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United States Department of Agriculture

Agricultural Research Service

Research Project: INTEGRATED AGRICULTURAL SYSTEMS FOR THE NORTHERN GREAT PLAINS Title: Sustainability of Switchgrass for Cellulosic Ethanol: Evaluating Net Energy, Greenhouse Gas Emissions, and Feedstocks Costs

Authors
item Schmer, Marty
item Vogel, Kenneth
item Mitchell, Robert
item Liebig, Mark
item Perrin, Richard -

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: July 1, 2009
Publication Date: July 15, 2009
Citation: Schmer, M.R., Vogel, K.P., Mitchell, R., Liebig, M.A., Perrin, R.K. Sustainability of Switchgrass for Cellulosic Ethanol: Evaluating Net Energy, Greenhouse Gas Emissions, and Feedstocks Costs. Symposium Proceedings.

Interpretive Summary: Perennial herbaceous plants such as switchgrass are being evaluated as cellulosic bioenergy crops. In this study, switchgrass was managed as a biomass energy crop in field trials on marginal cropland on ten farms across a wide precipitation and temperature gradient in the mid-continental USA to determine net energy and economic costs based on known farm inputs and harvested yields. Agricultural energy input costs, biomass yield, and estimated ethanol output, greenhouse gas emissions and net energy results are summarized in this presentation using life-cycle assessment (LCA). Switchgrass produced significantly more renewable energy than nonrenewable energy consumed. Estimated average greenhouse gas emissions from cellulosic ethanol derived from switchgrass were 94% lower than the estimated average production, refinement, and combustion of conventional gasoline. Commonly used modeled carbon sequestration rates by LCA can underestimate actual carbon storage by switchgrass. The overall sustainability of switchgrass grown for bioenergy and related GHG emissions are highly dependent on LCA assumptions and the expected conversion efficiency within a cellulosic ethanol plant. This study confirms that switchgrass can be grown in a sustainable manner for biofuel production to meet future U.S. energy demands.

Technical Abstract: Perennial herbaceous plants such as switchgrass are being evaluated as cellulosic bioenergy crops. Sustainability concerns with switchgrass (Panicum virgatum L.) and similar energy crops have been about net energy efficiency, potential greenhouse gas (GHG) emissions, and economic feasibility grown at the field-scale. All previous energy analysis reports are based on data from research plots and estimated inputs. In this study, switchgrass was managed as a biomass energy crop in field trials on marginal cropland on ten farms across a wide precipitation and temperature gradient in the mid-continental USA to determine net energy and economic costs based on known farm inputs and harvested yields. Agricultural energy input costs, biomass yield, and estimated ethanol output, greenhouse gas emissions and net energy results are summarized in this presentation using life-cycle assessment (LCA). Annualized costs across all farms were $59.10 Mg-1 for a 10 year rotation. Switchgrass produced significantly more renewable energy than nonrenewable energy consumed. Cellulosic ethanol from fully established switchgrass fields was estimated to displace 1240 L of gasoline ha-1. Estimated average greenhouse gas emissions from cellulosic ethanol derived from switchgrass were 94% lower than the estimated average production, refinement, and combustion of conventional gasoline. Commonly used modeled carbon sequestration rates by LCA can underestimate actual carbon storage by switchgrass. The overall sustainability of switchgrass grown for bioenergy and related GHG emissions are highly dependent on LCA assumptions and the expected conversion efficiency within a cellulosic ethanol plant. This is a baseline study that represents the genetic material and agronomic technology available for switchgrass production in 2000 and 2001 when the fields were planted. This study confirms that switchgrass can be grown in a sustainable manner for biofuel production to meet future U.S. energy demands.

Last Modified: 10/21/2014
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