Abstract:
A planar concentrator solar power module has a planar base, an aligned array of linear photovoltaic cell circuits on the base and an array of linear Fresnel lenses or linear mirrors for directing focused solar radiation on the aligned array of linear photovoltaic cell circuits. The cell circuits are mounted on a back panel which may be a metal back plate. The module includes a voltage stand-off layer and heat spreader layer. The cell circuit array may include multiple sets of cells formed by dividing planar silicon cells. The cell circuit area is less than a total area of the module. Each linear lens or linear mirror has a length greater than a length of the adjacent cell circuit. The circuit backplate is encapsulated by lamination for weather protection. The planar module is generally rectangular with alternating rows of linear cell circuits and linear lenses or linear mirrors.

Description:
[0001]     This application claims the benefit of U.S. Provisional Application No. 60/608,517 filed Sep. 10, 2004, which is incorporated herein by reference in its entirety.  
         [0002]     Co-pending U.S. application Ser. No. 10/209,900, filed Aug. 2, 2002, which claims benefit of U.S. Provisional application No. 60/374,808 filed Apr. 24, 2002 and U.S. Provisional Application No. 60/391,122 filed Jun. 25, 2002, are all incorporated herein by reference in each of their entireties.  
         [0003]     WO 2004/001859 A1 publication of PCT/US03/19524 is also incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0004]     Solar concentrators require very high investments to scale up production of a new concentrator cell. The investment required for manufacturing scale-up versions of a new cell is prohibitive. Another problem that needs to be solved is the cell-interconnect problem.  
         [0005]     There is a need for a solar concentrator module that is a retrofit for a planar module and that is easier and cheaper to make. The business infrastructure for trackers and lenses should already be in-place. The heat load should be easily manageable. Investment requirements should be manageable and it should not threaten existing cell suppliers. Cells to be used should be available with very minor changes relative to planar cells. Therefore, low cost cells should be available from today&#39;s cell suppliers. Finally, it should be usable in early existing markets in order to allow early positive cash flow.  
         [0006]     The demand for solar photovoltaic (PV) cells and modules has far outstripped PV cell supply.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention provides a 3-sun mirror module design that uses ⅓ the cells to triple module production at lower cost.  
         [0008]     A problem for concentrated sunlight PV systems has been the requirement for investment in special cell and module manufacturing facilities. The new concentrator module uses existing planar cells. Standard 125 mm×125 mm SunPower A300 cells are cut into thirds. The new module design uses standard circuit laminant fabrication procedures and equipment. A thin aluminum sheet is added at the back of the laminant for heat spreading. While a standard planar module contains rows of 125 mm×125 mm cells, the new concentration modules have rows of one-third cells. Each row is 41.7 mm wide. Linear mirrors with triangular cross sections are located between the cell rows. The mirror facets deflect the sun&#39;s rays down to the cell rows. The result is a 3-sun concentrator module. Since mirrors are over ten times cheaper than expensive single crystal cell material, these 3-sun modules can be made at half the cost of today&#39;s solar PV modules.  
         [0009]     These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the claims and the drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1A  is a perspective view of an assembled Planar Solar Cell Power Module.  
         [0011]      FIG. 1B  shows a cross section through the planar solar concentrator power module.  
         [0012]      FIG. 1C  shows a blow up section from  FIG. 1B  with a single lens and circuit element in more detail.  
         [0013]      FIG. 2A  shows a module with an exemplary laminar layer sequence  
         [0014]      FIG. 2B  shows a standard 1-sun module layer sequence.  
         [0015]      FIG. 2C  shows a mirror module layer sequence adding heat-spreader.  
         [0016]      FIG. 2D  shows standard 1-sun module laminant structure.  
         [0017]      FIG. 2E  shows a 3-sun module laminant structure.  
         [0018]      FIG. 3A  is a front view of a 1-sun cell.  
         [0019]      FIG. 3B  is a front view of a 1-sun cell cut into halves.  
         [0020]      FIG. 3C  is a back view of a 1-sun cell.  
         [0021]      FIG. 3D  is a back view of a 1-sun cell cut into thirds.  
         [0022]      FIG. 4A  is a back view of a triplet string with third cells.  
         [0023]      FIG. 4B  is a front view of the triplet string with third cells.  
         [0024]      FIG. 5A  is a front view of a laminant 4×9 cell array.  
         [0025]      FIG. 5B  is a back view of a laminant 4×9 cell array with an aluminum sheet heat spreader with slits or grooves.  
         [0026]      FIG. 6A  is an edge view of a mirror with two facets on each side.  
         [0027]      FIG. 6B  is a perspective view of the mirror shown in  FIG. 6A .  
         [0028]      FIG. 6C  is an edge view of an end mirror.  
         [0029]      FIG. 6D  is a perspective view of the mirror shown in  FIG. 6C .  
         [0030]      FIG. 7A  is a perspective view of a mirror array with end clips.  
         [0031]      FIG. 7B  is a perspective detail of the mirror array with end clips shown in  FIG. 7A .  
         [0032]      FIG. 7C  is a front view of the mirror array shown in  FIG. 7A .  
         [0033]      FIG. 7D  is an edge view of the mirror array with end clips shown in  FIGS. 7A, 7B  and  7 C.  
         [0034]      FIG. 8A  is a front view of the mirror module with the one-third photovoltaic cells mounted between the mirrors.  
         [0035]      FIG. 8B  is an edge view of the mirror module shown in  FIG. 8A .  
         [0036]      FIG. 8C  is a back view of the mirror module showing the aluminum sheet heat spreader.  
         [0037]      FIG. 9  shows a perspective of the two-faceted mirrors used with the one-third cells in a power module.  
         [0038]      FIG. 10  shows a top view of two planar cells wired in series.  
         [0039]      FIG. 11  shows a top view of two planar cells cut in half and operated at 2× concentration using mirrors.  
         [0040]      FIG. 12  shows an end view of the two planar cells cut in half and operated at 2× concentration using mirrors shown in  FIG. 10 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0041]     A photograph of the 2× mirror modules  10  is shown in  FIG. 1A .  
         [0042]      FIG. 1B  shows a cross section through a planar solar concentrator power module  1 . The cross section is perpendicular to the focal lines produced by the lenses and perpendicular to the circuit length dimension.  FIG. 1C  shows a blow up section from  FIG. 1B  showing a single lens  2  and circuit element  4  in more detail. The preferred planar concentrator solar module consists of a back panel of metal sheet  6  upon which linear silicon cell circuits  7  are mounted. In the exemplary embodiment depicted, for example, a metal frame  9 , for example aluminum frame, surrounds the module  1  with the cells  4  of the cell circuits  7  mounted on the back panel  6 . A lens array  3  of, for example, Fresnel lenses  5  is mounted on a glass front sheet  8  forming the front side of the planar concentrator solar module  1 . The array  3  of linear Fresnel lenses  5  produces lines of focused solar radiation that fall on an aligned array of linear photovoltaic power circuits. Bus  53  is provided on an edge of the cell circuit.  
         [0043]      FIG. 2A  shows an exemplary module  20  with a laminar layer sequence in which the layers may be sequentially arranged as follows: Glass substrate  11 , first EVA  14 , cell row(s)  12 , row spacer  13 , second EVA  15 , PET  16 , third EVA  17 , metal layer  18  (for example, aluminum heat spreader), and stress relief slit/slot/groove  19 .  
         [0044]      FIGS. 2B and 2D  show the layer sequence for a typical 1-sun module. Shown in  FIGS. 2C and 2E  is the addition of the heat spreader layer sequence employed when making the mirror modules.  
         [0045]      FIGS. 2B and 2D  show a standard 1-sun module layer sequence photovoltaic cell array  20  laminated between upper and lower EVA sheets  21 ,  23  with a glass cover layer  25  on the top and a Tedlar/TPT sheet layer  27  for a back  29 .  
         [0046]      FIGS. 2C and 2E  show a mirror module layer sequence adding heat-spreader  31 , with photo voltaic arrays  30  divided and laminated between upper and lower EVA sheets  21 ,  23  with a glass cover layer  25  on the top and a Tedlar sheet layer  27 . A heat spreader layer  31 , such as but not limited to aluminum sheet, is attached with, for example, an adhesive layer  33  to the Tedlar/TPT sheet layer  27 .  
         [0047]      FIG. 3A  is a back view of a 1-sun cell  37 .  FIG. 3B  is a back view of a 1-sun cell cut into halves  39 .  
         [0048]     The exemplary 3× mirror-module is described herein.  FIGS. 3C through 8C  describe this 3× embodiment in detail. This 3× embodiment reduces the module cost by reducing further the amount of single-crystal silicon cell material required.  
         [0049]     Recently, SunPower Corp has started to manufacture a new type of 1-sun cell. That cell  40  is shown in  FIG. 3C . Its metal grid  41  differs from earlier designs. This SunPower cell has both n and p collection grids  43 ,  45  on its back  47 . The n grid lines  43  run to an n bus  53  on one cell edge  51 . The p grid lines  45  run to a p bus  55  on the opposite edge  57 . Cutting those cells into thirds  50  is shown in  FIG. 3D .  
         [0050]     Both sets of grid lines  43 ,  45  are plated to a thickness that allows good current flow even at 3-sun current levels. That has been demonstrated via measurements with the following favorable results. 
 
Suns=2.998; Isc=5.755 A; Voc=0.703 V; FF=0.717; Pmax=2.9 W
 
Efficiency=19.46%. 
 
         [0051]     The one-third cells  50  are series connected  60  with connectors  61  between busses  53 ,  55  as shown in  FIGS. 4A  and B. Then the series connected cells  50  are laminated  63  into circuit assembles  65  as shown in  FIG. 5A  using the layer sequence shown in  FIG. 2B  and incorporating the metal heat spreader  31  on the circuit backside  29 . An important detail to note in  FIG. 5B  is that the 0.5 mm to 0.75 mm thick aluminum sheet heat spreader  31  has stress relief slits or grooves  35  to accommodate the difference in thermal expansion coefficient between the heat spreader sheet  31  and the other silicon and glass laminant materials shown in  FIGS. 2A and 2B . The slits or grooves  35  run from the cells  50  toward the mirrors so as not to interfere with the heat flow direction.  
         [0052]     We also note that the stress relief slits  35  can be discontinuous as shown in  FIG. 5B  such that the heat spreader sheet  31  remains as one large sheet or, alternatively, the stress relief slits can be continuous such that that heat spreader then consists of smaller rectangular tiles arranged in a pattern to form the heat spreader sheet  31 .  
         [0053]      FIG. 5A  shows a thirty-six cell circuit  65  with four rows  69  containing nine cells  50  each. The cells are approximately 5″ long each. This particular module has dimensions of approximately 20″ by 47″, preferably 21″ by 47″, and represents one of the popular sizes for 1-sun planar modules. Another popular size might contain seventy-two cells  50  with six rows  69  of twelve cells  50  each and have dimensions of approximately 30″ by 62″, preferably 31″ by 62″. Alternatively, there can be twelve rows  69  of six cells  50 . A large number of size variations are possible.  
         [0054]     FIGS.  6 A-D show the mirror constructions  71  for the 3× module  80 . Note that in contrast to the 2× design, these mirrors  73  have two facets  75 ,  77  per face  79 . The end mirrors  72  shown in  FIGS. 6C  and D have only one face  74  with two facets  75  and  77 . The mirrors can be folded sheet metal, silvered glass mounted onto plastic extrusions, or silvered tape coatings rolled onto aluminum sheets prior to bending into the proper shapes. Several different mirror types and coatings are viable.  
         [0055]     The mirrors  73  are then tied together in an array  70  using end clips  78  as shown in FIGS.  7 A-D. Finally, the mirror array  70  is screwed down onto a metal frame  83  that surrounds the laminated circuit as shown in FIGS.  8 A-D, completing the 3× mirror module. This feature allows for mirror replacement if required over time.  
         [0056]     The planar solar concentrator power module array  80  shown in  FIG. 9  replaces expensive single crystal cell areas with inexpensive mirror areas to reduce the cost of solar generated electricity.  
         [0057]      FIG. 9  shows a power module  80  bearing an array  70  of two-faceted linear mirrors with generally triangular cross sections located between the cell rows  69 . The mirror facets  75 ,  77  deflect the sun&#39;s rays down to the rows  69  of one-third cells  50 . An embodiment is shown in  FIGS. 10, 11 , and  12 .  
         [0058]      FIG. 10  shows two series connected planar photovoltaic cells  90  which can be centrally divided along line  91 . The grid lines  93  and  95  are connected to busses  103 ,  105 , and the busses are connected in series by extended connectors  107  cutting the cells  90  along line  91  forms the series-connected planar half cells  110  shown in  FIG. 11 .  FIG. 11  shows a solar concentrator power module  120  consisting of rows  121  of half solar cells  110  separated by rows  133  of mirrors  135 . The mirrors deflect sunlight down to the cells. The cells are mounted on a metal sheet heat spreader  131 . The cell and mirror array sunlight-collection-area is the same as the heat spreader sheet area. As shown in  FIG. 12  the heat spreader  131  moves heat from under the cells  110  to the area underneath the mirrors  135  for uniform heat removal by contact with air.  
         [0059]      FIG. 10  shows typical 1-sun silicon cells  90  available in high volume production today. The cell shown has a metal collection grid on its front side with grid lines  93 ,  95  connected to two current busing lines  103 , 105 . In one embodiment of the planar solar concentrator power module depicted in  FIG. 11 , the cells  90  are cut in half. Current busing lines  103 , 105  remain on each half as shown in  FIG. 11 . The half-cells  110  are separated by intermediate rows  133  of mirrors  135  as shown in  FIGS. 11 and 12 . The result is a 2× mirror-module  120  with double the power output for the same amount of silicon cell area shown in  FIG. 10 . A perspective view of the assembly of  FIG. 12  is shown in  FIG. 10 . Preferably, the width of the row spacer sets the cell row spacing equal to the mirror spacing which is set by the slots/grooves in the end clip. The cell row spacer sets the width between cells equal to the width between mirrors to within a tolerance of about±2 mm.  
         [0060]     Some specific features of the product include stress relief slits or grooves  35  in heat spreader sheet  31 , multi faceted mirrors  73 , replaceable mirrors  73 , SunPower cell segments  50 , and 3× module design  80 .  
         [0061]     This invention describes a solar photovoltaic module preferably for use on earth, though other uses are within the scope of this invention. This new photovoltaic module consists of a large weather proofed laminated PV-cell circuit containing periodic alternating rows of cells separated by row spacers. Said laminated circuit has a thin metal heat spreader on its backside for heat removal to the ambient air. An edge frame surrounds said laminated circuit and supports an array of linear concentrating elements above said laminated circuit. The laminated circuit and the linear sunlight concentrating elements are aligned such that sunlight is directed to the linear cell rows in the laminated circuit.  
         [0062]     The object of this invention is a dramatically lower cost photovoltaic module than today&#39;s most prevalent 1-sun solar photovoltaic module. Relative to today&#39;s PV modules, the invention includes three changes to accomplish this objective.  
         [0063]     The first step in accomplishing this low cost objective is to use the same silicon single crystal or cast multi-crystalline cells that are in high volume production today. These cells are simply cut into halves as shown in  FIG. 3A-3B  or thirds as shown in  FIGS. 3C-3D , or fourths, etc., as is evidently possible from  FIG. 3A  allowing use of one-half, one-third, etc., as much of the expensive cell material in our new module.  
         [0064]     The second key to our cost reduction strategy is to use the existing low-cost terrestrial module lamination process because it yields modules with proven durability. This produces cell-circuits that are dramatically different than those used on space satellites. There is typically a large glass plate on top of the laminated circuit that can be as large as 1.5 square meters and much too thick and heavy for use in space. It prevents corrosion of the circuit in the wet terrestrial environment.  
         [0065]     Starting with this low-cost terrestrial lamination concept, we then make some important changes in this lamination as shown in  FIGS. 2A, 2B , and  2 C.  FIG. 2B  shows the standard 1-sun laminated circuit and  FIGS. 2A and 2C  show the three changes we make for our new laminated circuit. Our first change is to use rows of half-cells or third-cells, etc., with row spacers ( FIG. 2A ) between the rows to set repeatable well-defined spaces between the rows.  
         [0066]     As we plan to concentrate the solar energy onto the cell rows, our second change is to add a thin metal heat spreader to the backside of the laminated circuit as shown in  FIGS. 2A and 2C . This metal sheet spreads the heat uniformly for air cooling from the backside of said laminated circuit. Since laminations are done with flat parts, finned heat sinks are not appropriate or necessary. A flat sheet heat spreader is sufficient for the low solar concentrations described here.  
         [0067]     The third change is to use thinner insulating layers between the back of the cells and the metal heat spreader while still maintaining the required voltage standoff. Experimentation has shown that these changes in the lamination are non-trivial. For example, because the aluminum sheet thermal expansion coefficient is much larger than that of the glass-cover plate, we found that the laminated circuit will bow unless we add stress relief slots in the aluminum sheet as shown in  FIG. 2A . However, given these stress relief slots, we have now shown that our new laminated circuits pass the standard terrestrial qualification tests that include survival through large numbers of thermal cycles.  
         [0068]     Given the new laminated circuit as described, various low cost linear solar concentrating elements can be used. This is the third key to our low cost module strategy since these concentrating elements are much cheaper than the solar cell material we have saved in the fabrication of our new laminated circuit. These concentrating elements can include either a linear Fresnel lens array or linear mirror funnels as shown in the figures.  
         [0069]     While the invention has been described with respect to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention, which is described in the following claims.