The numbers cited here seemed high to me, so I checked them. Primary energy consumption in the US[1] ~1 * 10 ^ 20 Joules. Divided by population and number of seconds in a year[2] is about 10000 Joules per person-second, so about 10kW per person. A kilowatt of peak solar power requires about 8 square meters of panels[3]. 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.

That being said, there is a lot of space where nobody lives in the US. There are some 28000 square meters per person in the US. Dedicating about 3% of that to solar panels doesn't seem impossible.

Some energy saving is also possible without changing the average lifestyle too much. Insulating homes helps quite a bit. Electric cars are more efficient that gas cars.

[1] https://www.eia.gov/energyexplained/?page=us_energy_home

[2] https://www.wolframalpha.com/input/?i=10%5E20+joules+%2F+(3....

[3] https://www.quora.com/How-much-solar-energy-can-be-tapped-in...