Abstract
Solar panels are typically in fixed positions. They're limited in their energy-generating ability because they cannot consistently take full advantage of maximum sunlight. For more effective solar energy systems, the solar panels should be able to align with sunlight as it changes during a given day and from season to season. This article examines the design advantages of creating an intelligent solar tracking system using an embedded processor and an FPGA in a system-on-a-chip (SOC) architecture.
Introduction
Solar energy is becoming increasingly attractive as we grapple with global climate changes. However, while solar energy is free, non-polluting, and inexhaustible, solar panels are traditionally fixed. As such, they cannot take advantage of maximum sunlight as weather conditions and seasons change. This article describes an FPGA- and embedded processor-based system-on-a-chip (SOC) implementation of a prototypical solar-tracking electricity generation system that improves the efficiency of solar panels by allowing them to align with the sun's movements.
Integrated design for faster development and greater flexibility
For optimal efficiency, solar panels should be perpendicular to sunlight where the illumination is strongest. But since the direction of sunlight changes during the course of a day – and from season to season – a high-performance solar tracking system can maximize usage of the panels.
A team of students from Yuan Ze University in Taiwan applied embedded design techniques and a SOC architecture to create an FPGA-based solar tracking system. This system uses two motors as the drive source, conducting an approximate hemispheroidal 3-D rotation on the solar array within a certain amount of space. This rotation allows the system to track the sun in real time to efficiently perform photoelectric conversion and production.
To reduce control problems, the two drive motors are decoupled, i.e., the rotation angle of one motor does not influence that of the other motor. Similarly, one motor does not bear the weight of the other. This implementation minimizes the system's power consumption during operation and increases efficiency and the total amount of electricity generated.
This application uses an Altera Nios II configurable embedded processor to perform solar tracking. The design combines the processor with the two-axis motor tracking controller, memory, and I/O interfaces into one Cyclone II FPGA. This integration accelerates development while maintaining design flexibility, reduces the circuit board costs with a single-chip solution, and simplifies product testing. The design includes three modes as follows:
- Balance positioning: A tilt switch prevents the solar panels from hitting the mechanism platform and damaging it or the motor.
- Automatic mode: The system receives sunlight onto the cadmium sulphide (CdS) photovoltaic cells where the CdS acts as the main solar tracking sensor. The sensor feeds back to the FPGA controller through an analog-to-digital (A/D) converter. The processor is the main control core and adjusts the two-axis motor so that the platform is optimally located for efficient electricity generation.
- Manual mode: This mode is available if the system requires maintenance or repair.
1. Solar tracking control architecture.
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The logic flow design of the system is implemented with an embedded processor control circuit, as shown in Fig 2. When the tracking control circuit is activated, the system performs tracking, energy conservation, and system protection, as well as system control and external anti-interference measures. External interference includes weather influences, such as wind, sand, rain, snow, hail, and salt damage (i.e. salt erosion on the mechanism).
2. Tracking control flowchart.
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Embedded processor in control
The embedded processor, as shown in Fig 3, acts as the control center and integrates the two-axis control chip. The system establishes what data is fed back to the FPGA using a photography sensor. It conducts the tracking control rule operation to calculate the angle required by the motor and adjusts the motor's current angle. It also moves the solar panel to achieve optimal power.
3. System architecture.
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