At 10:04 AM 03/28/2006, Robert C. McFarlane wrote:
Has anyone seen a clear answer (including input-output
aggregate energy balance) on whether a plug-in hybrid methanol (or ethanol)
powered vehicle fleet would reduce emisisons in the
Fortunately, this is the kind of thing where sheer logic can get you very far. But it depends on some assumptions, which really need to be spelled out.
If the electricity generation does not generate CO2, there would be a substantial reduction in CO2 emissions. More precisely, to a high degree of accuracy, gross CO2 emissions would be multiplied by:
(1) The ratio of CO2 per BTU of methanol or ethanol to the same for gasoline;
(2) The miles per BTU of today’s average car divided by that of a hybrid;
(3) The fraction of miles for which a plug-in driver would use the liquid fuel.
From what I have seen a reasonable guess would be:
1 * (1/2) * (1/2),
i.e. a reduction of gross CO2 by a factor of four.
Factor 1 I would look up in the Handbook of Chemistry and Physics if I were at home, but I would be surprised if it were not within about 10-20% of 1. (I actually did look it up about 20 years ago, when I ran EIA’s first carbon tax scenario, but memories do fade..)
Factor 2 depends on how good the hybrid is. There has been
hype in the press about the validity of the EPA mpg estimates, but I don’t
think it is relevant here, for several reasons. (Above all, it applies equally
to hybrid mpg and to conventional mpg, not changing the ratio much). For a best
state of the art hybrid—today’s
This leaves out two very big factors:
1. What about CO2 from electricity production?
2. What about CO2 ABSORBED from ethanol or methanol production?
Those in turn depend a whole lot on other very important decisions we need to make. We could do better than the gross calculation, or we could do worse, and it really depends on what we do.
If the ethanol or methanol (or DME or P-series) came from biofuels production, and if the biofuels production itself did not use CO2-based energy inputs, then the NET CO2 emission EITHER from conventional fuel-flexible cars or from fuel-flexible hybrids would be ZERO. Not just a four-fold reduction; ZERO.
But... the traditional distillation methods for ethanol today are highly energy-intensive. I don’t know exactly how reliable Pimentel’s estimates are... but if the CO2 per BTU of energy INPUT to ethanol production is as large as that of gasoline, we might as well be using gasoline, so far as CO2 is concerned. We are back to the gross CO2 calculation above. In that case, fuel flexibility buys more national security, but not a CO2 improvement.
On the other hand, if we insist on three-way (“GEM”) fuel flexibility, and cut the energy input requirements for biofuel production in half, we really would be doing twice as well as the gross CO2 calculation suggests. And besides... a factor of four is not so bad.
If we produced the electricity for plug-in hybrids or for biofuel production from traditional coal plants, we could get back to the situation where the only benefit to CO2 comes from the high mpg of hybrids. In fact, the overall CO2 benefit might be even less than that or nothing at all.
To do better, and to keep doing better and to meet our other needs, we really have only two large-scale solutions, in my view. One is a set of solutions involving Stirling technology—especially advanced solar Stirling, as a way to produce electricity at low cost in the daytime, and as a way to provide an energy input to “Cool Water” type Clean Coal plants, to permit zero CO2 emissions and zero long-term CO2 storage. Another is aggressive development of new options that have shown up for space solar power, which some serious aerospace people (in serious companies) believe could be giving us gigawatts in ten years. If truly rational, we would be pushing both as hard as we can (but NOT deviate from technology reality as in some of the historic fantasy technology projects, like perhaps the bulk of the Synfuels Corporation).
We could do it. That could totally zero out the CO2. But we aren’t doing it. For all the talk, we are still basically doing nothing. (Talk is sometimes an important first step but... ). It is certainly another example of how CO2 reduction and national security go hand in hand, extremely closely, once we get down to the reality level. If we ever do.
Best of luck to us all,