Aug 15, 2014 at 08:35 AM

Riding the Rails for Energy Storage

By Ares North America

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By Jonathan Marshall

While California studies high-speed rail to carry passengers up and down the state, a start-up in Nevada is exploring instead the potential for low-speed rail to carry tons of rocks up and down hills to store energy.

Advanced Rail Energy Storage (ARES) is putting a new twist on the ancient Greek myth of King Sisyphus, who was condemned forever to push an immense boulder up a hill, only to have it tumble back down again.

The Advanced Rail Energy Storage project is being tested on a short track in Tehachapi.

With the benefit of modern technology, ARES proposes to push hundreds of tons of rocks uphill aboard electrified rail cars, then create electricity as needed through regenerative braking as those cars roll back down the tracks.

The company is testing the system on an 880-foot track in Tehachapi and planning to build its first commercial 50 megawatt system on a 5.7-mile track in Pahrump, Nev., east of Death Valley.

“We use no water, we use no fuel, we produce no emissions, we use no hazardous or environmentally hazardous substances,” says ARES CEO James Kelly, former senior vice president of transmission and distribution for Southern California Edison.

Untold numbers of investors and entrepreneurs are looking at new technology options for capturing and releasing electricity on demand. Their goal is to make money off a huge new market opened up by California’s energy storage mandate, which requires electric utilities to purchase 1,325 megawatts of storage capacity by 2020.

Energy storage can serve a variety of functions, including lowering energy supply costs by letting utilities buy and store electricity when prices are low; reducing the need to purchase expensive transmission, by siting storage close to loads; and helping to cushion the swings of generation from intermittent sources such as wind and solar.

Batteries, which store energy in the form of chemical bonds, are proven in the field but, for now at least,  are expensive and ill-suited to large-scale storage needs. Storing energy in the form of compressed air underground, as PG&E is working to demonstrate, is a highly promising approach, but can take years to implement.  Other forms of energy storage include flywheels, molten salt, ice, and hydrogen.

ARES is harnessing the potential gravitational energy available from elevated masses. In concept, that’s much like the most prevalent form of bulk energy storage long used by PG&E and other utilities: pumped hydro. Utilities with such facilities pump water from a low reservoir up to an adjacent higher reservoir, usually at night when electricity costs are low, and then release it through a generator to serve peak demand when electricity is more valuable.

“Using the Earth’s gravitational field to store energy can be an excellent way to do it,” says Haresh Kamath, program manager for energy storage at the Electric Power Research Institute. “It’s relatively easy, and has been used for centuries.”

From water to compressed air to batteries, such as this demonstration storage project near Vacaville, PG&E continues to look into various ways to store energy. (Currents Archive Photo.)

Pumped hydro, however, is limited by the availability of suitable reservoir sites, and can take years to permit and build. Building or modifying a relatively short rail line up a hill promises to be much easier and quicker. And compared to many exotic storage R&D projects, “Rail is compelling because it uses well understood, off-the-shelf technology,” Kamath notes.

There’s no certainty that it will be commercially viable, however. Kamath hopes further testing will resolve his concerns about rail storage, which includes the efficiency losses from friction and mechanical stress on the rails, and the complication of having to put the generation system on moving rail cars.

A similar concept motivates another energy storage startup, Energy Cache. With funding from billionaire Microsoft founder Bill Gates, it is adapting technology from the mining and ski lift industries to carry motorized buckets of gravel up hills, then powering a generator as they come back down. If they can make it work, I’m sure King Sisyphus would be glad to go along for the ride.

Posted in ARES News.