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Comment by bombcar | Hacker News Reader

Electrifying yards could be worthwhile, but total US fuel usage for trains is about 3.5 billion gallons [346] out of about 46 billion gallons/yr [995].

[346] https://www.bts.gov/content/class-i-rail-freight-fuel-consum...

[995] https://www.eia.gov/energyexplained/diesel-fuel/use-of-diese...

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So ~7.5%? Seems worthwhile to me.

High-end estimates are $5m per mile, at 140,000 miles it would be $700 billion, throw in a bit more for some new locos (probably could switch existing somehow), cool trillion.

Could be better spent money than other things we do.

The far more practical method would be for trains to haul thier own batteries. A couple freight cars full of lithium would provide substantial range without electrifying the entire track. And trains have amazing potential for regeneration during braking, if one can find a way to do it practically.

Solar panels on top of the cars?

The amount of energy provided by the solar panels would be a rounding error compared to the total needed to move the train. Almost certainly not worth it.

Yeah you'd almost certainly be better installing electromagnets in yards to help get the train up to speed somehow ...

But a few cars of batteries wouldn't? Feels like that's not that much either but I haven't run the numbers.

Some very rough back of the envelope calculations, with apologies in advance for imperial units:

CSX says a "typical train" might be hauling 3000 tons of freight 500 miles, using about 3,000 gallons of diesel [1]. Batteries are about two orders of magnitude lower volumetric energy density, so 3,000 gallons of diesel has the same energy as about 300,000 gallons of batteries. Roughly 7.5 gallons per cubic foot, so that's 40,000 cubic feet. But the diesel engine only converts about a third of the energy in the diesel into usable form, while the batteries will be close to 100%, so we actually only need a third as many batteries. I'll round up to 15,000 cubic feet.

A standard boxcar is about 6,000 cubic feet interior volume [2], so that would be 2.5 boxcars full of batteries.

So battery cars might be feasible.

[1] https://www.csx.com/index.cfm/about-us/the-csx-advantage/fue...

[2] https://www.csx.com/index.cfm/customers/resources/equipment/...

This can work for a lightweight railcar, with a lot of sun, but is out of the question for a freight train.

https://en.m.wikipedia.org/wiki/Byron_Bay_Train

Or we could just go back to electrification, like much of the Milwaukee Road had prior to the 1970s, instead of feeling the perpetual techie desire for new vaporware tech.

Large American freights don’t much brake if they can avoid it.

You’d more get a benefit from using the power coasting down the Rockies to provide juice to climb it - electricification.

Some of the trains in the photograph use up to ~17MWs, to get 129MWh of batteries installed on the ground in the worlds largest battery array at the time, cost $90 million dollars and while a train could certainly pull it, it's a non-trivial addition. That battery array couldn't move the train for even a fraction of some journeys required by train engines, so I think it's a non-starter economically for these cross-country journeys.

https://en.wikipedia.org/wiki/Hornsdale_Power_Reserve

Not for cross-country journeys yet (at least not alone), but battery powered locomotives are picking up steam...

https://www.forbes.com/sites/alanohnsman/2022/03/01/the-new-...

Apparently they largely have regenerative breaking already but nowhere to store the energy so dump it through resistors to vent it as heat, if they had big battery arrays the savings could be significant.

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