<P> Polycrystalline silicon, also called polysilicon or poly - Si, is a high purity, polycrystalline form of silicon, used as a raw material by the solar photovoltaic and electronics industry . </P> <P> Polysilicon is produced from metallurgical grade silicon by a chemical purification process, called the Siemens process . This process involves distillation of volatile silicon compounds, and their decomposition into silicon at high temperatures . An emerging, alternative process of refinement uses a fluidized bed reactor . The photovoltaic industry also produces upgraded metallurgical - grade silicon (UMG - Si), using metallurgical instead of chemical purification processes . When produced for the electronics industry, polysilicon contains impurity levels of less than one part per billion (ppb), while polycrystalline solar grade silicon (SoG - Si) is generally less pure . A few companies from China, Germany, Japan, Korea and the United States, such as GCL - Poly, Wacker Chemie, OCI, and Hemlock Semiconductor, as well as the Norwegian headquartered REC, accounted for most of the worldwide production of about 230,000 tonnes in 2013 . </P> <P> The polysilicon feedstock--large rods, usually broken into chunks of specific sizes and packaged in clean rooms before shipment--is directly cast into multicrystalline ingots or submitted to a recrystallization process to grow single crystal boules . The products are then sliced into thin silicon wafers and used for the production of solar cells, integrated circuits and other semiconductor devices . </P>

Where does silicon for solar panels come from
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