Renewable energy sources have a lower energy density than conventional forms of energy, meaning that a given surface area of renewables will produce less power than that same surface area utilized by fossil fuels.
Renewables are nonetheless capable of powering the U.S. on a small amount of land. Researchers at the National Renewable Energy Laboratory estimated in 2008 that solar power could supply electricity to all Americans using just 0.6% of the country's land. They point out for comparison that solar power’s footprint would be less than 2% of farming and grazing land.
Researchers at Columbia University reported in 2009 that including life-cycle factors such as mining and waste storage, solar in sunny areas requires less surface area than coal or nuclear.
Estimates for wind are even lower: CleanTechnica suggested that wind turbines could power the U.S. on “about 0.01% of the land.”