Letters to the Editor
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A square of farmland 4700 kilometers on a side.
Andrew's article overlooks the real issue in the biofuels debate. Few serious people would deny that under the right circumstances, biofuels CAN yield more energy than they take to produce. To suggest otherwise is a bit of a straw man. (In any case, only four of the six studies cited suggest that they do.) The question is, can biofuels replace in any serious way our fossil fuel consumption?
And, from this model, the answer is pretty clearly no. Even the four positive-yield studies still produce results like (at best) 1.5 net energy ratio. (That is, 1.5 joules of ethanol and other fuels coming out for every joule of energy inputs.) For comparison, Alaska oil in 1996 is given at around 11.1 net energy ratio. (That's Odum 1996, which incidentally gave corn and sugarcane biofuels as 1.10 and 1.14 respectively, suggesting comparable system boundaries to the papers reviewed by ERG.) Figures for Texas oil from 1940's discoveries (from other studies and, admittedly, perhaps different system boundaries) give net energy ratios on the order of 28 to 100+! Tout court, our lifestyle is built around energy that's a hell of a lot easier to get at than biofuels. Replacing them with ethanol is gonna involve some serious compromises.
I won't get into the details of the individual models, because that's a bit outside of my competence. I'm just an urban planner. But I notice that the most optimistic study (Shapouri's, with the 1.5 net) shows a bunch of suspicious zeroes in the biorefinery phase. ("NR" means "not reported.") Perhaps I have missed something; perhaps all the energy comes from "primary energy" (i.e. solar) but I doubt it.
I also notice that none of the models include the energy cost of moving the products to market. How much will be used to move that ethanol from Iowa or Brazil or wherever to the gas tank in suburban Los Mengeles?
Finally--for the real reality check--how many hectares of farmland would have to be dedicated to producing fuels to meet our current needs? Shapouri (again the most optimistic of the papers) shows 73,424 net megajoules' yield per hectare. (Cell B49, Shapouri-adjusted) Currently, global petroleum use alone amounts to 30 billion barrels per year at about 6100 megajoules per barrel. That's 183 trillion megajoules of petroleum per year, of which something something on the order of one-tenth goes into producing more petroleum. So, call it 165 trillion megajoules' per year net petroleum energy. (I'm not even getting into the natural gas and coal here, right? I'm just talking about oil, which provides about 40% of traded energy worldwide.)
That works out to 2.25 billion hectares dedicated to biofuels to match our petroleum consumption. Or, a square of farmland 4700 kilometers on a side.