U.S. patent application number 13/588387 was filed with the patent office on 2013-05-09 for control and tracking system and method for a solar power generation system.
The applicant listed for this patent is Glenn A. Reynolds. Invention is credited to Glenn A. Reynolds.
Application Number | 20130112188 13/588387 |
Document ID | / |
Family ID | 47747045 |
Filed Date | 2013-05-09 |
United States Patent
Application |
20130112188 |
Kind Code |
A1 |
Reynolds; Glenn A. |
May 9, 2013 |
CONTROL AND TRACKING SYSTEM AND METHOD FOR A SOLAR POWER GENERATION
SYSTEM
Abstract
Embodiments of a solar reflector assembly and methods of
controlling a solar reflector assembly are generally described
herein. Other embodiments may be described and claimed.
Inventors: |
Reynolds; Glenn A.; (Long
Beach, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Reynolds; Glenn A. |
Long Beach |
CA |
US |
|
|
Family ID: |
47747045 |
Appl. No.: |
13/588387 |
Filed: |
August 17, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61525410 |
Aug 19, 2011 |
|
|
|
Current U.S.
Class: |
126/585 ;
126/601; 126/714 |
Current CPC
Class: |
F24S 40/52 20180501;
F24S 2020/23 20180501; F24S 50/20 20180501; F24S 23/74 20180501;
Y02E 10/47 20130101; F24S 50/40 20180501; Y02E 10/40 20130101; F24S
25/13 20180501; F24S 2025/013 20180501; F24S 30/425 20180501 |
Class at
Publication: |
126/585 ;
126/714; 126/601 |
International
Class: |
F24J 2/38 20060101
F24J002/38; F24J 2/12 20060101 F24J002/12 |
Claims
1. A method of controlling a solar reflector assembly comprising at
least one frame, at least one reflector mounted on the frame, a
control system configured to move the frame, and a tube having a
central axis and configured to have therein a heat transfer fluid
being heated by the reflector focusing sunlight onto a focal line
configured to be generally aligned with the central axis, the tube
coupled to the frame with at least one tube support, the method
comprising: determining an offset between the focal line and the
central axis; and moving the frame to move the central axis toward
the focal line to reduce the offset.
2. The method of claim 1, wherein the offset corresponds to a
position of the central axis relative to the focal line when at
least a portion of the tube support is deflected by a load on the
tube support.
3. The method of claim 1, wherein the offset corresponds to a
position of the central axis relative to the focal line when at
least a plurality of frame members of the frame is deflected by a
load on the frame.
4. The method of claim 1, wherein the offset corresponds to a
position of the central axis relative to the focal line when at
least one part of the frame is misaligned relative to another part
of the frame.
5. The method of claim 1, wherein the offset corresponds to a
position of the central axis relative to the focal line when the
frame is misaligned relative to another frame.
6. The method of claim 1, wherein determining the offset comprises
measuring the position of the central axis relative to the focal
line.
7. The method of claim 1, wherein determining offset comprises
computing the position of the central axis relative to the central
axis.
8. The method of claim 1, wherein determining the offset comprises
measuring an intensity of light focused on the tube by the
reflector with an optical sensor.
9. The method of claim 1, wherein determining the offset comprises
measuring a temperature of the heat transfer fluid.
10. A solar reflector assembly comprising: at least one frame; at
least one reflector mounted on the frame; a tube having a central
axis and configured to have therein a heat transfer fluid being
heated by the reflector focusing sunlight onto a focal line
configured to be generally aligned with the central axis, the tube
coupled to the frame with at least one tube support; and a control
system configured to move the frame, the control system comprising
a processor and a data storage device, wherein the processor is
configured to execute a code stored in the data storage device to:
determine an offset between the focal line and the central axis;
and move the frame to move the central axis toward the focal line
to reduce the offset.
11. The solar reflector assembly of claim 10, wherein the offset
corresponds to a position of the central axis relative to the focal
line when at least a portion of the tube support is deflected by a
load on the tube support.
12. The solar reflector assembly of claim 10, wherein the offset
corresponds to a position of the central axis relative to the focal
line when at least a plurality of frame members of the frame is
deflected by a load on the frame.
13. The solar reflector assembly of claim 10, wherein the offset
corresponds to a position of the central axis relative to the focal
line when at least one part of the frame is misaligned relative to
another part of the frame.
14. The solar reflector assembly of claim 10, wherein the offset
corresponds to a position of the central axis relative to the focal
line when the frame is misaligned relative to another frame.
15. The solar reflector assembly of claim 10, wherein determining
the offset comprises measuring the position of the central axis
relative to the focal line.
16. The solar reflector assembly of claim 10, wherein determining
offset comprises computing the position of the central axis
relative to the central axis.
17. The solar reflector assembly of claim 10, wherein determining
the offset comprises measuring an intensity of light focused on the
tube by the reflector with an optical sensor.
18. The solar reflector assembly of claim 10, wherein determining
the offset comprises measuring a temperature of the heat transfer
fluid.
19. A method of controlling a solar reflector assembly comprising
at least one frame, at least one reflector mounted on the frame, a
control system configured to move the frame, and a tube configured
to have therein a heat transfer fluid being heated by the reflector
focusing sunlight on the tube, the tube coupled to the frame with
at least one tube support, the method comprising: determining a
variable indicative of a temperature of the heat transfer fluid;
and moving the frame between a focused position wherein sunlight is
focused on the tube by the reflector and a defocused position
wherein sunlight is less focused on the tube by the reflector than
the focused position to control the temperature of the heat
transfer fluid.
20. The method of claim 19, wherein moving the frame comprises
moving the frame from the focused position to the defocused
position to reduce the temperature of the thermal fluid in the
tube.
21. The method of claim 19, wherein moving the frame comprises
oscillating the frame between the focused position and the
defocused position to provide a generally even heat distribution on
the tube.
22. The method of claim 19, wherein moving the frame comprises
oscillating the frame between a first defocused position lagging
the focused position and a second defocused position leading the
focused position to provide a generally even heat distribution on
the tube, wherein the focused position is between the first
defocused position and the second defocused position.
23. The method of claim 19, wherein the variable is determined by
measuring the temperature of the heat transfer fluid.
24. The method of claim 19, wherein the variable is determined by
measuring an intensity of light focused on the tube by the
reflector with an optical sensor.
25. A solar reflector assembly comprising: at least one frame; at
least one reflector mounted on the frame; a tube configured to have
therein a heat transfer fluid being heated by the reflector
focusing sunlight on the tube, the tube coupled to the frame with
at least one tube support; and a control system configured to move
the frame, the control system comprising a processor and a data
storage device, wherein the processor is configured to execute a
code stored in the data storage device to: determine a variable
indicative of a temperature of the heat transfer fluid; and move
the frame between a focused position wherein sunlight is focused on
the tube by the reflector and a defocused position wherein sunlight
is less focused on the tube by the reflector than the focused
position to control the temperature of the heat transfer fluid.
26. The solar reflector assembly of claim 25, wherein to move the
frame comprises to move the frame from the focused position to the
defocused position to reduce the temperature of the heat transfer
fluid.
27. The solar reflector assembly of claim 25, wherein to move the
frame comprises to oscillate the frame between the focused position
and the defocused position to provide a generally even heat
distribution on the tube.
28. The solar reflector assembly of claim 25, wherein to move the
frame comprises to oscillate the frame between a first defocused
position lagging the focused position and a second defocused
position leading the focused position to provide a generally even
heat distribution on the tube, wherein the focused position is
between the first defocused position and the second defocused
position.
29. The solar reflector assembly of claim 25, wherein the variable
is determined by measuring the temperature of the thermal fluid in
the tube.
30. The solar reflector assembly of claim 25, wherein the variable
is determined by measuring an intensity of light focused on the
tube by the reflector with an optical sensor.
Description
RELATED APPLICATION
[0001] The present application claims the benefit of the filing
date of U.S. Provisional Application Ser. No. 61/525,410, filed
Aug. 19, 2011, the entire disclosure of which is incorporated by
reference herein.
FIELD
[0002] This disclosure generally relates to solar power generation
systems, and more particularly, to a control system and method for
a solar power generation system.
BACKGROUND
[0003] Reflective solar power generation systems may either use a
number of spaced apart reflective panels that surround a central
tower and reflect sunlight toward the central tower or
parabolic-shaped reflective panels that focus sunlight onto a tube
at the focal point of the parabola defining the reflective panels.
The latter system may be referred to as a solar trough system. With
solar trough systems, the structures that support the reflective
panels and the tube may deflect due to static loads. Accordingly,
instead of focusing sunlight generally along a central axis of the
tube, the reflective panels may focus the sunlight at a location
that is offset relative to the central axis of the tube. Therefore,
the temperature of the heat transfer fluid in the tube may not
reach a required or preferred level. The noted deflections due to
static loads may be greater for large trough systems. In contrast,
when the sunlight is focused onto the tube, the heat transfer fluid
may become excessively hot and lose viscosity in trough systems
that use large reflectors. The control systems used for solar
trough systems may only track the position of the sun without
considering the noted deflections due to static loads and/or
maintaining the temperature of the heat transfer fluid at a certain
level or within a certain range.
SUMMARY
[0004] According to one aspect, a method of controlling a solar
reflector assembly is disclosed, where the solar reflector assembly
may include at least one frame, at least one reflector mounted on
the frame, a control system configured to move the frame, and a
tube having a central axis and configured to have therein a heat
transfer fluid being heated by the reflector focusing sunlight onto
a focal line configured to be generally aligned with the central
axis, the tube coupled to the frame with at least one tube support.
The method includes determining an offset between the focal line
and the central axis, and moving the frame to move the central axis
toward the focal line, to reduce the offset.
[0005] According to another aspect, a solar reflector assembly
includes at least one frame, at least one reflector mounted on the
frame, a tube having a central axis and configured to have therein
a heat transfer fluid being heated by the reflector focusing
sunlight onto a focal line configured to be generally aligned with
the central axis, the tube coupled to the frame with at least one
tube support, and a control system configured to move the frame,
the control system comprising a processor and a data storage
device. The processor is configured to execute a code stored in the
data storage device to determine an offset between the focal line
and the central axis, and move the frame to move the central axis
toward the focal line to reduce the offset.
[0006] According to another aspect, a method of controlling a solar
reflector assembly is disclosed. The solar reflector assembly may
include at least one frame, at least one reflector mounted on the
frame, a control system configured to move the frame, and a tube
configured to have therein a heat transfer fluid being heated by
the reflector focusing sunlight on the tube, the tube coupled to
the frame with at least one tube support. The method includes
determining a variable indicative of a temperature of the heat
transfer fluid, moving the frame between a focused position wherein
sunlight is focused on the tube by the reflector and a defocused
position wherein sunlight is less focused on the tube by the
reflector than the focused position to control the temperature of
the heat transfer fluid.
[0007] According to another aspect, a solar reflector assembly
includes at least one frame, at least one reflector mounted on the
frame, a tube configured to have therein a heat transfer fluid
being heated by the reflector focusing sunlight on the tube, the
tube coupled to the frame with at least one tube support, and a
control system configured to move the frame, the control system
comprising a processor and a data storage device. The processor is
configured to execute a code stored in the data storage device to
determine a variable indicative of a temperature of the heat
transfer fluid, and move the frame between a focused position
wherein sunlight is focused on the tube by the reflector and a
defocused position wherein sunlight is less focused on the tube by
the reflector than the focused position to control the temperature
of the heat transfer fluid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 shows a reflector frame assembly according to one
exemplary embodiment.
[0009] FIG. 2 shows a side view of the reflector frame assembly of
FIG. 1.
[0010] FIG. 3 shows a tube for carrying a heat transfer fluid in a
solar reflector power generation system.
[0011] FIG. 4 shows a side view of a frame having a reflector
according to one exemplary embodiment.
[0012] FIG. 5 shows the tube of FIG. 3 with reflective light rays
forming a radiation band thereon.
[0013] FIGS. 6-8 show three positions of the frame of FIG. 3.
[0014] FIG. 9 shows a side view of the reflector frame assembly of
FIG. 1 with static load deflections according to one exemplary
embodiment.
[0015] FIG. 10 shows a perspective compressed view of a frame with
static load deflections according to one exemplary embodiment.
[0016] FIG. 11 shows a reflector frame assembly according to one
exemplary embodiment.
[0017] FIG. 12 shows a control system according to one
embodiment.
[0018] FIG. 13 shows a method of controlling a reflector frame
assembly according to one embodiment.
[0019] FIG. 14 shows a bell-shaped curve representing the
distribution of reflected light rays striking a tube of the frame
assembly of FIG. 1 according to one embodiment.
[0020] FIG. 15 shows a curve represent the distribution of
reflected light rays striking a tube of the frame assembly of FIG.
1 according to another embodiment.
[0021] FIG. 16 shows three bell-shaped curves representing the
distribution of reflected light rays striking a tube of the frame
assembly of FIG. 1 when the frame is oscillated according to
another embodiment.
[0022] FIG. 17 shows a method of controlling a reflector frame
assembly according to one embodiment.
DETAILED DESCRIPTION
[0023] Referring to FIG. 1, a plurality of reflector frame
assemblies 100 forming a section of a solar power generation system
is shown. Each reflector frame assembly 100 includes a frame 102,
which is rotatably mounted on one or more support pylons 104 and
can rotate about a center axis or rotation axis 200 to track the
daily east to west movement of the sun. Referring also to FIG. 2,
each frame 102 has a concave or trough-shaped side, to which one or
more reflectors 106 (only one reflector is shown in FIG. 1) are
connected. In the embodiments described herein, the reflectors 106
are parabolic. The reflectors 106 may be constructed from any type
of rigid (e.g., glass) or flexible material (e.g., reflective film)
that provides a reflective surface. The reflectors 106 may be
constructed from a flexible reflective material that is mounted to
a backing structure. Examples of reflectors and backing structures
are described in US 2009/0101195 and US 2011/0094502, the entire
disclosures of which are expressly incorporated by reference. The
reflectors 106 can be connected to the frame by any device and/or
method. An example of a device and method for attaching the
reflectors to the frame is described in detail in U.S. patent
application Ser. No. 13/491,422, filed Jun. 7, 2012, the entire
disclosure of which is expressly incorporated by reference.
[0024] Referring to FIGS. 2-5, the reflectors 106 reflect and focus
sunlight onto a tube 110, which may extend generally along a focal
line 108 of one or more frames 102. A focal line 108 as disclosed
is a theoretical concept and may be in the form of a focal band in
practice (i.e., having length and width). However, a central axis
of such a focal band may be considered a focal line. In the example
of FIG. 1, the tube 110 is shown to extend generally along the
focal line 108 of four frames 102A-102D. The tube 110 may be
mounted with tube mounts 112 to each frame 102. When the reflectors
106 are directly facing the sun, a longitudinal central axis 111 of
the tube 110 may be generally coaxial with a focal line 108 of the
reflectors 106 (shown in FIG. 3). Accordingly, the reflectors 106
reflect the sunlight generally onto the tube 110 at a focal line
108 which may generally correspond to the longitudinal central axis
111 of the tube 110. The tube 110 serves as a conduit for carrying
a heat transfer fluid (HTF) that can transfer the heat generated by
the focused sunlight to a power generation section (not shown) of
the solar power generation system.
[0025] Each reflector frame assembly 100 includes a drive mechanism
113 and controller 114, which may be collectively referred to
herein as a control system 115. Each frame 102 is rotated about the
axis 200 (shown in FIG. 1) by the control system 115 to track the
daily movement of the sun. The direction of rotation is shown by
the arrow 202 in FIG. 2. The control system 114 may provide
continuous tracking of the sun, thereby providing continuous
focusing of sunlight onto the tube 110. Any type of analog and/or
digital control system utilizing classical and/or modern control
techniques may be used to provide continuous and or discrete solar
tracking of the reflector frames 102. An example of a control
system and methods for rotating the frame assemblies 100 and solar
tracking thereof is provided in U.S. Patent Application Publication
No. 2010/0229851, the entire disclosure of which is expressly
incorporated by reference.
[0026] The reflector 106 (only half of a reflector 106 is shown in
FIGS. 2 and 4) has a principal axis 204 and the focal line 108.
Light rays 208 that are parallel to the principal axis 204 are
focused onto the focal line 108. Because the tube 110 is positioned
such that the longitudinal central axis 111 passes through the
focal line 108, the light rays 208 striking the reflector 106 are
reflected and focused onto the longitudinal central axis 111 of the
tube 110 to form the focal line 108. However, the outer surface of
the tube 110 is spaced from the longitudinal central axis 111 by a
distance defined by the radius of the tube 110. Accordingly, with
reference to FIG. 5, the focused light rays 208 form a focal band
or radiation band 116 on the surface of the tube 110. Light rays
208 that are slightly offset from parallel or generally offset when
striking the reflector 106 may either strike the tube 110 outside
the radiation band 116 or completely miss the tube 110. For the HTF
in the tube 110 to reach the highest temperature possible
considering the contemporaneous physical conditions of the frame
assembly and the surrounding environmental conditions, the greatest
possible number of light rays 208 must be captured by the reflector
106 and focused onto the tube 110. To do so, the reflector 106 must
be oriented so as to be directly facing the sun such that the
principal axis 204 theoretically intercepts a center of the Sun.
The control system 115 may continuously rotate each frame 102 from
east to the west as shown by the three progressive positions of
FIGS. 6-8 (i.e., morning, noon and afternoon, respectively) so that
the reflector 106 is substantially directly facing the sun.
[0027] The control system 115 may utilize tracking algorithms for
tracking the location of the sun. Such tracking algorithms use
location and the angular position of the frames 102, and the date
and time of day to estimate the position of the sun. Each of the
frames 102 may include one or more inclinometers, which can provide
the control system 115 with the angular positions of the frame 102.
By having an estimated position of the sun and the location and
position of the frame 102, the control system 115 can rotate the
frame 102 to track the movement of the sun. Instead of or in
combination with using the solar tracking algorithm, the control
system 115 may also utilize thermocouples placed at one or more
locations along the tube 110 to measure the temperature of the tube
110 and/or the temperature of the HTF. The control system 115 can
then rotate the each or several frames 102 to generally maximize
the measured temperature, which may correspond to a generally
optimum tracking of the sun. As described in detail below, instead
of or in combination with the above tracking devices and methods,
the control system 115 may use one or more optical sensors to
continuously track the location of the sun.
[0028] When a reflector 106 is slightly offset from directly facing
the sun, the number of parallel light rays 208 (i.e., parallel to
the principal axis 204) is reduced as compared to a scenario where
the reflector is directly facing the sun. Accordingly, the number
of reflected light rays intercepting the focal line 10 is slightly
reduced. Therefore, the intensity of the radiation band 116 is
slightly reduced and the HTF in the tube 110 may not reach a
possible maximum temperature considering the contemporaneous
physical conditions of the frame assembly and the surrounding
environmental conditions. When the reflector 106 is even more
offset, the intensity of the radiation band 116 is further reduced.
Therefore, in order to achieve the highest possible temperature of
the HTF in the tube 110, each frame 102, hence the one or more
reflectors 106 mounted on each frame, must continuously track the
movement of the sun and directly face the sun throughout the day as
accurately as possible. As described in detail below, the control
115 may make solar tracking adjustments in order to compensate for
static loads, compensate for misalignment, defocus the reflectors
to reduce the temperature of the HTF, and/or provide generally
uniform heat distribution on the tube 110.
[0029] The components of a theoretically rigid solar reflector
assembly 100, such as the frame 102, tube mounts 112 and/or the
tubes 110 would not deflect under the static loads of the frame
members or objects mounted to the frame members or be misaligned
relative to each other. Accordingly, the longitudinal central axis
of the tube 110 would be coaxial with the focal line 108. However,
absolute rigidity cannot be achieved. Furthermore, a highly rigid
structure that diminishes any static load deflections to a
negligible level may not be practical considering the costs of
manufacturing, transportation, assembly, operation and maintenance.
Accordingly, the reflector frame assembly 100 may not be
constructed with such rigidity so as to relatively eliminate or
render negligible the effect of static loads on the frames 102.
Large reflector assemblies may also exacerbate such deflection
problems. Therefore, the static loads exerted by the frame members
and any objects attached to the frame members may deflect the frame
members themselves and/or the overall frame 102, thereby affecting
the above-described focusing function of the entire frame 102
depending on the angular position of the frames 102 about the
rotation axis 200.
[0030] Referring to FIG. 9, a frame 102 is shown in a position
where the principal axis 204 is generally horizontal. This position
may generally correspond to either the morning or late afternoon
positions of the frame 102. The position 220 of the tube mounts 112
and the tube 110 shown in FIG. 9 corresponds to a position when the
tube mounts 112 (and/or all components of the reflector assembly
100) are rigid. In position 220, the principal axis 204 may
generally intersect, the longitudinal central axis 111 of the tube
112. However, as shown in FIG. 9, the tube mounts 112 may be
defined by two cantilever beams that can deflect due to the loads
exerted thereon by the tube 110 and the HTF carried in the tube
110. Accordingly, as shown by position 222, the weight of the tube
110 including the weight of the HTF may cause the tube mounts 112
to deflect. This deflection is shown in an exaggerated manner in
FIG. 9. Depending on the degree of the deflection in the tube
mounts 112, some of the light rays reflecting from the reflectors
106 may slightly, significantly, or completely miss the tube 110.
Therefore, the deflection in the tube mounts 112 may result in the
HTF not reaching a certain temperature.
[0031] Referring to FIG. 10, the deflection of the tube mounts 112
may vary along the lengths of the frame assemblies 100. As shown in
FIG. 7, in the generally vertical position of the principal axis
204, which may correspond to the noon position of the frame 102,
the deflection in the tube mounts 112 may be small, or negligible.
Therefore, in the operating range of each frame 102, the deflection
of the tube mounts 112 may be highest in the morning and late
afternoon positions and diminish, as the frame 102 moves toward the
noon position.
[0032] As described further below, the control system 115 can
rotate the frame assembly 100 to compensate for the deflection in
the tube mounts 112. For example, referring to FIG. 9, the control
system 114 can rotate the frame assembly 100 in the direction of
the arrow 224 in order to move the tube 110 from position 222
toward position 220. Although the tube mounts 112 remain deflected
even near position 222, albeit slightly less than when in position
220, the tube 110 will be positioned closer to the tube of position
220, and therefore, intercepting more of the light, rays that are
reflected from the reflectors 106 as compared to the tube 110 of
position 222. Therefore, with the control system 115 making a
compensating, rotation in the direction of the arrow 224, the HTF
may reach a preferred temperature. The compensating rotation along
the arrow 224 may be highest at the extreme operating positions of
the frame 102 (i.e., morning and late afternoon positions) and
diminish toward the noon position.
[0033] Referring to FIG. 11, a frame 102 is partially shown. At
least some of the longitudinal frame members 118 are shown to be
deflected or sagging under their own weight. This deflection is
shown in an exaggerated manner in FIG. 11. The lateral frame
members 120 may also deflect under static loads including the
lateral members' own weight. All of the frame members may deflect
under their own weight and the loads exerted thereon by the weight
of the other frame members. Accordingly, the entire frame 102 may
deflect or sag. In the position of the frame assembly 100 shown in
FIG. 7, the left and right sides of the frame 102 may deflect or
sag nearly symmetrically about the axis of rotation 200.
Accordingly, the deflections of the frame members and/or the entire
frame 102 may depend on the angular position of the frame 102.
Although not shown, various frame members and/or the entire frame
102 may be slightly twisted so as to affect the focusing of the
light rays onto the tube 110.
[0034] As described in detail below, the control system 115 can
rotate a frame 102 or a plurality of connected frames 102A-D to
compensate for the deflection and/or twists in the frame members
and/or the entire frames 102. For example, the deflection or
sagging in the entire frame 102 as shown in FIG. 11 may cause at
least a section of the tube 110 to move to a position 222 as shown
in FIG. 9. The control system 115 can rotate the frame 102 in the
direction of the arrow 224 in order to move the tube 110 from
position 222 toward position 220. The deflections in the frame
members and/or the entire frame 102 may be measured and/or
numerically computed based on the physical and material properties
of the frame members and provided to the control system 115.
[0035] The frame assembly 100 may be constructed at the operating
site of the solar power generation system by onsite assembly of the
individual frame members of each frame 102 or onsite assembly of
preassembled sections of the frames 102. Due to possible
manufacturing inconsistencies, variations and/or defects of a few
or some of the parts of the frame assemblies 100, or improper
installation of the frame assemblies 100, the frame assemblies 100
may be misaligned when assembled on site. As a result, a few or
some of the frames 102 may be misaligned such as to cause slight
misalignment in the focusing of the light rays from the reflectors
106 onto the tube 110. An example of such a misalignment is
described in detail blow.
[0036] Referring back to FIG. 1, the frame assembly 100 is shown as
having four frames 102A-102D. All of the frames 102A-D may be
rotationally driven about the rotation axis 200 by a single drive
mechanism 113 of the control system 115 according to commands from
the controller 114 to track the daily movement of the sun. Thus,
the frames 102A-D rotate together during solar tracking. The frames
102A-D may be misaligned such that each frame is rotationally
offset relative to another frame 102A-D. For example, when the
frame 102A is positioned at an angle of 35 degrees relative to a
horizontal position, the frame 102B may also be positioned at an
angle of 35 degrees. The frames 102C and 102D, however, may be
positioned at 36 degrees and 37 degrees, respectively. As a result,
if the frames 102A and 102B are correctly positioned for tracking
the sun, the frames 102C and 102D are offset from the correct
tracking position by 1 and 2 degrees, respectively. The control
system 115 can rotate the frames 102A-D to compensate for the
misalignment in the frames 102A-102D by rotating the frames
102A-102D to an angle that corresponds to an average of the angles
of the frames 102A-102D. In the above example, the control system
115 can position the frames 102A-102D at an angle of 35.75 degrees,
which is the average of 35, 35, 36 and 37 degrees.
[0037] As described above, the control system 115 can rotate the
frame 102 to compensate for any misalignment, which is not limited
to the above example, and may include any misalignment between any
members and/or sections of each frame assembly 100. The
misalignment in the frame assemblies 100 can be measured on site
and the corresponding measurement data can be provided to the
control system 115.
[0038] Referring to FIG. 12, the control system 115 may include a
processor 300 and a data storage module 302 as parts of the
controller 114. The drive mechanism 113 may be coupled to the
processor 300 for receiving commands from the processor to actuate
or move one or more of the frames 102 (e.g., four frames 102 as
shown in FIG. 1). The drive mechanism 113 may include one or more
electric motors and any associated mechanisms such as gearing or
other mechanisms that convert rotational motion to linear motion or
a combination or rotational and linear motion. The drive mechanism
113 may also include hydraulic actuators such as linear hydraulic
actuators and associated mechanisms for converting the linear
motion of the hydraulic actuators to rotational motion or a
combination of rotational and linear motion. The control system 115
may also include one or more sensors, which are collectively shown
as sensor module 306. The sensor module 306 may include any type of
sensor that can detect the linear and/or angular position of the
frame, the position of the sun, the deflection of one or more frame
members (e.g., strain gage), temperature at one or more locations
on the tube 110, temperature of the HTF at one or more locations
along the tube 110, one or more optical sensors that can measure
the intensity and dimensions of the radiation band 116 and/or one
or more imaging sensors that capture images of the frames 102
and/or the tube 110. The sensors of the sensor module 306 may be
near the processor 300 and/or the data storage module 302. One or
more sensors of the sensor module 306 may be remotely located from
the processor 300 and/or the data storage module 302. For example,
strain gages may be positioned on several frame members to measure
the deflections of these frame members during operation of the
frame as disclosed. Such strain gages may then transmit data to the
processor 300 with wires or wireless communication. The control
system 115 may also include other components that may be required
for operation of the control system 115 as disclosed such as a
power supply or one or more input/output ports (not shown).
[0039] Referring to FIG. 13, a method 400 for controlling the frame
102 when compensating for static loads is shown. The method 400
determines an offset between the focal line 108 and the
longitudinal central axis 111 of the tube 110 (block 402). The
method then moves the frame to move the longitudinal central axis
111 toward the focal line 108 to reduce the offset. The method 400
may determine an actual position of the tube 110 and then move the
frame 102 to move the tube 110 from the actual position toward the
rigid position of the tube when the actual position is offset
relative to the rigid position. The method 400 may determine the
shift or offset in the position of one or more sections of the tube
110 relative to the corresponding sections of the focal line 108.
The method 400 then rotates the frame 102 to reduce the offset or
rotate the frame 102 toward the theoretically rigid position of the
frame to compensate for static loads exerted on the frame 102 and
the tube mounts 112. The shift or offset in the position of the
tube 110 relative to the focal line as described herein may be
referring to a shift in the position of a section or the entire
tube 110 relative to corresponding section or the entire focal line
108, respectively.
[0040] The shift or offset in the position of the tube 110 relative
to the focal line 108 may be caused by a deflection in any support
structure of the tube, such as deflection in the tube mounts 112,
generally the deflection of one or more frame members which may
cause the reflectors to shift the focal line 108, and/or any
misalignment in the components of the solar reflector assembly 100.
For example, a shift in the position of the tube 110 relative to
the focal line 108 may be caused by the static loads on the tube
mounts 112, the static loads of the tube itself, or the static
loads on one or more frame members. A shift in the position of the
tube 110 relative to the focal line 108 may be caused by a shift or
offset in the reflectors 106 due to static loads on one or more
frame members. The latter scenario may be a shift in the focal line
108 rather than a shift in the position of the tube 110. However, a
shift in both the position of the tube 110 and the focal line 108
may be caused by static loads on some or all parts of the frame
assembly 100.
[0041] Determining the shift in position of the tube 110 relative
to the focal line 108 may be based on actual measurements of
deflection in or more tube support members (e.g., tube mounts 112)
and/or actual measurements of deflection in or more parts of the
frame 102 with one or more sensors such as strain gages; actual
measurements of the temperature of the surface of the tube 110
and/or the HTF; measurements of the position of the tube 110 and or
positions of the reflectors, i.e., the focal line 108, using
various imaging techniques such as still or motion photography;
measurements of the intensity and size of the radiation band 116 on
the tube using light sensors or imaging techniques; and/or, any
other displacement sensing, imaging, or thermal measurement
techniques.
[0042] Determining the shift in position of the tube 110 relative
to the focal line 108 may be also be based on predetermined
measurement and/or computational data regarding the movement of the
tube 110 and/or the movement of the focal line 108 due to static
loads. For example, the frame 102 may be cycled through a daily
operation and the position of the tube 110 relative to the focal
line 108 at several locations along the tube 110 may be measured.
Furthermore, such measurements make take into account seasonal
variations and/or environmental conditions that may affect the
static loads, i.e., deflections in the tube support structure
and/or the frame members. In another example, deflections in the
tube support structure and/or the frame members may be modeled by
computational methods such as finite element analysis. Accordingly,
data regarding the deflections in the tube support structure and/or
the frame members may be virtually determined with sufficient
and/or high accuracy. Determining the shift in position of the tube
110 relative to the focal line 108 may also be determined based on
real-time data, historical data, predetermined measurement data
and/or other computational data.
[0043] According to the method 400, the amount by which to rotate
the frame 102 (block 404) may be determined based on data regarding
the shift in position of the tube 110 relative to the focal line
108 as described in detail above. Determining the amount by which
to rotate the frame 102 may be based on a difference between an
actual position of the tube 110 relative to an actual focal line
108, which as described in detail above may be determined in
real-time, historical data and/or computational data, and the
position of the tube 110 relative to the focal line 108 if the
frame 102 is rigid, which may be referred to herein as the rigid
position of the tube 110. The processor 300 may then send a command
to the drive mechanism 113 to rotate the frame 102 by the
determined rotation. For example, if the shift in the position of
the tube 110 relative to the focal line is 5.degree. ahead or
leading the rigid position of the tube 110, the frame 102 may be
rotated by -5.degree. to position the tube 110 relative to the
focal line 108 to a near rigid position.
[0044] The shift of offset in position of the tube 110 relative to
the focal line 108 may be different along the length of the tube
110. According to one example, the method 400 may compute an
average of the shift or offset in the position of the tube 110
relative to the focal line 108 along the length of the tube 110 to
determine the amount by which to rotate the frame 102. For example,
referring to FIG. 1, the shift in the position of the tube 110 may
be 1 degree for a first frame 102A, 4 degrees for a second frame
102B, 3 degrees for a third frame 102C and 4 degrees for a fourth
frame 102D. According to his example, the frames 102A-D may be
rotated by 3 degrees to position the tube 110 to a near rigid
position. Other algorithms for determining an overall amount by
which to rotate the frame may be used.
[0045] The method 400 may be performed by the processor 300
accessing data stored in the data storage device 302 and/or
executing one or more program codes stored in the data storage
device 302 to operate the drive mechanism 113. For example, the
data storage device 302 may include data regarding the rigid
position of the tube 110 and the actual position of the tube 110
relative to the focal line 108. During the operation of each frame
102 or a plurality of frames 102 that may be operated by the same
control system 115 (e.g., frames 102A-D of FIG. 1), the processor
300 may compute the amount by which to rotate the frame 102 by
subtracting the actual position of the tube 110 relative to the
focal line 108 from the rigid position of the tube 110, which may
be the same as the position of the focal line 108. Based on the
result of such computation, the processor 300 may then send a
command to the drive mechanism 113 to rotate the frame by the
computed amount.
[0046] In certain operating conditions, such as during hot summer
days, the focusing of sunlight onto the tube 110 may excessively
raise the temperature of the tube 110 so as to overheat the tube
110, thereby possibly causing deformation or damage to the tube 110
and/or overheating the HTF, which may adversely affect the
viscosity of the HTF. In order to maintain the HTF at an optimum or
near optimum temperature while preventing the tube 110 from
overheating, the control system 115 can operate in a slightly
defocused mode by lag, lead or lead-lag tracking of the sun. In the
lag tracking mode or lagging mode, the control system 115 can
position a frame assembly 102 slightly lagging from directly facing
the sun in order to reduce the number of reflected light rays that
strike the tube 110. As a result, the intensity of the focused
sunlight is reduced and the HTF is maintained a lower temperature
than if the control system 115 tracked the sun without any defocus
or lag. However, the lagging offset position may be controlled by
the control system 115 so as to maintain the HTF preferred or near
preferred temperature.
[0047] In the lead tracking mode or leading mode, the control
system 115 can position a frame 102 slightly leading ahead of
directly facing the sun in order to reduce the number of reflected
light rays that strike the tube 110. As a result, the intensity of
the focused light rays is reduced and the HTF is maintained at a
lower temperature than if the control system 115 tracked the sun
without any defocus or lead. However, the leading offset position
may be controlled by the control system 115 so as to maintain the
HTF at a preferred or near preferred temperature.
[0048] In the lead-lag tracking mode or leading-lagging mode, the
control system 115 can position a frame 102 slightly leading ahead
of directly facing the sun in order to reduce the number of
reflected light rays that strike the tube 110. Then, the control
system 115 does not move the frame 102 until the position of the
sun catches up with the leading position of the frame 102 and
passes the leading position such that the frame 102 will be
positioned in a lagging mode. The control system 115 then moves the
frame 102 to a leading position and this leading-lagging cycle is
repeated. As a result, the intensity of the focused light rays is
reduced and the HTF is maintained at a lower temperature than if
the control system 114 tracked the sun without any defocus or
lead-lag. However, the lead-lag cycle may be controlled by the
control system 115 so as to maintain the HTF at preferred or near
preferred temperature.
[0049] Referring back to the radiation band 116 of FIG. 5, the
distribution of light rays may not be uniform and have the highest
intensity at the center section of the tube 110, which is shown in
FIG. 5 as section H, while diminishing from the center section H
toward the lateral portions of the tube 110. Referring to FIG. 14,
the distribution of the reflected light rays that strike the tube
110 can be represented by a bell-shaped curve BC. The horizontal
axis in FIG. 14 represents the width of the radiation band and the
vertical axis represents the temperature of the tube 110 along the
width of the radiation band 116. Thus, according to the curve BC,
the center section H of the tube 110 experiences the highest
temperature in the radiation band 116, while the edge portions E
experience the lowest temperature of the radiation band 116. It may
be preferred to provide a more uniform heat distribution within the
radiation band 116, which may result in the transfer of more heat
to the fluid carried in the tube, while reducing the peak
temperatures that can occur at the center section H of the
radiation band 116. A more uniform heat distribution curve of the
radiation band 116 may resemble FIG. 15, which shows the peak
temperature to be lower, yet more heat being transferred to the
tube 110 (i.e., the transferred heat corresponds to the area under
the curve BC).
[0050] The control system 115 can dither or oscillate the frame
assembly 100 about the rotational axis 200 such that the center
portion H of the radiation band 116, which is the hottest portion
of the radiation band 116, oscillates laterally on the radiation
band 116. For example, when the frame 102 is rotated so as to be
slightly leading ahead of directly facing the sun, section H of the
radiation band 116 is shifted slightly off-center to one side of
the tube 110. Accordingly, the curve BC may resemble the curve BC+
of FIG. 16. Conversely, when the frame 102 is rotated so as to be
slightly lagging behind from directly facing the sun, section H of
the radiation band 116 is slightly shifted off-center to the other
side of the tube 110. Accordingly, the curve BC may resemble the
curve BC- of FIG. 16. When the control system 115 dithers or
oscillates the frame 102 between leading and lagging positions, the
oscillations of the curve BC over time as shown by the arrow DT may
resemble the curve of FIG. 15. In other words, the peak in the
curve BC of FIG. 14 is dithered or oscillated in order for the heat
distribution to resemble the curve of FIG. 15. Therefore, the heat
transfer to the HTF carried by the tube 110 is increased while
reducing the peak localized temperature on the tube 110.
[0051] Referring to FIG. 17, a method 500 for controlling the frame
102 when defocusing for overheating and/or dithering for uniform
heat distribution is shown. The method 500 includes determining a
variable indicative of the temperature of the fluid inside the tube
110 (block 502). The method 500 further includes moving the frame
102 between a focused position and a defocused position wherein
sunlight is less focused on the tube 110 by the reflector 106 than
the focused position to control the temperature of the heat
transfer fluid (block 504). Controlling the temperature of the
fluid may be performed by defocusing the frame assembly as
described above, or dithering the frame assembly to provide uniform
heat distribution on the tube 110.
[0052] The variable indicative of the temperature of the HTF may
represent the actual temperature of the HTF at a certain location
along the tube 110. Alternatively, the variable indicative of the
temperature of the HTF may represent the intensity of the radiation
band 116 across the width of the radiation band 116, which may be
measured by one or more optical sensors as described in detail
below. The intensity of the radiation band 116 across the width of
the radiation band 116 may correspond to certain temperature of the
HTF according historical, tabular, experimental and/or
computational data.
[0053] If the temperature of the HTF in the tube 110 approaches or
exceeds a certain threshold temperature, the control system 115 can
rotate the frame 102 to defocus the reflectors 106 and reduce the
intensity of the radiation band 116. Accordingly, the temperature
of the HTF may be reduced. Further, the control system 115 may
continuously dither the frame 102 to provide a uniform heat
distribution on the tube 110.
[0054] The method 500 may be performed by the processor 300 by
accessing data stored in the data storage device 302 and/or
executing one or more program codes in the data storage device 302
to operate the drive mechanism 113. For example, the data storage
device 302 may include tabular data correlating the intensity of
the radiation band 116 to the temperature of the HTF. The processor
300 may receive information from an optical sensor (described in
detail below), regarding the intensity of the radiation band 116 at
a certain location on the tube 110. If the data received by the
processor 300 corresponds to a temperature of the HTF approaching
or exceeding a certain threshold, the processor 300 sends a command
to the drive mechanism 113 to defocus the reflector or solar
assembly to reduce the temperature of the fluid. Furthermore, the
processor 300 may send a command to the drive mechanism 113 to
dither or oscillate the frame 102 to maintain the temperature of
the HTF at a certain level or to evenly distribute the reflected
sunlight on the radiation band 116
[0055] Referring back to FIG. 4, an exemplary embodiment of the
frame assembly 100 is shown. The frame assembly 100 is similar to
the frame assembly 100 described above and further includes an
optical sensor 122 positioned on the frame assembly 100 so as to
face the tube 110. At least one optical sensor 122 may be provided
for each frame assembly 100. However, any number of optical sensors
122 can be provided for each frame assembly 100. For example, each
frame 102 may include an optical sensor 122. The optical sensor 122
measures the light striking the tube 110. In other words, the
optical sensor 122 measures the light that strikes the tube 110 to
form the radiation band 116 including longitudinal and lateral
gradient information. Accordingly, the curve BC can be constructed
with the data obtained from the optical sensor 122.
[0056] The data from the optical sensor 122 can be used by the
control system 115 to perform the above-described functions of
compensating for static loads, compensating for misalignment,
defocusing and dithering. Thus, the control system 115 can rotate
the frame 102 to shift the peak of the curve BC shown in FIG. 16 to
achieve any preferred localized or distributed temperature profile
on the tube 110.
[0057] The data from the optical sensor 122 can also be used by the
control system 115 to track the movement of the sun without running
a sun tracking algorithm or receiving information from a sun
sensor. When the frame assembly 100 is facing the sun such that the
reflectors 106 are focused onto the tube 110, the curve BC
resembles the curve shown in FIG. 14. If the frame assembly 100
remains stationary, the curve shifts of center with the movement of
the sun. The control system 114 can continuously or discretely
receive data from the optical sensor 122 and rotate the frame
assembly 100 so as to keep the peak of the curve BC centered.
Therefore, by continuously or discretely centering the peak of the
curve BC, the control system 115 can track the movement of the sun
without resorting to a tracking algorithm, any sun sensors and/or
inclinometers. However, a tracking algorithm, a sun sensor and/or
an inclinometer can also be used for redundancy, calibration
purposes, and/or tracking confirmation.
[0058] Although a particular order of actions is described above,
these actions may be performed in other temporal sequences. For
example, two or more actions described above may be performed
sequentially, concurrently, or simultaneously. Alternatively, two
or more actions may be performed in reversed order. Further, one or
more actions described above may not be performed at all. The
apparatus, methods, and articles of manufacture described herein
are not limited in this regard.
[0059] While the invention has been described in connection with
various aspects, it will be understood that the invention is
capable of further modifications. This application is intended to
cover any variations, uses or adaptation of the invention
following, in general, the principles of the invention, and
including such departures from the present disclosure as come
within the known and customary practice within the art to which the
invention pertains.
* * * * *