Plug-In
Hybrid Electric Vehicle
A pug-in hybrid electric vehicle is a hybrid electric vehicle
that can be charged with electricity like a pure electric
vehicles and run under engine power like a hybrid electric
vehicle. This combination offers increased driving range with
potentially large fuel and cost savings, emissions reductions,
and other benefits. Plug-in hybrid electric vehicles (PHEVs)
are still at a pre-commercial stage of development. Research
and development efforts are bringing them closer to widespread
commercialization.
Like hybrid electric vehicles, PHEVs are powered by two energy
sources — an energy conversion unit (such as an internal combustion
engine or fuel cell) and an energy storage device (usually
batteries). The energy conversion unit can be powered by gasoline,
diesel fuel, compressed natural gas, hydrogen, or other fuels.
The batteries can be charged by plugging into a standard electrical
outlet - a capability conventional hybrid electric vehicles
do not have - in addition to being charged by the energy conversion
unit when needed.
PHEV have a larger battery pack than conventional hybrid electric
vehicles. During typical daily driving, most of a PHEV's power
comes from the stored electricity. For example, a PHEV driver
might drive to and from work on all-electric power, plug in
the vehicle to charge it at night, and be ready for another
all-electric commute in the morning. However, the engine can
be used when longer trips are required, and the PHEV does
not need to be plugged in to operate.
Vehicle-to-grid concept
Researchers are developing "vehicle-to-grid" technologies
that allow a two-way connection between the PHEV and the local
utility grid. While the vehicle is plugged in and not in use,
the utility could take advantage of the extra electrical storage
capacity in the vehicle batteries to help meet peak electricity
demand, provide grid support services, or respond to power
outages. PHEV owners could get paid by the utility for use
of their vehicles, which would only be used when needed and
without negative effects on the vehicle battery's state of
charge. Google.org's RechargeIT program is demonstrating vehicle-to-grid
technologies.
Benefits of plug-in hybrid electric vehicles
These advanced vehicles have the potential to cut fuel use
and costs, increase energy security, protect public health
and the environment, and enhance national electrical systems.
Electricity typically costs much less than gasoline or diesel
fuels. Because PHEVs use electric power much of the time,
and the batteries are recharged by plugging into the electrical
grid, they can significantly reduce fuel use and costs. For
example, if electricity costs $0.08 per kilowatt-hour and
gasoline costs $2.77 per gallon, a PHEV could drive on electric
power for 3 cents per mile compared with 13 cents per mile
for driving on gasoline. Combined operation might result in
a cost of about 6 to 8 cents per mile.
Plug-in hybrid electric vehicles also offer flexible fueling
options. Because PHEVs can be recharged at home much of the
time, drivers can limit their trips to the gas station.
The United States imports more than 60% of its petroleum,
two thirds of which is used to fuel vehicles in the form of
gasoline and diesel. The demand for petroleum imports is increasing.
With much of the worldwide petroleum reserves located in politically
volatile countries, the United States is vulnerable to supply
disruptions.
Plug-in hybrid electric vehicles are highly efficient - requiring
little petroleum-based fuel to drive - and can use electricity
derived from domestic fossil fuel, nuclear, and renewable
sources. PHEVs also could be designed to use renewable and
domestically produced alternative fuels instead of gasoline
or diesel.
Electricity is an energy carrier rather than a primary energy
source. Thus, the environmental benefits of PHEVs depend in
part on the source of electricity from which the PHEVs are
charged. If the electricity comes from efficient power plants,
the benefits can be substantial. One U.S. study projected
an average 42% carbon emissions reduction from mileage driven
on electricity instead of gasoline. Even transferring the
point of emissions from the tailpipe to the power plant could
be important for urban areas with severe automobile-related
air quality problems. Hybrid vehicles have additional features
that make them more environmentally friendly than conventional
vehicles.
Research and development
Several barriers are preventing widespread commercialization
of PHEVs, including the following:
Hybrid component mass, volume, cost, reliability, and safety
Lack of domestic sources for batteries
Consumer behavior and expectations
Robust operation in range of environmental conditions.
Government and industry research and development efforts are
aimed at overcoming these PHEVs have the potential to enhance
the nation's electrical generation and distribution system.
Electrical demand varies greatly; demand is generally high
during the day and low at night. Charging PHEV batteries at
night would take advantage of the low demand. If vehicle-to-grid
capabilities are developed, PHEV battery capacity also could
be used to help meet peak electricity demands. PHEV drivers
would charge their vehicles while demand and electricity prices
are low and, when their vehicles are idle, sell electricity
back to the utility when demand and prices are high. This
could help utilities avoid building extra generation capacity
to meet peak demands.
The national and global benefits of PHEVs are greatest when
the electricity used to power them comes from clean, renewable
sources. If vehicle-to-grid capabilities are developed, PHEVs
could help compensate for the intermittency of renewable energy
production. For example, wind-generated electricity could
be stored in PHEV batteries when the wind is blowing and demand
is low and drawn out when the wind slackens or demand is high.
A National Renewable Energy Laboratory report calculates that,
if half of U.S. vehicles were PHEVs, wind turbine electrical
generation would double.
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