Abstract:
A solar concentrator calibration tool that compensates for inconsistencies in the fabrication, assembly and installation of a solar collector system, permits the solar collector to perform optimally. The calibration tool provides feedback information to a supervisory control processor, allowing the processor to compare the expected position of the sun to the “actual” position found by the calibration tool. The processor then generates a calibration signal, thereafter used by the collector&#39;s movement control mechanism, to compensate the tracking of the solar collector to accurately follow the movement of the sun, unconstrained by the effects of the construction inconsistencies.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This U.S. patent application is a continuation application of U.S. patent application Ser. No. 13/897,268, filed May 17, 2013, now pending, which is a continuation of U.S. patent application Ser. No. 12/841,360, filed Jul. 22, 2010, now U.S. Pat. No. 8,466,400, issued Jun. 18, 2013, which claims the benefit of U.S. Provisional Application No. 61/228,440, filed Jul. 24, 2009, now expired. This patent application incorporates by reference, the entirety of U.S. patent application Ser. Nos. 13/897,268, 12/841,360, and 61/228,440. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to the installation of a solar collector and, more particularly, to a system for providing alignment between the sun and the collector, regardless of the physical characteristics of the solar collector support system. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the increasingly important field of renewable energy production, solar power is a highly promising technology. In some cases, this technology employs solar cells, also known as photovoltaic (PV) cells, to convert solar radiation into direct current electricity. Solar cells may be arranged into arrays of flat panels, in which sunlight directly impinges upon large surface areas of solar cells. Or, solar cells may be used in photovoltaic concentrators, in which mirrors and lenses reflect and focus solar energy onto a much smaller solar cell. In other cases, solar irradiance is concentrated and focused onto a cavity receiver to produce thermal energy. While the efficiency of any solar power system is largely quantified by the ability of the concentrator to convert solar energy into electricity, the ability of the solar energy system to track the sun&#39;s movements also has a large effect on a solar power system&#39;s efficiency. That is, it remains an important consideration in solar energy systems to be able to effectively and efficiently adjust the angle of the solar panel/collector to maximize the intensity of the sunlight being collected. 
         [0004]    One type of tracking system utilizes pedestal-mounted designs, in which a solar module is generally mounted on a vertical pole, or pedestal, which is itself inserted into the ground. Various mechanical linkages and motors are then used to tilt the panel on the support pole in one or two axes according to the sun&#39;s movements. 
         [0005]    In addition to pedestal-mounted designs, many other tracking systems have utilized combinations of sliding rails, pin joints, ball-and-sockets, rotating wheels, and more. These non-pedestal designs involve multiple supports, typically located around the perimeter of the solar module, to anchor and control the module&#39;s movement. For instance, one prior art arrangement comprises a circular, ring-mounted reflector which is supported by a pair of diametrically-opposing levers, with a third lever located below and mid-way between the connections of the lever pair. The three levers use an assembly of linkages to turn the reflector to its desired position, which can include turning the reflector face-down to a protective stowed position. 
         [0006]    While numerous tracking systems have been designed and implemented, problems remain with site preparation, “stack-up” tolerances as a result of the solar collector fabrication and assembly, as well as with the installation of the collector itself at the site. That is, solar collectors require the construction of a precise foundation and subsequent optical alignment in order to accurately align the collector with the sun during installation and thereafter track the sun&#39;s motion across the sky. The high costs associated with site preparation and fabrication of such a foundation impacts the economic viability of installing large-area solar collector fields (that is, an installation of a large number of separate collectors which are then operated as a “system”). 
       SUMMARY OF THE INVENTION 
       [0007]    The need remaining in the prior art is addressed by the present invention, which relates to the installation of a solar collector and, more particularly, to a calibration tool and procedure for creating “custom” tracking information that compensates for inaccuracies in an individual solar collector installation, thus maintaining alignment between the sun and the installed solar collector, regardless of various imperfections in the solar collector construction and installation. 
         [0008]    In particular, the calibration tool of the present invention comprises a system that is removably attached to a solar collector system upon installation. The tool performs a calibration function by: (1) collecting a body of data defining the locations of a collector as it initially moves to track the sun&#39;s movement; (2) comparing this actual movement data with “expected” movement data (taken from standard solar charts and latitude/longitude information); (3) creating an adjustment “overlay” (in the form of the “difference” between these two sets of data); and (4) storing the overlay information within the collector&#39;s movement control mechanism. 
         [0009]    The calibration tool comprises an alignment element (removably attached to the collector) used to sense the optimum alignment between the collector and the sun at any given point in time, a position encoder (also attached to the collector) to generate the collector&#39;s elevation and latitude information (in general, “position information”) at any given point in time, and a processor that collects and utilizes the information from both the alignment element and the position encoder, in conjunction with the “expected” sun movement information, to determine the offset between the actual and expected values and thereby generate the calibration information (offset data) used by the servomechanisms to control the movement of the collector. 
         [0010]    In operation, the calibration tool functions to initially provide alignment between the sun and the collector and determine the initial position information (e.g., elevation and azimuth) of the collector. Thereafter, a calibration routine (stored in the processor) is followed for a period of time sufficient to determine the offset between the expected location of the sun (relative to the optical axis of the collector—from known reference sources) and the actual location of the sun (relative to the optical axis of the collector—from the position encoder data). The offset information is used by the processor to determine the calibration adjustment that will be required to be performed by the collector&#39;s servomechanisms to keep that particular collector in alignment with the sun&#39;s path. The information is then transferred to the servomechanisms and the calibration tool is removed from the collector. 
         [0011]    It is an advantage of the arrangement of the present invention that the calibration tool is only required upon initial installation of a solar collector. Once the calibration is performed, the tool may be removed and is ready for use with another collector installation. 
         [0012]    Moreover, the use of a calibration tool to perfect the alignment between the sun and the collector has been found to reduce the accuracy required in preparing the installation site, constructing the individual components of the system and building the system in the field. These reductions yield a significant cost savings over prior art arrangements that relied on precise alignment upon installation. 
         [0013]    Other and further aspects and embodiments of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Referring now to the drawings, 
           [0015]      FIG. 1  illustrates an exemplary solar collector that may utilize the calibration tool of the present invention; 
           [0016]      FIG. 2  is a side view of the collector of  FIG. 1 ; 
           [0017]      FIG. 3  is a diagram of an exemplary calibration tool formed in accordance with the present invention; and 
           [0018]      FIG. 4  is a flowchart illustrating an exemplary process of performing solar collector calibration in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  is a simple illustration of an exemplary solar collector  10  that can be calibrated with the system of the present invention to provide a tracking program that overcomes imperfections that may exist in the system components, installation site preparation and/or on-site construction of the solar collector itself. In this particular example, solar collector  10  includes a concentrating reflector  12  for re-directing impinging solar radiation onto a receiver  14  (or a secondary reflector positioned at that location). At an installation site, collector  10  may be attached to, for example, a concrete pad  20 , or similar support structure. A mounting structure  30  is used to attach collector  10  to pad  20 . Although not explicitly shown in this view, structure  30  also includes servomechanisms used to move collector  10  so as to track the sun&#39;s movement during the course of the day. A side view of the arrangement of  FIG. 1  is shown in  FIG. 2 , which illustrates a particular configuration of mounting structure  30 . As discussed above, the variations in site preparation and concentrator assembly will impact the alignment between collector  10  and the sun. For example, a “level” platform upon which to mount a collector should not exhibit an offset from “level” no greater than “millimeters” over a platform several meters in width. Variations in the dimensions of mounting structure  30  may also impact the alignment between collector  10  and the sun. 
         [0020]      FIG. 3  illustrates an exemplary calibration tool  40  formed in accordance with the present invention to provide for a correction between the expected path of the sun&#39;s movements and the “actual” locations of the sun observed by receiver  14  as collector  10  moves to maintain alignment. As discussed above, the difference between the expected and actual values can be attributed to a variety of factors including, but not limited to, imperfections in the pad upon which the collector is installed, misalignment between system components, imperfections in the construction of the individual system components and/or construction imperfections in the actual installation of the solar collector system in the field. Calibration tool  40  is not permanently attached to solar collector  10 , but is only used upon installation to determine the offset between the predicted and actual values and create an adjustment signal thereafter used by the collector&#39;s servomechanisms to control the movement of collector  10 . Thereafter, calibration tool  40  is removed. 
         [0021]    As shown in  FIG. 3 , calibration tool  40  includes an alignment element  42 , a processor  44  and a position encoder  46 . Alignment element  42  is used to periodically re-adjust the position of collector  10  to maintain the collector&#39;s optical axis in alignment with the location of the sun. In one embodiment, alignment element  42  comprises a quadrant photodiode sensor array that will create a series of electrical output signals based upon the amount of solar radiation received by the array. Various other types of arrangements may be used to form alignment element  42  including, but not limited to, a matrix configuration of photodiodes, a set of thermocouples, a camera; in general, any type of instrumentation that will be affected by radiation from the sun. 
         [0022]    Processor  44  includes a control program that will cause the collector to adjust its position until alignment between the sun and alignment element  42  is achieved (i.e., when “maximum” solar radiance is measured by, for example, a photodiode array). Once alignment is achieved, the actual location information associated with the position of collector  10  (in terms of elevation and azimuth data) are recorded by position encoder  46  and transmitted to processor  44 . 
         [0023]    With this understanding of the operation of the elements forming calibration tool  40 , an exemplary calibration process as performed in accordance with the present invention will now be described in detail. 
         [0024]      FIG. 4  contains a flowchart of an exemplary process that can be used to implement the calibration process as provided in accordance with the present invention. The process begins at step  100  with the attachment of alignment element  42  and position encoder  46  to the solar collector system. In order to properly calibrate the alignment of the collector system with the location of the sun, alignment element  42  needs to be positioned along the optical axis of the system. In a preferred embodiment, alignment element  42  is positioned at receiver  14 , allowing for its relatively straightforward attachment and later removal. 
         [0025]    Once these elements are in place, the calibration process starts with an initial scan movement of collector  10  (step  110 ) and measurement of the optical signal (sun&#39;s radiance) impinging alignment element  42 . This step can be thought of as a “centering” process to initially line up receiver  14  of the solar collector system with the position of the sun. As shown in step  120 , the movement of collector  10  (under the control of the servomechanisms included in mounting structure  30 ) continues, with the power of the optical signal captured by alignment element  42  being transmitted to processor  44  until a signal associated with optimum alignment is achieved (e.g., maximum solar power is measured). At this point, an initial registration of collector  10  with the sun&#39;s location has been accomplished, and the location of collector  10  (elevation and azimuth) is transmitted from position encoders  46  to processor  44  (step  130 ). 
         [0026]    Inasmuch as the sun continuously traverses a path across the horizon, collector  10  must remain aligned with the sun&#39;s position to continue to receive maximum radiance. The art is replete with systems that provide such tracking, as mentioned above. However, these systems are known to utilize only the ‘predicted’ or ‘expected’ movement of the sun (for a given geographic location, time of year, etc.) and do not take into account any irregularities introduced into the tracking by the imperfections in the solar collector system itself. It is the purpose of the present invention to understand these irregularities and calibrate the “path” followed by the collector so as to remain in alignment with the actual location of the sun. 
         [0027]    Thus, the calibration process of the present invention continues at step  140  with the initiation of the calibration sequence. The sequence begins with the movement of collector  10  continuing to be controlled, for a predetermined period of time, by measuring the optical signal received by alignment element  42  so as to maintain alignment with the sun (step  150 ). As each movement is performed, the solar collector&#39;s location information from position encoders  46  (e.g., elevation and azimuth) is transmitted to processor  44  (step  160 ), which appends a timestamp to this location data and stores it in an included memory module (step  170 ). 
         [0028]    At this point, a decision is made (step  180 ) to determine if the calibration time period has expired. Presuming the calibration period has not expired, the process returns to step  150 , where the position of the collector is again re-aligned with the sun (using feedback from alignment element  42 ) and the associated elevation and azimuth information is transmitted to processor  44 . 
         [0029]    By repeating these steps for a predetermined period of time (measured in, perhaps, hours or minutes), a body of data is created that defines the actual position of the sun with respect to collector  10  that is required to maintain alignment therebetween. Once a sufficient amount of data has been gathered (as determined by the individual performing the calibration), the process moves on to step  190 , where processor  44  functions to compare the collected actual data regarding the elevation and azimuth of the sun to the expected values associated with the geographic information stored therein. 
         [0030]    Inasmuch as any installed solar collector will have one or more imperfections, the actual and predicted values will be different. Processor  44  then functions to determine this difference as an offset adjustment that needs to be made to the expected values of the sun&#39;s movements (associated with the movement over the course of an entire year) and transmits this offset adjustment as a calibration signal to the servomechanisms associated with mounting structure  30  (step  200 ). Once the calibration information has been stored in the servomechanisms, the calibration process is finished, and alignment element  42  and position encoder  46  are removed from the solar collector system (step  210 ). 
         [0031]    It is to be understood that calibration tool  40  may be extended to control a network of solar concentrators that have been co-located in a distributed fashion across an ‘open field’ area. In conventional arrangements, such concentrator arrays have to compromise between land usage and shadowing of neighboring concentrators. Solar thermal collection is conducted only when the sun is 30 degrees off the horizon, resulting in an average of 6.25 hours/day of solar collection over the year. The control/tracking method of the present invention can be configured to raise the dishes in sequence as the sun breaks the horizon without shadowing. This would result in a 4% increase in annual capacity factor. 
         [0032]    While the invention has been described with reference to the preferred embodiments, obvious modifications and alterations are possible by those skilled in the relevant art. Therefore, it is intended that the invention include all such modifications and alterations to the full extent that they come within the scope of the following claims or equivalents thereof.