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“ Electric (specifically grid-connected) trains also suddenly make a bit more sense.” On a first glance it would appear so, but it a terrible idea in practice.

by shsbsi 6y ago

“ Electric (specifically grid-connected) trains also suddenly make a bit more sense.” On a first glance it would appear so, but it a terrible idea in practice. At least for freight. Commuter trains are often electric (15 Hz? I forget), mostly for local air quality problems. Train engines are incredibly efficient. Only the largest marine engines are better. These engines are large enough that they approach the thermal efficiency of the thermal plant producing electricity. So no real gains for CO2 emissions. (Wind and solar don’t count at a first approx. since we’re talking about marginal E use. The train not connected on to the grid frees up production at a thermal plant to lower its production) But you also loose a lot of resiliency. In extremis, a diesel Trains don’t need anything to run. In case of an ice storm you have to rebuild big infrastructure. Train can help you transport that if they’re independent.

amluto 6y ago
Electric commuter trains have other major benefits. They stop and start frequently, and electric train sets can accelerate and decelerate faster than diesel. On the upcoming electric Caltrain, this will save quite a bit of time for long commutes. I believe that many electric trains can also regenerative brake. They can operate safely in long tunnels, unlike diesel. I suspect that diesel locomotives are considerably less efficient under the varying load conditions of a commuter train than they are for long freight routes. And, as far as I know, all major high speed trains are electric.
- donarb 6y ago
  > electric train sets can accelerate and decelerate faster than diesel All locomotives use electric motors for traction. Diesel locomotives have a motor that turns a generator to produce electricity for the traction motors on the wheels. A diesel locomotive can stop and start just as fast as a fully electric locomotive, but commuter trains are relatively lighter than freight trains. Diesel locomotives can also use regenerative braking.
  - amluto 6y ago
    > A diesel locomotive can stop and start just as fast as a fully electric locomotive, The Caltrain electrification plan respectfully disagrees. I am not remotely an expert, but I would guess there are two major factors at play. First, a lot of commuter electric trains are multiple units and have no locomotive. This means that more of the wheels can supply traction, which presumably increases the traction-to-weight ratio of the whole train set. Secondly, I think that efficient diesel generators tend to be most efficient at a specific output power, whereas a commuter train runs over a wide range of output powers. A grid-powered electric train set can briefly draw several MW from the grid without a major loss of efficiency.
    - Symbiote 6y ago
      To make a third factor a bit more explicit: there's a limit to the power you can apply to a wheel before it slips on the rail. Having more powered wheelsets means the total possible power is increased. Commuter trains usually use multiple units, and metro trains always do -- they start and stop often, so the improved acceleration is a benefit. Long distance trains can be multiple units, or a single locomotive: the time saving is less useful on a train that stops infrequently, so lower capital + maintenance costs win (plus passenger comfort, it's quieter inside).
willyt 6y ago
Electric locomotives on freight trains are pretty common in Europe probably because they can have a much higher power output in a smaller unit. A pair of TGV power cars, one at each end of the train, has a max power of 12MW at full acceleration, you would need about 14 of these diesel locos for the same output. The power here is 25kV at 50Hz apart from some commuter lines. Also modern electric trains can use regenerative braking to dump the braking energy back into the grid. It’s pretty common.
- gpvos 6y ago
  14 diesel locs for one TGV trainset; nice way of showing how energy-guzzling high speed trains are compared to classic trains. It's still better than an airplane, but not by that much.
  - owenversteeg 6y ago
    Actually it is a heck of a lot better than an airplane. 14 diesel locomotives sounds like a lot, but that is absolute maximum power, and a TGV carries a ton of people. On routes where they are very inefficient (London-Paris as an example), you're looking at around 10 times more emissions by plane (plane 122kg vs high speed train 11kg.) On routes where they are efficient, you're looking at more around 100x more emissions by plane (65kg Paris to Lyon by plane vs 0.7kg by TGV.) Data here: https://ressources.data.sncf.com/explore/dataset/emission-co2-tgv/table/?sort=-tgv_empreinte_co2e_kgco2e_voyageur https://ressources.data.sncf.com/explore/dataset/emission-co... You'll notice that you can cross the whole of France, 1001km Lille-Marseille, for just about 1.6 kilograms CO2 per person per trip. Try that in a plane!
  - willyt 6y ago
    Right but its pulling 12MW to accelerate you to 200MPH in a reasonable amount of time, it's not sitting at full power for the whole trip. I think they are capable of >300mph if you open it up to full power and see what happens. Also I got the number wrong a TGV duplex transports about 500 people with a max power of 8MW. A Eurostar is 750 people with max power of 12MW.

by shsbsi 6y ago

amluto 6y ago

Electric commuter trains have other major benefits. They stop and start frequently, and electric train sets can accelerate and decelerate faster than diesel. On the upcoming electric Caltrain, this will save quite a bit of time for long commutes. I believe that many electric trains can also regenerative brake. They can operate safely in long tunnels, unlike diesel. I suspect that diesel locomotives are considerably less efficient under the varying load conditions of a commuter train than they are for long freight routes. And, as far as I know, all major high speed trains are electric.

donarb 6y ago
> electric train sets can accelerate and decelerate faster than diesel All locomotives use electric motors for traction. Diesel locomotives have a motor that turns a generator to produce electricity for the traction motors on the wheels. A diesel locomotive can stop and start just as fast as a fully electric locomotive, but commuter trains are relatively lighter than freight trains. Diesel locomotives can also use regenerative braking.
- amluto 6y ago
  > A diesel locomotive can stop and start just as fast as a fully electric locomotive, The Caltrain electrification plan respectfully disagrees. I am not remotely an expert, but I would guess there are two major factors at play. First, a lot of commuter electric trains are multiple units and have no locomotive. This means that more of the wheels can supply traction, which presumably increases the traction-to-weight ratio of the whole train set. Secondly, I think that efficient diesel generators tend to be most efficient at a specific output power, whereas a commuter train runs over a wide range of output powers. A grid-powered electric train set can briefly draw several MW from the grid without a major loss of efficiency.
  - Symbiote 6y ago
    To make a third factor a bit more explicit: there's a limit to the power you can apply to a wheel before it slips on the rail. Having more powered wheelsets means the total possible power is increased. Commuter trains usually use multiple units, and metro trains always do -- they start and stop often, so the improved acceleration is a benefit. Long distance trains can be multiple units, or a single locomotive: the time saving is less useful on a train that stops infrequently, so lower capital + maintenance costs win (plus passenger comfort, it's quieter inside).

willyt 6y ago

Electric locomotives on freight trains are pretty common in Europe probably because they can have a much higher power output in a smaller unit. A pair of TGV power cars, one at each end of the train, has a max power of 12MW at full acceleration, you would need about 14 of these diesel locos for the same output. The power here is 25kV at 50Hz apart from some commuter lines. Also modern electric trains can use regenerative braking to dump the braking energy back into the grid. It’s pretty common.

gpvos 6y ago
14 diesel locs for one TGV trainset; nice way of showing how energy-guzzling high speed trains are compared to classic trains. It's still better than an airplane, but not by that much.
- owenversteeg 6y ago
  Actually it is a heck of a lot better than an airplane. 14 diesel locomotives sounds like a lot, but that is absolute maximum power, and a TGV carries a ton of people. On routes where they are very inefficient (London-Paris as an example), you're looking at around 10 times more emissions by plane (plane 122kg vs high speed train 11kg.) On routes where they are efficient, you're looking at more around 100x more emissions by plane (65kg Paris to Lyon by plane vs 0.7kg by TGV.) Data here: https://ressources.data.sncf.com/explore/dataset/emission-co2-tgv/table/?sort=-tgv_empreinte_co2e_kgco2e_voyageur https://ressources.data.sncf.com/explore/dataset/emission-co... You'll notice that you can cross the whole of France, 1001km Lille-Marseille, for just about 1.6 kilograms CO2 per person per trip. Try that in a plane!
- willyt 6y ago
  Right but its pulling 12MW to accelerate you to 200MPH in a reasonable amount of time, it's not sitting at full power for the whole trip. I think they are capable of >300mph if you open it up to full power and see what happens. Also I got the number wrong a TGV duplex transports about 500 people with a max power of 8MW. A Eurostar is 750 people with max power of 12MW.