Hillary Clinton wants half of all US gas stations to sell E85 by 2015. Robert @ The Oil Drum crunched some numbers and came to this conclusion:
Our annual gasoline consumption is up to almost 140 billion gallons. That means on a BTU equivalent basis, converting the entire US corn crop into ethanol would amount to 13.4% of our annual gasoline demand. It takes 77,228 BTUs of fossil fuel inputs to make 83,961 BTUs of "green, renewable" ethanol. That means that in reality, using our entire corn crop would only displace 1% of our annual gasoline consumption. We can't possibly produce enough E85 to justify putting in all those pumps.
Cyclelicious readers are a smart bunch, so you already know that Hillary talked about cellulosic ethanol, which can be made from switchgrass (among other things). I crunched the numbers before on cellulosic ethanol and switchgrass, figuring we need over 500 million acres of switchgrass to create enough ethanol to replace what we burn today. This commentor came up with a similar number. This comment is also good to read regarding some of the reality that we encounter when trying to figure out a way to fuel our automobiles.
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I've also crunched the numbers and it doesn't take long before you realise that there isn't enough arable land around to support either growing crops for fuel and food OR indeed for growing trees to offset greenhouse gas emissions. Should we also point out that there are almost NO environmental benefits in terms of reduced greenhouse gas emissions in using E85?
There are technologies being devoted that will allow ethanol to be produced from arable waste, so that land could feasibly be used for food and fuel. I don't know what the figures are on that, but it has to be closer to sustainable.
But, really, there's only one answer- use less fuel. Drive less, in more efficient cars, cycle, walk etc. etc.