Carbon Accounting and Vehicle Fuels: A Research Update

The Environmental and Energy Study Institute (EESI) held a briefing examining recent research regarding the carbon dioxide (CO2) intensity of transportation fuels, such as crude oil and ethanol. The panel also considered the economic costs and benefits of renewable fuels as a CO2 reduction strategy. There is a growing body of research concerning the carbon intensity of both petroleum-derived and renewable fuels. Carbon intensity refers to the amount of greenhouse gases (including CO2, nitrous oxide, and methane) that are released per unit of fuel. “Wells to wheels” assessments are calculated by adding the emissions at each production step. For biofuels, this includes emissions and/or carbon sequestration as well as impacts to land use associated with growing biofuel feedstocks.

• Dr. Michael Wang, Senior Scientist, Energy Systems, Argonne National Laboratory, said biofuels are one of the main fuel sources that the Department of Energy (DOE) is looking to invest in.
• The Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) Model developed by Argonne National Laboratory allows for the careful comparison of very diverse fuel feedstocks. Several factors are taken into consideration, including direct and indirect land use as well as carbon emissions during each different step of the production, commercialization, and end-use phases.
• Land Use Change (LUC) modeling has improved substantially over the past six years and finds that greenhouse gas emissions from corn ethanol are lower than previously estimated.
• The Life-Cycle Assessment (LCA) of greenhouse gas emissions from gasoline and biofuels shows that the latter have a much smaller carbon footprint. Transitioning to cellulosic biofuels will result in even greater greenhouse gas reductions.
• The quantity of chemicals/fertilizers used in U.S. corn farming has fallen significantly over the past 40 years, making the production of ethanol safer for ecosystems than extracting and using fossil fuels.
• A significant increase in crop yields and in the valuable co-products produced in biorefineries has resulted in a decrease in the area required for biofuel production. Producing biofuels has become a much more efficient process.
• DDGs (dried distillers grains), high protein animal feeds, and corn oil that can be used for biodiesel and other purposes are some of the valuable co-products of ethanol production, allowing much greater efficiency and return optimization.
• Dr. Steffen Mueller, Principal Economist at the University of Illinois at Chicago, Energy Resources Center, said that over the past 13 years, the amount of water necessary to produce one gallon of ethanol in factories has decreased from 5 gallons to 2.7 gallons of water. The amount of energy it takes to create ethanol has also decreased from 1.09 kWh/gallon to 0.75 kWh/gallon, while crop yields have steadily increased.
• The year 2014 is shaping up to be a record one for corn production. Despite persistent droughts, yields of more than 170 bushels per acre are expected. Corn yields have been increasing for the past five years.
• Many new technologies have contributed to these efficiency gains, with even greater gains emerging as new biorefineries use corn kernel fiber (previously a waste byproduct) to produce cellulosic ethanol.
• Being able to use corn stover as animal feed has also helped minimize waste. Higher corn yields have increased the amount of plant residue (known as stover), which is becoming a waste management issue. But by adding 5 percent lime (which aids in animals digestion), stover can be used as animal feed.
• Dean Drake, President, Defour Group said that since 2011, the cost per gallon of ethanol has been less than the cost per gallon of gasoline. This is due in part to the expiration of the tax credit and the lifting of the tariff on imported ethanol in 2011 and 2012: domestic producers rapidly came under a great deal of competitive pressure, and had to innovate and become much more efficient to survive. They are now reaping the benefits of their increased efficiency.
• Improvements made in the production of ethanol have not only seen increased profits, but also reductions in greenhouse gas emissions.
• Ethanol is a high octane fuel, which requires no additional substances to operate with high-efficiency engines. On the other hand, gasoline has a low octane number and requires additives to operate with such engines.
• Drake urged policymakers to be very skeptical of ethanol research studies conducted before the 2012 industry shake-up. Studies conducted prior to 2012 do not reflect the new reality on the ground.
• The gasoline we use today is about 10 percent ethanol. This means that the infrastructure is already in place to make a transition to higher levels of ethanol, and it also shows how essential ethanol has become in making common-day vehicle fuel.
• Using ethanol as a primary fuel source will allow for improvements in engine performance. It will allow for higher compression ratios, increasing engine efficiency and enhancing combustion, allowing the vehicle to do more with the same amount of fuel. Ethanol will also decrease tailpipe emissions by 7-10 percent.
• Ethanol is unique: it can displace current fossil fuels but can also save consumers money.

Currently, the U.S. transportation fuel supply contains approximately 10 percent ethanol, a renewable fuel intended to lower greenhouse gas (GHG) emissions and reduce dependence on petroleum. The primary feedstock for renewable ethanol is cornstarch, but other advanced feedstocks, such as agricultural and municipal solid waste, are now reaching commercial production levels. The Renewable Fuel Standard (RFS) mandates that corn ethanol must achieve greenhouse gas (GHG) reductions of 20 percent relative to petroleum-derived gasoline, while advanced biofuels and cellulosic biofuels must attain 50 to 60 percent GHG reductions, respectively. However, new research suggests that improvements in technology may achieve even higher reductions in GHG for ethanol and advanced biofuels.

Models such as the “Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation Model” (GREET) by Argonne National Laboratory, have demonstrated that the carbon intensity for ethanol has been steadily falling in the past decade. Recent GREET analyses have estimated that corn ethanol has a carbon intensity between 19 and 48 percent lower than conventional gasoline. Research conducted at the University of Illinois at Chicago has also shown that the corn ethanol industry’s energy use has declined 30 percent in a seven-year time period. Between 2008 and 2012, the yield of ethanol per bushel of corn has remained the same, whereas the thermal energy obtained per bushel has increased substantially.

In the ongoing search for a fuel blend that will meet increasing vehicle efficiency standards without significantly affecting consumer prices, ethanol provides many significant advantages in addition to its low carbon intensity. In particular, ethanol is home grown (decreasing our dependence on foreign countries), and its production results in many valuable byproducts, such as dry distiller’s grains (animal feed), corn oil, and fiber. Ethanol is also high in octane, which will become an increasingly important fuel characteristic as car manufacturers deploy increasingly efficient engine technologies. While ethanol has a lower overall energy content than gasoline, the decoupling of gasoline and ethanol prices means that fuels with high ethanol content, such as E85, are now at or close to price parity with gasoline on an energy content basis. This briefing is the first in a series this fall, set to examine renewable fuels.