The MaxTracker grid-tied photovoltaic positioning system, designed by Shingleton Design, LLC, in Auburn, NY embodies all the characteristics of large-scale economical solar energy collection. The balanced structural design provides a large capacity, modular PV generation system with a compact control configuration that makes use of available drive mechanisms and maximizes the 'Bang per Buck' ratio in this competetive market. This prototype system, installed at the Arizona Public Service's Solar Testing and Research (STAR) Center, has been in continuous operation without failures since the summer of 1999.
Using a single, linear actuator, capable of developing 15 tons of force, eight double-rows of panels, each nearly 150 feet long, are positioned about a single, North-South axis of rotation, connected together by a patented inter-row linkage system. Covering about a quarter-acre of land and producing about 115 kiloWatts of AC power through the inverters at the far end of each row, the MaxTracker has brought the PV electric generation industry to new levels of economic acceptability.
The MaxTracker positioning system makes use of the SolarTrak® 'BackTracking' strategy to maximize output while avoiding PV cell damage. The drive unit, located midway in the first row on the right, uses a single SolarTrak® controller implemented with a 4-wire SCR power control interface to drive the 1/2 horsepower, single-phase motor. The prototype control unit shown to the left separates the low voltage DC components from the high voltage AC to provide safety during the initial testing and demonstration of the new equipment.
As the production design evolved over the next year, several modifications were implemented to reduce costs and complexity while maintaining the high-level of dependability demonstrated by the prototype system.
Converting to a high-quality, 'Dirty Duty' TEFC 1/2-horsepower motor by Baldor corporation using the updated 3-wire power control interface (using only three SCR's instead of five), allowed all of the components to reside in the same junction box. To provide the necessary safety precautions, a 'finger guard' was added to cover all the high-voltage components.
This installation in Vallejo, CA, in the backyard of a local fire station, Reconfiguration of the original design while keeping the controller components unchanged, produced a modular array with smaller panels on each row, reducing the panel width and wind effects, while more than doubling the number of rows, 17 in this case.
Beginning with installed unit #22, the motor for the system was replaced with a NORD 3-phase gearmotor. This upgrade further reduced the cost of the drive unit by eliminating the costly intermediate speed-reducer gearbox while improving the efficiency of the motor drive power consumption and lowering the operating temperature dramatically from over 190 degrees F. to less than 100.
Using a stock motor-starter unit to monitor the 3-phase power input, the SolarTrak® sports a solid-state 3-phase power board that allows five off-the-shelf CRYDOM SCR solid-state relays to be installed in same size NEMA 4X junction box.
The inter-row link system and the compact, yet powerful drive unit powered by the SolarTrak® sun-tracking controller combine to support the current state-of-the-art single-axis tracking platform.
Once properly installed, these systems will offer years of trouble-free operation with high tolerance to grid failures, atmospheric events and even maintenance technicians.