Batteries can provide up to 2,000 horsepower to a locomotive. What's more, locomotives spend many minutes while dynamic braking, as opposed to cars that brake for only a few seconds at a time. The energy captured from regenerative braking can cut a locomotive's fuel use by 15%, equivalent to 25,000 – 30,000 gallons of diesel per vehicle per year, and eliminate more than 300,000 kg of CO2 emissions, equivalent to that from 2,600 cars. The reduction in NOx emissions is even more significant.
General Electric is currently modeling a sodium metal-chloride battery for use in hybrid locomotives as an alternative to the lithium and metal-hydride batteries used in cars. Key requirements for a locomotive battery are:
- Higher energy densities
- Ability to withstand the environment of a long-haul locomotive
- Tolerance of cell failures in high-voltage strings, where batteries with failed cells continue to operate safely and effectively.