A solar thought experiment

Update 7/30/07: Mr Rapier updated his figures, and so have I

Just how many solar panels would it take to power the entire United States? Blogger Robert Rapier takes on this hypothetical thought experiment and comes up with some interesting (and very rough) figures:

Area required: 72 miles by 72 miles 50 miles x 50 miles
Cost: $670 billion $309 billion per year over 10 years
Carbon emissions avoided: 2,375 million metric tons (a 1/3 reduction in "anthropogenic" emissions)

Context: the U.S. federal government has annual revenues of $2.4 trillion (it spends a few hundred billion more). This solar extravaganza would be about 1/4 13% of the annual budget.