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Energy Storage high speed trains sun

Published on April 2nd, 2013 | by Nicholas Brown

7

Gravity Energy Storage For The Electricity Grid

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April 2nd, 2013 by  

We have all heard of the saying “what goes up, must come down.” This rule of gravity is an important part of so many systems, and it can also be a nuisance sometimes. However, why not put it to more use?

high speed trains sun

High-Speed Trains.
Image Credit: Shutterstock

Gravity energy storage for the electricity grid involves using electricity from the grid to power a motor that lifts a weight upwards, and the weight is allowed to fall/roll down when electricity is needed.

When it rolls down, it can turn a gear or unreel a cable, causing a generator to turn.

Jim Kelly, who has 38 years of energy storage research and development experience at Southern California and Edison, decided that it is time to try to use gravity to aid energy storage.

His concept involves using an electric motor powered by surplus electricity available in the electricity grid to propel a train up a slope, and when the electricity is required during low-wind periods or cloudy weather, the train is allowed to roll back downhill, this rolling motion is used to turn the same motor that also acts as a generator.

The propulsion motor mentioned obtains its electricity via a third electrified rail, and when the motor generates electricity, it is fed through that same rail back into the electricity grid to help back up power plants.

Efficiency is expected to be about 90%.

A large-scale system of this type that could provide 500 MW of power (the energy storage capacity was not stated) would require about 8 miles of track.

While 8 miles sounds long, that is of course only the length of the track. The width is not much, so it doesn’t require as much space as it might appear at first. The energy to size ratio cannot be calculated without the energy storage capacity, though.

This project is to be executed on a ranch on the Tehachapi mountains.

Benefits of Gravity Energy Storage

  1. No self-discharge. Gravity systems can retain their energy forever without losing any of it.
  2. The ability to last decades.
  3. The systems can be highly efficient.
  4. Simplicity.
  5. No rare materials or conflict-minerals required.

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About the Author

writes on CleanTechnica, Gas2, Kleef&Co, and Green Building Elements. He has a keen interest in physics-intensive topics such as electricity generation, refrigeration and air conditioning technology, energy storage, and geography. His website is: Kompulsa.com.



  • Bob_Wallace

    There’s another system being investigated in which a large concrete weight is moved in a column water. That avoids the friction loss of hauling a weighted “train” up a track.

    It also requires less land. Just enough for a big hole in the ground.

  • Captain Obvious

    Water would seem easier and cheaper.

  • Bill_Woods

    “A large-scale system of this type that could provide 500 MW of power
    (the energy storage capacity was not stated) would require about 8 miles
    of track.”

    Potential energy = mgh. Eight miles of 8% grade is an elevation difference of 1 km. A 100-tonne rail car raised an elevation of 1 km will store 1e9 W-s. Enough to generate 500 MW for 2 seconds.

  • Matt Grason

    Brilliant in its elegance.

  • http://twitter.com/Kf_Lenz Karl-Friedrich Lenz

    The London subway has operated on that principle since 1863, with stations elevated relative to tracks between stations.

    One could also try to use elevators with this idea. Transport weights up in time slots where electricity is cheap, and down when it is expensive.

  • geoffderuiter

    Fill that train with used Li-ion or Lead acid batteries and you can have double plus energy!

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