U.S. patent application number 13/999275 was filed with the patent office on 2014-09-11 for method and apparatus for orienting arrays of mechanically linked heliostats for focusing the incident sunlight on a stationary object.
The applicant listed for this patent is Rajeev Pandit, Ravindra Patwardhan. Invention is credited to Rajeev Pandit, Ravindra Patwardhan.
Application Number | 20140251315 13/999275 |
Document ID | / |
Family ID | 51486273 |
Filed Date | 2014-09-11 |
United States Patent
Application |
20140251315 |
Kind Code |
A1 |
Patwardhan; Ravindra ; et
al. |
September 11, 2014 |
Method and apparatus for orienting arrays of mechanically linked
heliostats for focusing the incident sunlight on a stationary
object
Abstract
The present invention is a method and apparatus for periodic
orientation of arrays of mechanically linked heliostats positioned
on rotatable shafts such that incident sunlight is focused on a
stationary object. In each altitudinal orientation a minuscule
predefined push is given by an actuator and the time interval
between each altitudinal orientation is
2.times.(T.sub.2-T.sub.1)/n. For azimuthal reorientation, the
magnitude of rotation of rotatable shafts is determined by
(Y.times.Sin .gamma.)/2 degrees, and as per the position of the sun
in the sky, the determined magnitude in degrees is added/subtracted
to form angle .theta.'. The length `C` of the linear actuator with
its arm at angle .theta. can be extended/retracted to length
`C.sub.1` such that angle .theta.' is achieved, wherein an arm
affixed with each rotatable shaft and coupled with a linear
actuator provides the ability to rotate the rotatable shaft in
clockwise or anticlockwise direction.
Inventors: |
Patwardhan; Ravindra; (Pune,
IN) ; Pandit; Rajeev; (Parkland, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pandit; Rajeev
Patwardhan; Ravindra |
Parkland
Pune |
FL |
US
IN |
|
|
Family ID: |
51486273 |
Appl. No.: |
13/999275 |
Filed: |
February 6, 2014 |
Current U.S.
Class: |
126/714 ;
126/601 |
Current CPC
Class: |
F24S 50/20 20180501;
F24S 2030/11 20180501; Y02E 10/47 20130101 |
Class at
Publication: |
126/714 ;
126/601 |
International
Class: |
F24J 2/38 20060101
F24J002/38 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 6, 2013 |
IN |
588/MUM/2012 |
Claims
1. A method for synchronous orientation of mechanically-linked
heliostats to focus incident sunlight onto a central receiver, said
method comprising: a) dividing the sky into four imaginary
quadrants A, B, C and D via imaginary east-west line (from
90.degree. azimuth to 270.degree. azimuth) and north-south line
(from 0.degree. azimuth to 180.degree. azimuth) bisecting at the
zenith to form a three-dimensional grid for mapping altitudinal and
azimuthal trajectory of the sun across the sky with help of a
common art solar position calculation program/software; b) mapping
position of the sun and upon occurrence of a first predefined
event, recording corresponding time (T.sub.1) as start point; c)
mapping position of the sun and upon occurrence of a second
predefined event, recording the corresponding time (T.sub.2) as mid
point; d) determining altitudinal (elevational) displacement of the
sun to occasion suitable means to introduce a calibrated
compensation in heliostat orientation necessary to focus sunlight
onto said central receiver; e) determining azimuthal displacement
of the sun to occasion suitable means to introduce a calibrated
compensation in heliostat orientation necessary to focus sunlight
onto said central receiver; f) repeating steps a to e for continued
synchronous orientation of mechanically linked heliostats to
continuously focus sunlight onto said central receiver.
2. The method of claim 1, wherein the sun elevation, and sun
azimuth, values are periodically monitored at intervals ranging
from 30 seconds to 1800 seconds using said common art solar
position calculation program/software.
3. The method of claim 1, wherein said first predefined event is
said to occur upon reaching a user-defined eastern sun elevation in
degrees like 30.degree. eastern sun elevation.
4. The method of claim 1, wherein said second predefined event
indicative of the sun azimuth being 180.degree. or 360.degree..
5. The method of claim 1, wherein determination of apparent angular
displacement .gamma. of the sun with respect to said east west line
passing through the zenith is calculated by the formula
[90.degree.-azimuth value of the sun] when the sun is observed to
be present in quadrant A, which quadrant A is present in the north
east region of the sky.
6. The method of claim 1, wherein determination of apparent angular
displacement .gamma. of the sun with respect to said east west line
passing through the zenith is calculated by the formula [azimuth
value of the sun-90.degree.] when the sun is observed to be present
in quadrant B, which quadrant B is present in south east region of
the sky.
7. The method of claim 1, wherein determination of apparent angular
displacement .gamma. of the sun with respect to said east west line
passing through the zenith is calculated by the formula
[270.degree.-azimuth value of the sun] when the sun is observed to
be present in quadrant C, which quadrant C is present in south west
region of the sky.
8. The method of claim 1, wherein determination of apparent angular
displacement .gamma. of the sun with respect to said east west line
passing through the zenith is calculated by the formula [azimuth
value of the sun-270.degree.] when the sun is observed to be
present in quadrant D, which quadrant D is present in northwest
region of the sky.
9. The method of claim 1, wherein said means to introduce a
calibrated compensation in heliostat orientation according to
apparent altitudinal displacement of the sun is an actuator like a
linear stepper motor actuator with a pusher ball nut and lead screw
in operational linkage to said heliostats, wherein displaceable
said pusher ball nut travels on said lead screw for actuating a
pusher rod for rotating said heliostats from a mirror elevation of
predefined degrees eastern to a mirror elevation of predefined
degrees western orientation.
10. The method of claim 9, wherein actuation periodicity of the
said actuator for achieving orientation of heliostats necessary to
focus sunlight onto said central receiver is calculated by the
formula 2(T.sub.2-T.sub.1)/n where n is the number of consecutive
altitudinal orientations of said heliostats required in a day
necessary to track the sun from a predefined degrees of solar
elevation like 30.degree. eastern in the morning to a predefined
degrees of solar elevation like 30.degree. western in the
evening.
11. The method of claim 10, wherein said n number of altitudinal
orientations of the said heliostats required in a day necessary to
track the sun from predefined degrees of solar elevation (eastern)
in the morning to predefined degrees of solar elevation (western)
in the evening depends on total length of said lead screw on which
said displaceable pusher ball nut travels for actuating said pusher
rod for rotating said heliostats, pitch of the said lead screw, and
number of steps that said stepper motor rotates in each altitudinal
orientation.
12. The method of claim 1, wherein said means to introduce a
calibrated compensation in heliostat orientation according to
apparent azimuthal displacement of the sun is an east west
directional rotatable shaft in operational linkage to said
heliostats and further characterized in having a central/distal arm
affixed with said rotatable shaft and coupled with a drive means
providing ability to rotate said rotatable shaft in both clockwise
and anticlockwise directions.
13. The method of claim 12, wherein actuation periodicity of the
rotatable shaft for achieving orientation of heliostats necessary
to focus sunlight onto said central receiver is calculated by the
formula 2(T.sub.2-T.sub.1)/p where p is a user defined arbitrary
time unit, and wherein said formula 2(T.sub.2-T.sub.1)/p gives
total number of azimuthal orientations required in a functional
day.
14. The method of claim 12, wherein magnitude of rotation of said
rotatable shaft necessary to focus sunlight onto said central
receiver is calculated by the formula (Y.times.Sin .gamma.)/2
degrees, wherein Y is `90.degree.-sun elevation in degrees`.
15. The method of claim 12, wherein direction of rotation of the
said rotational shaft depends on whether it is the start of
operations or not the start of operations.
16. The method of claim 12, wherein at the start of the operation,
direction of rotation of the said rotational shaft is northward
when sun lies in the quadrant A at that instant, and direction of
rotation of the said rotational shaft is southward when sun lies in
the quadrant B at that instant.
17. The method of claim 12, wherein, in northern hemisphere,
direction of rotation of the said rotational shaft is southward
when the sun azimuth is .ltoreq.180.degree. and it is not start of
the operation.
18. The method of claim 15, wherein in northern hemisphere,
direction of rotation of the said rotational shaft is northward
when sun azimuth is >180.degree. and it is not start of the
operations.
19. The method of claim 1, wherein accumulated mechanical error is
negated by readjusting the altitudinal and azimuthal status after
every 120 minutes whereupon functionality extremes of the heliostat
orientation means are force-achieved via control check-loop.
20. An apparatus for orienting arrays of mechanically linked
heliostats for focusing the incident sunlight on a stationary
object, said apparatus comprising: a) a computer executable
software code housed in suitable computer readable medium for
embodying method of claim 1; b) a central processing unit (CPU)
means to execute said software code for generating controlling
commands for actuator/s for rotating pivotably rotatable mounts of
heliostats located on related rotatable shafts for tracking an
apparent altitudinal motion of the sun in the sky, and for
generating controlling commands for actuator/s for rotating related
rotatable shafts for tracking an apparent azimuthal motion of the
sun in the sky; c) a display means for alphanumerical display of
user information like time, date, system status, controlling
commands; c) a real time clock for supplying time data to be used
to control the time related parameters in method of claim 1; d)
input means for interacting with application software or entering
data like time data or Geographical location data; e) input/output
port for exchange of data with other devices; f) Mechanical linkage
as illustrated in the accompanying figure for orienting arrays of
mechanically linked heliostats for focusing the incident sunlight
on a stationary object.
Description
RELATED APPLICATIONS
[0001] Priority is claimed for US provisional patent application:
An application claiming the benefit under 35 USC 119(e) US
Provisional patent application number: U.S. 61/850,810 Filing date:
Feb. 25, 2013 Priority claimed: Yes Priority is also claimed for
two Indian patent applications (foreign patent applications): 1)
Provisional Patent Application number: 588/MUM/2012 Filing date: 7
Mar. 2012 Priority claimed: Yes
Country: IN (India)
[0002] 2) Nonprovisional Patent Application number: 588/MUM/2012
Filing date: 6 Mar. 2013
Country: IN (India)
[0003] Priority claimed: Yes
[0004] All of the aforementioned patent applications are
incorporated herein in their entirety by reference.
BACKGROUND OF THE INVENTION
[0005] Various technologies have been explored, developed, and
implemented for harnessing solar energy ranging from simple
trapping of incident sunlight to the more advanced conversion of
sunlight using photovoltaic and thermal means. Heliostats are one
such device which is based on the reflective-collection principle.
Heliostats are devices that include a plurality of plane or curved
reflectors that focus incident sunlight onto a stationary target.
Reflective surfaces of said reflectors have to be maintained to
remain perpendicular to the bisector of the angle between the solar
vector and the target vector as seen from the mirror.
[0006] Present day heliostats are generally controlled by
computers. Heliostats are periodically oriented with respect to the
moving sun and a fixed target such that the incident solar
radiation is focused on the fixed target. Computer Programs are
needed for automatically maneuvering reflector mirrors of the
Heliostats. A heliostat control computer program aims the
heliostats by periodically predicting the location of the sun in
the sky. Predictions are based on the date, time, longitude and
latitude. The position of each mirror of each heliostat is
periodically determined, wherein each mirror of each heliostat is
kept perpendicular to a bisector of an angle, wherein said angle is
formed by a solar vector and a target vector.
[0007] Generally a conventional heliostat is mounted on a pedestal
and is pivotally rotatable about altitudinal and azimuthal axes.
Each axis is equipped with a motorized limb that can pivotally
rotate the mirror of the heliostat to adjust its position.
[0008] The conventional heliostat control methods that are being
used in the prior art are developed for the conventional
heliostats. Such conventional heliostat control methods are of no
use for orienting arrays of mechanically linked heliostats (ganged
heliostats) positioned on rotatable shafts.
[0009] There is a need to develop a control method and an apparatus
for periodically orienting mechanically linked heliostats mounted
on rotatable shafts so as to accurately and continually concentrate
incident sunlight on a stationary locus.
[0010] Ravindra Patwardhan and Rajeev Pandit in their U.S. patent
application Ser. No. 12/798,847 titled `a solar central receiver
system employing common positioning mechanism for heliostats`
describe a system of concentrating and harvesting solar energy,
wherein such arrays of mechanically linked heliostats positioned on
rotatable shafts are included. Said U.S. patent application Ser.
No. 12/798,847 is incorporated herein in its entirety by reference.
The present invention is specifically intended for periodic
reorientation of such arrays of mechanically linked heliostats
positioned on rotatable shafts so as to accurately and continually
concentrate incident sunlight on a stationary locus.
[0011] In the said `solar central receiver system employing common
positioning mechanism for heliostats`, arrays of heliostats mounted
on rotatable shafts are required to be periodically oriented with
respect to a stationary object and the sun such that incident solar
radiation upon said heliostats is focused upon said stationary
object and thereby deliver concentrated solar radiation upon said
stationary object from dawn to dusk. Said solar central receiver
system comprises: A heliostat field consisting of flat or curved
light reflecting heliostats mounted on horizontal parallel arrays
of rotatable shafts. The rotatable shafts are positioned about a
stationary object. The stationary object is mounted at a predefined
height above ground level. Each rotatable shaft provides a linear
array of mounting means for mounting a linear array of heliostats.
The mounting means are linked mechanically. Each mounting means is
designed in a manner which permits individual pivotal movement of
mounted heliostat with respect to related rotatable shaft about a
first rotation axis. Each said rotatable shaft supports a rotation
mechanism (drive means) for synchronously rotating the linear array
of heliostats about the first rotation axis. Each said rotatable
shaft is rotatable about its axis and is coupled with a drive means
to rotate each said rotatable shaft about its axis such that when
each said rotatable shaft is rotated, said linear array of
heliostats rotates about a second rotation axis that is
perpendicular to said first rotation axis.
[0012] The present invention is specifically intended for periodic
orientation of mechanically linked (ganged) heliostats positioned
on a rotatable shaft. For illustrative purpose, one of the
embodiments as described by Patwardhan et al in `a solar central
receiver system employing common positioning mechanism for
heliostats` is reviewed in FIG. 1, wherein FIG. 1 schematically
depicts a slotted link and pusher mechanism for driving an array of
pivotably rotatable heliostats to synchronously rotate for tracking
the apparent motion of the sun in the sky. As depicted in FIG. 1, a
single shaft segment or pluralities of shaft segments 107 are
interconnected to form a shaft 101. Each shaft segment 107
preferably consists of a sturdy rotatable structure like a pipe
having a tubular/square cross-section and long enough to mount
preferably 4 to 6 heliostats (for example 3 to 5 meters long). At
each end of the shaft segment 107, end flanges 109 are fitted. Said
flanges 109 support circular projections 110 of the shaft segment
107. Each circular projection 110 is supported on bearing 108
mounted in a pedestal 102. Each half portion of flexible brake drum
coupling 103 is supported on adjoining circular projection 110 so
that all shaft segments 107 are coupled together. Or the adjoining
shaft segments 107 are connected by flexible couplings and one
brake is connected at the nondriving end of the shaft 101. An
actuating rod 111 is supported in end flanges 109 via bushes 112
such that the said actuating rod 111 can move to and fro in a
direction parallel to the axis of the shaft segment 107.
Additionally, the actuating rod 111 is supported on supporting
bushes 113 such that the deflection of actuating rod 111 is kept
minimum. In other embodiments, the actuating rod 111 can also be
supported on the outside surface of shaft segment 107. The
actuating rods 111 can be supported on the flanges 109 that are
projected above the outer surface of the shaft segment 107. An
actuator 124 is fitted at one end of the actuating rod 111. The
actuator 124, for example, a stepper motor ball screw linear
actuator, is connected with one end of the pusher rod. The
clockwise (or anticlockwise) rotation of the stepper motor achieves
forward movement of the ball nut which in turn pushes the pusher
rod forward and vice versa. A plurality of links 115 are rigidly
fitted on actuating rod 111 such that each link 115 is very close
to a supporting bush 113. Supporting bush 113 and link 115 project
out of the circular pipe 120 through slot 116 provided in said pipe
120. A plurality of supports 117 for the heliostats are pivoted by
pivot pins 118 on brackets 119. Said brackets 119 are rigidly
fitted on pipe 120. Support 117 can freely oscillate about said pin
118. A heliostat is to be mounted on each said support 117. Hence
oscillation of said support 117 about pin 118 rotates respective
heliostat (not shown in the figure) positioned over it. An arm 121
is rigidly fixed on support 117 such that it also oscillates along
support 117 about pivot pin 118. Pin 122 is permanently fitted on
arm 121 and the said pin 122 is engageable in a slot 123 formed in
the body of link 115.
[0013] When the actuating (pusher) rod 111 is linearly moved in the
eastern direction by the actuator 124, said link 115 moves said pin
122 towards eastern direction and this results in the clockwise
rotation of the arm 121 along support 117 about pin 118. Said
clockwise rotation is preferably up to 45.degree. or more than
45.degree. if needed depending on the movement of the actuating rod
111. Initially when the movement is zero, the said clockwise
rotation is zero and the support 117 is in the horizontal plane.
And said clockwise rotation increases as the said movement of
actuating rod 111 in eastern direction increases. However, the
ratio of the said clockwise rotation and the said linear motion may
or may not be constant. Similarly, when the actuating rod 111 is
linearly moved in the western direction, the arm 121 along with the
support 117 rotate in anticlockwise direction. And said
anticlockwise movement is preferably up to 45.degree. or more than
45.degree. if needed depending on the movement of said actuating
rod 111.
[0014] Each rotatable shaft is coupled with a drive means to drive
the rotatable shaft to rotate about its axis such that an array of
heliostats mounted on each said rotatable shaft rotates tracking an
apparent azimuthal motion of the sun in the sky. Referring to FIG.
2, at one end of the rotatable shaft 207 an arm 201 is rigidly
fitted. At the distal end of the arm 201 an extensible actuator arm
202 of a linear actuator 203 is coupled by a knuckle joint 204. The
proximal end of the linear actuator 203 is coupled with the
horizontal segment 206 of the pedestal by a knuckle joint 205.
Extension of the actuator arm 202 of the linear actuator 203 would
rotate the shaft in anticlockwise direction and vice versa.
[0015] An Array of heliostats is positioned on a linear array of
mounting means on each rotatable shaft. Each heliostat is
positioned with a defined angle of orientation and defined angle of
inclination according to its location in a heliostat field similar
to a facet of a Fresnel type reflector.
[0016] The angle of orientation at which a heliostat is positioned
on a rotatable shaft depends on minimal distance between a central
receiver and a longitudinal axis of said rotatable shaft. Said
minimal distance is a side opposite an angle of orientation in an
imaginary right angled triangle including the angle of orientation
as an acute angle. A distance between said stationary receiver and
a midpoint position on said heliostat is a hypotenuse in said
imaginary right angled triangle. And the sine of said angle of
orientation is equal to said length of a said side opposite divided
by length of said hypotenuse. The angle of inclination at which a
heliostat is fixedly positioned with respect to the rotatable shaft
varies according to a location of said heliostat in said heliostat
field. The angle of inclination at which a heliostat is fixedly
positioned with respect to the rotatable shaft is angle
.epsilon./2. An angle .epsilon. depends on a distance between said
central receiver to a midpoint of said heliostat in said heliostat
field, which distance is a length of a side opposite said angle
.epsilon. in an imaginary right angled triangle including the angle
.epsilon. as an acute angle. The height of said stationary object
from ground level, which height is a length of an adjacent side of
said angle .epsilon.. The angle .epsilon. is calculated by finding
tangent of said angle .epsilon., wherein said tangent of said angle
.epsilon. is equal to said length of said side opposite said angle
.epsilon. divided by said length of said adjacent side.
[0017] The sun path refers to the apparent positional changes of
the sun as the earth rotates and orbits around the sun. The sun
apparently travels a curved path in the sky while moving from east
to west. In the northern hemisphere, in winter, the sun rises south
east and sets south west. In summer, the sun rises north east,
crosses to the south of the east-west line during the day as it
rises, and then crosses back to the north side of the east-west
line as it sets and then sets north west. In the southern
hemisphere, it is vice versa. Solar noon occurs at the middle of
the arc shaped solar path across the horizon when the sun and
meridian cross paths. To be more specific, the solar noon occurs
when the sun azimuth is 180.degree. or the sun azimuth is
360.degree.. The solar noon is half way between sunrise and sunset
and occurs when the sun reaches its highest point in the sky.
[0018] In the northern hemisphere, from dawn to solar noon, as the
sun apparently moves from east to west, the azimuthal solar
movement is always southwards. Whilst from solar noon to dusk, as
the sun apparently moves from east to west, the azimuthal solar
movement is always northwards. In the southern hemisphere, it is
vice versa. Therefore, for each azimuthal tracking, it is necessary
to determine whether the azimuth movement of the sun is southward
or northward. Similarly, it is necessary to determine azimuthal
displacement of the sun from the east west line and to introduce a
calibrated compensation in heliostat orientation necessary to focus
sunlight onto a central receiver. As the arrays of heliostats in
the said solar central receiver system are in operational linkage
to the related rotatable shafts, rotating the rotatable shafts in
clockwise/anticlockwise direction would compensate the solar
azimuthal movement.
[0019] When arrays of mechanically linked heliostats, mounted on
horizontal parallel arrays of rotatable shafts, are to be
periodically oriented such that the incident sunlight is to be
focused on a stationary object, the conventional solar tracking
method for heliostats will not work.
[0020] For identifying the problem and finding the solution for
altitudinal and azimuthal tracking of arrays of mechanically linked
heliostats mounted on rotatable shafts, an example of various
values of solar altitude (elevation) and azimuth on 1 Jan. 2012 are
considered. On this day, at 9:40 hours, the solar altitude is
30.degree. and azimuth is 132.degree.. At 9:43 hours the solar
altitude is 30.5.degree. and azimuth is 132.6.degree.. At this
juncture, both the altitude and azimuth have changed. But on the
same day, at 12:26 hours, the solar altitude is 48.4.degree. and
azimuth is 176.degree.. At 12:29 hours the solar altitude is
48.4.degree. and azimuth is 177.degree.. At 12:32 hours the solar
altitude is 48.4.degree. and azimuth is 178.1.degree.. At 12:35
hours the solar altitude is 48.4.degree. and azimuth is
179.1.degree.. At 12:38 hours the solar altitude is 48.4.degree.
and azimuth is 180.2.degree.. At 12:41 hours the solar altitude is
48.4.degree. and azimuth is 181.2.degree.. At 12:44 hours the solar
altitude is 48.4.degree. and azimuth is 182.2.degree.. At 12:47
hours the solar altitude is 48.4.degree. and azimuth is
183.3.degree.. At 12:50 hours the solar altitude is 48.3.degree.
and azimuth is 184.3.degree..
[0021] From 12:26 to 12:47, the solar altitude remains 48.4.degree.
while solar azimuth changes from 176.degree. to 183.3.degree.. In
this situation, if one merely tries to track the changing solar
azimuth from 12:26 to 12:47, the mirrors of the ganged heliostats
would be misaligned and the system would fail to focus the incident
solar radiation on the fixed target. This is because from 12:26 to
12:47, the sun continues to travel westwards at a regular pace even
if the sun elevation is unchanged. In said `solar central receiver
system employing common positioning mechanism for heliostats`, in
northern hemisphere, the southward rotation of the rotatable shaft
tracks the changing solar azimuth from 90.degree. to 180.degree.
and the northward rotation of the rotatable shaft tracks the
changing solar azimuth from 180.degree. to 270.degree.. Therefore,
the changing solar azimuth from 12:26 to 12:47 (solar azimuth
176.degree. to 183.3.degree.) could only be tracked by southward
rotation of the rotatable shaft, if and only if, the heliostats
also move altitudinally along with the sun! In said `solar central
receiver system employing common positioning mechanism for
heliostats`, the eastward actuation by the actuator results in
synchronous westward rotation of the array of mounted heliostats
tracking the westward altitudinal movement of the sun.
[0022] For explanation purpose, as an example, it is assumed that
the arrays of mechanically linked ganged heliostats are positioned
in east west direction, and the sun elevation is 30.degree.
(eastern) in the morning at the start of the operation and the
mirror elevation is 45.degree. (eastern), wherein the solar
radiation is focused on the target. Let it be further assumed that
the arrays of mechanically linked ganged heliostats function from
sun elevation 30.degree. (eastern) to sun elevation 30.degree.
(western). The solar path from sun azimuth 180.degree. to dust is a
mirror image of the solar path from dawn to sun azimuth
180.degree.. Consequently, at the end of the operation, the sun
elevation would be 30.degree. (western) and the mirror elevation
would be 45.degree. (western). The altitudinal rotation of the
heliostats from heliostat mirror elevation 45.degree. (eastern) in
the morning to heliostat mirror elevation 45.degree. (western) in
the evening should be regular and should take the same time as the
time taken by the sun to move in the sky from 30.degree. in the
morning at the start of the operation to 30.degree. in the evening
at the end of the operation. This happens because all the installed
heliostats in the said solar central receiver system behave as a
dynamic flattened manifestation of a single parabolic reflector,
which is initially positioned to focus the solar radiation on a
stationary target for a fixed position of the sun (like the sun at
the zenith) in the sky.
[0023] On that 1.sup.st day of January 2012, the time taken by the
sun from sun elevation 30.degree. in the morning to sun elevation
30.degree. in the evening is 435 minutes. If the mirrors of the
heliostats are to be rotated every 3 minutes for altitudinal
tracking the sun, it is essential to regularly rotate the mirrors
such that the rotation of the mirrors should take the same 435
minutes to change the position of heliostat mirrors from mirror
elevation 45.degree. (eastern) in the morning to mirror elevation
45.degree. (western) in the evening.
[0024] The present inventors have examined heliostat control
programs available in the market or on internet. The available
heliostat control programs cannot be implemented in a system of
reflectors wherein the reflectors (mirrors) are arranged in arrays
and are mounted on rotatable shafts. Control of the arrays of
heliostats mounted on rotatable shafts for periodic orientation for
tracking an apparent movement of the sun in the sky requires a
considerably different premise, thus preserving the necessity to
invent for the present inventors.
[0025] What is needed, therefore, is an amalgamation of
astronomical and trigonometrical calculations from astronomical
theory to result in logic for maneuvering arrays of mechanically
linked heliostats positioned on horizontal and parallel rotatable
shafts. The present inventors, in cognizance of aforesaid needs,
have undertaken focused research and come up with novel solutions
to effectively address the same. The following description presents
one way of performing the present invention. A principle object of
the present invention is to provide a method and apparatus adapted
for synchronously controlling a field of mechanically-linked
(ganged) heliostats positioned on rotatable shafts to accurately
concentrate incident sunlight on a stationary locus.
[0026] Yet another object of the present invention is to provide a
method and apparatus adapted for synchronously controlling a field
of mechanically-linked (ganged) heliostats characterized in having
simple protocol of usage within skill level of ordinary person.
[0027] Yet another object of the present invention is to provide a
method and apparatus adapted for synchronously controlling a field
of mechanically-linked (ganged) heliostats characterized in having
low costs of materials, assemblage, maintenance and operations.
[0028] These together with other objects, advantages and their
attainment will become subsequently apparent in the details of
products, their preparation and application as more fully
hereinafter described and claimed hereinafter reference being had
to the accompanying figures. Thus, for tracking an apparent
movement of the sun in the sky, the altitudinal and azimuthal
orientation of the arrays of heliostats mounted on rotatable shafts
require a considerably different premise. The rationale of the
present invention as described in detail in the detailed
description is to provide many novel features that are not
anticipated or implied by any of the prior art.
BRIEF SUMMARY OF THE INVENTION
[0029] The present invention is specifically intended for periodic
orientation of mechanically linked (ganged) heliostats positioned
on rotatable shafts such that the incident sunlight is focused on a
stationary object. Method for altitudinal orientation comprises of
finding the total functional time 2.times.(T.sub.2-T.sub.1) in
seconds that is needed for altitudinal rotation of the heliostats
in a day to track the altitudinal movement of the sun, wherein the
mirrors of the heliostats rotate from a defined mirror elevation
(for example 45.degree. eastern) to a defined mirror elevation (for
example 45.degree. western). T.sub.1 is the time of the day wherein
the rotation of the heliostat starts at the said defined mirror
elevation. T.sub.2 is the time when the sun azimuth is 180.degree.
or 360.degree.. It is at the middle of the total functional time.
In each altitudinal orientation a minuscule push (or pull) is given
by an actuator. A calculated defined number (n) of altitudinal
orientations (minuscule pushes) by an actuator would result in
inducing the heliostats to rotate from the said defined mirror
elevation (eastern) to said defined mirror elevation (western). The
time interval between each altitudinal orientation would be
2.times.(T.sub.2-T.sub.1) divided by n.
[0030] For implementing the azimuthal orientation, at the scheduled
starting time T.sub.1, the computation means determines the solar
elevation and azimuth at that instant. When it is the start of the
operation, the magnitude of rotation [(Y.times.Sin .gamma.)/2
degrees] is determined. As per the position of the sun in the sky
at that instant, the determined value in degrees is
added/subtracted to angle .theta. to form angle .theta.'. A
central/distal arm affixed with each rotatable shaft and coupled
with a linear actuator (drive means) provides a capability to
rotate the related rotatable shaft in clockwise or anticlockwise
direction by extension/retraction of the length of the arm of the
linear actuator. The length of the said arm of the linear actuator
`C.sub.x` can be extended/retracted to `C.sub.1` such that angle
.theta.' is achieved.
[0031] If it is not the start of the operation, then the formula
2*(T.sub.2-T.sub.1)/p gives total number of azimuthal orientations
required in a total functional time of the day, where p is a user
defined arbitrary time unit like say 30 minutes (1800 seconds). Let
this value [2*(T.sub.2-T.sub.1)/p] be called as .DELTA.. The length
of the linear actuator C.sub.1 at T.sub.1 and the length of the
linear actuator C.sub.2 at T.sub.2 is determined and the difference
|C.sub.2-C.sub.1| millimeters is calculated and then divided by
.DELTA./2. Let this value be called as .OMEGA. mm. At each interval
of p seconds, subsequent to the primary azimuthal orientation at
the defined mirror elevation (eastern) till T.sub.2, the rotatable
shaft is to be rotated in southward direction such that the value
of the length the arm of the linear actuator is varied by .OMEGA.
mm. Similarly, at each interval of p seconds, from T.sub.2 to the
defined mirror elevation (western), the rotatable shaft is to be
rotated in northward direction such that the value of the length of
the said arm of the linear actuator is varied by .OMEGA.
millimeters.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0032] FIG. 1 schematically depicts one of the embodiments of the
solar central receiver system employing common positioning
mechanism for heliostats.
[0033] FIG. 2 schematically depicts a mechanism of rotation of the
rotatable shaft by a linear actuator.
[0034] FIG. 3 is a schematic representation of the arrangement of
essential components of an apparatus of a control system for
orienting arrays of ganged heliostats.
[0035] FIG. 4 illustrates a flowchart of the sequence of steps
pertaining to the process of altitudinal orientation.
[0036] FIG. 5 illustrates a method to determine the azimuthal
displacement of the sun from the east west line in the sky.
[0037] FIG. 6 illustrates the basis for determination of the
required magnitude and the direction of rotation of the rotatable
shaft to track the azimuthal movement of the sun in the sky.
[0038] FIG. 7 illustrates a flowchart of the sequence of steps
pertaining to the process of the azimuthal orientation.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO
DRAWINGS
[0039] Ravindra Patwardhan & Rajeev Pandit in their U.S. patent
application Ser. No. 12/798,847 have substantially described a
solar central receiver system titled a `solar central receiver
system employing common positioning mechanism for heliostats`. Said
solar central receiver system employing common positioning
mechanism for heliostats is intended for periodically orienting
arrays of heliostats positioned on rotatable shafts such that
incident solar radiation upon said arrays of heliostats is focused
upon a stationary object and thereby deliver concentrated solar
radiation upon the stationary object. Said patent application is
herein incorporated in its entirety with reference. The present
invention, namely, `a method and apparatus for orienting arrays of
mechanically linked heliostats for focusing the incident sunlight
on a stationary object` is specifically meant for a methodology and
an apparatus for orienting arrays of mechanically linked heliostats
(ganged heliostats) positioned on rotatable shafts as described by
Ravindra Patwardhan & Rajeev Pandit in their U.S. patent
application Ser. No. 12/798,847. Furthermore, Ravindra Patwardhan
& Rajeev Pandit, in their application for registration of US
copyrights titled `A method and apparatus for orienting arrays of
mechanically linked heliostats for focusing the incident sunlight
on a stationary object (The software for Solar fire)`, which is
accepted at the US Copyright Office and allotted open case No.
1-1062961501, have substantially described a methodology and
control means used to develop software and a control system for the
purpose of orientation of ganged heliostats (mechanically linked
heliostats) positioned on rotatable shafts to track the sun such
that the incident sunlight is focused on a stationary object. Said
application for registration of US copyrights (allotted open case
No. 1-1062961501) is also herein incorporated in its entirety with
reference.
[0040] The present invented method and the apparatus are to be
employed for tracking the altitudinal and azimuthal movement of the
sun, wherein arrays of ganged heliostats positioned on rotatable
shafts are periodically oriented with respect to the moving sun and
a fixed stationary object (receiver) such that incident solar
radiation on the said arrays of ganged heliostats is focused upon
the stationary object and thereby deliver concentrated solar
radiation upon said stationary object.
[0041] For the purpose of explanation only, certain assumptions are
made to explain the invented method for periodic orienting arrays
of mechanically linked heliostats mounted on horizontal parallel
arrays of rotatable shafts for focusing the incident sunlight on a
stationary object.
[0042] Assumptions:
[0043] The horizontal, parallel rotatable shafts of the said solar
central receiver system employing common positioning mechanism for
heliostats are placed in east west direction. The rigidly fitted
brackets of the mounting means on rotatable shafts are
perpendicular to the horizontal ground at the start of the
operation. While fixedly positioning the arrays of mirrors on the
pivotally rotatable mounts of the rotatable shafts, the position of
the mirror of each heliostat is such that rays perpendicular to the
horizontal ground [like the rays from the sun at the zenith (solar
azimuth 90.degree. and solar elevation 90.degree.)] incident on the
said mirror would be reflected on the target.
[0044] It is assumed that at the start of the operation, the mirror
elevation is 45.degree. and the sun elevation is 30.degree..
[0045] The mirrors of the heliostats rotate from 45.degree. mirror
elevation (eastern) to 45.degree. mirror elevation (western) while
tracking the sun from sun elevation is 30.degree. (eastern) to sun
elevation is 30.degree. (western).
[0046] A stepper motor ball screw linear actuator is connected with
the actuating rod on the western aspect of the rotatable shaft
& the clockwise rotation of the stepper motor achieves forward
(eastward) movement of the actuating rod which in turn causes
backward (westward) rotation of mounted heliostats and vice
versa.
[0047] As substantially described in the U.S. patent application
Ser. No. 12/798,847, all the installed heliostats in the said solar
central receiver system behave as a flattened dynamic manifestation
of a single parabolic reflector, which is initially positioned to
focus the solar radiation on a stationary target for a fixed
position of the sun in the sky. Hence the target elevation and
target azimuth are not assumed.
[0048] A southward projecting arm is affixed at right angle with
each rotatable shaft and positioned parallel to the ground and
coupled with a linear actuator, wherein retraction/extension of the
arm of the linear actuator would cause clockwise/anti-clockwise
rotation of the related rotatable shaft respectively resulting in
southward/northward rotation of the rotatable shaft
respectively.
[0049] The invented heliostat control software is run in a place in
northern hemisphere like Pune city, India.
[0050] Method for altitudinal orientation of arrays of mechanically
linked heliostats mounted on arrays of rotatable shafts for
continually focusing the incident sunlight on a stationary
object:
[0051] The position of a celestial object like the sun can be
defined by specifying its altitude (elevation) and its azimuth. The
altitude of an object is equal to its angle in degrees above the
horizon. The azimuth of an object is equal to its angle in the
horizontal direction, with north at 0.degree., east at 90.degree.,
south at 180.degree., and west at 270.degree.. As the Earth
rotates, the sun appears to rise and set, constantly changing its
altitude and azimuth. Sun's altitude and azimuth also varies
according to an observer's location on Earth. The sun rises in the
east and sets in the west everywhere on the Earth. The Earth's
rotation tilts about 23.5 degrees on its pole-to-pole axis,
relative to the plane of Earth's solar system orbit around our sun.
The sun's declination at the spring equinox is 0.degree.. It moves
up to 23.5.degree. in the summer, then drifts back down through
0.degree. at fall equinox, and down to -23.5.degree. in the winter.
As the Earth orbits the sun, this creates the 47 degree peak solar
azimuth angle difference and the hemisphere-specific difference
between summer and winter. In the northern hemisphere, the winter
sun rises in the southeast, peaks out at a low angle above the
southern horizon, and then sets in the southwest. In the northern
hemisphere in summer, the sun rises in the northeast, peaks out
nearly straight overhead (depending on latitude), and then sets in
the northwest.
[0052] In the present invention, the elevation angle and the
azimuth angle of the sun are the two key angles that are used in
the `method and apparatus for orienting arrays of mechanically
linked heliostats for focusing the incident sunlight on a
stationary object`. To calculate the sun's position throughout the
day, excellent algorithms are available.
[0053] Based on the equations of the astronomical ephemeris, and
the American ephemeris and nautical almanac, Pitman and Vant-Hull
presented formulae for the calculation of the ecliptic sun
coordinates, its declination and the equation of time. They
discussed about various phenomena affecting the Sun's position, and
estimated the errors resulting when these phenomena are
disregarded. Similarly, a solar vector can also be calculated with
the help of algorithms of Spencer, Walraven, and Michalsky.
[0054] "NOAA_Solar_Calculations_day.xls" file is available for
downloading on interne. The calculations in the NOAA (National
Oceanic & Atmospheric Administration) solar position
calculators are based on equations from Astronomical Algorithms by
Jean Meeus. The said program is available for downloading from the
following
websites:--http://www.esrl.noaa.gov/gmd/grad/solcalc/calcdetails.html
http://www.srrb.noaa.gov/highlights/sunrise/azel.html
[0055] A computer-control program for heliostats by Mr. David
Williams is
available--http://www.iwilltry.org/b/projects/build-a-heliostat-for-solar-
-heating-and-lighting/Heliostat control programs/algorithms are
also available: `Solar Position Algorithm for Solar Radiation
Applications`--a technical report by Ibrahim Reda and Afshin
Andreas of National Renewable Energy Laboratory, Department of
Energy (USA)=http://www.nrel.gov/docs/fy08osti/34302.pdf
[0056] The computation means for synchronous orientation of ganged
heliostats uses modified available software like
NOAA_Solar_Calculations_day.xls, wherein the solar elevation and
the solar azimuth are determined when the location specific date,
time, longitude, latitude are inputted. To keep down the price, a
low-cost microprocessor based controller is preferably used.
[0057] The computation means under its control program continuously
keeping track of the real time in the RTC, checks for the
occurrence of a scheduled starting time, say 8:00:00 AM. At the
occurrence of the scheduled starting time, the computation means
starts the operation. Corresponding to the occurrence of the
30.degree. eastern sun elevation, the time T.sub.1 is determined
and recorded as a first predefined event. Similarly, corresponding
to the occurrence of the solar azimuth 180.degree. or 360.degree.
(solar noon), the time T.sub.2 is determined and recorded as a
second predefined event. In fact, the solar path from sun azimuth
180.degree. (or 360.degree.) to dust is a mirror image of the solar
path from dawn to sun azimuth 180.degree. (or 360.degree.). The sun
azimuth 180.degree. or 360.degree. occurs at the middle of the
curved solar path in the sky. Therefore T.sub.2 occurs at the
middle of the westward solar path from solar elevation 30.degree.
eastern to the solar elevation 30.degree. western. Similarly,
T.sub.2 occurs at the middle of the westward mirror rotation from
mirror elevation 45.degree. eastern to a mirror elevation
45.degree.. Hence, the time 2.times.(T.sub.2-T.sub.1) in
seconds/minutes is the total time in seconds/minutes that a
heliostat is needed to regularly rotate to track the sun. While
tracking the sun from solar elevation 30.degree. eastern to the
solar elevation 30.degree. western, the arms of the supports of the
mirrors of the heliostats rotate from an elevation 45.degree.
eastern to an elevation 45.degree. western. This happens because
all the installed heliostats in the said solar central receiver
system behave as a dynamic flattened manifestation of a single
parabolic reflector, which is initially positioned to focus the
solar radiation on a stationary target for a fixed position of the
sun (like the sun at the zenith) in the sky. The target elevation
and azimuth is already considered when the reflectors are fixedly
positioned like Fresnel type reflectors. The alignment of said
single parabolic reflector receiving solar radiation from the sun
at solar elevation 30.degree. eastern and focusing the solar
radiation on a fixed target would be mirror image of the said
single parabolic reflector receiving solar radiation at solar
elevation 30.degree. western. Since each mirror of each heliostat
of the said solar central receiver system behaves as a part of that
said single parabolic reflector, mirror alignment receiving
sunlight from the sun at solar elevation 30.degree. eastern would
be mirror image of the mirror alignment for the solar elevation
30.degree. western.
[0058] It is assumed that the stepper motor ball screw actuator is
connected on the western aspect of the pusher (actuator) rod &
the clockwise rotation of the stepper motor achieves forward
movement of the ball nut on the lead screw that impels forward
movement of the pusher rod that causes westward rotation of the
heliostats. Let it be further assumed that the realizable forward
movement of the ball nut on the lead screw (5 mm pitch) is 200 mm
for rotating the heliostats from say mirror elevation 45.degree.
(eastern) at the start of the operation to the sun azimuth
180.degree. (or 360.degree. azimuth). This means that, for rotating
the heliostats from mirror elevation 45.degree. (eastern) at the
start of the operation to mirror elevation 45.degree. (western) at
the end of the operation, a total forward movement of the ball nut
on the lead screw (5 mm pitch) would be 400 mm in each day. Let it
be further assumed that at each altitudinal orientation, the
stepper motor is rotated 50 steps, wherein each step is 1.8.degree.
(that is, the stepper motor is rotated 1/4.sup.th of a circle). The
total rotations of a ball nut for traveling on a 400 mm length lead
screw having 5 mm pitch would be 80. For each altitudinal
orientation, the stepper motor is rotated by 1/4.sup.th of a circle
each time. Hence, there would be 320 altitudinal orientations in a
day. This means that the total number (n) of altitudinal
orientations in a day are fixed and depend on the length of the
lead screw that a ball nut travels for actuating the pusher rod,
pitch of the lead screw, and the number of steps (like 50 steps in
the present example) that a stepper motor rotates in each
altitudinal orientation. Hence, the time interval between each
altitudinal orientation would be 2.times.(T.sub.2-T.sub.1)
seconds/minutes divided by n. Consequently, from the occurrence of
the time of the day T.sub.1 [mirror elevation 45.degree.
(eastern)], n number of regular successive altitudinal orientations
(320 in the present case)--like 50 steps in the present example--at
interval of `2.times.(T.sub.2-T.sub.1)/n` seconds/minutes would
achieve 45.degree. mirror elevation (western) of the heliostat.
[0059] FIG. 3 schematically depicts an apparatus for periodically
orienting arrays of mechanically linked heliostats mounted on a
horizontal rotatable shaft for focusing the incident sunlight on a
stationary receiver. FIG. 3 depicts an apparatus that comprises of
a computing means capable of executing computer codes/programs that
define the operating system software or application software. Said
computing means includes a central processing unit (CPU) 301 that
preferably includes one or more processors/micro-processors and/or
one or more digital signal processors. The (CPU) 301 executes
routines for solar tracking utilizing stored application software
and/or various sensor inputs. An input/output port is included for
exchange of data with other devices. The CPU 301 is coupled to
memory means 302 that stores application software including
CPU-executable code. Input means like a keyboard 303 is for
interacting with the application software or entering data like
time data or Geographical location data etc. A display screen 304
is for alphanumerical display of user information like time, date,
Controlling actions taken etc. A Real Time Clock (RTC) or an
on-chip RTC 305 supplies time data to be used to control the time
related parameters. The CPU 301, the memory 302, and the
application software including CPU-executable code loaded in the
memory predict the location of the sun in the sky, and calculate
required azimuth and altitude axis rotation for heliostats using
predicted location of the sun in the sky. A SMPS 306 is used to
generate DC power supply and to convert high level AC signal to DC
signal for electronic circuits as per their requirement. When
supply ranges of volts and amperes are different, optical isolator
is used in between two stages to avoid interference that may be
caused by different power levels. The CPU 301 generates controlling
commands for the linear actuators 308 via actuator 307 for rotating
related rotatable shafts for tracking an apparent azimuthal motion
of the sun in the sky. The CPU 301 also generates controlling
commands for stepper motor linear actuator 310 via a drive unit 309
for rotating pivotably rotatable mounts of the heliostats located
on related rotatable shaft for tracking an apparent altitudinal
motion of the sun in the sky.
[0060] The said CPU 301 under its control program executes or
initiates execution of routines for solar tracking utilizing stored
application software and/or various sensor inputs. Said CPU, a
memory, and application software including CPU-executable code
loaded in said memory predict location of the sun in the sky. Each
prediction is based on date, time, longitude and latitude related
to location of said heliostats. The CPU receives feedback from
sensory means that comprise rotary encoders or optical sensors or
position-sensing detectors or optoelectric sensors or feedbacks
from drive motors. Said CPU, said memory, and said application
software including CPU-executable code loaded in said memory
periodically calculate required azimuth and/or altitude axis
rotation for heliostats using predicted location of the sun in the
sky, and feedbacks from sensory means. Said CPU generates
controlling commands for a single geared motor drive unit or a
plurality of gear motors drive units for rotating related rotatable
shaft/shafts to rotate about a first rotation axis for tracking an
apparent motion of the sun in the sky. Said CPU generates
controlling commands for a single actuator or a plurality of
actuators for synchronously rotating pivotably rotatable mounts of
said heliostats located on related rotatable shaft about a second
rotation axes that are perpendicular to said first rotation axis
for tracking an apparent motion of the sun in the sky. Said CPU
includes a set of logic programs for converting commands into
electronic drive signals.
[0061] As an example, one of the ways of creating application
software including CPU-executable code:--
[0062] An updated/modified version of the original
"NOAA_Solar_Calculations_day.xls" file is available for
downloading. The said program is available for downloading from the
following
websites:--http://www.esrl.noaa.gov/gmd/grad/solcalc/calcdetails.html
http://www.srrb.noaa.gov/highlights/sunrise/azel.html
The said excel worksheet ("NOAA_Solar_Calculations_day.xls" file)
is updated and modified to suit the requirement of the present
invention. In this `solar position calculation program/software`,
the data in the said updated and modified excel work sheet changes
as per the user inputs and is updated continuously as per the
position of the sun. The data that is required to be entered in the
solar position calculation program/software is latitude, longitude,
target azimuth, target elevation, time zone, time, date, sun
elevation to check (for example 30.degree. sun elevation), sun
azimuth to check (for example, 180.degree. azimuth), arm `A`
length, arm `B` length, length `C` at start position, start
position angle .theta., value of n, for azimuthal tracking value of
`p` etc.
[0063] FIG. 4 depicts a flow diagram illustrating one version of
process-flow to implement the altitudinal orientation of arrays of
mechanically linked heliostats mounted on arrays of rotatable
shafts for continually focusing the incident sunlight on a
stationary object. The operation starts at step 401. At step 402,
the computation means under its control program continuously
keeping track of the real time in the real time clock (RTC), checks
for the occurrence of a scheduled starting time, say 8:00 AM. At
step 403, at the occurrence of a scheduled starting time, the
computation means under its control program, determines T.sub.1 and
T.sub.2 and then determines the time interval between each
altitudinal orientation=2.times.(T.sub.2-T.sub.1)/n seconds. At
step 404, the computation means under its control program executes
n number of successive clockwise rotations--like 1/4.sup.th of a
circle in the present example--of the lead screw by the stepper
motor (n number of miniscule pushes) for altitudinal orientations
of the heliostats. At step 405, at the end of the
2.times.(T.sub.2-T.sub.1) time, the computation means under its
control program executes n/4 number of complete anticlockwise
revolutions of the lead screw by the stepper motor such that the
mirrors achieve the original position for the next day operation.
At step 406 the operation ends.
[0064] Method for azimuthal orientation of arrays of mechanically
linked heliostats mounted on arrays of rotatable shafts for
continually focusing the incident sunlight on a stationary
object:
[0065] The sun rises in the east and sets in the west everywhere on
the Earth. The Earth's rotation tilts about 23.5 degrees on its
pole-to-pole axis, relative to the plane of Earth's solar system
orbit around our sun. The sun's declination at the spring equinox
is 0.degree.. It moves up to 23.5.degree. in the summer, then
drifts back down through 0.degree. at fall equinox, and down to
-23.5.degree. in the winter. As the Earth orbits the sun, this
creates the 47 degree peak solar azimuth angle difference and the
hemisphere-specific difference between summer and winter. In the
northern hemisphere, the winter sun rises in the southeast, peaks
out at a low angle above the southern horizon, and then sets in the
southwest. In the northern hemisphere in summer, in a city like
Pune (India), the sun rises in the northeast, peaks out nearly
straight overhead (depending on latitude), and then sets in the
northwest. The sun travels a curved path while apparently moving
from east to west. Therefore, for each azimuthal tracking, it is
necessary to determine whether the azimuth movement of the sun is
southward or northward. For this purpose, as depicted in FIG. 5, it
is necessary to divide the sky 501 into 4 quadrants by drawing
imaginary lines from east (90.degree. azimuth) to west (270.degree.
azimuth)--line 503, and from north (0.degree. azimuth) to south
(180.degree. azimuth)--line 502. The 4 quadrants thus formed would
be:
1) From 0.degree. azimuth to 90.degree. azimuth=quadrant 504,
henceforth named as quadrant A. 2) From 90.01.degree. azimuth to
180.degree. azimuth=quadrant 505, henceforth named as quadrant B.
3) From 180.01.degree. azimuth to 270.degree. azimuth=quadrant 506,
henceforth named as quadrant C. 4) From 270.01.degree. azimuth to
0.degree. azimuth (or 360.degree. azimuth)=quadrant 507, henceforth
named as quadrant D.
[0066] Let the center of the sky at the cross section of the above
said imaginary lines be called as .beta.. Furthermore, here, it is
necessary to determine an angle .gamma., which is less than or
equal to 90.degree., and denotes the displacement of the sun from
the east west line. As depicted in FIG. 5, the angle 508 is an
example of angle .gamma.. The angle .gamma. is formed between the
east west line 503 and the line formed between the sun 509 and the
center .beta.. To determine the required azimuth rotation of the
rotatable shaft, one needs to find angle .gamma.. The software
yields the current solar azimuth. From the identified solar
azimuth, one can find the quadrant in which the sun lies at that
instant. With a known quadrant in which the sun lies and the solar
azimuth at that instant the angle .gamma. can be determined as
follows.
[0067] Determination of the angle .gamma.:--1) If the sun lies in
quadrant A, then angle .gamma.=90.degree.-azimuth value of the sun.
2) If the sun lies in quadrant B, then angle .gamma.=azimuth value
of the sun-90.degree.. 3) If the sun lies in quadrant C, then angle
.gamma.=270.degree.-azimuth value of the sun. 4) If the sun lies in
quadrant D, then angle .gamma.=azimuth value of the
sun-270.degree..
[0068] To introduce a calibrated compensation in heliostat azimuth
orientation according to the apparent azimuthal displacement of the
sun, wherein each east west directional rotatable shaft 207 (FIG.
2) that is in operational linkage to the mounted heliostats is
further characterized, as depicted in FIG. 2, in having an arm 201
affixed with each rotatable shaft 207. The said arm 201 is coupled
with a drive means like a linear actuator 203. Said linear actuator
203 provides the ability to rotate said rotatable shaft 207 in both
clockwise and anticlockwise directions by extension/retraction of
the arm 202 of the said linear actuator 203. Let it be assumed that
before the start of the actual operation at T.sub.1, the said arm
201 is parallel to the horizontal ground, projecting southward, and
making an angle of 90.degree. (angle .theta.) with the imaginary
perpendicular line from the center of the shaft 207 joining the
joint 205 (length A).
[0069] For a given longitude, latitude, time, and date, the
software determines the sun elevation and the sun azimuth values,
for that time of day. As an example, let it be assumed that at
T.sub.1 the value of the sun elevation is 30.degree. and the sun
azimuth is 110.degree.. From the identified solar azimuth, the
quadrant in which the sun lies at that instant can be determined.
From the determined solar azimuth and the quadrant in which the sun
lies, angle .gamma. can be determined as described hereinbefore. It
is necessary to determine angle .gamma. for determining the
required rotation of the rotatable shaft for tracking azimuthal
movement of the sun.
[0070] FIG. 6 depicts the conceptual basis for determining the
magnitude of the azimuth rotation. FIG. 6 schematically depicts the
sky 601 divided in 4 quadrants (as depicted in FIG. 5) by joining
the lines drawn from east to west and from north to south crossing
at zenith at P. While moving from east to west, the sun apparently
travels a curved path in the sky. For illustrative purpose, it is
assumed that the R, F, G, and H are the positions of the sun in the
sun's curved path in the sky on a particular day. From the
positions of the sun R, F, G, and H, perpendicular lines RL, FM,
GU, and HO are drawn on the east west line respectively. Triangles
are formed with respect to the positions of the sun R, F, G, and H,
namely, triangle RLP, triangle FMP, triangle GUP, and triangle HOP,
wherein angle .gamma. is formed, namely, angle RPL (angle
.gamma..sub.1), angle FPM (angle .gamma..sub.2), angle GPU (angle
.gamma..sub.3), and angle HPO (angle .gamma..sub.4)
respectively.
[0071] The said software also yields concurrent solar elevation at
the instant of the determination of angle .gamma.. Now the distance
of the sun in degrees from the center P can be ascertained as
90.degree.-concurrent solar elevation=Y degrees. Y is the length of
the hypotenuse of the triangle formed with respect to the position
of the sun like R, F, G, and H. Here, Sin .gamma.=length of the
side opposite divided by the length of the hypotenuse=length of the
side opposite/Y. Therefore the `length of the side opposite` in
degrees=Y.times.Sin .gamma.. For illustrative purpose, it is
assumed that the angle of elevation of the sun at position R is
10.degree., at position F is 30.degree., at position G is
48.degree., and at position H is 62.degree.. It is further assumed
that at the position R of the sun, it is the start of the actual
operation (time T.sub.1). The distance of the sun from the center P
can be defined as `90.degree.-concurrent sun elevation`=Y. Here,
{dot over (Y)} is the hypotenuse in the triangle formed with
respect to the position of the sun. The distance RP is the
hypotenuse in the triangle RPL and represents the distance of the
sun from the center P. Hypotenuse RP can be defined as
90.degree.-concurrent sun
elevation=90.degree.-10.degree.=80.degree.=Y.sub.1. Similarly,
hypotenuse FP=Y.sub.2=90.degree.-30.degree.=60.degree.. Similarly,
hypotenuse GP=Y.sub.3=90.degree.-48.degree.=42.degree.. Similarly,
hypotenuse HP=Y.sub.4=90.degree.-62.degree.=28.degree.. Therefore,
RL=Y.sub.1.times.Sin .gamma..sub.1, FM=Y.sub.2.times.Sin
.gamma..sub.2, GU=Y.sub.3.times.Sin .gamma..sub.3, and
HO=Y.sub.4.times.Sin .gamma..sub.4. For tracking the apparent
azimuthal position of the sun, the rotatable shaft should be
rotated such that the apparent lateral displacement of the sun,
like RL, from the east west midline is compensated. For the
position of the sun at R, the apparent displacement RL should be
compensated. As per the law of reflection, the rotatable shaft
should be rotated such that the shafts should rotate RL/2 degrees.
In other words, for the position of the sun at R, for tracking the
apparent azimuthal displacement RL, the rotatable shaft should be
rotated by (Y.sub.1.times.Sin .gamma..sub.1)/2 degrees. Now
RL/2=(Y.sub.1.times.Sin .gamma..sub.1)/2
degrees=(80.degree..times.Sin .gamma..sub.1)/2 degrees. If it is
assumed that solar azimuth at position R is 110.degree., then as
the sun lies in quadrant B, and
.gamma..sub.1=110.degree.-90.degree.=20.degree.. Therefore,
RL/2=(80.degree..times.0.342)/2=13.7.degree.. Thus, at the start of
the operation, the determined magnitude of rotation of the
rotatable shaft at the instant wherein the sun elevation is
10.degree. and sun azimuth 110.degree. is =13.7.degree.
[0072] To determine the direction of rotation of the rotatable
shaft for tracking the azimuthal movement of the sun:
[0073] If it is the start of the operation:
[0074] If it is the start of the operation and if the sun lies in
the quadrant B, then for tracking the azimuthal movement of the
sun, rotate the (east west directional) shaft in southward
direction. If it is the start of the operation and if the sun lies
in the quadrant A, then for tracking the azimuthal movement of the
sun, rotate the shaft in northward direction.
[0075] If it is not the start of the operation:
[0076] To determine the direction of rotation of the rotatable
shaft (east west directional) for each successive tracking of the
azimuthal movement of the sun: If it is not the start of the
operation and if the sun azimuth is .ltoreq.180.degree., then
rotate the shaft in southward direction. If it is not the start of
the operation and if the sun azimuth is >180.degree., then
rotate the shaft in northward direction.
[0077] To determine the magnitude of the required rotation of the
rotatable shaft for tracking the azimuthal movement of the sun:
[0078] If it is the start of the operation: At the actual start of
the operation at T.sub.1, when suppose the sun elevation is
10.degree., the sun azimuth 110.degree., and the mirror elevation
is 45.degree. (eastern), the determined magnitude of rotation of
the rotatable shaft for tracking the solar azimuth status will be
(Y.times.Sin .gamma.)/2 degrees, where the angle .gamma. is formed
between the east west line and the solar vector at that instant and
Y is the hypotenuse as described hereinbefore. At the start of the
operation at T.sub.1 it is necessary to rotate the rotatable shaft
for the entire magnitude of rotation=(Y.times.Sin .gamma.)/2
degrees towards the determined northern/southern direction as per
the sun's position in quadrant A or B.
[0079] For illustration, as per the example, at the start of the
operation at T.sub.1, the sun azimuth is 110.degree. and hence the
sun lies in the quadrant B. Therefore, the direction of rotation
should be southward. Inputting the values (as per the example) of Y
and .gamma. in (Y.times.Sin .gamma.)/2 degrees, the magnitude of
rotation will be (80.degree..times.0.342)/2=13.7.degree.. The
rotatable shafts are positioned in east west direction and the arm
201 is projecting in southward direction. As the sun lies in
quadrant B, The rotatable shaft is to be rotated in southward
direction. The retraction of the arm 202 would rotate the rotatable
shaft in southward direction, and would decrease the angle .theta..
To track for the determined solar azimuth 110.degree., the
rotatable shaft would have to be rotated by 13.7.degree. towards
south so that the mounted array heliostats rotate by 13.7.degree.
towards south. To achieve the 13.7.degree. rotation of the
rotatable shaft towards south, the arm 201 would have to be moved
in a clockwise manner in turn rotating the rotatable shaft by
13.7.degree., wherein the arm 202 of the linear actuator 203 would
have to be retracted to such an extent that the angle .theta. would
become from 90.degree. to 76.3.degree..
[0080] For azimuthal tracking:--
[0081] If it is not the start of the operation:
[0082] Determine the value of (T.sub.2-T.sub.1) seconds, and
2.times.(T.sub.2-T.sub.1) seconds.
[0083] Decide an arbitrary time interval p for azimuthal tracking
like say a time interval of 1800 seconds.
[0084] Determination of the required extension/retraction of the
arm 202 for the required rotation of the rotatable shaft for
tracking the azimuthal movement of the sun:
[0085] As already described, each east west directional rotatable
shaft is rotatable about its axis and is coupled with a drive means
to achieve clockwise/anti-clockwise rotation to track the azimuthal
movement of the sun. As depicted in FIG. 2, extension/retraction of
the arm 202 would cause anti-clockwise/clockwise rotation of
rotatable shafts respectively. As depicted in FIG. 2, the linear
actuator 203 with its arm 202 (length C), the arm 201 (length B),
and an imaginary line joining center of the shaft 207 & joint
205 (length A) form a triangle. Furthermore, as depicted in FIG. 2,
an angle .theta. is formed between the lengths A & B. Now the
length A and the length B of the said triangle are unchanging,
while the length C is changeable. The length C is changeable
because the arm 202 of the linear actuator 203 can be extended or
retracted. Extension/retraction of the length C would vary angle
.theta. (increase/decrease angle .theta.) resulting
anticlockwise/clockwise rotation of the rotatable shaft such that
the solar azimuth movement can be tracked.
[0086] In trigonometry, the law of cosines (cosine formula or
cosine rule) relates to the lengths of the sides of a plane
triangle to the cosine of one of its angles. Using notations with
reference to FIG. 2, in a triangle formed by the sides A, B, and C,
the law of cosines says C.sup.2=A.sup.2+B.sup.2-2AB cos .theta.,
where .theta. denotes an angle of a triangle contained between
sides of lengths A and B and opposite the side of length C.
(C.sup.2=A.sup.2+B.sup.2-2AB cos .theta. equation 1)
Inputting the known unchanging values of lengths A and B and the
determined angle .theta. in the equation 1, C.sup.2 can be
determined. With determination of C.sup.2, value of C can be
determined. Now to determine the needed value of requisite C', from
the original C, wherein the angle .theta. would be changed from
90.degree. to 76:3.degree., one would have to input the value
76.3.degree., which is henceforth called the angle .theta.' along
with the known values of A and B in the equation 1. Here, in this
cosine rule C'.sup.2=A.sup.2+B.sup.2-2AB cos .theta.', wherein the
values of A.sup.2+B.sup.2-2AB are constant and only the value of
cos .theta.' would be changed. Therefore, as per the example, by
inputting the value 76.3.degree. (.theta.') in the equation 1, the
value C'.sup.2 can be found. With the determination of C'.sup.2,
the value of requisite C' can be found. The decrease of the angle
.theta. means, as per the assumption, there would be a southward
rotation, wherein the arm of the linear actuator would be
retracted. In the present case, by finding the difference |C-C'|
millimeters, one can find the required length of the needed
retraction of the arm of the linear actuator.
[0087] The length of the `C` is known, which is the length of the
linear actuator with its arm at the start of the operation when
angle .theta. is 90.degree.. The hereinbove description exemplifies
and elucidates the methodology of determination of the length of
the `C.sub.1`, which is the length of the linear actuator with its
arm at the time T.sub.1, and the length, of the `C.sub.2`, which is
the length of the linear actuator with its arm at the time
T.sub.2.
[0088] Determine the length of the `C.sub.1` at T.sub.1 and the
length of the `C.sub.2` at T.sub.2, wherein, the length of the
linear actuator 203 with its arm 202 at time T.sub.1 is C.sub.1,
and the length of the linear actuator 203 with its arm 202 at time
T.sub.2 is C.sub.2. Once the values of C, C.sub.1 and C.sub.2 are
known, one can find |C-C.sub.1| mm and |C.sub.2-C.sub.1| mm.
[0089] Find |C.sub.2-C.sub.1| millimeters.
[0090] Determine the value of (T.sub.2-T.sub.1) seconds divided by
p seconds. Let this value be called as .DELTA.'. Here, .DELTA.'
value denotes the number of times one needs to perform the
azimuthal tracking from T.sub.1 to T.sub.2. By using the `floor or
ceiling function` on the value of .DELTA.' find the nearest
positive integer number, which is henceforth called as .DELTA..
Here, the minor mistake, which happens due to floor or ceiling
function can be easily compensated by the software.
[0091] Divide |C.sub.2-C.sub.1| mm by .DELTA.. Let this value be
called as .OMEGA. mm.
[0092] At each interval of p seconds, from the morning at T.sub.1
when the mirror elevation is 45.degree. (eastern) till T.sub.2, the
rotatable shaft is to be rotated in southward direction, wherein
the length of the linear actuator with its extensible/retractable
arm is varied by .OMEGA. mm.
[0093] Similarly, at each interval of p seconds, from T.sub.2 to
the evening till the mirror elevation is 45.degree. (western), the
rotatable shaft is to be rotated in northward direction, wherein
the length of the linear actuator with its extensible/retractable
arm is varied by .OMEGA. mm. The length of the linear actuator with
its extensible/retractable arm is varied such that if the sun
azimuth is .ltoreq.180.degree., then the rotatable shaft is rotated
in southward direction, and if the sun azimuth is >180.degree.,
then the rotatable shaft is rotated in northward direction. (It is
assumed that the rotatable shafts are positioned in east west
direction.).
[0094] FIG. 7 depicts a flow diagram illustrating one version of
process-flow to implement the azimuthal orientation of arrays of
mechanically linked heliostats mounted on arrays of rotatable
shafts for continually focusing the incident sunlight on a
stationary object. The initializing operation starts at step 701.
At step 702, the computation means under its control program
continuously keeping track of the real time in the RTC, checks for
the occurrence of a scheduled starting time, say 8:00 AM and start
the operation. At step 703, the computation means determines the
time T.sub.1 and T.sub.2, and determines the values of the sun
elevation and azimuth for the time T.sub.1 and T.sub.2. At decision
diamond 704, the computation means determines whether it is the
start of the operation, that is, time T.sub.1, or whether it is
time beyond T.sub.1. If it is the start of the operation (time
T.sub.1), then at step 705, the computation means determines
(Y.times.Sin .gamma.)/2 degrees and determines .theta.' and the
direction of rotation. The direction of rotation is determined as
per the position of the sun at that instant, which is whether the
sun lies in the quadrant A or B. At step 706, as per the cosine
rule, inputting the value of angle .theta. in the equation 1, the
new value of C, which is C.sub.1 is determined. By finding
|C.sub.1-C|, the extent of the retraction/extension of the arm of
the linear actuator is determined, and communicated to the linear
actuator for implementation. At decision diamond 704, when the
computation means determines it is not the start of the operation,
then at step 707, the value of (T.sub.2-T.sub.1)/p is determined
wherein the value of p is an arbitrary time interval for azimuthal
tracking like say a time interval of 1800 seconds. Let this value
(T.sub.2-T.sub.1)/p be called as .DELTA.'. Here, .DELTA.' value
denotes the number of times one needs to perform the azimuthal
tracking from T.sub.1 to T.sub.2. By using the `floor or ceiling
function` on the value of .DELTA.' find the nearest positive
integer number, which is called as .DELTA.. At step 707, the length
of the `C.sub.1` at T.sub.1 and the length of the `C.sub.2` at
T.sub.2 is also determined, wherein, the length of the linear
actuator with its arm at time T.sub.1 is C.sub.1, and the length of
the linear actuator with its arm at time T.sub.2 is C.sub.2. And
then the value of |C.sub.2-C.sub.1| in millimeters (mm) is
determined. At the step 708, the value of |C2-C1|
mm/.DELTA.=.OMEGA. mm is determined. At step 709, at each interval
of p seconds, from T.sub.1 to T.sub.2 and from T.sub.2 o T.sub.1,
the length of the linear actuator is varied by .OMEGA. mm such that
the rotatable shaft is rotated in southward/northward direction. If
the sun azimuth is .ltoreq.180.degree., then the rotatable shaft is
rotated in southward direction. And if the sun azimuth is
>180.degree., then the rotatable shaft is rotated in northward
direction. At decision diamond 710, the computation means
determines whether the total functional time
2.times.(T.sub.2-T.sub.1) is over or not. If over (yes), then at
step 711, the process ends. If not over (no), then go to step
709.
[0095] To overcome the accumulated mechanical error due to
conditions like mechanical backlash, in one of the embodiments, the
altitudinal and azimuthal status is re-adjusted at the interval of
say 90 or 120 minutes. Accumulated mechanical error is negated by
readjusting the altitudinal and azimuthal status whereupon
functionality extremes of the heliostat orientation means are
force-achieved via control check-loop. Using the sensors like
rotary encoder or a proximity switch, the starting position for the
shaft is achieved by instructing the DC motor linear actuator to
rotate till the position of the actuator arm extension is at its
original position, wherein the arm 201 (FIG. 2) is at right angle
with the imaginary line joining center of the shaft 101 & joint
205 (FIG. 2). Similarly, to achieve the altitudinal starting
position, the stepper motor is instructed to rotate such that the
reflectors of heliostats achieve the starting eastern elevation
position of 45.degree.. The altitudinal and azimuthal tracking is
then computed for that instant and the heliostats are rotated
accordingly. Once the current position is achieved, then the
process continues as is described hereinbefore as if it is not the
start of the operation.
[0096] The hereinabove mentioned embodiments of the method for
orienting arrays of mechanically linked heliostats for focusing the
incident sunlight on a stationary object are described as an
example only and those experts in the art can very well recognize
that numerous variations are possible without departing from the
main theme.
[0097] The present invention may, of course, be carried out in
other specific ways than those herein set forth without departing
from the spirit and essential characteristics of the invention. The
present embodiments are, therefore, to be considered in all
respects as illustrative and not restrictive, and all changes
coming within the meaning and equivalency range of the detailed
description are intended to be embraced therein.
* * * * *
References