Solar silicon production starts with the production of silicon
metal from quartz and carbon. Produced mainly for the aluminum and chemical industry the silicon metal has a purity of 98-99%. Contrary, the threshold for solar silicon in considered to be 99.9999%. Refining of silicon to solar silicon is mainly done via the gas-phase with high technical, energetic and financial efforts. Thus, novel routes to provide cost-effective and easy to scale alternatives for solar silicon production were developed. One of this routes is the direct carbothermic reduction of high-purity raw materials to produce solar silicon. However, due to a dramatic price decrease to $15/kg in the past years, many projects were stopped. Based on a review of project results published throughout the years in this field, we will present our approach for a low-cost solar silicon production by direct carbothermic reduction of renewable raw materials in a microwave furnace.