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How Will Electric Vehicles Impact Peak Demand? | Demand Response

Many skeptics argue that system capacity constraints will limit the viability of electric vehicles.  With all the attention that the industry pays to peak demand concerns, electric vehicles must complicate matters, right?  Wrong. When it comes to peak demand, electric vehicles will not have a noticeable impact for 10 or 20 years, even if charging is uncontrolled.

According to a UC Berkeley study that analyzes the effects of plug-in hybrid electric vehicle adoption on system load in California, “1 million compact car plug-in hybrid electric vehicles would not significantly affect the system peak.”  We may not see 1 million electric vehicles on the road in all of the United States for 5 or 10 years, so it will be at least 10 or 20 years before we see 1 million in California alone.  According to this study, even then, electric vehicles will not significantly affect the system peak.  System capacity constraints will become a real issue in 20 or 30 years, but we should not worry about it too much at this point.

A concern that is not overblown is how electric vehicles impact the distribution system.  There are two main issues with respect to the distribution system that electric utilities are concerned about.  The first issue is obvious.  The number one job of electric utilities is to keep the lights on.  Electric vehicles may not have much of an impact at a system wide level, but for a given circuit or transformer, a few electric vehicles charging at the same time may lead to an increase in localized outages.  Considering that adoption of electric vehicles will be concentrated in certain neighborhoods, electric utilities are concerned about maintaining the same level of reliability.

The second issue is less obvious.  According to an EPRI study, concentrated charging of electric vehicles will lead to an increase in transformer degradation.  The figure below plots the degradation of a given transformer as a function of the number of plug-in hybrids served.  According to the study, “These transformers typically serve 5-7 households.”  If a cluster of 5-7 households adopts 3 to 5 plug-in hybrids and charges them at 240 volts, transformer degradation increases precipitously.  This scenario will be quite common because adoption of electric vehicles will be concentrated in certain neighborhoods and 240 volt charging will be common (in fact, 240 volt charging will be required for LEAF owners).


Stephen Lacey of RenewableEnergyWorld.com recently interviewed Matt Nielsen, a senior researcher with GE.  He emphasizes many of the same points:

“Most people agree that we have enough generation capacity to meet the first wave [of electric vehicles]… One of the key stress points that folks are concerned about are the local points of connection for these vehicles, especially the local area transformers… They are designed such that they may be overloaded during the day, but then they have a cooling period at night so they can decrease their temperature and that doesn’t impact their overall lifetime.  So what does that mean?  Does that mean we then continue to add load to these transformers when we thought they were going to be cooling down, but now they are not cooling down?  Or do we charge them during the day and we add to the peak load that they see, stressing them even more?  A lot of the utilities are very proactive.  They are already trying to look at where they believe adoption will occur for the electric vehicles and then try to identify those stress points in their distribution system and proactively identify a plan to correct that.  So I think, on the utility side, one of the main challenges in on the distribution side.”

Like us humans, transformers need time to cool down.  If they are forced to work 24/7, their overall lifetime decreases.  This issue, as well as localized outages, are the key challenges that utilities will face as a result of electric vehicles.  Concerns about peak demand are overblown.  Concerns about the distribution system are real and need to be dealt with proactively.

To read more on how utilities can deal with these challenges, check out this white paper.  It highlights some of the electric vehicle work we did at Freeman, Sullivan & Co.