Abstract:
The present invention provides an apparatus and method for solar tracking. The solar tracking sensor array and method so disclosed can be used with any device that requires a specific orientation to the sun for optimal operation. The system relies upon a sun tracking mechanism which includes a plurality of phototransistors configured in a particular manner. The apparatus can further be used with an analog sensor circuit which is also disclosed herein. Although the device and method are disclosed in conjunction with a solar tracking device, which includes the analog sensor circuit, a drive assembly, and a power source, these components may be used independently of one another.

Description:
This application is a divisional application from U.S. application Ser. No. 11/236,695 and claims priority from the foregoing application. 
    
    
     FIELD OF THE INVENTION AND RELATED ART 
     This invention relates to sensor devices for solar tracking. Solar power is a renewable energy source derived from the conversion of sunlight to electricity. As the 21 st  century progresses, solar power continues to play a considerable role in the future of global energy production. 
     As solar-based devices rely upon the collection of sunlight, all such devices must be appropriately oriented so as to maximize their operation. Generally, each device operates most efficiently at some optimal orientation, which may vary depending on the location, setting, or geometry of the collection device, at which the solar device is best positioned to collect sunlight at any given time. 
     Consequently, solar based devices require orientation to maximize efficiency and operation. Many installations compromise efficiency by choosing an optimal fixed orientation, but tracking installations can be used instead to provide even greater output. Various techniques exist in the art for tracking the sun. These techniques include manual manipulation by a human operator, pre-set movement based upon expected positioning of the sun, and traditional shadow bar sensing. The present invention provides advantages over the existing devices and techniques as it allows for more precise tracking while minimizing tracking error and eliminating manual intervention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of the tracker assembly with photovoltaic panel and stand. 
         FIG. 2  is a perspective view of the sensor mount. 
         FIG. 3  is a top view of the sensor mount. 
         FIG. 4  is a schematic of the sensor circuit for controlling movement of the drive assembly. 
     
    
    
     SUMMARY AND OBJECTS OF THE INVENTION 
     The invention discloses a novel sun tracking apparatus and method which utilizes an arrangement of phototransistors to assist in the control of a drive assembly, or similar means, in a solar tracking device. The apparatus can further be used with an analog sensor circuit which is also disclosed herein. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The primary embodiment of the invention disclosed herein focuses on a single axis tracking system. That is, the system follows the sun in the azimuth (east to west) direction throughout the day, but does not have a second axis of motion to correct for the seasonally changing zenith (vertical) angle. This is because a middle value for the zenith angle can be chosen as the fixed angle of the tracker, maintaining a low margin of error throughout the year. In other words, the azimuth tracking substantially increases the energy output (by about 28%, depending mostly on the latitude of the site), while the zenith tracking would only provide a marginal improvement at twice the cost (an additional 4% or so). However, those skilled in the art will realize that the same design principles disclosed herein could be applied to a second axis of motion if desired. 
     Referring now to  FIG. 1 , the sensor array is shown as used in conjunction with a complete solar tracking assembly, including a drive mechanism and associated components. It will be realized that the sensor may be used independent of such an assembly if so desired. The solar tracking device may be categorized as having three primary components: a tracking assembly  1 , a photovoltaic panel  2 , and a base platform  3 . The photovoltaic panel  2  is disposed at the end of a rotatable output shaft  4 , which is designed to move in both forward and backward directions. The photovoltaic panel  2  and the tracking assembly, as a unit, are mounted on an adjustable stand that supports a base platform  3  that permits the adjustment and fixation of the zenith angle of the assembly. 
       FIGS. 2 and 3  show the sensor mount  28  which consists of a shade  29   a ,  29   b  and an overhanging portion  28   a . Two forward motion phototransistors, F 1 , F 2 , are mounted on one side, the forward side, of a shade  29   a  and two additional backward motion sensors, B 1 , B 2  are secured on the other side, the backward side, of the shade  29   b . These phototransistors are secured to a sensor mount  28  that is attached to the output shaft  4  so that it moves with the photovoltaic panel  2  throughout the day to follow the relative position of the sun. The sensor mount  28  includes an overhang portion  28   a.    
     The movement of the drive mechanism is controlled through the use of an analog sensing circuit  30 . The drive mechanism in this case is one or more actuators, but the drive mechanism may also consist of an electric motor or any other such device. Referring now to  FIG. 4 , in the embodiment described herein, different phototransistors  31  are used to activate separate parts of the circuit in order to control the different directions of motion. A 555-timer  32  is provided to control another transistor, the P-MOSFET, that allows current to flow from the battery  33  to the drive assembly. 
     The simplest method of controlling the movement of the drive mechanism is through an analog sensing circuit  30 . There must be at least one sensor for each direction of motion. In this design, different phototransistors  31  are used to turn on separate parts of the circuit  30  to control the different directions of motion. Multiple phototransistors can be used for each direction of motion by connecting them in parallel. The light-sensitivity of these phototransistors can be adjusted by changing the value of the resistor R 3 . Once a phototransistor activates the circuit, a 555-timer  32  controls another transistor that allows current to flow from a battery  33  to the drive assembly. The timer is used to convert a continuous “on” signal from the phototransistor to a cyclic “on-off” signal. The necessary “on-time” and “off-time” can be adjusted to the correct duration by the values of two resistors R 1 , R 2  and one capacitor C that are connected to the timer  32 . Also, the timer  32  itself receives no power without a signal from one of the phototransistors  31 , because of a break in the ground line, in order to minimize overall power consumption. In this arrangement, the current is drawn from a battery  33  that has been charged by the photovoltaic panel  2 , but it will be recognized that the power could also come from a photovoltaic panel directly, a bank of capacitors, an alternating current line, or any other electric power supply. 
     When the timer  32  is not grounded, it consumes no power, and the P-MOSFET breaks the circuit to the drive assembly, in this case the actuator  15 , so that no movement can happen. If F 1  or F 2 , or both, receive light, then the timer  32  becomes grounded and begins to count, by charging and discharging the capacitor C through R 1  and R 2 . Once the timer  32  has completed the first period of its two-step cycle, it toggles the output signal to close the P-MOSFET, allowing current to flow from the battery  33  (or photovoltaic panel, capacitor bank, AC, or any other power supply), through the P-MOSFET, then the drive mechanism, to the ground. When the timer has finished the second period of its cycle, the output of the timer is toggled once again, so the P-MOSFET breaks the circuit. If the previous cycle did not rotate the output shaft  4  far enough, then the forward sensors will still be in the light, and the cycle continues until they are shaded. When all the sensors are shaded, the timer ground is broken so no further action is taken. The backward part of the circuit works exactly the same way. It is identical in form, but may have different values for C, R 1 , or R 2 , for timing purposes, and can have physically different sensor positions and orientations. It will be recognized by those in the art that other controller types, including digital circuits, may be used to accomplish the foregoing tasks. 
     The layout of the phototransistors  31  determines the way that the motor responds to the sun. The two phototransistors, F 1 , F 2 , mounted on the forward side of the shade  29   a  detect the sun if it is getting ahead of the plane of the photovoltaic panel  2 . The other two sensors, B 1 , B 2  are used on the backward side of the shade  29   b  to detect the sun if it is far behind the photovoltaic panel  2 . This sensor mount  28  is oriented such that it moves with the photovoltaic panel  2  throughout the day. When the photovoltaic panel  2  is directly facing the sun, all phototransistors are shaded, so no motion is signaled (idle position). The width of the overhang structure  28   a  on the sensor mount  28  determines the range of the idle position. For example, if the panel  2  can be rotated in steps of four degrees then the overhang  28   a  should shade the forward sensors (F 1 , F 2 ) until the sun is overhead by two degrees thereby minimizing tracking error. 
     Referring to  FIGS. 5 and 6 , under normal operation, the forward facing sensors (F 1 , F 2 ) are triggered many times throughout the day, signaling the motor to inch along with the sun. Then at sunrise the next day, the backward facing sensors (B 1 , B 2 ) will detect the rising sun and signal the tracking device to return the panel  2  to its starting position. When it is cloudy, no signal is given, and so no power is wasted trying to chase the sun when nothing but diffuse light is available in the sky, in which case the angle of the photovoltaic panel has little importance. If it is cloudy for only the beginning or end of the day, then the sun might re-appear at any point relative to the photovoltaic panel, so multiple sensors are used to cover greater angles. If the sun appears far ahead of the photovoltaic panel  2 , then the motor will continue to cycle until the photovoltaic panel  2  is facing the sun, placing the forward facing sensors (F 1 , F 2 ) in the shade of the sensor mount  28 . If the sun appears behind the photovoltaic panel  2 , then the panel can adjust backwards, or return to the starting position and then catch up to the sun within a few minutes. Nevertheless, the return motion will still happen at most once per day. 
     In the embodiment shown herein, the circuit is configured such that forward movement of the drive assembly is effected by heating an actuator so that the contraction causes a rotation in the drive clutch (not shown) of the drive assembly. The circuit is further configured such that the backward or reverse movement of the drive assembly is accomplished through slightly different means, in that a contraction of the actuator serves to disengage the drive assembly and the panel is returned to its starting position through the use of a return spring. It will be noted that the circuit and drive mechanism may be configured to permit backward step motion in the same fashion as it is used to permit forward motion, if such movement is desired. 
     While the invention has been described in reference to certain preferred embodiments, it will be readily apparent to one of ordinary skill in the art that certain modifications or variations may be made to the system without departing from the scope of invention claimed below and described in the foregoing specification.