Concentrated Solar, Dual Axis-Tracking, Multi-junction GaAs Cell Photo-voltaic System Design for Efficient Solar Energy Conversion

摘要

Inexpensive photovoltaic (PV) arrays make use of inherently inefficient mono-junction solar cells. Higher efficiency multi-junction PV cells are available but in small sizes and at much higher cost. One method of reducing the overall cost yet yielding a high efficiency is through an inexpensive concentrating device which focuses large amounts of sunlight onto a small sized but efficiently working multi-junction PV cell and running it at high concentrations. Using this method greatly reduces the surface area of the multi-junction PV cell needed to collect the solar radiation; this in turn allows for the higher efficiency panels to be utilized economically. The primary goal of this work has been to design and build an inexpensive and experimental, dual-axis tracking concentrated solar photovoltaic system to show its economic feasibility. The secondary goal is to use the resulting sun-tracking mechanism as a platform on which other concentrated solar energy conversion devices (solar-thermo-electric, solar-thermo-mechanical, solar-thermo-chemical) can be tested for research and educational use in the future. Relatively inexpensive common materials and simple manufacturing processes demonstrated that using a parabolic dish to concentrate solar radiation onto a tiny 1/2 cm~2 multi-junction solar cell chip would produce an electrical output greater than 8 watts. Excess heat generated is dissipated via a heat sink assembly the solar cell chip is bonded to. The system is made up from a scalable parabolic mirror, a microprocessor controlled dual-axis tracking mechanism which is guided by a four-quadrant home-made light sensor, and the multi-junction solar cell assembly including its heat sink. The parabolic mirror is designed by combining strips of off-the-shelf aluminum coated polycarbonate mirror material, all bent, positioned and held in a frame to reflect the light at the focal point where the multi-junction cell is fixed. The system follows the celestial path of the sun within 1.6 degree. This project was completed as a senior capstone design project utilizing all of the education gained thus far in the engineering curriculum along with a large amount of self-directed learning. Every stage in the design and development of the project was an educational test that had to be overcome. Discussion on the short comings, challenges, and the use of the education received to resolve these issues are presented.