Although trucks carry a large portion of freight in North America, for long-distance transport trains are still carrying the lion’s share. Railroads account for 43% of all intercity freight traffic, which is more than any other single method. Every day, there are thousands of railcars and container cars crisscrossing the continent, carrying everything required by a consumer-oriented society.
All modern locomotives are already half-way to being hybrid vehicles. They are powered by massive diesel engines driving generators, which power the electric motors that actually drive the train. The diesel-electric locomotive is a robust design requiring relatively low maintenance, and has been in mainline service since 1929.
Diesel electric trains use dynamic braking, where the electric motors are used as brakes. In dynamic braking, the motors act as generators, creating large amounts of power. With a conventional diesel-electric locomotive, though, this power is wasted. Along the top of a locomotive are a series of heaters and blowers. Power from the brakes is fed into these heaters, and simply discarded as waste heat. (Locomotives also carry conventional brakes, as dynamic braking isn’t effective below about 16 km/h)
It would seem to be a straightforward idea to put a battery into this loop, and recapture some of this wasted power. After all, the diesel-electric is already half-way there. However, the brakes generate so much power that a conventional battery simply can’t handle it. Nor can a conventional battery provide enough current to get a train rolling again.
To cope with these immense energy demands, General Electric created a new class of battery. These monsters use molten salt, a combination of sodium and metal chloride, to create a battery than can absorb, and dump, over 2000 horsepower in less than a second. The 10-ton battery would capture brake energy and excess generator power, and store it for later use, like accelerating, or climbing a steep grade.
The ability to recapture some of a train’s braking energy is significant. A typical 200-ton locomotive loses enough energy to braking over the course of a year to power over 150 homes. Reducing this energy cost can have significant payoffs. A hybrid locomotive can reduce fuel consumption by up to 15% and emissions by up to 50%.
When these sorts of savings are applied to the entire fleet of locomotives operating across North America, you have the potential to cut NO2 emissions by the equivalent of taking 1/3 of North America’s cars off the road.
However, in tough economic times, the future of hybrid rail is uncertain. GE has only built the one test locomotive, and has none in service, while another company, Railpower Technologies, sought creditor protection in 2009.
In a greener world, rail would be the primary method of long-distance transportation, and the hybrid diesel-electric would come into its own as a green machine.