Solar cell assembly and fabrication of solar cell panels utilizing same

An assembly comprising a plurality of solar cells arrayed on and adhesively bonded to a sheet of non-woven heat-actuatable fabric is provided which offers significant advantages in the fabrication of solar cell panels, particularly fabrication of panels by vacuum lamination techniques.

FIELD OF THE INVENTION 
This invention relates generally to a solar cell assembly particularly 
useful in the fabrication of solar cell panels. 
BACKGROUND OF THE INVENTION 
In general, a solar cell panel consists of individual solar cells 
electrically interconnected and housed in a protective and supporting 
enclosure. 
Typically, the individual solar cells of the module are arranged in columns 
and rows and are interconnected by interconnector means which are 
positioned so as to connect the cells in the requisite series and/or 
parallel circuit arrangement. The circuit arrangement, of course, depends 
upon the desired output voltage and current at the panel peak power point. 
A protective enclosure or housing is used in order to protect the solar 
cells and the interconnector means from degrading as a result of 
environmental conditions such as humidity, pollutants, wind, snow, ice 
damage and the like. Typically, the housing consists of a rigid support 
structure on which solar cells are mounted and a top light transparent 
silicone encapsulant through which solar radiation passes before impinging 
upon the active solar cells. Generally a protective glass cover sheet is 
applied over the encapsulant. More recently, there has been a tendency to 
mount an array of solar cells to the bottom surface of an optically clear 
superstrate not only to protect the solar cell array against environmental 
hazards, but also to serve as the structural support for the solar cell 
array. The arrayed and so mounted cells also are encapsulated in a 
protective encapsulant at least on the underside thereof. 
In encapsulating solar cell arrays, one of two major methods typically is 
employed. In one method, a liquid encapsulant is poured into a mold or 
pumped into a cavity where it is cured. In a second method, sheets of 
encapsulant material are layed up with a solar cell array into an assembly 
which then is vacuum laminated under appropriate temperature conditions 
resulting in the fusing of the encapsulant into a single optically clear 
layer which encompasses the solar cell array and which layer also is 
bonded to any support material that is employed in forming the solar cell 
panel. In either technique, it is particularly important to assure that 
the encapsulant is free of air bubbles since panel defects such as 
delamination and cell cracking often are associated with bubbles present 
in the encapsulant. 
As will be appreciated, bubble formation in the encapsulant is more 
prevalent when solar panels are fabricated by the vacuum lamination method 
and numerous techniques have been devised in an attempt to provide for 
complete removal of air prior to the lamination of the sheets of 
encapsulant. For example, fiberglass scrim and similar sheets of woven 
fabrics frequently are used in vacuum lamination processes to hold the 
sheets of encapsulant apart during the evacuation step and prior to the 
fusing of the sheets of encapsulant. 
Another problem in fabricating solar cell panels is to assure precise 
alignment of the individual solar cells in the array. One standard 
technique for forming a panel begins with arranging individual solar cells 
in the appropriate rows and columns on an appropriate alignment or spacing 
jig. Next the metallic interconnectors are attached to the cell electrodes 
by soldering or welding. In typical solar cells, the interconnector 
extends from the top electrode of one cell to the bottom electrode of the 
next adjacent cell. Rows of adjacent cells, of course, are similarly 
connected. Consequently, there is a lot of handling and movement of 
individual cells in order to properly index or position the cells and 
complete the soldering and welding. This technique is described, for 
example, in U.S. Pat. No. 4,132,570. 
In U.S. Pat. No. 3,565,719, a method of forming a solar panel is disclosed 
in which the cells are arranged in a pre-alignment fixture having cavities 
therein, and the so-arrayed cells are thereafter bonded to a support 
structure and the pre-alignment fixture is removed. 
In U.S. Pat. No. 3,780,424, a process for making a solar panel is described 
in which an adhesive material is used to bond cells in permanent alignment 
to a substrate. 
In U.S. Pat. No. 4,154,998, yet another technique is disclosed for 
preparing a solar cell panel in which induction heating is used to fuse a 
plurality of silicon solar cells to their interconnectors and substrate. 
Notwithstanding the foregoing advantages, there remains a need for a 
simple, inexpensive technique for precisely aligning a plurality of 
silicon solar cells in an array which can be handled easily and used in 
numerous different types of solar panel structures rather than being 
limited, for example, to panels having superstrates or panels having 
substrates. 
SUMMARY OF THE INVENTION 
In its simplest sense, the present invention comprises a sheet of 
non-woven, thermoplastic, heat-actuatable fabric having a plurality of 
solar cells arrayed on and adhesively bonded to the top surface of the 
sheet material. 
The assembly is readily prepared by placing a sheet of non-woven, 
thermoplastic, heat-actuatable fabric on a work surface over a diagram of 
the desired cell layout. The sheet material is sufficiently thin and the 
openings between the fibers sufficiently wide that at least portions of 
the diagram below the sheet are visible, thereby permitting proper 
location of solar cells on the sheet. The individual solar cells, each 
having an interconnector attached to the bottom of the cell, are placed in 
their appropriate position on the sheet material in accordance with the 
cell layout. Then the cells are interconnected by soldering. Since the 
sheet material is heat actuatable, as the solar cells are soldered, the 
cell and the interconnector have their temperature raised sufficiently so 
that the sheet material fuses to the cell, thereby adhesively bonding the 
cell in a fixed position on the sheet. Thereafter the assembly can be used 
in preparing a solar cell panel. 
These and other embodiments of the invention are described with 
particularity in the detailed description.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, a solar cell assembly 10 in accordance with the 
present invention is shown in a fragmentary perspective view. As can be 
seen, the solar cell assembly 10 includes a plurality of solar cells 11 
arrayed upon and adhesively bonded to the top surface of a non-woven, 
heat-actuatable sheet material 12. Preferably the sheet material 12 will 
be of the same general dimensions of any solar cell panel which is to be 
formed from the solar cell assembly 10. The cells are provided with metal 
interconnectors 14. The interconnectors are attached to the cells, for 
example by soldering or welding, to provide the desired series and/or 
parallel arrangement for the array. As can be seen, the cells have a bus 
bar 15 and current collectors 16 on the top surface of the cell. The 
interconnectors 14 connect the bus bar on the top surface of one cell to 
the electrode (not visible) on the bottom surface of an adjacent cell. 
In forming the solar cell assembly of FIG. 1, the heat actuatable sheet 
material 12 of the requisite size is placed over a diagram 17 of the 
desired cell layout. The heat-actuatable sheet material suitable in the 
practice of the present invention preferably is sufficiently transparent 
when placed in contact with the cell layout diagram so that the desired 
position of the cells can be seen through the sheet material 12. 
Additionally, the sheet material preferably is thermally actuatable at 
temperatures generally in the range of about 90.degree. C. to about 
150.degree. C., although sheet material which is thermally actuatable at 
lower temperatures may be employed. In general, the heat-actuatable sheet 
material is formed from synthetic fibers such as polyester, polyamide and 
acrylic fibers which have a heat-actuatable adhesive on the surface 
thereof or the sheet material is formed from fibers or filaments of 
thermoplastic adhesive material. Such heat-actuatable sheet material is 
commercially available. Indeed, the commercially available heat-actuatable 
sheet materials are generally white in appearance and consequently, in an 
alternate embodiment of the present invention, the cell layout diagram is 
printed on the sheet material 12. 
After placing the sheet material 12 over the cell layout (or providing a 
sheet material with the cell diagram printed thereon), the individual 
cells are aligned in their proper position on top of the sheet material in 
accordance with the cell layout diagram 17. Since the non-woven sheet 
material has a slightly rough surface which will tend to grab any of the 
defects or roughness on the bottom of the solar cell placed upon it, the 
cells do not slide around or move about once they are placed in position 
on the surface of the sheet layer material 12. 
Additionally, as can be noted in FIG. 2, the individual solar cells 11 each 
have one end of the metal interconnector 14 soldered to the bottom 
electrode on solar cell 11. Consequently, the next step in preparing the 
solar cell assembly of the present invention is to solder the 
interconnector 14 of one cell to the top electrode or bus bar 15 of the 
next adjacent cell. During the soldering process, a portion of each cell 
being soldered gets sufficiently hot to cause the surface of sheet 
material 12 to fuse and adhere to the bottom of the solar cell. 
Consequently, each of the solar cells after they have been soldered to the 
next adjacent cell becomes permanently fixed in the position on the sheet 
material 12. After the cells are soldered one to the other, the entire 
assembly can be lifted and moved about and washed and dried just by 
picking it up at one of the ends of the sheet material. 
Referring now to FIG. 3, a solar panel utilizing the solar cell assembly 10 
of the present invention is fabricated by preparing a laminate including 
the support for the solar cell array. In the embodiment shown in FIG. 3, 
the support is a superstrate 18 made of a light transparent rigid sheet 
material such as glass. In order to bond the solar cell assembly 10 to the 
top support structure, a sheet of clear light transparent thermoplastic 
film 19 is interposed between the superstrate 18 and the solar cell 
assembly 10. Standard light transparent thermoplastic film materials used 
in the fabrication of solar cell panels can be employed in this invention. 
Thus, sheets of polyethylene vinylacetate or polyvinylbutyrate are 
eminently suitable in the practice of the present invention. In the 
laminate shown in FIG. 3, a backing sheet of thermoplastic film material 
20 is also provided so as to provide a protective back layer for the solar 
cells against exposure to the environmental atmosphere and hazards. 
Following the normal vacuum bag processing techniques, the assembly is 
placed in a vacuum bag and the bag evacuated under heat, thereby resulting 
in the requisite pressure to fuse the various components of the laminate 
into a panel structure. 
Included in the assembly as shown in FIG. 3 are strips of non-woven 
thermoplastic material 21 which are arranged linearly in the longitudinal 
alleys between the rows of individual solar cells. One of the advantages 
of placing such a non-woven sheet material in the longitudinal alleyways 
between the rows of individual solar cells is to permit adequate 
evacuation of the laminate prior to complete fusion of the thermoplastic 
material. Hence, air bubbles and the like are avoided, thereby enhancing 
the quality of the panel made with the solar assembly 10. 
Optionally a bottom layer of white sheet material (not shown) can also be 
applied to the assembly so that light which is incident on the areas 
between the individual solar cells will be scattered by the white 
diffusive surface and reflected upwardly to the top of the panel and 
internally reflected downwardly to the top of the individual solar cells 
(a similar laminate is shown in FIG. 4 with the exception that the rigid 
support structure 22 is provided for supporting the solar cells in the 
panel). This rigid support structure can be a white polyester material 
similar to that disclosed and claimed, for example, in U.S. Pat. No. 
4,132,570. In this embodiment, then, there is shown the cell supported on 
substrate 22. Nonetheless, a top glass cover 23 is provided in order to 
protect the cells against environmental hazards resulting from wind, rain, 
hail, etc. The top protective cover typically will be glass; however, it 
need not be of the same strength as the glass layer 18 of the embodiment 
shown in FIG. 3. 
Among the advantages of the assembly of the present invention is that (1) 
individual solar cells may be strung in an appropriate array and the array 
moved without the need for expensive fixtures; (2) because the cells do 
not readily move when placed on the surface of the heat fusible sheet 
material, they can be strung in a very close spaced pattern; (3) after 
bonding the array of cells on the top surface of the sheet material, the 
cells can be easily washed and hung to dry, thereby facilitating the 
removal of the flux used in soldering the cells; (4) cell spacing is 
maintained through the laminating process; and (5) the entire assembly can 
be primed, for example, by dipping the entire array thus insuring perfect 
coverage of all the elements of the assembly. These and other advantages 
should be readily apparent although no intention is made to be limited to 
the specific embodiments outlined in the detailed description; but, 
rather, it is intended that many other changes and modifications may also 
be made without departing from the spirit and scope of the invention as 
set forth herein.