Why we shouldn't electrify more of the UK

[marko2]

Battery tech is there to enable this already, but scale-ability and manufacturing capacity & cost are not. That will take a while.

Power transfer will be via a 3rd / 4 rail system or via a short OLE section turned on only when activated. This type of system is now common on European tram systems. It also allows very rapid power transfers, quicker and safer than charging cables.

Some power sources will be grid fed, hence locations of OLE where that works best whilst at station stops, battery packs will slow charge & dump the power to a train when it calls.

The issue with a discontinuous electrification scheme where power is delivered at station stops is that a large amount of power needs delivering in a short space of time.
Using the figures above of 3.5kWh / carriage-mile, and assuming 10 miles between stops, and a 4 carriage train, this equates to 140kWh that needs delivering during the station stop - assuming no losses.
If we assume the train is on the juice for 60s, this means we need a power supply that is capable of delivering 8.4MW continuously for 60s at each locations. This is fairly similar to the specification for specification for a continuous OHLE systems on a high-speed line. Remember that services 12-car trains rather than four.

This poses a whole bunch of engineering problems:
* How to get a suitable power supply to each station - we're probably looking at 50kV feeder. I suspect installing these would not be substantially cheaper than installing continuous OHLE
* The load is discontinuous, single-phase. How are the phases balanced?
* Intercity trains don't stop at every station and are longer.
* The drives in all of these systems are not perfectly efficient, and neither are batteries. All non-useful energy goes as heat. Even if the battery charger is 99% efficient, that leaves 84kW of heat to get rid of

DC rails are out for this application unless you fancy a conductor rail delivering 14kA at 600V and a rectification station to supply it (hint: 3rd rail territory has similar arrangements - and a still needs a 50kV feeder network between them).

There is clearly a milage in discontinuous electrification schemes for short formation, lightweight and low-speed services with large amounts of regenerative braking, or for very short sections of discontinuous electrification on majority electrified lines. The idea as described above suffers from being both impractical, and expensive.

 

[marko2]

The most efficient diesel engines can now (once warmed up and in perfect conditions) can convert ~40% of the fuel energy into power.
Once you include losses in the power train, production and transportation energy the well to power output to wheel is actually about 15% efficient.
Unfortunately, braking energy is wasted and much time is spend idling so the full well to rail / road efficiency is only about 5%

With electric cars / trains using regen power via OLE or batteries efficiency is around 90%.
Losses on the Power Station to vehicle are around 25% (source to power station is tiny now most is gas / renewable)
So the total efficiency from energy source to rail / road efficiency is about 70%

I understand that with today's grid mix an electric vehicle / train emits around 20% of the gases of a diesel powered vehicle

Don't forget that if comparing a diesel engine to electricity generated by a gas-powered power stations, Carnot's Theorem tells us that the maximum thermal efficiency of any heat engine is about ~67% - A practical gas turbine comes in at ~60%.

[https://www.bloomberg.com/news/arti...-dirt-on-clean-electric-cars?srnd=hyperdrive) has some interesting things to say about the whole life CO2 output of electric vehicles.

 

[Pigeon]

The way to do battery electrification is to not bother trying to recharge them in real time. Instead you simply swap either discharged battery packs (eg. with a large forklift), or complete locomotives (probably easier), for fully charged ones, and refill the empties at leisure. In a country the size of Britain, most runs are short enough that you can get all the way between one endpoint/reversal point and the next on one charge, ending up at an existing natural break/delay point which you can use to do the swap.

This has advantages beyond simply avoiding the difficulty of fast recharging, because the steady load of a bunch of chargers is easier to provide for than the rapidly-varying load with step changes of several megawatts that direct traction supply constitutes. It is also well suited to participation in load management schemes to ease the task of operating the grid, whereas direct traction supply has to be completely excluded from such schemes.

(Swapping of standardised battery packs is also how electric cars ought to be done, and would be if electric cars were not merely yet another instrument for channelling money to people who are already more than rich enough not to need it with a transport function tacked on the side to be touted as the primary reason for their existence and so provide an excuse. Let us not allow the bad design decisions taken in one area to blind us to the possibility of doing things better in the rail area.)

The most efficient diesel engines can now (once warmed up and in perfect conditions) can convert ~40% of the fuel energy into power.
Once you include losses in the power train, production and transportation energy the well to power output to wheel is actually about 15% efficient.
Unfortunately, braking energy is wasted and much time is spend idling so the full well to rail / road efficiency is only about 5%

With electric cars / trains using regen power via OLE or batteries efficiency is around 90%.
Losses on the Power Station to vehicle are around 25% (source to power station is tiny now most is gas / renewable)
So the total efficiency from energy source to rail / road efficiency is about 70%

I understand that with today's grid mix an electric vehicle / train emits around 20% of the gases of a diesel powered vehicle

40% for a train-sized diesel is about right (the "most efficient" ones get over 50%), but most of those figures are wrong, or at best dubious, so the real difference is a lot closer. The most glaring error is the complete omission of any figure for the efficiency of the generating plant, which is also somewhere in the region of 40% depending on which variety of prime mover it uses. That error being so large, I cba to post chapter and verse on the lesser ones.

 

[Pigeon]

Don't forget that if comparing a diesel engine to electricity generated by a gas-powered power stations, Carnot's Theorem tells us that the maximum thermal efficiency of any heat engine is about ~67% - A practical gas turbine comes in at ~60%.

Carnot's theorem does not put an upper limit on thermal efficiency. You can get arbitrarily close to 100% by making Tin-Tout large enough. The limitations are practical, not theoretical, and derive from things like the limited ability of materials to withstand high temperatures and the inevitability of heat losses.

Gas turbines are not really that impressive for efficiency, but you get a lot of misleading figures chucked around which derive from the assumption that you are using their rather large and high-quality waste heat output to some desirable end, which isn't always possible and isn't always done even where it is.

http://www.bloomberg.com/news/articles/2018-10-16/the-dirt-on-clean-electric-cars

Hopefully that's fixed the link

 

[swaldman]

Don't forget that if comparing a diesel engine to electricity generated by a gas-powered power stations, Carnot's Theorem tells us that the maximum thermal efficiency of any heat engine is about ~67% - A practical gas turbine comes in at ~60%.

[https://www.bloomberg.com/news/arti...-dirt-on-clean-electric-cars?srnd=hyperdrive) has some interesting things to say about the whole life CO2 output of electric vehicles.

To my eye, it says that if the electric car is manufactured and driven in the worst case (an electrical grid powered mostly by low-quality coal), then it reaches breakeven on CO2 emissions after about 3 years.

Given that the lifetime of a car is more than 3 years, that seems like good news to me. And our grid is quite a lot cleaner than the German one, so that breakeven point will come sooner.

 

[marko2]

Carnot's theorem does not put an upper limit on thermal efficiency. You can get arbitrarily close to 100% by making Tin-Tout large enough. The limitations are practical, not theoretical, and derive from things like the limited ability of materials to withstand high temperatures and the inevitability of heat losses.

Gas turbines are not really that impressive for efficiency, but you get a lot of misleading figures chucked around which derive from the assumption that you are using their rather large and high-quality waste heat output to some desirable end, which isn't always possible and isn't always done even where it is.

Indeed - it seems that the name-plate efficiency of state of the art combined-cycle gas turbine plants is 61% - with efficiency measured against electrical output being lower. Given the British public's general distaste for district heating schemes (the obvious application for the waste-heat) and the siting of plants well away from population centres, it's a fair bet that electricity thus derived has an efficiency of 50% at the point of delivery to the rail network (not including losses inherent in OHLE).

 

[reddragon]

Don't forget that if comparing a diesel engine to electricity generated by a gas-powered power stations, Carnot's Theorem tells us that the maximum thermal efficiency of any heat engine is about ~67% - A practical gas turbine comes in at ~60%.

[https://www.bloomberg.com/news/arti...-dirt-on-clean-electric-cars?srnd=hyperdrive) has some interesting things to say about the whole life CO2 output of electric vehicles.

That would be OK if CCGT was our prime power source, when even today in late autumn it only make 40% and far less in the summer.

Our grid is now dominated by Renewables (solar / wind etc) & nuclear and NR has always been contracted to Nuclear historically (not sure about now).

So for today generation losses are 16%, in the summer they were about 8%.

 

[reddragon]

The way to do battery electrification is to not bother trying to recharge them in real time. Instead you simply swap either discharged battery packs (eg. with a large forklift), or complete locomotives (probably easier), for fully charged ones, and refill the empties at leisure. In a country the size of Britain, most runs are short enough that you can get all the way between one endpoint/reversal point and the next on one charge, ending up at an existing natural break/delay point which you can use to do the swap.

This has advantages beyond simply avoiding the difficulty of fast recharging, because the steady load of a bunch of chargers is easier to provide for than the rapidly-varying load with step changes of several megawatts that direct traction supply constitutes. It is also well suited to participation in load management schemes to ease the task of operating the grid, whereas direct traction supply has to be completely excluded from such schemes.

(Swapping of standardised battery packs is also how electric cars ought to be done, and would be if electric cars were not merely yet another instrument for channelling money to people who are already more than rich enough not to need it with a transport function tacked on the side to be touted as the primary reason for their existence and so provide an excuse. Let us not allow the bad design decisions taken in one area to blind us to the possibility of doing things better in the rail area.)
.

The tech is moving fast that this will not be a problem in 5 years

 

[MarkyT]

The tech is moving fast that this will not be a problem in 5 years

Watering points for steam locos typically had to deliver enormous volumes in a very short time during station stops. In order to do this, they had to have large tanks which were replenished from local sources slowly between trains. Similarly, charging points for on board supercapacitors can be equipped with their own large battery bank that can be recharged slowly between trains from normal local mains supplies that could not otherwise be expected to meet the surges on their own. Storage changes everything.

 

[reddragon]

40% for a train-sized diesel is about right (the "most efficient" ones get over 50%), but most of those figures are wrong, or at best dubious, so the real difference is a lot closer. The most glaring error is the complete omission of any figure for the efficiency of the generating plant, which is also somewhere in the region of 40% depending on which variety of prime mover it uses. That error being so large, I cba to post chapter and verse on the lesser ones.

You are looking backwards at the worst possible figures for coal / CCGT etc which is being phased out.

Solar, wind, hydro, Nuclear do not have emission losses. Gas, which is much cleaner than coal / oil has not been practical on trains or cars.

CCGT / coal is today 40% and in the summer was much less as it is on windy days.

To say that generating power via the grid is 40% efficient, same as a diesel engine is utterly ridiculous as otherwise everyone would use diesel generators at home instead of grid power. It typically costs 5 times as much to use a generator with red diesel.

 

[cjmillsnun]

Electrification as it is currently carried out has a bunch of problems...

The overall conversion efficiency from chemical energy of fuel to mechanical output from the wheels is not a lot different whether you use a remote generating plant and transmit the electricity, or a local plant and transmit the fuel. You get some benefit from remote generation using nuclear or renewable sources, but since most of our electricity still does come from fossil fuel (all this crowing about "no coal" days but they never mention that the replacement for all those closed coal power stations was gas ones...) and since railways use only a minor percentage of the fossil fuel used for transport, it's nothing like as much of a benefit as it's made out to be.

There is a huge difference in efficiency. A CCGT (Combined Circuit Gas Turbine) is roughly 62% efficient, transmission losses are not too great because of the National Grid stepping the voltage up. The train (a typical EMU) carries one or two transformers and pantographs (depending on size) as well as a small amount for control circuitry along with the traction motors.

A diesel engine by comparison is 45% efficient maximum (most are roughly 40%), and there are one per car along with fuel tanks and generators and traction motors (using a DEMU as a comparison). So more engines that are less efficient plus carrying more weight and they are more likely to fail.

There are days where our generation is more than 50% low carbon (renewables, biomass and nuclear) and the carbon footprint is much smaller using CCGTs over coal on most days. So whilst the "long tailpipe" is a thing, it is doing far less environmental damage.

 

[swaldman]

There is a huge difference in efficiency. A CCGT (Combined Circuit Gas Turbine) is roughly 62% efficient, transmission losses are not too great because of the National Grid stepping the voltage up. The train (a typical EMU) carries one or two transformers and pantographs (depending on size) as well as a small amount for control circuitry along with the traction motors.

A diesel engine by comparison is 45% efficient maximum (most are roughly 40%), and there are one per car along with fuel tanks and generators and traction motors (using a DEMU as a comparison). So more engines that are less efficient plus carrying more weight and they are more likely to fail.

There are days where our generation is more than 50% low carbon (renewables, biomass and nuclear) and the carbon footprint is much smaller using CCGTs over coal on most days. So whilst the "long tailpipe" is a thing, it is doing far less environmental damage.

Note also that the engines on our train must react to the power demands of our train - whether that be running at full power, or idling, or somewhere in between. The prime movers of grid generation can (usually) be either i) at their most efficient rpm, or ii) off. I suspect that has at least as much influence as grid vs DMU-engine efficiency.

 

[reddragon]

The fundamental problem is that the oil / coal industry heavily promotes 'clean' fossil fuels with massive budgets to save their skin.

You cannot compare the 45% efficiency of the best diesel engine with the whole energy cycle of electricity.

There is the huge & growing energy / pollution cost in finding, exploiting, extracting, refining, transporting and storing oil which gets trillions per year of hidden subsidies.

Then this 45% figure. You can half that immediately as you cannot recover the energy from braking as is done with electricity, then there are the idling wastage's, that gets you down to 15%. Less the production cost = 5% efficiency and that is without the massive pollution / health damage done, lets say diesel is 1% efficient then, lol.

Compare like with like and do not selectively use figures.

 

[Pigeon]

This thread has become pointless to engage with further, as it has become infested with salesmen quoting sales figures, and stuff like this:

You cannot compare the 45% efficiency of the best diesel engine with the whole energy cycle of electricity.

...which I was not doing...

Then this 45% figure. You can half that immediately as you cannot recover the energy from braking as is done with electricity

...statements which are not only wrong, but trivially daft...

Compare like with like and do not selectively use figures.

...and cooking utensils disputing their relative levels of surface carbon contamination.

 

[najaB]

...statements which are not only wrong, but trivially daft.

How does regenerative braking work with a diesel engine?

 

[Pigeon]

About as well as it recovers half the energy from electric operation.

 

[najaB]

About as well as it recovers half the energy from electric operation.

Clearly that was badly worded (and somewhat tongue in cheek), but in metro-style operation it produces a very significant (something like a 30%) reduction in CO2 emission which is what we were discussing. What's the CO2 reduction of regenerative braking for diesel trains?

 

[gsnedders]

Battery trains, with 3rd rail at stations to provide a top-up charge will soon be very feasible.

Has anyone explored live running rail electrification? If the running rails were electrified and the wheels acted as the pickup shoes, it would negate many of the challenges of third rail in icy conditions.

If want want track-level electrification (which the ORR won't allow), we can much more easily solve the icing problems than by creating a new electrification scheme: bottom-contact third rail, as most third rail systems use (albeit not in the UK). (And the cost of converting from top-contact to bottom-contact is comparable with the cost of moving to OHLE, so that's not gonna happen.)

 

[sir_gummerz]

We all know the benefits of electrifying more of the UK but why should we NOT consider electrifying more of the UK?

Discuss.....

hydrogen trains may be coming our way soon. it may be pointless to electrify

 

[Class 170101]

But surely 'burning' hydrogen in a combustion engine on a train is still going to come up against the saqme problems as diesel when compared to 'burning' it in a power station and transmission?

 

[gsnedders]

But surely 'burning' hydrogen in a combustion engine on a train is still going to come up against the saqme problems as diesel when compared to 'burning' it in a power station and transmission?

It's similarly less efficient, yes, but the emissions aren't nearly as much of a concern.

 

[snowball]

But surely 'burning' hydrogen in a combustion engine on a train is still going to come up against the saqme problems as diesel when compared to 'burning' it in a power station and transmission?

The only combustion product is water, so no particulates, no oxides of nitrogen and no contribution to global warming.

At least, none of those things locally, but for the full story you have to consider where the hydrogen came from.

 

[najaB]

but for the full story you have to consider where the hydrogen came from.

Ding! Let's see what you've won. Indeed, burning hydrogen can be completely carbon neutral or it can be dirtier than using coal to generate the electricity directly (due to losses).

 

[xotGD]

There is no point in electrifying a line when over half the services that operate along it are still diesel trains. The ECML north of Doncaster, for example.

 

[GRALISTAIR]

There is no point in electrifying a line when over half the services that operate along it are still diesel trains. The ECML north of Doncaster, for example.

Disgraceful- what could be done to change this? Bimodes will help of course and what about the spur to Middlesbrough would that help?

 

[najaB]

There is no point in electrifying a line when over half the services that operate along it are still diesel trains

I suspect that more than half of trains using a non-electrified line would be diesel...

 

[gallafent]

There is no point in electrifying a line when over half the services that operate along it are still diesel trains. The ECML north of Doncaster, for example.

Doesn't that logic lead to an intractable eggchicken situation (unless of course a programme is put in place through which the lines, and the (vast majority of the) trains, are upgraded to be electric, or bi-mode, at the same time)? … but surely the DfT could never make that happen

 

[gallafent]

I suspect that more than half of trains using a non-electrified line would be diesel...

Succinctly put!

 

[gallafent]

How does regenerative braking work with a diesel engine?

Only possible with a Diesel-Electric transmission of course. Big resistor banks on the roof to dump the load (e.g. Voyagers, Meridians)

 

[Bletchleyite]

Only possible with a Diesel-Electric transmission of course. Big resistor banks on the roof to dump the load (e.g. Voyagers, Meridians)

Or a more environmentally friendly option would be to shove it into batteries either for providing ETH or for traction.