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April 19, 2007

Ethanol? Good? Bad? Ugly?

Category: Ethanol – Dan 9:29 pm

While hanging out at the Sierra Club’s booth at last weekend’s Step It Up event in San Francisco, someone asked me “Can you explain the deal with Ethanol? Is it a good idea or not.”

As with many things, the answer is “it depends”.

Drawing from “” (the industry group promoting corn-based ethanol):

Ethanol is a clean-burning, high-octane fuel that is produced from renewable sources. At its most basic, ethanol is grain alcohol, produced from crops such as corn. Because it is domestically produced, ethanol helps reduce America’s dependence upon foreign sources of energy.

Ethanol is grain alcohol, the same alcohol, in pure form, that you get from fermented grapes, wheat, potatoes, or rye. Instead of mixing it with water, it’s mixed with gasoline.

There’s two issues to discuss here. First, why do we care about ethanol. And the second, how do you make it.

Why do we care about ethanol?

Ethanol, like gasoline and diesel, is a high energy density liquid fuel. It’s a potential substitute for gasoline to power our vehicles. And unlike diesel or gas, it’s made from biomass. The theory here is that growing plants uses the energy of the sun to take CO2 out of the air and convert it into biomass, you then convert the biomass into ethanol, and you essentially have a carbon neutral energy source.

This is the big appeal of ethanol. That said, it’s not a perfect fuel by any means:

  • It has a lower energy density than gasoline or diesel (roughly a third less). If you got 300 miles on a tankful with gas, you’d only get 200 miles on a tank of ethanol.
  • Ethanol is not compatible with some fuel system components. This is one reason that cars need specific adaptations to use E85 fuel
  • Ethanol absorbs water, whereas gas and diesel do not. Most existing petroleum pipeline are (surprisingly) not water free (water is heavier, and can collect in low spots). Putting ethanol or gas/ethanol mixtures in these pipes causes the water and other contaminants to be taken up by the fuel. Consequently, ethanol today is transported by truck, not pipeline.[3]

OK, not perfect. But a reasonable choice for a liquid fuel based on renewable biomass.

How do you make ethanol?

In the US today, ethanol is almost synonymous with corn. But corn has two issues: first it’s a relatively water and energy intensive crop to grow, and second we currently only produce ethanol from the grain. The result is that it takes nearly as much energy (mostly fossil fuel energy) to create the ethanol as you get from it[4]. I guess you could call this dumb green energy.

Brazil is also making large investments in ethanol, but it’s based on using Sugar Cane. The overall energy yield is roughly 8 times what you put into it, making this a much greener source of liquid fuel.

But to really make ethanol successful, one needs to look at what crops yield the most potential fuel per acre for the least input of energy and water. Here are some choices:

Crop US Gallons/acre
Miscanthus 1500
Switchgrass 1150
Sugar Cane 662
Corn 370

This is why switchgrass is often mentioned as the long term ethanol feedstock. The challenge is in making production from non-starch based sources. The term for this is cellulosic ethanol. Much work is now being done to generate ethanol from these alternate sources, and if this can ramp up to an industrial scale, then ethanol has great promise as a future liquid fuel.