The Anonymous Widower

Funding Gives Weight To Idea For Storing Electricity

The title of this post, is the same as that of an article on Page 45 of today’s copy of The Times.

It talks of a company called Gravitricity, which has used the same principle as every weight-operated clock to store energy and especially energy generaed from intermittent sources like wind and solar power.

The company has just secured a £650,000 grant from Innovate UK.

In Solar Power Could Make Up “Significant Share” Of Railway’s Energy Demand, I looked at how solar farms and batteries could be used to power third-rail railway electrification.

Because of energy losses, third-rail electrification needs to be fed with power every three miles or so. This gives a problem, as connection of all these feeder points to the National Grid can be an expensive business.

A series of solar farms, wind turbines and batteries, controlled  by an intelligent control system, is an alternative way of providing the power.

In an article in the October 2017 Edition of Modern Railways, which is entitled Celling England By The Pound, Ian Walmsley says this in relation to trains running on the Uckfield Branch.

A modern EMU needs between 3 and 5 kWh per vehicle mile for this sort of service.

If I assume that trains are five cars and will be efficient enough to need only 3 kWh per vehicle mile, then to power a train along a ten mile section of track will take 150 kWh.

As the control system, only powers the track, when a train needs it, the whole system can be very efficient.

So why will Gravitricity battery ideas be ideal in this application?

Appropriate Size

By choosing the right weight and depth for the Gravitricity battery , appropriate energy storage can be provided at different points on a line.

Some parts of a journey, like accelerating away from stations will need more electricity than others, where trains are cruising along level ground.

Supposing my five-car example train is travelling at 60 mph, then to cover ten miles will take 10 minutes, with 15 kW being supplied in every minute.

If the train weighs 200 tonnes, then accelerating the train to 60 mph will need about 20 kWh.

I’m sure that a Gravitricity battery could handle this.

I would suspect that batteries of the order of 100 kWh would store enough power for the average third-rail electrified line.

A proper dynamic simulation would need to be done. I could have done this calculation in the 1960s, but I don’t have the software now!

Response Time

For safety and energy-efficiency reasons, you don’t want lines to be switched on, when there is no train present.

I suspect that if there is energy in the battery, response would be fast enough.

Energy Efficiency

The system should have a high efficiency.

How Big Would A 100 kWh Gravitricity Battery Be?

A quick calculation shows the weight would be 400 tonnes and the depth would be 100 metres.

Installing the batteries

Each battery will need a 100 metre deep hole of an appropriate diameter.

This sequence of operations would be performed.

  • A rail-mounted drilling rig would drill the hole.
  • The heavy weight of the battery would arrive by train and would be lifted into position using a rail-mounted crane.

As the equipment will generally be heavy, doing all operations from the railway will be a great help.

 

 

 

February 9, 2018 - Posted by | Transport | , , ,

1 Comment »

  1. A Class 700 train draws 3MW for an 8-car or 5MW for a 12 car. Most of this is used accelerating the train away from stations, so in reality some sort of storage in the train will be most efficient. You don’t need control circuitry to dynamically switch lines on an off, since losses are relatively low when there is no load (train) on it, although disconnecting third rail power in stations when not required would improve safety.

    Comment by Mark Clayton | February 9, 2018 | Reply


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