U.S. patent application number 12/200086 was filed with the patent office on 2010-03-04 for global solar tracking system.
Invention is credited to Sam Cowley, Qiang Xie.
Application Number | 20100051017 12/200086 |
Document ID | / |
Family ID | 41721822 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100051017 |
Kind Code |
A1 |
Xie; Qiang ; et al. |
March 4, 2010 |
GLOBAL SOLAR TRACKING SYSTEM
Abstract
A system may include determination of whether solar tracking of
a first period of time is to be performed in a first region of sky
or in a second region of sky, determination of a target tracker
position in a first coordinate system if the solar tracking of the
first period of time is to be performed in the first region of sky,
and determination of the target tracker position in a second
coordinate system if the solar tracking of the first period of time
is to be performed in the second region of sky. In some aspects,
determination of the target tracker position in the second
coordinate system includes subtracting 360.degree. from an azimuth
angle in the first coordinate system if the azimuth angle in the
first coordinate system is between +180.degree. and +360.degree.,
wherein the azimuth angle in the second coordinate system is
determined to be equal to the azimuth angle in the first coordinate
system if the azimuth angle in the first coordinate system is
between 0 and +180.degree..
Inventors: |
Xie; Qiang; (San Jose,
CA) ; Cowley; Sam; (Mountain View, CA) |
Correspondence
Address: |
BUCKLEY, MASCHOFF & TALWALKAR LLC
50 LOCUST AVENUE
NEW CANAAN
CT
06840
US
|
Family ID: |
41721822 |
Appl. No.: |
12/200086 |
Filed: |
August 28, 2008 |
Current U.S.
Class: |
126/600 ;
126/601 |
Current CPC
Class: |
G01J 1/0266 20130101;
H02S 20/00 20130101; F24S 50/20 20180501; H02S 20/32 20141201; Y02E
10/47 20130101; H01L 31/0547 20141201; G01J 2001/4266 20130101;
Y02E 10/52 20130101; H01L 31/0543 20141201 |
Class at
Publication: |
126/600 ;
126/601 |
International
Class: |
F24J 2/38 20060101
F24J002/38 |
Claims
1. A method comprising: determining whether solar tracking during a
first period of time is to be performed in a first region of sky or
in a second region of sky; determining a target tracker position in
a first coordinate system if the solar tracking during the first
period of time is to be performed in the first region of sky; and
determining the target tracker position in a second coordinate
system if the solar tracking during the first period of time is to
be performed in the second region of sky.
2. A method according to claim 1, wherein the determined target
tracker position comprises an azimuth angle, the method further
comprising: controlling a solar tracker to move to the determined
target tracker position during the first period of time.
3. A method according to claim 2, wherein the first region of sky
is primarily a northern portion of sky with respect to the solar
tracker, and wherein the second region of sky is primarily a
southern portion of sky with respect to the solar tracker.
4. A method according to claim 2, further comprising: determining a
second target tracker position in the first coordinate system if
the solar tracking during the first period of time is to be
performed in the first region of sky; determining the second target
tracker position in the second coordinate system if the solar
tracking during the first period of time is to be performed in the
second region of sky; and controlling the solar tracker to move to
the determined second target tracker position during the first
period of time.
5. A method according to claim 4, further comprising: determining
whether solar tracking during a second period of time is to be
performed in the first region of sky or in the second region of
sky; determining a third target tracker position in the first
coordinate system if the solar tracking during the second period of
time is to be performed in the first region of sky; determining the
third target tracker position in the second coordinate system if
the solar tracking during the second period of time is to be
performed in the second region of sky; and controlling the solar
tracker to move to the determined third target tracker position
during the second period of time.
6. A method according to claim 1, wherein determining the target
tracker position in the second coordinate system comprises:
determining an azimuth angle in the first coordinate system; and
determining an azimuth angle in the second coordinate system based
on the azimuth angle in the first coordinate system.
7. A method according to claim 6, wherein the first coordinate
system comprises azimuth angles between 0.degree. and +360.degree.,
and wherein the second coordinate system comprises azimuth angles
between -180.degree. and +180.degree..
8. A method according to claim 7, wherein determining the target
tracker position in the second coordinate system comprises:
subtracting 360.degree. from the azimuth angle in the first
coordinate system if the azimuth angle in the first coordinate
system is between +180.degree. and +360.degree., wherein the
azimuth angle in the second coordinate system is determined to be
equal to the azimuth angle in the first coordinate system if the
azimuth angle in the first coordinate system is between 0.degree.
and +180.degree..
9. A method according to claim 1, wherein determining whether solar
tracking during the first period of time is to be performed in the
first region of sky or in the second region of sky comprises:
determining an azimuth angle of the sun corresponding to noon of
the first period of time; determining that solar tracking during
the first period of time is to be performed in the first region of
sky if the azimuth angle of the sun corresponding to noon of the
first day is within the first region of sky; and determining that
solar tracking during the first period of time is to be performed
in the second region of sky if the azimuth angle of the sun
corresponding to noon of the first period of time is within the
second region of sky.
10. A method according to claim 1, wherein the determination of
whether solar tracking during the first period of time is to be
performed in the first region of sky or in the second region of sky
is performed before dawn and after 12:01 a.m. of the first period
of time.
11. A method according to claim 1, wherein determining whether
solar tracking during the first period of time is to be performed
in the first region of sky or in the second region of sky
comprises: determining a date on which a solar position changes
between the first region of sky and the second region of sky.
12. A system comprising: a solar tracker; and a control unit
coupled to the solar tracker and to: determine whether solar
tracking during a first period of time is to be performed in a
first region of sky or in a second region of sky; determine a
target tracker position in a first coordinate system if the solar
tracking during the first period of time is to be performed in the
first region of sky; and determine the target tracker position in a
second coordinate system if the solar tracking during the first
period of time is to be performed in the second region of sky.
13. A system according to claim 12, wherein the determined target
tracker position comprises an azimuth angle, the control unit
further to: control the solar tracker to move to the determined
target tracker position during the first period of time.
14. A system according to claim 13, wherein the first region of sky
is primarily a northern portion of sky with respect to the solar
tracker, and wherein the second region of sky is primarily a
southern portion of sky with respect to the solar tracker.
15. A system according to claim 13, the control unit further to:
determine a second target tracker position in the first coordinate
system if the solar tracking of the first period of time is to be
performed in the first region of sky; determine the second target
tracker position in the second coordinate system if the solar
tracking of the first period of time is to be performed in the
second region of sky; and control the solar tracker to move to the
determined second target tracker position during the first period
of time.
16. A system according to claim 15, the control unit further to:
determine whether solar tracking of a second period of time is to
be performed in the first region of sky or in the second region of
sky; determine a third target tracker position in the first
coordinate system if the solar tracking of the second period of
time is to be performed in the first region of sky; determine the
third target tracker position in the second coordinate system if
the solar tracking of the second period of time is to be performed
in the second region of sky; and control the solar tracker to move
to the determined third target tracker position during the second
period of time.
17. A system according to claim 12, wherein determining the target
tracker position in the second coordinate system comprises:
determining an azimuth angle in the first coordinate system; and
determining an azimuth angle in the second coordinate system based
on the azimuth angle in the first coordinate system.
18. A system according to claim 17, wherein the first coordinate
system comprises azimuth angles between 0.degree. and +360.degree.,
and wherein the second coordinate system comprises azimuth angles
between -180.degree. and +180.degree..
19. A system according to claim 18, wherein determining the target
tracker position in the second coordinate system comprises:
subtracting 3600 from the azimuth angle in the first coordinate
system if the azimuth angle in the first coordinate system is
between +180.degree.and +360.degree., wherein the azimuth angle in
the second coordinate system is determined to be equal to the
azimuth angle in the first coordinate system if the azimuth angle
in the first coordinate system is between 0.degree. and
+180.degree..
20. A system according to claim 12, wherein the determination of
whether solar tracking during the first period of time is to be
performed in the first region of sky or in the second region of sky
comprises: determining an azimuth angle of the sun corresponding to
noon of the first period of time; determining that solar tracking
during the first period of time is to be performed in the first
region of sky if the azimuth angle of the sun corresponding to noon
of the first period of time is within the first region of sky; and
determining that solar tracking during the first period of time is
to be performed in the second region of sky if the azimuth angle of
the sun corresponding to noon of the first period of time is within
the second region of sky.
21. A system according to claim 12, wherein the determination of
whether solar tracking during the first period of time is to be
performed in the first region of sky or in the second region of sky
is performed before dawn and after 12:01 a.m. of the first period
of time.
22. A method according to claim 12, wherein the determination of
whether solar tracking during the first period of time is to be
performed in the first region of sky or in the second region of sky
comprises: determining a date on which a solar position changes
between the first region of sky and the second region of sky.
Description
BACKGROUND
[0001] A solar collector may receive solar radiation (i.e.,
sunlight) and direct the solar radiation onto a photovoltaic (or,
solar) cell. A "concentrating" solar collector may also convert the
received solar radiation into a concentrated radiation beam prior
to directing the radiation onto the solar cell. The cell, in turn,
may generate electrical power based on photons of the received
radiation.
[0002] A solar collector is designed to generate power in response
to radiation which intercepts the solar collector within a certain
range of incidence angles. Power generation typically drops
significantly if incoming radiation deviates from the range of
incidence angles. The range depends on the design of the solar
collector, and typically narrows with increasing concentration
factors. For example, in some solar collector designs providing
approximately 500-fold concentration, the range of incidence angles
providing suitable power generation extends only one degree from
normal.
[0003] In operation, a solar tracker aligns a solar collector with
a radiation source (e.g., the sun) such that incoming radiation
intercepts the solar collector within its preferred range of
incidence angles. According to some systems, a solar collector is
associated with a central axis perpendicular to its reception
surface, and the above-mentioned alignment consists of moving the
solar collector so that the axis points directly toward the
apparent position of the sun in the sky.
[0004] FIG. 1 illustrates apparent solar positions 100A-100D within
sky 110. Each of solar positions 100A-100D corresponds to a
different time of day. Solar positions 100A-100D vary in both
azimuth angle and elevation angle. Horizon 120 may be defined as
the 0 degree elevation angle, and any direction may be defined as
the 0 degree azimuth angle. For locations north of the Tropic of
Cancer, apparent solar positions 100A-100D are always in the
southern part of the sky. For locations south of the Tropic of
Capricorn, apparent solar positions 100A-100D are always in the
northern part of the sky.
[0005] Solar tracker 200 includes support 210, alignment device 220
and alignment device 230. Alignment device 220 is mounted on
support 210 and is coupled to alignment device 230. Alignment
device 230 is coupled to solar collector 300. Alignment device 220
may be controlled to rotate solar collector 300 to a particular
azimuth angle, while alignment device 230 may be controlled to
rotate solar collector 300 to a particular elevation angle. Such
operation may be intended to align axis 310 of collector 300 with
an apparent solar position in sky 110.
[0006] For a typical solar tracker, the elevation angle cannot
exceed 90 degrees and the azimuth angle range of movement is
usually less than 360 (e.g., between 0 degrees and 355 degrees, 0
degree is North). Typically, these constraints are implemented by
mechanical limit switches and intended to prevent damage to tracker
200 and/or collector 300 due to malfunctions. These constraints may
also or alternatively take into account physical considerations
such as a length of cables within and attached to tracker 200.
However, in order for a tracker to be deployed globally, it needs
to be able to move to any azimuth angle (e.g., from 0 to 360
degree).
[0007] FIG. 2 is a graph illustrating solar paths during several
days of a particular year at a location between the Equator and the
Tropic of Cancer. The 0 degree azimuth angle represents North
(e.g., True North). For most of the year, an azimuth angle of solar
tracker 200 is moved through range A of angles shown in FIG. 2. On
some days (i.e., May 19, June 21, and July 24, as well as the days
in between), the azimuth angle of the solar position passes through
North. Even if a tracker is mechanically capable of a 360 degree
(or more) range of azimuth movement, according to conventional
solar tracking algorithms, the solar azimuth angle will change on
these days from 0 degrees to 360 degrees around noon. A
conventional solar tracking algorithm will treat this as a 360
degree change in azimuth angle and will cause tracker 200 to rotate
reversely through almost a 360 degree azimuth angle to continue
tracking.
[0008] Solar collector 300 delivers negligible power during the
large azimuthal rotation described above. Such a rotation may also
lead to excessive wear on the mechanical elements of solar tracker
200. Similar issues would arise if solar tracker 200 were located
between the Equator and the Tropic of Capricorn.
[0009] Moreover, conventional solar tracking algorithms are also
not suited for use at multiple global locations. For example,
locations North of the Tropic of Cancer require a solar tracking
algorithm for tracking in the Southern part of the sky and
locations South of the Tropic of Capricorn require a different
solar tracking algorithm for tracking in the northern part of the
sky. Similarly, solar tracker 200 would require another solar
tracking algorithm if located between the Equator and the Tropic of
Capricorn and yet another solar tracking algorithm if located
between the Equator and the Tropic of Cancer. Maintaining different
tracking algorithms for solar trackers located in different parts
of the world may be inefficient, costly, and prone to errors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a perspective view of a solar tracking system.
[0011] FIG. 2 is a graph illustrating elevation and azimuth
coordinates for various solar paths.
[0012] FIG. 3 is a flow diagram of a process according to some
embodiments.
[0013] FIG. 4 is a graph illustrating elevation and azimuth
coordinates for various solar paths according to some
embodiments.
[0014] FIG. 5 is a block diagram of a system according to some
embodiments.
[0015] FIGS. 6A through 6C illustrate azimuth angular movement of a
solar tracker according to some embodiments.
[0016] FIG. 7 is a flow diagram of a process according to some
embodiments.
[0017] FIG. 8 is a perspective view of a solar collector array
according to some embodiments.
DESCRIPTION
[0018] The following description is provided to enable any person
in the art to make and use the described embodiments and sets forth
the best mode contemplated for carrying out some embodiments.
Various modifications, however, will remain readily apparent to
those in the art.
[0019] FIG. 3 is a flow diagram of process 400 according to some
embodiments. Process 400 and all other processes described herein
may be executed by one or more hardware and/or software elements,
one or more of which may be located remotely from one another.
Although described herein with respect to specific systems, these
processes may be implemented and executed differently than as
described. According to some embodiments, process 400 may be
embodied in firmware and performed by a microcontroller executing
the firmware.
[0020] Initially, at S410, it is determined whether solar tracking
during a period of time is to be performed in a first region of sky
or a second region of sky. The period of time may encompass the
upcoming day, several upcoming days, or a portion of the upcoming
day. According to some embodiments, the determination at S410
occurs during a time at which no appreciable light is available
from which to generate electrical current (e.g., after dusk and
before dawn). Embodiments are not limited thereto, as the
determination may be performed at any time of day, and may be
performed more than once per day. In a particular example, S410 is
performed a few hours before dawn of the first day, and the
determination relates to whether solar tracking during the first
day is to be performed in a first region of sky or a second region
of sky.
[0021] The first region of sky may be a portion of sky which does
not include a particular direction (e.g., North), while the second
region of sky may be a portion of sky which includes the particular
direction. In this regard, the first region of sky and the second
region of sky may include some common directions. Using the example
of FIG. 2, the first region of sky may comprise a mostly-Southernly
region extending from 70 degrees from North, through South (e.g.,
True South), to 300 degrees from North, and the second region of
sky may comprise a Northernly region extending from 85 degrees from
North, through North, to 270 degrees from North.
[0022] The determination at S410 may be performed based on any
techniques that are or become known. According to some embodiments,
S410 comprises determining the solar noon azimuth angle for the
upcoming day. This determination may comprise receiving date and
location data via a Global Positioning System (GPS) receiver, and
determining the solar noon azimuth angle based on the date and
location data and on ephemeris equations and/or ephemeris tables.
If the noon azimuth angle is within the first region of sky, it is
determined that solar tracking during the first day is to be
performed in the first region of sky. If the noon azimuth angle is
within the second region of sky, it is determined that solar
tracking during the first day is to be performed in the second
region of sky.
[0023] According to some embodiments, S410 comprises receiving date
and location data as described above, and comparing the data with
stored information indicating solar tracking regions corresponding
to various dates and locations. For example, the information may
indicate that solar tracking is to be performed in the first region
on all dates for all locations North of the Tropic of Cancer, and
that that solar tracking is to be performed in the second region on
all dates for all locations South of the Tropic of Capricorn. The
information may further indicate a date for all locations between
the equator and the Tropic of Cancer at which the solar position
changes from the first region to the second region, a date for all
locations between the equator and the Tropic of Cancer at which the
solar position changes from the second region to the first region,
a date for all locations between the equator and the Tropic of
Capricorn at which the solar position changes from the second
region to the first region, and a date for all locations between
the equator and the Tropic of Capricorn at which the solar position
changes from the first region to the second region. Calculations of
such "transition dates" based on location data are known in the
art.
[0024] Flow proceeds to S420 if it is determined that solar
tracking for the period of time is to be performed in the first
region of sky. A tracker position in a first coordinate system is
determined at S420. The tracker position includes an elevation
angle and an azimuth angle intended to align a solar collector with
the sun at a given time. According to some embodiments, a solar
position at the given time is estimated using GPS data, ephemeris
tables and tracking error data as is known in the art.
[0025] The first coordinate system may be a coordinate system
through which a solar tracker may continuously track the sun over
the first region of sky. In one example, the 0 degree azimuth angle
corresponds to North and the first region of sky is the
mostly-Southernly region described above with respect to FIG. 2.
The first coordinate system may therefore include azimuth angles
which encompass this mostly-Southernly region.
[0026] According to some embodiments, the first coordinate system
includes azimuth angles within the range of 0 and 360 degrees. As
seen from FIG. 2, a solar tracker capable of continuous movement
through this range will also be capable of tracking the sun through
the first region of sky corresponding to range A. Since a solar
position determined according to conventional techniques includes
an azimuth angle within the range of 0 and 360 degrees, the
determination at S420 may simply comprise determining a solar
position using conventional techniques.
[0027] Flow proceeds from S410 to S430 if it is determined that
solar tracking for the period of time is to be performed in the
second region of sky. At S430, a tracker position in a second
coordinate system is determined.
[0028] The second coordinate system may be a coordinate system
through which a solar tracker may continuously track the sun over
the second region of sky. Continuing with the current example, the
0 degree azimuth angle corresponds to North and the second region
of sky is the Northernly region corresponding to range B of FIG.
2.
[0029] As described above, a solar tracking algorithm which
represents azimuth angle only in the first coordinate system (e.g.,
0 to 360 degree) is unable to continuously track the sun over range
B. FIG. 4 is an alternative representation of the solar paths of
FIG. 2. More specifically, the azimuth angles of range B are
depicted as mathematically-equivalent angles of range C. In the
present example, the second coordinate system includes azimuth
angles within the range of -180 and +180 degrees. As seen in FIG.
4, after transforming the azimuth angle from a first coordinate
system (e.g., 0 to 360 degrees) to a second coordinate system
(e.g., -180 to 180 degrees), the azimuth angle will change
continuously in the second coordinate system to allow continuous
tracking of the sun through the second region of sky corresponding
to range C.
[0030] According to this example, the tracker position determined
at S430 includes an azimuth angle in the range of -180 to +180
degrees. Some embodiments of S430 include determining a solar
position including an azimuth angle within the range of 0 and 360
degrees according to conventional techniques. The determined
azimuth angle is then converted to the second coordinate system.
Under the present assumptions, determined azimuth angles between 0
degrees and 180 degrees require no conversion (i.e., because the
second coordinate system includes this range of azimuth angles),
and determined azimuth angles between 180 degrees and 360 degrees
are decreased by 360 degrees in order to place them in the range
-180 degrees to 0 degrees.
[0031] S420 (or S430, depending on the result of the determination
at S410) may repeat throughout the day in order to update the
tracker position and thereby track the sun across the first region
(or second region) of sky.
[0032] In some embodiments, a tracker position is determined in a
coordinate system that is different from the first or the second
coordinate systems and is converted thereto as required by S420 or
S430.
[0033] Embodiments are not limited to the specific coordinate
systems or conventions (e.g., 0 degrees=North) described above. The
table below summarizes first and second coordinate systems that may
be employed for various first and second regions of sky and various
"0 degree" directions. The table also specifies a method to convert
an azimuth angle from each of the first coordinate systems to an
associated second coordinate system. Embodiments are not limited to
those represented in the table.
TABLE-US-00001 First coordinate Second coordinate First region
Second region system (azimuth system (azimuth of sky of sky angle
a) angle b) Conversion method Primarily Primarily 0.degree. to
360.degree. -180.degree. to 180.degree. If (a <= 180), b = a
Southern Northern (0.degree. is North) (0.degree. is North) If (a
> 180), b = a - 360 Primarily Primarily -180.degree. to
180.degree. 0.degree. to 360.degree. If (a > 0), b = a Southern
Northern (0.degree. is South) (0.degree. is South) If (a < 0), b
= a + 360 Primarily Primarily 0.degree. to 360.degree. -180.degree.
to 180.degree. If (a <= 180), b = a Northern Southern (0.degree.
is South) (0.degree. is South) If (a > 180), b = a - 360
Primarily Primarily -180.degree. to 180.degree. 0.degree. to
360.degree. If (a >= 0), b = a Northern Southern (0.degree. is
North) (0.degree. is North) If (a < 0), b = a + 360 Primarily
Primarily -90.degree. to 270.degree. -270.degree. to 90.degree. If
(a <= 90), b = a Southern Northern (0.degree. is East)
(0.degree. is East) If (a > 90), b = a - 360 . . . . . . . . . .
. . . . .
[0034] As is evident from the previous description, process 400 may
address the tracking discontinuity presented by conventional solar
tracking systems located in the Tropics. Moreover, process 400 may
be equally suited to application at locations North of the Tropic
of Cancer or South of the Tropic of Capricorn. Of course, at these
locations, S410 will always provide the same result (i.e., solar
tracking will always occur in the first region of sky or always in
the second region of sky) and the same coordinate system will
always be employed.
[0035] FIG. 5 is a block diagram of system 500 according to some
embodiments. System 500 may execute process 400 but embodiments are
not limited thereto. In addition, embodiments are not limited to
the elements and/or the configuration depicted in FIG. 5.
[0036] System 500 includes solar collector 510 and solar tracker
520. Solar collector 510 may comprise any system for receiving
solar radiation that is or becomes known. In some embodiments,
solar collector 510 comprises a concentrating solar collector for
receiving solar radiation, concentrating the solar radiation, and
directing the concentrated radiation onto a solar cell. Solar
collector 510 may comprise solar sensors such as Normal Incidence
Pyrheliometer (NIP) sensors in some embodiments. Solar collector
510 may comprise an array of individual solar collectors according
to some embodiments.
[0037] According to the illustrated embodiment, solar collector 510
generates direct current in response to received solar radiation.
Inverter 515 may receive the direct current and convert the direct
current to alternating current. Any suitable inverter may be
employed, including but not limited to an inverter employing a
maximum power point tracking servo. Inverter 515 supplies the
alternating current to intended load 525. Inverter 515 may not be
required in some embodiments, such as those employing the
aforementioned NIP sensors.
[0038] Intended load 525 may comprise any device, network, or
combination thereof intended to receive power generated by solar
collector 510. Intended load 525 may comprise a private or public
power grid to which solar collector 510 provides power. Intended
load 525 may be coupled to a dedicated motor or energy storage
device to be supplied power by solar collector 510, and/or may
comprise a general-purpose power grid.
[0039] Solar tracker 520 may comprise hardware and/or software for
moving solar collector 510 with respect to a position in the sky.
Some embodiments of solar tracker 520 comprise an azimuthal drive
to move solar collector 510 in the azimuth rotational plane and an
elevational drive to position solar collector 510 in the elevation
rotational plane. Solar tracker 520 may comprise
hydraulically-driven elements according to some embodiments. In
some embodiments, solar tracker 520 operates to position solar
collector 510 so that an axis thereof (e.g., a central axis normal
to a receiving surface) points at a desired position in the sky.
The desired position may comprise a position of the sun, but
embodiments are not limited thereto.
[0040] Control unit 530 includes processor 532 and storage 534.
Processor 532 may comprise one or more microprocessors,
microcontrollers and other devices to execute program code
according to some embodiments. In this regard, storage 534 stores
control program 535 comprising executable program code. Processor
532 may execute the program code of control program 535 in order to
operate system 500 according to one or more of the processes
described herein. In some embodiments of control unit 530, some or
all of storage 534 resides within processor 532.
[0041] Storage 534 also stores ephemeris tables 536 for determining
solar positions (and resulting tracker positions) corresponding to
various locations, dates and times. Determination of a solar
position in some embodiments may be based on ephemeris tables 536
as well as on ephemeris equations embodied in program code of
control program 535. Error correction data 537 may comprise data
used to correct for tracking errors as currently or hereafter
known.
[0042] GPS receiver 540 may receive date, time and location data
from the GPS network. Systems according to some embodiments may
implement additional or alternative systems to retrieve date, time
and/or position data, including but not limited to radio and
GPS-like systems. This data may be used in conjunction with
ephemeris equations and/or ephemeris tables 536 to determine a
solar position and a position of solar tracker 520 as is known in
the art. Date/time information may be obtained in some embodiments
from a battery-backed Real Time Clock (RTC) maintained within
system 500. Location data can be determined using a portable GPS
unit or online source during installation of system 500, which
would further include manual input of thusly-determined location
data into control unit 530.
[0043] FIGS. 6A through 6C illustrate ranges of angular movement
according to some embodiments, but embodiments are not limited to
the illustrated ranges. In some embodiments, a solar tracker such
as solar tracker 520 is capable of azimuthal movement through the
illustrated ranges.
[0044] FIG. 6A illustrates a 540 degree range (i.e., from -180
degrees to +360 degrees) of continuous azimuthal movement. Although
0 degrees is depicted as North, embodiments are not limited
thereto. Such a range may allow a solar tracker to move
continuously through two different azimuthal coordinate systems as
described above. The 540 degree range may be implemented by putting
two independent limit switches around an azimuth motor shaft with
proper rotation reduction rate, by placing the limit switches on a
slip-ring structure, or by other methods known to the art.
[0045] FIG. 6B illustrates continuous movement between azimuthal
angles 0 degrees and 360 degrees of the 540 degrees shown in FIG.
6A. The FIG. 6B movement may provide continuous tracking within a
first coordinate system (i.e., 0 degrees through 360 degrees) as
described with respect to process 400. Similarly, FIG. 6C
illustrates continuous movement between azimuthal angles -180
degrees and +180 degrees of the 540 degrees shown in FIG. 6A.
Movement between azimuthal angles -180 degrees and +180 degrees may
provide continuous tracking within a second coordinate system
(i.e., -180 degrees through +180 degrees) according to some
embodiments.
[0046] FIG. 7 is a flow diagram of process 700 according to some
embodiments. Process 700 may comprise an implementation of process
400, but embodiments are not limited thereto. Process 700 will be
described below with respect to system 500 and particular
directional conventions, but embodiments are also not limited
thereto.
[0047] At S710, it is determined whether solar tracking for the
upcoming day is to be performed primarily in the Northern sky or
primarily in the Southern sky. Solar tracking is performed
"primarily" in the Northern (or Southern) sky if the sun is in the
Northern sky (or Southern) for the majority of daylight time. The
determination at S710 may occur before dawn on the day in question.
For example, the determination at S710 may be performed at 1 a.m.
local time in some embodiments.
[0048] According to some embodiments, S710 comprises determining
the solar noon azimuth angle for the upcoming day. It is determined
that solar tracking for the upcoming day is to be performed in the
Northern sky if the determined noon azimuth angle is in the
Northern sky, and it is determined that solar tracking for the
upcoming day is to be performed in the Southern sky if the
determined noon azimuth angle is in the Southern sky.
[0049] As described with respect to S410, the determination of S710
may alternatively be based on stored information indicating that
solar tracking is to be performed in the Southern sky on all dates
for all locations North of the Tropic of Cancer, and that that
solar tracking is to be performed in the Northern sky on all dates
for all locations South of the Tropic of Capricorn. The stored
information may also specify the above-described transition dates
for locations between the equator and the Tropic of Cancer and for
locations between the equator and the Tropic of Capricorn. In some
embodiments, these dates are calculated on-the-fly during process
700.
[0050] A software flag is set to NORTH or SOUTH at S710 depending
on the result of the determination. Flow then pauses at S720 until
the upcoming day begins. In some embodiments, the day is determined
to begin when the sun is at a first position from which light can
be received and converted to electrical current. This position may
vary depending upon the solar collector used in conjunction with
process 700.
[0051] Process 700 may be initiated upon initialization of a system
according to some embodiments. For example, after installing a
solar tracker and a solar collector during daylight of a particular
day, S710 may be performed to determine whether solar tracking for
the particular day is to be performed primarily in the Northern sky
or primarily in the Southern sky. Since the particular day has
already begun, flow then proceeds from S720 to S730.
[0052] A target tracker position is determined at S730. The target
tracker position includes an elevation angle and an azimuth angle
intended to align a solar collector with the sun. According to some
embodiments of S730, a solar position is estimated using GPS data
from GPS receiver 540, ephemeris tables 536 and error correction
data 537 as is known in the art, and the target tracker position is
determined to be equal to the solar position.
[0053] According to some conventional techniques, the target
tracker position includes an azimuth angle between 0 degrees and
360 degrees, with 0 degrees being assigned to True North. The range
of azimuth angles and the actual direction associated with each
angle may differ from the present example.
[0054] Next, at S740, it is determined whether the software flag is
set to SOUTH. The 0 degree to 360 degree azimuth coordinate system
mentioned at S730 and illustrated in FIGS. 4 (i.e., range A) and 6B
is intended, according to the present example, to allow continuous
tracking of solar positions located primarily in the Southern sky.
Therefore, since the software flag is set to SOUTH and the
determined azimuth angle is between 0 degrees and 360 degrees, the
solar tracker is moved at S750 to the determined target tracker
position (i.e., to the determined azimuth angle and elevation
angle).
[0055] S750 may comprise transmitting appropriate commands from
control unit 530 to solar tracker 520 to ensure alignment of a
central axis of solar collector 510 with the determined target
tracker position. Such commands may include commands to rotate to
the determined azimuth angle and to the determined elevation
angle.
[0056] System 500 may employ any technique to move solar tracker
520 to a tracker position that is or becomes known. Some systems
operate in terms of "encoder counts" instead of angles and
therefore convert desired azimuth (and elevation) angles to encoder
counts. If the current azimuth count differs from the desired count
(i.e., angle) by more than a certain error threshold, solar tracker
520 is moved in an appropriate direction until the current azimuth
count matches the desired count. Control of the elevation angle may
proceed similarly.
[0057] Alternatively, flow proceeds from S740 to S760 if it is
determined that the software flag is not set to SOUTH. Such a
determination indicates that solar tracking is to be performed
primarily in the Northern sky. According to the present example,
and as illustrated in FIG. 6C and FIG. 4 (i.e., range C), azimuth
angles between -180 degrees and +180 degrees provide continuous
tracking of solar positions located primarily in the Northern sky.
Accordingly, the azimuth angle of the target tracker position
determined at S730 (i.e., between 0 degrees and 360 degrees) is
converted to an azimuth angle between -180 degrees and +180 degrees
at S760.
[0058] The conversion at S760 may proceed according to any suitable
technique. The conversion may depend upon the coordinate system in
which the azimuth angle was determined at S730 (i.e., 0 degrees to
360 degrees in the present example) and the coordinate system to
which the azimuth angle is to be converted (i.e., -180 degrees to
+180 degrees in the present example). According to some embodiments
of S760, the converted azimuth angle is equal to the azimuth angle
determined at S730 if the azimuth angle determined at S730 is
between 0 degrees and +180 degrees. The converted azimuth angle is
360 degrees less than the azimuth angle determined at S730 if the
azimuth angle determined at S730 is between +180 degrees and +360
degrees. For example, an azimuth angle of 120 degrees is converted
to 120 degrees, while an azimuth angle of 310 degrees is converted
to -50 degrees.
[0059] The solar tracker is then moved to the target tracker
position at S750 as described above. If flow reaches S750 from
S760, the target tracker position includes an elevation angle
(e.g., between 0 degrees and 90 degrees) and an azimuth angle
between -180 degrees and +180 degrees. According to some
embodiments, solar tracker 520 might not be moved at S750 if the
target tracker position is equal to or negligibly different from
the current position of solar tracker 520. For example, solar
tracker 520 may be moved at S750 only if at least one of the
currently-determined elevation angle and azimuth angle differs from
the corresponding angles of current position by 0.1 degree or more.
Flow then proceeds to S770 to determine if daylight has ended.
[0060] If daylight has not ended, it is determined at S780 whether
to update the target tracker position. S780 may be governed by a
timer that indicates a period (e.g., 5 sec.) which should pass
between tracker position updates. Flow returns to S730 once the
period has ended. Flow proceeds directly from S770 to S730 in some
embodiments to provide continuous execution of S730 through
S760.
[0061] In the illustrated embodiment, flow cycles from S730 through
S780 until an end of daylight is determined at S770. The end of
daylight may represent a time at which the sun is no longer at a
position from which light can be received and converted to
electrical current. The end of daylight may be determined based on
a comparison between the current time and any time indicating an
end of daylight (e.g., dusk, twilight, astronomical twilight,
etc.). The end of daylight may be determined based on the power
output by system 500 in some embodiments.
[0062] Flow returns to S710 once the end of daylight is determined
at S770. S710 may be performed again after a specified number of
hours have elapsed and/or at a specific time after the end of
daylight (e.g., 3 a.m. local time). Process 700 may then proceed as
described above with respect to a next day. Although process 700
depicts setting a software flag to NORTH or SOUTH prior to the
beginning of each day, embodiments are not limited thereto. Such a
software flag may be set every few days, and/or may be
predetermined for each calendar day (i.e., allowing S710 to be
omitted from the daily process).
[0063] FIG. 8 is a perspective view of solar collector 800
according to some embodiments. Solar collector 800 may comprise an
implementation of collector 510 and may generate electrical power
from incoming solar radiation. Collector 800 may be mounted on a
solar tracker such as solar tracker 520 to maintain a desired
position relative to the sun during daylight hours.
[0064] Solar collector 800 comprises sixteen instantiations 810a-p
of concentrating solar collectors. Each of concentrating solar
collectors 810a-p may be connected in series to create an
electrical circuit during reception of light by solar collector
800. Embodiments are not limited to the arrangement shown in FIG.
8.
[0065] As described in U.S. Patent Application Publication No.
2006/0266408, each of concentrating solar collectors 810a-p
includes a primary mirror to receive incoming solar radiation
substantially parallel to axis 815 and a secondary mirror to
receive radiation reflected by the primary mirror. Each secondary
mirror then reflects the received radiation toward an active area
of a solar cell within a corresponding one of collectors
810a-p.
[0066] A perimeter of each primary mirror may be substantially
hexagonal to allow adjacent sides to closely abut one another as
shown. In some embodiments, a perimeter of each primary mirror is
square-shaped. Each primary mirror may comprise low iron soda-lime
or borosilicate glass with silver deposited thereon, and each
secondary mirror may comprise silver and a passivation layer formed
on a substrate of soda-lime glass. The reflective coatings of the
primary and secondary mirrors may be selected to provide a desired
spectral response to the wavelengths of solar radiation to be
collected, concentrated and converted to electricity by collector
800.
[0067] Each primary mirror and secondary mirror is physically
coupled to substantially planar window or cover glazing 820. Each
of collectors 810a-p is also to coupled to backpan 830. Backpan 830
may comprise any suitable shape and/or materials and may provide
strength and heat dissipation to collector 800. The electrical
current generated by each of concentrating solar collectors 810a-p
may be received by external circuitry coupled to backpan 830 in any
suitable manner.
[0068] The several embodiments described herein are solely for the
purpose of illustration. Embodiments may include any currently or
hereafter-known versions of the elements described herein.
Therefore, persons in the art will recognize from this description
that other embodiments may be practiced with various modifications
and alterations.
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