A hybrid locomotive operates on the same principle as a hybrid motor vehicle. All propulsion power is derived directly from a large battery, with a smaller diesel generator providing recharges to the battery as its charge is depleted. A regenerative braking system can be integrated into the hybrid combination to convert kinetic energy back into electricity to be stored when braking.
There is limited Australian experience with these systems and the applicability is also low. US studies indicate that benefits may be accessible only when used in low horsepower switching operations, given that full power is needed only intermittently and for only relatively short periods. This limitation is supported by a general lack of linehaul applications using the technology.
As with genset locomotives, the use of hybrid switching locomotives in the US has been largely driven by Environmental Protection Agency regulations to reduce harmful pollutants affecting urban areas in close proximity to rail yards.
Limited opportunities have been identified to purchase or transfer technology to Australian operation beyond a Central Queensland coal haulage trial. The commercial linehaul hybrid being released in the US will not be suitable for non-standard gauge rail networks (much of Australia).
Some manufacturers claim a fuel consumption reduction of approximately 25%. Current experience suggests that hybrid switching locomotives can reduce diesel fuel use by around 15% and the next generation of locomotives could contribute to a 5–10% improvement in fuel efficiency for linehaul operations. In addition to regenerative braking, hybrids also benefit from allowing the diesel-generator to run at a constant speed (the most efficient operating point) to reduce fuel consumption by buffering energy demands with the battery.
Key implementation benefits
No purchases of hybrid locomotives were identified that did not have government grant support. US rail operators have indicated that current fuel savings do not meet their return on investment thresholds. Additionally some trials have encountered performance issues with defective battery components that required a locomotive recall after batteries over heated.
Examples of implementation
Union Pacific media release
This article provides information on air quality and fuel saving improvements form the purchase of 10 ‘Green Goat’ hybrid switch locomotives. Australian rail operators may identify useful metrics of performance improvement that Union Pacific presents publicly.
For more information see Union Pacific (2005) ‘Union Pacific orders 10 ‘Green Goat’ hybrid locomotives for Southern California
rail yard operations’
GE Transport fact sheet
This fact sheet identifies a current engineering prototype of a linehaul battery-hybrid. Potential fuel savings are expected to be 15% (GE Transport 2011).
For more information see GE Transport (2011) ‘Hybrid locomotive’ fact sheet (opens in a new window) PDF 416 KB.
Evaluation of battery-power boosted freight locomotives
This academic case study may be useful for coal haulage operators as it simulates gradient profile and distances that are common with this task. The simulations performed demonstrate upper and lower bounds of the effectiveness of regenerative braking in freight haul applications. Short trains showed higher regenerative efficiencies than longer trains on the same track. Experience over mildly undulating track demonstrated limited gains from regenerative braking of 0.2% to 4% (Bearham 2007).
For more information, see G.Bearham (2007) Evaluation of battery power boosted freight locomotives, G. Bearham (opens in a new window) PDF 350 KB
For the full report on fuel saving opportunities in the road and rail sectors, 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.