Last week the blogosphere was chattering about the two papers in Nature that addressed the issue of how much of the world’s remaining fossil fuels humanity could burn before we triggered an unacceptable level of climate change. In writing about those articles (It’s Crunch Time), I said:
Casting the situation as a limit on how much of the remaining fossil fuels we can burn in a given time window strikes me as extremely useful. I don’t mean to suggest that legislators and deniers around the world will suddenly slap themselves in the forehead and exclaim, “Oh! Now I get it! Let’s get to work!” But it does seem like a much more approachable way to frame the limits to our behavior than is talking about parts per million of CO2 in the atmosphere. (I’m assuming that the math all works out, and that the authors used reasonable, mainstream estimates for the recoverable reserves of fossil fuels.)
I remember quite clearly thinking how much that news felt like the study I’ve mentioned so many times, Ulf Bossel’s “E21″ paper, Does a Hydrogen Economy Make Sense? [PDF], that does a thorough analysis of the efficiency of a hydrogen fuel cell car vs. an EV.
We now have what feels like another article that seems to ring true in the same unmistakable way, this time concerning biofuels, as described in Green Car Congress: Study Finds Bioelectricity Better Option Than Liquid Biofuels for Transportation Output and GHG Emissions:
A new life cycle assessment comparing the performance of bioelectricity and ethanol from a variety of pathways with respect to transportation kilometers and GHG offsets achieved per unit area of biofuels cropland concludes that bioelectricity used to charge a battery electric vehicle outperforms ethanol for a combustion engine across a range of feedstocks, conversion technologies, and vehicle classes.
The study by University of California, Merced, Assistant Professor Elliott Campbell along with Christopher Field of the Carnegie Institution’s Department of Global Ecology and David Lobell of Stanford University, found that bioelectricity produces an average 81% more transportation kilometers and 108% more emissions offsets per unit area cropland than cellulosic ethanol. A paper on the work appeared in the 8 May issue of the journal Science.
The authors point out their study looked at only two criteria, kilometers travelled and greenhouse gas offsets, but did not examine the performance of electricity and ethanol for other policy-relevant criteria such as water consumption, air pollution or economic costs.
…
The net transportation output per hectare is larger for the bioelectricity case. With BEVs and ICVs of similar size, one can travel farther on biomass grown on a hectare of land when it is converted to electricity than when it is converted to ethanol…For this case, the gross transportation output per hectare is 85% greater for bioelectricity than cellulosic ethanol. This is largely due to fact that the small SUV BEV has an electric motor that is 3.1 times as efficient as the internal combustion engine of the small SUV ICV for highway driving.
-Campbell et al. (2009)
See GCC’s article for more results from the paper, which is not generally available to the public, as well as the university’s press release.
Just to take a blatant guess, I would say that the economic cost (see below) would have to be less for the bioelectricity case; once the crop is harvested (which has to be done no matter its intended use), I can’t imagine that transporting the crop to an electricity plant and burning it would cost more than converting it into ethanol and then transporting the ethanol to a gas station.
Water use might be a more problematic situation; converting the biomass into ethanol takes some water, but so does cooling the thermoelectric generator that burns biomass in the bioelectricity case.
I think we need at least one more study on this.
Related articles:
- Scientific American: What Is The Best Way to Turn Plants into Energy?
- Technology Review: Biofuels vs. Biomass Electricity
Of course, work on biomass to liquid technologies won’t end once word of this study spreads, nor should it, given how early we are in the transition away from petroleum based vehicle fuels. One big breakthrough hit the news feeds just yesterday, Biofuels Digest: Breakthrough at Mascoma holds potential for 60 percent drop in production cost of cellulosic ethanol; ‘golden dream’ of CBP is closer than thought:
In Massachusetts, Mascoma will announce later this morning a breakthrough that is reducing the cost of cellulosic ethanol production by up to 60 percent in lab tests.
The breakthrough relates to consolidated bioprocessing (CBP) – a transformational technology which the DOE/USDA 2006 Roadmap called “the ultimate low-cost configuration for cellulose hydrolysis and fermentation,” and which reduces or eliminates the need for added enzymes to process pretreated lignocellulose into ethanol.
Mascoma is reporting that, in the lab, based on multiple runs with reduced enzyme requirements, it is seeing normalized per gallon operating costs in March at just under 40 percent of the June 2008 baseline.
Assuming this 60% cost reduction is real, it’s a tremendous advance, although it wouldn’t seem to address the basic point of the study quoted above and “field to wheels” efficiency.
