Patent Application
20130247960
The present invention relates to apparatuses for collecting, concentrating and harvesting solar-light by total internal reflection.
Concentrating Photovoltaic (CPV) solar panels are known and they are used to generate electricity for industrial and personal use.
Optical concentrators for photovoltaic (PV) solar applications are well known and they use reflective, refractive, diffractive, TIR waveguides, luminescence optics or combinations of these optical elements.
Optical concentrators using planar or slab waveguides in conjunction with collecting and focusing refractive optical elements have been used to improve the solar energy concentration onto reduced size PV cells to reduce the cost of the PV cell and to minimize the height of the solar panels.
There is a need to further optimize the design, the manufacturing and the assembling operations related to concentrating photovoltaic (CPV) solar panels based on planar or slab waveguides that use total internal reflection and the corresponding optical focusing elements. Both the optical efficiency and the overall efficiency that depends on the efficiency of the PV cells needs further refinements. The design of the optical components needs to be done also by considering the current and the future advances in the PV cells designs and manufacturing coupled to the waveguide optics.
This invention discloses an optical solar concentrator having a focusing layer including focusing optical elements that concentrate sunlight onto the corresponding deflectors of a waveguide. The deflectors are located in the lower surface of the waveguide and in the focal plane of the focusing elements. The deflectors redirect the light inside the waveguide under total internal reflection conditions in order to collect the focused light and couple the sunlight to a photovoltaic cell. The sun light exiting from the waveguide is first redirected and further concentrated by a secondary optic that couple the light to the PV cell. The focusing optical elements and the deflectors are either longitudinal or annular and the PV cell is in several embodiments a multi-junction PV cell. The multi-junction cells have are designed for a spectral response that matches the spectrum of the light reaching the PV cell through the combined focusing elements, the waveguide and the secondary optical element.
The invention discloses several embodiments of the concentrators where the annular focusing elements and the annular deflectors have both circular and polygonal outer surfaces. The polygonal ouster surfaces allow for the better clustering of the optics to increase the active surface of the solar panels.
The invention also discloses a tray that that protects the optics and locates the PV cells relative to the optics. In some embodiments the material of the tray is similar to the material of the waveguide to allow the two parts to expand and shrink at the same rate during manufacturing and in the field and in the day and night conditions.
In some embodiments the tray is made of a polycarbonate that includes a carbon fiber filler to dissipate the heat from the PV cell. One such a material is Raheama made by Tejin Limited of Japan.
For a better understanding of the present invention, as well as other aspects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawings, where:
a is a cross-sectional view of the photovoltaic solar-light concentration apparatus of
b is a cross-sectional view of another embodiment of a photovoltaic solar-light concentration apparatus having a cladding layer;
a is a perspective view of another embodiment of the photovoltaic solar-light concentration apparatus;
b is a cross section view of the secondary optic show in
a-b-c-d-e-f-g illustrate another embodiment of the invention showing a hexagonal shaped photovoltaic solar concentrator with a secondary optic.
Referring to
The photovoltaic solar-light concentration apparatus 10 is generally rectangular in shape. It is contemplated the focusing layer 20 and the waveguide 30 could be generally square. A second embodiment of a photovoltaic solar-light concentration apparatus 10′ having a generally circular shape will be described in greater detail below with reference to
The photovoltaic solar-light apparatus 10 comprises a focusing layer 20 and a waveguide 30 separated by an air gap 40. The focusing layer 20 and the waveguide 30 are generally rectangular. The focusing layer 20 and the waveguide 30 are parallel to each other.
The focusing layer 20 comprises a plurality of longitudinal focusing elements 22 disposed an abutting side-by-side position. The plurality of longitudinal focusing elements 22 forms a plurality of stripes, wherein each stripe is a cylindrical lens. It is contemplated that the focusing elements 22 could be more elaborate and consists of various optical active facets of various shapes. Each focusing element 22 (i.e. stripe) collects concentrates (by focusing) solar-light 1 (shown in
The waveguide 30 is a planar slab of acrylic glass. The waveguide 30 is injection molded. It is contemplated that the waveguide 30 could be thermoformed or injection molded from one or more moldable materials. For example, the waveguide 30 could be molded from optical grade polycarbonate, such as CALIBRE™, IUPILON™, LEXAN™, MAKROLIFE™ MAKROLON™, PANLITE™, TARFLON™ or LBE™. The waveguide 30 could also thermoformed or injection molded from polymethyl methacrylate (Plastic Materials) such as any of POLICRIL™, PLEXIGLAS™, GAVRIELI™, VITROFLEX™, LIMACRYL™, R-CAST™, PER-CLAX™, PERSPEX™, PLAZCRYL™, ACRYLEX™, ACRYLITE™, ACRYLPLAST™, ALTUGLAS™, POLYCAST™, OROGLASS™, OPTIX™, LUCITE™ and ACRYLIC™. The focusing layer 20 is made of the same materials and using the same manufacturing methods as the waveguide 30. Materials for the focusing layer 20 and the waveguide 30 are selected from same or different materials selected from the materials listed before.
The waveguide 30 is optically coupled to the focusing layer 20. The waveguide 30 has an entry surface 32 disposed facing the focussing side 24 of the focusing layer 20, a reflecting surface 34 opposite to the entry surface, and an exit surface 36 at an end of the entry surface 32 and the reflecting surface 34.
A plurality of longitudinal deflectors 50 is disposed on the reflecting surface 34. The plurality of longitudinal deflectors 50 is integrally formed with the waveguide 30 by injection molding. It is contemplated that the plurality of longitudinal deflectors 50 could be formed by injection compression molding. The longitudinal deflectors 50 are parallel to each other and parallel to the exit surface 36. The plurality of longitudinal deflectors 50 consists in a plurality of adjacent spaced apart stripes. It is contemplated that the deflectors 50 can be equally spaced or can be spaced at variable distances one relative to the other or in clusters. It is also contemplated that the stripes could not be spaced apart. Each longitudinal deflector 50 (i.e. stripe) has a shape of a wedge. It is contemplated that the longitudinal deflectors 50 could have more elaborate shapes than a single wedge.
The plurality of deflectors 50 is arranged in a one-to-one optical relationship with respect to the plurality of focusing elements 22. The plurality of deflectors 50 is positioned in the focal plane of the focusing elements 22 so that each deflector 50 receives the solar-light 1 coming from a single corresponding one focusing element 22. It is contemplated that, the plurality of deflectors 50 could not be positioned in the focal plane of the focusing elements 22. The deflectors 50 have a deflecting surface 52 positioned at an angle with respect to the incoming solar-light 1 beam so as to redirect the solar-light 1 into the waveguide 30 at an angle that ensures total internal reflection. It is contemplated that the deflecting surface 52 could be flat, segmented, multi-faceted or curved. It is also contemplated that the deflecting surface 52 could be mirror-coated or uncoated. It is also contemplated that the deflecting surface 52 could be sized and positioned with respect to the focusing elements 22 to always capture and deflect the entire solar-light beam 1 so that no focused light passes by the deflecting surface 52. This prevents direct focused light 1 not intercepted by surface 52 from escaping from the waveguide 30. It is contemplated that the waveguide 30 and thus the deflecting surface 52 could be slightly closer to the focusing element 22 (short focus) or a little further from the focusing element 22 (far focus) for as long as no light escapes the deflecting surface 52. Starting with this first reflection at the deflecting surface 52, the solar-light 1 is reflected between the entry surface 32 and the reflecting surface 34 at angles that exceed the critical angle (hence ensuring total internal reflection). The solar-light 1 is therefore trapped into the waveguide 30, and the total internal reflections direct unidirectionally the solar-light 1 toward the exit surface 36 of the waveguide. This combination of a longitudinal focusing element 22 and a longitudinal deflecting element 50 that together generate a band or stripe shaped solar beams 1 advancing via total internal reflection in the waveguide 30 allows for the optimum concentration since no solar light 1 will be directed towards the lateral walls/surface of the waveguide 30 to lower the amount of solar light 1 advancing towards the exit surface 36, that happens in some other known planar waveguides 30 for light concentration.
A photovoltaic (PV) cell 60 is optically coupled to the waveguide and is disposed at the exit surface 36 of the waveguide 30 and collects the solar-light 1 trapped in the waveguide 30. The photovoltaic cell 60 in
As best seen in
Referring now to
The photovoltaic solar-light concentration apparatus 10′ has a focusing layer 20′ and a waveguide 30′ separated by an air gap 40′. It is completed that the air gap 40′ could be replaced by a cladding layer 70′ (see
The waveguide 30′ is disk-shaped and has the same size as the focusing layer 20′. The waveguide 30′ has an exit surface 36′ centrally located. The exit surface 36′ is positioned underneath the central portion 21′ of the focusing layer 20′ and has a radius of the central portion 21′.
The waveguide 30′ has a plurality of deflectors 50′ disposed on a reflecting surface 34′ of the waveguide 30′. The plurality of deflectors 50′ consists in annular wedges disposed concentrically. The deflectors 50′ are isolated with respect to each other. The plurality of deflectors 50′ is disposed in the waveguide 30′ so as to create a one-to-one relationship with the plurality of focusing elements 22′. Similarly to the solar-light concentration apparatus 10, the solar-light 1 is trapped into the waveguide 30′ and is directed unidirectional by total internal reflection toward the exit surface 36′.
A secondary optic 80′ is disposed at the exit surface 36′. The secondary optic 80′ is disk-shaped. The secondary optic 80′ directs and concentration the solar-light 1 coming radially from the exit surface 36′ into a spot. It is contemplated that the secondary optic 80′ could be omitted.
A photovoltaic cell 60′ is disposed underneath a center of the secondary optic 80′. The photovoltaic cell 60′ has a square shaped active area. It contemplated that photovoltaic cell 60′ could be circular.
a and 8b show a photovoltaic concentrator (800′) having a focusing layer (820′) with annular and concentric focusing elements (822′) and a planar slab waveguide (830′) having deflecting elements (850′) not shown but similar to item (50′) of
Referring back to
Referring to
Referring to
General comparison of concentrations for revolved and linear geometries for the concentrator of the current invention.
The formula for geometrical concentration is:
here C is the geometrical concentration factor of the revolved geometry, Ac is the sun collection area and Aa is the energy absorber area.
For the revolved and linear geometries, the collection area is the same. What differs is the area of the absorber.
For the linear geometry, the area of the absorber is equal to
A
a
=h·l
where l is the length of the linear focusing elements.
For the revolved geometry, the area of the absorber is equal to
Aa=2πrcentreh
where rcentre is the radius of hole at the centre of the optics and h is the height of the waveguide.
For the case where rcentre=20 mm, h=4 mm and l=200 mm, the revolved geometry has a concentration factor which is approximately 1.6 times the concentration of the linear geometry.
With numbers:
Therefore, for a collection area of approximately Ac=314 cm2, and the parameters as specified above, we have the following:
The concentration factor of the revolved geometry is 62.5 for the above scenario. Further concentration can be added by using a secondary optic with an additional concentration factor of 1.5. This increases the total concentration for the revolved optic to 93.75. With this concentration, a multi-junction pv cell at 40% efficiency can be used which has an area of 3.3 cm2.
The concentration factor of the linear geometry is approximately 39.3 for the above scenario. Since the absorber area of the linear geometry is very large (8 cm2 in this scenario), a PV cell with efficiency of 8% will have to be used, since multi-junction cells are too expensive to used to cover that much area.
The increased concentration of the revolved geometry in combination with the secondary optic and the possibility to use a multi-junction cell makes the revolved geometry a much more attractive design than the linear geometry. Also the fact that the deflection elements and the focusing elements can be diamond turned more efficiently makes the revolved geometry more attractive for higher concentration in many applications.
In particular,
The spectrum of the sunlight entering the focusing layer is partially absorbed by the poly-methyl methacrylate (or other materials) therefore altering the spectrum of the exiting light and this impacts the performance of the system since it requires a customized multi-junction PV cell. A planar waveguide ( ) slab is optically coupled to the focusing layer having a regular polygonal shape and an optically smooth flat upper surface ( ) and an opposed lower flat surface having a corresponding regular polygonal shape. The lower surface ( ) is parallel to the upper surface ( ) to create a waveguide of a constant thickness. Both surfaces are bare, that is they don't have any type of mirror coating to reduce the cost and the damage that can be caused in operation due to sun exposure or the humidity that will lower the reflections inside the waveguide.
The waveguide ( ) is separated from the focusing layer ( ) by a material having a lower index of refraction than the waveguide ( ). In this embodiment the waveguide has an annular-exit surface ( ) and a plurality of annular deflecting elements ( ) each located in the focal plane of a corresponding focusing element and along concentric circles on the lower surface of the waveguide. By placing the deflecting elements on the lower surface of the waveguide the optical coupling with the focusing elements is improved and less light escape through the waveguide. The annular deflecting elements are disposed to deflect the focused solar at an angle that causes total internal reflection of the solar-light inside the waveguide, the solar-light being conveyed toward the exit surface of the waveguide by multiple total internal reflections between the parallel upper and lower surfaces of the waveguide that are not mirror coated. The waveguide layer is molded of poly-methyl methacrylate or other moldable material. The spectrum of the sunlight entering the waveguide ( ) is partially absorbed by the poly-methyl methacrylate (or other materials) therefore further altering the spectrum of the light exiting the waveguide and this impacts the performance of the concentrating system since it requires a customized multi-junction PV cell responsive to this changed solar spectrum.
Because of the increased demand for high solar efficiency for a reduced foot print this invention shows the coupling of the waveguide optics to multi-junction cells that are not only smaller in size to increase the optical concentration but also they are more efficient and more flexible to be made for a specific and more customized input solar spectrum affected by the absorption caused by the focusing elements and the waveguide that are made of moldable plastic resins. Also the lengthy travel of the light trough the waveguide contributes to a larger spectrum absorption in the waveguide than in the focusing layer. A multi junction photovoltaic cell is disposed to receive the solar light emerging from the waveguide and the multi-junction PV cell is designed to provide an optimum electronic efficiency for the sunlight spectrum exiting the waveguide.
In some embodiments of the invention a disc shaped secondary optical element ( ) having an annular entry surface ( ) and a reflecting surface ( ) is located between the waveguide and the multi-junction PV cell as shown in
As shown in
Raheama consists of 50-200 micrometer fibers cut from a cylindrical graphite fiber stock measuring about 8 micrometers in diameter. It disperses well in plastic, allowing manufacturers to produce heat-radiation components of almost any shape. Raheama's thermal expansion coefficient is as low as that of ceramics, so compacts created with the material have exceptional dimensional stability. Raheama also offers high electrical conductivity, making it suitable for the prevention of static and shielding from radio waves.
Raheama has two standard specifications, R-A201 and R-A301, each boasting its own set of special features. R-A201 offers superior moldability and dispersion as a filler in plastic or rubber. It also combines with other fillers. R-A301 provides superior heat radiation, ranging from high levels of thermal conductivity using just small amounts of filler to extra-high levels as more filler is added.
Table with some of the item numbers.
Modifications and improvements to the above-described embodiments of the present invention may become apparent to those skilled in the art. The foregoing description is intended to be exemplary rather than limiting. The scope of the present invention is therefore intended to be limited solely by the scope of the appended claims.
This application is a continuation of U.S. patent application Ser. No. 13/053,184, filed Mar. 21, 2011 which claims the benefit of priority of U.S. Provisional Patent Application No. 61/315,744 filed Mar. 19, 2010; this application is a continuation-in-part of U.S. patent application Ser. No. 13/028,957, filed Feb. 16, 2011. Through the '957 Application, the present application is a continuation of U.S. patent application Ser. No. 13/007,910, filed Jan. 17, 2011, now U.S. Pat. No. 7,991,261. Through the '910 Application, the present application is a continuation of U.S. patent application Ser. No. 12/113,705, filed May 1, 2008, now U.S. Pat. No. 7,873,257. Through the '705 Application, the present application claims the benefit of priority of U.S. Provisional Patent Application No. 60/915,207 filed May 1, 2007; U.S. Provisional Patent Application No. 60/942,745 filed Jun. 8, 2007; and U.S. Provisional Patent Application No. 60/951,775 filed Jul. 25, 2007. Each of the foregoing applications is incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61315744 | Mar 2010 | US | |
| 60915207 | May 2007 | US | |
| 60942745 | Jun 2007 | US | |
| 60951775 | Jul 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13053184 | Mar 2011 | US |
| Child | 13892821 | US | |
| Parent | 13007910 | Jan 2011 | US |
| Child | 13028957 | US | |
| Parent | 12113705 | May 2008 | US |
| Child | 13007910 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13028957 | Feb 2011 | US |
| Child | 13053184 | US |
