U.S. patent application number 12/502085 was filed with the patent office on 2010-01-14 for tracking concentrator employing inverted off-axis optics and method.
Invention is credited to Robert Owen Campbell, Michael George Machado.
Application Number | 20100006088 12/502085 |
Document ID | / |
Family ID | 41504001 |
Filed Date | 2010-01-14 |
United States Patent
Application |
20100006088 |
Kind Code |
A1 |
Campbell; Robert Owen ; et
al. |
January 14, 2010 |
Tracking Concentrator Employing Inverted Off-Axis Optics and
Method
Abstract
Solar concentrators are arranged in an array to define an input
aperture such that the solar collector is positionable to face the
input aperture of the concentrators skyward. An input axis of
rotation extends through the aperture in the skyward direction, and
a focus region is smaller than the aperture. Each concentrator
includes at least one optical arrangement that is supported for
rotation about the input axis for tracking the sun within a
predetermined range of positions of the sun using no more than the
rotation of the optical arrangement around the input axis. An
optical concentrator is described in which a receiving direction
extends at an acute angle from an optical axis and in one azimuthal
direction outward from the optical axis such that a component of
the concentrator is rotatable about the optical axis for alignment
to receive input light. A previously unknown inverted off-axis lens
is described.
Inventors: |
Campbell; Robert Owen;
(Boulder, CO) ; Machado; Michael George; (Boulder,
CO) |
Correspondence
Address: |
PRITZKAU PATENT GROUP, LLC
993 GAPTER ROAD
BOULDER
CO
80303
US
|
Family ID: |
41504001 |
Appl. No.: |
12/502085 |
Filed: |
July 13, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61080554 |
Jul 14, 2008 |
|
|
|
Current U.S.
Class: |
126/573 |
Current CPC
Class: |
F24S 50/20 20180501;
Y02E 10/52 20130101; F24S 23/31 20180501; Y02E 10/47 20130101; H01L
31/0543 20141201; F24S 30/422 20180501 |
Class at
Publication: |
126/573 |
International
Class: |
F24J 2/38 20060101
F24J002/38 |
Claims
1. A solar collector comprising: one or more solar concentrators
arranged in an array such that each of said concentrators is in a
fixed position with a fixed alignment in said array and each of
said concentrators is configured to define (i) an input aperture
having an input area such that the solar collector is positionable
to face the input aperture of each concentrator in a skyward
direction such that said input aperture is oriented to receive
sunlight from the sun, (ii) an input axis of rotation that extends
through said aperture in said skyward direction, and (iii) a focus
region that is substantially smaller than said aperture area, and
each of said concentrators includes an optical assembly having at
least one optical arrangement that is supported for rotation about
said input axis for tracking the sun within a predetermined range
of positions of said sun using no more than said rotation of the
optical arrangement around the input axis such that said rotation
does not change the direction of the aperture from said skyward
direction, wherein for any specific one of said positions within
said predetermined range of positions, said optical arrangement is
rotatably oriented, as at least part of said tracking, at a
corresponding rotational orientation as at least part of
concentrating the received sunlight within said focus region, for
subsequent collection and use as solar energy.
2. The solar collector of claim 1 wherein for said specific one of
said positions of said sun, a rotational misalignment caused by
rotating the optical arrangement away from said corresponding
rotational orientation causes at least some of said received
sunlight to be directed outside of said focus region.
3. The solar collector of claim 1 wherein said optical arrangement
serves as an input arrangement for initially receiving the
sunlight, and said optical assembly includes an additional optical
arrangement following said input arrangement to accept the sunlight
from the input arrangement and configured for rotation about an
additional axis of rotation, and said input arrangement and said
additional arrangement are configured to cooperate with one another
in performing said tracking based at least in part on a
predetermined relationship between (i) said rotation of said input
arrangement about said input axis of rotation and (ii) rotation of
said additional arrangement about said additional axis of rotation
to focus the received sunlight into the focus region.
4. The solar collector of claim 3 wherein said additional axis of
rotation and said input axis of rotation are at least approximately
parallel with one another.
5. The solar collector of claim 3 wherein said additional axis of
rotation and said input axis of rotation are collinear with one
another.
6. The solar collector of claim 3 wherein said input optical
arrangement is configured for bending the received sunlight for
acceptance by said additional optical arrangement, and said
additional optical arrangement is configured for accepting and
redirecting the bent light to cause said focusing.
7. The solar collector of claim 3 including a group of two or more
of said solar concentrators and a drive mechanism rotatably couples
all of said input arrangements in said group to collectively rotate
all of said input arrangements while maintaining, during said
tracking, at least approximately the same rotational orientation
for all of the input arrangements as at least part of causing the
optical assemblies in the group to track the sun in a synchronized
way.
8. The solar collector of claim 7 wherein said drive mechanism is
further configured for rotatably coupling all of said additional
arrangements in said group to collectively rotate all of said
additional arrangements while maintaining, during said tracking, at
least approximately the same rotational orientation for all of the
additional arrangements as at least part of causing the optical
assemblies in the group to track the sun in said synchronized
way.
9. The solar collector of claim 8 wherein said additional
arrangement and said input arrangement of each concentrator are
rotatably coupled with one another through said drive arrangement
such that a first amount of rotation of one of said input
arrangement or said additional arrangement causes a second amount
of rotation in the other one of the input arrangement or the
additional arrangement, and the predetermined relationship is
maintained throughout said tracking at least in part as a result of
said coupling.
10. The solar collector of claim 3 wherein said optical assembly is
configured to define a receiving direction as a vector that is
characterized by a predetermined acute receiving angle with respect
to the input axis such that the input axis and the receiving
direction define a plane, and which receiving direction extends in
one azimuthal direction outward from the input axis in said plane,
such that said receiving direction is adjustable, based on a
coordinated rotation of said input arrangement and of said
additional arrangement, for performing said tracking of said
sun.
11. The solar collector of claim 10 wherein said input optical
arrangement is configured for bending the received sunlight for
acceptance by said additional optical arrangement, and said
additional optical arrangement is configured for accepting and
redirecting the bent light to cause said focusing.
12. The solar collector of claim 3 wherein said input arrangement
defines an at least generally planar configuration, and said input
arrangement includes a planar input surface that defines said input
aperture.
13. The solar collector of claim 12 wherein said input arrangement
is configured for bending the received light rays.
14. The solar collector of claim 13 wherein said additional
arrangement is a CPC following said input arrangement to accept the
light rays from the input arrangement, and the CPC is configured to
cause said focusing.
15. The solar collector of claim 14 wherein said CPC is a
reflective CPC configured for performing said focusing by
reflecting the light rays received from the input arrangement to
the focus region.
16. The solar collector of claim 13 wherein said optical assembly
includes an IOA following said input arrangement to accept the
light rays from the input arrangement, and the IOA is configured to
cause said focusing.
17. The solar collector of claim 1 wherein said optical arrangement
serves as an input arrangement for initially receiving the
sunlight, and said optical assembly includes an additional optical
arrangement following said input arrangement to accept the sunlight
from the input arrangement and configured for rotation about an
additional axis of rotation, and said input arrangement and said
additional arrangement are configured to cooperate in performing
said tracking based at least in part on said rotation of said input
arrangement about said input axis of rotation.
18. The solar collector of claim 17 wherein said optical assembly
is configured to define a receiving direction as a vector that is
characterized by a predetermined acute acceptance angle with
respect to the input axis such that the input axis and the
receiving direction define a plane, and which receiving direction
extends in one azimuthal direction outward from the input axis in
said plane, such that said receiving direction is rotatably
adjustable, based at least in part on said rotation of said input
arrangement.
19. The solar collector of claim 18 wherein said input optical
arrangement is configured for bending the received sunlight for
acceptance by said additional optical arrangement, and said
additional optical arrangement is configured for accepting and
redirecting the bent light to cause said focusing.
20. The solar collector of claim 17 wherein said input arrangement
defines an at least generally planar configuration, and said input
arrangement includes a planar input surface that defines said input
aperture.
21. The solar collector of claim 20 wherein said input arrangement
is configured for bending the received light rays for acceptance by
said additional arrangement.
22. The solar collector of claim 21 wherein said additional
arrangement is a CPC following said input arrangement to accept the
light rays from the input arrangement, and the CPC is configured to
cause said focusing.
23. The solar collector of claim 22 wherein said CPC is a
reflective CPC configured for performing said focusing by
reflecting the light rays accepted from the input arrangement to
the focus region.
24. An optical concentrator comprising an optical assembly having
one or more optical arrangements including an input optical
arrangement, and said optical assembly is configured for defining
(i) an input aperture having an input area for receiving a
plurality of input light rays, (ii) an optical axis passing through
a central region within said input aperture, (iii) a focus region
having a surface area that is substantially smaller than the input
area and is located at an output position along said optical axis
offset from the input aperture such that said optical axis passes
through said focus region, and (iv) a receiving direction defined
as a vector that is characterized by a predetermined acute
receiving position with respect to said optical axis such that the
optical axis and the receiving direction define a plane, and which
receiving direction extends in one azimuthal direction outward from
the optical axis in said plane such that at least the input
arrangement is rotatable about the optical axis for alignment of
the receiving direction to receive a plurality of input light rays
that are each at least approximately antiparallel with said vector,
and thereafter, focusing the plurality of input light rays to
converge toward said optical axis until reaching said focus region
such that the input light is concentrated at the focus region.
25. The optical concentrator claim 24 wherein said focus region
includes a given area and for at least some of said input light
that is characterized by at least a particular amount of
misalignment with the receiving direction, that input light is
rejected by falling outside of the given area of the focus
region.
26. The optical concentrator of claim 24 wherein said input
arrangement defines an at least generally planar configuration, and
said input arrangement includes a planar input surface that defines
said aperture.
27. The optical concentrator of claim 26 wherein said optical
assembly includes an additional optical arrangement following said
input arrangement, and said input arrangement is configured for
bending the received light rays for acceptance by said additional
arrangement.
28. The optical concentrator of claim 27 wherein said additional
arrangement is a CPC configured to accept the light rays from the
input arrangement, and the CPC is configured to cause said
focusing.
29. The optical concentrator of claim 27 wherein said CPC is a
reflective CPC configured for performing said focusing by
reflecting the light rays received from the input arrangement to
the focus region.
30. The optical concentrator of claim 27 wherein said additional
arrangement is an IOA configured to accept the light rays from the
input arrangement, and the IOA is configured to cause said
focusing.
31. The optical concentrator of claim 30 wherein said IOA is
configured for selective rotation about said optical axis, and said
input arrangement and said IOA are configured to cooperate with one
another in performing said receiving and said focusing based at
least in part on (i) said rotation of said input arrangement about
said optical axis and (ii) said rotation of said IOA.
32. An inverted off-axis lens, comprising: an optical arrangement
having an at least generally planar configuration defining (i) a
planar input surface having an input surface area and (ii) an axis
of rotation that is at least generally perpendicular thereto; and
said optical arrangement is configured for defining an acceptance
direction as a vector that is characterized by a predetermined
acute acceptance angle with respect to said axis of rotation such
that the axis of rotation and the acceptance direction define a
plane, and which acceptance direction extends in one fixed
azimuthal direction outward from the axis rotation in said plane
such that the optical arrangement is rotatable about the axis for
alignment of the acceptance direction to accept a plurality of
input light rays that are each at least approximately antiparallel
with said vector, and thereafter, transmissively passing the
plurality of input light rays through said optical arrangement
while focusing the plurality of input light rays to converge toward
one another until reaching a focus region that is substantially
smaller than the input surface area such that the input light is
concentrated at the focus region.
33. The inverted off-axis lens of claim 32 wherein said focus
region includes a given area and for at least some of said input
light that is characterized by at least a particular amount of
misalignment with the acceptance direction, that input light is
rejected by falling outside of the given area of the focus
region.
34. The inverted off axis lens of claim 32 wherein said focal
region is located along said axis of rotation offset from the input
surface area such that said axis of rotation passes through said
focal region.
35. The inverted off axis lens of claim 32 wherein said optical
arrangement further defines an output surface that is at least
generally parallel with said input surface and spaced therefrom by
a thickness, and at least part of said thickness refracts said
plurality of input light rays to cause the focusing of the light
rays.
36. The inverted off axis lens of claim 32 wherein said optical
arrangement is integrally formed of an optical material.
37. The inverted off axis lens of claim 36 wherein said optical
arrangement includes a plurality of optical prisms to accept and
focus said input light rays.
38. The inverted off axis lens of claim 35 wherein said optical
arrangement includes a plurality of optical prisms that are
configured to cooperate with one another to accept and the focus
said input light rays, and the prisms are integrally formed of an
optical material.
39. The inverted off axis lens of claim 38 wherein at least a
subset of said plurality of prisms is integrally formed with said
input surface.
40. The inverted off axis lens of claim 38 wherein at least a
subset of said plurality of prisms is integrally formed with said
output surface.
41. The inverted off axis lens of claim 38 wherein a first subset
of said plurality of prisms is integrally formed with said input
surface, and a second subset of said plurality of prisms is
integrally formed with said output surface,
42. The inverted off axis lens of claim 41 wherein said first and
second subsets of prisms are cooperatively configured to cooperate
with one another for accepting and focusing said input light rays,
and wherein said first subset of prisms is configured for bending
the input light rays for acceptance by said second set of prisms,
and said second subset of prisms is configured to cause said
focusing of said input light rays.
43. A solar concentrator for collecting and concentrating a
plurality of mutually parallel incoming rays of sunlight, said
solar concentrator including the inverted off axis lens of claim 32
arranged in a series relationship following an input optical
arrangement with the input surface of the off axis lens facing
towards the input arrangement, and the inverted off axis lens and
the input arrangement are each configured for selective rotation to
cooperate with one another such that the input arrangement
initially receives said incoming light rays and bends the incoming
light rays to produce intermediate light rays for acceptance by
said inverted off-axis lens such that the intermediate light rays
are at least approximately oriented antiparallel to said acceptance
direction, and said inverted off axis lens is aligned for accepting
said intermediate light rays such that said intermediate light rays
serve as said input light rays for said inverted off axis lens and
the inverted off axis lens concentrates the intermediate light rays
at said focus region of said inverted off-axis lens.
44. The solar concentrator of claim 43 wherein said input
arrangement is aligned with said axis of rotation, and said
inverted off axis lens and said input arrangement are configured to
cooperate with one another to define a receiving direction as a
vector that is characterized by a predetermined acute acceptance
angle with respect to the axis of rotation such that the axis of
rotation and the receiving direction define a plane, and which
receiving direction extends in one azimuthal direction outward from
the axis of rotation in said plane, such that said receiving
direction is rotatably adjustable, based on a coordinated rotation
of said input arrangement and of said additional arrangement.
45. The solar concentrator of claim 43 wherein said input
arrangement is concentrically aligned on said axis of rotation of
said inverted off axis lens such that said selective rotation of
said input arrangement revolves around said axis of rotation.
46. The solar concentrator of claim 45 wherein said input
arrangement includes an input axis of rotation that is skewed with
respect to said axis of rotation of said inverted off axis lens
such that said input arrangement is tiltable toward the sun.
47. The solar collector of claim 44 including a receiver following
said inverted off-axis lens, said receiver having a receiving
surface facing towards the off axis lens and aligned such that the
receiving surface at least partially overlaps said focus region,
and said receiver is configured such that at least some of the
concentrated input light is absorbed by said receiver and converted
into a form of energy.
48. The solar collector of claim 47 wherein said receiver is
configured for converting the absorbed input light into electrical
energy as said form of energy.
49. The solar collector of claim 48 wherein the receiver is
configured for converting the absorbed light into thermal energy as
said form of energy.
50. The solar collector of claim 49 wherein said receiver is in
thermal communication with a fluid and said receiver is configured
such that at least a portion of said thermal energy is transferred
to said fluid.
51. The solar collector of claim 50 wherein said receiver is
configured for passing a liquid therethrough, and at least some of
said thermal power is transferred to said liquid for subsequent use
outside of said receiver.
52. A multi-element inverted off-axis optical assembly, comprising:
an optical assembly having two or more optical arrangements
including a first arrangement that defines (i) an input aperture
having an input area and (ii) an axis of rotation that is at least
generally perpendicular thereto; and said optical arrangements are
configured to cooperate with one another for defining an acceptance
direction as a vector that is characterized by a predetermined
acute acceptance angle with respect to said axis of rotation such
that the axis of rotation and the acceptance direction define a
plane, and which acceptance direction extends in one azimuthal
direction outward from the axis of rotation in said plane, and at
least said first arrangement is supported for motion that is
limited to rotation about said axis of rotation for alignment of
the acceptance direction to accept said plurality of input light
rays that are each at least approximately antiparallel with said
vector, and thereafter, focusing the plurality of input light rays
to converge toward one another until reaching a focus region that
is substantially smaller than the input surface area such that the
input light is concentrated at the focus region.
53. The multi-element inverted off axis optical assembly of claim
52 wherein said first arrangement is positioned for initially
accepting said plurality of input light rays and said optical
assembly includes a second optical arrangement following said first
arrangement to collect the light rays from the first arrangement,
and said first arrangement and said second arrangement are
configured to cooperate in performing said accepting and said
focusing based at least in part on said rotation of said first
arrangement about said axis of rotation.
54. The multi-element inverted off axis optical assembly of claim
53 wherein said second optical arrangement is rotatably fixed such
that the second optical arrangement is not rotatable.
55. The multi element inverted off axis optical assembly of claim
53 wherein said first arrangement and said second arrangement are
fixedly attached to one another for simultaneous rotation such that
said first arrangement and said second optical arrangement
co-rotate together with one another as part of said alignment of
said acceptance direction.
56. The multi element inverted off axis optical assembly of claim
53 wherein said first optical arrangement is configured for bending
the received input light rays for acceptance by said second optical
arrangement, and said second optical arrangement is configured for
collecting and redirecting the bent light to cause said
focusing.
57. The multi-element inverted off axis optical assembly of claim
53 wherein said second arrangement is a CPC.
58. A solar concentrator for collecting and concentrating a
plurality of mutually parallel incoming light rays, said solar
concentrator including the multi-element inverted off axis optical
assembly of claim 52 arranged in a series relationship following an
input arrangement that is aligned on said optical axis of said
inverted off axis optical assembly with the input arrangement with
the input surface of the off axis optical assembly facing towards
the input arrangement, and the inverted off axis optical assembly
and the input arrangement are each configured for selective
rotation to cooperate with one another such that the input
arrangement initially receives said incoming light rays and bends
the incoming light rays to produce intermediate light rays for
acceptance by said inverted off-axis optical assembly such that the
intermediate light rays are at least approximately oriented
antiparallel to said acceptance direction, and said intermediate
light rays serve as said input light rays for said inverted off
axis optical assembly such that the inverted off axis optical
assembly concentrates the intermediate light rays at said focus
region of said inverted off-axis optical assembly.
59. The solar collector of claim 58 including a receiver having a
receiving surface facing towards the off axis optical assembly and
aligned such that the receiving surface at least partially overlaps
said focus region, and said receiver is configured such that at
least some of the concentrated input light is absorbed by said
receiver and converted into power.
60. A method for solar collection, said method comprising:
arranging one or more solar concentrators in an array to position
each of said concentrators in a fixed location with a fixed
alignment in said array and configuring each of said concentrators
for defining (i) an input aperture having an input area such that
the solar collector is positionable to face the input aperture of
each concentrator in a skyward direction with said input aperture
oriented to receive sunlight from the sun, (ii) an input axis of
rotation that extends through said aperture in said skyward
direction, and (iii) a focus region that is substantially smaller
than said input aperture; configuring each of said concentrators
with an optical assembly having at least one optical arrangement
and supporting said optical arrangement for rotation about said
input axis for tracking the sun within a predetermined range of
positions of said sun using no more than said rotation of the
optical arrangement around the input axis such that said rotation
does not change the direction of the aperture from said skyward
direction; and for any specific one of said positions within said
predetermined range of positions, rotatably orienting said optical
arrangement, as at least part of said tracking, to a corresponding
rotational orientation as at least part of concentrating the
received sunlight within said focus region, for subsequent
collection and use as solar energy.
61. A method for focusing collimated light, said method comprising:
configuring an optical IOA arrangement for defining (i) a planar
IOA input surface having an input surface area and (ii) an axis of
rotation that is at least generally perpendicular thereto; and
further configuring said optical IOA arrangement for defining an
acceptance direction as a vector that is characterized by a
predetermined acute acceptance angle with respect to said axis of
rotation such that the axis of rotation and the acceptance
direction define a plane, and which acceptance direction extends in
one fixed azimuthal direction outward from the axis rotation in
said plane such that the optical arrangement is rotatable about the
axis for alignment of the acceptance direction for accepting a
plurality of input light rays, as said collimated light, that are
each at least approximately antiparallel with said vector, such
that said plurality of input light rays transmissively pass through
said optical IOA arrangement and are concentrated by focusing the
plurality of input light rays to converge toward one another until
reaching a focus region that is substantially smaller than the
input surface area.
62. A method for concentrating a plurality of mutually parallel
rays of sunlight, said method comprising: providing an input
optical arrangement for initially receiving a plurality of incoming
rays of sunlight; positioning the optical IOA arrangement of claim
61 in a series relationship following the input arrangement with
the input surface of the optical IOA arrangement facing towards the
input optical arrangement; supporting the optical IOA arrangement
and the input arrangement for selective rotation to cooperate with
one another such that the input optical arrangement re-directs the
incoming rays of sunlight to produce a set of intermediate rays of
sunlight, for acceptance by said optical IOA arrangement, such that
said intermediate rays of light are at least approximately oriented
anti-parallel to said acceptance direction of said optical IOA
arrangement; and accepting said intermediate light rays with said
optical IOA arrangement such that said intermediate light rays
serve as said input light rays for said optical IOA arrangement and
(ii) concentrating the intermediate light rays at said focus region
of said inverted off-axis lens.
Description
RELATED APPLICATION
[0001] The present application claims priority from U.S.
Provisional Patent Application Ser. No. 61/080,554 filed on Jul.
14, 2008, entitled Tracking Concentrator Employing Inverted
Off-Axis Optics, which is incorporated herein by reference in its
entirety.
BACKGROUND
[0002] The present invention is generally related to collecting and
concentrating solar energy and, more particularly, to apparatus and
methods for receiving and concentrating light, for example
sunlight, for subsequent use as some form of power.
[0003] Applicants recognize that in the field of solar energy that
one of the greatest challenges to overcome is the diffuse or low
density nature of the energy from the sun. Roughly, on the Earth's
surface, each kilowatt of energy from the sun is spread over 1
square meter of area. Currently, the most common solar technologies
use the sunlight directly to convert the incoming solar radiation
into heat or electricity. At an energy density of only 1
kilowatt/m.sup.2, (100 milliwatts/cm.sup.2), the energy converter
often must cover large areas in order to gather and convert a
significant amount of energy. Applicants appreciate that the cost
of covering a large area with a traditional energy converter can be
prohibitive. For example, traditional photovoltaic panels often
utilize large areas of expensive semiconductor materials, and
solar-thermal converters often utilize large areas of costly
metals. In each of these examples, high costs may often render such
installations as impractical at least from the standpoint of
cost.
[0004] One approach to address this problem includes the use of
solar concentrators to allow a designer to leverage the energy
converter material through the use of relatively low cost
reflective or refractive material for focusing solar power to be
received by the converter in a more concentrated form as compared
to traditional non-concentrating solar collectors. The use of
concentrators may reduce the amount of expensive converter material
needed in a given application.
[0005] FIG. 1 illustrates a diagrammatic elevation view of a
conventional concentrating solar collector generally indicated by
reference number 10. Solar collector 10 utilizes a parabolic
reflector 13 that defines an input aperture having a circular input
area with diameter D aligned for receiving solar energy carried by
incoming rays sunlight 14. The parabolic reflector is configured
for receiving sunlight and focusing the sunlight within a focus
region 16 that is substantially smaller than the input area. A
receiver 19 is configured for collecting the focused sunlight and
for converting it to another form of energy (not shown). For
example the receiver could include a photovoltaic (PV) cell for
converting the energy directly into electricity, or the receiver
could include a solar liquid heater configured for heating water to
convert the solar energy into thermal energy.
[0006] It is noted that concentrators may be constructed using
refractive material. For example, a Fresnel lens may be used to
reduce the amount of material required. A description of Fresnel
lenses may be found in "Nonimaging Fresnel Lenses: Design and
Performance of Solar Concentrators" by Ralf Leutz and Akio Suzuki;
published by Springer and which is incorporated by reference.
[0007] Attention is now turned to FIG. 2 with ongoing reference to
FIG. 1. FIG. 2 illustrates a diagrammatic elevational view of a
concentrating solar collector, generally indicated by reference
number 20, utilizing a refractive Fresnel lens 23 as a
concentrator, having a circular input area with diameter D, aligned
for receiving incoming rays of sunlight 14 configured for
concentrating the sunlight to a focusing region 16 that is
substantially smaller than the input area. As discussed previously
with reference to solar collector 10, the focused sunlight is
collected by receiver 19 for conversion to a form of energy such as
heat or electricity.
[0008] As will be described at appropriate points hereinafter,
Applicants recognize that while conventional concentrators in some
cases may be advantageous from a cost standpoint, at least as
compared with systems utilizing non-concentrating collectors, they
are not entirely without problems. In some applications, the use of
concentrating collectors may introduce specific challenges that are
unique to concentrating systems. In other some cases the use of
concentration may at least exacerbate problems and/or challenges
that may be associated with conventional non-concentrating solar
collectors such as PV cells.
[0009] The foregoing examples of the related art and limitations
related therewith are intended to be illustrative and not
exclusive. Other limitations of the related art will become
apparent to those of ordinary skill in the art upon a reading of
the specification and a study of the drawings.
SUMMARY
[0010] The following embodiments and aspects thereof are described
and illustrated in conjunction with systems, tools, and methods
which are meant to be exemplary and illustrative, not limiting in
scope. In various embodiments, one or more of the above described
problems have been reduced or eliminated, while other embodiments
are directed to other improvements.
[0011] In general, a solar collector is described. In one
embodiment, one or more solar concentrators are arranged in an
array such that each of the concentrators is in a fixed position in
the array. Each of the concentrators is configured to define (i) an
input aperture having an input area such that the solar collector
is positionable to face the input aperture of each concentrator in
a skyward direction such that the input aperture is oriented to
receive sunlight from the sun, (ii) an input axis of rotation that
extends through the aperture in the skyward direction, and (iii) a
focus region that is substantially smaller than the aperture area.
Each of the concentrators includes an optical assembly having at
least one optical arrangement that is supported for rotation about
the input axis for tracking the sun within a predetermined range of
positions of the sun using no more than the rotation of the optical
arrangement around the input axis such that the rotation does not
change the direction of the aperture from the skyward direction.
Furthermore, for any specific one of the positions within the
predetermined range of positions, the optical arrangement is
rotatably oriented, as at least part of the tracking, at a
corresponding rotational orientation as at least part of
concentrating the received sunlight within the focus region, for
subsequent collection and use as solar energy.
[0012] In one feature, the optical arrangement serves as an input
arrangement for initially receiving the sunlight, and the optical
assembly includes an additional optical arrangement following the
input arrangement. The additional arrangement is positioned to
accept the sunlight from the input arrangement and is configured
for rotation about an additional axis of rotation. The input
arrangement and the additional arrangement are configured to
cooperate with one another in performing the tracking based at
least in part on a predetermined relationship between (i) the
rotation of the input arrangement about the input axis of rotation
and (ii) rotation of the additional arrangement about the
additional axis of rotation to focus the received sunlight into the
focus region.
[0013] In another feature, the input optical arrangement is
configured for bending the received sunlight for acceptance by the
additional optical arrangement, and the additional optical
arrangement is configured for accepting and redirecting the bent
light to cause the focusing.
[0014] In one embodiment of an optical concentrator, an optical
assembly includes one or more optical arrangements. One of the
optical arrangements is an input optical arrangement, and the
optical assembly is configured for defining (i) an input aperture
having an input area for receiving a plurality of input light rays,
(ii) an optical axis passing through a central region within the
input aperture, (iii) a focus region having a surface area that is
substantially smaller than the input area and is located at an
output position along the optical axis offset from the input
aperture such that the optical axis passes through the focus
region, and (iv) a receiving direction defined as a vector that is
characterized by a predetermined acute receiving angle with respect
to the optical axis such that the optical axis and the receiving
direction define a plane. The receiving direction extends in one
azimuthal direction outward from the optical axis in the plane such
that at least the input arrangement is rotatable about the optical
axis for alignment of the receiving direction to receive a
plurality of input light rays that are each at least approximately
antiparallel with the vector. The optical assembly is further
configured for focusing the plurality of input light rays to
converge toward the optical axis until reaching the focus region
such that the input light is concentrated at the focus region.
[0015] In one feature, the focus region includes a given area and,
for at least some of the input light that is characterized by at
least a particular amount of misalignment with the receiving
direction, that input light is rejected by falling outside of the
given area of the focus region.
[0016] In an additional feature, the optical assembly includes an
additional optical arrangement following the input arrangement, and
the input arrangement is configured for bending the received light
rays for acceptance by the additional arrangement. In one
implementation, the additional arrangement can be a CPC configured
to accept the light rays from the input arrangement, and the CPC is
configured to cause the focusing. In another implementation, the
additional arrangement can be an IOA configured to accept the light
rays from the input arrangement, and the IOA is configured to cause
the focusing.
[0017] In one aspect, an inverted off axis lens includes an optical
arrangement having an at least generally planar configuration
defining (i) a planar input surface having an input surface area
and (ii) an axis of rotation that is at least generally
perpendicular thereto. The optical arrangement is configured for
defining an acceptance direction as a vector that is characterized
by a predetermined acute acceptance angle with respect to the axis
of rotation such that the axis of rotation and the acceptance
direction define a plane. The acceptance direction extends in one
fixed azimuthal direction outward from the axis of rotation in the
plane such that the optical arrangement is rotatable about the axis
for alignment of the acceptance direction to accept a plurality of
input light rays that are each at least approximately antiparallel
with the vector. The inverted off axis lens is further configured
for transmissively passing the plurality of input light rays
through the optical arrangement while focusing the plurality of
input light rays to converge toward one another until reaching a
focus region that is substantially smaller than the input surface
area such that the input light is concentrated at the focus
region.
[0018] In one embodiment of a solar concentrator, the solar
concentrator includes the inverted off axis lens arranged in a
series relationship following an input optical arrangement with the
input surface of the off axis lens facing towards the input
arrangement. The inverted off axis lens and the input arrangement
are each configured for selective rotation to cooperate with one
another such that the input arrangement initially receives the
incoming light rays and bends the incoming light rays to produce
intermediate light rays for acceptance by the inverted off-axis
lens such that the intermediate light rays are at least
approximately oriented antiparallel to the acceptance direction.
The inverted off axis lens is aligned for accepting the
intermediate light rays such that the intermediate light rays serve
as the input light rays for the inverted off axis lens and the
inverted off axis lens concentrates the intermediate light rays at
the focus region of the inverted off-axis lens.
[0019] In one embodiment, the inverted off axis lens is a
multi-element inverted off-axis optical assembly including an
optical assembly having two or more optical arrangements. One of
the optical arrangements is a first arrangement that defines (i) an
input aperture having an input area and (ii) an axis of rotation
that is at least generally perpendicular thereto. The optical
arrangements are configured to cooperate with one another for
defining an acceptance direction as a vector that is characterized
by a predetermined acute acceptance angle with respect to the axis
of rotation such that the axis of rotation and the acceptance
direction define a plane. The acceptance direction extends in one
azimuthal direction outward from the axis of rotation in the plane,
and at least the first arrangement is supported for motion that is
limited to rotation about the axis of rotation for alignment of the
acceptance direction to accept the plurality of input light rays
that are each at least approximately anti parallel with the vector.
The optical arrangements are further configured for focusing the
plurality of input light rays to converge toward one another until
reaching a focus region that is substantially smaller than the
input surface area such that the input light is concentrated at the
focus region.
[0020] In addition to the exemplary aspects and embodiments
described above, further aspects and embodiments will become
apparent by reference to the drawings and by study of the following
descriptions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Exemplary embodiments are illustrated in referenced figures
of the drawings. It is intended that the embodiments and figures
disclosed herein are to be illustrative rather than limiting.
[0022] FIG. 1 is a diagrammatic view, in elevation, of a reflection
type prior art solar concentrator and its operation.
[0023] FIG. 2 is a diagrammatic view, in elevation, of a refractive
type prior art solar concentrator and its operation.
[0024] FIG. 3 is a diagrammatic perspective view, in elevation, of
one embodiment of an optical concentrator produced according to the
present disclosure, showing components of the concentrator and
aspects of its operation.
[0025] FIG. 4 is a diagrammatic view, in elevation, illustrating
the operation of one example of a conventional off-axis
concentrating lens.
[0026] FIG. 5 is a diagrammatic perspective view of one embodiment
of an Inverted Off-Axis lens (IOA), shown here to illustrate the
components of this embodiment of the IOA and its operation with
respect to bending and focusing input light.
[0027] FIG. 6 is a diagrammatic view, in perspective, shown here to
illustrate a number of aspects associated with rotational
orientation of the IOA.
[0028] FIGS. 7A and 7B are diagrammatic views, in perspective,
showing a single IOA solar collector system oriented for use in the
morning and afternoon, respectively, during a given day.
[0029] FIG. 8 is a diagrammatic view, in elevation, of one
embodiment of a bender shown here to illustrate the operation of
the bender with respect to receiving a plurality incoming rays of
light.
[0030] FIG. 9 is a diagrammatic view, in elevation, of one
embodiment of a bender shown here to illustrate the
three-dimensional nature of the bending action of the bender.
[0031] FIG. 10 is a diagrammatic perspective view, shown here to
illustrate the operation of a concentrator that is made up of a
bender combined with an IOA in accordance with the present
disclosure.
[0032] FIG. 11 is a diagrammatic view, in elevation, illustrating
one embodiment of a Bi-Rotational concentrator or BRIC and its
operation in the non-limiting instance of a particular orientation
of incoming light.
[0033] FIG. 12 is a diagrammatic perspective view illustrating a
bender and aspects of its operation with respect to incoming
light.
[0034] FIGS. 13A and 13B are diagrammatic views each illustrating
the field of view of the sky in relation to the sun for different
levels of concentration for a given track of the sun in each figure
for purposes of comparison.
[0035] FIG. 14 is a diagrammatic view, illustrating a field of view
that is stretched to advantageously match the sun's path.
[0036] FIG. 15 is a diagrammatic view, in elevation, illustrating a
linear concentrator configuration employing an array of two IOA's
configured for receiving input rays of light 14 and concentrating
the light along the axis of a linear target.
[0037] FIGS. 16A and 16B are perspective views of conventional two
axis solar collectors, shown here to illustrate details of their
structures.
[0038] FIGS. 17A-C are diagrammatic representations illustrating
three different fields of view each of which may be associated with
a different type of solar collector or concentrator.
[0039] FIG. 18A is a diagrammatic side view, in elevation, showing
one embodiment of an array of two concentrators, shown here to
illustrate details with respect to the operation of the array.
[0040] FIG. 18B is a diagrammatic end view, in elevation, showing
the concentrator array embodiment of FIG. 18A.
[0041] FIG. 18C is a diagrammatic plan view showing the
concentrator array embodiment of FIGS. 18A and 18B.
[0042] FIG. 19A is a diagrammatic side view, in elevation,
illustrating one embodiment of a split cell system having four
concentrators, shown here to illustrate details with respect to the
operation of the system.
[0043] FIG. 19B is a diagrammatic plan view still further
illustrating the split cell system of FIG. 19A, shown here to
illustrate still further details with respect to its operation.
[0044] FIG. 20A is a diagrammatic perspective view of a bender
according to the present disclosure, showing details with respect
to its operation.
[0045] FIG. 20B is a diagrammatic perspective view of one
embodiment of an IOA according to the present disclosure, showing
details with respect to its construction and operation.
[0046] FIGS. 21A and 21B are diagrammatic perspective views showing
yet another embodiment of an IOA that may be utilized for shaping
of the focus region
[0047] FIG. 22A is a diagrammatic perspective view of a refractive
arrangement for use with an IOA to further focus a redirected wedge
of light.
[0048] FIG. 22B is a diagrammatic perspective view of a reflective
arrangement for use with an IOA to further focus a redirected wedge
of light.
[0049] FIGS. 23A and 23B are diagrammatic views, in elevation,
showing different views of one embodiment of a concentrator taken
from orthogonal viewpoints to illustrate details of the operation
of the concentrator in different coordinate axis planes for a
special case wherein the input light is handled by the concentrator
in the planes of these figures.
[0050] FIG. 23C is a diagrammatic plan view of the concentrator of
FIGS. 23A and 23B, shown here to illustrate further details of the
operation of the concentrator.
[0051] FIGS. 24A and 24B are a diagrammatic views, in elevation,
showing different views of the concentrator of FIGS. 23A-23C taken
from orthogonal viewpoints to illustrate details of the operation
of the concentrator in different coordinate axis planes for an
exemplary case in which light enters skewed to the coordinate axes
planes.
[0052] FIG. 24C is a diagrammatic plan view of the concentrator of
FIGS. 24A and 24B, illustrating a projection of components of the
light onto a horizontal coordinate axis plane after the light
enters the concentrator.
[0053] FIG. 25A is a diagrammatic view, in elevation, illustrating
one embodiment of a bender, shown here to illustrate details with
respect to the structure and operation of the bender.
[0054] FIG. 25B is diagrammatic view, in elevation, illustrating
the bender of FIG. 25A, shown here to illustrate further details
with respect to shading which is dependent upon the incidence angle
of incoming light.
[0055] FIG. 26A is a diagrammatic view, in elevation, illustrating
one embodiment of a concentrator in which a multi-element IOA is
used.
[0056] FIG. 26B is a diagrammatic view, in elevation, illustrating
another embodiment of a concentrator which, in this example,
utilizes a single element IOA.
[0057] FIG. 26C is a diagrammatic view, in elevation illustrating
still another embodiment of a concentrator which, in this example,
utilizes an input optical arrangement and an additional optical
arrangement to cooperate for purposes of causing the input light to
be concentrated at a focus region.
[0058] FIG. 27 is a diagrammatic view illustrating coverage of the
sky, shown as a rectangle, that is traversed by the sun according
to annual and daily variations for a particular bender and IOA.
[0059] FIG. 28 illustrates details of the operation of a bender or
IOA with respect to certain variations in the configuration of its
structure.
[0060] FIGS. 29A and 29B are further enlarged views which
illustrate details of the operation of the bender or IOA of FIG. 28
with respect to sidewall slope (FIG. 29A) and apex rounding (FIG.
29B).
[0061] FIG. 30 is a diagrammatic view illustrating coverage of the
sky, shown as a rectangle, that is traversed by the sun according
to annual and daily variations, shown here to illustrate the effect
of variation in prism configuration in terms of loss of the field
of view for a particular bender and IOA.
[0062] FIG. 31 is a diagrammatic view of the sky that is traversed
by the sun showing annual and daily variation in the position of
the sun and shown here to illustrate a tradeoff between adding sky
coverage in the morning and evening with losing sky coverage for
specific days around noon.
[0063] FIG. 32 is a diagrammatic view of the sky that is traversed
by the sun showing annual and daily variation in the position of
the sun and shown here to facilitate a discussion of confined
ranges of bender and IOA rotation versus maintaining tracking
capability.
[0064] FIG. 33A is a diagrammatic elevational view of one
embodiment of a concentrator wherein the bender is tilted with
respect to an IOA.
[0065] FIG. 33B is a diagrammatic plan view of the concentrator of
FIG. 33A, shown here to illustrate further details of its structure
and operation.
[0066] FIG. 34 is a diagrammatic elevational view of another
embodiment of a concentrator having a tilted bender wherein the
bender and IOA can be controlled by a filament.
[0067] FIG. 35 is a diagrammatic elevational view of one embodiment
of a concentrator having a bender that is linked through a hub
attached with the IOA such that the bender is rotated on the
hub.
[0068] FIG. 36 is a diagrammatic view, in elevation, of one
embodiment of a concentrator showing a ramp method for tilting the
bender relative to the IOA.
[0069] FIG. 37 is a diagrammatic plan view which illustrates one
embodiment of an array of four concentrators that are rotatably
coupled with one another through a drive mechanism to cause the
benders to co-rotate about their associated axes using a flexible
drive member.
[0070] FIG. 38 is a diagrammatic plan view which illustrates
another embodiment of an array of four concentrators that are
rotatably coupled with one another through a drive mechanism to
cause the benders to co-rotate about their associated axes using a
geared type arrangement.
[0071] FIG. 39A is a diagrammatic plan view showing a solar
collector constructed as a panel enclosure housing a concentrator
array.
[0072] FIG. 39B is a diagrammatic elevational view of the solar
collector of FIG. 39A, shown here to illustrate further details of
its structure.
[0073] FIG. 40 is a diagrammatic plan view of one embodiment of a
concentrator having a bender, an IOA 32, and a concentrating
arrangement, shown here to illustrate details of its structure.
[0074] FIG. 41 is diagrammatic elevational view of a concentration
which utilizes a multi-element IOA.
DETAILED DESCRIPTION
[0075] The following description is presented to enable one of
ordinary skill in the art to make and use the invention and is
provided in the context of a patent application and its
requirements. Various modifications to the described embodiments
will be readily apparent to those skilled in the art and the
generic principles taught herein may be applied to other
embodiments. Thus, the present invention is not intended to be
limited to the embodiment shown, but is to be accorded the widest
scope consistent with the principles and features described herein
including modifications and equivalents, as defined within the
scope of the appended claims. It is noted that the drawings are not
to scale and are diagrammatic in nature in a way that is thought to
best illustrate features of interest. Descriptive terminology, such
as, for example, upper/lower, right/left, clockwise and
counter-clockwise and the like may be adopted for purposes of
enhancing the reader's understanding, with respect to the various
views provided in the figures, and is in no way intended to be
limiting.
[0076] As described previously in the background section,
Applicants recognize that while conventional concentrators in some
cases may be advantageous from a cost standpoint, at least as
compared with systems utilizing non-concentrating collectors,
conventional concentrators are not entirely without problems. In
some cases the use of concentrators can exacerbate problems and/or
challenges that may be associated with conventional
non-concentrating solar collectors such as PV cells. For example,
in photovoltaic panels, the efficiency of the PV cells generally
decreases with increasing temperature. While this is a common
concern in the design of non-concentrating panels heating is of yet
greater concern when concentrators are used to increase the
incoming light intensity by 10.times. or 100.times. or higher, and
under these circumstances management of heat-related factors can
become a serious challenge. In other cases, the use of
concentrating collectors may introduce specific challenges that are
commonly associated with concentrating systems. For example, many
concentrators require the light to enter with a certain angular
accuracy which may require that the concentrator move in order to
"track" in relation to a light source such as the sun. Conventional
tracking systems can be both costly and complex, and in some cases
the cost of a tracking system may substantially undermine cost
savings that may otherwise be enabled by the use of
concentration.
[0077] Applicants describe hereinafter a number of solar collectors
including optical concentrators that advantageously utilize
internal rotational motion for tracking the light arriving from a
movable source and concentrating the light onto a target such as a
receiver. The optical concentrators of the present disclosure cause
input light to pass through a series of one or more optical
arrangements, and typically at least one of the arrangements is
supported for rotation. In several examples described hereinafter,
at least one of the rotating optical elements can be configured as
an inverted off-axis lens arrangement that is configured for
rotation as at least part of allowing and/or causing the system to
track a moving light source. For example, this disclosure details a
number of solar collectors that utilize solar concentrators that
are configured to define a receiving direction that is adjustable,
for tracking motion of the sun, based on rotational orientation of
one or more optical arrangements so that, as the sun changes
position, the concentrated light exiting the system can be made to
continuously illuminate the receiver.
[0078] Turning now to the figures, wherein like components are
designated by like reference numbers whenever practical, attention
is now directed to FIG. 3 which is a diagrammatic perspective view,
in elevation, of one embodiment, generally indicated by reference
number 26, of an optical concentrator including an inverted off
axis lens arrangement 32 in a series relationship following an
optical bender arrangement 33. This bender arrangement serves as an
input arrangement defining an input aperture 31 having an input
surface area, and is configured for initially receiving incoming
rays of sunlight 14 and for bending the incoming rays of sunlight
to produce intermediate light rays 39 for acceptance by inverted
off-axis lens arrangement 32 such that the intermediate light rays
serve as input rays of light with respect to the IOA (Inverted
Off-Axis lens). The inverted off axis lens arrangement
transmissively passes the intermediate light rays such that these
rays converge towards one another until reaching a focus region 41
that is substantially smaller than the input surface area.
[0079] Each of the optical arrangements of optical concentrator 26
can be configured in a relatively flat, thin and generally planar
configuration that may be regarded as being analogous to a that of
a Fresnel lens, such that the combination of the two arrangements
may be implemented in a correspondingly flat and thin shape.
Concentrator 26 defines a receiving direction 34 for receiving the
incoming rays of sunlight 14 at an input orientation such that the
incoming rays of sunlight are anti-parallel therewith, while the
bender and the inverted off axis lens arrangement cooperate with
one another such that the optical concentrator receives and
concentrates the received light onto focus region 41. The bender
arrangement and the inverted off axis lens may be closely spaced
such that a substantial portion of the intermediate rays of light
leaving the bender arrangement will be accepted and concentrated by
the inverted off axis lens arrangement. As will be described in
detail at appropriate points hereinafter, the optical arrangements
including bender arrangement 33 and inverted off-axis lens
arrangement 32 can be rotatably oriented relative to one another
and with respect to the incoming rays of sunlight, so that the
light exiting the bender arrangement enters the inverted off-axis
lens at an angle appropriate to cause the inverted off axis lens to
accept and concentrate focus the intermediate light rays such that
they converge toward one another until reaching focal region 41. As
the direction of the incoming rays of sunlight changes, for example
as a result of motion of the sun, the two optical elements 32 and
33 can be rotated for tracking the motion of the sun so that a
correctly adjusted rotational relationship between them and
relative to the incoming rays of sunlight is maintained for
concentrated illumination of the focus region.
[0080] The embodiment of concentrator 26 illustrated in FIG. 3 can
be referred to as a Bi-Rotational Inverted off-axis Concentrator
(BRIC), and in many applications is well suited for use in a fixed
or movable solar panel for conversion of sunlight to a form of
energy such as thermal or electrical power. Applicants note that in
the case of a fixed solar panel, having an array of one or more
optical concentrators 26, the sun typically exhibits daily motion
relative to panel, for example between sunrise and sunset, as well
as seasonal motion, for example from winter to summer. As the sun's
position changes with respect to the panel, throughout a given day
and throughout seasonal variations, the direction of the incoming
rays of sunlight 14 entering the BRIC changes. As will be described
in greater detail hereinafter, the BRIC can track this direction
change by rotating the bender and the inverted off-axis lens such
that they cooperate with one another to continuously adjust the
orientation of receiving direction 34 to track the sun for
maintaining illumination of focal region 41. It is noted that a
receiver 19 may be introduced for converting the focused light into
a form of energy. For example a receiving surface of a PV cell may
be aligned to overlap the focal region such that a portion of the
focused light is converted by the PV cell into electricity.
[0081] Applicants recognize that in many applications, including a
number of solar collection applications, the use of a BRIC in a
solar PV panel provides a number of sweeping advantages as compared
to conventional solar panels. For example, as described above, a
concentrator can be configured such that the focusing and
concentrating of incoming rays of sunlight allows for the use of a
receiver (such as PV cell) having an area that is substantially
smaller than the input area of concentrator. As compared to
conventional non-concentrating PV cells, the systems and method for
tracking the sun and concentrating sunlight, as described above and
hereinafter throughout this application, can be employed for
reducing the required surface area of relatively expensive PV cells
required for a given application and therefore reduce the cost of a
solar collector at least as compared to a conventional panel.
Furthermore, the relatively flat and thin shape of a BRIC allows it
to be incorporated inside a panel enclosure having a relatively low
profile as compared to the profiles typically associated with
conventional concentrator systems. This may allow a concentrating
solar PV system to be packaged in an enclosure having a shape and
size that is based on conventional standards, and solar panels
constructed in accordance with this disclosure may be compatible
with existing installation infrastructures that have been
developed, for example, for the conventional panels including
non-concentrating solar PV panels.
[0082] With ongoing reference to FIG. 3, it is again noted that the
bender and the inverted off-axis lens of solar concentrator 26 are
both supported for rotation. In addition, a receiver 19 may be
positioned to provide a receiving surface as a stationary target
such that the receiving surface overlaps the focal region, and the
receiver may be configured such that at least some of the
concentrated light is absorbed by the receiver and converted to a
form of energy such as, for example, electrical or thermal power.
It is noted that in the context of this disclosure the phrase
"stationary target" refers to the fact that the target does not
rotate or otherwise move relative to other parts of the panel. If
the whole panel is moving to track the sun, then the BRIC will act
to concentrate the light on a stationary target attached to the
moving panel, and the target may remain stationary relative to the
panel enclosure, even in cases where the panel may be in motion. In
particular, as one example, an array of one or more solar
concentrators 26 may be supported in fixed positions in a
supporting structure (such as a solar panel enclosure) and relative
to one another, and the bender and the inverted off axis lens may
be supported for rotation as described above with reference to FIG.
3, while the receiver may be fixedly supported in relation to its
concentrator such that it is not rotated or otherwise moved at
least with respect to the supporting structure.
[0083] It is noted, as will be described in greater detail
immediately hereinafter, that the optical properties of inverted
off-axis lens 32 differs substantially as compared to the optical
properties of conventional off-axis lenses.
[0084] Attention is now directed to FIG. 4 which is a diagrammatic
view in elevation illustrating the operation of one example of a
conventional off-axis concentrating lens 44, which can be
implemented in a number of configurations including but not limited
to (i) a continuous surface lens or (ii) as a Fresnel lens. In this
example lens 44 is configured to define an optical axis 47, and to
receive input rays of collimated light 45 such that the collimated
light enters lens 44 in a parallel orientation with optical axis
47. Off-axis lens 44 is further configured to focus the light onto
an off-axis focus region 41 that is in an off-axis location such
that the focus region does not lie on optical axis 47. It is noted
that based on well known conventions, the designation of this lens
as an "off-axis" lens is premised on off-axis positioning of the
focal region as illustrated in FIG. 4.
[0085] It is further noted with reference to FIG. 4 and for
purposes of the remainder of this application, the term "optical
axis" refers to an at least generally central path along which
light tends to propagate through an optical system. In many
conventional optical systems, such as imaging systems, an optical
axis may be defined as a line through space around which the system
is rotationally symmetric. This is not necessarily the case in the
examples discussed throughout this disclosure, and it is further
noted that in order to perform their intended functions as
described herein, both benders as well as inverted off axis lenses
generally can be configured in a physically asymmetric manner at
least with regard to specific structural and/or optical material
properties. In this regard, it may be appreciated by one of
ordinary skill in the art that an optical axis of either a bender
or an inverted off axis lens can be associated with optical
properties of the arrangement and may not necessarily be defined
based on any apparent physical symmetry, incidental or otherwise.
Returning to discussions regarding nomenclature, it is noted that
the term `lens` will refer, hereinafter and throughout this
disclosure, to an optical arrangement that can modify the light
rays as they pass through the element. The modification, including
bending of the direction of the light, may or may not be uniform
over the surface of a given lens. Furthermore the modification of
light by a given lens may also affect the convergence or divergence
of the rays as the rays transmissively pass through the lens.
[0086] As will be described in detail immediately hereinafter, an
inverted off-axis lens defines an optical axis and is configured
such that a focal region of the inverted off-axis lens is on the
optical axis while the incoming light is entering in an off-axis
orientation. In particular, an inverted off-axis lens is configured
to accept incoming light at an angle relative to the optical axis.
Based on designations presented herein and used throughout the
remainder of this application, the use of the term "inverted"
refers to an inversion of the functional operation of an inverted
off-axis lens as compared with a conventional off-axis lens.
[0087] Summarizing with respect to the discussion above, a
conventional off-axis lens is configured to accept incoming light
that is on-axis while the focal region is generally positioned at
an off-axis location. By contrast, an inverted off-axis lens is
configured to accept incoming light that is incident at a skewed
angle with respect to the optical axis, and the focal region is
located on the axis.
[0088] It is noted that the term `Inverted Off-Axis lens` may be
referred to throughout this overall disclosure and in the appended
claims by the acronym `IOA`. With respect to this nomenclature, it
is further noted that the IOA may be an individual lens, consisting
of one optical element, or it may be configured as an optical
arrangement having two or more optical elements and/or
components.
[0089] Resuming the discussion, the focal region of an IOA may be
positioned along the optical axis such that the incoming light
arrives at an angle and is then bent and focused into focus region
41. As described above, and as will be described in greater detail
immediately hereinafter, an IOA may be regarded as performing two
optical functions: (i) bending the incoming light to direct the
light along the optical axis and towards the focal region, and (ii)
focusing the light for convergence onto the focal region.
[0090] Attention is now directed to FIG. 5, which is a diagrammatic
perspective view illustrating bending and focusing properties of
one embodiment of IOA 32. The IOA defines an input surface 54,
having an input surface area, and is configured for accepting a
plurality of parallel input rays 56, and for bending and focusing
the plurality of input light rays onto focal region 41. The IOA is
further configured for defining an acceptance direction 57
represented in FIG. 5 as a vector {right arrow over (A)} that
extends outward from the optical axis in one fixed azimuthal
direction having a fixed orientation with respect to the IOA such
that the optical axis and the vector define a plane. The IOA is
rotatable for orientation of acceptance direction 57 to accept the
plurality of input light rays such that the rays are each at least
approximately anti-parallel with the acceptance direction 57, and
the IOA is yet further configured for transmissively passing the
plurality of input light rays while focusing the light rays to
converge toward one another until reaching a focus region that is
substantially smaller than the input surface area.
[0091] While certain aspects of the immediately following points
are to be discussed in further detail hereinafter, it is to be
understood that (i) input rays of light 56 entering the IOA in the
direction that is at least approximately anti-parallel to the
acceptance direction are directed to the focal region, (ii) the
acceptance direction 57 is a physical characteristic of the IOA
that is structurally defined by the IOA itself, and (iii) any
misaligned input rays of light (not shown), entering the IOA in a
substantially misaligned direction that is sufficiently skewed with
respect to the acceptance direction, will be redirected by the IOA
to diverge away from the optical axis such that they pass outside
of the focal region, and increased misalignment will generally
result in correspondingly increased divergence of the bent light
way from the focus region.
[0092] With ongoing reference to FIG. 5, it is noted that there are
significant functional differences between the focal length of an
IOA as compared to a conventional focal length associated with a
conventional lens, and that for a conventional lens having a focal
length, collimated light typically must enter the lens parallel to
an optical axis of the lens in order to be directed to a focal
region that is removed from the lens by a distance corresponding to
the focal length. In cases where the light enters the conventional
lens at an angle that is skewed relative to the optical axis of the
conventional lens, the light will be typically directed off axis
and away from the focal region. By contrast, the IOA accepts
collimated light at a skewed angle relative to the optical axis,
and directs the light towards a focal region that is located along
the optical axis. Applicants recognize, as will be described in
greater detail hereinafter, that at least for use in solar
concentrators, the inverted off axis characteristics of the IOA, as
described immediately above and throughout the disclosure, results
in a number of sweeping advantages at least with respect to
applications relating to solar collectors having solar
concentrators that include one or more IOAs.
[0093] It should be appreciated by a person of ordinary skill in
the art, having this overall disclosure in hand, that the presence
of a unique acceptance direction, in accordance with the
immediately foregoing descriptions, implies that there is at least
some kind of rotational asymmetry that should be inherently present
in the physical structure and/or material properties of the IOA,
and in an absence of this form of asymmetry in the structure of the
IOA, it is not reasonably possible for the IOA to define a distinct
acceptance vector in a manner consistent with the descriptions
herein. For example, in one embodiment that will be described in
detail at appropriate points hereinafter, the IOA may include
prisms that are integrally formed therewith, and the prisms may be
oriented in parallel with one another along a reference direction
(not show in FIG. 5) and configured to cause the aforementioned
bending of the input rays of light. Prisms oriented in this manner
provide one example for satisfying the requirement for rotational
asymmetry in the IOA.
[0094] While acceptance direction 57 (represented in FIG. 5 as
vector {right arrow over (A)}) is defined by structural and/or
optical properties of the IOA, and therefore remains fixed in the
frame of reference of the IOA, it is to be understood that relative
to earth's frame of reference the acceptance direction only changes
if and when the IOA itself changes position. For example, when the
IOA is rotated, the acceptance direction rotates accordingly to
sweepingly define a surface of a cone, as will be described
immediately hereinafter. In view of the immediately foregoing
points, and for purposes of descriptive clarity, it is useful to
define an appropriate set of coordinates for describing the
acceptance direction as the IOA changes position, rotatably or
otherwise. In this regard, it is to be understood that the
acceptance direction of the IOA can be regarded as a 3D (three
dimensional) vector in the context of conventional three
dimensional space. In accordance with well known principles of
analytic geometry, any 3D vector that is solely utilized for
describing a direction in space can be designated to have an
arbitrary magnitude (most commonly 1, or "unity") and can be
henceforth designated using only two angular coordinates. The
acceptance direction of an IOA can be represented in accordance
with the standard practices with a fixed zenith angle .xi. (the
angle between vector {right arrow over (A)} and the optical axis),
and a fixed direction relative to the IOA represented in FIG. 5 as
vector D which is a projection 64 of vector {right arrow over (A)}
onto input surface 54. Using this system of coordinates in
accordance with the foregoing conventions, acceptance direction 57
(represented in FIG. 5 as vector {right arrow over (A)}) maintains
the aforedescribed constant magnitude of unity and the
aforedescribed constant angle .xi.. It is therefore clear that as
long as optical axis 47 remains fixed, the orientation in space of
acceptance direction 57, rotatably changing or not, can be fully
specified by angle .phi. with respect to reference axis 61. Since
the acceptance direction 57 is itself fixed with respect to the
frame of reference of the IOA, then it is equally appropriate to
describe the rotational orientation of the IOA according to the
same nomenclature, and the statement that the IOA is azimuthally
oriented with angle .phi. can be reasonably considered as being
synonymous with a statement that the acceptance direction is
azimuthally oriented with angle .phi..
[0095] It is further noted that the projection 64 (designated in
FIG. 5 as vector D) of acceptance direction 57 onto IOA surface 54
is also fixed with respect to the IOA, and is also oriented at
angle .phi. relative to reference direction 61. As one additional
aspect of nomenclature that may be used throughout this disclosure,
projection 64 is to be considered as a direction through space in
which the IOA is "pointing". Carrying this terminology one step
further, in order for the IOA to accept input rays of light 56, for
bending and concentrating, IOA 32 is pointed in an opposing
orientation as compared to the input rays of light such that a
projection of the input rays (not shown) onto surface 54 is
anti-parallel with projection 64 (represented in FIG. 5 as vector
D).
[0096] There are two conditions that can be met in order for input
rays 56 to be aligned anti-parallel with acceptance vector 57
thereby causing the IOA to accept the input rays of light for
bending and concentrating onto focus region 41, and these two
conditions may at times be designated hereinafter and throughout
this disclosure according to the following shorthand notation: (i)
the IOA is rotatably oriented to be pointed towards the input rays
of light, and (ii) the input rays of light enter the IOA at the
zenith angle .xi. of the IOA. Foreshortening the terminology yet
further, for use in subsequent descriptions, input rays of light 56
and IOA 32 may be regarded as being "aligned with one another" at
times when these conditions are met, and hereinafter throughout
this disclosure a statement that the IOA and the input rays of
light are aligned with one another is to be interpreted as stating
that these two conditions have been met at least to a reasonable
approximation. For purposes of further clarification, it is noted
that a statement that the IOA is pointed towards the input rays of
light, is only to be interpreted as stating that the first of the
two conditions has been met, and under these circumstances, the IOA
and the input rays may or may not be aligned with one another. For
purposes of descriptive clarity, two examples resulting in
misalignment will be discussed immediately hereinafter.
[0097] As a first example (not shown) resulting in misalignment, if
the IOA were to be rotated away from the appropriate rotational
orientation that is illustrated in FIG. 5, than the input rays of
light and the acceptance angle would become skewed relative to one
another, thus resulting in a misaligned condition such that the IOA
and the input rays of light are not aligned with one another.
[0098] As another example resulting in misalignment, if the IOA in
FIG. 5 were to be tilted, for example by pivoting the IOA about
reference direction 61, a sufficiently large tilt would result in a
mismatch (not shown) between the acceptance direction and the input
rays of light, and input rays of light and the acceptance direction
would be correspondingly skewed with respect to one another,
resulting in yet another condition such that the IOA and the input
rays are misaligned relative to one another.
[0099] Attention is now turned to FIG. 6 with ongoing reference to
FIG. 5, the former of which is a diagrammatic perspective view of
IOA 32 illustrating a number of aspects associated with rotational
orientation of the IOA. As described above in reference to FIG. 5,
the acceptance direction (represented in FIG. 5 as vector {right
arrow over (A)}) is defined by the IOA based on structural and/or
optical material properties of the IOA, and therefore acceptance
direction 57 remains stationary in a frame of reference of the IOA.
Therefore, as the IOA is rotated about its axis of rotation, the
acceptance direction may be regarded as sweeping a surface 60 of a
cone, indicated in FIG. 6 with dotted lines and hereinafter
referred to as an acceptance cone, associated with the IOA. As will
be described immediately hereinafter, the acceptance cone serves as
a conceptual and/or visual aid that will be referenced hereinafter
in the context of descriptions relating to performance of the IOA
especially in regard to cooperation between the IOA and other
optical arrangements. Employing terminology that is consistent with
the description of FIG. 5, it is to be understood that any input
ray of light 56 propagating toward the IOA, and having a direction
that lies on the surface 60 of the acceptance cone, can be accepted
by the IOA for bending and focusing, provided that the IOA is
rotated to an appropriate rotational orientation for accepting that
ray. In other words, adopting the shorthand terminology set used
previously in reference to FIG. 5, if (i) the input ray of light 56
lies on the acceptance cone of the IOA, and (ii) the IOA is
rotatably oriented such that the IOA is pointed toward the incoming
rays light, then the IOA is appropriately oriented to accept and
concentrate the input rays of light. By contrast, any misaligned
ray that has a substantially different direction that does not at
least approximately lie on the acceptance cone will be misaligned
with the IOA regardless of the specific rotational orientation of
the IOA.
[0100] As described above in reference to FIG. 5, the acceptance
direction, remains fixed with respect to the IOA, and motion of the
IOA that is restricted to rotation about one axis (such as the
optical axis of the IOA) can be described in the earth's frame of
reference and based on well-established conventions of analytic
geometry, with a zenith angle (represented in FIGS. 5 and 6 as
.xi.) and azimuth angle .phi.. As described previously, in cases
where the motion of a given IOA is solely limited to rotation about
the optical axis of the IOA, the zenith angle .xi. remains fixed
with respect to the IOA even while the IOA rotates, and therefore
the acceptance cone is characterized by zenith angle .xi..
[0101] As described above in reference to FIG. 3, and as will be
described in greater detail at various points throughout the
remainder of this disclosure, Applicants recognize that IOA 32 can
be combined with additional optical arrangements for continuously
tracking the sun throughout much of the day in a highly
advantageous manner that is limited to rotation of the optical
arrangements. It is noted however, that the mere use of an IOA does
not in itself insure the existence of a continuous tracking
capability, and that a single IOA configured solely for rotational
motion while being held in an otherwise fixed orientation, cannot
be utilized by itself (in an absence of additional optical
arrangements) for tracking the sun continuously throughout the day.
Nevertheless, for purposes of enhancing the readers understanding,
the use of a single IOA will be described below, in the context of
a solar collector system.
[0102] Attention is now directed to FIGS. 7A and 7B, which are
diagrammatic perspective views depicting a single IOA solar
collector system 80 positioned for use at two different times
(morning and afternoon) during a given day. The solar collector
illustrated in FIGS. 7A and 7B is in a fixed position, with a fixed
alignment, and includes an IOA 32 supported for rotation about an
optical axis 47. The IOA acts as a solar concentrator and is
configured such that input surface 54 of the IOA defines an input
aperture having an input area such that the solar collector is
positionable such that the input aperture faces in a skyward
direction such that the input aperture is oriented to receive
sunlight from the sun (the sun being indicated by reference number
73). The solar concentrator is further configured to define optical
axis 47 as extending through the aperture in the skyward direction,
and the solar concentrator is yet further configured to define a
focus region 41 that is substantially smaller than the aperture
area. The solar collector is in a fixed position with fixed
alignment, and for each of the morning and afternoon positions, as
will be described in detail immediately hereinafter, the IOA can be
rotatably oriented for receiving and concentrating received rays of
sunlight 14.
[0103] As described above, concentrator 80 is configured such that
rotation of the IOA lens about axis 47 rotates acceptance direction
57 thereby pointing the IOA in varying directions. FIGS. 7A and 7B
illustrate this principle by depicting a single concentrating IOA
lens being utilized as a solar concentrator. However, it is noted
that this solar concentrator functions ideally only twice per day:
once in the morning and once in the afternoon, as illustrated in
FIGS. 7A and 7B and as will be described immediately
hereinafter.
[0104] During the morning the solar concentrator will function
properly only at a particular time of the morning when the morning
sun is at a position 86 such that the rays of sunlight 14 are
aligned anti-parallel with acceptance direction 57, at which time
IOA 32 bends and focuses the rays sunlight toward focal region 41.
At other times during the morning, the IOA can be pointed towards
the incoming rays of sunlight, but the incoming rays of sunlight at
these other times nevertheless do not enter the IOA at the zenith
angle .xi. of the IOA, and therefore the IOA is misaligned with
respect to the incoming rays of sunlight.
[0105] Similarly, during the afternoon, the solar concentrator will
function properly only at a particular time of the afternoon when
the afternoon sun is at a position 86' such that the incoming rays
of sunlight 14 are aligned anti-parallel with acceptance direction
57, at which time IOA 51 bends and focuses the rays sunlight toward
focal region 41. At other times during the afternoon, the IOA can
be pointed towards the incoming rays of sunlight, but the incoming
rays of sunlight at these other times nevertheless do not enter the
IAO at the zenith angle .xi. of the IOA.
[0106] It is noted that single IOA tracker 80 can be used
successfully, for continuously tracking the sun throughout a
substantial portion of the day, only when utilized with an
additional 1- or 2-axis tracking system. One example of such an
arrangement, to be described in detail in a subsequent portion of
this disclosure, is a solar panel enclosure supporting an array of
one or more single-IOA trackers 80 (each tracker has one single
IOA) each of which trackers is attached to an external mechanical
tracker mechanism. In many conventional applications, a mechanical
tracker mechanism may be configured to move a conventional solar
panel for continuously pointing the panel such that the panel faces
directly towards the sun. In the arrangement under discussion,
having an array of single-IOA concentrators, a mechanical tracker
may be configured for facing the panel toward the sun within a
predetermined tolerance based on the bend angle of the IOA, and the
IOA can be rotated to correct for any mechanical misalignment
associated with the mechanical tracker.
[0107] Having described the basic operating principles of an IOA,
and having illustrated the use of a single-IOA solar concentrator
having only limited tracking abilities, the description is now
directed to optical properties and operating principles relating to
an optical arrangement that is configured as a bender. It is first
noted that a bender may be considered as being perhaps somewhat
analogous to an IOA to the extent that a bender shares certain
characteristics that are at least loosely analogous with associated
characteristics of an IOA. For example, as one analogous
characteristic, a bender receives incoming rays of light and
redirects the incoming rays by bending the rays through a given
angle and in a given direction with respect the bender and relative
to the incoming rays, such that the bender redirects the incoming
rays of light in a way that changes depending on the rotational
orientation of the bender relative to an orientation of the
incoming rays of light. It is noted however that a bender is not
configured to cause any focusing of the incoming rays of light.
Hence the name "bender". In this regard, a bender may perhaps be
considered as somewhat analogous to a limited special case of a
uniquely specified IOA-like device that has an infinite focal
length. While this consideration is regarded by Applicants as being
more or less a curiosity, the analogy may be nevertheless useful
for illustrative and descriptive purposes at least for helping to
establish consistent terminology for distinguishing benders from
IOA's while putting forth various descriptions relating to
cooperation between these two distinct classes of arrangements.
[0108] Having introduced a number of general considerations
relating to benders, attention is now directed to FIG. 8 which is a
diagrammatic perspective view illustrating the operation of a
bender 33 as it receives a plurality incoming rays of light 14. As
depicted in FIG. 8, and as will be described in greater detail
hereinafter, all of the rays of light are parallel with one
another, and bender 33 bends the rays in a way that may depend in
part on the rotational orientation of the bender with respect to
the incoming rays of light. Furthermore, unlike the IOA, the amount
and direction of bending typically does not depend on where a given
ray strikes the bender, and therefore each one of the plurality of
incoming parallel rays of light is bent in the same way as the
others such that the bender produces a plurality of output rays of
light 92 that are all parallel with one another.
[0109] It is noted, as described immediately above, that the
parallel relationship between the incoming rays of light is
maintained during the bending, regardless of the rotational
orientation of the bender, at least in part because (i) the
incoming rays of light are all parallel with one another, and (ii)
the incoming rays of light are all bent in the same way.
[0110] It will be appreciated by one of ordinary skill in the art
that while the bender may be configured to have a rotationally
symmetric overall shape, such as a circular shape as depicted in
FIG. 8, the bending performance requires that there should be some
functional form of asymmetry with respect to rotation about an
optical axis 47 of the bender. As was the case regarding IOAs this
asymmetry may be structural in nature (for example if the bender is
configured using prisms) or the asymmetry may relate to optical
properties of materials that are utilized within the bender. In
view of these considerations regarding asymmetry, the rotational
orientation of the bender can be characterized and described
utilizing similar conventions and terminology established
previously for specifying rotational orientation of IOA's.
[0111] As described immediately above, Bender 33 is configured to
exhibit different bending performance depending on the orientation
of the bender with respect to the incoming rays of light. In this
regard, it is useful to establish a bender direction 93 as a
reference direction that can be associated with the bender as
illustrated in FIG. 8 as a vector B. Once established and/defined
for a given bender, the bender direction is to be regarded as being
fixed with respect to the bender such that the bender direction can
serve as a reasonable reference for describing the orientation of
the bender with respect to the incoming rays of light and with
respect to the earths frame of reference. In view of the
immediately forgoing description regarding asymmetry of the bender,
and consistent with the disclosure as a whole, a person of ordinary
skill in the art will readily appreciate that it is helpful at
least for purpose of descriptive clarity to establish some form of
reference feature, in this case bender direction 93, as a
reasonable basis for specifying the orientation of the bender.
[0112] Since bender direction 93 remains fixed with respect to the
bender, it is clear that any rotation of the bender results in a
corresponding change of direction of bender direction 93, as
illustrated in FIG. 8 by an angle .rho. between the bender
direction and a spatial coordinate axis 61. It is noted that
coordinate axis 61 is to be regarded as being fixed in space, for
example in the earth's frame of reference. In other words, as
bender 33 rotates about optical axis 47, the rotational orientation
changes in a way that can be specified as a changing value of angle
.rho. relative to the spatially fixed axis 61. In this regard, the
angle .phi. can be used to specify the bender direction relative to
the optical axis of the bender. For descriptive purposes, certain
aspects of the foreshortened terminology defined for IOAs will also
be adopted for use in describing benders. In particular, the bender
direction may be regarded as the direction the bender is
"pointing". Furthermore, for a given plurality of parallel incoming
rays of light, and in terms of previously established nomenclature,
the bender can be considered as "pointing toward" the light. In
this regard, the bender is pointing toward the light if a
projection of the light onto the surface of the bender is collinear
with the bender direction. Furthermore, as will be described in
greater detail hereinafter, when the bender is pointing towards the
light in this manner, the bender performs in such a manner that the
bent light is bent by an angle .beta. and remains in a plane
defined by incoming ray of light 14 and bender direction 93.
Additionally, at times when these conditions apply with respect to
incoming rays of sunlight, then the bender may be considered as
pointing toward the sun.
[0113] Attention is now directed to FIG. 9 in conjunction with FIG.
8. FIG. 9 is a diagrammatic elevational view illustrating the 3D
nature of the bending action of bender 33. An incoming ray of light
14 encounters the bender at a point 101 and is bent in a way that
depends on the rotational orientation of the bender, as will be
described immediately hereinafter.
[0114] In a first orientation wherein the bender is rotated about
optical axis 47 so that the bender direction 93 points away from
the incoming light, as illustrated in FIG. 9, the incoming ray of
light 14 is redirected to produce an output ray of light 92 that is
bent by a bending angle 104 relative to an axis 105 that is a
collinear extension of input ray of light 14.
[0115] In a second orientation of the bender wherein the bender is
rotatatably oriented about axis 47 such that bender direction 93'
points toward the incoming light, as illustrated in FIG. 9, the
incoming ray of light 14 is redirected to produce an output ray of
light 92' that is bent by bending angle 104', between output ray
92' and axis 105, having the same angular value as angle 104 but
corresponding to a different orientation as compared to that of
output ray 92. In other words, based on the two different
orientations of the bender with respect to the incoming ray of
light, output ray 92 and 92' are bent by the same amount but in
opposite directions. It is noted that in these cases the direction
of bending differs, but the amount of bending corresponds to the
bending angle .beta..
[0116] In a third orientation the bender is rotated by ninety
degrees with respect to both of the first and second orientations
such that the bender direction (not shown) points out of the plane
defined by the figure. With this orientation of the bender the
incoming ray of light 14 is redirected to produce an output ray of
light 92'' that is bent by a bending angle 104'', between output
ray 92'' and axis 105, also having the same angular value as angle
104 but corresponding to a different orientation as compared to
both of output rays 92 and 92''. It is noted that magnitudes of the
bending angles 104, 104' and 104'' all have the value .beta.
corresponding to the bending angle of the bender.
[0117] In a manner that is consistent with the foregoing three
examples, rotation of the bender whilst maintaining incoming ray 14
in a fixed direction as illustrated in FIG. 8 causes the output ray
of light 92 to sweep out the surface of an exit cone 118 such that
the surface is defined as having the angle 104 with respect to axis
105.
[0118] With ongoing reference to FIGS. 8 and 9 it was generally
assumed, for purposes of descriptive clarity, that the amount of
bending relative to axis 105 remained constant and independent of
the angle at which light enters the bender. This assumption can be
invalid. For example, if the first bender is implemented using
refractive optics, then the nonlinear nature of Snell's law can
make the bending angle a function of the light ray entry angle and
direction. The system still can still function, however. The
non-constant nature of bending angle .beta. warps or otherwise
distorts the shape of the exit cone of the first bender optical
element at least to some extent. For purposes of clarifying the
foregoing point, it is again noted that in an ideal bender, that
does not have a distorted exit cone, angles 104,104', and 104'' all
have the same value P corresponding to the bending angle of the
bender. On the other hand, in the case of a non-ideal bender with a
warped exit cone, these angles may differ somewhat from one
another. This may add a certain degree of complexity to predictive
calculations required to determine where the exit and acceptance
cones intersect, and but the same basic principles are still in
play, since even a substantially warped and/or distorted surface
still bears substantial resemblance to that of a cone.
[0119] Having initially introduced concentrator 26 with reference
to FIG. 3, and having described the basic operating principles of
an IOA, with reference to FIGS. 5 and 6, and of a bender, with
reference to FIGS. 8 and 9, various aspects of the foregoing
descriptions relating to concentrator 26 will be re-introduced
immediately hereinafter in order to combine, clarify and expand
upon various details relating to the operation of concentrator
26.
[0120] Referring again to FIG. 3, and summarizing with respect to
operation of solar concentrator 26, based in part on terminology
set forth in the descriptions relating to FIGS. 5-9, optical
concentrator 26 includes IOA 32 in a series relationship following
a bender arrangement 33 with input surface 39 of the IOA facing
towards the bender arrangement. IOA 32 and bender 33 are each
configured for selective rotation to cooperate with one another
such that the bender arrangement initially receives incoming rays
of sunlight 14 and bends the incoming rays of sunlight, in a manner
that is consistent with the descriptions in reference to FIGS. 8
and 9, to produce intermediate light rays 39 for acceptance by the
IOA such that the intermediate light rays can be at least
approximately oriented anti-parallel to the acceptance direction of
the IOA. In one embodiment, the bender arrangement receives and
bends the incoming rays to change their direction without causing
any focusing of the incoming light rays, and in accordance with the
descriptions relating to FIGS. 8 and 9, the bender may be rotatably
oriented, at least with respect to the incoming rays of light, to
bend the incoming rays of light such that the resulting
intermediate rays of light have a direction that is aligned with
the surface of the acceptance cone of the IOA, and the IOA can be
rotatably oriented for accepting and concentrating the intermediate
rays of light. In all cases, at least for a predetermined range of
orientations of input rays of light 14, the bender arrangement (or
some other input element) and the IOA cooperate with one another
such that the bender is rotatably aligned in an orientation that
allows the intermediate rays to serve as input rays 56 of the IOA
(FIG. 5), and the IOA is rotatably oriented to accept the
intermediate light rays (as input rays) and concentrate the
intermediate light rays at focus region 41 in a manner that is
consistent with the descriptions of an IOA appearing above with
reference to FIGS. 5 and 6. In other words, the input element (for
example, a bender) and the IOA can be rotatably oriented, with
respect to one another and with respect to the input rays of
sunlight, to cooperate with one another such that the intermediate
light rays 39 are aligned to be at least approximately oriented
anti-parallel to the acceptance direction of the IOA.
[0121] Based on the forgoing descriptions in conjunction with the
disclosure taken as a whole, it may be appreciated that for a
bender-IOA combination to serve as a concentrator for properly
tracking the sun over a predetermined range of positions, such as,
for example, a given range of positions corresponding with apparent
motion of the sun throughout a given day, the aforementioned
cooperation, between a bender arrangement and the IOA, can be
reasonably achieved provided that the bender and the IOA are
configured at least generally in accordance with the criterion that
follow below.
[0122] Based in part on the descriptions relating to FIGS. 8 and 9
in conjunction with FIG. 3, for a given incoming ray of light that
is received through an input aperture defined by bender 33 and
incident on the input surface thereof, rotating of the bender about
it's associated optical axis causes the resulting output ray of
light to sweepingly define an exit cone such that for a given
rotational orientation of the bender, the incoming ray of light is
bent to produce an output ray of light that radiates away from a
point of incidence of the incoming ray of light, and radiates away
from the bender such that the output ray of light lies on the
surface of the exit cone. As described previously in reference to
FIG. 9, for a given incoming ray of light the corresponding exit
cone of the bender at least approximately delineates the range of
bending directions that may be selected, for a given input ray of
light, by selectively rotating the bender.
[0123] It is to be understood that in the context of concentrator
26, output ray 92 of FIG. 9, produced by the bender from the
incoming ray of light, is to be regarded as corresponding to
intermediate ray 39 of FIG. 3, and as described previously, the
intermediate ray in turn serves as the input ray of light for IOA
32 of FIG. 5. Combining and appropriately interpreting the
descriptions and terminology relating to FIG. 3, FIG. 9, and FIG.
5, it should be appreciated that the output ray produced by the
bender serves in the context of IOA 32 as the input ray that is to
be accepted for bending and focusing by the IOA.
[0124] Considering now FIGS. 5 and 6 in the context of the
immediately foregoing points, it will be appreciated by a person of
ordinary skill in the art that in order for the IOA to accept and
focus the output ray of light from bender 33, it is necessary that
(i) the output ray of light from the bender lies on the acceptance
cone of the IOA within some approximations, and (ii) the IOA may be
rotatably oriented such that the acceptance direction is oriented
to be anti-parallel with the output ray of light from the bender
within some approximation.
[0125] Attention is now turned to FIG. 10 the combined operation of
a concentrator comprising a bender combined with an IOA as
illustrated. FIG. 10 illustrates one embodiment of a bender-IOA
concentrator generally indicated by reference number 26' and
configured such that the bender and the IOA cooperate with one
another in the manner set forth previously. In order for
concentrator 26' to track the sun over a predetermined range of
positions, throughout a portion of the day and/or including
seasonal variations, bender 33 and IOA 32 are configured for
compatibility with one another such that for each anticipated
orientation of incoming rays of sunlight 14 (i) the associated exit
cone of the bender intersects the acceptance cone of the IOA along
a line of intersection 104 that extends from the bender to the IOA,
(ii) the bender is rotatably oriented such that the output ray of
the bender is collinear with the line of intersection at least to
an approximation, and (iii) the IOA is rotatably oriented such that
the acceptance direction of the IOA is collinear with the line of
intersection 104 and therefore is anti-parallel with the output ray
of light from the bender at least to an approximation. With the
bender and the IOA selectively rotated for cooperating with one
another in the manner set forth immediately above, the output ray
of light from the bender serves as the input ray of light for the
IOA, and the IOA bends and focuses this input ray of light for
passage to focus region 41.
[0126] It is noted that as the sun changes position, the
orientation of the incoming rays of sunlight changes and therefore
the exit cone of the bender shifts and/or changes correspondingly,
and the optical source can be tracked during these changes only for
as long as the line of intersection is actually present between the
two cones, and the tracking is achieved by adjusting the rotational
orientations of the bender-IOA combination such that they cooperate
with one another for receiving and concentrating the incoming rays
of sunlight in the manner set forth above with reference to FIG.
10. In view of the foregoing point, it can be appreciated by a
person of ordinary skill in the art that for a given position of
the sun, the aforedescribed cooperation between the bender and the
IOA can be achieved only insofar as the exit cone (of the bender)
and the acceptance cone (of the IOA) overlap one another such that
a line of intersection is present, and for each orientation of the
incoming rays of light, corresponding throughout the day to the
given position of the sun, this requirement for a line of
intersection between the two cones represents a criterion that
should be satisfied in order for the solar collector to concentrate
the incoming rays of sunlight. It will be further appreciated that
for a given day, at a particular geographic location, and at a
given time of the year and a given view of the sky available to the
concentrator, this criterion may in some cases set practical limits
as to what range of sun positions during the day will produce light
that can be tracked by the concentrator.
[0127] For further explanatory purposes, one example illustrative
of a special case in which the relationships between various
parameters are somewhat simplified as compared to more general
cases will now be described. For simplicity, it will be assumed
that for a given bender-IOA combination, all focus action is
performed by the IOA, and that the bender serves only to bend the
light by a particular bending angle .beta.. For additional
simplicity, it will be assumed in this example that the bending
angle .beta. is equal to the zenith angle .xi. defined by the
IOA.
[0128] Attention is now directed to FIG. 11 which is illustrative
of the special case under consideration. FIG. 11 is a diagrammatic
view, in elevation, depicting one embodiment as a special case of a
Bi-Rotational concentrator or BRIC generally indicated by reference
number 109. For purposes of descriptive clarity it is noted that
the view of FIG. 11 is taken in a plane that bisects the assembly
such that optical axis 47 lies in the plane as shown.
[0129] Bender 33 and an IOA 32 are configured for rotation around
optical axis 47. Furthermore, in the example at hand, the bender
and the IOA are specifically matched with one another such that the
IOA is configured with an acceptance direction (fixed with respect
to the IOA) characterized in part by a acceptance angle .xi. (the
zenith angle of the acceptance direction relative to the optical
axis) having a value equal to the bending angle .beta. of the
bender such that .xi.=.beta.. Furthermore, the incoming rays of
light 14 lie in the bisecting plane and are oriented to enter the
system at a receiving angle 2.beta., (twice the IOA zenith angle
.beta.), relative to the optical axis 47. It is noted that for
purposes of illustrative clarity the description with reference to
FIG. 11 will initially be restricted to consideration of incoming
rays of light 14 that lie in the plane of the cross section.
[0130] Bender 33 is configured, based on a particular design
configuration that will be presented in detail hereinafter, such
that the bending angle may be at least approximately constant
regardless of the angle of the arriving light rays. The bender is
rotatably oriented to be pointed towards the incoming light such
that bender direction 93 of the bender lies in the bisecting plane
and the bender receives the incoming rays of sunlight and bends
these rays by a bending angle .beta. having a magnitude equal to
the zenith angle .xi. of IOA 91 thereby producing intermediate rays
of light 39 that lie in the bisecting plane and which are tilted
with respect to the optical axis by angle .beta. to match the
zenith angle (.xi.=.beta. for the example at hand) defined by IOA
32.
[0131] IOA 32 is positioned and rotatably oriented such that the
acceptance direction 57 (represented by vector {right arrow over
(A)}) lies in the bisecting plane and is anti-parallel with respect
to the intermediate rays of light such that the IOA bends and
focuses the intermediate rays of light for concentration at a focal
region 41 of the IOA. While the foregoing description with respect
to FIG. 11 has been restricted to a particular set
[0132] incoming rays of light that lie in the bisecting plane, it
is noted that in view of the disclosure as a whole, based on the
operating principles set forth previously with respect to benders
and IOA's, a person of ordinary skill in the art will recognize
that a plurality of incoming light rays that are each oriented
parallel with respect to this particular set of light rays will
also be received and focused by concentrator 109 such that they are
directed through focus region 41.
[0133] Having described the operation of optical concentrator 109
with respect to a particular orientation of incoming rays of light
14, it is to be understood that concentrator 109 may be utilized
for receiving and concentrating other rays of light (not shown)
that are oriented at different angles. For example, in a case where
incoming rays of light 14 are oriented with the entrance angle
having a different value that is substantially smaller than
2.beta., then one or both of the bender and the IOA will need to be
rotated to different orientations in order that they cooperate with
one another to bend and focus the incoming rays of light in a
manner that is consistent with the operating principles described
with reference to FIG. 10 and previously in this disclosure.
[0134] For example, with respect to the embodiment of FIG. 11, for
a given plurality of mutually parallel incoming rays of light
having entrance angles substantially less than 2.beta., the bender
defines an exit cone, as described above in reference to FIG. 9,
based in part on the orientation of the incoming rays of light, and
the given plurality of incoming light rays is receivable, based on
the appropriate rotational orientations of the bender and the IOA,
as long as the previously described criterion is satisfied such
that exit cone intersects the acceptance cone of the IOA along a
line of intersection that extends from the bender to the IOA. It is
noted that for receiving and concentrating the plurality of
incoming light rays it is generally necessary to rotate the bender
to align the intermediate rays to be collinear with the line of
intersection, and it is also generally necessary to rotate the IOA
for directing the acceptance direction to be collinear with the
line of intersection in order that the IOA bends and concentrates
the intermediate rays of light.
[0135] With ongoing reference to FIG. 11, it is again noted that
the illustrated embodiment represents a special case wherein the
bender and the IOA are configured such that bending angle .beta.
(defined the bender) is equal to zenith angle .xi. (defined by the
IOA). Applicants recognize that with respect to this particular
embodiment, incoming rays of light that enter the concentrator in a
parallel orientation with optical axis 47 can be received and
concentrated regardless of the angular orientation of the bender.
As mentioned previously, bender 33 is configured, based on a
particular design configuration that will be presented in detail
hereinafter, wherein the bending angle has a value .beta. that may
be at least approximately constant regardless of the angle of the
arriving light rays. Therefore, incoming rays of light that enter
the concentrator parallel with the optical axis will produce
intermediate rays that are bent in the bender direction (the
direction in which the bender points) by the amount .beta.. In
other words the incoming rays of light are bent by an amount
towards the direction in which the bender is rotatably pointed.
And, for the special case of incoming rays of light 14 that are
parallel with optical axis 47, regardless of the orientation of the
bender, the IOA can be oriented such that the acceptance direction
of the IOA is anti parallel to the intermediate rays of light so
produced.
Vector Description of the BRIC
[0136] The following discussion describes a number of aspects
related to determination of the correct orientations for the two
IOAs to align the optical system to a given optical source. This
discussion again assumes that bend angle 104 of the bender is not a
function of input angle or direction, and that bend angle 104 has a
value that is equal to the azimuthal angle .xi. associated with the
acceptance direction of the IOA such that .xi.=.beta.. As will be
described immediately hereinafter, the operation of a bender may be
described mathematically by decomposing a vector representing the
incoming ray into three components, as based on a number of
definitions that will be described immediately hereinafter.
[0137] Attention is now turned to FIG. 12 which is a diagrammatic
perspective view illustrating one embodiment of bender 33. FIG. 12
illustrates an incoming ray of light 14 incident upon bender 33.
Incoming ray of light 14, and any other direction vector of
interest, may be mathematically represented, in accordance with
established principles of analytic geometry that will be familiar
to a person of ordinary skill in the art, by decomposing the ray
based on a coordinate system defined by three mutually orthogonal
axes including (i) a `u-axis` 126, a `v-axis` 127, and a `z-axis`
128. As illustrated in FIG. 12, z-axis 128 is aligned with the
optical axis of the optical arrangement, and the u and v axes lie
in a plane defined by an input surface 131.
[0138] The directional orientation of incoming ray of light 14 can
be represented by a unit input vector 103 (of unit length) pointing
in the direction of the incoming ray 14, and based upon the
immediately foregoing definitions unit input vector 103 may be
mathematically decomposed, in accordance with the aforementioned
established conventions, for representation as a 3-vector r
including u, v, and z components 126', 127' and 128', respectively,
with values r.sub.u, r.sub.v, and r.sub.z, with each value
corresponding to an associated projection of vector 103 onto the
u-axis, the v-axis, and the z-axis. While 3-vector r is graphically
depicted as pointing in opposition to incoming ray of light 14, it
is to be understood that this is to be considered as an arbitrary
convention defined for purposes of convenience, and that the
3-vector r, defined in this manner, corresponds with the
orientation of incoming ray of light 14, and is not intended as
corresponding with the direction of the incoming ray of light. In
the equations that follow, all orientations will be mathematically
represented based on this convention, and will be physically
interpreted accordingly. It is further noted that while the bender
itself may attenuate the light to some extent, the description at
hand relates only to the bending of the light and not to
attenuation and/or other modifications. In this regard, it will be
appreciated by a person of ordinary skill in the art that that
"normalized" vectors (of unit length) are appropriate for use as
input as well as output vectors at least insofar as their use is
restricted to descriptions relating to the bending, and not to
attenuation and/or other modifications to the light. Thus, any
incoming ray 103 can be mathematically represented using Cartesian
coordinates as 3-vector r (having unit length) that is decomposed
into u, v, and z components as follows:
r .fwdarw. = ( r u r v r z ) ( EQ 1 ) ##EQU00001##
[0139] Analytic geometry may be utilized in conjunction with
trigonometry and linear algebra in order to mathematically model
the effect of passing a ray through the bender. For example, with
the incoming ray entering the bender being represented by the
3-vector r of Eq. 1, the orientation of resulting output ray may be
described by the 3-vector s, (also having unit length) utilizing
the aforedescribed coordinates, as:
s .fwdarw. = ( s u s v s z ) = ( cos .beta. 0 - sin .beta. 0 1 0
sin .beta. 0 cos .beta. ) r .fwdarw. = ( cos .beta. 0 - sin .beta.
0 1 0 sin .beta. 0 cos .beta. ) ( r u r v r z ) ( EQ 2 )
##EQU00002##
[0140] The 3-vector s is a unit vector that merely describes the
orientation of output ray 93, and is not to be interpreted as
representing the physical ray itself. In particular, 3-vector s of
Equation 2 corresponds with the orientation of the output ray of
light, but is not intended for correspondence with the direction of
the output ray of light. A person of ordinary skill in the art will
readily appreciate that the foregoing matrix equation implies the
v-axis component remains unchanged during the bending such that
s.sub.v=r.sub.v, and therefore the bending action of the IOA may be
regarded as being restricted to lie within the u-z plane.
Furthermore, in view of this recognition and based on the foregoing
mathematical description, it can be appreciated that the U axis
corresponds with bender direction 93 in accordance with previous
descriptions in reference to FIG. 8, and as illustrated by the
presence in FIG. 12 of bender direction 93 overlying u-axis 126.
Using the terminology set forth previously in reference to FIG. 8,
if a particular in-plane input ray (not shown) lies in the u-z
plane, it will remain in the u-z plane during bending, and this
orientation of the bender direction relative to the incoming ray of
light corresponds with the previously described scenario wherein
the bender is pointed towards the incoming ray of light. Based on
previously introduced terminology, a case wherein the incoming ray
of light lies in the u-z plane of FIG. 12 represents a case where
the bender is to be regarded as pointing toward the incoming rays
of light.
[0141] While the bending action may be calculated in Cartesian
coordinates in accordance with the foregoing descriptions, a person
of ordinary skill in the art will readily appreciate that the
performance of the system may also be characterized based on other
systems of coordinates, even while the above mathematical technique
may be utilized, provided that the appropriate conversions between
coordinate systems are properly executed and are performed at an
appropriate step of any given overall determination. For example,
an orientation of the incoming ray of light 14 may be characterized
using a first angle .phi..sub.in (relative to the optical axis) and
a second angle .delta. (relative to the v-axis), as illustrated in
FIG. 12, and well known techniques may be employed for converting
this orientation to the system of Cartesian Coordinates defined
above, at which point the formula above may be employed for
characterizing the bending. The resulting 3-vector s can be
converted back to polar coordinates (again using well known
mathematical techniques) to find .phi..sub.out represented in FIG.
12 as the angle of the light 93 exiting bender 33 relative to the
optical axis. The resulting equation for .phi..sub.out is:
.phi. out = tan - 1 ( ( sin .phi. in cos .delta. cos .beta. - cos
.phi. in sin .beta. ) 2 + sin 2 .phi. in cos 2 .delta. sin .phi. in
cos .delta. sin .beta. + cos .phi. in sin .delta. ) ( EQ 3 )
##EQU00003##
[0142] It will be further appreciated by a person of ordinary skill
in the art, that these calculations may also be performed as
numerical computations by utilizing well known analytical optics
techniques. For example, in many cases ray tracing may be employed
for simulating the operation of a specific bender, IOA and/or
combination thereof.
[0143] Based on the analytical techniques described above, in
conjunction with well established techniques associated with
physical optics, and in view of this disclosure as a whole, a
person of ordinary skill in the art will appreciate that a special
case of a concentrator 109 described with reference to FIG. 11 may
be utilized for tracking the sun over a wide range of positions
throughout the day. For example, it may be readily appreciated that
concentrator 26', configured with .epsilon.=.beta.=22.5 degrees and
located in Boulder Colo. (with the concentrator facing such that is
tilted south at an angle of approximately 40 degrees from
horizontal), is capable of tracking the sun throughout a
substantial portion of a given day. It is again noted that
concentrator 26' is capable of achieving this performance based
solely on rotation of the bender and the IOA, and does not require
any additional tracking mechanism in order to achieve this
remarkable performance.
Shaping of IOA Acceptance Ray Profile
[0144] In the foregoing discussions, the term `focal region` rather
than `focal point` has been used to describe the location of
concentration of light rays from a lens. This distinction has been
made since the term `focal point` applies to a more traditional
imaging optics where collimated light focuses to a point. Instead
of being designed with techniques restricted to imaging optics, an
IOA can be constructed using analogous methods (such as non-imaging
Fresnel concentrating lens techniques), wherein the light rays are
directed into a focus region and never converge to a point. One
approach to accomplishing this is to directly incorporate a
non-imaging Fresnel concentrating lens as part of an optical IOA
arrangement. Another general approach is to employ non-imaging
optical principles in the design of the IOA. It is noted that a
good source on the design of non-imaging lenses can be found in
Nonimaging Fresnel Lenses: Design and Performance of Solar
Collectors by Leutz and Suzuki, which is incorporated herein by
reference. By employing non-imaging optical techniques in the
design of an IOA, it is possible to increase the range of
directions about the acceptance direction wherein light entering
the IOA will still be concentrated and directed into the focus
region. In other words, it is possible to exploit the nature of a
non-imaging IOA in order to decrease sensitivity to misalignment of
the incoming rays of light, such that within a predetermined range
of misalignment, the incoming rays of light are nevertheless
received and concentrated into the focal region.
[0145] As described in the reference by Leutz and Suzuki referred
to above, the design of a non-imaging lens involves processing the
boundary of the input aperture of the lens and designing the optics
so that an input ray of light that is misaligned will still be
directed into a particular region. The Leutz and Suzuki references
consider only the magnitude of misalignment and thus the range of
allowable misalignment is circularly symmetric. Applicants
recognize that this is not a requirement, and that by configuring
an optical arrangement such that misalignment design values are a
function of the direction of the incoming ray, non-imaging optical
arrangements can be created that have an asymmetric range of
allowable input rays. Applicants further recognize that by
utilizing these principles, an IOA can be designed so that the
incoming ray distribution can be more oval shaped, which can have
the advantage that the sun's path traverses the long axis of the
oval, thus requiring less frequent or less accurate movement to
track the sun.
[0146] For a concentrator comprising a given combination of optical
arrangements the design of a given concentrator acceptance range
may in many cases be complex, the required analytical techniques
are believed to be well described in the Luetz reference, and
applicants believe that a person of ordinary skill in the art
having this disclosure in hand, will be readily able to implement a
number of embodiments based on the descriptions herein. Introducing
foreshortened terminology for describing the functioning of a
concentrator such as concentrator 26, and variations thereof, a
concentrator may be regarded as defining a concentration ratio
based on the area of the focal region and the area on the input
aperture defined by the concentrator. Furthermore, a concentrator
that is configured with a given concentration ratio generally will
receive and concentrate rays that are within a given range of
misalignment angles. This range of misalignment angles can be
considered as defining a "field of view" of the concentrator
defined herein as a range of positions of the sun in the sky from
which light may be received and concentrated without employing any
tracking motion, rotational or otherwise. For example, the field of
view of concentrator 26 is that range of positions of the sun in
the sky for which concentrator 26 is capable of receiving and
concentrating light without performing any rotational adjustments.
It is to be understood that the field of view as described above
does not account for the question of whether the sun ever actually
occupies all the positions in the field of view, and that it is
possible to configure a solar concentrator to exhibit a field of
view that includes vacant positions that the sun never actually
occupies, regardless of the time of day or the time of year.
Applicants are aware that even non-imaging optical systems tend to
be governed by the well known and fundamental principles of optics
that impose theoretical limits with respect to field of view of
imaging and non-imaging systems alike. In this regard, a
concentrator system having a wide field of view that includes a
wide range of vacant positions in the sky may be perhaps be
considered as wasting at least a portion of the field of view.
Applicants recognize that a wide-field system having circular
symmetry may be inherently wasteful in this respect since the sun
tends to follow an at least somewhat linear trajectory, and that
such a system may be modified to change the shape of the field of
view to another shape that more closely matches a given path of the
sun in the sky, to account for daily and/or seasonal variation of
the position of the sun in the sky.
[0147] Concentrators function by taking the light from a given area
and focusing the light to a smaller area. A symmetrical circular
10.times. concentrator may receive sunlight through a circular
aperture defined by the concentrator, and may concentrate the
received sunlight by bending and focusing the light to a focus
region that is 1/10.sup.th as large as the input aperture. A solar
energy application represents a special case where the light source
is continuously moving but the path of the light source is known.
These applications typically employ concentrators that take the
sun's energy from a near circular area and concentrate it to a
smaller circular or square area. This requires that the optics
track the sun throughout the day. The greater the concentration,
the closer the input light area is to the size of the sun in the
sky and therefore the more stringent the tracking requirements. In
applications of low concentration, the tracking can be more
tolerant since the sun can move through the larger field of view
before adjustment of tracking is required.
[0148] Attention is now turned to FIGS. 13 A and 13 B which are
diagrams, generally indicated by reference number 130 and 130',
respectively, illustrating fields of view 133 and 133' including a
range of positions 136 of the sun as the sun moves through a
predetermined portion of a given day. It is noted that FIGS. 13A
and 13B both depict the same range of positions 136, but that field
of view 133' in FIG. 13B is substantially smaller than field of
view 133 in FIG. 13A. FIGS. 13A and 13B illustrate the concept that
tolerance in positioning is less critical for lower concentration,
based on the principle that a lower concentration system tends to
have a wider field of view, and it can be appreciated based on
FIGS. 13A and 13B that it is possible to avoid repositioning the
field of view for some time as the sun makes its way across the
field of view 133, while more frequent repositioning will be needed
in a higher concentration having field of view 133'.
[0149] With ongoing reference to FIG. 13A, based on the terminology
set forth above with regard to general discussions and definitions
for the field of view, it is noted that at least a portion of field
of view 133 may be regarded as being wasted since it appears to
include a substantial portion of vacant positions in the sky, and
Applicants recognize that it may be therefore be advantageous to
stretch the field of view to at least better match the sun's path
that is indicated by way of consecutive positions 136.
[0150] Attention is now directed to FIG. 14 with reference to FIG.
13A. FIG. 14 is a diagram, generally indicated by reference number
140, illustrating a field of view 146 that is stretched to match
the sun's path. A stretched Field of view 146 corresponds with a
magnification of roughly 10.times. and has an area that is
approximately the same as field of view 133 (field of view 133 is
initially shown in FIG. 14, overlaying field of view 146 and
represented with a dashed line). It is clear from FIG. 14 that a
modified concentrator exhibiting stretched field of view 146 covers
more of the sun's path as compared to an unmodified concentrator
exhibiting field of view 133, and therefore the modified
concentrator can maintain tracking of the sun in a way that
requires less repositioning. Thus, by designing the field of view
to match the sun's motion through the sky, it is possible to reduce
the tracking requirement of the panel and/or relax mechanical
performance specifications that relate to the associated tracking
mechanism. While it is possible to employ this approach in
conjunction with conventional solar collectors, Applicants
recognize that this approach may be especially advantageous when
employed in the context of concentrators described in this overall
disclosure, especially since the non-imaging optics utilized for
producing IOA's lends itself well to configuring the field of view
in a customized way.
[0151] For example, by modifying a concentrator to provide a field
of view that is stretched to match the path of the sun (or other
predictable light source) in the manner described immediately
above, the need to reposition can be reduced. For example, if IOA
32 of concentrator 26 is modified for producing a field of view
having a stretched shape similar to the field of view of FIG. 14,
it may be possible to relax certain specifications and/or
requirements related to tracking, especially with respect to
mechanical specifications and/or requirements that relate to
rotation of the IOA. For example, it may be possible to reduce a
required range of rotation, and to also reduce the number of times
during the day that the rotational orientation is adjusted. It is
noted that this approach can also be applied to mechanical tracking
systems or combined IOA/mechanical trackers. As one possible
simplification, it may be possible to configure a tracker for
tracking the sun based on a set of discreet `resting` positions as
opposed to a smooth and continuous profile of positions. For
example, concentrator 26 could be modified for rotational
orientation of one or more optical arrangements (benders and/or
IOAs) and the field of view could be sufficiently stretched such
that in order to track the sun throughout a given day the
concentrator is only required toggle between two receiving
directions--for example a first receiving direction for the
morning, and a second receiving direction for the afternoon.
Alternatively, concentrator 26 may be modified for defining a set
of discreet receiving directions and to change from one to the
other on an hourly basis. Applicants recognize that a tracker that
locks into fixed positions, at least generally in accordance with
the foregoing descriptions, may be less expensive to implement than
a continuous tracker.
IOA Tracking
[0152] It is to be appreciated that the method of tracking
disclosed herein provides a number of remarkable advantages as
compared with traditional concentrator systems and associated
methods. Perhaps the most significant advantages stem from the
simplicity of the drive mechanisms needed to implement this
technology. For example, in the context of concentrator 26, a
tracking concentrator system, for example including a bender and an
IOA, can utilize two sets of moving parts that are independent of
one another such that moving the IOA does not move the bender, and
vice versa. Furthermore, as described previously in reference to
FIG. 3, the configuration of the optical system can be compact, at
least along the direction of the optical axis, and does not change
position or form-factor as the system is tracking. This allows a
rotating drive mechanism (for rotating a bender and/or an IOA) to
be placed inside the product package, such as a low profile panel
and/or enclosure, for shielding the drive mechanism from weather
and wind. This in turn significantly reduces the requirements
related to environmental resistance, at least for any actuators,
drive mechanisms and/or control systems that are required for
rotatably adjusting the IOA and the bender. The use of optical
concentrators that track the sun based solely on rotational motion
may significantly reduce the cost of optical tracking and enable
its use in applications that were previously impractical at least
for reasons relating to cost and/or size of conventional
trackers.
[0153] Applicants recognize that there are yet further advantage
associated with configurations that rely solely on rotation for
tracking the sun. At least with regard to mechanical
considerations, it is noted that rotation is often easier to
accomplish than translation, and can therefore be achieved at lower
cost. In addition, moving mechanical components that rotate are
capable of being balanced. For example, at least with respect to
embodiments that are configured such that the rotating optical
arrangements (benders and/or IOAs) are inherently balanced, the
system may be arranged such that the only torque required by the
tracking actuators is the torque required for acceleration and
overcoming friction. If the optical tracking application is fairly
slow, as it generally is in solar applications, then the torque
requirements become minimal. This further reduces the size,
complexity, and cost of the implementation.
[0154] Applicants further recognize that it may be advantageous to
modify a low cost conventional concentrator, at least with the
addition of an IOA, in order to improve tracking performance while
relaxing certain requirements with respect to the associated
tracking mechanism. A person of ordinary skill in the art, having
this disclosure in hand, may identify a concentrating system with a
simple low cost tracking mechanism, and may then improve the system
at least by addition of an IOA such that the modified system
includes a fine adjustment, in part resulting from the use of the
IOA for improving tracking performance.
[0155] Another class of advantages of the IOA-based optical
trackers is that the target of the optical system need not move.
For example, in an IOA tracking solar photovoltaic (PV)
concentrator, the target of the concentrated light, the PV cell,
does not move as the system tracks. A stationary optical path is
clearly easier, and therefore less expensive, to implement.
Additionally, in the solar concentrator example, the stationary PV
cell can eliminate the need for moving the conductors that carry
the power away from the cell and can significantly simplify the
removal of excess heat from the target.
[0156] As described in greater detail hereinafter, a solar
collector may be configured that utilizes an array of one or more
concentrators to redirect and focus the sun's rays on receivers
that are configured for absorbing the concentrated light for
conversion to a form of power such as electricity or thermal power.
Each concentrator may include at least one optical element (IOA or
bender) that is supported for rotation as at least part of focusing
the sun's rays onto an unmoving target. If more than one optical
arrangement (such as an IOA and/or bender) is utilized, then the
first optical arrangement to interact with the incoming light may
serve as an input arrangement for initially receiving incoming rays
of sunlight. In effect, the concentrators act as a solar tracker so
that the target, electrical connections and support structure of
the assembly need not move and the only moving parts are rotatable
optical arrangements in the concentrators, and their associated
drive mechanisms and components thereof. Applicants recognize that
the panel can be movable (e.g. with an external 1- or 2-axis
tracker) and in this case the internal target tracking could be
used as a secondary tracker or as an integral part of the whole
tracking system. Thus, one approach is to utilize an external
mechanical tracker as a coarse (not highly accurate) tracker with
an internal BRIC tracker/concentrator acting as a fine tracker
utilizing rotation of optical arrangements as described throughout
this disclosure. This particular approach may be utilized to relax
requirements associated with the external mechanical tracker to
allow the tracker to be designed with a lower cost
configuration.
[0157] Having described the operation of concentrator 26, and
having described various details with respect to the operation and
characteristics of benders and IOA's. A number of general system
level considerations relating to solar concentrators will be
presented immediately hereinafter.
One-IOA Systems
[0158] Overall concepts relating to two distinct one-IOA designs
will be described hereinafter. A first one-IOA embodiment is a
1-dimensional array having one or more IOAs for focusing light onto
a linear target. The concentration gain is not as great as compared
with a 2-dimensional concentrator (such as concentrator 26).
However, Applicants recognize that this first embodiment may
provide advantages at least for use with solar-thermal systems
where the target may be linear in nature, such as a pipe, though
this first embodiment may also be applicable for use with a linear
array of PV cells. The IOA itself may include a bender followed by
a concentrator. The concentrator may be a 2-dimensional
(point-type) concentrator (such as a conventional lens), or a
1-dimensional (line-type) concentrator (such as a cylindrical lens)
that is mounted parallel to the 1-dimensional target. Thus, the
concentrator may be physically independent of the rotatable IOA, or
may be partially combined with the rotatable IOA.
[0159] Attention is now directed to FIG. 15 which is a diagrammatic
representation, in elevation, of a linear concentrator
configuration, generally indicated by reference number 150 and
employing an array of two IOA's 32 configured for receiving input
rays of light 14 concentrating the light along the axis of a linear
target 153.
[0160] The IOA's are controlled, for example by a drive mechanism
(not shown) to rotate and to continuously point towards the
incoming rays of sunlight and to direct the exit rays to the target
153. IOA output rays 156 may move up and down the target (left and
right in FIG. 15) since there is only one IOA per concentrator to
correct for one axis of the sun's position. Typically, the IOA
output rays striking the target will be incident at an angle (not
perpendicular) to the target, however the IOA output rays may enter
perpendicular to the target at specific times during the day when
the sun's ray angle matches the IOA bend angle such that the IOA
output rays leave perpendicular to the IOA and are directed towards
the target.
[0161] As one aspect of the operation of concentrator system 150,
with the target oriented East-West, then seasonal North-South
variation of the sun can be fully corrected. Four examples are
worth noting to understand this system. When the sun is in the east
with no northern or southern displacement, then the IOA may rotate
so that the light is bent toward the target--with no north or south
bending since the sun is already on a target-IOA plane. When the
sun is in the north and the day and the time are such that sun is
positioned along the acceptance direction of the IOA, then the
incoming rays of sunlight will bend downward to the target with no
east or west component. A similar configuration occurs when the sun
is in the south. These last two examples result in the sun's rays
entering the target perpendicularly.
[0162] Of interest are the cases when the IOA bend angle is less
than the sun angle, or when the IOA bend angle is more than the sun
angle. In these cases, the sun angle of concern is the angle
between the sun's rays and the plane made by the target line-IOA
line. With an east-west orientation of the target, the important
sun angle is the north-south angle since any east-west angle will
not need to be corrected in order for output rays 156 to strike the
target, since the sun's rays will be allowed to strike the target
with an angle along the target axis (east-west). If the IOA bend
angle is less than the sun angle, then the IOA will correct part of
the sun's angle, but not all of it and so the rays may strike the
target at an angle, but the rays will strike the target at a
steeper angle (more perpendicular) than if the IOA were not
present. Alternatively, if the IOA bend angle is greater than the
sun angle, then the incoming rays of light are focused on the
target, but will strike the target at an angle in the opposite
direction than if no IOA were present. In fact, there should be a
point such that the angle of the sun equals the bend angle and then
the rays that fall on the target will be directly below the exit
rays from the IOA. For example, if the IOA bend angle is 30
degrees, then the sun's position should be at 30 degrees to have
the light rays striking perpendicularly to the target. This 30
degree angle is the total angle made up of the vector sum of the
east-west angle and the north-south angle.
[0163] As can be seen, the rays will strike the target
perpendicularly two times during the day (when the sun is east at
the bend angle, and when the sun is west at the bend angle). Thus,
if the panel assembly of the IOAs is continuously rotated, then it
may be possible for the rays exiting the IOA to strike the target
perpendicularly at all times. This in effect becomes a 2-axis
tracker with one axis external to the panel that moves the whole
panel, and one axis internal to the panel that bends the light to
the target. Note: the two axes are not necessarily orthogonal.
IOA with Mechanical Tracker
[0164] This second embodiment separates the tracking motion of the
panel into two different tracking methods. Traditionally, a solar
panel is either fixed (not moving) or is moving so that it is
pointed toward the sun--this is generally referred to as
"tracking". (The solar panel has a "direction" which is the
perpendicular to the surface of the panel in the direction of the
incoming light: thus when the solar panel is pointed toward the
sun, the panel is positioned so that the light enters the panel at
right angles.) Oftentimes, depending on the configuration of a
given solar collector, there may be at least two motivations for
tracking the sun: (i) when tracking the sun, the amount of sunlight
that enters the panel may be increased as compared to a fixed
non-moving panel, and (ii) typical concentrating solar panels often
require the sunlight to enter the panel at a constant angle at all
times--thus as the sun moves across the sky, the panel can rotate
in relation to this movement such that the panel points directly
toward the sun. By contrast, a fixed non-moving panel receives less
light in the morning and evening due to the shallow angle of the
light entering the panel which is commonly called the `cosine
effect`. This is such a large effect that a number of manufacturers
of traditional solar panels presently offer tracking on their
panels to recover this lost morning/evening power.
[0165] Attention is now directed to FIG. 16A, which illustrates a
perspective view of one embodiment of a conventional one axis
tracker generally indicate by reference number 160. Different
levels of tracking are common: one relatively simple case is a
one-axis tracker where the panel is pointed (its direction normal
to the surface where the light enters the panel) about the
East-West direction of the sun's daily motion, but not the
North-South direction of the sun's seasonal motion as shown in FIG.
16A. Thus, in the morning, the panel can be pointed to the east in
the general direction of the sun, and throughout the day the panel
may rotate about a north-south axis of rotation so that the panel
will be pointed to the west during the evening. (The axis of
rotation is commonly tilted to further improve the amount of light
entering the panel, and this tilt is often preferably arranged to
be comparable to the latitude of the installation.) Because the
sunlight may not enter the panel perpendicularly at all times
throughout the year, this method may not be suitable for
concentrated solar panels that typically require the light to enter
nearly perpendicular to the panel surface. If the panel has a
one-axis tracker, then seasonal variations may result in a +/-23.5
degree entrance angle to the panel with an additional possible
daily angle error if the panel is tilted too far in front of the
sun or too far behind the sun. Thus a one-axis tracker in some
cases may not applicable for a concentrating system.
[0166] Attention is now turned to FIG. 16B, which illustrate
perspective views of a conventional two axis tracker generally
indicated by reference numbers 160'. The two axis tracker shown in
FIG. 16B rotates to follow the sun in the east-west daily motion as
well as the north-south seasonal motion. Thus it is possible for
the sunlight to enter the panel in a fixed (perpendicular)
direction at all times of the year and throughout at least a
substantial portion of each day. Due to typical construction
techniques, a given two axis tracker may be much more complex and
costly than a given one axis tracker. Thus, a two-axis tracker is
primarily used for concentrator panels where the panel can point
toward the sunlight with a very small angle error and one-axis
trackers are primarily used for non-concentrator panels where the
light may enter off of the panel.
[0167] Attention is now directed to FIGS. 17A, 17B, and 17C which
are diagrammatic representations illustrating three different
fields of view generally indicated by 170, 170' and 170'',
respectively, that may be each associated with a different solar
collector (or solar concentrator). FIG. 17A illustrates effective
field of view 170 that may be associated with a non-tracked (fixed)
solar collector such as a conventional PV solar panel. FIG. 17B
illustrates a field of view 170' that may be associated with a
solar collector (or solar concentrator) that employs one-axis
tracking, and FIG. 17C illustrates a field of view that may be
associated with a solar collector (or solar concentrator) that
employs two-axis tracking. In FIG. 17A, the associated solar
collector may receive and collect incoming rays of sunlight with
the sun in locations from +/-23.5 due to seasonal variation 173 and
from +/-90 due to daily variation 176.
[0168] FIG. 17B illustrates field of view 170' associated with a
collector wherein a one-axis tracker has been incorporated such
that field of view 170' associated with viewing and/or with
receiving and concentrating sunlight during daily variation is
reduced as compared to field of view 170 (FIG. 17A) such that field
of view 170' covers an annual seasonal variation 176 where the sun
is high in the summer and low in the winter as illustrated in FIG.
17B by a double headed arrow representing seasonal variation 176,
and it is to be understood that the associated one axis tracker may
be configured for tracking daily variation 173 indicated by a
double arrow in FIG. 17B.
[0169] FIG. 17C illustrates field of view 170'' associated with a
solar collector wherein a two-axis tracker has been incorporated
such that field of view 170'' associated with viewing and/or with
receiving and concentrating sunlight during daily variation is
reduced as compared to field of view 170' (FIG. 17B) such that
field of view 170'' covers no seasonal or daily variation, and it
is to be understood that the associated two axis tracker may be
configured to track seasonal variation 173 and daily variation
176.
[0170] With ongoing reference to FIG. 17B it is noted that if the
associated one axis tracker exhibits a certain degree of error,
then an IOA can be utilized in accordance with previous
descriptions, to compensate for this error. Referring to FIG. 17C
it is noted that the associated tracker is required to track the
motion of the sun at all times during the day and throughout the
year. The accuracy of tracking typically required for this form of
two axis tracking may be prohibitively expensive and may require a
mechanically stiff structure to maintain the required orientation
while supporting an array of panels. It is noted that IOAs may be
incorporated in the associated collector such that IOAs are able to
contribute to correcting errors in the overall tracking to allow
for relaxed specifications relating to tracking requirements, for
example as described in reference to FIGS. 13 and 14.
[0171] Returning to FIGS. 17B and 17C, the assumed one or two axis
tracking is compatible with an associated embodiment of a solar
collector that that utilizes at least one solar concentrator having
field of view 170' or 170'', respectively. By incorporating a light
bending optical arrangement, such as a bender or an IOA, the
incoming rays of light may be redirected toward a receiver, such as
a PV cell or light/heat gathering elements. Thus, an angle between
the optical axis of the concentrator and the incoming rays of
sunlight is the bend angle of the IOA, and the incoming rays of
sunlight may be redirected to the target receiver. Previously, it
was demonstrated how two optical arrangements may be configured to
redirect the light so that light entering a concentrator anywhere
within a range of receiving directions can be received and
concentrated. This same method can be used here so that as the
concentrator is moved by a one axis tracker, an IOA can correct for
any non-normal sunlight angle so that the light exiting a given IOA
is normal to the receiver surface. In fact, since the tracker may
be regarded as relaxing the requirements as to the receiving range
of the concentrator, the optical arrangements may be rotatably
aligned to correct for a smaller angle error. Thus the tracker may
be made at a lower cost or with different requirements with the
understanding that any smaller tracking errors may be compensated
by rotation of the optical arrangements. Furthermore, for a tracker
that supports a plurality of IOA and/or bender or bender equipped
concentrators, since each IOA and/or bender-equipped concentrator
can independently correct for tracking errors, mechanical
specifications and/or requirements of the tracker may be relaxed so
that angular variations across the tracker from one concentrator to
another can be corrected separately in each of a plurality of
concentrators used in a given multi-concentrator system. With this
in mind, it is recognized that an associated tracker could be
configured in a cost-reduced manner such that it does not move
smoothly throughout the day and perhaps has fixed positions that it
rests in and `ratchets` between these fixed positions throughout
the day.
[0172] If a single optical arrangement (such as a bender or an IOA)
can bend the light more than the seasonal variation
(+/-23.5.degree.), then the single optical arrangement can correct
for the North-South seasonal error while the 1- or 2-axis tracker
will correct for the daily sun position. The addition of the
optical arrangement allows for the 1- or 2-axis external tracker to
be simpler in design and less accurate in its positioning. In the
simple case of Spring Equinox when the sun is passing directly over
and perpendicular to the panel, at noon, the optical axis of a
panel may be tilted east or west (relative to the sun location) by
the bend angle so that the input optical arrangements thereon would
see the sunlight entering at the bend angle and bend the light so
that it is normal to the surface inside the panel and can
subsequently be concentrated onto the target. Since the optical
arrangement may correct for any light entering at the bend angle
and the seasonal variation is less than the bend angle, then there
is a panel orientation such that the light will enter the panel at
the bend angle so that the optical arrangement can bend the light
and concentrate the light onto the target. (Note: at Winter
Solstice when the sun is 23.5.degree. below (south) of the normal
of the panel, then the 1-axis tracker would point the panel toward
the sun direction--in the east-west direction--and the optical
arrangement would correct for the low sun entrance angle.) Thus the
1-axis tracker may adjust so that the sun is entering at the angle
that is required by the optical arrangement in order to provide the
needed corrections with respect to tracking the sun, and a single
optical arrangement combined with a 1-axis tracker can be used to
orient the sunlight in the panel for use in a solar concentrator.
Similarly using an IOA-bender configuration may allow a greater
range of sun angle corrections and permit the panel to be oriented
perpendicular to the sun without requiring a panel offset to
compensate for the IOA bending angle.
[0173] As another embodiment of this method, a light bending film
could be applied over an entire solar panel that supports a
plurality of concentrators, such that light entering all the
concentrators in the panel is pre-compensated (or "biased") with a
bend angle. If the panel is mounted so that the seasonal variation
is not symmetric, (the winter angle is not equal to the summer
angle), then the incoming rays of light could be bent by a fixed
angle such that the light in the panel is symmetric with respect to
seasonal variation. For example, if the panel is mounted 20.degree.
too far northward (e.g. panel tilt of 20.degree. when mounted
equatorially), then the seasonal variation will be from 3.5.degree.
North to 43.5.degree. South and the optical arrangements (such as
benders and/or IOAs) would need to correct for the worst case of
43.5.degree.. If a fixed 20.degree. light bending film is added to
the panel, then the light angle may be reduced by 20.degree.
resulting in a symmetric north/south variation of +/-23.5.degree..
This simplifies the overall design by reducing the worst case angle
correction and balances the system. Note, that due to well known
variations of sunlight intensity during the seasons (more intensity
during the summer and less intensity during the winter), it may be
advantageous to have the panel tilted with a north-south offset to
maximize the total amount of energy captured during the year. This
is especially true with a one-axis tracker where the only
north-south correction is performed by the IOAs and not by a
physical movement of the panel.
Dual Optical Arrangements
[0174] A bender-IOA embodiment of an optical concentrator may
include (i) an input bender, which changes the direction of light
rays that pass therethrough and (ii) a lower IOA that accepts rays
of light at a given off-axis (off-normal) direction and focuses
these rays to a receiver (generally centered) below the lens. The
combination of these two rotatable optical arrangements permits the
sun's rays to be directed to a single unmoving receiver when the
sun is anywhere within a range of receiving directions relative to
the concentrator. The extent of this range of receiving directions
is a function of the two optical arrangements and is normally made
to be as large as possible. The lower IOA has many configurations
such as a light bender with a reflective concentrator, a light
bender with an embedded refractive concentrator, or a combination
with the concentration being accomplished by refraction and/or
reflection.
[0175] Attention is now directed to FIGS. 18A, 18B and 18C which
are diagrammatic illustrations of elevational, end, and plan views
respectively of an array of two concentrators 26 and 26' each
including input bender 33, lower IOA 32 and the receiver 189. In
the end view, the second concentrator is not visible behind the
front concentrator. Note that input rays of sunlight 14 entering
the input bender are in different directions on the two views. This
is due to the separation of the sun's ray vector into two
components (a side view component and a front view component). The
actual sun ray angle is the vector sum of these two components.
[0176] The Lower IOA's 32 and 32' may be constructed with a
circular light bending IOA followed by a square or other shaped
concentrator arrangement 187 (represented in FIG. 18C using a
dashed line) to acquire the light that falls between the IOA's.
This configuration has the advantage of using the sun's rays when
the sun is nearly directly overhead. This concentrator design,
while shown as square, could be any shape. For example if the panel
is designed as a hexagonal pattern, then a hexagonal concentrator
would be preferred as compared to the square. In fact, the
arrangement of the light benders, the arrangement of concentrators
and the arrangement of the receivers do not have to be linear or
one-to-one. For example, a 2-by-2 array of light benders could send
light rays to two concentrators which could then send the light
rays to one receiver. Alternatively, a single IOA light bender
could send rays to multiple concentrators and receivers.
Split-Cell
[0177] A split cell embodiment may be based on an array of
concentrators with receiver locations that are not centered with
respect to the concentrators. In particular, when the receivers are
located between the concentrators, in a plan view, then it may be
possible to concentrate light rays that do not pass through an IOA
within the concentrator, but that pass between the IOAs, as will be
described immediately hereinafter.
[0178] Attention is now turned to FIGS. 19A and 19B which
illustrate elevational and plan views, respectively, of a
split-cell system having four concentrators 26. The plan view of
FIG. 19B shows receivers 189 located directly between the
concentrators so that the light rays collected on the receivers can
be from four different IOAs and from the space between the IOAs
(the inter-IOA gap). Thus, input rays of sunlight 14 that enter
between the IOAs in the inter-IOA gap may be combined with the
sun's rays from the four IOAs to create a greater light intensity
than that without the inter-IOA contribution. Since receiver 189
collects all of the light from it's associated square as compared
to just the light from its associated circle, the increase of light
intensity can be 20% or more depending upon the design efficiency.
Note that as the sun increases its angle, then some of the
inter-IOA gap contribution will decrease and possibly result in no
contribution; however, the design could also be optimized to
collect the light at an off-normal angle and reduce the light
collected when the light is directly above each concentrator. Note
also, that the total amount of light entering each receiver need
not be less than the design in FIG. 18.
[0179] In the following example it may be easier to implement the
light bending independently from the concentration. Furthermore,
the shape of the receiver does not have to be circular as is
described next.
[0180] Attention is now directed to FIGS. 20A and 20B which are
diagrammatic perspective views of a bender 200 and IOA 203,
respectively. FIG. 20A depicts a circular shaped bender that
rotates on its axis of rotation (optical axis 47) to align the
incoming sunlight to its angled surfaces (in the form of prisms and
represented by the parallel lines in the diagram) which redirect
that light. It is assumed that all the prisms are at the same angle
and therefore bend the incoming light by the same angle. In this
case, a cylindrical column of light 202 is coming out from bender
200.
Shaping of the Focus Region
[0181] If an IOA is formed by modifying a bender by changing the
prism angle of each prism, a line or rectangle can form focus
region. FIG. 20B shows the effect of an angle change for each prism
moving from the left side to the right side; it is seen that the
light on the left is bent more to the right and the light on the
right is bent more to the left. The light exiting IOA 203 forms a
wedge that can be approximated as a single line or rectangle at a
distance below IOA 203. The varied redirection is shown in FIG.
20B. The effect of this varied prism angle IOA is analogous to a
combination including a conventional IOA combined with a
cylindrical lens which has the ability to concentrate the light to
a more rectangular shaped focus region.
[0182] Attention is now directed to FIGS. 21A and 21B which are
diagrammatic views, in perspective, showing two different
illustrations of yet another embodiment of an IOA 203' that may be
utilized for shaping of the focus region. An additional
concentrator, either reflective or refractive, can be used to
change the line(s) of light or rectangle(s) of light into another
shape such as a circle or small rectangle by concentrating the
light in different directions. One simple method of implementing
this is by using an A-frame refractor or reflector (not shown)
following IOA 203'. FIGS. 21A and 21B show an implementation
resulting in wedges of light 205 from two different
perspectives.
[0183] Attention is now directed to FIGS. 22A and 22B which
illustrate yet two more applications related to shaping of the
focus region. FIG. 22A illustrates a refractor and FIG. 22B
illustrates a reflector design using this concept to further focus
and redirect wedges of light 205 in other directions as compared to
FIGS. 21A and 21B. The tent shaped piece illustrated in FIG. 22A is
a refractor 206 that rotates with an optical arrangement 210 (a
bender or an IOA) which bends the wedges of light exiting optical
arrangement 210 to focus them at a point or small rectangle.
Similarly, the system in FIG. 22B utilizes a reflector 206',
schematically represented in FIG. 22B as an upside down tent that
is suspended from the edge of the optical arrangement. This
performs the same function as the refractor concentrator--it
concentrates the light from the wedges to the focus region using
reflection rather than refraction. Thus the optical arrangement may
be configured to perform a one dimensional concentration along one
axis and the secondary concentrator (refractor or reflector) may
perform a second concentration along the perpendicular (or other)
axis. The combination of both one dimensional concentrations
results in a two dimensional concentration resulting in a shaped
focal region as illustrated in FIGS. 22A and 22B. It is noted that
it may be easier and less expensive to implement the light bending
and concentration in two separate functions rather than combining
all functions in one optical interface.
[0184] Another option is to configure optical arrangement 210 as an
IOA that provides concentration in the second direction. This may
avoid additional interfaces and therefore additional optical
losses. In this case, the IOA could have a complex configuration
attained by convolving the light bending function with the
concentrating function. The light exiting the IOA would be
redirected refractively or reflectively, providing the same
function as the "tents" in the previous examples without adding an
additional optical layer.
[0185] Another method of 2D concentration is to use upper and the
lower surface of the IOA for a combined concentration. One simple
method of doing this is to use the same variable angle prism walls
as discussed previously with reference to FIG. 20B on a lower IOA
surface 215 (see FIG. 20B) and a similar variable angle prism wall
on the upper IOA surface 216 (see FIG. 20B) where the direction of
the prisms is rotated 90 degrees as compared to the lower IOA.
Also, the tilt angle for the upper IOA prisms may be set to a
nominal of zero degrees so that no light bending occurs for this
direction. For example, the upper IOA surface may be configured to
concentrate in the X-axis and the lower IOA surface may be
configured to concentrate in the Y-axis to result in a
2-dimensional concentration using one IOA.
[0186] These methods along with variations of these methods can be
used to direct light from a moving source to a single location or
multiple locations. Varying levels of concentration can also be
achieved. The shape of the illuminated area can also be varied.
Furthermore the distance to the focus region can be reduced by
focusing the light to multiple points. Using multiple smaller focus
regions may also reduce the heat gain at each focus region location
which could have a direct benefit for PV applications. All of these
have benefits in applications that have limitations in spacing,
that have requirements in light concentration, spot size
requirements or light location requirements.
Bender-IOA Combination
[0187] Attention is now turned to FIGS. 23A and 23B which are
diagrammatic representations showing two plan views of the same
concentrator generally indicated by the reference number 26. In
this example, an upper bender 33 has a bending angle
.beta.=30.degree. for bending incoming rays of light 14 by 30
degrees, and a lower IOA 32 has an acceptance direction with a
zenith angle of .xi.=30 degrees in order to focus the rays to the
target. Thus, the upper bender can be rotationally configured so
that its exit rays are 30 degrees from normal in order to match the
lower IOA.
[0188] FIGS. 23A and 23B may be regarded as illustrating a
particular mode of operation wherein the sun's rays entering at the
normal to the concentrator. (The sun is positioned so that it is
intersected by the optical axis). If it is assumed that the bender
has been rotated so that its bend direction is oriented to the
right along the positive x-axis, then the intermediate rays 39 exit
the upper bender at a 30 degree angle from the optical axis to be
collected by the lower IOA which is rotated to point towards the
intermediate rays so that these rays will be focused to the focus
region. Thus, if the bender bends the rays of light to the right,
then the lower IOA will be rotatably pointed so that it bends the
rays of light to the left resulting in the rays exiting the lower
IOA normal to the IOA surface and parallel to optical axis 47.
[0189] As a second example that cannot be easily visualized in a
single plane, attention is now turned to FIGS. 24A, 24B and 24C,
which are diagrammatic representations illustrating elevational,
end and plan views, respectively of an embodiment of a concentrator
generally indicated in all three views by reference number 26. If
the input rays of sunlight 14 enter bender 33 at an angle of 45
degrees from normal as seen from the front, then the bender may be
rotatably oriented so that intermediate rays 39 exit at 30 degrees
from optical axis 47 making them more vertical. Since this is a two
dimensional problem with rotation, the change of direction of the
rays from 45 degrees to 30 degrees may not be accomplished in one
plane. In this example, the light rays will change direction out of
the plane made by the 45 degree incoming rays and optical axis 47.
It can be seen from the top view in FIG. 24C that in this
perspective, the input rays of light 14 may be regarded as entering
from the side and being successively bent first by the bender to a
first angled direction as indicated in the top view by intermediate
rays 39, and then by the IOA in a second angled direction as
indicated in the plan view by IOA output rays 220.
[0190] To better understand this rotation, referring to FIG. 24A,
first consider the bender rotated so that its bend direction points
to the right in the direction of the positive x-axis. The 30 degree
bend angle (.beta.=30.degree.) of the bender will bend the ray
downward so that the ray will exit the bender at 15 degrees from
optical axis 47. If the bender then rotates 90 degrees so that its
bend direction is pointed away, into the paper, and in the
direction of the positive y-axis, the bender will now add its 30
degree bend component in the direction of the y-axis which cannot
be seen from the front view--the front view would show the ray
passing the bender without any change of angle. The side view,
however, will show the ray entering normal to the bender and then
bending 30 degrees upon exiting the bender. Thus, the ray will
continue at 45 degrees as seen from the front view since there has
been no bending in this dimension and add a bend of 30 degrees as
seen from the side view. The result is that the ray has a new
direction, 45 degrees sideways and 30 degrees forward (or
backward). The vector sum of these two angles is 54 degrees from
normal which is too shallow. Thus, by rotating the bender, the ray
direction has changed from being too steep at 15 degrees to being
too shallow at 54 degrees. Since the ray direction will change
smoothly and continuously with the bender rotation, then there will
be a certain bender rotation angle that results in a 30 degree exit
angle from the bender. This is the rotation angle that is required
for bender 33 to prepare the ray for entering IOA 32. IOA 32 is
then rotated to be pointed towards the intermediate rays of light
for concentration by the IOA into the focal region 41.
One Embodiment of a Bender
[0191] Attention is now directed to FIG. 25A, which is a
diagrammatic plan view illustrating one embodiment of a bender
generally indicated by reference number 230. The use of a prism
array provides one approach for configuring a bender. A prism array
may consists of a 1 dimensional array of prisms 233 as illustrated
in FIG. 25A. Typically each prism of the prism array will have a
vertical wall 236 and a sloped wall 239 on a prismatic side 242 of
the array. A flat surface 241 faces towards the incoming rays of
light. This is similar in structure and manufacture to a
conventional Fresnel lens, although it is not circularly symmetric
as in the case of many Fresnel lenses. It should also be noted that
the principles and techniques taught hereafter can equally well be
employed by a practitioner of ordinary skill in the art to embody a
bender with two prismatic sides, or more specifically a bender with
both sides defining separate 1 dimensional arrays of prisms.
[0192] In one orientation, as illustrated in FIG. 25A, flat side
241 faces towards incoming rays of light 14 and prismatic side 242
faces toward output rays of light 92. It is assumed that the
incoming rays of light are parallel with one another, and that the
orientation of the rays will bend as they enter the higher index of
refraction material. Note that if the rays were to then exit a
surface parallel to the first surface as in flat glass, then the
rays would return to their original angle. However, when the output
rays exit the prismatic side of the prism array, they may leave
through the vertical wall or the sloped wall. In this embodiment,
the bender is configured so that the optical axis 47 is aligned
parallel to a normal axis 301 that is perpendicular (normal) to
flat surface 241, and the incoming rays of light enter the bender
at an incoming angle .theta..sub.in as illustrated in FIG. 25A.
[0193] It is noted that for incoming rays of light that enter from
the left and not from the right, then the exiting rays will exit
the bender through the sloped wall only, and will not exit the
bender through the vertical walls. For a given set of incoming rays
of light (parallel with one another and entering with incoming
angle .theta..sub.in) the bender produces output rays of light 92
(parallel with one another and exiting the prism array with an
output angle .theta..sub.out). It is further noted that output
angle .theta..sub.out is related to, but not equal to, the incoming
angle .theta..sub.in, and that the bending angle .beta. can be
derived, based on the values of .theta..sub.in and .theta..sub.out
in conjunction with the geometry illustrated in FIG. 25A. As
described previously in reference to FIGS. 8 and 9, in the context
of a particular incoming ray of light, the term bending angle
refers throughout this disclosure to the change of angle of the
rays of light caused by the bender, and may be regarded as the
angle .beta. of output ray 92 relative to extension 105 of incoming
ray of light 14. For example, consistent with this definition, and
by inspection of FIG. 25A, it is evident that bender 230 bends
incoming ray of light 14 by the bending angle of
.beta.=.theta..sub.in+.theta..sub.out. It is noted that this is a
special case, and it is not to be assumed that the bending angle
.beta. is a constant for all possible values of .theta..sub.in.
[0194] A person of ordinary skill in the art will recognize that
the amount of bending can be determined, based on well know
principles of optics, by the angle of the sloped wall, the
refractive index of the bender material, and the application of
Snell's Law. With ongoing reference to FIG. 25A, with the angle of
the sloped wall relative to the flat surface represented as angle
.PSI., and with the index of refraction of the bender material
represented as index n, then .theta..sub.out may be expressed as
follows:
.theta. out = .PSI. + sin - 1 ( n sin ( sin - 1 ( 1 n sin ( .theta.
in ) ) - .PSI. ) ) = .PSI. + sin - 1 ( sin ( .theta. in ) cos (
.PSI. ) - n 2 - sin 2 ( .theta. in ) sin ( .PSI. ) ) ( EQ 4 )
##EQU00004##
[0195] In the following three examples, we will consider the angle
of (i) the incoming rays of the light 14 entering the bender (ii)
internal rays of light 239 passing through the bender and (iii)
output rays of light 92 exiting the bender are considered assuming
a bender index of refraction n=1.5 and a prism angle
.PSI.=40.degree. from flat.
[0196] For the sun directly overhead and incoming rays of light 14
entering at angle of .theta..sub.in=0.degree. (from optical axis
47), the internal ray angle inside the bender will also be
0.degree. but the ray angle upon exiting the bender
(.theta..sub.out) will be -34.6.degree. (to the left). This
corresponds, for this particular incoming ray of light, with a
bending angle of .beta.=34.6 degrees.
[0197] For incoming rays of light entering at (.theta..sub.in)
angle of 10.degree. (from optical axis 47), the internal ray angle
will be 6.6.degree., and the rays upon exiting (.theta..sub.out)
will be -15.6.degree. (to the left). This example is the situation
as depicted in FIG. 25. This corresponds with a bending angle of
.beta.=25.6 degrees.
[0198] For incoming rays of light entering at (.theta..sub.in)
angle of 22.3.degree. (from optical axis 47), the internal ray
angle will be 15.degree., and the rays upon exiting
(.theta..sub.out) will be 0.degree. (relative to the optical axis).
This corresponds with a special case wherein the bender bends the
incoming rays of light so that they exit the bender parallel to the
optical axis, and bending angle
.beta.=.theta..sub.in=22.3.degree..
[0199] While the assumption of a constant bending angle has served
as a useful approximation for descriptive and illustrative
purposes, it is again noted that this is only an approximation, and
does not necessarily represent the precise bending performance of a
given bender, as illustrated above in the context of a specific
embodiment. Nevertheless, this approximation tends to be
sufficiently realistic such that it is useful to characterize a
given bender as exhibiting a specific "bend angle" even if this
number is subject to variation based on the orientation of incoming
rays of light, and in the context of this disclosure, a given
bender may be specified as having a specific bend angle, even in
cases where that bend angle may vary. In order for a specific bend
angle to serve as a useful reference, it is helpful to maintain
consistency, from one bender to another, as to the definition of
bend angle. In view of the foregoing points, the "bend angle" of
any given bender, when specified as a single value, is to be
associated throughout this disclosure with the special case when
output rays are oriented parallel to the optical axis of the
bender, for example in the way that is described in the third
example set forth immediately above.
[0200] For example, while the bender embodiment of the present
discussion exhibits variations depending on the orientation of the
incoming rays of light, the bender embodiment illustrated in FIG.
25A is to be specified, based on this convention, as exhibiting a
"bending angle" of .beta.=22.3.degree. such that the incoming rays
of light are bent so that the resulting output rays are parallel
with the optical axis.
[0201] The following table specifies a number of embodiments that
are assumed to utilize the geometry illustrated in FIG. 25A, with
each bender embodiment exhibiting a different bending angle
(specified in the table as "bend angle") in accordance with the
definition set forth immediately above. The upper row corresponds
to a desired bending angle, with each column being associated with
bending angles 15, 20, 25, 30, 35 and 40 degrees, and the second
and third rows specify prism angles .PSI. required to achieve the
desired bending angle in benders that utilize two different
materials, Acrylic and Polycarbonate, respectively. It is assumed,
as noted in the table, that acrylic has a refractive index of
approximately 1.49 and polycarbonate has an refractive index of
approximately 1.58.
TABLE-US-00001 TABLE 1 Bend Angle (deg) Material Index 15 20 25 30
35 40 Acrylic 1.49 29 37 45 51 57 62 Polycarbonate 1.58 25 32 39 45
51 55
[0202] Attention is now turned to FIG. 25B, which illustrates the
operation of bender 33 with respect to incoming rays of light 14
that are oriented to cause shading as will be described in further
detail at one or more appropriate points hereinafter. Input rays of
light 14 enter at angle .theta..sub.in of 40.degree. from the
optical axis; the internal ray angle .phi. may be 25.4.degree. and
the rays upon exiting may have .theta..sub.out=17.8.degree.
directed to the right as shown in FIG. 25B. In this example, light
is bent by a bend angle of .beta.=22.2 degrees, however some of the
exiting light rays encounter vertical wall 236 and are refracted
off in a different direction (not shown), to cause shading.
One Embodiment of a Solar Concentrator
[0203] Attention is now drawn to FIG. 26A, which is a diagrammatic
plan view illustrating one embodiment of a solar concentrator,
generally indicated by reference number 26'' that utilizes a multi
element IOA 32''. A bender 33 initially receives incoming rays of
light 14 and redirects the incoming rays of light for acceptance by
multi-element IOA 32'' configured for accepting and concentrating
the rays by focusing the rays into focus region 41. Multi-component
IOA 32'' includes a bender 234 and a Fresnel lens 235, and bender
33 and IOA 32'' are both supported for rotation about optical axis
47. It is noted that the Fresnel lens can be either fixed in
position, or it can be supported for rotation about the optical
axis 47, and may be configured as a converging or concentrating
lens for focusing light that enters normal to its upper surface so
that it is directed to pass through focal region 41.
[0204] It is noted that bender 234 and Fresnel lens 235 cooperate
with one another to function as an IOA in accordance with previous
descriptions in reference to FIGS. 5 and 6, and the references
herein describing IOA 32'' as a "multi-element" IOA are premised on
the presence of two or more elements therein. As discussed in
reference to FIG. 8, FIG. 9 and FIG. 25, bender 234 may receive
intermediate rays of light 39 and bend the intermediate rays of
light by bending angle .beta. (of bender 234) to be parallel with
optical axis 47, and the Fresnel lens concentrates the intermediate
rays of light into focal region 41.
[0205] A specific embodiment of concentrator 26'' will be described
immediately hereinafter. This specific embodiment is capable of
concentrating the sunlight by at least approximately 10:1, and is
capable of tracking the sun within a cone of approximately +/-45
degrees around the optical axis. While the concentrator is tracking
the sun and concentrating the light onto the receiver, the
concentrator can remain fixed in position and orientation, and the
only movement can be restricted to the rotation of the two
benders.
[0206] It may be useful to refer to FIG. 25A and the corresponding
description to better understand the specific description of the
benders. Bender 33 may be configured as an acrylic disk with a
circular input surface (as flat side 241) of 120 mm in diameter and
a bend angle of .beta.=20.degree.. Input surface 241 of bender 33
defines an input aperture for the concentrator, and has an aperture
area of approximately 113 cm.sup.2. A bottom surface 247 of bender
33 is a linear prism array with a pitch of 1 mm and with the
vertical walls (FIG. 25 236) angled 2.degree. to promote overall
ease-of-manufacturing. From the previous table of bender designs,
the sloped wall portion of the bottom side of the bender (FIG. 25,
reference number 239) may have an angle v of approximately
37.degree..
[0207] Bender 234 can be chosen to be an acrylic disk with an input
area of 120 mm in diameter, and the bend angle can be chosen to be
30.degree.. The larger bend angle for the second bender is chosen
to enable the concentrator to target the sun when the sun is near
or on the optical axis. During this situation, the sunlight enters
the topmost bender nearly normal, which tends to increase the
amount of bending that will occur. Increasing the bend angle of the
bottommost bender allows it to restore light entering the
concentrator nearly parallel to the optical axis to parallel again
before entering the Fresnel lens. The bend angle of the bottommost
bender should be increased until it approximately matches the
increased bend angle of the topmost bender for light entering that
bender from normal. As with bender 33, bottom surface 247 of bender
234 is a linear prism array with a pitch of 1 mm and with the
vertical walls (FIG. 25, item 236) angled at 2.degree. to aid
manufacturing. Again, from the previous table of bender designs,
the sloped wall portion of the bottom side of the bender (FIG. 25,
item 239) can have an angle v of approximately 51.degree..
[0208] It may be advantageous to place the two benders as close
together as manufacturing and operational tolerance allow and still
permit rotation for maintaining a small gap 242 between bender 33
and bender 234 FIG. 26A. If the two benders are not closely spaced,
a portion of the light leaving the first bender, which is at an
angle relative to the optical axis, may miss the second bender, and
light could be wasted. For the specific implementation under
discussion, the gap may be readily configured to be under 1 mm and
this maintains such wasted light to less than approximately 1%.
[0209] The Fresnel lens may have a diameter equal to or larger than
that of the bottommost bender in order to not lose (and therefore
waste) any further light energy. For example, a non-imaging Fresnel
lens, as described in Leutz and Suzuki, may be used as this
provides a reasonably efficient configuration. However, a more
commonly available imaging Fresnel lens, such as is available from
Fresnel Technologies (101 W. Morningside Drive, Fort Worth, Tex.
76110, 817-926-7474, www.fresneltech.com), can be used as well.
Lower pitch Fresnel lenses may be preferred as they can have fewer
edges and corners which may scatter light and correspondingly
reduce efficiency, however as pitch drops--lenses often become
thicker. One reasonable choice for this specific embodiment is the
Fresnel Technologies Item #18.2 lens that has a pitch of 25/inch
and focal length of 6 inches. It is noted that Fresnel lenses are
generally not reversible and that this lens is designed to be
placed grooved-side up which is the opposite from the depiction of
the Fresnel lens in FIG. 26A which indicates it is placed flat-side
up. This particular lens also operates flat side up at low
concentration ratios, such as is the case here. However, the
effective focal length is shorter when reversed.
[0210] Still referring to FIG. 26A, the concentration factor of
solar concentrator 26'' may be determined by the square of the
ratio of the Fresnel lens focal length to the distance from the
focal length to the receiver. Thus, assuming the focus region is
located 4.5 inches below the Fresnel lens, the concentration factor
is (6/1.5).sup.2 or 16:1. The receiver should be at least 1/16 the
aperture area of the concentrator, or at least 30 mm in diameter.
However, this does not imply that the receiver will receive light
with an intensity 16.times. as great as sunlight. Losses from
reflection at the interface of each refractive material,
imperfections in the optics (particularly in the sharp corners),
and losses from light intersecting the vertical walls and bending
the incorrect direction may limit the optical efficiency to below
70% for this embodiment. Thus, this concentrator may intensify the
light hitting the receiver by a factor approximately of
10-11.times..
[0211] Attention is now directed to FIG. 26B in conjunction with
FIG. 26A. FIG. 26B is a diagrammatic plan view of a concentrator,
generally indicated by reference number 244, utilizing a
single-element IOA 245. An input surface 248 of single-element IOA
245 may include a bender prism array configured to serve as a
bender for receiving and bending intermediate rays 239 in a way
that is analogous to the operation of bender 234 in FIG. 26A, and
an output surface 255 may include a focusing prism array configured
to cause focusing in a way that is analogous to the operation of
Fresnel lens 235 of FIG. 26A. The bender prism array and the
focusing prism array may cooperate with one another to serve as an
IOA as described previously with reference to FIGS. 5 and 6.
Applicants believe that a person of ordinary skill in the art,
having this disclosure in hand, will be readily able to modify the
designs presented previously and throughout this disclosure to
configure a single element IOA as described with reference to FIG.
26B. In particular, configuring the output surface as a Fresnel
lens may be achieved in accordance with well known design
techniques associated with Fresnel lenses. With regard to the input
surface, Applicants believe that a person of ordinary skill in the
art may readily adapt and incorporate the teachings herein in order
to configure the input surface for bending in an appropriate way
such that the input and output surfaces cooperate with one another
to serve as an IOA in the manner described herein.
[0212] Furthermore, for reasons of illustrative clarity the
forgoing example describes the operation of a concentrator with a
single-element IOA that operates analogously with the concentrator
of FIG. 26A such that the bending and focusing functions of IOA 245
are performed separately and by opposing faces of the IOA. In this
regard, applicants further recognize that there is no requirement
that the bending and focusing action must be separated between the
input and output surfaces, respectively, and these two opposing
surfaces may be configured to cooperate with one another in a
variety of complex combinations to perform the bending and focusing
functions as described herein, and Applicants believe that a person
of ordinary skill in the art, having the present disclosure in
hand, may readily generate a variety of configurations that will
perform in a manner that falls within the scope these
descriptions.
[0213] As described immediately above in reference to FIG. 26B, the
bending and focusing functions may be combined in a variety of
complex ways between the opposing surfaces of single element IOA
245. Applicants further recognize that there is no requirement that
the input optical arrangement should be limited to receiving and
bending, or that an additional optical arrangement (following the
input optical arrangement) should be limited to serving solely as
an IOA (for accepting and concentrating), and that all of the
functions of the solar concentrator may be combined in complex ways
and distributed or re-distributed across among multiple optical
arrangements. It is noted that these functions include, but are not
limited to, (i) the initial receiving and bending previously
described with respect to the bender, and (ii) the accepting and
concentrating previously described with respect to the IOA.
[0214] Attention is now directed to FIG. 26C which is a
diagrammatic elevational view of one embodiment of a concentrator
244' including an input optical arrangement 252 and an additional
optical arrangement 255. The concentrator is configured for
defining (i) an input aperture 260 for example as an outer
periphery of the input arrangement having an input area for
receiving incoming rays of light 14, (ii) an optical axis 47
passing through a central region 105 of the input aperture, (iii) a
focus region 41 having a surface area that is substantially smaller
than the input area and is located at an output position along the
optical axis offset from the input aperture such that the optical
axis passes through the focus region, and (iv) a receiving
direction 34 defined as a vector that is characterized by a
predetermined acute receiving angle .omega. with respect to the
optical axis and one or both of the optical arrangements is
rotatable about the optical axis for alignment of the receiving
direction to receive the incoming rays of light. The input
arrangement and the additional arrangement are further configured
to cooperate with one another for focusing the plurality of input
light rays to converge toward the optical axis until reaching the
focus region such that the input light is concentrated at the focus
region.
[0215] While a number of embodiments described herein utilize a
bender as the input arrangement, and an IOA as the additional
arrangement, it is again noted that there is no requirement that
the arrangements be disposed in this order. However, Applicants
recognize that if a given concentrator is modified by re-arranging
the order of the arrangements, in many cases, it may be necessary
to substantially re-configure the arrangements themselves in order
that they cooperate with one another to receive and concentrate the
incoming rays of light in a manner that is at least generally
consistent with the performance of optical concentrators (for
example optical concentrator 26) described herein and throughout
this overall disclosure. While substantial modifications of the
optical arrangements may be required in conjunction with any
particular re-ordering of the optical arrangements, Applicants
believe that a person of ordinary skill in the art, having this
disclosure in hand, may implement concentrator 244' in a variety of
ways, utilizing a variety of optical arrangements, in accordance
with the teachings herein and without adhering to any particular
restriction as to ordering of the arrangements. For example, in one
embodiment, as described previously, the input arrangement may be a
bender, and the additional arrangement may be an IOA. In another
embodiment, the input arrangement and the additional arrangement
may both be configured as IOAs. It is further noted that there is
no requirement that optical arrangements 252 and 255 should consist
of only one optical component, ands that one or both of these
optical arrangements may include a plurality of optical
components.
Prism Wall Slope
[0216] Referring again to FIGS. 25A and 25B, and considering the
embodiment of bender 233 illustrated therein, it is again noted
that in cases when the incoming rays of light enter bender 233 at
an incoming angle that is equal to the bending angle (such that
.theta..sub.in=.beta.) then the output rays will exit the bender
parallel with the optical axis thereof. Returning now to this
description, the case where .theta..sub.in is increased beyond
.beta. will be examined immediately hereinafter.
[0217] Attention is again turned to FIG. 25B, which, as described
previously, illustrates the operation of bender 33 with respect to
incoming rays of light 14 that are oriented to cause shading as
will be described in further detail at appropriate points
hereinafter. Input rays of light 14 enter at angle .theta..sub.in
of 40.degree. from the optical axis; the internal ray angle .phi.
may be 25.4.degree. and the rays upon exiting may have
.theta..sub.out=17.8.degree. directed to the right as shown in FIG.
25B. In this example, light is bent by a bend angle of .beta.=22.2
degrees, however some of the exiting light rays encounter vertical
wall 236 and are refracted off in a different direction, to cause
shading, as will be discussed in greater detail immediately
hereinafter.
[0218] If the angle is sufficiently increased, then there will be a
shading effect where some of the rays of light are interfered with
by part of the bender, and these rays of light may no longer be
parallel to the non-interfered rays of light. This shading effect
is shown in FIG. 25B where the exiting rays of light designated by
the reference numbers 92 are not limited. However, the output rays
of light 92'' may be at least partially blocked, and output rays
92''' are at least partially blocked. This shading effect can be
minimized or removed by several methods including changing the
slope of the vertical prism wall or modifying the top or bottom of
the bender surface.
[0219] Establishing the optimal slope of the prism walls is not a
trivial matter and may be different for the bender than for an
associated IOA. In the case above, for the 23.degree. entering
angle of light, the exit light was normal to the bender. This is
the design case for the associated IOA. In this case, the internal
ray angle was found to be 15.degree., thus the vertical wall could
be sloped up to this 15.degree. angle with no negative effects.
Thus, under normal operation, this part of the associated IOA
(between vertical and 15.degree. should never transmit any light
rays). This design freedom can be used to improve the prism
performance by adjusting the prism corners (from vertical to slope
and back to vertical) so that the area of the prism that interacts
with the light will be more optimally oriented. In a similar
manner, the bender can have its vertical wall modified to improve
performance, however there are more trade-offs for the upper
bender.
[0220] In order to examine the prism wall effects, related aspects
of operation of the operation of concentrators are observed. At
least within a reasonable approximation, as described previously, a
BRIC includes a bender that can be oriented to redirect the
incoming light onto an exit cone followed by an IOA that accepts
this light and redirects it to the target. In this basic
embodiment, the illumination entering the bender is essentially
redirected as it travels through the two optical arrangements (the
bender and the IOA). In this description, the bender rotates as
frequently as needed to keep the sun within its field of view. The
IOA rotates in relation to the bender as needed to maintain the
light on the target. The amount of rotation required is determined
by the sun's movement through the sky in its daily and annual
cycle. For an ideal location on earth, the sun's path moves +/-23.5
degrees north to south to north annually and +/-90 degrees as it
moves east to west daily.
[0221] Attention is now directed to FIG. 27 which is a diagrammatic
view generally indicated by the reference number 240, illustrating
the coverage of the sky where the horizontal axis of the rectangle
corresponds with a daily tracking range 249 representing a portion
of a given day from sunrise to sunset and the vertical axis of the
rectangle corresponds with a seasonal tracking range 251
representing seasonal variation from summer to winter. The diagram
(FIG. 27) depicts this space and how the bender and the IOA
cooperate with one another if the bender has a bending angle of
30.degree. and if the IOA has a acceptance direction fixed at an
angle of 30.degree. relative to its associated optical axis. It is
expected that the sun will traverse a straight line from left to
right in the rectangular box each day, and this line will move from
the top of the rectangle in winter to the bottom of the rectangle
in the summer. The IOA coverage, as shown by the central circle 243
for the IOA and the series of circles 246 for the bender, is shown
centered on the rectangle. This is the ideal configuration, but any
particular installation may shift this configuration to be centered
above or below the center of the rectangle.
[0222] Here it can be seen that a system, having a bender and an
IOA, configured with the bender and the IOA matched with one
another such that .xi.=.beta.=30.degree., exhibits a lack of
coverage in the morning and the evening (near sunrise and sunset).
While the sunlight angle at these times is non-optimum for energy
collection, it would still be beneficial to collect this energy
since this represents a loss of potential energy conversion on a
daily basis.
[0223] The IOA in FIG. 27 may be composed of Prism-like Fresnel
lens, as will, be described immediately hereinafter. In this
regard, attention is now directed to FIG. 28 which illustrates
three different variations of bender and/or IOA cross-sections that
may be employed as will be described immediately hereinafter. Each
variation is shown in a region labeled as regions A-C separated by
dashed lines. The central region B in FIG. 28 is shown with
vertical walls and sharp angles (i.e. not beveled) as the ideal
configuration although not required. Practical manufacturing
constraints, such as those imposed by injection molding or other
plastic forming methods, make it more likely that the vertical
walls will have a small slope (as shown to the left in Region A
with one such slope indicated in the figure as a "non-vertical
wall") and/or that the sharp corners will be rounded (as shown to
the right in Region C). The sunlight comes from the top of FIG. 28,
and of particular interest is the effect of the non-vertical wall
(as in Region A), a "top apex 250 and a bottom apex 253 as shown.
Depending on the time of day and day of the year, the sunlight can
impinge on the associated bender or IOA at various angles, but at
any given moment, the rays are parallel to each other. The bender
or IOA is rotated so that the impinging rays strike the sloped
surfaces and are redirected by an angle that is a function of the
sloped wall. However, when the sun is directly over the bender or
IOA, the sun's rays will enter the bender or IOA in a perpendicular
direction and be parallel to the vertical walls. The sunlight will,
however, strike the non-vertical wall, because of it's a small
sloped angle, at approximately noon on the equinoxes. When the sun
is east or west (early or late in the day compared to noon), or
north or south (early or late in the year compared to the Spring or
Autumn equinox) then the sun will enter the bender or IOA with an
angle and may not strike the non-vertical wall.
[0224] If the vertical walls are perfectly vertical and top apex
250 and bottom apex 253 are perfectly sharp (not rounded), there
will be no optical shading loss--i.e. nearly all of the light
entering the bender or IOA will exit the bender or IOA in the
preferred direction. However, cases where there is a slight slope
to the vertical wall and/or the top apex and/or the bottom apex are
not perfectly sharp, some of the incoming light will be redirected
in a manner not consistent with the design expectation and will
result in "shading" loss. These cases are shown in FIG. 28 wherein
the areas the light that is not transmitted properly is noted at
the non-vertical walls (as I.sub.A in Region A), and for the
non-sharp top apex 250' and non-sharp bottom apex 253' (as I.sub.C
in Region C). In these cases, the angle formed between the sunlight
and the surface is not the expected or designed angle, and the
light will not be sent in the appropriate direction, and this loss
of sunlight can be mapped into a hole in the bender or IOA's
coverage of the sky, as will be described hereinafter.
[0225] Attention is now directed to FIGS. 29A and 29B which are
diagrams depicting the shading loss for the near vertical sunlight
entry normally at the equinoxes when the sun entry angle is normal
to the bender or IOA surface.
[0226] FIGS. 29A and 29B shows that the loss due to shading is
limited to certain times of the year and then only at certain times
of the day for the non-vertical wall and the non-ideal angles. When
the amount of energy produced throughout the year is optimized, it
is potentially advantageous to reduce the performance at certain
times of the day and on certain days of the year if the gains in
performance at other times and day are larger. Specifically, the
design should call for and tolerate small angles on the vertical
wall and curvature or non-sharp angles for the bottom apex of the
bender and or IOA if these result in overall cost reductions or
performance improvement when measured over the lifetime of the
panel. Thus, a slight loss in performance for a short period of
time on a few days of the year may be a good tradeoff if
performance is enhanced by a greater amount at other times
throughout the year.
[0227] Attention is now directed to FIG. 30 which is a diagram
showing the loss of coverage for a 2 degree angle on the vertical
wall and can also be used to understand the loss due to control of
sharpness of the prism angles. Notice that an area 250 is a
corresponding area of loss that is a nearly negligible loss
compared to the total area of the collector. Even though it occurs
during the prime solar energy time of day, it is for a very short
time and for very few days, thus when averaged over the year, this
is a very small loss of total energy production.
[0228] It is important to understand that sunlight at shallow
angles near sunrise and sunset has less energy potential for a
fixed panel design since the shallow angle reduces the amount of
energy impinging upon the panel. Therefore it is more important to
collect the light in the prime hours, and in the diagram above,
this means centering coverage ring 243 horizontally unless there
are other special conditions that may modify the theoretical
sunlight distribution. The example shown in FIG. 30 assumes a
bender with bend angle design of 30.degree. and an IOA with an
acceptance angle having zenith angle of 30.degree. which means
coverage of the first 30.degree. of sun in the morning and the last
30.degree. of light before sunset are lost (since the two
arrangements each are assumed to track 30.degree. for a total of
60.degree. out of a total of 90.degree. for sunrise to noon and for
noon to sunset). This loss can be regained by increasing the bend
angle and the zenith angle to 45.degree. for the bender and the
IOA, respectively, as one example, but there is a limit to the
total amount of bending that one optical arrangement can perform.
When the two optical arrangements are designed to different
associated bender and zenith angles, the coverage of the morning
and evening sunlight can be increased at the cost of a hole in the
center. The hole in the center would have a radius nearly
equivalent to the difference in angles between the two IOAs. So
combining a bender with a 30.degree. bender angle and IOA with a
45.degree. zenith angle would result in a 15.degree. hole--or half
the diameter of the current center circle.
[0229] Additionally, while the IOA often is associated with a
requirement that the light exiting it should normally be centered
below it, the bender does not have this requirement. Thus the IOA
has a fundamental optimal angle for the vertical wall based on the
fact that the light entering the IOA is pre-determined and the
light exiting the IOA (in the absence of concentration) must be
vertical, this sets the vertical wall angle limits. Referring back
to the discussions around FIG. 25B, it was noted that for a
properly designed IOA (with an exit ray angle normal to the IOA),
the internal ray angle was 15.degree. for that particular example;
thus for that example, the vertical wall could have a slope as
large as 15.degree. and still not create a shadowing effect. For a
refractive IOA, the vertical wall limit is a function of the index
of refraction of the IOA, the wall angle of the IOA, and acceptance
zenith angle .beta. of the IOA. Since the bender does not require
the light to exit normal to the surface, it has a different
requirement for the vertical wall angle. This vertical wall angle
can be adjusted to trade off performance at low angle as compared
to high (near vertical) angles. Thus a shallower vertical wall
angle 252 (See FIG. 28) may perform better when the sun is at a low
entrance angle (as shown in FIG. 25B) since the shadowing effect
will be reduced, but when the sun is directly overhead, this same
shallow vertical wall angle will now cause a shadowing effect. As
can be seen in FIG. 25B, when the vertical wall is truly vertical,
there is a shading effect at low entrance angles, and this can be
removed by adding a slope to the vertical wall. The penalty of
adding a slope is that when the sun is directly overhead, the rays
may hit the non-vertical wall and be misdirected. However since the
sun is directly overhead only a few minutes a day for a few days
per year, this loss of performance may improve overall (annual)
performance due to the increased performance at morning and evening
for all days of the year. (Also, as described later, if the bender
has a tilt associated with it, then the sun's rays may never enter
normal to the surface, so there may be no performance penalty
associated with adding a slope to the vertical wall.
[0230] Attention is now directed to FIG. 31 which illustrates the
coverage of the sky where the horizontal axis of the rectangle
corresponds to a daily tracking range 249 representing a portion of
a given day from sunrise to sunset and the vertical axis of the
rectangle corresponds to a seasonal tracking range 251 representing
a given year from summer to winter. This shows the tradeoff between
adding sky coverage in the morning and evening balanced against
losing sky coverage for specific days around noon. The diagram is
scaled for degrees in both the vertical and horizontal directions.
However, if the actual time spent by the sun in each position of
the rectangle is considered as well as the angle of the sun in each
position (which translates to how much energy is convertible), it
is seen that the vertical axis of +/-23.5.degree. actually
represents 365 days of the year while the horizontal axis
represents only 1 day. Further, the spacing between days on the
vertical axis is not uniform--that is the sun does not move the
same number of degrees each day towards the north and south. In
fact, the sun moves faster around solstice (center of the vertical
axis) and slows down at the winter and summer (ends of the vertical
axis). So a small dot of non-coverage in the center does not impact
very many days. The convertible energy from the sun is greatest in
the midday sun (center of the horizontal axis) and least at the
beginning and end of the day (ends of the horizontal axis). There
is also a summer-winter effect where there is more convertible
energy in the summer than the winter. When these are considered,
there is an optimal combination of sky coverage near sunrise and
sunset tradeoff with loss of coverage for a short period around
noon for a few days around solstice. Accordingly, one angle can be
used for the bender to limit shading losses while increasing the
angle of the IOA to cover a greater portion of the sky each morning
and evening.
[0231] Thus it may be desirable to reduce the noon optimal
performance of a system in order to gain performance at other times
of the day or year.
Method of Rotation of IOA
[0232] As described above, the optical arrangements (for example
the bender and the IOA) may be selectively rotated such that a set
of two or more optical arrangements in a given concentrator
cooperate with one another in order to continuously compensate for
the sun's motion for maintaining concentration of the sun's rays on
a fixed (stationary) target, and one method of moving a particular
optical arrangement is by rotation about the center axis of the
arrangement. It is noted that, in all previous descriptions,
rotation of the optical arrangements has been described with
respect to the optical axis of each of the aforedescribed optical
arrangements, and it is to be understood that the optical axis in
the foregoing examples has been aligned to be collinear with an
axis of rotation such that both the optical axis and the axis of
rotation may be considered as equivalent for the descriptive
purpose of serving as a reference axis in space. While as few as
one concentrator may comprise a solar collector, it is also
possible to construct a panel of multiple concentrators containing
many optical arrangements wherein groups of optical arrangements
can be rotatably controlled together using one or more drive
mechanisms. The optical arrangements may be physically supported
about their center, suspended by their edges, suspended in a fluid,
or in any manner such that they may rotate in a controlled way.
Limits of Rotation
[0233] In order to consider a number of rotation methods and
apparatus that are possible, it may be helpful to consider the
requirement of the rotation needed to track the sun. In particular,
if the rotation can be limited to less than 360 degrees, then this
may simplify the motion and allow other forms of rotation. The
amount of rotation required is determined by the sun's movement
through the sky in its daily and annual cycle having seasonal
variations. For any location on earth, the sun's path moves within
a range of +/-23.5 degrees north to south to north annually and it
moves +/-90 degrees (nominally) as it moves east to west daily.
[0234] Attention is now directed to FIG. 32 which is a diagram
schematically depicting this space and how the two optical
arrangements cooperate with one another to cover this space in an
example where the bender has a bend angle of .beta.=30.degree. and
the IOA has an acceptance direction with a zenith angle of
.xi..sub.A=30.degree. such that the range of receiving directions
for the collector describe a receiving cone with an area that is
approximated in FIG. 32 as a circle. It is expected that the sun
will traverse a straight line from left to right in rectangular box
257 each day, and this line will move from the top of the rectangle
to the bottom of the rectangle and back to the top throughout the
year. The IOA coverage 243, as shown by the circle for the IOA and
the overall coverage of the series of circles 246 for the bender is
shown centered on the rectangle. This is the ideal configuration,
but it is not required and any given installation may shift this
configuration to be centered above or below the center of the
rectangle.
[0235] The pair of pointing directions 256 and the pair of pointing
directions 259 on the same diagram show how there are two distinct
solutions for the orientations of the optical arrangements for a
light source at any particular point in the range of operation. By
evaluating the extremes of +/-23.5.degree. (winter to summer) and
the center line (solstice), it can be determined if the range of
angles of the optical arrangements can be limited.
[0236] Notice that for a given concentrator including a particular
bender-IOA combination, it is possible to bend the light from the
incoming angle to the target by two different methods. In the
context of FIG. 32, it is possible to use a configuration that
includes an IOA that is not pointing upward when the sun is located
in the lower half of the diagram (from 0 to -23.degree.). This
means that we can confine the IOA to a 180 degree rotation plus the
additional approximately 140 to accommodate the reverse rotation to
the summer and the same approximately 14.degree. to accommodate the
reverse rotation to the winter. The 14.degree. is found by taking
the Tangent of the angle described by the east-west motion
(90.degree.) and the north-south motion (23.degree.) which provides
14.degree.. This means that the IOA can be confined to
approximately a 208.degree. rotation which is much less than the
full 360.degree. and permits simple linkages and other limited
rotation methods to be used to orient the IOA.
[0237] It is observed that the bender can be confined to a similar
rotational limit if the two optical arrangements are properly
paired (with bend angle equal to zenith angle as described above)
since their function can be reversed as shown by the two pointing
directions illustrated in FIG. 32. However, if the two optical
arrangements (the bender and the IOA) are not compatible in this
regard, then the limits may be different for the two IOAs.
[0238] In order to confine the rotation to these limited levels, it
may require a discontinuity in angle orientation of the optical
arrangements sometime during the day to switch the direction of
thereof, although this can be accomplished fairly rapidly in
comparison to the motion of the sun.
Rotational Methods
[0239] Two methods of rotating the IOA in an array configuration
are disclosed. The bender is typically mounted as an array so that
all of the benders in an array are rotated, for example by a first
drive mechanism, synchronously with one another for maintaining the
same orientation as one another. The IOAs may be configured in a
separate array that such that all the IOA's are rotated, for
example by a second drive mechanism, independently from the bender
array, but controlled in a similar manner.
[0240] Attention is now turned to FIGS. 33A and 33B which
illustrate diagrammatic elevational and plan views, respectively,
of one example of a concentrator having a bender 33 that is tilted
with respect to an IOA 32. The bender may be tilted, relative to
the IOA to improve the acceptance angles allowed for the
concentrator by a fixed tilt angle 261 that is set so that optical
axis 47 of the bender is at least approximately aligned to the
acceptance direction of the IOA. Thus, if the IOA exhibits an
acceptance direction having a zenith angle of 30 degrees, then the
bender may be tilted at a tilt angle of approximately 30 degrees or
less. This allows the top bender to function in a way that is
analogous to a bender used in conjunction with a concentrating lens
to implement an IOA, as was depicted in FIG. 31. As has been
discussed previously, the bender in a multi-element (bender+lens)
IOA is operated with light rays exiting it parallel to the optical
axis, which significantly reduces shading losses. A top bender
operating at a tilt approximately equal to the acceptance direction
of the following IOA operates under the same condition: light rays
will exit it parallel to the bender's tilted optical axis and
shading losses will be significantly reduced. However, in order to
facilitate this desirable arrangement, as the IOA rotates to track
the sun, the tilted optical axis of the bender can rotate to stay
aligned with the acceptance direction of the IOA.
[0241] A single drive mechanism can be configured for rotating both
the bender and the IOA in a coordinated way to maintain tracking by
causing the tilt direction to follow the acceptance direction of
the lower IOA. The bender would also be allowed to rotate around
its own optical axis. Thus two rotations are still required: (i)
the full concentrator rotation of both IOAs about the IOAs optical
axis 47' and (ii) the rotation of the bender about its own tilted
axis 47. A filament 264 can serve as at least a part of a drive
mechanism to provide rotation of IOA 32 and the bender such that
the IOA and the bender are rotatably coupled with one another. The
tilt angle can be reduced, but should be larger than zero to gain
an advantage in accepting lower angle sunlight and in reducing the
effect of the non-vertical walls of the IOA, if a prism array
configuration is used.
[0242] Attention is now directed to FIG. 34 which illustrates
another example of a concentrator wherein a bender 33 can be
controlled by wrapping a filament 264 such that it extends around a
peripheral edge of IOA 32 first, then wraps around and grips a
peripheral edge of bender 33 to provide bender control. The
filament is routed from the IOA to the bender at a junction 269
where the two optical arrangements are nearest. Filament 264 can be
firmly gripping (and/or fixedly attached with) the bender so that
it rotates the bender without affecting the IOA.
[0243] Attention is now directed to FIG. 35 which represents a
concentrator having a bender that is linked through a hub 270
attached with the IOA such that the bender rides on the hub as
shown in FIG. 35. The illustration of FIG. 35 is schematic in
nature, and it is to be understood that the illustrated
configuration can be achieved in a number of different
configurations.
[0244] Attention is now directed to FIG. 36 which is a schematic
diagram showing some examples of bender-IOA tilt by utilizing a
ramp method. The ramp method uses a first ramp 272 on the upper
part of the IOA and a second ramp 275 on the bottom of the bender.
Thus, when the two optical arrangements are pointed in the same
direction the ramps add in height and tilt the bender; when the
optical arrangements are pointed in opposite directions (such as
when the sun is directly overhead), then the ramps cancel and the
arrangements are parallel to each other.
[0245] When we consider the function of the bender, there is a
tradeoff between increasing the top angle, which in turn increases
the amount of the early morning and late evening sun that is
accessible, and shading loss, which increases with increasing top
angle.
[0246] Attention is now directed to FIG. 37 which is a plan view
showing an array of four concentrators that are rotatably coupled
with one another through a drive mechanism including a filament
264, typically thread, chain, and/or wire, that can be wrapped
around a portion of each bender in the array so that as the
filament is moved, it causes the benders to rotate about their
associated axes. The pattern of the filament is made so that there
may be little or no slippage of the benders and each bender rotates
the same amount; a serpentine pattern can be used in this
embodiment. A groove or slot in the circumference of the benders
may be used to keep the filament in place around the optical
arrangement. Alternatively, the filament may be self centering by
using a band or tape or similar method.
[0247] The filament is moved by a motor 267 which drives the
filament in a controlled manner to rotate the benders to the proper
angle. At least one motor for each array may be used, or one motor
268 with a shifting transmission to connect the motor to either one
of the arrays may be used. The filament may wrap around an output
shaft of the motor, and then proceed around each of the benders in
the array. Center posts 271 may be used to wrap the filament a
half-turn so that the filament changes direction after leaving one
lens and before entering the next lens. If a larger array is
needed, then additional center posts could be added. Thus if the
filament is moving down from the right side of one lens, then it
can be guided such that it moves up as it enters the left side of
the adjacent lens. While FIG. 37 is a plan view, and therefore
illustrates only benders which are positioned as input arrangements
for initially receiving input rays of light (not shown), it is
recognized that the same techniques may be applied with respect to
IOA's (not shown in FIG. 37) and that the same filament may wrap
around IOA, for example in accordance with FIGS. 33 and 34.
[0248] Attention is now turned to FIG. 38 which is a schematic
representation illustrating yet another example of a drive
mechanism for rotating the optical arrangements 280 using gears
where each optical arrangement could have a set of teeth (not
shown) that mesh with a drive gear 283. In the present example, a
central gear 283 with gear teeth (not shown) around the outside of
the gear may rotate, causing optical arrangements 280 that are
meshed with central gear 283 to rotate. It is noted that this same
method of rotation could be expanded for any number of optical
arrangements such that the optical arrangements have gear teeth
that would mesh with the central gear to allow for rotation.
Furthermore, one or more additional gears (or filaments) could
connect some of the drive gears to, or each gear could be driven by
its own distinct motor.
[0249] Attention is now turned to FIGS. 39A and 39B which are
diagrammatic plan and elevational views, respectively, of a solar
collector constructed as a panel enclosure and generally indicated
by reference number 289. The panel enclosure houses a concentrator
array. As discussed previously, the concentrators may be organized
into the array in patterns that are rectangular, hexagonal, or of
any other shape that may provide for a high areal efficiency in the
packing of the concentrators. Control filaments (not shown) may run
in a fashion that rotatably couples the concentrators so that
selected optical arrangements within each concentrator rotate
synchronously with the corresponding selected optical arrangements
in the other concentrators. For example, filaments may link the
rotation of benders in each concentrator so that they synchronously
rotate together and additional filaments may similarly
synchronously link the rotation of the IOAs within each
concentrator. Therefore, at least in the example at hand, when one
bender rotates 10 degrees clockwise, then all benders rotate 10
degrees clockwise, and the IOAs do not rotate. Or, when one IOA
rotates 60 degrees counter-clockwise, then all IOAs rotate 60
degrees counter-clockwise, and the benders do not rotate. In this
regard, the drive mechanism is to be considered as rotatably
coupling all the benders with one another, and as rotatably
coupling all the IOAs with one another. The side view of FIG. 39B
also shows reflective concentrators 291 below the IOA.
[0250] Attention is now directed to FIG. 40 which is a diagrammatic
plan view of a concentrator having a bender 33, an IOA 32, and a
concentrating arrangement 300. The optical arrangements including
the bender, the IOA, and the concentrating arrangement are set
above focus region 41 at a distance such that the light energy is
uniformly illuminating the focus region as seen in FIG. 40. This
distance is variable and is a trade-off between lens efficiency
(longer is better) and compact panel size (shorter is better).
[0251] Bender 33 can utilize an array of prisms with each prism
having a width, or pitch, of 1 mm. Each prism indicates a sloped
wall that is at an angle of approximately 40 degrees relative to
the surface tangent, and a vertical wall that is approximately 90
degrees to the surface tangent. This sloped-wall/vertical-wall
pattern repeats over the full surface of the bender.
[0252] At least with respect to the example at hand, it may be
desirable for the sloped wall angle to be maximized to produce the
largest acceptance angle possible given the index of refraction of
the material. The maximum angle is calculated when the rays of
light enter vertically and are bent as far as possible, which is
given by the critical (Total Internal Reflection) angle. This angle
is .THETA.(prism)=arcsin(1/n), where n is the index of refraction.
Thus, for an index of refraction of 1.5, the maximum angle is 41.8
degrees. If the prism includes a 90 degree vertical angle, then the
prism ramp angle generally should not exceed this and should be
less than this angle to allow for tolerance and a larger field of
view of the sun. One exemplary design choice is the use of a 40
degree angle, though with a higher index of refraction material,
the angle can be different.
[0253] The vertical side wall of each prism may also be modified if
direct light above the lens is not to be completely concentrated to
the target. This may be useful in examples wherein the top lens is
tilted with respect to the line connecting the center of the lens
to the center of the target. This may also be useful if more of the
lower angle performance can be gained at the expense of the near
vertical performance, which only occur a few minutes a day for a
few days per year.
[0254] The pitch (prism width) can be adjusted based upon the
sharpness of the corners of the prism (more rounded corners of the
prism produce losses so a larger pitch may be preferred) and the
volume of material of the prism (a larger pitch require more
material which is more costly and will produce more optical
aberrations).
[0255] By way of example, the bender can be a disk of acrylic with
a diameter of 120 mm and maximum thickness of 2 mm with a 3 mm hole
centered for support, and the prisms can be integrally formed with
the disk. The bender disk rotates about a center hole. The outer
rim of the disk can include a slot to accept a filament that
provides for rotation. The flat side of the bender can face towards
the sun and the prismatic side is facing the target. This bender
may be made by standard casting or injection molding techniques.
Any suitable dimensions can be used so long as the device functions
consistent with these descriptions.
[0256] In the example at hand, concentrator 300 immediately follows
the IOA. The concentrator can be configured such that that it
causes a focus region spot size of 30 mm at the design distance of
12 cm. In one embodiment, the IOA and the concentrator are
integrated into one optical element which removes two optical
interfaces. This IOA will have a complex surface related to the
convolution of the light bending prisms and the concentrating
Fresnel and should be numerically modeled for optimal efficiency.
The examples described herein are in no way intended to be
limiting, and it is to be understood that there are innumerable
solutions to this lens shape, that are considered to enable overall
performance, as described. The IOA may be fabricated using a
variety of well-known manufacturing techniques, including but not
limited to injection molding and the like. It is to be understood
that the concentrator need not be integrally fabricated with the
rotating IOA refractive element, and that in another embodiment,
the concentrator may be a compound parabolic concentrator (CPC) or
similar reflective concentrator that can be arranged as a separate
and distinct component from the rotating IOA refractive element.
Additionally, the IOA could be completely reflective where the
reflective element bends the light and concentrates the light; thus
the system could comprise one refractive IOA bender and one
reflective IOA as the complete optical system.
[0257] In the example at hand, the bender can be rotated about its
axis by filament 264 and the IOA may be rotated about its axis by
filament 264'. A PV solar cell 303 of 30 mm diameter can be fixedly
centered under the concentrator so that it may be fully
illuminated. The PV solar cell can be attached to a metal backing
plate (not shown) which may serve as a heat sink for the thermal
energy added by the concentrated solar radiation. Note, that as
compared to a standard non-concentrating solar panel, this BRIC
method has nearly the same solar density and thermal density, thus
the thermal penalty for a BRIC panel should be no greater than that
of a standard solar panel without concentration.
[0258] This design has a theoretical concentration of 16 as the
sun's rays are captured over a 120 mm diameter area and
concentrated over a 30 mm diameter area resulting in a 4.times.
reduction in diameter and a 16.times. reduction in area. However,
due to an approximate 4% reflective loss on each lens interface, (6
optical interfaces), the lens efficiency is approximately 78%, and
a protective cover layer (not shown) is typically about 90%
efficient, resulting in a concentration factor of about 11. All
values are for demonstration only and any suitable values may be
used so long as the device functions consistent with these overall
descriptions.
[0259] Control circuitry (not shown) may be configured to direct
the filaments 264 and 264' to move causing the bender and the IOA
to rotate in such a manner that the sun's rays are illuminating
focus region 41 for reception by PV cell 303 at least at times when
the rays are within the range of receiving angles of the
concentrator.
[0260] Variations with respect to FIG. 40 include: combining the
IOA and the concentrator into one integral optical arrangement;
tilting the bender to point more closely towards the sun; using a
different rotational method other than the outer diameter drive
filaments 264 and 264'; replacing the PV cell with multiple
receivers; removing a central rotation hub 306 and supporting each
of the three optical arrangements by their respective edges or
sides; using multiple concentrators in side-by-side relationships
with one another to concentrate onto one single target and so
on.
[0261] Attention is now directed to FIG. 41 in conjunction with
FIG. 22B and FIGS. 26A and 26B. FIG. 41 is a diagrammatic
elevational view of a concentrator, generally indicated by
reference number 310 utilizing a bender 33 (as an input optical
arrangement) followed by a multi element IOA 32''' (indicated in
the figure with a dashed box). The multi-element IOA includes a
bender 234 and a reflector 206'' having a parabolic contour. Bender
234 accepts intermediate rays of light 39 and redirects the
accepted rays for collection by reflector 206'' which collects and
concentrates the redirected light into focus region 41, as
illustrated in FIG. 41.
[0262] In one embodiment, bender 33 and bender 234 may be
configured to cooperate with one another such that output rays 92'
exiting bender 234 may be collimated (parallel with one another) in
an orientation that is at least approximately parallel with optical
axis 47. With regard to this embodiment, Applicants believe that a
person of ordinary skill in the art will recognize that there are a
variety of well known techniques for utilizing parabolic reflective
surface for collecting and concentrating collimated light. For
example, reflector 206'' may be configured as a concentric
parabolic concentrator (CPC) according to well known techniques.
These techniques are discussed in "Nonimaging Optics" by Roland
Winston, Juan C. Minano, and Pablo Benitez; published by Elsevier
Academic Press and which is incorporated herein by reference. While
an example utilizing collimated output rays 92' has been presented
herein for purposes of descriptive clarity, it is to be appreciated
that there is no requirement that output rays 92' should be
collimated and/or parallel with optical axis 47, and a person of
ordinary skill in the art, having this overall disclosure in hand,
may readily implement a variety of configurations in which
reflector 206'' can be configured to collect output rays 92' that
have been received and bent by bender 234 and are neither
collimated nor parallel with optical axis 47. However, it is to be
appreciated, based on well known principles of optics, that a given
reflector 206'', in order to collect and concentrate the light as
described herein, may require that output rays 92' fall within some
predetermined range of angles relative to optical axis 47.
[0263] With ongoing reference to FIG. 41 it is noted that bender 33
and bender 234 may be selectively rotated with respect to one
another and relative to the orientation of the incoming rays of
light, in order for the bender and the multi element IOA to
cooperate with one another, in accordance with the descriptions in
this overall disclosure, for receiving and concentrating incoming
rays of light 14. It is further noted that in one variation of the
embodiment described herein, reflector 206'' may be attached to
bender 234 such that bender 234 and reflector 206'' co-rotate. In
another variation, reflector 206'' may be stationary in the earth's
frame of reference such that it does not rotate with bender
234.
[0264] While a number of exemplary aspects and embodiments have
been discussed above, those of skill in the art will recognize
certain modifications, permutations, additions and sub-combinations
thereof. It is therefore intended that the following appended
claims and claims hereafter introduced are interpreted to include
all such modifications, permutations, additions and
sub-combinations as are within their true spirit and scope.
* * * * *
References