Abstract:
An array of solar collectors track the sun based on measured values of power output from the array and from a sun sensor on the array. The sun is tracked by periodically adjusting the altitude and azimuth of the array so the collectors remain pointed at the sun to maximize an amount of solar flux reflected from the collectors. The sun sensor, which detects alignment of the sun, recognizes when relative movement of the sun causes about a 10% reduction in power output of the array. The altitude and azimuth of the array are readjusted based on output from the sun sensor. While the array is being reoriented, power output from the array is monitored, and values for power output versus orientation of the array are recorded. Offset values between the power output, sun sensor output, and the ephemeral equations are calculated by comparing these values during operation.

Description:
BACKGROUND 
     1. Field of Invention 
     The invention relates to maximizing output from a concentrated photovoltaic (CPV) system. More specifically, the invention relates generally to a method of identifying an offset for positioning solar collectors in an orientation so a maximum amount of solar energy reflects from the solar collectors. 
     2. Description of Prior Art 
     Converting solar energy into electricity is often accomplished by directing the solar energy onto one or more photovoltaic cells. The photovoltaic cells are typically made from semiconductors, that can absorb energy from photons from the solar energy, and in turn generate electron flow within the cell. A solar panel is a group of these cells that are electrically connected and packaged so an array of panels can be produced; which is typically referred to as a flat panel system. An array of panels used together is typically referred to as a solar flat panel photovoltaic (PV) system. Solar systems are typically positioned so that on the average they receive rays of light directly from the sun. 
     Some solar energy systems, which are referred to as Concentrated Photo Voltaic (CPV) systems, concentrate solar radiation onto a solar cell. CPV systems include solar collectors with a curved reflective surface that when exposed to sunlight reflects the light into a concentrated and focused image onto the solar cell. However, unless the collectors are substantially aligned with the sun, the image becomes unfocused to cause a corresponding reduction of power output from the CPV system. While tracking systems are generally included with CPV systems to maintain alignment of the solar collectors with the sun; misalignments can remain due to inherent manufacturing tolerances in CPV systems. 
     SUMMARY OF THE INVENTION 
     Provided herein is a method of positioning an array of solar collectors. In an example, the method includes monitoring an output from a sun sensor positioned on the array, identifying when the output from the sun sensor reaches a designated value, reorienting the array based on the designated value, monitoring a power output from the array, estimating an offset value based on a comparison between the output from the sun sensor and the power output from the array, and adjusting orientation of the array based on the offset value. In this example, the step of monitoring a power output from the array can occur when the array is being reoriented. In an example, the sun sensor has an acceptance angle that is greater than an acceptance angle of the solar collectors. Optionally, the step of reorienting the array includes adjusting an elevation of one end of the array and adjusting an azimuthal orientation of the array. In an alternative, estimating an offset value includes estimating a difference between an orientation of the array when the output from the sun sensor is at about a maximum value, and an orientation of the array when the power output from the array is at about a maximum value. In this example, the orientation of the array can be its elevation, its azimuth, or both. The method may further include identifying an orientation of the array corresponding to a maximum power output of the array to define a maximum power orientation, comparing the maximum power orientation with an ephemeral orientation to define an ephemeral offset, and adjusting orientation of the array based on the ephemeral orientation and the ephemeral offset. In this example, the method can continue to orient the array for maximum power output when the sun sensor is obscured by clouds or other obstructions. Alternatively, the solar collectors reflect light from the sun to generate power, and when reorienting, the array is moved into an orientation that is ahead of an on-axis orientation with the sun, so that the solar collectors will be on-axis with the sun at a future time due to relative movement of the sun. 
     Also disclosed herein is another method of orienting an array of solar collectors with a path of the sun. This method includes sensing an intensity of the sun at a particular location on the array, adjusting an orientation of the array when the sensed intensity is at a designated value, monitoring a power output from the array and the sensed intensity as the orientation of the array is being adjusted, identifying an orientation of the array when the power output is at a maximum value to define a maximum power orientation, and identifying an orientation of the array when the sensed intensity is at a maximum value to define a maximum intensity orientation, estimating a sensing offset by comparing the maximum power orientation with the maximum intensity orientation, and further adjusting the orientation of the array by the sensing offset. The steps of this example method can be repeated so that the array is at an on-axis orientation with the sun. Optionally, an axis of rays from the sun is aligned with an edge of an acceptance angle of the array, and the array is positioned so that the path of the sun moves the axis to an opposite edge of the acceptance angle of the array. In an example, the intensity of the sun is measured with a sun sensor having an acceptance angle having a value at least twice of a value of an acceptance angle of the array. The array can include modules, and the method can further include monitoring an output power from each of the modules. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view of an example embodiment of an array of solar collectors mounted on a moveable frame in accordance with the present invention. 
         FIG. 2  is a side view of the array of  FIG. 1  showing an example of an elevation means for tilting the array in accordance with the present invention. 
         FIG. 3  is a front view of the array of  FIG. 1  showing an example of an azimuthal orientation means in accordance with the present invention. 
         FIG. 4  is a schematic illustration of the array of  FIG. 1  with positioning means in accordance with the present invention. 
         FIG. 5  is a graphical illustration of the array of  FIG. 1  in example orientations over a period of time and corresponding plots of elevation and azimuth in accordance with the present invention. 
         FIG. 6A  is a perspective view of an example of a sun sensor for use with the array of  FIG. 1  in accordance with the present invention. 
         FIG. 6B  is a plan view of the sun sensor of  FIG. 6A  in accordance with the present invention. 
         FIG. 7  is a graphical illustration of solar flux generated by a solar collector with respect to elevation and azimuth of the solar collector and in accordance with the present invention. 
         FIG. 8  is a graphical illustration in a plan view of the flux plot of  FIG. 7 . 
     
    
    
     While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF INVENTION 
     The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. 
     It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the improvements herein described are therefore to be limited only by the scope of the appended claims. 
       FIG. 1  is a perspective view of a solar conversion system  10  that includes a solar array  12  made up of modules, where a module is a grouping of solar collectors  14 . The array  12  is mounted on a frame  16 , and suspended over the collectors  14  are receivers  18  that mount on rails  20  shown extending lengthwise and supported by frame  16 . In one embodiment, the collectors  14  are arranged into groups that define a module  17 . In the example of  FIG. 1 , the array  12  includes  4  modules  17 , wherein each module  17  includes  12  collectors  14 . A vertical monopole  22  is shown set into a surface, such as the ground, a rooftop, or other structure, and supports the frame  16  at an elevation above grade and positioned for unobstructed movement. Further illustrated in the example of  FIG. 1  is an elevation motor  24  for elevating one end of the array  12  for positioning the array  12  in a designated orientation. Further in the example of  FIG. 1 , sidewalls  25  may be provided around each module  17 . 
     A side view of the solar conversion system  10  provided in  FIG. 2  and illustrates the elevation motor  24  depending downward from the frame  16  and mounted to a bracket  26 . In the example of  FIG. 2  the bracket  26  is elongate and depends from a hub  28  and generally oblique to monopole  22 . The hub  28  is mounted on an upper end of monopole  22  and can rotate with respect to the monopole  22 . The embodiment of the hub  28  of  FIG. 2  has an opening on its lower end for receiving the upper end of the monopole  22 . The frame  16 , which has a generally rectangular outer periphery, pivotingly mounts on an upper end of hub  28  by clevis members  30  ( FIG. 3 ) and hinge rod  32 . The clevis members  30 , which are generally planar members, each have an end attached to an upper end of hub  28 . The end rod  32  is received in bores formed laterally through the clevis members  30  and that orients substantially parallel to frame  16 . Elevation motor  24  has a selectively extendable leg  34  that projects from its upper end and pivotingly attaches to a pivot beam  35  that is shown attached to a lower surface of frame  16 . Leg  34  is urged upward for pushing upward one end of frame  16 , thereby allowing for tilting of the array  12  as illustrated by the curved arrow. 
     In  FIG. 3  a front view is shown of an example of the solar conversion system  10  that depicts an azimuthal motor  36  next to the monopole  22  and hub  28 . The azimuthal motor  36  provides relative rotation of the hub  28  with respect to monopole  22 , thereby azimuthally orienting array  12  as illustrated by the curved arrow around monopole  22 . Hinge member  38  mounts on a lower end of frame  16  and depends downward to between the clevis members  30 . A bore through hinge member  38  registers with the bores through the clevis members  30 , so that the hinge rod  32  can engage clevis members  30  to hinge member  38 , and allow pivoting movement of clevis members  30  with respect to hub  28 . 
       FIG. 4  provides a schematic illustration of the solar conversion system  10  and wherein the array  12  is subdivided into a number of modules  46   1 ,  46   2 ,  46   3 , . . . ,  46   n , where n can be any value greater than 3. In an example, each of the modules  46   1 ,  46   2 ,  46   3 , . . . ,  46   n  includes twelve solar collectors  14 . Lines  48   1 ,  48   2 ,  48   3 , . . . ,  48   n  are shown extending from the modules  46   1 ,  46   2 ,  46   3 , . . . ,  46   n  and to a power combiner  50 , where the lines  48   1 ,  48   2 ,  48   3 , . . . ,  48   n  provide communication for electricity generated within the receivers  18  ( FIG. 1 ). In an example, the electricity from the modules  46   1 ,  46   2 ,  46   3 , . . . ,  46   n  is combined in series within the power combiner  50 . Further illustrated in the example of  FIG. 4  is a controller  52  that is in communication with power combiner  50  via line  54 . In an example, the controller  52  can monitor power delivered to the power combiner  50 . A light sensor  56  is schematically illustrated on the frame  16  and in communication with controller  52  via link  58 . Examples of the link  58  include wiring, wireless signals, telemetry and other forms of signal communication. Additional links  60 ,  62  illustrate communication between the controller  52  and elevation motor  24  and azimuthal motor  36 . As such, in one example signals generated within controller  52  may be transmitted via link  60  for actuating leg  34  attached to elevation motor for pivoting the panel  16  thereby adjusting orientation of the array  12 . Similarly, signals via link  62  from controller  52  to azimuthal motor, may azimuthally orient frame  16  via connection  66  to azimuthally adjust orientation of the array  12 . Further illustrated in the example of  FIG. 4  is a circuit  68  connecting to power combiner  50  that includes lines  70 ,  72  that by communication between the power combiner  50  and a load  74 . The load can be anything consuming electricity, as well as means for storing electricity for later use. 
       FIG. 5  is a graph  76  that illustrates a measured on-axis plot  78  that represents values of azimuth and elevation of array  12  over time. In an example, elevation is the angle of the array  12  with respect to vertical, and azimuth is the angle a centerline projecting from the array  12  varies from true North. The azimuth and elevation values used to create plot  78  are those that result in a maximum power output of the array  12 . Also provided on the graph  76  is a sensor on-axis plot  80 , shown in dashed outline, which represents an example of azimuth and elevation values to orient an array  12  over the course of a day wherein a sun sensor would yield a maximum output. The spatial difference between plot  78 ,  80  defines an offset  82 , which as described in more detail below may be compensated for to maximize power output from the array  12 . 
     In  FIG. 6A  provides a perspective view of one example of a sun sensor  84  shown having photo-transistors  86  set in a planar base  88 , and a stand  90  on the base  88  set between the transistors  86 .  FIG. 6B  is a partial sectional view of the sun sensor  84  and taken along lines  6 B- 6 B. Shown in the embodiment of  FIG. 6B  recesses  91   1 ,  91   2 ,  91   3 ,  91   4  are formed into the lateral side walls of the stand  90  and extend from a lower end of the stand  90  to roughly a mid-portion of stand  90 . The photo-transistors  86   1 ,  86   2 ,  86   3 ,  86   4  are set on the base  88  such that at least a portion of each transistor  86   1 ,  86   2 ,  86   3 ,  86   4  extends into a corresponding recess  91   1 ,  91   2 ,  91   3 ,  91   4 . The photo-transistors  86   1 ,  86   2 ,  86   3 ,  86   4  are numbered to indicate an example of a location. To illustrate, an embodiment exists wherein photo-transistor  86   1  is referred to as an upward transistor and oppositely disposed photo-transistor  86   3  is designated as a downward transistor. Similarly, photo-transistor  86   2 , which is on a lateral side of the stack  90  and adjacent both photo-transistor  86   1  and photo-transistor  86   3 , is referred to as an east transistor. Similarly, photo-transistor  86   4  is designated as a west transistor. In an example, the transistors  86   1 ,  86   2 ,  86   3 ,  86   4  are wired so that if one of the transistors is fully exposed to sunlight, and the oppositely disposed transistor is fully shaded, the transistors yield a signal output of about 100%. In contrast, if an oppositely disposed photo-transistor is fully illuminated by sunlight and the original transistor is shaded, the transistors are configured to give an output of around 0%. In conditions where each transistor has roughly an equal amount of sunlight exposure, the total output will be around 50%. As such, knowing the orientation of the oppositely disposed photo-transistors with respect to orientation of a solar panel, alignment of the panel can be approximated by monitoring an output value of the photo-transistors. In one specific example, when a signal output from photo-transistors  86   1 ,  86   3  is about 100%, photo-transistor  86   1  is fully illuminated, and photo-transistor  86   3  is substantially fully shaded, whereas signal output of zero indicates an opposite orientation, e.g. photo-transistor  86   3  is fully illuminated, and photo-transistor  86   1  is substantially fully shaded. Following the same reasoning for signal outputs of photo-transistors  86   2  and  86   4 , monitoring the output of these transistors provides a general indication of an orientation of the solar array on which the sun sensor  84  is mounted. Thus, orienting a solar array based solely on measured output from sun sensor  84 , an orientation of an associated array  12  would be adjusted so that each of the pairs of photo-transistors would yield signal values of around 50%. Moreover, knowing that signal outputs of greater than 50 or less than 50 for either pair means at least one of the photo-transistors is shaded and to achieve an on-axis orientation, adjusting the elevation and/or azimuth of the array  12  could be undertaken to achieve an on-axis orientation. Knowing the magnitude of the signal output yields an indication of in which direction the adjustment should take place. 
     Included in  FIG. 7  is a 3-dimensional graph  92  where an example azimuth axis  94  and elevation axis  96  are shown in a plane P, and a plot  98  extends over axis  94 ,  96 . The example plot  98  is shown having an apex  100  centered over the intersection of axis  94 ,  96 . Also illustrated is a line L that extends from the intersection of axis  94 ,  96 , in a direction substantially normal to plane P and intersects plot  98 . In the example of  FIG. 7 , where line L intersects plot  98  represents the flux produced by solar array when the array is “on-axis” with the sun. Thus, in an on axis condition, line L would be coaxial with an axis of a path of direct sunlight onto the array. Further illustrated in  FIG. 7 , is how changes in angular orientation along one or both of the azimuth axis  94  and elevation axis  96  can affect the magnitude of the flux. In one example, an acceptance angle θ is shown where these variations and rotation on either axis  94 ,  96  does not substantially affect magnitude of the flux. In an example embodiment, an acceptance angle of about 0.5 degrees correlates to maintaining about 90% of the maximum flux. Thus, optimizing the power output of a solar array can include monitoring orientation of the array so that offset angle between the on-axis configuration is kept within the acceptance angle. 
     As is known, relative movement between a solar array  12  and the sun requires repositioning of the array so that an on-axis orientation can be maintained. While the sun sensor of  FIGS. 6A and 6B  may provide an on-axis orientation of the sun sensor  84 , manufacturing tolerances and other possible misalignments, can limit the ability of a sun sensor to accurately access an on-axis orientation of a solar array. To overcome these misalignments, output of the sun sensor  84  and the power output from the solar array  12  may be monitored to determine an offset  82 . In one example of operation, signal output from the sun sensor  84  is monitored over time, and when the signal output reaches a designated threshold value, the array is moved about its azimuth angle and/or elevation angle. Moreover, as described above, signal output values from the sun sensor  84 , e.g., greater than or less than 50%, can indicate in which direction the array  12  should be moved. Referring back to  FIG. 7 , because a range of orientation of a solar array  12  is limited to its acceptance angle θ, the array  12  is moved until it is at an edge of its acceptance angle θ with the sunlight. Thus in one example, an acceptance angle of the sensor  84  may be greater than that of the acceptance angle θ of the solar array  12 . For the purposes of discussion herein, an acceptance angle of the sun sensor  84  described an angle of rotation in either an azimuthal or elevational orientation, wherein output of one of the pairs of photo-transistors varies from about 0% to about 100%. In one example embodiment, the acceptance angle for the sun sensor  84  is around 3 degrees, wherein an acceptance angle θ of a corresponding solar array  12  is around 0.5 degrees. 
     An example method of using the sun sensor  84  for positioning of the solar array includes simultaneously monitoring outputs from the sun sensor  84  and monitored power from the array  12 ; also recorded are the azimuthal and elevational orientations of the array  12  when the outputs are monitored. This step of monitoring can occur as the array  12  is being moved to adjust for relative movement of the sun. These monitored outputs with respect to orientation can then be compared to one another for assessing or estimating an offset  82 . For example, if signals from the sun sensor  84  indicate an on-axis orientation at an azimuth elevation that is different from an azimuth elevation where the solar array  12  has a maximum power output, the difference in these respective azimuths in elevations can define an offset value  83 . As such, knowing the offset value  83 , the sun sensor  84  can be used for orienting the solar array  12 , and then the array can be further adjusted by a value of the offset  82 . 
     To illustrate an example of estimating an offset value, an overhead view of the plot  98  is provided in  FIG. 8 . In this example, a path P O  illustrates an example of movement of the intersection of the azimuth and elevation axis  94 ,  96  of  FIG. 7  and how this movement is maintained within the boundaries of the apex  100 . As such, containing this orientation within the apex  100  results in a continuous output of power as close as possible to the maximum power output of the solar conversion system  10 . To contrast an example, a path P I  shown in dashed outline has start and end points outside the apex  100 , path P I  illustrates an example of orienting solar array  12  based on outputs from sun sensor  84  and without applying an offset value; as such, an overall drop off in system power output is experienced if the offsets are not accounted for. 
     A similar offset may be utilized in situations when shading from clouds or other obstructions limit the ability to acquire an on-axis orientation by use of the sun sensor  84  or power output from the array  12 . In this example, actual on-axis positions are monitored during use, and these positions are compared to an ephemeral equation based on the location of the solar array  12  and date and time in question. Manufacturing tolerances in addition to settling of the ground beneath the array  12  will likely produce some differences between the actual on-axis condition in those predicted by the ephemeral equation. Thus by maintaining a history of the offsets when clouds obstruct the view of the sun, a threshold value is determined by the controller  52 , and the tracking of the sun can switch to the ephemeral equation and be adjusted by the estimated ephemeral offset. 
     The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.