How much area would be required to power the world (with solar panels alone)

I came across this particular pic which really made me think. I don’t know if they did the math right, but if they did, with a surface as big as the plastic island floating around in the Pacific covered with solar panels, the whole world could be powered. If we consider other sources of clean energy (hydro plants for example),

Electricity from trees

Researchers have figured out a way to ‘plug’ into electrical power generated by trees. It has been a well known fact for years that plants can conduct electricity (humans can too, take care kids), and now scientists from MIT found out just how much they can pack up: 200 millivolts of electrical power (=0.2 volts). The lemon and potato battery