Is electric powered transpo the answer? 2

[Dinosaur]

I have read many things here where folks appear to think highly of electrical transportation. I don't think much of it because the energy needed is much higher than traditional solutions. On another thread, it was reported that only 15-20% of the input energy at an electrical power plant was used at the final destination (e.g. the fuel content at the electrical plant contained 5 to 6.7 times the energy used in the home). This is because they are unable to capture all the energy in the fuel, there are productiion losses such as friction in the generators and turbines, and there are transmission losses. I do not know what the ratio is for petroleum IC engines, but I am under the impression it is much better than this. Are there any automotive engineers here that can provide some comparisons? Thanks.

 

[LCruiser]

There's no way to tell right now. If fusion becomes viable, electrically powered cars become viable. If CO2 turns out not to be a problem and the scammers are overruled, gasoline (rather probably diesel) made from coal will keep us going for centuries.

 

[moltenmetal]

At least with electric transport (hopefully mostly trains with SOME cars) there is a HOPE of using renewable energy sources to supply them. The special needs of transportation (ie. lightweight, high energy density storage or a distribution grid usable by the vehicle while travelling) make the direct use of renewables as fuels very difficult. So what you get are over-hyped pseudo-alternatives like corn ethanol and canola biodiesel- taking food and turning it into fuel.

There's not enough agricultural biomass generated on earth, forgetting about our food needs, to eliminate our dependance on fossil fuels at CURRENT levels of consumption.

That we haven't maximized the use of renewables for our stationary energy requirements yet is a direct result of the economics being skewed toward processes which dump stuff for free into the atmosphere (ie. coal). Until wind costs LESS than burning coal, there's no incentive to do anything else other than to burn coal, so that's what we will do.

 

[LCruiser]

Of course another way to look at "dumping stuff for free" into the atmosphere is that we are increasing the potential biomass in the biosphere by increasing the level of CO2 in the atmosphere, as CO2 is the base of the food chain.

It could be, once we know more about the carbon cycle and climate change feedbacks, that emission of CO2 is a positive thing, increasing the food supply - especially for third world countries.

 

[moltenmetal]

It ain't called the greenhouse effect for nothin'- ask anyone who runs a greenhouse what kind of increased agricultural production you can get out of doubling CO2...

 

[zdas04]

I don't know anyone who runs a greenhouse, could you enlighten us?

David

 

[SomptingGuy]

I don't get the joke .. if there is one.

Big glass shed full of (possibly legal) plants.

- Steve

 

[KENAT]

As others have previously posted, with the current technology it's probably easier to have stationary power (electrical) generation that's either 'green' or at least free of imported oil (or whatever your justification for changing the status quo is) than to put it straight into personal transport.

Potentially this could then free up natural gas from being used in stationary power which can relatively easily be used in existing car technology etc.

Of course, we've gone and spent the money & effort on those gas power stations and aren't going to stop using them anytime soon(even if we could build alternative sources quick enough), probably not before their natural end of life in a few decades, due to the investment made.

By the time we could stop using it for stationary power natural gas will probably be in a similar boat to what oil is currently, so you're back to square one.

Maybe we've already missed the boat for this line of thought.

KENAT, probably the least qualified checker you'll ever meet...

 

[btrueblood]

Some numbers awhile back bugged me a bit... the quote from the OP is ~ "15-20% of the input energy at an electrical power plant was used at the final destination".

Ok. But, then:

"figure 33% of the fuel energy can end up as mechanical energy at the flywheel for a 4cyl Honda"

Hmm. Both statements are apparently true. But I think the comparison is unfair. The electrical efficiency assumes all losses incurred (conversion, transmission, re-conversion to useful work), essentially an end-to-end efficiency. The automotive engine gets 33% (arguable, but maybe possible with today's turbocharged, multi-valve motors) only at its best operating point, which is essentially near-redline with near-wide-open-throttle. Since that is not how most of those Hondas are operated, the efficiency of the engine is significantly lower in actual driving use due to operation at part-load, part-throttle "cruise" conditions (maybe more like 20-25%? But I'd bet a bit less than that even). Also, to be fair, the auto example should add in conversion losses thru the drivetrain, reducing the figure to something closer to 15-20% for an overall efficiency. These are just WAG numbers, obviously, since actual drive cycles could (and do) cause a lot of variation in the average efficiency of the vehicle.

It's always bothered me that fuel-burning locomotives actually run the engine to generate electricity, which is then applied to the electric traction motors to move the train... But it's obvious when you think about it, a DC motor can provide ample torque at zero speed, while a diesel engine would have to have a relatively inefficient torque converter with gobs of slip to allow it to move the train from a dead stop. But why lug the weight and fuel around for the diesel? Was told long ago that weight for a locomotive is beneficial, since it provides traction... but that arguement does not hold for passenger rail systems where all cars have drive wheels, or are so light that high traction force from the loco is not required. I think the real answer is that diesel used to be really, really cheap. So, no point in installing expensive overhead power lines for cross-country travel.

If electrical power is locally generated, through a distributed network of small powerplants (of whatever ilk), are transmission losses across the grid consequently reduced? Does that argue in favor of wind/solar/small hydro/farm methane etc. etc. generation?

Hmmm.

 

[KENAT]

btrue, I was thinking similar a while back about the distributed power for an electrified train line.

I saw an article in Popular Mechanics or Popular Science about high speed rail. One possible route was LA to Las Vegas.

I was thinking that if they set up solar power plants and wind turbines along the line (seeing as it's in the desert and pretty windy at least in parts) that would cut down transmission losses etc as well as being nice & green.

Another issue in why diesal electric not electric, what are the costs in electrifying a line & the transmission losses if far from the power plants? Some of the lines out my way in the desert are pretty remote and very long.

KENAT, probably the least qualified checker you'll ever meet...

 

[cranky108]

The quote from above about vehicles and MW load:
"vehicles on the road represent something like a 1,200,000 MW load--does anyone think that we have anything like that much spare generating capacity or the werewithal to build it?"
Question: how many of these are operating at one time? I know mine is turned off for more than 22 hours a day. Also a good deal of time it is just keeping it self going as I wait at a stop light. It really dosen't generate all that much power, except on vacations.

 

[LCruiser]

The power required to keep a car or train moving is mostly fighting wind resistance. There is additional power required to do the work of climbing hills, but mostly it's the wind resistance. The additional work required to lift a heavy locomotive vs. a light locomotive is negligible compared to lifting the entire train itself. So it doesn't matter if you're carrying a lot of fuel around. The line losses in overhead power lines, in addition to their construction and maintenance, costs more for overland travel.

They are used in urban commuter rail.

Running off an electric motor has an advantage in that the diesel can be run at optimum efficiency, which more than offsets the little additional weight of the motor compared to the train.

What I think they should do is every rail car have a battery bank so when the train's going downhill it stores up the energy from braking...

 

[KENAT]

LCruiser, that brings up a good point.

I understand that Electric/Diesal electric use the motors for breaking, i.e. turn them into generators to load the wheels. However, based on a show I saw the other day I got the impression that this energy is then dissapated as heat (at least by diesal electric) rather than stored/used/returned to the track.

Does anyone know anything about this? First is my understanding correct and secondly the resoning etc, I can guess part of the reasons at least historically have been financial but I wonder what technical aspects there are?

KENAT, probably the least qualified checker you'll ever meet...

 

[moltenmetal]

The experiment's been done, folks. Google a bit and you'll see the results. Double the CO2 and you get a 15-20% increased yield of crop fruits/seeds with a decrease in the average nutritive content thereof.

You also get an increased yield of weeds.

What you get in natural ecosystems when you do this on what amounts to an evolutionary blink of the eye is unknown.

What IS known is that biomass yield nowhere nearly doubles with doubling atmospheric CO2 as implied in a previous post (as a wishful thought I guess). The carbon cycle is complex but it's clear that CO2 in the atmosphere versus plants on the land and in the seas represents nowhere nearly a self-regulating system- certainly not on a timescale of human significance.

And unlike global warming itself, where the complexity of climate models leads lots of people to deny the risk, nobody is denying that we're headed toward doubling our atmospheric carbon dioxide concentration, nor that we humans are responsible for this change.

 

[RossABQ]

Trains have a ironic twist compared to cars; the locomotive HAS to be heavy, as tractive force is a function of weight. There is absolutely no incentive to design a lightweight loco. I took a Railroad Engineering course as my senior elective and it was a fascinating course. Winds affect trains more than you'd think, the worst situation is a quartering wind: it pushes the flanges of the wheels against the far side rail, greatly increasing friction.

PS -- the perenial winner of the "lowest utilization award" for machinery is the automobile. As noted, not used anywhere near capacity. The index is meant to track production tool utilization, but vehicles are considered a capital tool.

 

[KENAT]

Ross, I saw something on high speed trains recently where it seemed mass was an issue, presumably due to acceleration demands (I can't recall), and so they made efforts to reduce their mass.

KENAT, probably the least qualified checker you'll ever meet...

 

[RossABQ]

If you are talking about self-propelled (train) cars, where each car has its own motive power (typical of some light rails), weight might be an issue. Chicago's EL trains are each self-powered this way, allows for more flexibility (adding cars).

 

[KENAT]

I think what I was looking at was about the TGV & 'Bullet' train etc.

KENAT, probably the least qualified checker you'll ever meet...

 

[LCruiser]

High speed trains are people movers. I think we've been talking about freight trains.

 

[Xtal2012]

Diesel-electric locomotives dissipate braking energy as heat because there's no easy way to store it. There are many possible storage methods such as batteries, supercapacitors, flywheels, thermal storage using molten salt, etc., but given the relatively low cost of diesel it's much easier and cheaper at the moment to simply dump the heat as waste.

If locomotives ran on hydrogen it would be possible to use the waste electricity from braking to generate hydrogen and oxygen from the electrolysis of water, which could be used as fuel later.

Fully electric trains (relying on remotely transmitted power) can and do contribute their braking energy back to the 'grid'.

It's my opinion that an immediate policy shift towards electrified rail could save the US a lot of grief in the coming decades.

 

[moltenmetal]

You can make a train more efficient by supplying the loco with electricity so it can do regenerative braking back to the grid.

That said, diesel is still so cheap that an enormous fraction of North American freight is moved by truck rather than by train. Hell, the city of Toronto currently TRUCKS its garbage to a landfill in Michigan, since there's no direct rail link- oh yeah, and because the roads are funded through public taxes whereas the railroads have to maintain their own rails...