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Producing solar grade silicon the environmentally friendly way

A new method for the production of SOLar Grade SILicon at low Cost (SOLSILC) has been achieved through the creation of a two-step high temperature process that increases the competitive market price.

Industrial Technologies

The primary objective of this project was to produce commercial solar grade silicon with a market price below 20 Euros per kilogram. This entailed the testing, processing and the efficiency of SOLSILC cells, as well as the evaluation and investigations of the relevant technical, environmental and economic aspects. Thus the final objective is to operate a pilot demonstration producing solar grade silicon at a rate of 5000 tonnes per year and therefore achieve a competitive market price. This two-step high-temperature process produces silicon metal from high-purity quartz and pure carbon black, with silicon carbide as an intermediate product. The process begins in a rotary plasma furnace where pellets of quartz and carbon black are reacted to produce silicon carbide. The second furnace is an electric arc furnace where the silicon melt is formulated from the reaction of the quartz and silicon carbide. The resultant silicon melt saturated with carbon is reduced from several hundred ppmw to 2-5ppmw via a combination of three purification processes. The first of which is a controlled SiC precipitation, followed by the purging of gaseous oxidations and finally directional solidification. Furthermore, individual purification tests of the different purification methods have been performed on the solar grade silicon, and their effectiveness has been demonstrated. The minimum specifications for solar grade silicon have also been derived from the chemical analysis of commercially available PV wafers, whilst the chemical composition of SOLSILC silicon has also been estimated. In addition, the cell tolerance performance for specific impurities has been investigated and the end results indicate the possibility of achieving good cell performance on wafers made of SOLSILC silicon. Finally, the project evaluated the environmental impact of the SOLSIOLC process when compared to solar grade silicon production techniques. It discovered that with the availability of resources, energy consumption, and safety and emission standards, this process is probably one of the most environmentally friendly manufacturing process of all.

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