TABLE 3.1 Approximate Charging Time as a Function of Vehicle Size and Electric Driving Range (hours)





Level 1




Economy vehicle




Midsize vehicle




Light-duty truck/SUV




Level 2




Economy vehicle




Midsize vehicle




Light-duty truck/SUV




NOTE: Numbers rounded by the committee.

SOURCE: Morrow et al., 2008.

home service to allow PHEV charging, whether desired or required, is estimated to range from slightly less than $1,000 to slightly more than $2,000. PHEV-40s are more likely to need costly new circuitry for 220 volts.

PHEV subsidies may soften the financial concerns associated with this issue, and in some cases (especially for meter upgrades), utilities may pay for such upgrades and amortize the costs over a series of electric bills. However, an open question remains: To what extent will these additional costs, or just the inconvenience of making the modifications, dissuade potential PHEV buyers?

Public Charging

As PHEVs proliferate, there will be a growing demand for public charging, much of which could occur during day-time hours, when electric power costs are higher. It seems likely that some office complexes will install chargers for their employees and visitors, and shopping malls may install chargers to attract customers. In some cases, businesses may not even charge for the electric power, treating it instead as a promotional expense.

As an indication of interest in public charging, one company, Electric Transportation Engineering Corp., was recently awarded a stimulus grant of nearly $100 million from the Department of Energy to build 12,800 charging stations for electric vehicles and PHEVs in Arizona, Washington, Oregon, California, and Tennessee (DOE, 2009b).


The committee identified some related issues that are beyond the scope of this study and will require detailed assessment to understand the impact of PHEVs on the grid and vice versa:

  • Outlet access. An accurate estimate is needed of the number of existing homes and buildings where charging would be easy. About 35 percent of housing units do not have a garage or carport, which is probably essential for an outlet for home charging (Bureau of the Census, 2008). PHEV owners without ready access to an outlet would need a public charging infrastructure; it is uncertain how many consumers would be willing to rely on public charging.

  • Charging at 440 V. Some carmakers may be interested in 440-V charging to reduce charging times (Carney, 2009). The cost and potential extent of such service needs study.

  • Distribution system upgrades. In some areas, local utility electric distribution capacity may not be adequate for the simultaneous charging of many PHEVs on one circuit, particularly for fast charges. These areas should be identified and plans for upgrading developed.

  • Safety. Safety issues associated with charging PHEVs must be thoroughly studied and problems minimized.

  • Energy stored in PHEVs. It has been suggested that the electric grid might use the electric energy stored in PHEVs to help meet peak demand (when the costs of producing power are very high) and replace it later, when costs are lower. The willingness of PHEV owners to allow this, and the benefits to them of doing so, need to be assessed. Conditions and terms under which this might be feasible and beneficial need to be developed. Alternatively, a charged PHEV might be used to provide electric power to a home during a blackout. It would be useful to know the viability of these options.

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