The capacity factor of new utility scale solar deployed in the US in 2010 was 24%. By 2012 it had risen to roughly 30%.
The rising capacity factor of new solar projects is part of why the cost of electricity from new solar is dropping faster than the installed cost per watt. Installing solar at a 30% capacity factor produces a quarter more electricity than the same number of watts of solar deployed at 24%. The rise in capacity factor effectively reduces the price of electricity by 20%.
The chart and data are from an excellent Lawrence Berkeley National Labs study, Is $50/MWh Solar for Real? Falling Project Prices and Rising Capacity Factors Drive Utility-Scale PV Toward Economic Competitiveness
The EIA shows similar numbers, showing that the capacity factor of the entire solar PV fleet in the US in 2014 (including projects deployed before 2012) was 27.8%.
As newer projects come online, they’ll likely move the average capacity factor of the total fleet upwards.