Train-Based Gravity Energy Storage Could Stabilize Electricity Grid

First Posted: Apr 04, 2013 09:55 PM EDT

In an interesting twist on the old concept of gravity energy storage, mostly practiced in pumped-storage hydropower currently, Jim Kelly, CEO of Advanced Rail Energy Services in California, is looking forward to actually test the method of using trains instead of water - driving them uphill with excess electricity, and recouping electricity similar to a hybrid car when letting them roll back down.

An engineer with Southern California Edison for 38 years, Kelly and his team at ARES intend to store excess energy, created by photovoltaic solar panels and wind turbines, by moving trains powered by electric engines and weighed down by many cars filled with gravel.

When demand in the grid reaches a peak, the trains can be allowed to roll down the hill at about 55 kilometers per hour. The electric motor that used electricity from the power grid to push the train uphill would become a dynamo, slowing down the train and pumping electricity back into the grid.

The idea operates on the same principle as pumped-storage hydropower, where the generator (dynamo) and turbine (pump) of such a plant are reversed to push large quantities of water in an uphill reservoir when there is excess energy in the grid. Then, when the energy is needed, the direction can be rapidly switched and water released to go back through the turbine.

The latter method works so well that it currently “accounts for 93 percent of energy storage worldwide,” according to Slate, but it takes a lot of water stored in a surface reservoir, which can be difficult in places that are hot and dry.

Kelly’s train project would require eight miles of track to store 500 megawatt hours of electricity, which would be quite an effective and interesting system if it works out like that and is easy enough to maintain.

The city of Los Angeles is considering Kelly’s proposal as one of a series to build a more advanced and clean electricity grid.

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