U.S. patent application number 11/282959 was filed with the patent office on 2011-04-21 for lightweight, low cost solar energy collector.
Invention is credited to Michael K. Costen, Eric B. Hochberg.
Application Number | 20110088686 11/282959 |
Document ID | / |
Family ID | 43878334 |
Filed Date | 2011-04-21 |
United States Patent
Application |
20110088686 |
Kind Code |
A1 |
Hochberg; Eric B. ; et
al. |
April 21, 2011 |
Lightweight, low cost solar energy collector
Abstract
A lightweight solar concentrator of the reflecting parabolic or
trough type is realized via a thin reflecting film, an inflatable
structural housing and tensioned fibers. The reflector element
itself is a thin, flexible, specularly-reflecting sheet or film.
The film is maintained in the parabolic trough shape by means of a
plurality of tensioned fibers arranged to be parallel to the
longitudinal axis of the parabola. Fiber ends are terminated in two
spaced anchorplates, each containing a plurality of holes, which
lie on a desired parabolic contour. In a preferred embodiment,
these fibers are arrayed in pairs with one fiber contacting the
front side of the reflecting film and the other contacting the back
side of the reflecting film. The reflective surface is thereby
slidably captured between arrays of fibers, which control the
shape, and position of the reflective film. Gas pressure in the
inflatable housing generates fiber tension to achieve a truer
parabolic shape. A plurality of bridges and or retention clips may
be employed in certain embodiments to maintain the position of the
reflective surface relative to the fibers.
Inventors: |
Hochberg; Eric B.;
(Altadena, CA) ; Costen; Michael K.; (Milford,
CT) |
Family ID: |
43878334 |
Appl. No.: |
11/282959 |
Filed: |
November 19, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10601923 |
Jun 19, 2003 |
6994082 |
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11282959 |
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60412518 |
Sep 20, 2002 |
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Current U.S.
Class: |
126/600 ;
126/697 |
Current CPC
Class: |
Y02E 10/47 20130101;
F24S 30/425 20180501; F24S 25/50 20180501; F24S 2030/15 20180501;
F24S 23/745 20180501 |
Class at
Publication: |
126/600 ;
126/697 |
International
Class: |
F24J 2/46 20060101
F24J002/46; F24J 2/12 20060101 F24J002/12 |
Goverment Interests
ORIGIN OF THE INVENTION
[0002] The invention described herein was made in the performance
of work under a NASA contract, and is subject to the provisions of
public law 96-517 (35 USC 202) in which the contractor has elected
to retain title.
Claims
1. A solar concentrator comprising: a membrane reflector having a
unitary line focus; a transparent tubular housing enclosing said
reflector; and a plurality of strings extending within said tubular
housing, wherein said plurality of strings shape said reflector to
have a substantially stepless parabolic cross-section.
2. (canceled)
3. The concentrator recited in claim 1 wherein said strings are in
a state of tension.
4. The concentrator recited in claim 1 wherein said strings are
arranged in pairs, each such pair having a string on front and back
surfaces of said reflector.
5. The concentrator recited in claim 4 wherein said string pairs
are in a state of tension.
6. The concentrator recited in claim 1 wherein said housing is
internally pressurized above external atmospheric pressure by a gas
within said housing.
7.-8. (canceled)
9. The concentrator recited in claim 1 wherein said housing
comprises opposed end plates, a gas in said housing being
pressurized to cause said endplates to be extended further from one
another; and wherein said reflector is shaped by a plurality of
string pairs, each said pair supporting said reflector on front and
back surfaces of said reflector, said string pairs being connected
to said endplates and being subjected to tension depending on the
separation between said endplates.
10. (canceled)
11. The concentrator recited in claim 1 further comprising a solar
energy receiver extending along at least a portion of said line
focus.
12. The concentrator recited in claim 1 further comprising means
for rotating said housing to control the orientation of said
reflector relative to incident sunlight.
13.-15. (canceled)
16. The concentrator recited in claim 1 wherein said membrane
reflector is slidably received by said strings without any
significant tension being applied to said membrane reflector.
17. The concentrator recited in claim 9 wherein said endplates each
comprise an axially flexible material.
18. The concentrator recited in claim 1 further comprising at least
one bridge operatively positioned at an interval along the length
of the strings to provide means to maintain the string positions in
a desired parabolic shape.
19. The concentrator recited in claim 1 wherein said membrane
reflector comprises a plurality of adjacent membrane reflector
sections.
20. The concentrator recited in claim 19 further comprising at
least one retention clip operatively connected to said adjacent
membrane reflector sections to operatively position said reflector
sections relative to the strings.
21.-22. (canceled)
23. A parabolic trough solar energy concentrator comprising a
stepless parabolic reflector shaped by a plurality of tensioned
string pairs extending along said reflector, each said tensioned
string pair having respective strings positioned on opposed
surfaces of said reflector.
24. The concentrator recited in claim 23 further comprising a
gas-tight tubular transparent housing enclosing said reflector.
25. The concentrator recited in claim 23 wherein said reflector
comprises a film having a reflective surface and wherein said film
is received between said pairs of strings without any significant
tension being applied to said film.
26. The concentrator recited in claim 24 wherein said housing is
hermetically sealed by a pair of opposed endplates, each such
endplate comprising an axially flexible material.
27. (canceled)
28. The concentrator recited in claim 24 wherein a gas inside said
housing is under pressure and wherein said pressure at least
partially contributes to said tension of said strings.
29. (canceled)
30. The concentrator recited in claim 24 further comprising means
for rotating said concentrator to control the orientation of said
reflector and receiver relative to incident sunlight.
31. (canceled)
32. The concentrator recited in claim 23 wherein said reflector
comprises a plurality of reflector sections.
33. The concentrator recited in claim 32 further comprising at
least one retention clip operatively connected to two or more
reflector sections to operatively position said reflector sections
relative to the strings.
34. The concentrator recited in claim 32 further comprising at
least one bridge operatively positioned at an interval along the
length of the strings and between a pair of adjacent reflector
sections to provide means to maintain the string positions in a
desired parabolic shape.
35. (canceled)
Description
CROSS-REFERENCE TO CORRESPONDING APPLICATIONS
[0001] This application takes priority from provisional patent
application Ser. No. 60/412,518 filed on Sep. 20, 2002 and from
utility patent application Ser. No. 10/601,923 filed on Jun. 19,
2003.
BACKGROUND OF THE INVENTION
[0003] 1. Technical Field
[0004] The present invention relates generally to the field of
solar collectors having a parabolic trough to collect and
concentrate solar energy. The invention pertains more specifically
to an extremely lightweight and low cost parabolic trough solar
collector.
[0005] 2. Background Art
[0006] Parabolic trough technology is currently the most advanced
solar thermal electric generating technology. This is primarily due
to nine large commercial-scale solar power plants, the first of
which has been operating in the California Mojave Desert since
1984. These plants, which continue to operate on a daily basis,
range in size from 14 to 80 MW and represent a total of 354 MW of
installed electric generating capacity. These plants, which were
all built with government support, have explored the lifetime costs
of operating large solar energy collection systems. A dominant
finding from building and operating these solar power plants is
that commercial viability has not yet been attained and that
commercial viability depends upon reducing the per wattage capital
required to build the solar collectors. Reducing the per wattage
capital required to build a solar collector is a prime motivator
for this invention.
[0007] The following issued U.S. patents appear to constitute
relevant prior art:
TABLE-US-00001 U.S. PATENT NO. PATENT DATE INVENTOR 4,173,397 Nov.
6, 1979 Simpson 4,432,342 Feb. 21, 1984 Lucas 4,051,834 Oct. 4,
1977 Fletcher 4,318,394 Mar. 9, 1982 Alexander 4,071,017 Jan. 31,
1978 Russell 4,920,033 Apr. 11, 1989 Sick 4,243,019 Jan. 6, 1981
Severson 4,454,371 Jun. 12, 1984 Folino 4,077,392 Mar. 7, 1978
Garner 4,515,148 May 7, 1985 Boy-Marcotte 4,359,041 Nov. 16, 1982
Snodgrass 4,293,192 Oct. 6, 1981 Bronstein 4,291,677 Sep. 29, 1981
Monk
[0008] Of the foregoing prior art patents, the patent to Russell
(U.S. Pat. No. 4,071,017) and to Simpson (U.S. Pat. No. 4,137,397)
appear to be the most relevant.
[0009] Russell discloses a nonparabolic discontinuous (stepped)
flat faceted mirror, which is supported by tensioned cables that
are fixed to the ground via concrete and steel anchors. An
embodiment uses a flexible reflective film, which is weaved through
the cables and tensioned to generate a discontinuous flat faceted
mirror. Being that the mirror is fixed to the ground, the receiver
moves to maintain coincidence with the focus over the course of a
day.
[0010] Simpson discloses a parabolic reflector sheet that is placed
in tension against a plurality of tensioned wires to form a
continuous, stepless, flat faceted parabolic mirror. The tensioned
wires are supported by a pair of arcuate base members, which are
mounted to ground or other structure such as a roof via suitable
supports. The sheet is attached to bars at both ends. Torsion
applied to one of the bars generates tension in the sheet.
[0011] Neither of these patents discloses a continuous, stepless,
unfaceted, parabolic sheet reflector. Also, neither such patent
discloses a transparent tubular enclosure that is pressurized to
generate the tension in the fibers. Additionally, neither patent
discloses a structure, which is of comparable light weight or low
cost.
SUMMARY OF THE INVENTION
[0012] A lightweight solar concentrator of the reflecting parabolic
cylinder or trough type is realized via a unique combination of
thin reflecting film, an inflatable structural element and
tensioned fibers. The reflector element itself is a thin flexible,
specularly-reflecting sheet or film. (Aluminized polyester sheet,
for example). The reflector element is not self-supporting.
[0013] The film is maintained in the parabolic trough shape by
means of a plurality of tensioned fibers (high strength carbon, for
example) arranged to be parallel to the longitudinal axis of the
parabola. Fiber ends are terminated in two spaced anchorplates,
each containing a plurality of holes, which lie on the desired
parabolic contour.
[0014] In the preferred embodiment, these fibers are arrayed in
pairs with one fiber directly above the reflecting film and the
other immediately behind the reflecting film. The reflective
surface is thereby captured between arrays of fibers. The fibers
might constrain the membrane by other arrangements. These fibers
control shape and position of the reflective membrane.
[0015] The anchorplates are centrally fastened to circular
endplates. These endplates also serve to seal the ends of a
transparent thin film cylindrical enclosure tube, which functions
as a housing. The enclosure tube may be seamless or may comprise
one or more seams which enable the enclosure tube to be formed from
a flat flexible sheet. Once sealed, raising the pressure of the gas
(air) inside the enclosure tube increases the stiffness of the
enclosure tube. With only a modest internal pressure the enclosure
becomes structurally stable with the capability to provide a
weather tight housing for the internal mirror, receiver and other
components. In addition, the inflated enclosure is designed with
endplates that impart a portion of their pressure load into the
anchor plates and hence the reflector forming fibers. In this
manner, tension is provided to the fibers without using additional
costly structure.
[0016] Because of the tension, sag or deformation of the array of
fibers can be minimized even in the presence of the gravitational
load represented by the reflector sheet. As tension is increased,
deformation of both fiber and reflector is reduced and the
reflector is even further constrained to follow the specific
parabolic contour defined by the array of fiber-locating holes.
[0017] Thus, the tension resulting from pressurization of the gas
inside the cylindrical envelope forces the reflector sheet into the
parabolic trough shape enabling a line focus to be created above
the reflector. The location of this focal line is determined by the
array of holes and the particular parabolic form they follow. In
most embodiments the focal line is created inside the transparent
cylindrical envelope, including being coincident with the axis of
the cylindrical envelope, although it can otherwise be arranged to
fall outside the cylinder.
[0018] A substantially line like receiver of the focused
concentrated solar direct beam radiation is located at the line
focus of the trough reflector. This receiver can be a conduit
containing a flowing gas or liquid to which the radiant energy will
be transferred and thereby be captured and utilized. Alternately, a
photovoltaic receiver may be located at the position of this focal
line for the purpose of converting the radiant energy directly into
an electrical form. Alternatively, a hybrid receiver having both
thermal and electrical outputs may be placed at this line
focus.
[0019] Concentrators are fastened to the ground via brackets at the
endplates only. The collector design allows a two axis polar
mounting configuration to enable maximum energy collection over the
day and the year in any location. Hourly or azimuth sun tracking is
accomplished via rotation or the cylindrical collector about the
cylindrical axis, while elevation tracking is accomplished via
vertical tilting of the collector or array of collectors.
[0020] As used herein the terms "string", "fiber" and "wire" are
interchangeable and each refers to an elongated membrane support
member.
[0021] As used herein, the terms "reflector sheet", "reflector
film", "membrane" and "reflector" are interchangeable and each
refers to an ultra-thin, ultra-light, non-self-supporting member
having at least one highly reflective surface.
[0022] As used herein the terms "housing", "enclosure",
"cylindrical tube", "enclosure tube", "envelope", "transparent
film", are interchangeable and each refers to a transparent
cylindrical tubular member that encloses and structurally supports
the parabolic membrane.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The aforementioned objects and advantages of the present
invention, as well as additional objects and advantages thereof,
will be more fully understood herein after as a result of a
detailed description of a preferred embodiment when taken in
conjunction with the following drawings in which:
[0024] FIG. 1 is a three-dimensional view of a preferred embodiment
of the present invention;
[0025] FIG. 2 is an enlarged view of an anchorplate illustrating
the string anchoring technique used therein;
[0026] FIG. 2a is a view of the bridges and reflector film
retention clips;
[0027] FIG. 3 is an enlarged view of the spring-based interface
between the string anchorplate and the hub;
[0028] FIG. 4 is a view of a bolted interface between the string
anchorplate and the hub;
[0029] FIG. 5 is a view of the hub from outside the enclosure;
[0030] FIG. 6 is a cross section view of the hub and endplates;
[0031] FIG. 7 is an enlarged view showing the retention of the
strings into the anchorplate;
[0032] FIG. 8 is a simplified illustration of the preferred string
pair film support system;
[0033] FIGS. 9-11 illustrate a first alternative film supporting
technique;
[0034] FIGS. 12 and 13 illustrate a second alternative film
supporting technique; and
[0035] FIGS. 13-17 illustrate the manner in which the enclosure
tube is secured to the endplates.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0036] Referring to the accompanying figures and initially FIGS. 1
and 2 in particular, it will be seen that a lightweight parabolic
trough solar concentrator 10 is shown. Concentrator 10 comprises an
inflatable transparent enclosure tube 12 terminating at its axial
ends in a pair of circular endplates 18 each supported at its
center by a hub 33. Within enclosure tube 12 is a string-supported
reflector 14 configured by tensioned strings 15 to form a parabolic
shape having a line focus. The reflector 14 may comprise a single
reflector sheet or a plurality of adjacent reflector sheet
sections.
[0037] A receiver 16 is positioned along the line focus of the
parabolic reflector and may be configured as a pipe carrying a
liquid to be heated by the concentrated sunlight or may be
configured as a surface supporting a line array of photovoltaic
cells. The ends of the strings 15 terminate in and are secured by
an anchorplate 20 at each axial end of the concentrator 10. FIG. 1
shows two concentrators 10 ganged together for a joint elevation
tracking as well as azimuth sun tracking.
[0038] Extending internally along a radius of each end plate 18 is
a pipe member 23 connecting receiver 16 to a central hub 33. A
counterweight 24 compensates for the weight of receiver 16. Gas
pressure within enclosure tube 12 causes the endplates 18 to
separate the anchorplates and place the strings under tension. The
array of holes 31 in each anchorplate 20 follows the desired
parabolic form thereby causing the strings 15 and reflector 14 to
form the same parabolic shape. As the gas pressure in the tubular
housing 12 increases, the strings become more taut and thus more
precisely conform to the desired shape along their entire
lengths.
[0039] In certain embodiments one or more bridges 80 are located at
intervals along the length of the tensioned strings 15 to provide
means to maintain the tensioned strings 15 in a desired parabolic
shape. Shown in FIG. 2a, a bridge 80 is shown in combination with a
retention clip 81. One or more retention clips 81 provide means to
ensure the reflector sheets do not slide out of the tensioned
strings 15 and provide a connection between two adjacent reflector
sheets with a bridge 80 caught in between. A clearance 82, is
provided between the clip 81 and the bridge 80. This clearance
ensures the reflector 14 can slidably adjust its position relative
to the strings and maintain a smooth undistorted surface regardless
of thermal growth or other disparity. If a reflector 14 attempts to
slide too far relative to the tensioned strings 15, the retention
clip 81 will contact the bridge and prevent the reflector sheet
from exiting the tensioned strings 15.
[0040] FIG. 2 illustrates an anchorplate 20 in an enlarged view. As
shown therein, anchorplate 20 comprises a bent rectangular tube
having a plurality of through-holes 31. The holes 31 are arranged
along a substantially parabolic curve to receive and secure strings
15. A cross bar 32 is bolted to the anchorplate at two locations
and is integral to a hub faceplate 34, which is secured to a
central hub 33. Rotation of the endplate 18 will rotate the hub 33,
the anchorplate 20, the pipe 23 and the counter-weight 24 along
with the receiver 16. The reflector 14 will also rotate so that its
focal line remains coincident with receiver 16.
[0041] FIGS. 3 and 4 illustrate two embodiments used to secure
anchorplate 20 to the hub 33. The first embodiment, shown in FIG. 3
utilizes springs to enhance axial compliance between the reflector
assembly and transparent enclosure tube assembly. As shown therein,
four symmetrically located shoulder bolts 28 extend through a pair
of spaced anchorplate hubs 34 which are welded to the anchorplate
crossbar 32. Each shoulder bolt 28 supports a corresponding helical
spring 25 between hub 34 and a retainer 30. This arrangement
precisely positions the anchorplate 20 relative to the hub 33 in
all directions and rotations except along the hub axis. In the
direction of the hub axis, the compliance of the helical springs 25
allow the anchorplate 20 to attain an optimal position relative to
the hub 33 for maintaining string tension under a variety of the
pressure and thermal loadings.
[0042] The second embodiment, shown in FIG. 4 depends upon an
endplate 18 and or strings 15 and or enclosure tube 12 to provide
axial compliance between the reflector assembly and tube assembly.
As shown therein, the anchorplate 20 is attached to the hub 33 via
a pinned and bolted joint. The pins 27 precisely position the
anchorplate 20 relative to the hub 33 in all directions and
rotations. The bolts 29 transfer loads from the anchorplate 20 to
the hub 33.
[0043] FIGS. 5 and 6 illustrate the manner in which the hub 33 is
attached and sealed from air leakage to the endplate 18. FIG. 5
provides a cross section view of the hub 33 to endcap 18 interface.
As shown therein, the hub 33, is reduced in diameter to provide a
shoulder 41 for axial positioning and sealing against the endcap
18. A gasket 39 is provided to ensure the seal and provide a soft
interface with the endcap 18. A bolt ring 20 and gasket 42 are
located on the outside of the collector enclosure. Bolts 43 secure
the bolt ring 40, gaskets 39 and 42 and endplate 18 and against the
shoulder 41 of the hub 33 and generate an airtight seal. FIG. 6
provides an isometric view of the hub 33 operatively connected to
an endplate 18 interface.
[0044] FIG. 7 illustrates the manner in which each pair of strings
15 in anchored to anchorplate 20. As shown therein, each such
string pair is terminated by a ferrule 36, which is received in a
split collet 38 having an internal retaining shoulder 22. A portion
of the split collet 38 is tapered to be received and retained in a
corresponding tapered hole 31 in the anchorplate. Tapered hole 31
has a flat 44, which in conjunction with a flat 37 on the split
collet 38 controls the rotational orientation of the strings. The
collet also includes an external shoulder feature for limiting the
depth of penetration of the collet into its corresponding tapered
hole 31.
[0045] The cross-section view of FIG. 8 illustrates the preferred
reflector/string interface wherein string pairs 15 support the
reflector 14 between the strings 15. The string pairs 15 are spaced
apart by a gap slightly greater than the thickness of the reflector
14. The reflector 14, which is untensioned and allowed to slide
relative to the strings 15, is guided by the strings to take a
parabolic shape. By allowing sliding relative to the strings 15,
the reflector 14 is not impacted by thermal growth differences or
other disturbance that will negatively impact the parabolic mirror
shape. In addition, by allowing sliding relative to the strings 15,
the reflector 14 will avoid faceting and form a surface that is
much closer to a parabola, which has the desired optical
performance.
[0046] Another embodiment 50 of a reflector/string interface is
shown in FIGS. 4-6. As shown therein, the reflector 50 comprises a
plurality of reflector segments 52, each of which is welded along
an edge to a tubular hinge piece 54, which is hingedly attached to
a single fiber or string 56. The fibers 56 serve the same purpose
as the strings 15 of FIG. 2, namely to locate and shape the
reflective surface.
[0047] Still another membrane embodiment 60 is shown in FIGS. 12
and 13 wherein a reflective membrane 62 employs an integral
backside sleeve 64 through which a single fiber 66 is threaded.
Sleeve 64 may be integrally formed by welding the membrane
surfaces. In one such embodiment, reflective membrane 62 is about
0.001 inches thick and sleeve 63 is about 0.010 to 0.030 inches in
diameter. However, because in this embodiment the sleeves do not
obstruct the reflective surface of the membrane, the sleeve
diameter can be virtually any practical size.
[0048] FIGS. 14-18 illustrate the manner in which the tubular
housing 12 shown in FIG. 16 is secured to each endplate 18 shown in
FIG. 14. As shown therein, the circumferential edge 70 of each
endplate has a regular convoluted shape. This edge is surrounded by
a ring assembly 72 (see FIG. 15), which comprises a clamping ring
74, a plurality of shoes 76 and a clamp 78. As seen best in FIGS.
17 and 18, the end of tube 12 is positioned and hermetically bound
to the endplate edge 70. This is done by tightening clamps 78 until
the plurality of shoes 76 engage the tube end and endplate edge.
The convolutions cause the tube to be circumferentially stretched
to ensure a wrinkle-free and hermetic assembly.
[0049] Various aspects of the disclosed embodiments have been
omitted to avoid obfuscation of the more salient features. By way
of example, it will be understood that the inflatable tubular
assembly may have one or more sealed seams and a pressure valve.
Furthermore, also not shown explicitly is a drive mechanism for
slowly rotating the collector assembly to keep the direct beam
solar radiation on the receiver as the Earth rotates. Moreover, the
ancillary interfaces for the receiver are well known in the art and
are also not shown.
[0050] Having thus described various embodiments of the present
invention, it will now be evident that many modifications and
additions are contemplated. Accordingly, the scope hereof is
limited only by the appended claims and their equivalents.
* * * * *