Friday, May 6, 2016

Gravity Grid-Scale Storage System Using Trains

Subtitle:  A New Approach to Grid-Scale Energy Storage

There are several different technologies for storing electricity, or the functional equivalent, at grid-scales.  The most common is pumped storage hydroelectric, also the list includes batteries of various designs, super-capacitors, high-speed flywheels, compressed air energy storage, and molten materials of various compositions.  

A new system caught my attention this week, by Ares North America see link,  that uses excess power from the grid to power
Figure from Ares' Biological Assessment Report (2016) 
electric locomotives pulling heavy rail cars up a hill to a holding yard.  When power is needed on the grid, the locomotives and train of heavy cars rolls back down the hill to another storage yard.  The downhill journey has the brakes on, with the brakes being electric motor/generators that operate in generator mode.   The company has patents for the system. 

The first project received environmental approval about one week ago, and is to be built in Nevada just west of Las Vegas near the town of Pahrump.   The project is to have 50 MW capacity, but only 12.5 MWh of storage.   The local grid is the California Independent System Operator, CAISO.  Ares Nevada will provide load-leveling to CAISO.  

The train has two electric locomotives and rail cars loaded with a large concrete block for weight.  Power is provided via an overhead catenary system.   A bit of quick math shows that, for a 5.5 mile long track, and one train, the train speed is approximately 20-25 mph.  One must allow some distance for stopping at each end.  

Advantages of such a system are readily apparent, compared to other forms of energy storage.  No water is required, nor is a lake at a high elevation and another at a low elevation.   An Ares gravity storage system can be built anywhere there is a sufficient slope.  Those who advocate for wind-turbines in the UK, for example, may be having a look over the various hills and low mountains in that country.   Spain may also have a keen interest.  Germany, too, although the mountains are far from the industrial areas. 

Ares also lists advantages as no emissions, no fossil fuels required, no water required, no hazardous wastes produced, no harmful extraction of minerals, and no adverse decommissioning required to restore the land.  The system is also claimed to be easily scalable and expandable, and cost approximately 60 percent of a similar-sized pumped storage hydroelectric system.   

I would add these advantages: nothing to blow up, no dams to burst with fatal flooding, no danger of catching fire, no wildlife harmed, slow speed, quiet operation, no high pressure to leak or blow out, and well-proven principles. 

This appears to be a viable solution to grid-scale energy storage.   It is one to watch.  It would be useful in areas where wind-energy is great at night during periods of low demand.  One can easily imagine such systems all along the Front Range of the US Rocky Mountains, with the high end in the foothills, and the track running east into the plains.  The great wind corridor in the US, from north Texas to the Canadian border, could have the wind energy stored when necessary via the gravity storage systems, then returned to the grid as needed.  

As engineers would say, That's pretty slick. 

Roger E. Sowell, Esq.
Marina del Rey, California
copyrignt © 2016 by Roger Sowell, all rights reserved

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