U.S. patent application number 12/901289 was filed with the patent office on 2011-02-10 for solar collection apparatus and methods using accelerometers and magnetics sensors.
Invention is credited to Mark S. Olsson.
Application Number | 20110030672 12/901289 |
Document ID | / |
Family ID | 43533819 |
Filed Date | 2011-02-10 |
United States Patent
Application |
20110030672 |
Kind Code |
A1 |
Olsson; Mark S. |
February 10, 2011 |
Solar Collection Apparatus and Methods Using Accelerometers and
Magnetics Sensors
Abstract
A mirror or other reflecting surface is used for collecting and
reflecting incident solar radiation. The mirror is supported for
independent motion about a pair of axes. An accelerometer generates
signals representative of an amount and direction of motion of the
mirror about each of the axes. Motors or other drive mechanisms
independently drive the mirror about each of the axes. A tracking
device provides information about the current position of the Sun.
A control is connected to the accelerometer, the motors and the
tracking device for maintaining a predetermined optimum orientation
of the mirror as the Sun moves across the sky. Position sensors
that sense the position of the mirror relative to the earth's
magnetic field may also be employed.
Inventors: |
Olsson; Mark S.; (La Lolla,
CA) |
Correspondence
Address: |
MICHAEL H JESTER
505 D GRAND CARIBE CAUSEWAY
CORONADO
CA
92118
US
|
Family ID: |
43533819 |
Appl. No.: |
12/901289 |
Filed: |
October 8, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11763267 |
Jun 14, 2007 |
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12901289 |
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60807456 |
Jul 14, 2006 |
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Current U.S.
Class: |
126/574 ;
126/601; 126/605 |
Current CPC
Class: |
Y02E 10/52 20130101;
Y02B 10/20 20130101; Y02E 10/47 20130101; E04D 13/033 20130101;
F24S 2030/133 20180501; F24S 2030/15 20180501; H01L 31/0547
20141201; F24S 30/45 20180501; F24S 50/20 20180501; F24S 23/70
20180501 |
Class at
Publication: |
126/574 ;
126/605; 126/601 |
International
Class: |
F24J 2/40 20060101
F24J002/40; F24J 2/38 20060101 F24J002/38 |
Claims
1. A solar tracking apparatus, comprising: means for collecting and
reflecting incident solar radiation; means for supporting the solar
radiation collecting and reflecting means for independent motion
about a pair of axes; accelerometer means for generating signals
representative of an amount and direction of motion of the solar
radiation collecting and reflecting means about each of the axes;
motor means for independently driving the solar radiation
collecting and reflecting means about each of the axes; tracking
means for providing information about the current position of the
Sun; and control means connected to the accelerometer means, the
motor means and the tracking means for maintaining a predetermined
optimum orientation of the solar radiation collecting and
reflecting means as the Sun moves across the sky.
2. The solar tracking apparatus of claim 1 wherein the solar
radiation collecting and reflecting means is configured for
concentrating incident solar radiation.
3. The solar tracking apparatus of claim 1 wherein the
accelerometer means is mounted on the solar radiation collecting
and reflecting means.
4. The solar tracking apparatus of claim 1 wherein the support
means includes a pair of pivot mechanisms.
5. The solar tracking apparatus of claim 1 wherein the
accelerometer means includes a MEMS accelerometer device
6. The solar tracking apparatus of claim 1 wherein the motor means
includes first and second electric motors and first and second
drive linkages for coupling the electric motors, respectively, to
the support means.
7. The solar tracking apparatus of claim 1 wherein the solar
radiation collecting and reflecting means is supported so that both
axes are substantially in the same horizontal plane when the solar
radiation collecting and reflecting means is in a horizontal
orientation.
8. The solar tracking apparatus of claim 7 wherein the solar
radiation collecting and reflecting means is a mirror with a
configuration selected from the group consisting of planar,
parabolic and parabolic trough.
9. The solar tracking apparatus of claim 1 and further comprising
means for sensing a reference position of the solar radiation
collecting and reflecting means relative to the earth's magnetic
field vector and for generating signals representative of the
reference position and supplying them to the control means.
10. The solar tracking apparatus of claim 9 wherein the
accelerometer means and the reference position sensing means are
provided by three-axis sensors.
11. A heliostat mirror pointing system employing both accelerometer
and magnetic sensors to determine mirror position relative to the
earth's gravitational vector and the earth's magnetic field
vector.
12. The heliostat mirror pointing system of claim 11 wherein one
axis of rotation is approximately vertical.
13. The heliostat mirror pointing system of claim 11 wherein one
axis of rotation is approximately horizontal.
14. The heliostat mirror pointing system of claim 11 wherein the
magnetic sensor is used to sense rotation around said vertical
axis.
15. The heliostat mirror pointing system of claim 11 wherein the
accelerometer sensor is used to sense rotation around said
horizontal axis.
16. The heliostat mirror pointing system employing 3-axis magnetic
sensors to determine mirror position relative to the earth's
magnetic field vector.
17. The heliostat mirror pointing system of claim 16 wherein one
axis of rotation is approximately vertical.
18. The heliostat mirror pointing system of claim 16 wherein one
axis of rotation is approximately horizontal.
19. The heliostat mirror pointing system of claim 16 wherein the
magnetic sensor is used to sense rotation around horizontal and
vertical axis.
20. A heliostat mirror control system employing both accelerometer
and magnetic sensors to determine mirror position relative to the
earth's gravitational vector and the earth's magnetic field
vector.
21. The heliostat mirror control system of claim 20 wherein said
control system is a member of a mesh network.
22. The heliostat mirror control system of claim 20 wherein said
control system uses a wireless control means
23. The heliostat mirror control system of claim 20 wherein
photovoltaic devices are used to provide power to said control
system.
24. The heliostat mirror control system of claim 20 wherein
photovoltaic devices are used to store energy in one or more
capacitors to provide power for said control system.
25. The heliostat mirror control system of claim 20 wherein
photovoltaic devices are used to store energy in one or more
rechargeable batteries to provide power for said control
system.
26. A solar tracking apparatus, comprising: a reflective surface
for collecting and reflecting incident solar radiation; a pivot
mechanism that supports the reflective surface for independent
motion about a pair of axes; an accelerometer that generates
signals representative of an amount and direction of motion of the
reflective surface about each of the axes; at least one motor
coupled to independently drive the reflective surface about each of
the axes; a data source that provides information about the current
position of the Sun; and a control circuit connected to the
accelerometer, the motor and the data source for maintaining a
predetermined optimum orientation of the reflecting surface as the
Sun moves across the sky.
27. The solar tracking apparatus of claim 26 wherein the reflective
surface is configured for concentrating incident solar
radiation.
28. The solar tracking apparatus of claim 26 wherein the
accelerometer is mounted on the reflective surface.
29. The solar tracking apparatus of claim 26 wherein the reflective
surface is supported by a pair of pivot mechanisms.
30. The solar tracking apparatus of claim 26 wherein the
accelerometer is a MEMS accelerometer device.
31. The solar tracking apparatus of claim 29 wherein the apparatus
includes first and second electric motors and first and second
drive linkages for coupling the electric motors to corresponding
ones of the pair of pivot mechanisms.
32. The solar tracking apparatus of claim 26 wherein the reflective
surface is supported so that both axes are substantially in the
same horizontal plane when the reflective surface is in a
horizontal orientation.
33. The solar tracking apparatus of claim 26 wherein the reflective
surface is a mirror with a configuration selected from the group
consisting of planar, parabolic and parabolic trough.
34. The solar tracking apparatus of claim 26 and further comprising
means for sensing a reference position of the solar radiation
collecting and reflecting means relative to the earth's magnetic
field vector and for generating signals representative of the
reference position and 4 supplying them to the control circuit.
35. The solar tracking apparatus of claim 34 wherein the
accelerometer and the reference position sensing means are provided
by three-axis sensors.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a Continuation-in-Part of U.S.
application Ser. No. 11/763,267 of Mark S. Olsson, filed Jun. 14,
2007.
[0002] This application also claims benefit under 35 USC Sections
119(e) and 120 to the filing date of U.S. Provisional Application
Ser. No. 60/807,456 filed by Mark S. Olsson on Jul. 14, 2006.
FIELD OF THE INVENTION
[0003] The present invention relates to systems and methods for
utilizing the energy of the Sun, and more particularly, to systems
and methods for tracking the Sun to re-direct and concentrate
incident solar radiation for lighting, heating and photovoltaic
applications.
BACKGROUND OF THE INVENTION
[0004] Increased usage of renewable energy sources such as solar
radiation is important in reducing dependence upon foreign sources
of oil and decreasing green house gases. Devices have been
developed in the past that track the motion of the Sun to re-direct
and concentrate incident solar radiation. FIG. 1 illustrates one
example of a prior art device that utilizes a parabolic dish mirror
10 with a central axis 12 that is pointed generally toward the Sun
14. Incident solar radiation 22 is received and reflected by the
parabolic dish mirror 10 and concentrated at its focus 16, where a
thermal target (not illustrated) can be mounted so that it can be
heated. The parabolic dish mirror 10 is supported for independent
movement by a two-axis tracking support 18 mounted atop a
supporting structure 20 such as a tower. Optical encoders (not
illustrated) associated with the tracking support 18 provide
signals indicative of the direction and amount of rotation of the
parabolic dish mirror 10 so that motor drives and a control system
(not illustrated) can be used to track the Sun and increase the
efficiency of the energy transfer.
[0005] FIG. 2 illustrates another example of a prior art device
similar to the device of FIG. 1 except that the device of FIG. 2
utilizes a parabolic trough mirror 30. Dashed line 32 illustrates a
common plane of the focal line 36 of the parabolic trough mirror 30
and the Sun 14. A single axis tracking support 38 carries the
parabolic trough mirror 30 and is mounted atop a tower 40. Incident
light rays from the Sun such as 42 are collected and reflected by
the parabolic trough mirror 30 and concentrated on a pipe (not
illustrated) that extends along the focal line 36. This allows a
heat transfer fluid such as water or liquid sodium to be heated.
The heating efficiency can be improved by mechanisms (not
illustrated) that cause the parabolic trough mirror 30 to pivot and
track the Sun. FIG. 3 illustrates another prior art device that
utilizes a heliostat flat mirror 50 that receives incident light
rays 52 from the Sun 14 and reflects them against a thermal target
58 atop a tower 59. Another tower 54 carries a two-axis tracking
support 56 which supports a flat mirror 50. Drive and control
mechanisms (not illustrated) allow the flat mirror 50 to be
independently moved about a rotate axis 60 (azimuth) and about a
tilt axis 62 (elevation) to ensure that the Sun's rays are
reflected onto the target 58 as the Sun moves across the sky. There
are many variations of the foregoing devices, but to date, none has
been widely adopted due to the complexity, reliability, accuracy
and/or expense of the tracking mechanisms.
SUMMARY OF THE INVENTION
[0006] In accordance with the present invention a solar tracking
apparatus has a mirror or other reflecting surface for collecting
and reflecting incident solar radiation. The mirror is supported
for independent motion about a pair of axes. An accelerometer
generates signals representative of an amount and direction of
motion of the mirror about each of the axes. Motors or other drive
mechanisms independently drive the mirror about each of the axes. A
tracking device provides information about the current position of
the Sun. A control is connected to the accelerometer, the motors
and the tracking device for maintaining a predetermined optimum
orientation of the mirror as the Sun moves across the sky.
[0007] According to another aspect of the present invention, one or
more magnetic field sensors are used to sense rotation around an
approximately vertical axis and one or more accelerometers are used
to sense tilt around an approximately horizontal axis to provide
signals indicative of heliostat mirror position in a coordinate
system to a control system. The control system allows for precise
positioning of a heliostat mirror and the directing of solar energy
in a desired direction.
[0008] According to another aspect of the present invention, three
orthogonal magnetic field sensors are used to sense rotation around
an approximately vertical axis and three orthogonal accelerometers
are used to sense tilt around an approximately horizontal axis to
provide signals indicative of heliostat mirror position in a
coordinate system to a control system. The control system allows
for precise positioning of a heliostat mirror and the directing
solar energy in a desired direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIGS. 1-3 illustrate examples of prior art solar radiation
collecting and redirecting devices.
[0010] FIG. 4 illustrates a first embodiment of the present
invention that utilizes a flat mirror to heat a target.
[0011] FIG. 5 illustrates a second embodiment of the present
invention that utilizes an array of mirrors to reflect solar
radiation through a skylight.
[0012] FIG. 6 illustrates an alternate embodiment wherein an array
of flat tracking mirrors reflects incident solar radiation through
the windows of a house to provide light and heat.
[0013] FIG. 7 illustrates another embodiment that utilizes an array
of heliostat mirrors to heat a thermal target.
[0014] FIG. 8 illustrates another embodiment that utilizes a
plurality of heliostat mirrors to reflect solar radiation onto a
high temperature photovoltaic panel.
[0015] FIG. 9 is a block diagram of another embodiment in which a
network controller controls a plurality of mirror nodes.
[0016] FIG. 10 illustrates another embodiment in which a heliostat
mirror is positioned to reflect incident solar radiation onto a
target via a vertical array of photo-sensors.
[0017] FIG. 11 is a block diagram illustrating one embodiment of
the mirror controller network node of the embodiment of FIG. 4.
[0018] FIG. 12 is a flow diagram illustrating one embodiment of a
method of operation of the control of FIG. 11.
[0019] FIG. 13 is a flow diagram of another embodiment of a method
of operation of a solar tracking 20 device in accordance with the
present invention.
[0020] FIG. 14 is a front isometric view of another embodiment that
utilizes a weight-tensioned device to pivot the mirror.
[0021] FIG. 15 is a back isometric view of the embodiment
illustrated in FIG. 14.
[0022] FIG. 16 is a front elevation view of the embodiment
illustrated in FIG. 14.
[0023] FIG. 17 is a back elevation view of the embodiment
illustrated in FIG. 14.
[0024] FIG. 18 is a side elevation view of the embodiment
illustrated in FIG. 14.
[0025] FIG. 19 is an exploded back isometric view of the embodiment
illustrated in FIG. 14.
[0026] FIG. 20 is a vertical sectional view (stepped cut) of the
embodiment illustrated in FIG. 14 showing internal components
thereof.
[0027] FIG. 21 illustrates another embodiment that employs magnetic
sensors and accelerometers.
[0028] FIG. 22 is a block diagram of the control system of the
embodiment of FIG. 21.
[0029] FIG. 23 is a block diagram of control circuitry.
[0030] FIG. 24 is a flow chart of data integration of magnetic
sensor and accelerometer data and their resolution.
DETAILED DESCRIPTION
[0031] The entire disclosure of U.S. patent application Ser. No.
11/763,267 of Mark S. Olsson, filed Jun. 14, 2007, and published
Jan. 17, 2008 as US-2008-0011288-A1 is hereby incorporated by
reference.
[0032] FIG. 4 illustrates a first embodiment of the present
invention that utilizes a flat mirror to heat a target. A solar
tracking apparatus has a reflective surface in the form of a mirror
70 for collecting and reflecting incident solar radiation 82 from
the Sun 14. The mirror in this embodiment has a planar
configuration, although this embodiment could be adapted to use
other mirror configurations including parabolic dish, parabolic
trough, etc. in order to concentrate the incident solar radiation.
The mirror could be conventional silver coated glass, or could be
plastic, or could be Mylar.RTM. polyester film on a support
substrate, or some other form of reflective material that is
durable, lightweight and inexpensive.
[0033] The mirror 70 (FIG. 4) is supported by a pair of pivot
mechanisms 72 for independent motion about a pair of tilt axes 88
and 90. The pivot mechanisms 72 are mounted atop a support or tower
76. An accelerometer 74 generates signals representative of an
amount and direction of motion of the mirror about each of the axes
88 and 90. In effect the Earth's gravity is sensed and used to
provide an indication of the current orientation of the mirror 70.
Electric motors 78 (only one of two illustrated) independently
drive the mirror 70 about each of the axes utilizing, for example,
a worm gear 80 and a circular rack gear 81. A mirror controller
network node 86 includes a tracking device, typically an electronic
processor, that provides information about the current position of
the Sun 14. The mirror controller network node 86 also includes a
control that is connected to the accelerometer 74, the motors 78
and the tracking device for maintaining a predetermined optimum
orientation of the mirror as the Sun moves across the sky. The
architecture and method of operation of the mirror controller
network node 86 are discussed hereafter in greater detail. Incident
solar radiation with an angle of incidence 96 is reflected off the
surface of the mirror 70 at an angle of reflection 94 so that it
strikes a thermal target 84 such as a container or conduit of a
heat transfer fluid or an array of photovoltaic cells.
[0034] The accelerometer 74 (FIG. 4) is preferably a
micro-electro-mechanical systems (MEMS) accelerometer device.
Utilizing micro-fabrication techniques a position sensor component
and signal conditioning circuit can be fabricated on a single
integrated circuit chip. Such MEMS accelerometer devices are
relatively inexpensive, durable and sufficiently accurate for
purposes of manufacturing commercial embodiments of the present
invention. Suitable MEMS accelerometer devices are the KXM52-1040
dual-axis (XY) MEMS accelerometer device and the KXM52-1 050
tri-axis (XYZ) MEMS accelerometer device, both of which are
commercially available from Kionix, Inc., 36 20 Thronwood Drive,
Ithica, N.Y. 14850 USA. See U.S. Pat. Nos. 6,149,190 granted Nov.
21, 2000 to Galvin et al. and 6,792,804 granted Sep. 21, 2004 to
Adams et al., both of which are assigned to Kionix, Inc., the
entire disclosures of which are hereby incorporated by reference.
Also suitable are the ADXL321 (two-axis) and ADXL330 (three-axis)
MEMS accelerometer devices, both of which are commercially
available from Analog Devices, Inc., One 25 Technology Way,
Norwood, Mass. 02062 USA. See U.S. Pat. Nos. 6,837,107 granted Jan.
4, 2005 to Green and 6,845,665 granted Jan. 25, 2005 also to Green,
both of which are assigned to Analog Devices, Inc., the entire
disclosures of which are hereby incorporated by reference.
[0035] While it is possible over certain rotational limits, with
appropriate calibration and alignment to use single axis sensors,
it is desirable to use three axis sensors for both magnetic field
and gravity. It is anticipated with ongoing reductions in the cost
of sensors and greater system integration that three axis sensors
will be widely available at low cost. For example, an Aichi Steel
Corporation, Electro-Magnetic Products, AMI601 sensor would be
suitable for this application. See
http://www.aichi-mi.com/3_products/ami%20catalogue%20e.pdf.
[0036] The AMI602, which would also serve in this application, is
also from Aichi and is a 6-axis motion sensor which incorporates
3-axis magnetometer and 3-axis accelerometer. The controller IC of
the AMI602 consists of a circuit for sensor elements, an amplifier
capable of compensating each sensors offset and setting appropriate
sensitivity values, a temperature sensor, a 12 bitAD converter, an
PC serial output circuit, a constant voltage circuit for power
control and an 8032 micro-processor controlling each circuit.
[0037] Again referring to FIG. 4, the pivot mechanisms 72 are
configured and arranged so that throughout the useful range of
tracking tilts, the accelerometer 74 is not rotated in an unknown
fashion about a vertical axis. If the accelerometer is rotated
about a vertical axis, the pointing direction of the mirror 70
becomes ambiguous or indeterminate. The addition of a magnetic
sensor in an alternate embodiment avoids this problem, as discussed
later. Modern compass MEMS devices which combine accelerometers
with magnetic compass sensors are known in the art, and allow the
array to be corrected for tilt, and such a device could be used in
place of the accelerometer 74.
[0038] It will be understood that a wide variation of modifications
of the embodiment illustrated in FIG. 4 are possible. For example,
the accelerometer 74 need not be directly mounted to the mirror but
could be coupled thereto through a mechanical or optical linkage.
The pivot mechanisms 72 could be replaced with an alternate pivot
mechanism such as a ball and socket or flexible joint, instead of
those employing independently movable mechanical pivots. Thus the
mirror 70 need not strictly rotate about two axes, as is the case
with the embodiment of FIG. 4 wherein rotation of the mirror 70
about one axis rotates the other axis. It will be appreciated that
it is not necessary that both axes of tilt are substantially in the
same horizontal plane when the mirror 70 is in a normal or
horizontal orientation. Other forms of motor means for driving the
mirror 70 can be employed besides the electric motor 78 and gears
80 and 81, such as hydraulic and pneumatic systems. The mirror 70
need not move in azimuth and elevation, it being sufficient that it
be capable of independent movement about two non-parallel axes.
[0039] FIG. 5 illustrates a second embodiment of the present
invention that utilizes an array 104 of individual mirrors 106 to
reflect solar radiation 110 through a skylight 102 on the roof of a
building 100 to provide internal lighting. This greatly increases
the amount of solar radiation otherwise directly entering the
interior of the building through the skylight 102 as illustrated by
incident light rays 108. The mirrors 106 may each be independently
supported and moved as illustrated in FIG. 4 or they may be
simultaneously supported and moved by a common tracking system so
that reflected light 114 strikes a fixed angle target mirror 112
and is reflected as downwardly projected light 116. The skylight
102 may be of the type sold under the SOLATUBE.RTM. trademark which
employs a conduit with a highly reflective surface. Optionally a
hot mirror 118 may be inserted in to the reflected light
transmission path to reflect away the infrared component during the
summer to avoid unwanted heating of the interior of the building
100.
[0040] FIG. 6 illustrates an alternate embodiment wherein an array
144 of flat tracking mirrors 142 reflect incident solar radiation
146 as reflected radiation 148 that passes through the window 140
of a house to provide light and heat. Again the mirrors 142 are
supported and moved in the fashion described in connection with
FIG. 4.
[0041] FIG. 7 illustrates another embodiment that utilizes an array
170 of heliostat mirrors 168 to heat a thermal target 162. The
amount of incident solar radiation 164 that is redirected as
reflected solar radiation 166 is maximized by mounting an
accelerometer 160 on each heliostat mirror 168 and using its
signals, along with tracking information to tilt each mirror 168
about its two-axis tilting support 172.
[0042] FIG. 8 illustrates another embodiment that utilizes a
plurality of heliostat mirrors 206 equipped as described in
connection with FIG. 4 in order to re-direct a maximum amount of
incident solar radiation 202 as reflected radiation 204 onto a high
temperature photovoltaic panel 200.
[0043] FIG. 9 is a block diagram of another embodiment in which a
network controller 222 controls a plurality of mirror nodes 220.
The network controller 222 may be connected to the mirror nodes 220
by a network link 226 which may be wired or wireless, fiber optic,
laser or any other well known data communications scheme. One
example is the ZIGBEE.TM. data link. Bluetooth links or other
wireless means could be used as well according to the scale of the
application. An optional mirror node training interface 224 is
provided that can be used to load the network controller 222 with
tracking data from local or remote sources that give the predicted
location of the Sun throughout the day for a given latitude,
longitude, date and time. This information is used by the
controller to compare the actual position of the mirrors with their
optimum positions so that they can be moved to maximize the
collection and/or concentration of solar radiation. Alternatively
this information may be preprogrammed into the network controller
222 or the mirror controller network node 86 (FIG. 4).
[0044] The present invention differs from conventional heliostats
that require a vertical tracking axis. In the present invention,
the Sun is tracked in both azimuth and elevation, however, tracking
is required in both axes as neither component is separately
derived.
[0045] FIG. 10 illustrates another embodiment in which a heliostat
mirror 246 is positioned to re-direct incident solar radiation 250
as reflected solar radiation 252 to strike a target 248 utilizing
mechanisms similar to those described in connection with FIG. 4. A
vertical array of photo-sensors 240 detect reflected radiation 252
and their signals are used to position the mirror 246 so that the
reflected radiation will strike the target 248. A Sun hood 254 may
be used with each photo-sensor 240 to prevent it from detecting
significant amounts of incident solar radiation 250. The spacing
242 between the photo-sensors 240 can be optimized relative to the
dimension 244 of the mirror 246.
[0046] FIG. 11 is a block diagram illustrating one embodiment of
mirror controller network node 86 of the embodiment of FIG. 4. A
PIC micro-computer based control 300 provides the basic
intelligence and control through appropriate input/output
interfaces. Position information is received from the accelerometer
302. First and second axis motors 304 and 306 are appropriately
driven. AC power or some other power source 310 such as solar or
battery power provides power to the control 300. In order for the
mirror to be optimally pointed, it is necessary for the control 300
to compare the actual position of the mirror to the current
position of the Sun and make the appropriate adjustments. Data
regarding the predicted location of the Sun is pre-programmed into
the control 300, in which case a user interface (not illustrated)
is necessary for a user to enter the correct latitude, longitude,
date and time during initial set up. This interface could be a
keypad or a connection to a PC or PDA, for example. Optionally, a
Global Positioning System (GPS) and time base receiver 312 may be
connected to the control 300 to provide this information. A wired
or wireless network link 308 connects the control to a remote
location for monitoring or control.
[0047] FIG. 12 is a flow diagram illustrating one embodiment of a
method of operation of the control of FIG. 11. Initially in step
314 the starting parameters are acquired, including latitude and
longitude, time, tilt axis orientation to the North, and the
estimated azimuth and elevation of the mirror. Latitude, longitude
and time can be obtained via the network. In step 316 the processor
calculates the position of the Sun. In step 318, using signals from
the accelerometer, and data from a look up table, the control
calculates the movement of the mirror about each axis necessary to
achieve the optimum orientation. In step 320, the motors are driven
by the control the move the mirror as needed to obtain the optimum
orientation. If the accelerometer signals do not indicate mirror
motion, an ERROR message is generated and transmitted and/or
displayed. In step 322, the control continues to track the Sun in
order to engage the target.
[0048] FIG. 13 is a flow diagram of another embodiment of a method
of operation of a solar tracking device in accordance with the
present invention.
[0049] FIGS. 14-20 illustrate another embodiment of the present
invention that utilizes weight-tensioned mechanisms to pivot the
mirror. The embodiment 400 includes a planar square mirror 402
whose corners are supported by four cable hook corners 404. A small
yoke 406 (FIGS. 15 and 19) has a square surface which is secured to
the center of the rear side of the mirror 402 by suitable adhesive.
Small yoke 406 is connected for independent rotation about two axes
to a tall yoke 408 by a cross piece 410. The base of the tall yoke
408 is secured by screws 412 and nuts 414 (FIG. 19) to a
cylindrical cap plate 416. The cylindrical cap plate 416 is mounted
on the upper end of a support structure in the form of a hollow
vertical support post 418.
[0050] A lower tension wire 420 (FIG. 18) has one end connected to
the uppermost cable hook corner 404 and its other end connected to
the lowermost cable hook corner 404. An upper tension wire 422
(FIGS. 18 and 19) has an intermediate segment wrapped around an
upper drive pulley 424 (FIG. 20) and its ends connected to
respective ones of the laterally spaced cable hook corners 404. The
lower tension wire 420 is connected to a lower counter-weight drive
assembly 426 (FIG. 20). The upper tension wire 422 is connected to
an upper counter-weight drive assembly 428 on which the upper drive
pulley 424 is mounted. The lower tension wire 420 passes through
large rectangular apertures 430 (FIG. 18) on opposite sides of the
lower portion of the support post 418. The upper tension wire 422
passes through large rectangular apertures 432 formed on opposite
sides of the upper portion of the support post 418, and spaced
ninety degrees from the apertures 430. The intermediate segment of
the lower tension wire is wrapped around a lower drive pulley 434
(FIG. 20) mounted on the lower counter-weight drive assembly
426.
[0051] Each of the counter-weight drive assemblies 426 and 428
(FIG. 19) has a similar construction, and therefore, only one need
be described. The lower counter-weight drive assembly 426 includes
a lower micro-motor 436 (FIG. 20), a lower rotation restraint
mechanism 438, a shaft connector 440, and a lower worm gear drive
442. These mechanisms allow the lower tension wire 420 to be driven
by the lower drive pulley 434 to pivot the mirror 402 about a
horizontal axis. Similar mechanisms in the upper counter-weight
drive assembly 428 allow the upper drive pulley 424 to drive the
upper tension wire back and forth to pivot the mirror 402 about a
tilted (off vertical) axis. The lower counter-weight drive assembly
426 includes a cylindrical drive mount 444 (FIG. 20) and a
ring-shaped counter-weight 446. The cylindrical drive mount 444 has
oval apertures 448 (FIG. 14) formed on opposite sides thereof to
allow ingress and egress of the lower tension wire 420.
[0052] The lower and upper counter-weight drive assemblies 426 and
428 are capable of reciprocal vertical motion within the bore of
the support post 418. A control circuit (not illustrated) receives
input from a MEMS accelerometer as previously described and causes
the micro-motors of the lower and upper counter-weight drive
assemblies 426 and 428 to move the mirror 402 into the optimum
position for reflecting solar radiation onto a target (not
illustrated in FIGS. 14-20), such as a photovoltaic array, heat
exchanger, etc.
[0053] Referring now to FIG. 21, a heliostat mirror (1000) is
supported by a vertical tubular support (1002). A motorized tilt
mechanism (not shown) provides rotation around an approximately
horizontal axis (1004) for tracking solar elevation. A second
motorized rotation mechanism (not shown) provides rotation around
an approximately vertical axis (1006) for tracking the sun (1018)
in azimuth across the sky. The mirror need not be flat but might
have some curvature in one or more directions to allow the solar
energy to be brought to a tight focus. A sensor and control package
(1008) can be mounted anywhere on the mirror or the supporting
structure. Preferably, all the sensors and controls are integrated
into a single package to reduce cost and the need for
interconnecting cables. In this case, the sensor and control
package needs to be mounted so that it is subject to both tilt and
rotation during mirror positioning. One or more magnetic sensors
1010 are used to sense the earth's magnetic field (1012) to
determine rotational position around an approximately vertical
axis. One or more accelerometers included in the sensor package
1008 are used to sense the gravity vector (1014) and determine
rotational position around an approximately horizontal tilt axis
1004. The magnetic sensor may be a three-axis magnetic field sensor
which provides x, y, and z data in response to measurement of the
earth's magnetic field.
[0054] A separate sensor such as the Honeywell HMC5843 available
from Honeywell International Inc., 101 Columbia Road, Morristown,
N.J. 07962 or the AK8973S available from Asahi Kasei Microsystems
(AKM Semiconductor) at 1731 Technology Drive, San Jose, Calif.
95110, are examples which would serve. Alternatively a combined
integrated circuit including both three-axis accelerometer and
three-axis compass, such as the AMI602 6-axis motion sensor which
incorporates 3-axis magnetometer and 3-axis accelerometer
(available from Aichi Steel Corporation at 1 Wano-wari, Arao-machi,
Tokai-shi, Aichi-ken, 476-8666 Japan) or the STMicroelectronics
LSM303DLH geomagnetic module combining magnetic-field and
linear-acceleration sensing would serve. Where a combined sensor
unit is used, separate magnetic sensors 1010 are dispensed with as
both the gravitic vector 1014 and the magnetic vector 1012 are
measured by the combined unit.
[0055] For maximum durability, the sensor and control package can
be mounted behind an uncoated transparent section of glass mirror.
Optical sensors to determine the position of the sun can be
integrated into the sensor and control package. The same suite of
optical sensors can further be used to determine the relative
position of the solar energy target. Various means of building
optical sensors to sense light direction are known in the art.
Optionally, photovoltaic cells can be integrated into the sensor
and control package or optionally mounted in an adjacent fashion
(1011). Batteries or capacitors can be used to store the energy
from the photovoltaic cells to provide power to operate both
motorized rotation axes. Alternatively wired power (not shown) can
be used. A wireless link (1016) or a wired link (not shown) can be
used to remotely control each mirror and exchange data between each
mirror's control system and a centralized control facility. If a
wireless link is employed, a mesh networking topology is preferably
used to allow data and control signals to be communicated across a
heliostat array of large area extent. A large heliostat array might
be usefully employed to produce hydrogen fuel by photo-catalytic
means.
[0056] Control signals from the mirror control system to each
motorized rotation axis might be by wireless means. For lowest
possible cost and long terms reliability it is desirable to reduce
the number of cables, wires, and connectors as possible. Power to
run the axis rotation motors may be provided by a hardwired means
while control might be provided by wireless means. Rotation motors
may alternatively each have their own small photovoltaic panel and
energy storage means.
[0057] FIG. 22 illustrates a block diagram of the control system
for the embodiment of FIG. 21. In FIG. 22, a controller block
(2216) receives data from magnetic sensors (2200) which sense
rotation around an approximately vertical axis and acceleration
sensors (2202) to sense tilt around an approximately horizontal
axis to provide signals indicative of heliostat mirror position.
Optionally, photo sensors (2204) may be used to establish the
position of the heliostat relative to the sun, or to a target with
an optical beacon. In FIG. 22, the option of using photovoltaics to
power the system is illustrated including photovoltaic cells
(2218), a power-conditioning block (2220), and a power storage unit
(2222) which in turn communicates and supplies power to the
controller block (2216). Further, in FIG. 22, the controller block
(2216) is illustrated with a communication link via a ZigBee module
(2214) which in turn is in communication with a mesh network (2224)
allowing coordination of the local system with a remote solar array
controller (2226). The dashed line represents an alternative energy
source (2230) by usual wired connection to the energy grid, a local
generator, or other energy supply. The controller block (2216), by
means of emitted control signals, governs the activation of a motor
drive (2208) which in turn controls two axes, one approximately
vertical (2210) and one approximately horizontal (2212). An
optional wireless link (2232) is also shown for data relay between
the controller block and the motor control electronics if separate
power is available.
[0058] FIG. 23 illustrates a detailed block diagram of exemplary
components of magnetic sensors and accelerometers and their
relationship to the axis motors of an embodiment similar to FIG.
21. In FIG. 23 an integrated circuit system 2314 contains both
magnetic sensors and accelerometers and their appropriate
circuitry. In FIG. 23 the integrated circuit 2314 is an AMI602
6-axis sensor with integrated amplifier, 12-bit analog-digital
converter and an 8032 microprocessor controlling the circuits of
the integrated circuit 2314.
[0059] Three sensors measure values for magnetic orientation
relative to the earth's magnetic field on an X axis 2318, a Y axis
2320, and a Z axis 2320. Three accelerometer sensors measure
acceleration at the same time along the X axis 2324, Y axis 2326,
and Z axis 2328. These sensor signals are processed through a
converter into digital data transmitted to a microcontroller 2310.
In FIG. 23, the microcontroller 2310 is a 64-pin PIC 18F6722
available from Microchip Technology Inc., 2355 West Chandler Blvd.,
Chandler, Ariz., USA 85224-6199. The microcontroller 2310
communicates with the AMI602 integrated circuit 2314 through a
standard I.sup.2C bus 2323. A real-time clock chip 2316 also
communicates with the microcontroller 2310 on the I.sup.2C bus
2323. In FIG. 23 the real-time clock chip 2316 is a DS 1340C with
built-in calendar and clock, available from Maxim/Dallas
Semiconductor, at Maxim Integrated Products, Inc., 120 San Gabriel
Drive, Sunnyvale, Calif. 94086.
[0060] The microcontroller 2310 also receives digital GPS time base
information from an optional GPS/time base receiver 2312;
alternatively it may receive data streams from an onboard clock
2316 and perform look-up operations using an on-board or remote
data lookup table. An optional ZigBee communication module 2319 and
the optional GPS/time base receiver 2312 communicate to the
microcontroller 2310 by means of an on-board universal
synchronous/asynchronous receiver/transmitter, or USART 2321. The
microcontroller 2310 is capable of sending pulse-width modulated
data on two output pins, P3A and P3D, shown in FIG. 23 as a
combined PWM port 2325. Motor control commands are transmitted by
means of the PWM port 2325 to a first axis motor 2327 controlling
the horizontal axis of the solar collector, and a second axis motor
2329 controlling the vertical axis thereof.
[0061] FIG. 24 is a flow chart of the control logic. By calculating
the present orientation of the sun and the measured present
orientation of the line-of-direction axis of the mirror such as
1000 in FIG. 21, the microprocessor may derive delta values for
each axis to align the mirror 1000 (FIG. 21) with the sun 1018
(FIG. 21). These delta values are in turn used to compute motor
commands to drive the horizontal axis motor 2326 and the vertical
axis motor 2334 in FIG. 23. In FIG. 24 the control cycle begins
with a step 2402 of getting the real-time clock value and a
following step 2404 of looking up the sun's real-time position and
translating to azimuth and elevation values. A test step 2406 is
done to determine whether the sun is over the horizon or not; if it
is not, the mirrors are parked (step 2408) and a sleep timer is
initiated (step 2410). The system is placed in a sleep state 2412
until such time as a sleep timer interrupt 2401 occurs. The sleep
timer interrupt may be caused by passage of a specified period, or
by an external signal, or a pre-defined clock moment, or by a
photo-sensor trigger event, for example. If test step 2406
determines the sun is over the horizon, the system must then get
the zero baseline value for the accelerometers (step 2414) and
their current values (step 2416). Likewise, it gets baseline values
for the magnetic sensors (step 2418) on three axes, and their
current values (step 2420). Based on these values the system
computes current azimuth and elevation in Step 2422, and compares
them to the required azimuth and elevation in step 2424. A test is
then done in Step 2426 to determine whether the delta between the
required azimuth and elevation and their present values is below a
pre-defined tolerance threshold. If the delta is within tolerable
limits the motors are halted (step 2428) and the sleep timer
initiation step 2410 is executed. If the delta exceeds tolerable
limits the system must then compute the amount of change required
in azimuth and elevation (step 2430) and translate that change into
a change for the horizontal axis and the vertical axis (step 2432).
These values must in turn be translated into motor control values
in Step 2434 resulting in motor control transmissions sent to the
first axis motor 2326 (FIG. 23) and the second axis motor 2328
(FIG. 23) in Step 2436.
[0062] It will be clear to one skilled in the art that the use of
other particular sensors and other configurations will also prove
workable. The particular components described are mentioned as
examples of different embodiments.
[0063] While several preferred embodiments of the present invention
have been described, and some variations thereof, further
modifications will occur to those skilled in the art. For example,
any of the embodiments described herein can utilize accelerometers
alone, or accelerometers and magnetic sensors. Therefore the
protection afforded the subject in invention should only be limited
in accordance with the following claims.
* * * * *
References