U.S. patent application number 09/902033 was filed with the patent office on 2001-11-29 for double reflecting solar concentrator.
Invention is credited to Frazier, Scott.
Application Number | 20010045212 09/902033 |
Document ID | / |
Family ID | 25415218 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010045212 |
Kind Code |
A1 |
Frazier, Scott |
November 29, 2001 |
Double reflecting solar concentrator
Abstract
A double reflecting solar concentrator utilizing a primary
reflective surface which reflects incident light toward a secondary
surface. The incident light reflects off the secondary surface away
from the primary surface's natural focus point toward a secondary
focal point positioned on or substantially near the surface of the
primary reflective surface.
Inventors: |
Frazier, Scott; (Littleton,
CO) |
Correspondence
Address: |
JENKENS & GILCHRIST, PC
1445 ROSS AVENUE
SUITE 3200
DALLAS
TX
75202
US
|
Family ID: |
25415218 |
Appl. No.: |
09/902033 |
Filed: |
July 10, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09902033 |
Jul 10, 2001 |
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09579537 |
May 24, 2000 |
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6276359 |
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Current U.S.
Class: |
126/686 ;
126/600 |
Current CPC
Class: |
F24S 23/80 20180501;
F24S 23/74 20180501; Y02E 10/47 20130101; F24S 23/77 20180501; F24S
30/45 20180501; F24S 23/79 20180501; Y02E 10/40 20130101; F24S
30/425 20180501 |
Class at
Publication: |
126/686 ;
126/600 |
International
Class: |
F24J 002/38 |
Claims
What is claimed is:
1. A solar concentrator comprising: a substantially planar primary
reflective surface; and a secondary reflective surface having a
substantially parabolic curvature, the secondary reflective surface
positioned adjacent to the primary reflective surface such that at
least a portion of the light incident on the primary reflective
surface is reflected to the secondary reflective surface and
reflected from the secondary reflective surface to a focal line
substantially on the primary reflective surface.
2. The solar concentrator of claim 1 wherein the primary reflector
is positioned relative to the secondary reflector such that light
incident on the primary reflector is reflected substantially
parallel to a line between the directrix of the secondary reflector
and the focus of the secondary reflector.
3. The solar concentrator of claim 1 further comprising a support
system for rotating said solar concentrator about a rotational axis
that is substantially parallel to the focal line and near the
primary reflector.
4. The solar concentrator of claim 3 wherein the rotational axis is
near the focal line.
5. The solar concentrator of claim 3 wherein the rotational axis is
between the focal line and the secondary reflector.
6. The solar concentrator of claim 1 wherein the rotational axis is
substantially on the secondary reflector.
7. The solar concentrator of claim 1 wherein the primary and
secondary reflectors are adjoining.
8. The solar concentrator of claim 1 further comprising a solar
receiver on the focal line.
9. A solar concentrator assembly comprising: a parabolic reflector
having a parabolic curvature; a planar reflector being
substantially planar and positioned adjacent to the parabolic
reflector; a focal line on one of the parabolic and the planar
reflectors; and a support structure that supports the parabolic and
the planar reflectors to rotate together about a rotational axis
substantially parallel to the focal line.
10. The solar concentrator assembly of claim 9 wherein the
rotational axis is near the focal line.
11. The solar concentrator assembly of claim 10 wherein the focal
line is substantially on the parabolic reflector.
12. The solar concentrator assembly of claim 10 wherein the focal
line is substantially on the planar reflector.
13. The solar concentrator assembly of claim 9 wherein the focal
line is substantially on the parabolic reflector and the rotational
axis is between the focal line and the planar reflector.
14. The solar concentrator assembly of claim 9 wherein the
parabolic and the planar reflectors are adjoining.
15. The solar concentrator assembly of claim 9 further comprising a
solar receiver on the focal line.
Description
[0001] This application is a continuation in-part of co-pending
application Ser. No. 09/579,537 filed on May 24, 2000, which is
hereby incorporated by reference as if reproduced herein.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field of the Invention
[0003] The present invention relates to solar concentrators and
solar collector systems. More particularly, the present invention
relates to a linear solar concentrator which utilizes a portion of
a parabolic arc or a planar surface for a first reflection surface
and a planar or a parabolic secondary reflection surface for
concentrating solar energy in a substantially linear fashion on a
predetermined portion of the first reflection surface.
[0004] 2. Description of Related Art
[0005] Solar concentrators work by collecting sunlight from a large
area and concentrating sunlight into a smaller area. There are
identifiable techniques for converting solar energy into useable
forms, but whether or not the solar energy is collected and
converted on a substantial scale is controlled by economics. If the
cost of installing and maintaining a solar energy collection system
is lower than the alternatives, then widespread use of the solar
energy collection system is possible. The bulk of the cost for
solar energy collection systems is in the initial investment. Thus,
solar systems must begin to pay for themselves when the system is
utilized.
[0006] Presently, there exist large linear solar concentrators.
FIG. 1 depicts an exemplary prior art linear concentrator. The
depicted concentrator was the result of the EUCLIDES project which
was subsidized by the European Union. Dual parabolic trough
portions cast a beam irradiance onto a strip of solar cells
positioned linearly along the Dual parabolic trough portion's focal
line. Drawbacks of this prior art type of linear concentrator
relate to the size and shape of the concentrator as well as the
position of the focal line. The geometry of such concentrators
requires that the linear trough must "stick-up" high above the
ground in order to focus the solar energy to the focal lines of the
trough. The parabolic surfaces become a large "sail" and require
substantial support due to subjection to the strength of strong
winds. The singular parabolic shape of the concentrator is not
easily reinforceable and is easily twisted or flexed out of its
required parabolic shape such that the reflected solar energy
misses the prescribed linear conglomerate of solar cells.
[0007] Furthermore, the focal line positioning of the solar
collectors requires its own separate supporting structure such that
the solar collectors are held on the focal line associated with
each parabolic solar concentrator.
[0008] Cooling of the solar collectors is a difficult task due to
the movement of the focal line as the linear parabolic trough
tracks the sun. The focal line will move along a defined arc as the
depicted linear parabolic trough collector pivots on a line
parallel with the focal line. Such a situation requires flexible
plumbing pieces that connect to the solar collection area. The
flexible plumbing carries coolant, such as water, to cool the solar
collector devices while the solar energy is being concentrated on
them. Flexible plumbing tends to crack, degrade and leak when it is
used in outdoor conditions. Thus, one of the major repair costs for
prior art solar concentrator/collection systems is the repair and
maintenance of the associated flexible plumbing for cooling the
collector area of the solar concentrator.
[0009] What is needed is a solar concentrator configuration that
has a relatively low manufacturing cost, that is structurally more
rigid than a simple linear parabolic trough, and that maintains a
profile close to the ground such that the solar concentrator
structure is less likely to sustain damage due to high winds.
SUMMARY OF THE INVENTION
[0010] The present invention overcomes the foregoing and other
problems by providing a double reflecting linear trough style solar
concentrator that is relatively inexpensive to manufacture and
provides a structure that is substantially more rigid than a simple
parabolic surface.
[0011] Exemplary embodiments of the present invention provide a
double reflecting solar concentrator that comprises a primary
parabolic surface and a secondary planar surface. Incident light
reflects off the primary parabolic surface toward the parabolic
surface's natural focal line. Prior to reaching the natural focal
line, the incident light is reflected off the secondary planar
surface toward a secondary focal line which is located
substantially on the primary parabolic surface.
[0012] Exemplary embodiment also encompass a double reflecting
solar concentrator that comprises a substantially planar primary
reflective surface and a secondary reflective surface having a
substantially parabolic curvature. The secondary reflective surface
can be positioned adjacent the primary reflective surface such that
at least a portion of the light incident on the primary reflective
surface is reflected to the secondary reflective surface and
reflected from the secondary reflective surface to a focal line
substantially on the primary reflective surface.
[0013] The optical path of the exemplary embodiments results in a
narrower field of view at the receiver which can improve the costs
of some receiver devices. The parabolic reflector also acts to
redirect slightly unfocussed sunlight back onto the receiver which
reduces system pointing accuracy requirements. Furthermore, this
technique for focusing allows the solar concentrator to track the
sun by pivoting substantially on the focal line of the exemplary
double reflecting trough. A cooling system can cool the solar
collectors positioned on the focal line. Since the focal line is
substantially stationary, flexible plumbing for cooling the area
about the focal line is substantially eliminated. The exemplary
solar concentrator can pivot at other locations depending on the
needs of the specific application.
[0014] Furthermore, exemplary solar concentrators that are in
accordance with the present invention are structured to comprise a
profile that is low to the ground such that wind effects are
limited. Such a low profile design eliminates the prior art's need
for "beefy" structural support.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] A more complete understanding of the method and apparatus of
the present invention may be obtained by reference to the following
Detailed Description when taken in conjunction with the
accompanying Drawings wherein:
[0016] FIG. 1 is a prior art parabolic trough solar
concentrator;
[0017] FIG. 2 is a generic parabola and its focus;
[0018] FIG. 3 depicts a section of a parabolic curve;
[0019] FIG. 4 depicts an exemplary portion of a parabolic curve
with light reflecting off of the parabolic surface;
[0020] FIG. 5 depicts an exemplary side view of an exemplary double
reflecting parabolic solar concentrator;
[0021] FIG. 6 depicts a closer view of FIG. 5;
[0022] FIG. 7 depicts another exemplary embodiment of a double
reflecting solar concentrator comprising a second parabolic
surface;
[0023] FIG. 8 depicts an exemplary double reflecting solar
concentrator with a second parabolic surface and how further
depicts light reflects across the second parabolic surface;
[0024] FIG. 9 depicts another exemplary double reflecting solar
concentrator with a grazing concentrator;
[0025] FIG. 10 depicts exemplary "open" and "closed" configurations
of exemplary double reflecting solar concentrators;
[0026] FIG. 11 depicts various exemplary double reflecting solar
concentrators which place the focal line of the concentrator near
the bottom of the parabolic section;
[0027] FIG. 12 depicts an exemplary side view of an exemplary
double reflecting solar concentrator having a planar primary
reflector;
[0028] FIG. 13 depicts exemplary side view of another exemplary
double reflecting solar concentrator having a planar primary
reflector;
[0029] FIG. 14 depicts yet another exemplary side view of yet
another exemplary double reflecting solar concentrator having a
planar primary reflector;
[0030] FIGS. 15A and B depict a three-dimensional views each of an
exemplary double reflecting solar concentrator mounted on a support
structure; and
[0031] FIGS. 16A-D depict schematics of various exemplary mounting
configurations of exemplary solar concentrators.
DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENTS OF THE
PRESENT INVENTION
[0032] The exemplary embodiments provide a double reflecting solar
concentrator which has useful optical and construction properties
which lend itself to low construction costs, installation costs,
and operational costs.
[0033] The exemplary concentrators geometrically comprise a
predetermined portion of a parabolic mirror in combination with a
planar mirror that allows light to be focused on and along a
predetermined portion of the surface of the parabolic mirror, or
alternately along a predetermined portion of the surface of the
planar mirror.
[0034] FIG. 2 depicts a traditional generic parabolic shape 10 and
focal point 12. A parabola is the set of points, in a plane that
are equidistant from a focus point and a line in the plane (the
line is sometimes called a directrix). The exemplary embodiments of
the present invention utilize a portion of the parabolic arc 10. It
is understood that virtually any parabolic arc (parabolic equation)
can be utilized in the present invention. FIG. 3 depicts a section
of the parabolic arc 30 and its focus 12. FIG. 4 depicts incident
light 40 impinging on a surface of the section of parabolic arc 30
and reflecting off a reflective surface (not specifically shown) to
the focus 12 of the parabolic arc section 30.
[0035] FIGS. 5 and 6 depict a first embodiment of the present
double reflecting solar concentrator 50. A first reflecting surface
52 comprises a predetermined portion of a parabolic curve 30. A
second reflective surface 54 is perpendicular to a directrix
associated with the parabolic curve. The exemplary parabolic curve
is normalized such that the focal point 12 is positioned at X=0,
Y=2 and the second reflective surface is positioned at X=2.
[0036] The incident light 40 reflects off the primary surface 52
and proceeds toward the focal point 12. Prior to reaching the focal
point 12, the incident light reflects off the secondary surface 54
and is focused at the secondary focus 56. The secondary reflective
surface 54, is preferably positioned on the parabolic curve of the
primary reflective surface 52. In the exemplary embodiment the
primary and secondary focal points 12, 56 are each positioned at
the same Y-coordinate position.
[0037] By placing the secondary surface 54 between the primary
reflective surface 52 (the parabolic curve) and the focus, the
secondary surface 54 will shift the focus to a point equally
distant in front of it as the distance to the focal point 12 behind
it. Therefore, if the secondary surface 54 is put in an X-position
that is equal to the Y-position of the focus 12 height, the focus
will be shifted to a secondary focus point 56 located on the
parabolic curve and the primary reflective surface 52. FIG. 5
depicts the secondary focus 56 to be on the primary surface
directly to the right of the focus 12. The incident light 40 that
is focused to the secondary focal point 56 must be perpendicular to
the directrix of the parabolic curve.
[0038] With the understanding that FIG. 6 represents a "normalized"
cross section of an exemplary trough-style double reflecting solar
concentrator 50, it is plain to see that the secondary focal point
56 is essentially a focal line that extends the length of the
exemplary double reflecting concentrator's length. Photovoltaic
(PV) cells can be placed linearly along to focal line to collect
the solar energy.
[0039] FIG. 7 depicts another exemplary embodiment of the present
invention. FIG. 7 depicts a double reflecting solar concentrator
having two parabolic surfaces 70. This embodiment provides a solar
concentrator having a more compact profile then the first exemplary
embodiment. A second parabolic reflector 72 is positioned between
the primary reflective surface 52 and the secondary reflective
surface 54. The second parabolic reflector 72 has a focal point
that coincides with the secondary focal point 56. The second
parabolic reflector 72 allows the corner 74 to be removed thereby
decreasing the overall height of the double reflecting parabolic
concentrator 70. FIG. 8 depicts a preferable position for the
second parabolic reflector 72. Ideally, the second parabolic
reflector 72 is positioned such that it does not interfere with the
reflection of incident light 40 as it reflects from the primary
surface 52 to the secondary surface 54. In other words, the
preferable position for the second parabolic surface 72 is such
that light incident on the primary surface 52 is reflected toward
the secondary surface 54 without being obscured or reflected by the
second parabolic surface 72.
[0040] Again, the exemplary embodiment 70 is normalized such that
the original focus of the parabolic curve is at X=0, Y=2. One with
skill in the art could determine and calculate the positioning of
the secondary reflective surface 54 and the second parabolic
reflector 72 for a variety of parabolic curves.
[0041] FIG. 9 depicts another exemplary embodiment of the present
invention 90 which includes a grazing concentrator 92 positioned
adjacent to the secondary focal point 56. A receiving surface 94
can be positioned at the secondary focal point 56 to collect the
solar energy focused there.
[0042] The grazing concentrator 92 is substantially flat and at a
steep enough angle to reflect the incident light onto the receiving
surface (solar cell) 94. The grazing concentrator uses an
additional surface 92 and the original primary reflector 52 which
allows for incident light 40, that is slightly out of focus, to be
reflected back toward the secondary focal point (line) 56. This
feature allows for a lower tolerance pointing system for the solar
concentrator. Thus, a more expensive and more accurate solar
concentrator pointing system may not be required with the present
exemplary embodiment of the present invention. Furthermore, this
embodiment 90 may be better able to collect diffused or stray light
found on partly hazy or lightly cloudy days. The grazing
concentrator 92 helps a receiver, collector or PV 94 collect rays
that are slightly off focus.
[0043] Other embodiments of the present double reflecting solar
concentrator can be utilized to move the secondary focal point to
other positions on or near the primary parabolic surface. FIG. 10
depicts two embodiments of the present invention wherein the
secondary reflective surface is not perpendicular with the
directrix of the parabolic surface or parallel with the Y-axis. The
spacing, from the focal point 12, of the secondary reflective
surface 102a, 102b may also change. The combination of the
non-parallel (canted) and moved secondary reflective surfaces 102a,
102b move the secondary focus 56a, 56b to other locations that may
be more useful than the original secondary focus 56. Canting the
secondary focus 102a may result in a portion of the primary surface
being shadowed 104 by the canted secondary surface 102a and result
in an inefficiency of the resulting exemplary solar
concentrator.
[0044] FIG. 11 depicts an exemplary embodiment of the present
double reflecting solar concentrator 110 wherein the secondary
focus 112 is at the bottom of solar concentrator 110. Here the
incident light 40 reflects first off the primary reflective surface
52 toward the secondary surface 114. The secondary surface 114 is
held in place by a support surface or leg 116. The surface 114 is
positioned such that it does not cast a shadow on the primary
surface 52 by interfering with incident light 40. The secondary
surface 114 reflects the incident light to the secondary focal
point 112 at the bottom of the solar concentrator trough 110.
[0045] FIG. 12 depicts a schematic of an exemplary embodiment of
the present double reflecting solar concentrator 140 configured
such that the first or primary reflective surface 142 is planar and
the secondary reflective surface 144 is a predetermined portion of
a parabolic curve. Thus, incident light 40 reflects off the planar
primary reflector 142 into the parabolic secondary reflector 144
and to a focus 146 on or near the planar primary reflective surface
142. The focus 146 is representative of a focal line that extends
the length of the solar concentrator 140. The planar primary
reflective surface 142 can be angled in relation to the parabolic
secondary reflector 144 to reflect light into the parabolic
secondary reflector 144 substantially parallel to a line passing
through both the focus 146 and the parabola's directrix.
[0046] As seen in FIGS. 13 and 14 the focus 146 need not be near
the upper edge of the planar primary reflector 142, but can be at
various locations along or near the surface of the primary
reflector 142. In FIG. 13, the focus 146 is near the middle of the
planar primary reflector 142. In FIG. 14, the focus 146 is closer
to the bottom of the planar primary reflector 142. Also, as seen in
FIG. 14, the planar primary reflector 142 need not adjoin the
parabolic secondary reflector 144. For example, in cases where the
focus is near the base of the primary reflector 142, the planar
primary reflector 142 may be adjacent to and spaced outward from
the parabolic secondary reflector 144.
[0047] FIGS. 15A and B depict exemplary solar concentrators 120 in
accordance with the present invention. Incident light 40 reflects
off the primary reflective surface 122 toward the secondary
reflective surface 124 and then toward a solar collector 126
located at the focal line (also 126) of the exemplary double
reflecting solar concentrator 120. FIG. 15A depicts an exemplary
embodiment having a parabolic primary reflective surface 122a and
planar secondary reflective surface 124a, and FIG. 15B depicts an
exemplary embodiment having a planar primary reflective surface
122b and a parabolic secondary reflective surface 124b. The solar
collector 126 can be a photovoltaic or other solar energy
collection device. A cooling system can be installed along or
adjacent to the focal line 126. The cooling system can be a fluid
pipe which carries a cooling fluid such as water, propylene glycol,
antifreeze or any other acceptable fluid.
[0048] A support structure supports and aims the exemplary solar
concentrator toward the sun such that incident rays 40 are
substantially perpendicular to the primary reflective surface 122
or the directrix of the parabolic primary reflective surface 122. A
screw jack, cam or hydraulic system 130 may raise and lower the
exemplary solar concentrator such that it rotates substantially
about support elements 132.
[0049] In FIGS. 15A and B, the exemplary solar concentrator is
rotably supported on or near the focal line 126 by support elements
132. Thus, a cooling system mounted near the focal line 126 does
not require flexible plumbing. Furthermore, the collector 126 may
be mounted directly to the support structure at the focal line of
the exemplary solar concentrator 120.
[0050] Referring to FIGS. 16A-D, the exemplary solar concentrator
can be rotably supported at various locations on or near the
concentrator. Moving the axis of rotation away from the edges of
the concentrator decreases the height of the overall assembly as
the solar concentrator 120 is rotated through its range of motion.
Minimizing the overall height of the assembly, minimizes the
profile of the solar concentrator 120 to wind, and thus minimizes
the effect of wind loads. A rotational axis away from the edges of
the concentrator 120, also decreases the force that is required to
rotate the solar concentrator 120, because more of its weight is
supported by the support elements 132.
[0051] FIGS. 16A-D schematically depict the effect of different
rotational axis locations on the height of the solar concentrator.
As is discussed above, to minimize the movement of the cooling
system plumbing (not specifically shown) the solar concentrator can
be configured to rotate about the focus 126 (FIG. 16A). A
rotational axis located intermediate of the focus 126 and the
bottom of the primary reflector 122a has the most compact profile
(FIG. 16B), and the force required to rotate the solar concentrator
is minimized. However, depending on the location of the focus 126,
this configuration may require flexible plumbing for the cooling
system. FIGS. 16C and 16D depict additional configurations. Note
that FIG. 16D depicts the rotational axis on or near the secondary
reflector 124a. The rotational axis can be at virtually any
location on or near the secondary reflector 124a. Also, though each
of the figures depicts a parabolic primary reflector 122a, the
concepts illustrated are equally applicable to a solar concentrator
that has a planar primary reflector 122b and parabolic secondary
reflector 124b. In all of the above figures, the rotational axis
may be displaced from the surface of the solar concentrator, for
example, by a mounting bracket (not specifically shown) joining the
support elements 132 and solar concentrator 120, without departing
from the scope of this invention.
[0052] Some advantages of the present exemplary embodiments are
that the concentrator's trough shape has a natural torsion
stiffness which is greater than that of a plane parabolic surface.
Ribs or other stiffening elements can be added to the structure to
further stiffen the structure. A clear cover 136 can be placed over
the top of the exemplary solar concentrator to increase the
stiffness of the apparatus and further help keep the reflective
surfaces clean. The resulting exemplary double reflecting solar
concentrator is relatively low in overall height when compared to
prior art linear solar concentrators.
[0053] To manufacture an exemplary double reflecting solar
concentrator the parabolic primary surface can be rolled or formed.
The secondary reflective surface is planar and can be formed from
the same piece of metal as the primary surface by being folded at
the lower corner.
[0054] The fixed receiver and plumbing provide additional
manufacturing and operating cost savings. As the sun changes
position throughout the day or year the exemplary solar
concentrator must move so that the sun rays are always incident on
the concentrator at the same angle. The exemplary solar
concentrator rotates substantially about the focal line of the
concentrator. The focal line can be just off the rotational axis.
Thus, the solar collectors (PV's) may be fixed on or near the
surface of the primary reflective surface along the focal line.
Furthermore, the plumbing which cools the solar collectors may flow
through or near the fixed rotational axis of solar collector
thereby eliminating a need for flexible plumbing.
[0055] Although various preferred embodiments of the present double
reflecting solar concentrator have been shown and described, it
will be appreciated by those skilled in the art that changes may be
made to these embodiments without departing from the principles and
the spirit of the invention, the scope of which is defined in the
appended claims.
* * * * *