Development of a Two-Axis Solar Tracker for Daylighting and CPV(Concentrator Photovoltaics)

An embedded two-axis solar tracker was developed using AVR micro controller in order to enhance the efficiency of daylighting systems and CPV(Concentrator Photovoltaic). Such systems use either one or two solar concentrators to collect and focus solar light to desired spot, which require high accuracy of tracking. The system consists of an Atmega128 micro controller, two step motors, two micro-step motor driver, Cadmium Sulfide (CdS) sensors, GPS module and other accessories needed for functional stability. This system is controlled by astronomical method and optical method. Initial operation is performed by the result from the astronomical method and followed by fine controlled operation using the signals from CdS sensors. The GPS generates UTC, longitude and latitude data where the solar tracker is installed. A database of solar altitude, azimuth, and sunrise and sunset times is provided by UART (Universal Asynchronous Receiver/Transmitter) to AVR micro controller. A small parabolic concentrator (<30cm) was developed, which mounted to the tracker for CPV. A secondary reflector and an optical cable were used for daylighting. Ray-tracing simulation on the small concentrator module was conducted to analysis its performance. Solar position and sunrise and sunset times in the database were compared with those of the Astronomical Applications Department of the U.S. Naval Observatory. The differences were found to be negligible.