Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
Hybrid Electric Vehicles
Overview
Hybrid Electric Vehicles (HEV) combine
the internal combustion (IC) engine of a
standard vehicle with the motor and
battery technology of an electric vehicle.
This combination offers reduced fuel
consumption and GHG emissions when
compared to conventional vehicles, with
no appreciable reduction in range or
power. The two primary benefits of
drivetrain hybridization include
recouping energy that would otherwise
be wasted during braking, and allowing
the engine to spend more of its running
time at its most efficient operating point.
Various HEV configurations utilize one
or both of these efficiency improvement strategies. Essentially all hybrid systems also
shut down their IC engines at idle to further save fuel. Light-duty HEVs have
significantly better fuel economy than conventional gasoline engines, with passenger cars
typically ranging from 30 to 50 mpg, while retaining comparable vehicle range and overall
performance.
Gasoline HEVs have been commercially available in the United States for several years,
including the Toyota Prius and the Ford Escape hybrid models. The estimated number of
passenger HEVs in the United States in 2008 was 970,000, while HEV light trucks were
estimated at 280,000, corresponding to approximately 0.5 percent of the 2008 U.S. LDV
fleet. 19
All hybrid vehicle designs rely on dedicated batteries as a storage medium for additional
power delivery beyond that of the IC engine. Typically, hybrid drivetrain configurations
are classified in three types, according to the way that power flows through them: series,
parallel, and power-split. A series hybrid uses an IC engine to directly power an electric
generator which, in turn, powers one or more electric motors to drive the vehicle. This
type of system has the advantage of allowing the engine to run continuously at its most
3-40
HEV options are expected to be offered for an increasing number of LDV models
in the United States over the next few years, including pickups and SUVs, although the
benefit of hybridization for heavier trucks with significant towing requirements will likely
be less than that of lighter vehicles (Bandivadekar et al., 2008). Certain HEVs currently
also are eligible for tax credits of up to $3,000 per vehicle, offered through the end of 2010
by the Internal Revenue Service (IRS, 2009).
19 AEO 2009, Table 58.
Hybrid Electric Vehicles
Per Vehicle GHG Reduction: 26-54%
Confidence in Estimates: Moderate
• Cost-effectiveness and market penetration will
depend on fuel prices
Feasibility: High
• Proven, in-use technology
Key Policy Options:
• Financial or regulatory incentives for improved
fuel efficiency