Solar panels on trains (or, really, just about anything that moves) is pointless. You can do it, but as a general guideline, you shouldn't - solar panels don't like moving. They're quite brittle in the efficient forms (silicon and glass), and while they can be made quite strong, that doesn't extend to "regular flexing and motion." Plus, anything that moves is likely to have terrible pointing of panels on a regular basis.

Just electrify the rail lines. There are strict sizing requirements for train cars such that they can fit through tunnels, so putting wires up just outside this and retracting the pickups for tunnels is perfectly doable. Most locomotives are diesel electric already, so they're not a big shift to convert to battery/electric, with some battery cars for the stretches that can't be electrified. Or just run the diesels for that chunk. It's still a huge win to electrify rail.

> It's still a huge win to electrify rail.

Alternatively, just ignore rail for now. It's ridiculously efficient (about 3-4x the efficiency of truck freight). If you phase-in a tax on carbon, more freight will immediately shift from truck to rail because of this comparative advantage... and it will provide incentive for small energy wins on rail, too.

Later, after we shift more cargo away from trucks and remaining trucks become more efficient, we can worry about fully making rail carbon neutral.

(And even then-- can ignore batteries for awhile in favor of just electrification of high-traffic segments).

Wow. I wasn't aware that so little rail is electrified in some countries. I was especially surprised about my own country Poland that has barely over 60% rail electrified, with European average being roughly similar. USA is below 2% vs China with over 60% electrification of the network of nearly exactly same length. I have no idea why almost nobody talks about that. I know rail is superbly efficient, but it still would be a huge win if USA could bring up their electrification to at least first world countries average.

Mexico and Canada have even more abysmal rates. I guess entire continent of North America was sleeping when the world started doing electric trains.

I always thought that nearly all rail was electrified and have trouble even imagining rails without wiring.

Solar panels that you can fit on a train won't provide a fraction of the energy required for the train. Luckily, we have a solution since 19th century: https://en.wikipedia.org/wiki/Railway_electrification_system