U.S. patent application number 13/442740 was filed with the patent office on 2013-05-09 for solar energy receiver.
This patent application is currently assigned to Cool Earh Solar. The applicant listed for this patent is Paul Dentinger, Robert Lamkin, John Liptac, James Page, Tom Reynolds. Invention is credited to Paul Dentinger, Robert Lamkin, John Liptac, James Page, Tom Reynolds.
Application Number | 20130112239 13/442740 |
Document ID | / |
Family ID | 48222870 |
Filed Date | 2013-05-09 |
United States Patent
Application |
20130112239 |
Kind Code |
A1 |
Liptac; John ; et
al. |
May 9, 2013 |
SOLAR ENERGY RECEIVER
Abstract
Embodiments of the present invention may utilize one or more
techniques, alone or in combination, to maximize a surface area of
a receiver that is configured to convert light into another form of
energy. One technique enhances collection efficiency by controlling
a size, shape, and/or position of a cell relative to an expected
illumination profile under various conditions. Another technique
positions non-active elements (such as electrical contacts and/or
interconnects) on surfaces likely to be shaded from incident light
by other elements of the receiver. Another technique utilizes
embodiments of interconnect structures occupying a small footprint.
According to certain embodiments, the receiver may be cooled by
exposure to a fluid such as water or air.
Inventors: |
Liptac; John; (Mountain
House, CA) ; Dentinger; Paul; (Sunol, CA) ;
Lamkin; Robert; (Pleasanton, CA) ; Page; James;
(Oakland, CA) ; Reynolds; Tom; (Livermore,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Liptac; John
Dentinger; Paul
Lamkin; Robert
Page; James
Reynolds; Tom |
Mountain House
Sunol
Pleasanton
Oakland
Livermore |
CA
CA
CA
CA
CA |
US
US
US
US
US |
|
|
Assignee: |
Cool Earh Solar
Livermore
CA
|
Family ID: |
48222870 |
Appl. No.: |
13/442740 |
Filed: |
April 9, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61475483 |
Apr 14, 2011 |
|
|
|
Current U.S.
Class: |
136/246 ;
136/251 |
Current CPC
Class: |
H01L 31/035281 20130101;
H01L 31/0201 20130101; F24S 50/20 20180501; G01S 3/7861 20130101;
H01L 31/048 20130101; H01L 31/042 20130101; H01L 31/022433
20130101; H01L 31/0525 20130101; H02S 20/32 20141201; H01L 31/0547
20141201; Y02E 10/47 20130101; H01L 31/0508 20130101; Y02E 10/52
20130101 |
Class at
Publication: |
136/246 ;
136/251 |
International
Class: |
H01L 31/052 20060101
H01L031/052; H01L 31/05 20060101 H01L031/05; H01L 31/042 20060101
H01L031/042 |
Claims
1. A solar energy receiver comprising: a support structure; a
plurality of active photovoltaic (PV) devices disposed on the
support structure, each PV device including an active receiver
element and one or more non-active elements; wherein the plurality
of PV devices are arranged such that active receiver element of a
first PV device at least partially hides a non-active element of a
second PV device from incident light.
2. The solar energy receiver of claim 1 wherein the second PV
device is adjacent to the first PV device.
3. The solar energy receiver of claim 1 wherein the plurality of
active PV devices comprise back contact PV cells.
4. The solar energy receiver of claim 3 wherein the back contact PV
cells include at least one of: through silicon via (TSV) cells,
emitter cells, or metallization wrap through cells.
5. The solar energy receiver of claim 1 wherein the plurality of
active PV devices comprise front contact PV cells.
6. The solar energy receiver of claim 5 wherein: a busbar of a
first front contact PV cell is in electrical communication with a
back contact of a second front contact PV cell through an
electrically conducting adhesive.
7. The solar energy receiver of claim 6 wherein the electrically
conducting adhesive includes a solder.
8. The solar energy receiver of claim 1 wherein the active receiver
element comprises a reflector and wherein the reflector comprises a
central reflector and/or a peripheral reflector.
9. The solar energy receiver of claim 1 wherein the non-active
element comprises an electrical interconnect between two adjacent
active PV devices.
10. The solar energy receiver of claim 9 wherein the plurality of
the active PV devices comprise front contact PV cells and wherein
the front contact PV cells are arranged in an annulus.
11. The solar energy receiver of claim 1 wherein the support
structure comprises: a thermally conducting substrate having an
upper surface and an opposing lower surface; a metal layer disposed
on the lower surface; one or more cooling channels coupled to the
lower surface; and a printed circuit board (PCB) coupled to the
upper surface.
12. The solar energy receiver of claim 1 wherein each of the
plurality of active PV devices are non-square in shape.
13. The solar energy receiver of claim 1 wherein the one or more
non-active elements comprise an interconnect, a busbar, a contact,
a through hole, or a diode.
14. The solar energy receiver of claim 1 wherein the plurality of
active PV devices are disposed in an annular arrangement.
15. A solar energy receiver comprising: a first photovoltaic (PV)
device comprising: a first front surface and a first front contact
disposed on the first front surface, the first front contact having
a first electrical polarity, wherein the first front contact
occupies a portion of the first front surface; and a first back
surface and a first back contact disposed on the first back
surface, the first back contact having a second electrical polarity
opposite to the first electrical polarity, wherein the first back
contact occupies a portion of the first back surface; and a second
PV device comprising: a second front surface and a second front
contact disposed on the second front surface, the second front
contact having a third electrical polarity, wherein the second
front contact occupies a portion of the second front surface; and a
second back surface and a second back contact disposed on the
second back surface, the second back contact having a fourth
electrical polarity opposite to the third electrical polarity,
wherein the second back contact occupies a portion of the second
back surface; wherein the second front contact of the second PV
device underlies the first back contact of the first PV device and
wherein only the portion of the first back surface of the first PV
device overlies the second front surface of the second PV
device.
16. The solar energy receiver of claim 15 further comprising: a
third photovoltaic (PV) device comprising: a third front surface
and a third front contact disposed on the third front surface, the
third front contact having a fifth electrical polarity, wherein the
third front contact occupies a portion of the third front surface;
and a third back surface and a third back contact disposed on the
third back surface, the third back contact having a sixth
electrical polarity opposite to the fifth electrical polarity,
wherein the third back contact occupies a portion of the third back
surface; and wherein the second back contact of the second PV
device overlies the third front contact of the third PV device and
wherein only the portion of the second back surface of the second
PV device overlies the third front surface of the third PV
device.
17. The solar energy receiver of claim 15 wherein the first PV
device, the second PV device, and the third PV device are disposed
in a shingle arrangement.
18. The solar energy receiver of claim 15 wherein the second front
contact of the second PV device is electrically connected to the
first back contact of the first PV device using an electrically
conducting adhesive.
19. The solar energy receiver of claim 15 wherein the second front
contact of the second PV device is electrically connected to the
first back contact of the first PV device using a connection
stack.
20. The solar energy receiver of claim 19 wherein the connection
stack comprises a plurality of layers.
21. The solar energy receiver of claim 15 further comprising a
substrate configured to support the first PV device and the second
PV device.
22. The solar energy receiver of claim 21 wherein the substrate
comprises one or more facets and each PV device is aligned in a
facet.
23. The solar energy receiver of claim 22 wherein a first facet is
disposed in a first plane and a second facet is disposed in a
second plane different from the first plane.
24. The solar energy receiver of claim 15 wherein a shape of the
first PV device is one of: a rectangle, a trapezoid, or a
polygon.
25. The solar energy receiver of claim 15 further comprising one or
more extent sensors configured to track a position of sun.
26. A system comprising: a solar energy receiver including a
plurality of photovoltaic (PV) devices; a plurality of extent
sensors coupled to the solar energy receiver; and a tracking
mechanism coupled to the solar energy receiver, wherein the
plurality of extent sensors are configured to track a position of
the sun in the sky and provide the position information to the
tracking mechanism; and wherein the tracking mechanism is
configured to orient the solar energy receiver based on the
position information received from the plurality of extent sensors,
the tracking mechanism comprising: a tracking control unit
configured to receive the position information from the plurality
of extent sensors and determine an orientation for the solar energy
receiver; and a motor control unit configured to receive
coordinates for the orientation from the tracking control unit and
operate one or more motors to orient the solar energy receiver in
the determined orientation.
27. The system of claim 26 wherein the solar energy receiver has an
associated illumination region and wherein the plurality of extent
sensors are located along a periphery of the illumination
region.
28. The system of claim 26 wherein the solar energy receiver has an
associated illumination region and wherein the plurality of extent
sensors are used to control an area of the illumination region.
29. The system of claim 26 wherein the plurality of extent sensors
are mounted on the solar energy receiver.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims benefit under 35 USC .sctn.119(e) to
U.S. Provisional Patent Application No. 61/475,483 filed on Apr.
14, 2011, the disclosure of which is incorporated by reference
herein in its entirety for all purposes.
BACKGROUND OF THE INVENTION
[0002] Solar radiation is the most abundant energy source on earth.
However, attempts to harness solar power on large scales have so
far failed to be economically competitive with most fossil-fuel
energy sources.
[0003] One reason for the lack of adoption of solar energy sources
on a large scale is that fossil-fuel energy sources have the
advantage of economic externalities, such as low-cost or cost-free
pollution and emission. Another reason for the lack of adoption of
solar energy sources on a large scale is that the solar flux is not
intense enough for direct conversion at one solar flux to be cost
effective. Solar energy concentrator technology has sought to
address this issue. For example, solar radiation energy is easily
manipulated and concentrated using refraction, diffraction, or
reflection to produce solar radiation energy having many thousands
of times the initial flux. This can be done using only modest
materials such as refractors, diffractors and reflectors.
[0004] Specifically, solar radiation is one of the most easy energy
forms to manipulate and concentrate. It can be refracted,
diffracted, or reflected to many thousands of times the initial
flux utilizing only modest materials.
[0005] With so many possible approaches, there have been a
multitude of previous attempts to implement low cost solar energy
concentrators. So far, however, solar concentrator systems cost too
much to compete unsubsidized with fossil fuels, in part because of
large amounts of material and large areas that that solar
collectors occupy. The large amounts of materials used to make
solar concentration systems and the large areas that are occupied
by solar concentration systems render solar concentration systems
unsuitable for large-scale solar farming.
[0006] Accordingly, there is a need in the art for improved
apparatuses and methods for the collection of solar energy.
SUMMARY
[0007] Embodiments of the present invention may utilize one or more
techniques, alone or in combination, to maximize a surface area of
a receiver that is configured to convert light into another form of
energy, for example, electricity. One embodiment of the present
invention provides a technique that enhances collection efficiency
of the receiver by controlling a size, shape, and/or position of a
photo-sensitive cell relative to an expected illumination profile
under various conditions. Another technique described herein
positions non-active elements (such as electrical contacts and/or
interconnects) on surfaces likely to be shaded from incident light
by other elements of the receiver. Another technique utilizes
embodiments of interconnect or contact structures occupying a small
footprint. According to certain embodiments, the receiver may be
cooled by exposure to a fluid such as water or air.
[0008] Another embodiment of the present invention provides a solar
energy receiver that includes location sensors for determining
location of the Sun at any given time and providing the location
information to a tracking system that can orient the solar receiver
optimally.
[0009] Certain embodiments of the present invention provide a solar
energy receiver. The solar energy receiver includes a support
structure, a plurality of active photovoltaic (PV) devices disposed
on the support structure. Each PV device includes an active
receiver element and one or more non-active elements. The plurality
of PV devices are arranged such that active receiver element of a
first PV device at least partially hides a non-active element of a
second PV device from incident light. In some embodiments, the
active receiver element comprises a reflector and wherein the
reflector comprises a central reflector and/or a peripheral
reflector. In some embodiments, the support structure further
comprises a thermally conducting substrate having an upper surface
and an opposing lower surface, a metal layer disposed on the lower
surface, one or more cooling channels coupled to the lower surface,
and a printed circuit board (PCB) coupled to the upper surface. In
some embodiments, the active PV cells are non-square in shape. In
one embodiment, the plurality of active PV devices are disposed in
an annular arrangement.
[0010] Another embodiment of the present invention provides a solar
energy receiver that includes a first photovoltaic (PV) device and
a second PV device. The first PV device comprises a first front
surface and a first front contact disposed on the first front
surface and having a first electrical polarity. The first front
contact occupies a portion of the first front surface. The first PV
device further includes a first back surface and a first back
contact disposed on the first back surface that has a second
electrical polarity opposite to the first electrical polarity. The
first back contact occupies a portion of the first back surface.
The second PV device comprises a second front surface and a second
front contact disposed on the second front surface and having a
third electrical polarity. The second front contact occupies a
portion of the second front surface. The second PV cell also
includes a second back surface and a second back contact disposed
on the second back surface and having a fourth electrical polarity
opposite to the third electrical polarity. The second back contact
occupies a portion of the second back surface. In some embodiments,
the second front contact of the second PV device underlies the
first back contact of the first PV device and wherein only the
portion of the first back surface of the first PV device overlies
the second front surface of the second PV device.
[0011] In some embodiments, the solar energy receiver includes a
third photovoltaic (PV) device that includes a third front surface
and a third front contact disposed on the third front surface and
having a fifth electrical polarity. The third front contact
occupies a portion of the third front surface. The third PV device
also includes a third back surface and a third back contact
disposed on the third back surface and having a sixth electrical
polarity opposite to the fifth electrical polarity. The third back
contact occupies a portion of the third back surface. In this solar
energy receiver, the second back contact of the second PV device
overlies the third front contact of the third PV device and wherein
only the portion of the second back surface of the second PV device
overlies the third front surface of the third PV device. In some
embodiments, the shape of the first and/or the second PV device can
be non-square such as a rectangle, a trapezoid, or a polygon.
[0012] In some embodiments, the second front contact of the second
PV device is electrically connected to the first back contact of
the first PV device using an electrically conducting adhesive. In
other embodiments, the second front contact of the second PV device
is electrically connected to the first back contact of the first PV
device using a connection stack. In an embodiment, the connection
stack can be multi-layered.
[0013] Other embodiments of the present invention provide a system
that includes a solar energy receiver, a plurality of extent
sensors coupled to the solar energy receiver, and a tracking
mechanism coupled to the solar energy receiver. The solar energy
receiver may include a plurality of active PV devices. The
plurality of extent sensors are configured to track a position of
the sun in the sky and provide the position information to the
tracking mechanism. The tracking mechanism is configured to orient
the solar energy receiver based on the position information
received from the plurality of extent sensors. The tracking
mechanism further includes tracking control unit configured to
receive the position information from the plurality of extent
sensors and a positioning structure and determine an orientation
for the solar energy receiver and a motor control unit configured
to receive coordinates for the orientation from the tracking
control unit and operate one or more motors to orient the solar
energy receiver in the desired orientation.
[0014] These and other embodiments of the present invention, as
well as its features and some potential advantages are described in
more detail in conjunction with the text below and attached
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIGS. 1A-1B show perspective views of front-contact
photovoltaic (PV) cells according to an embodiment of the present
invention.
[0016] FIG. 2 shows a simplified plan view of a receiver according
to an embodiment of the present invention.
[0017] FIG. 2A is a simplified exploded view showing the placement
of one active cell on the support of the receiver according to an
embodiment of the present invention.
[0018] FIGS. 2A1-2A3 show various views of another embodiment of a
multi-prong contact structure according to an embodiment of the
present invention.
[0019] FIG. 2B shows a simplified generic cross-sectional view of a
receiver structure according to an embodiment of the present
invention.
[0020] FIG. 2C shows an enlarged view of a portion of the receiver
showing the serial connection of the cells according to an
embodiment of the present invention.
[0021] FIG. 2D shows a more detailed cross-sectional view of the
receiver according to an embodiment of the present invention.
[0022] FIG. 2E shows a plan view of an embodiment a single ring of
cells according to an embodiment of the present invention.
[0023] FIG. 2F shows a simplified generic cross-sectional view of
an alternative embodiment of a receiver employing multiple printed
circuit boards.
[0024] FIG. 3A shows a simplified cross-sectional view a receiver
employing the shingling technique according to an embodiment of the
present invention.
[0025] FIG. 3B shows a simplified cross-sectional view of an
alternative embodiment of a receiver employing the shingling
technique.
[0026] FIG. 4 shows a simplified plan view of another alternative
embodiment utilizing the shingling approach, with shaped cells
arranged in an annular manner.
[0027] FIG. 4A shows a perspective view of a shaped cell utilized
in the embodiment shown in FIG. 4.
[0028] FIG. 4B shows a simplified perspective view of a shaped cell
utilized in the embodiment shown in FIG. 4.
[0029] FIG. 4C shows a simplified cross-sectional view of a shaped
cell utilized in the embodiment shown in FIG. 4.
[0030] FIG. 4C1 shows a simplified cross-sectional view of a
connection stack, in accordance with an embodiment of the present
invention.
[0031] FIG. 4C2 shows a simplified cross-sectional view of another
connection stack, in accordance with another embodiment of the
present invention.
[0032] FIG. 4C3 shows a simplified cross-sectional view of a
connection stack, in accordance with yet another embodiment of the
present invention.
[0033] FIG. 4C4 shows a simplified cross-sectional view of a
connection stack, in accordance with still another embodiment of
the present invention.
[0034] FIG. 4C5 shows a simplified cross-sectional view of a
connection stack in order to access positive and negative terminals
of an annulus of cells in accordance with still another embodiment
of the present invention.
[0035] FIG. 5 shows a simplified schematic diagram of a solar
receiver with extent sensors positioned outside the illuminated
area according to an embodiment of the present invention.
[0036] FIG. 5A shows a simplified schematic diagram of a solar
receiver with extent sensors positioned straddling the illuminated
area according to an embodiment of the present invention.
[0037] FIG. 6 shows a simplified control schematic for closed loop
error processing of extent sensor signals according to an
embodiment of the present invention.
DETAILED DESCRIPTION
[0038] Embodiments of receivers in accordance with the present
invention may be employed in connection with optical collector
devices, including but not limited to those utilizing inflatable
concentrators as described in U.S. patent application Ser. No.
11/843,531, filed Aug. 22, 2007, which is incorporated by reference
in its entirety herein for all purposes.
[0039] U.S. patent application Ser. No. 13/227,093, filed Sep. 7,
2011, disclosing a solar collector having a receiver positioned
external to an inflation space or volume, is incorporated by
reference in its entirety herein for all purposes. Embodiments of
the present invention may share one or more characteristics in
common with the apparatuses disclosed in that patent
application.
[0040] U.S. patent application Ser. No. 12/720,429, filed on Mar.
9, 2010, describing mounting structures and other concepts, is also
incorporated by reference in its entirety herein for all
purposes.
[0041] U.S. patent application Ser. No. 13/015,339 filed on Jan.
27, 2011 describing mounting structures and other concepts is also
incorporated by reference in its entirety herein for all
purposes.
[0042] Receivers according to particular embodiments may share one
or more features with those described in U.S. Patent Publication
No. 2008/0135095, which is also incorporated by reference herein
for all purposes.
[0043] Further incorporated by reference herein for all purposes,
is U.S. Patent Publication No. 2010/0295383, which describes
various embodiments of power plants. Embodiments of receivers in
accordance with the present invention may be incorporated into
power plants exhibiting one or more features disclosed in that
patent application.
[0044] Embodiments of the present invention relate to receiver
structures for use in harnessing solar energy. Receivers typically
comprise an array of individual active elements that are sensitive
to incoming light.
[0045] FIG. 1A shows a perspective view of one such active element
including a front-contact photovoltaic (PV) cell 100. Front-contact
PV cell 100 receives incident light 101 through front surface 102,
and generates electrical power therefrom.
[0046] The electrical power generated within cell 100 flows through
conducting fingers 104 in electrical communication with busbar 106,
which together form a comb-like structure 107 as illustrated in
FIG. 1B. Busbar 106 typically serves as the negative node of the
front contact PV cell. Back surface 108 of front-contact PV cell
100 bears conducting layer 110 serving as the positive node of the
front-contact PV cell.
[0047] Individual solar cells can have relatively low voltages
determined by the band gap of the semiconductor(s) used, and
non-idealities present within PV devices. For example if the PV
cell of FIG. 1A comprises silicon, then an output voltage of about
0.6 V can be expected. Multi junction cells can have higher
voltages. Accordingly, a receiver may comprise multiple solar cells
connected in series in order to obtain a higher output voltage.
[0048] One challenge in developing a multi-element receiver for
Concentrated Photovoltaic (CPV) applications is reducing or
eliminating surface area of the receiver that is occupied by
non-active elements. As used herein, the term `grout` refers to
illuminated receiver area that is incapable of converting light
into electricity. Typically grout comprises busbars, interconnects,
traces, and the spacing between solar cells.
[0049] Accordingly, embodiments of the present invention employ
various methods, alone or in combination, to minimize or eliminate
the grout. In certain embodiments, the shapes of the active cells
are chosen to minimize grout. In certain embodiments, elements of
the receiver are positioned to hide non-active elements under other
elements of the receiver, for example, reflectors or active
elements. Other techniques which may be employed include the use of
an interconnect structure having a small footprint, the use of an
interconnect as an optical element itself, the use of back contact
cells, and the use of shingling wherein non-active portions of the
cells overlap one another. These are described in detail below.
[0050] Solar cell manufacturing techniques allow PV cells to be in
non-rectangular shapes. A shaped PV cell may be tessellated so as
to minimize the spacing between cells and grout.
[0051] Attachment of a PV cell to the receiver and the associated
electrical connections may greatly influence the function of a CPV
receiver. The attachment vehicle may be a conducting or an
insulating adhesive depending on the type of electrical
communication desired. As used herein the term "electrically
conducting adhesive" or ECA includes but is not limited to solder,
epoxy, acrylic, polyimide, polyurethanes, cyanate esters, silicone,
or the like and combinations thereof that allow electrical
communication through the material. As used herein the term
"insulating adhesive" includes but is not limited to epoxy,
acrylic, polyimide, polyurethanes, cyanate esters, silicone, or the
like and combinations thereof that does not allow electrical
communication through the material.
[0052] For example, FIGS. 2-2D shows simplified views of a receiver
200 according to one embodiment of the present invention. Receiver
200 comprises a support 202 bearing a plurality of discrete active
elements 204 that are connected in series. In this particular
embodiment, receiver 200 includes an inner ring 206 and an outer
ring 208 which support a plurality of front-contact PV cells 210
having busbars 211.
[0053] As illustrated in FIG. 2, each PV cell 210 is in the shape
of a trapezoid comprising approximately the same area, such that a
uniform illumination profile will generate approximately the same
amount of current in each cell. In this embodiment, PV cells 210
may be shaped as angular wedges or trapezoids in order to create a
circle-like shape. As front contact cells are used, busbars 211 may
be grouped together on inside ring 206 and/or outside ring 208,
where they can underlie optical elements such as central reflector
240 or peripheral reflector 242 in such a way as to avoid shading
of the active cell area. For example, the corresponding exploded
view of receive 200 as illustrated in FIG. 2A shows a portion of
the central reflector 240 overhanging the busbar 211 of the front
contact cell.
[0054] In certain embodiments, single or multiple rings of cells
may be used in such a way as to minimize grout by covering with
inner and outer optical elements. Here, for example, two annuli of
cells are combined, with series connections made cell-to-cell
around the inner and outer rings. Inner ring 206 and outer ring 208
may be connected in series on a single layer PCB using a through
hole 252 connection on the inside of the inner ring as illustrated
in FIG. 2. Hiding busbars 211 and other non-active components (such
as bypass diodes 250, through hole connections 252, or temperature
sensors 254) under optical elements in this manner, minimizes grout
by reflecting or refracting light that would usually be lost back
onto the cell active area.
[0055] FIG. 2A is a simplified exploded view showing the placement
of one active cell on the support 202 according to an embodiment of
the present invention. In particular, a first portion 212a of
conductor layer 212 that is present on the surface of support 202
extends from underneath the cell to establish electrical
communication with the positive node through a layer 215 of
conducting adhesive. Soldermask 260 can also be present over
conductor layer 212 and dielectric 224 (shown in FIG. 2B).
[0056] FIG. 2A shows that a second conductor 220 extends upward to
establish electrical communication with busbar 211 on the top
surface of the cell, again through conducting adhesive layer 215.
In one embodiment, grout is minimized by creating a compact
electrical connection from the top of a cell to the PCB level. FIG.
2A shows that conductor 220 exhibits a multi-prong structure with
one or multiple legs 220a in order to minimize the area needed to
create a two terminal connection from a front contact cell. This
small footprint interconnect method provides the needed electrical
connectivity, while being flexible enough to allow for thermal
expansion mismatch between differing materials.
[0057] FIGS. 2A1-2A3 show various views of an elongated embodiment
of a multi-prong contact structure 290, which may be used to make
contact with a busbar of a larger cell. In particular, the portion
290a of the elongated multi-prong contact facing the cell extends
along close to a full expected length of the busbar, to maximize
electrical contact therewith. By contrast, the opposite portion
290b of the elongated multi-prong contact 290 facing the support
220a (and conducting traces patterned thereon) does not extend the
full length of the busbar, leaving space on the PCB trace for the
contact with the backside of the cell.
[0058] In certain embodiments, contacts (including the
multi-pronged contact) and/or interconnects may themselves comprise
an optical element. For example in some embodiments, the shape of
the non-active element can be chosen to minimize shading. Also,
particular embodiments may have the contact or interconnect be
configured to reflect light back onto the active cell area of the
receiver. The multi-pronged contact may be combined with the cell
to create a package, using a conducting adhesive. In addition to
conducting adhesives, techniques such as ultrasonic or laser
welding may be used. Such combination of the contact and cell into
a single package may facilitate high volume production utilizing
simple automated assembly through the use of pick and place
technology. The underside contact of the package may be attached to
the board using conducting adhesive. Connections may be made for
series, parallel, or combinations thereof
[0059] FIG. 2B shows a simplified generic cross-sectional view of a
receiver 200 according to an embodiment of the present invention.
In particular, this figure shows the cell 210 in contact with
support 202 through solder/adhesive layer 215. Support 202
comprises a Printed Circuit Board (PCB) 218 in contact with a
substrate 222 having favorable thermally conducting and physical
structural support properties. In some embodiments, substrate 222
can include thermally conductive material such as aluminum or
copper.
[0060] PCB 218 in turn comprises conductor layer 212 (typically
patterned traces) such as copper, overlying a dielectric layer 224
(which may have through holes penetrating there through). Examples
of materials that may be used for the dielectric layer include but
are not limited insulating adhesives with high thermal
conductivity, ceramics such as alumina, aluminum nitride, or
proprietary compounds such as COOLAM.TM. available from DuPont of
Wilmington, Del., and THERMAL CLAD.RTM. available from The
Bergquist Company of Chanhassen, Minn. An encapsulant 219 and
transmissive optical element 221 seal and weatherize the receiver
as well as provide mechanical protection for the cells. Sealing the
cells and interconnects is important in order to minimize
performance degradation that can arise, for example, from corrosion
or electromigration of the solar cell metallization. The
encapsulation material is chosen to match the index of refraction
of the transmissive element and minimize reflection. Examples of
materials that can be used as encapsulant 219 include but are not
limited to silicones, ionomers, or ethylene vinyl acetate
(EVA).
[0061] As illustrated in FIG. 2B, the backside of substrate 222
includes integral raised portions 222a defining channels 226
in-between two adjacent portions 222a. Channels 226 increase the
surface area of substrate 222 and increase heat transfer for
natural or forced convection cooling. Such channels may also be
formed through reliefs. Skiving may also be used to increase the
surface area of substrate 222. A fluid (such as air or water) can
be circulated through these channels and can constitute a cooling
system that can be used to control the temperature of the
receiver.
[0062] FIG. 2C shows an enlarged view of the inner ring portion of
the receiver showing the serial connection of the cells according
to an embodiment of the present invention. The positive terminal of
a first cell 220 is coupled to a connector 256 through trace 212b.
From there on, each adjacent cell has its positive node 212a
connected to the negative node of the next cell around the ring. At
the final cell in the inner ring the negative node is also coupled
to connector 256 via trace 212c. The rings also may be in serial
connection with one another. Wires can be routed from connector 256
through hole 252 to connect the inner ring in series with the outer
ring via a connector of the outer ring. Outer ring connections can
be made in a similar manner as that of the inner ring described
above.
[0063] FIG. 2D shows a more detailed cross-sectional view of
receiver 200 taken along line D-D' of FIG. 2. FIG. 2D shows that
resulting positive and negative nodes for the inner and outer
strings of active devices can be connected with each other and with
external circuitry through hole 252 and using wires from connectors
256. Positive node 276 from the outer ring can be connected with
the negative node 272 of the inner ring producing a serial
connection of all the cells with the remaining leads 274 and
278.
[0064] Transmissive optical element 221 may be refractive and/or
shaped include and/or homogenizing properties. Homogenizing
properties can be obtained through coatings or surface treatments,
which minimize loss. Central reflector element 240 and peripheral
reflector element 242 can have homogenizing properties as well.
Examples of materials that can be used as transmissive optical
element 221 include but are not limited to low iron tempered glass,
fluoropolymers, fused silica, silicone, etc. Certain embodiments of
the present invention may include traces and or interconnects
across the top surface of the support. This grout can also be
covered with optical elements used to reflect or refract light back
onto the active area.
[0065] FIG. 2D also shows receiver 200 as further comprising
central reflecting element 240 and peripheral reflecting element
242. These reflecting elements serve to re-direct light incident on
the central and peripheral portions to the active elements for
collection. This further enhances the collection efficiency of
receiver 200 and also increases tolerance for tracking the source
of illumination (e.g. the sun moving across the sky).
[0066] In the particular embodiment illustrated in FIGS. 2-2D,
busbars 211 and connections between the active devices on each ring
are positioned proximate to the corresponding (central or
peripheral) reflecting element. In this manner, the surface area of
receiver 200, which is prone to shading by a reflecting element,
can be allocated for the necessary but non-active function of
routing electrical power between the photo-sensitive elements. This
in turn frees up other surface area on receiver 200 to be occupied
by the active elements able to convert incident light into
electrical energy. Such allocation of receiver surface area to
active elements increases collection efficiency.
[0067] FIG. 2E shows an embodiment of a solar receiver 200 composed
of a single ring 207 of dual busbar cells 264. The embodiment
illustrated in FIG. 2E offers better conversion efficiency for
non-uniform illumination profiles. In this embodiment, the
multi-prong contact 220 is reduced to a single leg. Receiver 200
also incorporates extent sensor elements 255, which are described
in detail below. Embodiments illustrated in FIGS. 2-2E provide
close contact between the PV cells through bonding of layers from
PV cell 210, solder/adhesive 215, conductor 217, dielectric 224,
and substrate 222 (which together form a thermal stack). This
minimizes contact resistance and thermal resistance leading to a
lower cell temperature and more efficient cell operation.
[0068] It is desirable to have a high concentration of solar
radiation on the photovoltaic cells because it reduces the amount
of expensive photovoltaic material in the system. This also
increases the conversion efficiency of the cells. The portion of
the incident sunlight not converted to electricity by the
photovoltaic cells is absorbed and converted to heat.
[0069] Since the conversion efficiency of common photovoltaic cells
decreases with increasing temperature, it may be desirable that the
system include a heat exchanger that can remove the heat from the
cells to keep their temperature as low as possible. In fact, at
very high solar concentrations, system survival may depend upon
efficient heat removal. One technique for efficient heat removal
may be to keep the distance over which the heat must flow as small
as possible. One possible mechanism is to provide heat exchangers
with small physical dimensions, in particular thin layers of
materials comprising the thermal stack. The back side of the PCB or
the metal substrate that is in thermal communication with the PV
cells may feature pins, channels or other geometrical features to
enhance heat transfer, as described above. Such geometrical
features in combination with a flow of cooling fluid such as air or
water, may serve to keep the temperature of the receiver within
desirable levels.
[0070] In order to reduce the overall receiver module cost as well
as the cost of the cooling system and its operation, it may be
desirable to cool the solar module at the lowest possible fluid
flow rate and pressure drop. Turbulent flow may be used to draw hot
liquid from the wall chaotically through the bulk of the liquid.
Most liquid heat exchangers for solar cooling employ cooling tubes,
which require a high Reynolds number to benefit from eddy-based
transport of hot liquid from the wall. If the channel is reduced in
size to increase the Reynolds number to improve eddy transport, the
pressure drop increases. If the channel diameter is increased at
constant Reynolds number, the flow rate increases. Natural
convection of heat from the PC board and/or substrate can be
enhanced by any combination of eddying, forced convection, nucleate
boiling, and film boiling. Moreover, a surface area of the PCB
and/or substrate available for heat transfer can be increased by
techniques such as texturing or molding. In some embodiments,
forced convection techniques may also be employed.
[0071] The present invention is not limited to the particular
receivers of FIGS. 2-2E, and one skilled in the art will realize
that variations are possible. For example, while the embodiments
disclosed above include a single PCB, this is not required and
alternative embodiments could employ multiple PCBs as is shown
generically in FIG. 2F. In embodiments utilizing multiple PCBs,
patterning of the conductor and conducting vias in the various
layers can accommodate a variety of routing paths in a manner
analogous to the interconnect metallization schemes commonly
implemented in integrated circuit design. Such flexibility in
routing may afford further opportunity for placement and sizing of
active devices to maximize collection efficiency.
[0072] The various techniques employed by embodiments of the
present invention may be used on single or multilayer interconnect
levels. Single layer designs reduce cost and simplify thermal
stack, enhancing heat transfer. Multilayer designs may allow for
more complex topologies and smaller critical footprints. While
FIGS. 2-2E illustrates embodiments of receivers comprising a
plurality of front contact cells, the present invention is not
limited to this particular form of active element. According to
alternate embodiments, back contact cells may be connected directly
onto the substrate and routed to give the desired circuit
configuration using a single or multilayer PCB with minimal grout
loss. Back contact cells may have various contact patterns
according to their type. Back junction, emitter wrap through, or
metallization wrap through PV cells may be used in conjunction with
the PCB, in order to create desirable combinations of connections
on a single layer or on multiple layers. PV cells formed utilizing
through hole contacts or vias may also be used. This process is
generally known as "through silicon via" or TSV.
[0073] It is to be noted that the present invention is not limited
to embodiments utilizing active devices (e.g., PV cells) of any
particular shape or arranged in any particular spatial orientation.
For example, the receiver 200 of FIGS. 2-2E comprises a plurality
of trapezoidal active elements arranged in an annular fashion on a
circular support, however, this is not required. Alternative
embodiments could utilize active devices having other shapes,
arranged in a different manner, and/or on supports that are other
than circular in shape, and still remain within the scope of the
present invention.
[0074] FIGS. 3A and 3B illustrate a receiver according to another
embodiment of the present invention. The embodiments illustrated in
FIGS. 3A-3B employ a "shingling" technique where a bottom contact
340 of one cell 300 is attached to a busbar 311 of another cell
300. This creates a step height difference equal to the thickness
of cell 300, plus the thickness of any attachment medium. The
overlap is designed such that the bottom cell is not shaded and
additional contacts are not required to produce a series
connection. The tilted spatial orientation of the embodiments of
FIGS. 3A-3B allows a region of the active area of a front contact
PV cell 300 to overlap non-active busbar 311 of next front contact
PV cell 305, increasing collection efficiency. It also eliminates
the need for a multi-prong structure for adjacent cell connections
thereby reducing cost. Further, the shingling method allows contact
along the long direction of the cells, allowing grid lines to
traverse the cell, thereby minimizing series resistance.
[0075] Receiver topologies and interconnects based on the shingling
technique described above can utilize thermally conducting and
insulating adhesives and combinations thereof In the embodiments of
FIGS. 3A-3B, the PV cells are connected electrically using the
conducting adhesive 340, and are isolated from each by direct
mounting in the thermally conductive but electrically insulating
adhesive 342. Substrate 302 may be faceted to create a flat surface
as in FIG. 3A, or it may not be as shown in FIG. 3B. Conducting
adhesive 340 and insulating adhesive 342 may be chosen based upon
chemical compatibility with the cell metallization and other metals
that they contact in order to avoid corrosion issues.
[0076] Different rows or annuli of cells can be connected together
using a thin sheet of conductive metal chemically compatible with
the adhesive. The thin sheet metal connections may be used to
create different series/parallel interconnect topologies as
desired. Such an approach eliminates certain steps in conventional
substrate fabrication and cell packaging processes, resulting in
cheaper and faster production of multi-element receivers with
minimal grout.
[0077] Embodiments of the present invention may employ the
shingling technique described above to create receivers that have a
square or rectangular shape, or other shapes including circular.
Shingling may be used with active cells of rectangular or other
shapes such as polygons, angular wedges (trapezoids having opposite
surfaces curved), and others depending on the area that is to be
covered. According to particular embodiments, trapezoids or angular
wedges may be shingled together to produce a circular topology with
minimal grout. FIG. 4 shows such an embodiment utilizing cells
arranged in an annular manner. Such a configuration may be useful
where the illumination profile is expected to be circular in
shape.
[0078] Shingling may also be used on three dimensional surfaces to
create non-flat surfaces. For example, FIG. 3A shows a planar
substrate. A non-planar dielectric material 342 is formed between
front contact cells 300 and the planar surface 302a of substrate
302. The edge of one cell 300 overlaps a portion of the adjacent
cell 305, to which it is electrically connected through conducting
adhesive 340 and busbars 311. An encapsulant 380 overlies the
cells. A transmissive optical element 333 overlies encapsulate 380.
In some embodiments, cells may be arranged in shapes to approximate
cylinders, polyhedra, or other complex shapes of arbitrary
geometry.
[0079] FIG. 3B shows another embodiment utilizing shingling. As
illustrated in FIG. 3B, the top surface of substrate 302 is not
planar, but rather comprises a plurality of inclined facets. This
embodiment, similar to the one illustrated in FIG. 3A, allows the
non-active receiver elements (e.g., busbar 311, conducting adhesive
340, etc.) to be shaded by an overlapping portion of the adjacent
active receiver element thereby enhancing the utilization of
receiver surface area and increasing efficiency. A non-planar
substrate surface as shown in FIG. 3B can reduce the average
thickness of adhesive 342 which in turn can improve heat transfer
and reduce temperature difference between cells 300, 305 and
substrate 302 which improves efficiency and mechanical robustness.
In some embodiments, faceted surfaces reduce the thickness of the
dielectric material and improve thermal performance.
[0080] FIG. 4 shows a simplified plan view of a receiver according
to another embodiment of the present invention. As illustrated,
receiver uses the shingling technique to approximate an annular
shape. A single ring is composed of a plurality of shaped solar
cells 400. This ring may or may not be used with a central
reflector 410 and a peripheral reflector 412.
[0081] FIG. 4A shows an individual shaped cell 400 according to an
embodiment of the present invention. Cell 400 includes a non-active
busbar 406, a plurality of fingers, 404, and an active area 402.
Busbar 406 and fingers 404 form a comb-like structure 407. The
bottom region of the cell contains a metallization layer 409 with a
contact surface 408. The edge of the cell 405 is shown. Cell 400
can utilize a short finger length reducing electrical communication
distance to the busbar, which minimizes losses due to non-uniform
illumination. This finger spacing 403 can be adjusted to provide
optimal efficiency for a given concentration ratio. In some
embodiments, the optimal finger spacing may be non-uniform along
the length of cell 400.
[0082] FIG. 4B shows a perspective view of the tiling or shingling
of the cells into a receiver. Electrical communication between
cells is established via a connection stack 440. A dielectric 442
insulates the cells from substrate 430 and provides thermal
communication between cells 400 and substrate 430. Dielectric 442
may be a thermally conductive insulating adhesive. Substrate 430
may or may not be actively cooled by circulating a fluid and may or
may not be faceted. In this particular embodiment, the shingling
angle is higher on the inside of the ring than on the outside. In
some embodiments, the shingling angle is a function of receiver
radius. Edge 405 of each cell is also an active element. This
particular embodiment results in a very low grout loss, approaching
zero, and eliminates the need for a multi-prong interconnect
structure, and may lead to a cheaper manufacturing process.
[0083] FIG. 4C shows a more detailed, but still simplified, side
view of the receiver of FIG. 4 according to an embodiment of the
present invention. As illustrated in FIG. 4C, the receiver includes
a transmissive optical element 433 overlying an encapsulant
480.
[0084] Encapsulant 480 is used to bind the various PV cells
together and provide structural support to the receiver. Electrical
communication between the PV cells is established through
connection stack 440 which is in contact with cell metallization
surface 408 and busbar 406. Stack 440 may be composed of three or
more layers, 440a, 440b, and 440c. Composition of each layer 440a,
440b, and/or 440c can be varied according to the type of electrical
connection to be made. Connections may be made for series,
parallel, or combinations thereof.
[0085] Examples of composition of stack 440 are illustrated in
FIGS. 4C1 through 4C4 according to an embodiment of the present
invention. For example, FIG. 4C1 shows that stack 440 can include
three identical layers of electrically conducting adhesive 450 in
contact with the back surface metallization of one cell and the
busbar 406 of an adjacent cell. Such a connection provides for a
series connection between cells.
[0086] FIG. 4C2 illustrates a connection stack 440 that includes a
thin conducting metal layer 452 sandwiched between two layers of
electrically conducting adhesive 450 thereby electrically
connecting adjacent cells. In some embodiments, the thin conducting
metal 452 can be used to provide electrical communication to
external circuitry such as bypass diodes. Metal 452 extends
radially in the view shown in FIG. 4. FIG. 4C3 and 4C4 show
examples of connection stacks 440 and how power output terminal
connections may be made. An electrically insulating adhesive 454
electrically isolates the back surface metallization 408 and busbar
region of 406 of adjacent cells. This allows for a single terminal
or polarity to be connected to an external circuit. The stack shown
in FIG. 4C4 may be connected to the same back side metallization
surface 408 of cell in FIG. 4C3, as illustrated in FIG. 4C4. This
allows the opposite polarity terminal to 4C3 to be connected to an
external circuit. Dielectric 442 insulates the thin metal conductor
452 from electrical communication with other cells or the
substrate.
[0087] FIG. 4C5 shows a flattened perspective view of FIG. 4C
illustrating the use of a connection stack to provide access to
positive and negative circuit terminals. The backside metallization
surface is typically positive polarity (+), while busbar, 406 is
negative (-) for common p-type front contact solar cells. For a
single annulus of cells to all be connected in series, access to
the busbar of first cell 415 in the series and access to back
contact of the last cell in series 416 is needed. This is obtained
by the use of two electrically conducting adhesive layers
connecting two metal foil or ribbon layers 452 that extend beyond
the extent of the cells 400. These two metal layers are isolated
electrically from one another by the use of an electrically
insulating adhesive 454.
[0088] As is well known, the position of the sun in the sky
continually changes during the daytime as the earth rotates. In
order to receive the maximum amount of radiation from the sun, it
is desirable that the receiver directly faces the sun as much as
possible. In order to determine the optimal position of the
receiver with respect to the sun, it is advantageous to determine
the position of the sun at any given time. Once the position of the
sun is determined, the receiver can be moved/focused accordingly to
receive the maximum radiation from the sun.
[0089] The position of the sun in the sky can be calculated
directly using the date, time, and geographical location of the
receiver. In practice; however, variations in such factors as
terrain, manufacturing, and/or assembly of the receiver limit the
tracking accuracy of this purely analytical approach. A more
accurate tracking system utilizing sensors can provide a more
robust system capable of the tight tracking tolerances required for
CPV power generation. The sensors can help more accurate tracking
of the sun thereby increasing receiver power output."
[0090] FIG. 5 illustrates a solar receiver including tracking
sensors according to an embodiment of the present invention. As
illustrated in FIG. 5, fine tracking extent sensor elements 501 are
placed just outside the illuminated region 500 on a solar receiver
502. Extent sensors 501 make use of the printed circuit board
functions of the solar receiver. In some embodiments, extent
sensors 501 can be electrically and mechanically connected to
traces or pads via the printed circuit board of the receiver
substrate. In this embodiment, extent sensors 501 are placed in
symmetric co-linear pairs along an X axis and a Y axis.
[0091] Sensors 501 may be optical or thermoelectric devices
including but not limited to photovoltaic cells, photodiodes,
thermopiles, or pyroelectrics. Using photovoltaic cell material may
be beneficial due to the cell's ability to withstand concentrated
sunlight and produce an electrical signal that is proportional to
the illumination level. If sensors 501 are identical or calibrated,
they will give the same response for a given illumination intensity
and function as follows. For example, when the receiver is pointed
ideally, the signals from sensors 501 at the extent of the spot
will be equal and minimal The position error of a mispointed
receiver can be resolved into orthogonal basis vector components.
When the receiver is mispointed, the signal from the perimeter
sensor pairs in the x- and/or y-axis will be unequal. The magnitude
of the difference in signals from any sensor pair will vary
proportionally to the degree of the mispointing component along
that particular axis. The characteristic curve of the difference in
power signals along each axis can easily be linearized for small
pointing errors.
[0092] For concentrating systems with variable focal length, extent
sensors 501 may also be used to control the size (e.g., area) and
disposition of illuminated region 500. For example, when the solar
spot is of ideal size, the signal from the four perimeter sensors
501 will be equal and minimal. The solar spot size is proportional
to the sums of the signals of the four sensors. Thus, minimizing
differences between the sensor pairs and bounding the value of the
sum of the sensor signals can yield an illuminated region that is
both centered and of the desired illumination intensity.
[0093] In some embodiments, the extent sensors may be used to
provide continuous spatial position information over a given range
or to provide binary information. For example, when sensors 501 are
deployed as continuous spatial measurement devices, a balance
between sensors 501 on each axis is sought.
[0094] When the sensors are deployed as discrete spatial
measurement devices, a threshold energy for each extent sensor may
be defined such that when the threshold is met the signal goes from
`off`, binary 0 to `on`, binary 1. The sum and difference equations
required for control can then be represented in boolean form for a
binary system.
[0095] There are many different arrangements of extent sensors as
shown in FIGS. 5 and 5A. Extent sensors may be located in, out, or
straddling the illumination region. FIG. 5A illustrates sensors 501
straddling illumination region 500. In some embodiments,
symmetrical or asymmetrical configurations for the sensors may be
used with an even or odd number of extent sensor elements. In some
embodiments, sensors may also be rotated at an angle relative to
the principle axes.
[0096] FIG. 6 illustrates an example feed-back control scheme
utilizing both coarse and fine tracking according to an embodiment
of the present invention. Coarse elevation and azimuth ("ELE" and
"AZI) are calculated given the geographical position of the
structure and the time and date. Extent sensor electrical signals
are read and interpreted. Adjustments are then made to the position
of the structure by actuating ELE or AZI motors. This loop runs
continuously or at specified time intervals providing accurate
position control of the illumination region on the solar
receiver.
[0097] Positioning structure 606 includes a frame on which a solar
receiver can be mounted. Thus, positioning structure 606 provides
the support for the solar receiver and associated electronics.
Positioning structure 606 has an associated geographical location
and elevation information. In in application, we refer to the
geographical location for positioning structure 606 is referred to
as the "coarse" position. Usually, positioning structure 606 is
placed on the ground and may have associated elevation
information.
[0098] Sensors 501 (e.g., extent sensors described above) may be
mounted directly on the solar energy receiver and may determine
position information for the Sun. The position information
determined by sensors 501 is communicated to tracking control
system 602. Tracking control system 602 receives inputs from
sensors 501 about the location of the Sun and the geographical
location of positioning structure 606. Based on that information,
tracking control system 602 determines the optimal orientation for
the solar receiver. Once the optimal orientation is determined,
tracking control system 606 drives motors 608 and 610 via motor
driver 604 to orient the solar receiver in the desired
orientation.
[0099] Tracking control system 602 continually receives position
information from positioning structure 606 and sensors 501 and
based on that, adjusts the positioning structure so that the solar
receiver is oriented in a manner so as to collect maximum solar
energy.
[0100] The tracking system illustrated in FIG. 6 can be deployed in
either online tracking or offline calibration to account for
terrain variation. In some embodiments, the tracking system can be
directly integrated into the online closed-loop control algorithm
or it can be used simply as a range governor during online
tracking. In some applications the tracking system may be used in
an offline closed-loop calibration process, in which data gathered
is used to create an open-loop calibration transform applied to
either the position command or the observed error.
[0101] Having thus described exemplary embodiments of the present
invention, it should be noted by those skilled in the art that the
within disclosures are exemplary only and that various other
alternatives, adaptations, and modifications may be made within the
scope of the present invention. Accordingly, the present invention
is not limited to the specific embodiments as illustrated herein,
but is only limited by the following claims.
* * * * *