Series connected photovoltaic module and method for its...

Batteries: thermoelectric and photoelectric – Photoelectric – Panel or array

Reexamination Certificate

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C136S251000, C136S256000, C136S255000, C136S249000, C257S433000, C257S458000, C257S457000, C257S443000, C438S080000, C438S098000, C438S067000, C438S072000, C438S074000

Reexamination Certificate

active

06803513

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to photovoltaic devices. More specifically, the invention relates to photovoltaic modules comprised of two or more electrically interconnected photovoltaic cells. Most specifically, the invention relates to photovoltaic power generating modules, and methods for their manufacture, wherein the number of electrical interconnections between the cells comprising the module are minimized.
BACKGROUND OF THE INVENTION
Photovoltaic devices are nonpolluting and silent in operation. They are readily adapted to either a centralized or distributed power generating system, and growing in popularity as an alternative to fossil or nuclear powered electrical generation systems. The high cost and small size of single crystal photovoltaic devices has heretofore limited their utility; however, high volume processes for the manufacture of thin film semiconductor devices are now in commercial production, and very large area photovoltaic materials are being manufactured in continuous, roll-to-roll processes. The photovoltaic material produced in such processes is generally cut to size and fabricated into power generating modules which are comprised of a number of electrically interconnected photovoltaic cells selected to provide a desired output voltage and current. Such modules should have high power generating efficiency, and toward that end it is desirable to maximize the photovoltaically active surface of each cell. In addition, such modules should be rugged, low in cost and easy to fabricate. In addition, many applications require that such power generating modules be as light in weight as possible.
In view of these criteria, the prior art has developed a number of processes for fabricating large area photovoltaic materials into individual power generating cells and/or modules comprised of interconnected cells. U.S. Pat. Nos. 5,457,057; 5,681,402; and 5,759,291, the disclosure of which are incorporated herein by reference, show particular configurations of photovoltaic cells in which current collecting grid wires are employed to convey photovoltaically generated currents to a bus bar member. The disclosed structures maximize the photovoltaically active area of the devices; and in addition, are reliable, rugged and easily fabricated.
Referring now to
FIGS. 1 and 2
, there is shown a photovoltaic cell
20
of the prior art, which is generally similar to cells specifically disclosed in the U.S. Pat. No. 5,759,291 patent.
FIG. 1
is a top plan view of the cell
20
, and
FIG. 2
is a cross-sectional view of that cell
20
taken along line
2

2
of FIG.
1
. As is best seen in
FIG. 2
, the cell
20
includes a substrate electrode
22
having a body of photovoltaic material
24
disposed upon a topmost surface thereof. A top electrode
26
is disposed upon the upper surface of the photovoltaic body
24
.
The photovoltaic body
24
is typically comprised of a number of layers of semiconductor material, and it operates to absorb incident photons and generate electron-hole pairs which are collected by the substrate electrode
22
and top electrode
26
to generate a photocurrent. The patents incorporated by reference herein describe some specific materials and configurations for the photovoltaic body; although, it is to be understood that the present invention may be implemented using various photovoltaic materials.
The substrate electrode
22
is, in some instances, fabricated from a sheet of electrically conductive material, such as a sheet of stainless steel, aluminum, electrically conductive polymer, cermet, degenerate semiconductor or the like, and it may include further layers thereupon, such as light reflective layers, texturizing layers and the like as is known in the art. In other instances, the substrate
22
may comprise a composite substrate such as a body of polymeric material having an electrically conductive coating, such as a coating of metal, non-metallic conductor or the like thereupon. Such composite substrates are particularly advantageous where the weight of the finished device is a concern. Again, the present invention may be implemented with all of such substrates. The top electrode
26
is transmissive of photovoltaically active wavelengths. One particularly preferred group of top electrode materials comprises transparent, electrically conductive oxide (TCO) material such as indium oxide, tin oxide, mixed oxides of indium and tin, and the like.
As is also seen in
FIG. 2
, a current collecting grid wire
28
is disposed upon the top, light incident, surface of the top electrode
26
. This grid wire serves to collect photogenerated currents and convey them to a pair of current collecting bus bars
30
a
,
30
b
. Inclusion of this grid wire
28
is important, since the electrical conductivity of most TCO materials is fairly low; hence, the series resistance of the photovoltaic device
20
would be very high if the photocurrents had to travel laterally very far through the top electrode material. The grid wire
28
shortens this current path and provides a high conductivity conduit for the photo currents.
As further illustrated in
FIG. 2
, the bus bars
30
a
,
30
b
, as well as the end portions of the grid wire
28
, are supported by an electrically insulating body
32
a
,
32
b
disposed upon the semiconductor body
24
. This insulating body prevents the bus bar
30
and grid wire
28
from short circuiting through to the substrate
22
. In one particularly preferred embodiment, and as is described in the '291 patent, this insulating body
32
is comprised of a double-sided adhesive tape which is applied to the semiconductor body
24
prior to the deposition of the top electrode material
26
thereupon. In other embodiments, and as is described in the patents incorporated by reference herein, this insulating body
32
may be disposed upon the substrate
22
. Also, in some instances, the bus bars
30
may be directly affixed to the semiconductor body
24
, and the grid wires bonded between the bus bar and semiconductor or atop the semiconductor body.
Referring now to
FIG. 1
, there is shown a top plan view of the device of FIG.
2
. Visible in the figure is the top electrode material
26
, grid wires
28
a
-
28
e
, bus bars
30
a
,
30
b
and edge portions of the substrate
22
.
As is described in the patents incorporated by reference herein, the photovoltaic cell material of
FIGS. 1 and 2
can be electrically interconnected to form multi-cell modules. Such modules are typically configured as a series connected group of cells, and in that regard, an electrical connector is employed to establish a current path between the bus bar of one cell and the substrate of an adjacent cell. These interconnectors are typically soldered or welded, and
FIGS. 11 -13
of the '057 patent illustrate such interconnections. As is known and described in the art, the interconnected cells are typically laminated with an encapsulant material to produce a finished module.
While prior art technology as described hereinabove has produced high quality, high efficiency modules, the inventors hereof have recognized that the steps and structures associated with the formation of interconnections in accord with the prior art can be improved upon so as to maximize the efficiency, reliability and ease of fabrication of such photovoltaic modules.
As will be described in detail hereinbelow, the present invention provides a photovoltaic module in which the number of soldered or welded joints in the module is minimized thereby decreasing the likelihood of device failure and simplifying its manufacture. In addition, the structures of the present invention provide a highly redundant current path through the device which further enhances its reliability. The structures of the present invention are readily adaptable to the manufacture of very lightweight photovoltaic generator devices having ultra lightweight composite substrates. These and other advantages of the present invention will be apparent from the drawings, discussion and description which

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