Caltrain is in the process of adopting electric trains.

http://www.caltrain.com/projectsplans/CaltrainModernization....

You obviously haven't ridden it recently because signs are posted up at the major stations about it.

That's great to hear! I haven't ridden it in years, you are right. Back then they made a survey on how much it would cost & the price tag was something ludicrous. Hundreds of millions or maybe a billion? I dunno. That was when I formulated the idea that this is lame. Much poorer countries manage electric trains. etc etc. Good to hear they are making the switch.

A local branch line (UK) has been testing battery powered trains this year, to save the expensive of electrifying the line. They charge the batteries on the electrified main line. Hopefully this will take off on other branch lines.

I wonder how much % of its electricity consumption a sunny-californian train could generate if one were to tile its roof with PV panels.

My intuition tells me it wouldn't even be close, but let's do the math since it's pretty straightforward.

Caltrain uses cars that are 26 meters long and 3 meters wide[1]. That's 78m^2 of area to catch sunlight. The largest trains have 6 passenger cars and one locomotive. Let's cover all 7 in solar cells, giving 532m^2 of sunlight. At noon on the equator, approximately 1kW/m^2 of energy hits the earth. The bay area is around 37ºN latitude. sin(37º) ≈ 0.6x the energy per unit area. While 600 watts per square meter sounds like a lot of power, we must also account for solar panel efficiency. The best commercially-feasible panels are around 19% efficient. That gives us 114 watts per square meter. Multiply by the total area and we have 60kW of power at noon on a cloudless day. To compare with your car: 60kW is 80 horsepower. The locomotives used by Caltrain put out 3600-4000 horsepower[2].

To sum up: 26m * 3m * 7 * 1kW/m^2 * sin(37º) * 0.19 ≈ 60kW.[3]

On a cloudless day at noon, with no tunnels or shade on the tracks, solar cells could generate 2-3% of the train's needed power. As I thought, not even close.

1. http://en.wikipedia.org/wiki/Bombardier_BiLevel_Coach

2. http://en.wikipedia.org/wiki/MPI_MPXpress

3. http://www.wolframalpha.com/input/?i=26m+*+3m+*+7+*+1kW%2Fm%...

While you're basically correct, there's one point worth correcting: Caltrain locos need to put out 4000 hp because diesel trains built to US standards are ridiculously heavy, see eg. https://bikeeastbay.org/rail/fra.html. A modern EMU is much lighter and consequently needs a lot less power.

Yes, these suggestions of powering cars / trains with the solar panels stuck to their rooftops is ludicrous. I sometimes imagine that these "great ideas" are actually introduced & elaborated by the dirty energy companies to make the clean energy folks look like a bunch of drifting dreamers. Sadly it's probably well meaning people without any sort of science understanding.

I also think it's also well-meaning people without science understanding, or that didn't do the math. Intuition for those things is hard. While the result for this calculation is roughly where I expected it to be, I know that my intuition fails me wrt. houses - I just can't believe, without doing the math, that a typical solar installation people put up is sufficient to actually power a household, with washing machine, fridge and computer equipment.

Thanks for doing the math. The results are what I expected them to be, but it's cool to know the approximate number :).

Next time, please do the math yourself. It only took me a few minutes, and much of that was spent fact-checking.

To me, failing to perform such basic calculations is just as annoying as not reading an article, then asking a question related to its contents.