Suggested Citation:
Davies, Jamie (2011) Impact of Observed Travel and Recharging Behavior, Simulated Workplace Charging Infrastructure, and Vehicle Design on PHEV Utility Factors (UF), Total Charge Depleting (CD) Driving and Time of Day (TOD) Grid Demand: Scenarios Based on Consumers' Use of a Plug-in Hybrid Electric Vehicle (PHEV) Conversion. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-11-03

Plug-in hybrid electric vehicles (PHEVs) can run on gasoline or grid electricity and have been widely touted as promising more future societal and environmental benefits than hybrid electric vehicles (HEVs). However, since the charging of PHEVs will place new loads on the electrical grid, how much and the time of day (TOD) at which users plug in their vehicles will have implications for electricity providers who must meet the additional electrical load required to charge a fleet of PHEVs. PHEV charging could place new burdens on existing electrical infrastructure (substations and transformers) and generating capacity. Information about consumers’ recharging behavior can help utilities and interested parties better plan for PHEVS in the marketplace. To date, analysts have made assumptions as to the design of PHEVs that will be purchased, and the travel and recharging behavior of the future users. Furthermore, since PHEVs can run in charge depleting (CD) and charge sustaining (CS) modes there is uncertainty as to how much travel will be completed in each mode due to the variety of possible vehicle designs, access to charging infrastructure, and travel and recharging behavior of PHEV users. Accounting for the amount of travel in each mode is crucial in order to accurately assess the fuel economy (FE) benefits, green house gas (GHG) emissions and costs of PHEVs. In 2001, the Society of Automotive Engineers (SAE) promulgated standard J2841 defining the utility factor (UF) as the percentage of travel that can be completed in CD mode for a PHEV fleet with a given CD range. As such, the SAE standard J2841 has a substantial influence on policies regarding PHEVs and their assumed benefits and costs, and has been used by analysts, industry, and policy makers to calculate PHEV corporate average fuel economy (CAFE), GHG emissions, operating costs and Zero Emission Vehicle (ZEV) credits. My analysis challenges J2841by calculating the observed UF for a fleet of PHEVs driven by 25 Plausible Early Market (PEM) PHEV buyers in a demonstration and market research project. To estimate the potential effects on the UF of additional charging infrastructure, I model a workplace charging scenario in which each of the 25 households recharges the PHEV at their workplace as well as at home. Lastly, hypothetical consumer-designed PHEVs, solicited from each PEM household, are used to create and compare future market scenarios in which consumers are offered a wide variety of makes and body styles of PHEVs—thus simulating a plausible future market in which a variety of PHEVs are offered for sale. The results suggest that promoting “short range” PHEVs and focusing on popular vehicle-types, rather than upon achieving high CD ranges, could lead to greater total benefits from PHEVs in the early market, through more widespread adoption of PHEVs. 

Compared to SAE J2841, the observed UFs from the PEM demonstration data are 10 percentage points higher for PHEVs of up to 40 miles of CD range. At 40 miles CD range, J2841 stipulates a UF of 62%; I calculate a UF of 72% from the observed data. The increase in CD driving from adding simulated workplace charging varies by vehicle range, with the largest percentage point increases in CD driving occurring below 20 miles. Workplace charging changes the TOD distribution of power needed to charge a fleet of vehicles, producing a new maximum at 9:30 a.m. The addition of workplace charging under the conditions modeled here does not change the evening peak power demand.