AN IMPROVED PHOTOVOLTAIC CONCENTRATOR AND A METHOD OF
FABRICATING THE SAME
FIELD OF THE INVENTION
The present invention, in general relates to an improved photovoltaic
concentrator and a method of fabricating the same and in particular to a
photovoltaic concentrator having an improved back pan and to a method of its
fabrication, whereby a cost effective solution for thermal management is
achieved.
BACKGROUND OF THE INVENTION
It is traditionally known that a plurality photovoltaic cells are connected to form a photovoltaic module, while an array constitutes a plurality of photovoltaic modules. Now, high concentration photovoltaic modules, apply a concentrator such as a mirror to concentrate sunlight on the solar cells. Each high concentration photovoltaic module includes a plurality of interconnected receivers, each receiver having one or more photvoltaic cells adapted to be connected to similar receivers, electrically.
Optica! concentrators or photovoltaic concentrators, as they are popularly known, comprise optical systems, for concentrating the sun's radiation on to the receiver. Photovoltaic concentration panels employ lens and mirrors to concentrate sun's radiation on the solar cell, to ensure maximum utilization of solar energy and its conversion in to electrical energy, thereby reducing panel cost. However, concentration of Sun's radiation on the solar cell, reduces the cell area required for energy conversion. Furthermore, concentration also increases the temperature of the solar cell, which decreases the conversion efficiency. Hence, effective thermal management is, one of the important aspects , which need to be addressed by photovoltaic concentrators. For that purpose, the two most popular techniques applied are active and passive cooling. Active cooling involves, convective or conductive heat transfer, applying heat exchangers or fans. Active cooling is invariably cumbersome and suffers from lack of reliability.

Passive cooling involves application of large thermal mass and high thermal conductivity materials, for quick heat transfer. Often recourse is taken to expensive high conductivity materials like aluminum, copper and so on. Hence, not only is the process cumbersome, but also it is expensive. Furthermore, in this regard, the back panel of photovoltaic concentrators is designed, such that it comprises 2.5 mm thickness of aluminum alloy. Aluminum is used for its low weight and high thermal conductivity, for heat transfer. Aluminum also has high coefficient of thermal expansion, which causes significant self contraction and expansion due to rise and fall of the environment temperature. However, aluminum alloy is expensive as stated before and is not as widely available as steel.
Accordingly, over the years there was a long felt need for providing a cost-effective and technically sound back pan for photovoltaic concentrators, whereby an effective thermal management is achieved In a technically sound and an economically significant manner, in the area of photovoltaic modules having high concentration photovoltaic concentrators.
The present invention meets the aforesaid long felt need.
All through out the specification, reference has been made to "Mirrors", "Lenses"
"receiver", "assembly", "photovoltaic cells" for the sake of understanding, but is
not to limited to those and the present invention embraces all similar items in the
field referred to by other names, as may be understood by persons skilled in the
art.
OBJECTS OF THE INVENTION
It is the principal object of the present invention to provide an Improved
photovoltaic concentrator for high concentration photovoltaic modules, having a
cost-effective and technically sound back pan, whereby an effective thermal
management is achieved in a technically sound and an economically significant
manner.

It is yet another object of the present invention to provide an improved back pan design for photovoltaic concentrators of high concentration photovoltaic modules, whereby a cost-effective solution for ensuring the mechanical integrity and effective heat dissipation of thermal energy is achieved. It is a further object of the present invention to provide an improved back pan design for photovoltaic concentrators of high concentration photovoltaic modules, whereby cost-reduction is achieved without compromising on the performance of photovoltaic concentration modules.
It is a further object of the present invention to provide an improved back pan design for photovoltaic concentrators of high concentration photovoltaic modules, in the form of a robust back pane! of steel material, with high stiffness property. It is yet another object of the present invention to provide an improved back pan design for photovoltaic concentrators of high concentration photovoltaic modules, whereby no supply chain constraint is encountered due to wider availability of raw material at reasonable price.
It is a further object of the present invention to provide a high concentration photovoltaic module incorporating at least an improved photovoltaic concentrator. It is yet another object of the present invention to provide a method of fabricating an improved photovoltaic concentrator for high concentration photovoltaic modules, having a cost-effective and technically sound back pan, whereby an effective thermal management is achieved in a technically sound and an economically significant manner.
How the foregoing objects are achieved and the other aspects of the present invention will be clear from the following description which Is purely by way of understanding and not by way of any sort of limitation.

SUMMARY OF THE INVENTION
Accordingly, the present invention provides an improved photovoltaic
concentrator for high concentration photovoltaic modules, having at least a back
pan adapted to accommodate the mechanical stresses acting on it, wherein said
back pan is predominantly made up of steel material of optimum thickness
whereby a cost-effective and technically sound back pan is achieved adapted to
facilitate thermal management in a technically sound and an economically
significant manner.
In accordance with preferred embodiments of the photovoltaic concentrator of the
present invention.
-said back pan has an aluminum coating along its inner surface.
-said back pan includes a steel sheet having a maximum 0.1 mm thick aluminum
coating.
-said back pan includes aluminum coated steel sheet.
-said back pan includes a 1,5mm thick steel material having a 0.1 mm thick aluminum coat, the ambient temperature being 35 degrees Celsius and maximum cell temperature being 61.57 degrees Celsius.
-said back pan includes a 1.2mm thick steel material having a 0.1 mm thick aluminum coat, the ambient temperature being 35 degrees Celsius and maximum cell temperature being 58.77 degrees Celsius.
-said back pan includes a 1.2mm thick steel material having a 0,013 mm thick aluminum coat ambient temperature being 35 degrees Celsius and maximum cell temperature being 61.55 degrees Celsius.
The present invention also provides a method of fabricating an improved photovoltaic concentrator for high concentration photovoltaic modules, having at least a back pan adapted to accommodate the mechanical stresses acting on it, said method including forming a back pan of steel material of optimum thickness

by sheet bending and welding operations whereby a cost-effective and technically sound back pan is achieved adapted to facilitate thermal management in a technically sound and an economically significant manner.
In accordance with a preferred embodiment of the aforesaid method, it includes coating said steel material in the form of sheet with an aluminum coating by thermal spray processing, the optimum thickness of the steel and aluminum layer to be applied being predetermined by Finite Element Stress and Thermal analysis.
The present invention also provides a photovoltaic module incorporating at least one photovoltaic concentrator as described hereinabove.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The nature and scope of the present invention will be better understood from the accompanying drawings, which are by way of illustration of some preferred embodiments and not by way of any sort of limitation. In the accompanying drawings,
Figure 1 illustrates a preferred embodiment of the back pan in accordance with the present invention.
Figure 2 illustrates a design of a conventional back pan.
Figure 3 illustrates another design of a conventional back pan.
Figure 4 illustrates another preferred embodiment of the back pan in accordance with the present invention.
Figure 5 illustrates another preferred embodiment of the back pan in accordance with the present invention.

Figure 6 illustrates another preferred embodiment of the back pan in accordance with the present invention.
Figure 7 illustrates another design of a conventional back pan in accordance with the present invention.
Figure 8 illustrates another preferred embodiment of the back pan in accordance with the present Invention.
BRIEF DESCRIPTION OF THE INVENTION
The following describes some preferred embodiments of the present invention, which are purely for the sake of understanding the performance of the invention, and not by way of any sort of limitation.
As stated before, traditionally, the back panel of photovoltaic concentrators comprises 2.5 mm thickness of aluminum alloy. Aluminum is selected mainly, for its low weight and high thermal conductivity for heat transfer, the main objective being effective thermal management. Aluminum also has high coefficient of thermal expansion, which causes significant self contraction and expansion, due to rise and fall of the environment temperature. However, aluminum alloy is expensive as stated before and is not as widely available as steel. In general, an aluminum back pan weighs about 9.8Kgs and its cost is Rs 160 to 180 per Kg. Figures 2, 3 and 7 Illustrate examples of conventional back pan designs for photovoltaic concentrators. Figure 3 illustrates 2.5 mm thick aluminum back pan, ambient temperature being 35 degrees Celsius and maximum cell temperature being 60.65 degrees Celsius, Figure 7 illustrates that the conventional 2.5mm thick aluminum back pan has undergone displacement due to dead weight, the maximum displacement being 0.0348mm.
The existing aluminum back pan, which apply 2.5 mm thick aluminum alloy sheet, is formed using a sheet metal forming process. The back pan has three steel stiffner bars, suitably located to keep the strain within the permissible limits. The aluminum receives heat from the heat spreader and spreads it over a large

area from which the heat is transferred by convective heat flow. The back pan is so designed such that the mechanical stresses acting on the back pan is accommodated by the thickness of aluminum sheet and the disposition of the three steel stiffners.
The present invention aims at providing a cost-effective innovative material or material combinations for substituting the present aluminum alloy back pan. It suggests a cost effective solution, for thermal management.
The object of the present invention is to come up with a cost-effective innovative
material or material combinations for substituting the present aluminum alloy
back pan.
The present design uses steel as the material of construction.
For that purpose, some of the important characteristics of aluminum and steel
were analyzed and the results obtained are as follows:
Density (gm/cc): 2.7(AI) and 7.85(Steel)
Modulus (Gpa): 68(AI) and 200{Steel)
Thermal conductivity (W/mK): 200
The above results clearly corroborate the suitability of steel for its application in
the manufacture of back pans of photovoltaic concentrators of high concentration
photovoltaic modules, in as much as the issue of achieving an effective thermal
management, in a technically sound and an economically significant manner is
concerned.
Preferably, in order to facilitate heat transfer, the inner surface of the back pan is
provided with an aluminum coating. The aluminum coating helps to spread heat
over the large area before natural air cooling takes over by convective heat
transfer. The optimum thickness of the steel and aluminum layer is deciphered by
Finite Element Stress and Thermal analysis. There may be several options, such
as using a steel sheet which is provided with 0.1 mm thick aluminum coating by
the thermal spray process. Alternatively, an aluminum coated steel sheet may be
applied. Steel is of course more weldable than aluminum and the back pan may
be manufactured by sheet bending and welding operations.

Figure 1 illustrates a back pan, in accordance with the present invention. Figure 4 illustrates a back pan in accordance with the present invention, comprising a 1.5mm thick steel material having a 0.1 mm thick aluminum coat, the ambient temperature being 35 degrees Celsius and maximum cell temperature being 61.57 degrees Celsius,
Figure 5 illustrates a back pan in accordance with the present invention, comprising a 1.2mm thick steel material having a 0.1 mm thick aluminum coat, the ambient temperature being 35 degrees Celsius and maximum cell temperature being 58.77 degrees Celsius,
Figure 6 illustrates a back pan in accordance with the present invention, comprising a 1.2mm thick steel material having a 0.013 mm thick aluminum coat, the ambient temperature being 35 degrees Celsius and maximum cell temperature being 61.55 degrees Celsius,
Figure 8 Illustrates that the back pan in accordance with the present invention made up of 1.2mm thick steel material having 0.013mm thick aluminum coat, has undergone displacement due to dead weight, the maximum displacement being 0,0038031 mm.
On application of photovoltaic concentrators having back pans in accordance with the present invention, it has been thus found, that the back pan is cost-effective and technically sound and it facilitates such optical concentrators in accordance with the present invention, to provide an effective thermal management, in a technically sound and an economically significant manner. So, the present invention highlights on the application of aluminum coated steel or application of an aluminum coating on the steel substrate to improve the heat dissipation. The optimum thickness of the steel and aluminum layer is deciphered by Finite Element Stress and Thermal analysis. The technical advancement and economic significance achieved by the present invention were hitherto not known and not conceived by persons skilled in the art.

In a nutshell following are some of the vital advantages, which the photovoltaic concentrators in accordance with the present invention achieve,
1. The cost of manufacturing back pans is substantially reduced without compromising on the mechanical and thermal stresses.
2. Thermal management is achieved with greater degree of precision.
3. A cost-effective solution for ensuring the mechanical integrity and effective heat dissipation of thermal energy is achieved.
4. A robust back pan predominantly made of steel material with high stiffness property is achieved.
5. Supply chain constraint is permanently removed because of wider availability of raw materials.
The present invention has been described with reference to some drawings and preferred embodiments, purely for the sake of understanding and not by way of any limitation and the present invention includes all legitimate developments within the scope of what has been described hereinbefore and what has been claimed hereinafter.

WE CLAIM
1. An improved photovoltaic concentrator for high concentration photovoltaic modules, having at least a back pan adapted to accommodate the mechanical stresses acting on it, wherein said back pan is predominantly made up of steel material of optimum thickness whereby a cost-effective and technically sound back pan is achieved adapted to facilitate thermal management in a technically sound and an economically significant manner.
2. The improved photovoltaic concentrator as claimed in claim 1 wherein said back pan has an aluminum coating along its inner surface.
3. The improved photovoltaic concentrator as claimed in claim 1 wherein said back pan includes a steel sheet having a maximum 0.1 mm thick aluminum coating.
4. The improved photovoltaic concentrator as claimed in claim 1 wherein said
back pan includes aluminum coated steel sheet.
5.The improved photovoltaic concentrator as claimed in claim 3 wherein said back pan includes a 1.5mm thick steel material having a 0.1 mm thick aluminum coat, the ambient temperature being 35 degrees Celsius and maximum cell temperature being 61.57 degrees Celsius.
6. The improved photovoltaic concentrator as claimed in claim 3 wherein said back pan includes a 1.2mm thick steel material having a 0.1 mm thick aluminum coat, the ambient temperature being 35 degrees Celsius and maximum cell temperature being 58.77 degrees Celsius.
7. The improved photovoltaic concentrator as claimed in claim 3 wherein said back pan includes a 1.2mm thick steel material having a 0.013 mm thick aluminum coat, ambient temperature being 35 degrees Celsius and maximum cell temperature being 61.55 degrees Celsius.

8. A method of fabricating an Improved photovoltaic concentrator for high
concentration photovoltaic modules, having at least a back pan adapted to
accommodate the mechanical stresses acting on It, said method including
forming a back pan of steel material of optimum thickness by sheet bending and
welding operations whereby a cost-effective and technically sound back pan is
achieved adapted to facilitate thermal management in a technically sound and an
economically significant manner.
9. The method of fabricating an improved photovoltaic concentrator for high
concentration photovoltaic modules as claimed in claim 8 further comprising
coating said steel material in the form of sheet with an aluminum coating by
thermal spray processing ,the optimum thickness of the steel and aluminum layer
to be applied being predetermined by Finite Element Stress and Thermal
analysis.
10. A photovoltaic module incorporating at least one photovoltaic concentrator as
claimed in any one of the claims 1 to 7.