Battery powered train

[watercooled]

That flywheel was just for short uses, as I said for higher-density devices, gyroscopic forces could be a huge barrier to their use considering trains tend to accelerate in more than one plane. It's not unreasonable to assume some super-flywheel capable of powering a train for a decent amount of time would be more than capable of throwing it off the rails as soon as it hits a small dip in the rails.

Of course, it would be theoretically possible to negate such problems with sort of gimbal system, but being able to transfer the energy effectively would pose some challenges. And then it comes back to size/weight/cost.

Even in stationary installations, huge flywheels have to be installed taking into account the Earth's rotation so as to avoid unnecessary friction.

[Gerrard]

Well, flywheels are used in motorsport: -

http://www.williamshybridpower.com/#...cations%2Faudi
http://www.williamshybridpower.com/#...ions%2Fporsche
(it would appear the links don't automatically go to the right part of the page )


Yes, they are considerably smaller and lighter, but would experience more force (again, probably doesn't scale that well compared to the size of the flywheel). However, they are looking at buses, trams and trains but very much from the start/stop point of view rather than trying to power something solely on it.

[wasabi]

Good link - but there are plenty of solutions for short term energy storage. Regenerative braking is only a tiny part of the equation, but one of the big tickboxes car manufacturers are pushing. Because is it relatively easy to solve. The 30 seconds between pulling up at a junction and pulling away is in storage terms, easy.

As Jeremy Clarkson keeps reminding us, range and recharge time on leccy vehicles still sucks.

[badass]

I’d be sceptical about an electric train being more efficient than a diesel one. Sure the actual train might be more efficient but it needs to get its electricity from power stations which are around 45% efficient. Then there’s the efficiency of the electricity transmission, the charging efficiency of the trains battery (~85%) and finally the efficiency of the train’s electric engine (~65%). This would place the efficiency of an electric train at just under 25%. A diesel engine has an efficiency of 25% - 40% and I’d guess a large engine like a train’s would be at the upper end of that. This is a very rough estimate I know but even if I’m off a bit in my estimations and an electric train is more efficient there can’t be much in it. Not enough to justify setting up the infrastructure for electric trains.
People see electric transport as being green because the actual vehicle doesn’t produce fumes. The truth is that they still require burning fuels somewhere, be it in the vehicle or at a power station. In terms of efficiency it’s better to have your energy source close to where it’s being used.

And there was me thinking that electric motors were over 90% efficient over 20 years ago ;-)

[watercooled]

Well there's also that. IIRC it's not unusual to have decent induction motors running at >95% efficiency under certain conditions. Of course there are still going to be some losses in the transmission, but in reality it's likely to be far less than the losses in a diesel system, whether it's mechanical or hydraulic.

[TheAnimus]

I feel as if I'm somehow the flywheel fanboy.... I am not, I am just genuinely curious how the technology pans out! I mean a Tesla or something might be used for a few hours per day, but this thing is going to be in almost continuous daytime use. Does that mean they are aware of the lifespan of the battery and working around it, or have they something more clever planned, I've no idea.

But it will be interesting to see the end article.

[TheAnimus]

Good link - but there are plenty of solutions for short term energy storage. Regenerative braking is only a tiny part of the equation, but one of the big tickboxes car manufacturers are pushing. Because is it relatively easy to solve. The 30 seconds between pulling up at a junction and pulling away is in storage terms, easy.

As Jeremy Clarkson keeps reminding us, range and recharge time on leccy vehicles still sucks.

You make it sound like it's a problem that can't be solved.

Myself renting the battery would be a favourable proposition, because I would know entirely the costs.

[watercooled]

I feel as if I'm somehow the flywheel fanboy....

Sorry if I played a part in that, it wasn't intentional.

I am not, I am just genuinely curious how the technology pans out! I mean a Tesla or something might be used for a few hours per day, but this thing is going to be in almost continuous daytime use. Does that mean they are aware of the lifespan of the battery and working around it, or have they something more clever planned, I've no idea.

But it will be interesting to see the end article.

I agree it would be interesting to see if something like that would work well, it's certainly a different approach. Still, I remain somewhat wary about a flywheel storing enough energy to drive a train considering even my Powerball gets scary if you put some effort into it! I know batteries have the potential to release the stored energy dangerously, but it tends to be more gradual even in catastrophic failure.

Not that I'm completely against the idea if a suitable/practical form of containment could be used of course.

They do seem to be looking into some interesting types of batteries though, like the molten salt. Although, I'm still sceptical about the practicality for anything other than fairly short routes/gaps even for chemical batteries.

[watercooled]

You make it sound like it's a problem that can't be solved.

Myself renting the battery would be a favourable proposition, because I would know entirely the costs.

Battery swapping is certainly a more practical solution, however I'm still sceptical (as usual) about the practicality and environmental impact of huge-scale lithium battery production.

[TheAnimus]

Yup, this is the problem, diesel or petrol has some very useful properties, its easy to convert, good density, there is also infrastructure in place.

However as someone who cycles in London, shifting the pollution someplace other than the road is a great idea. Not too mention it becomes then a larger market for the power storage arms race. Even if the overall energy efficiency is less.

[Funkstar]

I've read a couple of pieces about companies installing banks of flywheel energy storage units along with wind turbines to help even out or delay their power delivery to the grid.

Windy through the night when you don't actually need the power? Spin up the flywheels and save it for the morning power spike instead.

[peterb]

But the original post was about railway rolling stock - not road vehicles.

The mass of a car with 4 people in it is around 1 to 1.5 tonnes. The mass of a modern 450 class train 170 tonnes per unit - for a 4 unit train that is 780 tonnes! The energy required to accelerate that is considerably more than that required to accelerate a car, and although some of that energy could be regained by regenerative braking, the losses will be considerably greater.

Secondly, a train tends to travel relatively long distances between stops, unlike a car which is constantly accelerating and braking, particularly in towns, but also on congested motorways.

The point of the battery train experiment is to look at the feasibility of running electric rolling stock on partially or non electrified lines.

A bit of maths - a 740 tonne train travelling at 80Km/hr has a momentum of mv or 59.2*10^9 Kg/m/s

The momentum of a flywheel is I*w where I is the moment of inertia and w is the angular velocity in radians/second or 2*pi*I in revolutions/second

The moment of inertia for a flat solid disk is .606*m*r^2 where m is the mass and r is the radius. So to make the maths easy, lets assume the flywheel has a radius of 1 metre. The moment of Inertia, I is then m*.606 if we take the flywheel angular rotation to be 60,000 rpm, or 1000 rps or 6200 radians/sec, the mass of the flywheel needs to be about 1.6*10^7 Kg or 1.6*10^4 tonnes. Those are just the momentum figures using the principle of conservation of momentum (and ignoring the linear momentum stored in flywheel)

I'll leave it as an exercise to work out the kinetic energy a the train travelling at that speed has and the mass of an equivalent 1 metre radius flywheel- but you will find that the flywheel with the same kinetic energy needs to be massive, apart from the difficulties of getting that energy in and out of the flywheel.

(I think it is around 2*10^5 tonnes, but given the lateness of the hour, I'm quite willing to concede that I may have made an error or two)

Of course energy is not conserved, so the energy required to accelerate the train to that speed will be even greater.