While the U.S. federal government has clean energy targets, they are not binding. Most economically developed countries have mandatory policies designed to bolster renewable electricity production. Because the U.S. lacks an enforceable federal mandate for renewable electricity, individual states are left to develop their own regulations. 

Marilyn Brown, Regents’ and Brook Byers Professor of Sustainable Systems in Georgia Tech’s School of Public Policy; Shan Zhou, an assistant professor at Purdue University and Georgia Tech Ph.D. alumna; and Barry Solomon, a professor emeritus of environmental policy at Michigan Technological University, investigated how clean electricity policies affect not only the states that adopt them, but neighboring states as well. Using data-driven comparisons, the researchers found that the impact of these subnational clean energy policies is far greater — and more nuanced — than previously known. 

Their research was recently published in the journal Proceedings of the National Academy of Sciences. 

“Analysts are asking if the U.S. should have a federal renewable mandate to put the whole country on the same page, or if individual state policies are sufficient,” Brown said. “To answer that question, it is useful to know if states with renewable energy policies are influencing those without them.”

Brown, Solomon, and Zhou examined a common clean energy policy tool: the Renewable Portfolio Standard (RPS). Adopted by more than half of U.S. states, RPSs are regulations requiring a state’s utility providers to generate a certain percentage of their electricity from renewable resources, such as wind or solar. Many of these standards are mandatory, with utility companies facing fines if they fail to reach targets within a given time.

To investigate the influence of these policies across state lines, the researchers first created a dataset that included 31 years (1991-2021) of annual renewable electricity generation data for 48 U.S. states and the District of Columbia. They then used the dataset to generate pairs of states linking each state to its geographic neighbors or electricity trading partners, allowing them to examine the influence of the RPS policy adopted by one of the pair on the renewable energy generation of the other — a total of 1,519 paired comparisons. 

“By only looking at the pairs, we can see if an RPS in one state directly affects renewable electricity generation in another state, and, if that’s the case, whether it is because they are geographic neighbors or if it’s because they are participating in the same wholesale electricity market,” Zhou said. 

Looking into the electricity market is important, because states often purchase electricity from other states through wholesale markets rather than exclusively producing their own power, and the purchased power can be generated from renewables. Utilities in some states may be allowed to meet their own RPS requirements by purchasing renewable energy credits based on the renewable electricity generated in other states. 

In their analyses, the team also considered the concept of “policy stringency.” A stringency measure evaluates a state’s renewable electricity targets relative to the amount currently produced in the state. For example, if a state requires electric utilities to generate 30% of their electricity from renewable sources by 2030 and the state already has 25%, it isn’t a very stringent policy. On the other hand, if a state has a 30% target and only uses 10% renewables currently, it has a more ambitious and stringent RPS.

Though policy experts have used the metric in related work for over a decade, the research team improved the design. 

“Our stringency variable includes interim targets as well as the existing share of renewable energy generation,” Solomon said.

The team found that the amount of renewable electricity generation in a state is not only influenced by whether that state has its own RPS, but also by the RPS policies of neighboring states. 

“We also learned that the stronger a neighboring state’s RPS policy is, the more likely a given state is to generate more renewable electricity,” Brown said. “It’s all a very interactive web with many co-benefits.”

The authors were surprised to find that a given state’s electricity trading partners did not hold the most influence over renewable generation, but rather the geographical proximity to RPS states. They suggest that past RPS policy research focusing on within-state impacts likely underestimated an RPS’s full impact. While the researchers have not yet identified all factors that can cause spillover effects, they plan to investigate this further. 

“The spillover effect is very significant and should not be overlooked by future research, especially for states without RPSs,” Zhou said. “For states without policies, their renewable electricity generation is very heavily influenced by their neighbors.”

Citation: Shan Zhou, Barry D. Solomon, and Marilyn A. Brown, “The spillover effect of mandatory renewable portfolio standards.” PNAS (June 2024). 
DOI: https://doi.org/10.1073/pnas.2313193121
 

The federally funded IAC program provides small to mid-sized industrial facilities in the region with free assessments for energy, productivity, and waste, while also supporting workforce development, recruitment, and training.

“This IAC is a great example of the ways in which Georgia Tech is serving all of Georgia and the Southeast,” said Tim Lieuwen, executive director of Georgia Tech’s Strategic Energy Institute (SEI) and Regents’ Professor and holder of the David S. Lewis, Jr. Chair in the Daniel Guggenheim School of Aerospace Engineering.

“We support numerous small and medium-sized enterprises in rural, suburban, and urban areas, bringing the technical expertise of Georgia Tech to bear in solving real-world problems faced by our small businesses.”

Georgia Tech’s IAC, which serves Georgia, South Carolina, and North Florida, is administered jointly by the George W. Woodruff School of Mechanical Engineering and the Georgia Manufacturing Extension Partnership (GaMEP), part of the Enterprise Innovation Institute (EI2). The organization has performed thousands of assessments since its inception in the 1980s – usually at rate of 15 to 20 per year – and typically identifies upwards of 10% in energy savings for clients.

The assessment team, overseen by IAC associate director Kelly Grissom, comprises faculty and student engineers from Georgia Tech and the Florida A&M University/Florida State University College of Engineering.

In addition, Georgia Tech leads the Southeastern IACs Center of Excellence, which partners the institution with fellow University System of Georgia (USG) entity Kennesaw State University, local HBCU Clark Atlanta University, and neighboring state capital HBCU Florida A&M University.

Although mechanical engineering has historically been the chief area of concentration for IAC’s interns, the program currently accepts students across a range of disciplines. “Increased diversity from that standpoint enriches the potential of the recommendations we can make,” said Grissom.

Students are integral to the program, as is Grissom’s role in facilitating their experiences with client engagement and technical recommendations.

“Kelly is the reason our program has been recognized,” said Randy Green, energy and sustainability services group manager at GaMEP. “He works tirelessly to ensure that assessments are accomplished with success for our manufacturers and students.”

“We also recognize our partnership with the Woodruff School of Mechanical Engineering and with IAC program lead Comas Haynes, Ph.D., who works diligently to keep us on track and connected with our sponsors at the U.S. Department of Energy,” Green added.

The DoE accolade represents “a ‘one Georgia Tech’ win,” symbolic of the synergistic relationships forged across the Institute, said Haynes, who also serves as the Hydrogen Initiative Lead at Georgia Tech’s Strategic Energy Institute (SEI) and Energy branch head in the Intelligent Sustainable Technologies Division at the Georgia Tech Research Institute. Haynes specifically cited Green’s “technical prowess and managerial oversight” as another key to the IAC program’s success.

Said Devesh Ranjan, Eugene C. Gwaltney, Jr. School Chair and professor in the George W. Woodruff School of Mechanical Engineering, “It is truly an honor for Georgia Tech to be named the Department of Energy Industrial (Training and) Assessment Center of the Year. Clean energy and manufacturing have been a focus for the Institute and the Woodruff School for a long time, and GTRI, EI2, and SEI have collaboratively done phenomenal work in helping manufacturers save energy, improve productivity, and reduce waste.”

To check eligibility and apply for assistance from Georgia Tech’s IAC, click here.

Christine Conwell has been named interim executive director of the Strategic Energy Institute (SEI), effective Sept. 10. 

A principal research scientist, Conwell has served as SEI’s director of planning and operations since 2020. In this role, she oversaw strategic and annual planning within SEI and partnered with campus researchers and units to create and execute strategic programs and events. Most recently, she led the development of a new five-year action plan and launched a signature initiative to build energy-focused research partnerships with historically Black colleges and universities and minority-serving institutions.  

Before her role at SEI, Conwell was managing director of the $40 million NSF-NASA Center for Chemical Evolution (CCE) in the School of Chemistry and Biochemistry, where she oversaw daily operations, fostered collaborations between 12 universities and other partners, and developed outreach and educational programs. Annually, she worked with more than 80 faculty, postdoctoral researchers, and students and advised on key opportunities to maximize the center's impact. She served as a key leader within CCE’s management team and, in 2020, she was awarded Georgia Tech’s prestigious Outstanding Achievement in the Research Enterprise Award for her leadership.

“Christine has been instrumental in the growth and expansion of the Strategic Energy Institute,” said Julia Kubanek, vice president of Interdisciplinary Research at Georgia Tech. “The strong research ties she has built as a long-standing member of the Georgia Tech research community, along with her outstanding leadership during the past few years, makes her the natural choice for SEI’s interim executive director.”

Conwell holds a B.S. in molecular biology and chemistry from Westminster College in Pennsylvania and a Ph.D. in biochemistry from Georgia Tech. She has authored several peer-reviewed manuscripts, book chapters, and grants on her research in DNA biophysics and non-viral gene delivery, and was a postdoctoral recipient of the NIH Ruth Kirschstein National Research Service Award. During her time at Georgia Tech, Conwell has served as a member of the Research Faculty Senate and the Faculty Executive Board, and she was selected as a member of the fifth Leading Women at Georgia Tech cohort.

“I am honored to serve as the interim executive director of the Strategic Energy Institute during this pivotal moment for energy research,” she said. “As we navigate an exciting period of innovation at the local, regional, and national levels, I am eager to build on our current momentum and deepen collaborations with our exceptional researchers, faculty, and staff to further advance our energy community and drive progress in the field.”

- Written by Benjamin Wright -

Yuanzhi Tang knows firsthand how much of an impact BBISS can make through its programs. The associate professor in the School of Earth and Atmospheric Sciences answered a BBISS call for faculty fellowships, and later seed funding for a project related to sustainable resources. That project grew into a collaboration with Georgia Tech’s Strategic Energy Institute; the Center for Critical Mineral Solutions (CCMS), supported by the College of Sciences and co-sponsored by BBISS; SEI; the Institute for Electronics and Nanotechnology (IEN); and the Institute for Materials (IMat and IEN are now combined into the Institute for Matter and Systems). The goal of the center is to develop sustainable solutions for the grand challenges associated with critical metals and materials essential for the clean energy transition.

During her time as a faculty fellow within BBISS, Yuanzhi became familiar with the people in the organization and had the opportunity to evaluate student and faculty fellow applications. When the opportunity arose to take on the role of associate co-director of interdisciplinary research for BBISS, she was happy to accept so she could help others access resources that had shaped her growth as a researcher at Georgia Tech.

“Being part of a community of people who value interdisciplinary research on sustainability-related topics, I benefited from the interactions and engagement with BBISS and I hope to carry that forward, particularly for young faculty. They are often eager to connect but might not know where to begin. BBISS can be a starting point for them.”

With a background in geochemistry and degrees from Peking University, Stony Brook University, and a postdoc at Harvard, Yuanzhi has gained a breadth of experience that has earned her a variety of awards and recognition. As she joins BBISS in a formal role, she has some advice for early-career colleagues.

“Go to seminars, events, and organized activities, as the best ideas often come through communicating and networking with others, and that’s how you discover that your expertise is needed in other fields. Be confident in who you are as a scholar, but also go out and find ways to collaborate. Georgia Tech places value on interdisciplinary research, and this is a unique strength that you should leverage.”

Away from the office, classroom, and lab, Yuanzhi is a wife and mother of two young children. She enjoys cuddle time with the kids and navigating parenthood in an academically driven household. Her husband is also a Georgia Tech professor and together they juggle the challenges of their careers with spending quality time with the children. “We try to keep work minimal on weekends and get out of the house and enjoy what Atlanta has to offer. We love nature and appreciate that we can be close to campus, close to the city, and still have so many green places to be outside.”

As she embarks on her new role with BBISS, Yuanzhi sees parallels between being a parent, professor, and now an administrator.

“The world is changing rapidly with the explosion of information and technology. It’s a struggle to know what to teach my kids and my students. How do we prepare them for five, 10, or even 20 years from now? This feeling of responsibility connects my work and personal life. It’s challenging, but also very exciting to see how we can help them embrace changes.”

Timothy Lieuwen has been appointed interim executive vice president for Research (EVPR) by Georgia Tech President Ángel Cabrera, effective September 10. 

Lieuwen is a Regents’ Professor, the David S. Lewis, Jr. Chair in the Daniel Guggenheim School of Aerospace Engineering, and executive director of the Strategic Energy Institute. His research interests range from clean energy and propulsion systems to energy policy, national security, and regional economic development. He works closely with industry and government to address fundamental problems and identify solutions in the development of clean energy systems and alternative fuels. 

A proud Georgia Tech alumnus, Lieuwen (M.S. ME 1997, Ph.D. ME 1999) has had a remarkable academic career. He is a member of the National Academy of Engineering and is a fellow of the American Society of Mechanical Engineers, the American Institute of Aeronautics and Astronautics, the American Physical Society, the Combustion Institute, and the Indian National Academy of Engineering (foreign fellow). He has received numerous awards, including the ASME George Westinghouse Gold Medal and the AIAA Pendray Award. He serves on governing or advisory boards of three Department of Energy national labs: Oak Ridge National Laboratory, Pacific Northwest National Laboratory, and the National Renewable Energy Laboratory and was appointed by the U.S. Secretary of Energy to the National Petroleum Council. 

Lieuwen has authored or edited four books on combustion and over 400 scientific publications. He also holds nine patents, several of which are licensed to industry, and is founder of an energy analytics company, Turbine Logic, where he acts as chief technology officer.

In Lieuwen’s appointment announcement, President Cabrera said, “Tim’s extensive experience and knowledge of Georgia Tech makes him uniquely suited to lead our research enterprise as we search for a permanent EVPR. I am grateful for his willingness to serve the Institute during this period of remarkable growth, and I look forward to working with him and the rest of the team.”

From keeping warm in the winter to doing laundry, heat is crucial to daily life. But as the world grapples with climate change, buildings’ increasing energy consumption is a critical problem. Currently, heat is produced by burning fossil fuels like coal, oil, and gas, but that will need to change as the world shifts to clean energy. 

Georgia Tech researchers in the George W. Woodruff School of Mechanical Engineering (ME) are developing more efficient heating systems that don’t rely on fossil fuels. They demonstrated that combining two commonly found salts could help store clean energy as heat; this can be used for heating buildings or integrated with a heat pump for cooling buildings.

The researchers presented their research in “Thermochemical Energy Storage Using Salt Mixtures With Improved Hydration Kinetics and Cycling Stability,” in the Journal of Energy Storage.

Reaction Redux 

The fundamental mechanics of heat storage are simple and can be achieved through many methods. A basic reversible chemical reaction is the foundation for their approach: A forward reaction absorbs heat and then stores it, while a reverse reaction releases the heat, enabling a building to use it.

ME Assistant Professor Akanksha Menon has been interested in thermal energy storage since she began working on her Ph.D.  When she arrived at Georgia Tech and started the Water-Energy Research Lab (WERL), she became involved in not only developing storage technology and materials but also figuring out how to integrate them within a building. She thought understanding the fundamental material challenges could translate into creating better storage.

“I realized there are so many things that we don't understand, at a scientific level, about how these thermo-chemical materials work between the forward and reverse reactions,” she said.

The Superior Salt

The reactions Menon works with use salt. Each salt molecule can hold a certain number of water molecules within its structure. To instigate the chemical reaction, the researchers dehydrate the salt with heat, so it expels water vapor as a gas. To reverse the reaction, they hydrate the salt with water, forcing the salt structure’s expansion to accommodate those water molecules. 

It sounds like a simple process, but as this expansion/contraction process happens, the salt gets more stressed and will eventually mechanically fail, the same way lithium-ion batteries only have so many charge-discharge cycles. 

“You can start with something that's a nice spherical particle, but after it goes through a few of these dehydration-hydration cycles, it just breaks apart into tiny particles and completely pulverizes or it overhydrates and agglomerates into a block,” Menon explained. 

These changes aren’t necessarily catastrophic, but they do make the salt ineffective for long-term heat storage as the storage capacity decreases over time. 

Menon and her student, Erik Barbosa, a Ph.D. student in ME, began combining salts that react with water in different ways. After testing six salts over two years, they found two that complemented each other well. Magnesium chloride often fails because it absorbs too much water, whereas strontium chloride is very slow to hydrate. Together, their respective limitations can mutually benefit each other and lead to improved heat storage.

“We didn't plan to mix salts; it was just one of the experiments we tried,” Menon said. “Then we saw this interactive behavior and spent a whole year trying to understand why this was happening and if it was something we could generalize to use for thermal energy storage.”

The Energy Storage of the Future

Menon is just beginning with this research, which was supported by a National Science Foundation (NSF) CAREER Award. Her next step is developing the structures capable of containing these salts for heat storage, which is the focus of an Energy Earthshots project funded by the U.S. Department of Energy’s (DOE) Office of Basic Energy Sciences.

A system-level demonstration is also planned, where one solution is filling a drum with salts in a packed bed reactor. Then hot air would flow across the salts, dehydrating them and effectively charging the drum like a battery. To release that stored energy, humid air would be blown over the salts to rehydrate the crystals. The subsequently released heat can be used in a building instead of fossil fuels. While initiating the reaction needs electricity, this could come from off-peak (excess renewable electricity) and the stored thermal energy could be deployed at peak times. This is the focus of another ongoing project in the lab that is funded by the DOE’s  Building Technologies Office.

Ultimately, this technology could lead to climate-friendly energy solutions. Plus, unlike many alternatives like lithium batteries, salt is a widely available and cost-effective material, meaning its implementation could be swift. Salt-based thermal energy storage can help reduce carbon emissions, a vital strategy in the fight against climate change.

“Our research spans the range from fundamental science to applied engineering thanks to funding from the NSF and DOE,” Menon said. “This positions Georgia Tech to make a significant impact toward decarbonizing heat and enabling a renewable future.”

This partnership in the advancement of AI and mathematical optimization to address pressing energy transformations in Latin America and the U.S. has formed between the NSF Artificial Intelligence (AI) Research Institute for Advances in Optimization (AI4OPT) at Georgia Tech and PSR, Inc. - Energy Consulting and Analytics. 

PSR is a global leader in analytical solutions for the energy sector, providing innovative technical consultancy services and state-of-the-art power systems planning software. Their tools are used for detailed modeling of entire countries or regions and are utilized in over 70 countries. Together with AI4OPT, they aim to leverage advancements in AI and mathematical optimization to address pressing energy transformations in Latin America and the U.S.

Latin America boasts abundant renewable energy resources, especially hydropower, leading to one of the largest shares of renewables in its energy mix. However, expanding renewable energy capacity in Latin America and the U.S. to meet decarbonization goals will require system operational advances and new technologies that can adapt to current needs.

One focus of this collaboration will be studying how to efficiently incorporate pumped storage into the resource mix as a solution for long-duration storage. These plants act as large batteries, pumping water to higher reservoirs during low demand periods and generating electricity during high demand with minimal energy loss over time. This technology supports both short-term and long-term energy storage, making it crucial for managing the variability of intermittent renewables like solar and wind.

The complex and large-scale nature of the expansion problem, exacerbated by inherent uncertainty and time-coupled decisions, traditionally requires sophisticated optimization techniques. AI innovations now provide faster solutions and better representations of non-linear dynamics, leading to more cost-effective operations and optimized energy mix selection for the energy transition.

This collaboration plans to use machine learning to enhance power system operators' ability to perform faster security checks and screenings. As renewable energy sources introduce more variability, traditional methods struggle with the increasing number of scenarios needed for grid stability. Machine learning offers a solution by expediting these analyses, supporting the integration of more renewable energy into the system.

About PSR

PSR is a global provider of analytical solutions for the energy sector, spanning from insightful and innovative technical consultancy services to state-of-the-art specialized power systems planning software applied to the detailed modelling of entire countries or regions. Having its products applied in over 70 countries, PSR contributes to the research and development of optimization and data analytics’ tools for guaranteeing a reliable and least-cost operation of power systems, helping the countries achieve their decarbonization targets.

About AI4OPT

The Artificial Intelligence (AI) Research Institute for Advances in Optimization, or AI4OPT, aims to deliver a paradigm shift in automated decision-making at massive scales by fusing AI and Mathematical Optimization (MO) to achieve breakthroughs that neither field can achieve independently. The Institute is driven by societal challenges in energy, logistics and supply chains, resilience and sustainability, and circuit design and control. To address the widening gap in job opportunities, the Institute delivers an innovative longitudinal education and workforce development program.