The aim of the new process which is followed since autumn 2008 is also to produce solar grade silicon out of metallurgical grade silicon as cost-effective as possible. Key feature of the underlying process is a multilevel method for the separate reduction of phosphorous (P), boron (B) and other metals with which purity in the range of 99.9999 percent can actually be achieved, and this is also under the prerequisite that the raw materials can tolerate wider fluctuations in quality. The process allows the use of a wider range of marketable so-called commodity materials and therefore provides cost reduction advantages in purchasing.