U.S. patent application number 13/159388 was filed with the patent office on 2011-10-06 for modular solar panels with heat exchange.
This patent application is currently assigned to SUNMODULAR, INC.. Invention is credited to Mark V. Brillhart, Ana M. Corrales, Eugenia M. Corrales.
Application Number | 20110240098 13/159388 |
Document ID | / |
Family ID | 57860020 |
Filed Date | 2011-10-06 |
United States Patent
Application |
20110240098 |
Kind Code |
A1 |
Corrales; Eugenia M. ; et
al. |
October 6, 2011 |
Modular Solar Panels with Heat Exchange
Abstract
A photovoltaic module with photovoltaic cell and a heat sink.
The heat sink is attached on a side of the cell opposite to the
light-receiving side of the photovoltaic cell. The heat sink can
remove heat caused by light absorbed by the photovoltaic cell but
not converted to electricity as well as heat generated by
resistance to high current passing through electrodes of the
photovoltaic cell. A photovoltaic module formed of such cells can
exhibit greater energy conversion efficiency as a result of the
ability to dissipate the heat. A method of making a solar module
involves e.g. laminating a heat sink to a photovoltaic cell.
Inventors: |
Corrales; Eugenia M.; (Los
Altos, CA) ; Brillhart; Mark V.; (Palo Alto, CA)
; Corrales; Ana M.; (Los Altos, CA) |
Assignee: |
SUNMODULAR, INC.
Los Altos
CA
|
Family ID: |
57860020 |
Appl. No.: |
13/159388 |
Filed: |
June 13, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11788456 |
Apr 19, 2007 |
|
|
|
13159388 |
|
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|
Current U.S.
Class: |
136/246 ;
165/185 |
Current CPC
Class: |
B29C 45/1671 20130101;
Y02B 10/10 20130101; Y10T 29/49114 20150115; Y02B 10/12 20130101;
H01M 14/005 20130101; H02S 40/42 20141201; B29C 45/14639 20130101;
Y02E 10/50 20130101; H02S 20/23 20141201; H02S 20/25 20141201; H01L
31/052 20130101; H02S 40/36 20141201; Y10T 29/49112 20150115; Y02B
10/20 20130101 |
Class at
Publication: |
136/246 ;
165/185 |
International
Class: |
H01L 31/052 20060101
H01L031/052; F28F 3/04 20060101 F28F003/04 |
Claims
1. A system for cooling a set of photovoltaic cells located in a
photovoltaic module, the system comprising: a heat sink base
configured to draw heat from said photovoltaic cells; and a
plurality of protrusions attached to said heat sink base in a
pattern, said protrusions forming a first set of channels parallel
with a first axis, said pattern including a set of discontinuities,
said discontinuities forming a second set of channels; wherein all
of said channels in said second set of channels are non-orthogonal
to said first axis.
2. The system of claim 1, further comprising a thermal interface
layer between said heat sink base and said photovoltaic cells.
3. The system of claim 1, wherein said photovoltaic module is a
non-concentrating photovoltaic module.
4. The system of claim 1, wherein said channels in said second set
of channels are herringbone shaped.
5. The system of claim 1, wherein said protrusions are one of
pyramids, cylinders, square pegs, and cones.
6. A photovoltaic module with a set of photovoltaic cells
comprising: a heat sink base configured to heat from said
photovoltaic cells; a plurality of heat dissipating shapes attached
to said heat sink base in a pattern, said plurality of heat
dissipating shapes forming a first set of channels being parallel
to each other along an axis; and a second set of channels formed by
a set of discontinuities in said pattern, said second set of
channels having at least one channel; wherein said second set of
channels are not parallel to said axis, and are non-orthogonal to
said axis.
7. The module of claim 6, further comprising a thermal interface
layer between said heat sink base and said photovoltaic cells.
8. The module of claim 7, wherein said heat sink base and said heat
dissipating shapes comprise the same material.
9. The module of claim 6, wherein said heat dissipating shapes are
one of pyramids, cylinders, square pegs, and cones.
10. The module of claim 6, wherein said second set of channels are
herringbone shaped.
11. The module of claim 6, wherein said photovoltaic module is a
non-concentrating photovoltaic module.
12. The module of claim 10, wherein: said photovoltaic module is
configured to be mounted on a rooftop; and said axis is
perpendicular to a ridgeline of said rooftop when said photovoltaic
module is mounted on said rooftop.
13. A photovoltaic module with a set of photovoltaic cells
comprising: a heat sink base configured to heat from said
photovoltaic cells; a plurality of protrusions attached to said
heat sink base, said protrusions being parallel to each other along
an axis, and said protrusions being segmented by a plurality of
discontinuities; and a set of direct air escape and entry channels
formed by said plurality of discontinuities, said set of direct air
escape and entry channels having at least one channel; wherein said
set of direct air escape and entry channels are not parallel to
said axis, and are non-orthogonal to said axis.
14. The module of claim 13, further comprising a thermal interface
layer between said heat sink base and said photovoltaic cells.
15. The module of claim 13, wherein said set of direct air escape
and entry channels are herringbone shaped.
16. The module of claim 13, wherein said photovoltaic module is a
non-concentrating photovoltaic module.
17. The module of claim 13, wherein said heat sink base is in
thermal communication with an unexposed surface of said
photovoltaic cells.
18. The module of claim 17, wherein said photovoltaic module is a
non-concentrating photovoltaic module.
19. The module of claim 18, wherein said heat sink base and said
protrusions comprise the same material.
20. The module of claim 17, wherein said protrusions are one of
pyramids, cylinders, square pegs, and cones.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 11/788,456, entitled "Modular Solar Panels with Heat Exchange"
filed Apr. 19, 2007, which is incorporated by reference in its
entirety herein as if it was put forth in full below.
BACKGROUND OF THE INVENTION
[0002] Solar energy is a renewable energy source that has gained
significant worldwide popularity due to the recognized limitations
of fossil fuels and safety concerns of nuclear fuels. The
photovoltaic (PV) solar energy demand has grown at least 25% per
annum over the past 15 years. Worldwide photovoltaic installations
increased by 1460 MW (Megawatt) in 2005, up from 1,086 MW installed
during the previous year (representing a 34% yearly increase) and
compared to 21 MW in 1985.
[0003] Most growth in the field of solar energy has focused on
solar modules fixed on top of an existing roof. Rooftops provide
direct exposure of solar radiation to a solar cell and structural
support for photovoltaic devices. Despite increased growth, the
widespread use of conventional roof-mounted solar modules has been
limited by their difficulty and cost of installation, lack of
aesthetic appeal, and especially their low conversion
efficiency.
[0004] Most conventional roof-mounted solar modules are constructed
largely of glass enclosures designed to protect the fragile silicon
solar cells. These modules are complex systems comprising separate
mechanical and electrical interconnections that are then mounted
into existing rooftops, requiring significant installation time and
skill. Available modules are also invasive in the aesthetics of
homes and commercial buildings, resulting in limited use. A few
manufacturers have fabricated more aesthetically pleasing and less
obstructive solutions, but the systems are not price competitive
largely due to installation difficulties and poor total area
efficiency. Lower module efficiency levels are correlated to higher
photovoltaic system costs because a greater module area is required
for a given energy demand.
[0005] The efficiency of converting light into electricity for a
typical crystalline-silicon roof-mounted solar cell is
approximately 13%. Some systems have seen efficiency increases (up
to 18-20%) by modifications such as the use of anti-reflective
glass on the cell surface to decrease optical reflection, use of
textured glass on the cell surface to increase light trapping, and
the use of improved materials like thin film silicon or germanium
alloy. Despite these improvements, solar cell conversion efficiency
remains limited, in part, by high solar cell temperatures. The
efficiency of a photovoltaic device decreases as the temperature
increases. Part of the energy radiated onto the cell is converted
to heat, which limits the electrical energy output and overall
conversion efficiency of the cell. Fabrication of a system capable
of removing heat from the photovoltaic cell would greatly increase
total efficiency.
[0006] There is significant interest in and need for a photovoltaic
module that addresses the above problems.
BRIEF SUMMARY OF THE INVENTION
[0007] Described herein are various solar modules that produce
energy from the sun's radiation as well as various methods employed
in fabrication of those solar modules. Some of the modules have
increased efficiency in converting solar energy to electricity.
Some modules are aesthetically attractive and well suited for
installation over top of conventional roofs.
[0008] In one instance, the photovoltaic module has photovoltaic
cells, a frame retaining the photovoltaic cells and adapted to
mount on a finished rooftop, and a heat sink to remove heat from
the photovoltaic cells. The heat sink has fins positioned parallel
along a heat sink base and parallel to each other. The heat sink
base has a thickness of between 0.05'' and 0.5'', and the fins each
have a height between 0.25'' and 7'', a center to center spacing
between 0.05'' and 1'', and a width between 0.001'' and 0.25'', and
the center to center spacing is sufficient to provide a channel
between said fins for cooling air to enter. In another instance,
the heat sink base has a thickness of between 0.1'' and 0.25'', and
the fins each have a height between 0.75'' and 5'', a center to
center spacing between 0.2'' and 0.5'', and a width between 0.007''
and 0.1''. In another instance, the heat sink base has a thickness
of between 0.1'' and 0.2'', and the fins each have a height between
0.9'' and 2'', a center to center spacing between 0.3'' and 0.4'',
and a width between 0.02'' and 0.05''.
[0009] In other instances, the photovoltaic module has a thermal
interface layer between the heat sink and photovoltaic cells to
improve heat dissipation. In other instances, the module has a
conformal coating on the photovoltaic cells.
[0010] In other instances, the frame of the module does not extend
beyond the base of the heat sink, allowing unimpeded access of
ambient air to fins of the heat sink.
[0011] In other instances, the heat sink has a length, thickness,
fin height, fin spacing and fin width to maintain the photovoltaic
cell at a temperature below about 150.degree. F. in quiescent
ambient air at a temperature of 70.degree. F.
[0012] In other instances, the heat sink has of fins positioned
substantially parallel to a long axis of the heat sink. In other
instances, the fins are positioned substantially perpendicular to a
long axis of the heat sink.
[0013] In other instances, the heat sink is positioned
substantially parallel to a long axis of the photovoltaic module.
In other instances, the heat sink is positioned substantially
perpendicular to a long axis of the module. In other instances, the
heat sink has a length sufficient to span greater than 3/4 the
width of the module. In other instances, the heat sink has a length
sufficient to span greater than 3/4 the length of the module.
[0014] In other instances, the heat sink is constructed of extruded
aluminum. In other instances, the heat sink is constructed of black
anodized aluminum. In other instances, heat sink base is
constructed of a thermally conductive polymer. In other instances,
the heat sink base is constructed of elastomer.
[0015] In other instances, the fins are discontinuous along a long
axis of the heat sink base to form air escape and entry channels.
In other instances, the channels are herringbone shape.
[0016] The present invention is better understood upon
consideration of the detailed description below in conjunction with
the accompanying drawings and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a perspective view of a photovoltaic module with
heat sinks
[0018] FIG. 2 is a partial side view of a FIG. 1.
[0019] FIG. 3 is a bottom view of a heat sink.
[0020] FIG. 4A-1 is a cross-sectional view of an upper jig and a
lower jig used to construct a photovoltaic module.
[0021] FIG. 4A-2 is a bottom view of an upper jig.
[0022] FIG. 4B is the view shown in FIG. 4A-1 with a photovoltaic
cell and a heat sink.
[0023] FIG. 4C is the view shown in FIG. 4B with an interface
layer.
[0024] FIG. 4D illustrates the apparatus shown in FIG. 4C where the
upper jig and lower jig are compressed.
[0025] FIG. 4E shows a side view of a photovoltaic module produced
by the described process.
DETAILED DESCRIPTION
[0026] The following description is presented to enable a person of
ordinary skill in the art to make and use the invention.
Descriptions of specific materials, techniques, and applications
are provided only as examples. Various modifications to the
examples described herein will be readily apparent to those of
ordinary skill in the art, and the general principles defined
herein may be applied to other examples and applications without
departing from the spirit and scope of the invention. Thus, the
present invention is not intended to be limited to the examples
described and shown, but is to be accorded the scope consistent
with the appended claims.
[0027] FIGS. 1 and 2 illustrate an example of a photovoltaic (PV)
module 100 of the present invention. The photovoltaic module 100
comprises a photovoltaic array of interconnected photovoltaic cells
110 positioned within a frame 120, which may be adapted to mount
the module on a finished rooftop. Each photovoltaic cell is
positioned within the frame 120 to allow exposure of a cell's
light-receiving surface to solar radiation.
[0028] Each photovoltaic cell 110 may be any currently used in the
art or developed in the future, such as a silicon-based wafer
photovoltaic cell, a thin film photovoltaic cell, or a conductive
polymer that converts photons to electricity. Such cells are
well-known and include wafer-based cells formed on a
monocrystalline silicon, poly- or multicrystalline silicon, or
ribbon silicon substrate. A thin-film photovoltaic cell may
comprise amorphous silicon, poly-crystalline silicon,
nano-crystalline silicon, micro-crystalline silicon, cadmium
telluride, copper indium selenide/sulfide (CIS), copper indium
gallium selenide (CIGS), an organic semiconductor, or a light
absorbing dye.
[0029] Each photovoltaic cell 110 may be of any shape (e.g. square,
rectangular, hexagonal, octagonal, triangular, circular, or
diamond) and located in or on a surface of a module. A photovoltaic
cell in a module is one recessed within the module frame with
essentially only the top surface of the cell exposed to the light
source. A photovoltaic cell on a module is one placed directly on
top of the frame with essentially only the bottom surface not
exposed to the light source.
[0030] The electrical configurations between individual
photovoltaic cells 110 as well as the electrical connections
between individual modules may independently be configured as
series, parallel, or mixed series-parallel as is well known in the
art to achieve the desired operating current and voltage. For
example, individual photovoltaic cells within a module are
connected in series to increase the total operating voltage of the
module. If the voltage produced by each individual photovoltaic
cell within a module is sufficient, then the cells may be connected
to adjacent cells in parallel to maintain voltage and increase
current.
[0031] The photovoltaic module comprises one or more heat sinks 130
in thermal communication with the unexposed surface of the
photovoltaic cells 110 to dissipate the waste heat from the cells.
As illustrated in FIG. 2, each heat sink may comprise a base 200
attached to the flat surface of the unexposed surface of the solar
cells and a plurality of fins 210 extending substantially
perpendicular to a large surface of the base and substantially
parallel to the long axis of each other. The base and fins may be
constructed separately and later joined, or constructed as one unit
from the same material source. The heat sink may be in direct
physical contact with the solar cells or may have one or more
intervening layers. An example of an intervening layer is an
intervening thermal interface layer 220, which can be made of any
material used in the art, such as thermally conductive grease or
adhesive (e.g. conductive epoxy, silicone, or ceramic) or an
intervening thermally conductive polymer, such as a thermally
conductive polymer available from Cool Polymers, Inc. The
intervening layer may be of any material commonly used in the art
(e.g. ethyl-vinyl-acetate (EVA), polyester, Tedlar.RTM., EPT). The
thermal interface layer may be constructed of material that is both
electrically isolative and thermally conductive. The thermal
interface layer may be a thin layer of polymer that is not
intrinsically thermally conductive but, due to its thinness,
conducts heat at a sufficient rate that it is considered thermally
conductive. Other layers may be present separately or in addition
to an intervening thermal interface layer, such as one or more
electrically insulating layers. The intervening layer may be in
simultaneous contact with both the solar cell(s) and the heat
sink.
[0032] The heat sinks may be positioned substantially parallel or
substantially perpendicular to the long axis of the module 100 and
may span portions of or the entire length or width of the module.
Likewise, multiple heat sinks may be aligned in tandem, with or
without intervening space, to span the portions of or the entire
length or width of the module, if desired. In one variation a heat
sink has sufficient length to span greater than 3/4 of the length
of the module. In another variation a heat sink has sufficient
length to span greater than 3/4 of the width of the module. In some
variations different heat sinks on the module will be positioned
substantially perpendicular to one another.
[0033] The base 200 and fins 210 of each heat sink can be
independently constructed of one or more thermally conductive
materials, such as aluminum or aluminum alloy (e.g. 6063 aluminum
alloy, 6061 aluminum alloy, and 6005 aluminum alloy), copper,
graphite, or conductive polymer (such as conductive elastomer as
available from, e.g. Cool Polymers, Inc.), and may be of any color,
such as blue, black, gray, or brown. Dark colors may improve heat
sink performance. A heat sink constructed of metal may be anodized
or plated. Heat sinks may be constructed by common manufacturing
techniques such as extrusion, casting, or injection molding, or may
be constructed using a combination of manufacturing techniques to
construct hybrid heat sinks (e.g. aluminum fins molded into a
conductive polymer base).
[0034] FIG. 2 illustrates dimensions of a heat sink 130. A base 200
may have a thickness designated as t. Fins 210 may independently
have a height designated h, a center to center spacing designated
as s, and a width designated as w. The width w of any fin may be
independently less than 1 inch, or less than 0.75'', or less than
0.5'', or less than 0.3'', or less than 0.2'', or less than 0.15'',
or less than 0.1'', or less than 0.05'', or less than 0.025'', or
less than 0.01'', or less than 0.005'', or less than 0.0025'', or
less than 0.001'', or between 0.001'' and 0.25'', or between
0.002'' and 0.1'', or between 0.005'' and 0.075'', or between
0.01'' and 0.06'', or between 0.02'' and 0.05'', or 0.02''. The
height h of any fin may be independently greater than 0.1'', or
greater than 0.25'', or greater than 0.5'', or greater than 0.75'',
or greater than 1'', or greater than 2'', or greater than 3.5'', or
between 0.25'' and 7'', or between 0.5'' and 6'', or between 0.75''
and 5'', or between 0.8'' and 2.5'', or between 0.9'' and 2'', or
between 0.9'' and 1.25'', or 1''. The center to center spacing s
between fins may be independently between 0.05'' and 1'', or
between 0.075'' and 0.9'', or between 0.1'' and 0.8'', or between
0.2'' and 0.7'', or between 0.2'' and 0.5'', or between 0.25'' and
0.45'', or between 0.25'' and 0.4'' or between 0.3'' and 0.4'', or
between 0.3'' and 0.45'', or between 0.35'' and 0.4''. The
thickness t of the base of each heat sink may be independently less
than 1'', or less than 0.75'', or less than 0.5'', or less than
0.4'', or less than 0.3'', or less than 0.2'', or less than 0.15'',
or less than 0.1'', or less than 0.05'', or between 0.05'' and
0.5'', or between 0.075'' and 0.35'', or between 0.1'' and 0.25'',
or between 0.1'' and 0.2'', or 0.1'', or 0.15'', or 0.2''. The
ratio of center to center spacing (s) to the fin height (h) (i.e.
s/h) may be independently 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4,
0.45, 0.5, 0.5, 0.6, 0.65, 0.7, or between 0.1 and 0.7, or between
0.15 and 0.5, or between 0.2 and 0.4, or between 0.2 and 0.35, or
between 0.25 and 0.3. The dimensions of any fin may be identical or
different from the dimensions of any other fin on the same heat
sink. The dimensions of any fin or base may be identical or
different from the dimensions of any other fin on another heat
sinks. The dimensions of all heat sink bases on a module may be the
same. The dimensions of all heat sink fins of all heat sinks on a
module may be the same. The dimensions of all heat sink fins of an
individual heat sink may be the same. The height of all fins of a
heat sink may be the same. The height of all fins of a heat sink
may be different. The average height of all fins of a heat sink may
be of any dimension described above. The average center to center
spacing of all fins of a heat sink may be of any dimension
described above. The average width of all fins of a heat sink may
be of any dimension described above.
[0035] The dimensions of each heat sink may independently be any
combination of the dimensions described above, such as w between
0.002'' and 0.1'', h between 0.75'' and 5'', s between 0.2'' and
0.5'', and t between 0.1'' and 0.25''; w between 0.001'' and
0.25'', h between 0.75'' and 5'', s between 0.2'' and 0.5'', and t
between 0.1'' and 0.25''; w between 0.02'' and 0.05'', h between
0.75'' and 5'', s between 0.2'' and 0.5'', and t between 0.1'' and
0.25''; w between 0.002'' and 0.1'', h between 0.25'' and 7'', s
between 0.2'' and 0.5'', and t between 0.1'' and 0.25''; w between
0.002'' and 0.1'', h between 0.9'' and 2'', s between 0.2'' and
0.5'', and t between 0.1'' and 0.25''; w between 0.002'' and 0.1'',
h between 0.75'' and 5'', s between 0.05'' and 1'', and t between
0.1'' and 0.25''; w between 0.002'' and 0.1'', h between 0.75'' and
5'', s between 0.3'' and 0.4'', and t between 0.1'' and 0.25''; w
between 0.002'' and 0.1'', h between 0.75'' and 5'', s between
0.2'' and 0.5'', and t between 0.05'' and 0.5''; and w between
0.002'' and 0.1'', h between 0.75'' and 5'', s between 0.2'' and
0.5'', and t between 0.1'' and 0.2''.
[0036] A long axis of fins 210 may be substantially parallel or
substantially perpendicular to a long axis of the base.
Substantially parallel is when two referenced axes form an angle of
less than 10.degree.. Substantially perpendicular is when two
referenced axes form an angle between 85.degree. and 95.degree.. A
long axis is an axis parallel to the longest straight edge of the
object referenced. A long axis is implied if no axis is referenced.
The fins may run continuously along most or all of the length of
the base. Fins may form different angles with respect an axis of
the heat sink (e.g. a fan orientation), so that air may pass freely
through many of the channels formed by adjacent fins regardless of
wind direction. Surfaces of fins may also have features such as
ridges or bumps that help induce eddies in air flowing past the
fins to help convection.
[0037] A heat sink may be designed such that a first volume
(defined as a volume of a heat sink including its associated heat
sink base) is a percentage of a second volume (defined as a volume
from a top-down projected surface area of the heat sink base and a
third dimension, wherein the third dimension is defined by the
least squares determination from the heights of each protrusion on
the heat sink base (such as cones, fins, etc.)). For example, if
all protrusions of a heat sink are of equal dimensions then the
first volume would be the heat sink base volume added to the
product of the volume of each protrusion and the number of
protrusions; and the second volume would be the top-down projected
surface area of the heat sink base (e.g. width.times.length, if the
heat sink base were rectangular) multiplied by the protrusion
height (i.e. the third dimension). If the heights of protrusions
within a heat sink are different, then the least squares
determination of all protrusion heights would determine the third
dimension used in the example above. The percent volume is the
first volume divided by the second volume.times.100. The percent
volume may be, for example, between 10% and 50%, between 15% and
45%, between 20% and 40%, between 25% and 35%, between 20% and 30%,
between 25% and 30%, between 30% and 35%, between 35% and 40%,
between 40% and 45%, between 45% and 50%, between 20% and 25%,
between 15% and 20%, between 10% and 15%, between 10% and 20%,
between 15% and 25%, between 25% and 35%, between 30% and 40%,
between 35% and 45%, between 40% and 50%, between 10% and 25%,
between 15% and 30%, between 20% and 35%, between 25% and 40%,
between 30% and 45%, between 35% and 50%, between 10% and 12.5%,
between 12.5% and 15%, between 15% and 17.5%, between 17.5% and
20%, between 20% and 22.5%, between 22.5% and 25%, between 25% and
27.5%, between 27.5% and 30%, between 30% and 32.5%, between 32.5%
and 35%, between 35% and 37.5%, between 37.5% and 40%, between 40%
and 42.5%, between 42.5% and 45%, between 45% and 47.5%, or between
47.5% and 50%.
[0038] FIG. 3 is a top-down view of a heat sink 130 with optionally
present channels 300 formed by segmented heat sink fins 320. Each
channel provides an additional opening to the interior of the heat
sink and allows increased airflow to the internal fins. Channels
may be of any pattern, such as general cross-cut, herringbone, or
undulating. The fins may also be replaced with other heat
dissipating shapes attached to the base, such as pyramids
(including frustum pyramids), cylinders, square pegs, or cones
(including frustum cones).
[0039] The heat sink may be configured to reduce the temperature of
a photovoltaic cell in ambient quiescent air that is at standard
temperature and pressure and an irradiance (E) by white light
individually or in any combination of 800 W*m.sup.-2, 1000
W*m.sup.-2, or 1200 W*m.sup.-2 by at least 1.degree. C.; or by at
least 2.degree. C.; or by at least 5.degree. C.; or by at least
7.degree. C.; or by at least 10.degree. C.; or by at least
12.degree. C.; or by at least 15.degree. C.; or by at least
20.degree. C. as compared to an identical cell lacking the heat
sink. The size, number, and spacing of fins, the size of the base
portion, and the materials of construction of the heat sink may be
selected based on the desired decrease in temperature over the
comparative PV cell.
[0040] The heat sink may be configured to maintain a photovoltaic
cell at a temperature below about 175.degree. F., or below about
160.degree. F., or below about 150.degree. F., or below about
140.degree. F., or below about 130.degree. F., or below about
120.degree. F., or below about 110.degree. F., or below about
100.degree. F., or below about 90.degree. F., or below about
80.degree. F. in quiescent ambient air at a temperature of
70.degree. F. at standard pressure.
[0041] The heat sink may be configured to increase the energy
conversion efficiency (defined by the equation:
.eta.=(P.sub.m/(E.times.A.sub.c)), where P.sub.m is maximum
electrical power in watts, E is the input light irradiance in
W*M.sup.-2 and A.sub.c is the surface area of the solar cell in
m.sup.2) or total-area efficiency of a photovoltaic cell (which may
be defined by the relative change in current (I) and/or voltage (V)
or relative change in the product of I and V) in ambient quiescent
air that is at standard temperature and pressure and an irradiance
(E) by white light individually or in any combination of 800
W*m.sup.-2, 1000 W*m.sup.-2, or 1200 W*m.sup.-2 by at least 0.5%;
or by at least 1%; or by at least 1.5%; or by at least 2%; or by at
least 2.5%; or by at least 3%; or by at least 3.5%; or by at least
4%; or by at least 4.5%; or by at least 5%; or by at least 5.5%; or
by at least 6%; or by at least 6.5%; or by at least 7%; or by at
least 7.5%; or by at least 8%; or by at least 8.5%; or by at least
9%; or by at least 9.5%; or by at least 10% as compared to an
identical cell lacking the heat sink.
[0042] If desired, the heat sink may be subjected to forced airflow
provided by any means, e.g. one or more fans, to increase airflow
over the heat sink and increase cooling effectiveness of the
photovoltaic cell. A fan may deliver the forced air to the heat
sink by direct exposure or remotely through a duct system.
[0043] The module may contain a protective layer 230 as shown in
FIG. 2 adjacent to the light-receiving surface of each photovoltaic
cell to protect the photovoltaic cells from damage (caused, for
example, from moisture, dust, chemicals, and temperatures changes),
while allowing the transmission of sunlight. The protective layer
may conform to the surface shape of the photovoltaic cells and may
be made of any suitable material, such as glass (e.g. low-lead
tempered glass) or polymer (e.g. parylene or ethyl-vinyl-acetate).
The protective layer may be a film (clear or colored) and be made
of e.g. acrylics, epoxies, urethanes, and silicones. The protective
layer may optionally be an antireflective coating, such as silicon
nitride.
[0044] As shown in FIGS. 1 and 2, a photovoltaic module may have a
frame 120 with mounting fixtures such as screw holes, tabs, and/or
electrical connections that are suitable to mount the module in
framework that is attached to a finished roof-top so that heat from
the solar cells may be dissipated into ambient air. The frame may
surround the photovoltaic cells and, optionally, may surround
additional layers that may be present adjacent to cells. It is
preferable for roof-top mounting that little or none of the frame
of the module blocks access to the heat sinks 130 so that
relatively cool air may flow freely through the cooling fins. In
one experiment, blocking access to the heat sink via a frame
resulted in decreased photovoltaic efficiency. FIGS. 1 and 2
illustrate how the fins and channels there between are free of the
frame so that air may travel through the channels unimpeded by the
frame (e.g. allowing horizontal access to the heat sink).
[0045] The frame may comprise a flange or lip 102 (straight or
curved) as shown in FIG. 1 oriented to direct air flowing through
the heat sink upward upon exiting the module. This feature may
prevent hot air generated from a heat sink from entering an
adjacent module. Likewise, a flange or lip may be oriented to force
fresh cold air flowing above a module or adjacent module into a
heat sink. A feature of this orientation may be particularly useful
to permit cool air to enter the underside of a module when multiple
modules are arranged with minimal intervening space. Multiple
flanges and/or lips may be incorporated into a single frame to
direct cool air into a heat sink and to direct hot air away from a
heat sink.
[0046] Optionally, legs 140 may be provided to permit the module to
be set upon a flat surface during handling and prior to
installation, thus supporting the weight of the module 100 and
preventing compression of the fins. Legs 140 may also be used to
mount the module to a surface such as a rooftop. Legs may be
sufficiently long that they elevate the module a sufficient
distance from the surface to which they are mounted that air flows
freely beneath and through channels through and past the fins to
provide improved energy conversion efficiency over a similar
construction in which the fins touch the surface of the roof
top.
[0047] The frame 120 and legs 140 may be independently constructed
of one or more materials capable of supporting the photovoltaic
module, such as metal (e.g. aluminum), ceramic, cement, composite,
or polymer (e.g. conductive polymer). The frame and heat sink may
be constructed as one mold from a conductive polymer, if desired.
The frame may have an extended configuration to cover the heat sink
wherein the frame may also include a screen or perforations along
the sides to allow air flow to the heat sinks.
[0048] The framework into which modules may be inserted typically
has footers especially adapted to mount to common roofing materials
such as composite roofing or wood battens forming part of the roof
structure. Often, the framework has a height such that fins of the
module's heat sink just touch or are just above the surface (e.g.
rooftop) on which the framework is mounted. Alternatively, the
framework may elevate the module over the rooftop a sufficient
distance that air may flow sufficiently freely beneath and through
the channels between fins to provide improved efficiency over a
similar construction in which the fins touch the rooftop.
[0049] A photovoltaic module may be formed in standard lengths of
approximately e.g. 3 feet, 4 feet, 5 feet, 6 feet, 7 feet, 8 feet,
9 feet, 10 feet, or 1 meter, 1.5 meter, 2 meter, 2.5 meter, 3
meter, 3.5 meter, or 4 meter. The photovoltaic module may be formed
in standard widths of approximately e.g. 1 foot, 1.5 feet, 2 feet,
2.5 feet, 3 feet, 3.5 feet, 4 feet, 4.5 feet, 5 feet, or 0.25
meter, 0.5 meter, 0.75 meter, 1 meter, 1.25 meter, 1.5 meter, 1.75
meter, or 2 meter.
[0050] Photovoltaic modules typically contain 3, 6, 9, 12, 15, 18,
21, 24, 27, 30, 20, 24, 28, 32, 36, 40, 25, 36, 45, 50, 42, 48, 54,
60, or 72 PV cells arranged in rows and columns. PV cells may be
arranged, for instance, 4.times.9, 6.times.8, 6.times.9,
6.times.12, or 8.times.12. A module may, for example, have from
five to ten heat sinks in instances where a single heat sink is in
contact with cells across an entire row of PV cells in the
module.
[0051] A typical photovoltaic module may have an overall width of
between 35'' and 40'', an overall length of between 50'' and 60'',
photovoltaic cells in a 6.times.9 configuration, and 9 heat sinks
each spanning a column of photovoltaic cells across the width of
the module. When viewing the solar-cell side of the module in which
light receiving surfaces of the cells are visible ("top-down") the
width of a module is the minor axis or the shortest distance
between opposite walls of the frame. Columns span the module width,
while rows span the module length. In another configuration, a
photovoltaic module may have an overall width of between 35'' and
40'', an overall length of between 45'' and 55'', photovoltaic
cells in a 6.times.8 configuration, and 8 heat sinks each spanning
a column of photovoltaic cells across the width of the module. In
another configuration, a photovoltaic module may have an overall
width of between 20'' and 30'', an overall length of between 50''
and 60'', photovoltaic cells in a 4.times.9 configuration, and 8
heat sinks each spanning a column of photovoltaic cells across the
width of the module. In another configuration, a photovoltaic
module may have an overall width of between 30'' and 40'', an
overall length of between 50'' and 55'', photovoltaic cells in an
8.times.12 configuration, and 12 heat sinks each spanning a column
of photovoltaic cells across the width of the module. Other module
configurations described within (such as heat sinks spanning the
length of the module) may be applied to the examples above.
[0052] In one example, a module was constructed containing 36
photovoltaic cells in a 4.times.9 configuration of moncrystalline
silicon (225 .mu.m thickness). The cells were laminated with glass
using an SPI-laminator (Spire, Inc.) and heat sinks attached using
Omegabond.RTM. 101 epoxy cement. Heat sinks contained fins with the
following dimensions: w=0.06'', h=0.9375'', s=0.3'', and t=0.1''.
Each heat sink contained eight fins and had an overall width of
2.5''. Two heat sinks were abutted such that the overall width of
the joined heat sinks was 5'' in order to cover the width of each
photovoltaic cell.
[0053] Often anywhere from 4 to 20 modules are installed in a solar
module on the roof-top of a house, depending on the amount of
south-facing (in the northern hemisphere) rooftop that is
available. Many more solar modules may be installed on the larger
roofs of commercial buildings, for instance.
[0054] The photovoltaic modules described herein may be linked
together by any method and/or using any apparatus known in the art.
Photovoltaic modules may also be designed to interlock mechanically
and/or electronically, as described in U.S. Provisional Application
No. 60/874,313, entitled "Modular Solar Roof Tiles And Solar Panels
With Heat Exchange" filed Dec. 11, 2006, which is incorporated by
reference in its entirety. Modules may also be separated from one
another with sufficient space to allow increased airflow between
the modules to improve cooling of photovoltaic cells.
[0055] Another feature of the present invention is a method of
manufacturing a photovoltaic module. FIGS. 4A-4E are different
views during the described fabrication process of a photovoltaic
module.
[0056] FIG. 4A-1 illustrates a cross-sectional view of a system
used to construct a photovoltaic module. An upper jig 400 comprises
an optionally present depression 410 designed to complement one or
more photovoltaic cells. The depression may have a depth 420
roughly the thickness of the photovoltaic cell(s), or less than the
thickness of the cell or cells. Vacuum channels 487 in any shape,
number, and configuration may be present to allow a vacuum source
through the upper jig to the photovoltaic cell(s). A vacuum source
may allow the photovoltaic cells(s) to be temporarily held within
the depression 410 during the manufacturing process. FIG. 4A-2
shows the upper jig 400 from a bottom view. Each depression 410 is
shown with its corresponding width 482 and length 484. The width
and length can independently have roughly the same dimensions as
the largest surface of the cell or cells, or have slightly larger
dimensions. The number of depressions 410 may be united or
separated and any number desired for the module, such as 1, 2, 3,
4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or
25. The shape of a depression may be of any shape of photovoltaic
cell or cells, such as square, rectangular, hexagonal, octagonal,
triangular, circular, or diamond.
[0057] A lower jig 440 shown in FIG. 4A-1 may comprise a base
depression 450 and fin depressions 460. The base depression 450 and
fin depressions 460 may be designed to collectively compliment a
heat sink such that the heat sink may be inserted into the lower
jig and is incapable of substantial horizontal movement following
insertion. The base depression may have a depth 470 roughly the
thickness of a heat sink base or slightly less than the thickness
of a heat sink base, and a width roughly the same as the heat sink
base or slightly larger than the heat sink base. The base
depression may be optionally present. Each fin depression 460 may
have roughly the same dimensions as the heat sink fins or slightly
larger dimensions to allow uninhibited insertion of the heat sink.
The lower jig 440 may also be designed to complement any number of
heat sink designs describe herein, such as pyramids (including
frustum pyramids), cylinders, square pegs, or cones (including
frustum cones). Vacuum channels (not shown) may be present to
provide a vacuum source through the lower jig to the heat sink, as
described for the upper jig.
[0058] The material of the upper and lower jig may be independently
any material known in the art, such as aluminum, copper, ceramic,
and polymer. The upper jig and the lower jig may be in reverse
orientation, such that the upper jig is below the lower jig.
[0059] The photovoltaic module manufacturing process may begin by
placing the photovoltaic cell(s) and the heat sink into their
respective jigs, as illustrated in FIG. 4B. The upper jig 400
houses one or more photovoltaic cells 486 inserted into each
depression 410 such that a flat surface of each cell 488 is exposed
while most of the remaining surface area of each cell is housed
within depression. Each cell may be made of any material described
herein or known in the art, such as wafer-based cells formed on a
monocrystalline silicon, poly- or multicrystalline silicon, or
ribbon silicon substrate, and may be of any shape, such as square,
rectangular, hexagonal, octagonal, triangular, circular, or
diamond. The cell(s) may be temporarily fixed to the upper jig 400
by gravity, vacuum (using e.g. optionally present vacuum channels
478), or any common adherent. The lower jig 440 houses the heat
sink 490 such that a flat surface of the heat sink 492 is exposed
while most of the remaining surface area, such as the fins, is
housed within depression. The heat sink may be made of any
thermally conductive material known in the art and/or described
herein, such as aluminum or aluminum alloy (e.g. 6063 aluminum
alloy, 6061 aluminum alloy, and 6005 aluminum alloy), copper,
graphite, or conductive polymer (such as conductive elastomer), may
be of any color (e.g. blue, black, gray, or brown) and may comprise
cooling surfaces configured of any geometry, such as pyramids
(including frustum pyramids), cylinders, square pegs, or cones
(including frustum cones). The heat sink may be temporarily fixed
to the lower jig 440 by gravity, vacuum, or any common
adherent.
[0060] FIG. 4C illustrates how an intervening layer 494 may be
added to the exposed surface of the heat sink 492 or to the exposed
surface(s) of the cell(s). The intervening layer may be a thermal
interface layer, such as thermally conductive grease (e.g.
conductive epoxy, silicone, or ceramic) or an intervening polymer
such as a thermally conductive polymer. The intervening layer may
be of any material commonly used in the art (e.g.
ethyl-vinyl-acetate (EVA), polyester, Tedlar.RTM., EPT). The
thermal interface layer may be, for example, constructed of any
material that is both electrically isolative and thermally
conductive and may be a compound or mixture of compounds that
chemically react when exposed to air, heat, and/or pressure. The
intervening layer may comprise multiple layers, such as an
electrically isolating layer next to PV cells and a thermally
conductive layer next to a heat sink, or may be absent. The layer
may be in simultaneous contact with both the photovoltaic cell(s)
and the heat sink.
[0061] As illustrated in FIG. 4D, both jigs house the heat sink
490, optionally present intervening layer 494, and photovoltaic
cell(s) 486 are sandwiched together to allow simultaneous contact
of the optionally present intervening layer 494 with the heat sink
and the photovoltaic cell(s). Sufficient pressure may be applied to
either the upper jig 400, lower jig 440, or both, in a direction
toward the photovoltaic components to allow pressure between the
cell(s) and the heat sink, and force intimate contact of their
surfaces. Because the upper jig is complementary to the housed
cell(s) 486, the resulting applied pressure is distributed across
the area of a cell-upper jig interface, thus preventing the
likelihood of damage to the cell(s). Likewise, because the lower
jig is complementary to the housed heat sink, the applied pressure
may be less likely to damage the heat sink fins (e.g. crushing or
warping the fins). Sufficient heat may also be applied during the
process, separately or in conjunction with sufficient pressure, to
intimately join the heat sink to the photovoltaic cell(s). This
process of temporarily applying pressure and/or heat to unite two
or more materials together, also known as laminating, may allow the
surface(s) of the cell(s) to more closely contact an adjacent
material at a microscopic level and allow increased conductive heat
transfer away from the cell(s). A vacuum may be applied to decrease
air pressure before, during, and/or after applying pressure and/or
heat to aid in removing pockets of air between layers. Removing
trapped air may allow a more intimate contact between layers
resulting in increased thermal transfer.
[0062] Conditions during lamination may vary depending on the
photovoltaic module configuration. In one instance the lamination
temperature is approximately 155.degree. C., decreased air pressure
is applied for five minutes, and one atmosphere of pressure is
applied by the jigs to force the heat sink and photovoltaic cell(s)
between the jigs together for seven minutes. In another instance,
the lamination temperature is between 100.degree. C. and
200.degree. C., or between 125.degree. C. and 175.degree. C., or
between 135.degree. C. and 155.degree. C. In another instance 1.25,
1.5, 2, 2.5, 3, 3.5, 4, 4.5, or greater than 5 atmospheres of
pressure is applied by the jigs to force the heat sink and
photovoltaic cell(s) between the jigs together. In another
instance, pressure is applied by the jigs for 1 to 30 minutes, 2 to
20 minutes, 5 to 15 minutes, or greater than 30 minutes. In another
instance decreased air pressure is applied for 1 to 30 minutes, 2
to 20 minutes, 5 to 15 minutes, or greater than 30 minutes.
[0063] FIG. 4E illustrates a photovoltaic module following removal
of the upper jig and the lower jig.
[0064] The process may comprise additional layers known in the art
(e.g. ethyl-vinyl-acetate (EVA), polyester, Tedlar.RTM., EPT) on or
within the module, such as a protective layer (e.g. conformal
coating), as described herein.
[0065] The process may further comprise the addition of a frame,
with or without legs, as described herein, to permit airflow
through direct horizontal access to the heat sinks.
* * * * *