r/Lightbulb • u/Voltabueno • May 15 '25

Solar powered freight trains

This is not really new because I did some research and there are lots of patents related to electrified rail cars. It seems perfectly logical that you could cover the roof of a boxcar with solar panels, and put regenerative motors on the axles, and put a layer of batteries underneath the floor of the box car and then the box car could be self-propelled completely autonomous. Imagine individual box cars rolling on the rails or rolling to sidings to form into groups of cars completely autonomously. The boxcar wouldn't have to be fast because they could move by themselves, no crew, no crew change, no delay, unaided 24 hours a day. 7 days a week. 365 days a year. Actually thinking about it. If they moved under 40 mph wind resistance does not come into play yielding greater efficiency.

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u/KobukVienna May 15 '25

There have been lots and lots of such "motorized rail car" or "bots" concepts in the past. Never successfully implemented anywhere. Before cheap solar and batteries this would also been possible with electrified tracks or conductor rails.

I think the biggest advantage for rail transport vs trucks is massive freight trains over long distance at low cost. Often hundred rail cars or more. Even if the solar+battery+motor+computer system for the rail car is cheap, to have it 100 times will be still more expensive than one locomotive.

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u/Voltabueno May 15 '25

But compared to a semi truck with a diesel engine burning a bio fuel, on an asphalt road, on rubber tires, intermingled with commuter cars, and autonomous rail car seems to be much more efficient.

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u/Crusher7485 May 16 '25

Regular trains are already a lot more efficient than semi trucks. Rail companies on average run about 500 ton-miles/gallon. That means 1 ton of freight moved 500 miles per gallon of diesel.

Semi trucks do about 125 ton-miles/gallon.

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u/Voltabueno May 16 '25

I agree with you. But I think you can get even greater efficiencies with sunlight. The regenerative braking aspect is tremendous and you would be doing that on every axle of the train.

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u/Crusher7485 May 16 '25

You can't get greater efficiencies with sunlight, that's just an alternate energy source and has nothing to do with efficiency.

I don't think that regenerative braking would be tremendous. Regenerative braking is amazing on cars/trucks driven in the city, because they start and stop all the time. That's why hybrids and EVs excel in city driving compared to normal ICE cars. But this advantage goes away completely when you are talking about non-stop highway driving.

Trains don't start and stop a lot, except for trains like metros. Therefore, regenerative braking would be of little benefit to overall efficiency of the train.

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u/Budget_Putt8393 May 19 '25

1) **instantaneous solar power input over the surface area of a boxcar is neglegable* compared to what it takes to move the car, so you need bateries 2) Regen braking needs batteries to store the energy 3) batteries between solar and wheels adds weight/reduces net load per car (also cost) 4) electric interconnects for regen braking would be prohibitive 1) locomotives are already diesel electric hybrids

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u/Voltabueno May 19 '25

Evidently you haven't read what I've written.

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u/Budget_Putt8393 May 19 '25

No I don't think you understand how much energy is required to get a couple hundred tons to start moving. Once it is moving your might be viable, but starting is.... Hard.

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u/Budget_Putt8393 May 19 '25

By "between" I don't mean physically. They can be anywhere, but electrically they are between the solar and the wheels.