Now there's a big difference between what's technically possible and what's technically, politically, and financially practical, but a new study of the solar power potential of the US should give great pause.
PV Magazine reports that NREL's new analysis of the technical potential of solar photovoltaics and concentrating solar power in the US places the total amount that can be installed just under 200,000 GW, capable of generating just under 400,000 Terawatt-hours annually—hugely exceeding the electricity generating capacity of the US for 2010 of 4,125 TWh.
Breaking that down along different methods of generating solar power, the report found that rooftop PV alone could generate 818 TWh of electricity each year, roughly 20% of current demand; utility-scale PV in urban areas could generate 2,232 TWh, or 56% of demand; concentrating solar power has a potential of just over 116,000 TWh. But utility-scale solar PV in rural areas is really where the actions at, with 280,613 TWh of electricity technical capable of being generated each year.
The full report also goes into the potential of other renewable energy sources, but these far trail the technical potential of solar power.
Onshore wind power was found to have the technical potential of generating 32,700 TWh annually; offshore wind power, 17,500 TWh. Enhanced geothermal power could generate 31,300 TWh. Biomass power, not taking into account anything diverted for liquid fuel production, could generate 500 TWh. Exploiting hydropower to the greatest extent technically possible would generate 300 TWh each year
All of which is to say, from a technical perspective, for electricity generation renewable energy sources (totally excluding nuclear power) could produce several, several times the amount of electricity currently generated in the United States.
Again, technologically possible is different that politically or financially possible—and doesn't really take into account distribution issues (not every place is as ideally suited for solar power as California and Texas, both singled out in the report)—but even a small percentage of reaching this technologically potential would allow the US to have carbon-free power at current consumption levels, even allowing a generous expansion of electricity usage.