Ethanol yields 25% more energy than the energy invested in its production, whereas biodiesel yields 93% more. Compared with ethanol, biodiesel releases just 1.0%, 8.3%, and 13% of the agricultural nitrogen, phosphorus, and pesticide pollutants, respectively, per net energy gain. Relative to the fossil fuels they displace, greenhouse gas emissions are reduced 12% by the production and combustion of ethanol and 41% by biodiesel. Biodiesel also releases less air pollutants per net energy gain than ethanol. These advantages of biodiesel over ethanol come from lower agricultural inputs and more efficient conversion of feedstocks to fuel. Neither biofuel can replace much petroleum without impacting food supplies. Even dedicating all U.S. corn and soybean production to biofuels would meet only 12% of gasoline demand and 6% of diesel demand.
In English, soy is better primarily because, as a legume, it is on the soil enriching side of the nitrogen cycle, rather than the soil depleting side. This is important because when we really need biofuels, oil based fertilizers may even more expensive than they are now.
Hat Tip to Science News.
2 comments:
I can't get to the linked article, but I wonder if it considers ethanol from sources other than corn? I have read (and perhaps you've mentioned it in the past) that ethanol from sugar cane is more efficient, and would be more cost effective, if not for the import tariffs. If legislators are serious about alternative energy, perhaps they'll reconsider.
These same tariffs are responsible for the widespread use of high-fructose corn syrup. Back when I drank soda, I lamented Coca Cola's change to "new Coke," and then to the corn syrup-based "classic." (A friend and I did a taste test, and we could tell the difference between old and classic Coke.) It was a treat to find a store that sold bottles imported from Mexico, where sugar is still used.
The article this post is based on considers only soy and corn.
I suspect that soy would still come out ahead of sugar cane, but sugar cane depletes soils greatly, and thus, would require fertilizer, which is the factor that also hurts corn.
But, since the demand for biofuels far exceeds the supply of corn, soy and sugar cane combined, it may not matter much.
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