I read where a 100 mile by 100 mile square area in the US desert could provide all the necessary energy for the entire country.
Wishful thinking.
The most advanced and largest Solar installation in the world is in the Mojave Desert. (SEGS). It covers 1600 acres (2.5 sq mi) and has a peak output of 324 Mw. For comparison, the state of California averages ~40,000Mw of electricity each day.
So, if the facility size were expanded by 150x (375 sq miles or 240,000 acres) you would begin to supply the State of California on a given day during peak conditions (4 hrs a day).
Despite this massive array you would still need 100% backup capacity (i.e. backup power plants) to supplement for non peak times of the day - morning, evening & nightime.
Consider too the environmental implications of such an enormouse land area occupied by an industrial complex.
Additionally the manufacturing process uses heavy metals and nasty chemicals and requires a large energy input.
There's a reason that Solar generated electricity is not more widely used. It must be heavily subsidized to approach affordability. Even then, what exactly are you gaining?