PV Panels

How They are Made

• http://www.sunlightcontractors.com/img/sw/Solar%20World-Understanding.pdf

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

Phosphorus

• Phosphine - [1] - dopant. 40 l cylinder - $700 - [2]. 0.2 ppm is required for doping PV. [3]

• If a PV panel, 285W, weighs 19 kg and maybe 1.5 kg silicon - [4] - 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.

• $5/lb - [5]

Boron

• Diborane gas - used in doping. [6]. $1400 per tank - [7]
• $500/kg - [8]
• Borax - 25 cents/lb