Other tech: holographic solar concentrators

Holograms can concentrate by about ten times and can reduce the amount of silicon needed by 25-85%. Currently there is supply shortage of suitable silicon for solar power. the first generation system will be somewhat cost competitive with new alternatives in solar power ($2.40 per watt) and the second generation could be competitive with other forms of energy ($1.50 per watt)

$3 per watt installed is key threshhold price for more rapid adoption.