US20120227729A1

US20120227729A1 - Sun tracking control system for solar collection devices

Info

Publication number: US20120227729A1
Application number: US13/064,197
Authority: US
Inventors: Robert D. Lundahl; Robert Wesley Cutlip; Michael Selzler
Original assignee: Advanced Technology and Research Corp
Current assignee: Advanced Technology and Research Corp
Priority date: 2011-03-09
Filing date: 2011-03-09
Publication date: 2012-09-13
Also published as: WO2012122509A2; WO2012122509A3

Abstract

This invention presents a robust design for a sun tracking control system where a capacitor(s) is charged from the solar panel and used to power a tracking control system and motor actuator(s). The control system periodically moves the solar array to a calculated sun position. The control system also monitors the energy stored in the capacitor(s) and makes its move decisions contingent on the level of stored energy. This added level of energy based decisions provide the tracking system a robust operating behavior to accommodate real world operating conditions with a simple rule set.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention:

This invention relates to sun tracking solar energy collection systems and specifically to the design of a tracking control system that is self powered, robust, and adaptive to different changing sun conditions.
2. Brief Description of Prior Art
Sun tracking is a common technique used to increase the energy yield of solar energy collection systems. Many such devices are described in prior art and nearly all of them can be classified as one (1) or two (2) axis trackers depending on the different freedom of movements of their tracking mechanism.
The equatorial mount is a common example of a one (1) axis tracker where the solar array is rotated around a single axis that is oriented parallel to the earth's rotational axis. The rotation of the solar array is controlled to match the rotation of the earth so that the solar array tracks the sun as the sun moves from East to West throughout the day. A typical one (1) axis tracker follows the same path every day and does not automatically accommodate the changes in the elevation of the sun path as it changes throughout the year. This small pointing error limits the ultimate efficiency of one (1) axis trackers by several percent. Previous art also show many different two (2) axis systems where the solar array is actively positioned in azimuth and elevation. These two (2) axis systems allow the solar array to be perfectly aimed at the sun throughout the year and thereby realize their maximum solar energy collection efficiency.
Nearly all one (1) and two (2) axis tracking systems use electric motors to position the solar array as the sun moves across the sky on its celestial path. The number of motors depends on the number of axis of motions and the specific mechanical configuration of the tracking mechanism.
Prior art shows several different methods to power the motors that move the panels and perform the sun tracking function. Some solutions power the motors directly while others use the solar panels to charge a local battery that is then used to drive the positioning motors.
One popular “direct drive” approach is to use a cluster of photo-diodes in a shading fixture attached to the solar array where the outputs of the photo-diodes are proportional to the amount of sun they are each receiving. The shading fixture is physically configured such that the outputs are balanced when pointed at the sun and unbalanced when pointed off-axis to the sun. An electrical circuit controls the power to the motor(s) in response to the balanced output of the photo-diodes so that panel positioning is automatic as the system constantly tries to “balance” itself. These solutions are simple and low cost. However, the pointing accuracy is limited and the system can be easily fooled on partly cloudy days, extraneous lighting, and the ambiguity of where to go at the end of the day. These “balancing” systems are also not very energy efficient. Motor power is always “ON” as the system is always actively trying to balance itself.
Previous art also shows many examples of solar panels re-charging a battery that in turn is used to power motors and a control system that actively calculates where to point the array based on the time of day. These systems are more energy efficient and cannot be fooled by optical sensors. However they are also very susceptible to power outages, power surges, and a host of other conditions that can interrupt the proper functioning of the control processor. Battery life is highly unpredictable and even a temporary failure will cause the tracking system to stop working and require some sort of restart procedure. Recovery can be difficult if the panel was stopped in a bad position and re-starting may require a technician with advanced skills and tools to travel to a remote site for servicing.

SUMMARY OF THE INVENTION

This invention describes a tracking system controller that is more robust than previous designs. This tracking control system is the “micro-controller” type that actively calculates the suns position and activates the electric motor(s) to move the array to the correct position. This controller can be used for both 1 (one) and 2 (two) axis systems.
This invention describes a robust control approach that uses capacitor(s) rather than batteries as an energy storage device to store power for a microprocessor and the positioning motors. The capacitor storage device is not intended for long term or as high a capacity of energy storage as a battery. A unique power management logic adapts the tracking function to the different power levels of the capacitor and anticipates the total loss of power everyday. When power is restored the controller will automatically re-initialize itself and return to complete functionality. This regular and periodic “re-boot” will automatically fix and recover from any errors on a daily basis as part of its normal operating sequence.
The microprocessor uses an embedded Global Positioning System (GPS) circuit to accurately determine the system location, date, and time of day. This information is available upon power up and provides the tracking system with all the necessary information and does not require any manual data input during the initialization procedure. The initialization function is automatic.
In operation, the control program monitors the available power of the capacitor(s) and modifies the tracking program to reliably track the sun during the day and to “fail safe” under low power conditions and recover automatically upon the restoration of power. The simple rule set can be summarized as follows:

- If power levels are maintained, the tracking function will continue.
- If power levels drop through a pre-programmed set point, the control program will park the solar array in a due South position.
- If power levels regain and move back above the set point, the control program will resume the tracking function.
- If power levels do not regain and drop below a secondary lower set point, the processor will shut down and power off completely.
- When the panels begin to generate energy again, and power levels rise above a set point, the processor automatically turns power on, re-initializes itself, and resumes the tracking control program automatically.

This robust tracking control logic anticipates the changes in available power and automatically synchronizes the tracking function with the normal daily cycle of the available energy from the sun. This logic simplifies the beginning and end of day logic of when to start or stop the tracking function and the mid day logic of how to deal with low energy conditions caused by atmospheric conditions.
When available power is above a pre-set threshold the controller will execute the required move and then wait for the next cycle. However, whenever the available power is below a pre-programmed threshold, the controller will move to a due South position instead and wait for sufficient power before continuing to the calculated solar position.
The control system of this invention plans on the regular loss of power to the controller and the orderly re-initialization of functions when power is returned. This will happen every day as the sun sets and the power drops through the pre-programmed threshold and the panel(s) will be positioned to the due South position. The due South position is chosen since this is the optimum position for fixed panels. Without sufficient sunshine the power will continue to drop until the processor shuts down leaving the panel(s) pointed in the due South position. When sufficient sunshine returns, the processor will turn back on, all systems will re-initialize and the solar array will drive to the current calculated position of the sun. This regular and periodic “re-boot” of the system controller has a purging and self correction effect to automatically fix any system anomalies on a frequent and regular basis.
It should be obvious to one skilled in the art that the same control approach could be used with batteries to store energy instead of capacitors and still be within the spirit of this invention where fluctuations in available power are used to make power management decisions for the microprocessor and for repositioning the solar array. The typical charge and discharge characteristics of a battery can be different than those of a capacitor, however they both will support the same control logic of the invention.

OBJECT OF THE INVENTION

The object of this invention is to provide a solar tracking controller that can be powered directly from a solar array and exhibits a robust and self correcting logic.
A further object of this invention is to provide a solar tracking controller that can be applied to both 1 (one) and 2 (two) axis controllers.
A further object of this invention is to provide a solar tracking controller that can incorporate capacitor(s) as an energy storage device for the control system.
A further object of this invention is to provide a solar tracking controller that is inexpensive to manufacture.
A further object of this invention is to provide a solar tracking controller that is inexpensive to maintain.
A further object of this invention is to provide a solar tracking controller that will accommodate a wide range of input voltages and currents typical for solar collectors.
A further object of this invention is to provide a solar tracking controller that does not require battery storage to provide power or maintain volatile memory or setup parameters.
A further object of this invention is to provide a solar tracking controller that can output a high current level to operate high powered positioning motors.
A further object of this invention is to provide a solar tracking controller that takes advantage of the daily loss of solar power to reset the controller.
A further object of this invention is to provide a solar tracking controller that isn't constantly on and using power and searching for the sun position.
A further object of this invention is to provide a solar tracking controller that is self initializing for its installation location to facilitate a world wide deployment.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 Tracking Control Electrical Interface—This illustration shows how the tracking control system interfaces with the solar array.

FIG. 2 Tracking Control Processor Functions—This illustration shows the functions of the tracking control processor.

FIG. 3 Voltage sensing switch logic—This illustration shows the internal logic for the voltage sensing switch and the conditions that make the switch turn off, remain off, turn on, and remain on.

DETAILED DESCRIPTION OF THE INVENTION

The following sections describe only one embodiment of this invention where the application is for a solar panel tracking system. It should be obvious that this invention could be utilized in other applications where a control processor is powered from an electrical source that is variable and has a wide range in outputs including 0 volts.
FIG. 1 shows how the tracking control electronics interface with a solar panel to share the generated power. The solar panel (1) is producing DC electrical power (2) to the end user (3). The tracking control system (4) receives its power by tapping into the output of the solar panel (1). Inside the tracking control system (4) is a capacitor(s) charging circuit (5). The charge resister (6) limits the current flow across the capacitor (7) to safely charge it up to its maximum voltage.
The tracking control is performed by the microprocessor (8) which is connected to the capacitor(s) (5) as its power source. The microprocessor (8) is also connected to a Global Positioning System (GPS) (9), positioning motor(s) (10), and position sensor(s) (11). The program running in the microprocessor (8) calculates the position of the sun based on the date, time, and location of the system as determined by the GPS (9). The position sensor(s) (11) tell the microprocessor the current orientation of the solar array. Based on the calculated position of the sun and the current position of the solar array, the microprocessor will activate the positioning motor(s) (10) to correctly position the solar array with respect to the sun for maximum energy conversion.
To save power and minimize wear, the solar array can be positioned periodically instead of constantly being adjusted. Many update cycles are possible. A good compromise is to try and update the position of the solar array every 15 minutes during the daylight hours. This provides sufficient accuracy for the performance of a standard multi-crystalline solar panel. A focusing array may need much more accuracy and for these applications the update rate can be increased to one update per minute or more. Many different options for the control program are possible and anticipated.
Using the capacitor(s) (5) as a power supply provides tremendous flexibility to accommodate a wide range of input voltages and currents from the solar panel (1) and output power for the microprocessor (8). Using the capacitor(s) (5) as a power supply also provides the high amperage that can be used by the positioning motors (10) when needed for additional power to overcome the forces of wind loading, snow, etc.
The capacitor(s) (5) also allows the solar panel (1) to collect electricity at low levels that could not power the motors directly. Lower voltages can be used to trickle charge the capacitor (5) and store up enough energy to move the panel with a shorter burst of higher power.
It is important to note that there are many possible configurations for the capacitor charging circuit (5) and they are anticipated by this invention where solar power is used to store energy in a capacitor (7) that is in turn used to power a microprocessor (8) and positioning motor(s) (10).
FIG. 2 illustrates the tracking control processor functions and show how the different energy management features are incorporated to provide the robustness and reliability of this tracking control solution.
The solar panel (12) provides power to charge the capacitor(s) (13) which stores power and provides it to the microprocessor (14) through the voltage sensing switch (15). The voltage sensing switch (15) checks the capacitor (13) voltage to determine the available power and then makes a decision to turn power ON (16), maintain power ON (17), or turn power OFF (18) for the microprocessor (14). The internal logic of the voltage sensing switch (15) is discussed more thoroughly in the detailed description of FIG. 3.
When power “turned ON” (16), the processor will automatically re-boot (19) the control program, re-initialize all functions and prepare the processor to wake up (20). This is an important step in the robustness of this control approach and will likely happen on a daily basis. A power off/power on restart of the processor is a powerful technique to correct just about any program execution errors that could have been caused by any kind of power surges, static discharges, jams or other error conditions.
If the power is simply maintained ON (17) the control program will run in its program loop waking up (20), updating position, going to sleep (27).
When the power is turned OFF (18), all power is removed from the microprocessor (14) and both the control program and microprocessor will shut down completely. Restarting the control program will require the processor to re-boot and re-initialize (19).
When the microprocessor (14) is running its control cycle with the power maintained ON (17), the processor will maintain its control cycle. The processor will wake up (20), check the current location, date, and time (21), it will calculate the current sun position (22), and it will check the current panel position (23) using the panel position sensor(s) (24). The processor will compare the calculated position with the current position and determine if a move is needed (25) to better align the panel with the sun.
If the position of the panel is within the pre-programmed tolerance, no move will be needed (26), and the processor program will be put into a “sleep” mode for a pre-programmed number of “n” seconds (27). After the time has expired, the processor program will wake up (20) and the process will repeat itself.
If the panel position is outside of the pre-programmed tolerance, a move will be needed (28). However, before any move is executed, the program will check the capacitor voltage (29) to see if sufficient power is available in the capacitor(s) (13) to accomplish the move, and still get back to the due South position if no additional power were available. This check of capacitor voltage (29) will assure that the panel will not be driven to a new position where it could get stuck without enough power to get back to the safe, due South position. The power required to move and return to a due South position is determined during the design phase and stored as set points used in the move decision (30).
If the available voltage is above the required set point (31), the processor will move the panel to the new position (32) and the program will go into “sleep” mode for “n” seconds (27). After “n” seconds, the processor program will wake up (20) and the process will repeat itself.
If the available voltage is below the required set point (33), the processor will move the panel to the due South position (34) and the program will go into “sleep” mode for “n” seconds (27). After “n” seconds, the processor program will wake up (20) and the process will repeat itself.
The electrical output of the solar panel (12) can vary widely from environmental conditions as well as the normal on and off cycle caused by the cycles of day and night. The capacitor(s) (13) is not intended to store an excess of power. The “voltage sensing switch” (15), the “check capacitor voltage” (29), and the “move where” (30) decisions logically work together to provide a robust operation. If the electrical output of the panel (12) drops too low for too long, regardless of reason, the solar panel will first be moved to the south position (34). This parking position is in the middle of the daily solar cycle and thus the “safe” to park the panel and be ready to start collecting energy regardless of when the energy is available in the day. Moving the panel to this “safe” South position (34) assures that it will not get stuck in an extreme position (Far East or West) where it might take several days to collect enough power to re-start the tracking function. This functionality is in effect even when the processor is in sleep mode (27) waiting for the next cycle.
If the electrical output of the panel continues to drop as at the end of the day, the voltage sensing switch (15) will eventually turn power off (18) and shut down the control program and microprocessor. This power off condition will cause the processor to re-boot, and re-initialize (19) when power is turned ON (16) in the future. This cycle will be performed automatically everyday and provides a robust autonomy necessary for a device that is not serviced regularly.
FIG. 3 illustrates the functions within the voltage sensing switch (35) and the logic involved to provide a hysteresis effect between power on and power off states. It is important to note that this “logic” may be performed with the hard logic of an electronic circuit where a configuration of components will provide the logic for the power on and power off states automatically.
The voltage sensing switch (35) will check the capacitor voltage (36) and compare it with a pre-determined low voltage set point (37). If the answer is NO (38) and the voltage is not above the low voltage set point (37) the power will turn OFF (39). If the answer is YES (40) and capacitor voltage is above the low voltage set point (37) than an additional comparison is made to determine if the voltage is above the high set point (41). If YES (42), the power will turn ON (43). If NO (44), then another check is made to see if the voltage has ever been above the high set point (45) since the last time the processor was started. If the answer is YES (46) then the power has been turned on (43) in a previous cycle and the power will remain on (47). If the answer is NO (48), the power will remain off (49).
It is this logic that provides a hysteresis effect to maximize the productive time for the system and yet avoids unnecessarily cycling of the control system. The power turns off (39) at a relatively low set point (37) and the power turns on (43) at a different and higher set point (41). Requiring the voltage to rise above the higher set point before restarting (43) avoids an ambiguous state between on and off However, allowing the processor to run as the voltage is falling from the high set point to the low set point, after it has reached the high set point, maximizes the opportunity for the processor to run and the system to collect power.

Claims

1. A control system to activate motors and move one or more solar panels to track the sun where the control system incorporates,

a super-capacitor energy storage device,

a charging circuit that uses power from said solar panel(s) to charge said super-capacitor,

a microprocessor that is powered by said super-capacitor,

at least one motor powered by said super-capacitor to move the said solar panel(s),

at least one position sensor to determine the relative position of said solar panel(s),

a Global Position Sensor,

a voltage sensing circuit

whereas said voltage sensing circuit will monitors the voltage of said super-capacitor and communicate said voltage level to said microprocessor and based on pre-determined set point, logically decide to continue providing power, turn on power, or turn off power to said microprocessor based on said voltage level and,

a logical program that runs in said micro-processor that,

will automatically initialize start up upon the application of power and,

will periodically read the position, time, and date from said Global Position Sensor and,

will calculate the relative current position of the sun and,

will determine the current position of said solar panel(s) from said position sensor(s) and,

will determine if the position of said solar panel(s) needs to be changed to face the sun and,

will goes into a “sleep” mode for a set period of time if no change in position is required and,

will determine the available power in said super-capacitor if a change in position is required and,

will logically determine weather to move said solar panel(s) to a new position or move said panel to a due South position based on available power stored in said microprocessor and,

will cease program execution without damage when power is removed from said micro-processor.

2. A control system in accordance with claim 1 where the logical control exhibited by said voltage sensing circuit is provided by the hard logic inherent in an electronics circuit.

3. A control system in accordance with claim 1 where a battery is used instead of said super-capacitor.

4. A control system in accordance with claim 1 where the position information is manually input to said microprocessor and the time and date information are provided by an internal clock.

5. A control system in accordance with claim 4 where the position information is manually input to said microprocessor and the time and date information are provided by external data transmitted over radio frequency.

6. A control system in accordance with claim 1 where the position, time and date information are provided by an external source.

7. A control system in accordance with claim 1 where the charging voltage for the said super-capacitor energy storage device is supplemented in whole or in part from an external source other than said tracking solar panel.

8. A control system in accordance with claim 3 where the charging voltage for the battery energy storage device is supplemented in whole or in part from an external source other than said tracking solar panel.

9. A control system in accordance with claim 1 where said motor(s) are driven by some other power source and only the control logic of said control system is provided as control signals only.