Photovoltaic module

A photovoltaic panel is supported, sealed and isolated from the environment by being encased in a reaction injection molded elastomer which encapsulates the back, sides and a portion of the front side of the photovoltaic panel.

FIELD OF THE INVENTION 
The invention relates to photovoltaic cells for converting light into 
electrical energy and more particularly to an elastomer-encased 
photovoltaic panel which offers significant advantages in manufacturing 
and weather resistance. 
BACKGROUND AND SUMMARY OF THE INVENTION 
It has long been desirable to capture radiation, particularly visible 
light, to convert it directly into electrical energy through the 
utilization of photovoltaic cells. Many types of photovoltaic cells, often 
referred to as solar cells, have been considered and constructed. For 
example, single-crystal cells have been produced, as well as those 
produced from gallium arsenide and other similar materials. In addition, 
thin film cells have been fabricated from microcrystalline, amorphous, 
compound or semiconductor material other than single crystal semiconductor 
material, deposited in situ upon a substrate by chemical vapor deposition, 
sputtering or other similar means. In use, these cells are assembled in 
photovoltaic panels and modules which must withstand the rigors of the 
environment and handling in commerce. 
As used herein, the term photovoltaic panel or panel refers to a 
combination of a sheet of transparent material or other lamina, an array 
or group of photovoltaic cells interconnected to provide an output of 
electrical energy, and any backing sheet or material, which forms a device 
capable of transforming incident radiation to electrical current. Such 
panels are traditionally comprised of a transparent front or 
radiation-facing sheet such as a glass or transparent polymer, laminated 
with layers of transparent conductors, photovoltaic materials, 
cell-connecting circuits, metals and other lamina which together comprise 
an operative photovoltaic panel. Thus, photovoltaic panels have 
traditionally included a sheet of glass or other rigid transparent 
material to protect the photovoltaic cell, and a back sheet of steel or 
aluminum metal or foil, with the various lamina being bonded together by a 
dielectric layer of plasticized polyvinyl butyryl or ethylene 
vinylacetate. In instances where a totally transparent photovoltaic panel 
is desired, such as in a solar cell which serves as an automobile sun 
roof, a front and back sheet both of rigid transparent material is 
employed. 
After the initial assembly of the laminates which comprise the photovoltaic 
panel, the edges of the panel have traditionally been smoothed to provide 
a flush edge surface, and sealed with a non-conductive varnish followed by 
one or more layers of polyester and/or polyurethane tape. After this 
sealing of the edges, the panel is enclosed in a peripheral frame of 
aluminum, steel, molded polymer or other rigid frame material. This method 
of sealing and framing the periphery of the panel has been necessary to 
isolate the solar cell from the environment, and to provide a frame for 
the strengthening of the panel and to provide a border to permit ease of 
handling and the attachment of connector boxes and the like for attachment 
of the photovoltaic cell to an external electrical circuit. For example, a 
solar panel with a hardened foil back layer sandwiched between polyvinyl 
fluoride resin sheets, and framed in rigid peripheral framing is shown in 
U.S. Pat. No. 4,401,839. This combination of a photovoltaic panel with the 
frame, sealing means, connection means and ancillary supporting structures 
is referred to herein as a photovoltaic module. 
While existing methods for the production and framing of photovoltaic 
panels have provided significant improvements in solar cell technology 
over the years, it has been a desideratum to simplify the lamination and 
manufacture of such panels and provide for a stronger module and a more 
perfect seal to protect the edges or back panel of photovoltaic panels. 
For example, the lamination steps have previously required a considerable 
expenditure of labor, and the metal backing sheets previously used to 
protect the back of the panel may allow electrical leakage which turns a 
photovoltaic cell into a capacitor. 
According to the invention, a photovoltaic module is provided which 
comprises a panel having front and back sides and edges forming a 
perimeter and at least one photovoltaic cell capable of converting 
radiation incident on the front of the panel to electrical energy, with 
the panel being partially encapsulated in a unitary, reaction-injected 
molded elastomer which forms a seal against a portion of the front side of 
the panel bordering the perimeter, and continues around the perimeter and 
seals against at least a portion of the back side. In one embodiment, the 
module further comprises means for establishing external electrical 
connection to the photovoltaic cell, including an internal portion 
electrically connected to the cell and an external portion extending from 
the panel, and the unitary elastomer further encapsulates at least the 
internal portion of such connecting means. 
The elastomeric casing is formed on a predetermined portion of a 
photovoltaic panel by placing the panel in a mold having interior walls 
which cooperate with the predetermined portion to define a cavity 
encompassing the perimeter and at least a portion of the front and back of 
the panel, introducing a flowable reaction injection molding material into 
the cavity and curing the material to form the casing. For example, the 
panel could be placed in a mold including two cooperating mold sections 
having surfaces defining a chamber for receiving the panel, with one of 
the mold sections having seal means positioned to be adjacent the 
periphery of the front side of the panel to support the panel within the 
panel receiving chamber and seal the portion of the panel located 
interiorly of the seal means against the influx of fluid. The facing 
surfaces of the mold sections located exteriorly of the seal means are 
provided with a casing shaping portion which cooperates with the seal 
means and the predetermined portion of the panel to define a cavity when 
the mold sections are in contacting relationship. 
The mold also includes inlet means for introducing the flowable reaction 
injection molding material into the cavity when the mold sections are 
contacting to form a closed mold. The casing shaping portion of the mold 
may also define a cavity portion which includes at least the internal 
portion of the connecting means of the panel so that a portion of the 
connecting means is imbedded in the cured reaction injection molding 
material. Preferably, the reaction injection molding elastomer 
encapsulates the back and perimeter edges of the panel and forms a seal 
against a portion of the front side of the panel bordering the perimeter. 
If desired, a stiffening structure such as metal, fibrous or polymeric 
sheets or girders may be included within the elastomer to add to the 
rigidity of the photovoltaic module. 
In a preferred embodiment, the module comprises a first sheet having a 
first radiation-incident side and having a photovoltaic cell formed 
thereon; a second backing sheet, preferably having a comparable modulus of 
thermal expansion, adjacent and spaced from a back side of the first 
sheet; and a unitary, reaction injection molded elastomer disposed between 
the back side of the first sheet and the second, the elastomer partially 
encapsulating the first sheet, forming a seal against a portion of the 
front side of the first sheet bordering the perimeter, continuing around 
the perimeter of the first sheet and sealing against at least a portion of 
the second sheet. The term unitary elastomer, as used herein, refers to a 
one-piece elastomer, one that is formed by a single injection of an 
elastomer-forming material as described.

DETAILED DESCRIPTION 
A wide variety of photovoltaic panels may be encapsulated in an elastomer 
produced by reaction injection molding (RIM). Any such panel having a 
front transparent substrate bearing at least one photovoltaic cell may be 
advantageously encapsulated according to the invention. In the preferred 
embodiment, there is illustrated in FIGS. 1-3 a photovoltaic module 
embodying the present invention, designated generally 10. The module 10 
comprises a laminated central panel 12, including an array of photovoltaic 
cells 14, surrounded by a border 16 which is formed from a RIM elastomer. 
Turning now to FIG. 2, the module 10 is seen to include a transparent 
sheet or substrate 18, formed from various materials such as glass or 
transparent polymers, through which incident light illustrated at 20 
passes. The module 10 includes a thin film semiconductor material 22. The 
thin film material 22 may be, for example, a PIN microcrystalline thin 
film silicon-hydrogen cell array, a thin film amorphous silicon panel or 
an array of single crystal photovoltaic cells. Methods for the production 
of photovoltaic panels are known in the art and will not be discussed 
further herein, other than to incorporate by reference U.S. Pat. No. 
4,638,111 to Gay. The RIM process is particularly advantageous in 
encapsulating photovoltaic panels since RIM is a thermosetting polymer 
formed from the reaction of injected liquid polymeric precursors at low 
temperature (less than 200.degree. F.), thus preventing heat damage to the 
thin film material which would occur if high temperature injection molding 
techniques were employed. In addition, the use of the RIM elastomer 
permits the insertion of various fastener receiving means in the elastomer 
during the molding process, as will be apparent from the following 
description, which will accept fasteners for the attachment of the module 
to various structures. 
On either side of the thin film semiconductor material 22 are thin films of 
electrical conductors 24 which are patterned with a laser or otherwise, 
and staggered to form front and back overlapping electrodes which collect 
charge from the cell array in series. For example, a film of zinc oxide or 
indium tin oxide (ITO) may be employed for a transparent front film. 
Aluminum and/or nickel for a non-transparent or zinc oxide or ITO for a 
transparent back film may be employed. Methods for the production and 
utilization of such conductor films are also known in the art. If the 
bottom conductor layer 24 is transparent a partially reflective layer 26, 
for example, a coating such as a layer of white or light-colored paint, 
may be used which causes a portion of the incident light to be reflected 
again through the thin film semiconductor material 22 after striking the 
reflective layer 26. 
In FIG. 2, a unitary elastomer 30 is seen to encapsulate the photovoltaic 
panel 12, forming a seal against a portion 32 of a front side 34 bordering 
a perimeter 36 of the panel 12, and continuing around the perimeter 36 and 
sealing against a back side 38 of the panel 12. The encapsulation of all 
but the light incident portion of the front side 34 of the panel 12 is a 
significant benefit since it eliminates the lamination step previously 
required in the assembly of photovoltaic modules. 
In FIG. 3 only a portion 40 of the back side 38 which is adjacent the 
perimeter 36 is encapsulated by the elastomer. In this FIG., the panel 12 
is seen to include the transparent sheet 18, thin film material 22 and 
transparent electrical conductors 24 as described above in FIG. 2. Behind 
these lamina, an additional transparent sheet 19 is included which 
protects the lamina 22 and 24 which comprise the array of photovoltaic 
cells and permits the further transmission of the incident radiation 
through the panel 12 as shown to provide a totally transparent panel. 
In FIG. 3, the charge-carrying transparent conductors 24 are seen to extend 
from the left edge of the panel 12, where they are connected by soldering 
or otherwise to means for establishing external electrical connection to 
the panel 12, here shown as leads 44 and 46. These leads are seen to 
include internal portions 48 and 50, which are encapsulated by the unitary 
elastomer 30, and external portions 52 and 54 which extend from the 
elastomer 30 for connection to an external electrical circuit, not 
specifically shown, for utilization of the current produced by the 
photovoltaic module 10. In both FIGS. 2 and 3, the internal edge portion 
of the elastomer 30 which is adjacent the front of the panel 12 tapers 
outwardly from the panel to permit rain water or condensation to drain 
easily from the front of the panel when the module is placed in operating 
position, that is, angled toward the sun. 
In a similar manner which will be recognized by those skilled in the art, 
FIG. 2 shows an electrical connection means comprising connectors 60 and 
62 having internal portions 64 and 66 connected to the transparent 
conductors 24, which establish the circuit within the photovoltaic panel 
12, by soldering or other means which are known in the art. The internal 
portions 64 and 66 are seen to be embedded in the elastomer 30 so that the 
internal laminations of the panel 12 are sealed against the penetration of 
moisture, and the connectors 60 and 62 are thus held in congruence with 
the conductors 24. The connectors 60 and 62 also include external portions 
68 and 70 which extend from the internal portions 64 and 66 into an 
essentially square cavity 72 formed in the elastomer 30. This cavity 72 
serves as a terminal box or junction box for use with a connector plug or 
cover plate whereby the connectors 60 and 62, and the connections 
therewith, are isolated from the environment. For example a cover plate, 
not shown, bearing sealed wires for connection to an external electrical 
circuit may be inserted in the recess 74 provided about the edges of the 
cavity 72 and secured by adhesive or other fastener means. If such wires 
are employed, the external portions 68 and 70 may be threaded or otherwise 
adapted to receive wire-connecting means. Alternatively, the cavity 72 may 
be adapted to receive an elastomeric plug which, in turn, receives the 
external portions 68 and 70 for connection with the external circuit. The 
general construction of terminal assemblies for prior art photovoltaic 
panels is known in the art, and a particularly useful assembly is shown in 
U.S. Pat. No. 4,371,739 to Lewis, et al., which is incorporated herein by 
reference. 
Significant advantages are provided through the use of the RIM elastomer 
module-forming method in that significant additional rigidity may be 
provided to the photovoltaic module 10. For example, the thickness of the 
unitary elastomer overlying the back side 38 in FIG. 2, as well as the 
uniform sealing of the elastomer against the abutting portions of the 
panel 12, add significant rigidity to the photovoltaic module 10. 
Structural ridges formed in the elastomer 30 across the back side 38 may 
be employed to add significant structural stiffness without increasing the 
weight of the module. Alternatively, internal structural members may be 
employed to stiffen the module. For example, FIG. 3 shows an L-shaped 
stiffening structural member 80 at the right side of the drawing, and an 
I-beam shaped stiffener 82 at the left. The stiffeners 80 and 82 are shown 
in the drawing as being formed from carbon fibers, although a wide variety 
of shapes, sizes and materials may be employed for the structural 
reinforcing members. For example, these members may be made of polymeric 
material, steel or aluminum. 
While reaction injection molding (RIM) has not previously been employed in 
the encapsulation of photovoltaic panels, RIM is a well established 
process for molding block polymers, and a wide variety of RIM machines is 
in existence and known in the art. The RIM machine meters, mixes and 
dispenses reactive chemicals into a mold, where a chemical reaction occurs 
and the desired part is formed. Polyurethanes, polyamines, epoxies, 
polyesters, nylon and hybrid block polymers may be formed by RIM 
technology and adaptable to the formation of the elastomer-encapsulated 
photovoltaic panels of the invention. With respect to the polymers formed 
around the photovoltaic panels, an elastomer is preferred to minimize 
unequal thermal expansion which might otherwise stress the laminations of 
the photovoltaic panel or break the glass substrate of the panel. 
Preferably, an elastomer having a modulus of elasticity of from 200 to 
10,000 p.s.i. is preferred. Since polyurethane technology is developed and 
easily adaptable to the encapsulation of photovoltaic panels, the use of 
polyurethane resins in RIM technology will be discussed in this preferred 
embodiment. However, other polymer systems are equally adaptable to the 
invention upon the reading of this description. A description of the RIM 
technology for a wide variety of polymers is set forth in Sweeney, 
Reaction Injection Molding Machinery and Processes, Marcel Dekker, Inc., 
New York (1987) and Kresta, Reaction Injection Molding and Fast 
Polymerization Reactions, Polymer Science and Technology, Volume 18, 
Plenum Press, New York (1982). Both of these publications are incorporated 
herein by reference. 
Commercial RIM polyurethane polymer precursors are based on isocyanates, 
polyols, extenders, catalysts and blowing agents. The extenders are 
usually glycols or amines or some combination of the two. The most common 
isocyanate is diphenylmethane diisocyanate (MDI) and has been found to be 
a preferred isocyanate in the production of the photovoltaic modules of 
the invention. The polyol may be either a polyether or polyester chain 
compound having reactive hydroxyl end groups. Preferably, a polyol 
comprising a mixture of diol-triol, or an all triol polyol, having a 
molecular weight of about 4,000 is preferred. Diamine extenders such as 
diethyl toluene diamine have been found to be particularly useful, as have 
triamine catalysts, organo-tin or tin oxide catalysts. The elastomers of 
the invention may be either solid elastomers, or include a freon expanding 
agent to form a foam or semifoam elastomer. Either the solid or expanded 
elastomer is equally adaptable to encapsulating the photovoltaic panels of 
the invention. In addition, a wide variety of fillers may be employed to 
form a reinforced reaction injection molding (RRIM) elastomer. Fillers 
such as carbon black or fine limestone may be added as pigments to the 
elastomer. Plate-like fillers such as the mineral wollastonite may be 
employed as reinforcing fillers. In addition, needle-like or long fibrous 
fillers such as glass fibers may also be employed to provide structural 
rigidity to the elastomer. 
Solid elastomers or structural RIM foam are equally adaptable to the 
invention. Solid elastomers are formulated with no expanding agent and the 
mold is completely filled with the polyurethane precursors. Structural 
foam is produced by using a chemical system containing a relatively large 
amount of an expanding agent such as freon. Heat from the chemical 
reaction vaporizes the expanding agent, causing the reactants to foam, 
adding additional expansion pressure to fill and pack the mold. The rate 
of the polymerization reaction is adjusted catalytically to allow the 
foaming to occur before viscosity increases excessively. 
Polyurethane precursors which are prepared specifically for use in reaction 
injection molding are available from BASF Wyandotte Corporation, Dow 
Chemical Company, ICI (Rubicon), Mobay Chemical Corporation, Olin Chemical 
Company, Texaco Chemicals, Union Carbide Corporation and the Upjohn 
Company. RIM polyurethane preparations sold under the trade names Mobay MP 
5000 and Dow Spectrim 5 have been found to be particularly useful in the 
encapsulation of solar panels. 
RIM machines for dispensing reactants are available from a number of 
suppliers, and are widely known and used in the art for the formation of a 
wide variety of products. One source for RIM machines is Admiral 
Equipment, Incorporated of Akron, Ohio. The RIM dispensing machine 
performs four functions: (a) conditions the elastomer precursors to 
control density and viscosity, (b) meters the precursors as required by 
the stoichiometry of the chemical system, (c) mixes the reactants by high 
pressure impingement within the mixing head, and (d) recirculates the 
reactants to maintain pressure, density and viscosity. The metering pumps 
on RIM machines may be linear, axial or rotary piston pumps, or lance 
pistons. The elastomer precursors are fed at high pressure to a mixing 
head which mixes the reactants by impingement during shots, recirculates 
the reactants between shots, develops the pressures needed for good mixing 
and self-cleans the mixing chamber using a cleanout piston. 
As mentioned, the mixing of the reactants occurs in the mix head and 
continues after injection within the mold. The mold shapes the part, 
directs reactants into the mold cavity, directs the flow of reactants, 
controls the exotherm temperature produced by the molding process by 
removing heat, and contains devices to facilitate holding the part to be 
molded in position and facilitating part removal. 
FIG. 4 shows a cross-sectional view of a mold 100 for forming the 
encapsulated photovoltaic panel of the invention. The mold 100 includes a 
first mold section 102 and a second mold section 104 which have facing 
surfaces, detailed more specifically herein, which cooperate to define a 
chamber for receiving the photovoltaic panel 12 and forming an 
encapsulated elastomer around the panel. An overhead view of the mold 
section 102 is shown in FIG. 5. The mold sections 102 and 104 are seen to 
be adaptable to be brought into a contacting relationship wherein facing 
surfaces 106 and 108 abut. Mold carrying clamps for this purpose are known 
in the art and may comprise hydraulic or mechanical means for moving the 
mold sections in opposite directions as shown in FIG. 4, or may involve a 
hinged book-type opening method. Such mold clamps provide the forces which 
hold the mold together during filling, provide the breakaway forces 
necessary to open the mold after the reactants have polymerized, move the 
mold from a loading position to a shot position during the molding cycle 
and open and close the mold for insertion of materials and removal of the 
polymerized part. One source for such mold carrying devices is Urethane 
Technology, Incorporated of Grand Haven, Mich. 
A chamber for molding the encapsulated photovoltaic module 10 which is 
shown broadly in FIG. 2 is defined in FIG. 4 by a cavity 110 in the mold 
section 102. The cavity 110 includes a border cavity portion which 
encompasses the perimeter 36 of the panel 12 and overlies a portion of the 
front side 34 of the panel 12 bordering the perimeter 36. Seal means 116 
are positioned in the mold section 102 to be adjacent the periphery of the 
front side of the panel 12, when the panel is in place within the mold 
100, to support the panel and seal the portion of the panel 2 located 
interiorly of the seal means, that is, the area of the front surface 34 
above and interior cavity portion 118, against the influx of the reactive 
molding fluid. 
Several types of material may be used to make RIM molds. Epoxy molds are 
easy to make and inexpensive compared to metals, but suffer from a low 
heat transfer rate and a high coefficient of thermal expansion. Most 
commonly, metal molds such as nickel shell, spray metal, cast aluminum, 
cast zinc alloy (Kirksite), machined aluminum or machined steel are 
preferred. Regardless of the mold material employed, it may be desirable 
to include a plurality of tubes or passages, shown schematically by the 
reference numeral 120 in FIG. 4, which are uniformly spaced throughout the 
mold sections and provide for the circulation of a heat-transfer fluid in 
order to control the temperature at appropriate portions of the mold to 
control chemical reaction rates. The seal means 116 and other 
cavity-defining portions of the mold are preferably machined or otherwise 
formed from metal, although resilient seal means such as silicone rubber 
seals may be employed. 
During the molding process, the panel 12 is held against the seal means 116 
by a vacuum in the interior cavity portion 118 which is produced, in the 
mold shown in FIG. 4, by a vacuum chuck means 122, or a plurality of 
individual vacuum cups, are employed to hold the panel 12 in a sealing 
relationship with the seal means 116. The vacuum chuck 122 is seen to 
include a threaded tap 124 for attachment of a vacuum hose, not shown. 
When the panel 12 is thus held against the seal means 116 and the mold 
sections 102 and 104 are brought into an abutting relationship, a core 
portion 128 of the mold section 104 is seen to be adapted to form a 
portion of the elastomer 30 which overlies the back side 38 of the panel. 
If a transparent module such as that shown in FIG. 3 is desired, a module 
wherein the elastomer borders only a portion of the back side 38 of the 
panel 12, seal means similar to the means 116 are included in the core 
128. 
The mold section 102 also includes an inlet sprue 130, which is adapted to 
receive the mixing and injection valve of the RIM machine, not 
specifically shown. Communicating with the sprue 130 is a runner 132 which 
preferably extends longitudinally along the length of the panel 12 and 
which is adapted to receive the incoming fluid from the sprue 130. Upon 
filling, the runner 132 creates a reservoir of increased pressure whereby 
the fluid elastomer precursors quickly flow over a restricted inlet gate 
134 into the nearest border cavity portion 112 and the core 128 of the 
mold section 104. The inlet gate 134 provides a clearance against the 
facing surface 108 of about 30/1000ths of an inch. Thereafter, the fluid 
fills the circumferential border cavity 112 and flows over an outlet gate 
136, on three sides of the panel, and into a dump well 138. It should be 
understood that gates 134 and 136 cooperate to extend around the periphery 
of the border 16 of the module 10 to form flash portions of the elastomer 
which are then trimmed from the module. An exit sprue 139 for excess 
elastomer-forming reactants may also be provided leading from the dump 
well 138. It should be understood that the abutting perimeter portions of 
the mold sections 102 and 104 provide sufficient clearance for the escape 
of air from the mold cavity. Generally, a clearance of from 5/1000ths to 
10/1000ths of an inch is sufficient clearance between the mold sections at 
136 to allow the escape of air during the influx of the fluid. 
It will be appreciated by those of skill in the art that mold design can 
vary significantly with respect to the dumping of excess elastomer-forming 
precursors, depending on factors such as the size of the panel to be 
encapsulated and the particular formulation employed. For example, while 
panels have been formed using the peripheral dump well 138 as is shown in 
FIG. 5, other panels have been formed in molds wherein the dump well is 
deleted and the border cavity 112 communicates across the outlet gate 136 
directly with the exit sprue 139. Other molds have been employed wherein 
the mold-facing surfaces 106 and 108 are in such close contact at the gate 
136 that virtually all of the elastomer flows through a single exit sprue. 
This provides for significant advantages in demolding and finishing the 
encapsulated photovoltaic module. Such variations will be apparent to 
those with skill in the art without departing from the spirit of the 
invention. 
The mold sections 102 and 104 may also be adapted, according to means known 
in the art, to form the cavity 72 or other portions of the elastomer 30 
necessary to form connector means or junction boxes around the external 
portion of the terminal assemblies which are electrically connected to the 
panel 12. For example, to form the cavity 72 in FIG. 2, an essentially 
square (from an overhead view) mold plug 140, shown in FIG. 4 and in some 
detail in FIG. 6, is inserted over the terminal means. The plug 140 may be 
made from a resilient material which is coated with a mold-released 
formulation, and is seen to include cylindrical perforations 142 and 144 
which cover and seal against the exposed, external portions 68 and 70 of 
the connectors 60 and 62. When the mold sections 102 and 104 are closed, a 
top 146 of the mold plug 140 is seen to contact the top of the core 128 so 
that the cavity 72 in the elastomer 30 (as shown in FIG. 2) is formed. 
Other means for forming connector means or terminal boxes will be apparent 
to one of ordinary skill in the art having read this disclosure. It is to 
be noted with respect to the plug 140 that the edges thereof are tapered 
inwardly at a draft angle of at least 1.5..degree., and preferably from 
3.degree. to 5.degree. from perpendicular. This draft angle should also be 
noted with respect to the edges of the elastomer 30 in FIGS. 2 and 3. 
Similar draft angles are also shown with respect to the cavity 110 and the 
core 128 in FIG. 4. 
Should it be desired to include structural means such as those shown by the 
reference numerals 80 and 82 within the elastomer, these members are 
attached, by elastomeric adhesive or other means, to the panel 12 and the 
incoming elastomer-forming fluid easily flows about the structural members 
and any voids between the members and the panel to form a rigid, stiffened 
solar module. 
In the method of the invention, the glass or transparent polymer with the 
photovoltaic cells or films attached, as well as the structural stiffening 
members and terminal members if desired, is first primed in all areas to 
which the elastomer is to adhere. This prime coating may or may not be 
tinted to provide a partially reflective coating to the photovoltaic panel 
such as that shown by the reference numeral 26 in FIG. 2. The primer is 
deposited about 1/4 of an inch around the edge of the front surface of the 
panel, the edges and the back. If a transparent panel is desired, only a 
portion of the back surface is primed and coated with elastomer. Primers 
for use in reaction injection molding are known in the art, but the 
inclusion of an amino-silane coupling agent is preferred. Epoxy-silane is 
also useful as is any other molecule having a portion which bonds to the 
elastomer and another portion which bonds to the panel. Following the 
priming of the panel, the mold cavity is sprayed with a mold release agent 
which may include a paint which colors the exterior of the elastomer. Such 
in-mold coatings are also known in the art. 
Following the priming of the panel and the in-mold coating, the primed 
panel is placed in the mold, the mold closed and clamped, and a vacuum 
applied to the vacuum chuck means to hold the panel securely against the 
seals. The clamped mold is then rotated to position the air vents at the 
highest point, usually with the fluid input at the lowest point, and the 
fluid elastomer precursors are mixed in the mix head during the injection 
process and the reacting solution is injected into the inlet sprue. The 
impingement pressure necessary to mix the incoming streams of 
polyurethane-forming precursors in the mix head is about 2,000-3,000 
p.s.i., although the pressure in the mold cavity after flow through the 
runner and across the inlet gate is only about 20-50 p.s.i. During the 
polyurethane-forming reaction, the temperature produced by the 
polyurethane exotherm is maintained at about 150.degree.-160.degree. F. by 
the mold and the heat transfer fluid in the passages 120. The volume of 
the fluid injected into the mold is calculated so that the 
elastomer-forming fluid fills the mold cavity, extends across the land or 
flash areas above the peripheral gates 134 and 136, and penetrates 
slightly into the dump well. Following the curing of the elastomer, which 
generally occurs within thirty seconds, the encapsulated panel is removed 
when the mold opens. If desired, knockout pins or knockout pads may be 
inserted in the mold section which retains the panel to facilitate part 
removal. After removal from the mold, the encapsulating elastomeric 
material has a form which is shown schematically, in cross-section, in 
FIG. 7. The panel 12 is there shown to be encased in a unitary elastomer 
30 which extends across the back side 38 of the panel 12, around the 
perimeter 36 and overlying and sealing against a portion of the front side 
34 of the panel bordering the perimeter. The portion of the elastomer 
which has cured within the inlet sprue 130 and the runner 132 is seen as 
being attached to the module 10 by an inlet flash portion 150. The portion 
of the elastomer which has escaped into the dump well 138 is seen to be 
attached to the module 10 by a peripheral outlet flash portion 152. These 
flash portions are thereafter trimmed or torn from the module 10 as is 
known in the art. 
A particularly advantageous embodiment of the module 10 is shown in FIG. 8. 
In this figure, the module 10 is seen to include a first or front 
transparent sheet 160, having front and back sides and edges forming a 
perimeter as shown above with respect to the sheet of substrate 18, and 
having an plurality of photovoltaic cells 162 arrayed on the back side 
thereof which are capable of converting radiation incident on the front 
side of the sheet 160 to electrical energy. As with all transparent sheets 
employed in the construction of solar panels, the sheet is preferably 
plain glass having a thickness of about 2 mm rather than tempered glass 
since the temperature associated with the processing of the photovoltaic 
cells thereon destroys the temper of tempered glass. 
The module in FIG. 8 also includes a second or back sheet 164, also having 
front and back sides and edges forming a perimeter, the second sheet being 
disposed essentially planar to and adjacent the back side the first sheet. 
The sheet 164 is preferably a tempered window glass sheet having a 
thickness of about 1/8 inch, the tempered glass being employed to provide 
greater strength to the module in this embodiment. 
The module further includes a reaction injection molded elastomer 170 which 
is seen in the FIG. to have an edge portion 172 which encapsulates the 
perimeter edges of the first and second sheet, and a portion of the front 
side of the first sheet bordering the perimeter. At least the edges of the 
second sheet are encapsulated, although the elastomer can be continued 
behind the back of the sheet 164 if desired to add strength to the module. 
Of particular note in this embodiment is the fact that the elastomer 170 
includes a portion 174 which forms a "sandwich" between the back side of 
the first sheet, that is, the side which includes the cell array 162, and 
the front side of the second sheet 164. Preferably, this portion 174 has a 
thickness of from about 0.060 to about 0.10 inches, or greater, and is 
unitary with all edge portions 172 which form the perimeter of the module. 
This double sheet-elastomer core construction provides significant 
advantages of added strength and durability. Since tempered glass cannot 
be used for photovoltaic panels, modules without RIM encapsulated edges 
can suffer breakage of the panel simply by the torsional stress of lifting 
the module by one end. The single sheet RIM encapsulated panels are more 
durable in that the elastomer of the invention provides an advantageous 
soft edge for protection of the panel, but in tests breakage of an 
elastomer encapsulated single-panel has occurred if such a panel is 
dropped on a carpet from a height of twenty inches. In identical tests the 
double sheet-elastomer core construction module shown in FIG. 8 was 
dropped from a height of greater than six feet on a concrete floor without 
breakage of either panel. 
Further, the double sheet-elastomer core construction is balanced from a 
thermal standpoint when sheets of comparable modulus are used in that both 
sheets expand or contract equally with temperature variations. In 
addition, the use of glass as a backing sheet is useful in that the 
penetration of water vapor, which penetrates polyurethane to some extent, 
is minimized. 
The double sheet-elastomer core module may be formed in a mold similar to 
the mold 100 by spacing the sheet 160 from the sheet 164 with double sided 
tape of sufficient thickness, for example, a closed cell polyurethane foam 
tape with acrylic adhesive on both sides. Flow restrictors may be provided 
on the edges of the mold cavity, if necessary, so that flow of the 
elastomer precursors between the sheets is accomplished without the 
formation of air bubbles. Alternatively, vacuum chuck means may be 
provided in both of the mold sections to space the sheets sufficiently for 
the influx of the RIM precursors. 
The module in FIG. 8 also includes an alternative connection means 180 for 
establishing electrical connection to the photovoltaic array 162. This 
connector means includes an internal portion, not specifically shown, 
connected to the conductors in the cell array, and an external portion 
which includes insulated wires 182 and 184 which are sealed in the 
elastomer 170, and a plug 186 comprising a shaft-like connector 188 and a 
shaft-receiving connector 190. A connector-receiving means is formed in 
the top edge 172 of the elastomer 170, and includes a first cavity portion 
190 positioned where the wires exit the elastomer, a plug-receiving cavity 
192, and a first wire-receiving channel 194 therebetween which includes 
wire retaining flanges 196. 
In use, the plug 186 is connected to a mating plug which will conduct 
electricity from the module to an external device. These two plugs are 
sized so that the mated plug combination, when inserted in the cavity 192, 
is securely retained by the resilient elastomer 170. The wires which lead 
from the mating plug are retained in a second wire-receiving channel 200, 
including retaining flanges 202, and lead to the edge of the module. 
Depending upon the desired position of the module, the wires and plug 186 
may lead upwards from the module as shown by the phantom lines 204 for 
connection to the mating plug, or behind the back of the module as 
displayed in that Figure. 
The connector-receiving means, that is, cavities 190 and 192 and the 
channels 194 and 200, may be formed by the use of a mold plug of 
appropriate form, similar to the mold plug 140 shown in FIG. 6. The 
external portion of the wires 182, 184 are positioned in grooves in the 
outlet gate of the mold, for example, grooves with an elastomeric seal 
which seal tightly against the wires, and the plug 186 is positioned 
outside the mold cavity during the molding process. 
From the foregoing description, one skilled in the art can readily 
ascertain the essential characteristics of the invention and, without 
departing from the spirit and scope thereof, can adapt the invention to 
various usages and conditions. Changes in form and the substitution of 
equivalents are contemplated as circumstances may suggest or render 
expedient, and although specific terms have been employed herein, they are 
intended in a descriptive sense and not for purposes of limitation, the 
purview of the invention being delineated in the following claims.