Wednesday, 26 April, 2006

Ethanol? Who are you kidding?

According to the media, the new fuels to save us all will be--wait for it--alcohol (ethanol and methanol).  That's right.  No more sucking dead dinosaurs out of the ground.  No.  Instead we'll make our fuel from corn, cane sugar, or some other fermentable sugar.  It's a nice dream.  Too bad it won't work.

Why won't it work?  There are at least two arguments against ethanol:

The first argument is simple math:

  1. U.S. gasoline consumption is about 320,500,000 gallons per day.
  2. Ethanol is made primarily from corn.  You get about 2.7 gallons of ethanol per bushel of corn.
  3. Average corn yield is about 150 bushels per acre.

From (2) and (3), we can easily determine that you get about 405 gallons of ethanol per acre (2.7 gallons per bushel * 150 bushels per acre).  That's per year, by the way.  It's not common to get more than one crop of corn per year.

At 405 gallons of ethanol per acre, it would take 791,000 acres of corn to produce enough ethanol for one day of gasoline.  It would take 240,000,000 acres of corn to replace the U.S. gasoline consumption with ethanol.  The current planted acreage of corn in the U.S. is 80,000,000 acres, and that's already used for other things.  240,000,000 acres makes up the total U.S. acreage of grains, oilseeds, and cotton.  There's just not enough farmland to grow enough corn to replace the gasoline.

Okay, nobody serious is recommending that we replace all of our gasoline consumption with ethanol.  I just threw out the above to get rid of the alternate fuel groupies who glom onto any new idea without even trying to understand the ramifications.  Besides, the numbers above assume that we can replace gasoline with ethanol on a gallon-for-gallon basis.  We can't, because ethanol is less energy-rich than gasoline.

Argument number two is based on practical considerations.

Ethanol has long been used as an additive to gasoline.  It increase the oxygen content of gasoline to help burn the gasoline more completely and reduce tailpipe emissions.  Ethanol is being used increasingly to replace MTBE as an oxygenate because of the perceived harmful effects of MTBE on the environment.  (Search for "effects of MTBE" if you want to read the literature.)  There is some argument about whether ethanol is a suitable replacement for MTBE.

Existing automobile engines can burn fuel that is 90% gasoline and 10% ethanol.  Flexible fuel vehicles (FFVs) with specially modified engines can burn an 85-15 mixture, but those engines are not common.  At best, ethanol could replace 10% of our gasoline consumption today, and if FFVs became more common, perhaps we could replace up to 15% of our gasoline with ethanol.

Pure ethanol is not a very practical fuel at all.  Ethanol absorbs water, which dilutes the fuel and makes it less effective.  Ethanol also is very corrosive and very hard to store or transport.  More importantly, ethanol has 37% less energy per gallon than does gasoline.  That is, it requires burning 1.6 gallons of ethanol to get the same amount of energy that you get from burning one gallon of gasoline.  Methanol, by the way, is more corrosive than ethanol, and has 55% less energy than gasoline.

It's simply not possible to replace gasoline with alcohol.  We can maybe reduce our gasoline consumption by up to 10% by using blended fuels, but that's the best we'll be able to do with alcohol.  Even if it were possible, I think you'll find that the cost would be prohibitive.

The other fuel that's being hyped to death lately is biodiesel.  That won't work, either, but I'm too tired right now to explain why.  Go look for the reasons yourself, or wait until I get around to writing it.