Meeting the Challenge of Accurate Solar Tracking
Photovoltaic technology is an emerging major power source due to its numerous environmental and economic benefits and proven reliability. Automation and control solutions for solar tracking devices are at the forefront of this renewable energy technology. Concentrated photovoltaic (CPV) systems are designed to capture sun rays at their highest intensity by concentrating the beam of light through solar cells at an optimized angle. In comparison, traditional fixed position solar panels require a larger area and a great number of arrays arranged into one system for maximum energy efficiency. Using advanced solar tracking technology, CPV systems can achieve 30% more power output and reduce the amount of space required. CPV systems also provide the ability to store generated electricity for usage at a later time. CPV cells are normally set up as flat panel assemblies that can be mounted on rooftops for residential use or larger sun-exposed areas such as deserts or fields for commercial use. One of their greatest features is that they have a long lifetime and require very little maintenance. Since CPV systems are part of a recently emerging technology where the market is highly cost-driven, engineers continue to seek the most efficient method of integrating the various components that make up this system and drive its technology. In order to provide maximum efficiency to solar power generation, various challenges must be overcome. If the sun were to move just a few millimeters, the beam of light being tracked at the solar cell would no longer be positioned at its highest intensity, tremendously decreasing efficiency. Therefore, considerations range from sensor module precision, complex calculation algorithms, data logging, control solutions and overall system integration. Hence a very precise tracking system which meets all of these challenges is required. The solar tracker unit ensures that the PV panel which converts sunlight energy into electricity is constantly at the optimum angle to maximize the efficiency of the system; it is a critical component of the entire CPV system, and is typically mounted on the rear of the panel itself. Panasonic provides the key components that enable a photovoltaic tracking system:
- Tilt sensor module
- Minas series Servo System
- FP-X series PLC
- GT series HMI
The Tilt sensor module is designed to detect the horizontal and vertical movements of the solar tracker and provide its precise angular position as well as alerting the PLC of intense weather conditions such as strong winds or earthquakes. The tilt sensor’s main features include:
- Angular detection accuracy
- Universal protocol
- Waterproof & dust resistance
- Adjustable offset
- Adjustable upper & lower limits
The tilt sensor module comes with an acceleration sensor as well as a microprocessor and power supply circuit for an all in one package module. The acceleration sensor uses the solar tracker’s position as a frame of reference and determines its movement based on the difference of the gravitational shifts. Previous solar tracking technologies have been dependent on absolute encoders to provide absolute angular detection. Absolute encoders detect angular degree based on the position of the solar tracker and require an extra sensor to detect the horizontal “zero” degree position. Panasonic’s tilt sensor detects the absolute angle by gravity and does not require an additional sensor to determine when the tracker is positioned horizontally at angle “zero.
Since solar tracking requires very high accuracy for sunlight beam intensity, the tilt sensor module is designed to provide angular accuracy of up to 0.05 degrees, detecting even the smallest movement of the solar tracker in both the vertical and horizontal direction. For ease of setup and communication the tilt sensor connects through an RS-485 serial port and uses MODBUS RTC as its communication protocol to the PLC.
Since the sensor is designed for outdoor usage, it is rated IP67 which means its case is robustly designed to protect the inner parts from dust and water. The adjustable offset comes as a special feature to provide ease of installation so that any angle can be set as a zero point frame of reference. However the maximum detection range under the adjustable offset mode is +/- 45 degrees as shown in the diagram below.
Because of unpredictable weather conditions such as strong winds or earthquakes, the CPV system must be able to determine the difference between the movement of the solar tracker from such weather conditions or from the movement caused by the sun rays shifting direction. Therefore an alert system is required to communicate that information to the PLC so that the tracker is set back in place. The adjustable upper and lower limits of the tilt sensor module are designed for that reason. Using a PhotoMOS relay that turns ON or OFF when one of the angular limits is crossed, it generates a signal to the PLC notifying it that the limits have been passed and it must recalculate the position of the solar tracker.
The MinasA4 series servo system is used to automatically move the solar tracker based on the direction commands provided by the PLC. The Panasonic FP-X series PLC provides the solar industry with a compact yet powerful programmable controller that provides reliable and fully automated operation of the solar tracker. Panasonic’s solution takes into account several environmental factors using date and time to calculate the sun’s position. The algorithm complex programmed in the PLC uses the date and time to determine the sun’s altitude and azimuth as variables to determine which direction to move the solar tracker. Panasonic also provides a GT series HMI which allows technicians to adjust and monitor the settings from a touch panel with a user-friendly interface. Logged data can also be saved on an SD memory card in CSV format.
With complete system integration that provides a tilt sensor module with precise angular detection, a PLC system with robust calculation algorithms as well as an automated servo system providing controlled movement and an easy to use touch panel, Panasonic is able to overcome the various challenges that CPV systems face today providing a system for maximum efficiency to solar power generation.