Solar photovoltaic (PV) modules capture more sunlight per unit area when they are pointed at the sun, as its position in the sky changes during the day. Sun tracking PV systems result in increased annual energy production compared to PV modules mounted on a fixed structure. ViaSol Energy Solutions designed an economical, elevated, single-axis-tracking PV system, currently deployed on top of two parking garages at Arizona State University in Tempe, AZ. ViaSol's horizontal single-axis-tracking technology rotates the PV modules on a north-south axis, from east to west following the path of the sun from sunrise to sunset. With this tracker, the panels will produce approximately 30 percent more energy (normalized) than fixed horizontal systems on rooftops.
In addition to producing clean electricity from the sun, these tracking systems provide much-appreciated shade from the hot Arizona sun each summer. Elevated tracking PV systems also allow dual use of valuable urban real estate, such as the top decks of parking structures and parking lots.
To maximize tracking reliability, reduce maintenance and improve uptime, ViaSol designed the controller using the IDEC MicroSmart Pentra PLC system. The MicroSmart Pentra system was selected for its robustness, control flexibility and economic value. The entire controller is built using commercial off-the-shelf (COTS), UL-listed components. The PLC-based controller logic consists of a finite state machine implemented using ladder logic. User-controlled setpoints customize controller operation. The finite state machine implements manual operation modes and error-handling logic.
The position of the sun is calculated using a simplified, modified version of the "Solar Position Algorithm" (National Renewable Energy Labs.), an astronomical algorithm that estimates the position of the sun with an uncertainty of 0.00003 degree. The simplified algorithm estimates sun angles within ±0.05 degrees from the solar position algorithm. The logic calculates the optimum tilt angle every five minutes using the MicroSmart real-time clock (RTC) feature. A wind stow algorithm moves the PV modules flat during high winds. MicroSmart Data Link (RS485) protocol is used to network multiple controllers in master-slave mode. An IDEC MicroSmart Web server module is used for Internet-based control, monitoring and maintenance of the tracking system.
The tracker drive system consists of COTS, agricultural, hydraulic cylinders, three-phase induction motors, pumps and fluid reservoirs. Environmentally friendly, biodegradable fluids are used in the hydraulic system. A VFD protects the motor and provides soft start and stop. The MicroSmart Pentra controls the VFD and hydraulic valve stack. ViaSol's unique controller logic design optimizes system operation for maximum reliability and minimum parasitic power losses. Annually, less than 0.1 percent of produced energy is used for the tracker operation.
The MicroSmart Pentra from IDEC is also known for its speed, flexibility and power. Now with the introduction of a new 12V dc model, MicroSmart Pentra is the perfect choice for eco-friendly solar applications.
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