Quantifying the Flow of Exergy and Carbon through the Natural and Human Systems
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Quantifying the Flow of Exergy and Carbon through the Natural and Human Systems Richard E. Sassoon1, Weston A. Hermann2, I-Chun Hsiao1, Ljuba Miljkovic1, Aaron J. Simon3 and Sally M. Benson1 1 Global Climate and Energy Project (GCEP), Stanford University, The Jerry Yang & Akiko Yamazaki Environment and Energy Building – 4230, 473 Via Ortega, Suite 324, Stanford, CA 94305 2 Tesla Motors, 1050 Bing Street, San Carlos, CA 94070 3 Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551-0808
ABSTRACT Exergy is the useful portion of energy that allows us to do work and perform energy services. While energy is conserved, exergy is not; some exergy is destroyed whenever energy undergoes a conversion. We gather exergy from distinct, energy-carrying resources that are found in the natural world. These resources are converted into energy carriers that are convenient to use in our factories, vehicles, and buildings for heating, lighting and mechanical services. While there is no shortage of exergy resources, there are considerable environmental, economic, and other constraints associated with the manner and magnitude of their use. This article describes an approach to examining and presenting data on energy use at a global scale. It provides insights into the efficiencies and carbon emissions of many energy pathways, and can provide a basis for an examination of future energy options. In this study, we trace the flow of exergy and carbon through the natural and human systems, revealing the major destructions of exergy, the exergy efficiency of engineered energy processes, and the processes with the highest associated atmospheric carbon emissions. These data have been collected in a relational database available online at http://gcep.stanford.edu/research/exergy/data.html and are presented here in a set of exergy and carbon flow charts.
INTRODUCTION Delivering energy services to a growing population and economy without significantly impacting the environment is a grand challenge of this century. Reducing emissions of carbon dioxide to the atmosphere is a major component of this challenge and it will likely take a wide range of technological advances promoted by forward-looking investments to simultaneously reduce the energy requirement of our energy services and decouple carbon dioxide emissions from the energy we use. Discussions of the benefits or drawbacks of future energy choices often lack the context of the relative magnitudes of the resources and energy conversion involved. In addition, they often focus on the flow of energy, rather than exergy, and therefore lack a consistent basis for comparison of energy resources or conversion processes in terms of their thermodynamic potential. This study traces exergy, the useful portion of energy that can be converted to work, from primary resources in the natural system to energy services. The interface between exergy use and the global carbon cycle is also explored. The maps of inter-connected data developed
here capture the current state of the
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