UPDATE: In 2015 the price of solar modules had dropped to $0.57 / Watt.
By Clayton Handleman
It has been observed for that for manufactured products, each time the total amount of that product is doubled, the cost declines by a certain percentage. This was first observed in the aircraft industry and since then has been seen in products from calculators to flat panel televisions and even solar modules. For silicon solar modules the cost reduction per doubling is 17%. Graphs showing this are called experience curves. There is a long historical precedent for this in photovoltaics but it also has occurred with wind power and is now happening with Li-ion batteries.
See More Links at the bottom of this post.
UPDATE: Solar now coming in under $30 / MWhr
PV Experience Curve, PV Cost Curves
UPDATE July 2015: PPA signed for PV power under $40 / MWhr HERE
And PV Installed costs are dropping as well with Germany leading the way.
McKinsey – Grid Parity is coming .
See Also – Capacity Increases
Lots of graphics on Cost of Solar
Mainstream sources consistently underestimate growth of renewables.
Clayton Handleman, EV Battery Experience Curves, Li-Ion Cost Curves, Battery Cost Curves