Investigation of an octagon-shaped chimney solar power plant

Abstract

South Africa has limited reserve electricity resources and many parts of the country have limited access to electricity, while electricity production capacity is at maximum and almost every gigawatt is accounted for. The energy crisis has highlighted the need to increase electricity generation capacity and to search for alternative energy sources. This study focuses on the solar chimney concept, which harnesses both solar and wind energy to generate electricity, especially in the sunny Northern Cape Province and Karoo regions of South Africa. The concept is an alternative design focusing on very low wind power, where an effective cone solar frustum power plant is able to generate sufficient wind flow to turn a turbine and produce electricity. The study focused on different chimney designs (cylindrical and octagon shapes) to evaluate the best performance. Simulations were performed to find the optimum design configuration to focus the research. The simulations evaluated the shape of the tower, tower base, heat transfer surface areas and efficiencies of the system. The results showed that the octagonal chimney outperformed the normal cylindrical one, mainly due to an increased airflow and the turbine being positioned at the outlet of the chimney (whereas it is at the bottom of a cylindrical chimney). The addition of mirrors increased the performance due to solar radiation from all the directions around the chimney. The results were confirmed by a pilot plant that was operated continuously for 24 months.