SYNCHRONIZED SOLAR CONCENTRATOR ARRAY
A solar energy collecting device includes a rotation axis to be mounted parallel to the earth's polar axis, a solar energy collector mounted for rotation around the rotation axis at a predetermined rotation speed, the solar energy collector defining a tilt angle with respect to the rotation axis, and a tilt angle adjustment mechanism for automatically and intermittently adjusting the tilt angle. Various configurations of the solar energy collector are possible, and the rotation speed may be one revolution per day or half a revolution per day depending on the solar energy collector configuration. Many drive modes are possible, including rotating continuously throughout a day or rotating during daylight hours and rotating backward or forward at night. The tilt angle adjustment mechanism includes a handle fixed to the solar energy collector and a tilt angle change guide.
1. Field of the Invention
This invention relates to solar energy collection, and in particular, to solar tracking and sunlight concentration and collection.
2. Description of the Related Art
Effective use of solar energy has been an important research subject. Various applications on concentrated or non-concentrated solar energy have been invented. The main obstacle is the cost. There is no successful for-profit solar utility exists today. Recently solar panels have been widely installed on roof tops, however, solar panel is still expensive because it uses photovoltaic solar cells at non-concentrated solar illumination condition. Photovoltaic solar cell, made from semiconductor materials such as silicon or gallium arsenide, is the most expensive part of the solar panel. It would use much less solar cell if sunlight is first concentrated; also the sunlight to electricity conversion efficiency of the solar cell can be improved under the concentrated sunlight intensity.
Solar concentrator can reduce the energy receiver size and cost. However, solar concentrator usually needs to track sun's motion, and tracking systems tend to be bulky, complicated, expensive, and unreliable and awkward to implement. One type of solar tracking systems uses dual axial tracking, where continuous rotation around two non-parallel axes is required. Another type of tracking systems uses polar tracking, where the solar energy receiver or concentrator rotates around a polar axis, i.e. an axis parallel to the rotation axis of the earth. For example, U.S. Pat. No. 6,284,968 describes a “solar-tracking system that provides a polar rotation at a constant velocity of 366.25 revolutions clockwise per year, and orbital revolution that is one revolution per year in the counter-clockwise direction. The support for the orbital drive system is tilted from polar drive system at an angle of 23.45 degrees, and is constant, which angle is equal to the earth's axis tilt from orbital axis.” (Abstract.) U.S. Pat. No. 5,632,823 also describes a solar tracking system using polar tracking, where the inclination angle (i.e. the angle between the solar collector and the polar rotation axis) is adjusted empirically: “The sun shadow of a pointer normal to the solar collector panel serves to properly align the panel. Alternately, the current generated by the solar cells is measured and its maximum indicates that the solar panel is properly aligned with the sun.” (Abstract.)
The present invention is directed to a solar energy collecting device and system that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a polar tracking system for solar energy collection that has a simple structure and is easy to implement.
Additional features and advantages of the invention will be set forth in the descriptions that follow and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention provides a solar energy collecting device which includes a rotation axis; a solar energy collector mounted for rotation around the rotation axis, the solar energy collector defining a tilt angle with respect to the rotation axis; a driving mechanism for driving the solar energy collector to rotate around the rotation axis at a predetermined rotation speed during at least part of a day; and a tilt angle adjustment mechanism for automatically and intermittently adjusting the tilt angle. Various configurations of the solar energy collector are possible, and the rotation speed may be one revolution per day or half a revolution per day depending on the solar energy collector configuration. Various drive modes are possible, including rotating continuously throughout a day or rotating during daylight hours and rotating backward or forward at night to a starting position and restarting the rotation the next day.
One embodiment of the tilt angle adjustment mechanism includes a handle fixed to the solar energy collector and a tilt angle change guide.
In another aspect, the present invention provides a solar energy collecting system comprising a plurality of such solar energy collecting devices, the system further including a base on which the rotation axes of the plurality of solar energy collecting devices are mounted and an enclosure for enclosing the plurality of solar energy collecting devices.
In yet another aspect, the present invention provides a method for collecting solar energy, the method including mounting a rotation axis parallel to a polar axis of the earth; mounting a solar energy collector for rotation around the rotation axis, the solar energy collector defining a tilt angle with respect to the rotation axis; rotating the solar energy day; and automatically and intermittently adjusting the tilt angle.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
Embodiments of the present invention provide a solar energy collection system that uses a polar tracking method to track the sun. In one embodiment, the solar energy collection system is formed by a plurality of solar energy collection unit 300. As shown in
As another alternative (not shown), the solar energy collection units may include only an energy receiver without a solar energy concentrator. In this disclosure, the term “solar energy receiving surface” refers to the surface of the solar energy concentrator if one is present, or refers to the surface of the target energy receiver if no solar energy concentrator is present. The descriptions below use the solar energy collection units 300 of
As shown in
The solar energy collection unit 300 is mounted on a tracking structure for tracking the position of the sun. The solar energy collection unit 300 may tolerate certain margin of error in tracking. As shown in
The principles of polar coordinate system and polar tracking are described below.
As shown in
According to embodiments of the present invention, the solar energy collection units 300 are mounted to rotate around a rotation axis that is parallel to the polar axis in an installed solar energy collection system. (In the instant disclosure, the rotation axis is sometimes referred to as the polar axis where the context makes the meaning clear.) The solar energy collection units 300 rotate along the polar axis 400 at a speed of approximately one turn per day to track the sun. Looking from the celestial North Pole, the rotation direction is clockwise to counter the effect of the earth rotation, so that the solar energy collection unit 300 is always facing the sun at the same angle.
In a simple implementation, the solar energy collection unit 300 may rotate around the rotation axis 400 continuously at a substantially constant speed of approximately one revolution per day. Alternatively, it may rotate at a speed of approximately one revolution per day during the day to collect the solar energy, and rotate backward or forward at a different speed during the night (non-collection time) to an appropriate position, and re-start the rotation at an appropriate time of the day for the next day's operation.
The solar energy collection unit 300 is mounted on rotational axis with a tilt angle that is adjustable. Some examples of the tilt angle adjustment mechanism are described with reference to
In the example shown in
A tilt angle change guide 360 is provided to engage the distal portion of the handle 350 during some part of daily rotation to change the tilt angle of the rigid body 330. In
One example of a tilt angle change guide 360 is illustrated in
The rigid body 330 is fixedly attached to the crossbar 410 by a clamp, latch or other suitable tilting attachment most of the time so that it rotates around the rotation axis 400 at a fixed tilt angle, except during the brief period when the handle 350 is engaged with the tilt angle change guide 360. During that period, the tilting attachment loosens, so that the rigid body 330 can rotate around the crossbar 410 (i.e. change the tilt angle) as the handle 350 is pushed by the tilt angle change guide 360. After the handle exits the tilt angle change guide, the tilting attachment is re-fastened. In practice, if the rigid body 330 is designed to be well balanced, and the friction between the rigid body and the crossbar 410 is strong enough to hold the tilt angle unchanged, yet weak enough to allow the tilt angle to change when the handle is pushed by the tilt angle change guide 360, the tiling attachment may not necessarily need to be explicitly loosened and re-fastened.
An example of a tilting attachment is shown in
Tilt angle adjustment may be automatically carried out at a desired time of day. In the embodiment shown in
For a given tilt angle adjustment schedule, the amount of tilt angle change for each adjustment is determined by the season (time of the year) and the length of time between successive adjustments. For each adjustment, the tilt angle change guide 360 is re-positioned so that its entrance location approximately corresponds to the current tilt angle and its exit location corresponds to the target tilt angle. At the entrance end, a flared shape may be provided (see
One example for re-positioning the tilt angle change guide 360 is shown in
Another example of a tilt angle change guide 360′ is shown in
The handle and the tilt angle change guide may be implemented in many forms in addition to the examples described above. For example, an alternative design is shown in
In the polar tracking system, the rotation around the polar axis is synchronized to the sun's position relative to the earth. By using counters and comparators, accurate angular control can be monitored and controlled at various stages of the transmission between the motor and the slow rotating array, so that precise rotation motion of the axes will match the predicted position of the sun. It may be used for an accurate adjustment for different daylight length, sunrise time, etc. Correct timing and reliability are important, and redundancy, sense and feedback can help to keep the tracking system accurate and reliable.
With the input of latitude and longitude of the installation location and accurate date and time, it is easy to set the initial tracking direction. For example, the sun passes the meridian at noon local time. Once tracking started, the apparatus can turn at one rotation per day continuously, or back and forth during night and day to reset positions.
A suitable control circuit, which preferably employs a self-calibrated clock, may be used to control the motion of the solar energy collection units. Optionally, a universal standard time source, such as the GPS time signals or standard radio time source, may be used to eliminate any time error accumulation. Preferably, software control is used. A solar sensor could also be used for auxiliary tracking.
In one implementation, an array of the solar energy collection unit mounted on their rotation axes are connected together by means of chains, gears, or other synchronization means, which may be driven by one power source. All units rotate continuously at the same speed. Because of the slow and continuous rotation at the speed of one turn per day, and the very slow tilt angle adjustment, an array of such solar energy collection units can be driven simultaneously and continuously by a low powered motor.
To allow the panel to operate independently of external power sources, a small but sufficient energy storage device, such as a rechargeable battery or a super capacitor is preferably provided as an energy source to allow the motor in the tracking mechanism to continue to work during night and cloudy/rainy days. It may contain a control circuitry described earlier. Both such energy storage device and control circuitry can also be external, particularly when multiple similar panels are installed at the same location.
The panel 371 must be constructed and mounted in a way such that the rotation axes 400 are parallel to the polar axis of the earth. In one embodiment, the panel is constructed so that all rotation axes 400 are parallel to the base 372 of the enclosure. Such a panel should be installed such that the base is tilted up with respect to the horizontal plane with an angel equal to the latitude at the installation location, and the rotation axes 400 are oriented along a north-south direction in the top view, as shown in
As shown in
As shown in
In an embodiment employing stationary target energy receivers 210 (either centralized or distributed) as shown in
Similar to solar energy collection units 300 using moving target energy receivers 200, an energy collection unit using stationary target energy receivers 210 may be arranged in an array and enclosed in an enclosure with a transparent cover in a similar manner as shown in
In an array of solar energy collection units, one structural element may partially block the incident sunlight on another solar energy concentrator during certain times. For some applications, such as solar thermal, non-uniform illumination on the energy receiver is acceptable; for other applications, such as photovoltaic (PV) which require uniform light illumination for optimal performance, a non-imaging concentrator, which could produce uniform output illumination when input sun light is partially blocked, is preferably used.
Many different variations of a solar energy collection system are described above. One common feature of the different variations is that a solar energy collector (which is either a solar energy concentrator (100/110) for directing sunlight to a solar energy receiver (200/210), or a solar energy receiver without a concentrator) is mounted to rotate around a polar axis at a predetermined rotation speed during at least a part of a day, with automatic and intermittent tilt angle adjustment. The variations include:
The predetermined rotation speed is approximately one revolution per day if the solar energy collector is a solar energy concentrator (100) used with a solar energy receiver (200) that rotates with the concentrator, or if the solar energy collector is a solar energy receiver without a concentrator (not shown in the drawings). The predetermined rotation speed is approximately half a revolution per day if the solar energy collector is a solar energy concentrator (110) used with a stationary solar energy receiver (210) that is fixed in space. “To rotate at a predetermined rotation speed during at least part of a day” includes various drive modes such as rotating continuously throughout a day (i.e. 24 hours a day), or rotating during a part of the day (e.g., during daylight hours) and rotating backward or forward (preferably at a faster speed) to a starting position so that it can restart the rotation the next appropriate angle once every short time period such as a minute, as long as the average speed is the predetermined rotation speed. “Approximately one revolution per day” or “approximately half a revolution per day” means the rotation speed may deviate from an ideal value of 360 degrees (or 180 degrees) per 24 hours. Generally, a relatively inexpensive timing device (clock) can achieve an accuracy of ±1 degree per 24 hours (equivalent to ±4 minutes per 24 hours). Accumulated timing error may be corrected from time to time using a universal standard time source, such as the GPS time signals or standard radio time source. Further, although more accurate tracking results in more efficient solar energy collection, tracking (rotation) speed may deviate from the ideal speed by a larger amount (e.g. 10 or even 20 degrees per 24 hours) if a less-than-optimized energy collection efficiency can be accepted. Moreover, the solar energy collector may be designed so that collection efficiency remains relatively high for a large range of sunlight incident angle, in which case an even larger tracking error may be acceptable. Thus, it should be understood that the above described deviations from the ideal case of a constant rotation at a speed of 360 (or 180) degrees per 24 hours fall within the scope of the present invention. In addition, due to the finite eccentricity (0.0167) of the earth's orbit around the sun, the exact length of each day can be longer or shorter than 24 hours. The tracking device may be designed to adjust to this variation of the length of the day, either by changing the rotation speed or by correcting for accumulated errors from time to time. All of such variations in the rotation speed of the tracking system are within the scope of the present invention.
“Automatic and intermittent tilt angle adjustment” means the adjustment occurs automatically without human intervention, and occurs more than once a day, once a day or less frequently than once a day. The advantage of intermittent tilt angle adjustment is that it can be achieved with relatively simple mechanical structures, such as the handle 350 in the illustrated embodiments.
Also described is a solar energy collecting system in which a plurality of such solar energy collectors are mounted on a base and driven by a common power source to rotate at the same speed. The solar energy collector can be any one of the above variations. The plurality of solar energy collectors can be enclosed in an enclosure which can then be installed as a unit.
As seen from the above descriptions, a synchronized solar concentrator array according to embodiments of the present invention has only one set of fixed axis, but can array rotate at the same speed and direction, around their own fixed axes; therefore, no complex control mechanism is required. Each concentrator does not need to be large or bulky. Using repetitive, small, and simple module can reduce manufacturing cost. As a result, the overall system cost can be reduced. In addition, the energy collection units can rotate at a constant speed (although it's not a requirement) and can be synchronized to a universal standard time source (such as GPS signals or a standard radio time source), eliminating problem associated with systems using a solar sensor or a local clock.
By using concentrators, solar cell material usage for a panel of the same power rating can be significantly reduced. By using an effective solar tracking method, the overhead cost from solar tracking is insignificant. Because each solar energy collection unit can have a small size, an array of them can be arranged in a plane and a low profile flat panel can be constructed.
One particular application of panels constructed related to
Advantages of solar energy collection systems according to embodiments of the present invention are as follows:
-
- one fixed axis tracking for accurate solar energy collection;
- individual axis or arrays of axes are all parallel to the earth rotation axis
- using less solar energy conversion element because of concentrator;
- array of synchronized solar concentrators could be driven by one small power source;
- synchronized rotation at controlled, nearly constant, slow speed;
- seasonal tilt angle slight adjustment as needed
- could be used in both distributed energy receiver, or in a centralized energy receiver;
- with a cover, it will look like a static flat panel, or a static heliostat.
It will be apparent to those skilled in the art that various modification and variations can be made in the solar energy collection system of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents.
Claims
1. A solar energy collecting device comprising:
- a rotation axis;
- a solar energy collector mounted for rotation around the rotation axis, the solar energy collector defining a tilt angle with respect to the rotation axis;
- a driving mechanism for driving the solar energy collector to rotate around the rotation axis at a predetermined rotation speed during at least part of a day; and
- a tilt angle adjustment mechanism for automatically and intermittently adjusting the tilt angle.
2. The solar energy collecting device of claim 1, wherein the tilt angle adjustment mechanism comprises:
- a handle fixed to the solar energy collector and rotates with it around the rotation axis;
- a tilt angle change guide having an elongated opening adapted to receive a part of the handle, the tilt angle change guide being positioned such that the handle enters a first end of the opening, slides along the opening, and exits a second end of the opening during a portion of the rotation of the solar energy collector, wherein the tilt angle of the solar energy collector is a first value when the handle enters the first end of the opening and a second value when the handle exits the second end of the opening; and
- a tilt angle change guide adjusting mechanism for seasonally adjusting the position of the tilt angle change guide.
3. The solar energy collecting device of claim 2, further includes a clamp or latch for fixing the solar energy collector to the rotation axis at a fixed tilt angle, wherein the clamp or latch is disengaged when the handle enters the first end of the opening of the tilt angle change guide, and reengaged when the handle exits the second end of the opening.
4. The solar energy collecting device of claim 2, wherein the handle and the tilt angle change guide are located such that the handle enters the opening of the tilt angle change guide during non-energy collection time.
5. The solar energy collecting device of claim 1, wherein the solar energy collector is a solar energy receiver, and wherein the predetermined rotation speed is approximately one revolution per day.
6. (canceled)
7. (canceled)
8. (canceled)
9. The solar energy collecting device of claim 1, wherein the drive mechanism drives the solar energy collector to rotate continuously throughout a day.
10. The solar energy collecting device of claim 1, wherein the drive mechanism drives the solar energy collector to rotate during daylight time of a day and to rotate backward or forward during night time to a starting position and restarts the rotation the next day.
11. (canceled)
12. (canceled)
13. The solar energy collecting device of claim 1, further including a control circuit for controlling the driving mechanism, the control circuit receiving a universal standard time signal for synchronizing the rotation of the solar energy collector to the rotation of the earth relative to the sun.
14. (canceled)
15. A solar energy collecting system comprising a plurality of solar energy collecting devices of claim 1, the system further comprising:
- a base on which the rotation axes of the plurality of solar energy collecting devices are mounted; and
- an enclosure for enclosing the plurality of solar energy collecting devices.
16. The solar energy collecting system of claim 15, wherein the rotation axes of the plurality of solar energy collecting devices are parallel to each other, the system further comprising:
- a power source for providing a drive power; and
- a drive system for transmitting the drive power to the driving mechanisms of the plurality of solar energy collecting devices to drive them to rotate at the same speed.
17. The solar energy collecting system of claim 16, further comprising:
- a control circuit for controlling the drive system; and
- an energy storage device for storing energy for the power source,
- wherein the control circuit and the energy storage device are located outside the enclosure.
18. The solar energy collecting system of claim 15, wherein the rotation axes of the plurality of solar energy collecting devices are parallel to the base.
19. The solar energy collecting system of claim 15, wherein the rotation axes of the plurality of solar energy collecting devices are tilted with respect to the base by a predetermined angle.
20. The solar energy collecting system of claim 15 further comprising a stationary solar energy receiver, wherein the solar energy collector of each solar energy collecting device is a solar energy concentrator that directs sunlight to the solar energy receiver.
21. The solar energy collecting system of claim 15, wherein each solar energy collecting device further includes a solar energy receiver, wherein the solar energy collector of each solar energy collecting device is a solar energy concentrator that directs sunlight to the respective solar energy receiver.
22. A method for collecting solar energy, comprising:
- mounting a rotation axis parallel to a polar axis of the earth;
- mounting a solar energy collector for rotation around the rotation axis, the solar energy collector defining a tilt angle with respect to the rotation axis;
- rotating the solar energy collector around the rotation axis at a predetermined rotation speed during at least part of a day; and
- automatically and intermittently adjusting the tilt angle.
23. A solar energy collecting device comprising:
- a rotation axis;
- a solar energy collector mounted for rotation around the rotation axis, the solar energy collector defining a tilt angle with respect to the rotation axis;
- a driving mechanism for driving the solar energy collector to rotate around the rotation axis at a predetermined rotation speed during at least part of a day; and
- a tilt angle adjustment mechanism for automatically adjusting the tilt angle, tilt angle adjustment mechanism including:
- a handle fixed on the solar energy collector and rotates with it around the rotation axis,
- a tilt angle change guide engaging the handle during at least a part of the rotation of the handle around the rotation axis, and
- a tilt angle change guide adjusting mechanism for seasonally adjusting the position of the tilt angle change guide.
24. The solar energy collecting device of claim 23, wherein the tilt angle change guide has an elongated opening adapted to receive a part of the handle, the tilt angle change guide being positioned such that the handle enters a first end of the opening, slides along the opening, and exits a second end of the opening during a portion of the rotation of the solar energy collector, wherein the tilt angle of the solar energy collector is a first value when the handle enters the first end of the opening and a second value when the handle exits the second end of the opening.
25. The solar energy collecting device of claim 24, wherein the tilt angle change guide has a plurality of parallel openings.
26. The solar energy collecting device of claim 23, wherein the handle has a circular shape and the tilt angle change guide engages the handle constantly.
Type: Application
Filed: Jun 2, 2007
Publication Date: Oct 29, 2009
Applicant: RENEWATT CORPORATION (Rowland Heights, CA)
Inventor: Datong Chen (Fremont, CA)
Application Number: 12/303,361