Navigant Research Blog

Hydraulic Hybrids Seek Commercial Users

David Alexander — October 29, 2013

Hydraulic hybrid technology, which uses compressed gas as the medium to store and reuse energy, has been available for some years and has been tested in U.S. heavy duty fleets since 2003.  So far it has yet to capture the imagination of commercial vehicle manufacturers and fleet operators for widespread implementation, even though all the testing so far has reported significant fuel economy and efficiency improvements at a cost increment a fraction of that required for electric hybrids.  While some fleets are beginning to commit to small purchases, the volumes are still tiny even when compared with hybrid electric commercial vehicles.

As with all hybrids, the best ROI will come from vehicles with a drive cycle that includes a lot of stopping and starting.  Shuttle buses, delivery trucks, and garbage pickup trucks are the initial target markets.  The major selling point for hydraulic hybrid technology is its high power density, which is essential to recover the maximum energy from heavier vehicles.  Small startup companies such as Lightning Hybrids in Colorado, NRG Dynamix in Michigan, and RDS Technologies in Australia are all working with local customers to upgrade existing fleet vehicles to demonstrate the benefits of their systems in practice.

Not For Everyone

In recent years, hybrid electric vehicles have also had a hard time breaking into the commercial vehicle market, but cost has been the main factor along with the inability of batteries to handle the large energy flows in slowing and accelerating large vehicles.  The relatively recent introduction of natural gas as a clean fuel for commercial vehicles, thanks to the low-cost availability as a liquid fuel, means that attention has again been diverted from the potential of the hydraulic hybrid.  However, automakers really should get more interested in the technology because although natural gas is clean, its energy density is much lower than diesel or gasoline.  Adding a hydraulic hybrid system in parallel can allow vehicles for some drive cycles to use clean fuel without needing to increase the engine size to maintain on-road performance.

Hydraulic hybrid technology is not a solution for all vehicles.  It makes a good partner with gasoline (or natural gas) engines to deliver high torque performance similar to that of a diesel engine at lower total cost and equivalent economy while producing fewer harmful emissions – as long as the vehicle usage includes stopping and starting.  However, the 2013 project announcement in Europe from PSA Peugeot Citroën and Bosch indicates that there is potential for a new approach to efficiency in small city cars.

Navigant Research’s report Hydraulic Hybrid Vehicles outlines two quite different potential scenarios: slow incremental growth based on heavy duty fleets or a surge of interest as a way to support engine downsizing in consumer vehicles.  This segment is going to be fascinating to watch.

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