Abstract:
A solar array concentrator assembly includes a first solar array panel configured to receive solar energy and a first adjustable concentrator coupled to the first solar array panel. The first adjustable concentrator reflects solar energy toward the first solar array panel. A first drive shaft is coupled to the first adjustable concentrator. The first drive shaft is configured to rotate the first adjustable concentrator relative to the first solar array panel to maximize the solar energy reflected toward the first solar array panel.

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application Ser. No. 60/324,183, filed Sep. 21, 2001, entitled Solar Array Concentrator. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention relates to a solar array concentrator system and method, and more particularly to a solar array having adjustable concentrators for varying the relative angle between a solar array panel and the concentrator. 
     BACKGROUND OF THE INVENTION 
     Solar arrays convert sunlight into electricity. Such conversion results in an economical power source for many applications, such as spacecraft. In general, the more sunlight received by a solar array, the more power. Solar arrays operate most effectively when receiving a maximum of available solar energy. However, the position of the solar array with reference to incoming solar energy does not always enable the array to receive maximum energy. Some systems presently in use position the solar array to enable the array to receive maximum solar energy. These systems are heavy and utilize somewhat complicated mechanisms. When a solar array is used in an application where weight is an important factor, the mechanism for adjusting the solar array becomes an unacceptable portion of the total weight of the assembly. 
     Concentrators, or reflectors, may be added to solar arrays in order to focus sunlight on the arrays, thus providing more power output from the arrays. However, fixed concentrators tend to shadow the array at certain angles and may cause overheating of substrates. The fixed concentrator on a solar array driven by a solar array drive is one efficient method of producing power. However, one disadvantage with a fixed concentrator on a driven solar array is the high cost of building solar array drives and the mechanisms needed to track sun and command the drives. 
     SUMMARY OF THE INVENTION 
     The present invention provides a solar array concentrator system and method that substantially eliminates or reduces at least some of the disadvantages and problems associated with previous systems and methods. 
     In accordance with a particular embodiment of the present invention, a solar array concentrator assembly includes a first solar array panel configured to receive solar energy and a first adjustable concentrator coupled to the first solar array panel. The first adjustable concentrator reflects solar energy toward the first solar array panel. A first drive shaft is coupled to the first adjustable concentrator. The first drive shaft is configured to rotate the first adjustable concentrator relative to the first solar array panel to maximize the solar energy reflected toward the first solar array panel. 
     The solar array concentrator assembly may include a positioning motor coupled to the first drive shaft, the positioning motor adjusting the position of the first concentrator relative to the first solar array panel to maximize the amount of solar energy reflected toward the first solar energy panel. The assembly may further include a second solar array panel configured to receive solar energy, wherein the second solar array panel is foldably coupled to the first solar array panel. A second adjustable concentrator may be coupled to the second solar array panel, the second adjustable concentrator reflecting solar energy toward the second solar array panel. A second drive shaft may be coupled to the adjustable concentrator, wherein the second drive shaft is configured to rotate the second adjustable concentrator relative to the second solar array panel to maximize the solar energy reflected toward the second solar array panel. A draw mechanism may be coupled to the first and second drives, wherein the draw mechanism is configured to engage the first drive shaft with the second drive shaft to form a continuous drive shaft and hinge between the first and second solar array panels. 
     Technical advantages of particular embodiments of the present invention include an adjustable concentrator hinged to a solar array panel to vary the relative angle between the concentrator and the solar array panel. Thus, more energy is provided onto the panel than would be available without the concentrator. A further technical advantage of the present invention is the elimination of a mechanism coupled to the solar array to position the array to receive more energy. Such mechanisms for the solar array panels tend to be costly and complicated drives. The adjustable concentrator of the present invention provides a lighter weight and less costly assembly than assemblies used to drive the solar arrays thereby making the adjustable concentrators of the present invention a logical choice for applications such as a spacecraft or other vehicle where weight is a factor and where maneuverability is important. 
     Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some or none of the enumerated advantages. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of particular embodiments of the invention and their advantages, reference is now made to the following descriptions, taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 illustrates a system having adjustable concentrators coupled to solar array panels, in accordance with an embodiment of the present invention; 
     FIGS. 2A,  2 B and  2 C illustrate the adjustable concentrators of FIG. 1 in different positions relative to solar array panels, in accordance with an embodiment of the present invention; 
     FIG. 3 illustrates a system comprising an adjustable concentrator coupled to a solar array panel, in accordance with an embodiment of the present invention; 
     FIG. 4 illustrates a spring for the system of FIG. 3 that aids in the deployment of the concentrator coupled to the solar array panel, in accordance with an embodiment of the present invention; 
     FIG. 5 illustrates a motor and drive shaft for the system of FIG. 3 for rotating the concentrator relative to the solar array panel, in accordance with an embodiment of the present invention; 
     FIG. 6 illustrates solar array panels and adjustable concentrators coupled to the main body of a spacecraft, in accordance with an embodiment of the present invention; 
     FIG. 7 illustrates the deployed adjustable concentrators and solar array panels coupled to the main body of a spacecraft, in accordance with an embodiment of the present invention; 
     FIG. 8 illustrates the main body of a spacecraft with solar array panels and concentrators in a folded position, in accordance with an embodiment of the present invention; 
     FIG. 9 illustrates the main body of a spacecraft with solar array panels and concentrators in a partially deployed position, in accordance with an embodiment of the present invention; 
     FIG. 10 illustrates a draw wire through hollow drive shaft segments of a drive shaft for rotating concentrators relative to solar array panels, in accordance with an embodiment of the present invention; 
     FIG. 11A illustrates the draw wire of FIG. 10 in a folded position, in accordance with an embodiment of the present invention; and 
     FIG. 11B illustrates the draw wire FIG. 10 in an unfolded position, in accordance with an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a system  11  for improving the power output from solar array panels in accordance with an embodiment of the present invention. Solar array panels  10  are coupled to concentrators  12 . The solar array panels  10  comprise conventional solar cells responding to solar energy for converting incoming solar energy to electrical energy. Solar array panels  10  may be electrically coupled to an object, such as a spacecraft, to provide power at a certain voltage and current for the object. Concentrators  12  reflect solar energy to solar array panels  10 . Such reflection provides more solar energy to solar array panels  10 , thus improving the power output from solar array panels  10 . The concentrators  12  are hinged to the solar array panels  10  and are adjustable by means of stepper drive motors  24  coupled to drive shafts forming hinge elements between the solar array panels  10  and the concentrators  12 . Using adjustable concentrators  12  allows the concentrators to be moved and positioned to optimize that amount of solar energy reflected to solar array panels  10 . Moreover, adjustable concentrators can decrease the shading of solar array panels that may occur by a fixed solar array panel/concentrator assembly. 
     FIGS. 2A-2C are side views of system  11  of FIG. 1 wherein concentrators  12  are positioned at different angles to reflect solar energy  16  to solar array panels  10 . As illustrated, the concentrators  12  may be adjusted relative to the position of the solar array panels  10 , depending on the direction from which the solar energy  16  is received. Thus, the concentrators  12  may be adjusted based on the position of the solar array panels  10  relative to the sun. 
     FIG. 3 illustrates a system comprising a solar array panel  10  coupled to a concentrator  12  through a drive shaft assembly  18  with a drive shaft  20 . As a motor (not shown) coupled to the drive shaft  20  turns the drive shaft, the angle between the concentrator  12  and the solar array panel  10  will be changed, thus allowing solar energy to be reflected onto solar array panel  10 . The motor drives the drive shaft  20  against a spring  22 . 
     FIG. 4 illustrates the spring  22  of FIG. 3 in a neutral, relaxed position. When spring  22  is in such neutral position, the concentrator  12  is at an angle of 180° relative to solar array panels  10 , or in alignment with solar array panel  10 . At such position, no solar energy will be reflected onto solar array panel  10 , and concentrator  12  will not shadow solar array panel  10 . Rotating the drive shaft  20  against the spring  22  tends to dampen out vibrations which may occur in the concentrator  12  during operation. 
     As the motor drives the drive shaft  20  past the 180° position described above, the drive force will be against the tension of the spring  22 . Should the motor fail, the spring  22  will return to a neutral position such that the concentrator  12  is in alignment with the solar array panel  10 . This neutral position assures that the solar array panel  10  is not covered or shaded preventing full power output from the solar array panel  10  in the event of an anomaly in the system. 
     Spring  22  may also be used to deploy the concentrator  12  from a stowed position in some applications, such as when the concentrator is coupled to a solar array panel  10  of a spacecraft as further discussed below. The concentrator  12  may be folded back behind the solar array panel  10  when in a stowed position, and upon deployment of the solar array panel  10 , the spring  22  may deploy to a neutral position, thereby rotating the concentrator  12  to the 180° position discussed above. 
     FIG. 5 is a diagram illustrating a positioning motor  24  coupled to a drive shaft  20  that functions as a hinge thereby enabling rotation of concentrator  12  relative to solar array panel  10 . As the positioning motor  24  rotates the shaft  20 , the angle between the concentrator  12  and the solar array panel  10  is changed so that solar energy is reflected off of the concentrator  12  onto the solar array panel  10 . The motor  24  may be controlled by an automatic control system. For example, a computer may determine the optimal position of the concentrator  12  relative to the solar array panel  10  based on the positions of the solar array panel  10  and the sun. The computer outputs instruction signals to control the motor  24  such that the motor  24  rotates the concentrator  12  to an optimal position determined by inputs to the computer. In particular embodiments in which the solar array panel  10  is coupled to a spacecraft, the computer may be onboard the spacecraft. 
     As stated above, in particular embodiments of the present invention, the concentrators and the solar array panels described herein are coupled to a spacecraft in order to provide power to the spacecraft generated from solar energy. In such cases, the navigational systems of the spacecraft may adjust the angles of the concentrators relative to the solar array panels based on the movement and direction of the spacecraft for optimizing receipt and reflection of solar energy onto the solar array panels. Similar systems are currently used for adjustment of solar array drives during flight. 
     As the spacecraft orbits the earth (or travels in some other orbit), the angle of the spacecraft to the sun continually changes. The onboard computer of the spacecraft reads the rate of change from the onboard gyros and generates the proper signals to the motor  24  that rotates the drive shaft  20 . The motor  24  rotates the drive shaft  20  to move the concentrator  12  relative to the solar array panel  10 , thus optimizing the amount of solar energy reflected onto the solar array panels. 
     While some embodiments described herein include a motor rotating a drive shaft in order to change the position of the concentrators relative to the solar array panels, it should be understood that other methods of changing the position of the concentrators may be used in other embodiments. Moreover, other embodiments may include methods other than a spring as described herein to provide deployment of the concentrators. 
     FIG. 6 is a diagram illustrating a spacecraft  28  with a main body  30 . Spacecraft  28  includes solar array panels  10  folded in a stowed, launch position. Concentrators  12  are folded behind solar array panels  12  in order to conserve space and to avoid shading of the solar array panels  10  if the concentrators  12  do not deploy correctly. As illustrated, the spacecraft  28  is placed on a booster, and a fairing or shroud placed over it for protection during launch. Once the spacecraft has been launched and reaches the desired altitude, the fairing is jettisoned. Subsequently during flight, the spacecraft  28  is separated from the booster, and the solar array panels may be deployed. 
     FIG. 7 illustrates spacecraft  28  with solar array panels  10  in a deployed position. Concentrators  12  are also illustrated in a deployed position for reflection of solar energy onto solar array panels  10 . The illustrated position of concentrators  12  in FIG. 7 is similar to the position of concentrators  12  illustrated in FIG.  2 A. Once the solar array panels  10  have been deployed, a signal from the onboard computer of spacecraft  28  releases and deploys the concentrators  12 . The motor  24  and springs  22  (illustrated and described above) will cause the drive shaft  20  to rotate and deploy the concentrators  12  to an operational position for reflecting solar energy to solar array panels  10 . The concentrators  12  may be further adjusted based on the relative position of the solar array panels  10  and the sun. 
     FIG. 8 illustrates a spacecraft  40  with a main body  42  having solar array panels  10  folded in a stowed position for launch. By using a combination of hinges and springs, the solar array panels  10  may be folded thereby reducing the space needed on a booster for the spacecraft  40 . Concentrators  12  may be coupled to the solar array panels  10  by a folding drive shaft that functions to rotate the concentrators as further described below. 
     FIG. 9 illustrates spacecraft  40  showing a position of solar array panels  10  during deployment of the panels from their stowed position shown in FIG.  8 . Once the solar array panels  10  are fully deployed (in a position approximately perpendicular to main body as sown in FIG. 7) and oriented towards the sun, the concentrators  12  may be deployed. Such deployment of the concentrators  12  may occur as a result of the rotational force exerted by the springs described above with respect to FIGS. 3 and 4 as they move to a neutral position. The motors  24  may then be activated to rotate the drive shaft  20  (see FIG. 5) that hinges the concentrators  12  relative to the solar array panels  10  so that the concentrators may be rotated to an optimal position for reflection of solar energy onto solar array panels. 
     In order to fold the solar array panels  10  of FIG. 1 as described in the embodiment illustrated in FIGS. 8 and 9, the drive shaft  20  which hinges the concentrators  12  to the solar array panels  10  and rotates the concentrators  12  relative to the solar array panels  10  using the motor  24  (as illustrated in FIG. 5) may also be folded. The foldable drive shaft comprises hollow drive shaft segments with a draw wire running through the segments. FIG. 10 illustrates a hollow drive shaft  55  with splined segments  50  having a draw wire  52  running through the segments. The drive shaft segments  50  include splined ends  53  that engage a mating splined end of an adjacent segment  50  to form a continuous drive shaft that hinges the solar array panels  10  and the concentrators  12 . 
     FIGS. 11A and 11B illustrate the operation of the drive shaft  55 . FIG. 11A illustrates the drive shaft  55  in a folded position. The draw wire  52  is threaded through the hollow drive shaft segments  50 , as illustrated in FIG.  10 . Referring to FIG. 1, each drive shaft segment  50  hinges a concentrator  12  to a respective solar array panel  10 . Draw wire  52  is visible between the hollow drive shaft segments  50 . As illustrated, sufficient slack is provided in the draw wire  52  and some free play is provided between each of the drive shaft segments  50  to insure that the draw wire  52  is not tensioned until the solar array panels  10  begin to unfold. Motors  24  are coupled to the ends of the drive shaft  55 . Motors  24  include a wire draw mechanism  61  for tensioning the draw wire  52  to bring the drive shaft segments  50  together to form a unitary drive shaft  55 . 
     FIG. 11B illustrates the drive shaft  55  after unfolding to form a rotary shaft. In operation, when the solar array panels  10  unfold (as illustrated in FIG.  9 ), the drive shaft segments engage an adjacent segment to form the drive shaft  55  thereby enabling the concentrators to be rotated into a desired position for reflection of solar energy. The drive shaft  55  is coupled to the solar array panels and the concentrators (as illustrated in FIG. 5 with respect to drive shaft  20 , concentrators  12  and solar array panels  10 ). When the drive shaft  55 , including the drive shaft segments  50  and draw wire  52 , is unfolded, the wire draw mechanism  61  operates to pull the draw wire  52  tight from the ends so that the drive shaft segments  50  lock into place by engagement of adjacent splined end sections. Thus, drive shaft  55  becomes a rigid shaft that hingedly couples the solar array panels and the concentrators. Wire draw mechanism  61  includes a wire pull assembly for this function. Such wire pull assembly may occur by any of a number of mechanisms, such as by a wound spring assembly attached to a spool that, when released, provides a pulling motion to the draw wire  52 . 
     Two motors  24  are illustrated (one on each end of the drive shaft  55 ) so that if one motor  24  fails, there is an additional motor to pull the draw wire  52  and rotate the concentrators. The motors  24  may be constructed with a solenoid assembly that couples the motors to the drive shaft  55 . Thus, if there is a power or computer failure, the motors  24  would disengage from the drive shaft  55 , and the concentrators would move to a fail-safe position so as not to shadow the solar array panels. 
     With the motors  24  disabled and the draw wire  52  holding the drive shaft segments  50  together into a continuous segment drive shaft, the spring  22 , as illustrated in FIG. 3, rotates the drive shaft segments  50  to position the concentrators in alignment with the solar array panels. To position the concentrators into an optimal light-reflecting position based on the position of the sun relative to the solar array panels, the motor is activated to drive against the spring  22 , as discussed above. As the drive shaft segments  50  are rotated, the angle between the concentrators and the solar array panels varies thereby enabling reflected light to be focused on the solar array panels. Examples of such angle variations are illustrated in FIGS. 2A,  2 B and  2 C. In particular embodiments, the range of motion of the concentrators may be approximately 150 degrees from a position of alignment, that is, in line with the solar array panels. 
     Particular embodiments of the present invention described above provide for rotation of concentrators that reflect solar energy onto solar array panels. The concentrators may be adjusted for optimum reflection of solar energy based on the position of the sun relative to the concentrators and the solar array panels. The solar array panels may be kept fixed while the concentrators may be adjusted. This is an advantageous alternative to driving the solar array panels relative to the concentrators, because costly and complicated drives for the solar array panels are avoided. Moreover, the mechanisms described herein for adjusting the concentrators are lighter than mechanisms for positioning the solar array panels, thus saving weight and adding maneuverability in applications where such mechanisms are used, such as spacecraft applications. Moreover, while particular embodiments described herein discuss the use of adjustable concentrators rotatably coupled to solar array panels for use in a spacecraft application, it should be understood that adjustable concentrators rotatably coupled to solar array panels may be used in other applications as well. For example, such adjustable concentrators may be used in various other applications where solar energy is received for conversion to power, such as in solar-powered automobiles. 
     Although the present invention has been described in detail, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as falling within the scope of the appended claims.