From Cornell University News:
An acre of U.S. corn yields about 7,110 pounds of corn for processing into 328 gallons of ethanol.
That's 3,225 kg and 1241 liters.
Let's assume that the "large SUV" has a twenty gallon (76 litre) tank. So that's 7110 pounds divided by about 16. That comes out to 433 pounds (196 kg) of corn.
From the Washington Post:
[...] each pound of corn yields about 1,566 calories.
That's .45kg and 6.56 MJ.
Multiplying by 1566 and dividing by 365 gives us about 1860 calories (7.8 MJ). That's sufficient calories per day for a sedentary forty year old woman (as per WebMD). If our large SUV instead had a thirty gallon (114 litre) tank, that would bring things up to around 2790 calories (11.7 MJ), enough for a moderately active man.
This obviously ignores any nutritional deficiencies in corn. In reality an all corn diet would likely be short on some key nutrients, like protein. But given that caveat, the comparison is numerically accurate.
Why it seems off
Since it definitely costs me more in a year to eat than it would to fill the tank of an SUV, something must be off here. What am I missing?
I don't know your actual shopping and dietary habits, but I suspect:
- You don't buy corn in bulk from farmers. As such, if you bought 433 pounds (196 kg) of corn, you'd pay more than the $21 (US; see the Cornell link for the $1.05 per gallon price).
You have higher standards for your corn than ethanol producers do.
- You want your corn juicy, not dry.
- You want all of the husk removed, including the silk strands.
- You want all of the cob removed.
Ethanol producers don't care as much about that stuff. Corn is preferable, but it's not like they're eating it. So processing corn for ethanol can take shortcuts that food processors can't.
- Food corn that is not perfect is removed and not sold as food for people. It may be fed to animals or turned into ethanol.
- A lot of the food that you eat is more expensive than corn. Corn is a staple crop. It's one of the cheapest foods around. You'd pay a lot more for a steak made from a cow (probably fed with corn). But even a decent vegan diet is going to cost more than corn does. It's not like you eat raw soybeans, corn, wheat, oatmeal, and various vegetables. You typically add spices, sweeteners, etc. as well as the cost of preparation.
- On average, your food probably travels farther than corn does to become ethanol. This is because the ethanol producers can locate close to the corn to save on shipping costs. And they don't need their corn fresh. Some of your food probably comes from the other side of the equator, where it is freshly grown and shipped quickly to you.
- You probably spend a significant amount of your food budget on packaging and preservation rather than the contents. You can get a bushel (25.4 kg) of corn for about $1, but that might buy you a small bag of frozen corn.
TL;DR: you likely have a more expensive diet than just corn bought in bulk directly from the farmer.