5 ms·
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 mete
by ggreer 11y ago
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 http://en.wikipedia.org/wiki/Bombardier_BiLevel_Coach
2. http://en.wikipedia.org/wiki/MPI_MPXpress http://en.wikipedia.org/wiki/MPI_MPXpress
3. http://www.wolframalpha.com/input/?i=26m+*+3m+*+7+*+1kW%2Fm%5E2+*+sin%2837%C2%BA%29+*+0.19 http://www.wolframalpha.com/input/?i=26m+*+3m+*+7+*+1kW%2Fm%...
- jpatokal 11y agoWhile 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 https://bikeeastbay.org/rail/fra.html. A modern EMU is much lighter and consequently needs a lot less power.
- codecamper 11y agoYes, 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.
- TeMPOraL 11y agoI 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.
- TeMPOraL 11y agoThanks for doing the math. The results are what I expected them to be, but it's cool to know the approximate number :).
- ggreer 11y agoNext 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.