Meet the New GREET

Source: By Cindy Zimmerman, AgWired • Posted: Tuesday, October 19, 2021

The U.S. Department of Energy Argonne National Laboratory (ANL) has just released its latest update to the Greenhouse gas and Regulated Emissions and Energy use in Transportation (GREET) model, the standard tool used to audit the energy and environmental effects of transportation fuels such as ethanol and gasoline.

The 2021 GREET model includes a number of significant updates, especially for corn ethanol. Recognizing that the corn ethanol industry has significantly evolved in the past two decades, they conducted a retrospective analysis evaluating the changes from 2005 to 2019.

The results show that corn grain yield has increased while fertilizer inputs per acre have remained constant, which led to a decrease in fertilizer intensities per bushel of corn harvested. In addition, increased corn grain ethanol yield and reductions in energy use have reduced the life-cycle greenhouse gas (GHG) emissions per megajoule (MJ) of corn grain ethanol produced and used. Based on the results of this study, we have updated the time-series values of relevant parameters for the corn ethanol pathway in GREET 2021.

American Coalition for Ethanol (ACE) CEO Brian Jennings thanked Dr. Michael Wang and his team at Argonne for making updates to the GREET model which will help farmers, ethanol producers, and government agencies better understand how farming practices play a pivotal role in reducing the overall carbon intensity of corn ethanol. “Given the growing support for new clean fuel markets at the state and federal level, particularly among Midwestern states, these timely updates to the GREET model should help us advocate for policies that give credit to farmers for practices which further reduce corn ethanol’s carbon footprint.”

The 2020 version of GREET created a new Feedstock Carbon Intensity Calculator (FD-CIC) to help quantify the soil carbon sequestration benefits of corn and other biofuel feedstocks. In response, ACE, along with corn grower groups, provided recommendations to modify the calculator to measure crop-specific impacts on soil carbon and reduce nitrous oxide (N2O) emissions from fertilizer use. The 2021 update included our request to account for the nitrous oxide reducing impacts of 4R (Right rate, Right form, Right place, Right time) nitrogen management methods, and enhanced efficiency nitrogen fertilizer (EEF) use. The information ACE provided to Argonne showed full implementation of 4R management along with EEF could reduce N2O emissions by up to 40 percent relative to GREET estimates.

ACE board member Ron Alverson with Dakota Ethanol says the FD-CIC has been extremely helpful in evaluating the effect farming practices have on ethanol’s GHG emissions because it accounts for corn yield and energy, fertilizer, and chemical use factors for individual farms instead of relying on default values and can be used by biofuel feedstock producers to determine how best to reduce their carbon intensity. “We look forward to continuing to collaborate with Dr. Wang and the Department of Energy scientists to incorporate additional updates to GREET in the future, specifically regarding corn transportation distances, energy use factors for corn ethanol facilities, lime use rates, and crediting the use of biofuels by biofuel feedstock producers,” said Alverson.

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