One of the greatest challenges facing today’s policymakers is to find ways to meet the growing global demand for energy and to do so in more sustainable ways. To make informed decisions, they rely upon the expertise of scientists and engineers who advise them on energy issues. Prominent among these international experts is the Energy Systems Analysis Group (ESAG), a research center within the Princeton Environmental Institute (PEI) at Princeton University.
ESAG uses science- and engineering-based systems analysis to help clarify the environmental and economic implications of various alternative energy options and to identify energy technologies and strategies that could put the global energy system on a more sustainable path. The knowledge they generate raises the level of the energy policy debates and is helpful to policymakers in making energy choices.
Led by senior research physicist Robert Williams, the group includes engineer Eric Larson and chemist Tom Kreutz. ESAG communicates directly with high-level government policymakers and private-sector leaders, informing energy policy in the U.S. (on both federal and state levels), China, India, Brazil, several European countries, and also influences decision-making at multilateral organizations such as the World Bank and the United Nations.
Members of ESAG publish their findings in academic journals, reports and book chapters, and present their work at conferences. They also advise Princeton undergraduates, Ph.D. students and post-doctoral fellows on their research projects, and teach courses in the School of Engineering and Applied Science, PEI and the Woodrow Wilson School of Public and International Affairs. ESAG’s research interests are broad and varied, and have followed the international energy sector’s growth and development over the last forty years. “ESAG has investigated energy use in homes, in commercial buildings, and in industrial processes,” said Larson. “On the supply side,” Kreutz added, “we’ve studied fuel cells, solar and hydrogen production and use, wind energy systems coupled to compressed air energy storage, biomass (plant matter) energy, coal and natural gas electricity generation, the production of synthetic transportation fuels, carbon (CO2) capture and storage (CCS), and other topics.”
The history of ESAG began in 1971, when Robert Socolow, professor of mechanical and aerospace engineering, joined the Princeton faculty with a mandate to “invent” interdisciplinary environmental research at Princeton. That year, Socolow helped the University establish the Center for Environmental Studies [later known as the Center for Energy and Environmental Studies (CEES)].
“In the early 1970s, similar to today, it was nearly universally acknowledged that the problems of energy and the environment challenged the most fundamental assumptions about humanity’s roles on this planet. Princeton and a few other universities understood the need to transcend the traditional disciplines – such as bringing together physics, biology, ethics, and economics. Our Center recruited a remarkable set of scholars who have worked alongside one another doing interdisciplinary research for over four decades,” said Socolow.
According to Socolow, the Center's energy systems analysis work took off when Bob Williams arrived in 1975. Larson joined in 1983 and Kreutz in 1996. Williams, Larson and Kreutz moved from CEES in the Engineering School to PEI in Guyot Hall in 2001, where the team has become known as the Energy Systems Analysis Group.
During the 1990s, Williams and Larson participated in a comprehensive review of renewable energy options that was commissioned as a contribution to the 1992 United Nations Conference on Environment and Development, held in Rio de Janeiro. Williams was a co-editor of the resulting book, "Renewable Energy: Sources for Fuels and Electricity," which has provided much of the analytical basis for the now widely held view that renewable energy can come to play a major role in the world’s energy economy.
Since the completion of that study, much of the ESAG research relating to renewables has been an exploration of opportunities to exploit synergisms that arise from hybrids of fossil energy and renewable energy systems—a promising but, thus far, largely overlooked endeavor.
One such hybrid involves coupling wind power systems to natural gas-fired compressed air energy storage systems (CAES) and long-distance high voltage transmission lines. “Although there is more than enough high-quality wind to satisfy total electricity demand, wind power is only intermittently available, and most good wind resources are remote from areas where electricity is needed,” says Williams.
The wind/CAES/high voltage transmission concept makes it feasible to address these challenges simultaneously. ESAG’s research indicates that low greenhouse gas (GHG)-emitting electricity provided by such a system is likely to be competitive under a carbon mitigation policy with coal power systems using carbon capture and storage (CCS) technology.
During the last several years, ESAG has explored fossil/renewable energy synergisms that focused mainly on exploiting simultaneously opportunities for biomass energy (energy derived from plant matter) and CCS.
The conversion of biomass (plant matter) into electricity and synthetic fuels has been a continuing focus of ESAG research. “In the 1990s, this research was motivated by the prospect that biomass energy can be nearly “carbon neutral,” because every ton of CO2 emitted as a result of conversion or combustion is compensated by the extraction of a ton of CO2 from the atmosphere during photosynthesis if the biomass is provided on a renewable basis,” said Williams. Among other impacts, ESAG’s work in this period (much of it Larson’s) influenced the establishment of national policies in Brazil that now encourage electricity exports from sugarcane biomass.
CCS is a carbon mitigation option that would enable continuing roles for fossil fuels (which account for about 80% of total global energy consumption) with greatly reduced emissions of CO2 to the atmosphere. Much of the CCS effort has been aimed at identifying fundamental transformations relating to coal, the least costly and most abundant fossil fuel, to make its production and use minimally disruptive of the global climate and the environment more generally.
However, ESAG is investigating CCS not only for fossil fuels but for biomass as well, both in systems supplied only with biomass and in systems that coprocess biomass with a fossil fuel.
Tom Kreutz has recently developed a powerful software tool (Energy Systems Evaluation Software) that greatly facilitates ESAG’s ability to analyze such complex systems and compare them to more conventional energy systems. Kreutz explained, “This tool allows us to explore systematically how the economics of an energy system are impacted by variables such as the size of a production plant, cost of the inputs, the price of oil, the pricing of CO2 emissions, and other considerations, and to make comparisons of different energy conversion systems with respect to a wide range of performance criteria.”
One of ESAG’s major ongoing activities involves investigating systems that coprocess biomass with natural gas or coal to make synthetic liquid transportation fuels (known as “synfuels”) and also to coproduce fuels and electricity in the same facility via systems with CCS. A goal of this research is to find ways to decarbonize transportation fuels as well as electricity at attractive costs. According to Williams, the current bullishness about shale gas resources suggests the importance of understanding the prospects for making synthetic liquid transportation fuels from natural gas.
ESAG’s interest in coal and coproduction stems largely from the many trips Williams and Larson began making to China in the early 1990s in conjunction with activities of the China Council for International Cooperation on Environment and Development (CCICED). During these visits it became clear to Williams and Larson that carbon-friendly ways of using coal in a carbon constrained world are needed, as it is unlikely that the rest of the world will be able to wean China from coal. These trips also catalyzed a collaboration between ESAG and a Tsinghua University group led by Prof. Li Zheng that continues to this day. The coproduction focus is based on intense Chinese interest in the “polygeneration” concept that involves coproducing electricity, synthetic fuels and chemicals in the same facility.
Based on its extensive earlier biomass energy research, ESAG has added biomass coprocessing to the polygeneration concept, emphasizing the benefits of “negative” CO2 emissions of biomass energy with CCS that can offset the detrimental “positive” CO2 emissions of fossil fuel burning. Williams points out that a significant preliminary finding of this research is the suggestion that, “In principle at least, addressing the climate and energy security challenges for transportation and electricity simultaneously might be easier than addressing these challenges separately.”
ESAG's findings for synfuels made from coal, from biomass, and from coal plus biomass, with and without CCS, were showcased in a major 2009 study by the US National Research Council (NRC), "America’s Energy Future: Technology and Transformation." Socolow was a member of the NRC committee charged by Congress with conducting the study, and ESAG contributed analysis that helped make sense of major transportation fuel options with the aim of both helping mitigate global warming and reducing oil-import dependence.
Currently, ESAG members are participating in a major international study, "The Global Energy Assessment," which addresses current and future energy challenges and describes technological options and pathways. The results are compiled in a 25-chapter book, involving several hundred authors and reviewers from around the world. It will be published by Cambridge University Press in 2012. Larson, Prof. Li Zheng, and Williams are the lead authors of the fossil energy systems chapter. Additionally, Larson is a lead author for a chapter on renewable energy systems.
Even though Congress has yet to enact comprehensive carbon mitigation legislation, and the near-term prospects of getting such legislation passed seem unlikely, Williams believes there are ways to advance the energy conversion concepts ESAG has been developing in the absence of such a policy framework.
“In 2011, the United States Supreme Court ruled that the Environmental Protection Agency (EPA) has the authority to regulate carbon emissions and I believe such regulations might offer a way forward. Coproduction technologies coprocessing less than 10% biomass for which captured CO2 is used for enhanced oil recovery (EOR) would be in compliance with the recent (March 2012) EPA-proposed carbon emissions rules for new power plants. If these rules are codified, first-generation coproduction technologies could be launched in the market in this decade, because these technologies would be very competitive in CO2 EOR markets,” said Williams.
In the CO2 EOR process, CO2 is injected into suitable mature oil fields to enable more oil production (typically CO2 dissolves in the oil, reducing its viscosity and enabling more oil to flow to the well bore for recovery). EOR currently provides approximately 6% of U.S. crude oil production annually by injecting into mature oil fields about 50 million tons of CO2 delivered to oil fields through 3600 miles of CO2 pipelines. Most projects use naturally occurring geologic CO2, for which supplies are limited. “If supplies could be supplemented by CO2 captured at energy conversion plants, U.S. oil recovery via CO2 EOR could be increased perhaps 10-fold over the next 10 to 15 years. CO2 EOR makes it possible to displace oil that would otherwise be imported, while enabling carbon mitigation at plants providing the CO2,” said Williams.
In March 2012, Steven Chu, the United States Secretary of Energy, asked the National Coal Council (NCC) to prepare a report on CCS for coal energy conversion systems (including synfuel systems) for which captured CO2 is used for EOR. For this study, Williams has the lead responsibility for the synfuels analysis. “One of my goals for the study is a recommendation to the Energy Secretary that ways be found to enable building now a first-of-a-kind commercial-scale coproduction plant coupled to CO2 EOR,” says Williams.
Commenting upon ESAG’s evolution and many contributions, Socolow said, “The ESAG experience at Princeton has shown that energy systems analysis can be a powerful tool for guiding policymakers in shaping new policies to deal with the interrelated challenges facing our current unsustainable energy system, for guiding private sector investments in the face of emerging new energy policies, and for prioritizing fundamental energy research. It has also informed our teaching curriculum.”
ESAG is currently supported by the BP-sponsored Carbon Mitigation Initiative, the Edgerton Foundation, the National Energy Technology Laboratory (NETL) and the Siebel Energy Challenge.