>Since the sun doesn't shine all the time and you don't get peak output all the time 750 square meters per person doesn't seem terribly unrealistic.
At current prices, that much PV capacity would cost around 25 trillion dollars. That price doesn't include any storage capacity.
The climate is changing far too rapidly for us to hope for science fiction solutions. We need a major reduction in emissions now, which means both a vast increase in renewable production and a vast reduction in overall consumption.