How Efficient is Steam?

[76020]

Does anybody know how efficient steam power is as regards to Diesel and Electric?

We are told that an 25KV Electric train running costs are just under 50% of a Diesel train, also an Electric train running on 25KV costs 20% less than an electric train running on 750V 3rd rail, so how does 25KV versus steam line up?

 

[gordonthemoron]

does it not depend on whether the steam is being used to run a steam loco or generating electricty to run electric trains?

 

[455driver]

As the rest of his post has "train" in it a few times it doesnt take a genius to work it out does it! :roll:

I think steam LOCOs are between 7 and 15% efficient (and very labour intensive), a diesel electric loco is about 80% and a straight electric loco 95% on pure fuel in to power out measures.

25KV overhead is a very efficient way of power distibution and needs a substation every 50-75 miles (more where there are lots of trains running).
I think that is right, its been ages since I looked into this.

750V DC is very inefficient and needs a substation every 3 miles (again more where there are lots of trains running).

 

[Spaceflower]

As the rest of his post has "train" in it a few times it doesnt take a genius to work it out does it! :roll:

I think steam LOCOs are between 7 and 15% efficient (and very labour intensive), a diesel electric loco is about 80% and a straight electric loco 95% on pure fuel in to power out measures.

25KV overhead is a very efficient way of power distibution and needs a substation every 50-75 miles (more where there are lots of trains running).
I think that is right, its been ages since I looked into this.

750V DC is very inefficient and needs a substation every 3 miles (again more where there are lots of trains running).

95%? That's awfully efficient. Are you sure?

 

[starrymarkb]

Why not have both as in this infamous picture

[Alt Text - Image shows a Swiss Tank Engine with Pantograph for immersion heating]

 

[455driver]

95%? That's awfully efficient. Are you sure?

On pure "fuel in" (ie electricity) to "power out" (traction power plus all the other electrical load) it is over 90% with the rest dissipated as heat (I am 99% certain of that ), its been ages since I looked into this stuff though so it could be a load of rubbish but these figures are in my head from somewhere, of course if you start using the efficiency loses of the transmission system it all gets skewed all over the place and you can make the statistics say what you want.
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Why not have both as in this infamous picture

[Alt Text - Image shows a Swiss Tank Engine with Pantograph for immersion heating]

That thing doesnt count!

 

[Yew]

Your figures do not include the efficiency of the prime mover, and the electricity generator.

 

[Spaceflower]

For electrically powered trains, one should not only consider the efficiency of the electric motors on the train, but the energy loss in transmitting the electric energy from the power plant to the train. Of course, the efficiency of the power plant in converting fossil fuel energy into electricity must be counted too.

So what are typical values for such efficiency? It turns out that for both trains and autos this efficiency is roughly 30% under the best conditions. This is also the case for electric trains. Thus if thermal efficiency is roughly the same, the comparison of vehicle resistance will give a good indication of the fuel consumption of different vehicles (under the best conditions).

A quick web search found this. I'm not sure of its authenticity, but would guess it to be closer to the mark than the 95% earlier quoted.

 

[HSTEd]

CCGT and CWS fueled low speed diesels have obtained electrical efficiency above 50% and are approaching 60% in some cases.

Even once you account for resistive losses you have a good chance of beating 40% overall end to end.
And you don't have to worry about carrying whatever fuel it uses around.

 

[Lee_Again]

And let's not forget that electric trains are lighter which means quicker acceleration and reduced maintenance costs. So it's not just the efficiency of the power, there's other stuff to take in to account.

I should imagine that solar powered trains (in the future) would be the most efficient but they'd likely weigh the same as a small mountain.

So..

Steam=heavy, labour intensive, not instant (no on switch!!)

Diesel = heavy, expensive to fuel (but can go anywhere), switch on ability

electric = light, cheap (but only if there's power), switch on ability
AC = excellent at long distance transmission, expensive to put up
DC=huge power loss over short distances, cheap to install

 

[Spaceflower]

And electric trains can take advantage of multiple sources of power generation, including renewables.

A solar powered train? Don't we suffer from enough weather related disruption?

 

[Lee_Again]

A solar powered train? Don't we suffer from enough weather related disruption?

"...due to the wrong kind of Sun."

Solar Power very unlikely but just iidle speculation about the most efficient power source and adding to the debate that efficiency of power supply is not the only factor. I wouldn't be surprised if coal, diesel and elctricity were all about the same once you factored in all parts of the supply chain. It's largely coal that supplies the electricy afterall.

 

[HSTEd]

Mostly its natural gas that supplies the "juice" these days.

And hopefully, if the madness abates, it will be uranium.

 

[455driver]

A quick web search found this.

For electrically powered trains, one should not only consider the efficiency of the electric motors on the train, but the energy loss in transmitting the electric energy from the power plant to the train. Of course, the efficiency of the power plant in converting fossil fuel energy into electricity must be counted too.

So what are typical values for such efficiency? It turns out that for both trains and autos this efficiency is roughly 30% under the best conditions. This is also the case for electric trains. Thus if thermal efficiency is roughly the same, the comparison of vehicle resistance will give a good indication of the fuel consumption of different vehicles (under the best conditions).
I'm not sure of its authenticity, but would guess it to be closer to the mark than the 95% earlier quoted.

Do you want to include mining the coal and transporting it, do you want to include sucking up the crude oil, refining it and transporting it?

Do you want to include the costs of searching for them in the first place?
How far do you want to go?

 

[Spaceflower]

I don't want to go anywhere at the minute, I'm busy with stuff. However 95% sounds awfully efficient, too efficient to be real in fact.

 

[455driver]

As I put in my post, I was referring to the loco only and couldnt remember exactly what the totals were!

Its a pity you didnt answer the post first with all your knowledge as it would have saved me bothering, oh wait you havent actually answered the OP have you but just argued about my figures! :roll:

 

[Spaceflower]

I was questioning your figures. Any machine with a 95% energy efficiency sounds pretty remarkable. I'd rather not argue over this though, it's not worth it.

Besides, I'm certainly no expert in the field.

 

[route:oxford]

On a single diagram, with regenerative braking, isn't there the possibility that an electric (or battery-hybrid) loco would be more than 100% efficient?

 

[SS4]

On a single diagram, with regenerative braking, isn't there the possibility that an electric (or battery-hybrid) loco would be more than 100% efficient?

No, that would violate the first law of thermodynamics

 

[142056]

You'd never get a loco/train whatever you like to be entirely silent, which means it can't be 100% efficient..you'd at least have energy wasted to sound.

 

[455driver]

I was questioning your figures. Any machine with a 95% energy efficiency sounds pretty remarkable. I'd rather not argue over this though, it's not worth it.

so I am wrong but you cant post any info yourself!

Dont know why I bother sometimes!:roll:

 

[dcsprior]

According to "Encyclopedia of Electrochemical Power Sources" (viewable on google books here) quotes 85% efficiency for the conversion from electric -> kinetic energy (i.e. the bit that happens on the train).

Wikipedia says "Electric locomotives benefit from the high efficiency of electric motors, often above 90%", and although there's no reference to a primary source, its close enough to the 85% I found elsewhere that I find it credible. If they routinely exceed 90%, it would be reasonable to expect that the best were 95% efficient.

 

[bnm]

so I am wrong but you cant post any info yourself!

Dont know why I bother sometimes!:roll:

Having your figures questioned doesn't mean you are wrong. 95% efficiency in any powered motive system is pretty remarkable. Energy will be lost in transmission and to friction, sound and heat in the motor(s).

A figure plucked from the depths of memory with no citation is rightly going to challenged. Particularly when it is one as high as 95%.

 

[Zamracene749]

To sort of help the debate, I trawled the net and dug up this recent letter from Bombardier transportation clarifying the relative environmental merits of diesel and electric freight haulage.
It details comparative efficiencies between diesel and electric locomotives (though sadly not steam), they seem closer than I might have guessed, makes fascinating reading if you are into this sort of thing.

http://www.qca.org.au/files/R-Bombardier-Submission-QRNetworkETSDAAU-1012.pdf

One thing I did notice whilst searching is that locomotive builders seem reluctant to quote energy efficiency for their products online on their web pages, probably due to the differing efficiencies over a range of duties.

Now if only somebody can come up with something for a modern steam locomotive, even tonnes of coal used for a long trip would help....

 

[HSTEd]

Having your figures questioned doesn't mean you are wrong. 95% efficiency in any powered motive system is pretty remarkable. Energy will be lost in transmission and to friction, sound and heat in the motor(s).

A figure plucked from the depths of memory with no citation is rightly going to challenged. Particularly when it is one as high as 95%.

With modern permanent magnet motors starting to appear in traction applications, efficiencies in that part of the chain above 98% start to look reasonable.

Then there is the advances in power semi conductors that will take the efficiency of the electric locomotive over 90% with ease.

We live in interesting times.

 

[theageofthetra]

As far as I know steam is just a power transmission method, its in how that steam is produced that the efficiency factors come in. Although one was probably never officially built a small nuclear reactor powering a steam turbine would have interesting efficiency figures. I can't believe given their huge loading gauge and distances that the Soviets didn't at least consider this.

 

[HSTEd]

As far as I know steam is just a power transmission method, its in how that steam is produced that the efficiency factors come in. Although one was probably never officially built a small nuclear reactor powering a steam turbine would have interesting efficiency figures. I can't believe given their huge loading gauge and distances that the Soviets didn't at least consider this.

They did some time in the 60s.

They then decided electrification was a better deal.

 

[bnm]

With modern permanent magnet motors starting to appear in traction applications, efficiencies in that part of the chain above 98% start to look reasonable.

Then there is the advances in power semi conductors that will take the efficiency of the electric locomotive over 90% with ease.

We live in interesting times.

That's a maybe from pantograph to wheel. But there's also the losses in generation and transmission.

That generation and transmission needs to be factored in when comparing with Diesel and steam locomotives.

 

[HSTEd]

That's a maybe from pantograph to wheel. But there's also the losses in generation and transmission.

That generation and transmission needs to be factored in when comparing with Diesel and steam locomotives.

Typical losses from the 132kV/400kV circuit to the pantograph are ~10% at most.
Losses on the supergrid are effectively negligible.

Which puts us at somewhere at 80% from power plant to wheel.
Large hydrogen cooled turbo-generator sets are capable of efficiencies approaching 99%.

So its about 80% from the turbine in the power plant to the wheel.

Once you account for the regenerative braking saving of ~20% for comparison purposes with diesel you end up having effectively similar losses between the power plant turbine and the engine crankshaft in a diesel plant.

And large turbines in power plants are far better at producing mechanical energy than modern medium and high speed diesel engines.

 

[12CSVT]

Why not have both as in this infamous picture

[Alt Text - Image shows a Swiss Tank Engine with Pantograph for immersion heating]

You could call that an electric kettle