Can we use big batteries to power our trains?

An eastbound manifest freight swoops through an S curve in Lombard Canyon, just east of Toston, Montana, on September 11, 2011. The tracks here snake along the Missouri River between Toston and Lombard.
Enlarge / An eastbound manifest freight swoops through an S curve in Lombard Canyon, just east of Toston, Montana, on September 11, 2011. The tracks here snake along the Missouri River between Toston and Lombard.

With the rapid pace of development in electric vehicles, we will likely get to a place where eliminating carbon emissions from one form of transport is possible. But cleaning up the remaining major modes—planes, trains, and ships—appears to be considerably more challenging. A new analysis suggests we have a good idea of how to improve one of those.

The study, performed by California-based researchers, looks at the possibility of electrifying rail-based freight. It finds that the technology is pretty much ready, and under the right circumstances, the economics are on the verge of working out. Plus, putting giant batteries on freight cars has the potential to create some interesting side benefits.

Giving freight a jolt

Right now, most freight in the US is moved by diesel-powered locomotives. In a typical year, these locomotives produce about 35 million tonnes of carbon dioxide, and the rest of the pollutants they make are estimated to cause 1,000 premature deaths and $6.5 billion in health damages.

Researchers have considered a few options for cutting the trains’ emissions. One would involve electrifying the whole system by stringing wires above the tracks, but that would involve a significant up-front expense and ongoing maintenance costs. An alternative would be powering fuel cells with hydrogen. That solution has the potential to be relatively cheap, but it requires the development of significant hydrogen production capacity, ideally involving splitting water using renewable electricity. That capacity is likely many years away from becoming a reality.

The last option is to use batteries, which could be integrated with the existing system. Most diesel locomotives use the diesel to power an electric generator, which then powers the motors. A change in wiring could potentially allow locomotives to accept an outside power source, such as a battery.

Scientists looked into this possibility some years back, but it was rejected on both technological and economic grounds. Since that time, batteries have gotten considerably larger, and they have dropped in price by 87 percent over the last decade. The researchers behind the new study decided it was worth taking another look.

A battery on wheels

In the US, the typical freight car travels an average of 241 kilometers per day when in operation. So the researchers created a battery big enough to move that distance as part of a large freight train (four locomotives, 100 freight cars, and about 7,000 tonnes of payload). They found that lithium ferrous phosphate would let each of the four locomotives be serviced by a single freight car configured as a giant battery. The battery would only occupy 40 percent of the volume of a typical boxcar and would be seven tonnes below the weight limit imposed by existing bridges.

Because of the efficiency of direct electric power, the train would use only half the energy consumed by an internal combustion engine driving an on-board generator. And while an above-average trip wouldn’t work on a single charge, freight trains normally stop several times a day to change crew and refuel, providing an opportunity to boost the range with some fast charging. And if longer breaks are possible, the battery cars themselves could be swapped out.

While the system wouldn’t require new locomotives, the batteries and charging infrastructure it would need make for some substantial up-front costs. The researchers added up all these costs and then calculated the price of electricity that would be needed to make the whole thing price-competitive with diesel.

Source: Ars Technica

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