U.S. patent application number 11/500053 was filed with the patent office on 2008-02-07 for terrestrial solar power system using iii-v semiconductor solar cells.
Invention is credited to Arthur Cornfeld, Daniel McGlynn, Paul R. Sharps, Mark A. Stan.
Application Number | 20080029151 11/500053 |
Document ID | / |
Family ID | 39027972 |
Filed Date | 2008-02-07 |
United States Patent
Application |
20080029151 |
Kind Code |
A1 |
McGlynn; Daniel ; et
al. |
February 7, 2008 |
Terrestrial solar power system using III-V semiconductor solar
cells
Abstract
A system for generating electrical power from solar radiation
utilizing a III-V compound multijunction semiconductor solar cell;
a concentrator for focusing sunlight on the solar cell, including a
concave trough-shaped reflector; and a heat spreader connected to
the solar cell for cooling the cell.
Inventors: |
McGlynn; Daniel;
(Albuquerque, NM) ; Sharps; Paul R.; (Albuquerque,
NM) ; Cornfeld; Arthur; (Sandia Park, NM) ;
Stan; Mark A.; (Albuquerque, NM) |
Correspondence
Address: |
Casey Toohey;Emcore Corporation
1600 Eubank Blvd. SE
Albuquerque
NM
87123
US
|
Family ID: |
39027972 |
Appl. No.: |
11/500053 |
Filed: |
August 7, 2006 |
Current U.S.
Class: |
136/249 |
Current CPC
Class: |
Y02E 10/52 20130101;
H01L 31/0725 20130101; H01L 31/0735 20130101; H01L 31/052 20130101;
H01L 31/0521 20130101; H01L 31/06875 20130101; H01L 31/0547
20141201; F24S 20/20 20180501; Y02E 10/544 20130101 |
Class at
Publication: |
136/249 |
International
Class: |
H01L 31/042 20060101
H01L031/042 |
Claims
1. A system for generating electrical power from solar radiation
comprising: a III-V compound semiconductor solar cell; a
concentrator for focusing sunlight on the solar cell, including a
concave trough-shaped reflector; a solar tracker coupled to said
concentrator so as to align the concentrator with the rays of the
sun as the sun traverses the sky so that the sunlight is focused on
the solar cell; a heat spreader connected to said solar cell for
cooling said cell; and an electrical circuit connected to said
solar cell for transferring electrical energy from said cell.
2. A system as defined in claim 1, wherein said heat spreader is a
metal structure with cooling fins.
3. A system as defined in claim 1, wherein said heat spreader is
water cooled.
4. A system as defined in claim 1, wherein said solar cell is an
inverted metamorphic cell with an insulated via extending
therethrough so that the anode and cathode contacts are on one side
thereof.
5. A thin, flexible solar cell comprising a semiconductor body
including a first solar subcell on the substrate having a first
band gap; a second solar subcell disposed over the first subcell
and having a second band gap smaller than the first band gap; a
grading interlayer disposed over the second subcell having a third
band gap larger than the second band gap; a third solar subcell
disposed over the second solar subcell such that the third solar
subcell is lattice mis-matched with respect to the second subcell
and the third subcell has a fourth band gap smaller than the third
band gap; and a support for mounting the solar cell in a non-planar
configuration so as to capture the parallel rays of the incoming
sunlight in a concentrator so that the rays are substantially
perpendicular to the surface of the semiconductor body.
6. A solar cell module comprising: a thin film semiconductor body
including a multijunction solar cell and first and second
electrical contacts on the back surface thereof; a support for
mounting said solar cell and making electrical contact with said
first and second contacts; and a heat spreader attached to said
support for dissipating heat from said semiconductor body.
7. A module as defined in claim 6, wherein said semiconductor body
is composed of a III-V compound semiconductor.
8. A module as defined in claim 7, wherein said support is composed
of copper and has first and second electrically isolated regions
for making electrical contact with said first and second contacts
respectively.
9. A module as defined in claim 6, wherein said heat spreader
includes cooling fins.
10. A multijunction solar cell comprising: a semiconductor body; a
first solar subcell in said body having a first band gap; a second
solar subcell in said body disposed adjacent said first subcell in
said body and having a second band gap smaller than said first band
gap; a grading interlayer disposed adjacent said second subcell in
said body and having a third band gap greater than said second band
gap; and a third solar subcell disposed adjacent said interlayer in
said body and not being lattice mis-matched with respect to said
second subcell and having a fourth band gap smaller than said third
band gap.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to co-pending U.S. patent
application Ser. No. 11/109,016 filed Apr. 19, 2005, and Ser. No.
11/280,379 filed Nov. 16, 2005.
[0002] This application is also related to co-pending U.S. patent
application Ser. No. 11/45,793 filed Jun. 2, 2006 and assigned to
the common assignee.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention.
[0004] The present invention relates generally to terrestrial solar
power systems for the conversion of sunlight into electrical
energy, and, more particularly, to the use of III-V compound
semiconductor solar cells in conjunction with reflector
concentrators which are connected in an array for unitary movement
to track the sun.
[0005] 2. Description of the Related Art.
[0006] Commercially available silicon solar cells for terrestrial
solar power application have efficiencies ranging from 8% to 15%.
Compound semiconductor solar cells, based on III-V compounds, have
28% efficiency in normal operating conditions and 32.6% efficiency
under concentration. Moreover, it is well known that concentrating
solar energy onto the photovoltaic cell increases the cell's
efficiency.
[0007] Terrestrial solar power systems currently use silicon solar
cells in view of their low cost and widespread availability.
Although compound semiconductor solar cells have been widely used
in satellite applications, in which their power-to-weight
efficiencies are more important than cost-per-watt considerations
in selecting such devices, such solar cells have not yet been
designed and configured for terrestrial systems, nor have
terrestrial solar power systems been configured and optimized to
utilize compound semiconductor solar cells.
[0008] In conventional solar cells constructed with silicon (Si)
substrates, one electrical contact is typically placed on a light
absorbing or front side of the solar cell and a second contact is
placed on the back side of the cell. A photoactive semiconductor is
disposed on a light-absorbing side of the substrate and includes
one or more p-n junctions, which creates electron flow as light is
absorbed within the cell.
[0009] The contact on the face of the cell where light enters is
generally expanded in the form of a grid pattern over the surface
of the front side and is generally composed of a good conductor
such as a metal. The grid pattern does not cover the entire face of
the cell since grid materials, though good electrical conductors,
are generally not transparent to light.
[0010] The grid pattern on the face of the cell is generally widely
spaced to allow light to enter the solar cell but not to the extent
that the electrical contact layer will have difficulty collecting
the current produced by the electron flow in the cell. The back
electrical contact has not such diametrically opposing
restrictions. The back contact simply functions as an electrical
contact and thus typically covers the entire back surface of the
cell. Because the back contact must be a very good electrical
conductor, it is almost always made of metal layer.
[0011] The placement of both anode and cathode contacts on the back
side of the cell simplifies the interconnection of individual solar
cells in a horizontal array, in which the cells are electrically
connected in series. Such back contact designs are known from PCT
Patent Publication WO 2005/076960 AZ of Gee et al. for silicon
cells, and U.S. patent application Ser. No. 11/109/016 filed Apr.
19, 2005, herein incorporated by reference, of the present
assignee, for compound semiconductor solar cells.
[0012] Another aspect of terrestrial solar power system is the use
of concentrators (such as lenses and mirrors) to focus the incoming
sun rays onto the solar cell or solar cell array. The geometric
design of such systems also requires a solar tracking mechanism,
which allows the plane of the solar cell to continuously face the
sun as the sun traverses the sky during the day, thereby optimizing
the amount of sunlight impinging upon the cell.
[0013] Still another aspect of concentrator-based solar power cell
configuration design is the design of heat dissipating structures
or coolant techniques for dissipating the associated heat generated
by the intense light impinging on the surface of the semiconductor
body. Prior art designs, such as described in PCT Patent
Application No. 02/080286 A1, published Oct. 10, 2002, utilize a
complex coolant flow path in thermal contact with the (silicon)
photovoltaic cells.
[0014] Still another aspect of a solar cell system is the physical
structure of the semiconductor material constituting the solar
cell. Solar cells are often fabricated in vertical, multijunction
structures, and disposed in horizontal arrays, with the individual
solar cells connected together in an electrical series. The shape
and structure of an array, as well as the number of cells it
contains, are determined in part by the desired output voltage and
current. One type of multijunction structure useful in the design
according to the present invention is the inverted metamorphic
solar cell structures, such as described in U.S. Pat. No.
6,951,819, M. W. Wanless et al, Lattice Mismatched Approaches for
High Performance, III-V Photovoltaic Energy Converters (Conference
Proceedings of the 31.sup.st IEEE Photovoltaic Specialists
Conference, Jan. 3-7, 2005, IEEE Press, 2005) and U.S. patent
application Ser. No. 11/445,793 of the present assignee, filed Jun.
2, 2006, and herein incorporated by reference
[0015] Although a variety of design features described above have
been known for use in solar cell arrays and solar energy systems,
they have not been utilized together or adapted in an integrated
manner in a terrestrial solar energy system prior to the present
invention.
SUMMARY OF THE INVENTION
1. Objects of the Invention
[0016] It is an object of the present invention to provide an
improved multijunction solar cell for terrestrial power
application
[0017] It is another object of the invention to provide an inverted
metamorphic solar cell for terrestrial power applications.
[0018] It is still another object of the invention to provide an
inverted metamorphic solar cell as a thin, flexible film that
conforms to the non-planar support of a solar concentrator.
[0019] It is still another object of the invention to provide a
solar cell as a thin, flexible film that conforms to the non-planar
support of a heat spreader.
[0020] It is still another object of the invention to provide a
solar cell as a thin, flexible film that conforms to the non-planar
image plane of a solar concentrator.
[0021] It is still another object of the invention to provide a
III-V semiconductor solar cell with a reflective or refractive
solar concentrator for terrestrial power applications.
[0022] It is still another object of the invention to provide a
III-V semiconductor solar cell with a solar tracker for terrestrial
power applications.
2. Features of the Invention
[0023] Briefly, and in general terms, the invention provides a
system for generating electrical power form solar radiation
utilizing a III-V compound semiconductor solar cell, a concentrator
for focusing sunlight on the solar cell, including a concave
trough-shaped reflector, a solar tracker coupled to said
concentrator so as to align the concentrator with the rays of the
sun as the sun traverses the sky so that the sunlight is focused on
the solar cell, a heat spreader connected to said solar cell for
cooling said cell, and an electrical circuit connected to the solar
cell for transferring electrical energy from the cell.
[0024] In another aspect, the present invention provides a thin,
flexible solar cell including a semiconductor body having an upper
surface; a multijunction solar cell disposed on the upper surfaces;
a first solar subcell on the substrate having a first band gap; a
second solar subcell disposed over the first subcell and having a
second band gap smaller than the first band gap; and a grading
interlayer disposed over the second subcell interlayer having a
third band gap larger than the second band gap, and a third solar
subcell over the second solar subcell such that the third solar
subcell is lattice mismatched with respect to the second subcell
and the third subcell has a fourth band gap smaller than the third
band gap, and a support for mounting the solar cell in a non-planar
configuration so as to capture the sunlight in a concentrator.
[0025] In one aspect, the present invention provides a solar cell
including a semiconductor structure that includes a first III-V
semiconductor region forming a first surface of the semiconductor
structure and having a first polarity and a second III-V
semiconductor region forming a second surface of the semiconductor
structure and having a second polarity. The structure further
includes at least one insulating via formed in the semiconductor
structure from the first surface to the second surface, an
electrical connection extending through the via and an insulated
contact pad on the first surface of the semiconductor structure,
the electrical connection extending from the second semiconductor
region to the insulated contact pad so as to form a terminal of the
second semiconductor region on the first surface, and a heat
dissipating support on which the solar cell is mounted.
[0026] In another aspect, the present invention provides a solar
cell module including a thin film semiconductor body including a
multijunction solar cell and having first and second electrical
contacts on the back surface thereof, a support for mounting the
solar cell and making electrical contact with the first and second
contacts, and a heat spreader attached to the support for
dissipating heat from the semiconductor body.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 shows a highly simplified block diagram of a
terrestrial solar cell system under an illustrated embodiment of
the invention;
[0028] FIG. 2 shows a cross-sectional view of an inverted
metamorphic solar cell that may be used in the present
invention;
[0029] FIG. 3 shows an enlarged cross-sectional view of a first
embodiment of the collection optics used in the present invention;
and
[0030] FIG. 4 shows a cross-sectional view of a second embodiment
of the collection optics used in the present invention.
[0031] Additional objects, advantages, and novel features of the
present invention will become apparent to those skilled in the art
from this disclosure, including the following detailed description
as well as by practice of the invention. While the invention is
described below with reference to preferred embodiments, it should
be understood that the invention is not limited thereto. Those of
ordinary skill in the art having access to the teachings herein
will recognize additional applications, modifications and
embodiments in other fields, which are within the scope of the
invention as disclosed and claimed herein and with respect to which
the invention could be of utility.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0032] Details of the present invention will now be described
including exemplary aspects and embodiments thereof. Referring to
the drawings and the following description, like reference numbers
are used to identify like or functionally similar elements, and are
intended to illustrate major features of exemplary embodiments in a
highly simplified diagrammatic manner. Moreover, the drawings are
not intended to depict every feature of the actual embodiment nor
the relative dimensions of the depicted elements, and are not drawn
to scale.
[0033] The present invention relates generally to terrestrial solar
power systems for the conversion of sunlight into electrical
energy, and to the use of Ill-V compound semiconductor solar cells
in conjunction with optical components such as reflectors or
concentrators which are connected in an array for unitary movement
to track the sun.
[0034] In one aspect, the invention relates to the design of a
solar power system as depicted in FIG. 1. FIG. 1 depicts the sun
100 traversing the sky along a path 101 which varies with latitude
and day of the year. Solar collectors 102 are pointed at the sun so
as to maximize the exposure of the solar cells (not shown) directly
to the sun's parallel incoming rays. The collectors 102 may be
organized as an array which is mounted on a rotatable platform 103
to allow the array to track the sun 100 as the sun moves during the
day. The platform 103 is in turn mounted on a fixed support 104
which may be mounted on a building or other terrestrial structure.
The support 104 may include electrical circuitry to transfer the
electrical current supplied by the array 102 to a battery, power
distribution system, or grid.
[0035] A solar tracking arrangement 106 is provided which may
either store solar angle data in a database, or utilize
photodetectors or other optical components 107 to detect the
position of the sun 100. The tracking arrangement processes the
stored or detected sun angle information, and transmits appropriate
control signals to the support 104 to cause the platform 103 and
collector optics array 102 to be continuously positioned both in
azimuth and altitude angles by means of a drive 105, schematically
shown in the Figure. A variety of solar tracking arrangements are
known to those skilled in the art, and therefore need not be
described in detail here.
[0036] FIG. 2 depicts the multijunction inverted metamorphic solar
cell that may be used in one embodiment of the present invention,
including three subcells A, B and C. More particularly, the solar
cell is formed using the process in U.S. patent application Ser.
No. 11/445,793 filed Jun. 2, 2006. As shown in the Figure, the top
surface of the solar cell includes grid lines 501 which are
directly deposited over the contact layer 105. An antireflective
(ARC) dielectric layer is deposited over the entire surface of the
solar cell. An adhesive is deposited over the ARC layer to secure a
cover glass. The solar cell structure includes a window layer 106
adjacent to the contact layer 105. The subcell A, consisting of an
n+ emitter layer 107 and a p-type base layer 108, is then formed on
the window layer 106.
[0037] In the preferred embodiment, the n+ type emitter layer 107
is composed of InGA(Al)P, and the base layer 108 is composed of
InGa(Al)P.
[0038] Adjacent to the base layer 108 is deposited a back surface
field ("BSF") layer 109 used to reduce recombination loss. The BSF
layer 109 drives minority carriers from the region near the
base/BSF interface surface to minimize the effect of recombination
loss.
[0039] On the BSF layer 109 is deposited a sequence of heavily
doped p-type and n-type layers 10 which forms a tunnel diode, a
circuit element that functions to electrically connect cell A to
cell B.
[0040] On the tunnel diode layers 110 a window layer 111 is
deposited. The window layer 111 used in the subcell B also operates
to reduce the recombination loss. The window layer 111 also
improves the passivation of the cell surface of the underlying
junctions. It should be apparent to one skilled in the art, that
additional layer(s) may be added or deleted in the cell structure
without departing from the scope of the present invention.
[0041] On the window layer 111 of cell B are deposited: the emitter
layer 112, and the p-type base layer 113. These layers are
preferably composed of InGaP and In.sub.0.015GaAs respectively,
although any other suitable materials consistent with lattice
constant and band gap requirements may be used as well.
[0042] On cell B is deposited a BSF layer 114 which performs the
same function as the BSF layer 109. A p++/n++ tunnel diode 115 is
deposited over the BSF layer 114 similar to the layers 110, again
forming a circuit element that functions here to electrically
connect cell B to cell C. A buffer layer 115a, preferably InGaAs,
is deposited over the tunnel diode 115 and has a thickness of about
1.0 micron. A metamorphic buffer layer 116 is deposited over the
buffer layer 115a which is preferably a compositionally step-graded
InGaAlAs series of layers with monotonically changing lattice
constant to achieve a transition in lattice constant from cell B to
subcell C. The bandgap of layer 116 is 1.5 ev constant with a value
slightly greater than the bandgap of the middle cell B.
[0043] In one embodiment, as suggested in the Wanless et al. paper,
the step grade contains nine compositionally graded steps with each
step layer having a thickness of 0.25 micron. In the preferred
embodiment, the interlayer is composed of InGaAlAs, with
monotonically changing lattice constant, such that the bandgap
remains constant at 1.50 ev.
[0044] Over the metamorphic buffer layer 116 is a window layer 117
composed of In.sub.0.78GaP, followed by subcell C having n+ emitter
layer 118 and p-type base layer 114. These layers are preferably
composed of In.sub.0.30GaAs.
[0045] A BSF layer 120 is deposited over base layer 119. The BSF
layer 120 performs the same function with respect to cell C as BSF
layers 114 and 109.
[0046] A p+ contact layer 121 is deposited over BSF layer 120 and a
metal contact layer 122, preferably a sequence of Ti/Au/Ag/Au
layers is applied over layer 121.
[0047] FIG. 3 is a view of a first embodiment of the present
invention using a Cassegrain reflector arrangement. In such an
arrangement, the solar cell 204 may be mounted in the center of the
reflector 301, and a passive heat spreader 302, with cooling fins
303, may be provided.
[0048] In most general terms, the solar cell module is a thin film
semiconductor body including a multijunction solar cell having
first and second electrical contacts on the back surface thereof.
The module includes a support for mounting the solar cell and
making electrical contact with the first and second contacts. A
heat spreader is attached to the support of the reflector 301 for
dissipating heat from the semiconductor body.
[0049] FIG. 4 is an enlarged view of a parabolic trough solar
collector 400 according to a second embodiment of the present
invention. The trough 401 is one embodiment of the collector optics
102, the trough 401 is positioned to face the sun so that the
incoming parallel rays are focused at a focal point along a line,
approximately at the center of tube element 402. In one embodiment,
the solar cell 406 (such as described in FIG. 2) may be mounted and
supported by the tube 402. The tube 402 may be composed of two
electrically isolated elements 403 and 404 supported by a
dielectric outer support 405. The metallic elements 403 and 404
function as a heat spreader, and may be filled with a circulating
liquid to provide even greater cooling to the solar cell 406. The
tube 402 is suspended at the focal point by means of a support
bracket 408.
[0050] One aspect of the present invention depicted in FIG. 4 is
that the solar cell 406 is a flexible thin film and shaped so as to
conform to the surface of the tube 402, which has a non-planar
configuration, in this embodiment being cylindrical. The design of
the solar cell 406 may include a metal via 407 which makes an
electrical connection between the top surface of the cell 406 and
element 404. The bottom surface of the cell 406 makes electrical
contact with element 403.
[0051] Although this invention has been described in certain
specific embodiments, many additional modifications and variations
would be apparent to those skilled in the art. The present
invention is therefore considered in all respects to be
illustrative and not restrictive. The scope of the invention is
indicated by the appended claims, and all changes that come within
the meaning and range of equivalents thereof are intended to be
embraced therein.
[0052] It will be understood that each of the elements described
above, or two or more together, also may find a useful application
in other types of constructions differing from the types described
above.
[0053] While the invention has been illustrated and described as
embodied in a solar power system using III-V compound
semiconductors, it is not intended to be limited to the details
shown, since various modifications and structural changes may be
made without departing in any way from the spirit of the present
invention.
[0054] Without further analysis, the foregoing will so fully reveal
the gist of the present invention that others can, by applying
current knowledge, readily adapt it for various applications
without omitting features that, from the standpoint of prior art,
fairly constitute essential characteristics of the generic or
specific aspects of this invention and therefore, such adaptations
should and are intended to be comprehended within the meaning and
range of equivalence of the following claims.
* * * * *