Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.
South Africa has the largest and most developed economy and the highest energy consumption on the continent. 72% of the primary energy is provided by coal, making South Africa the leading carbon dioxide emitter in Africa and the 13th largest in the world. As the amount of South Africa’s proved crude oil reserves is very small, synthetic fuels derived from coal and natural gas in its coal-to-liquid and gas-to-liquid plants make up roughly 90% of the country’s domestic petroleum production. However, just one third of the total petroleum demand can be met by the production and the other two third has to be imported and processed in the local oil refineries. Using Concentrated Solar Thermal (CST) technology, especially solar tower systems, could have the potential to substitute fossil fuels by solar energy, as South Africa is exposed to one of the highest direct normal irradiance (DNI) in the world. There are several technologies able to deliver high temperature heat. They differ by heat transfer media, system temperature and the system pressure. Direct or indirect heat storing allows a high solar share while an easy hybridization with fossil fuels guarantees 100% availability. One promising technology, for example, uses small ceramic particles as heat transfer and storage media. The particles can be heated up to 1000°C and later be used for production of hot air. A very simple and therefore robust technology uses ambient air which is heated up to 750°C for direct use in a pre- heating process or storing the heat in regenerator storage. Another technological approach uses the rejected heat of a solarized gas turbine with temperatures up to 650°C as process heat. The benefit of such a system is the combined generation of electricity and heat. Storage can be included at the pressurized side allowing high solar share or by using a regenerator on the hot exhaust stream. The diversity of processes and consumers requires an individual selection of the technology and a layout adapted to the specific consumer needs. The paper presents the different available technologies to show the potential using CST for process heat using air with temperatures above 600°C.
