Solar module having reflector between cells

A photovoltaic module comprising an array of electrically interconnected photovoltaic cells disposed in a planar and mutually spaced relationship between a light-transparent front cover member in sheet form and a back sheet structure is provided with a novel light-reflecting means disposed between adjacent cells for reflecting light falling in the areas between cells back toward said transparent cover member for further internal reflection onto the solar cells. The light-reflecting comprises a flexible plastic film that has been embossed so as to have a plurality of small V-shaped grooves in its front surface, and a thin light-reflecting coating on said front surface, the portions of said coating along the sides of said grooves forming light-reflecting facets, said grooves being formed so that said facets will reflect light impinging thereon back into said transparent cover sheet with an angle of incidence greater than the critical angle, whereby substantially all of the reflected light will be internally reflected from said cover sheet back to said solar modules, thereby increasing the current output of the module.

FIELD OF THE INVENTION 
This invention relates to an improved solar cell module having reflector 
means designed to utilize light impinging on areas between the cells which 
would normally not be utilized in photoelectric conversion, thereby 
increasing the power output of the cell. 
BACKGROUND OF THE INVENTION 
Photovoltaic solar cells for directly converting radiant energy from the 
sun into electrical energy are well known. The manufacture of photovoltaic 
solar cells involves provision of flat semiconductor substrates having a 
shallow p-n junction adjacent one surface thereof (commonly called the 
"front surface"). Such substrates are often referred to as "solar cell 
wafers". A typical solar cell wafer may take the form of a rectangular 
EFG-grown polycrystalline silicon substrate of p-type conductivity having 
a thickness in the range of 0.010 to 0.018 inches and a p-n junction 
located about 0.3-0.5 microns from its front surface. Circular or square 
single crystal silicon substrates and rectangular cast polycrystalline 
silicon substrates also are commonly used to make solar cells. The solar 
cell wafers are converted to finished solar cells by providing them with 
electrical contacts (sometimes referred to as "electrodes") on both the 
front and rear sides of the semiconductor substrate, so as to permit 
recovery of an electrical current from the cells when they are exposed to 
solar radiation. These contacts are typically made of aluminum, silver, 
nickel or another metal or metal alloy. A common preferred arrangement is 
to provide silicon solar cells with rear contacts made of aluminum and 
front contacts made of silver. The contact on the front surface of the 
cell is generally in the form of a grid, comprising an array of narrow 
fingers and at least one elongate bus (commonly called a "bus bar") that 
intersects the fingers. The width and number of the fingers and bus bars 
are selected so as to maximize the output current. 
Further, to improve the conversion efficiency of the cell, it is accepted 
practice to form on the front surfaces of the solar cells an electrically 
non-conducting anti-reflection ("AR") coating that is transparent to solar 
radiation. In the case of silicon solar cells, the AR coating is often 
made of silicon nitride or an oxide of silicon or titanium. Typically the 
AR coating is about 800 Angstroms thick. The AR coating overlies and is 
bonded to those areas of the front surface of the cell that are not 
covered by the front contact, except that at least a portion of the front 
contact (usually a bus bar) is not covered with the AR coating, so as to 
permit making a soldered connection to that contact. 
Photovoltaic solar cells (e.g., silicon solar cells) are relatively small 
in size, typically measuring 2-4 inches on a side in the case of cells 
made from rectangular EFG-grown substrates, with the result that their 
power output also is small. Hence, industry practice is to combine a 
plurality of cells so as to form a physically integrated module with a 
correspondingly greater power output. Several solar modules may be 
connected together to form a larger array with a correspondingly greater 
power output. 
The usual practice is to form a module from two or more "strings" of solar 
cells, with each string consisting of a plurality of cells arranged in a 
straight row and electrically connected in series, and the several strings 
being arranged physically in parallel with one another so as to form an 
array of cells arranged in parallel rows and columns with spaces between 
adjacent cells. The several strings are electrically connected to one 
another in a selected parallel and/or series electrical circuit 
arrangement, according to voltage and current requirements. A common 
practice is to use solder coated copper wire, preferably in the form of a 
flat ribbon, to interconnect a plurality of cells in a string, with each 
ribbon being soldered to the front or back contact of a particular cell, 
e.g., by means of a suitable solder paste. 
For various reasons including convenience of manufacture and assembly, cost 
control, and protection of the individual cells and their 
interconnections, it has been common practice for such modules to have 
laminated structures. These laminated structures consist of front and back 
protective sheets, with at least the front sheet serving as a cover and 
being made of clear glass or a suitable plastic material that is 
transparent to solar radiation, and the back sheet serving as a support 
for the cells and being made of the same or a different material as the 
front sheet. Disposed between the front and back sheets so as to form a 
sandwich arrangement are the solar cells and a light-transparent polymer 
material that encapsulates the solar cells and is also bonded to the front 
and back sheets so as to physically seal off the cells. The laminated 
sandwich-style structure is designed to mechanically support the cells and 
also to protect the cells against damage due to environmental factors such 
as wind, snow, rain, ice, and solar radiation. The laminated structure 
typically is fitted into a metal frame which provides mechanical strength 
for the module, and facilitates combining it with other modules so as to 
form a larger array or solar panel that can be mounted to a support that 
is arranged to hold the array of cells at the proper angle to maximize 
reception of solar radiation. 
The art of making solar cells and combining them to make laminated modules 
is exemplified by the following U.S. Pat. Nos.: 4,751,191 (R. C. 
Gonsiorawski et al.); 5,074,920 (R. C. Gonsiorawski et al.), 5,118,362 (D. 
A. St. Angelo et al.); 5,178,685 (J. T. Borenstein et al.); 5,320,684 (J. 
Amick et al); and 5,478,402 (J. I. Hanoka). The teachings of those patents 
are incorporated herein by reference thereto. 
Unfortunately, when a plurality of cells are arrayed in a module, the total 
active surface area of the array (i.e., the active area of the front faces 
of the solar cells) is less than the total area exposed to radiation via 
the transparent front protective sheet. For the most part this is due to 
the fact that adjacent cells do not touch each other and also the cells at 
the periphery of the array may not extend fully to the outer edges of the 
front protective sheet. Consequently less than all of the solar radiation 
which is received by the module impinges on active solar cell areas, with 
the remainder of the received solar radiation impinging on any inactive 
areas that lie between the cells or border the entire array of cells. 
As noted in U.S. Pat. No. 4,235,643, issued Nov. 25, 1980 to James A. Amick 
for "Solar Cell Module", a number of techniques have been proposed for 
increasing the efficiency and effectiveness of solar cell modules by 
concentrating incident solar radiation onto active cell areas. For 
example, U.S. Pat. No. 2,904,612 describes a reflector-type device in 
which the land areas between the circular solar calls consist essentially 
of inverted intersecting frustums of cones circumscribing the cells. 
Another technique employed to enhance solar cell module output is the use 
of lenses. Thus U.S. Pat. No. 3,018,313 describes a solar cell module 
which has an array of lenses covering the module so as to concentrate the 
light impinging on the cover of the solar cell array to converge 
downwardly toward the active solar cell area. In U.S. Pat. No. 4,053,327, 
yet another light focusing arrangement is described wherein the cover of a 
solar cell module comprises a plurality of converging lenses arranged so 
as to direct the light incident on the module so that it does not fall on 
the grid lines of the front electrode of the solar cells in the array. 
The Amick patent discloses an improvement over such prior efforts which 
comprises providing between adjacent cells an optical medium having a 
plurality of light-reflective facets that are angularly disposed so as to 
define a plurality of grooves having a depth in the range of 0.001" to 
0.025", with the angle at the vertex formed by two mutually converging 
facets being between 110.degree. and 130.degree., preferably about 
120.degree., with the result that light impinging on those facets will be 
reflected back into the transparent front cover member at an angle .phi. 
greater than the critical angle, and then reflected again internally from 
the front surface of the cover member so as to impinge on the solar cells. 
The term "critical angle" refers to the largest value which the angle of 
incidence may have for a ray of light passing from a more dense optical 
medium to a less dense optical medium. If the angle of incidence .phi. 
exceeds the critical angle, the ray of light will not enter the less dense 
medium (e.g, air) but will be totally internally reflected back into the 
denser medium (e.g., the transparent cover sheet). 
Amick U.S. Pat. No. 4,235,643 suggests (in column 4) that the faceted 
region is substantially coplanar with the solar cells and preferably the 
vertical height of a facet will be equal to the thickness of the solar 
cell. In column 5 of the Amick patent it is stated that the grooves are 
machined or molded in the optical medium. 
Further information about the Amick invention is provided by the technical 
paper published by James A. Amick and William T. Kurth, "V-Groove Faceted 
Reflector For Enhanced Module Output", pp. 1376-1381, Record of IEEE 
Photovoltaic Specialists Conference--1981. In said article, the authors 
disclose that the faceted reflector was made of acrylic plastic and had a 
thin aluminum reflecting layer, with the repeat spacing (peak-to-peak 
spacing) of the facets being 0.070 inches. 
However, the Amick reflector invention was not a commercial success. A 
primary limitation of the Amick invention was the inability to provide a 
satisfactory reflector medium at an acceptable cost. 
Consequently, notwithstanding the advantages made in the recent years in 
increasing the energy conversion efficiency of solar cells, there still 
remains a very definite need for improving the ability of a solar cell 
module to capture and use available light energy and, more importantly, do 
so using a reflector medium that is relatively inexpensive to manufacture 
and is easy to use. 
OBJECTS AND SUMMARY OF THE INVENTION 
A primary object of the present invention is to provide an improved 
photovoltaic solar cell module having novel reflector means for increasing 
its power output. 
Another object of the present invention is to provide an improved solar 
cell module comprising a plurality of solar cells arrayed in rows and 
columns between first and second support sheets, at least one of said 
sheets being transparent to solar radiation, and novel flexible reflector 
means disposed between said cells for increasing the amount of radiation 
received by said cells through said transparent sheet. 
Still another object is to provide a module of the type described that 
comprises one or more concentrator members in the form of a thermoplastic 
film having a plurality of parallel grooves coated with a light-reflecting 
coating. 
Another object is to provide a method of improving a solar module by 
incorporation therein of a novel solar energy reflector that operates so 
as to cause an increase the module's output current. 
A further object is to provide an improved method of manufacturing a solar 
module. 
These and other objects and advantages of the invention are achieved by 
providing a novel photovoltaic module comprising an array of electrically 
interconnected photovoltaic cells disposed in a planar and mutually spaced 
relationship between a transparent front planar cover member in sheet form 
and a back support structure, with at least said front cover member being 
transparent to solar radiation, and a novel light-reflecting means 
disposed between adjacent cells for reflecting light falling in the area 
between cells back toward said transparent cover member for further 
internal reflection onto the solar cells. More specifically, the solar 
cell module of the present invention comprises a plurality of 
mutually-spaced solar cells arrayed in a planar arrangement of rows and 
columns on a planar surface of the back sheet structure, with areas of 
said planar surface between the solar cells being covered by a novel 
optically-reflective textured sheet material having a plurality of facets 
disposed in a predetermined angular relationship with respect to said 
cover member and each other, so that light impinging thereon through the 
front cover member will be reflected upwardly back to the transparent 
cover member and then backwards toward active areas of the cells. In 
accordance with this invention, the optically reflective textured sheet 
material has a thickness substantially less than the thickness of the 
solar cells and comprises (1) a substrate in the form of a thin and 
flexible thermoplastic film that has been embossed so as have a plurality 
of substantially flat-sided grooves of predetermined configuration, and 
(2) a light-reflecting coating on said substrate in the form of a metallic 
film (or a reflective film comprised of multiple dielectric layers, as 
further described hereinafter) that extends along said grooves and forms a 
plurality of discrete light-reflecting facets, said grooves having a 
geometry such that incident light normal to the solar cell module will be 
reflected from said facets back into said transparent planar cover member 
and the angle of incidence of such reflected lighter at said transparent 
cover member will be greater than the critical angle, whereby 
substantially all of said reflected light will be directed by further 
reflection from said transparent cover member back to said solar cells, 
thereby increasing the power output of the module. Preferably the 
light-reflecting coating is a thin film of a metal having a high 
reflectivity, e.g., silver and aluminum. 
In one preferred embodiment the optically reflective sheet material is 
formed with grooves running in a single direction, but pieces of said 
material are positioned in the spaces between cells so that the grooves 
extend in one direction between rows of cells and in a different direction 
between columns of said cells. Another embodiment is characterized by 
having (1) a sheet of said optically reflective material, with grooves all 
running parallel to one another, underlying all of the solar cells and 
extending across the spaces between the cells, and (2) strips of said same 
material disposed between rows (or columns) of said cells so that the 
grooves in said strips extend at a right angle to the grooves in said 
sheet underlying said cells. In other embodiments the textured material is 
made or arranged with grooves running in at least two different 
directions. Other embodiments, features and advantages of the invention 
will be apparent from the following specification and the drawings wherein 
like numerals are used throughout to identify like parts.

In the several drawings, the relative thicknesses of the plastic film and 
metal layer that make up the flexible light-reflective laminated material 
are exaggerated in relation to the other solar module components solely 
for convenience of illustration. 
FIGS. 1 and 2 illustrate a conventional solar cell module 2 comprising a 
plurality of rectangular solar cells 4. The kind of solar cells used in 
the module may vary. Preferably, but not necessarily, the module comprises 
silicon solar cells. Although not shown, it is to be understood that each 
solar cell comprises a front contact on its front surface in the form of a 
grid comprising an array of narrow, elongate parallel fingers 
interconnected by one or more bus bars, and a rear contact on its rear 
surface, with the cells made substantially as illustrated and described in 
said above-identified U.S. Pat. Nos. 4,751,191, 5,074,920, 5,118,362, 
5,178,683, 5,320,684 and 5,478,402. The module also comprises a back 
protector member in the form of a sheet or plate 6 that may be made of 
various materials and may be stiff or flexible. Preferably the back 
protector sheet 6 is an electrically insulating material such as glass, a 
plastic, a plastic reinforced with glass fibers or a wood particle board. 
A preferred back protector member is Tedlar.RTM.. The solar cells are 
arranged in parallel rows and columns and are interconnected by electrical 
leads 8 which usually are in the form of flat copper ribbons. The usual 
practice in making a solar module is to interconnect the cells in each row 
in series so as to form strings, and then connect the strings in series or 
in parallel, or in some series/parallel combination, according to the 
voltage and current requirements of electrical system into which the 
module is to be installed. Referring to FIG. 2, adjacent cells in a string 
are connected in series by soldering one end of a flexible copper ribbon 8 
to the back electrode of one solar cell and soldering the opposite end of 
the same ribbon to a bus bar of the front contact on the next succeeding 
solar cell. 
Overlying the cells is a stiff or rigid, planar light-transmitting and 
electrically non-conducting cover member 10 in sheet form that also 
functions as part of the cell support structure. Cover member 10 has a 
thickness in the range of about 1/8" to about 3/8", preferably at least 
about 1/4", and has an index of refraction between about 1.3 and 3.0. By 
way of example, cover member 10 may be made of glass or a suitable plastic 
such as a polycarbonate or an acrylic polymer. 
Interposed between back sheet 6 and transparent cover member 10 and 
surrounding the cells 4 and their electrical connector ribbons 8 is an 
encapsulant 14 which is made of suitable light-transparent, electrically 
non-conducting material. Preferably encapsulant 14 is the ethylene vinyl 
acetate copolymer known in the trade as "EVA", or an ionomer. A common 
practice is to introduce the encapsulant in the form of discrete sheets 
that are positioned below and on top of the array of solar cells, with 
those components in turn being sandwiched between the back sheet 6 and the 
cover member 10. Subsequently that sandwich is heated under vacuum, 
causing the encapsulant sheets to become liquified enough to flow around 
and encapsulate the cells and simultaneously fill any voids in the space 
between the front cover member and the rear support that may result from 
evacuation of air. On cooling the liquified encapsulant solidifies and is 
cured in situ to form a transparent solid matrix that envelops the cells 
and fully fills the space between the back sheet 6 and cover member 10 
that is not occupied by the mutually spaced cells and the components that 
form their electrical interconnections. The encapsulant adheres to the 
front and back sheets 6 and 10 so as to form a laminated subassembly. 
Regardless of how the laminated subassembly is made, it usually is provided 
with and secured to a surrounding frame 16, with a sealant 18 usually 
disposed between the frame and the edges of the laminated subassembly. The 
frame may be made of metal or molded of a suitable material such as an 
organic plastic or elastomer material. Although not shown, it is to be 
understood that a conventional module such as shown in FIGS. 1 and 2 also 
is provided with electrical terminals for connecting the module to another 
module or directly into an electrical circuit, with the terminals usually 
being affixed to the rear support sheet 6. 
The present invention improves upon the Amick invention by substituting a 
less expensive but equally performing reflecting means for Amick's 
reflecting means with its machined or molded grooves. For convenience the 
invention is described and illustrated hereinafter in the context of 
adding a novel textured reflector material to the conventional module 
structure shown in FIGS. 1 and 2, so that the textured material extends 
along the spaces between adjacent cells and also any spaces bordering the 
array of cells. 
FIG. 3 is a side elevation of a portion of a preferred form of textured 
material 20 that is used as a reflector means according to the present 
invention. The reflector material is textured by the presence of grooves 
as hereinafter described so that it is capable of reflecting light which 
normally impinges on the land areas between and around the cells in the 
module at an angle such that the reflected radiation, when it reaches the 
front surface of the cover member, will be totally internally reflected 
back down to the array of solar cells. The textured material comprises a 
substrate in the form of a thin and flexible thermoplastic film 22 that is 
coated on one side with a light reflecting metal film 24. The substrate is 
formed with a plurality of contiguous V-shaped grooves 26 each defined by 
a pair of flat mutually converging surfaces 27A, 27B that extend at a 
predetermined angle to one another in the range of 110.degree. to 
130.degree., preferably about 120.degree., with the result that the 
portions 24A and 24B of the metal coating on those surfaces form 
light-reflecting facets. Since the angle between said facets is between 
110.degree. and 130.degree., each facet extends at an angle of between 
25.degree. and 35.degree. relative to the plane of said cover member. 
The textured material 20 is produced in several steps. First, the film 22 
that serves as the substrate is manufactured as a continuous or extended 
web having flat front and back surfaces, and that continuous web is then 
wound onto a roll for subsequent processing, or it may be passed directly 
to subsequent processing stages. The subsequent processing comprises first 
embossing the film so as to form the V-shaped grooves on one side, and 
then metallizing the grooved surface of the film. Preferably, the 
embossing is accomplished by passing the film between a pinch roller and 
an embossing roller, the pinch roller having a smooth cylindrical surface 
and the embossing roller having a plurality of contiguous V-shaped ridges 
on its cylindrical surface with the ridges extending around the periphery 
of the embossing roller. The embossing roller ridges are reverse 
(negative) images of the desired V-shaped grooves in shape and depth. The 
film is heated so that as it passes between the two rollers it is soft 
enough to be shaped by the ridges on the embossing roller. The grooves 
formed by the ridges are fixed in shape on cooling of the film. After 
formation of grooves 26, the plastic film is subjected to a metallizing 
process wherein the adherent metal film 24 is formed. Preferably, but not 
necessarily, this is done by a conventional vapor deposition process on a 
continuous basis as a second stage in a high speed machine that includes 
an embossing first stage and means for transporting the continuous plastic 
film through its various stages at a relatively high speed. The metallized 
film is wound on a roll for subsequent use as a light reflector means as 
herein described. Subsequently pieces are cut from the rolled metallized 
film for use as light reflector means according to the invention. 
Still referring to FIG. 3, the substrate is made of a plastic film material 
which is thermoplastic and which may be transparent, translucent or 
opaque. For reasons of cost and ease of use, a readily available plastic 
film is preferred for the substrate 22, with the film being sufficiently 
flexible to allow it to be stored in roll form. One suitable substrate 
material is polyethylene terephthalate, one form of which is sold as a 
transparent film wound in rolls under the trademark Mylar.RTM.. Other 
plastic films also may be used. By way of example but not limitation, the 
substrate may be a film made of other polyesters or a polyolefin such as 
polyethylene or polypropylene. Still other plastic films will be obvious 
to persons skilled in the art. 
It has been determined that a satisfactory flexible textured reflector 
sheet can be made using as the substrate a plastic film having a thickness 
in the range of 4 to 10 mils (0.004 to 0.010 inch). Preferably the 
substrate has a thickness of about 5 mils. Currently aluminum is preferred 
as the reflective metal coating for reason of cost, but silver may become 
the preferred coating since its reflectivity is sufficiently higher than 
aluminum to offset the difference in cost. In this context it should be 
noted that aluminum has a reflectivity of about 80-85% while silver has a 
reflectivity of 95-98%. The metal is applied in a very thin coating in the 
order of Angstrom units, preferably having a thickness in the range of 300 
.ANG. to 1000 .ANG., more preferably between 300 .ANG. to 500 .ANG.. By 
way of example, in a substrate having a thickness of about 0.005 inch and 
V-shaped grooves with an included angle between 110.degree. and 
130.degree., the grooves have a depth of about 0.002 inch and a repeat 
(peak-to-peak) spacing of about 0.007 inch. 
The textured material 20 is disposed so that it occupies the spaces ("land 
areas") between cells in a module. Because of the above-described geometry 
of grooves 26, light reflected from one facet is not blocked by any 
adjacent facet and instead light reflected from the facets and passing 
into the transparent cover member will strike the front face of the cover 
member at an angle exceeding the critical angle, with the result that 
substantially all of the reflected light is reflected internally back 
toward the solar cells, thereby substantially improving the module's 
electrical current output. 
FIG. 4 illustrates how the textured laminated reflector material of FIG. 3 
is used in a module. Essentially the laminated sheet material 20 is 
disposed in the areas 30A between adjacent rows of cells and the areas 30B 
between adjacent columns of cells, and also in the areas 30C and 30D that 
border the array of cells. The textured material is disposed so that in 
FIG. 4, for example, the grooves 26 extend horizontally in the areas 30A 
and 30D and vertically in areas 30B 30C. For convenience and simplicity, 
only some of the grooves 26 are shown in FIG. 4 and then only part of 
their full length. However, it is to be understood that the grooves extend 
for the full expanse of the land areas 30A, 30B, 30C and 30D. 
FIG. 5 illustrates one way that the arrangement shown in FIG. 4 can be 
achieved. In this case, a sheet 20A of the laminated reflector film 
material of FIG. 3 is placed under the array of cells, the sheet being 
large enough to protrude beyond the periphery of the array, with the 
grooves of that sheet extending in the same direction in land areas 30A, 
30B and 30C. Then an additional length of the same laminated reflector 
film material is cut into strips 20B with the grooves running lengthwise 
of the strips, and those strips are then placed over sheet 20 in those 
portions of areas 30A that lie between adjacent areas 30B and also between 
areas 30B and 30C, and the areas 30D between areas 30C so that the grooves 
of members 20A and 20B provide a pattern as shown in FIG. 4. More 
specifically, a plurality of grooves are disposed between and extend 
parallel to vertical columns of cells while additional grooves are 
disposed between and extend parallel to the cell rows. This arrangement 
has been found to be advantageous in that only one form of texturized 
reflector sheet material is required to be used, while having the grooves 
between adjacent rows oriented at a right angle to the grooves between 
columns improves the amount of light that is internally reflected from the 
areas between the cells back onto the front surfaces of the cells. 
FIG. 6 illustrates a second way to obtain a patterned groove arrangement as 
shown in FIG. 4 using a laminated plastic film as shown in FIG. 3. In this 
case, the laminated sheet 20A is omitted and instead the laminated plastic 
film having parallel grooves running along its length is cut into a 
plurality of strips 20B, each having the grooves 26 running lengthwise, 
and one of those strips is placed in each of the land areas 30A and 30D so 
that their grooves extend horizontally as viewed in FIG. 4, and additional 
like strips (not shown) are placed in areas corresponding to land areas 
30B and 30C of FIG. 41 so that their grooves extend vertically as seen in 
FIG. 4. It should be appreciated that at the intersections of land areas 
30B and 30C with land areas 30A and/or 30D, the grooves may extend either 
horizontally or vertically. 
FIG. 7 is a fragmentary plan view of a preferred form of laminated plastic 
film reflector material 20C. It is to be understood that material 20C also 
comprises a plastic film that has grooves formed by embossing as above 
described and also a metal film covering and following the contour of the 
grooves. However, in this case the embossing roll (not shown) is designed 
to emboss a rectangular pattern of grooves 28 that have a cross-sectional 
shape like grooves 26, certain of the grooves 28A extending lengthwise in 
one direction and the remaining grooves 28B extending at a right angle to 
grooves 28A, thereby leaving rectangular flat areas 29 each of which is 
sized so that a solar cell 4 will fit in that area. The laminated film 
material can be made wide enough so that the number of rectangular areas 
29 formed across its width is equal to the number of cells in a row or 
column of cells in an intended module, in which case the web of laminated 
film can be severed into discrete pieces having areas 29 equal in number 
to the number of cells in an intended module. 
FIG. 8 shows another form of laminated plastic film 20D. In this case the 
film is embossed with a herringbone pattern of grooves 32A and 32B. This 
material may be used in place of sheet 20A in which case strips 20B may be 
omitted from the embodiment of FIG. 5, or it may be cut into strips and 
used in place of strips 20B in the embodiment of FIG. 6. 
An example of the manufacture of modules incorporating the laminated 
plastic film material provided by this invention is accomplished according 
to the following method and the technique illustrated in FIG. 6. An array 
of cells are disposed on the back sheet 6 over a sheet of encapsulant such 
as EVA or ionomer. The cells are interconnected to one another and also to 
output terminals on the back sheet as previously described. Then pieces of 
said laminated plastic film material, cut into suitable shapes, are 
positioned in the spaces between the cells as described in connection with 
FIG. 6. Next another sheet of encapsulant is placed over the cells and 
covered by a transparent front cover sheet made of glass or plastic. 
Finally the module is heated under vacuum to cause the two sheets of 
encapsulant to fuse to one another and to the exposed surface areas of the 
back sheet, the front cover, the cells and the laminated plastic film 
material. This module is then available for mounting in a frame for 
subsequent use. 
Alternatively, the module may be assembled in reverse fashion, with the 
transparent glass or plastic sheet serving as the support for the module 
components during module assembly. In this method a layer of encapsulant 
would be placed over the transparent sheet with the cells placed face down 
on this layer. A second relatively thin layer of encapsulant would be laid 
over the rear of the cells, and a textured sheet as in FIG. 7 laid face 
down over the second encapsulant sheet with its grooves facing down. Then 
a third thin encapsulant sheet is placed over the textured reflector sheet 
and that is covered by a back sheet made of glass. Then the foregoing 
sandwich is laminated under heat and vacuum as previously described. 
The following demonstrates the amount of improvement provided by this 
invention. Ten cell coupons were made using EVA as the encapsulant and 
0.25 inch thick glass as the front cover sheet. Each coupon comprised one 
solar cell measuring 100 mm. on each side. Each cell was surrounded by 4 
strips of laminated reflector material, one strip along each side of the 
cell, with the grooves running in one direction along two opposite sides 
of the cell and at a second direction at a right angle to the first 
direction along the other two sides of the cell, essentially in a pattern 
like that of FIG. 4. The laminated reflector material consisted of 0.005 
inch thick Mylar.RTM. film having an aluminum coating approximately 400 
.ANG. thick on its top surface. The Mylar.RTM. film had been embossed 
before being metallized, the embossing producing V-shaped grooves having 
an included angle of about 120.degree., a depth of about 0.002 inch and a 
repeat spacing of about 0.007 inch. Each strip of laminated film measured 
about 25 mm. wide. These coupons, and another coupon having no reflector 
material but with an opaque mask surrounding it, were tested by 
illuminating each cell with a solar simulator light source and measuring 
the short circuit current. The 10 coupons having the laminated reflecting 
plastic film showed improvements in output power ranging from 20.8 to 
25.6% greater than the power output of the cell that did not have the 
novel reflecting medium. It has been found also that a like cell 
surrounded by a flat white surface showed an output power increase no 
better than about 10% greater than the cell having no reflecting medium. 
The invention also includes the concept of replacing the reflective metal 
coating on the plastic film with a dielectric stack comprising multiple 
layers of inorganic materials such as SiO.sub.2, and Si.sub.3 N.sub.4 
arranged so as to form a reflecting mirror. Dielectric mirrors are well 
known; see A. Scherer et al, "Reactive Sputter Deposition of High 
Reflectivity Dielectric Mirror Stacks", J. Vac. Sci. Technol. (1993). 
Plastic film with dielectric mirror coatings are available commercially 
from various companies. 
The invention also contemplates installing the laminated reflecting 
material consisting of a transparent plastic film substrate and a metal 
coating on its grooved surface so that the metal coating is facing away 
from the transparent cover sheet so as to avoid any possibility of the 
metal film short circuiting the cells. 
The invention is not limited in its application to any particular kind of 
solar cell, or solar cell encapsulant or cover sheet or back sheet. The 
invention is susceptible of various modifications that will be obvious to 
persons of ordinary skill in the art.