An Energy Analysis Of Merseyrail’s New Trains
Various factors come into this anaysis and I’ll detail them first.
Merseyrail’s New Trains
- The trains will have regenerative braking.
- The trains will weight in at 99 tonnes.
- The trains will have a capacity of 486 passengers.
- The trains are four cars and 64 metres long.
It should also be noted that the current trains have a maximum speed of 121 kph, although the Northern Line has a maximum speed of 97 kph and the Wirral Line one of 110 kph.
I also suspect that the trains will be pretty good aerodynamically, as most modern trains are. My linked article quotes an energy saving of twenty per cent.
Merseyrail’s tunnels date from the Loop and Link Project of the 1970s, where the three electrified lines coming into Liverpool, were connected together.
- The Loop Line allows trains from the other side of the Mersey to access four stations in Central Liverpool and gave a substantial capacity increase.
- The Link Line joined the Northern suburban lines to Kirkby, Ormskirk and Southport to the Southern suburban line to Hunts Cross.
Currently, the Loop Line is having a major upgrade with slab track and other goodies and if it is not to the same standard, I wouldn’t be surprised to see the Link Line improved as well.
I suspect that when the work is finished, Merseyrail’s tunnels will not offer much resistance to the trains passing through.
If the new trains use regenerative braking with batteries, there is one big advantage in the tunnels.
Some braking energy is stored on the train and used to accelerate the train when needed. So hopefully, the flow of electricity between track and train is reduced, which means less heat generation in the tunnel as the currents flow through to and from the train.
Let’s assume that a train running at line speed in a tunnel has X KwH of kinetic energy. For a stop, this energy must be absorbed by the regenerative brakes and turned into electrical energy. It won’t be 100 % of the energy but I suspect that with modern systems it could be as high as 80%. Batteries are an efficient way to store this energy and I suspect, with the best systems, virtually every KwH you put in the battery can be retrieved later, if the battery is large enough.
Unlike Manchester, Liverpool is not surrounded by hills, so I would expect that most of the lines have fairly gentle gradients.
These are a few altitudes.
- Aintree – 13 m.
- Chester – 32 m.
- Garston – 23 m.
- Hunts Cross – 40 m.
- John Lennon Airport – 24 m.
- Kirkby – 26 m.
- New Brighton – 43 m.
- Ormskirk – 52 m.
- Southport – 6 m.
- West Kirby – 9 m.
These examples, show that the network is not an arduous one. I suspect that the lowest part of the network is in the tunnels under Liverpool. Judging by the escalator lengths, I suspect it could be around thirty metres below ground.
Kinetic Energy Of A Full Train
The mass of a train is 99 tonnes plus say 70 kg for each of 486 passengers.
This gives a mass of 133 tonnes for the fully-loaded train.
Suppose it is travelling at 100 kph.
This gives a kinetic energy of 51.3 MJ.
Or converting that to everyday units we get 14.25 KwH.
As a typical transport battery for somethig like a hybrid bus is around 75 KwH, I would think that such a battery could handle regenerative braking on the trains with ease.
How Far Could A Train Run On Batteries Away From Electrification?
This is a bit like asking the old question about how long is a piece of string.
Merseyrail’s lines are generally fairly flat and if the trains have regenerative braking with batteries, I suspect the range could be longer than expected.
Other factors will also affect the range.
- Driving aids.
- Wheel-slip protection.
- Good driving.
- The weather.
- Accurately-positin slab track.
I also think the range on batteries will be deliberately restricted to a conservative distance, as running out of energy, would not be tolerated.
I would also expect the achievable range to get longer, as the operator and its drivers, learn how to conserve energy.