Rail Energy Storage Harnesses the Power of Gravity All the Livelong Day

A California startup is repurposing trains and rail cars to help renewable energy utilities compete with fossil fuels.

What goes up must come down. This principle applies to most things in our current gravitational setup — college tuition being a conspicuous exception — and it could provide a significant boost to green energy initiatives, too.

A California-based company called Advanced Rail Energy Storage (ARES) is using the power of gravity to help renewable energy utilities compete with coal and gas. The idea is to help solve the perennial problem of energy storage. Because wind and solar installations can't always generate energy on demand — sometimes it's cloudy and the air is still — green utilities need a reliable method of storing surplus energy.

There are several ways to do this using high-tech industrial batteries, flywheels, or hydroelectric facilities, but these approaches tend to be expensive and complicated.

ARES's solution? Run some old trains up and down a hill.

The company harnesses the power of potential and kinetic energy to help utilities add and subtract to the energy grid as needed. When the wind or solar farm is producing excess energy, that power is shuttled over to the adjacent ARES facility. The surplus energy is used to power repurposed electric locomotives, which in turn haul enormously heavy railroad cars to the top of a hill.

When less energy is being produced but more is needed for the grid, the railroad cars roll back down, turning potential energy back into kinetic energy by powering onboard generators with the force of their descent. The technique is similar to the regenerative braking system that is used in electric and hybrid vehicles, which routes deceleration energy to the vehicle’s battery.

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The system is also similar to existing hydroelectric (“pumped hydro”) solutions that essentially do the same things with water — pumping water uphill and capturing downhill flow. A benefit of the rail energy storage solution is that it doesn't need to be near a large source of water. That’s good for wind and solar installations, which are often located in remote areas.

It's cheaper, too. Ares contends that its rail energy solution costs about half as much as competing energy storage solutions, and has less of an environmental impact.

“We use no water, burn no fossil fuel, produce no emissions, and use no hazardous or environmentally troubling materials like lithium,” ARES CEO James Kelly told Seeker. “We are excited to be a green storage solution that can enable higher penetration of intermittent renewable resources — like wind and solar — in the US and around the world.”

Pushing rocks up a hill might seem like a curiously low-tech approach to energy storage, but Kelly said that this very simplicity is what gives rail energy storage an edge. Building a railroad loop is a lot simpler than maintaining a giant battery farm, and the ARES system can easily use repurposed locomotives and freight cars. An ARES site can be quickly and cleanly decommissioned and restored in months rather than years or decades, Kelly said.

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None of this matters unless the system is efficient. Rail energy storage has about an 80 percent efficiency rate, meaning that the descending railroad cars can output 80 percent of the energy that was initially used to get them up that hill.

That's better than pumped-storage hydroelectricity, Kelly noted, which typically runs in the 60 percent range. Batteries can return a higher efficiency, but their capacity degrades over time.

“The real question is how much you get out when you need the energy,” Kelly said. “If you discharge your storage batteries tomorrow, you will probably get 90 units out. If you discharge in six months, you may get 40 or 50 units. ARES units have essentially infinite cycles with no degradation.”

“What we've done with ARES is harness the inexhaustible, entirely reliable power of gravity,” he added.

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The company currently runs two facilities, a testbed operation near their headquarters in Santa Barbara, Calif., and a new installation outside the town of Pahrump, Nevada.

In April of last year, the Nevada Bureau of Land Management granted environmental approval and a land lease to ARES for its first commercial operation. Construction on the Nevada facility will begin early next year and will initially help local utilities make small adjustments to the regional power grid.

Once the facility is fully operational, it will have a total power capacity of 50 megawatts — enough to help renewable energy providers manage their intermittent energy problems and better compete with coal and gas facilities.

According to Kelly, ARES currently holds an exclusive patent on its rail energy storage system in the US and 52 other countries, including the European Union and, as of last week, China.

“ARES has also recently received unsolicited requests to consider applications of our technology across the US, in Australia, China, Europe, South America, and South Africa,” Kelly said. “It's an exciting time.”

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