A hybrid drivetrain involves the hybridisation of two or more different power sources in the same vehicle. The most commonly used arrangement uses an electric motor coupled with an internal combustion engine (together creating an electric hybrid). This is the type of system found in most commercially available hybrid vehicles.
Most hybrid systems also incorporate a regenerative braking feature which captures some of the energy normally wasted during vehicle braking.
Hybrid vehicles can deliver a significant fuel saving when matched carefully to the right application. They are best suited to urban freight applications with frequent stop-start conditions, which maximises the benefit of regenerative braking.
However, hybrid electric vehicles are not considered suitable for regional linehaul applications due to extended periods without braking. In such applications the benefits of regenerative braking and supplementary battery power are often outweighed by the penalty of carrying the additional weight of these components.
The main motivation for using hybrids relates to lower fuel consumption and reduced emissions.
Isuzu reports that in trials, fuel consumption savings of over 20% were achieved on inner city runs, and almost 10% on a mixed urban run. TNT has reported real-world fuel and emissions reductions of 14% in its fleet.
These savings translate to reduced fuel expenditure; however, it should be noted that battery life is currently uncertain and replacement may be required during the service life of the vehicle.
Key implementation considerations
The potential benefits of hybrid vehicles are highly dependent on the duty cycle of the vehicle. While the technology has provided up to 20% fuel savings in some Australian fleets, the savings are highly variable. For example, the city of Toronto experienced fuel savings of 10% compared with the predicted 20–30%, and a battery life of 18 months compared with the four years estimated.
Experience from Australian trials in the bus industry suggests that a failure to match hybrid system with duty cycle can actually increase fuel consumption compared to a conventional vehicle.
Examples of implementation
The Crown Coaches website provides information on the potential fuel savings experienced by a hybrid coach operator when compared to equivalent diesel coaches (Crown Coaches 2011). The Crown Coaches hybrid in pre-release testing reported a fuel economy of 3.73 km/L compared to 2.75 km/L for conventional buses.
It should be noted that although a coach may have a similar tare weight to road freight vehicles, duty cycles and payloads are likely to be different.
For more information, see Crown Coaches Pty Ltd (2011) Crown Coaches presents Australia’s 1st hybrid bus.
This case study highlights the potential fuel savings that may be realised through the use of hybrid trucks in a courier application. Using one of the first hybrid trucks in Australia, Barnett couriers has achieved a 32% fuel saving in its initial three months of operation (Truck World 2008).
Back-to-back comparison with a similar-sized solely diesel-powered truck on the same route has revealed a reduction in average fuel use from 27.8 L per 100 km to 18.8 L per 100 km (32%).
For more information, see Truck World (2008) Hybrid delivers economy message to courier company.
This fleet planning and management presentation demonstrates the potential for fuel efficiency benefits with the use of hybrid trucks in a delivery application.
Trialling a 2 tonne hybrid electric vehicle from 2003, the postal service experienced a 21% improvement in fuel efficiency. Battery life continues to be monitored.
For more information, see USPS (2007) ‘Fleet planning and management’.
New York City Transit
This evaluation report provides insights into the potential improvements in fuel economy that may be experienced with the implementation of hybrid electric technology in buses.
The City trialled 10 hybrid electric buses alongside its conventional diesel bus fleet. The hybrid bus fuel economy was found to be 34–40% better than that of the diesel fleet. It should be noted that this case study refers to buses being used under a particular application.
For more information, see New York City Transit (2006) Hybrid and CNG transit buses: final evaluation results (Opens in new window) PDF 1.1 MB.
Toronto Transit Commission
This news article discusses the disappointing fuel economy and battery life experienced by the City of Toronto when implementing hybrid buses.
The lead-acid batteries have required replacing after 18 months instead of four years, and the buses are providing only a 10% diesel fuel saving instead of the marketed 20–30% saving. The cost premium for each bus was almost 50%. It was acknowledged that the buses operate on uncongested residential routes that do not provide optimal conditions for hybrid buses.
Note: This case study details the experience of a fleet that was in a climate significantly colder than that in Australia, which is known to adversely impact battery power.
For more information, see The Star.com (2008) TTC going diesel again after hybrid bus glitch.
For the full report, see Fuel for Thought – Identifying potential energy efficiency opportunities in the Australian road and rail sectors (opens in a new window) PDF 1.5 MB.