U.S. patent application number 13/087724 was filed with the patent office on 2011-08-18 for wire network for interconnecting photovoltaic cells.
This patent application is currently assigned to MIASOLE. Invention is credited to Steven Thomas Croft.
Application Number | 20110197947 13/087724 |
Document ID | / |
Family ID | 44368794 |
Filed Date | 2011-08-18 |
United States Patent
Application |
20110197947 |
Kind Code |
A1 |
Croft; Steven Thomas |
August 18, 2011 |
WIRE NETWORK FOR INTERCONNECTING PHOTOVOLTAIC CELLS
Abstract
Provided are novel interconnect wire network assemblies and
methods of fabricating thereof. An assembly may include conductive
portions/individual wires that, in certain embodiments, are
substantially parallel to each other. The assembly also includes
two or more carrier films (i.e., the front side and back side
films) attached to opposite sides of the wires. The films are
typically attached along the wire ends. The films are made from
electrically insulating materials and at least the front side film
is substantially transparent. The front side film is used to attach
the wires to a photovoltaic surface of one cell, while the back
side film is used for attachment to a substrate surface of another
cell. These attachments electrically interconnect the two cells in
series. In certain embodiments, one or both carrier films extend
beyond two end wires and form insulated portions that allow much
closer arrangements of the cells in a module.
Inventors: |
Croft; Steven Thomas; (Menlo
Park, CA) |
Assignee: |
MIASOLE
San Clara
CA
|
Family ID: |
44368794 |
Appl. No.: |
13/087724 |
Filed: |
April 15, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12566555 |
Sep 24, 2009 |
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13087724 |
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12052476 |
Mar 20, 2008 |
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12566555 |
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Current U.S.
Class: |
136/244 ; 156/52;
174/113R |
Current CPC
Class: |
B32B 15/04 20130101;
H01L 31/0512 20130101; Y02E 10/50 20130101; B32B 2307/412 20130101;
B32B 15/20 20130101; H01L 31/0508 20130101; B32B 2307/732 20130101;
B32B 15/02 20130101; H01L 31/188 20130101; H01L 31/1876 20130101;
B32B 2307/202 20130101; B32B 2457/12 20130101 |
Class at
Publication: |
136/244 ; 156/52;
174/113.R |
International
Class: |
H01L 31/05 20060101
H01L031/05; H01B 13/18 20060101 H01B013/18; H01B 7/00 20060101
H01B007/00 |
Claims
1. An interconnect wire network assembly comprising: a plurality of
conductive portions extending substantially parallel to each other,
the plurality of conductive portions having a first set of ends
defining a first edge and a second set of ends defining a second
edge, the plurality of conductive portions configured for current
collection from a front side surface of a first photovoltaic cell
and electrical connection with a back side surface of a second
photovoltaic cell; a first carrier film comprising a first
substantially transparent electrically insulating layer, the first
carrier film coupled to the plurality of conductive portions along
the first edge and configured to attach the plurality of conductive
portions to the front side surface of the first photovoltaic cell
to form a first electrical connection between the front side
surface and the plurality of conductive portions; and a second
carrier film comprising a second substantially transparent
electrically insulating layer, the second carrier film coupled to
the plurality of conductive portions along the second edge and
configured to attach the plurality of conductive portions to the
back side surface of the second photovoltaic cell to form a second
electrical connection between the back side surface and the
plurality of conductive portions.
2. The interconnect wire network assembly of claim 1, wherein the
first carrier film is positioned on another side of the plurality
of conductive portions with respect to the second carrier film, and
wherein the first carrier film and the second carrier film form an
overlap.
3. The interconnect wire network assembly of claim 1, wherein the
first carrier film is positioned at a predetermined distance from
the second carrier film.
4. The interconnect wire network assembly of claim 1, wherein an
outside edge of the first carrier film substantially coincides with
the first edge of the plurality of conductive portions.
5. The interconnect wire network assembly of claim 1, wherein the
first carrier film extends past the first edge of the plurality of
conductive portions.
6. The interconnect wire network assembly of claim 1, wherein the
plurality of conductive portions extends past two edges of the
first carrier film.
7. The interconnect wire network assembly of claim 1, wherein the
first carrier film comprises one or more materials selected from
the group consisting of: polyethylene terephthalate, polyethylene
co-methacrylic acid, polyamide, and polyetheretherketone.
8. The interconnect wire network assembly of claim 1, wherein the
plurality of conductive portions comprises one or more materials
selected from the group consisting of: copper, aluminum, nickel,
and chrome.
9. The interconnect wire network assembly of claim 1, wherein the
plurality of conductive portions comprises multiple individual
wires.
10. The interconnect wire network assembly of claim 9, wherein the
multiple individual wire are between 24 gauge and 56 gauge.
11. The interconnect wire network assembly of claim 9, wherein the
multiple individual wires are spaced apart by between about 2
millimeters and about 5 millimeters.
12. The interconnect wire network assembly of claim 9, wherein each
wire of the multiple individual wires is electrically insulated
from other wires prior to attaching the interconnect wire network
assembly to the first photovoltaic cell or the second photovoltaic
cell.
13. The interconnect wire network assembly of claim 9, wherein the
multiple individual wires comprise a strip of foil attached to the
second edge and electrically interconnecting the multiple
individual wires.
14. The interconnect wire network assembly of claim 1, wherein the
first carrier film extends past two end wires of the plurality of
conductive portions forming two side insulating regions.
15. The interconnect wire network assembly of claim 1, wherein the
first carrier film extends past and folds over two end conductive
portions of the plurality of conductive portions, forming
insulating shells around the two end conductive portions.
16. A method of fabricating an interconnect wire network assembly
comprising: unwinding multiple individual wires from corresponding
multiple wire rolls; extending the multiple individual wires along
an unwinding direction substantially parallel to each other at a
predetermined distance from each other, wherein the multiple
individual wires form a first surface and a second surface, with
the first surface and the second surface spaced apart by a
cross-sectional dimension of the multiple individual wires;
applying a first carrier film onto the first surface of the
multiple individual wires; and applying a second carrier film onto
the second surface of the multiple individual wires.
17. The method of fabricating an interconnect wire network assembly
of claim 16, wherein the first carrier film and the second carrier
film are applied substantially perpendicular to the unwinding
direction.
18. The method of fabricating an interconnect wire network assembly
of claim 16, further comprising: forming a roll of interconnect
wire network subassemblies; unwinding the roll of interconnect wire
network subassemblies; and cutting the multiple individual wires
substantially perpendicular to the multiple individual wires to
form the interconnect wire network assembly.
19. The method of fabricating an interconnect wire network assembly
of claim 16, further comprising cutting the multiple individual
wires substantially perpendicular to the multiple individual wires
to form the interconnect wire network assembly.
20. The method of fabricating an interconnect wire network assembly
of claim 19, wherein cutting the multiple individual wires
comprises cutting the first carrier film or the second carrier
film.
21. The method of fabricating an interconnect wire network assembly
of claim 16, wherein applying the first carrier film comprises
passing an electric current through a portion of the multiple
individual wires that is in contact with the first carrier film in
order to heat this portion.
22. A photovoltaic module comprising: a first photovoltaic cell
comprising a front side surface; a second photovoltaic cell
comprising a back side surface; and an interconnect wire network
assembly comprising: a plurality of conductive portions extending
substantially parallel to each other and in electrical
communication with the front side of the first photovoltaic cell
and the back side of the second photovoltaic cell, the conductive
portions having a first set of ends defining a first edge and a
second set of ends defining a second edge; a first carrier film
comprising a first substantially transparent electrically
insulating layer, the first carrier film coupled to the plurality
of conductive portions along the first edge and attaching the
plurality of conductive portions to the front side surface of the
first photovoltaic cell; and a second carrier film comprising a
second substantially transparent electrically insulating layer, the
second carrier film coupled to the plurality of conductive portions
along the second edge and attaching the plurality of conductive
portions to the back side surface of the second photovoltaic cell.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 12/566,555, entitled "INTERCONNECT ASSEMBLY",
filed Sep. 24, 2009, (Attorney Docket MSOLP009X1), which is a
continuation-in-part of U.S. patent application Ser. No.
12/052,476, entitled "INTERCONNECT ASSEMBLY", filed Mar. 20, 2008,
(Attorney Docket MSOLP009), both of which are incorporated herein
by reference in their entirety for all purposes.
BACKGROUND
[0002] In the drive for renewable sources of energy, photovoltaic
technology has assumed a preeminent position as a cheap and
renewable source of clean energy. For example, photovoltaic cells
using a Copper Indium Gallium Diselenide (CIGS) absorber layer
offer great promise for thin-film photovoltaic cells having high
efficiency and low cost. Of comparable importance to the technology
used to fabricate thin-film cells themselves is the technology used
to collect electrical current from the cells and to interconnect
one photovoltaic cell to another to form a photovoltaic module.
[0003] Just as the efficiency of thin-film photovoltaic cells is
affected by parasitic series resistances, photovoltaic modules
fabricated from multiple cells are also impacted by parasitic
series resistances and other factors caused by electrical
connections to the absorber layer and other electrical connections
within the modules. A significant challenge is the development of
current collection and interconnection structures that improve
overall performance of the module. Moreover, the reliability of
photovoltaic modules is equally important as it determines their
useful life, cost effectiveness, and viability as reliable
alternative sources of energy.
SUMMARY
[0004] Provided are novel interconnect wire network assemblies and
methods of fabricating thereof. An assembly may include conductive
portions/individual wires that, in certain embodiments, are
substantially parallel to each other. The assembly also includes
two or more carrier films (i.e., the front side and back side
films) attached to opposite sides of the wires. The films are
typically attached along the wire ends. The films are made from
electrically insulating materials and at least the front side film
is substantially transparent. The front side film is used to attach
the wires to a photovoltaic surface of one cell, while the back
side film is used for attachment to a substrate surface of another
cell. These attachments electrically interconnect the two cells in
series. In certain embodiments, one or both carrier films extend
beyond two end wires and form insulated portions that allow much
closer arrangements of the cells in a module.
[0005] In certain embodiments, an interconnect wire network
assembly includes a plurality of conductive portions extending
substantially parallel to each other, a first carrier film having a
first substantially transparent electrically insulating layer, and
a second carrier film having a second substantially transparent
electrically insulating layer. The plurality of conductive portions
having a first set of ends defining a first edge and a second set
of ends defining a second edge. The plurality of conductive
portions is configured for current collection from a front side
surface of a first photovoltaic cell and electrical connection with
a back side surface of a second photovoltaic cell. The first
carrier film is coupled to the plurality of conductive portions
along the first edge and configured to attach the plurality of
conductive portions to the front side surface of the first
photovoltaic cell to form a first electrical connection between the
front side surface and the plurality of conductive portions. The
second carrier film is coupled to the plurality of conductive
portions along the second edge and configured to attach the
plurality of conductive portions to the back side surface of the
second photovoltaic cell to form a second electrical connection
between the back side surface and the plurality of conductive
portions.
[0006] In certain embodiments, a first carrier film is positioned
on another side of the conductive portions with respect to the
second carrier film. The two films may overlap. In other
embodiments, the two films may be positioned at a predetermined
distance from the second carrier film. An outside edge of the first
carrier film may substantially coincide with the first edge of the
plurality of conductive portions. In other embodiments, the first
carrier film extends past the first edge of the conductive
portions. In certain embodiments, conductive portions extend past
two edges of the first carrier film.
[0007] One or both carrier films may be made from one or more of
the following materials: polyethylene terephthalate, polyethylene
co-methacrylic acid, polyamide, and polyetheretherketone. In the
same or other embodiments, conductive portions may be made from one
or more of the following materials: copper, aluminum, nickel, and
chrome. Conductive portions may include multiple individual wires.
These individual wires may be between 24 gauge and 56 gauge. The
individual wires may be spaced apart by between about 2 millimeters
and about 5 millimeters. Each wire may be electrically insulated
from other wires prior to attaching the interconnect wire network
assembly to the first photovoltaic cell or the second photovoltaic
cell. In certain embodiments, multiple individual wires have a
strip of foil attached to the second edge and electrically
interconnecting the multiple individual wires.
[0008] In certain embodiments, the first carrier film extends past
two end wires of the plurality of conductive portions forming two
side insulating regions. The first carrier film may extend past and
folds over two end conductive portions of the plurality of
conductive portions, forming insulating shells around the two end
conductive portions.
[0009] Provided also a method of fabricating an interconnect wire
network assembly. The method involves unwinding multiple individual
wires from corresponding multiple wire rolls, extending the wires
along an unwinding direction substantially parallel to each other
at a predetermined distance from each other, applying a first
carrier film onto the first surface of the wires, and applying a
second carrier film onto the second surface of the wires. The two
first carrier films may be applied substantially perpendicular to
the unwinding direction. Applying the first carrier film may
involve passing an electric current through a portion of the
multiple individual wires that is in contact with the first carrier
film in order to heat this portion.
[0010] The method may also involve forming a roll of interconnect
wire network subassemblies, unwinding the roll of interconnect wire
network subassemblies, and cutting the multiple individual wires
substantially perpendicular to the multiple individual wires to
form the interconnect wire network assembly. In certain
embodiments, the method involves cutting the multiple individual
wires substantially perpendicular to the multiple individual wires
to form the interconnect wire network assembly. Such cutting may
also involve cutting the first carrier film or the second carrier
film.
[0011] Provided also a photovoltaic module that includes a first
photovoltaic cell having a front side surface, a second
photovoltaic cell having a back side surface, and an interconnect
wire network assembly. The assembly may include a plurality of
conductive portions extending substantially parallel to each other
and in electrical communication with the front side of the first
photovoltaic cell and the back side of the second photovoltaic
cell. The assembly also includes a first carrier film coupled to
the plurality of conductive portions along the first edge and
attaching the plurality of conductive portions to the front side
surface of the first photovoltaic cell. Furthermore, the assembly
includes a second carrier film coupled to the plurality of
conductive portions along the second edge and attaching the
plurality of conductive portions to the back side surface of the
second photovoltaic cell. The conductive portions include a first
set of ends defining the first edge and a second set of ends
defining the second edge. The first carrier film is made from a
first substantially transparent electrically insulating layer,
while the second carrier film is made from a second substantially
transparent electrically insulating layer.
[0012] These and other embodiments are described further below with
reference to the figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic representation of a photovoltaic
module having multiple photovoltaic cells electrically
interconnected with each other using interconnect wire network
assemblies, in accordance with certain embodiments.
[0014] FIG. 2 is a schematic top view of an interconnect wire
network assembly, in accordance with certain embodiments.
[0015] FIG. 3A is a schematic side view of an interconnect wire
network assembly depicted in FIG. 2, in accordance with certain
embodiments.
[0016] FIG. 3B is a schematic side view of another interconnect
wire network assembly, in accordance with different
embodiments.
[0017] FIG. 3C is a schematic side view of yet another interconnect
wire network assembly, in accordance with different
embodiments.
[0018] FIG. 4 illustrates a process flowchart corresponding to a
method of fabricating an interconnect wire network assembly, in
accordance with certain embodiments.
[0019] FIG. 5 illustrates a schematic view of an apparatus for
fabricating an interconnect wire network assembly, in accordance
with certain embodiments.
[0020] FIG. 6A is a schematic representation of a technique for
cutting a subassembly to form an interconnect wire network
assembly, in accordance with certain embodiments.
[0021] FIG. 6B is a schematic representation of another technique
for cutting a subassembly to form an interconnect wire network
assembly, in accordance with different embodiments.
[0022] FIG. 7 illustrates a schematic side view of two photovoltaic
cells electrically interconnected using an interconnect wire
network assembly, in accordance with certain embodiments.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0023] In the following description, numerous specific details are
set forth in order to provide a thorough understanding of the
present invention. The present invention may be practiced without
some or all of these specific details. In other instances, well
known process operations have not been described in detail so as to
not unnecessarily obscure the present invention. While the
invention will be described in conjunction with the specific
embodiments, it will be understood that it is not intended to limit
the invention to the embodiments.
[0024] To provide a better understanding and context for the
description of various features of interconnect wire network
assemblies, an example of a photovoltaic module will now be
described. FIG. 1 is a schematic representation of a photovoltaic
module 100 having multiple photovoltaic cells 104, in accordance
with certain embodiments. Photovoltaic cells 104 are electrically
interconnected in series using multiple interconnect wire network
assemblies 106. Specifically, each pair of cells 104 is
interconnected using one assembly 106. FIG. 1 shows eight
photovoltaic cells interconnected with seven assemblies; however,
it will be understood that any number of cells may be used in a
module. In certain embodiments, a module includes at least 10 cells
or, more specifically, at least 15 cells interconnected in series.
In particular embodiments, a module includes 22 cells
interconnected in series. Furthermore, one set of cells
interconnected using wire network assemblies may be further
connected to one or more similar sets in the same module. For
example, a module may include two sets, each set including 22
interconnected cells. The connections between the sets may be
provided by wire network assemblies or other components.
[0025] Multiple cells may be interconnected in series when
individual cells do not provide an adequate output voltage. The
output voltage requirement may be driven by electrical current
transmission and other factors. For example, a typical voltage
output of an individual CIGS cell is between 0.4V and 0.7V. A
module built from CIGS cells is often designed to provide a voltage
output of at least about 20V or even higher. In addition to
interconnecting multiple cells in series, a module may include one
or more module-integrated inverters. Interconnect wire network
assemblies 106 may be also used to provide uniform current
distribution and collection from one or both contact layers, as
further explained below. It should be understood that these
assemblies may also be used to provide parallel electrical
connections or a combination of in-series and parallel
connections.
[0026] As shown in FIG. 1, each interconnect wire network assembly
106 (with the exception of the bottom assembly, which is further
described above) extends over a front side of one cell and under a
back side of another cell. One or both cells in this pair may be
connected to other cells and so on. As such, most cells may have
one interconnect wire network assembly extending over its front
side and another interconnect wire network assembly extending under
its back side. An end cell in the set (e.g., the top-most cell in
FIG. 1) may have only one interconnect wire network assembly
extending over one of its surfaces, typically over the front side.
In this embodiment, a bus bar 108 may be connected directly to the
cell (i.e., to its back side). In some embodiments, an end cell
(e.g., the bottom-most cell in FIG. 1) may still have two
interconnect wire network assemblies. A bus bar 110 may be attached
to one of these assemblies. Specifically, bus bar 110 may be
attached to a portion of the interconnect wire network assembly
extending outside of the cell perimeter. Such attachment may
involve welding, soldering, and other forms of attachments, which
are generally not suitable for attachment directly to the
cells.
[0027] When an interconnect wire network assembly extends over a
front side of the photovoltaic cell, it makes an electrical
connection with that side or, more specifically, with a top layer
arranged on that side. In certain embodiments, a photovoltaic cell
includes one or more transparent conductive oxides (TCO), such as
zinc oxide, aluminum-doped zinc oxide (AZO), indium tin oxide
(ITO), and gallium doped zinc oxide, disposed over the front side
of the photovoltaic cell. A typical thickness of a top conductive
layer is between about 100 nanometers to 1,000 nanometers (for
example between about 200 nanometers and 800 nanometers), with
other thicknesses within the scope. The TCO provides an electrical
connection between the entire photovoltaic layer and a portion of
the interconnect wire network assembly extending over the front
side of the cell. Due to the limited conductivity of the TCO layer,
the interconnect wire network assembly typically extends uniformly
over the entire front side surface of the cell and provides uniform
current distribution and collection from this surface. As such, an
interconnect wire network assembly is sometimes referred to as a
current collector. Various characteristics of interconnect wire
network assemblies allowing uniform current distribution and
collection are described below in the context of FIG. 2.
[0028] An interconnect wire network assembly extending under a back
side of the cell makes an electrical connection with that side or
more specifically with a conductive substrate supporting the
photovoltaic stack. Some examples of photovoltaic stacks include
CIGS cells, cadmium-telluride (Cd--Te) cells, amorphous silicon
(a-Si) cells, micro-crystalline silicon cells, crystalline silicon
(c-Si) cells, gallium arsenide multi-junction cells, light
adsorbing dye cells, and organic polymer cells. Some examples of
conductive substrates include stainless steel foil, titanium foil,
copper foil, aluminum foil, beryllium foil, a conductive oxide
deposited over a polymer film (e.g., polyamide), a metal layer
deposited over a polymer film, and other conductive structures and
materials. In certain embodiments, a conductive substrate has a
thickness of between about 2 mils and 50 mils (e.g., about 10
mils), with other thicknesses also within the scope. Generally, a
substrate is sufficiently conductive such that a uniform and
extensive distribution of interconnect wire network assembly wires
is not needed for uniform current collection on this side. As such,
a portion of the wire network assembly extending under the back
side of one cell may be smaller than a corresponding portion
extending over a front side of an adjacent cell.
[0029] As shown in FIG. 1 and further explained below with
reference to FIG. 2, interconnect wire network assemblies may
include conductive portions, such as multiple individual wires,
extending substantially parallel to each other. When installed into
the module, conductive portions extend under photovoltaic cells and
are illustrated with dashed line in FIG. 1. The other part of the
conductive portions extends over front sides of adjacent cells and
is shown with solid lines. When cells are spaced apart as shown in
FIG. 1, a part of the conductive portions extends between the
cells. In other embodiments, cells in the module may be adjacent to
each other (e.g., have a minimal or no gap) or even overlap
(sometimes referred to as a "shingle" arrangement). Interconnect
wire network assemblies also have insulating carrier films, which
allow various insulation schemes that in turn allow these various
cell arrangements, as will be now described in more detail.
[0030] FIG. 2 is a schematic top view of an interconnect wire
network assembly 200, in accordance with certain embodiments.
Assembly 200 includes conductive portions 202 and two carrier films
(i.e., a first carrier film 204 and a second carrier film 206).
Since these films 204, 206 are cut to a predetermined length, these
films 204, 206 may be also referred to as carrier strips or decals.
A portion of conductive portions 202 extends under first carrier
film 204 from the top view perspective presented in FIG. 2. As
such, this portion is shown with dashed lines. In certain
embodiments, conductive portions 202 include multiple individual
wires continuously extending between two edges (i.e., the first
edge and the second edge) defined by ends of the wires along
direction X. In certain embodiments, these wires extend
substantially parallel to each other. Specifically, an angle
between any pair of adjacent wires may be less than about 5.degree.
or, more specifically, less than about 1.degree.. However, wires
may extend in other directions and/or cross-over.
[0031] Substantially parallel wires are shown in FIG. 2 and may be
arranged and spaced apart along the length of assembly 200, or
direction Y. This arrangement may be characterized by a pitch 209,
which, for purposes of this document, is defined as a distance
between the centers of two adjacent wires. The pitch determines the
distance an electrical current travels through the conductive top
layer of the cell prior to reaching more conductive wires of the
interconnect wire network assembly 200. Reducing the pitch
increases the current collection characteristics of assembly 200.
However, a smaller pitch also decreases the useful surface area of
the cell by covering the photovoltaic layer with non-transparent
wires. In certain embodiments, pitch 209 is between about 2
millimeters and 5 millimeters (e.g., about 3.25 millimeters),
although other distances may be used, as appropriate.
[0032] Conductive portions 202 are typically made from thin, highly
conductive metal stock and may have round, flat, and other shapes.
As mentioned above, conductive portions 202 are generally more
conductive than the TCO layer and are used to improve current
collection from the front surface of the cell. Examples of wire
materials include copper, aluminum, nickel, chrome, or alloys
thereof. In some embodiments, a nickel coated copper wire is used.
In certain embodiments, the wire is 24 to 56 gauge, or in
particular embodiments, 32 to 56 gauge (for example, 40 to 50
gauge). In specific embodiments, the wire has a gauge of 34, 36,
40, 42, 44, or 46. Additional wire examples are described in U.S.
patent application Ser. No. 12/843,648, entitled "TEMPERATURE
RESISTANT CURRENT COLLECTORS FOR THIN FILM PHOTOVOLTAIC CELLS,"
filed Jul. 26, 2010, (Attorney Docket MSOLP039/IDF156), which is
incorporated herein by reference in its entirety for purposes of
describing additional wire examples.
[0033] Carrier films 204 and 206 are coupled to conductive portions
202 along two edges defined by the ends of conductive portions 202,
such as ends of wires shown in FIG. 2. These edges extend along the
length of the assembly in direction Y and may be generally parallel
to each other. Various positions of carrier films 204 and 206 with
respect to these edges are explained below with reference to FIGS.
3A, 3B, and 3C. As noted, during fabrication of a module, one
carrier film is configured to attach wires 202 to a photovoltaic
surface of one photovoltaic cell and may be referred to as a top
carrier film or a top decal. Another carrier film is configured to
attach wires 202 to a substrate surface of another photovoltaic
cell and may be referred to as a bottom carrier film or a bottom
decal. Either one of carrier films 204 and 206 can be a top carrier
film, while another one can be a bottom carrier film. These
designations are explained in more detail with reference to FIG. 7,
which shows two photovoltaic cells interconnected using an
interconnect wire network assembly. The attachments provided by the
carrier films form electrical connections between conductive
portions 202 and the photovoltaic and substrate surfaces of two
cells.
[0034] Both top and bottom carrier films are made from electrically
insulating materials. The top carrier film should also be
substantially transparent so as to allow the sunlight to reach the
photovoltaic layer. In certain embodiments, both carrier films are
substantially transparent electrically insulating layers. Some
examples of suitable carrier film materials include thermoplastic
materials, such as polyethylene terephthalate (PET), ionomer resins
(e.g., poly(ethylene-co-methacrylic acid)), polyamide,
polyetheretherketone (PEEK), or combinations of these. One
particular example is SURLYN.RTM., available from E. I. du Pont de
Nemours and Company in Wilmington, Del. In certain embodiments, one
or both carrier films have a layered structure. For example, a
carrier film may have three polymers layers, such as a co-extruded
stack containing SURLYN.RTM., PET, and another layer of SURLYN.RTM.
(with the PET layer positioned in between the two SURLYN.RTM.
layers). In certain embodiments, a suitable carrier may be a
thermoplastic material or materials curable using ultra violet (UV)
or other techniques.
[0035] FIG. 3A is a schematic side view of the interconnect wire
network assembly 200 depicted in FIG. 2, in accordance with certain
embodiments. This side view further illustrates various
arrangements of the assembly that may not be easily appreciated
from the top view in FIG. 2. Specifically, FIG. 3A shows carrier
films 204 and 206 attached to opposite sides of conductive portions
202. With reference to direction Z, carrier film 204 is positioned
on the top side of conductive portions 202, while carrier film 206
is positioned on the bottom side of conductive portions 202. This
orientation does not necessarily correspond to carrier film 204
being a top carrier film in the module assembly. In this
orientation and reference, the bottom surface of carrier film 204
may be an adhesive surface and used for securing carrier film 204
to conductive portions 202. Furthermore, the same adhesive surface
is used to secure carrier film 204 to the cell (e.g., to a
photovoltaic surface if carrier film 204 is a top carrier film)
after integration of assembly 200 into the module. Correspondingly,
carrier film 206 has a top adhesive surface for securing carrier
film 206 to conductive portions 202 and, after installation, to the
cell (e.g., to a substrate surface if carrier film 206 is a bottom
carrier film). Adhesion between the carrier films and conductive
portions, during fabrication of the assembly, may be achieved by
applying pressure between these components and/or heat to one or
both components. These features are further described below with
reference to FIG. 4.
[0036] FIG. 3A illustrates carrier films 204 and 206 forming an
overlap 208 in the middle portion of assembly 200. This overlap may
be used, in part, to prevent electrical shorts in the assembled
module and for other purposes. At overlap 208, carrier films 204
and 206 may be adhered to each other in the areas between adjacent
conductive portions and outside of end conductive portions to
provide additional structural integrity to assembly 200. Further,
conductive portions 202 are shown to extend past the outside edges
of carrier films 204 and 206 (in direction X) and have exposed ends
205 and 207.
[0037] Other arrangements of wires and carrier films in
interconnect wire network assemblies are possible. FIG. 3B is a
schematic side view of another assembly 300, in accordance with
different embodiments. Carrier films 304 and 306 extend past the
wire ends (in direction X) and form insulating regions or flaps 305
and 307. There may be a need to protect the ends of the wires to
prevent their sharp corners from causing electrical shorts.
Furthermore, carrier films 304 and 306 do not overlap in the middle
portion of assembly 300. Instead carrier films 304 and 306 form a
gap 308 in that portion and expose a portion of wires 302. This gap
308 may help to improve the flexibility of assembly 300 around this
portion and may reduce the overall thickness of assembly 300.
[0038] FIG. 3C is a schematic side view of interconnect wire
network assembly 310, in accordance with different embodiments.
Outside edges of carrier films 314 and 316 of this assembly
coincide with the ends of wires 312. This type of arrangement may
be formed by cutting wires 312 together with carrier films 314 and
316 during fabrication of the assembly, as described below with
reference to FIG. 6B. Furthermore, carrier films 314 and 316 do not
overlap in the middle portion of the assembly. Instead, the inside
edges of carrier films 314 and 316 coincide.
[0039] In general, respective positions of the carrier films'
outside edges relative to the wires' ends are independent from
respective positions of the inside edges. Various combinations of
these respective positions are not limited to the examples
presented in FIGS. 3A, 3B, and 3C and described above. Other
combinations are possible (e.g., extended outside edges (as shown
in FIG. 3B) combined with overlapped inner edges (as shown in FIG.
3A), a middle gap (as shown in FIG. 3B) combined with exposed wire
ends (as shown in FIG. 3A), and so on).
[0040] Returning to FIG. 2, carrier films 204 and 206 are shown to
extend beyond end wires 202a and 202b in Y direction. These
extensions form two side insulating regions 211a and 211b, which
may be referred to as insulating flaps. Insulating regions 211a and
211b do not have any conductive materials and may include only one
or both carrier films. As such, insulating regions 211a and 211b
can be used to insulate the edges of corresponding photovoltaic
cells after fabrication of the module. For example, this insulation
allows a closer arrangement of cells within a module along Y
direction. It should be noted that only one carrier film may extend
beyond end wires 202a and 202b to form insulating regions 211a and
211b. In certain embodiments, there is not gap between two adjacent
cells (not accounting portions of the interconnect assemblies
attached to these cells) in this direction. The cells may even
overlap in certain embodiments. Carrier films of the interconnect
assemblies may be used to insulate edges of the two adjacent cells.
For example, one portion of the carrier film may be attached to the
front light incident side of the first cell, while another portion
may extend outside of the first cell boundary and under the back
side of the adjacent cell. This extension insulated the two
adjacent edges of the cells with respect to each other.
[0041] In certain embodiments, conductive portions include
individual wires such that each wire is electrically insulated from
other wires. For example, the wires may extend substantially
parallel to each other and/or do not touch each other. One having
ordinary skills in the art would understand that such wires remain
electrically insulated only until attachment of the assembly to a
photovoltaic cell, during which the wires become interconnected by
a front side, back side, or both. In other embodiments, wires may
be interconnected by a strip of foil or other wires. The
interconnection may be provided along one set of wires' ends,
similar to an example presented in FIG. 1. The interconnecting
element (e.g., a foil strip) may then be used for connection to bus
bars and/or other electrical components of the module. In certain
embodiments, an interconnecting element may be used to enhance an
electrical connection to a back side of the photovoltaic
module.
[0042] FIG. 4 illustrates a flowchart corresponding to a process
400 of fabricating an interconnect wire network assembly, in
accordance with certain embodiments. Process 400 may start with
unwinding multiple individual wires from wire rolls or spools in
operation 402. In certain embodiments, multiple wires provided in
operation 402 may be interconnected and provided as a woven mesh.
However, it would be understood by one having ordinary skills in
the art that other types of conductive portions may be used in
addition or instead of individual wires. Various examples of wires
are described above. The number of wires depends on a size of the
assembly (and a photovoltaic cell) and a pitch between the wires.
The wires may have different profiles (e.g., a round profile or a
flat profile).
[0043] Process 400 may proceed with extending the wires along the
same direction (i.e., "an unwinding direction") in operation 404.
The wires may be substantially parallel during this operation and
positioned at a predetermined distance from each other. In other
embodiments, wires may be arranged in other configurations and may
even overlap. During this operation, the wires may be arranged
within substantially the same plane by, for example, applying a
tension to the wires. In general, the multiple wires extended in
this operation may be characterized as having a first surface and a
second surface regardless of whether these surfaces are planar or
not. These two surfaces are spaced apart by a cross-sectional
dimension of the wires, such as wire diameters for round wires or
wire thicknesses for flat wires.
[0044] FIG. 5 illustrates a schematic view of an apparatus 500 for
fabricating an interconnect wire network assembly, in accordance
with certain embodiments. Apparatus 500 includes multiple spools
502 providing multiple wires 504. Wires 504 remain under tension
provided by a rewind roller 508, which is used for the winding of
sub-assemblies. The pitch between wires 504 may be specific to the
positioning of spools 502 and/or a guiding mechanism (not
shown).
[0045] Returning to FIG. 4, process 400 then continues with
applying one carrier film onto the first surface of the wires in
operation 406 and applying another carrier film onto the second
surface of the wires in operation 408. These operations may be
performed in parallel or in series. For example, one carrier film
may be initially attached to the wires followed by a separate
operation in which another carrier film is attached to the wires.
In another example, both films are applied in the same operation.
Edges of the two films can be aligned during this part of the
process. Furthermore, in certain embodiments, one or both films are
applied substantially perpendicular to the unwinding direction.
Finally, this part of the process may also involve cutting the
carrier films, if the films are supplied from continuous rolls.
Overall, in certain embodiments, a product of this part of the
process is a set of continuous wires with two strips of carrier
film attached to the opposite sides of this set of wires. It should
be noted that the operation of applying carrier film strips
continues as wires are being unrolled and fed through the
application area.
[0046] As shown in FIG. 5, apparatus 500 also includes two carrier
film rolls 506a and 506b, which supply the two films onto the two
surfaces of the extended wires 504. A mechanism (not shown) may be
employed for grabbing free ends 507a and 507b of the carrier films
to extend these films from rolls 506a and 506b and into position
with respect to wires 504. A cutting mechanism (not shown) may be
employed for cutting the carrier films from the rolls 506a and 506b
along a cutting line 509. A roll-type or guillotine-type cutter can
be used for these purposes. Cutting forms carrier film strips 510a
and 510b, which are carried by wires 504 to sub-assembly roll
508.
[0047] In certain embodiments, applying a carrier film to the wires
involves passing an electric current through at least a portion of
the wires that is in contact with the carrier films. The electrical
current heats this portion of the wires, which may help to adhere
the carrier film to the wires. For example, two metal rollers may
be put in temporary contact with wires in the post-application zone
512. A predetermined voltage may be applied to the rollers at least
during the contact period to drive current through the wires and
heat the wires. Further, a pressure may be applied between wires
504 and carrier film strips 510a and 510b by, for example, passing
a subassembly through nip rollers (e.g., heated rollers) in the
post-application zone.
[0048] Returning to FIG. 4, process 400 may proceed with an
optional operation 410, during which continuous wires with carrier
film films may be formed into a roll as, for example, shown in FIG.
5. This roll is considered to be a sub-assembly and may be stored
prior to further processing, which involves unwinding the toll and
cutting the wires to form interconnect wire network assemblies.
Process 400 may then proceed with cutting wires across their length
(e.g., in a direction substantially perpendicular to the wires) to
form the interconnect wire network assembly in operation 412. It
should be noted that operation 412 may proceed without forming an
intermediate subassembly (i.e., without an intermediate optional
operation 410). A guillotine-type of cutter may be used for this
purpose. Operation 412 may involve cutting only the wires in the
areas free of the carrier films. An example of such an operation is
shown in FIG. 6A. Cutting lines 602 are depicted with heavy dashed
lines (thin dashed lines correspond to the hidden edge of one
carrier film strip). Cutting lines 602 pass through wires 504 but
not through either one of carrier films 510a and 510b. In other
embodiments, operation 412 may involve cutting both the wires and
one or more carrier films. An example of such an operation is shown
in FIG. 6B where cut lines 604 go through both wires and initial
carrier film strips 610a and 610b. After cutting, carrier strip
610a is divided into new carrier strips 612a and 614a, while
carrier strip 610b is divided into new carrier strips 612b and
614b. New carrier strips 612a and 612b together with a portion of
wires 606 attached to these strips form an interconnect wire
network assembly.
[0049] FIG. 7 illustrates a schematic side view of two photovoltaic
cells 702 and 706 and an interconnect wire network assembly 710
electrically connecting these two cells, in accordance with certain
embodiments. Assembly 710 includes wires 712 and two carrier films
(i.e., top carrier film 714 and bottom carrier film 716). In
certain embodiments, top carrier film 714 and bottom carrier film
716 are the same type of films (in terms of thickness and
composition). The dimensions of top carrier film 714 and bottom
carrier film 716 may be the same or different. Top carrier film 714
and bottom carrier film 716 are shown to overlap in the area 718.
However, other embodiments described above with reference to FIGS.
3A, 3B, and 3C are possible. Photovoltaic cell 702 includes a
substrate 703 and a photovoltaic layer 704 positioned on a front
surface of a substrate. Similarly, photovoltaic cell 706 includes a
substrate 707 and a photovoltaic layer 708 positioned on a front
surface of a substrate. A portion of bottom carrier film 716
extends beyond the edge of photovoltaic cell 702 and over
photovoltaic layer 704 of this cell. This feature may be used to
prevent short circuits between photovoltaic layer 704 and substrate
703 and caused by wires 712.
[0050] Although the foregoing invention has been described in some
detail for purposes of clarity of understanding, it will be
apparent that certain changes and modifications may be practiced
within the scope of the appended claims. It should be noted that
there are many alternative ways of implementing the processes,
systems and apparatus of the present invention. Accordingly, the
present embodiments are to be considered as illustrative and not
restrictive, and the invention is not to be limited to the details
given herein.
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