The point at which solar power becomes economically viable is probably driven more by the rising cost of fossil fuels rather than the slow and steady advances in efficiency and affordability in solar power itself. At some point, those graph lines - the falling cost of solar and the rising cost of oil - are going to cross over, and that's when solar will start to become far more important to the primary energy production companies of Earth.
Mokalus of Borg
PS - I'd like it if solar were important to them already.
PPS - However, I think that misses the fact that money is their motivator, not environmental concern.