I agree with your general point. But I think this example may be a tad hyperbolic.
According to this site, it would take 2907 acres of panels.
http://www.boemre.gov/omm/pacific/kids/Power-Your-City/bookmark-1-page%20side-by-side.pdf
I don't know that's right either, but I believe MA has a lot more acres than that.
If you have an actual number for the power consumed by this imaginary city of 100,000 we can do some calculations.
I am wondering how well those 2907 acres of solar panels would do powering the city of 100,000 during the night. My guess is...not very well.
According to your numbers it would take ~14000 square miles to power the United States. A square of ~118 miles on each side.