[fizigura]

Well, most land is either farmland, forest or desert. Forest is out of the question for any solar installations unless you want to cut down the trees. Desert is not easily accessible for most parts of the world and provides terrible conditions for solar cells that have sharply declining efficiency with heat and don't like dust.

Leaves farmland, if you want to do this kind of thing at any sort of required scale. (Sure you can put solar cells on barn roofs, but the premise was scale magnitudes beyond that.)