 |
Description  |
|
|
BACKGROUND OF THE INVENTION
The present invention relates to a device for tracking the apparent motion
of the sun across the sky and concentrating the radiant energy received
from the sun on a fixed target area. More particularly, the invention
relates to what may be described as a "ganged heliostat", that is, an
array of heliostats controlled by a single mechanism such that each
heliostat redirects rays of the sun toward a common fixed target area and
thereby concentrates the rays of the sun received over a large area to a
smaller target area.
The efficient utilization of solar energy is a problem receiving widespread
attention in industry today. One potential solution is in the development
of solar cells by the semi-conductor and allied industries for converting
the radient energy of the sun into electrical power. Most, if not all,
conventional solar cells are quite expensive and in order to be
economically viable, they must have a high efficiency. One method of
improving the efficiency of solar cells is by concentrating incident
sunlight received over a large area onto the cells. Another method is to
have the cell or associated equipment for the cell track the apparent
motion of the sun across the sky so as to maximize the amount of incident
sunlight received per cell unit area over the course of a day.
While various devices are known in the art for concentrating sunlight on a
particular solar device and/or for tracking the apparent motion of the
sun, such mechanisms have various inherent disadvantages such as being
complex, expensive, difficult to maintain and prone to gradually work out
of proper adjustment for maximum utility. Examples of these known devices
are those disclosed in U.S. Pat. Nos. 913,051 to Pope, 1,219,372 to
Butterfield, 1,938,003 to Arthuys et al, 1,876,428 to Arthuys et al,
2,022,144 to Nicholson, 2,135,997 to Arthuys, 2,712,772 to Trombe,
3,656,844 to Botskor, and 3,951,510 to Lloyd.
It is therefore an object of the present invention to provide a device for
tracking the apparent motion of the sun across the sky and for
concentrating the rays received therefrom on a fixed target area.
Another object of the present invention is to provide a device which is
relatively uncomplicated, requires a minimum amount of maintenance, is
relatively inexpensive to manufacture and requires relatively small
amounts of energy for operation.
Yet another object of the present invention is to provide a device which is
able to be adjusted so to compensate for the changes in the apparent
motion of the sun from day to day.
The invention in its broadest aspect comprises a device adapted for
tracking the motion of the sun and reflecting and thereby concentrating
rays of the sun to a fixed target area which includes at least two members
each having a reflective surface and being rotatably mounted in a frame on
an axis which passes through the center point of the member, each frame
being rotatably mounted in a common support on an axis which passes
through the center point of the member and is at a right angle to the axis
of the member, a control rod having a longitudinal axis attached to each
member such that the axis of the control rod is normal to the reflective
surface of the member and passes through the center point of the member,
guide frame means in engagement with each control rod, driving means for
moving the guide frame such that each member rotates about one axis and is
thereby capable of tracking the apparent motion of the sun, and adjusting
means for moving the guide frame means such that each member rotates
relative to the other axis.
Further objects, advantages, and features of the present invention will
become more fully apparent from a detailed consideration of the
arrangement and construction of the constituent parts as set forth in the
following specification taken together with the accompanying drawing.
DESCRIPTION OF THE DRAWING
In the drawing
FIG. 1 is a perspective view of a device in accordance with the present
invention;
FIG. 2 is a perspective view of a member and frame which form a part of the
device shown in FIG. 1;
FIG. 3 is a perspective view of the device of FIG. 1 with portions of the
device cut away;
FIG. 4 is a detailed perspective view of an offset assembly shown in FIG.
3;
FIG. 5 is a detailed perspective view of a swivel assembly shown in FIG. 3;
FIG. 6 is a sectional view of the device of FIG. 1 taken along line 6--6;
FIG. 7 is a sectional view of the device of FIG. 1 taken along line 7--7.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, there is shown a perspective view of a device 10
in accordance with the concepts of the present invention. Device 10
includes a support frame 12 on legs 14 having a major surface 18 inclined
with respect to horizontal. The support frame 12 is of a generally
rectangular configuration and has a plurality of square shaped apertures
16 on surface 18. Mounted for rotation within each aperture 16 is a member
20 having a planar reflective surface 22 such as a mirror or the like and
a frame 24 about the member. The interrelationship among member 20, frame
24 and support frame 12 is more clearly shown in FIG. 2.
In operation, device 10 is adapted to track the motion of the sun and
reflect and thereby concentrate rays from the sun to a common fixed target
area, for example, a fluid heater or a solar collector 25 containing solar
cells as shown in FIG. 1. Each reflective surface 22 of the respective
members 20 is positioned to be in a different plane so as to direct the
rays of the sun toward the collector 25. As is apparent, device 10 is
capable of directing the sunlight incident on a large area to a much
smaller area where solar energy devices such as solar cells may be used to
their full advantage.
As the sun apparently progresses across the sky during a day, the device 10
is capable of shifting the plane of each of the reflecting surfaces 22 of
the members 20 so that the rays of the sun are continually reflected
toward the collector 25. The capability of the device 10 to have the plane
of each reflective surface 22 of the members 20 changed with respect to
the support frame 12 is partially shown in FIG. 2 where the member having
the reflective surface is rotatably mounted within frame 24. The axis 26
about which member 20 is able to rotate with respect to the frame 24
passes through the center point 28 of the member. Frame 24 includes pivot
mounts 30 which are on an axis 31 which also passes through the center
point 28 of the member 20. Pivot mounts 30 are received by apertures in
the support frame (not shown) such that the frame 24 is pivotly mounted
therein.
Attached to member 20 is a control rod 32 having a longitudinal axis 34.
The control rod 32 is positioned such that its axis 34 is normal to the
surface of member 20 and passes through center point 28 of the member. The
length of control rod 32 is not believed to be critical, however, the
longer the control rod, the more precise is the control that can be
exercised over the member 20.
FIG. 3 is a cut-away view of the device 10 of FIG. 1 which illustrates a
mechanism for controlling the movement of the members 20 of the device 10.
Extending through both sides of support frame 12 are shafts 36 and 38
which are able to rotate about their respective longitudinal axes. Shaft
36 is driven by motor 40 and rotation of shaft 36 is transferred to shaft
38 by a suitable means such as by the shown cable and pulley arrangement
42.
Suspended from shafts 36 and 38 are four offset assemblies 44 which in turn
support the guide frame 46. The construction of an offset assembly 44 is
more clearly shown in FIG. 4. The guide frame 46 includes shafts 48 and
50, each having a longitudinal axis parallel to the axis of shafts 36 and
38. Shafts 48 and 50 each pass through longitudinal members 52 of guide
frame 46 which are securely attached to cross members 54. Shafts 48 and 50
are able to rotate within longitudinal members 52 but are restrained from
axial movement by bushings 55 on each shaft.
Located on the longitudinal members 52 of the guide frame 46 are a
plurality of swivel assemblies 56, each swivel assembly adapted to engage
a control rod 32. The structure of a swivel assembly 56 is more clearly
shown in FIG. 5. Also attached to guide frame 46 is adjusting means 58 for
shifting and then fixing the guide frame 46 in directions parallel to the
longitudinal axes of shafts 48 and 50. One embodiment of an adjusting
means 58 is shown in FIG. 7.
FIG. 4 is a detailed perspective view of offset assembly 44 shown in FIG.
3. An offset assembly may be defined as an assembly which transfers
rotational motion of the driven shaft 36 or 38 to another shaft 48 or 50
and allows for axial movement of the shaft 48 or 50 relative to the driven
shaft. In this embodiment, offset assembly 44 comprises blocks 60, each
pivotably mounted by pins 62 within offset frame 64. Shaft 36 extends
through one of the blocks 60 and is securely mounted therein by set screw
66. Shaft 48 extends through the other block 60 and is also securely
mounted therein in the same manner. As is apparent, when shaft 36 is
caused to rotate by drive motor 40, this rotational movement will be
transferred by offset assembly 44 to shaft 48 and thus to guide frame 46.
In addition, offset assembly 44 allows shaft 48 and thus guide frame 46 to
be shifted in an axial direction relative to shaft 36.
FIG. 5 is a detailed perspective view of swivel assembly 56 shown in FIG.
3. A swivel assembly may be defined as an assembly which allows motion of
the guide frame, considering the guide frame 46 as a plane, in directions
within the plane to be transferred to the control rod 32 but motion normal
to the plane is not transferred to the control rod. In this embodiment,
swivel assembly 56 comprises base plate 70 attached to longitudinal member
52 by screws 72, a yoke member 74 attached to the base plate by pivotal
joint 76, and swivel block 78 pivotably mounted in yoke member by pins 80.
Located in the center of swivel block 78 is a bore through which a control
rod 32 passes. Control rod 32 may rotate with respect to swivel block 78
and may also slide longitudinally within the block.
The operation of the device 10 in accordance with the present invention may
be more clearly understood by reference to FIGS. 6 and 7. FIG. 6 is a
cross-sectional view of the device 10 of FIG. 1 taken along line 6--6 and
FIG. 7 is a cross-sectional view of the device 10 of FIG. 1 taken along
line 7--7.
In FIG. 6, offset assemblies 44 are shown in various positions
corresponding to various degrees of rotation of shafts 36 and 38 during an
operational cycle of the device 10. Position A, shown in phantom lines,
indicates the position of offset assembly 44 during the initial part of
the cycle of device 10. Position B represents approximately the midpoint
in the cycle and position C represents a final point in the cycle. As is
apparent from FIG. 6, at each position of the offset assemblies 44, guide
frame 46 and thus the members 20 are displaced to different positions as
shafts 36 and 38 rotate thus allowing the device to track the apparent
motion of the sun across the sky.
FIG. 7 illustrates the function of adjusting means 58 to the operation of
the device 10. In this embodiment, adjusting means 58 comprises a control
member such as a cord or cable 82 having one end suitably attached to
guide frame 46 and the other end attached to crank assembly 84 mounted on
a portion of support frame 12. By appropriate adjustment of the crank
assembly 84, the effective length of cable 82 is either lengthened or
shortened. To facilitate precise adjustment of the cable 82, a pointer 86
is attached to the cable 82 and a read-out scale 88 fastened to a portion
of the support 12.
Because of the upper or major surface 18 of support frame 12 is at an angle
from horizontal, offset assemblies 44 will be in the position shown by the
phantom lines if no tension is applied to cable 82. By shortening the
effective length of cable 82, offset assembly 44 and guide frame 46 will
assume the position shown in heavy lines. Thus by appropriate adjustment
of the adjusting means 58, the angle of the reflective surfaces of members
20 relative to horizontal can be fixed so as to properly reflect rays from
the sun to the target area.
The above described device 10 operates as a recognition of the following
general principles. The apparent motion of the sun during a day is, to an
observer on a particular point, a circle. On the day of an equinox, the
apparent path of the sun is along a great circle beginning at due east and
ending at due west and having an angular rate of travel of one revolution
per 24 hours. This apparent path of the sun on a day of an equinox lies in
a plane called the "equatorial plane". On days other than an equinox, the
sun appears to move in non-great circles in planes parallel to the
equitatorial plane.
The axis of the circle representing the apparent path of the sun on the day
of an equinox corresponds to the observer's line of sight toward the North
Star (Polaris). Thus the device as shown in FIG. 1 may be positioned such
that the edges of the support frame 12 are directed toward the North Star
and the major surface 18 is therefore perpendicular to the equitorial
plane.
The angular distance of circles representing the apparent motion of the sun
or non-equinox days from the equitorial plane is commonly known as the
declination angle. The declination angle varies more or less sinusoidally
during a year between limits of about .+-. 23-1/2.degree.. Thus by knowing
the declination angle for a particular day of the year, the device may be
set to accurately track the apparent motion of the sun by adjusting the
adjustment means for the proper setting for that day. While the
declination angle changes very slightly during the course of a day, these
changes are not of sufficient magnitude to adversely affect the operation
of the device.
For general purposes, the apparent rate of travel of the sun can be
considered to be one revolution per 24 hours. However, there is actually a
very slight variation in the angular rate of the sun from one revolution
per 24 hours. While in any given day, this variation is not significant,
in time these variations accumulate into significant differences between
apparent solar time and clock time. On a particular day, the sun may be
ahead or behind the clocks by as much as sixteen minutes although over the
period of a year, the variations, called equation of time, average out to
zero. By knowing the declination, the equation of time may be determined
from commonly available plots.
In the device of the present invention, these variations may be compensated
for, when using a drive motor having an output of one revolution per 24
hours, by adjusting the daily starting time of the drive motor to thereby
reflect the annual variation in the equation of time. Alternatively, a
variable speed drive motor may be utilized having an output which may be
more or less than one revolution per 24 hours or which may be programed to
vary its output during a day to compensate for the variations.
As is well known, an incident ray of light striking a reflective surface
will reflect in a plane at an angle from a normal from the reflective
surface equal to the angle of the incident ray from normal. Thus a ray
from the sun on a line S striking a reflective surface having a normal N
is reflected on a line T at an angle 0 from normal N equal to the angle
between line S and normal N. The components of the device of the present
invention are set up such that the center point of the member is on both
lines N and T. The intersection of a shaft and block of an offset assembly
and the intersection of a shaft and the other block of offset assembly
points is on line S. All four offset assemblies are arranged so as to move
in parallel with one another and thus each point on the guide frame is
offset from a fixed point in space by a fixed length representing line S.
Each of the swivel assemblies mounted on the guide frame is then
positioned such that the point in space that is offset from the
intersection of control rod and block of the assembly is also located the
same distance away from the center point of the member that corresponds to
the line T for that member. Thus the device is able to reflect rays of the
sun S toward a fixed target on a line T by proper adjustment of the normal
N from each member.
In operation, the device is positioned such that the edges of the support
frame are directed toward the North Star and the adjusting means set to
correspond to the declination angle for the particular day. The drive
motor is set for the proper rate of rotation and then activated. The
device is then able to direct multiple sun images onto a common target
area while continually tracking the apparent motion of the sun during a
day.
While the present invention has been described with reference to a
particular embodiment thereof, it will be understood that numerous
modifications may be made by those skilled in the art without actually
departing from the spirit and scope of the invention as defined in the
appended claims.
* * * * *
|
|
 |
|
 |
Description |
|
