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SolarTrak® Development Milestones

Continuing in his effort to assist industry in the implementation of his cyber-progeny, Mr. Maish, pictured to the left with an Entech Corporation 860 Watt linear Fresnel concentrator, produced yet another version of his controller that ran off of batteries charged by a similar 5-watt panel (near the center of the frame) and consuming only an average (including the intermittant motor-on power) 12 milliamps of current throughout the day. These units were capable of running for months and even years in remote areas without the need of human intervention.

Part of the reason the units could maintain operation and accuracy for such long periods was the implementation of clock correction algorithms that systematically adjusted the time of day by a few seconds per day and another few seconds per week. Proper calibration of those correction values produced clock accuracies in the neighborhood of less than a minute per year of error. To further improve on that accuracy, an additional, seasonal correction for average temperature changes across winter and summer was included, bringing the error down to less than 30 seconds per year.

The next step in the implementation of the SolarTrak® technology was to allow off-grid (non-AC-powered) control systems for residential and light commercial applications. A single-axis PV positioner, known as the 'Delta Tracker' for its triangular shape, became the first battery-powered application. A small, 5-Watt PV panel, at the lower tip of the array, provides all the charging power necessary for long-term operation of the linear actuator (like on a satellite dish) that moves the array from side ot side. With the array tilted up in the air, the solar insolation hits the panels at very nearly the ideal direct-normal angle. As the array leans over to its limit in the early morning and late afternoon, the triangular shape prevents the panels from hitting the ground while maximixing its range of motion.
Page 2 - Low Power Sytems
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The 'Entech Version' of the SolarTrak® control board (shown to the right) is all that is required to run the two-module, two-axis postioner (above) which uses two 24" Von Weise linear actuators (below) for the mechanical power.
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This compact little board, measuring only 4" x 5" including the attached LCD monitor, contains everything necessary to drive and manipulate a low-power (<40V at 2 amps) tracking device. It has two motor drivers to deliver power to the screwjacks, four function switches to select manual operation, an emergency stow position and other installation-specific operations and a joystick for moving the unit under the manual operation mode.
The on-board, real-time clock device has a power backup supplied by a 'Super Cap', a special capacitor, much like a deep-cycle marine battery, that can run the clock while the unit is powered down for over a month. The micro-controller unit (MCU) at the center of the board contains all the computer code (> 30,000 lines), memory and parameter storage necessary for its operation. A mere ten electrical connections are necessary to run things.
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This basic controller technology has been designed to accomodate most mechanical positioning geometries. The four basic geometries are Azimuth/Elevation, where the primary axis (the one fixed to the Earth) is coincident with a line running through the center of the Earth, Polar/Declination, where the primary axis is parallel to the Earth's axis of rotation, and two Tilt/Roll versions, one with the primary axis aligned East-West and the other North-South. In all cases the secondary axis is orthogonal (perpendicular) to and rotates about the primary axis allowing the positioner to point anywhere in 3-dimentional space within the physical limitations of the mechanical range of motion.

In order to define the mathematical characterization of these various geometries, the size and the position (orientation) with respect to the Earth, there are actually over one hundred parameters that are stored in non-volitile (won't go away when the power is off) memory within the MCU. Most of these parameters are defined when the SolarTrak® is configured for a particular mechanical device but several are specific to where in the world that device will be installed.

The bulk of these parameters are set using a serial interface with either a PC running special software or a companion board (teaching pendant) referred to as the User Interface Module (UIM). The remaining, site-specific parameters and several calibration settings are accessible through the use of the LCD monitor and three buttons located just above the monitor anf to the right of the MCU. These three buttons funtion in a fashion very similar to a digital watch where the 'Item' button chooses which parameter to view, the 'Adjust' button selects the parameter for modification and the 'Value' button actually changes the number.

This version of the SolarTrak® Control board has become the foundation of all subsequent control system designs built by EEInc. When power requirements exceed the low-power limits of the basic board, a higher power motor interface circuit is included to accomodate the needs of large systems.