Energy-Storing Train Gets Nevada Approval by David Z. Morris @FortuneMagazine May 22, 2016, 12:10 PM EDT E-mail Tweet Facebook Linkedin Share icons One of the biggest challenges of the shift to renewable energy like solar and wind is energy storage. The wind or sun don’t always generate power exactly when it’s needed, so infrastructure needs to bridge the gap. Batteries are the most frequently discussed solution, but there are other options out there, many of them surprisingly low-tech. Get Data Sheet, Fortune’s technology newsletter. In April, the Nevada Bureau of Land Management granted environmental approval and a land lease to Advanced Rail Energy Storage (ARES), a startup with an energy storage solution that’s both novel and old-school. Apparently taking some inspiration from the myth of Sisyphus, ARES proposes to use excess off-peak energy to push a heavily-loaded train up a grade. Then, when the grid needs that energy back, the cars will be rolled back down the slope—but in a significant improvement on the myth, that return trip will generate energy and put it back on the grid. ARES’ solution is related to an already common kind of energy storage known as pumped-storage hydropower, which pumps water uphill, then captures the power of its downhill flow as needed. The obvious advantage of the ARES approach is that it’s more adaptable, without the need for lots of water. ARES has also said its solution costs about half as much as other storage technologies, and claims 80% efficiency in energy reclamation, similar to or slightly above typical hydro-storage efficiency. For more on renewable energy, watch our video. The project is also further evidence for Nevada’s emergence as a leading region for innovative transportation and energy projects. The state is already the home of the Tesla gigafactory and Hyperloop One’s testing facility. ARES says construction on its Nevada project will begin in Spring of 2017, at a projected cost of $55 million.