Turning plants into fuel might sound good, but crunching the numbers makes it look kind of pathetic. According to energy journalist Robert Bryce in his latest book, Power Hungry, the U.S. uses 320 billion gallons of oil each year. So let's see what it would take to replace ten percent - 32 billion gallons — with biomass-derived ethanol.
Ethanol has about two-thirds the energy density of gas, so we would need 48.5 billion gallons of ethanol. Companies pioneering cellulosic ethanol say they can get about 100 gallons of ethanol from a ton of cellulose-based biomass. So we would need 485 million tons of biomass.
And how much is that? If a 48-ft trailer can hold 15 tons of biomass, it would only take 32.2 million of them, which, if lined up (without trucks attached), would stretch over 293,000 miles, long enough to circle the world at the Equator eleven times.
And how much land would it take to grow that biomass? Researchers at Oak Ridge National Laboratory calculate that an acre of switchgrass can create 11.5 tons of biomass annually. To get 485 million tons, it would therefore take 42.1 million acres planted in nothing but switchgrass. That's about 65,800 square miles, or nearly the size of Oklahoma. It would also represent 10% of America's cropland now under cultivation.
So if we devote 100% our croplands to switchgrass, we can totally replace gasoline. Unfortunately, we also won't have any homegrown food.
