The continuation of the solar cell and battery cost curves are pretty darn impressive. Costs halving about once a decade, for several decades, is pretty darn impressive. One more decade until solar is cheaper than coal is today,
Do you have a cost curve for the price of watts delivered to the grid, instead of solar cell costs?
Going on the wikipedia price per watt: http://en.wikipedia.org/wiki/Price_per_watt
Solar panels are currently selling for as low as US$0.70c a watt (7-April-2012) in industrial quantities, but the balance of system costs put the systems closer to $4 a watt.
So even if the panels were free, it's still $3.30 per watt to actually make it happen.
BOS costs have so far kept rough pace with cell costs, and the DOE has fairly credible roadmaps and prototypes for further reductions, as with cells. Part of these are regulatory costs (pointless permitting demands and the like) which can be relaxed, and have been in places like Germany.
A while ago I wrote briefly on why the Singularity might not be near and my estimates badly off. I saw it linked the other day, and realized that pessimism seemed to be trendy lately, which meant I ought to work on why one might be optimistic instead: http://www.gwern.net/Mistakes#counter-point
(Summary: long-sought AI goals have been recently achieved, global economic growth & political stability continues, and some resource crunches have turned into surpluses - all contrary to long-standing pessimistic forecasts.)