Finally, we can calculate how much land is needed to power the entire US with
photovoltaics (neglecting the storage issue). The US used about 3.6 × 1012 kWh of
electricity in 2000. This could be met with 2 × 1010 m2. If we compare with the area
of paved roads across the country, of about 3.6 × 106 km and assume an average width of 10 m this leads to 3.6 × 1010 m2