## How Big Would Batteries Need To Be On A Train For Regenerative Braking?

Let’s assume that we have a Class 710 train, trundling around North East London at up to 120 kph.

To calculate the kinetic energy in the train, which will have to be transferred to the battery, we need the mass of the train and its velocity.

I’ll start with the velocity of the train.

As it approached a station, it will be at whatever is the appropriate line speed, which to make things easy I’ll assume is 100 kph or just under 28 metres per second.

In most cases after stopping and discharging and loading a few passengers, it will probably return to a similar line-speed to go to the following station.

The mass of each car of an Aventra, is found at several places on the Internet, including this entry in Wikipedia which gives it as 30-35 tonnes. So the four-car Class 710 train could have a mass of 130 tonnes. Add 100 passengers at an average of 80 kg. each and this would make the mass 138 tonnes

Applying the standard formula gives a kinetic energy of 53240741 joules or in common-or-garden units 14.8 kilowatt hours. So the energy of an Aventra going at 100 kph could power a one bar electric fire for fifteen hours.

To get a better handle on how much energy is involved let’s look at these specifications for a Nissan Leaf car.

Nissan talks about 24 and 30 kWh versions of the car, So if this is the battery size, then one of Nissan’s batteries could store all the braking energy of a four-car Class 710 train.

Even a fully-loaded Class 345 train would only need a 50kWh battery.

Assuming of course, I’ve got the maths correct.

I have a feeling that using batteries to handle regenerative braking on a train could be a very affordable proposition.

As time goes on, with the development of energy storage technology, the concept can only get more affordable.

Why bother to store it, just pump it back into the power system to power other trains that are not braking

Comment by John Wright | September 5, 2016 |

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[…] In How Big Would Batteries Need To Be On A Train For Regenerative Braking?, I calculated that the energy of a fully-loaded Class 710 train travelling at 100 kph is around 15 KwH. […]

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