Current and theoretical maximum well-to-wheels exergy efficiency of options to power vehicles with natural gas Michael G. Waller, Eric D. Williams ⇑ , Schuyler W. Matteson, Thomas A. Trabold Golisano Institute for Sustainability, Rochester Institute of Technology, 1 Lomb Memorial Dr., Rochester, NY 14623, United States highlights  Calculated current and theoretical maximum well-to-wheel exergy efficiencies.  Current efficiency ranking: battery electric > internal combustion > fuel cell.  Theoretical limit ranking: fuel cell > battery electric > internal combustion.  Efficiency limiting steps include heat engines, methane reforming and fuel cells. article info Article history: Received 14 October 2013 Received in revised form 17 March 2014 Accepted 31 March 2014 Available online 3 May 2014 Keywords: Well-to-wheels Exergy analysis Compressed natural gas vehicle Battery electric vehicle Fuel cell electric vehicle Hydraulic fracturing abstract Lower prices and increased supply of natural gas from hydraulic fracturing could lead to widespread use of natural gas in transportation. There are three primary ways that natural gas could be used in personal vehicles: compressed natural gas (CNG) in a combustion engine, as a source of hydrogen for a fuel cell electric vehicle (FCEV), and to generate electricity for a battery electric vehicle (BEV). In this work, we compare these three paths by analyzing their current and theoretical maximum well-to-wheels (WTW) exergy efficiencies. Each pathway begins with the extraction of natural gas and ends with deliv- ery of work to the vehicle’s wheels. The best current and theoretical maximum well-to-wheels exergy efficiencies for CNG, FCEV, and BEV pathways are found to be 31%/63%, 25%/87% and 44%/84% respec- tively. The largest exergy destruction for the CNG pathway occurs within the vehicle’s internal combus- tion engine (ICE) plant, which has a best current efficiency of 35%. For the FCEV pathway the main current sources of exergy destruction are the reforming stage and within the fuel cell engine plant, with best cur- rent efficiencies of 69% and 50% respectively. For the BEV pathway, the largest exergetic loss occurs dur- ing the conversion from natural gas to electricity at a combined cycle power plant, with a best current efficiency of 59%. While the theoretical maximum succeeds in identifying process steps that limit effi- ciency, it does not inform how much progress could be made to improve efficiency with what effort. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The automotive transportation sector consumes approximately 27% of U.S. total energy demand, translating to 32% of national greenhouse gas emissions and generating a dependence on for- eign oil [1,2]. Consumption of petroleum and its negative side effects not only result from onboard automotive combustion, but also from the entire fuel supply chain including fuel extrac- tion, transport, production, and distribution. In order to address the environmental and social externalities of petroleum, we must transition to a sustainable energy system relying on alternative fuel chains. In the long term, transportation needs to be based on renewable energy sources. In the meantime, natural gas may serve as an inter- mediate stage in the transition away from oil as the primary trans- port fuel [3]. Recently, there has been renewed interest in the cost and future supply of natural gas (NG) due to advances in horizontal drilling and hydraulic fracturing. These advances that began to be widely used in 2005, allow local industries to economically tap into vast reserves of unconventional gas deposits, such as shale gas [4]. Since 1989, the number of onshore natural gas wells has nearly doubled from 2,60,000 to 5,14,637 in 2011 [5]. Additionally, it was estimated that 60% of all new oil and gas wells since 2010 were hydraulically fractured. By 2035, natural gas production in http://dx.doi.org/10.1016/j.apenergy.2014.03.088 0306-2619/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Present/permanent address: Golisano Institute for Sustainability, Rochester Institute of Technology, 1 Lomb Memorial Dr., Rochester, NY 14623, United States. Tel.: +1 585 475 7211; fax: +1 585 475 5455. E-mail address: exwgis@rit.edu (E.D. Williams). Applied Energy 127 (2014) 55–63 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy