IEEE Electrification Magazine - June 2014 - 10

finite capacity to meet ever-growing electricity needs, and
the majority of this system is powered by coal and natural
gas generators.
v2G technology makes it possible
for vehicles to become valuable grid
resources while conserving energy
and supporting clean, renewable energy sources. For example, solar photovoltaics' variable nature and
concentration of electricity output in
the middle of the day pose limitations,
and the high cost of Pev batteries can
constrain the cars' market potential.
When deployed together, however,
these technologies can provide mutual benefits. if solar energy sources can
increase the availability of peakperiod midday charging, powering
Pevs can be made more affordable. at
the same time, Pevs can store photovoltaic energy during periods of
low demand.
nreL is working with the U.s.
Department of Defense and the U.s.
army corps of engineers to explore
how v2G systems can integrate photovoltaics, Pevs, and renewable energy management with a microgrid
system at Fort carson, a large army facility in colorado. as
part of this project, nreL's new energy systems integration Facility is being used in tandem with the lab's vehicle

testing and integration Facility to explore system-scale
interaction among renewable energy sources, vehicles, the
electricity grid, buildings, and transportation infrastructure. research is also helping to identify the impact of grid functions on
vehicle battery life span.
researchers are exploring three
other features of technology that present significant promise: smart charging, v2G communications, and fast
charging. automated smart charging
systems use information about the
grid frequency, voltage, availability of
renewably generated power, and pricing to determine when and how much
power to deliver to Pevs. as shown in
Figure 1, this helps Pev drivers ensure
batteries are always adequately
charged at the most affordable rate.
these systems also provide grid operators with a highly flexible load to buffer disturbances, increase reliability,
and enable increased adoption of
intermittent renewable resources.
v2G communications pair smart
charging capabilities with features
allowing Pevs to feed energy back to
the grid. Bidirectional charging gives
electric vehicles the potential to balance variable production
from intermittent renewable sources, supply emergency
backup power, and act as grid-tied energy storage devices.
today, fast charging makes it possible to recharge an electric vehicle
from empty to 80% of its total capacity in 20-30 min. Future technology
may shorten recharge time to as little
as 5 min. this makes Pevs more
competitive with conventional gasoline-powered vehicles in terms of
fueling times.
Devising a way for electric-drive
vehicles to automatically connect with
the grid for charging without needing
to be plugged in can also mitigate
some of the barriers to Pev adoption.

V2G technology
makes it possible to
store energy in and
source energy from
vehicle batteries to
balance intermittent
renewable resources,
enhance grid
stability, and/or
reduce demand
for costly grid-fed
electricity at
peak hours.

NREL Campus Power Demand (kW)

2,000
1,800
Typical
Daily Peak

1,600
1,400
1,200

Daily Drop Due to
On-Site Solar Production

1,000
800
0:00

6:00

12:00

18:00
0:00
6:00
Time of Day

12:00

18:00

0:00

Buildings + PEVs (20%, Immediate Charging) Unmanaged = US$11.50/vehicle/mo
Buildings + PEVs (20%, Staggered Charging) Staggered = US$4.50/vehicle/mo
Campus Net Load with PV
Buildings + PEVs (2% Adoption)
Figure 1. How managed power can deliver more than 60% savings in energy costs while integrating renewables with the grid.

I E E E E l e c t r i f i c ati o n M agaz ine / j un e 2014

Cutting the Cord:
Wireless Power Transfer
vehicle charging needs to become
more convenient and cost effective
for a larger number of people to buy
Pevs. Wireless power transfer (WPt)
takes this v2G communication one
step further. While Pev owners
might have the means to plug in
vehicles at home or at work, charging

Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2014