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\\\"everything about ethanol is good, good, good,\\\" crows Iowa Senator Chuck Grassley, echoing the conventional wisdom that corn-based ethanol will help us kick the oil habit, line the pockets of farmers, and usher in a new era of guilt-free motoring. But despite the wishes of Iowans (and the candidates courting them) the \\\"dot-corn bubble\\\" is too good to be true.
"Ethanol Production Using Corn, Switchgrass, and Wood;
Biodiesel Production Using Soybean and Sunflower"
by David Pimentel1,3 and Tad W. Patzek2
Several physical and chemical factors limit the production of liquid fuels such as ethanol and biodiesel using plant biomass materials.These include the following:
(1) An extremely low fraction of the sunlight
reaching America is captured by plants. On
average the sunlight captured by plants is
only about 01.%, with corn providing 0.25%.
These low values are in contrast to photovoltaics
that capture from 10% or more sunlight,
or approximately 100-fold more sunlight
than plant biomass.
(2) In ethanol production the carbohydrates
are converted into ethanol by microbes,
that on average bring the concentration of
ethanol to 8% in the broth with 92% water.
Large amounts of fossil energy are required
to remove the 8% ethanol from the 92%
(3) For biodiesel production, there are two problems:
the relatively low yields of oil crops
ranging from 1,500 kg/ha for sunflower to
about 2,700 kg/ha for soybeans; sunflower
averages 25.5% oil, whereas soybeans average
18% oil. In addition, the oil extraction
processes for all oil crops is highly energy
intensive as reported in this manuscript.
Therefore, these crops are poor producers of