Net energy debate

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Bioenergy > Issues > Controversies > Net energy debate

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One of the controversies surrounding biofuels is the question of net energy (also referred to as "energy balance"). Net energy compares the energy value of the fuel produced with all of the energy inputs that went in: nitrogen fertilizer (often made from petroleum, the fuel that powered the tractors, trucks and other machines, and the energy source for the plant that produced the fuel. It also takes into account the energy value of the co-products from production. Net energy value is not intrinsic to a certain fuel or feedstock but is heavily influenced by the efficiency of the industry and the technologies used. Net energy is usually calculated by using some form of life-cycle analysis.


US Corn ethanol

The US corn ethanol industry has seen debate over whether the net energy balance is positive.

  • New Perspectives on the Energy Return on (Energy) Investment (EROI) of Corn Ethanol: Part 1 of 2, 26 July 2010 by The Oil Drum: "The following is the first of two posts based on a recent paper published under the same title in the journal Environment, Development, and Sustainability."
    • "Over the past decade there has been considerable debate on corn ethanol, most focused on whether it is a net energy yielder. The argument is generally that if the Energy Return on Investment (EROI) of corn ethanol is positive then it should be pursued. On one side are Pimentel (2003) and Patzek (2004) who claim that corn ethanol has an EROI below one energy unit returned per energy unit invested, and on the other side are a number of studies claiming that the EROI is positive, reported variously as between 1.08 and 1.45....Even with numerous publications on this issue, disagreement remains as to whether corn ethanol is a net energy yielder."
    • "[M]ost analyses to date...use optimal (i.e. Iowa) values for corn yield, fertilizer, and irrigation, despite the fact that each of these have large geographical (as well as other) variation. Because of this they fail to represent the variable nature of corn production across space, and by extension the subsequent variability in the EROI of corn ethanol."
    • "The results from our meta-error analysis indicated that the average EROI for corn ethanol was 1.07 with a standard error of 0.1....EROI values calculated in the spatial analysis ranged from 0.36 in less optimal corn-growing areas, for example southern Texas, to 1.18 in optimal areas, for example Nebraska...If we apply the same confidence calculated in the meta-error analysis to the results of the county EROI analysis, we find that none of the counties had an EROI that was high enough (1.20) to conclude that corn ethanol was produced at an energy profit."[1]




  • A wiki for the biofuels research community, 29 October 2010 by "Researchers at the U.S. Department of Energy's Joint BioEnergy Institute (JBEI) have created a technoeconomic model that should help accelerate the development of a next generation of...biofuels....This on-line, wiki-based model enables researchers to pursue the most promising strategies for cost-efficient biorefinery operations by simulating such critical factors as production costs and energy balances under different processing scenarios."
    • "'The high production cost of biofuels has been the main factor limiting their widespread adoption,' says JBEI's Daniel Klein-Marcuschamer. 'We felt that a model of the biorefinery operation that was open, transparent about the assumptions it uses, and updatable by the community of users could aid in guiding research in the direction where it is most likely to reduce the production cost of biofuels.'"
    • "Klein-Marcuschamer, a post-doctoral researcher in JBEI's Deconstruction Division, was the lead author of a paper describing this research that was published in the journal Biomass and Bioenergy. The paper is titled "Technoeconomic analysis of biofuels: A wiki-based platform for lignocellulosic biorefineries (PDF file).'"
    • "The initial JBEI technoeconomic model is formulated to simulate a lignocellulosic ethanol biorefinery that uses corn stover feedstock. Model input factors include the cost of transporting the stover to a refinery, the use of acid pre-treatments to break down lignin and enzymes to break down cellulose into simples sugars, and the fermentation of these simple sugars into ethanol using yeast. From such inputs, users can calculate the resulting energy and greenhouse gas output."[2]

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