U.S. patent application number 13/286047 was filed with the patent office on 2012-02-23 for solar collector.
This patent application is currently assigned to SKYLINE SOLAR, INC.. Invention is credited to Mang V. Chau, Marc A. Finot, Brian J. Ignaut, Tamir Lance, Cameron G. Wylie.
Application Number | 20120042932 13/286047 |
Document ID | / |
Family ID | 43973229 |
Filed Date | 2012-02-23 |
United States Patent
Application |
20120042932 |
Kind Code |
A1 |
Wylie; Cameron G. ; et
al. |
February 23, 2012 |
SOLAR COLLECTOR
Abstract
The present invention relates to a solar energy collector
suitable for use in a solar energy collection system. The solar
energy collection system includes the collector, a stand that
supports the collector and a tracking system that causes the
collector to track movements of the sun along at least one axis.
The collector includes one or more reflector panels, one or more
solar receivers, and a space frame support structure that
physically supports the reflector panels and solar receivers. In a
particular embodiment, the space frame support structure includes
struts that extend through a gap between the reflector panels to
support the one or more receivers.
Inventors: |
Wylie; Cameron G.; (San
Mateo, CA) ; Lance; Tamir; (Los Gatos, CA) ;
Ignaut; Brian J.; (San Mateo, CA) ; Finot; Marc
A.; (Palo Alto, CA) ; Chau; Mang V.; (San
Jose, CA) |
Assignee: |
SKYLINE SOLAR, INC.
Mountain View
CA
|
Family ID: |
43973229 |
Appl. No.: |
13/286047 |
Filed: |
October 31, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12982703 |
Dec 30, 2010 |
8071930 |
|
|
13286047 |
|
|
|
|
61362591 |
Jul 8, 2010 |
|
|
|
Current U.S.
Class: |
136/246 |
Current CPC
Class: |
Y02E 10/47 20130101;
Y02E 10/52 20130101; F24S 23/74 20180501; F24S 23/80 20180501; H01L
31/0547 20141201; Y02E 10/40 20130101; F24S 30/425 20180501; F24S
25/13 20180501 |
Class at
Publication: |
136/246 |
International
Class: |
H01L 31/052 20060101
H01L031/052 |
Claims
1. A photovoltaic solar energy collector suitable for use in a
solar energy collection system that includes the collector, a stand
that supports the collector and a tracking system that causes the
collector to track movements of the sun along at least one axis,
the collector comprising: a plurality of reflector panels including
first and second reflector panels that are separated by a gap and
that extend in a longitudinal direction; at least one solar
receiver that is positioned above the gap between the first and
second reflector panels, each solar receiver including at least one
photovoltaic cell, the plurality of reflector panels being arranged
to direct incident sunlight to the at least one solar receiver; and
a space frame support structure that physically supports the
plurality of reflector panels and the at least one solar receiver,
the space frame support structure including a multiplicity of
linear struts that are connected at nodes to form a repeating
geometric pattern wherein the multiplicity of linear struts include
a first strut and a second strut that physically support the at
least one solar receiver, the first and second struts slanting
downward and outward from the at least one solar receiver and
extending through the gap between the first and second reflector
panels.
2. A photovoltaic solar energy collector as recited in claim 1
wherein: the reflector panels have concave reflective surfaces that
face inward towards a central region of the collector; and there is
an aperture between the first and second support struts that allows
air to flow therethrough.
3. A photovoltaic solar energy collector as recited in claim 1
wherein the first and second reflector panels are arranged
symmetrically about a reference plane that extends in said
longitudinal direction and wherein the first and second struts are
also arranged symmetrically about the reference plane.
4. A solar collector as recited in claim 1, further comprising: a
longeron that extends in said longitudinal direction, the at least
one solar receiver being attached with the longeron; the nodes of
the space frame support structure include a plurality of nodes that
are separated by gaps and that are arranged along the length of the
longeron; and a plurality of the struts are coupled to each of the
nodes on the longeron and extend diagonally downward from the node
to help support the at least one solar receiver.
5. A solar collector as recited in claim 1, wherein: the first and
second reflector panels each include an inner edge and an outer
edge that extend in a longitudinal direction, the inner edges of
the first and second reflector panels being positioned closer to
one another than the outer edges of the first and second reflector
panels, the first and second reflector panels being arranged such
that the outer edges of the first and second reflector panels are
positioned higher than the inner edges of the first and second
reflector panels; and the at least one solar receiver includes
first and second solar receivers that are positioned adjacent to
one another over a region that is between the inner edges of the
first and second reflector panels, respectively.
6. A solar collector as recited in claim 5, wherein: the collector
further comprises a upper longeron, the first and second struts
being connected with and helping to support the upper longeron, the
upper longeron being positioned higher than the first and second
reflector panels and extending in said longitudinal direction, the
first and second solar receivers being mounted on the upper
longeron; the nodes of the space frame support structure includes a
plurality of top nodes that are separated by gaps and that are
arranged along the length of the upper longeron, the top nodes
being positioned higher than the first and second reflector panels;
and the first and second struts are attached to the top node on the
upper longeron and extend diagonally downward therefrom to pass
between the first and second reflector panels to help support the
first and second solar receivers.
7. A solar collector as recited in claim 5, wherein: the second
solar receiver is positioned over and shades the first solar
receiver; and the second reflector panel is positioned higher than
the first reflector panel.
8. A solar collector as recited in claim 5, wherein: the plurality
of reflector panels further includes a third reflector panel and a
fourth reflector panel, each reflector panel having a backside and
a reflective frontside, the third reflector panel being positioned
outside the outer edge of the first reflector panel, the fourth
reflector panel being positioned outside the outer edge of the
second reflector panel, each reflector panel having a concave shape
that curves outward from a central region between the first and
second reflector panels; and the at least one solar receiver
further includes a third solar receiver and a fourth solar
receiver, the third and fourth solar receivers being positioned on
the backsides of and at the outer edges of the first and second
reflector panels, respectively, wherein the reflective frontsides
of the third and fourth reflector panels are arranged to direct
incident light to the third and fourth solar receivers,
respectively.
9. A solar energy collection system as recited in claim 1, wherein
each strut is formed from one selected from a group consisting of
roll formed steel sections, hot rolled steel sections and tubular
aluminum extruded members.
10. A solar energy collection system as recited in claim 1,
wherein: the collector further comprises an upper longeron that
extends in the longitudinal direction and a connector, the
connector being an integrally formed metal piece that at least
partially encircles and is secured to the upper longeron, the
connector having engagement features for receiving the first and
second struts; the solar collector is substantially symmetrical
along a bisecting plane; and the upper longeron and the attached
connector are positioned on the bisecting plane.
11. A photovoltaic solar energy collector as recited in claim 1
wherein: each of the plurality of reflector panels has a concave
shape; and the multiplicity of linear struts includes a plurality
of reflector support struts that underlie, are adjacent to and
physically support the plurality of reflector panels wherein the
plurality of reflector support struts are straight and do not match
the concave shape of the reflector panel.
12. A photovoltaic solar energy collection system comprising: a
solar energy collector including, at least one reflector panel that
extends in a longitudinal direction, at least one solar receiver,
each solar receiver including at least one photovoltaic cell, the
plurality of reflector panels being arranged to direct incident
sunlight to the at least one solar receiver, and a space frame
support structure that physically supports the at least one
reflector panel and the at least one solar receiver, the space
frame support structure including a multiplicity of linear struts
that are connected at nodes to form a repeating geometric pattern;
and a stand that pivotally supports the collector for pivotal
movement around a pivot axis; and a tracking system that causes the
collector to pivot around the pivot axis to track movements of the
sun along at least one axis wherein the range of motion around the
pivot axis is one selected from a group consisting of: 1) at least
150 degrees; 2) at least 160 degrees; and 3) at least 170
degrees.
13. A solar energy collection system as recited in claim 12 wherein
the pivot axis is positioned away from the center of gravity of the
collector to facilitate said range of motion.
14. A solar energy collection system as recited in claim 12 wherein
neither the solar receiver nor any support structure in the
collector shades the at least one reflector panel.
15. A photovoltaic solar energy collector suitable for use in a
solar energy collection system that includes the collector, a stand
that supports the collector and a tracking system that causes the
collector to track movements of the sun along at least one axis,
the collector comprising: at least one reflector panel that extends
in a longitudinal direction; at least one solar receiver, each
solar receiver including at least one photovoltaic cell, the
plurality of reflector panels being arranged to direct incident
sunlight to the at least one solar receiver; and a space frame
support structure that physically supports the at least one
reflector panel and the at least one solar receiver, the space
frame support structure including a multiplicity of linear struts
that are connected at nodes to form a repeating geometric pattern
wherein the repeating geometric pattern repeats along the
longitudinal axis and wherein the longitudinal period of the
repeating geometric pattern does not equal the length of any
reflector panel or solar receiver in the collector.
16. A solar energy collector as recited in claim 15 further
comprising at least one stringer that extends in a longitudinal
direction and underlies a reflector panel of the at least one
reflector panel, each stringer including a plurality of attachment
points for attaching to the overlying reflector panel.
17. A solar energy collector as recited in claim 15 wherein: the
multiplicity of struts further includes a plurality of reflector
support struts that extend out from a central region of the
collector towards the periphery of the collector; the reflector
support struts underlie the reflector panels and the stringers,
each stringer being attached with at least two of the reflector
support struts.
18. A solar energy collector as recited in claim 17, wherein: the
collector further comprises a central node, an upper longeron, a
lower longeron and a side longeron that all extend substantially
parallel to one another in a longitudinal direction and that are
all connected with one another using at least some of the struts;
and the at least one reflector support strut includes a first
reflector support strut and a second reflector support strut, the
first reflector support strut extending from the central node in
the space frame support structure to the side longeron, the second
reflector support strut extending from the lower longeron to the
side longeron, wherein the first and second reflector support
struts are arranged to help physically support the at least one
reflector.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] The present invention claims priority U.S. patent
application Ser. No. 12/982,703, entitled "Solar Collector Having A
Spaced Frame Support Structure With A Multiplicity Of Linear
Struts," filed Dec. 30, 2010, which is incorporated herein by
reference in its entirety for all purposes and claims priority to
U.S. Provisional Application No. 61/362,591, entitled "Optimized
Solar Collector," filed Jul. 8, 2010, which is incorporated herein
in its entirety for all purposes.
FIELD OF THE INVENTION
[0002] The present invention relates to solar technologies. More
specifically, the present invention relates to various collector,
reflector and support structure designs for use in concentrating
photovoltaic systems.
BACKGROUND OF THE INVENTION
[0003] Typically, the most expensive component of a photovoltaic
(PV) solar collection system is the photovoltaic cell. To help
conserve photovoltaic material, concentrating photovoltaic (CPV)
systems use minors or lenses to concentrate solar radiation on a
smaller cell area. Since the material used to make the optical
concentrator is less expensive than the material used to make the
cells, CPV systems are thought to be more cost-effective than
conventional PV systems.
[0004] One of the design challenges for any CPV system is the need
to balance multiple priorities. For one, a CPV system requires a
support structure that arranges the optical concentrators and the
photovoltaic cells such that incoming sunlight is efficiently
converted into electricity. This support structure should also
accommodate a tracking system and provide for the adequate
dissipation of heat. Another consideration is the cost of
manufacturing, installing and repairing the CPV system. Existing
CPV designs address these issues in a wide variety of ways.
Although existing CPV systems work well, there are continuing
efforts to improve the performance, efficiency and reliability of
CPV systems.
SUMMARY OF THE INVENTION
[0005] One aspect of the present invention relates to a
photovoltaic solar energy collector suitable for use in a solar
energy collection system that includes a stand and a tracking
system. The solar collector includes multiple reflector panels that
each extend in a longitudinal direction, one or more solar
receivers, and a space frame support structure. In this aspect of
the present invention, there is a gap between two of the reflector
panels. At least one solar receiver is positioned above the gap
between the reflector panels. The reflector panels are arranged to
direct incident sunlight to the solar receiver(s). The space frame
support structure physically supports the reflector panels and the
solar receiver(s). The space frame support structure also includes
multiple linear struts that are connected at nodes to form a
repeating geometric pattern. At least two of these struts slant
downward and outward from the solar receiver(s) and extend through
the gap between the reflector panels to help support the solar
receiver(s).
[0006] In another aspect of the present invention, a photovoltaic
solar energy collector will be described. The solar collector
includes at least one reflector panel that extends in a
longitudinal direction, one or more solar receivers and a space
frame support structure. The space frame support structure
physically supports the reflector panel(s) and the receiver(s). The
space frame support structure includes multiple linear struts that
are connected at nodes to form a repeating geometric pattern. The
repeating geometric pattern repeats along the longitudinal axis.
The longitudinal period of the repeating geometric pattern does not
equal the length of any reflector panel or solar receiver in the
collector.
[0007] In another aspect of the present invention, a photovoltaic
solar energy collection system will be described. The solar energy
collection system includes a solar energy collector, a stand and a
tracking system. The solar collector includes one or more reflector
panels, one or more solar receivers and a space frame support
structure. The space frame support structure includes multiple
linear struts that are connected at nodes to form a repeating
geometric pattern. The stand pivotally supports the collector for
pivotal movement around a pivot axis. The tracking system causes
the collector to pivot around the pivot axis to track movements of
the sun along at least one axis. In various embodiments, the range
of motion around the pivot axis is at least 150 degrees, 160
degrees and/or 170 degrees.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The invention and the advantages thereof, may best be
understood by reference to the following description taken in
conjunction with the accompanying drawings in which:
[0009] FIGS. 1A and 1B are diagrammatic perspective and
cross-sectional views of a solar collector according to a
particular embodiment of the present invention.
[0010] FIG. 2A is a diagrammatic side view of a reflector panel
with a convex shape according to a particular embodiment of the
present invention.
[0011] FIG. 2B is a diagrammatic side view of a reflector made of
multiple reflector panels according to a particular embodiment of
the present invention.
[0012] FIG. 2C is a diagrammatic side view of the reflector panel
illustrated in FIG. 2A.
[0013] FIGS. 3A-3D are diagrammatic cross-sectional views of solar
receivers and reflector panels according to various embodiments of
the present invention.
[0014] FIGS. 4A and 4B are diagrammatic perspective and
cross-sectional views of a collector unit according to a particular
embodiment of the present invention.
[0015] FIGS. 5A-5C and 6A-6C are diagrammatic cross-sectional views
of various collectors that are formed from different arrangements
of the collector units illustrated in FIGS. 4A and 4B.
[0016] FIGS. 7A-7D are diagrammatic cross-sectional and perspective
views of a solar collector with a space frame support structure in
accordance with various embodiments of the present invention.
[0017] FIGS. 8A and 8B are diagrammatic perspective views of a
connector suitable for use in a space frame support structure
according to a particular embodiment of the present invention.
[0018] FIGS. 9A and 9B are diagrammatic cross-sectional and
perspective views of a solar collector with a space frame support
structure in accordance with another embodiment of the present
invention.
[0019] FIGS. 10A and 10B are diagrammatic cross-sectional and
perspective views of a reflector panel according to a particular
embodiment of the present invention.
[0020] FIG. 11 is a diagrammatic perspective view of multiple solar
collectors that are arranged to form a solar collector row in
accordance with a particular embodiment of the present
invention.
[0021] FIG. 12 is a diagrammatic cross-sectional view of a solar
collector that is suitable for pivoting around an axis in
accordance with a particular embodiment of the present
invention.
[0022] FIGS. 13A and 13B are diagrammatic cross-sectional and
perspective views of a solar collector with a support cable in
accordance with a particular embodiment of the present
invention.
[0023] In the drawings, like reference numerals are sometimes used
to designate like structural elements. It should also be
appreciated that the depictions in the figures are diagrammatic and
not to scale.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] The present invention relates generally to concentrating
photovoltaic systems. The assignee for the present application,
Skyline Solar, Inc., has received multiple patents related to such
technologies, such as U.S. Pat. No. 7,709,730, entitled "Dual
Trough Concentrating Solar Photovoltaic Module," filed Apr. 10,
2008, which is hereby incorporated by reference in its entirety for
all purposes and is hereinafter referred to as the '730 patent.
[0025] The '730 patent describes various solar collector designs
that involve a trough-shaped reflector that directs incident
sunlight to a string of photovoltaic cells. The described designs
work well for many applications. During the course of installing,
manufacturing and operating solar energy collection systems,
however, the assignee has identified various areas in which the
designs could be further improved. For example, ordinary wear and
tear can form gaps in the reflector. This can skew the reflection
of light by the reflector and may reduce the collection of solar
energy. It would also be desirable to develop an improved support
structure for the collector that is resilient, lightweight and
cost-effective. The present application contemplates a wide variety
of design concepts relating to collectors, support structures,
reflector panels, power plants and tracking systems that address
these and other concerns.
[0026] Initially, with reference to FIGS. 1A and 1B, a
concentrating photovoltaic solar collector 100 according to a
particular embodiment of the present invention will be described.
The solar collector includes multiple solar receivers 102 and
reflector panels 104 that each have a compound curvature. The
reflector panels 104 are arranged in one or more rows that extend
along the longitudinal axis 106. Each row includes multiple,
adjacent reflector panels that cooperate to form a reflector 108
with a substantially continuous reflective surface. The solar
receivers 102 each have at least one photovoltaic cell 118 and are
arranged to form a string of photovoltaic cells 118. A space frame
support structure 110 physically supports the reflector panels 104
and the solar receivers 102. A tracking system causes the collector
to pivot to track the movements of the sun. FIG. 1B is a
diagrammatic cross-sectional view of the solar collector 100
illustrated in FIG. 1A.
[0027] Foundation settling, differential thermal expansion, and
mechanical tolerances in the manufacturing and installation of a
reflector can cause undesirable gaps to open up between the
reflector panels 104 in the reflector. If the reflective surface
becomes non-continuous, then the flux line that forms on the string
of photovoltaic cells 118 may include gaps and become
non-continuous as well. As a result, the exposure of the
photovoltaic cells to concentrated sunlight will be less uniform,
which can substantially reduce the cell strings' efficiency.
[0028] Various embodiments of the present invention relate to
reflector panels 104 that are designed to address this problem.
More specifically, each reflector panel 104 incorporates two
different curvatures along two different axes. Along a plane
defined by an x axis 114 and a y axis 112, the reflector panel 104
has a concave shape. Along another axis (e.g., the longitudinal
axis 106, which goes into the page in FIG. 1B and is perpendicular
to the x-y plane), the reflector panel has a convex shape. The
concave shape is arranged to direct incident light 116 to the solar
receivers 102, as shown by the arrows in FIG. 1B. The convex shape
causes the light that is reflected by the panel 104 to be reflected
in a wider arc along the longitudinal axis 106. That is, the convex
shape of each panel 104 forms a wider flux line (as measured along
the longitudinal axis 106) than would be the case if the panel were
flat along the longitudinal axis. As a result, gaps in the flux
line that are formed by gaps in the reflective surface are covered
up or washed away. This can produce a more continuous, uniform flux
line, which contributes to greater cell string efficiency.
[0029] Another notable feature of the collector 100 illustrated in
FIGS. 1A and 1B is the space frame support structure 110 that
supports the solar receivers and reflector panels. The space frame
support structure includes multiple linear struts 120 that are
connected with nodes 122 to form repeating geometric shapes (e.g.,
triangles, pyramids, tetrahedrons, etc.) This arrangement offers
various advantages. For one, the large apertures in between the
struts 120 allow the free flow of air and reduce wind load on the
collector. The use of repeating components, such as the nodes 122
and the struts 120, can streamline the manufacturing, installation
and repair of the space frame. The longitudinal period of the
repeating geometric pattern does not have to correspond to the
longitudinal length of either a receiver or reflector panel,
allowing flexibility in receiver and reflector panel design.
[0030] Additionally, the space frame support structure 110 in FIGS.
1A and 1B is designed to operate as a unitary structure. That is,
struts that support different components of the collector are
interlocked with the rest of the space frame and are therefore more
stable and resistant to stress and bending. In the illustrated
embodiment, for example, the support for the solar receivers is not
a single, isolated column or pedestal. Instead, it is arranged in
the form of multiple receiver support struts 124 that are connected
to nodes 122 that in turn connect with and help support other
struts and components, such as the reflector panels 104. The struts
are arranged to firmly anchor important components of the collector
within the support structure, reduce or eliminate bending, and form
multiple paths through which mechanical loads may be dispersed.
[0031] The struts 120/124 and nodes 122 of the space frame
structure may take a variety of forms. By way of example, the
struts 120/124 may be cylinders, tubes, pipes, roll formed steel
sections, hot rolled steel sections, etc. Many of the struts may
have similar circumferences and may be formed using the same or
similar manufacturing processes. The struts 120/124 may be
connected with one another at the nodes 122 in any suitable manner,
including the use of welding, metal clinching, adhesive, rivets,
bolts and nuts, fasteners, etc. In some embodiments, the nodes 122
include connectors that are formed from extruded aluminum, sheet
metal, forged steel spheres or other materials.
[0032] Preferably, the space frame support structure is designed to
be compatible with many different types of reflector panels and
solar receivers. In the illustrated embodiment, for example, the
struts 120 underneath the reflector panels 104 form a stable base
platform for physically supporting the reflector panels. This base
platform is not arranged to be compatible only with a reflector
panel of a highly specific length and curvature. That is, the base
platform is not necessarily form fitted to the dimensions of a
particular reflector panel. Instead, with minimal modifications
(e.g., the drilling of holes, the securing of fasteners, etc.), the
base platform can be configured to accommodate reflector panels of
varying lengths, shapes and/or curvatures as long as the reflector
panels, when lined up along the length of the collector, generally
fit the dimensions of the space frame support structure.
[0033] The reflector panels 104 and solar receivers 102 may be
arranged in a wide variety of ways, depending on the needs of a
particular application. In the illustrated embodiment, for example,
the reflector panels 104 form a U-like shape. The solar receivers
102 are arranged in two adjacent rows that are positioned higher
and over a region that is between the reflectors. The two rows of
solar receivers 102 support strings of photovoltaic cells 118 that
face away from one another and towards the reflectors 104. When
sunlight is incident on one of the longitudinally extended
reflectors 104, a longitudinally extended flux line is formed on
the corresponding string of photovoltaic cells 118. In another
embodiment, the solar receivers 102 are positioned at the periphery
of the collector 100, and the reflector panels 104, rather than
directing incident light inward towards the center of the collector
100, instead direct light outward towards the periphery of the
collector 100.
[0034] The reflector panels 104 may be made from any suitable
reflective material. For example, metalized glass and aluminum work
well as materials for the reflector panels 104. Each solar receiver
102 may include or be attached with a wide variety of components,
such as a heat sink, fins, base plates, etc. In some embodiments,
the heat sink and/or the solar receiver include a fluid conduit.
The sunlight that is reflected onto the solar receivers 102 may be
used to heat a liquid that is flowing through the fluid conduit. A
wide variety of possible solar receiver, heat sink and fin designs
are described in U.S. Pat. No. 7,820,906, entitled "Photovoltaic
Receiver", filed May 20, 2008, and U.S. patent application Ser. No.
12/340,379, entitled "Solar Receiver," filed Dec. 19, 2008, which
are hereby incorporated in their entirety for all purposes.
[0035] Referring next to FIG. 2A and 2C, a reflector panel 200 with
a compound curvature according to a particular embodiment of the
present invention will be described. The reflector panel has a
convex shape in one direction and a concave shape in another. FIGS.
2A and 2C are diagrammatic side views of the reflector panel 200
that show its convex shape. The convex shape is defined in part by
a distance d, which measures the amount of maximum displacement of
the convex shape relative to a flat reference surface, and a
longitudinal length l. While the reflector panel in FIGS. 2A and 2C
is shown as having a single convex bow, the reflector panel may
also include multiple convex regions. In some embodiments, these
convex regions may be interspersed with concave and/or flat
regions. When properly utilized in a suitable collector, the convex
shape of the reflector panel 200 may substantially improve the
efficiency and performance of the collector.
[0036] As discussed earlier in connection with FIG. 1A, the present
invention contemplates collector designs where multiple reflector
panels 200 are arranged together along a longitudinal axis 106 to
form a reflector 202 with a curved reflective surface. The
reflective surface receives incident sunlight and directs it to a
string of one or more photovoltaic cells. As a result, a flux line
(e.g., a strip or band of concentrated illumination formed by the
reflected light) is formed on the string of cells. The shape and
dimensions of the flux line are defined in large measure by the
shape of the reflector panel 200.
[0037] When the reflector panels are flat along the longitudinal
axis, the flux line will tend to mirror the continuity of the
reflective surface. That is, if the reflective surface is
continuous, then the flux line tends to be continuous. However, if
the reflective surface has gaps, then the flux line will also tend
to have gaps (e.g., portions of the cell face within the periphery
of the flux line that do not receive light from the reflective
surface.)
[0038] Since the movement of the sun throughout the day causes
light to be reflected by the reflector panels at a variety of
angles, the effect of any gap between the reflector panels may
appear almost anywhere along the length of the cell string. That
is, a gap between two reflector panels could prevent a central
portion of one of the photovoltaic cells from being illuminated by
reflected light. This can substantially reduce cell efficiency,
particularly when the cells are electrically connected in series.
Unfortunately, it is not uncommon for gaps to develop between the
reflective panels that make up the reflective surface. The gaps may
arise due to errors in manufacturing, installation, operation or
constant thermal expansion and contraction.
[0039] The convex shape of the reflector panels 200 helps to
eliminate gaps in the flux line. FIGS. 2A and 2C illustrate how
incoming sunlight 204 is reflected when it strikes the convex
curvature of the reflector panel 200. The reflected light tends to
spread or fan out from the reflector panel 200. Depending on the
direction of the incoming sunlight, the reflected light may spread
out on both sides of the reflector panel (e.g., as in FIG. 2A,
where the incoming light is perpendicular to the longitudinal axis
106) or more to one side (e.g., as in FIG. 2C, where the incoming
light is coming in at an angle.) Generally, the reflected light
forms a wider flux line (along the longitudinal axis) then would be
the case if the reflector panel 200 were flat.
[0040] Referring next to FIG. 2B, a reflector 202 made of the
reflective panels 200 illustrated in FIGS. 2A and 2C will be
described. The reflective panels 200 are arranged adjacent to one
another along a longitudinal axis 106. Collectively, the reflective
panels 200, each with length 1, form a reflector 202 with a length
L. The reflector includes multiple convex shapes, where each
reflective panel 200 forms one of the concave shapes. When multiple
reflector panels are arranged together in this manner, the
aforementioned spreading out of the reflected light washes out or
eliminates gaps in the flux line that would be normally be caused
by gaps between the reflector panels. As a result of the washing
out effect, the flux line on the photovoltaic cells is more
continuous and uniform.
[0041] Various designs involve a reflector 202 where at least two
or more adjacent reflector panels 200 of the reflector 202 have the
same concave shape (e.g., as seen in FIG. 2B.) In some embodiments,
the convex shape of each reflector panel 200 is also substantially
symmetrical and the axes of symmetry 206 of the convex shapes of
the reflector panels 200 run substantially parallel to one another.
This arrangement promotes the spreading of light on both sides of
each reflector panel 200, which can be particularly effective in
washing out the effects of gaps between the reflector panels
200.
[0042] It should also be appreciated that the amount of convex
curvature in each reflector panel 200 of a reflector 202 need not
be the same. By way of example, the end reflector panels 200 shown
in FIG. 2B may have a greater amount of convex curvature than the
other reflector panels, since there may be a larger gap between
these reflector panels and reflector panels on a longitudinally
adjacent solar collector than the gap between adjacent reflector
panels on the same solar collector.
[0043] The convex curvature of the reflector panel 200 may be
different near the lower edge of a reflector panel 200 (e.g., the
displacement d may be greater or lower) than it is near the upper
edge of the reflector panel 200. The variation in convex curvature
may be inversely related to the distance variation between the
reflector panel and receiver. In particular the lower edge of the
reflector panel may be closer to the receiver than the upper edge
of the reflector panel. The convex curvature may thus be larger
near the lower edge of the reflector panel and smaller near the
upper edge of the reflector panel. This variation in convex
curvature across the reflector panel may result in a longitudinally
more uniform flux line.
[0044] It should be noted that in the figures, the degree of convex
curvature is exaggerated for the purpose of clarity. Generally, the
concavity of the reflector panel 200 is significantly greater than
the convexity of the reflector panel (e.g., the concave radius of
curvature may be 20 or more times less than the convex radius of
curvature.) Note that a smaller radius of curvature corresponds to
more curvature or a higher degree of concavity or convexity.
Various embodiments involve a reflector panel with a convex radius
of curvature for the reflector panel 200 that is approximately
between 50 and 70 m, although the degree of curvature may be lower
or higher for other implementations. In particular reflector panels
200 having a longer length in the longitudinal direction may
generally have a larger convex radius of curvature.
[0045] Referring next to FIGS. 3A-3D, solar receiver and reflector
arrangements according to various embodiments of the present
invention will be described. FIG. 3A is a diagrammatic
cross-sectional view of an arrangement 300 including a reflector
panel 302 and a solar receiver 304. From this vantage point, the
reflector panel 302 has a concave shape. The solar receiver
includes one or more photovoltaic cells 306. The reflector panel
302, whose optical aperture has a width w, is arranged to direct
incident sunlight to the solar receiver.
[0046] This arrangement 300 offers various advantages. For one, the
solar receiver is positioned outside of the optical aperture 308 of
the reflector panel 302. In the illustrated embodiment, for
example, the solar receiver 304 (and any associated support
structure) does not directly overlie the reflector panel 302 and
does not shade the reflector panel 302 during the normal operation
of the solar collector. This lack of shadowing helps maximize the
energy output of the photovoltaic cells 306 by increasing the
amount of light that is reflected to the cells.
[0047] Also, the arrangement 300 allows the reflector panel 302 to
be positioned relatively close to the solar receiver 304. If the
reflected light has to traverse a shorter distance between the
reflector and the solar receiver, less precision is required from
the collector and the tracking system. By way of example, assume
that f.sub.avg is the average distance between all the points on
the surface of the reflector panel 302 and the photovoltaic cell
306. Various collector designs arrange the solar receiver 304 and
the reflector panel 302 such that f.sub.avg is approximately
between 0.5 m and 1.5 m, although larger or smaller values of
f.sub.avg may be used.
[0048] The size and shape of the reflector panel 302 may be
adjusted so that light is concentrated on the photovoltaic cell 306
to the desired degree. The optical concentration factor, which may
be defined as the ratio of the width Iv, of the reflector panel 302
to the height of the photovoltaic cell h, relates to the average
increase in the sunlight intensity as compared to the intensity of
the incoming sunlight 315. Since the photovoltaic cell 306 is
typically the most expensive component of a collector, if a larger
reflective surface can be used to focus light on a smaller
photovoltaic area, there may be substantial cost savings. In
various embodiments of the present invention, the reflector panels
and solar receivers of the collector are arranged to have an
optical concentration factor of approximately between 5 and 50.
[0049] The efficiency of the solar collector may also be improved
by controlling the width w.sub.s of the solar receiver. If the
receiver width w.sub.s along the x axis is reduced relative to the
width w of the optical aperture, a greater proportion of the total
collector area can be taken up by the reflectors, which in turn
results in the direction of more light to the photovoltaic cells of
the collector. Some implementations of the present invention
contemplate a receiver width that is less than approximately 10%,
15% or 20% of the optical aperture width w.
[0050] Referring next to FIG. 3B, a variation on the solar receiver
and reflector arrangement of FIG. 3A according to another
embodiment of the present invention will be described. The concave
reflective surface of FIG. 3A, instead of being formed by a single
reflector panel, is instead formed by multiple reflector panels
310a/310b/310c that are arranged side by side. That is, the
reflector panels 310a/310b/310c form strips that extend
substantially parallel to one another down the longitudinal length
of the collector. For some applications, it is more cost-effective
to manufacture a larger amount of smaller reflector panels as
opposed to a smaller amount of larger ones.
[0051] Although three separate reflector panels are shown, it
should be appreciated that the concave reflective surface may be
formed from almost any number of reflector panels. The reflector
panels may be attached in any suitable manner. In the illustrated
embodiment, for example, the edges of the reflector panels
310a/310b/310c overlap one another and can be secured together
using any suitable means, such as a fastener, a bolt, an adhesive,
a latch, welding, etc. Various implementations involve multiple
reflective panels that are each curved such that they cooperate to
form a single reflective surface with a concave and/or parabolic
shape. In other embodiments, each reflective panel 310a/310b/310c
is substantially flat in the x-y plane, but are angled such that
they collectively approximate a single concave or parabolic curve.
They may have a slight convex curvature along the longitudinal
axis.
[0052] Referring next to FIGS. 3C and 3D, a solar receiver and
reflector arrangement 320 according to another embodiment of the
present invention will be described. In FIGS. 3A-3B, the solar
receivers 304 were generally positioned higher than the highest
edge of the associated reflector panel 302. By contrast, FIG. 3C
illustrates a solar receiver 304 that is positioned at a height
than is in between the heights of the lower and upper edges 312 and
314 of the reflector panel. Since the solar receiver 304 is more
centrally located relative to the reflector panel 302, the angles
of incidence (in a plane defined by the x axis 114 and the y axis
112) of reflected light on the cell face may be smaller than in
other designs where the solar receiver 304 is positioned
particularly low or high relative to the reflector panel 302. A
reduced angle of incidence may cause less of the light to be
reflected off the face of the cell, which helps increase the
collection of solar energy. In the illustrated embodiment, the face
of the photovoltaic cell 306 on the solar receiver 304 is
substantially perpendicular to the optical aperture 308 of the
reflector panel 302, although in other embodiments it may be
tilted.
[0053] Referring now to FIG. 3D, possible arrangements of a
reflector panel and a solar receiver according to various
embodiments of the present invention are described. FIG. 3D
illustrates a parabolic curve 322, which represents the shape of
one or more possible reflector panels along a plane defined by a y
axis 112 and a x axis 114. The focus 324 indicates a location of a
photovoltaic cell where these possible reflective panels direct
incident sunlight. A first portion 326 of the parabolic curve
approximates the shape and the position of the reflector panel in
FIG. 3A. A second portion 328 of the parabolic curve approximates
the shape and position of the reflector panel in FIG. 3C. Any
number of reflector panels can be imagined that have reflective
surfaces that conform substantially with the parabolic curve, which
is arranged to direct substantially all incoming incident sunlight
to the focus 324. A review of FIG. 3D indicates that the degree of
curvature of a reflector panel may be affected by whether the solar
receiver is positioned high, low or centrally relative to those
solar receivers. It should be appreciated that FIG. 3D is
applicable only to some of the embodiments contemplated by the
present invention and that the present invention contemplates other
embodiments in which the reflector panels have other curvatures,
arrangements and/or shapes.
[0054] Referring next to FIGS. 4A and 4B, a collector unit 400
according to a particular embodiment of the present invention will
be described. The collector unit 400 may represent a stand alone
structure, or it may be understood as a basic building block for
many other designs. That is, multiple collector units 400 may be
arranged together to form a wide variety of collector designs, some
of which are described in FIGS. 5A-5C and FIGS. 6A-6C. FIG. 4A
illustrates a diagrammatic perspective view of a collector unit 400
that includes one or more solar receivers 402 and one or more
reflector panels 404. FIG. 4B illustrates a cross-sectional view of
the collector unit 400, which may also have any of the features
described in connection with FIGS. 2A-2C and 3A-3D. The collector
unit 400 is arranged such that the reflector panels 404 direct
incident sunlight 410 to the solar receivers 402. The reflected
light forms a flux line on the receivers 402 that extends
longitudinally down the length of the collector unit.
[0055] As discussed previously with respect to other embodiments,
the design of the collector unit 400 offers several advantages.
Because the reflective surface of the reflector panels 404 is
positioned in close proximity to the solar receivers 402, the light
need not traverse a long distance between the reflector panels 404
and the solar receivers 402, which improves mechanical and tracking
tolerances for the collector. Additionally, the solar receivers 402
are positioned over a region just outside a lower edge 406 of the
reflective surface. As a result, the solar receiver 402 (and any
associated support structures) do not shade the reflective surface
and do not prevent incident sunlight from reaching the reflective
surface.
[0056] Some collector units involve multiple solar receivers and
reflector panels that are arranged in rows that run parallel to one
another along a longitudinal axis. In the illustrated embodiment,
for example, multiple longitudinally adjacent reflector panels 404
cooperate to form a reflector 408 with a substantially continuous
reflective surface. The solar receivers 402 are also arranged
longitudinally adjacent to one another to form a solar receiver row
that extends in the longitudinal direction 106. The length of the
solar receiver row is generally substantially similar to that of
the length L of the reflector. In various implementations, however,
the solar receiver row may be somewhat longer or shorter than the
reflector. It should be appreciated that although the figure
illustrates ten solar receivers 402 in the solar receiver row and
seven reflector panels 404 forming the reflector, almost any
suitable number or combination of solar receivers and reflector
panels may be used.
[0057] Multiple collector units 400 may be arranged in a wide
variety of ways to form different types of solar collectors. Some
examples are provided in FIGS. 5A-5C. FIG. 5A illustrates a solar
collector 500 made of two collector units 400a and 400b in which
the first and second reflectors 502a/502b are arranged with their
backsides to one another in a tent-like arrangement. In the
illustrated embodiment, the first and second reflectors 502a/502b
are arranged substantially symmetrically around the center of the
collector. A reflective surface on each reflector 502a/502b has a
parabolic or otherwise curved shape. The first and second
reflectors 502a/502b are arranged to form an A-like shape, i.e. the
inner edges 503a/503b of the reflectors 502a/502b are positioned
adjacent to one another at the middle of the collector, the
reflectors 502a/502b curve inward relative to one another, and the
outer edges 506a/506b of the reflectors 502a/502b are positioned at
the periphery of the collector 500 and at a lower height than the
inner edges 503a/503b of the reflectors 502a/502b. The first and
second solar receivers 504a/504b are positioned above a peripheral
region outside the outer edges 506a/506b of the first and second
reflectors 502a/502b, respectively, and are physically supported by
receiver support structures. An advantage of this implementation is
the location of the solar receivers 504a/504b at the periphery of
the collector 500, which allows easy access to the receivers for
installation, cleaning and repair. Additionally, the solar
receivers 502a/502b are somewhat removed from other collector
components, which may facilitate heat dissipation.
[0058] FIG. 5B illustrates a different way of arranging two
collector units 400a/400b. In the illustrated embodiment, the first
and second reflectors 522a/522b, which may have a curved or
parabolic shape, are substantially symmetrically arranged and curve
outward to form a trough- or U-like shape. That is, the inner edges
523a/523b of the reflectors 522a/522b are positioned closer to the
middle of the collector 520, while the outer edges 526a/526b of the
reflectors 522a/522b are positioned at the periphery of the
collector 520. The outer edges 526a/526b are positioned higher than
the inner edges 523a/523b, which results in the formation of a
U-type design. Two solar receivers 524a/524b, whose respective
photovoltaic cells face away from one another, are positioned over
a central region between the inner edges 523a/523b of the
reflectors 522a/522b. An advantage of this implementation is that
the two solar receivers 524a/524b are positioned at a single
location, which means that fewer structures are required to
physically support them then if they were separated across the
width of the collector 520.
[0059] FIG. 5C illustrates a collector 540 in which the collector
units 400a/400b are staggered at different heights. Rather than
being arranged side-by-side, the second solar receiver 544b is
positioned over and shades the first solar receiver 544a. To
maintain its proper alignment with the second solar receiver 544b,
the second reflector 542b is positioned higher than the first
reflector 542a. That is, the collector 540 is generally symmetrical
between the two collector units 400a/400b, except that the
collector units are offset along the vertical y axis 112. An
advantage of this design is that the solar receivers 544a/544b take
up less space along the x axis 114. A review of FIG. 5C indicates
that the pairs of solar receivers 524a/524b and 544a/544b of FIGS.
5B and 5C take up a distance G and G', respectively, which extends
along the x axis 114. Because the two solar receivers 544a/544b in
FIG. 5C are stacked over one another, the distance G' of the
collector 540 in FIG. 5C is substantially less than the distance G
of the collector 520 in FIG. 5B. As a result, the ratio of the
reflective area of the collector to the total area of the collector
is increased, which means that for the same amount of real estate,
more light is directed to the photovoltaic cells of the collector
540 in FIG. 5C.
[0060] Referring next to FIGS. 6A-6C, extended solar collectors in
accordance with various embodiments of the present invention will
be described. Each extended solar collector involves multiple
collector units that are coupled with a common base. The common
base allows a larger number of reflectors and solar receivers to be
part of a single collector structure that can be pivoted to track
the movements of the sun.
[0061] FIG. 6A relates to an extended collector 600 that is an
extended version of the A-type collector illustrated in FIG. 5A.
That is, in addition to the reflectors 502a/502b and solar
receivers 504a/504b illustrated in FIG. 5A, the extended collector
includes at least a third reflector 502c and a fourth reflector
502d. The third and fourth reflectors 502c/502d are positioned
outside the outer edges of the first and second reflector panels
502a/502b, respectively, and are oriented in a similar manner
(e.g., curving inwards towards a central region of the collector,
with the inner edges being higher than the outer edges.) Each
reflector has a reflective surface and an opposing backside
surface. The reflective surface of each reflector is arranged to
direct incident light to one of the solar receivers. The first and
second solar receivers 504a/504b are positioned near the inner
edges and on the backsides of the third and fourth solar receivers
502c/502d, respectively. As a result, it is not necessary to use a
separate structure to support the solar receivers 504c/504d, since
the reflectors 502c/502d can be used to hold the solar receivers in
position. In the illustrated embodiment, there are two more
reflectors and two more solar receivers in the collector beyond the
ones described above, that essentially repeat the aforementioned
receiver-reflector arrangement (e.g., each reflector is arranged to
direct sunlight to a solar receiver that is on the backside of the
next reflector, except for the solar receivers at the far ends of
the collector 600.) It should be appreciated that fewer or more
reflectors and solar receivers may be used. All of the reflectors
and receivers are mounted on a common base structure 602 that can
be pivoted along at least one axis to track incident sunlight.
[0062] FIG. 6B relates to an extended collector 620 that is an
extended version of the U-type collector 520 illustrated in FIG.
5B. That is, in addition to the reflectors 522a/522b and solar
receivers 524a/524b illustrated in FIG. 5B, the extended collector
520 includes at least a third reflector 522c and a fourth reflector
522d. The third and fourth reflectors 522c/522d are positioned
outside the outer edges of the first and second reflectors
522a/522b, respectively, and are oriented in a similar manner
(e.g., curving outwards away from a central region of the
collector, with the outer edges being higher than the inner edges.)
Additional third and fourth solar receivers 524c/524d are attached
with the backsides of the first and second reflectors 522a/522b.
The third and fourth reflectors 522c/522d are arranged to direct
incident light into the third and fourth solar receivers 524c/524d,
respectively. The solar receivers 524a-524d and reflectors
522a-522d are mounted on a common base structure 604 that is
arranged to pivot in order to track movements of the sun.
Additional reflector panels and solar receivers may be attached
with the common base structure 604 in the manner of the third and
fourth solar receivers 524c/524d and the third and fourth
reflectors 522c/522d to further expand the reflective area and
power generating capacity of the solar collector 620.
[0063] FIG. 6C illustrates an extended collector according to
another embodiment of the present invention. The features of the
collector 640 are almost identical to those of the collector 600 in
FIG. 6A, except that at least some of the reflectors 502a-502d are
at different heights. In the illustrated embodiment, for example,
the collector 640 is symmetrical along a bisecting axis 608 and the
common base structure 606 supports at least some of the reflectors
on each side of the bisecting axis 608 such they are offset from
one another along the vertical y axis 112.
[0064] It should be appreciated that FIGS. 5A-5C and 6A-6C provide
only a few of the possible arrangements of reflectors and solar
receivers that are contemplated in the present invention. Although
most of the figures involve substantially symmetrical collector
designs, in some embodiments the designs may instead be
asymmetrical. The reflector panels and solar receivers of each
solar collector may or may not have substantially identical
dimensions and/or shapes in the same collector. The common base
structures 602/604/606 of FIGS. 6A-6C are drawn diagrammatically as
platforms with flat surfaces, but it should be appreciated that a
base structure may take a wide variety of forms, including a space
frame support structure, multiple separate support structures,
etc.
[0065] Referring next to FIGS. 7A-7C, a space frame support
structure 702 for use in a solar collector 700 according to a
particular embodiment of the present invention will be described.
FIG. 7A illustrates a diagrammatic cross-sectional view of an
U-type collector 700 (e.g., as described in FIGS. 1A-1B and 5A),
which includes a space frame support structure 702 that physically
supports the solar receivers 706a/706b and the reflector panels
704a/704b. FIGS. 7B and 7C illustrate diagrammatic perspective
views of the collector 700, with some of the reflector panels
removed to reveal more of the underlying space frame. The space
frame support structure 702 includes multiple struts that are
connected at nodes. The struts 708 include one or more receiver
support struts 714a/714b/714c and one or more reflector support
struts 712a/712b.
[0066] The space frame support structure 702 is arranged to
disperse loads originating at the solar receivers 706a/706b and the
reflector panels 704a/704b. In the illustrated embodiment, for
example, the receiver support struts 714a/714b/714c are linear
pipes, tubes, or cylinders that extend diagonally out from a
location immediately underneath the solar receivers to one or more
nodes within the space frame. As a result, loads originating at the
solar receivers are largely converted into compressive or tensile
forces on one or more of the underlying struts, which are better
tolerated. Additionally, the structures that are supporting the
receiver and reflector panels are not physically isolated from the
rest of the rest of the space frame support structure, which may
render them more vulnerable to bending or damage. Instead,
components such as the receiver support structures are integrated
into the overall space frame support structure such that the loads
from the solar receivers are carried not only by the structures
that are in direct contact with them, but also by the rest of the
space frame support structure. The space frame support structure
702 may be viewed as a unitary structure, since it supports and
distributes the loads from both the solar receivers 706a/706b and
the reflector panels 704a/704b in an integrated or unitary
fashion.
[0067] Various implementations involve a space frame support
structure 702 that is made of linear struts that are connected at
nodes to form multiple geometric shapes, such as pyramids,
tetrahedrons, etc. These shapes help to disperse stresses from
carried components through multiple paths within the space frame.
The space frame support structure has large apertures 716 and
internal spaces that allow the passage of air, which substantially
reduces wind load on the collector 700. The large apertures 716
also facilitate cleaning of and access to the space frame support
structure 702 and are less likely to catch debris.
[0068] Generally, the space frame support structure 702 is arranged
to minimize or eliminate any shading of the reflector panels
704a/704b. In some embodiments, no portion of the solar receivers,
the space frame support structure or any part of the solar
collector shades the reflector panels 704a/704b during the normal
operation of the solar collector.
[0069] The space frame support structure may include multiple,
longitudinally extended longerons that form a base framework for
the rest of the space frame support structure. The longerons may be
continuous tubes substantially equal in length to the collector
length. The tube cross-section may be square, rectangular,
circular, or some other shape. Struts are attached to nodes on the
longerons to create an integrated, web-like, highly resilient
structure. (The term "longeron" may be understood in the present
application as any suitable type of linear member that extends in a
longitudinal direction.) For example, FIGS. 7B-7C illustrate a
space frame support structure 702 that includes an upper longeron
718, side longerons 720 and lower longerons 722. Each longeron is a
linear member that extends along a longitudinal axis 106. The upper
longeron 718 is arranged to physically support one or more solar
receivers 706a/706b. The side longerons 720 are positioned near the
outer edges 724 of the reflector panels 704a/704b and may
indirectly help to support the panels. The lower longerons 722 are
arranged at a bottom portion of the space frame support structure
702. All of the longerons extend substantially parallel to one
another along the longitudinal axis 106.
[0070] Each of the longerons have multiple nodes that are separated
by gaps and are distributed along the length of the longeron. The
nodes are connecting points for multiple additional struts that can
cause forces to be dispersed through multiple paths. For example,
the upper longeron 718 has multiple upper nodes 726 along its
length. In some embodiments, each upper node 726 is adjacent to and
directly underlies one or more solar receivers 706a/706b, although
this is not a requirement. Multiple receiver support struts
714a/714b/714c extend diagonally downward from each upper node 726
to help support the solar receivers 706a/706b. While the upper
longeron 718 may experience some bending force, the receiver
support struts 714 are subject primarily to tensile or compressive
loads. Force that is applied to the solar receivers 706a/706b is
dispersed through multiple, suitably angled receiver support struts
714a/714b/714c, rather than a single support member.
[0071] The solar receivers 706a/706b may be attached at multiple
points along the upper longeron 718. The attachment points may be
located at regular intervals along the longeron. These attachment
points need not correspond with space frame nodes. If the longeron
is formed from a rectangular tube, the attachment to the longeron
may include a U-shaped channel that fits over the longeron. Both
the longeron and the U-shaped may include holes. The U-shaped
channel may be secured to the longeron by aligning these holes and
inserting a fastener through the holes.
[0072] In some designs, the receiver support struts 714 fan out
from the upper nodes 726 and connect to various nodes deeper within
the space frame support structure. By way of example, in FIG. 7A,
one receiver support strut 714b extends straight down and directly
underneath the solar receivers 706a/706b and is coupled to a
central node 728 in the space frame support structure. Two other
receiver support struts 714a/714c extend diagonally downward to
lower nodes 730a/730b, respectively, which are coupled to the lower
longerons 722 at the bottom of the collector 700. In the
illustrated embodiment, the lower nodes 730a/730b are positioned
below the reflector panels. While FIG. 7A illustrates three
receiver support struts 714a/714b/714c extending out an upper node
726, it should be appreciated that there may also be more or fewer
receiver support struts extending out of the upper node or any
single node.
[0073] There are also multiple side nodes 732 that are separated by
gaps and are distributed along the length of each side longeron
720. Multiple reflector support struts 712a/712b extend diagonally
out from each side node 732 to help physically support the
reflector panels. One of these struts 712a, which extends towards
and is coupled to the side longeron 720, is coupled to the central
node 728. Another is coupled to the lower node 730b and also
extends to the side longeron 720. The two reflector support struts
712a/712b are attached to the side longeron 720 via the same side
node 732.
[0074] The reflector support struts 712a/712b cooperate to form a
base upon which the reflector panels 704a/704b may be positioned.
Various implementations involve reflector support struts 712a/712b
that extend in a direction substantially perpendicular to the upper
and side longerons 718/720. To further facilitate the mounting of
reflector panels 704a/704b to the space frame support structure
702, one or more stringers 734 may be positioned over the
aforementioned receiver support struts 712a. In the illustrated
embodiment, for example, the stringers 734 overlie and extend
perpendicular to the receiver support struts 712a. Each stringer
734 includes one or more attachment points for attaching to an
overlying reflector panel. The stringers 734 provide additional
stiffness to facilitate more accurate alignment of the reflector
panel. Together with the reflector support struts 712a/712b, the
stringers 734 also help to distribute the load of the reflector
panels more evenly over the space frame. Generally, stringers 734
facilitate the mounting of different sized reflector panels, since
they may be substantially invariant along the longitudinal
direction, attachment points between the stringers and reflector
panels may be installed at any location. In some embodiments,
stringers are not used and the reflector panel is attached with a
different support member (e.g., a receiver support strut 712a.)
[0075] The struts and nodes may take a wide variety of forms,
depending on the needs of a particular application. They may be
made of almost any suitably resilient material, such as aluminum or
steel. For example, tubular aluminum extruded members, roll formed
steel sections and hot rolled steel sections work well as struts in
the space frame support network. The nodes may be understood as
connecting points for multiple struts. Struts can be connected at
nodes without a connector (e.g., by form fitting or crushing the
struts together, bending the struts around one another, fabricating
through holes in one strut for the insertion of another strut, or
any other suitable technique.) Welding, metal clinching, adhesive,
rivets and bolts may be used to connect struts, connectors and/or
nodes of the space frame support structure. In some embodiments,
each node includes a separate connector that helps secure the
incoming struts. The connector may take any suitable form, such as
a metal sphere, a hub, etc. In some implementations, the connector
is arranged such that the long axes of the incoming struts are
arranged to meet substantially at a single point within the node
and/or connector. Struts may be attached to the connector using
various mechanisms, including pins, fasteners, bolts, etc.
[0076] In the illustrated embodiment, the gap G between the
reflector panels 704a/704b is utilized to provide extra structural
support for the solar receivers 706a/706b. By widening this gap
appropriately, room can be made for multiple receiver support
structures 714a-714c that help to stabilize the position of the
solar receivers. In any case, a large portion of the gap G is
covered by the solar receivers 706a/706b, and thus cannot be used
for the reflection of sunlight. In some prior art concentrating
photovoltaic systems, this gap between the reflector panels
704a/704b is either non-existent or not wide enough to accommodate
a substantial support framework.
[0077] The length of the receiver support struts 714a-714c may be
adjusted to help make the overall collector more symmetrical around
its pivot axis 736. That is, the upward extension of the receiver
support struts 714a-714c helps to balance out the lateral extension
of the reflector panels 704a/704b. Thus, in various embodiments,
the height h to width w ratio of the collector 700 (as measured
along a plane defined by the x axis 114 and the y axis 112) is
greater than approximately 0.4. A more symmetrical arrangement
helps reduce the buildup of stresses on a particular portion of the
space frame support structure, even when it is rotated to track
movements of the sun.
[0078] Referring next to FIG. 7D, a solar collector according to
another embodiment of the present invention will be described. FIG.
7D is a diagrammatic cross-sectional view of a solar collector 740
that includes a space frame support structure 742 with a different
arrangement of struts, nodes and longerons than what was shown in
FIGS. 7A-7C. The space frame support structure 742 includes side
longerons 752, a single upper longeron 754 and a single lower
longeron 750. The upper longeron 754, which is attached to one or
more solar receivers 744a/744b through upper node 762, is supported
by two receiver support struts 748a/748b that extend diagonally
down from the upper longeron 754 and are coupled to two central
nodes 756a/756b. Two additional struts 758a/758b connect the
central nodes 756a/756b with the single lower longeron 750 to form
a diamond shape between the upper longeron 754 and the lower
longeron 750. In the illustrated embodiment, the collector 740 is
symmetrical along a bisecting plane 759, and both the upper and
lower longerons 754/750 are on this bisecting plane 759. Multiple
reflector support struts 760a/760b are coupled to and extend from
the central and lower nodes 756a/756b/750 to each side longeron
752, where they are attached to the side longeron 752 via the same
side node 762. Similar to the space frame support structure 702
illustrated in FIG. 7A, the interconnections and structures
illustrated in FIG. 7D may be repeated down the length of the
longitudinally extended collector 740 (e.g., there are multiple
upper nodes and side nodes arranged along the longitudinal lengths
of the upper and side longerons, which may each have the same
interconnections as described above.) A notable feature of this
space frame design is that any node is limited to a relatively low
number of connecting struts (e.g., in the case of FIG. 7D, only
four.) For some applications, this feature is desirable, since it
makes the node somewhat easier to handle, install and repair.
[0079] It should be appreciated that there is almost an infinite
number of ways to arrange the longerons, struts and nodes of the
space frame support structure. FIGS. 7A-7D should be understood as
merely exemplary and should not be interpreted as limiting the
range of space frame support structures that are contemplated in
the present application.
[0080] The use of struts and nodes also makes the space frame
support structure relatively easy to ship and assemble. By way of
example, individual struts and nodes may be first compactly stored
in a shipping container so that they can be assembled almost
entirely on-site. Alternatively, portions of the space frame
support structure (e.g., interconnected nodes and struts that form
a plane of the space frame support structure) may be preassembled
prior to shipping. They may be preassembled in planar trusses that
can be assembled in the field. Some portions of the space frame
support structure (e.g., a planar combination of struts and nodes)
may be arranged to be collapsible for shipment and fold out in the
field. In particular the planar trusses may be collapsible such
that the struts are allowed to pivot about the nodes in such a way
as for the planar parts of the truss to collapse into a smaller
volume. In another approach, the main body of the space frame
supporting structure may be preassembled at the factory, and
peripheral components are added on site.
[0081] Referring next to FIG. 8A, a connector for use at a node of
the space frame support structure according to a particular
embodiment of the present invention will be described. FIG. 8A
illustrates a connector 800 that includes a body 802 and multiple
connector fins 806. The body 802 is arranged to accept a longeron
810, such as one of the longerons described in connection with
FIGS. 7A-7D. Each connector fin 806 is a solid sheet or planar
surface that extends out of the body 802. Preferably, the body 802
and fins 806 have simple geometries (e.g., cylinders, planes,
holes, slots, etc.) so that they are cost-effective to
manufacture.
[0082] The body 802 of the connector 800 includes a feature for
engaging a longeron 810 In the illustrated embodiment, for example,
the body 802 is a hollow cylinder with open ends that is arranged
to accept a longeron 810. The body 802 may be secured to the
longeron 810 using any suitable means, including a pin 814, a bolt,
fastener, a latch, adhesive, welding, etc. If a pin is used, the
pin may be stepped and the hole diameter in the strut and connector
appropriately sized so that each pin step has substantially equal
engagement with the hole in the strut or connector.
[0083] Each fin 806 is arranged to securely engage one or more
additional struts 808. This may be performed in a variety of ways.
By way of example, each strut 808 may be a metal tube, bar, rod or
cylinder whose end has a slot 812. The edge of the fin 806 of the
connector 800 is arranged to slide into the slot 812 of the strut
808. By lining up alignment holes 804 in the fin 806 and the end of
the strut 808 and extending a pin 816 through the holes and the
slot 812, the strut 808 can be secured to the fin 806. Preferably,
the struts 808 contact the connect 800 at substantially different
angles to avoid mechanical interference. In some embodiments, a
connector 800 and its connected struts 808 are arranged such that
the long axes of the incoming connecting struts 808 meet at
substantially the same point, which may or may not be in the
connector 800.
[0084] Referring next to FIGS. 9A-9B, a solar collector 900 with a
space frame support structure 902 according to another embodiment
of the present invention will be described. FIG. 9A is a
diagrammatic cross-sectional view of a space frame support
structure 902 suitable for use in A-type solar collector, such as
the one described in connection with FIG. 5A. FIG. 9B is a
diagrammatic perspective view of the space frame space structure
902 illustrated in FIG. 9A. In the illustrated embodiment, the
space frame support structure 902 is substantially symmetrical
along a bisecting plane 904, although this is not a requirement.
The solar collector 900 is arranged to be rotated around pivot axis
921 to track movements of the sun.
[0085] The solar collector includes an upper longeron 910, two side
longerons 912 and two lower longerons 914 that extend parallel
along the longitudinal axis 106 of the solar collector 900. The
upper longeron 910, in contrast to the upper longeron 718 of the
space frame support structure 702 of FIGS. 7A-7C, does not have
attachment sites for solar receivers. Multiple upper nodes 920 are
separated by gaps and arranged along the length of the upper
longeron 910. Multiple support struts 922a/922b/922c fan downward
from each upper node 920. Each of these struts 922a/922b/922c are
connected to one of the lower nodes 924a/924b/924c. Reflector
support struts 926a/926b also extend from the upper node 920 and
help physically support and underlie the reflector panels
908a/908b.
[0086] The solar receivers 906a/906b are coupled to various
attachment sites that are on each side longeron 912. The side
longeron 912 is supported by receiver support struts 928a/928b that
are positioned at the periphery of the solar collector 900. In the
illustrated embodiment, for example, each solar receiver is
physically supported by a first receiver support strut 928a and a
second receiver support strut 928b. The first receiver support
strut extends upward from a lower node 924c to the side node 930.
The second receiver support strut extends upward from a peripheral
node 932 to the side node 930.
[0087] The above arrangement of nodes and support struts are
repeated at various points along the length of the longerons and
the space frame support structure 902. That is, there are multiple
upper nodes 920, which are separated by gaps, along the length of
the upper longeron 910. Support structures 922a-922c fan downward
from each of these upper nodes 920 in the manner described above.
Similarly, there are side nodes 930, separated by gaps, along the
length of each side longeron 912. Receiver support struts 928a/928b
extend diagonally downward from each of these side nodes 930 to
corresponding lower and peripheral nodes 924c/932. As a result, a
lattice of interlocking struts and nodes is formed that helps to
prevent too much stress from building up on a narrow portion of the
support structure.
[0088] Referring next to FIGS. 10A and 10B, a reflector panel 1000
suitable for coupling to the space frame support structure
according to a particular embodiment of the present invention will
be described. FIG. 10A is a diagrammatic side view of the reflector
panel 1000. FIG. 10B is a diagrammatic perspective view of the
reflector panel 1000. The reflector panel 1000 may be understood as
an enlarged view of one of the reflector panels illustrated in the
previous figures. By way of example, the length l of the reflector
panel 1000 may correspond with the length l of the reflector panel
200 illustrated in FIG. 2A. The width w.sub.r of the reflector
panel 1000 may correspond with the width w.sub.r of the reflector
panel 300 illustrated in FIG. 3A. As previously discussed, the
reflector panel 1000 may have a compound curvature e.g., a convex
curvature in a plane including the longitudinal axis 106, and a
concave curvature along a plane defined by the x and y axes
112/114. The reflector panel has a reflective frontside 1002 and a
backside 1003.
[0089] The backside 1003 of the reflector panel 1000 includes
attachment features 1004 for coupling the panel to the space frame
support structure. In various embodiments, for example, the
attachment features are used to secure the reflector panel 1000 to
the stringers 734 illustrated in FIG. 7B. In still other
embodiments, the attachment features are used to secure the
reflector panel 1000 to a reflector support strut or other support
member. The attachment features may use any suitable means to
securely fasten the backside 1003 of the reflector panel 1000 to
the underlying support structure. By way of example, the attachment
features 1004 may involve adhesive, glue pads, holes, fasteners or
threaded screw holes.
[0090] The reflector panel 1000 may have a variety of different
compositions and dimensions, depending on the needs of a particular
application. Any reflective material, such as metalized glass,
aluminum, etc, may be used to form the reflector panel. The
reflective panel 1000 may be rectangular, curved, parabolic, flat,
and/or arranged in the form of rectangular sheets or longer strips
(e.g., as shown in FIG. 3B). In various embodiments, all of the
reflector panels of a particular solar collector have the same
dimensions and curvatures, although in other embodiments the panels
may differ in their shape and size.
[0091] Referring next to FIG. 11, a solar collector row 1100
according to a particular embodiment of the present invention will
be described. FIG. 11 is a diagrammatic perspective view of a solar
collector row 1100 that includes multiple solar collectors 1102
that have been arranged adjacent to one another along a
longitudinal axis 106. Multiple mounting posts 1106 form a stand,
which physically support the solar collector row for pivotal motion
1104, are positioned at the ends and at various points along the
length of the collector row. The illustrated collectors may be any
of the collectors described in the present application.
[0092] Preferably, the solar collectors 1102 are coupled together
such that they pivot together in tandem to track movements of the
sun. Coupling devices (not shown) are positioned underneath
adjacent collectors 1102 to help link the collectors 1102 together.
Some embodiments of the collector include a space frame support
structure with short tube assemblies at the longitudinal ends of
the collector, which are each arranged to be connected with a
coupling device. Each coupling device is in turn supported by one
of the mounting posts 1106, which physically supports the solar
collector row 1100. When torque is applied to one of the
collectors, the torque is transferred through the coupling devices
may rotate the entire solar collector row 1100. Various
implementations of this approach are described in U.S. patent
application Ser. No. 12/846,620, entitled "Manufacturable Dual
Trough Solar Collector," filed Jul. 29, 2010, which is incorporated
herein in its entirety for all purposes.
[0093] The present invention also contemplates a power generation
plant that includes multiple solar collectors 1102 and solar
collector rows 1100. The solar collector rows 1100 may be arranged
in any suitable manner (e.g., in an array, side by side in a
parallel formation, etc.) In some embodiments, multiple solar
collectors 1102 are positioned on a common carousel type platform
that can be rotated to track movements of the sun. All the
collectors on the carousel rotation axis may rotate about a common
rotation axis. The rotation axis may be substantially vertical. In
various embodiments, the collector longitudinal axes may lie in a
substantially horizontal plane, or the collector longitudinal axes
may have a fixed, oblique tilt angle relative to the rotation axis.
Alternatively, the collectors may be rotated about two axes. Such
approaches are described in greater detail in U.S. patent
application Ser. No. 12/642,704, entitled "High Ground Cover Ratio
Solar Collection System," filed Dec. 18, 2009, which is hereby
incorporated in its entirety for all purposes.
[0094] Referring next to FIG. 12, the tracking and pivoting of a
solar collector or solar collector row according to a particular
embodiment of the present invention will be described. FIG. 12 is a
diagrammatic end view of solar collectors 1102 that are at the ends
of two of the solar collector rows 1100 illustrated in FIG. 11. The
two solar collector rows 1100 are arranged in parallel and extend
in a longitudinal direction (i.e., into the page). A mounting post
1204 physically supports each solar collector for pivotal movement
around a pivot axis 1206 that also extends in the longitudinal
direction. The mounting posts 1204 may be anchored into the ground
or a common base 1210 (e.g., a roof top, car park cover, etc.) A
tracking system is arranged to pivot the solar collector to track
the movements of the sun, such that the incoming sunlight 1212 is
substantially incident on the optical aperture of the collector
1102.
[0095] Various designs involve a pivot axis 1206 that substantially
passes through the center of gravity of each collector in a solar
collector row 1100. That is, the weight of the various components
of the collector 1102 are distributed evenly around the pivot. As a
result, less force is required to rotate the collector 1102. The
location of the center of gravity of the collector 1102 depends on
the weights of the various components. By way of example, it may be
located along a bisecting plane 1216 of the collector and/or
between the reflector panels 1214a/1214b. Some embodiments involve
adding weights to the bottom of the collector 1102 to push the
center of gravity lower. An economical and simple way to do so is
to fill some of the lower struts or longerons with solid material,
such as gravel, cement, sand, earth or steel balls.
[0096] The solar collector 1102 is arranged to accommodate a wide
range of motion around the pivot axis. In some embodiments, for
example, the tracking system, stand and solar collector 1102 are
arranged to pivot the solar collector at least 170 degrees, or at
least 160 degrees, or at least 150 degrees, while keeping the pivot
axis 1206 substantially at the center of gravity of the collector.
Some implementations involve a pivot range of at least 120 or 140
degrees. The pivot range can be increased by pushing the pivot axis
1206 further from the center of gravity. The pivot range may be
adjusted to be lower or higher, depending on the solar insolation
characteristics of a particular solar power plant site.
[0097] Referring next to FIGS. 13A-13B, a solar collector 1300 with
a support cable 1306 according to a particular embodiment of the
present invention will be described. FIG. 13A is a diagrammatic
cross-sectional view of the solar collector 1300, which may be
understood as the A-type collector 500 illustrated in FIG. 5A. A
support cable 1306 extends across the span of the collector 1300 to
couple together the solar receivers 1302a/1302b and/or the receiver
support struts 1308 on either side of the collector. FIG. 13B is a
diagrammatic perspective view of the solar collector illustrated in
FIG. 13A.
[0098] The support cable 1306 is arranged to provide additional
support for the solar receivers 1302a/1302b and their associated
support structures. Preferably, the support cable 1306 has a small
diameter so that it only minimally shades the underlying reflector
panels 1304a/1304b. For example, a diameter of less than
approximately 3 mm works well for various applications. Moreover,
the effect of any shading by the cable 1306 on the reflector panel
can be further reduced if the reflective panel has a convex
curvature. That is, even when portions of the reflective panel are
rendered unable to reflect light, there may be few or no breaks in
the flux line formed by the reflective panel, for the reasons
previously discussed in connection with FIGS. 2A-2C.
[0099] The support cable 1306 may be made of any suitably resilient
material, such as a metal wire. It may be attached directly to
opposing solar receivers 1302a/1302b, to a portion of the support
structure for the solar receivers, are some other suitable portion
of the collector 1300. Various embodiments of the present invention
involves a support cable 1306 that extends diagonally multiple
times across the span of the collector (e.g., as seen in FIGS.
13B), rather than directly across (e.g., in a direction that is
perpendicular to the longitudinal axis 106 of the collector.)
[0100] Although only a few embodiments of the invention have been
described in detail, it should be appreciated that the invention
may be implemented in many other forms without departing from the
spirit or scope of the invention. In the foregoing description,
components in one figure can be modified or replaced based on
corresponding elements in another figure. For example, the features
of the reflector panel 1000 illustrated FIG. 10 may be included in
any figure that references a reflector panel, including but not
limited to FIGS. 1A, 2A-2C and 3A-3D. It should also be noted that
the axes may be understood as having a consistent meaning across
all the figures. That is, the x, y, and z axes are perpendicular to
one another. Additionally, it should be noted that the axes may be
used to understand the design of various embodiments that are based
on more than one figure. For example, FIG. 2B illustrates a line of
convex shaped reflector panels that extend along a longitudinal
axis. FIG. 1B illustrates a relatively zoomed out view of a
collector in which the panels are illustrated in less detail.
Therefore, the present invention also contemplates a particular
embodiment where the features of the reflector panels of FIG. 2B
are included in the reflector panels of FIG. 1A. In understanding
this embodiment, the longitudinal axes 106 of FIGS. 1A and 2B may
be used as a common reference point to understand how the reflector
panels of FIG. 2B are used in the collector of FIG. 1A.
Additionally, the specification and claims sometimes refer to "the
normal operation of the solar collector." This generally refers to
a mode in which the collector is tracking the movement of the sun
(e.g., as shown in FIG. 12). However, it should be appreciated that
the collector does not necessarily always track the sun during
normal operation. For example, in some implementations the
collector does not track the sun in the early morning. Therefore,
the present embodiments should be considered as illustrative and
not restrictive and the invention is not limited to the details
given herein, but may be modified within the scope and equivalents
of the appended claims.
* * * * *