It might generate enough power if you could find a way to get the Sun to go supernova but then we wouldn't need the trains, would we?

Greensleep, you're new here, so I think you've missed the repeated speeches by engineers regarding photovoltaic. The problem isn't that there aren't enough places to put them--the reason people don't use them is that they don't generate much electricity and they cost a whole lot.

For father's day, I bought my dad one of the p-v top off-chargers (mentioned here before) that keeps a car battery charged. It cost $43 plus tax and it provides 4.5 watts. Since 1 horsepower equals 746 watts, you could get the equivalent power of a GE AC4400 (4400 horsepower) locomotive using 3.2 million of the chargers I just mentioned. If it takes three locomotives to pull a train, that's 9.8 million battery chargers. Times $44 each and that's $433 million. And your train stops when the sun goes behind a cloud.

Also, you'd need huge wires up and down the train and they would be heavy, so more weight, more failures, lots of problems--but all solvable.

But the point is, solar cells are far from cost effective--they're pretty much useless when you need any kind of real power. Keep thinking.

hrench,trains are made of metal.but i'm talking about making NEW TRAINS putting people to work in the USA!

by the way you know trains use a generator to power the electric drive system!replace the gen with solar & batterys, your done! AND NO BIG WIRES, RAIL IS GROUND AND COUPLER IS HOT ,some enginer!

Greensleep, I'm one of the few engineers that has designed big wires to go down trains--for the purpose of EABS--electronic train brakes.

http://findarticles.com/p/articles/mi_m1215/is_n3_v199/ai_20460338

If you make the earth the return, the couplers would all have to be isolated electrically from the train. That would be nearly impossible, since really only steel will carry these loads efficiently. Also, the outsides of the couplers would need to be really well insulated to protect people from dying. When we did EABS, we started with 48V and discovered that we really needed higher--in the end we used 240VDC (yes, direct) to get the power down the train without loss (it's a mile!) Isolated from ground (two wires) because we can't rely on conduction between the couplers (they bounce) or the wheels to ground when the stopping of the train is at stake.

Yes, I Am an engineer, but I don't know everything. "The problem with the world is that fools are cocksure and the intelligent are full of doubt." -Russell.

One way you could use solar power on a train would be to install a motor on the wheels of the individual cars and use the power from the PV cells on the car to power itself. There would be no need to transmit power from car to car. Of course, this would not supply enough power to move the train at a satisfactory speed, but it would reduce the amount of power needed from the locomotive and could thereby save fuel. This wouldn't be cost effective right now, but maybe someday...

hrench, have you considered reverse centrifical (clutch)brakes.Using low voltage you could hold shoes away from drum with solinoids,releasing them for momentum friction braking.?

greensleep, the railroads are very pleased with air-actuated brakes, so whatever I would propose to change would never be realized. The article I referenced discusses that we were controlling the air brakes with an electronic signal and a set of very tiny 1-watt solenoids on each car (the solenoids ran larger valves). Each car had a computer and a battery and a way to talk to the main computer, but the brakes still had a 'trainline' of air pressure. This change may make it to the real-world some day, but the airbrake companies bought us and killed it in the 90's when I was working on it. Decreased stopping distances (1/3 less), less wear, cheaper car-equipment, but air brake companies have simpler equipment and a legacy to sell $3000 of equipment per car. They don't want cheaper.

With air brakes, on a train, if cars ever get separated, the pressure is lost and it causes the emergency brakes to apply to the whole train automatically. It prevents that runaway-train scenario that you see on the movies.

Most train cars have no brake drums or disks, the shoes act directly on the running surface of the wheels. Semi trucks use the reverse-brake principle you discuss, but they apply the brakes with springs and release them with air. The air set-up on traincars equates to a reverse-brake setup--if no pressure on the line, the brakes are applied--if pressure, no brakes applied, but the brakes are actually applied with air stored on each car. Many tons of force.

Self actuating drum-brakes have been well understood for a long time--my horse trailer has them-plus, a small solenoid makes a shoe drag which applies the brakes. But they use more than a few watts. I'm not sure if that's what you mean by 'reverse centrifugal' but that's my guess.

BTW, I don't mean to be pedagogical--I just figure this is a subject most people don't know so-much about. Maybe you already know much about this.

It would help but the real challenge is to create efficient and inexpensive solar cells that can power more than a radio.

A freight train might have three 4400 HP locomotives as the motive power. That's 10 MW. At 10 watts per square foot, that's 1,000,000 square feet. If the train is 10 feet wide, you'd need 19 miles of linear solar panels to generate those 10 MW.

You'd be better off simply electrifying the freight rail right-of-way and having it powered by a solar-thermal power plant.