U.S. patent application number 12/823138 was filed with the patent office on 2010-12-30 for 1-axis and 2-axis solar trackers.
Invention is credited to Datong Chen.
Application Number | 20100326427 12/823138 |
Document ID | / |
Family ID | 43369461 |
Filed Date | 2010-12-30 |
![](/patent/app/20100326427/US20100326427A1-20101230-D00000.png)
![](/patent/app/20100326427/US20100326427A1-20101230-D00001.png)
![](/patent/app/20100326427/US20100326427A1-20101230-D00002.png)
![](/patent/app/20100326427/US20100326427A1-20101230-D00003.png)
![](/patent/app/20100326427/US20100326427A1-20101230-D00004.png)
![](/patent/app/20100326427/US20100326427A1-20101230-D00005.png)
![](/patent/app/20100326427/US20100326427A1-20101230-D00006.png)
![](/patent/app/20100326427/US20100326427A1-20101230-D00007.png)
United States Patent
Application |
20100326427 |
Kind Code |
A1 |
Chen; Datong |
December 30, 2010 |
1-axis and 2-axis solar trackers
Abstract
A one-axis sun position tracking device with its rotation axis
parallel to the rotation axis of the Earth, rotates perpetually at
a constant speed in the opposite direction of the Earth's rotation.
This device comprises a shaft that is aligned to the Earth's polar
axis, one or more crossbars are rigidly attached to and
perpendicular to the shaft, solar energy collectors are mounted on
the crossbar and could rotate around the crossbar that defines
declination angle. A self-latched declination angle adjustment
mechanism keeps the declination angle constant at most of time. A
drive mechanism keeps this solar tracker to rotate perpetually. An
automatic and abrupt declination angle change will keep the
declination angle updated to correct value each day. A similarly
configured two-axis tracker that continuously updates its
declination angle by a mechanism derived from a differential
coaxial rotation. Two independent driving mechanisms control the
speed and/or duration of the two coaxial rotations, and are
programmed to eliminate all tracking errors from various
sources.
Inventors: |
Chen; Datong; (Fremont,
CA) |
Correspondence
Address: |
Datong Chen
741 Saltillo Pl
Fremont
CA
94536
US
|
Family ID: |
43369461 |
Appl. No.: |
12/823138 |
Filed: |
June 25, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61269462 |
Jun 26, 2009 |
|
|
|
Current U.S.
Class: |
126/601 ;
126/607 |
Current CPC
Class: |
Y02E 10/47 20130101;
G05D 3/105 20130101; F24S 2030/137 20180501; F24S 30/458 20180501;
H02S 20/30 20141201; F24S 30/428 20180501; Y02E 10/50 20130101;
F24S 2030/134 20180501; H02S 20/00 20130101 |
Class at
Publication: |
126/601 ;
126/607 |
International
Class: |
F24J 2/40 20060101
F24J002/40; F24J 2/38 20060101 F24J002/38 |
Claims
1. A 1-axis solar tracking device consists: a rotating shaft with
one or multiple crossbars perpendicularly attached to it, this
shaft is mounted along the celestial rotation axis of the Earth,
rotates continuously and perpetually at constant speed of one turn
per day, in the opposite direction of the Earth's rotation solar
energy collectors mounted on the crossbar and can rotate around
this crossbar for at least .+-.231/2.degree., this rotation defines
declination angle, a self-latch mechanism keeps the declination
angle constant most of the day, an automatic and non-continuous
declination angle update mechanism.
2. The 1-axis solar tracking device of claim 1, the mechanism that
determines the declination angle of the solar energy collectors
consists: a gear, which is mounted on a beam that is rigidly
attached to the main rotating shaft, a rod with one end pivot
connected to this gear and the other end pivot connected the solar
energy collector, a steady rotation of the gear translates into an
approximate sinusoidal oscillation of the declination angle of the
solar energy collector through the mechanic linking rod, the
amplitude of the oscillation of the declination angle is
231/2.degree..
3. The 1-axis solar tracking device of claim 1, the self-latch
mechanism that keeps the declination angle constant consists: a
spring loaded ball pushes against the notch between two adjacent
teeth of a gear, prevents the gear from rotating freely, the
strength of the spring and the gear tooth slope determine the
workload of this latch, an additional worm gear stage provides a
unidirectional and stronger latch of the declination angle,
4. The 1-axis solar tracking device of claim 1, the automatic and
non-continuous declination angle update mechanism consists: an open
worm tooth which is spiral shaped, its cross section matches that
of the worm gear, the open worm tooth which is fixedly mounted on
the ground, sits roughly in a plane that is perpendicular to the
main rotating shaft, the distance between one end of the open worm
tooth to the center of the main rotating shaft is different from
the distance between the other end of the open worm tooth to the
center of the main rotating shaft, the difference is one tooth
pitch of the worm gear, during most time of a day, the open worm
tooth does not engage with anything; at a pre-determined time of
the day, the open worm tooth engages with the worm gear, and forces
the worm gear to turn one notch during the engagement.
5. The 1-axis solar tracking device of claim 1, once the initial
declination angle is set correctly, and the gear ratio is set close
enough to 365.242199, perpetual rotation of the main rotating shaft
will provide a very good solar tracking. However, if the gear ratio
is set slightly different from the ideal number 365.242199,
periodical manual adjustments is needed to reset the accumulated
error in declination angle. For example, if the gear ratio is set
to 365, then only one manual declination angle adjustment every
four years is needed, which is simply to manually turn the self
latched gear by one notch once every four years; similarly, if the
gear ratio is set to 366 or 364, then 3 or 5 manual adjustments
every four years are needed, so on and so forth.
6. The 1-axis solar tracking device of claim 1, to correct the
error due to non-uniform day length, that is because each day is
not exact 24 hour, the main rotating shaft may be programmed to
rotate a little faster or slower from day to day to counter such
variance, or only to rotate a little faster or slower during a
portion of night time is enough to compensate the day length
variance problem.
7. A variance of the 1-axis solar tracking device of claim 1, if a
ratchet is incorporated in the declination angle adjustment
mechanism, the main rotating shaft could have an option to rotate
back and forth while the declination angle is still updated as if
the main rotating shaft was rotate perpetually, with all the
benefit of its declination angle fixed during each day, and
abruptly updates its declination angle daily and automatically.
8. A 2-axis solar tracking device consists: a rotating shaft with
one or multiple crossbars perpendicular attached to it, this shaft
is mounted essentially along the celestial rotation axis of the
Earth, rotates continuously and perpetually at constant speed of
one turn per day, in the opposite direction of the Earth's
rotation, solar energy collectors mounted on the crossbar and can
rotate around this cross bar for at least .+-.231/2.degree., this
rotation defines declination angle, a co-axial rotation mechanism,
though mechanical link, changes the declination angle continuously,
an error correction program controls both rotations.
9. The 2-axis solar tracking device of claim 8, the mechanism that
determines the declination angle of the solar energy collectors
consists: a gear, which is mounted on a beam that is rigidly
attached to the main rotating shaft, a rod with one end pivot
connected to this gear and the other end pivot connected the solar
energy collector, a steady rotation of the gear translates into an
approximate sinusoidal oscillation of the declination angle of the
solar energy collector through the mechanic linking rod, the
amplitude of the oscillation of the declination angle is
231/2.degree..
10. The 2-axis solar tracking device of claim 8, the mechanism that
continuously changes the declination angle consists: a gear, which
rotates coaxially with the main rotating shaft, engages with the
other gear whose rotation causes the oscillation of the declination
angle, two independent driving mechanisms that drive this gear and
the main rotating shaft, the differential rotation speed between
this gear and the main rotating shaft, combines with the gear ratio
in the drive train, continuously changes the declination angle.
11. The 2-axis solar tracking device of claim 8, the error
correction program controls both rotations can slightly adjust both
rotation speed and/or duration; that will compensate polar tracking
errors from all sources. Those small errors are well known and
could be tabulate into control programs.
12. A variance of the 2-axis solar tracking device of claim 8, the
driving mechanism have an option to rotate the main rotating shaft
back and forth with all the benefit of accurate polar tracking
during the daylight time.
13. A variance of the 2-axis solar tracking device of claim 8, the
error correction program can be extended to counter tracking error
when this 2-axis solar tracker is not mounted in polar orientation.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of provisional
application Ser. No. 61/269,462, filed 2009 Jun. 26 by the present
inventor.
FEDERALLY SPONSORED RESEARCH
[0002] Not applicable
SEQUENCE LISTING
[0003] None
BACKGROUND
[0004] 1. Field
[0005] This invention relates to solar energy collections,
specifically to sun position tracking that is used in sunlight
concentration and collection.
[0006] 2. Prior Art
[0007] Sun position tracking is very important to solar energy
collection, especially for solar concentrators. Different
implementations have been invented, they could be categorized as
1-axis tracking and 2-axis tracking. 1-axis tracking is simple,
however, it is commonly believed that 1-axis tracking has a poor
tracking capability, that is not true in a special case; 2-axis
tracking can have a very good tracking accuracy, however, it is
usually very complicated because of the coupled rotation of
2-axis.
[0008] Most 2-axis tracking methods are using local coordinate
system, or called horizontal mount. It offers convenience of low
profile of installation, however, the angular motion control is
very complicated. The first rotation axis is typically
perpendicular to the local horizontal plane, a platform is built
rotating around this axis, which sets the azimuth of the solar
tracker; and the second rotation axis is built on this platform and
determines the elevation of the solar tracker. Rotation around both
axes are nonlinear motions, usually servo motors with input from
sun position sensor are used to drive the tracker.
[0009] 2-axis tracking can also be done in polar coordinate system,
or called equatorial mount. It offers convenience of simple
tracking. The first rotation axis is typically parallel to the
rotation axis of the Earth, a platform is built rotating around
this axis; and the second rotation axis is built on this platform
and follows the seasonal change of the declination of the Sun.
Rotation of the first axis is very close to constant speed of one
turn per day, usually a clock motor is good enough to drive this
axis; rotation of the second axis is sinusoidal and very slow,
oscillates once per year, occasional manual adjustment or some kind
of automatic rotation were proposed.
[0010] In U.S. Pat. No. 4,202,321, Volna described a hybrid solar
tracking device, which he used both local and polar coordinate
systems. He used azimuth (axis 13) and elevation (axis 16) angles
in a local coordinate system to define the orientation of his solar
energy collector 29, however, he used polar axis 23 and declination
"point axis 27" to describe his drive mechanism in a polar
coordinate system, and used spindle 26 to connect both as "A
coordinate transformation apparatus" (claim 8). In this way, he
avoided the complex rotation control in the local coordinate
system. All four axes: azimuth axis 13, elevation axis 16, polar
axis 23, and declination "point axis 27" need to intersect at the
same point so that he could use it as an axis converter. In the
polar coordinate system, he proposed a generic concept of manual or
automatic adjustment of the declination angle by sliding the
"spindle 26", hence the "pointing axis 27", back and forth by
.+-.231/2.degree.. In column 4, line 49, "Alternatively, in a more
sophisticated and automatic embodiment of the invention,
appropriate drive mechanisms may be connected to automatically
slide bearing blocking 25 over datum surface 24 in timed
relationship with the days of the year." However, he did not give
any specific method to implement such automatic adjustment of the
declination angle. Also, Volna's implementation is an axis
converter, not a polar tracking device, it has mechanical
limitation of rotations that the device he proposed could not
rotate over 360.degree., or rotate perpetually since the circular
sector arm 20 collides with the pedestal 11 at certain angle. It
has to rotate back and forth each day, which defeats one of the
major advantages of polar tracking.
[0011] In U.S. Pat. No. 4,402,582, Rhodes described a polar
tracking device and a method to automatically adjust the
declination angle. However, the continuous declination angle
adjustment mechanism is only approximately sinusoidal, there is no
way mentioned to correct such error. In addition, the gear ratio is
set to be 365:1, which will lead to accumulation of error since a
year is not exact 365 days, and it is not easy to implement a more
accurate gear ratio into such parasitic driven apparatus. Also, the
parasitically powered adjustment only works when it rotates
continuously, it cannot have the option of rotating back and
forth.
[0012] In U.S. Pat. No. 4,368,962, Hultberg described a polar
tracking device and a more sophisticate method to adjust the
declination angle, and he further implemented error correction
mechanism to correct various errors which compensates the errors
from the imperfect drive train, eccentricity of the earth's orbit
around the sun, etc. It is a very complicate implementation with
too many gears, and multi-section coaxial rotations. The mechanical
link "space crank" requires that four axes to intersect at one
point. All make it difficult to practice.
[0013] 3. Objects and Advantages
[0014] To overcome the limitation of solar tracker in these prior
arts, and to simplify the implementation method, first, a 1-axis
solar tracker in polar orientation with a latched declination angle
is invented, and this declination angle is only updated abruptly
periodically and automatically, it offers the simplicity of
implementation and reasonably good tracking accuracy. Second, a
solar tracker with slight different implementation that
incorporates differential coaxial rotation is invented, it is
particularly applicable to polar tracking, and could be further
generalized to any 2-axis solar tracking configuration.
SUMMARY
[0015] As known in the prior arts, polar tracking has advantage of
simple driving and control requirement, while the rotation around
the polar axis is almost at steady speed: 360 degrees per day, the
declination angle change is very slow, only changes
.+-.231/2.degree. back and forth per year. It would be a good
approximation that the declination angle could be kept constant for
a day. As a matter of fact, the declination angle change rate
varies, its fastest change rate is less than .+-.0.1.degree. for
.+-.6 hour, while the sun itself has a .+-.0.267.degree. angular
size. So if we could set the declination angle at correct value,
keep it fixed through the day while we track the sun using only one
axis polar tracking, we still have good enough tracking accuracy.
Of course we have to set the next correct declination angle for the
next day, a manual adjustment is tedious, a continuous adjustment
is an overkill as others already proposed in the prior arts and is
unnecessary. An automatic, non-continuous, and abrupt adjustment of
the declination angle of the polar tracker is an object of the
present invention.
[0016] The proposed apparatus has a rotatable shaft orientated
substantially parallel to the rotation axis of the earth. One or
more crossbars are rigidly and perpendicularly attached to this
shaft, solar energy collectors are mounted on these crossbars and
could rotate around these crossbars to define different declination
angle. Those solar energy collectors are connected to a set of
gears by a mechanical link, and different position of the gears
determines the declination angle of the solar energy collectors.
One gear in the gear chain is usually latched, for example, by a
spring load ball against a notch, which causes the whole gear chain
and the declination angle to be kept at a fixed position. When
correctly forced at the correct time, the latched gear will be
unlatched, turned to the next correct position, and reapply the
latch. In this example, the spring will be compressed, the ball
yields its way of blocking the notch so that the gear could rotate
until the ball falls into the next notch; at that time, the
external force is removed and the spring loaded ball latches the
gear at the new position, which defines the next declination angle
for the solar tracker.
[0017] This 1-axis polar tracking with automatic and non-continuous
declination angle update should provide enough accurate sun
position tracking with simple implementation requirement. In order
to further improve sun position tracking, this non-continuous
declination angle adjustment is not enough. This basic tracking
apparatus can be modified to implement more error correction
mechanism, a coaxial differential rotation method could achieve
that goal, with both rotations near constant speeds. While the main
shaft with solar energy collector(s) rotates at the constant speed
of one turn a day, the same as mentioned above, a gear that rotates
coaxially either faster or slower than the main shaft, this
relative motion, goes though mechanical link, can continuously turn
the declination angle. Both rotation speeds and durations can be
controlled by simple counters, that small adjustments of rotation
speeds and/or durations could easily provide error correction for
earth's eccentric orbit around the sun and for all other causes,
both yearly and daily.
DRAWINGS
Figures
[0018] FIG. 1 is a perspective view of a 1-axis solar tracker,
[0019] FIG. 2A is a zoom in view of the gear with self-latch
mechanism,
[0020] FIG. 2B shows a cross-section view of the self-latch gear,
when it is in latched position,
[0021] FIG. 2C shows a cross-section view of the self-latch gear,
when the latch starts to yield under force,
[0022] FIG. 2D shows a cross-section view of the self-latch gear,
when it is in un-latched position,
[0023] FIG. 2E shows a cross-section view of the self-latch gear,
when it is latched in a new position,
[0024] FIG. 3A shows a perspective view of the worm gear starts to
engage with the "open worm tooth",
[0025] FIG. 3B shows a bottom view at start of the engagement of
the worm gear with the open worm tooth,
[0026] FIG. 3C shows a bottom view at the finish of the engagement
of the worm gear with the open worm tooth,
[0027] FIG. 4 is a perspective view of a 2-axis solar tracker,
REFERENCE NUMERALS
[0028] 10 rotatable shaft, [0029] 11 driving motor, [0030] 12 lower
support, [0031] 14 upper support, [0032] 15 polar axis, [0033] 20,
22 crossbars, [0034] 30 solar energy collector, [0035] 35 plate,
[0036] 37 universal joint, [0037] 40 rod, [0038] 50, 70 worm gears,
[0039] 51, 65 gears, [0040] 52, 62 beams, [0041] 60 worm, [0042] 61
motor, [0043] 63 slot, [0044] 64 spring, [0045] 66 ball, [0046] 71,
72, 73 inner teeth of a worm gear, [0047] 80 open worm tooth,
DETAILED DESCRIPTION
[0048] A 1-axis polar solar tracker is shown in FIG. 1, a rotatable
shaft 10 is installed between a lower mount 12 and an upper support
14. Both 12 and 14 are fixed on the ground, and are installed in
such a way that the shaft 10 can rotate along axis 15, which is
essentially parallel to the celestial rotation axis of the Earth.
Crossbars 20 and 22 are rigidly attached to the rotatable shaft 10,
and the crossbars 20 and 22 are perpendicular to the rotatable
shaft 10. There are more support beams 52 and 62 rigidly attached
to the rotatable shaft 10. Solar energy collector 30 is mounted on
the crossbar 20 and it could rotate around the crossbar 20 for at
least .+-.231/2.degree., which defines the declination angle. If we
establish xyz coordinates here, center line of the shaft 10 as
y-axis, center line of the crossbar 20 as x-axis, then we clearly
know the z-axis is perpendicular to both x and y. the angle between
the normal of the solar energy collector surface and the z-axis is
the declination angle. More solar energy collectors could be
similarly mounted on crossbar 22 and are omitted for illustration
simplicity. One side of the solar energy collector 30 is attached
to plate 35, which is pivot connected to one end of a rod 40 by a
universal joint 37, the other end of the rod 40 is pivot connected
to a worm gear 50, which is mounted on the beam 52. As the worm
gear 50 turns, when the rod 40 goes down to the lowest point
corresponds to 23.5.degree. declination angle of the solar energy
collector 30, and when the rod 40 goes up to the highest point
corresponds to -23.5.degree. declination angle of the solar energy
collector 30. In a very good approximation, a steady rotation of
the worm gear 50 translates into a sinusoidal oscillation of the
declination angle of the solar energy collector 30 through the
mechanic link 40. The worm gear 50 is driven by a worm 60, which is
connected to another worm gear 70. The worm gear 70 is mounted on
beam 62, and is usually latched to the beam 62 as explained in the
next paragraph. Everything mentioned above forms a temporary rigid
body on shaft 10, and is driven by motor 11 to rotate at a constant
speed along polar axis 15 perpetually. There is an "open worm
tooth" 80 which is fixedly mounted on the ground, and is shown not
touch any other part.
[0049] FIGS. 2A, 2B, 2C, 2D, and 2E illustrate a generic self-latch
mechanism of the gear 70 on the beam 62. FIG. 2A is a zoom-in 3D
view of the tracker near the gear 70, a latching ball 66 is
visible. FIG. 2B shows a cross-section view of the gear 70 on the
beam 62. The gear 70 has the same number of outer teeth as that of
inner teeth. 20 teeth on the gear 70 are shown for illustration
purpose only, exact number of teeth varies by design. A spring 64
is housed inside a slot 63 which is positioned in radial direction
of the beam 62, this spring 64 pushes a ball 66 outward, against
the notch between two adjacent inner teeth 71 and 72 of the gear
70, prevents the gear 70 from rotating around the beam 62 freely.
The strength of the spring 64 and the inner tooth slope determine
the workload of this latch. When enough tangential force is applied
to gear 70, the inner tooth 72 will push the ball back to the slot
63, as shown in FIG. 2C. If the gear 70 continue to rotate, as
shown in FIG. 2D, the spring loaded ball 66 has no latch function
to the gear 70 until one tooth interval has been rotated, as shown
in FIG. 2E, at this time, the ball 66 will be pushed out by the
spring 64 again, positioned between the inner teeth 72 and 73 of
the gear 70. If the tangential force is removed, the gear 70 is now
latched at a new position.
[0050] As seen in FIG. 1, this latched gear 70 is connected to worm
60, which in turn drives the gear 50. The position of gear 50
determines the declination angle of the solar energy collector 30
through the link rod 40, so the declination angle is latched to a
particular value. The whole assembly is rotating together on the
shaft 10 along the polar axis 15, one turn per day drive by a
single motor 11, as a 1-axis solar tracker. However, at a
pre-determined time of the day, the worm gear 70 started to be in
contact with the "open worm tooth" 80 which is fixed on the ground.
A zoom-in 3D perspective view is shown in FIG. 3A.
[0051] The "open worm tooth" 80 is a spiral shaped tooth, its cross
section matches that of the worm gear 70 as seen in FIG. 3A. This
"open worm tooth" 80 sits roughly in a plane that is perpendicular
to the polar axis 15. In this plane, as shown in FIGS. 3B and 3C,
the distance between one end of the "open worm tooth" 80 to the
center of the shaft 10 is different from the distance between the
other end of the "open worm tooth" 80 to the center of the shaft
10, the difference is one tooth pitch of worm gear 70. When the
1-axis solar tracker rotates, the worm gear 70 engages with the
"open worm tooth" 80, which forces worm gear 70 to turn one notch
during the engagement. Once the worm gear 70 leaves the "open worm
tooth" 80, the worm gear 70 is latched at a new position, one tooth
advance from the previous position.
[0052] We could choose the appropriate gear ratios so that a close
approximation of 365.242199 turns of the shaft 10 will result in
one turn of the gear 50. In theory one stage of worm gear is
enough. A 2-stage worm gear is illustrated in FIG. 1 to provide a
stronger latch of the declination angle enhanced by worm 60 to worm
gear 50, and this latch strength enhancement is unidirectional
which is a bonus feature; and to provide more accuracy and design
flexibility of gear ratio choices. More stages of gears could be
used for the same purpose; if a ratchet is incorporated, the shaft
10 could rotate back and forth while the declination angle is still
updated as if the shaft 10 rotates perpetually. This is a one axis
solar tracker in polar mount with its declination angle fixed
during each day, and abruptly updates its declination angle daily
and automatically.
[0053] To further enhance the tracking accuracy, a two-axis
tracking method is needed, that means the tracker has to adjust its
declination angle continuously. As seen in FIG. 4, a rotatable
shaft 10 is installed between a lower mount 12 and an upper support
14. Both 12 and 14 are fixed on the ground, and are installed in
such a way that the shaft 10 can rotate along axis 15, which is
essentially parallel to the celestial rotation axis of the Earth.
Crossbars 20 and 22 are rigidly attached to the rotatable shaft 10,
and the crossbars 20 and 22 are perpendicular to the rotatable
shaft 10. There is a support beam 52 rigidly attached to the
crossbar 10. Solar energy collector 30 is mounted on the crossbar
20 and it could rotate around the crossbar 20 for at least
.+-.231/2.degree., which defines the declination angle. If we
establish xyz coordinates here, center line of the shaft 10 as
y-axis, center line of the crossbar 20 as x-axis, then we clearly
know the z-axis is perpendicular to both x and y. the angle between
the normal of the solar energy collector surface and the z-axis is
the declination angle. More solar energy collectors could be
similarly mounted on crossbar 22 and are omitted for illustration
simplicity. One side of the solar energy collector 30 is attached
to a plate 35, which is pivot connected to one end of a rod 40 by a
universal joint 37, the other end of the rod 40 is pivot connected
to a gear 51, which is mounted on the beam 52. As the gear 51
turns, when the rod 40 goes down to the lowest point corresponds to
23.5.degree. declination angle of the solar energy collector 30,
and when the rod 40 goes up to the highest point corresponds to
-23.5.degree. declination angle of the solar energy collector 30.
The gear 51 is driven by another gear 65, which is rotating
coaxially with the shaft 10. Motor 11 drive the shaft 10 at a speed
of one turn a day; motor 61 drives the gear 65 at a different
speed. The differential rotation speed between the shaft 10 and the
gear 65, combines with the gear ratio of gears 65 and 51, turns the
gear 51 to rotate one turn per year. For example, if the gear 51
has 20 teeth and the gear 65 has 50 teeth, then the gear 65 turns
at speed of (365.242199.+-.1)/365.242199*20/50=1.00109516 or
0.9989048 turns per day.
[0054] With the help of two independent rotations of the shaft 10
and the gear 65, error correction for various causes could be done.
The earth orbit around the Sun is not a perfect circle, so that the
declination angle change is not a strict sinusoidal function of
time, neither is every day exact 24 hours. The simple mechanical
link 40 between the gear 51 and the solar energy collector 30 (via
the plate 35 and the universal joint 37) will not translate the
circular motion of the gear 51 into an exact sinusoidal angular
motion of the declination angle. All small angular errors for polar
axis rotation and for declination angle change, from above
mentioned causes and other causes not yet elaborated, can be easily
corrected by small adjustment of rotation speed and duration of the
shaft 10 and the gear 65, which are in turn driven by motors 11 and
61. A preferred embodiment is to let both motors 11 and 61 operated
at constant speeds at most time of a day, say 23 hours, speed up or
down a little bit at the remaining 1 hour to compensate any angular
errors for that particular day. Those small errors are well known
and could be tabulate into control programs.
[0055] If this 2-axis solar tracker is mounted in such a way that
the shaft 10 is not parallel to the celestial rotation axis of the
Earth, polar tracking assumption is no longer valid. However, with
the help of two independent rotations of the shaft 10 and the gear
65, accurate sun position tracking still can be achieved when it is
operated as a generic 2-axis solar tracker. This is particularly
useful when the orientation of the shaft 10 only slightly deviates
from the polar axis. In this case, the shaft 10 should rotate close
to constant speed, and the "declination angle" of the tracker
should change a small amount during the day. All these small
variance are well known and can be tabulate into control programs.
This optional operation mode may have new applications for this
2-axis tracker.
Operation
[0056] For the 1-axis solar tracker that is shown in FIG. 1, once
the initial declination angle and polar angle are set correctly,
motor 11 starts to drive the shaft 11 at constant speed at one turn
per day, in the opposite direction of the Earth's rotation. If the
gear ratio is set close enough to 365.242199, perpetual rotation of
shaft 10 will provide very good solar tracking. In practice, if the
gear ratio is set to 365, then only one manual declination angle
adjustment every four years is needed, which is simply to manually
turn the self latched gear 70 by one notch once every 4 years;
similarly, if the gear ratio is set to 366 or 364, then 3 or 5
manual adjustments every four years are needed, so on and so forth.
To correct the error due to non-uniform day length, that is because
each day is not exact 24 hour, this driving motor 11 may be
programmed to rotate a little faster or slower from day to day to
counter such variance, or only to rotate a little faster or slower
during a portion of night time is enough to compensate the day
length variance problem.
[0057] For the 2-axis solar tracker that is shown in FIG. 4, once
the initial declination angle and polar angle are set correctly,
motor 11 starts to drive the shaft 10 at constant speed at one turn
per day, and motor 61 starts to drive the gear 65 at constant speed
slightly faster or slower than one turn per day. In the previously
mentioned example, with gear ratio of 50 to 20, gear 65 rotates at
constant speed of 1.00109516 or 0.9989048 turns per day. Perpetual
rotation of shaft 10 and gear 65 will provide very good solar
tracking; rotate back and forth will also do the job. To correct
the error due to non-uniform day length, that is because each day
is not exact 24 hour, the driving motor 11 may be programmed to
rotate a little faster or slower from day to day to counter such
variance, or rotates a little faster or slower during a portion of
night time is enough to compensate the day length problem. To
correct non-exact sinusoidal declination angle change, the driving
motor 61 may be programmed to rotate a little faster or slower from
day to day to counter such variance. The error correction program
can be further extended to counter the non-uniform rotations when
the shaft 10 is mounted not exactly parallel to the celestial
rotation axis of the Earth, the variance is well known.
* * * * *