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Comment by sudosysgen | Hacker News Reader

Is it really better to have batteries on them than to run powerlines?

Power lines are way worse than batteries IMO. You need literally thousands of miles of them for the freight network, which is costly. Much of which is extremely far from population centers (and the ability to repair them). Battery powered freight trains — swapped out at places near cheap energy, like random wind farms and hydro plants — could potentially be a leap in reducing the cost of freight.

They're not mutually exclusive. Batteries could be good in combination with a partially-electrified train network. Recharge in places where installing a third rail is cheap, discharge in places where installing a third rail is expensive.

Can they even fit the batteries on the trains?

I know there are a lot of variables involved, by all my napkin math gets me to somewhere around half a megawatt-hour of battery capacity required to move a monster train (e.g. ~18 kilotons) 1 mile.

Read the article. The idea is about batteries and motors on each car.

Apparently this attacks the inefficiencies in joining/splitting up cars at their destinations.

Right, but will this leave any room in the car for actual cargo? I'd like to see actual numbers (kg of battery / mile) here, my gut feeling is that lithium ion batteries are not good enough for this application, and they'll just end up using mostly diesel.

From the article:

> Parallel Systems cars can carry 128,000 pounds, or 2.8 times more than a semitruck. They also recharge in an hour: Without being plugged in or pulled off the track, the wheels can be recharged to drive another 500 miles.

Is this saying that a single charge can move a full load of cargo 500 miles?

I dont think it needs to pull all of it by itself.

I can imagine a system where in the areas the Train needs to stop/reload/whatever being surrounded by electrical infrastructure that at all moments is shoving electricity into the battery as fast as possible.

Then during departure, for the first few miles, electrical lines follow the track continuing to recharge the train while it gets up to speed. Afterwards, the battery is only really needed to overcome air resistance and friction, since so much kinetic energy has been given to the train for "free"

This is all just a random thought really, no idea if this is anything like what they are going for.

EDIT: should have used rolling resistance, not friction, so the final figure here is at least an order of magnitude too big, maybe two.

To me, the numbers just don't add up. Let's assume

- 0.2 as the coefficient of kinetic friction between the wheels and the rail [1]

- the car holds 100 tons [2]

- batteries can store 250 Wh/kg [3]

How much battery is needed to combat friction for one mile? (normal force times friction coefficient times distance, then scaled to battery capacity)

> (100 tons * 10 m/s^2 * 0.2 * 1 mile) / (250 Wh/kg)

> = 324 kg

So, 324 kg of lithium ion battery is needed per mile? Am I doing something wrong here because this looks completely untenable.

[1]: https://the-contact-patch.com/book/rail/r1717-friction-betwe...

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

[3]: https://www.cei.washington.edu/education/science-of-solar/ba...

I don't see how the limit of friction is relevant here. Trains don't drag their wheels along the rail; the whole point of a wheel is that it rolls. A useful calculation would be based on rolling resistance.

totally forgot about that part. Rolling resistance seems to be at least an order of magnitude lower than friction so that does bring the numbers into a reasonable range.

wikipedia indeed says the rolling resistance for rail cars is indeed 0.002, so you are off by a factor of a round 100. 3.24 kg/mile is not that bad. Actually even 10kg/mile sounds very acceptable to me, so they may end up being able to use cheaper batteries like NiMH.

Rolling resistance, for trains, is just a small part of the equation. Air resistance and changes in altitude are also quite significant.

The article, with pictures, has a better description. This isn't about replacing diesel train engines with battery engines. Instead, it gives each individual car a battery and motors to propel that one car.

Trains don’t really have a hard weight or length limit. Just stick another few battery cars on it.

but they can't have exactly 256 axles !

> Trains in Switzerland are not allowed to have 256 axles

https://twitter.com/standupmaths/status/1185544321933758467

I presume the costs to convert enough of our existing rail networks to support electric trains (in the US) would be extremely high, especially considering so much of the freight rail network is owned by a few companies.

Freight rail seems like a great use case for large scale wireless charging in certain areas... have "rest stops" every X miles on key lines where trains can automatically charge up in the middle of a haul.

Im sure they could also take advantage of induction braking on the downhill section of mountain passes.

> especially considering so much of the freight rail network is owned by a few companies.

Why does it makes cost high? I thought easier than what if many companies have rails.

And because the route/topology would already be known the energy budget could be rather easy to calculate, e.g., enough to get it up and over the mountain.

The US currently has only 1% of the rail network electrified, so running power lines is going to be a huge project. Europe went the other way and has on average 54% electrified. With the Benelux / DACH / France region even around 70% or so.

At only 1% electrified network is makes a lot more sense to put batteries on the train. At 70% it makes more sense to continue electrification where needed.

I think it depends on the country. The US has very long distances and the margin on trains is very small and competition fierce. They're also not subsidized. The trains need to be as cheap to run as existing trains and they can't afford a massive electrification effort.

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