actually he did. He estimated that if we cover a landmass of the size of spain with solar collectors, it would power the world.
Put those panels in a desert and it's not really space people need
other sources: here
I worked as a solar technician for a couple years and I think it's doable. Solar panels are even the weakest part of the chain when it comes to reusable energy with one solar panel giving between 150 and 220 kwats/h while one wind energy unit can provide up to 1.3 megawatts.
So i think we could even power the world with less space than spain