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The combination of high oil costs, concerns about oil security and availability, and air quality issues related to vehicle emissions are driving interest in "plug-in" hybrid electric vehicles (PHEVs). PHEVs are similar to conventional hybrid electric vehicles, but feature a larger battery and plug-in charger that allows electricity from the grid to replace a portion of the petroleum-fueled drive energy. PHEVs may derive a substantial fraction of their miles from grid-derived electricity, but without the range restrictions of pure battery electric vehicles. As of early 2007, production of PHEVs is essentially limited to demonstration vehicles and prototypes. However, the technology has received considerable attention from the media, national security interests, environmental organizations, and the electric power industry. The use of PHEVs would represent a significant potential shift in the use of electricity and the operation of electric power systems. Electrification of the transportation sector could increase generation capacity and transmission and distribution (T&D) requirements, especially if vehicles are charged during periods of high demand. This study is designed to evaluate several of these PHEV-charging impacts on utility system operations within the Xcel Energy Colorado service territory. SUBJECT TERMS

Plug-in hybrid electric vehicles (PHEVs) have received considerable recent attention for their potential to reduce petroleum consumption significantly and quickly in the transportation sector. Analysis to aid the design of such vehicles and predict their real-world performance and fuel displacement must consider the driving patterns the vehicles will typically encounter. This paper goes beyond consideration of standardized certification cycless by leveraging state-of-the-art travel survey techniques that use Global Positioning System (GPS) technology to obtain a large set of real-world drive cycles from the surveyed vehicle fleet. This study specifically extracts 24-h, second-by-second driving profiles from a set of 227 GPS-instrumented vehicles in the St. Louis, Missouri, metropolitan area. The performance of midsize conventional, hybrid electric, and PHEV models is then simulated over the 227 full-day driving profiles to assess fuel consumption and operating characteristics of these vehicle technologies over a set of real-world usage patterns. In comparison to standard cycles used for certification procedures, the travel survey duty cycles include significantly more aggressive acceleration and deceleration events across the velocity spectrum, which affect vehicle operation and efficiency. Even under these more aggressive operating conditions, PHEVs using a blended charge-depleting energy management strategy consume less than 50% of the petroleum used by similar conventional vehicles. Although true prediction of the widespread real-world use of these vehicles requires expansion of the vehicle sample size and a refined accounting for the possible interaction of several variables with the sampled driving profiles, this study demonstrates a cutting-edge use of available GPS travel survey data to analyze the (highly drive cycle–dependent) performance of advanced technology PHEVs. This demonstration highlights new opportunities for using innovative GPS travel survey techniques and sophisticated vehicle system simulation tools to guide vehicle design improvements and to maximize the benefits offered by energy efficiency technologies.

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Plug-in hybrid electric vehicles (PHEVs) have emerged as a promising technology that uses electricity to displace petroleum consumption in the vehicle fleet. This paper presents a comparison of the costs (vehicle purchase costs and energy costs) and benefits (reduced petroleum consumption) of PHEVs relative to hybrid electric and conventional vehicles. A detailed simulation model is used to predict petroleum reductions and costs of PHEV designs compared to a baseline midsize sedan. The analysis finds that petroleum reductions exceeding 45% per vehicle can be achieved by PHEVs equipped with 20 mi (32 km) or more of energy storage. However, the long-term incremental costs of these vehicles are projected to exceed US$8,000. A simple economic analysis is used to show that high petroleum prices and low battery costs are needed to make a compelling business case for PHEVs in the absence of other incentives. However, the large petroleum reduction potential of PHEVs provides strong justification for governmental support to accelerate the deployment of PHEV technology.

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This work was funded by the Advanced Vehicle Technology Analysis and Evaluation activity in support of the FCVT Program of the Office of Energy Efficiency and Renewable Energy within the U.S. DOE. We wish to thank our sponsor, Lee Slezak, for his guidance and support. Terry Penney, as NREL's FCVT technology manager, and Matt Thornton, as task leader for NREL's Vehicle Systems Analysis Task, supported this project.We would also like to express our appreciation to the members of the FreedomCAR Vehicle Systems Analysis Technical Team: Larry Laws (GM), Mark Biernacki (DaimlerChrysler), and Asi Perach (Ford) for providing technical insight and industry review.Tony Markel, project leader iii 1. Proposed improvements to the existing test procedure for reporting PHEV fuel economy 2. A thorough exploration of the PHEV design space, including an evaluation of the trade-offs between cost and fuel consumption 3. The application of real-world driving data to quantify the impacts of travel behavior on the potential benefits of PHEVs 4. The optimization of energy management strategies focusing on petroleum displacement.The NREL research team has participated in many key industry meetings, and its research has been documented in eight formal presentations and five technical papers that have been published or have been submitted for publication within the next 6 months. This milestone report is a compilation of these papers and presentations for future reference.The following is a summary of important insights that emerged from the four areas of emphasis. Plug-In Hybrid Electric Vehicle Fuel Economy Reporting MethodsPHEVs differ significantly from existing vehicles. They consume two fuels (petroleum and electricity) at rates that depend on the distance driven and the aggressiveness of the cycle. The Society of Automotive Engineers J1711 Recommended Practice, created in 1999, provides the fundamentals for measuring fuel economy of off-vehicle charge-capable vehicles (i.e., plug-in hybrids and electric vehicles). Seven years later, with a much better understanding of how PHEVs will likely operate, some improvements to the original procedure are recommended. The team's specific recommendations are:• Report gasoline and electricity consumption separately, which allows the reported results to be used for vehicle operating cost comparisons, fuel consumption, and CO 2 emissions estimates.• Revise the end-of-test criteria to more accurately determine the distance driven in chargedepleting mode, fully capture the petroleum displacement potential of longer-range PHEVs, and improve the reporting accuracy for short-range PHEVs. 1• Assume that vehicles will be fully charged once per day because there is an economic incentive for consumers to recharge their vehicles at least once per day, if not more often.The recommended improvements to the fuel economy reporting methods have been adopted in our analyses, and the team intends to work with other labs and regulatory agencies to enact similar improvements in their procedures. The analysis also ...