Pumped hydro is a simple and effective way to store energy — you just pump water back up over the dam — but building new dams isn’t easy. All the good spots have already been taken, and the regulatory hurdles keep growing. There are other ways to apply the same simple principles though:
Instead of trying to build new pumped hydro facilities, the founders of ARES — William Peitzke, Matt Brown and John Robinson — asked themselves, “How can we do pumped storage hydro-electric, but without any water?” The answer they found was basically the opposite of water: rocks. Or more specifically, rocks on trains.
“We realized the solution was right in front of us,” said Kelly. “The railroad industry had developed an incredibly efficient way to move mass.” One ARES engineer determined that the coefficient friction of steel wheels on railroad track is lower than the coefficient friction of ice skates on ice.
The ARES system uses excess energy from the grid to pull 140-ton railcars up hills (total train weight: 1,350 tons). When the grid needs that power back, they simply let gravity take the weighted cars back down. Regenerative braking — similar to what you find in a Toyota Prius, or in Japanese subways — captures the energy the trains produce along the way
ARES built a test facility in California to prove the concept, and now they’re in the final stages of building a 50 megawatt facility in Nevada, which will come online in 2016. For comparison, this facility alone will add more energy storage than was built across the entire US in 2013 (44.2 megawatts), according to a recent recent report by US Energy Storage Monitor. The same report suggests that 220 megawatts will be deployed in 2015, twice the capacity of the previous two years combined.