By Susanne Retka Schill
Producing four-star biofuels may give producers a leg up when the United
States develops a carbon cap-and-trade system. Methods to quantify
greenhouse gas emissions and rate biofuels are being proposed and tested
in an attempt to incorporate the multiple facets of cropping systems,
conversion processes and industry and consumer needs.
All biofuels are not created equal. Renewable fuels have different
carbon footprints, depending on the feedstock that's used to produce it,
how that feedstock was grown, how far it was transported and how it was
converted to ethanol. Before ethanol producers can join cap-and-trade
programs or sell offset credits on the Chicago Climate Exchange, the
hurdle to quantify and express greenhouse gas performance must be
cleared. Although there are several systems and models being developed,
EPM talked to researchers involved in two projects that are tackling the
challenge from different angles. One is focused on a biofuels rating
system, the other models a life cycle assessment of biofuels to provide
a glimpse of what the future may hold for biofuels marketing.
Assigning one, two, three or four stars to biofuels based on how the
feedstocks used were raised and the biofuels produced might seem a bit
simplistic, but Alex Farrell, director of the University of California,
Berkeley, Transportation Sustainability Research Center, favors that
system from among the several that have been examined. He co-authored a
study titled "Creating Markets for Green Biofuels: Measuring and
Improving Environmental Performance," which was released in April 2007.
"We've identified what we think are the key factors and ways of
incorporating them into a system," Farrell says. That system would be
useful for consumers, producers or the government if they wanted to
regulate biofuels in some way, he adds.
Farrell suggests that star ratings be assigned using a Green Biofuels
Index that incorporates the global warming intensity (GWI) rating
associated with each batch of biofuel. The combined GWI of the feedstock
biorefining process plus a more simplified feedstock rating would be
computed into an index value. One star would be awarded for each 40
value units. "Feedstocks are very difficult to measure because they vary
from county to county and even from farm to farm," Farrell says. He
suggests there are capabilities already developed that can be adapted to
a biofuels rating system to account for different cropping systems, such
as the three-tier system developed by the USDA's Conservation Security
Program. The tiers represent increasing levels of conservation practices.
Assigning a star and an index value number to biofuels could help
blenders and consumers. "A company might use a value number in blending
biofuels to hit its target," Farrell suggests. "But consumers might not
want to learn what a 60 is, or an 83, so a star rating system is what
the fuel could be marketed under." A company wanting to market a
two-star biofuel could blend higher and lower index numbers to reach its
target star rating.
Such a system could provide market incentives for producing greener
biofuels, or provide a framework for a regulatory system if the
government decided to go that route. At the very least, Farrell says
their study can help improve the discussion around the environmental
qualities of biofuels.
Life Cycle Assessments of Biofuels
Rating biofuels implies that one can quantify life cycle greenhouse gas
(GHG) emissions. While many researchers have studied GHG emissions from
corn production to the ethanol production process in the short term, a
new study incorporates computer modeling to help quantify the greenhouse
gas sinks and sources from several energy cropping systems and project
affects over the long term. Sinks sequester carbon as opposed to
sources, which emit greenhouse gases.
Biofuels advocates believe that renewable fuels have near-zero net
emissions of greenhouse gases because the carbon is recycled, says Paul
Adler, a research agronomist at the USDA Agricultural Research Service
(ARS) in University Park, Pa. "However, growing the crops requires
energy," he says. Adler cites the energy requirements for machinery and
crop inputs, as well as the energy requirements for transporting
feedstocks and the biofuels conversion itself. The picture gets even
more complicated when considering farming practices, which affect the
amount of carbon that the soil can sequester, and that greenhouse gases
far more powerful than carbon dioxide are released during feedstock
production. "We constructed a model which included the many factors
contributing to life cycle greenhouse gas," Adler says. "This allowed us
to compare the different energy crops and determine which ones reduce
[greenhouse gases] the most."
He partnered with Bill Parton, senior research scientist at the Natural
Resource Ecology Laboratory at Colorado State University in Fort
Collins, Colo., and Stephen DelGrosso, a research soil scientist at the
USDA ARS in Fort Collins, to design their unique analysis. Adler's work
in cropping systems and trace greenhouse gas emissions from bioenergy
cropping systems in Pennsylvania, and conducting life cycle assessments,
was combined with the Colorado scientists' work in developing the
ecological model called DAYCENT. DAYCENT is a process-based computer
model, which simulates plant growth and the microbial processes in soil
that lead to nitrous oxide and methane emissions.
They examined several energy crops and crop rotations: hybrid poplars,
switchgrass, reed canary grass, corn-soybean rotations using
conventional tillage, corn-soybean rotations with no-till methods, and
corn-soybean-alfalfa rotations under both tillage systems. The cropping
systems data was added to the current best estimates for the inputs and
yields associated with cellulosic ethanol. When assessing corn, the
model assumed that 50 percent of the corn stover was used to produce
ethanol. Coproducts were assigned credits for energy and emissions
because they displace competing products that require energy to make.
"These numbers will evolve as the technology matures," says Adler. "It
gives us a first look at how these systems will compare."
In the end, the winners in the greenhouse gas reduction comparisons
aren't surprising, but the numerical values are interesting. Switchgrass
and hybrid poplar energy crops transformed into biofuels provide the
most greenhouse gas reductions when compared with gasoline and diesel,
at about a 115 percent reduction, in the long term when soil carbon
levels are at equilibrium and no longer sequestering additional amounts.
Reed canary grass reduced greenhouse gas emissions by 85 percent. The
different rotations and tillage systems for corn and soybean rotations
reduced greenhouse gas emissions around 40 percent. These numbers
compare with current analyses of the corn-to-ethanol production process
showing a 20 percent greenhouse gas reduction, Adler says.
The greatest impact on reducing the amount of greenhouse gases
associated with energy use by switching to biofuels came from
eliminating the life cycle greenhouse gases from fossil fuel use,
followed by the storage of carbon in the soil from perennial crops.
People most often think of carbon when considering greenhouse gases, but
agricultural systems release methane from the soil, which is 23 times
more active than carbon dioxide as a greenhouse gas, and nitrous oxide,
which is 300 times more powerful, Parton explains. Plus, the carbon
sequestration effect of no-till or perennial crops has a relatively
short-term positive effect on greenhouse gas emissions. "It's a positive
for 20 years, then you reach a new equilibrium," Parton says.
These first attempts at biofuels comparisons are interesting, but more
significant is the scientists' work to devise an assessment model that
incorporates so many variables of the entire system. The report
describing their methodology was published in the April 2007 Ecological
Applications, a journal of the Ecological Society of America. Future
work with the model will look at the potential impact of plowing up
Conservation Reserve Program acres and planting the acreage to corn
rotations, the impact of biofuels grown in different ecological regions
and how climate change might impact biofuels.
© 2007 BBI International Media
Check for earlier Pacific Biofuel posts: http://pacbiofuel.blogspot.com/