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Charging and Its Correlation to 'Gasoline Starts'

By: Morgan Davis
August 2011

One of the main benefits of Plug-in Hybrid Electric Vehicles (PHEVs) is the ability to displace petroleum use with electricity; these vehicles can use electricity as their primary fuel source.  Use of electricity results in lower emissions, and saves vehicle owners on maintenance and fueling costs.  In order to maximize cost savings and minimize emissions, it is important to understand how fast and how frequently to charge these vehicles.  This simulation study analyzes three scenarios: home charging only, home and work charging, and charging whenever the vehicle is parked (regardless of location).  Vehicle charging is modeled at both level 1 (1.44 kW) and level 2 (6.6 kW) for three near-term all-electric ranges (AERs): PHEV10, PHEV40, and PHEV100. The vehicles are simulated using the 2009 National Household Travel Survey dataset.  The results of the simulation are shown in Figure 1; the horizontal axis represents the scenario analyzed, and the vertical axis shows the percentage of days within the dataset during which there were no gasoline starts.

Vehicle Days with No Gasoline Starts
Figure 1 vehicle days with no gasoline starts

Not surprisingly, the vehicles with the highest AER have the most days with no gasoline starts.  Also, with the increase in charging availability, the percentage of gasoline starts decreases.  The impact of increased charging availability is more significant than the increase in charging power, especially for the more near-term scenarios (home only, and home + work). Figure 2 shows the reduction in gasoline starts for three near-term scenarios.

Reduction in Gasoline Starts
Figure 2 reduction in gasoline starts

The largest reduction of gasoline starts results from increased charging availability for low-AER vehicles. From an emissions standpoint, the reduction in gasoline starts is the most important environmental benefit of PHEVs. In order to maximize this benefit, increased charging availability, even at low power, is important.

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