Skip navigation to main content.
NREL - National Renewable Energy Laboratory
About NRELEnergy AnalysisScience and TechnologyTechnology TransferTechnology DeploymentEnergy Systems Integration

Hydraulic Hybrid Drive Systems

NREL's Fleet Test and Evaluation Team conducts performance evaluations of hydraulic hybrid drive systems in delivery vehicles. Because hydraulic hybrids feature highly efficient regenerative braking systems and "engine off at idle" capabilities, they are ideal for parcel delivery applications where stop-and-go traffic is common.

Hydraulic hybrid systems can capture up to 70% of the kinetic energy that would otherwise be lost during braking. This energy drives a pump, which transfers hydraulic fluid from a low-pressure reservoir to a high-pressure accumulator. When the vehicle accelerates, fluid in the high-pressure accumulator moves to the lower-pressure reservoir, which drives a motor and provides extra torque. This process can improve the vehicle's fuel economy by 25% to 30% compared to its non-hybrid equivalent.

UPS Hydraulic Hybrid Delivery Vans

The Fleet Test and Evaluation Team is evaluating the performance of 20 hydraulic hybrid delivery vans operated by the United Parcel Service (UPS) in the Baltimore, Maryland, area. UPS added the vans to its fleet in 2012. Because UPS started using gasoline engines in all of its non-hybrid delivery vans in 2010, NREL is comparing the new hybrid vans, which run on diesel, to similar conventional gasoline vans.

The on-road portion of this evaluation includes collecting and analyzing duty cycle, use, fuel economy, reliability, and other vehicle performance data. The in-lab portion involves dynamometer testing at NREL's Renewable Fuels and Lubricants Laboratory to determine the fuel economy and emissions impact of hybridization.