neighborhood clusters (May and Johnson, 2011). According to this “cul-de-sac effect,” plug-in vehicles tend to gravitate toward wealthy neighborhoods and environmentally conscious communities. The consequence can overload local circuits and transformers. Consider, for example, a Nissan Leaf recharging on a 240-volt, 15-amp circuit. This imposes a 3.3-kW load on the circuit, which is greater than the load of the average home in Berkeley, California. Similarly, a Chevy Volt recharging on a 240-volt, 30-amp circuit imposes a 6.6-kW load, about the average for homes in San Ramon, California (May and Johnson, 2011, p. 56). Since utility circuits and transformers tend to be sized to accommodate five or six homes, just a few vehicles can change the power loading of a circuit markedly. Thus, the charging issues posed by clusters of activity could challenge many early-adopter communities and utilities.

Second, regarding time, the chief concern of vehicle users is the worry about becoming stranded with a depleted battery. And so vehicle owners have an incentive to recharge their vehicles’ batteries at every opportunity: while at work, in parking garages, while parked at airports, and so forth. Thus, utility planners cannot assume that all charging will be done at night when the electric grid has off-peak power.

Third, the prospect for fast charging (see the section below) could make the plug-in vehicle much more desirable for customers to own because the charging could be completed in 15 or so minutes instead of many hours. Thus, fast charging might accelerate market penetration if it can be accommodated on the vehicle. However, this practice poses a power challenge, as distinct from an energy challenge, to the grid. Recharging a 10-kWh battery in, say, 15 minutes would require more than 40 kW of power. Larger batteries could impose a power requirement exceeding 50 kW per charge. And since the probable high cost of the early fast chargers would appear to prohibit their use in residences, fast charging would most likely be done in public places and hence while the vehicle is in daily use. Thus fast charging could exacerbate the peak-demand problem in some localities.

Finally, smart-grid technologies applied to the home could enable consumers to manage their vehicle recharging like any other appliance, and respond easily to price signals. The extent to which they adopt and use this capability and the extent to which such response might offset the local challenges posed by plug-in vehicle charging remain unknown.

Technology Uncertainty

In May 2012, eight automotive OEMs announced their adoption of a standard charging system, the Combined Charging System. The standard is a product of the Society of Automotive Engineers (SAE) and the European Automobile Manufacturers’ Association (ACEA). Operating under this standard, Combined Charging Systems would integrate the following into one vehicle connector: (1) regular



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