The ARES is pretty simple, as cutting-edge energy storage technology goes. A lot of rocks. A few railcars that, if they weren't traveling up and down the same 5.5-mile track on a Nevada hillside, would probably be hauling ore around a mining operation. Throw in an electric generator, and you've got the future of the American energy grid.

Well, one possible future. Energy storage is a hot topic, because federal and state guidelines are fast pushing utility companies to ramp up their use of renewable energy sources. (California's supply, for example, has to be 50 percent renewable by 2030.)

The problem is, today's coal and natural gas guzzling grid doesn't hold onto the electricity it generates. Utilities immediately deliver whatever they produce, and produce exactly what's needed, from moment to moment.

Renewables, though, don't work that way. The wind doesn't always blow, the sun doesn't always shine. So utilities are in search of ways to store surplus energy when they've got it, so they can distribute it later, when it's needed.

The most "duh" approach to energy storage is very big batteries like the ones Elon Musk peddles, which are poised to become a lot cheaper in the next five years. Pumped hydroelectric facilities are another option. Or you can move compressed air around underground caves. But none of these options has emerged as the best way to fix the grid.

Then there's rail energy storage, which is about to get its grand debut. In April, the Bureau of Land Management approved an ARES—that's Advanced Rail Energy Storage—project, conceived by a Santa Barbara-based energy startup called, well, ARES. By 2019, ARES operations head Francesca Cava says, the facility will occupy 106 acres in the excellently-named town of Pahrump, Nevada. By running a train up and down a hill, ARES can help utilities add to and subtract from the grid as needed.

ARES

It's a wonderfully simple idea, a 19th century solution for a 21st century problem, with some help from the abundant natural resource that is gravity. When the local utility's got surplus electricity, it powers up the electric motors that drag 9,600 tons of rock- and concrete-filled railcars up a 2,000-foot hill. When it's got a deficit, 9,600 tons of railcar rumble down, and those motors generate electricity via regenerative braking—the same way your Prius does. Effectively, all the energy used to move the train up the hill is stored, and recouped when it comes back down.

ARES may not like the term pilot project—it's already built a demonstration track in California—but Pahrump's new $55 million energy storage system has a lot to prove. This first official outing will start small, providing only ancillary services—that is, helping 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.”

And while the science behind ARES—rocks and gravity, mostly—is low-tech, that doesn't make for a cheap project. The company needs to pour money into the on-the-ground electronics and telecommunications equipment, and into bringing railcars up to their specifications. Andy Lubershane, a senior analyst with IHS Emerging Energy Research, says the setup is more expensive per kilowatt-hour "than almost anything else on the market today."

Ravi Manghani, a senior energy storage analyst at GTM Research, urges a "wait and watch approach." "Any new technology has to go through some big hurdles," he says.

And yet, the simplicity of this setup is appealing. Train goes up, train comes down. If only you could catch a ride, too—which ARES says is a very bad idea. "This is a different scenario in terms of safety and weight," Cava says, meaning you can’t just run these trains through DC Metro's infrastructure. They're way too heavy. Sorry to say the future of energy storage won't look like Magic Mountain at all.