How They are Made
How is Silicon Produced
- Carbothermal reduction - Si02 is heated with Carbon (charcoal) in an arc furnace to produce metallurgical grade (impure) silicon
- This silicon can be drawn into a round billet from a melt
- Metallurgical grade silicon is purified to solar grade silicon (not as pure as semiconductor grade) by zone refining in vaccuum 
- This is an induction heater traveling up a billet of silicon
- Vaccuum sucks out light impurities
- Heavy impurities are travel up the melt zone as melt zone travels up the billet
- Phosphine -  - dopant. 40 l cylinder - $700 - . 0.2 ppm is required for doping PV. 
- If a PV panel, 285W, weighs 19 kg and maybe 1.5 kg silicon -  - then .2 ppm -> then 0.3 mg of phosphine per panel. If a bottle of phosphine contains 10 kg phosphine, then one bottle is sufficient for - 30,000,000 panels! Thus, phosphine costs per panel are negligible - 0.002 cent per panel. This may be reduced for inefficiency of diffusion - but still likely to be way under 1 cent per panel.
- Diborane gas - used in doping. . $1400 per tank - 
- $500/kg - 
- Borax - 25 cents/lb
- Wanxiang 230 Watt 60 Cells Poly Silver Frame UL. 16 of these would be 3680W. . Company - . Panel specs - . The site shows panels as low as 20 cents. Is there a USA source at similar cost?