New study shows biofuel is useful and woody (straw) component is crucial to energy efficiency.

Ethanol Can Contribute to Energy and Environmental Goals

To study the potential effects of increased biofuel use, we evaluated six representative analyses of fuel ethanol. Studies that reported negative net energy incorrectly ignored coproducts and used some obsolete data. All studies indicated that current corn ethanol technologies are much less petroleum-intensive than gasoline but have greenhouse gas emissions similar to those of gasoline. However, many important environmental effects of biofuel production are poorly understood. New metrics that measure specific resource inputs are developed, but further research into environmental metrics is needed. Nonetheless, it is already clear that large-scale use of ethanol for fuel will almost certainly require cellulosic technology.


Survey of Earlier Energy studies on the corn to ethanol fuel process:
Two of the [earlier] studies stand out from the others because they report negative net energy values and imply relatively high GHG emissions and petroleum inputs (11, 12). The close evaluation required to replicate the net energy results showed that these two studies also stand apart from the others by incorrectly assuming that ethanol coproducts (materials inevitably generated when ethanol is made, such as dried distiller grains with solubles, corn gluten feed, and corn oil) should not be credited with any of the input energy and by including some input data that are old and unrepresentative of current processes, or so poorly documented that their quality cannot be evaluated (tables S2 and S3).

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This New Study
We used EBAMM to (i) add coproduct credit where needed, (ii) apply a consistent system boundary by adding missing parameters (e.g., effluent processing energy) and dropping extraneous ones (e.g., laborer food energy), (iii) account for different energy types, and (iv) calculate policy-relevant metrics (19). Figure 1 shows both published and commensurate values as well as equivalent values for the reference, conventional gasoline.
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Our best point estimate for average performance today is that corn ethanol reduces petroleum use by about 95% on an energetic basis and reduces GHG emissions only moderately, by about 13%. Uncertainty analysis suggests these results are robust (10)....Given adequate policy incentives, the performance of corn ethanol in terms of GHG emissions can likely be improved (20). However, current data suggest that only cellulosic ethanol offers large reductions in GHG emissions.
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This analysis illustrates the major contribution of agricultural practices to life-cycle GHG emissions (34% to 44%) and petroleum inputs (45% to 80%) to corn ethanol, suggesting that policies aimed at reducing environmental externalities in the agricultural sector may result in significantly improved environmental performance of this fuel. For example, conservation tillage reduces petroleum consumption and GHG emissions as well as soil erosion and agrichemical runoff (20, 21).

...and Cellulosic [Process variant] , which assumes that production of cellulosic ethanol from switchgrass becomes economic as represented in one of the studies (16).

The Cellulosic case presented here is a preliminary estimate of a rapidly evolving technology and is designed to highlight the dramatic reductions in GHG emissions that could be achieved. In addition, other biofuel technologies and production processes are in active development and, as the data become available, should be the subject of similar energy and environmental impact assessments.

In addition, future analysis of fuel ethanol should more carefully evaluate ethanol production from cellulosic feedstocks, not least because cellulosic ethanol production is undergoing major technological development and because the cultivation of cellulosic feedstocks is not as far advanced as corn agriculture, suggesting more potential for improvement. Such advances may enable biomass energy to contribute a sizeable fraction of the nation's transportation energy, as some studies have suggested (23, 24).

Science 27 January 2006:
Vol. 311. no. 5760, pp. 506 - 508
DOI: 10.1126/science.1121416
Alexander E. Farrell,1* Richard J. Plevin,1 Brian T. Turner,1,2 Andrew D. Jones,1 Michael O'Hare,2 Daniel M. Kammen1,2,3


See also Straw to sugar breakthrough
Overview of biomass to ethanol
May 2006:
GMO Pundit's Post on the Abengoa straw to ethanol plant in Spain has been extensively updated and extended

Update:
The following even more recent report reinforces the conclusions reported at the start.


Ethanol’s Energy Return on Investment: A Survey of the Literature 1990-Present
R O E L H A M M E R S C H L A G
Institute for Lifecycle Environmental Assessment,
P.O. Box 22437, Seattle, Washington 98122
Environ. Sci. Technol. 2006, 40, 1744-1750

Various authors have reported conflicting values for the energy return on investment (rE) of ethanol manufacture.
Energy policy analysts predisposed to or against ethanol frequently cite selections from these studies to support their positions. This literature review takes an objective look at the disagreement by normalizing and comparing the data sets from ten such studies. Six of the reviewed studies treat starch ethanol from corn, and four treat cellulosic ethanol. Each normalized data set is also submitted to a uniform calculation of rE defined as the total product energy divided by nonrenewable energy input to its manufacture.
Defined this way rE > 1 indicates that the ethanol product has nominally captured at least some renewable energy, and rE > 0.76 indicates that it consumes less nonrenewable energy in its manufacture than gasoline.
The reviewed corn ethanol studies imply 0.84 <>