U.S. patent application number 11/638793 was filed with the patent office on 2007-04-26 for concentrator solar photovol taic array with compact tailored imaging power units.
Invention is credited to Gary D. Conley, Stephen John Horne.
Application Number | 20070089778 11/638793 |
Document ID | / |
Family ID | 37461916 |
Filed Date | 2007-04-26 |
United States Patent
Application |
20070089778 |
Kind Code |
A1 |
Horne; Stephen John ; et
al. |
April 26, 2007 |
Concentrator solar photovol taic array with compact tailored
imaging power units
Abstract
Solar panels and assembled arrays thereof include a collection
of relatively compact, high-capacity power units. Optical
components of each power unit include a front window or surface
glazing, a primary mirror, secondary mirror and receiver assembly.
Primary and secondary mirrors are defined by respective perimeters,
at least a portion of which may be substantially coplanar and in
contact with the front window. Some primary mirrors are configured
with a perimeter of alternating full and truncated sections, and
are curved to a base portion forming a pilot hole therein. Receiver
assembly mechanical components include an alignment tube for mating
with the primary mirror's pilot hole and for housing a photovoltaic
solar cell. A base plate provided adjacent to the alignment tube
serves to radiate heat emitted by the solar cell, and in some
embodiments an additional heat sink provides further passive
cooling. A tapered optical rod also provided within the receiver
assembly directs received sunlight to the solar cell where
electrical current is generated.
Inventors: |
Horne; Stephen John; (El
Granada, CA) ; Conley; Gary D.; (Saratoga,
CA) |
Correspondence
Address: |
DORITY & MANNING, P.A.
POST OFFICE BOX 1449
GREENVILLE
SC
29602-1449
US
|
Family ID: |
37461916 |
Appl. No.: |
11/638793 |
Filed: |
December 14, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11138666 |
May 26, 2005 |
|
|
|
11638793 |
Dec 14, 2006 |
|
|
|
Current U.S.
Class: |
136/246 |
Current CPC
Class: |
G02B 19/0028 20130101;
H01L 31/0547 20141201; G02B 19/0042 20130101; H01L 31/052 20130101;
F24S 23/79 20180501; G02B 19/0033 20130101; F24S 23/12 20180501;
Y02E 10/52 20130101; Y02E 10/40 20130101 |
Class at
Publication: |
136/246 |
International
Class: |
H02N 6/00 20060101
H02N006/00 |
Claims
1-19. (canceled)
20. A power unit for a solar panel, comprising: a primary mirror
formed to define a pilot hole at the base thereof and curving out
from said pilot hole to a first perimeter portion; and a receiver
assembly, comprising: an alignment element for mating with the
pilot hole of said primary mirror; and a solar cell configured to
receive sunlight directed to said receiver assembly and to produce
a resultant electrical current flow.
21. The power unit of claim 20, wherein said receiver assembly
further comprises a base plate provided adjacent to said alignment
element and configured to radiate heat emitted by said solar
cell.
22. The power unit of claim 21, wherein said alignment element
comprises a tapered tube portion and a substantially wider base
portion, said substantially wider base portion provided adjacent to
said base plate, and wherein said solar cell is mounted in said
alignment element.
23. The power unit of claim 21, wherein said base plate is
configured as a substantially planar conductive element.
24. The power unit of claim 21, wherein said base plate is formed
with a series of substantially concentric circular portions therein
to facilitate flexibility within said base plate.
25. The power unit of claim 21, wherein said receiver assembly
further comprises a substrate to which said solar cell is mounted,
said substrate comprising electrical connections for relaying the
electrical current generated within said solar cell.
26. The power unit of claim 20, wherein said receiver assembly
further comprises a heat sink provided adjacent to said solar cell
for dissipating heat emitted by said solar cell.
27. The power unit of claim 20, wherein said receiver assembly
further comprises an optical rod fitted at least partially within
said alignment element, said optical rod configured to guide
sunlight received by said power unit to said solar cell.
28. The power unit of claim 27, further comprising an
anti-reflective coating provided on at least a portion of said
optical rod.
29. The power unit of claim 27, wherein said optical rod is tapered
away from an entrance surface thereof.
30. The power unit of claim 20, further comprising a front surface
provided adjacent to and adhered to at least part of the first
perimeter portion of said primary mirror, said front surface
characterized by a plurality of edges.
31. The power unit of claim 30, further comprising a housing for
receiving selected edges of said front surface.
32. The power unit of claim 30, further comprising an
anti-reflective coating provided on said front surface.
33. The power unit of claim 30, wherein said receiver assembly
further comprises a base plate provided adjacent to said alignment
element and configured to radiate heat emitted by said solar cell,
and wherein said base plate is coupled to said housing.
34. The power unit of claim 33, further comprising a plurality of
coil springs for coupling said base plate to said housing.
35. The power unit of claim 30, further comprising a secondary
mirror having a second perimeter portion provided in contact with
said front surface, wherein said second mirror is positioned in a
substantially linear relationship with the pilot hole of said
primary mirror.
36. The power unit of claim 20, further comprising at least one
mounting ring provided around said alignment element, said at least
one mounting ring being configured to mate with the pilot hole
formed in said primary mirror.
37-55. (canceled)
56. The power unit for a solar panel of claim 20, wherein the first
perimeter portion has a near-square shape.
57. The power unit for a solar panel of claim 20, wherein the first
perimeter portion has a near hexagonal shape.
Description
BACKGROUND OF THE INVENTION
[0001] It is generally appreciated that one of many known
technologies for generating electrical power involves the
harvesting of solar radiation and its conversion into direct
current (DC) electricity. Solar power generation has already proven
to be a very effective and "environmentally friendly" energy
option, and further advances related to this technology continue to
increase the appeal of such power generation systems.
[0002] A particular type of module utilized in conventional solar
systems employs photovoltaics or "PV" cells, in which an electrical
field is created at the P-N junction of a silicon wafer or other
semiconductive material. PV cells may be configured into modules
and arrays that convert impinging solar radiation into electrical
power, and can be employed in a wide variety of applications, such
as charging batteries, operating motors, powering electrical loads,
etc. As a power generation and distribution solution, PV modules
can provide an alternative or a supplement to traditional
grid-supplied electricity or can serve as a stand-alone source of
power in remote regions or other locations where conventional power
options may be unavailable or infeasible to implement.
[0003] In accordance with the pursuit for further advancement in
the field of photovoltaics and related solar generation
technologies, it is desired to provide solar panel and array
configurations that are increasingly efficient in their conversion
levels. In addition to achieving a design that is efficient in both
performance and size, it is also desirable to provide power units
and corresponding solar panels that are characterized by reduced
cost and increased levels of mechanical robustness. Although many
PV assemblies and related solar systems have been developed, no
single design has captured the above preferences and others
associated with the present subject matter. A better appreciation
of the aspects and advantages of the presently disclosed technology
will be attained from the remainder of the specification.
SUMMARY OF THE INVENTION
[0004] In view of the recognized features encountered in the prior
art and addressed by the present subject matter, new features and
steps associated with solar system technology have been developed.
More particularly, exemplary power units such as those including a
photovoltaic (PV) cell have been developed, as well as modular
configurations of such power units into solar panels and
corresponding arrays. The power units and collective assemblies
thereof are characterized by many particular features and
advantages, several of which will now be discussed.
[0005] Many embodiments of the presently disclosed technology
provide for a power unit design that is axially compact (such as
less than about 20 cm in some embodiments). Reduced dimensions and
cost as well as relative ease of assembly are some of the many
advantages afforded by select embodiments of the presently
disclosed technology.
[0006] Yet another advantage in accordance with certain embodiments
of the present invention concerns the completely passive cooling
options offered in each power unit design. The concentrator
assembly of each power unit is positioned at the back of each power
unit, thus providing it in a location that can be readily cooled.
Concentrator units may include a heat spreading element consisting
of a relatively large base plate that functions as a simple heat
spreader and serves to provide certain mechanical functionality for
the assembly as well to radiate heat emitted by the concentrator
assembly's solar cell. In some embodiments, an additional heat sink
element may also be provided adjacent to each solar cell for
further passive cooling.
[0007] A still further advantage of some embodiments of the present
technology concerns the relatively liberal optical tolerances that
are a result of the precise design and configuration of optical
components in each power unit. The size and position of primary and
secondary mirrors relative to one another and relative to an
optical rod in each concentrator assembly yields an arrangement in
which received sunlight can be concentrated to a given focal point
with some degree of flexibility and potential misalignment.
[0008] Exemplary embodiments of the present invention also offer
optimized combinations of mechanical rigidity and panel area
efficiency. Primary mirror shapes and arrangements are presented
that minimize structural weakness along a front panel surface while
also ensuring that a maximum amount of space is available for
exposure to potential sunlight. One particular exemplary embodiment
employs near-hexagonal shaped primary mirrors that are collectively
arranged in a honeycomb array that provides a strong and relatively
lightweight configuration that is potentially frameless and is
characterized by high levels of panel efficiency.
[0009] Different embodiments for selectively achieving the above
exemplary advantages will now be discussed. In one exemplary
embodiment of the present invention, a power unit includes several
optical components, such as a substantially planar surface (i.e., a
front window), a curved primary mirror and a secondary mirror. The
curved primary mirror has a first perimeter formed in a radially
symmetric fashion about a first axis, wherein at least a portion of
the first perimeter is provided in contact with the substantially
planar surface. The secondary mirror has a second perimeter formed
in a radially symmetric fashion about a second axis, wherein at
least a portion of the second perimeter is also provided in contact
with the substantially planar surface. The first and second axes
are substantially coaxial. In some embodiments, the first and
second perimeters are substantially coplanar and are sometimes both
circular.
[0010] In some more particular embodiments of the above exemplary
power unit, the first and second perimeters are characterized by
respective first and second diameters, where the first diameter is
sufficiently larger than the second diameter. In some embodiments,
the first and second mirrors may be radially symmetric about a
single axis that is substantially perpendicular to the
substantially planar surface. In other embodiments, the first
perimeter is defined by n full sections and n truncated sections
provided in an alternating fashion, where n is an integer number
between three and nine. The full sections of such a perimeter are
provided in contact with and/or are attached to the substantially
planar surface, and in some cases mounting tabs may be provided at
each full section to provide additional surface area for such
attachment. Each truncated section of the primary mirror's first
perimeter forms an arc that extends away from the substantially
planar surface, wherein the arc exists in a plane that is
substantially perpendicular to the substantially planar
surface.
[0011] Another exemplary embodiment of the present subject matter
corresponds to a solar panel that includes a plurality of power
units, such as those described above. Each power unit includes a
respective primary and secondary mirror and a receiver assembly.
Various exemplary shapes and arrangements of the mirrors may be as
previously described, with primary mirrors of adjacent power units
selectively provided in contact with one another. More
particularly, when a primary mirror perimeter is defined by n full
sections (for contact/attachment to a front window) and n truncated
sections (respectively formed in an arc away from the front window
and in a plane perpendicular to a front window), at least two
truncated sections of each primary mirror are respectively provided
adjacent to a truncated section of another adjacently positioned
primary mirror. In some embodiments, a single power unit is
surrounded by n other power units such that each of the n truncated
sections partially defining the primary mirror's first perimeter of
that single power unit is adjacent to a truncated section of one of
the n other power units. In more particular exemplary embodiments,
the receiver assembly of each power unit may selectively include
such components as an alignment feature, an optical rod and a
photovoltaic cell. An alignment feature may be used in combination
with optional mounting rings to guide and position the receiver
assembly relative to a pilot hole formed in each primary mirror. An
optical rod may be configured to receive sunlight from a power
unit's corresponding secondary mirror, and direct it to a
photovoltaic cell provided at the base of the optical rod.
[0012] Yet another exemplary embodiment of the present subject
matter concerns a power unit including such elements as a primary
mirror and a receiver assembly. The primary mirror may be formed to
define a pilot hole at the base thereof and then curve out from the
pilot hole to a first perimeter portion. The receiver assembly may
include an alignment element for mating with the pilot hole of the
primary mirror as well as a solar cell configured to receive
sunlight directed to the receiver assembly and to generate a
resultant electrical current flow therein. In more particular
embodiments, the receiver assembly may also include a base plate
provided adjacent to the alignment element to radiate heat emitted
by the solar cell (which may be mounted within the alignment
element). In some embodiments, the base plate may be provided in a
substantially flat and planar configuration. In other embodiments,
the base plate may correspond to a spring plate that provides a
flexible support mechanism by being formed with a series of
substantially concentric circular portions therein. The receiver
assembly may also include a substrate for mounting the solar cell
and for providing electrical connections for relaying the
electrical current generated in the solar cell. A heat sink may
also be provided at the base of the solar cell to further dissipate
heat. Some receiver assemblies may include an optical rod, which
may be tapered in some embodiments and configured for receiving and
guiding sunlight to the solar cell. Still further embodiments
selectively include such elements as a front window provided
adjacent to and adhered to at least a portion of the primary
mirror's first perimeter, a secondary mirror provided in contact
with a front window and positioned relative to the primary mirror's
pilot hole, and/or a housing for receiving select edges of the
front window.
[0013] A still further exemplary embodiment of the present
invention may relate to a solar array including at least one panel
(e.g., four panels in some embodiments) of power units provided in
a substantially planar and adjacent relationship with one another
and also a motorized assembly. Each power unit includes a primary
mirror, secondary mirror and receiver assembly. Primary mirrors may
be provided in a variety of shapes, such as but not limited to a
circular, near-square or near-hexagonal shape. The motorized
assembly is coupled to the at least one panel and is configured for
orienting the panel relative to a direction of applied sunlight.
The receiver assembly of each power unit may selectively include
one or more of the previously described exemplary components. The
solar array may also include such additional elements as a mounting
pole, a microcontroller for storing data corresponding to the
desired direction of orientation of the panel at different times
during the day, a communication link for receiving data from a
locally linked computing device or from a networked remote device
and a sun sensor for receiving sunlight and providing additional
information regarding the desired direction of orientation.
[0014] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate one or more
embodiments of the present subject matter, and together with the
description serve to explain certain principles of the disclosed
technology. Additional embodiments of the present subject matter
may incorporate various steps or features of the above-referenced
embodiments, and the scope of the presently disclosed technology
should in no way be limited to any particular embodiment.
Additional objects, features and aspects of the present subject
matter and corresponding embodiments are discussed in greater
detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] A full and enabling disclosure of the present subject
matter, including the best mode thereof, directed to one of
ordinary skill in the art, is set forth in the specification, which
makes reference to the appended drawings, in which:
[0016] FIG. 1 provides a perspective illustration of an exemplary
array embodiment in accordance with aspects of the present
invention, including multiple solar panels provided in a
pole-mounted configuration;
[0017] FIG. 2 provides a detailed perspective view of one exemplary
solar panel from the array of FIG. 1, including a representation of
a close-packed configuration of multiple power units within the
solar panel;
[0018] FIG. 3A provides a plan view of an exemplary primary and
secondary mirror configuration for use in accordance with a power
unit of the present invention, particularly illustrating an
exemplary near-hexagonal primary mirror design;
[0019] FIG. 3B provides a perspective view of an exemplary power
unit embodiment in accordance with aspects of the present
invention, including a near-hexagonal shaped primary mirror such as
also depicted in FIG. 3A;
[0020] FIG. 4A provides a plan view of an exemplary primary and
secondary mirror configuration for use in accordance with a power
unit of the present invention, particularly illustrating an
exemplary circular primary mirror design;
[0021] FIG. 4B provides a perspective view of an exemplary power
unit embodiment in accordance with aspects of the present
invention, including a circular-shaped primary mirror such as also
depicted in FIG. 4A;
[0022] FIG. 5A provides a plan view of an exemplary primary and
secondary mirror configuration for use in accordance with a power
unit of the present invention, particularly illustrating an
exemplary near-square primary mirror design;
[0023] FIG. 5B provides a perspective view of an exemplary power
unit embodiment in accordance with aspects of the present
invention, including a near-square shaped primary mirror such as
also depicted in FIG. 5A;
[0024] FIG. 6 provides a graphical view of exemplary size
relationships among cross-sectional representations of the primary
mirror, secondary mirror and focal plane components of a power unit
in accordance with aspects of the present invention;
[0025] FIG. 7 provides a detailed cross-sectional view of a power
unit embodiment in accordance with aspects of the present
invention, including the respective optical components, receiver
assembly and housing components thereof;
[0026] FIG. 8A provides an exploded perspective view of a first
exemplary receiver assembly embodiment in accordance with aspects
of the present invention; and
[0027] FIG. 8B provides an exploded and partially cutaway
perspective view of a second exemplary receiver assembly embodiment
in accordance with aspects of the present invention.
[0028] Repeat use of reference characters in the present
specification and drawings is intended to represent same or
analogous features or elements of the present subject matter.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0029] Reference will now be made in detail to presently preferred
embodiments of the disclosed technology, one or more examples of
which are illustrated in the accompanying drawings. Each example is
provided by way of explanation of the present technology, not
limitation of the present technology. In fact, it will be apparent
to those skilled in the art that modifications and variations can
be made in the present technology without departing from the spirit
and scope thereof. For instance, features illustrated or described
as part of one embodiment may be used on another embodiment to
yield a still further embodiment. Thus, it is intended that the
present subject matter covers such modifications and variations as
come within the scope of the appended claims and their
equivalents.
[0030] With reference to FIG. 1, a basic unit in accordance with
certain aspects of the presently disclosed technology corresponds
to an array 10 that includes a plurality of solar panels 12
provided in a substantially planar configuration. In the example of
FIG. 1, four solar panels 12 collectively form array 10, but it
should be appreciated that any number of solar panels may be
employed, from a single solar panel to many more than four panels.
Each panel 12 houses a matrix of power units 14 that convert
sunlight, or solar radiation, to electricity. In the exemplary
illustration of FIG. 1, thirty-two power units 14 are shown in each
solar panel 12, although this depiction should not be unnecessarily
limiting to the present subject matter. A fewer or greater number
of power units may be provided in each solar panel, and such power
units may be provided in a variety of particular configurations.
Each power unit has a mechanical arrangement which focuses solar
energy to an optical rod, which conducts it to a single
photovoltaic (PV) cell. These and other particular aspects of the
power units will be described later in more detail.
[0031] In one embodiment, each panel 12 of array 10 measures
approximately one meter by two meters and is provided with a
relatively compact depth of about 10 cm, due in part to the
efficiency of the optical components of each power unit. A
collective assembly of four panels as depicted in FIG. 1 may form a
substantially rectangular shape measuring about 2.25 meters by 4.25
meters and also characterized by a depth of 10 cm. A depth of
between about two and thirty cm is generally provided in some of
the disclosed exemplary embodiments. These dimensions are provided
for example only and should not be limiting to the present subject
matter.
[0032] In one exemplary embodiment, there are two outputs per
panel, each rated at approximately 48V and 5.3 A, resulting in a
peak power output for one panel 12 of approximately 500 W,
representing about 25% panel efficiency under maximum direct sun.
Such exemplary panel outputs can be connected at mounting pole 16
or some other collection point to provide a single output of 384 V,
5.3 A DC, corresponding to about 2 kW for a four-panel array 10. An
electricity generator utilizing the presently disclosed technology
may be used quite effectively when large numbers of arrays are
grouped together on top of large buildings or ground mounted, to
produce medium to large amounts of power. In one embodiment, an
aggregation of arrays into banks of twenty arrays each provides
7.78 kV and 5.3 A per bank to a grid intertie point. For fields of
less than 41 kW, accommodation of a smaller voltage may be
arranged.
[0033] The array 10 of FIG. 1 is positioned atop a mounting pole
16, which in some embodiments may be about 2.5 meters tall. A
structural frame 21 is provided along the array 10 to help maintain
planarity and rigidity of the assembly. Structural frame 21 is
connected to a torque bar 11 that serves to rotate the assembly of
solar panels 12 about its center in two axes: a front-back axis and
a left-right axis. A motorized gear drive assembly 15 provided at
the top of mounting pole 16 is coupled to torque bar 11 via pivot
point connections 17. Gear drive assembly 15 is also coupled to a
controller 19, which may correspond to a microcontroller in some
embodiments. Gear drive assembly 15, controller 19, torque bar 11
and mounting pole 16 all combine to form a tracker for the solar
panel array.
[0034] The tracker components illustrated in FIG. 1 collectively
function to orient the respective power units 14 in optimum
direction for receiving sunlight such that the PV cells therein can
operate most effectively. The motorized gear assembly 15 is
operated by controller 19 based on input received from a narrow
range sun sensor 20 that provides accurate pointing information. In
one embodiment, sun sensor 20 operates over a range of about five
degrees, and is used to zero array 10 to the sun for large pointing
errors. In some embodiments, sun sensor 20 is not required, such as
instances where the array is generally positioned within the
capture angle of certain optical components of the power units.
[0035] An array 10 such as illustrated in FIG. 1 is designed for
relatively easy installation and subsequent operation in a mostly
unattended state, making it especially ideal for operation in
remote areas. Each array 10 can be configured to monitor its own
health and efficiency, local weather conditions, and other
predetermined parameters. In some embodiments, monitoring and
control may be locally implemented, such as via a communication
link to a PDA or other handheld computing device provided with GPS
capabilities. Alternatively, monitoring and control of array 10 may
be effected remotely, such as via a communication link to the
Internet. Further, a camera may be mounted and web cast to allow
remote viewing of the system(s). In some embodiments, local control
will disable remote control, but the telemetry features of the
array can still be viewed remotely even during manual control
operations. The system controls of array 10 can be configured to
post an alarm or take itself offline if a problem occurs. In
addition, automatic calibration features that may be run on a
periodic basis to maximize power output may also be provided.
Telemetry data indicating where the array 10 should be positioned
throughout the day can be downloaded or provided and stored in
memory associated with microcontroller 19. A calibration procedure
may also be utilized to determine the orientation of the array to
the sun that produces maximum power output. When sunlight is not
available to the array 10, such as during night or in inclement
weather conditions, array 10 may be positioned upside down,
generally parallel to the ground. Such a position will offer the
least wind resistance and also reduces exposure of the front
surface of array 10 to dust and secretions, thus minimizing the
need for washing.
[0036] It should be appreciated that many other array and tracker
configurations are applicable for use with the presently disclosed
technology, including but not limited to ganged arrays of panels
for a low profile roof mount application. Such arrays could be
equatorial mounted and polar aligned so as to allow near-single
axis tracking. These too could be configured to park in a downward
facing position each evening or during other predetermined
conditions to minimize environmental particulate accumulation and
to afford further protection to the system.
[0037] Referring now to FIG. 6, select exemplary optical components
of each power unit will now be described. Certain aspects of the
optical components are tailored for maximum efficiency under
imaging optics theory. The main optical elements of each power unit
14 are a primary mirror 22, a secondary mirror 24, a protective
front surface 26, such as a window or cover glazing, and a receiver
assembly defining a nominal focal plane (f). As depicted in the
cross-sectional view of such elements in FIG. 6, the primary and
secondary mirror contours are tailored to eliminate all zeroth and
first-order aberrations (aplanatic), thereby allowing the
attainment of high flux at high collection efficiency. Protective
front surface 26 is a substantially planar surface, such as a
window or other glazed covering, that provides structural integrity
for a power unit and protection for other components thereof.
[0038] FIG. 6 also provides a general exemplary representation of
the size of the main optical components relative to one another. As
can be seen, the diameter of the primary mirror is about five times
that of the secondary mirror, and in some embodiments is greater
than about four times that of the secondary mirror. In another
example, it can be noted that the area of the primary mirror shaded
by the secondary mirror is about 3.2%. A receiver assembly (see
FIG. 7) defining focal plane (f) typically includes a tapered
optical rod (to be discussed later in more detail) to extract and
further concentrate impinging sunlight onto a solar cell that
resides just behind the apex of primary mirror 22. The
configuration of optical components generally described in FIG. 6
yields an axially compact design that can be easily cooled since
the solar cell of the receiver assembly is provided at the rear of
the unit.
[0039] Referring now to FIG. 7, another cross-sectional view is
provided of the optical as well as select mechanical components of
an exemplary power unit in accordance with embodiments of the
present invention. Sunlight, represented by the dashed-line ray
traces 30, enters the power unit 14 through a substantially planar
front window 26. The concave surface of primary mirror 22 then
reflects a majority of the received sunlight to the convex surface
of secondary mirror 24, where it is further reflected to a focal
point (f). Focal point (f) can be generally defined as the central
portion or upper surface of an optical rod 32 or a point at or
beyond the apex of the primary mirror. Optical rod 32 may be
tapered in some embodiments away from the focal point (f) and
employs total internal reflectance to provide optimal transmission
of the solar flux towards a solar cell 34. The configuration of the
optical components in FIG. 7 yields a sufficiently high exit
numerical aperture that can tolerate sufficient mechanical
misalignment. By providing optical rod 32 with a sufficiently wide
entrance diameter, the focal point of concentrated sunlight can
wander around the rod surface with some degree of flexibility and
still be collected at a solar cell 34 provided at the base of
optical rod 32. An upper surface defining the entrance for optical
rod 32 may also be provided with an antireflective coating to
reduce Fresnel reflection losses. The inside and outside surfaces
of the front window, as well as select portions of the optical rod,
may be subjected to any type of anti-reflection treatment, such as
but not limited to a nano-coating material, to increase optical
efficiency over a generally wide solar spectrum.
[0040] Referring still to FIG. 7, the primary mirror 22 and
secondary mirror 24 are both illustrated as curved elements,
although it should be appreciated that a substantially flat
secondary mirror may be utilized in some embodiments. In one
embodiment, primary mirror 22 is a second surface mirror using
silver, and slump-formed from soda-lime glass. The utilization of
silver in primary mirror 22 helps to accommodate a desired spectral
response to the ultraviolet levels of light harvested by the solar
cell 34 in collector assembly 28. Primary mirror 22 may weigh
approximately 500 grams in one exemplary embodiment. Secondary
mirror 24 is a first surface mirror using silver and a passivation
layer, approximately 50 mm in diameter, formed on a substrate of
soda-lime glass. Secondary mirror 24 may weigh approximately 45
grams in one exemplary embodiment. The respective perimeters of the
first and second mirrors 22, 24 may be formed to define a variety
of different shapes, although it should be appreciated that at
least a portion of the perimeter of first mirror 22 and the
perimeter of second mirror 24 is provided in contact with the
inside surface of front window 26. The portions of primary mirror
22 and secondary mirror 24 that are in contact with front window 26
may be physically attached thereto by one of many attachment means,
such as but not limited to compression, welding or an adhesive
bonding. In some embodiments, primary mirror 22 and secondary
mirror 24 may each be radially symmetric about an axis running
through the centers of both mirrors and generally perpendicular to
the front window 26.
[0041] The perimeter of each primary mirror 22 may be formed in a
variety of different fashions, and select exemplary embodiments
depicting several options will now be presented and discussed with
reference to FIGS. 3A-5B, respectively. In a first embodiment, such
as illustrated in the plan view of FIG. 4A and the perspective view
of FIG. 4B, the perimeter of primary mirror 22b is formed in a
generally circular configuration. With a generally circular
configuration, the entire perimeter of the primary mirror 22b may
be substantially coplanar with the perimeter of secondary mirror 24
and both circular perimeters may be in contact with and/or adhered
to the inner surface of front window 26. In one particular
embodiment of the disclosed technology, the perimeter of generally
circular primary mirror 22b is formed with an exemplary diameter 60
of about 280 mm, the perimeter of generally circular secondary
mirror 24 is formed with an exemplary diameter 62 of about 50 mm,
and the depth 64 of primary mirror 22b (see FIG. 4B) is formed to
be about 70 mm.
[0042] A second embodiment depicting an exemplary shape for primary
mirror 22 is provided in the plan view of FIG. 3A and perspective
view of FIG. 3B, in which the perimeter of primary mirror 22a is
formed in a near-hexagonal fashion. The perimeter of primary mirror
22a is defined by six full sections 66 and six truncated sections
68. Full sections 66 are substantially coplanar with one another
such that they may be provided in contact with and/or adhered to
the inner surface of front window 26. The distance 70 measured in a
straight line from the edge of adjacent full sections 66 is about
132 mm in one exemplary embodiment of the present technology. The
distance 72 measured across the diameter of the perimeter of
primary mirror 22a may be about 300 mm in one exemplary embodiment.
Each truncated section 68 of the perimeter of primary mirror 22a is
formed to define a generally arched segment that extends away from
front window 26. Each truncated section 68 exists in a respective
vertical plane that is substantially perpendicular to front window
26. Selected truncated sections 68 of each primary mirror 22a may
be provided in contact with and/or adhered to a matched truncated
section of an adjacent power unit's primary mirror. This matching
of adjacent truncated sections 68 can be visualized in the
illustration of FIG. 2, where the primary mirror of each power unit
14 is provided adjacent to a portion of at least two other primary
mirrors.
[0043] A third embodiment depicting an exemplary shape for primary
mirror 22 is provided in the plan view of FIG. 5A and the
perspective view of FIG. 5B, in which the perimeter of primary
mirror 22c is formed in a near-square configuration. The perimeter
of primary mirror 22c is defined by four full sections 74 and four
truncated sections 76. Full sections 74 are substantially coplanar
with one another such that they may be provided in contact with
and/or adhered to the inner surface of front window 26, while each
truncated section 76 exists in a respective plane that is
substantially perpendicular to front window 26 when the primary
mirror is adjacent thereto. The distance 80 measured across the
perimeter of primary mirror 22c may be about 250 mm in one
exemplary embodiment.
[0044] It should be appreciated in some embodiments of the
disclosed technology that the respective perimeters (or portions
thereof) of the primary and secondary mirrors may not be precisely
arranged in a coplanar fashion. Effective operation of a power unit
may still be achieved with a slightly staggered arrangement along
the coaxial alignment of primary and secondary mirrors within a
predetermined limit.
[0045] Referring to FIG. 5B, substantially flat mounting tabs 78
may be provided for each full section 74 to further facilitate
provision of a sufficient mating area for contact with or adherence
to front window 26. Dimensions for each mounting tab 78 may be
about 1.5 mm by about 5.0 mm in one exemplary embodiment. It should
be further appreciated that mounting tabs (such as tabs 78
illustrated in FIG. 5B) may be utilized with a primary mirror
perimeter of any shape and size when it is desired to increase the
amount of surface area for adhesion to front surface 26. For
example, such tabs may be used at each full section 66 in the
near-hexagonal configuration of FIGS. 3A and 3B even though it is
not illustrated.
[0046] It should be appreciated that although FIGS. 3A-5B,
respectively, depict only three exemplary embodiments for the shape
of primary mirror 22, many other options may be employed in
accordance with the present invention. For example, the perimeter
of primary mirror 22 may be formed as any near-polygonal shape
defined by n full sections and n truncated sections, where n is an
integer number generally within a range of between three and nine.
As with the above examples, each of the full sections in such
embodiments is typically in contact with and/or adhered to the
inner surface of a front window. Each truncated section is formed
as a circular arc that extends away from the front window and that
exists in a respective plane that is substantially perpendicular to
the front window. Each truncated section may be in contact with
and/or adhered to a truncated section of an adjacent power unit's
primary mirror.
[0047] It should be appreciated by one of ordinary skill in the art
that the decision of what shape to use for the perimeter of primary
mirror 22 is often dependent on a tradeoff between panel area
efficiency and mechanical rigidity. A panel having primary mirrors
formed in a near-square configuration (such as represented in FIGS.
5A and 5B) may be a good choice for embodiments in which the panel
area is to be most efficiently utilized. In such configurations and
others, one or more stiffening beams may be provided across the
front window 26 in order to improve device rigidity. It should be
appreciated that the more features added to increase rigidity such
as front support beams could shade some sunlight from entering the
power units. With reference to FIG. 2, a panel configuration of
near-hexagonal power units (such as individually represented in
FIGS. 3A and 3B) are capable of providing a good amount of panel
area efficiency, while also providing a structure that is uniformly
quite rigid in all directions since there are no lines of weakness
running across a given panel surface.
[0048] Referring again to FIG. 7, the receiver assembly 28 of the
exemplary power unit 14 will now be discussed. A photovoltaic (PV)
solar cell 34 is mounted inside a cell module that includes a base
plate 36 and an alignment tube 38. Alignment tube 38 may be formed
of aluminum or copper in some embodiments. Alignment tube 38 is
surrounded by first and second concentrically aligned and generally
circular mounting rings 56 and 58 that are connected to base plate
36 by bolts 60. In some embodiments, mounting ring 58 is
characterized by a slightly larger diameter than that of mounting
ring 56. Mounting rings 56, 58 may correspond to metal washers in
some particular exemplary embodiments. Tapered optical rod 32 is
also located by the alignment tube 38, and is glued or adhered by
other means to the PV cell 34. In one exemplary embodiment, optical
rod 32 is ground and molded from Corning BK7 borosilicate glass. In
other exemplary embodiments, optical rod 32 is molded from acrylic
or polyolephin. An anti-reflection coating accommodating a
relatively wide bandwidth may be provided on the entrance surface
of optical rod 32.
[0049] The removable receiver assembly 28 is installed by orienting
alignment tube 38 in the X-Y plane (as depicted by the directional
legend of FIG. 7, where the Y vector is generally perpendicular to
the X-Z plane) such that fits through a pilot hole formed in
primary mirror 22. A shoulder is formed by mounting rings 56 and 58
to contact the bottom surface of primary mirror 22, thus aligning
itself in a direction defined by the Z axis of FIG. 7. The base
plate 36 of receiver assembly 28 is loaded against front window 26
and primary mirror 22 by coil springs 62. Wing nuts 64 are used to
fasten the coil springs 62 relative to housing 40. Front window 26
is sealed to housing 40 with an extruded rubber gasket 44, in a
fashion similar to the attachment of a car windshield, or by other
suitable connection sealing means. The housing 40 with the mounted
cell modules and front window 26 are held flat and rigid with the
tines of the tracker frame 21 (as shown in FIG. 1).
[0050] Housing 40 may be built from more than one piece of
material, such as but not limited to stamped metal or polyethylene
terepthalate (PET) and is designed to accommodate the total number
of power units provided in a given solar panel. The sides 41 of
housing 40 (only one of four sides being illustrated in FIG. 7) may
all be formed from a single manufacturing stamping process on a
first piece of material and will contain a lip 43 on the top edge
of sides 41 that allows the front surface glass 26 to be mounted.
There may be an overlap between front window 26 and the mounting
lip 43 so that the force from the spring loaded primary mirrors is
transferred evenly to housing 40. Beads may be stamped into each
face of housing 40 to aid in rigidity of the structure. The backing
45 of housing 40 may be separately formed from a second piece of
material that can be bolted, screwed or connected in some other
fashion to the sides 41 of housing 40. Backing 45 may be formed
with enough receiver assembly mount points stamped into it to
accommodate the total number of power units per panel (e.g.,
thirty-two units in the exemplary embodiment of FIGS. 1 and 2). In
some embodiments, backing 45 may be made of a metallic material. In
other embodiments, such as when the respective base plates 36 of
each power unit in a solar panel are utilized as the positive
output for each solar cell, backing 45 may be made of an insulative
material such as fiberglass, plastic, or a polymer coated metal. A
weather-proof junction box (not shown) may be provided at the
exterior of backing 45 to house the power outputs 47 from each
cell, enclose any needed bypass diodes and allow external power
lines to be connected.
[0051] Additional description of the receiver assembly 28 will now
be presented with respect to FIGS. 8A and 8B. A first exemplary
receiver assembly embodiment 28, such as the one illustrated in
FIG. 7, is presented in the exploded view of FIG. 8A. Referring to
FIG. 8A, base plate 36 forms a relatively large square-shaped base
for receiver assembly 28 in order to serve as a heat spreading
element. In some exemplary embodiments, base plate 36 may be formed
of phosphor-bronze or an aluminum alloy. A photovoltaic (PV) solar
cell 34 is provided on an aluminum nitride substrate 48 which
contains the connection points for the power wires. In one
particular exemplary embodiment, PV cell 34 corresponds to a
triple-junction concentrator cell such as manufactured and sold by
Spectrolabs, Inc. PV cell 34 is configured to receive sunlight
directed to the cell via optical rod 32, and produce a resultant
electrical current flow based on an electrical field generated upon
sunlight hitting the different layers in the cell 34. Optical rod
32 may be formed with a generally circular entrance that tapers to
a smaller and generally square-shaped base. In one exemplary
embodiment, the surface area of PV cell 34 measures about 100
mm.sup.2. In one exemplary embodiment optical rod 32 measures about
29 mm in length, has a 19 mm diameter round entrance and a 9 mm by
9 mm square base.
[0052] Referring still to FIG. 8A, the cell 34, substrate 48 and
power wires may be assembled then mounted in alignment tube 38 with
and thermally bonded to a passive copper heat sink (not
illustrated). In some embodiments when base plate 36 serves to
dissipate enough heat or operation of the receiver assembly
otherwise remains within predetermined thermal limits, an
additional cooling element such as a heat sink may not be
necessary. Passive cooling that keeps the cell temperature within
or below a maximum range of 75-100 degrees Celsius has been deemed
appropriate for certain applications. Once the cell 34, substrate
48 and optical rod 32 are secured within alignment tube 38, a
spring clip 55 is attached to the top of the assembly. Spring clip
55 is fitted into a circular groove 57 that is formed near an upper
end of alignment tube 38 such that fingers 59 on the spring clip
grab the edges of optical rod 32 and compress it onto the PV cell
34. Fingers 59 also provide a centering force because spring clip
55 is set just below the entrance face of optical rod 32.
[0053] An alternative embodiment 28' of a receiver assembly in
accordance with the present invention is illustrated in FIG. 8B.
Receiver assembly 28' of FIG. 8B includes several elements that are
substantially the same as those described with respect to the
receiver assembly 28 of FIG. 8A. In such instances, like reference
numerals are used; prime designations are used to reference
elements having at least some variation thereto. Receiver assembly
28' includes a base plate 36' that is formed as a spring plate
having a concentric concertina spring stamped therein to provide a
certain level of mechanical flexibility for reducing component
stress. Such a spring design is seen in the partially cutaway view
of FIG. 8B. Alignment tube 38' is formed with a stepped smaller
diameter to form a shoulder 42 that contacts the bottom surface of
primary mirror 22 when receiver assembly 28' is oriented through
the pilot hole of the primary mirror. Alignment tube 38' is mounted
to the raised center ridge 46 of spring plate 36' and may be
physically mated thereto by an adhesive glue, bolting, friction
fit, or other suitable connection means. A bayonet mount
represented by tab elements 52 may be stamped into the spring plate
36'. Two or more of such tabs 52 can be provided to mate with slots
in the back of the power unit housing. The spring loading will help
ensure that mating between the tabs 52 and slots of the housing
will not loosen. A specialized mounting tool may be employed to
install or remove the receiver assembly by locking into slots 54
provided at one or more select locations around the periphery of
spring plate 36'.
[0054] While the specification has been described in detail with
respect to specific embodiments of the invention, it will be
appreciated that those skilled in the art, upon attaining an
understanding of the foregoing, may readily conceive of alterations
to, variations of, and equivalents to these embodiments. These and
other modifications and variations to the present invention may be
practiced by those of ordinary skill in the art, without departing
from the spirit and scope of the present invention, which is more
particularly set forth in the appended claims. Furthermore, those
of ordinary skill in the art will appreciate that the foregoing
description is by way of example only, and is not intended to limit
the invention.
* * * * *