How much surface area would be needed to power the whole world with solar panels?
496,805 Square kilometers or 191,817.483 square miles
Just to give you an idea of what this would actually look like, take a look at the image below.
This info-graphic shows the cumulative surface area required to power the entire planet with solar in 2030 (678 quadrillion BTU), given that solar panels will have 20% operating efficiencies. This includes all electrical consumption, down to machinery and transportation.