When it comes to assessing fuel efficiency and environmental impacts, the old days are gone. Once we were satisfied with vehicle MPGs and tailpipe emissions ratings, but no longer.

Today, transportation fuels and vehicle technologies are the subject of life cycle analysis (LCA), which assesses the impact of each stage of their production and use—cradle to grave, or in fuel-expert shorthand, “well to wheels.”

Michael Wang of Argonne National Laboratory is the driving force behind GREET (Greenhouse gases, Regulated Emissions and Energy use in Transportation). An LCA modeling tool with humble beginnings, GREET today is the gold standard for evaluating and comparing advanced fuels, vehicle technologies and their many combinations.

Why did you develop GREET?
A project we were doing in 1994 for the Department of Energy required us to examine energy and emissions implications of different transportation fuels and vehicle technologies. Mark Delucchi, a friend from graduate school, had generated a model that I thought I could use. But it was in Lotus 1-2-3 on the Mac, and I couldn’t open and use it. So I put together an Excel spreadsheet, just to finish the project. Afterward, DOE asked if we could make it available for others. That was the start of GREET.

How does it work for fuels?
The purpose is to put all fuel options on a comparable basis. To do that, you have to consider each stage of the whole life cycle of each option. For example, for petroleum it’s recovery, refining, gas distribution, and so on. For biofuels, we look at fertilizer production, feedstock farming, feedstock transportation, fuel production, fuel distribution, etc. We simulate energy use and emissions at each stage, and then make overall comparisons.

Since the first version in 1996, how has the tool evolved?
Each new version is more complicated, with more fuel and vehicle options and more issues to address. The ongoing effort is to get the best, most up-to-date data and our LCA research results into GREET—this is what life cycle analysis is all about. The area is evolving very fast. We have to be open-minded and keep abreast of new technology developments. On the other hand, we have to evaluate new information carefully, especially when so much is disseminated on the web. You have to do your homework and make judgment calls on what is credible.

People trust the information we use and put into GREET, and we have to be extra careful on our default data and parameters in GREET.

GREET is a free tool, available to anyone—do you monitor its use?
Having GREET in the public domain, on the web and in Excel, has made it transparent, a step-by-step form to follow. If I’ve made any contribution in this field, it has been to popularize LCA and demystify it. GREET has a large user base, and most just download and use it themselves. We do not have full control of how they use it, and Argonne does not endorse user results. When you change the parameters of GREET, the results are yours.

A 2008 study partially using GREET concluded that the impacts of biofuels on global land use would be dire, and advocated halting biofuel development. You challenged that study in a letter to Science magazine. Did the episode affect your thinking about GREET?
Land use change has been a major issue in expanding GREET’s system boundaries for biofuel analysis. It’s complicated. You have economic, social, political, even cultural factors in different countries and regions. To use only economic factors to simulate land use change, to me, is too limited. That’s what was done in the study I challenged. Even in the context of economic modeling of land use change, I challenged in my letter to Science that several key economic factors need to be taken into account and need to be researched. We did not feel comfortable that available models could quantify land use change then. Since then, we, and others, spent a considerable amount of effort to address a few critical economic issues in modeling of land use changes. Though many improvements were made, we are still not 100 percent satisfied with our efforts, and others’ efforts, in this area.  

What do we need to know that life cycle analysis can’t tell us?
Most models, including ours, cannot tell you the economics of technologies, technology readiness, or the social factors that determine consumer acceptance of new technologies. And new infrastructure needs are not now part of LCA comparisons. For example, if we’re going to have battery-powered electric vehicles, we know we’ll need to have a recharge infrastructure, either at home or at fast-charge stations. With LCA models now available, you still only get a piece of the puzzle.

How will GREET develop in the future?
We continue to expand GREET. On the biofuels front, we’re working on algae-based pathways, and to update the land use change module that we recently added to GREET, technology improvement, and other complicated factors for evaluating biofuels. For vehicle technologies, we are going to build into GREET modeling of new regulations that are now on board or proposed, such as the new national fuel economy standards, starting in model year 2015, and the heavy-duty truck fuel economy standard proposed in late October, so that people can compare technologies to meet those standards.

With such scrutiny of biofuels, can any ever measure up?

There is no denying that biofuels are being scrutinized more than any other transportation fuels. This is healthy evaluation as the society pursues fuel options with truly realizable energy and environmental benefits.

I hope we’re going to use the same scrutiny to examine all of the transportation fuels on this level of detail, so we can truly pursue sustainable fuel and technology options. On the other hand, I do worry that if we tend to become perfectionists, we may lose opportunity of adopting certain technologies with immediate, though incremental, benefits. Loss of realizable opportunity is a risk that many have not thought about.


Affiliation: Joined Argonne in 1993, and now senior scientist and manager of the Systems Assessment Section of its Center for Transportation Research.

Education: Holds his Ph.D. in environmental science from the University of California, Davis (1992), and a B.S. in agricultural meteorology from China Agricultural University in Beijing (1982).

Impact: Advises governments and companies in the U.S., China, Europe, South Africa, Southeast Asia, and Japan; 14,000 GREET users worldwide.

Outside the office: Hikes, bikes, jogs. (GREET analysis not available).

Planet-saving advice: “Public transportation is definitely the way to go.”



Bioenergy Connection welcomes comments on content we publish. While we encourage differing points of view,comments should move the conversation forward constructively. We reserve the right to restrict comments that contain inappropriate content, such as offensive language, verbal abuse, etc.

Post a Comment