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Top 10 EV Challenges

Utilities prepare for a bumpy road.

Fortnightly Magazine - June 2011

3.3-kW load, which is greater than the average home in Berkley, Calif. The Chevy Volt, at 240 v on a 30-amp circuit, draws 6.6 kW, equal to the average San Roman home load. The problem isn’t a lack of generation or transmission capacity, but capacity in the last 50 feet of the distribution system. Secondary transformers have been properly sized to accommodate the load of between three and six homes on average in the United States.

Consider a hot, humid day with air conditioners blazing. At the same time, not one, but multiple EVs are pulling into the garages, feeding from the same distribution transformer—each with the equivalent load of a single home—plugging-in and requesting a rapid charge. These are the makings for a localized brownout.

Some might believe this is the perfect storm that will drive the long-overdue overhaul of our nation’s grid. Others believe the odds of that storm occurring are slim to none, and it’s too costly to build a distribution system for worst-case scenarios. In either case, the problem has the potential to arise much sooner in older, established neighborhoods where transformers were sized for small homes (100 amp service versus the typical 200 amp service in newer homes) or in areas of the country where the peak demand of air conditioning wasn’t a distribution system design requirement.

In some areas of the country, a single level-1 EV charger ( i.e., a slow charger, using a 120 v circuit) per transformer won’t be an issue as long as the charging occurs during off-peak periods. Add a second level-1 charger and an overload condition will arise in a few areas. Introduce a level-2 charger ( i.e., a fast charger, using a 240 v circuit) and the issue has the potential to escalate.

Now add two EVs per home. Will neighbors be expected to negotiate who charges when? Will they have to choose between charging and keeping their home air conditioners running during EV charge times? When should EVs be charged if many people are plugging in at the same time, and how can the charging be smoothed out to avoid blowing a transformer or contributing to a peak event?

A Department of Energy study found that the idle capacity of today’s electric power grid could supply 70 percent of the energy needs of today’s cars and light trucks without adding to generation or transmission capacity—if the vehicles charged during off-peak times, somewhere between the hours of 9:00 p.m. and 6:00 a.m. However, currently nighttime rates aren’t low enough compared to daytime rates to change habits. Incentive-based pricing to motivate off-peak charging is important but not sufficient. Consumers will plug-in whenever they get the chance due to fear of a depleted battery—a phenomenon referred to as “range anxiety.”

Pure battery electric vehicles will serve as a secondary vehicle for most households, while plug-in hybrids, with their long driving range, can serve as the primary vehicle. Pike Research states that demand for EVs will begin increasing in 2012 as owners begin to travel further with their vehicles and become