PV Panels

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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 [1]
  • 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

Phosphorus

  • Phosphine - [2] - dopant. 40 l cylinder - $700 - [3]. 0.2 ppm is required for doping PV. [4]
  • If a PV panel, 285W, weighs 19 kg and maybe 1.5 kg silicon - [5] - 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.

Boron

  • Diborane gas - used in doping. [7]. $1400 per tank - [8]
  • $500/kg - [9]
  • Borax - 25 cents/lb