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NREL shows heavy duty hybrid trucks deliver on fuel economy


September 11, 2012
By Anthony Capkun

September 11, 2012 – A performance evaluation of Class 8 hybrid electric tractor trailers compared with similar conventional vehicles by the U.S. Department of Energy’s (DoE’s) National Renewable Energy Laboratory (NREL) shows significant improvements in fuel economy.

“During our 13-month study, the hybrid tractors demonstrated 13.7% higher fuel economy than the conventional tractors, resulting in a 12% reduction in fuel costs for the hybrids,” said NREL senior project leader Michael Lammert.

The hybrid tractors featured hybrid propulsion systems with 44 kW electric motors. The systems included regenerative braking and lithium-ion batteries that provided energy storage. Energy that is normally lost during braking is captured, stored in the batteries, and used to power the electric motor.

The NREL team collected and analyzed fuel economy, maintenance and other vehicle performance data on five hybrid and five conventional Class 8 tractor trailers operated by Coca-Cola Refreshments for delivery service in the Miami, Fla., area.

“We see cost as the number one barrier to companies using advanced technologies,” Lammert said. “Testing likes this helps companies understand whether these vehicles are going to save them money over the long run.”

In addition to field testing, the NREL team performed dynamometer testing at its Renewable Fuels and Lubricants (ReFUEL) Research Laboratory. During dynamometer testing, the hybrids demonstrated up to a 30% improvement in fuel economy, depending on drive cycle, and up to a 32.1% improvement in ton-miles-per-gallon. The comparable conventional tractors were approximately the same age and operated in similar conditions in the same facility.

NREL has been tracking and evaluating new propulsion systems in transit buses and trucks for more than 10 years. These evaluations are part of the U.S. DoE’s Advanced Vehicle Testing Activity, which conducts “comprehensive, unbiased evaluations of advanced technology vehicles” operating in fleets across the nation.