UT Energy Symposium: I, Widget: Why It’s Nearly Impossible to Trace Physical Flows Through the U.S. Economy, And What That Means for Industrial Energy Modeling
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Engineering Education and Research Center (EER), 3.646, Travis
Heather Liddell Assistant Professor of Mechanical Engineering, and Sustainability Engineering & Environmental Engineering, Harrington Fellow Speaker Biography: Heather Liddell is an Assistant Professor at Purdue University with joint appointments in Mechanical Engineering and Sustainability Engineering & Environmental Engineering. She studies energy and environmental impacts in manufacturing, integrating economy-level and technology-level modeling approaches. Before joining Purdue in 2023, Dr. Liddell was a group leader at the energy consulting firm Energetics, where she worked closely with the U.S. Department of Energy to develop strategies for resource-efficient and decarbonized manufacturing in the United States. She holds BS and MS degrees in mechanical engineering and a PhD in materials science from the University of Rochester and completed postdoctoral training at the U.S. Naval Research Laboratory. As a UT Harrington Fellow for the 2026-2027 academic year, she is collaborating with colleagues at the Energy Institute to develop new energy systems modeling approaches for a rapidly evolving industrial economy. Abstract: In Leonard Read’s famous 1958 essay “I, Pencil,” the eponymous narrator insists, rather gleefully, that no single person on Earth knows how to make a wooden pencil. Manufacturing know-how is scattered across complex global supply chains, with each entity contributing only a tiny piece. The story captures a marvel of economics. But for industrial system modelers, this marvel is simultaneously a conundrum. Individual firms may know what they make and in what quantities—but because U.S. statistical agencies do not comprehensively compile that information, this knowledge is similarly scattered. In this talk, I will show how sparse and decentralized data on physical production can limit our ability to build accurate mass-balanced models of the national production economy. Energy intensity (energy per unit of output) underpins how we track industrial efficiency and evaluate policy, but without physical output data these metrics must be assessed with a monetary-unit denominator. A monetary basis blurs energy efficiency gains with market price volatility and inflation. I will describe our group’s effort to build physically and environmentally extended input-output (IO) models of U.S. goods-producing industries, including approaches we have developed for operating under severe data sparsity and uncertainty. Lastly, I will explore how industrial energy use has shifted over time, and what that means for model obsolescence. About the UT Energy Symposium: The UT Energy Symposium is a weekly guest lecture series that is both free and open to the public and available for course credit. In an effort to provide a multi-disciplinary platform for UT faculty and students to interact on the most pressing energy issues facing our world, the Energy Institute sponsors the UT Energy Symposium (UTES), which will enter its 30th semester in spring 2026. The UTES serves as a “convener” for the campus community, uniting students interested in energy issues with faculty and others working on sustainable energy security. Students who register for the symposium receive one credit hour for the 15-week seminar course, which is open to both undergraduate and graduate students. Ongoing themes for UTES include climate change policy, innovation and diffusion of energy technologies, low-carbon technology options and status, and behavioral aspects of energy consumption. Each UTES talk will be recorded and posted on this page and on the Energy Institute YouTube channel following the event.