Electric Vehicles Present Challenges For Distribution
Oct. 16, 2011 - Dr. Russell Lefevre - renewgridmag.com
Increased worldwide interest in electric-vehicle
(EV) deployment has led many researchers to consider
the effects wide-scale adoption will have on the
electric grid. Most experts have concluded that there
is enough generation and transmission capacity to
accommodate the expected number of EVs, at least
in the near term.
However, the distribution system could present a
significant challenge, and the critical element is
In the U.S., the average pole-mounted transformer
serves seven to eight homes. Many who have examined
the issues have concluded that even small numbers
of EVs in a limited area could cause difficulties.
The effects will be very scenario-dependent, but
many studies show potential problems. For example,
Saifur Rahman, director of the Virginia Tech Advanced
Research Institute, recently indicated that in the
case of a 25 kVA transformer serving three houses
- with each house quick-charging a plug-in hybrid
vehicle at 6 p.m. - just flipping on a clothes dryer
would severely overload the transformer.
Another concern - one originally highlighted a couple
years ago at a California Energy Commission meeting
- is that simply charging EVs at night, when power
demand is significantly reduced, is not necessarily
The problem is that many utility distribution grids
employ undersized transformers that are designed
to cool overnight. If a high number of EVs charge
at night, when transformers are supposed to be getting
a break, the sustained excess current will eventually
cook a transformer's copper windings, causing a short
and blacking out the local loads it serves.
During the IEEE-USA Electric Vehicle Workshop held
this spring in Austin, Texas, Karl Rabago, vice president
of distributed energy services at Austin Energy,
spoke about the anticipated influx of EVs and the
need to prepare for the impact on utilities.
One projection indicates that Austin could have
as many as 192,000 EVs on its roads in 10 years.
To address the issues associated with this growth,
the utility has initiated a program called Plug-In
Partners, which is intended to support the installation
of home charging stations within the city. The program
provides a rebate of up to $1,500 toward the purchase
and installation of a Level 2 (240 V) charging station.
For the utility, the most important condition of
the agreement is customer participation in a charge-management
pilot program. This program is specifically designed
to enable Austin Energy to determine the actual effects
EVs will have on the grid as more cars come online.
Also, Honda's Electric Vehicle Demonstration Program,
launched late last year in Torrance, Calif., is designed
to help utilities prepare for large numbers of EVs.
The program includes research into customer behavior
and usability, public charging infrastructure planning
and sustainability initiatives. Stanford University
and Google are also involved in the program.
Undoubtedly, the growing market for EVs will continue
to spur innovation in areas such as battery technology
and charging infrastructure, but there are still
many challenges to overcome in order to achieve mass-market