U.S. patent application number 12/198970 was filed with the patent office on 2010-03-04 for modular fresnel solar energy collection system.
Invention is credited to Danny F. Ammar.
Application Number | 20100051016 12/198970 |
Document ID | / |
Family ID | 41723500 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100051016 |
Kind Code |
A1 |
Ammar; Danny F. |
March 4, 2010 |
MODULAR FRESNEL SOLAR ENERGY COLLECTION SYSTEM
Abstract
A modular linear Fresnel solar energy collection system
comprises one or more reflector units having a number of spaced,
elongated solar panels that extend between a pair of opposed,
light-weight aluminum beams. A first drive mechanism rotates the
solar panels at angles progressively increasing from the center of
the two beams to their ends so that each panel reflects incident
sunlight to a secondary reflector located above the panels. The
secondary reflector, in turn, reflects the sunlight it receives
from the solar panels onto a receiver tube mounted in a fixed
position substantially concentric to a central axis extending
between the two aluminum beams. A second drive mechanism is coupled
to one of the beams which is operative to pivot the assembly of
beams, solar panels and secondary reflector between a generally
easterly direction and westerly direction in order to track the
apparent movement of the sun during the course of a day.
Inventors: |
Ammar; Danny F.;
(Windermere, FL) |
Correspondence
Address: |
GRAY ROBINSON, P.A.
P.O. Box 2328
FT. LAUDERDALE
FL
33303-9998
US
|
Family ID: |
41723500 |
Appl. No.: |
12/198970 |
Filed: |
August 27, 2008 |
Current U.S.
Class: |
126/600 |
Current CPC
Class: |
F24S 23/77 20180501;
F24S 30/425 20180501; F24S 20/20 20180501; Y02E 10/40 20130101;
F24S 23/80 20180501; F24S 23/79 20180501; Y02E 10/47 20130101; F24S
2023/872 20180501 |
Class at
Publication: |
126/600 |
International
Class: |
F24J 2/38 20060101
F24J002/38 |
Claims
1. A solar energy collection system, comprising: a first beam and a
second beam; a number of solar panels each having a reflective
surface, said solar panels extending between said first and second
beams; at least one drive mechanism coupled to said solar panels
and being operative to tilt respective solar panels into a position
to reflect sunlight on said reflective surface thereof; a receiver
tube within which a heat transfer fluid is circulated; a secondary
reflector positioned so as to receive sunlight reflective from said
solar panels and to reflect said sunlight onto said receiver tube
to heat the heat transfer fluid therein.
2. The system of claim 1 in which said at least one drive mechanism
comprises a number of drive mechanisms each including a motor
having an output coupled to one end of a solar panel, said motors
being operative to pivot a respective solar panel at an angle
relative to said secondary reflector.
3. The system of claim 2 in which each of said drive mechanisms
operates independent of the other.
4. The system of claim 1 in which said at least one drive mechanism
comprises a worm gear drivingly connected to a number of follower
gears each coupled to one of said solar panels, said worm gear
being operative to rotate said follower gears to tilt respective
solar panels relative to said secondary reflector.
5. A solar energy collector system, comprising: a first beam and a
second beam; a number of solar panels, each of said solar panels
including a first section formed of a light-weight honeycomb
structure, a second section having a reflective surface and a third
section connecting said first and second layers, said solar panels
extending between said first and second beams; at least one drive
mechanism coupled to said solar panels and being operative to tilt
respective solar panels into a position to reflect sunlight on said
reflective surface thereof; a receiver tube within which a heat
transfer fluid is circulated; a secondary reflector positioned so
as to receive sunlight reflected from said solar panels and to
reflect said sunlight onto said receiver tube to heat the heat
transfer fluid therein.
6. The system of claim 5 in which said light-weight honeycomb
structure is honeycomb aluminum.
7. The system of claim 5 in which said first section has opposed
sides, said first section being formed in a concave shape between
said opposed sides.
8. A solar energy collection system, comprising: a first beam and a
second beam; a number of solar panels each having a reflective
surface, said solar panels extending between said first and second
beams; a first drive mechanism coupled to said solar panels and
being operative to tilt respective solar panels into a position to
reflect sunlight on said reflective surface thereof; a second drive
mechanism operative to pivot said first and second beams between a
first position in which said solar panels face a generally easterly
direction, and second position in which said solar panels face a
generally westerly direction; a receiver tube within which a heat
transfer fluid is circulated; a secondary reflector positioned so
as to receive sunlight reflected from said solar panels and to
reflect said sunlight onto said receiver tube to heat the heat
transfer fluid therein.
9. The system of claim 8 in which said at least one first drive
mechanism comprises a number of drive mechanisms each including a
motor having an output coupled to one end of a solar panel, said
motors being operative to pivot a respective solar panel at an
angle relative to said secondary reflector.
10. The system of claim 8 in which said at least one first drive
mechanism comprises a worm gear drivingly connected to a number of
follower gears each coupled to one of said solar panels, said worm
gear being operative to rotate said follower gears to tilt
respective solar panels relative to said secondary reflector.
11. A solar energy collection system, comprising: a first beam and
a second beam; a number of solar panels each having a reflective
surface, said solar panels extending between said first and second
beams; a first drive mechanism operative to pivot said first and
second beams between a first position in which said solar panels
face a generally easterly direction, and second position in which
said solar panels face a generally westerly direction; a number of
second drive mechanisms coupled to at least one of said first and
second beams, each of said second drive mechanisms mounting a group
of said solar panels and being operative to tilt said solar panels
within a respective group in a generally northerly direction and in
a generally southerly direction to reflect sunlight incident on
said reflective surface thereof; a receiver tube within which a
heat transfer fluid is circulated; a secondary reflector positioned
so as to receive sunlight reflective from said solar panels and to
reflect said sunlight onto said receiver tube to heat the heat
transfer fluid therein.
12. The system of claim 11 in which each of said solar panels
comprises a first section formed of a light-weight honeycomb
structure, a second section having a reflective surface and a third
section connecting said first and second layers.
13. The system of claim 11 in which said light-weight honeycomb
structure is honeycomb aluminum.
14. The system of claim 11 in which said first section has opposed
sides, said first section being formed in a concave shape between
said opposed sides.
15. A solar energy collector system, comprising: a number of
reflector units oriented side-by-side, each of said reflector units
comprising: (i) a first beam and a second beam; (ii) a number of
solar panels each having a reflective surface, said solar panels
extending between said first and second beams; (iii) at least one
first drive mechanism coupled to said solar panels and being
operative to tilt respective solar panels into a position to
reflect sunlight on said reflective surface thereof; (iv) a
receiver tube within which a heat transfer fluid is circulated; (v)
a secondary reflector positioned so as to receive sunlight
reflected from said solar panels and to reflect said sunlight onto
said receiver tube to heat the heat transfer fluid therein.
16. The system of claim 15 in which said at least one first drive
mechanism of each reflector units comprises a number of drive
mechanisms each including a motor having an output coupled to one
end of a solar panel, said motors being operative to pivot a
respective solar panel at an angle relative to said secondary
reflector.
17. The system of claim 15 in which said at least one first drive
mechanism of each of said reflector units is operative to tilt each
of said solar panels individually, each of said reflector units
further including a second drive mechanism operative to pivot said
first and second beams in an easterly direction and in a westerly
direction.
18. The system of claim 15 in which said solar panels of each
reflector unit comprises a first section formed of a light-weight
honeycomb structure, a second section having a reflective surface
and a third section connecting said first and second layers.
19. The system of claim 18 in which said light-weight honeycomb
structure is honeycomb aluminum.
20. The system of claim 18 in which said first section has opposed
sides, said first section being formed in a concave shape between
said opposed sides.
21. A solar energy collector system, comprising: a number of
reflector units oriented side-by-side, each of said reflect units
comprising: (i) a first beam and a second beam; (ii) a number of
solar panels each having a reflective surface, said solar panels
extending between said first and second beams; (iii) a first drive
mechanism operative to pivot said first and second beams between a
first position in which said solar panels face a generally easterly
direction, and second position in which said solar panels face a
generally westerly direction; (iv) a number of second drive
mechanisms each mounting a group of said solar panels and being
operative to tilt said solar panels within a respective group in a
generally northerly direction and in a generally southerly
direction to reflect sunlight incident on said reflective surface
thereof; (v) a receiver tube within which a heat transfer fluid is
circulated; (vi) a secondary reflector positioned so as to receive
sunlight reflected from said solar panels and to reflect said
sunlight onto said receiver tube to heat the heat transfer fluid
therein.
22. The system of claim 21 in which said solar panels of each
reflector unit comprises a first section formed of a light-weight
honeycomb structure, a second section having a reflective surface
and a third section connecting said first and second layers.
23. The system of claim 22 in which said light-weight honeycomb
structure is honeycomb aluminum.
24. The system of claim 22 in which said first section has opposed
sides, said first section being formed in a concave shape between
said opposed sides.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the generation of electrical
energy through solar thermal power collection, and, more
particularly, to a modular Fresnel solar energy collection system
that employs a secondary reflector, light-weight solar panels and a
fixed linear receiver through which a heat transfer fluid is
circulated.
BACKGROUND OF THE INVENTION
[0002] Systems for the generation of electricity by collecting
solar thermal radiation were first introduced in 1914, and have
become increasingly popular with the rise in fossil fuel costs and
concerns over global warming. A majority of solar energy collection
systems currently in use employ parabolic, trough-shaped reflectors
that focus the sun's energy on a receiver such as an engine.
Recently, a new type of system has emerged known as a linear
Fresnel reflector that includes a series of long, narrow mirrors
having a shallow curvature, or none at all, which focus light onto
one or more linear receivers positioned above the mirrors. The
concept of large reflectors being broken down into many Fresnel
sub-elements to improve manageability was advanced by Baum et al.
(1957), and in the 1960's, important development work was
undertaken by the solar pioneer Giovanni Francia (Francia, 1968) of
the University of Genoa, who developed both linear Fresnel
reflector systems and Fresnel point focus systems. Typically, a
linear Fresnel reflector focuses sunlight at 80 to 100 times its
normal intensity on the receiver. The concentrated energy heats a
heat transfer fluid flowing through the receiver, which, in turn,
is used to generate steam to power a turbine that drives an
electric generator.
[0003] Instead of a large parabolic surface, Fresnel reflectors use
many smaller mirrors which are more manageable, easier to install,
less expensive to maintain and aim to reduce overall costs by
sharing a receiver between several mirrors while still using simple
line-focus geometry with one axis of tracking, i.e., the individual
mirrors can pivot in a generally easterly and westerly direction.
Despite these advantages, there is more heat loss due to the larger
width dimension of the receiver which is needed to compensate for
the lack of curvature in the mirrors. Another disadvantage of
current linear Fresnel reflectors is that although they work well
when the sun is nearly vertical in the sky, e.g. between about
10:00 a.m. to 2:00 p.m., rapid performance degradation occurs at
other times during the day. As the sun incident angle increases,
the solar collection efficiency drops quickly because while the
mirrors are pivotal, the framework supporting them is
stationary.
[0004] The goal of any solar collection system is to reduce the
cost of electricity generated. There are fundamentally two ways to
do this, namely, reduce the cost of the solar field and annual
operating expenses, and, to increase system efficiency. Solar field
optical efficiency is dependent upon a number of factors,
including, without limitation, sunlight incident angle effects,
collector tracking error, the geometric accuracy of the mirrors to
focus light on the receiver tubes, mirror reflectivity, cleanliness
of the mirrors, the creation of shadows across the mirrors,
transmittance of solar energy into the receiver tubes, cleanliness
of the receiver tubes, absorption of solar energy by the receiver
tubes, end losses and the creation of shadows between rows of
mirrors. While current systems produce electricity at a cost in the
range of $0.12 to $0.18 per kilowatt-hour, it is desirable to
achieve a cost level of about $0.05 per kilowatt-hour to be more
competitive with present fossil-fuel based systems.
SUMMARY OF THE INVENTION
[0005] This invention is directed to a linear Fresnel solar energy
collection system that improves solar field efficiency, lowers
operational and maintenance costs, and therefore reduces the
overall cost of generating electricity per kilowatt-hour.
[0006] One aspect of this invention is predicated on the concept
providing a simple, modular linear Fresnel solar energy collection
system comprising one or more reflector units each fabricated using
light-weight materials arranged in a construction that is highly
accessible, easily maintained, and lower in initial cost. In one
embodiment, each reflector unit comprises a number of spaced,
elongated solar panels, having a slightly curved or flat reflective
surface, that extend between a pair of opposed, light-weight
aluminum beams. A first drive mechanism rotates the solar panels at
angles progressively increasing from the center of the two beams to
their ends so that each panel reflects incident sunlight to a
secondary reflector located above the panels. The secondary
reflector, in turn, reflects the sunlight it receives from the
solar panels onto a receiver tube mounted in a fixed position
substantially concentric to a central axis extending between the
two aluminum beams. A second drive mechanism is coupled to one of
the beams which is operative to pivot the assembly of beams, solar
panels and secondary reflector between a generally easterly
direction and westerly direction in order to track the apparent
movement of the sun during the course of a day.
[0007] Preferably, each solar panel comprises a honeycomb aluminum
section and a highly reflective silver-metallized surface connected
together by an adhesive layer. The solar panels are strong,
durable, light-weight and efficiently reflect incident sunlight
many times its normal intensity onto the secondary reflector. The
reflective surface of such panels may be washed to maintain
cleanliness which enhances the efficiency with which they reflect
incident sunlight to the secondary reflector.
[0008] A heat transfer fluid is circulated through the receiver
tube for heating by the sunlight directed thereto from the
secondary reflector. Because the receiver tube is fixed relative to
the pivoting beams, it may be connected to a fixed transfer conduit
that communicates with a steam generator and turbine. Since both
the receiver tube and transfer conduit are mounted in a fixed
position, heat losses resulting from the transfer of fluid out of
the receiver tube are minimized and maintenance problems are
reduced.
[0009] In an alternative embodiment, a reflector unit includes
solar panels that are formed in smaller segments and mounted to a
number of shafts extending between the opposed beams described
above. The shafts are operative to tilt the segmented solar panels
at a desired latitude angle, e.g. in a generally northerly or
southerly direction, dependent upon the geographic location of the
system. This allows the system of this invention to account for the
varying incidence angle of the sun with the earth as the seasons
change so that the solar panels more directly face the sun
throughout the year. An improvement in solar collection efficiency
of at least 5% may be realized by this enhancement of the present
invention.
[0010] The several embodiments of this invention are modular in
construction in the sense that several reflector units may be
mounted side-by-side, and their receiver tubes connected, to form a
linear Fresnel solar collection system with increased capacity and
overall efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The structure, operation and advantages of the presently
preferred embodiment of this invention will become further apparent
upon consideration of the following description, taken in
conjunction with the accompanying drawings, wherein:
[0012] FIG. 1 is a perspective view of one embodiment of a
reflector unit employed in the Fresnel solar energy collection
system of this invention;
[0013] FIG. 2 is a perspective view of a solar panel of this
invention;
[0014] FIG. 3 is an enlarged, partially disassembled view of the
encircled portion of the solar panel depicted in FIG. 2;
[0015] FIG. 4 is a perspective view of the receiver tube employed
in the system herein;
[0016] FIG. 5 is a schematic, end view of the solar panels and
secondary reflector of the system depicted in FIG. 1, illustrating
the angular orientation of the solar panels;
[0017] FIG. 6 is a schematic view of one embodiment of a first
drive mechanism for tilting a solar panel at an angle such as
depicted in FIG. 5;
[0018] FIG. 7 is a schematic view of an alternative embodiment of a
first drive mechanism for tilting a number of solar panels at the
same time;
[0019] FIG. 8 is a perspective view of a second drive mechanism for
collectively pivoting the beams, solar panels and secondary
reflector;
[0020] FIG. 9 is an end view of the second drive mechanism
illustrated in FIG. 8;
[0021] FIG. 10 is a perspective view of a solar collection system
according to this invention in which a number of reflector units
shown in FIG. 1 are oriented side-by-side;
[0022] FIG. 11 is a perspective view of an alternative embodiment
of the solar collection system of this invention wherein the
opposed beams, solar panels and secondary reflector are not
collectively pivotal;
[0023] FIG. 12 is a perspective view of the solar panels and beams
of an alternative embodiment of a solar energy collection system
according to this invention;
[0024] FIG. 13 is an enlarged, side view of a portion of FIG. 12
illustrating the manner in which solar panels are mounted on a
shaft for tilting movement relative to the opposed beams; and
[0025] FIG. 14 is a view similar to FIG. 15 showing solar panels
tilted after rotation of the shaft.
DETAILED DESCRIPTION OF THE INVENTION
[0026] Referring now to the drawings, one embodiment of a reflector
unit 10 for the solar energy collection system 12 of this invention
is illustrated with reference to FIGS. 1-10. The unit 10 is
initially generally described, followed by a discussion of
individual aspects of the design. Finally, an alternative
embodiment of a solar energy collection system according to this
invention is discussed with reference to FIG. 12-14.
[0027] With reference initially to FIG. 1, the reflector unit 10
comprises a pair of opposed beams 14 and 16, preferably formed of a
light-weight, durable and weather resistant material such as
aluminum. The beams 14, 16 may be reinforced by a truss structure
18, a portion of which is shown in FIGS. 1 and 8, that is also
preferably formed of aluminum or similar material. The beams 14, 16
are spanned by a number of elongated solar panels 20 which are
separated from one another so that there is at least some spacing
between the side edges of adjacent panels 20. The solar panels 20
pivot relative to the beams 14, 16, in a manner described below. A
secondary reflector 22 is located above the solar panels 20, as
discussed below, and is supported in that position at each end by
rods 23 extending from the beams 14, 16 and truss structure 18. The
solar panels 20 and secondary reflector 22 collectively form
structure for receiving incident sunlight and reflecting it onto a
receiver tube 24 within which a heat transfer fluid is circulated
for heating by the sunlight. The receiver tube 24 is preferably
located in a fixed position at an axis substantially coincident
with the centerline 26 of the two beams 14, 16. See FIG. 5.
[0028] The reflector unit 10 may be supported above ground level by
pylons 28 secured on a foundation such as concrete footers (not
shown) that can support the weight of the unit 10 and wind loading
applied to it. As described in detail below, in one embodiment the
beams 14, 16, solar panels 20 and secondary reflector 22 may be
collectively tilted by operation of a first drive mechanism in a
generally easterly and westerly direction.
[0029] Referring now to FIGS. 2 and 3, a solar panel 20 according
to this invention is shown in greater detail. Each solar panel 20
is generally rectangular in shape having opposed side edges 30 and
32. The panels 20 have a slight concave curvature in a direction
from one side edge 30 to the other side edge 32, which may be
slightly different from one panel 20 to another as described below.
Each panel 20 comprises a base section 34, a top section 36 and an
intermediate section 38 sandwiched between the sections 34, 36. The
base section 34 is preferably formed of a honeycomb aluminum, or
similar light-weight, weather resistant and durable material that
may be bent in the slight curvature noted above and shown in FIG.
2. The top section 36 is preferably a highly-reflective,
silver-metallized film comprising multiple layers of polymer film
with an inner layer of pure silver to provide a reflective surface
40 having high specular reflectance. One suitable material for top
section 36 is commercially available from ReflecTech, Inc. of Wheat
Ridge, Colo. under the trademark "ReflecTech" solar film. The
intermediate layer 38 is preferably a layer of pressure sensitive
adhesive. Layer 38 may be affixed on one side to the top section 36
and include a peel-off backing (not shown) which is removed prior
to attachment to the base section 34. In one presently preferred
embodiment, the solar panels 20 have a length dimension of about
4064 mm, a width dimension of about 460 mm and a thickness of about
25 mm.
[0030] The receiver tube 24 is a component employed in prior art
solar collection systems and is readily commercially available. As
shown in FIG. 4, it comprises a stainless steel housing 42 having a
solar-selective absorber surface surrounded by an anti-reflective,
evacuated glass sleeve 44. Typically, the housing 42 has a length
of 4 meters and a diameter of 70 mm, and the glass sleeve 44 is 115
mm in diameter. A heat transfer fluid such as oil or water is
circulated through the housing 42 where it is heated by reflected
sunlight, as discussed below. The receiver tube 24 has
glass-to-metal seals and metal bellows (not shown) to accommodate
differing rates of thermal expansion between the stainless steel
housing 42 and glass sleeve 44, and to help maintain the
vacuum-tight enclosure. This reduces heat losses at high operating
temperatures and protects the solar-select absorber surface of the
housing 42 from oxidation.
[0031] As noted above, the solar panels 20 and secondary reflector
22 collectively function to direct incident sunlight onto the
receiver tube 24 to elevate the temperature of heat transfer fluid
circulating within the receiver tube 24 to a level sufficient to
operate a steam generator (not shown) for the production of
electricity. The positioning of the solar panels 20 with respect to
the secondary reflector 22, and the configuration of the solar
panels 20 and secondary reflector 22, are both important in
maximizing the efficiency of the reflector unit 10. The discussion
that follows concerns this aspect of the present invention.
[0032] A parabola is a geometric shape defined by the locus of
points that are equidistant from a point (the focus) and a line
(directrix) that lie in the same plane. Reflective surfaces having
the shape of a parabola have been commonly used in solar power
collection systems because incident sunlight may be reflected to a
collection device located at the focus or directrix of the
parabola. The unit 10 of the present invention is designed to tale
advantage of this property of a parabola, but in a much more
efficient, less expensive and practical manner than taught in the
prior art.
[0033] The standard mathematical equation defining a parabola is as
follows:
[0034] Where:
y=x.sup.2/4f
[0035] f=the focal point
[0036] x=horizontal distance from the center
[0037] y=vertical distance
[0038] In the presently preferred embodiment of reflector unit 10,
each of the solar panels 20 is formed with a curvature according to
the above equation. The parabolic effect of focusing rays of light
to a focus or directrix of the parabola, discussed above, can be
used in a linear arrangement. As viewed in FIG. 5, the beam 14 is
shown with the receiver tube 24 depicted within an opening 46
formed in the beam 14, substantially concentric to a centerline 26
of the two beams 14, 16, and the secondary reflector 22 is located
at a position spaced from the receiver tube 24. A first array 50 of
solar panels 20 extends from the receiver tube 24 to one end of the
beams 14, 16, and a second array 52 of solar panels 20 extends from
the receiver tube 24 to the opposite end of beams 14, 16. The solar
panels 20 within the two arrays 50, 52, each having a parabolic
cross section as noted above, are oriented at an angle relative to
the secondary reflector 22 such that incident sunlight is reflected
onto a focal line 54 or directrix coincident with the secondary
reflector 24. This ensures an efficient transfer of thermal energy
from the solar panels 20 to the secondary reflector 24.
[0039] The manner in which the solar panels 20 may be oriented at
the appropriate angles depicted in FIG. 5, is illustrated with
reference to FIGS. 6 and 7. One embodiment of a first drive
mechanism according to this invention is illustrated in FIG. 6. An
end of each a solar panel 20 is fixed within a slot 56 of a
mounting fixture 58 which is coupled to the output 60 of a torque
motor 62 mounted to the beam 16. The opposite end of panel 20 is
pivotally mounted to beam 14. In response to operation of the motor
62, the fixture 58 rotates causing the solar panel 20 it supports
to tilt at an angle relative to the secondary reflector 22.
[0040] An alternative embodiment of the first drive mechanism of
this invention is shown in FIG. 7 wherein a number of solar panels
20 may be rotated at the same time. One end of each panels 20 is
mounted to a shaft 64 protruding from one of the beams 14, 16. Each
shaft 64, in turn, mounts a follower gear 66. A worm gear 68 having
external threads 70 is drivingly connected to each of the follower
gears 66 such that rotation of the worm gear 68 causes the follower
gears 56 to rotate thus tilting the solar panels 20. In order to
tilt the solar panels 20 at different angles relative to the
secondary reflector 22, as seen in FIG. 5, the diameter of the
follower gear 66 associated with each panel 20 may vary such that
the same extent of rotation of the worm gear 68 results in a
different amount of rotation of each follower gear 66, and,
therefore, a lesser or greater tilting of the respective solar
panel 20.
[0041] As noted above with reference to FIG. 5, the first and
second arrays 50, 52 of solar panels 20 reflect incident light to a
directrix 54. The secondary reflector 22 is located along the
directrix 54 and is constructed to reflect the light received from
solar panels 20 onto the receiver tube 24 to elevate the
temperature of heat transfer fluid circulating therein. In one
presently preferred embodiment, the secondary reflector 22 is
approximately 200 mm to 250 mm in width with a reflective surface
72 in the shape of a hyperbola. The exact geometry of the
reflective surface 72 is derived from the Cassegrain Equations for
a primary parabolic-shaped reflective surface, which, in this
instance, is the parabolic-shaped reflective surface of each solar
panel 20, and a secondary hyperboloid reflective surface. The
secondary reflector 22 may be constructed of a honeycomb panel
having the appropriate hyperboloid shape noted above connected by
an adhesive layer to the same material that forms the top section
36 of solar panels 20.
[0042] Referring now to FIGS. 8 and 9, it is advantageous for the
solar panels 20 to be track the position of the sun throughout the
course of a day in order to maximize the efficiency with which the
sunlight is reflected to the secondary reflector 22, and, in turn,
to the receiver tube 24. In the presently preferred embodiment of
this invention, a second drive mechanism is provided for
collectively pivoting the beams 14, 16, solar panels 20 and
secondary reflector 24 at an angle of at least about +/-30.degree.
relative to horizontal. This limited rotation improves the solar
energy collection in the early hours of day and late in the
afternoon by tilting the solar panels 20 toward the sun. However,
by limiting the rotation angle lower height pylons 28 may be used
and the spacing required between rows of panels 20 may be reduced
to avoid shadowing. This second drive mechanism comprises a support
frame 74 connected to a pylon 28 which rotatably mounts three
rollers 76, 78 and 80 spaced approximately 120.degree. apart. These
rollers 76-80 receive and support a drive wheel 82 which is
connected by a link chain 84, or other suitable drive means such as
a belt, to the output shaft of a motor 86. The drive wheel 82 is
connected by a plate 88 to the rods 23 which support the secondary
reflector 22 at one end, and connect to the beams 14, 16 and truss
structure 18 at the opposite end. In response to operation of the
motor 86, the drive wheel 82 rotates with respect to the rollers
76-80. The rods 23 and beams 14, 16 rotate with the drive wheel 82,
thus pivoting relative to the pylons 28.
[0043] In the presently preferred embodiment, the receiver tube 24
remains in a fixed position with respect to the beams 14, 16 and
drive wheel 82 throughout the pivotal motion of the beams 14, 16,
solar panels 20 and secondary reflector 22. As described above, the
receiver tube 24 may extend through an openings 46 formed in each
beam 14, 16. A protruding end of receiver tube 24 enters a bore 90
formed in the plate 88, and a central bore 92 formed in the drive
wheel 82 where it is received and supported by a bearing 94 that
allows the receiver tube 24 to remain in a fixed position during
rotation of the drive wheel 82. This construction has the advantage
of allowing the receiver tube 24 to be connected to a fixed
transfer conduit coupled to a steam generator (not shown).
Consequently, the expensive and leak-prone connections between the
moving receiver tubes and transfer conduits employed in some prior
art systems are eliminated in this invention.
[0044] The solar energy collection system 12 of this invention is
modular in construction. As shown in FIG. 10, a number of
individual reflector units 10 depicted in FIG. 1 and described
above may be located side-by-side to increase capacity and overall
efficiency of the solar field. In such arrangements, a second drive
mechanism of the type described above in connection with a
discussion of FIGS. 8 and 9 may be located in between adjacent
units 10 such that each end of the output shaft of motor 86 may be
coupled to the drive wheel 82 of one of the units 10 in the manner
described above. Further, the receiver tube 24 of one unit 10 may
be coupled to the receiver tube 24 of an adjacent unit 10 to
transmit heat transfer fluid to one or more conduits (not shown)
for the combined collection system.
[0045] As discussed above with reference to FIGS. 8-10, the
reflector units 10 of this invention may be provided with a second
drive mechanism to collectively tilt the beams 14, 16, solar panels
20 and secondary reflector 22 to track the position of the sun. In
an alternative embodiment shown in FIG. 11, the same reflector
units 10 described above and shown in FIG. 1 are employed but in a
solar collection system 95 in which the units 10 are secured in a
fixed position, side-by-side, to supports posts 96. The individual
panels 20 within each unit 10 of the system in FIG. 11 pivot as
described above, but the beams 14, 16 are held in a fixed position
to the posts 96. The receive tubes 24 of adjacent units 10 may be
connected to one another, as in the embodiment of FIGS. 8-10.
[0046] A still further embodiment of a solar energy collection
system according to this invention having one or more reflector
units 100 is illustrated in FIGS. 12-14. The reflector units 100
are similar to units 10 in many respects except for structure that
permits adjustment of the position. of solar panels about a second
axis. As discussed above, individual solar panels 20, as well as
the entire assembly of the beams 14, 16, panels 20 and secondary
reflector 22, may be pivoted relative an axis generally coincident
with the centerline 26 of the beams 14, 16. Such motion is in an
easterly to westerly direction consistent with the apparent
movement of the sun across the sky during the daylight hours. As is
well known, the earth tilts on its axis during the course of a year
causing the change of seasons and altering the angle of inclination
of the sun's rays. The unit 100 of this embodiment is designed to
not only track the sun's daily path but its annual inclination.
[0047] The same beams 14, 16 described above are employed in unit
100, but instead of elongated solar panels 20 extending between the
two beams 14, 16, a plurality of shorter, segmented solar panels
102 are provided. The solar panels 102 are divided into groups, and
each group of panels 102 essentially takes the place of a single
solar panel 20 in the embodiment of FIGS. 1-11. As best seen in
FIG. 12, one group of several panels 100 is mounted within each of
a number of sub-frames 104, e.g. a generally rectangular-shaped
structure having opposed ends and opposed sides. One end of each
sub-frame 104 is pivotally mounted to one of the beams 14 or 16,
and the opposite end thereof is connected to a mounting fixture
(not shown) secured to the other beam 14 or 16, such as the fixture
58 described above in connection with a discussion of FIG. 6. The
sub-frames 104 are pivoted relative to the beams 14, 16 by
operation of torque motors, such as motors 62, at the same angles
relative to the secondary reflector 22 as solar panels 20 described
above. See FIGS. 5 and 6.
[0048] In one embodiment, as shown in FIGS. 13 and 14, the panels
100 within each group may be coupled to a threaded shaft 106,
which, in turn, is rotatably mounted to the end walls of a
sub-frame 104. A lever arm 108 may extend from each panel 100 and
connect to an internally threaded sleeve 110 which threads onto the
shaft 106. In response to rotation of the shafts 106, either
manually by turning a knob 112 or by operation of a motor (not
shown), the sleeves 110 move axially along the shafts 106 causing
the panels 124 to tilt. The direction of rotation of the shaft 106
determines the direction of tilting of the panels 100. In this
manner, the panels 100 may be tilted in a northerly direction or a
southerly direction according the angle of inclination of the sun.
The remainder of the structure and operation of the solar
collection system depicted in FIGS. 12-14 is essentially the same
as that described above in connection with a discussion of the
system shown in FIG. 10.
[0049] While the invention has been described with reference to a
preferred embodiment, it should be understood by those skilled in
the art that various changes may be made and equivalents
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
[0050] For example, the receiver tube 24 is depicted in FIGS. 5, 11
and 12 as being positioned at the center of the beams 14 and 16 and
substantially concentric to the centerline 26. As shown in FIGS. 1,
8 and 10, the receiver tube 24 may also be located slightly above
the center of the beams 14, 16. In both instances, the receiver
tube 24 is located substantially at the center of rotation of the
beams 14, 16 and generally at the center of gravity of the
reflector units 10 or 100.
[0051] Therefore, it is intended that the invention not be limited
to the particular embodiment disclosed as the best mode
contemplated for carrying out this invention, but that the
invention will include all embodiments falling within the scope of
the appended claims.
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