Little Engines That Can

For storing renewables, take it back to the tracks

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An artist’s rendering of an upcoming ARES project in Pahrump, Nevada.—ARES image

One of the newest developing technologies in the renewable energy sector is regenerative braking, and the potential for applying it to a centuries-old industry and its infrastructure: train tracks. The basic principle is to gather energy used to move a train uphill and store it, recovering that same energy on the return trip downhill.

Rail energy storage represents another blossoming technology that is fast approaching real world application. In April, the Bureau of Land Management approved an Advanced Rail Energy Storage project from Santa Barbara-based energy startup ARES (yep, the acronym matches on purpose). By 2019, ARES operations head Francesca Cava says, the facility will occupy 106 acres in Nevada. By running a train up and down a hill, ARES can help utilities add to and subtract from the grid as needed. Or, as Lloyd Alter of Treehugger.com described Monday, storing energy by turning motors into generators.

WIRED magazine’s Aarian Marshall calls it “a wonderfully simple idea, a 19th century solution for a 21st century problem.” Gravity is essential. Utilities use their stored electricity to power electric motors that drag tons (literally; 9,600 of them) of rock or concrete-filled railcars up a 2,000-foot hill. When it’s got a deficit, the cars move downhill, and those motors generate electricity via regenerative braking—such as with an electric motor vehicle. “Effectively, all the energy used to move the train up the hill is stored, and recouped when it comes back down,” Marshall says.

The pilot project includes a demonstration track constructed in California and is expected to cost $55 million. This first official run will essentially be in test mode, providing ancillary services to help utility companies make relatively minor adjustments in their electricity output and input.

The Nevada project has a power capacity of 50 megawatts and can produce 12.5 megawatt-hours of energy. That’s relatively large, especially compared to a lot of battery storage projects. But it might not be large enough to make money. “Fifty megawatts doesn’t get us to economies of scale,” ARES CEO James Kelly admitted in an interview with UtilityDive. “We are more efficient as we get larger.”

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