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Bertram31.com General Bulletin Board
Re: Bio Diesel - Life cycle analysis of Biodiesel *LINK*
Posted By: Rawleigh In Response To: Re: Bio Diesel (Capt. Dave Kosh)
Date: Friday, 19 August 2005, at 4:17 p.m.
Response to David Pimentel Biodiesel Life Cycle Analysis
National Biodiesel Board
July 2005
Understanding the Life Cycle or “Well-to-Wheel” Concept
When evaluating a fuel, many people often focus on the fuel’s energy use or emissions
only when it is burned or utilized in a vehicle engine. Consequently, too little attention
is given to the technology or the infrastructure that helped create the fuel and
delivered it to market. For example, fuels that show very low pollutant emissions from
the vehicle may emit mightily during their production phases. Fuels very suitable for use
in combustion engines may be difficult and costly to transport and store.
The effect of biodiesel on overall consumption of petroleum and other fossil fuels can
only be understood in the context of biodiesel’s “life cycle”—the sequence of steps
involved in making and using the fuel from the extraction of all raw materials from the
environment to the final end-use of the fuel in a diesel vehicle. The chain has five
stages: feedstock production, feedstock transportation, fuel production, fuel distribution
and, finally, vehicle use.
The effect of biodiesel on overall consumption of petroleum and other fossil fuels can
only be understood in the context of this fuel’s energy balance, or “life cycle.”
Life Cycle Studies
The U.S. Department of Energy and the U.S. Department of Agriculture have performed
a life cycle study of the energy balance of biodiesel produced from soybeans in the
U.S. This is the most comprehensive, credible and thoroughly peer reviewed study
available on biodiesel produced from soybeans. Among its key findings:
• For every one unit of fossil energy used in this entire production cycle, 3.2 unit of
energy are gained when the fuel is burned, or a positive energy balance of
320%.
• The energy balance for biodiesel produced from soybeans is so high because
the starting component, soybean oil, is already high in energy content. Oils and
fats are nature’s preferred way to store high density energy.
• This study started with bare soil and took into account all the energy inputs
associated with growing and harvesting soybeans: transporting and processing
the soybeans into oil and meal, transportation and production of the soybean oil
into biodiesel, and transportation of the biodiesel to the end user.
This study can be found at www.nrel.gov/docs/legosti/fy98/24089.pdf.
Additionally, the International Energy Agency recently conducted a review of several
biofuel life cycle studies.1 The results of these studies all indicate that biodiesel has a
very good fuel process energy efficiency rating. While these studies apply to biodiesel
made from rapeseed and may differ slightly from soybean oil based biodiesel, they
establish the fact that biodiesel has a positive energy balance.
Fuel production process efficiency is a measure of how much process fuel is required to
grow crops, transport them to production plants, produce biodiesel and deliver it to
refueling stations. Studies that estimate better process efficiencies are represented by a
lower number in the table below.
Feedstock Fuel Process Energy
Efficiency (energy
in/out)
Net Energy Balance
Conversion
GM et al., 2002 Rapeseed 0.33
3.00 to 1
Levington, 2000 Rapeseed 0.40 2.50 to 1
Levelton, 1999
Altener, 1996 Rapeseed-a 0.55 1.82 to 1
Altener, 1996 Rapeseed-b 0.41 2.44 to 1
ETSU, 1996 Rapeseed 0.82 1.22 to 1
Levy, 1993 Rapeseed-a 0.57 1.75 to 1
Levy, 1993 Rapeseed-b 0.52 1.92 to 1
Note: When a range of estimates is reported by a paper, “a” and “b” are shown in the feedstock column
to reflects this. The inverse of fuel process production efficiency (1/fuel process production efficiency) is an
approximation of the net energy balance.
Response to Pimentel and Patzek Paper
It is the National Biodiesel Board’s position that the David Pimentel study, which claimed
a negative energy balance for biodiesel, contains some serious flaws. This study
cannot be deemed technically credible for the following reasons:
• In general, the authors do not provide enough details in the paper to determine
how they reached their controversial conclusion. Since this result is the
exception to the rule, scientific protocol would dictate that the researchers
provide a detailed description of their assumptions and their data sources.
However, their entire discussion on making biodiesel from soybean oil was limited
to one and a half pages. In contrast, a 1998 study conducted by the U.S.
Department of Agriculture and the Department of Energy called the Life Cycle
Inventory of Biodiesel and Petroleum Diesel for Use in an Urban Bus contained
286 pages of charts, tables, detailed data descriptions, and an in-depth
discussion of the assumptions that were used to determine that the net energy
balance of biodiesel was 3.2 to one.
• The study overestimates the energy used to grow soybeans because it uses data
from 15 years ago. The input data listed in table 6 is based on a 1990 study by
Ali and McBride. This USDA study reports survey data on the energy used to grow
soybeans in 1990. The USDA survey that collects this information is conducted
about every 4 years, and the latest data available is 2002. Why did the authors
1 International Energy Agency, Biofuels for Transport: An International Perspective, 2004.
use data from 15 years ago, when data on the 2002 crop year is readily
available? It is important to use the most current data available, since energy
use on farms decreases overtime as farmers adopt new methods to reduce
energy costs.
• Soybean production practices are inaccurate. For example, the researchers’
assumption regarding the use of lime (calcium carbonate) does not reflect
current farming practices. Lime inputs account for over 36% of the total energy
inputs for soybean production in Pimentel and Patzek study. While the use of
lime on acidic soils may help improve yields, its use is dependent upon the
requirements of the soil and is not a universal input for soybean production.
Moreover, in most parts of the country, the use of lime is limited and, if used, is
not applied on an annual basis. Therefore energy requirements, at a minimum,
must be allocated over multiple years.
• The study includes labor has an energy input. Even though the calories
consumed by farm workers can be converted to energy equivalents, most
researchers do not treat the calories as fossil energy. Labor associated with
soybean production has no significant effect on the total number of calories
consumed in the United States and calories are not considered to be a scarce
resource. Moreover, people must consume food to sustain life, regardless of their
occupation. Labor performed by farm workers requires an insignificant amount
of fossil energy, and has no direct effect on oil imports or energy security.
Including labor as an energy input results in an overestimation of the energy
required to produce soybeans.
• The study overvalues the energy inputs for soybean oil. Biodiesel production
results in three products: the soybean oil used for biodiesel, glycerin, and
soybean meal that is used primarily for animal feed. None of the energy used for
producing the meal should be included in the energy balance calculations for
biodiesel. While soybeans are approximately 80% protein meal and 20% oil, the
study allocates 79% of the energy inputs for growing soybeans to the oil. Other
studies have allocated a much greater amount of energy to the production of
soybean meal, which would lower the amount of energy needed to produce
soybean oil.
• The study does not acknowledge that producing biodiesel also results in the
production of glycerin, a highly valued product used in pharmaceuticals, soaps,
and other products. To be accurate, biodiesel’s energy balance should have
been credited for the glycerin co-product.
• The study overestimates the energy requirements for secondary inputs, such as
steel and cement. It is unusual for a life cycle study to include the energy used
to manufacture construction materials for biodiesel plants and farm equipment.
While most researchers recognize that there is energy embodied in these
materials, the amount is generally viewed as insignificant. Perhaps the reason
this study reports unusually high values for these secondary inputs is that it uses a
1979 study to derive energy estimates for the energy required to manufacture
construction materials and farm equipment. The U.S. manufacturing sector has
increased energy efficiency dramatically over the past 25 years. There is no
comparison between modern production facilities and farm equipment today
and those constructed in 1979.
• Pimentel erroneously reports that the USDA/DOE life cycle study concluded that
the net energy balance of biodiesel was negative. The Pimentel study
misrepresents the 1998 joint study by U.S. researchers from the Department of
Energy and U.S. Department of Agriculture. The study actually concluded that
biodiesel made from soybean oil resulted in an energy savings of more than 3 to
1. This study can be found at www.nrel.gov/docs/legosti/fy98/24089.pdf. It is the
prevailing study cited for biodiesel’s positive energy balance, so it is difficult to
understand how it could be misrepresented in a peer reviewed journal article.
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