, these provide added durability and reliability in case of a defect such as an air bubble or void in one of the layers
For ease of handling and assembly, photovoltaic cell circuit 49 can be bonded to dielectric film layer 46 using a thermally loaded adhesive in first adhesive layer 45 and then bonded to carrier 42 using a second thermally loaded adhesive layer 47, and carrier 42 which is itself attached to bottom 14 of container 10 using another layer, e.g. a third layer, of thermally loaded adhesive.
Encapsulating layer 43 is attached to a top portion of photovoltaic cell circuit 49, and one or more prism covers 44 are attached to encapsulating layer 43 to aid in focusing incident light energy onto photovoltaic cell circuit 49. In a preferred embodiment, clear encapsulating layer 43 comprises silicone material, such as Dow Corning Sylgard® 184, and prismatic cell cover 44 comprises silicone material such as Dow Corning Sylgard 184®. In preferred embodiments, prismatic cell cover 44 reduces the shadowing loss of metal gridlines on the top surface of photovoltaic cells 41 by refracting focused sunlight away from these gridlines onto active solar cell material instead. Prismatic cell cover 44 is typically molded into or attached to clear encapsulating layer 43 over each photovoltaic cell 41 to eliminate gridline shadowing loss.
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Waste heat may therefore be efficiently collected by insulating heat sink 50 to minimize heat losses to the environment and also by delivering the heat absorbed by the fluid to a nearby heat load, such as may be appropriate for use as hot water for an industrial or commercial application. The insulation material can also wrap around the sides and top edges of heat sink 50, leaving only the active solar cell material of receiver 40 exposed to the focus of Fresnel lens concentrator 30. If multiple heat sinks 50 are used in photovoltaic concentrator panel 1, corresponding to multiple photovoltaic cell circuits 49 under multiple Fresnel lens concentrators 30, fluid carriers 52 can be connected to insulated manifolds or other insulated fluid distribution system elements at the ends of the photovoltaic concentrator panel 1, using materials and designs well known to those of ordinary skill in the art in solar heat collection. In one embodiment, the thermal insulation material comprises an isocyanurate foam or other thermally insulating foam, materials well know to those of ordinary skill in the art of solar heat collection.
In some of these embodiments, when the waste heat generated within receiver 40 is to be dissipated to the surroundings, bottom 14 also acts as a heat exchanger and comprises a thermally conductive material, e.g., aluminum, which acts as a heat sink for receiver 40 as well as for transferring the waste heat to the surroundings such as by convection and radiation. Thus, in these embodiments bottom 14 may act as a backplane radiator for ambient air-cooling. To minimize the radiator temperature for the air-cooling approach, the surfaces of the backplane radiator should be reflective of solar wavelengths and absorptive/emissive of infrared wavelengths, which can be achieved with clear anodizing of aluminum or with white paint.
In another preferred embodiment of these embodiments, when the waste heat generated within receiver 40 is to be collected and used, bottom 14 comprises a low-cost, durable enclosure bottom made of a material such as glass or a suitable metal which may also act as a support for a thermally insulated, liquid-cooled receiver 40. A glass back material has an additional advantage of allowing diffuse sunlight to be transmitted completely through top 12 and bottom 14 of photovoltaic concentrator panel 1, reducing both the temperature of Fresnel lens concentrators 30 inside photovoltaic concentrator panel 1 and the external surfaces of photovoltaic concentrator panel 1.
Moreover, the configuration and relatively small size of receiver 40 is amenable to use of high-quality, proven solar cell and semiconductor circuit assembly fabrication equipment and methods and can be fully automated, producing assemblies at a higher-speed and lower cost and better quality.
Small receiver 40 or photovoltaic cell circuit 49 assemblies are more efficient than large receiver 40 or photovoltaic cell circuit 49 assemblies, due to the smaller currents and the smaller distances that the currents must be conducted, making the disclosed receivers 40 more efficient than receivers 40 in conventional larger concentrating photovoltaic modules. Further, small apertures make waste heat rejection simpler and less costly, due to the small quantity of waste heat and the small distances this waste heat needs to be conducted for dissipation, resulting in lower cell temperatures and higher cell efficiencies than for conventional larger concentrating photovoltaic modules
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The foregoing disclosure and description of the inventions are illustrative and explanatory. Various changes in the size, shape, and materials, as well as in the details of the illustrative construction and/or illustrative method may be made without departing from the spirit of the invention. For example, while the above illustrations and descriptions have been directed to include line-focus arched Fresnel lenses and silicon cells arranged in linear photovoltaic receivers in the focal lines of the arched lenses, the spirit of the invention applies equally to point-focus dome-shaped lenses and multi-junction cells arranged in a pattern corresponding to the focal spots of the dome lenses.
This application claims priority from U.S. Provisional Patent Application No. 61/177,498 filed on May 12, 2009 and U.S. Provisional Patent Application No. 61/178,341 filed on May 14, 2009.
Number | Date | Country | |
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61177498 | May 2009 | US | |
61178341 | May 2009 | US |