Abstract:
The present invention describes a solar panel system tracker that closely approximates the output levels of an actively tracked system but at significantly reduced levels of complexity and cost. The present invention is comprised of a clock that generates a five degree step function which moves the solar panel system in five degree increments over the period of the solar day. This provides approximately thirty-five separate adjustments throughout the day, yielding an aggregate output performance of approximately 90 percent compared to a fully tracked system.

Description:
[0001]    This non-provisional utility patent application claims the benefit of priority for U.S. Provisional patent application No. 61/002,045 filed Nov. 06, 2007. 
     
    
     BRIEF DESCRIPTION 
       [0002]    The subject of this invention relates to the alternative energy arts. Specifically, the present invention discloses a solar tracker that operates on the principle of a clock operated step function which provides energy capture performance of near real time tracking systems but at a very economical cost. 
       BACKGROUND OF THE INVENTION 
       [0003]    Power generation by means of photovoltaic cells (PV) is not new. Individual cells are normally configured in an array of multiple cells to create a specific desired output power. For example, a series/parallel array to provide and output rating of 12 volts at 1.5 amps. This series/parallel arrangement is referred to as a “solar panel,” and power output from the panel is customarily expressed in watts, thus in the preceding example the panel formed by the array would have a nominal rating of 18 watts. Common system design practice is to combine a number of panels to construct larger arrays to create a power source capable of delivering high levels of useful power. This is done by mounting a plurality of solar panels to a common frame. Typical contemporary systems range from two to five kilowatts, but as will be recognized, virtually any output power level can be obtained by increasing the number of panels that are interconnected. 
         [0004]    As mentioned panel systems vary enormously in their output capability, however, one common factor is the efficiency of the PV system. It is well understood in the art that a PV cell will produce peak output power output only when the sun&#39;s rays are impinging directly on the cell. Any off angle, whether longitudinal or lateral, will result in a rapid decline of the output power. It follows then that the power output of a panel system will suffer in the same way and to the same degree as the individual cells that comprise the system. Of course there are other factors that impact cell output including junction temperature, basic cell transfer efficiency and so forth, but for purposes of the disclosed invention, the discussion is limited to impinging angle issues. 
         [0005]    Since the power decrease phenomenon is so well understood, a number of methods have been used to compensate for the time variation of the impinging angle due to the sun&#39;s path over time. These methods include simply over-sizing a fixed panel system to account for power loss due to impinging solar angle variation, using focusing means to concentrate the impinging solar light to compensate for solar angle variation, and trackers that move the panel system to constantly face the sun in order to maximize the time the array is subjected to direct impinging light. Each of these, while functional, has one or more serious drawbacks. 
         [0006]    The over-sizing of a fixed panel system is highly inefficient and very costly. The theory of this method is to generate enough power during the relatively short period of time when the system is at or near its peak output to compensate for less than maximum output at all other times. As will be discussed in detail below, a 3.6 kilowatt panel system will deliver on average only 65 percent, or 23.4 kilowatts of power on a given day and under similar conditions when compared to a fully tracked panel system. 
         [0007]    Focusing methods exist in several different variants; for example, parabolic reflectors or mirror array reflectors. The fundamental way that these systems work is to concentrate the impinging solar light on a target, either a PV array or, more commonly, a boiler. Regardless of the target, the theory is to extract a greater amount of energy in a short period of time by amplifying the incoming solar light. Some of these focusing methods are used in tandem with tracking schemes, described just below. 
         [0008]    The focusing method suffers from two serious problems. First, focusing methods cause a buildup of heat on the surface of the panel or target, thus raising the junction temperature of the individual cells. This causes a decrease in output simply due to semiconductor physics. To compensate, cooling methods must be added to maintain a stable junction temperature. This is expensive and complex. Second, while the focusing method increases the output with respect to a fixed panel system, unless it is tracked it, too, has inefficiencies for the same reasons discussed just above. 
         [0009]    As is the case for focusing methods, tracking mechanisms come in numerous variants. Common to all of them is the ability of the mechanism, or “tracker”, to follow the sun as it transits the daytime sky. This is accomplished by providing a means for detecting where the sun is in the sky, then driving the solar panel array until it is perpendicular to the impinging light. This method is referred to as active tracking. The primary feature of active tracking is that the solar panel array is moved almost continually as the sun transits its daily arc, keeping the impinging light at an almost exact ninety degree angle to the surface of the array. 
         [0010]    Tracking methods also suffer from multiple problems. First, they are complex, requiring specialized knowledge to install and maintain. Second, they are very expensive. Third, in general they exhibit a high failure rate when compared with the other methods described. This is due to the complex mechanisms, use of exotic substances and difficulty in maintaining alignment under certain conditions. The vast majority of the current trackers require bright sunlight in order to track correctly. This is because they operate on a temperature differential—that is, the panels move when an element is exposed to direct sunlight. On overcast days trackers of this type become misaligned in short order. 
         [0011]    What would be desirable would be a method and apparatus that will approximate the output levels of an actively tracked panel system while not exhibiting the high cost, high maintenance and loss of alignment problems normally associated with these types of trackers. What would be further desirable would be a system that accomplishes the above yet is simple enough for average alternative energy users to install. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention describes a solar panel system tracker that closely approximates the output levels of an actively tracked system but at significantly reduced levels of complexity and cost. The present invention utilizes a clock that generates a five degree step function which moves the solar panel system in five degree increments over the period of the solar day. This provides approximately thirty-five separate adjustments throughout the day, yielding an aggregate output performance of approximately 90 percent compared to a fully tracked system. 
         [0013]    The present invention is comprised of a clock, a motor, a set of sensors, a battery and a control system. The control system is further comprised of a charge controller, a power controller, a motor controller and related sensor logic. Sensors used by the system include an AM (morning) sensor, a PM (afternoon) sensor, an AM limit switch, and a PM limit switch. Each of these components is mounted on a clutch plate so that the apparatus of the present invention may be quickly installed or removed for maintenance or relocation. 
         [0014]    The clutch plate is formed by a pair of disks: a fixed disk and a movable disk that is free to rotate on top of the fixed disk. The fixed disk has stop holes drilled at five degree increments, into which a pin controlled by a solenoid drops once a given step has occurred. This pin-and-hole combination is used to provide the requisite stability under windy conditions. 
         [0015]    The clutch plate assembly attaches to a fixed post via the lower fixed disk. The solar panel system, mounted on a frame, attaches to one end of a panel boom. The center of the panel boom attaches to the moveable disk. A counterweight is attached to the end of the panel boom opposite the solar panel system to create a balance point that is centered over the center of the moveable disk, thereby minimizing the load on the motor. 
         [0016]    In operation, the combination of the sensors and the control logic first ascertain that the solar panel system is in the morning position. If not, the logic activates the motor and drives the panels until the AM limit switch disengages the motor. Once in the correct position the clock logic begins the step function process. Each time a step is required the stabilizing pin is lifted, the motor is activated and the panels are moved exactly five degrees. The stabilizing pin is dropped into the next succeeding hole and the process waits until the time has been reached for the next step. At sunset the PM sensor instructs the logic to drive the panels to the morning position and the system goes to sleep until again awakened by the AM sensor. 
         [0017]    The method and apparatus of the present invention offer several advantages over the prior art. Among these are much lowered cost, good energy capture performance when compared to actively tracked systems and superior performance when compared with fixed systems. As well as these advantages, the present invention has other advantages discussed in detail below in conjunction with the drawings and figures attached. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1 : is a block diagram of the control system of the present invention. 
           [0019]      FIG. 2 : is a detailed block diagram of the motor controller of the system of the present invention. 
           [0020]      FIG. 3 : is a high level flow chart of the method of the present invention. 
           [0021]      FIG. 4 : is a detailed flow chart of the motor step function of the method of the present invention. 
           [0022]      FIG. 5 : provides details of the clutch mechanism of the apparatus of the present invention. 
           [0023]      FIG. 6 : shows the apparatus of the present invention in its normal operational mounting. 
           [0024]      FIG. 7 : is a schematic of a typical solar day. 
           [0025]      FIG. 8 : is a graphical representation of the performance of the present invention as compared to other contemporary solutions. 
           [0026]      FIG. 8 : is a typical output table comparing the performance of the present invention to other contemporary solutions. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0027]    The method and apparatus of the present invention form a system for economically optimizing the amount of energy captured from the sun using a solar panel array. Each of the various components of the apparatus will be discussed in detail in following paragraphs, however, a review of  FIG. 6  will provide the reader with an understanding of the basic architecture of the system. 
         [0028]    Looking briefly at  FIG. 6 , the apparatus of the present invention is comprised of three major parts: an array of solar panels  10 , a clutch assembly  800 , and an array boom and counterweight assembly  900 . Generally, the solar panel array  10  faces the sun and converts incoming light energy to direct current electrical energy. Clutch assembly  800  serves a number of purposes including acting as a mounting platform for the control electronics and battery as well as providing the wind stabilized pivot point needed for tracking the sun during a typical solar day. The array boom and counterweight assembly acts to center the weight of the apparatus at precisely the center point of the supporting post  910  thereby minimizing the load on the motor. Finally, AM sensor  920  and PM sensor  930  provide positional information for the control unit, becoming activated when the sun is detected in the morning and evening respectively. 
         [0029]    With the foregoing general description as a background,  FIG. 1  presents a block diagram of the control electronics of the system of the present invention. Control system  100  is comprised of numerous elements, but only the main elements will be discussed in detail here to aid in clarity. Elements not discussed are well known in the art and do not pertain directly to the present invention, thus need not be presented for a complete understanding of the invention. 
         [0030]    Solar panel array  10  is coupled to motor  150  via clutch  800 . Motor controller  200  uses information from various sensors and switches to determine when and in what direction the motor  150  should run. Solar panel array  10  is also connected electrically to array load  15  and charge controller  20 . Array load  15  can be any number of load devices including, but not limited to, batteries, pumps, inverters and DC driven generators. Charge controller  20  is used to manage the charge level of the battery  25 . 
         [0031]    Battery  25  is dedicated to providing power for the present invention and is not used for external load purposes. In a preferred embodiment, battery  25  is a 3 amp hour sealed lead acid type such as model PS1230 from Power-Sonic Corporation, San Diego, Calif. Power from battery  25  is delivered to motor  150  and to power controller  110 . Power controller  110  then regulates the incoming raw battery voltage and delivers it to the electronic portions of the system including the motor controller  200 , clock  120  and sensors  130  and  140 . 
         [0032]    Clock  120  is free running and outputs pulses at the rate of six KHz. These pulses are used by the logic contained within motor controller  200  to deliver the proper run time to motor  150 . In a preferred embodiment clock  120  is a CDCE913 from Texas Instruments, Dallas, Tex. AM sensor  140  and PM sensor  130  are photo sensitive devices that react to the light of the sun. In a preferred embodiment AM sensor  140  and PM sensor  130  are both type QSE113 from Fairchild Semiconductor, San Jose, Calif. AM sensor  140  is positioned such that early morning light causes it to change state and PM sensor  130  is positioned to cause it to change state in the evening. As detailed below, the combination of these sensors is used to assist in the correct positioning of the solar panel array  10 . 
         [0033]    Also used to assist in the positioning of solar panel array  10  are limit switches  145  and  135 . AM limit switch  145  is used to indicate to the logic of the motor controller  200  that the solar panel array  10  has reached its easterly most orientation. PM limit switch  135  is used to indicate to the logic of the motor controller  200  that the solar panel array  10  has reached its westerly most orientation. Both AM limit switch  145  and PM limit switch  135  are MS5-R from Velleman Inc., Fort Worth, Tex. 
         [0034]    Referring now to  FIG. 2 , the motor controller  200  is shown in greater detail. Sensor buffers  210  and limit switch buffers  215  receive the raw signals form the AM/PM sensors and AM/PM limit switches respectively and de-bounce them. De-bouncing is a term of art that means simply that the raw incoming signal is conditioned to a shape and level suitable for use in the core logic of the motor controller  200 . Counter logic and motor control block  300  contains the circuit level components that make the logical decisions needed to drive the motor and position the solar panel array. Motor power switching block  250  is comprised of the high power switching transistors required to activate the motor. Lastly, clutch driver  220  provides the control signals necessary to activate and deactivate the solenoid that mechanically stabilizes the solar panel array during times when the array is not being moved. 
         [0035]      FIGS. 3 and 4  provide a discussion of the method of the present invention. Starting with  FIG. 3 , the process is entered at step  510 . At step  515  a power on and initialization routine occurs. This routine is executed only once at the time that power is connected to the system. For example, after installation the solar panel array is approximately positioned and the battery terminals are connected. At this time all the logic is set to a known state and the clock starts delivering pulses to the motor control logic circuits. 
         [0036]    Initial alignment of the solar panel array need only be approximate. In fact, it can be completely in error without damage to the system. This is so because once the clock starts delivering pulses to the motor control logic the system will step five degrees every 20 minutes. Supposing that the solar panel array was initially positioned toward the west, an evening setting, when it should have been positioned near the center, a noon time setting, the system will run until the PM limit switch  560  is activated. At this time the logic will check the PM sensor  555  to determine if the sun is indeed in the west. If not, the solar panel array will simply wait until the sun “catches up” to the array position. At that time the array will be driven to the morning position and wait until dawn when the system will now be in time sync with the sun. Thus one advantage of the present invention is that it will self correct for misalignment of the array. 
         [0037]    Now suppose that the solar panel array was set to approximately the correct time of day with respect to the position of the sun. The motor control logic checks to see if the AM sensor  520  is active at step  520 . If the answer is no, process flow passes to the PM sensor decision  555  to see if the PM sensor  555  is active. If the answer is no, the solar panel array must be somewhere between morning and evening, thus control passes to the reset counter process  535  and the process proceeds as described just above. However, if the AM sensor  520  is active, the yes path is followed to the reset counter process  535  since if the AM sensor  520  is active then the solar panel array must be pointed at the morning sun and the process should proceed normally. 
         [0038]    At reset counter step  535  the step counter is set to  600 . This number is determined by the run time necessary to move the solar panel array approximately six degrees, and represents 100 pulses per one degree step. The clock  120  contains an internal divider that reduces the internal six KHz rate to the 100 pulses per degree required by the motor. As explained in detail below, the six degree run time is necessary to ensure that the solenoid shaft  862  drops into the next successive five degree step hole. The process flow passes to decrement counter step  540  where the value of the counter is decremented by one. At counter=0 decision  545  the process checks to see if the counter has been decremented to zero. If not, it is not yet time to move the solar panel array, and the process loops back to the decrement counter step  540 . If the counter has been decremented to zero it is time to move the solar panel array five degrees, so process flow passes to the step array process  600 . 
         [0039]    Looking now at  FIG. 4 , the step array process  600  is shown. The step array process is entered via enter step  610 . The method of the present invention checks to see if the array has activated the PM limit switch ( 894  of  FIG. 5B ). This is required because, as discussed above, if the array was initially mis-positioned, or if cloudy conditions have caused the array to be out of sync with the sun, the array will be driven to the evening position and wait for the sun to activate the return to the morning position. If the evening position has been reached, the yes path is followed and the process flow returns since no further action is required until the sun catches up with the array. 
         [0040]    If the evening position has not been reached, the No path is followed to the lift clutch pin step  620 . At lift clutch pin step  620  the solenoid that controls the clutch pin is activated, lifting the pin and allowing the top half of the clutch to move. At step motor step  630  the motor is activated and the solar panel array begins to turn. Just after the motor is activated the process passes to release clutch pin step  640 . Here the pin, which is spring loaded, tries to drop into the next five degree hole in the lower half of the clutch. Once the top half of the clutch has moved five degrees the pin drops, the motor is stopped and the process returns via return step  650 . It must be noted, however, that the motor run time is set to six degrees in order to ensure that the array has moved the complete five degree step. Since the solenoid shaft  862  is spring loaded, it will seat in the five degree hole just prior to the cessation of the motor run time. 
         [0041]    The process reenters the main flow at PM sensor decision  555 . Here the process checks to see if the sun has reached the evening position in the sky. If the answer is no, the process loops back to the reset counter step  535  and the systems waits for the next five degree time to expire. 
         [0042]    This loop will continue until the PM sensor decision  555  returns a yes answer. This means that the sun has reached the evening position in the sky. But in order to guarantee that the solar panel array has also reached its evening limit process flow passes to the PM limit decision  560 . If the PM limit switch ( 135  of  FIG. 1 ) has been activated, process flow transfers to the move to AM limit step  525  discussed below. If not, a no answer is followed out of PM limit decision  560  to the power decision  565 . If power has been lost for some reason, the process ends at end step  570 . If power is still on the system, and if the PM sensor is active but the PM limit switch is not, that must mean that the solar panel array has not yet reached its evening limit position. This can occur due to the sensitivity of the photo sensor or diffusion of the impinging light. In this case process flow passes back to reset counter step  535  in order to move the array another five degrees to the west. This loop will recur until the PM limit switch has been activated. 
         [0043]    Returning to PM limit decision  560 , and assuming that the PM limit switch has been activated, the system now moves the solar panel array to the morning position in anticipation of the next daily cycle. At move to AM limit step  525 , the necessary actions are taken to move the solar panel array to the morning position. These include reversing the drive motor, lifting the clutch pin, and moving the array toward the morning position. At AM limit decision  530  the process checks to see if the solar panel array has arrived at the morning position. If not, control passes back to move to AM limit step  525 . This loop will be prosecuted until the AM limit decision  530  returns a yes answer. This will occur as soon as the AM limit switch is activated. 
         [0044]    Once the AM limit decision  530  returns a yes answer, process flow passes to the AM sensor decision  532 . If the AM sensor decision  532  returns a no answer, a loop is set up that causes the system to enter a wait state. This occurs because once the solar panel array has reached the AM position, it is dark and no process activity is required until the sun rises to initiate the next daily cycle. As soon as the morning sun activates the AM sensor, a yes answer is returned from AM sensor decision  532  that passes process control to reset counter step  535  which begins the next daily cycle as just described. 
         [0045]    One of the key features of the present invention is the clutch mechanism that both assures an accurate five degree step per twenty minute period and provides the necessary physical stability for the solar panel array during windy conditions. The former is needed to provide predictable array performance and the later is needed to compensate for the large sail area of the solar panels themselves.  FIG. 5  provides the details of the clutch mechanism  800 . Looking first at  FIG. 5A , a side view of clutch  800  is shown. Clutch  800  is comprised of a lower plate  850 , an upper plate  830  and a separator bushing  820 . The upper plate  830  is moveable with respect to the lower plate  850 . Array shaft stub  810  is fixably attached to upper plate  830  by bolts  815  in the customary manner. Likewise, mounting shaft  840  is fixably attached to the lower plate  850  by bolts  845  in the customary manner. Upper plate  830  and lower plate  850  are made from aluminum, but as will be understood, any suitable material could be sued without departing from the spirit of the invention. For example, plastic or PVC could be used for these plates. Separator busing  820  is made from Delrin® (from DuPont) in a preferred embodiment, however, as with the clutch plates, any suitable material could be used. 
         [0046]    Mounted on the upper plate  830  are drive motor  870 , solenoid  860 , and electronics assembly  880 . The purpose of the drive motor  870  is to move the upper plate  830  with respect to the lower plate  850 . In a preferred embodiment the drive motor  870  is a Series 148 from Hansen Corporation, Princeton, Ind. The purpose of the solenoid  860  is to lift the stabilizing pin (discussed in detail below). In a preferred embodiment, the solenoid  860  is a model C-4 from Deltrol Controls, Milwaukee, Wis. The electronics assembly  880  is discussed below in connection with  FIG. 5B , however, contained within this assembly are the battery and the logic board that implements the method of the present invention. 
         [0047]    Turning now to  FIG. 5B , a sectional view of clutch  800  is shown. Array shaft stub  810  attaches to upper plate  830  by means of a flange  814  that is threaded to accept the threads  812  on shaft stub  810 . The drive shaft of drive motor  870  passes through upper plate  830 . The terminal end of the drive shaft has a gear  875  that engages the inner circumference of separator bushing  820 . The inner circumference of separator bushing  820  has mating teeth that accept the drive shaft gear such that upon application of power to the motor the upper plate  830  moves with respect to the lower plate  850 . Since the lower plate  850  is mounted to a mast, and hence stationary, the solar panel array attached to the array shaft stub  810  will also move with respect to the lower plate  850 . In this way the solar panel array is made to track the path of the sun over the period of a day. 
         [0048]    Also mounted to upper plate  830  is solenoid  860 . Solenoid  860  is of the type that, when power is applied, its shaft is retracted into the solenoid body. In the absence of power, the shaft  862  of the solenoid  860  drops into one of 35 receiving holes  855  disposed at five degree intervals near the outer circumference of the lower plate  850 . Each time the solar panel array is stepped, the solenoid  860  is activated, the shaft  862  is retracted, and the array moved. Near the end of the movement time the solenoid  860  is deactivated and the shaft  862  drops into the next succeeding receiving hole. Once the shaft  862  has seated, the solar panel array is held in a stable physical configuration. In this way the apparatus of the present invention provides the solar panel array with the ability to withstand windy conditions. 
         [0049]    Upper plate  830  has mounted to it electronics assembly  880 . Within this assembly are battery  882  and logic board  884 . The battery is used to provide enough storage to move the array from the evening position to the morning position and to maintain the process of the method of the present invention in an idle sate for a period of ten hours. This provides enough time to keep the process alive in the dark hours between sunset and sunrise. In a preferred embodiment, the battery is of the solid lead acid (SLA) type and is approximately 3 amp hours, for example, a PS1230 form Power-Sonic Corporation, San Diego, Calif. 
         [0050]    Logic board  884  is comprised of the necessary logic circuits to implement the process presented in  FIGS. 3 and 4  above. In a preferred embodiment the logic board  884  uses very low power integrated circuitry, for example, CMOS, such as that supplied by Motorola Inc. from Schaumburg, Ill., but it will be understood by those of skill in the art that any logic circuitry could be used. Moreover, while the apparatus of the present invention implements the logic in discreet integrated circuits, a field programmable logic array (FPLA) or other fully integrated solution could be used without departing form the spirit of the invention. 
         [0051]    As mentioned briefly above, mounting shaft  840  attaches to lower plate  850 . This is accomplished by means of flange  844  having internal threads that accept matching threads on shaft  840 . Unlike the array shaft stub  810 , however, the threads  842  of the mounting shaft  840  are located a distance inward from the terminal end of the shaft. This is done to allow mounting shaft  840  to protrude slightly into upper plate  830 . A keeper ring  846  of the “c-clip” type then captures the mounting shaft  840 . In this way a constant pressure is applied to separator bushing  820  which then maintains the contact between the gear  875  and the teeth on the inner circumference of the separator bushing  820 . In turn, separator bushing  820  is attached to the lower plate  850  by means of screws  822 . 
         [0052]    The final main components of the clutch  800  are the limit switches. AM limit switch  890  and PM limit switch  894  are mounted in the upper plate  830 . Thus when the upper plate moves with respect to the lower plate  850 , the switches move also. Located at appropriate positions in the lower plate  850  are two pins  892  and  896 . Pin  892  activates the AM limit switch  890  when the upper plate travels to the morning position. Pin  896  activates the PM limit switch  894  when the upper plate moves to the evening position. The purpose of these switches is to inform the process that the solar panel array has reached the end of its travel. As mentioned above, in a preferred embodiment AM limit switch  890  and PM limit switch  894  are both model MS5-R from Velleman Inc., Fort Worth, Tex., however, it will be recognized by those of skill in the art that other limit switches could be used without departing from the spirit of the invention. 
         [0053]    While not shown, mounting shaft  840  attaches to a mast by means of an adjustable bracket. This bracket allows the apparatus of the present invention to be tilted to accommodate seasonal variations in the solar azimuth angle. Since this adjustable bracket is well understood in the art, and since it is not a critical part of the present invention, the details of the bracket are left out for clarity. However, the lack of a detailed discussion of the angle adjustment should not be read as a limitation on the scope of the invention.  FIG. 6  provides an overview  1  of the major parts of the present invention as well as how they relate to a typical solar panel array system. The solar panel array  10  is comprised of one or more solar panels attached to a frame in the conventional manner. The solar panel array is then attached to the array shaft stub ( 810  of  FIG. 5A ). Because the array has significant mass, a counterweight  900  is used to balance that mass and thus place the load force from the apparatus directly over the mast  910 . Mast  910  is of the conventional type and may be of any suitable material. Clutch  800  has the solar panel array  10  and counterweight assemblies mounted to it and thence mounted to the mast  910  via an adjustable bracket (not shown). Also mounted to the mast are AM sensor  920  and PM sensor  930 . These sensors provide the signal to the logic board to inform the process that the sun is in either the morning or evening position. In a preferred embodiment the sensors are type QSE113 from Fairchild Semiconductor, San Jose, Calif., however, it will be understood by those of skill in the art that other sensors could be used without departing from the spirit of the invention. Each of these sensors is mounted in a conical housing in order to disallow ambient daytime light form triggering the sensor. The angle of the cone is set, in a preferred embodiment, at 10 degrees from the centerline of the cone. Thus if the sun has traversed past the first five degree step, the sensor will not be triggered. 
         [0054]      FIGS. 7 ,  8  and  9  provide the technical/theoretical basis for the operation of the present invention. Starting with  FIG. 7 , the parameters of a typical operational situation are shown. The apparatus of the present invention is located at point A. Both AM tree-line  600  and PM tree-line  610  represent the obstacles to impinging sunlight typical of most installations. Usable impinging light from the sun along solar arc  620  is thus limited to that clear exposure between the two tree-lines. A typical five degree step  650  is shown at some point mid-morning. Leading edge  652  is the point at which the apparatus of the present invention has just completed a step function. Approximately twenty minutes will pass at which time the sun will be at the trailing edge  654  of the five degree step. At this time the method of the present invention, under control of the clock, will again cause the solar panel array to step to the next position. 
         [0055]    The calculation  660  in the inset provides the derivation of the five degree step size and timing. Assuming a generally horizontal horizon and generally twelve hours of daylight in any given day, the solar arc will cover 180 degrees in twelve hours. It is recognized that a set of variables particular to each installation, for example tree lines  600  and  610 , will reduce the horizon and time, however, for purposes of discussion, the above assumptions can be applied. Since there are 36 five degree steps in 180 degrees, and since there are 720 minutes in twelve hours, then each five degree step represents 20 minutes. This 20 minute period is the amount of time the solar array spends at each five degree step. 
         [0056]    Referring now to  FIG. 8 , a graphical comparison of three methods discussed above is presented. The methods include a fixed array, a fully tracked array and the step function tracked array of the present invention. Line  720  describes the light energy captured during a solar day by the fixed array method. As can be seen, as the sun&#39;s angle becomes more and more perpendicular to the array, the amount of energy captured increases. However, both before and after perpendicularity is achieved the energy captured drops off significantly. As detailed in the table of  FIG. 9 , a fixed array can be expected to capture only about 65% of the energy of a fully tracked array. 
         [0057]    Line  700  in  FIG. 8  presents the light energy captured by a fully tracked array. As can be seen, once the sun has cleared the tree-line the captured energy rises quickly to near its peak value. This is because the impinging sunlight is striking the solar array at approximately 90 degrees. This peak value will be maintained for the balance of the solar day until the sun passes below the PM tree-line. The table of  FIG. 9  presents the data for this type of system and is the 100 percent reference for the other array data. 
         [0058]    Line  710  of  FIG. 8  presents the light energy captured by the method and apparatus of the present invention. The primary difference between the fully tacked array method and the method of the present invention is the appearance of a saw-tooth energy capture function along the top portion of the curve. Like the fully tracked method, the method of the present invention reaches its near maximum energy capture as soon as the sun has cleared the AM tree-line. This is because, as a result of the clock control, the impinging sunlight is striking the solar array at approximately 90 degrees. Also like the fully tracked method, the method of the present invention stops producing energy at the time the sun passes below the PM tree-line. 
         [0059]    The primary difference is detailed in the inset of  FIG. 8 . Once the step function has been completed under control of the method of the present invention, the energy captured peaks, such as at  712 . This relates directly to the leading edge of the five degree step ( 652  of  FIG. 7 ). As the sun continues its path along the solar arc, the energy captured will decrease as shown by line  714 . The decrease will continue until the next step function is completed. The average of the peaks and valleys of the saw-tooth is shown by line  716 . It is the average of the saw-tooth that represents the total energy captured by the step function tracked method. As shown in the data in the table of  FIG. 9 , the step tracked method will produce nearly 90 percent of the energy captured by a fully tracked method. Of course a step size of other than five degrees could be used without departing from the spirit of the invention. If a larger step size is used, a lower average power output will occur. Conversely, if a smaller step size is used the output will mote closely approximate that of the fully tracked array. 
         [0060]    The primary advantages of cost and simplicity make the sacrifice of 10 percent attractive for many, if not most applications. For example, remote pumping applications that traditionally use a fixed array can make use of the present invention to increase the output flow. Other applications such as portable lighting, remote communications and landscape lighting may also benefit. 
         [0061]    A first advantage of the present invention is that the apparatus is relatively inexpensive when compared to a fully tracked method. Depending on the exact technology involved, contemporary full tracked systems range in cost from the low thousands of dollars to upwards of ten thousand dollars. Given the simple, yet stable mechanical design, coupled to the inexpensive control method, the step tracker of the present invention could be manufactured at a cost of less than half of the least expensive fully tracked method. 
         [0062]    A second advantage of the present invention is that it is simpler than fully tracked methods. Contemporary fully tracked systems operate on one of several different principles. Some use inert gas, some use fluid pressure and still others use thermally sensitive metals to detect the need to move the array in response to a temperature change brought about by the sun&#39;s rays striking some part of the mechanism. Each of these is complex and requires special skill to install and maintain. The apparatus of the present invention, in contrast, requires only simple installation process. 
         [0063]    A third advantage of the present invention is that it is self correcting when a positional error occurs. If for some reason, power to the system is lost, or more likely, the mechanism became improperly oriented, a single day/night cycle will allow the method of the present invention to realign the array and carry forward normally.