I revisited the topic in 2014.
The boom and bust cycles continue. The latest example is mainly in China where massive overbuilding in the first half of 2016 have forced a halt to new construction for the second half of 2016. This is causing major problems for PV panel makers as oversupply is causing prices to collapse.
Link1, Link2, Link3
The root cause of this continuing boom and bust cycle is the continuing dependence on substantial government subsidy. This means the PV market is driven by political forces and not market forces. Government subsidy policies determine the scale of investment.
World clean energy Investment has stayed within a narrow range since 2010/2011. The graph above from Bloomberg (BNEF) shows the latest downturn, presumably caused by the turmoil in the Chinese market.
PV is clearly still far from economic viability and the flat level of spending for the last five plus years (around $250B/y) seems to be about as much as the world is currently willing and able to spend on subsidizing clean energy. This level only allows for slow growth in clean energy and a limited affect on CO2 emissions. Optimists need to come to terms with this reality and start considering alternatives like StratoSolar that show an economically viable clean energy solution based on today's PV is possible. Economic viability is the key to breaking out of the political boom and bust cycle.