California's target for greenhouse gas reduction in part relies on the development of viable low-carbon fuel alternatives to gasoline. It is often assumed that cellulosic ethanol--ethanol made from the structural parts of a plant and not from the food parts--will be one of these alternatives. This study examines the physical viability of a switchgrass-based cellulosic ethanol industry in California from the point of view of the physical requirements of land, water, energy and other material use. Starting from a scenario in which existing irrigated pastureland and fiber-crop land is converted to switchgrass production, the analysis determines the total acreage and water supply available and the resulting total biofuel feedstock output under different assumed yields. The number and location of cellulosic ethanol biorefineries that can be supported is also determined, assuming that the distance from field to biorefinery would be minimized. The biorefinery energy input requirement, available energy from the fraction of biomass not converted to ethanol, and energy output is calculated at various levels of ethanol yields, making different assumptions about process efficiencies. The analysis shows that there is insufficient biomass (after cellulose separation and fermentation into ethanol) to provide all the process energy needed to run the biorefinery; hence, the purchase of external energy such as natural gas is required to produce ethanol from switchgrass. The higher the yield of ethanol, the more external energy is needed, so that the net gains due to improved process efficiency may not be positive. On 2.7 million acres of land planted in switchgrass in this scenario, the switchgrass outputproduces enough ethanol to substitute for only 1.2 to 4.0percent of California's gasoline consumption in 2007.
[1]
D. Post,et al.
The long and short of food-chain length
,
2002
.
[2]
Michael P. Popp,et al.
Assessment of Alternative Fuel Production from Switchgrass: An Example from Arkansas
,
2007,
Journal of Agricultural and Applied Economics.
[3]
K. Paustian,et al.
Energy and Environmental Aspects of Using Corn Stover for Fuel Ethanol
,
2003
.
[4]
Michel Loreau,et al.
Food-web constraints on biodiversity–ecosystem functioning relationships
,
2003,
Proceedings of the National Academy of Sciences of the United States of America.
[5]
T. Patzek.
Can We Outlive Our Way of Life
,
2020
.
[6]
B. Drossel,et al.
Modelling Food Webs
,
2002,
nlin/0202034.
[7]
Andrew D. Jones,et al.
Supporting Online Material for: Ethanol Can Contribute To Energy and Environmental Goals
,
2006
.
[8]
M. Wu,et al.
Mobility chains analysis of technologies for passenger cars and light duty vehicles fueled with biofuels : application of the Greet model to project the role of biomass in America's energy future (RBAEF) project.
,
2008
.
[9]
Thomas W. Schoener,et al.
Food Webs From the Small to the Large: The Robert H. MacArthur Award Lecture
,
1989
.
[10]
A. Pessoa,et al.
ACID HYDROLYSIS OF HEMICELLULOSE FROM SUGARCANE BAGASSE
,
1997
.
[11]
D. Stern,et al.
Aggregation and the role of energy in the economy
,
2000
.